Metal-plastic composite structure, preparation method therefor and use thereof

Abstract

A metal-plastic composite structure, a preparation method therefor, and a use thereof. The metal-plastic composite structure comprises a first metal layer and a second metal layer which are stacked, and satisfies at least one of the following: comprising a first transition oxide film layer, a first porous oxide film layer and a first plastic layer which are sequentially stacked on the surface of the first metal layer that is not attached to the second metal layer, and a second transition oxide film layer, a second porous oxide film layer and a second plastic layer which are sequentially stacked on the surface of the second metal layer that is not attached to the first metal layer; the first metal layer and the second metal layer being metal layers of different materials; the porosity of the first transition oxide film layer being less than that of the first porous oxide film layer; and the porosity of the second transition oxide film layer being less than that of the second porous oxide film layer.

Description

Metal-plastic composite structure, preparation method and application thereof

[0001] Cross-reference to Related Applications

[0002] This application claims priority to Chinese patent application No. CN202410718466.9, filed on June 4, 2024, the contents of which are incorporated herein in their entirety as part of this application. TECHNICAL FIELD

[0003] The present application relates to the field of metal materials, in particular to a metal-plastic composite structure, a preparation method and application thereof. BACKGROUND

[0004] Currently, in order to meet the requirements of high strength and light weight at the same time, electronic device shells are prepared by using composite metals. However, since metals can shield signals, it is necessary to open slots in the metal shell and perform injection molding to solve the problem of signal shielding. In related technologies, in order to improve the bonding ability of metals and plastics, the metal is first subjected to surface treatment to form holes, and then a plastic layer is formed on the surface of the metal by injection molding. However, for composite metal shells, the performance differences between different metals will increase the difficulty of surface treatment, and the surface treatments of different metals will affect each other, making it difficult to achieve industrialization. Therefore, it is necessary to provide a metal-plastic composite structure scheme that is environmentally friendly, simple, and can achieve strong bonding of composite metals and plastics. SUMMARY

[0005] In view of this, the present application provides a metal-plastic composite structure, a preparation method and application thereof. The metal-plastic composite structure has strong bonding ability between the plastic layer and the metal layer, high structural reliability, simple preparation process, environmental friendliness, and is conducive to industrial production.

[0006] In a first aspect, the present application provides a metal-plastic composite structure, comprising a first metal layer and a second metal layer connected to each other, and at least one of: comprising a first transition oxide film layer, a first porous oxide film layer and a first plastic layer which are sequentially stacked on a surface of the first metal layer not connected to the second metal layer, and comprising a second transition oxide film layer, a second porous oxide film layer and a second plastic layer which are sequentially stacked on a surface of the second metal layer not connected to the first metal layer; the first metal layer and the second metal layer are metal layers of different materials; the first transition oxide film layer and the first porous oxide film layer contain a first metal oxide, the first porous oxide film layer contains a second metal oxide, at least one metal element in the first metal oxide, the second metal oxide and the first metal layer is the same, and the porosity of the first transition oxide film layer is less than the porosity of the first porous oxide film layer; the second transition oxide film layer contains a third metal oxide, the second porous oxide film layer contains a fourth metal oxide, at least one metal element in the third metal oxide, the fourth metal oxide and the second metal layer is the same, and the porosity of the second transition oxide film layer is less than the porosity of the second porous oxide film layer.

[0007] In some embodiments, the first metal oxide and the second metal oxide are oxides of the metal material of the first metal layer.

[0008] In some embodiments, the third metal oxide and the fourth metal oxide are oxides of the metal material of the second metal layer.

[0009] In some embodiments, the first metal layer has a first surface and a second surface arranged opposite to each other, the second metal layer has a third surface and a fourth surface arranged opposite to each other, the second surface and the third surface are connected to each other in a manner of being attached to each other, the first surface has a first transition oxide film layer, a first porous oxide film and a first plastic layer which are sequentially stacked, and the fourth surface has a second transition oxide film layer, a second porous oxide film layer and a second plastic layer which are sequentially stacked.

[0010] In some embodiments, the side surface of the first metal layer is sequentially stacked with a first transition oxide film layer, a first porous oxide film and a first plastic layer, and the side surface of the second metal layer is sequentially stacked with a second transition oxide film layer, a second porous oxide film layer and a second plastic layer.

[0011] In some embodiments, the first metal layer has a first surface and a second surface arranged oppositely, the second metal layer has a third surface and a fourth surface arranged oppositely, the second surface and the third surface are connected to each other in a manner of being attached to each other; at least one of the following is satisfied: the first surface has a first transition oxide film layer, a first porous oxide film layer, and a first plastic layer arranged in a manner of being stacked; and the fourth surface has a second transition oxide film layer, a second porous oxide film layer, and a second plastic layer arranged in a manner of being stacked.

[0012] In some embodiments, the material of the first metal layer is titanium, magnesium, titanium alloy, magnesium alloy, or stainless steel, and the material of the second metal layer is aluminum or aluminum alloy.

[0013] In some embodiments, the total area ratio of the nano-pores on the surface of the first transition oxide film layer close to the first plastic layer is less than or equal to 1%, and the total area ratio of the nano-pores on the surface of the first porous oxide film layer close to the first transition oxide film layer is 40%-80%.

[0014] In some embodiments, the total area ratio of the nano-pores on the surface of the second transition oxide film layer close to the second plastic layer is less than or equal to 1%, and the total area ratio of the nano-pores on the surface of the second porous oxide film layer close to the second transition oxide film layer is 45%-70%.

[0015] In some embodiments, the thickness ratio of the first porous oxide film layer to the first transition oxide film layer is (0.2-2.5):1, and the thickness ratio of the second porous oxide film layer to the second transition oxide film layer is (0.2-2.5):1.

[0016] In some embodiments, the thickness of the first transition oxide film layer is 24 nm-3.5 μm, and the thickness of the first porous oxide film layer is 60 nm-700 nm.

[0017] In some embodiments, the thickness of the second transition oxide film layer is 24 nm-3.5 μm, and the thickness of the second porous oxide film layer is 60 nm-700 nm.

[0018] In some embodiments, the surface roughness Ra of the side of the first porous oxide film layer close to the first plastic layer is greater than or equal to 1 μm.

[0019] In some embodiments, the surface roughness Ra of the side of the second porous oxide film layer close to the second plastic layer is greater than or equal to 2 μm.

[0020] In some embodiments, the first porous oxide film layer includes a plurality of first nano-pores.

[0021] In some embodiments, the first nanopores have a pore size of 20-100 nm.

[0022] In some embodiments, the first porous oxide film layer has a percentage of the first nanopores of 45-55%.

[0023] In some embodiments, the second porous oxide film layer comprises a plurality of second nanopores.

[0024] In some embodiments, the second nanopores have a pore size of 20-40 nm.

[0025] In some embodiments, the second porous oxide film layer has a percentage of the second nanopores of 50-60%.

[0026] In some embodiments, at least part of the first nanopores are filled with plastic material; at least part of the second nanopores are filled with plastic material.

[0027] In some embodiments, the shear strength between the first plastic layer and the first metal layer is greater than or equal to 20 MPa.

[0028] In some embodiments, the shear strength between the second plastic layer and the second metal layer is greater than or equal to 25 MPa.

[0029] In some embodiments, the first metal layer and the second metal layer further comprise a connecting layer.

[0030] In some embodiments, the connecting layer comprises metal or resin.

[0031] In some embodiments, the connecting layer has a thickness greater than or equal to 0.05 mm.

[0032] The metal-plastic composite structure provided by the present application has a transition oxide film layer and a porous oxide film layer, the porous oxide film layer has a greater porosity than the transition oxide film layer, which can improve the bonding ability of the plastic layer and the metal layer and enhance the reliability of the metal-plastic composite structure.

[0033] In a second aspect, the present application provides a preparation method of a metal-plastic composite structure, comprising:

[0034] providing a to-be-injection-molded composite metal material, the to-be-injection-molded composite metal material comprising a third metal layer and a fourth metal layer connected to each other;

[0035] satisfying at least one of: performing first etching on a surface of the third metal layer not connected with the fourth metal layer to form a fifth metal layer; and performing second etching on a surface of the fourth metal layer not connected with the third metal layer to form a sixth metal layer, to obtain an etched-to-be-injection-molded composite metal material;

[0036] satisfying at least one of: sequentially performing first anodic oxidation treatment and second anodic oxidation treatment on the etched-to-be-injection-molded composite metal material, so that a surface layer of the fifth metal layer not connected with the sixth metal layer sequentially forms a first porous oxide film layer and a first transition oxide film layer from outside to inside; and so that a surface layer of the sixth metal layer not connected with the fifth metal layer sequentially forms a second porous oxide film layer and a second transition oxide film layer from outside to inside, to obtain an oxidized-to-be-injection-molded composite metal material;

[0037] satisfying at least one of: performing injection molding on the oxidized-to-be-injection-molded composite metal material to form a first plastic layer on a surface of the first porous oxide film layer; and forming a second plastic layer on a surface of the second porous oxide film layer, to obtain a metal-plastic composite structure.

[0038] In some embodiments, the material of the third metal layer is titanium, magnesium, titanium alloy, magnesium alloy, or stainless steel, and the material of the fourth metal layer is aluminum or aluminum alloy.

[0039] In some embodiments, the first etching uses a first etching solution, and the first etching solution includes at least one of hydrofluoric acid, acetic acid, carbonic acid, hypochlorous acid, phosphoric acid, sodium fluoride, calcium fluoride, ammonium hydrogen fluoride, sodium citrate, sodium chloride, and ferric chloride.

[0040] In some embodiments, the concentration of the first etching solution is 5 g / L-30 g / L, the pH value of the first etching solution is 2-5, and the conductivity of the first etching solution is 100 mS / cm-500 mS / cm.

[0041] In some embodiments, the second etching uses a second etching solution, and the second etching solution includes at least one of nitric acid, sulfuric acid, hydrochloric acid, potassium chloride, ferric chloride, ferrous chloride, copper chloride, magnesium chloride, and sodium chloride.

[0042] In some embodiments, the concentration of the second etching solution is 100 g / L-300 g / L, the pH value of the second etching solution is less than or equal to 2, and the conductivity of the second etching solution is 400 mS / cm-1000 mS / cm.

[0043] In some embodiments, the first anodic oxidation treatment uses a first electrolyte, and the first electrolyte includes at least one of potassium dichromate, hydrogen peroxide, hydrofluoric acid, sulfuric acid, phosphoric acid, sodium fluoride, ammonium hydrogen fluoride, and sodium sulfate.

[0044] In some embodiments, the concentration of the first electrolyte is 3-20 g / L, and the pH value of the first electrolyte is 3-6.

[0045] In some embodiments, the temperature of the first anodization treatment is 10-60℃, the voltage of the first anodization treatment is 5-100 V, and the current of the first anodization treatment is 1-50 A.

[0046] In some embodiments, the second anodization treatment uses a second electrolyte, and the second electrolyte comprises at least one of oxalic acid, citric acid, sodium citrate, sodium sulfate, acetic acid, and phosphoric acid.

[0047] In some embodiments, the concentration of the second electrolyte is 15-25 g / L, and the pH value of the second electrolyte is 1-4.

[0048] In some embodiments, the temperature of the second anodization treatment is 20-40℃, the voltage of the second anodization treatment is 15-50 V, and the current of the second anodization treatment is 15-50 A.

[0049] In some embodiments, the temperature of the injection molding is 230-320℃, and the pressure of the injection molding is 80-120 MPa.

[0050] The preparation method of the metal-plastic composite structure provided by the present application is novel, simple, environmentally friendly, and has excellent performance.

[0051] In a third aspect, the present application provides a preparation method of a metal composite structure, comprising:

[0052] providing a composite metal material, wherein the composite metal material comprises a third metal layer and a fourth metal layer connected to each other;

[0053] satisfying at least one of the following: performing a first etching on the surface of the third metal layer that is not connected to the fourth metal layer to form a fifth metal layer; and performing a second etching on the surface of the fourth metal layer that is not connected to the third metal layer to form a sixth metal layer, thereby obtaining an etched composite metal material;

[0054] The etched composite metal material is sequentially subjected to a first anodic oxidation treatment and a second anodic oxidation treatment; at least one of the following is met: the surface layer of the fifth metal layer not connected with the sixth metal layer is formed from outside to inside in sequence as a first porous oxide film layer and a first transition oxide film layer; and the surface layer of the sixth metal layer not connected with the fifth metal layer is formed from outside to inside in sequence as a second transition oxide film layer and a second porous oxide film layer, to obtain a metal composite structure; the first transition oxide film layer and the first porous oxide film layer comprise oxides of the material of the first metal layer, the first transition oxide film layer comprises a first metal oxide, the first porous oxide film layer comprises a second metal oxide, at least one metal element in the first metal oxide, the second metal oxide and the first metal layer is the same, and the porosity of the first transition oxide film layer is less than the porosity of the first porous oxide film layer; the second transition oxide film layer comprises a third metal oxide, the second porous oxide film layer comprises a fourth metal oxide, at least one metal element in the third metal oxide, the fourth metal oxide and the second metal layer is the same, and the porosity of the second transition oxide film layer is less than the porosity of the second porous oxide film layer.

[0055] The surface treatment method of the metal composite structure provided by the application is simple, has low processing cost, is friendly to the environment, has wide application range, and can be produced on a large scale.

[0056] In a fourth aspect, the application provides an application of the metal-plastic composite structure in the first aspect or prepared by the preparation method in the second aspect or the metal composite structure prepared by the preparation method in the third aspect in electronic devices, vehicles and electrical appliances.

[0057] The metal-plastic composite structure or the metal composite structure provided by the application has wide application scenarios, which is conducive to its commercial application.

[0058] In a fifth aspect, the application provides a structural member, which comprises the metal-plastic composite structure in the first aspect or prepared by the preparation method in the second aspect or the metal composite structure prepared by the preparation method in the third aspect.

[0059] The structural member provided by the application has high structural stability, long service life and low preparation cost, which is conducive to its large-scale application.

[0060] In some embodiments, the structural member comprises an electronic device shell.

[0061] In a sixth aspect, the application provides an electronic device, which comprises the structural member in the fifth aspect.

[0062] The electronic device provided by the application has good comprehensive performance and strong product competitiveness. BRIEF DESCRIPTION OF DRAWINGS

[0063] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. The specific embodiments described herein are only used to explain the present application, and are not used to limit the present application.

[0064] Fig. 1 is a schematic diagram of the cross-sectional structure of a metal-plastic composite structure provided by an embodiment of the present application;

[0065] Fig. 2 is a schematic diagram of the cross-sectional structure of a metal-plastic composite structure provided by another embodiment of the present application;

[0066] Fig. 3 is an enlarged view of region A in Fig. 1;

[0067] Fig. 4 is a schematic diagram of a shear strength test principle of a metal-plastic composite structure provided by an embodiment of the present application;

[0068] Fig. 5 is a flowchart of a preparation method of a metal-plastic composite structure provided by an embodiment of the present application;

[0069] Fig. 6 is a scanning electron microscope (SEM) image of the surface of the first porous oxide film layer close to the first plastic layer side provided by embodiment 1-1 of the present application;

[0070] Fig. 7 is a scanning electron microscope (SEM) image of the first nanopore provided by embodiment 1-1 of the present application;

[0071] Fig. 8 is a cross-sectional scanning electron microscope (SEM) image of the first transition oxide film layer and the first porous oxide film layer provided by embodiment 1-1 of the present application;

[0072] Fig. 9 is a scanning electron microscope (SEM) image of the surface of the second porous oxide film layer close to the second plastic layer side provided by embodiment 1-1 of the present application;

[0073] Fig. 10 is a scanning electron microscope (SEM) image of the second nanopore provided by embodiment 1-1 of the present application;

[0074] Fig. 11 is a cross-sectional scanning electron microscope (SEM) image of the second transition oxide film layer and the second porous oxide film layer provided by embodiment 1-1 of the present application;

[0075] Fig. 12 is a schematic diagram of the adhesive of the first plastic layer after the shear strength test provided by embodiment 1-1 of the present application;

[0076] Fig. 13 is a schematic diagram of the adhesive of the second plastic layer after the shear strength test provided by embodiment 1-1 of the present application;

[0077] Fig. 14 is a schematic diagram of the cross-sectional structure of a metal-plastic composite structure provided by an embodiment of the present application;

[0078] Fig. 15 is a schematic diagram of a cross-sectional structure of a metal-plastic composite structure according to another embodiment of the present application;

[0079] Fig. 16 is an enlarged view of region B in Fig. 14;

[0080] Fig. 17 is a schematic diagram of a shear strength test of a metal-plastic composite structure according to an embodiment of the present application;

[0081] Fig. 18 is a flowchart of a method for preparing a metal-plastic composite structure according to an embodiment of the present application;

[0082] Fig. 19 is a scanning electron microscope image of a first oxide film layer of a metal-plastic composite structure prepared according to Example 2-1 of the present application;

[0083] Fig. 20 is a cross-sectional scanning electron microscope image of the first oxide film layer of the metal-plastic composite structure prepared according to Example 2-1 of the present application;

[0084] Fig. 21 is a scanning electron microscope image of a second oxide film layer of the metal-plastic composite structure prepared according to Example 2-1 of the present application;

[0085] Fig. 22 is a cross-sectional scanning electron microscope image of the second oxide film layer of the metal-plastic composite structure prepared according to Example 2-1 of the present application;

[0086] Fig. 23 is a schematic diagram of a cross-sectional structure of a composite metal according to an embodiment of the present application;

[0087] Fig. 24 is a schematic diagram of a concave-convex structure of a composite metal according to an embodiment of the present application;

[0088] Fig. 25 is a metallographic characterization of a cross-sectional morphology of a concave structure of some embodiments of the present application along a thickness direction of the composite metal;

[0089] Fig. 26 is a flowchart of a method for preparing a composite metal according to an embodiment of the present application;

[0090] Fig. 27 is a scanning electron microscope image of a nano-substructure of a concave-convex structure surface of a first metal TC4 titanium alloy according to Example 3-1 of the present application;

[0091] Fig. 28 is a metallographic characterization of a concave-convex structure of the first metal TC4 titanium alloy according to Example 3-1 of the present application;

[0092] Fig. 29 is a metallographic characterization of a cross-sectional structure of the composite metal along a thickness direction according to Example 3-1 of the present application;

[0093] Fig. 30(a) is a metallographic representation of the interface bonding of the first metal TC4 titanium alloy and the connecting metal A380 aluminum alloy in Example 3-1 of the present application; (b) is the EDS (Energy Dispersive Spectroscopy) representation result of the interface bonding;

[0094] Fig. 31 is a schematic diagram of a partial cross-sectional structure of an electronic device shell according to an embodiment of the present application;

[0095] Fig. 32 is a flow chart of a preparation method of an electronic device shell according to an embodiment of the present application;

[0096] Fig. 33 is a top view of a plane to be punched of a composite metal to be punched according to an embodiment of the present application;

[0097] Fig. 34 is an enlarged side view of the thickness direction of region A of the composite metal to be punched in Fig. 33;

[0098] Fig. 35 is a schematic diagram of a partial cross-sectional structure of a punching die according to an embodiment of the present application;

[0099] Fig. 36 is a metallographic representation of the cross-sectional bonding of the outer metal layer and the inner metal layer of the electronic device shell prepared in Example 4-1 of the present application;

[0100] Fig. 37 is a metallographic representation of the grain structure of the extruded region of the outer metal layer and the non-extruded region of the outer metal layer of the electronic device shell prepared in Example 4-1 of the present application;

[0101] Fig. 38 is an EDS (Energy Dispersive Spectroscopy) representation result of the interface bonding of the outer metal layer and the inner metal layer of the electronic device shell prepared in Example 4-1 of the present application.

[0102] Label explanation: metal-plastic composite structure 100, first metal layer 11, second metal layer 12, first transition oxide film layer 13, first porous oxide film layer 14, first plastic layer 15, second transition oxide film layer 16, second porous oxide film layer 17, second plastic layer 18, first oxide film layer 19, second oxide film layer 20, composite metal 200, connecting layer 21, electronic device shell 30, outer metal layer 301, inner metal layer 302, punching die 31, lower die 311, upper die 312, outer metal layer precursor 201, inner metal layer precursor 202, composite metal to be punched 300. DETAILED DESCRIPTION

[0103] With reference to the drawings of the embodiments of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0104] In a first aspect, the present application provides a metal-plastic composite structure 100, comprising a first metal layer 11 and a second metal layer 12 connected to each other, and at least one of: comprising a first transition oxide film layer 13, a first porous oxide film layer 14 and a first plastic layer 15 which are sequentially stacked on the surface of the first metal layer 11 not connected to the second metal layer 12; and comprising a second transition oxide film layer 16, a second porous oxide film layer and a second plastic layer 18 which are sequentially stacked on the surface of the second metal layer 12 not connected to the first metal layer 11; the first metal layer 11 and the second metal layer 12 are metal layers of different materials; the first transition oxide film layer 13 and the first porous oxide film layer 14 contain a first metal oxide, the first porous oxide film layer 14 contains a second metal oxide, at least one of the first metal oxide, the second metal oxide and a metal element in the first metal layer 11 is the same, the porosity of the first transition oxide film layer 13 is less than the porosity of the first porous oxide film layer 14; the second transition oxide film layer 16 contains a third metal oxide, the second porous oxide film layer contains a fourth metal oxide, at least one of the third metal oxide, the fourth metal oxide and a metal element in the second metal layer 12 is the same, and the porosity of the second transition oxide film layer 16 is less than the porosity of the second porous oxide film layer.

[0105] In some embodiments, the first metal oxide and the second metal oxide are oxides of the metal material of the first metal layer 11.

[0106] In some embodiments, the third metal oxide and the fourth metal oxide are oxides of the metal material of the second metal layer 12.

[0107] In some embodiments, the first metal layer 11 has a first surface and a second surface arranged opposite to each other, the second metal layer 12 has a third surface and a fourth surface arranged opposite to each other, the second surface and the third surface are connected to each other in a pasting manner, the first surface has the first transition oxide film layer 13, the first porous oxide film layer 14 and the first plastic layer 15 stacked thereon, and the fourth surface has the second transition oxide film layer 16, the second porous oxide film layer and the second plastic layer 18 stacked thereon.

[0108] In some embodiments, the side of the first metal layer 11 is sequentially stacked with a first transition oxide film layer 13, a first porous oxide film, and a first plastic layer 15, and the side of the second metal layer 12 is sequentially stacked with a second transition oxide film layer 16, a second porous oxide film layer, and a second plastic layer 18.

[0109] In some embodiments, the first metal layer 11 has a first surface and a second surface arranged opposite to each other, and the second metal layer 12 has a third surface and a fourth surface arranged opposite to each other, and the second surface and the third surface are bonded to each other.

[0110] At least one of the following is satisfied: the first surface has a first transition oxide film layer 13, a first porous oxide film layer 14, and a first plastic layer 15 stacked thereon; and the fourth surface has a second transition oxide film layer 16, a second porous oxide film layer, and a second plastic layer 18 stacked thereon.

[0111] In some embodiments, the material of the first metal layer is titanium, magnesium, titanium alloy, magnesium alloy, or stainless steel, and the material of the second metal layer is aluminum or aluminum alloy.

[0112] In some embodiments, the total area ratio of nano-pores on the surface of the first transition oxide film layer close to the first plastic layer is less than or equal to 1%, and the total area ratio of nano-pores on the surface of the first porous oxide film layer close to the first transition oxide film layer is 40%-80%.

[0113] In some embodiments, the total area ratio of nano-pores on the surface of the second transition oxide film layer close to the second plastic layer is less than or equal to 1%, and the total area ratio of nano-pores on the surface of the second porous oxide film layer close to the second transition oxide film layer is 45%-70%.

[0114] In some embodiments, the thickness ratio of the first porous oxide film layer to the first transition oxide film layer is (0.2-2.5):1, and the thickness ratio of the second porous oxide film layer to the second transition oxide film layer is (0.2-2.5):1.

[0115] In some embodiments, the thickness of the first transition oxide film layer is 24nm-3.5μm, and the thickness of the first porous oxide film layer is 60nm-700nm.

[0116] In some embodiments, the thickness of the second transition oxide film layer is 24nm-3.5μm, and the thickness of the second porous oxide film layer is 60nm-700nm.

[0117] In some embodiments, the surface roughness Ra of the side of the first porous oxide film layer close to the first plastic layer is greater than or equal to 1μm.

[0118] In some embodiments, the second porous oxide film layer has a surface roughness Ra of greater than or equal to 2 μm on a side close to the second plastic layer.

[0119] In some embodiments, the first porous oxide film layer includes a plurality of first nanopores.

[0120] In some embodiments, the first nanopores have a pore size of 20 nm-100 nm.

[0121] In some embodiments, the first nanopores have an area percentage of 45%-55% in the first porous oxide film layer.

[0122] In some embodiments, the second porous oxide film layer includes a plurality of second nanopores.

[0123] In some embodiments, the second nanopores have a pore size of 20 nm-40 nm.

[0124] In some embodiments, the second nanopores have an area percentage of 50%-60% in the second porous oxide film layer.

[0125] In some embodiments, at least part of the first nanopores are filled with plastic material; at least part of the second nanopores are filled with plastic material.

[0126] In some embodiments, the shear strength between the first plastic layer and the first metal layer is greater than or equal to 20 MPa.

[0127] In some embodiments, the shear strength between the second plastic layer and the second metal layer is greater than or equal to 25 MPa.

[0128] In some embodiments, the first metal layer 11 and the second metal layer 12 further include a connecting layer 21.

[0129] In some embodiments, the connecting layer includes metal or resin.

[0130] In some embodiments, the connecting layer has a thickness of greater than or equal to 0.05 mm.

[0131] The metal-plastic composite structure provided in the present application has a transition oxide film layer and a porous oxide film layer, and the porous oxide film layer has a greater porosity than the transition oxide film layer, which can improve the bonding capacity of the plastic layer and the metal layer and enhance the reliability of the metal-plastic composite structure.

[0132] In a second aspect, the present application provides a method for preparing a metal-plastic composite structure 100, comprising:

[0133] A to-be-injection-molded composite metal material is provided, which comprises a third metal layer and a fourth metal layer connected to each other;

[0134] At least one of the following is satisfied: a first etching is performed on a surface of the third metal layer which is not connected to the fourth metal layer, to form a fifth metal layer; and a second etching is performed on a surface of the fourth metal layer which is not connected to the third metal layer, to form a sixth metal layer, to obtain an etched to-be-injection-molded composite metal material;

[0135] The etched to-be-injection-molded composite metal material is sequentially subjected to a first anodization treatment and a second anodization treatment, at least one of the following is satisfied: a surface layer of the fifth metal layer which is not connected to the sixth metal layer is sequentially formed from outside to inside with a first porous oxide film layer 14 and a first transition oxide film layer 13, and a surface layer of the sixth metal layer which is not connected to the fifth metal layer is sequentially formed from outside to inside with a second porous oxide film layer and a second transition oxide film layer 16, to obtain an oxidized to-be-injection-molded composite metal material;

[0136] The oxidized to-be-injection-molded composite metal material is subjected to injection molding, at least one of the following is satisfied: a first plastic layer 15 is formed on the surface of the first porous oxide film layer 14; and a second plastic layer 18 is formed on the surface of the second porous oxide film layer, to obtain a metal-plastic composite structure 100.

[0137] In some embodiments, the material of the third metal layer is titanium, magnesium, titanium alloy, magnesium alloy or stainless steel, and the material of the fourth metal layer is aluminum or aluminum alloy.

[0138] In some embodiments, the first etching uses a first etching solution, and the first etching solution comprises at least one of hydrofluoric acid, acetic acid, carbonic acid, hypochlorous acid, phosphoric acid, sodium fluoride, calcium fluoride, ammonium hydrogen fluoride, sodium citrate, sodium chloride and ferric chloride.

[0139] In some embodiments, the concentration of the first etching solution is 5 g / L-30 g / L, the pH value of the first etching solution is 2-5, and the conductivity of the first etching solution is 100 mS / cm-500 mS / cm.

[0140] In some embodiments, the second etching uses a second etching solution, and the second etching solution comprises at least one of nitric acid, sulfuric acid, hydrochloric acid, potassium chloride, ferric chloride, ferrous chloride, copper chloride, magnesium chloride and sodium chloride.

[0141] In some embodiments, the concentration of the second etching solution is 100 g / L-300 g / L, the pH value of the second etching solution is less than or equal to 2, and the conductivity of the second etching solution is 400 mS / cm-1000 mS / cm.

[0142] In some embodiments, the first anodization process employs a first electrolyte, the first electrolyte comprising at least one of potassium dichromate, hydrogen peroxide, hydrofluoric acid, sulfuric acid, phosphoric acid, sodium fluoride, ammonium hydrogen fluoride, and sodium sulfate.

[0143] In some embodiments, the first electrolyte has a concentration of 3-20 g / L and a pH value of 3-6.

[0144] In some embodiments, the first anodization process has a temperature of 10-60℃, a voltage of 5-100 V, and a current of 1-50 A.

[0145] In some embodiments, the second anodization process employs a second electrolyte, the second electrolyte comprising at least one of oxalic acid, citric acid, sodium citrate, sodium sulfate, acetic acid, and phosphoric acid.

[0146] In some embodiments, the second electrolyte has a concentration of 15-25 g / L and a pH value of 1-4.

[0147] In some embodiments, the second anodization process has a temperature of 20-40℃, a voltage of 15-50 V, and a current of 15-50 A.

[0148] In some embodiments, the injection molding has a temperature of 230-320℃ and a pressure of 80-120 MPa.

[0149] The method for preparing the metal-plastic composite structure 100 is novel, simple, environmentally friendly, and produces a product with excellent performance.

[0150] In a third aspect, the application provides a method for preparing a metal composite structure, comprising:

[0151] providing a composite metal material, the composite metal material comprising a third metal layer and a fourth metal layer connected to each other;

[0152] satisfying at least one of the following: performing a first etching on a surface of the third metal layer that is not connected to the fourth metal layer to form a fifth metal layer; and performing a second etching on a surface of the fourth metal layer that is not connected to the third metal layer to form a sixth metal layer, to obtain an etched composite metal material;

[0153] The etched composite metal material is sequentially subjected to a first anodization treatment and a second anodization treatment; at least one of the following is met: the surface layer of the fifth metal layer not connected with the sixth metal layer is formed from outside to inside in sequence with a first porous oxide film layer 14 and a first transition oxide film layer 13; and the surface layer of the sixth metal layer not connected with the fifth metal layer is formed from outside to inside in sequence with a second transition oxide film layer 16 and a second porous oxide film layer, to obtain a metal composite structure; the first transition oxide film layer 13 and the first porous oxide film layer 14 comprise oxides of the material of the first metal layer 11, the first transition oxide film layer 13 comprises a first metal oxide, the first porous oxide film layer 14 comprises a second metal oxide, the first metal oxide, the second metal oxide and at least one metal element in the first metal layer 11 are the same, the porosity of the first transition oxide film layer 13 is less than the porosity of the first porous oxide film layer 14; the second transition oxide film layer 16 comprises a third metal oxide, the second porous oxide film layer comprises a fourth metal oxide, the third metal oxide, the fourth metal oxide and at least one metal element in the second metal layer 12 are the same, and the porosity of the second transition oxide film layer 16 is less than the porosity of the second porous oxide film layer.

[0154] The surface treatment method of the metal composite structure provided by the application is simple, low in processing cost, friendly to the environment, wide in application range, and can be mass-produced industrially.

[0155] In a fourth aspect, the present application provides a metal-plastic composite structure 100, comprising a first metal layer 11 and a second metal layer 12 connected to each other, and satisfying at least one of: comprising a first oxide film layer 19 and a first plastic layer 15 sequentially stacked on a surface of the first metal layer 11 not connected to the first metal layer 11; and comprising a second oxide film layer 20 and a second plastic layer 18 sequentially stacked on a surface of the second metal layer 12 not connected to the first metal layer 11; the first metal layer 11 and the second metal layer 12 are metal layers of different materials; the first oxide film layer 19 comprises a fifth metal oxide, at least one metal element in the fifth metal oxide being the same as at least one metal element in the first metal layer 11, the second oxide film layer 20 comprises a sixth metal oxide, at least one metal element in the sixth metal oxide being the same as at least one metal element in the second metal layer 12, the first oxide film layer 19 and the second oxide film layer 20 are the same or different; at least one of: the first oxide film layer 19 comprises a plurality of third nanometer holes, and the shortest distance between adjacent two third nanometer holes is less than or equal to 50 nm; and the second oxide film layer 20 comprises a plurality of fourth nanometer holes, and the shortest distance between adjacent two fourth nanometer holes is less than or equal to 50 nm.

[0156] In some embodiments, the metal element in the fifth metal oxide is the same as the metal element in the first metal layer.

[0157] In some embodiments, the metal element in the sixth metal oxide is the same as the metal element in the second metal layer.

[0158] In some embodiments, the first metal layer 11 has a first surface and a second surface arranged opposite to each other, the second metal layer 12 has a third surface and a fourth surface arranged opposite to each other, the second surface and the third surface are connected to each other in a pasting manner, the first surface has the first oxide film layer 19 and the first plastic layer 15 stacked thereon, and the fourth surface has the second oxide film layer 20 and the second plastic layer 18 stacked thereon.

[0159] In some embodiments, the side surface of the first metal layer 11 has the first oxide film layer 19 and the first plastic layer 15 stacked thereon in sequence, and the side surface of the second metal layer 12 has the second oxide film layer 20 and the second plastic layer 18 stacked thereon in sequence.

[0160] In some embodiments, the first metal layer 11 has a first surface and a second surface arranged opposite to each other, the second metal layer 12 has a third surface and a fourth surface arranged opposite to each other, the second surface and the third surface are connected to each other in a pasting manner;

[0161] at least one of: the first surface has a first oxide film layer 19 and a first plastic layer 15 stacked; and the fourth surface has a second oxide film layer 20 and a second plastic layer 18 stacked.

[0162] In some embodiments, the material of the first metal layer 11 includes titanium or titanium alloy, and the material of the second metal layer includes aluminum or aluminum alloy.

[0163] In some embodiments, the average pore diameter of the third nanopores is 10-70 nm, the average center-to-center distance between two adjacent third nanopores is less than or equal to 150 nm, and the pore depth of the third nanopores is 100-1000 nm.

[0164] In some embodiments, the average pore diameter of the fourth nanopores is 10-50 nm, the average center-to-center distance between two adjacent fourth nanopores is less than or equal to 100 nm, and the pore depth of the fourth nanopores is 100-3000 nm.

[0165] In some embodiments, the difference between the average pore diameter of the third nanopores and the average pore diameter of the fourth nanopores is less than or equal to 30 nm.

[0166] In some embodiments, the porosity of the first oxide film layer is 20-90%.

[0167] In some embodiments, the surface roughness Ra of the side of the first oxide film layer close to the first plastic layer is 0.1-20 μm.

[0168] In some embodiments, the thickness of the first oxide film layer is 100-1000 nm.

[0169] In some embodiments, the porosity of the second oxide film layer is 20-90%.

[0170] In some embodiments, the surface roughness Ra of the side of the second oxide film layer close to the second plastic layer is 0.1-50 μm.

[0171] In some embodiments, the thickness of the second oxide film layer is 100-3000 nm.

[0172] In some embodiments, the third nanopores and the fourth nanopores are filled with plastic material.

[0173] In some embodiments, the thickness of the first plastic layer and the second plastic layer is 0.1-200 mm.

[0174] In some embodiments, the shear strength between the first plastic layer and the first metal layer is greater than or equal to 20 MPa.

[0175] In some embodiments, the shear strength between the second plastic layer and the second metal layer is greater than or equal to 25 MPa.

[0176] In some embodiments, the first metal layer 11 and the second metal layer 12 further comprise a connecting layer 21.

[0177] In some embodiments, the connecting layer comprises metal or resin.

[0178] In some embodiments, the thickness of the connecting layer is greater than or equal to 0.05 mm.

[0179] The metal-plastic composite structure provided by the present application has strong bonding force between the plastic layer and the metal layer and high structural stability.

[0180] In a fifth aspect, the present application provides a preparation method of a metal-plastic composite structure, comprising:

[0181] providing a to-be-injection-molded composite metal material, the to-be-injection-molded composite metal material comprising a seventh metal layer and a fourth metal layer connected to each other; placing the to-be-injection-molded composite metal material in a fluorine-containing electrolyte, and after an anodic oxidation treatment, at least one of the following is met: forming a first oxide film layer on a surface layer of the seventh metal layer that is not connected to the fourth metal layer; and forming a second oxide film layer on a surface layer of the fourth metal layer that is not connected to the seventh metal layer, to obtain an oxidized to-be-injection-molded composite metal material; injection molding the oxidized to-be-injection-molded composite metal material, at least one of the following is met: forming a first plastic layer on the surface of the first oxide film layer; and forming a second plastic layer on the surface of the second oxide film layer, to obtain a metal-plastic composite structure.

[0182] In some embodiments, the material of the seventh metal layer comprises titanium or titanium alloy, and the material of the fourth metal layer comprises aluminum or aluminum alloy.

[0183] In some embodiments, the fluorine-containing electrolyte comprises fluoride and corrosion inhibitor.

[0184] In some embodiments, the fluoride comprises at least one of potassium fluoride, sodium fluoride, ammonium fluoride, ammonium bifluoride, fluorozirconate, fluoroborate, hydrofluoric acid, fluorozirconic acid, and fluoroboric acid.

[0185] In some embodiments, the corrosion inhibitor is an oxidizing corrosion inhibitor or a non-oxidizing corrosion inhibitor.

[0186] In some embodiments, the voltage of the anodization treatment is 5V-50V, the time of the anodization treatment is 1min-60min, and the temperature of the anodization treatment is 5℃-80℃.

[0187] In some embodiments, the temperature of the injection molding is 200℃-500℃, and the pressure of the injection molding is 75MPa-300MPa.

[0188] The preparation method of the metal-plastic composite structure provided by the application is novel, simple, and can produce a metal-plastic composite structure with strong bonding force between the metal layer and the plastic layer.

[0189] In a sixth aspect, the application provides a preparation method of a metal composite structure, comprising: providing a composite metal material, wherein the composite metal material comprises a seventh metal layer and a fourth metal layer connected to each other;

[0190] The composite metal material is placed in a fluorine-containing electrolyte, and after anodization treatment, at least one of the following conditions is met: a surface layer of the seventh metal layer that is not connected to the eighth metal layer forms a first oxide film layer 19; and a surface layer of the eighth metal layer that is not connected to the seventh metal layer forms a second oxide film layer 20, to obtain an oxidized injection-molding composite metal material; the first metal layer 11 and the second metal layer 12 are metal layers of different materials; the first oxide film layer 19 comprises a fifth metal oxide, at least one metal element in the fifth metal oxide being the same as at least one metal element in the first metal layer 11, the second oxide film layer 20 comprises a sixth metal oxide, at least one metal element in the sixth metal oxide being the same as at least one metal element in the second metal layer 12, the first oxide film layer 19 and the second oxide film layer 20 being the same or different; at least one of the following conditions is met: the first oxide film layer 19 comprises a plurality of third nanoholes, and the shortest distance between adjacent two third nanoholes is less than or equal to 50nm; and the second oxide film layer 20 comprises a plurality of fourth nanoholes, and the shortest distance between adjacent two fourth nanoholes is less than or equal to 50nm.

[0191] The preparation method of the metal composite structure provided by the application is simple, has low preparation cost, and produces a metal composite structure with excellent performance.

[0192] In a seventh aspect, the present application provides a composite metal 200, comprising a first metal layer 11 and a second metal layer 12 arranged in a stack, and a connecting layer 21 arranged between the first metal layer 11 and the second metal layer 12, the first metal layer 11 and the second metal layer 12 being different metal layers; at least one of the following conditions is satisfied: a surface of the first metal layer 11 combined with the connecting layer 21 is provided with at least one concave-convex structure, and a surface of the second metal layer 12 combined with the connecting layer 21 is provided with at least one concave-convex structure; and at least one of the following conditions is satisfied: the concave-convex structure comprises at least one concave structure, and at least one convex structure.

[0193] In some embodiments, at least one of the following conditions is satisfied: the concave-convex structure comprises a plurality of concave structures, and a plurality of convex structures.

[0194] In some embodiments, a distance between two adjacent concave structures is 0.1 mm-0.5 mm.

[0195] In some embodiments, a depth of the concave structure is 100 μm-500 μm, and a lateral dimension of the concave structure is 50 μm-350 μm.

[0196] In some embodiments, a cross-sectional shape of each concave structure along a thickness direction of the composite metal is rectangular, trapezoidal, triangular, or T-shaped.

[0197] In some embodiments, an inner surface of at least one concave structure is provided with a first nano-substructure; the first nano-substructure comprises nano-holes, and a diameter of the nano-hole is 50 nm-500 nm.

[0198] In some embodiments, an outer surface of at least one convex structure is provided with a second nano-substructure; the second nano-substructure comprises nano-holes, and a diameter of the nano-hole is 50 nm-500 nm.

[0199] In some embodiments, at least one of the following conditions is satisfied: a surface roughness of the concave structure is 10 μm-25 μm, and a surface roughness of the convex structure is 10 μm-25 μm.

[0200] In some embodiments, the connecting layer comprises metal or resin; the metal comprises at least one of magnesium and its alloy, aluminum and its alloy, zinc and its alloy, copper and its alloy; and the resin comprises at least one of polybutylene terephthalate, polyphenylene sulfide, polyamide, polyphthalamide, polypropylene, polycarbonate, polyphenylene sulfone, polyether ether ketone.

[0201] In some embodiments, the connecting layer comprises a metal, and the ratio of the hardness of the connecting layer to the hardness of the metal layer with smaller hardness among the first metal layer and the second metal layer is 1:(0.8-1.2).

[0202] In some embodiments, the coefficient of thermal expansion of the connecting layer is 2x10-5 / K-2.7x10-5 / K, and the ratio of the coefficient of thermal expansion of the connecting layer to the coefficient of thermal expansion of the metal layer with larger coefficient of thermal expansion among the first metal layer and the second metal layer is 1:(0.8-1.2).

[0203] In some embodiments, the connecting layer and the first metal layer are different metal layers, and the intermetallic diffusion depth at the interface between the connecting layer and the first metal layer is 1-10 μm; the connecting layer and the second metal layer are different metal layers, and the intermetallic diffusion depth at the interface between the connecting layer and the second metal layer is 1-10 μm.

[0204] In some embodiments, the shear strength between the first metal layer and the second metal layer is greater than or equal to 100 MPa.

[0205] In some embodiments, the first metal layer comprises at least one of magnesium and its alloys, aluminum and its alloys, copper and its alloys, iron and its alloys, zirconium and its alloys, titanium and its alloys, manganese and its alloys, chromium and its alloys, and zinc and its alloys.

[0206] In some embodiments, the second metal layer comprises at least one of magnesium and its alloys, aluminum and its alloys, copper and its alloys, iron and its alloys, zirconium and its alloys, titanium and its alloys, manganese and its alloys, chromium and its alloys, and zinc and its alloys.

[0207] In some embodiments, the first metal layer comprises at least one of iron and its alloys, zirconium and its alloys, and titanium and its alloys.

[0208] In some embodiments, the second metal layer comprises at least one of magnesium and its alloys, aluminum and its alloys, copper and its alloys, and zinc and its alloys.

[0209] In some embodiments, the first metal layer comprises a titanium alloy, the second metal layer comprises a 6013 aluminum alloy, and the connecting layer comprises an A380 aluminum alloy.

[0210] In some embodiments, the thickness of the first metal layer is greater than or equal to 0.2 mm; the thickness of the second metal layer is greater than or equal to 0.2 mm; and the thickness of the connecting layer is greater than or equal to 0.05 mm.

[0211] The composite metal provided by the application effectively improves the combination between the first metal layer and the second metal layer of the composite metal by arranging the concave-convex structure on the surface of the first metal layer and the second metal layer and connecting through the connecting layer, thereby improving the performance of the composite metal in processing and forming, and meeting the higher processing requirements.

[0212] In an eighth aspect, the application provides a preparation method of the composite metal provided in the seventh aspect, comprising:

[0213] performing roughening treatment on the surfaces to be combined of the first metal and the second metal, so that the surfaces to be combined of the first metal and the second metal form a plurality of concave-convex structures;

[0214] placing the surfaces with the concave-convex structures of the first metal and the second metal opposite to each other, and compositely connecting a connecting layer between the first metal and the second metal through solid-liquid combination; and obtaining a composite metal.

[0215] In some embodiments, the surface roughening treatment comprises at least one of milling processing and laser engraving.

[0216] In some embodiments, the surface roughening treatment further comprises chemical etching, and at least one of the following is satisfied: the chemical etching is performed after the milling processing, and the chemical etching is performed after the laser engraving processing.

[0217] The preparation method of the composite metal provided by the application is novel, the preparation process is simple, and the combination performance between the heterogeneous metals of the composite metal prepared is excellent.

[0218] In a ninth aspect, the application provides an application of the metal-plastic composite structure provided in the first aspect or the fourth aspect, or the metal-plastic composite structure prepared by the preparation method provided in the second aspect or the sixth aspect, or the metal composite structure provided in the third aspect or the seventh aspect, in electronic devices, vehicles and electrical appliances.

[0219] The application scenarios of the metal-plastic composite structure or the metal composite structure provided by the application are wide, which is beneficial to the commercial application thereof.

[0220] In a tenth aspect, the application provides a structural member, and the application provides an application of the metal-plastic composite structure provided in the first aspect or the fourth aspect, or the metal-plastic composite structure prepared by the preparation method provided in the second aspect or the sixth aspect, or the metal composite structure provided in the third aspect or the seventh aspect, in electronic devices, vehicles and electrical appliances.

[0221] The structural member provided by the application has high structural stability, long service life and low preparation cost, which is beneficial to large-scale application thereof.

[0222] In some embodiments, the structural member comprises an electronic device shell.

[0223] In some embodiments, the electronic device housing 30 comprises an outer metal layer 301 and an inner metal layer 302 arranged in a stack, the outer metal layer 301 and the inner metal layer 302 are metal layers of different materials; the electronic device housing 30 has at least one first R corner, the first R corner is greater than or equal to 0.1 mm; at the first R corner, the cross-section junction of the outer metal layer 301 and the inner metal layer 302 has a junction line, the straightness of the junction line is less than 0.1 mm.

[0224] In some embodiments, at the interface junction of the outer metal layer 301 and the inner metal layer 302, the diffusion depth between the metals is 0.1-10 μm.

[0225] In some embodiments, the average grain size deviation of the outer metal layer is less than or equal to 10%.

[0226] In some embodiments, the thickness of the outer metal layer is greater than or equal to 0.2 mm.

[0227] In some embodiments, the outer metal layer comprises at least one of aluminum and its alloys, titanium and its alloys, iron and its alloys, and zirconium and its alloys; the inner metal layer comprises at least one of aluminum and its alloys, copper and its alloys, zinc and its alloys, and magnesium and its alloys.

[0228] In some embodiments, the elastic modulus of the outer metal layer is greater than or equal to 70 GPa, and the elastic modulus of the outer metal layer is greater than that of the inner metal layer.

[0229] In some embodiments, the yield strength of the outer metal layer is greater than or equal to 150 MPa, and the strength of the outer metal layer is greater than that of the inner metal layer.

[0230] In some embodiments, the thermal conductivity of the inner metal layer is greater than or equal to 100 W·m-1·k-1, and the thermal conductivity of the inner metal layer is greater than that of the outer metal layer.

[0231] In some embodiments, the density of the inner metal layer is greater than or equal to 1.2 g / cm3, and the density of the inner metal layer is less than that of the outer metal layer.

[0232] In some embodiments, the bonding strength of the inner metal layer and the outer metal layer is greater than or equal to 70 MPa.

[0233] The electronic device shell provided by the application has a small R angle, can form a structure close to a right angle, the thickness of the outer metal layer and the inner metal layer is uniform, the straightness of the bonding line at the interface is small, and the comprehensive mechanical property of the electronic device shell is excellent.

[0234] In some embodiments, the application provides a method for manufacturing an electronic device shell, comprising:

[0235] A composite metal to be punched is provided, which comprises a first metal layer and a second metal layer arranged in a stack; the first metal layer is used to form the outer metal layer, and the second metal layer is used to form the inner metal layer;

[0236] The composite metal to be punched is placed in a punching die for punching treatment, and then subjected to heat treatment to obtain an electronic device shell blank;

[0237] The electronic device shell blank is milled to obtain an electronic device shell.

[0238] In some embodiments, the edge of the first metal layer 11 away from the second metal layer 12 has at least one second R angle, which satisfies 3t1≤second R angle≤6t1; the edge of the second metal layer 12 away from the first metal layer 11 has a third R angle at the corresponding position of the second R angle, which satisfies 7t2≤third R angle≤13t2, wherein t1 is the thickness of the first metal layer 11, and t2 is the thickness of the second metal layer 12.

[0239] In some embodiments, the second R angle transitions to the third R angle at the corresponding position of the second R angle to form a slope, and the thickness gradually decreases from the second metal layer 12 to the first metal layer 11 in the direction of the slope.

[0240] In some embodiments, the slope angle is greater than or equal to 10° and less than or equal to 40°, the distance L1 from the vertex of the second R angle to the vertex of the third R angle is greater than or equal to 2t, and the slope height h is less than or equal to t, wherein t is the thickness of the composite metal to be punched.

[0241] In some embodiments, the punching die 31 comprises an upper die 312 and a lower die 311, the lower die 311 comprises a groove, a convex portion is arranged around the position where the inner wall bottom of the groove is connected with the side wall, the first metal layer 11 of the composite metal to be punched 300 is in contact with the groove of the lower die 311, the convex portion comprises a horizontal boss, the width L2 of the horizontal boss is greater than or equal to t2, and the height D of the horizontal boss satisfies 1 / 4t1≤D≤t1.

[0242] In some embodiments, the stamping temperature T1 of the stamping process satisfies: 1 / 4Tm≤T1<Tm, wherein Tm is the minimum of the melting point of the outer metal layer 301 and the melting point of the inner metal layer 302; the stamping time of the stamping process is 3s-15s; and the pressure holding time of the stamping process is 30s-60s.

[0243] In some embodiments, the temperature T2 of the heat treatment satisfies: T2≤1 / 3Tm; and the time of the heat treatment is 30min-120min.

[0244] In some embodiments, the milling is followed by an injection molding process.

[0245] The method for preparing the electronic device shell provided in the present application is novel. By specially designing the to-be-stamped composite metal, the stamping die, and the parameters of stamping and heat treatment, the thickness of the outer metal layer and the inner metal layer of the prepared electronic device shell is uniform, the straightness of the bonding line at the cross-section bonding site is small, the comprehensive mechanical properties of the electronic device shell are excellent, and the grain structure of the electronic device shell is uniform, which facilitates subsequent uniform coloring.

[0246] In some embodiments, the electronic device shell is used in an electronic device middle frame.

[0247] In an eleventh aspect, the present application provides an electronic device comprising the structural member of the tenth aspect.

[0248] The structural member (electronic device shell) of the electronic device provided in the present application has excellent mechanical properties and heat dissipation performance and is low in density and light in weight, and has good mechanical properties, good user experience, and long service life.

[0249] Referring to FIG. 1, a schematic diagram of a cross-section structure of a metal-plastic composite structure according to an embodiment of the present application is shown. The metal-plastic composite structure 100 according to the present application comprises a first metal layer 11 and a second metal layer 12 connected to each other, and comprises a first transition oxide film layer 13, a first porous oxide film layer 14 and a first plastic layer 15 sequentially stacked on a surface of the first metal layer 11 not connected to the second metal layer 12, and comprises a second transition oxide film layer 16, a second porous oxide film layer 17 and a second plastic layer 18 sequentially stacked on a surface of the second metal layer 12 not connected to the first metal layer 11; the first metal layer 11 and the second metal layer 12 are metal layers of different materials; the first transition oxide film layer 13 comprises a first metal oxide, the first porous oxide film layer 14 comprises a second metal oxide, at least one metal element in the first metal oxide, the second metal oxide and the first metal layer 11 is the same, the porosity of the first transition oxide film layer 13 is less than the porosity of the first porous oxide film layer 14; the second transition oxide film layer 16 comprises a third metal oxide, the second porous oxide film layer 17 comprises a fourth metal oxide, at least one metal element in the third metal oxide, the fourth metal oxide and the second metal layer 12 is the same, the porosity of the second transition oxide film layer 16 is less than the porosity of the second porous oxide film layer 17. The metal-plastic composite structure according to the present application has a transition oxide film layer and a porous oxide film layer, wherein the porous oxide film layer has a greater porosity than the transition oxide film layer, which can improve the bonding force between the plastic layer and the metal layer and improve the comprehensive performance of the metal-plastic composite structure; and the transition oxide film layer has a smaller porosity and a higher strength than the porous oxide film layer, which can be used as a transition layer to connect the porous oxide film layer and the metal layer, avoid the shedding of the porous oxide film layer, improve the bonding force between the metal and the plastic, and at the same time make the composite structure have a high intrinsic strength, so as to balance the strength and the bonding force of the composite structure.

[0250] In the embodiment shown in FIG. 1, the first metal layer has a first surface S1 and a second surface S2 arranged oppositely, the second metal layer has a third surface S3 and a fourth surface S4 arranged oppositely, the second surface S2 is attached to the third surface S3 to connect to each other, the first surface S1 has the first transition oxide film layer 13, the first porous oxide film layer 14 and the first plastic layer 15 stacked thereon, and the fourth surface S4 has the second transition oxide film layer 16, the second porous oxide film layer 17 and the second plastic layer 18 stacked thereon.

[0251] In the embodiment of the present application, the transition oxide film layer and the porous oxide film layer can be arranged on the surface of the first metal layer 11 only or the second metal layer 12 only. In this case, the metal-plastic composite structure 100 comprises the first metal layer 11 and the second metal layer 12 connected to each other, and the first transition oxide film layer 13, the first porous oxide film layer 14 and the first plastic layer 15 arranged on the surface of the first metal layer 11 not connected to the second metal layer 12 in sequence. Alternatively, the metal-plastic composite structure 100 comprises the first metal layer 11 and the second metal layer 12 connected to each other, and the second transition oxide film layer 16, the second porous oxide film layer 17 and the second plastic layer 18 arranged on the surface of the second metal layer 12 not connected to the first metal layer 11 in sequence. In the embodiment of the present application, the transition oxide film layer and the porous oxide film layer can be arranged on the surface of the first metal layer 11 and the second metal layer 12 simultaneously. In this case, the metal-plastic composite structure 100 comprises the first metal layer 11 and the second metal layer 12 connected to each other, and the first transition oxide film layer 13, the first porous oxide film layer 14 and the first plastic layer 15 arranged on the surface of the first metal layer 11 not connected to the second metal layer 12 in sequence, and the second transition oxide film layer 16, the second porous oxide film layer 17 and the second plastic layer 18 arranged on the surface of the second metal layer 12 not connected to the first metal layer 11 in sequence.

[0252] It should be noted that the specific shape and size of the first metal layer 11 and the second metal layer 12 in the embodiment of the present application are not limited, and can be designed according to actual needs. The first metal layer 11 and the second metal layer 12 can have regular shapes or irregular shapes, and can have uniform thickness or non-uniform thickness.

[0253] In the embodiment of the present application, the first transition oxide film layer 13, the first porous oxide film layer 14 and the first plastic layer 15 can be arranged on part or all of the surface of the first metal layer 11 not connected to the second metal layer 12 in sequence as needed. The second transition oxide film layer 16, the second porous oxide film layer 17 and the second plastic layer 18 can be arranged on part or all of the surface of the second metal layer 12 not connected to the first metal layer 11 in sequence as needed.

[0254] Referring to FIG. 2, a cross-sectional structural schematic diagram of the metal-plastic composite structure 100 provided by another embodiment of the present application is shown. In this embodiment, the metal-plastic composite structure 100 includes the first metal layer 11 and the second metal layer 12 which are arranged in layers, and includes the first transition oxide film layer 13, the first porous oxide film layer 14 and the first plastic layer 15 which are arranged in layers on the side of the first metal layer 11, and includes the second transition oxide film layer 16, the second porous oxide film layer 17 and the second plastic layer 18 which are arranged in layers on the side of the second metal layer 12. In the embodiment shown in FIG. 2, the metal-plastic composite structure 100 includes both the first plastic layer 15 and the second plastic layer 18, and the first plastic layer 15 and the second plastic layer 18 are arranged adjacently on the same side, at this time, the first plastic layer 15 and the second plastic layer 18 are an integral structure, and the first plastic layer 15 and the second plastic layer 18 are of the same material. In some embodiments, the transition oxide film, the porous oxide film layer and the plastic layer are arranged on the side of the first metal layer 11 and the second metal layer 12, and at the same time, at least one of the following conditions is met: the first transition oxide film layer 13, the first porous oxide film layer 14 and the first plastic layer 15 are arranged on the first surface S1, and the second transition oxide film layer 16, the second porous oxide film layer 17 and the second plastic layer 18 are arranged on the fourth surface S4.

[0255] The metal-plastic composite structure 100 provided by the present application has the first metal layer 11 and the second metal layer 12, and the first metal layer 11 and the second metal layer 12 are different metals, which can have the performance advantages of different metal materials and is beneficial to improve the comprehensive performance of the metal-plastic composite structure 100. In an embodiment of the present application, the material of the first metal layer 11 can be but is not limited to titanium, magnesium, titanium alloy, magnesium alloy or stainless steel, and the material of the second metal layer 12 can be but is not limited to aluminum or aluminum alloy. Titanium or titanium alloy, stainless steel and magnesium or magnesium alloy have characteristics such as wear resistance, corrosion resistance and small density, and aluminum material has good thermal conductivity, is easy to process and has low cost, which is beneficial to improve the strength and light weight of the metal-plastic composite structure 100. Specifically, the grade of the titanium alloy can be but is not limited to TA1, TA2, TA3, TA4, TA5, T6, TA7, TA8, TA18, TB2, TB3, TB4, TB5, TB6, TC1, TC2, TC3, TC4 or TC6, etc.; the grade of the stainless steel can be but is not limited to 201, 202, 304, 316L, 420 or 440, etc.; the grade of the magnesium alloy can be but is not limited to AZ31B, AZ91D or ZK61M, etc.; and the grade of the aluminum alloy can be but is not limited to ADC10, ADC12, GM55, 1016, 1024, 5005, 5052, 6013, 6063, 6061, 7075 or 7550, etc. In an embodiment of the present application, the material of the first metal layer 11 can be TA5, and the material of the second metal layer 12 can be 6061.

[0256] In an embodiment of the present application, the connecting layer 21 is arranged between the first metal layer 11 and the second metal layer 12, the connecting layer 21 comprises metal or resin, and the thickness of the connecting layer 21 is greater than or equal to 0.05 mm, which can improve the bonding capacity between the first metal layer 11 and the second metal layer 12. The detailed description of the connecting layer 21 is given below.

[0257] In an embodiment of the present application, the first transition oxide film layer 13 and the first porous oxide film layer 14 comprise oxides of the metal material of the first metal layer 11, the first transition oxide film layer 13 comprises a first metal oxide, the first porous oxide film layer 14 comprises a second metal oxide, and at least one metal element in the first metal oxide, the second metal oxide and the first metal layer 11 is the same. For example, when the metal material of the first metal layer 11 is titanium, the first transition oxide film layer and the first porous oxide film layer 14 comprise titanium oxide; when the metal material of the first metal layer 11 is magnesium, the first transition oxide film layer and the first porous oxide film layer 14 comprise magnesium oxide.

[0258] In the present application, the first transition oxide film layer 13 is close to the first metal layer 11, and the porosity of the first transition oxide film layer 13 is less than the porosity of the first porous oxide film layer 14. The porosity of the first transition oxide film layer 13 is characterized by the total area ratio of the nano-pores on the surface of the first transition oxide film layer 13 close to the first porous oxide film layer 14, and the total area ratio of the nano-pores on the surface of the first transition oxide film layer 13 close to the first porous oxide film layer 14 is less than or equal to 1%, wherein the nano-pores are pores with a pore size less than or equal to 100 nm, which can be obtained by scanning electron microscopy (SEM) scanning the surface of the first transition oxide film layer 13 close to the first porous oxide film layer 14. The first transition oxide film has high strength and is a dense structure, which can be used as a transition layer to connect the first porous oxide film layer 14 and the first metal layer 11, avoid the shedding of the first porous oxide film layer 14, improve the metal-plastic bonding force, and at the same time make the composite structure have high intrinsic strength, so as to balance the strength and bonding force of the composite structure. Specifically, the total area ratio of the nano-pores on the surface of the first transition oxide film layer 13 close to the first porous oxide film layer 14 can be but not limited to less than or equal to 1%, less than or equal to 0.8%, less than or equal to 0.7%, less than or equal to 0.6% or less than or equal to 0.5%, etc. In an embodiment of the present application, the total area ratio of the nano-pores on the surface of the first transition oxide film layer 13 close to the first porous oxide film layer 14 can be less than or equal to 0.5%. In another embodiment of the present application, the total area ratio of the nano-pores on the surface of the first transition oxide film layer 13 close to the first porous oxide film layer 14 can be less than or equal to 0.3%.

[0259] In an embodiment of the present application, the thickness of the first transition oxide film layer 13 is 24 nm-3.5 μm. The suitable first transition oxide film layer 13 can prevent the first porous oxide film layer 14 from falling off, thereby improving the bonding ability between the first metal layer 11 and the first plastic layer 15. Specifically, the thickness of the first transition oxide film layer 13 can be, but is not limited to, 24 nm, 90 nm, 100 nm, 500 nm, 1000 nm, 2 μm, 3 μm or 3.5 μm, etc. In an embodiment of the present application, the thickness of the first transition oxide film layer 13 can be 24 nm-1 μm. In another embodiment of the present application, the thickness of the first transition oxide film layer 13 can be 1 μm-3.5 μm.

[0260] In an embodiment of the present application, the total area ratio of the nano-pores on the surface of the first porous oxide film layer 14 close to the first plastic layer 15 is 40%-80%, and the first porous oxide film layer 14 is a loose porous structure. The total area ratio of the nano-pores on the surface of the first porous oxide film layer 14 close to the first plastic layer 15 represents the porosity of the first porous oxide film layer 14, wherein the nano-pores are pores with a pore size less than or equal to 100 nm, which can be obtained by scanning the surface of the first porous oxide film layer 14 close to the first plastic layer 15 by scanning electron microscopy (SEM). The suitable porosity can improve the bonding ability between the first metal layer 11 and the first plastic layer 15, and improve the bonding ability of the metal-plastic composite structure 100. Specifically, the total area ratio of the nano-pores on the surface of the first porous oxide film layer 14 close to the first plastic layer 15 can be, but is not limited to, 40%, 50%, 60%, 70% or 80%, etc. In an embodiment of the present application, the total area ratio of the nano-pores on the surface of the first porous oxide film layer 14 close to the first plastic layer 15 can be 40%-70%. In an embodiment of the present application, the total area ratio of the nano-pores on the surface of the first porous oxide film layer 14 close to the first plastic layer 15 can be 60%-80%.

[0261] In an embodiment of the present application, the thickness ratio of the first porous oxide film layer 14 and the first transition oxide film layer 13 is (0.2-2.5):1. The suitable first porous oxide film layer 14 and the first transition oxide film layer 13 can make the first dense oxide layer have a certain strength, prevent the first porous oxide film layer 14 from falling off, and improve the bonding force between the first metal layer 11 and the first plastic layer 15. Specifically, the thickness ratio of the first porous oxide film layer 14 and the first transition oxide film layer 13 can be, but is not limited to, 0.2:1, 0.5:1, 0.7:1, 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1, or 2.5:1, etc. In an embodiment of the present application, the thickness ratio of the first porous oxide film layer 14 and the first transition oxide film layer 13 can be (0.2-1.8):1. In another embodiment of the present application, the thickness ratio of the first porous oxide film layer 14 and the first transition oxide film layer 13 can be (1.5-2.5):1.

[0262] In an embodiment of the present application, the thickness of the first porous oxide film layer 14 is 60nm-700nm. The suitable first porous oxide film layer 14 can improve the bonding ability between the first metal layer 11 and the first plastic layer 15. Specifically, the thickness of the first porous oxide film layer 14 can be, but is not limited to, 60nm, 100nm, 200nm, 400nm, 600nm, or 700nm, etc. In an embodiment of the present application, the thickness of the first porous oxide film layer 14 can be 60nm-500nm. In another embodiment of the present application, the thickness of the first porous oxide film layer 14 can be 400nm-700nm.

[0263] Referring to FIG. 3, which is an enlarged view of the area A in FIG. 1, it can be seen that the surface of the first porous oxide film layer 14 is an uneven surface, and the surface roughness Ra of the side of the first porous oxide film layer 14 close to the first plastic layer 15 is greater than or equal to 1μm, which increases the specific surface area of the side of the first porous oxide film layer 14 close to the first plastic layer 15, and the concave-convex interlocking structure formed between the first plastic layer 15 and the first porous oxide film layer 14 is beneficial to improve the reliability of the metal-plastic composite structure 100. Specifically, the surface roughness Ra of the side of the first porous oxide film layer 14 close to the first plastic layer 15 can be, but is not limited to, greater than or equal to 1μm, greater than or equal to 1.5μm, greater than or equal to 2μm, greater than or equal to 2.5μm, or greater than or equal to 3μm, etc. In an embodiment of the present application, the surface roughness Ra of the side of the first porous oxide film layer 14 close to the first plastic layer 15 can be greater than or equal to 2.3μm. In another embodiment of the present application, the surface roughness Ra of the side of the first porous oxide film layer 14 close to the first plastic layer 15 can be greater than or equal to 2.5μm.

[0264] In an embodiment of the present application, the first porous oxide film layer 14 includes a plurality of first nanopores, and at least part of the first nanopores are filled with plastic material, so as to improve the bonding force between the first metal layer 11 and the first plastic layer 15. In some embodiments, all the first nanopores in the first porous oxide film layer 19 are filled with plastic material. In other embodiments, at least part of the first nanopores are completely filled with plastic material, and at least part of the first nanopores are partially filled with plastic material.

[0265] In an embodiment of the present application, the first nanopores have a pore size of 20 nm to 100 nm. The appropriate pore size of the first nanopores increases the specific surface area of the first nanopores, promotes the entry of plastic material, and improves the bonding force between the first metal layer 11 and the first plastic layer 15. Specifically, the pore size of the first nanopores can be, but is not limited to, 20 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, or 100 nm, etc. In an embodiment of the present application, the pore size of the first nanopores can be 20 nm to 80 nm. In another embodiment of the present application, the pore size of the first nanopores can be 60 nm to 100 nm.

[0266] In an embodiment of the present application, the first nanopores have a pore depth of 60 nm to 700 nm. The appropriate pore depth can promote the entry of plastic material into the pores, thereby improving the bonding force between the first metal layer 11 and the first plastic layer 15. Specifically, the pore depth of the first nanopores can be, but is not limited to, 60 nm, 90 nm, 100 nm, 200 nm, 400 nm, 600 nm, or 700 nm, etc. In an embodiment of the present application, the pore depth of the first nanopores can be 60 nm to 550 nm. In another embodiment of the present application, the pore depth of the first nanopores can be 500 nm to 700 nm.

[0267] In an embodiment of the present application, the thickness and shape of the first plastic layer 15 can be designed according to actual needs. The first plastic layer 15 can have a regular shape or an irregular shape, and can be a layer structure with uniform thickness or non-uniform thickness.

[0268] In an embodiment of the present application, at least part of the first porous oxide film layer 14 is covered by the first plastic layer 15. That is, the covering mode of the first plastic layer 15 can be set according to actual needs. The first plastic layer 15 can cover all the first porous oxide film layers 14, or the first plastic layer 15 can cover part of the first porous oxide film layers 14.

[0269] Referring to FIG. 4, a shear strength test principle diagram of the metal-plastic composite structure 100 provided by an embodiment of the present application is shown. The shear strength between the first plastic layer 15 and the first metal layer 11 is greater than or equal to 20 MPa, which improves the bonding capacity between the first plastic layer 15 and the first metal layer 11. The test process is as follows: a 4 mm x 4 mm x 4 mm plastic block is injection molded on the surface of the first porous oxide film layer 14, a push force tester is used to push the side of the plastic block, and the maximum force during the pushing process is recorded to calculate the maximum stress, which is the shear strength between the first plastic layer 15 and the first metal layer 11. Specifically, the shear strength between the first plastic layer 15 and the first metal layer 11 can be, but is not limited to, greater than or equal to 20 MPa, greater than or equal to 21 MPa, greater than or equal to 22 MPa, greater than or equal to 23 MPa, greater than or equal to 24 MPa, or greater than or equal to 25 MPa, etc. In an embodiment of the present application, the shear strength between the first plastic layer 15 and the first metal layer 11 can be greater than or equal to 23 MPa. In another embodiment of the present application, the shear strength between the first plastic layer 15 and the first metal layer 11 can be greater than or equal to 25 MPa.

[0270] In an embodiment of the present application, after the shear strength test, the residual area of the first plastic layer 15 on the surface of the first metal layer 11 is greater than or equal to 95%. That is, the bonding force between the first plastic layer 15 and the first metal layer 11 is large, and after the shear strength test, the first plastic layer 15 and the first metal layer 11 cannot be completely separated, and at least part of the plastic material remains on the surface of the first metal layer 11. Specifically, after the shear strength test, the residual area of the first plastic layer 15 on the surface of the first metal layer 11 can be, but is not limited to, greater than or equal to 95%, greater than or equal to 96%, greater than or equal to 97%, greater than or equal to 98%, or greater than or equal to 99%, etc. In an embodiment of the present application, after the shear strength test, the residual area of the first plastic layer 15 on the surface of the first metal layer 11 can be greater than or equal to 96%.

[0271] In an embodiment of the present application, the second transition oxide film layer 16 and the second porous oxide film layer 17 comprise oxides of the material of the second metal layer 12. The second transition oxide film layer 16 comprises a third metal oxide, and the second porous oxide film layer 17 comprises a fourth metal oxide. The third metal oxide, the fourth metal oxide, and at least one metal element in the second metal layer 12 are the same. For example, when the metal material of the second metal layer 12 is aluminum, the second transition oxide film layer and the second porous oxide film layer 17 comprise aluminum oxide.

[0272] In the present application, the second transition oxide film layer 16 is close to the second metal layer 12, and the porosity of the second transition oxide film layer 16 is less than the porosity of the second porous oxide film layer 17. The porosity of the second transition oxide film layer 16 is characterized by the total area ratio of the nanopores on the surface of the second transition oxide film layer 16 close to the second plastic layer 18. The total area ratio of the nanopores on the surface of the second transition oxide film layer 16 close to the second porous oxide film layer 17 is less than or equal to 1%. The nanopores are pores with a pore size less than or equal to 100 nm, which can be obtained by scanning electron microscopy (SEM) scanning the surface of the second transition oxide film layer 16 close to the second porous oxide film layer 17. The second transition oxide film has high strength and is a dense structure, which can be used as a transition layer to connect the second porous oxide film layer 17 and the second metal layer 12, avoid the shedding of the second porous oxide film layer 17, improve the metal-plastic bonding force, and at the same time make the composite structure have high intrinsic strength, so as to balance the strength and bonding force of the composite structure. Specifically, the total area ratio of the nanopores on the surface of the second transition oxide film layer 16 close to the second porous oxide film layer 17 can be but not limited to less than or equal to 1%, less than or equal to 0.8%, less than or equal to 0.7%, less than or equal to 0.6%, or less than or equal to 0.5%, etc. In an embodiment of the present application, the total area ratio of the nanopores on the surface of the second transition oxide film layer 16 close to the second porous oxide film layer 17 can be less than or equal to 0.5%. In another embodiment of the present application, the total area ratio of the nanopores on the surface of the second transition oxide film layer 16 close to the second porous oxide film layer 17 can be less than or equal to 0.2%.

[0273] In an embodiment of the present application, the thickness of the second transition oxide film layer 16 is 24 nm-3.5 μm, and the appropriate second porous oxide film layer 17 can improve the bonding capacity between the second metal layer 12 and the second plastic layer 18. Specifically, the thickness of the second transition oxide film layer 16 can be but not limited to 24 nm, 100 nm, 120 nm, 150 nm, 180 nm, 1800 nm, 2000 nm, 3000 nm, or 3.5 μm, etc. In an embodiment of the present application, the thickness of the second transition oxide film layer 16 can be 24 nm-2800 nm. In another embodiment of the present application, the thickness of the second transition oxide film layer 16 can be 2000 nm-3.5 μm.

[0274] In an embodiment of the present application, the total area ratio of the nano-pores on the surface of the second porous oxide film layer 17 close to the second plastic layer 18 is 45%-70%, and the second porous oxide film layer 17 is a loose porous structure, and the porosity of the second porous oxide film layer 17 is determined by the total area ratio of the nano-pores on the surface of the second porous oxide film layer 17 close to the second plastic layer 18, wherein the nano-pores are pores with a pore size less than or equal to 100 nm, and the nano-pores on the surface of the second porous oxide film layer 17 close to the second plastic layer 18 can be obtained by scanning electron microscopy (SEM). A suitable porosity can improve the bonding capacity of the second metal layer 12 and the second plastic layer 18, and improve the bonding capacity of the metal-plastic composite structure 100. Specifically, the total area ratio of the nano-pores on the surface of the second porous oxide film layer 17 close to the second transition oxide film layer 16 can be, but is not limited to, 45%, 50%, 60%, 65%, or 70%, etc. In an embodiment of the present application, the total area ratio of the nano-pores on the surface of the second porous oxide film layer 17 close to the second transition oxide film layer 16 can be 45%-60%. In an embodiment of the present application, the total area ratio of the nano-pores on the surface of the second porous oxide film layer 17 close to the second transition oxide film layer 16 can be 50%-70%.

[0275] In an embodiment of the present application, the thickness ratio of the second porous oxide film layer 17 and the second transition oxide film layer 16 is (0.16-2.5):1, and a suitable second porous oxide film layer 17 and second transition oxide film can make the second dense oxide layer have a certain strength while improving the bonding force of the second metal layer 12 and the second plastic layer 18. Specifically, the thickness ratio of the second porous oxide film layer 17 and the second transition oxide film layer 16 can be, but is not limited to, 0.16:1, 0.5:1, 0.7:1, 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1, or 2.5:1, etc. In an embodiment of the present application, the thickness ratio of the second porous oxide film layer 17 and the second transition oxide film layer 16 can be (0.16-1.8):1. In another embodiment of the present application, the thickness ratio of the second porous oxide film layer 17 and the second transition oxide film layer 16 can be (1.5-2.5):1.

[0276] In an embodiment of the present application, the thickness of the second porous oxide film layer 17 is 60 nm-700 nm, and a suitable second porous oxide film layer 17 can improve the bonding capacity between the second metal layer 12 and the second plastic layer 18. Specifically, the thickness of the second oxide film layer 20 can be, but is not limited to, 60 nm, 100 nm, 200 nm, 400 nm, 600 nm, or 700 nm, etc. In an embodiment of the present application, the thickness of the second oxide film layer 20 can be 30 nm-500 nm. In another embodiment of the present application, the thickness of the second oxide film layer 20 can be 500 nm-700 nm.

[0277] In an embodiment of the present application, the surface of the second porous oxide film layer 17 is a rough surface, and the surface roughness Ra of the side of the second porous oxide film layer 17 close to the second plastic layer 18 is greater than or equal to 2 μm. The surface roughness Ra of the side of the second porous oxide film layer close to the second plastic layer is greater than or equal to 2 μm, which increases the specific surface area of the side of the second porous oxide film layer close to the second plastic layer, and the concave-convex interlocking structure is formed between the second plastic layer and the second porous oxide film layer, which is beneficial to improve the reliability of the metal-plastic composite structure. Specifically, the surface roughness Ra of the side of the second porous oxide film layer close to the second plastic layer can be, but is not limited to, greater than or equal to 2 μm, greater than or equal to 2.2 μm, greater than or equal to 2.5 μm, greater than or equal to 2.8 μm, or greater than or equal to 3 μm, etc. In an embodiment of the present application, the surface roughness Ra of the side of the second porous oxide film layer close to the second plastic layer can be greater than or equal to 2.3 μm. In another embodiment of the present application, the surface roughness Ra of the side of the second porous oxide film layer close to the second plastic layer can be greater than or equal to 2.5 μm.

[0278] In an embodiment of the present application, the second porous oxide film layer includes a plurality of second nanopores, and at least part of the second nanopores are filled with plastic material, which can improve the bonding force between the second metal layer and the second plastic layer. In some embodiments, all the second nanopores in the second porous oxide film layer are filled with plastic material. In other embodiments, at least part of the second nanopores are completely filled with plastic material, and at least part of the second nanopores are partially filled with plastic material.

[0279] In an embodiment of the present application, the pore size of the second nanopore is 20 nm-40 nm, and the appropriate pore size increases the specific surface area of the second nanopore, promotes the entry of plastic, and improves the bonding force between the second metal layer and the second plastic layer. Specifically, the pore size of the second nanopore can be, but is not limited to, 20 nm, 25 nm, 30 nm, 34 nm, 38 nm, or 40 nm, etc. In an embodiment of the present application, the pore size of the second nanopore can be 20 nm-35 nm. In another embodiment of the present application, the pore size of the second nanopore can be 30 nm-20 nm.

[0280] In an embodiment of the present application, the pore size ratio of the first nanopore and the second nanopore is 1:(3-10). The suitable pore size ratio can make the specific surface area of the first porous oxide film layer and the second porous oxide film layer similar, improve the bonding capacity between the plastic layer and the metal layer, avoid the imbalance of the bonding force between the first plastic layer and the first metal layer and the bonding force between the second plastic layer and the second metal layer, and reduce the structural reliability of the metal-plastic composite structure. Specifically, the pore size ratio of the first nanopore and the second nanopore can be, but is not limited to, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, or 1:10, etc. In an embodiment of the present application, the pore size ratio of the first nanopore and the second nanopore is 1:(3-7). In another embodiment of the present application, the pore size ratio of the first nanopore and the second nanopore is 1:(5-10).

[0281] In an embodiment of the present application, the pore depth of the second nanopore is 60nm-700nm. The suitable pore depth can improve the bonding capacity between the second metal layer and the second plastic layer. Specifically, the pore depth of the second nanopore can be, but is not limited to, 60nm, 100nm, 200nm, 400nm, 600nm, or 700nm, etc. In an embodiment of the present application, the pore depth of the second nanopore can be 60nm-600nm. In another embodiment of the present application, the pore depth of the second nanopore can be 500nm-700nm.

[0282] In an embodiment of the present application, the thickness and shape of the second plastic layer 18 can be designed according to actual needs. The second plastic layer 18 can be a regular shape or an irregular shape, and can be a layer structure with uniform thickness or non-uniform thickness.

[0283] In an embodiment of the present application, at least part of the second porous oxide film layer 17 is covered by the second plastic layer 18. That is, the covering mode of the second plastic layer 18 can be set according to actual needs. The second plastic layer 18 can cover all the second porous oxide film layers 17, or the second plastic layer 18 can also cover part of the second porous oxide film layers 17. In some embodiments, the materials of the first plastic layer 15 and the second plastic layer 18 can be the same or different.

[0284] In an embodiment of the present application, the shear strength between the second plastic layer 18 and the second metal layer 12 is greater than or equal to 25 MPa, thereby improving the bonding capacity between the second plastic layer 18 and the second metal layer 12. Specifically, the shear strength between the second plastic layer and the second metal layer can be, but is not limited to, greater than or equal to 25 MPa, greater than or equal to 26 MPa, greater than or equal to 27 MPa, greater than or equal to 28 MPa, greater than or equal to 29 MPa, or greater than or equal to 30 MPa, etc. In an embodiment of the present application, the shear strength between the second plastic layer and the second metal layer can be greater than or equal to 25.6 MPa. In another embodiment of the present application, the shear strength between the second plastic layer and the second metal layer can be greater than or equal to 28 MPa.

[0285] In an embodiment of the present application, after the shear strength test, the residual area of the second plastic layer on the surface of the second metal layer is greater than or equal to 95%. That is, the bonding force between the second plastic layer and the second metal layer is large, and after the shear strength test, the second plastic layer and the second metal layer cannot be completely separated, and at least part of the plastic material remains on the surface of the second metal layer. Specifically, after the shear strength test, the residual area of the second plastic layer on the surface of the second metal layer can be, but is not limited to, greater than or equal to 95%, greater than or equal to 96%, greater than or equal to 97%, greater than or equal to 98%, or greater than or equal to 99%, etc. In an embodiment of the present application, after the shear strength test, the residual area of the second plastic layer on the surface of the second metal layer can be greater than or equal to 96%.

[0286] Referring to FIG. 5, a flow chart of a method for preparing a metal-plastic composite structure according to an embodiment of the present application is provided, which includes the following steps:

[0287] S101: providing a to-be-injection-molded composite metal material, the to-be-injection-molded composite metal material comprising a third metal layer and a fourth metal layer connected to each other;

[0288] S102: satisfying at least one of the following: performing first etching on a surface of the third metal layer that is not connected to the fourth metal layer to form a fifth metal layer; and performing second etching on a surface of the fourth metal layer that is not connected to the third metal layer to form a sixth metal layer, thereby obtaining an etched to-be-injection-molded composite metal material;

[0289] S103: sequentially performing first anodic oxidation treatment and second anodic oxidation treatment on the etched to-be-injection-molded composite metal material, and satisfying at least one of the following: forming, from outside to inside, a first porous oxide film layer and a first transition oxide film layer on a surface layer of the fifth metal layer that is not connected to the sixth metal layer; and forming, from outside to inside, a second porous oxide film layer and a second transition oxide film layer on a surface layer of the sixth metal layer that is not connected to the fifth metal layer, thereby obtaining an oxidized to-be-injection-molded composite metal material;

[0290] S104: injection molding the metal-plastic composite structure after the oxidation, to form a first plastic layer on the surface of the first porous oxidation film layer and a second plastic layer on the surface of the second porous oxidation film layer, to obtain the metal-plastic composite structure. The preparation method provided in the application forms a transition oxidation film layer, a porous oxidation film layer and a plastic layer on the surfaces of the first metal layer and the second metal layer after etching and anodic oxidation treatment. The transition oxidation film layer can prevent the porous oxidation film layer from cracking and falling off, the porous oxidation film layer can improve the bonding force between the metal layer and the plastic layer, and the mechanical properties of the metal-plastic composite structure are improved. The preparation method of the metal-plastic composite structure provided in the application is novel, simple, mild and environmentally friendly, and the metal-plastic composite structure prepared has high bonding strength.

[0291] In the application, the fifth metal layer in the metal-plastic composite structure to be injection molded after etching is subjected to anodic oxidation treatment, so that the surface layer of the fifth metal layer is oxidized to form a first transition oxidation film layer and a first porous oxidation film layer. At this time, the unoxidized part of the fifth metal layer forms a first metal layer of the metal-plastic composite structure. Similarly, the sixth metal layer in the metal-plastic composite structure to be injection molded after etching is subjected to anodic oxidation treatment, so that the surface layer of the sixth metal layer is oxidized to form a first dense oxidation layer and a first porous oxidation film layer. At this time, the unoxidized part of the sixth metal layer forms a second metal layer of the metal-plastic composite structure.

[0292] In an embodiment of the application, the material of the third metal layer can be but is not limited to titanium, magnesium, titanium alloy, magnesium alloy or stainless steel, and the material of the fourth metal layer can be but is not limited to aluminum or aluminum alloy. Titanium or titanium alloy, stainless steel and magnesium or magnesium alloy have the characteristics of wear resistance, corrosion resistance and small density, and aluminum material has the characteristics of good heat conductivity, easy processing and low cost, which is beneficial to improve the strength and light weight of the metal-plastic composite structure. In an embodiment of the application, the material of the third metal layer can be TA5, and the material of the fourth metal layer can be 6061. In some embodiments, the third metal layer and the first metal layer are made of the same material, and the fourth metal layer and the second metal layer are made of the same material.

[0293] In an embodiment of the present application, the first etching liquid is used to etch the third metal layer to form the fifth metal layer, which can remove the oxide film naturally formed on the surface of the third metal layer, increase the surface roughness Ra of the fifth metal layer, and increase the specific surface area of the fifth metal layer, thereby improving the reliability of the metal-plastic composite structure. Specifically, the surface roughness Ra of the fifth metal layer can be greater than or equal to 2 μm, greater than or equal to 2.2 μm, greater than or equal to 2.5 μm, greater than or equal to 2.8 μm, or greater than or equal to 3 μm, etc. In an embodiment of the present application, the surface roughness Ra of the fifth metal layer can be greater than or equal to 2.3 μm. In another embodiment of the present application, the surface roughness Ra of the fifth metal layer can be greater than or equal to 2.5 μm.

[0294] In an embodiment of the present application, the first etching liquid can include at least one of hydrofluoric acid, acetic acid, carbonic acid, hypochlorous acid, phosphoric acid, sodium fluoride, calcium fluoride, ammonium hydrogen fluoride, sodium citrate, sodium chloride, and ferric chloride, but is not limited thereto. In an embodiment of the present application, the first etching liquid can be ammonium hydrogen fluoride. In another embodiment of the present application, the first etching liquid can be ferric chloride.

[0295] In an embodiment of the present application, the concentration of the first etching liquid is 5 g / L to 30 g / L, the pH value of the first etching liquid is 2 to 5, and the conductivity of the first etching liquid is 100 mS / cm to 500 mS / cm. The appropriate parameters of the first etching liquid can increase the surface roughness of the fifth metal layer, increase the surface area of the fifth metal layer, and improve the reliability of the metal-plastic composite structure. Specifically, the concentration of the first etching liquid can be 5 g / L, 10 g / L, 15 g / L, 20 g / L, 25 g / L, or 30 g / L, etc., but is not limited thereto; the pH value of the first etching liquid can be 2, 2.5, 3, 3.5, 4, 4.5, or 5, etc., but is not limited thereto; and the conductivity of the first etching liquid can be 100 mS / cm, 200 mS / cm, 300 mS / cm, 400 mS / cm, or 500 mS / cm, etc., but is not limited thereto. In an embodiment of the present application, the concentration of the first etching liquid can be 5 g / L to 15 g / L, the pH value of the first etching liquid can be 2 to 3, and the conductivity of the first etching liquid can be 100 mS / cm to 300 mS / cm.

[0296] In an embodiment of the present application, the fourth metal layer is etched by the second etching liquid to form the sixth metal layer, which can remove the natural oxide film formed on the surface of the fourth metal layer and improve the surface roughness Ra of the sixth metal layer without adversely affecting the first etching effect on the third metal layer. The surface roughness Ra of the sixth metal layer is greater than or equal to 2 μm, which increases the specific surface area of the sixth metal layer and is conducive to improving the bonding force of the metal-plastic composite material. Specifically, the surface roughness Ra of the sixth metal layer can be, but is not limited to, greater than or equal to 2 μm, greater than or equal to 2.2 μm, greater than or equal to 2.5 μm, greater than or equal to 2.8 μm, or greater than or equal to 3 μm, etc. In an embodiment of the present application, the surface roughness Ra of the sixth metal layer can be greater than or equal to 2.3 μm. In another embodiment of the present application, the surface roughness Ra of the sixth metal layer can be greater than or equal to 2.5 μm.

[0297] In an embodiment of the present application, the second etching liquid can include, but is not limited to, at least one of nitric acid, sulfuric acid, hydrochloric acid, potassium chloride, ferric chloride, ferrous chloride, cupric chloride, magnesium chloride, and sodium chloride. In an embodiment of the present application, the second etching liquid can be nitric acid. In another embodiment of the present application, the second etching liquid can be potassium chloride.

[0298] In an embodiment of the present application, the concentration of the second etching liquid is 100 g / L-300 g / L, the pH value of the second etching liquid is less than or equal to 2, and the conductivity of the second etching liquid is 400 mS / cm-1000 mS / cm. Suitable parameters of the second etching liquid can improve the surface roughness of the sixth metal layer, increase the surface area of the sixth metal layer, and be conducive to improving the reliability of the metal-plastic composite structure. Specifically, the concentration of the second etching liquid can be, but is not limited to, 100 g / L, 150 g / L, 200 g / L, 250 g / L, or 300 g / L, etc.; the pH value of the second etching liquid can be, but is not limited to, less than or equal to 2, less than or equal to 1.8, less than or equal to 1.5, less than or equal to 1.2, or less than or equal to 1, etc.; and the conductivity of the second etching liquid can be, but is not limited to, 400 mS / cm, 500 mS / cm, 600 mS / cm, 700 mS / cm, 800 mS / cm, 900 mS / cm, or 1000 mS / cm, etc. In an embodiment of the present application, the concentration of the second etching liquid can be 150 g / L-200 g / L, the pH value of the second etching liquid is less than or equal to 1.78, and the conductivity of the second etching liquid is 400 mS / cm-700 mS / cm.

[0299] In an embodiment of the present application, the first electrolyte is used for the first anodization treatment. The first electrolyte can be used to simultaneously treat the fifth metal layer and the sixth metal layer with different materials, and form the first porous oxide film layer and the second porous oxide film layer on the surfaces of the fifth metal layer and the sixth metal layer, respectively. The first electrolyte can include, but is not limited to, at least one of potassium dichromate, hydrogen peroxide, hydrofluoric acid, sulfuric acid, phosphoric acid, sodium fluoride, ammonium hydrogen fluoride, and sodium sulfate. In an embodiment of the present application, the first electrolyte can be hydrofluoric acid. In another embodiment of the present application, the first electrolyte can be phosphoric acid.

[0300] In an embodiment of the present application, the concentration of the first electrolyte is 3 g / L-20 g / L, and the pH value of the first electrolyte is 3-6. The appropriate parameters of the first electrolyte can promote the formation of the porous oxide film layer. Specifically, the concentration of the first electrolyte can be, but is not limited to, 3 g / L, 5 g / L, 8 g / L, 10 g / L, 15 g / L, 18 g / L, or 20 g / L, etc.; and the pH value of the first electrolyte can be, but is not limited to, 3, 3.5, 4, 4.5, 5, 5.5, or 6, etc. In an embodiment of the present application, the concentration of the first electrolyte can be 3 g / L-15 g / L, and the pH value of the first electrolyte can be 3-5. In another embodiment of the present application, the concentration of the first electrolyte can be 10 g / L-20 g / L, and the pH value of the first electrolyte can be 4.5-6.

[0301] In an embodiment of the present application, the temperature of the first anodization treatment is 10℃-60℃, the voltage of the first anodization treatment is 5V-100V, and the current of the first anodization treatment is 1A-50A. The appropriate conditions of the first anodization treatment can promote the formation of the porous oxide film layer, and are beneficial to the plastic entering the pores, thereby improving the bonding force between the plastic layer and the metal layer. Specifically, the temperature of the first anodization treatment can be, but is not limited to, 10℃, 20℃, 30℃, 40℃, 50℃, or 60℃, etc.; the voltage of the first anodization treatment can be, but is not limited to, 5V, 10V, 20V, 40V, 60V, 80V, or 100V, etc.; and the current of the first anodization treatment can be, but is not limited to, 1A, 5A, 10A, 20A, 30A, 40A, or 50A, etc. In an embodiment of the present application, the temperature of the first anodization treatment can be 10℃-40℃, the voltage of the first anodization treatment can be 5V-70V, and the current of the first anodization treatment can be 1A-35A. In another embodiment of the present application, the temperature of the first anodization treatment can be 30℃-60℃, the voltage of the first anodization treatment can be 60V-100V, and the current of the first anodization treatment can be 30A-50A.

[0302] In an embodiment of the present application, the second electrolyte is used for the second anodization treatment. The second electrolyte can be used to simultaneously treat the fifth metal layer and the sixth metal layer with different materials. The second electrolyte can continue to oxidize at least one of the surfaces of the fifth metal layer and the sixth metal layer through the pores in the porous oxide film layer, and form the first transition oxide film layer and the second transition oxide film layer, respectively, thereby improving the structural stability of the porous oxide film layer and preventing the cracking and peeling of the porous oxide film layer. Specifically, the second electrolyte can include, but is not limited to, at least one of oxalic acid, citric acid, sodium citrate, sodium sulfate, acetic acid, and phosphoric acid. In an embodiment of the present application, the second electrolyte can be citric acid. In another embodiment of the present application, the second electrolyte can be phosphoric acid.

[0303] In an embodiment of the present application, the concentration of the second electrolyte is 15 g / L-25 g / L, and the pH value of the second electrolyte is 1-4. The appropriate parameters of the second electrolyte can promote the formation of the transition oxide film layer. Specifically, the concentration of the second electrolyte can be, but is not limited to, 15 g / L, 16 g / L, 18 g / L, 20 g / L, 22 g / L, 24 g / L, or 25 g / L, etc.; and the pH value of the second electrolyte can be, but is not limited to, 1, 1.5, 2, 2.5, 3, 3.5, or 4, etc. In an embodiment of the present application, the concentration of the second electrolyte can be 15 g / L-20 g / L, and the pH value of the second electrolyte can be 1-3. In another embodiment of the present application, the concentration of the second electrolyte can be 18 g / L-25 g / L, and the pH value of the second electrolyte can be 2.5-4.

[0304] In an embodiment of the present application, the temperature of the second anodization treatment is 20℃-40℃, the voltage of the second anodization treatment is 15V-50V, and the current of the second anodization treatment is 15A-50A. The appropriate conditions of the second anodization treatment can promote the formation of the transition oxide film layer and be beneficial to improving the structural stability of the metal-plastic composite structure. Specifically, the temperature of the second anodization treatment can be, but is not limited to, 20℃, 25℃, 30℃, 35℃, 38℃, or 40℃, etc.; the voltage of the second anodization treatment can be, but is not limited to, 15V, 18V, 20V, 30V, 40V, 45V, or 50V, etc.; and the current of the second anodization treatment can be, but is not limited to, 15A, 20A, 30A, 40A, or 50A, etc. In an embodiment of the present application, the temperature of the second anodization treatment can be 20℃-30℃, the voltage of the second anodization treatment can be 15V-35V, and the current of the second anodization treatment can be 15A-35A. In another embodiment of the present application, the temperature of the second anodization treatment can be 25℃-40℃, the voltage of the second anodization treatment can be 30V-50V, and the current of the second anodization treatment can be 30A-50A.

[0305] In an embodiment of the present application, the first electrolyte and the second electrolyte further comprise an inhibitor, which can slow down the etching speed of the metal layer and avoid serious damage to the metal layer. The inhibitor can be an oxidizing inhibitor or a non-oxidizing inhibitor. Specifically, the zinc oxide inhibitor can be, but is not limited to, at least one of chromate, dichromate, molybdate, tungstate, permanganate, hydrogen peroxide, ozone, hypochlorous acid, hypochlorite and trivalent iron ions. The non-oxidizing inhibitor comprises at least one of aldehydes, amines, organic sulfides, heterocyclic compounds, organic acids and organic acid salts. Specifically, the non-oxidizing inhibitor can be, but is not limited to, at least one of amino acids, benzotriazole, chitosan, hexadecylamine, quinoline, mercaptobenzothiazole, methylbenzotriazole, imidazoline, thiazoline, sodium sulfate, ethylenediaminetetraacetic acid and its salts, gluconate and its salts, malate and its salts, oxalate and its salts (such as sodium oxalate), citrate and its salts (such as sodium citrate), succinate and its salts, lactic acid and its salts, malonic acid and its salts, adipic acid and its salts, and diphenyl disulfide. In an embodiment of the present application, when the inhibitor is a zinc oxide inhibitor, the inhibitor can be potassium permanganate. In another embodiment of the present application, when the inhibitor is a non-oxidizing inhibitor, the inhibitor can be malonic acid. In some embodiments, the inhibitor in the first electrolyte and the inhibitor in the second electrolyte can be the same or different.

[0306] In an embodiment of the present application, the first electrolyte and the second electrolyte further comprise an auxiliary agent, which comprises at least one of a pH buffer and a surfactant, and can reduce the surface tension of the fluorine-containing electrolyte, improve the wettability, and promote the consistency and uniformity of the anodizing process. Specifically, the pH buffer can be, but is not limited to, at least one of carbonates, bicarbonates, acetic acid and its salts, phosphoric acid and its salts, and pyrophosphoric acid and its salts; and the surfactant can be, but is not limited to, at least one of sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, sodium dodecyl sulfonate, cetyltrimethylamine and carboxymethyl cellulose. In an embodiment of the present application, when the auxiliary agent is a pH buffer, the auxiliary agent can be a carbonate. In another embodiment of the present application, when the auxiliary agent is a surfactant, the auxiliary agent can be sodium dodecyl sulfonate. In some embodiments, the auxiliary agent in the first electrolyte and the auxiliary agent in the second electrolyte can be the same or different.

[0307] In an embodiment of the present application, the first electrolyte and the second electrolyte further comprise a solvent. Specifically, the solvent can be, but is not limited to, at least one of water, ethylene glycol, propylene glycol, glycerol, 1,3-butanediol, ethanol and propanol. In an embodiment of the present application, the solvent can be water and propylene glycol. In some embodiments, the solvent in the first electrolyte and the solvent in the second electrolyte can be the same or different.

[0308] In an embodiment of the present application, the first etching is preceded by a pretreatment, which includes oil removal, water washing, neutralization, water washing, alkali etching, water washing, acid etching, water washing, ash removal, water washing, and ultrasonic water washing, etc. The pretreatment can remove the surface oxidation film and impurities of the metal-plastic composite structure to be injection molded, improve the surface roughness, and facilitate the etching and anodizing process.

[0309] In an embodiment of the present application, in the pretreatment, the purpose of oil removal is to remove the oil stains on the surface of the metal-plastic composite structure to be injection molded. An alkaline solution is used for oil removal, and the concentration of the alkaline solution is 10 g / L-80 g / L. Specifically, the alkaline solution can include, but is not limited to, at least one of NaOH, Na2CO3, NaHCO3, and Na3PO4, and the concentration of the alkaline solution can be, but is not limited to, 10 g / L, 20 g / L, 40 g / L, 60 g / L, or 80 g / L, etc. In an embodiment of the present application, the alkaline solution can be NaOH, and the concentration of the alkaline solution can be 20 g / L-40 g / L, which is conducive to the removal of oil stains on the surface of the metal-plastic composite structure to be injection molded. In some embodiments, the alkaline solution further includes a surfactant, and the mass percentage of the surfactant is 1%.

[0310] In an embodiment of the present application, in the pretreatment, the neutralization treatment is used to neutralize the residual alkaline solution and impurities in the oil removal. An acidic solution is used for neutralization, and the concentration of the acidic solution is 5 g / L-100 g / L. Specifically, the acidic solution can include, but is not limited to, at least one of oxalic acid, nitric acid, sulfuric acid, hydrochloric acid, perchloric acid, acetic acid, and citric acid, and the concentration of the acidic solution can be, but is not limited to, 5 g / L, 10 g / L, 20 g / L, 40 g / L, 60 g / L, 80 g / L, or 100 g / L, etc. In an embodiment of the present application, the acidic solution is acetic acid, and the concentration of the acidic solution can be 40 g / L-60 g / L.

[0311] In an embodiment of the present application, in the pretreatment, the alkali etching treatment can remove the natural oxidation film of the second metal layer. An alkali etching solution is used for alkali etching treatment, the concentration of the alkali etching solution is 10 g / L-80 g / L, and the temperature of the alkali etching is 40°C-80°C. Specifically, the alkali etching solution can include, but is not limited to, at least one of NaOH, Na2CO3, NaHCO3, and Na3PO4, and the concentration of the alkali etching solution can be, but is not limited to, 5 g / L, 10 g / L, 20 g / L, 40 g / L, 60 g / L, 80 g / L, or 100 g / L, etc.; and the temperature of the alkali etching can be, but is not limited to, 40°C, 50°C, 60°C, 70°C, or 80°C, etc. In an embodiment of the present application, the concentration of the alkali etching solution can be 20 g / L-40 g / L, and the temperature of the alkali etching is 40°C-60°C, which is conducive to the removal of the natural oxidation film of the second metal layer.

[0312] In an embodiment of the present application, in the pretreatment, the acid etching treatment is used to remove the natural oxide film of the first metal layer, and the acid etching solution is used for the acid etching treatment, and the acid etching solution can include, but is not limited to, at least one of sulfuric acid, hydrochloric acid, hydrofluoric acid, phosphoric acid and nitric acid. In an embodiment of the present application, the acid etching solution can be a mixed solution of hydrochloric acid, nitric acid, phosphoric acid and sulfuric acid with a mass ratio of 3:1:4:1.

[0313] In an embodiment of the present application, after the second anodization treatment, air cutting and baking are further included, the temperature of the air cutting is 40-70°C, and the temperature of the baking is 70-150°C, which is beneficial to remove the excess moisture on the surface of the metal-plastic composite structure to be injection molded. Specifically, the temperature of the air cutting can be, but is not limited to, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C or 70°C, etc., and the temperature of the baking can be, but is not limited to, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 140°C or 150°C, etc. In an embodiment of the present application, the temperature of the air cutting can be 40-60°C, and the temperature of the baking can be 70-100°C, which is beneficial to remove the surface moisture.

[0314] In an embodiment of the present application, the temperature of the injection molding is 230-320°C, and the pressure of the injection molding is 80-120 MPa, which can promote the melting of the plastic and the entry of the plastic into the pores in the porous oxide film layer, and is beneficial to improve the bonding force between the plastic layer and the metal layer. Specifically, the temperature of the injection molding can be, but is not limited to, 230°C, 250°C, 260°C, 280°C, 290°C, 310°C or 320°C, etc., and the pressure of the injection molding can be, but is not limited to, 80 MPa, 85 MPa, 90 MPa, 95 MPa, 100 MPa or 120 MPa, etc. In an embodiment of the present application, the temperature of the injection molding can be 230-290°C, and the pressure of the injection molding can be 80-100 MPa, which is beneficial to improve the bonding force between the plastic layer and the metal layer. In another embodiment of the present application, the temperature of the injection molding can be 280-320°C, and the pressure of the injection molding can be 95-120 MPa.

[0315] In an embodiment of the present application, the material of the injection molding includes plastic and glass fiber, and the plastic can include, but is not limited to, at least one of polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), acrylonitrile-styrene-diene copolymer (ABS), polyamide (PA), polyphthalamide (PPA), polypropylene (PP), polyethylene terephthalate (PET), polycarbonate (PC), polyphenylene sulfone resin (PPSU), polyaryletherketone (PEAK) and polyether ether ketone (PEEK). In an embodiment of the present application, the material of the injection molding can be polybutylene terephthalate (PBT).

[0316] In an embodiment of the present application, the mass percentage of the glass fiber in the material for injection molding is less than or equal to 55%. Specifically, the mass percentage of the glass fiber can be, but is not limited to, less than or equal to 55%, less than or equal to 50%, less than or equal to 45%, less than or equal to 40%, less than or equal to 35%, less than or equal to 30%, or less than or equal to 20%, etc. In an embodiment of the present application, the mass percentage of the glass fiber can be 40%.

[0317] In an embodiment of the present application, after the second anodization treatment, cleaning and baking are further included, which can remove the fluorine-containing electrolyte remaining on the surface of the oxide film layer after the anodization treatment, and is beneficial to the injection molding.

[0318] The present application also provides a preparation method of a metal composite structure, comprising: providing a composite metal material, the composite metal material comprising a third metal layer and a fourth metal layer connected to each other; at least one of the following is satisfied: performing first etching on a surface of the third metal layer not connected to the fourth metal layer to form a fifth metal layer; and performing second etching on a surface of the fourth metal layer not connected to the third metal layer to form a sixth metal layer, to obtain an etched composite metal material; sequentially performing first anodization treatment and second anodization treatment on the etched composite metal material, at least one of the following is satisfied: the surface layer of the fifth metal layer not connected to the sixth metal layer is formed from outside to inside in sequence as a first porous oxide film layer and a first transition oxide film layer; and the surface layer of the sixth metal layer not connected to the fifth metal layer is formed from outside to inside in sequence as a second transition oxide film layer and a second porous oxide film layer, to obtain a metal composite structure; the first transition oxide film layer and the first porous oxide film layer comprise oxides of the material of the first metal layer, and the porosity of the first transition oxide film layer is less than the porosity of the first porous oxide film layer; the second transition oxide film layer and the second porous oxide film layer comprise oxides of the material of the second metal layer, and the porosity of the second transition oxide film layer is less than the porosity of the second porous oxide film layer.

[0319] The preparation method of the metal composite structure provided by the present application has a wide range of applications, a simple preparation process, low preparation cost, and is easy to industrialize.

[0320] Referring to FIG. 14, a schematic diagram of a cross-section structure of a metal-plastic composite structure according to an embodiment of the present application is shown. The metal-plastic composite structure 100 includes a first metal layer 11 and a second metal layer 12 connected to each other, a first oxide film layer 19 and a first plastic layer 15 sequentially stacked on a surface of the first metal layer 11 not connected to the second metal layer 12, and a second oxide film layer 20 and a second plastic layer 18 sequentially stacked on a surface of the second metal layer 12 not connected to the first metal layer 11. The first metal layer 11 and the second metal layer 12 are metal layers of different materials. The first oxide film layer 19 includes a fifth metal oxide, and at least one metal element in the fifth metal oxide is the same as at least one metal element in the first metal layer 11. The second oxide film layer 20 includes a sixth metal oxide, and at least one metal element in the sixth metal oxide is the same as at least one metal element in the second metal layer 12. The first oxide film layer 19 and the second oxide film layer 20 are the same or different. The first oxide film layer 19 includes a plurality of third nanometer pores, and the shortest distance between any two adjacent third nanometer pores is less than or equal to 50 nm. The second oxide film layer 20 includes a plurality of fourth nanometer pores, and the shortest distance between any two adjacent fourth nanometer pores is less than or equal to 50 nm.

[0321] The metal-plastic composite structure provided by the present application has a first metal layer and a second metal layer, and the materials of the first metal layer and the second metal layer are different. The two layers are metal layers of different materials, and the composite material has the performance advantages of different metal materials, which is conducive to the wide use of the metal-plastic composite structure. At least one of the following conditions is met: the first metal layer has a first oxide film layer and a first plastic layer, and the surface of the second metal layer has a second oxide film layer and a second plastic layer; the first oxide film layer and the second oxide film layer both have nanometer pores arranged closely, and the specific surface area of the oxide film layer is large, which is conducive to improving the bonding force between the first plastic layer and the first metal layer, the bonding force between the second plastic layer and the second metal layer, and the structural stability of the metal-plastic composite structure.

[0322] In the embodiment shown in FIG. 14, the first oxide film layer 19 and the first plastic layer 15 are sequentially stacked on a surface of the first metal layer 11 away from the second metal layer 12, and the second oxide film layer 20 and the second plastic layer 18 are sequentially stacked on a surface of the second metal layer 12 away from the first metal layer 11.

[0323] In an embodiment of the present application, the oxide film layer can be arranged on the surface of the first metal layer 11 or the second metal layer 12 only, in which case the metal-plastic composite structure 100 comprises the first metal layer 11 and the second metal layer 12 connected to each other, and the first oxide film layer 19 and the first plastic layer 15 arranged in sequence on the surface of the first metal layer 11 not connected to the second metal layer 12; or the metal-plastic composite structure 100 comprises the first metal layer 11 and the second metal layer 12 arranged in sequence, and the second oxide film layer 20 and the second plastic layer 18 arranged in sequence on the surface of the second metal layer 12 not connected to the first metal layer 11. In an embodiment of the present application, the oxide film layer can be arranged on the surface of the first metal layer 11 and the second metal layer 12 simultaneously, in which case the metal-plastic composite structure 100 comprises the first metal layer 11 and the second metal layer 12 connected to each other, and comprises the first oxide film layer 19 and the first plastic layer 15 arranged in sequence on the surface of the first metal layer 11 not connected to the second metal layer 12, and the second oxide film layer 20 and the second plastic layer 18 arranged in sequence on the surface of the second metal layer 12 not connected to the first metal layer 11.

[0324] In an embodiment of the present application, the first metal layer 11 has a first surface and a second surface, and the second metal layer 12 has a third surface and a fourth surface, the second surface and the third surface are connected to each other, the first surface has the first oxide film layer 19 and the first plastic layer 15 arranged in sequence, and the fourth surface has the second oxide film layer 20 and the second plastic layer 18 arranged in sequence.

[0325] It should be noted that the specific shape and size of the first metal layer 11 and the second metal layer 12 in the embodiments of the present application are not limited, and can be designed according to actual needs, which can be regular or irregular, and the first metal layer 11 can be a layer structure with uniform or non-uniform thickness, and the second metal layer 12 can be a layer structure with uniform or non-uniform thickness.

[0326] In an embodiment of the present application, the first oxide film layer 19 and the first plastic layer 15 can be connected to each other in sequence on part or all of the surface of the first metal layer 11 not connected to the second metal layer 12 as needed; and the second oxide film layer 20 and the second plastic layer 18 can be arranged in sequence on part or all of the surface of the second metal layer 12 not connected to the first metal layer 11 as needed.

[0327] Referring to FIG. 15, a cross-sectional structure diagram of a metal-plastic composite structure 100 according to another embodiment of the present application is provided. The metal-plastic composite structure 100 includes a first metal layer 11 and a second metal layer 12 connected to each other, and at least one of the following conditions is satisfied: a first oxide film layer 19 and a first plastic layer 15 are sequentially arranged on the side of the first metal layer 11, and a second oxide film layer 20 and a second plastic layer 18 are sequentially arranged on the side of the second metal layer 12. In the embodiment shown in FIG. 15, the metal-plastic composite structure 100 includes both the first plastic layer 15 and the second plastic layer 18, and the first plastic layer 15 and the second plastic layer 18 are arranged on the same side. In this case, the first plastic layer 15 and the second plastic layer 18 are integrated, and the first plastic layer 15 and the second plastic layer 18 are made of the same material. In some embodiments, a transition oxide film, a porous oxide film layer, and a plastic layer are arranged on the side of the first metal layer 11 and the second metal layer 12, and at least one of the following conditions is satisfied: a first transition oxide film layer, a first porous oxide film layer, and a first plastic layer are arranged on the first surface, and a second transition oxide film layer, a second porous oxide film layer, and a second plastic layer are arranged on the fourth surface.

[0328] In an embodiment of the present application, the material of the first metal layer 11 includes titanium or a titanium alloy, and the material of the second metal layer 12 includes aluminum or an aluminum alloy. Titanium or a titanium alloy has the characteristics of wear resistance, corrosion resistance, and small density, and aluminum or an aluminum alloy has the characteristics of good thermal conductivity, easy processing, and low cost, which is beneficial to improve the strength and light weight of the metal-plastic composite structure. The grade of the titanium alloy can be, but is not limited to, TA1, TA2, TA3, TA4, TA5, T6, TA7, TA8, TB2, TB3, TB4, TB5, TB6, TC1, TC2, TC3, TC4, or TC6, and the grade of the aluminum alloy can be, but is not limited to, 1016, 1024, 5005, 5052, 6013, 6063, 6061, 7075, 7550, ADC10, ADC12, or GM55. In an embodiment of the present application, the material of the first metal layer can be TA5, and the material of the second metal layer can be 6061.

[0329] In an embodiment of the present application, a connecting layer is further arranged between the first metal layer and the second metal layer.

[0330] In an embodiment of the present application, the first oxide film layer 19 is close to the first metal layer 11, and the first oxide film layer 19 includes a fifth metal oxide, at least one metal element in the fifth metal oxide being the same as at least one metal element in the first metal layer. In some embodiments, the metal element in the fifth metal oxide is the same as the metal element in the first metal layer.

[0331] In an embodiment of the present application, the thickness of the first oxide film layer 19 is 100 nm-1000 nm. The suitable first oxide film layer 19 can improve the bonding capacity between the first metal layer 11 and the first plastic layer 15. Specifically, the thickness of the first oxide film layer can be, but is not limited to, 100 nm, 200 nm, 400 nm, 600 nm, 800 nm, or 1000 nm, etc. In an embodiment of the present application, the thickness of the first oxide film layer can be 100 nm-600 nm. In another embodiment of the present application, the thickness of the first oxide film layer can be 500 nm-1000 nm.

[0332] In an embodiment of the present application, the total area ratio of the nano-pores on the surface of the first oxide film layer 19 close to the first plastic layer 15 is 20%-90%. The first oxide film layer is a loose porous structure. The total area ratio of the nano-pores on the surface of the first oxide film layer close to the first plastic layer represents the porosity of the first oxide film layer, wherein the nano-pores are pores with a pore size less than or equal to 100 nm, which can be obtained by scanning the surface of the first oxide film layer close to the first plastic layer by scanning electron microscopy (SEM). The suitable porosity can improve the bonding capacity between the first metal layer and the first plastic layer, and improve the bonding capacity of the metal-plastic composite structure. Specifically, the total area ratio of the nano-pores on the surface of the first oxide film layer close to the first plastic layer can be, but is not limited to, 20%, 40%, 50%, 60%, 70%, 80%, or 90%, etc. In an embodiment of the present application, the total area ratio of the nano-pores on the surface of the first oxide film layer close to the first plastic layer can be 20%-70%. In an embodiment of the present application, the total area ratio of the nano-pores on the surface of the first porous oxide film layer close to the first plastic layer can be 60%-90%. Please refer to FIG. 16, which is an enlarged view of region B in FIG. 14. It can be seen that the first oxide film layer 19 is a non-flat surface. The surface roughness Ra of the side of the first oxide film layer close to the first plastic layer is 0.1 μm-20 μm, which increases the specific surface area of the side of the first oxide film layer close to the first plastic layer. The concave-convex interlocking structure is formed between the first plastic layer and the first oxide film layer, which is beneficial to improve the strength and reliability of the metal-plastic composite structure. Specifically, the surface roughness Ra of the side of the first oxide film layer close to the first plastic layer can be, but is not limited to, 0.1 μm, 1 μm, 2 μm, 5 μm, 10 μm, 12 μm, 15 μm, or 20 μm, etc. In an embodiment of the present application, the surface roughness Ra of the side of the first oxide film layer close to the first plastic layer can be 0.1 μm-10 μm. In another embodiment of the present application, the surface roughness Ra of the side of the first oxide film layer close to the first plastic layer can be 8 μm-20 μm.

[0333] In an embodiment of the present application, the first oxide film layer 19 includes a plurality of third nanopores, the third nanopores are closely arranged in the first oxide film layer, and at least part of the third nanopores are filled with plastic material, so as to improve the bonding force between the first plastic layer and the first metal layer. In some embodiments, all the third nanopores in the first oxide film layer are filled with plastic material. In other embodiments, at least part of the third nanopores are completely filled with plastic material, and at least part of the third nanopores are partially filled with plastic material.

[0334] In an embodiment of the present application, the average pore diameter of the third nanopores is 10 nm-70 nm. The appropriate pore diameter increases the specific surface area of the third nanopores, promotes the entry of plastic, and improves the bonding force between the first metal layer and the first plastic layer. Specifically, the average pore diameter of the third nanopores can be, but is not limited to, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, or 70 nm, etc. In an embodiment of the present application, the average pore diameter of the third nanopores can be 10 nm-50 nm. In another embodiment of the present application, the average pore diameter of the third nanopores can be 40 nm-70 nm.

[0335] In an embodiment of the present application, the pore depth of the third nanopores is 100 nm-1000 nm. The appropriate pore depth can improve the bonding capacity between the first metal layer and the first plastic layer. Specifically, the pore depth of the third nanopores can be, but is not limited to, 100 nm, 200 nm, 400 nm, 600 nm, 800 nm, or 1000 nm, etc. In an embodiment of the present application, the pore depth of the third nanopores can be 100 nm-600 nm. In another embodiment of the present application, the pore depth of the third nanopores can be 500 nm-1000 nm.

[0336] In the present application, the shortest distance between two adjacent third nanopores is less than or equal to 50 nm. The shortest distance between two adjacent third nanopores is the straight-line shortest distance between the edge positions of two adjacent third nanopores. Specifically, the shortest distance between two adjacent third nanopores can be, but is not limited to, less than or equal to 50 nm, less than or equal to 40 nm, less than or equal to 30 nm, less than or equal to 20 nm, or less than or equal to 10 nm, etc. In an embodiment of the present application, the shortest distance between two adjacent third nanopores can be less than or equal to 35 nm. In another embodiment of the present application, the shortest distance between two adjacent third nanopores can be less than or equal to 20 nm.

[0337] In an embodiment of the present application, the center-to-center distance between adjacent third nanopores is less than or equal to 150 nm. Since the nanopores are approximately circular or / and elliptical, taking the circular shape as an example, the center-to-center distance refers to the shortest distance between the centers of two adjacent third nanopores. The smaller the distance, the tighter the arrangement of the third nanopores, which is conducive to improving the bonding force between the first metal layer and the first plastic layer. Specifically, the center-to-center distance between adjacent third nanopores can be, but is not limited to, less than or equal to 150 nm, less than or equal to 140 nm, less than or equal to 130 nm, less than or equal to 120 nm, less than or equal to 110 nm, or less than or equal to 100 nm, etc. In an embodiment of the present application, the center-to-center distance between adjacent third nanopores can be less than or equal to 130 nm. In another embodiment of the present application, the center-to-center distance between adjacent third nanopores can be less than or equal to 110 nm.

[0338] In an embodiment of the present application, the thickness of the first plastic layer 15 is 0.1 mm-200 mm. Specifically, the thickness of the first plastic layer can be, but is not limited to, 0.1 mm, 10 mm, 20 mm, 40 mm, 60 mm, 80 mm, 100 mm, 150 mm, 180 mm, or 200 mm, etc. In an embodiment of the present application, the thickness of the first plastic layer can be 0.1 mm-80 mm. In another embodiment of the present application, the thickness of the first plastic layer can be 70 mm-200 mm. In some embodiments, the thickness and shape of the first plastic layer can be designed according to actual needs, which can be regular or irregular shapes, and the first plastic layer can be a layer structure with uniform or non-uniform thickness.

[0339] In an embodiment of the present application, at least part of the first oxide film layer 19 is covered by the first plastic layer 15. That is, the covering method of the first plastic layer can be set according to actual needs. Specifically, the first plastic layer can cover all the first oxide film layer, or the first plastic layer can also cover part of the first oxide film layer.

[0340] In an embodiment of the present application, the plastic material in the first plastic layer 15 is the same as the plastic material in part of the third nanopores.

[0341] Referring to FIG. 17, a schematic diagram of a shear strength test of the metal-plastic composite structure according to an embodiment of the present application is shown. The shear strength between the first plastic layer 15 and the first metal layer 11 is greater than or equal to 20 MPa, which improves the bonding ability between the first plastic layer 15 and the first metal layer 11. Specifically, the shear strength between the first plastic layer and the first metal layer can be, but is not limited to, greater than or equal to 20 MPa, greater than or equal to 22 MPa, greater than or equal to 24 MPa, greater than or equal to 26 MPa, greater than or equal to 28 MPa, or greater than or equal to 30 MPa, etc. In an embodiment of the present application, the shear strength between the first plastic layer and the first metal layer can be greater than or equal to 25.6 MPa. In another embodiment of the present application, the shear strength between the first plastic layer and the first metal layer can be greater than or equal to 27.5 MPa.

[0342] In an embodiment of the present application, after the shear strength test, the residual area of the first plastic layer on the surface of the first metal layer is greater than or equal to 95%. That is, the bonding force between the first plastic layer and the first metal layer is large, and after the shear strength test, the first plastic layer and the first metal layer cannot be completely separated, and at least part of the plastic material remains on the surface of the first metal layer. Specifically, after the shear strength test, the residual area of the first plastic layer on the surface of the first metal layer can be, but is not limited to, greater than or equal to 95%, greater than or equal to 96%, greater than or equal to 97%, greater than or equal to 98%, or greater than or equal to 99%, etc. In an embodiment of the present application, after the shear strength test, the residual area of the first plastic layer on the surface of the first metal layer can be greater than or equal to 96%.

[0343] In an embodiment of the present application, the second oxide film layer 20 is adjacent to the second metal layer 12, the second oxide film layer 20 comprises an oxide of the material of the second metal layer 12, the second oxide film layer 20 comprises a sixth metal oxide, and at least one metal element in the sixth metal oxide is the same as at least one metal element in the second metal layer. In some embodiments, the metal element in the sixth metal oxide is the same as the metal element in the second metal layer.

[0344] In an embodiment of the present application, the thickness of the second oxide film layer 20 is 100 nm-3000 nm, and the suitable second oxide film layer 20 can improve the bonding ability between the second metal layer 12 and the second plastic layer 18. Specifically, the thickness of the second oxide film layer can be, but is not limited to, 100 nm, 200 nm, 800 nm, 1000 nm, 1800 nm, 2000 nm, 2800 nm, or 3000 nm, etc. In an embodiment of the present application, the thickness of the second oxide film layer can be 100 nm-1800 nm. In another embodiment of the present application, the thickness of the second oxide film layer can be 1500 nm-3000 nm.

[0345] In an embodiment of the present application, the total area ratio of the nano-pores on the surface of the second oxidation film layer close to the second plastic layer is 20%-90%. The second oxidation film layer is a loose porous structure, and the porosity of the second oxidation film layer is characterized by the total area ratio of the nano-pores on the surface of the second oxidation film layer close to the second plastic layer, wherein the nano-pores are pores with a pore size less than or equal to 100 nm, which can be obtained by scanning the surface of the second oxidation film layer close to the second plastic layer by scanning electron microscopy (SEM). A suitable porosity can improve the bonding capacity of the second metal layer and the second plastic layer, and improve the bonding capacity of the metal-plastic composite structure. Specifically, the total area ratio of the nano-pores on the surface of the second oxidation film layer close to the second plastic layer can be, but is not limited to, 20%, 40%, 50%, 60%, 70%, 80%, or 90%, etc. In an embodiment of the present application, the total area ratio of the nano-pores on the surface of the first plastic layer in the second oxidation film layer can be 20%-70%. In another embodiment of the present application, the total area ratio of the nano-pores on the surface of the first plastic layer in the second porous oxidation film layer can be 60%-90%.

[0346] In an embodiment of the present application, the second oxidation film layer 20 is a non-flat surface, and the surface roughness Ra of the side of the second oxidation film layer close to the second plastic layer is 0.1 μm-20 μm, which increases the specific surface area of the side of the second oxidation film layer close to the second plastic layer, and forms a concave-convex interlocking structure between the second plastic layer and the second oxidation film layer, which is beneficial to improve the strength and reliability of the metal-plastic composite structure. Specifically, the surface roughness Ra of the side of the second oxidation film layer close to the second plastic layer can be, but is not limited to, 0.1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 30 μm, 40 μm, or 50 μm, etc. In an embodiment of the present application, the surface roughness Ra of the side of the second oxidation film layer close to the second plastic layer can be 0.1 μm-30 μm. In another embodiment of the present application, the surface roughness Ra of the side of the second oxidation film layer close to the second plastic layer can be 28 μm-50 μm.

[0347] In an embodiment of the present application, the second oxidation film layer 20 includes a plurality of fourth nano-pores, the fourth nano-pores are closely arranged in the second oxidation film layer, and at least part of the fourth nano-pores are filled with plastic material, which can improve the bonding force between the second plastic layer and the second metal layer. In some embodiments, all the fourth nano-pores in the second oxidation film layer are filled with plastic material. In other embodiments, at least part of the fourth nano-pores are completely filled with plastic material, and at least part of the fourth nano-pores are partially filled with plastic material.

[0348] In an embodiment of the present application, the average pore size of the fourth nanopores is 10-50 nm. The appropriate pore size increases the specific surface area of the fourth nanopores, promotes the entry of the plastic, and improves the bonding force between the first metal layer and the first plastic layer. Specifically, the average pore size of the fourth nanopores can be, but is not limited to, 10 nm, 20 nm, 30 nm, 35 nm, 40 nm, 45 nm, or 50 nm, etc. In an embodiment of the present application, the average pore size of the fourth nanopores can be 10-35 nm. In another embodiment of the present application, the average pore size of the fourth nanopores can be 30-50 nm.

[0349] In an embodiment of the present application, the difference between the average pore size of the third nanopores and the average pore size of the fourth nanopores is less than or equal to 30 nm. Controlling the difference between the average pore size of the third nanopores and the average pore size of the fourth nanopores can keep the specific surface areas of the first metal layer and the second metal layer similar, improve the bonding ability between the plastic layer and the metal layer, and avoid the imbalance between the bonding ability between the first plastic layer and the first metal layer and the bonding ability between the second plastic layer and the second metal layer, which leads to the decline of the mechanical properties of the metal-plastic composite structure. Specifically, the difference between the average pore size of the third nanopores and the average pore size of the fourth nanopores can be, but is not limited to, less than or equal to 30 nm, less than or equal to 30 nm, less than or equal to 25 nm, less than or equal to 22 nm, less than or equal to 20 nm, less than or equal to 17 nm, or less than or equal to 15 nm, etc. In an embodiment of the present application, the difference between the average pore size of the third nanopores and the average pore size of the fourth nanopores can be less than or equal to 20 nm. In another embodiment of the present application, the difference between the average pore size of the third nanopores and the average pore size of the fourth nanopores can be less than or equal to 15 nm.

[0350] In an embodiment of the present application, the pore depth of the fourth nanopores is 100-3000 nm. The appropriate pore depth can improve the bonding ability between the first metal layer and the first plastic layer. Specifically, the pore depth of the fourth nanopores can be, but is not limited to, 100 nm, 200 nm, 800 nm, 1000 nm, 1800 nm, 2000 nm, 2800 nm, or 3000 nm, etc. In an embodiment of the present application, the pore depth of the fourth nanopores can be 100-1600 nm. In another embodiment of the present application, the pore depth of the fourth nanopores can be 1500-3000 nm.

[0351] In the present application, the shortest distance between two adjacent fourth nanopores is less than or equal to 50 nm. The shortest distance between two adjacent fourth nanopores is the straight-line shortest distance between the edge positions of the two adjacent fourth nanopores. Specifically, the shortest distance between two adjacent fourth nanopores can be, but is not limited to, less than or equal to 50 nm, less than or equal to 40 nm, less than or equal to 30 nm, less than or equal to 20 nm, or less than or equal to 10 nm, etc. In an embodiment of the present application, the shortest distance between two adjacent fourth nanopores can be less than or equal to 35 nm. In another embodiment of the present application, the shortest distance between two adjacent fourth nanopores can be less than or equal to 20 nm.

[0352] In an embodiment of the present application, the average center-to-center distance of adjacent fourth nanopores is less than or equal to 100 nm. Since the pore type of the nanopore is approximately circular or / and elliptical, taking the circular shape as an example, the center-to-center distance refers to the distance between the centers of two adjacent fourth nanopores. The smaller the distance, the tighter the arrangement of the fourth nanopores, which is beneficial to improve the bonding force between the second metal layer and the second plastic layer. Specifically, the average center-to-center distance of adjacent fourth nanopores can be, but is not limited to, less than or equal to 150 nm, less than or equal to 140 nm, less than or equal to 130 nm, less than or equal to 120 nm, less than or equal to 110 nm, or less than or equal to 100 nm, etc. In an embodiment of the present application, the average center-to-center distance of adjacent fourth nanopores can be less than or equal to 130 nm. In another embodiment of the present application, the average center-to-center distance of adjacent fourth nanopores can be less than or equal to 110 nm.

[0353] In an embodiment of the present application, the thickness of the second plastic layer 18 is 0.1 mm-200 mm. Specifically, the thickness of the second plastic layer can be, but is not limited to, 0.1 mm, 10 mm, 20 mm, 40 mm, 60 mm, 80 mm, 100 mm, 150 mm, 180 mm, or 200 mm, etc. In an embodiment of the present application, the thickness of the second plastic layer can be 0.1 mm-80 mm. In another embodiment of the present application, the thickness of the second plastic layer can be 70 mm-200 mm. In some embodiments, the thickness and shape of the second plastic layer can be designed according to actual needs, which can be regular or irregular shapes, and the second plastic layer can be a layer structure with uniform or non-uniform thickness.

[0354] In an embodiment of the present application, at least part of the second oxide film layer 20 is covered by the second plastic layer 18. That is, the covering mode of the second plastic layer 18 can be set according to actual needs. Specifically, the second plastic layer 18 can cover all the second oxide film layer 20, or the second plastic layer 18 can also cover part of the second oxide film layer 20.

[0355] In an embodiment of the present application, the first plastic layer 15 and the second plastic layer 18 can be made of the same material or different materials.

[0356] In an embodiment of the present application, the plastic material in the second plastic layer 18 is the same as the plastic material in the fourth nano-pores.

[0357] In an embodiment of the present application, the shear strength between the second plastic layer 18 and the second metal layer 12 is greater than or equal to 25 MPa, thereby improving the bonding capacity between the second plastic layer 18 and the second metal layer 12. Specifically, the shear strength between the second plastic layer and the second metal layer can be, but is not limited to, greater than or equal to 25 MPa, greater than or equal to 26 MPa, greater than or equal to 27 MPa, greater than or equal to 28 MPa, greater than or equal to 29 MPa, or greater than or equal to 30 MPa, etc. In an embodiment of the present application, the shear strength between the second plastic layer and the second metal layer can be greater than or equal to 25.6 MPa. In another embodiment of the present application, the shear strength between the second plastic layer and the second metal layer can be greater than or equal to 28 MPa.

[0358] In an embodiment of the present application, after the shear strength test, the residual area of the second plastic layer on the surface of the second metal layer is greater than or equal to 95%. That is, the bonding force between the second plastic layer and the second metal layer is large, and after the shear strength test, the second plastic layer and the second metal layer cannot be completely separated, and at least part of the plastic material remains on the surface of the second metal layer. Specifically, after the shear strength test, the residual area of the second plastic layer on the surface of the second metal layer can be, but is not limited to, greater than or equal to 95%, greater than or equal to 96%, greater than or equal to 97%, greater than or equal to 98%, or greater than or equal to 99%, etc. In an embodiment of the present application, after the shear strength test, the residual area of the second plastic layer on the surface of the second metal layer can be greater than or equal to 96%.

[0359] Please refer to FIG. 18, which is a flow chart of a method for preparing a metal-plastic composite structure according to an embodiment of the present application, including:

[0360] S201: providing a to-be-injection-molded composite metal material, the to-be-injection-molded composite metal material including a seventh metal layer and an eighth metal layer connected to each other;

[0361] S202: placing the to-be-injection-molded composite metal material in a fluorine-containing electrolyte, and after an anodic oxidation treatment, at least one of the following is satisfied: forming a first oxide film layer on the surface layer of the seventh metal layer that is not connected to the eighth metal layer, and forming a second oxide film layer on the surface layer of the eighth metal layer that is not connected to the seventh metal layer, to obtain an oxidized to-be-injection-molded composite metal material;

[0362] S203: Injection molding is performed on the oxidized composite metal material to be injection molded, satisfying at least one of the following: a first plastic layer is formed on the surface of the first oxide film layer, and a second plastic layer is formed on the surface of the second oxide film layer, to obtain a metal-plastic composite structure. The preparation method provided in this application can simultaneously form nanoporous oxide film layers on metal surfaces with different etching properties through only one anodizing treatment, shortening the preparation process, reducing preparation costs, and facilitating industrial production. The preparation method of the metal-plastic composite structure provided in this application is novel, with a simple process, mild conditions, simple surface treatment, and high bonding strength of the obtained metal-plastic composite structure.

[0363] In one embodiment of this application, the seventh metal layer of the composite metal material to be injection molded is a titanium alloy and the eighth metal layer is an aluminum alloy, and anodizing treatment is performed using a fluorine-containing electrolyte. In this case, the composite metal material to be injection molded serves as the anode, and during the anodizing treatment, the main reaction on the surface of the seventh metal layer (titanium alloy) is Ti + 2H₂O - 4e⁻. - =TiO2 + 4H + A first oxide film layer, mainly composed of titanium oxide, is formed. On the surface of the eighth metal layer (aluminum alloy), the reaction 2Al + 3H₂O → 6e⁻ occurs. - =Al2O3 + 6H + A second oxide film, primarily composed of alumina, is formed. The fluorinated electrolyte contains fluoride ions, which react with hydrogen ions on the surface of the titanium dioxide film to form hydrogen fluoride, exhibiting excellent etching effects and creating densely packed third nanopores within the first oxide film. While hydrofluoric acid has a weak etching effect on aluminum or aluminum alloys, the hydrogen ions generated during the formation of the alumina film have a strong etching effect, creating densely packed fourth nanopores within the second oxide film. Different etching principles are employed for the seventh and eighth metal layers, allowing for simultaneous pore formation in both layers, thus forming a nanoporous oxide film on the surfaces of the first and second metal layers of the composite metal material to be injection molded.

[0364] In one embodiment of this application, after the seventh metal layer in the injection-molded metal-plastic composite structure is anodized, the surface of the seventh metal layer is oxidized to form a first oxide film layer. At this time, the unoxidized portion of the seventh metal layer forms the first metal layer of the metal-plastic composite structure. Similarly, after the eighth metal layer in the injection-molded metal-plastic composite structure is anodized, the surface of the eighth metal layer is oxidized to form a first oxide film layer. At this time, the unoxidized portion of the eighth metal layer forms the second metal layer of the metal-plastic composite structure.

[0365] In an embodiment of the present application, the material of the seventh metal layer can be but is not limited to titanium or titanium alloy, and the material of the eighth metal layer can be but is not limited to aluminum or aluminum alloy, etc. Titanium or titanium alloy has the characteristics of wear resistance, corrosion resistance, small density, etc., and aluminum material has the characteristics of good heat conductivity, easy processing and low cost, which is beneficial to improve the strength and light weight of the metal-plastic composite structure. In an embodiment of the present application, the material of the seventh metal layer can be TA5, and the material of the eighth metal layer can be 6061. In some embodiments, the seventh metal layer and the first metal layer are made of the same material, and the eighth metal layer and the second metal layer are made of the same material.

[0366] In an embodiment of the present application, the fluoride-containing electrolyte includes fluoride and corrosion inhibitor, which is beneficial to industrial production under mild conditions. Specifically, the fluoride can include but is not limited to at least one of potassium fluoride, sodium fluoride, ammonium fluoride, ammonium hydrogen fluoride, fluorozirconate, fluoroborate, hydrofluoric acid, fluorozirconic acid and fluoroboric acid. In an embodiment of the present application, the fluoride can be potassium fluoride.

[0367] In an embodiment of the present application, the concentration of fluoride ions in the fluoride-containing electrolyte is 0.5 g / L-10 g / L. Specifically, the concentration of fluoride ions in the fluoride-containing electrolyte can be but is not limited to 0.5 g / L, 1 g / L, 2 g / L, 4 g / L, 6 g / L, 8 g / L or 10 g / L, etc. In an embodiment of the present application, the concentration of fluoride ions in the fluoride-containing electrolyte can be 0.5 g / L-6 g / L. In another embodiment of the present application, the concentration of fluoride ions in the fluoride-containing electrolyte can be 5 g / L-10 g / L.

[0368] In an embodiment of the present application, the pH value of the fluoride-containing electrolyte is 2-12. Specifically, the pH value of the fluoride-containing electrolyte can be but is not limited to 2, 4, 6, 8, 10 or 12, etc. In an embodiment of the present application, the pH value of the fluoride-containing electrolyte can be 2-6. In another embodiment of the present application, the pH value of the fluoride-containing electrolyte can be 7-12.

[0369] In an embodiment of the present application, the corrosion inhibitor can slow down the etching speed of the metal layer, and avoid causing serious damage to the metal layer. The corrosion inhibitor can be an oxidizing corrosion inhibitor or a non-oxidizing corrosion inhibitor. Specifically, the zinc oxide corrosion inhibitor can be, but is not limited to, at least one of chromate, dichromate, molybdate, tungstate, permanganate, hydrogen peroxide, ozone, hypochlorous acid, hypochlorite, and trivalent iron ions. The non-oxidizing corrosion inhibitor includes at least one of aldehydes, amines, organic sulfides, heterocyclic compounds, organic acids, and organic acid salts. Specifically, the non-oxidizing corrosion inhibitor can be, but is not limited to, at least one of amino acids, benzotriazole, chitosan, hexadecylamine, quinoline, mercaptobenzothiazole, methylbenzotriazole, imidazoline, thiazoline, ethylenediaminetetraacetic acid and its salts, gluconate and its salts, malate and its salts, oxalate and its salts, citrate and its salts, succinate and its salts, lactate and its salts, malonate and its salts, adipate and its salts, and diphenyl disulfide. In an embodiment of the present application, when the corrosion inhibitor is an oxidizing corrosion inhibitor, the corrosion inhibitor can be potassium permanganate. In another embodiment of the present application, when the corrosion inhibitor is a non-oxidizing corrosion inhibitor, the corrosion inhibitor can be malonic acid.

[0370] In an embodiment of the present application, the fluoride-containing electrolyte further includes an auxiliary agent. The auxiliary agent includes at least one of a pH buffer and a surfactant, and can reduce the surface tension of the fluoride-containing electrolyte, improve the wettability, and promote the consistency and uniformity of the anodization reaction. Specifically, the pH buffer can include, but is not limited to, at least one of carbonates, bicarbonates, acetic acid and its salts, phosphoric acid and its salts, and pyrophosphoric acid and its salts. The surfactant can include, but is not limited to, at least one of sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, sodium dodecyl sulfonate, cetyltrimethylamine, and carboxymethyl cellulose. In an embodiment of the present application, when the auxiliary agent is a pH buffer, the auxiliary agent can be phosphoric acid. In another embodiment of the present application, when the auxiliary agent is a surfactant, the auxiliary agent can be sodium dodecyl sulfonate.

[0371] In an embodiment of the present application, the fluoride-containing electrolyte further includes a solvent. Specifically, the solvent can include, but is not limited to, at least one of water, ethylene glycol, propylene glycol, glycerol, 1,3-butanediol, ethanol, and propanol. In an embodiment of the present application, the solvent can be water and propylene glycol.

[0372] In an embodiment of the present application, in the anodization process, the heterogeneous composite metal serves as an anode, and the cathode can include, but is not limited to, stainless steel, platinum, iridium, or graphite plate, etc. In an embodiment of the present application, the cathode can be a graphite plate.

[0373] In an embodiment of the present application, the voltage of the anodization treatment is 5-50V, the time of the anodization treatment is 1-60min, and the temperature of the anodization treatment is 5-80℃. The suitable voltage, time and temperature of the anodization treatment can promote the formation of the oxide film layer and improve the bonding capacity between the metal layer and the plastic layer. Specifically, the voltage of the anodization treatment can be, but is not limited to, 5V, 15V, 25V, 35V, 45V or 50V, etc.; the time of the anodization treatment can be, but is not limited to, 1min, 10min, 20min, 30min, 40min, 50min or 60min, etc.; and the temperature of the anodization treatment can be, but is not limited to, 5℃, 15℃, 25℃, 45℃, 55℃, 65℃, 75℃ or 80℃, etc. In an embodiment of the present application, the voltage of the anodization treatment can be 5-40V, the time of the anodization treatment can be 1-40min, and the temperature of the anodization treatment can be 5-60℃. In another embodiment of the present application, the voltage of the anodization treatment can be 35-50V, the time of the anodization treatment can be 30-60min, and the temperature of the anodization treatment can be 55-80℃.

[0374] In an embodiment of the present application, the temperature of the injection molding is 200-500℃, and the pressure of the injection molding is 75-300MPa, which can promote the plastic to enter the nanopores in the oxide film layer and improve the bonding capacity between the plastic layer and the metal layer. Specifically, the temperature of the injection molding can be, but is not limited to, 200℃, 250℃, 300℃, 350℃, 400℃, 450℃ or 500℃, etc.; and the pressure of the injection molding can be, but is not limited to, 75MPa, 100MPa, 150MPa, 200MPa, 250MPa or 300MPa, etc. In an embodiment of the present application, the temperature of the injection molding can be 250-380℃, and the pressure of the injection molding can be 120-200MPa, which can improve the bonding capacity between the plastic layer and the metal layer. In another embodiment of the present application, the temperature of the injection molding can be 350-500℃, and the pressure of the injection molding can be 175-300MPa.

[0375] In an embodiment of the present application, different molds can be used according to the actual use requirements during the injection molding, and the temperature of the mold is 80-350℃. Specifically, the temperature of the mold can be, but is not limited to, 80℃, 100℃, 120℃, 180℃, 200℃, 250℃ or 350℃, etc. In an embodiment of the present application, the temperature of the mold can be 130-230℃, which can improve the effect of the injection molding. In another embodiment of the present application, the temperature of the mold can be 200-350℃.

[0376] In an embodiment of the present application, the material of the injection molding includes plastic and glass fiber, and the plastic can include, but is not limited to, at least one of polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), acrylonitrile-styrene-diene copolymer (ABS), polyamide (PA), polyphthalamide (PPA), polypropylene (PP), polyethylene terephthalate (PET), polycarbonate (PC), polyphenylene sulfone resin (PPSU), polyaryletherketone (PEAK) and polyether ether ketone (PEEK). In an embodiment of the present application, the material of the injection molding can be polybutylene terephthalate (PBT).

[0377] In an embodiment of the present application, the mass percentage of the glass fiber in the material of the injection molding is less than or equal to 55%. Specifically, the mass percentage of the glass fiber can be, but is not limited to, less than or equal to 55%, less than or equal to 50%, less than or equal to 45%, less than or equal to 40%, less than or equal to 35%, less than or equal to 30% or less than or equal to 20%, etc. In an embodiment of the present application, the mass percentage of the glass fiber can be 40%.

[0378] In an embodiment of the present application, the pretreatment before the anodization treatment includes degreasing, alkali etching, sanding, chemical polishing, neutralization, cleaning, etc., which can remove the surface impurities of the heterogeneous composite metal 200, improve the surface roughness, and facilitate the anodization treatment.

[0379] In an embodiment of the present application, the cleaning and baking after the anodization treatment can remove the fluorine-containing electrolyte remaining on the surface of the oxide film layer after the anodization treatment, and facilitate the injection molding.

[0380] The application further provides a preparation method of a metal composite structure, comprising: providing a composite metal material, the composite metal material comprising a seventh metal layer and an eighth metal layer connected to each other; placing the composite metal material in a fluorine-containing electrolyte, and after an anodic oxidation treatment, forming a first oxide film layer on the surface of the seventh metal layer not connected to the eighth metal layer, and forming a second oxide film layer on the surface of the eighth metal layer not connected to the seventh metal layer, to obtain an oxidized injection-molding composite metal material; the first metal layer and the second metal layer are metal layers of different materials; the first oxide film layer comprises a fifth metal oxide, at least one metal element in the fifth metal oxide being the same as at least one metal element in the first metal layer, the second oxide film layer comprises a sixth metal oxide, at least one metal element in the sixth metal oxide being the same as at least one metal element in the second metal layer, the first oxide film layer being the same as or different from the second oxide film layer; the first oxide film layer comprises a plurality of third nanopores, and the shortest distance between any two adjacent third nanopores is less than or equal to 50 nm; and the second oxide film layer comprises a plurality of fourth nanopores, and the shortest distance between any two adjacent fourth nanopores is less than or equal to 50 nm. The preparation method of the metal composite structure provided by the application is simple, has low preparation cost, and the prepared metal composite structure has excellent comprehensive performance.

[0381] At present, in order to make the electronic product shell have good mechanical properties and light weight, a method of compounding a metal with small density such as an aluminum alloy and a metal with good mechanical properties such as stainless steel is usually adopted, so that the density of the obtained composite metal is greatly reduced compared with stainless steel, and the stiffness and strength are greatly increased compared with aluminum alloy. Although the heterogeneous metal obtained by the composite metal has the advantage of one-piece forming, due to the difference in metal fluidity between the two different metals, when a product is prepared by one-piece forming such as die casting or casting in a large area, the deformation of the product is large, the interface between the two heterogeneous metal layers in the composite metal cannot form a clear and regular boundary line, and the thickness of the two heterogeneous metal layers is uneven, thereby causing poor combination between the heterogeneous metal layers, making it difficult to meet the mechanical property requirements of subsequent processing and being easy to separate and fall off during use; it also causes the overall mechanical properties of the obtained composite metal to be uneven, the range of the R angle obtained by stamping the composite metal is limited, and local deformation is easy to occur during use; and it also causes the color of the final product to be uneven due to uneven distribution of the heterogeneous metal layers during anodic oxidation coloring, affecting the appearance of the product.

[0382] In view of the above problems, the application provides a composite metal 200, which is connected by arranging a concave-convex structure on the surfaces of a first metal layer 11 and a second metal layer 12 and by a connecting layer 21, effectively improving the combination between the first metal layer and the second metal layer of the composite metal, and thereby improving the performance of processing and forming, and meeting higher processing requirements.

[0383] Referring to FIG. 23, a schematic diagram of a cross-sectional structure of a composite metal 200 according to an embodiment of the present application is shown. The composite metal 200 according to the present application includes a first metal layer 11 and a second metal layer 12 arranged in a stack, and a connecting layer 21 arranged between the first metal layer 11 and the second metal layer 12. In the embodiment of the present application, the first metal layer 11 and the second metal layer 12 are different metal layers, and at least one of the following conditions is satisfied: the surface of the first metal layer 11 combined with the connecting layer 21 is provided with at least one concave-convex structure, and the surface of the second metal layer 12 combined with the connecting layer 21 is provided with at least one concave-convex structure, wherein at least one of the following conditions is satisfied: the concave-convex structure includes at least one concave structure, and the concave-convex structure includes at least one convex structure. The composite metal according to the present application includes a first metal layer and a second metal layer of different materials, so that the composite metal has high strength and light weight, thereby improving the applicability of the composite metal in various fields, especially in electronic device housings. The composite metal according to the present application further includes a connecting layer between the first metal layer and the second metal layer, and the surface of the first metal layer combined with the connecting layer and the surface of the second metal layer combined with the connecting layer are both provided with a plurality of concave-convex structures, so that the concave-convex structure part in the connecting layer is embedded in the first metal layer and the second metal layer through mechanical combination, thereby being tightly and closely combined with the first metal layer and the second metal layer, forming a firmly combined composite metal whole, significantly improving the bonding force between the first metal layer and the second metal layer, prolonging the service life of the composite metal, and more favorably meeting the demand for mechanical properties of the forming process of the composite metal in actual production and application. In addition, the connecting layer serves as a transition layer between the first metal layer and the second metal layer, and the connecting layer is provided with concave-convex structures on the combined surfaces of the first metal layer and the second metal layer, which can effectively buffer the problems such as uneven thickness of the first metal layer and the second metal layer and unclear boundary line at the combined interface caused by different flowabilities of the two different materials during the forming process, thereby effectively improving the comprehensive mechanical properties of the composite metal, widening the application scenarios thereof, for example, improving the forming limit of the R angle during stamping forming, thereby forming a nearly right-angle structure.

[0384] It should be noted that the specific shape and size of the first metal layer 11 and the second metal layer 12 in the embodiments of the present application are not limited, and can be designed according to actual needs. The first metal layer 11 can be a regular shape or an irregular shape, and can be a layer structure with equal thickness or unequal thickness at different positions. The second metal layer 12 can be a regular shape or an irregular shape, and can be a layer structure with equal thickness or unequal thickness at different positions.

[0385] In an embodiment of the present application, the composite metal can be a metal processing raw material, which can be subsequently formed into a product according to actual use requirements. In an embodiment of the present application, the shape of the composite metal is not required, and the composite metal can be, for example, a plate, a profile or a casting according to different use requirements. In an embodiment of the present application, the plate includes but is not limited to a thick plate, a foil, a strip (coiled material).

[0386] Referring to FIG. 24, FIG. 24 is a schematic diagram of the concave-convex structure of the bonding surface of at least one of the connecting layer 21 and the first metal layer 11, and the connecting layer 21 and the second metal layer 12 in the composite metal 200 provided in an embodiment of the present application; the concave-convex structure satisfies at least one of the following: including at least one concave structure, and including at least one convex structure. In some embodiments, one convex structure is formed between every two adjacent concave structures, and the concave structures and the convex structures are continuously arranged. In other embodiments, the concave structures and the convex structures are independently arranged structures, and the concave structures and the convex structures are discontinuous.

[0387] In some embodiments, one convex structure is formed between every two adjacent concave structures, and the distance D1 between the two adjacent concave structures is the minimum straight-line distance between the edges of the two adjacent concave structures. In an embodiment of the present application, the distance D1 between the two adjacent concave structures is 0.1 mm-0.5 mm, and the suitable distribution of the concave structure can be more conducive to the concave-convex structure part of the connecting layer being embedded in the first metal layer and the second metal layer, thereby improving the bonding force between the connecting layer and the first metal layer and the second metal layer. Specifically, the distance D1 between the two adjacent concave structures can be, but is not limited to, 0.1 mm, 0.15 mm, 0.2 mm, 0.25 mm, 0.3 mm, 0.35 mm, 0.4 mm, 0.45 mm or 0.5 mm, etc.

[0388] In an embodiment of the present application, the depth H of the concave structure is the absolute value of the difference between the vertical distance between the highest point of the convex structure and the lowest point of the concave structure. In an embodiment of the present application, the depth H of the concave structure is 100 μm-500 μm. A suitable depth of the concave structure can improve the bonding performance between the connecting layer and the first metal layer and the second metal layer. Specifically, the depth H of the concave structure can be, but is not limited to, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, 350 μm, 400 μm, 450 μm or 500 μm, etc. In an embodiment of the present application, the lateral dimension D2 of the concave structure is 50 μm-350 μm. A suitable size of the concave structure can optimize the design of the concave-convex structure and improve the bonding force between the connecting layer and the first metal layer and the second metal layer. In an embodiment of the present application, the lateral dimension of the concave structure specifically refers to the diameter or side length of the cross-sectional shape of the concave structure in the direction perpendicular to the thickness direction of the composite metal. Specifically, the lateral dimension D2 of the concave structure can be, but is not limited to, 50 μm, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, 350 μm.

[0389] In an embodiment of the present application, the cross-sectional shape of each concave structure in the thickness direction of the composite metal can be rectangular, trapezoidal, triangular or T-shaped. In an embodiment of the present application, the cross-sectional shapes of the plurality of concave structures in the thickness direction of the composite metal can be the same or different. As shown in FIG. 25, in some embodiments of the present application, the cross-sectional shape of the concave structure in the thickness direction of the composite metal can be rectangular, as shown in (a) of FIG. 25. The rectangle can be a rectangle, as shown in (b) of FIG. 25, or a square. In an embodiment of the present application, as shown in (c) of FIG. 25, the cross-sectional shape of the concave structure in the thickness direction of the composite metal can be triangular. In an embodiment of the present application, as shown in (d) of FIG. 25, the cross-sectional shape of the concave structure in the thickness direction of the composite metal can be T-shaped. When the cross-sectional shape is T-shaped, it can be beneficial to form a "barb" structure at the bonding interface between the connecting layer and the first metal layer and the second metal layer, thereby improving the bonding force between the connecting layer and the first metal layer and the second metal layer, and thus improving the bonding force between the first metal layer and the second metal layer.

[0390] As shown in FIG. 2, the surface of the concave-convex structure is further provided with a nano secondary structure. In some embodiments, the inner surface of at least one of the concave structures is provided with a first nano secondary structure, and the inner surface of the concave structure includes the sidewall of the concave structure and the bottom surface of the concave structure. In an embodiment of the present application, the first nano secondary structure includes a nanopore, and the diameter of the nanopore is 50 nm-500 nm. Specifically, the diameter of the nanopore can be, but is not limited to, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, or 500 nm, etc. In some embodiments, the outer surface of at least one of the convex structures is provided with a second nano secondary structure, and the outer surface of the convex structure includes the sidewall of the convex structure and the top surface of the convex structure. In an embodiment of the present application, the second nano secondary structure includes a nanopore, and the diameter of the nanopore is 50 nm-500 nm. Specifically, the diameter of the nanopore can be, but is not limited to, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, or 500 nm, etc. Continuously providing a nano secondary structure on the surface of the micro-level concave-convex structure can optimize the design of the concave-convex structure, improve the surface roughness of the concave-convex structure, and thus improve the bonding force between the connection layer and the first metal layer and the second metal layer.

[0391] In an embodiment of the present application, at least one of the following is satisfied: the surface roughness of the concave-convex structure is 10 μm-25 μm, i.e., the concave structure, and the surface roughness of the convex structure is 10 μm-25 μm. The surface roughness of the concave-convex structure is caused by the nano secondary structure on the surface of the concave-convex structure. Controlling the surface roughness of the concave-convex structure within a suitable range can improve the bonding force between the first metal layer and the second metal layer.

[0392] In an embodiment of the present application, the connection layer 21 includes a metal or a resin. In some specific embodiments, the metal can be, but is not limited to, at least one of magnesium and its alloy, aluminum and its alloy, zinc and its alloy, copper and its alloy. When the connection layer includes a metal, at least one of the following is satisfied: the connection layer and the first metal layer are different metal layers, and the second metal layer is a different metal layer. In other specific embodiments, the resin includes, but is not limited to, at least one of polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), polyamide (PA), polyphthalamide (PPA), polypropylene (PP), polycarbonate (PC), polyphenylene sulfone (PPSU), polyether ether ketone (PEEK).

[0393] In an embodiment of the present application, the connecting layer 21 comprises metal. The ratio of the hardness of the connecting layer to the hardness of the metal layer with smaller hardness among the first metal layer and the second metal layer is 1:(0.8-1.2). The smaller the hardness of the metal, the poorer the deformation resistance of the metal, and the greater the deformation of the metal under external force. Therefore, when the connecting layer is metal, the present application controls the hardness of the connecting layer to be close to the hardness of the metal layer with smaller hardness among the first metal layer and the second metal layer, so as to minimize the difference in deformation between the connecting layer and the first metal layer and the second metal layer, improve the deformation coordination between the heterogeneous metals, and improve the connecting buffering effect of the connecting layer and the combination between the connecting layer and the first metal layer and the second metal layer. Specifically, the ratio of the hardness of the connecting layer to the hardness of the metal layer with smaller hardness among the first metal layer and the second metal layer can be, but is not limited to, 1:0.8, 1:0.9, 1:1, 1:1.1, or 1:1.2, etc.

[0394] In an embodiment of the present application, the ratio of the thermal expansion coefficient of the connecting layer 21 to the thermal expansion coefficient of the metal layer with larger thermal expansion coefficient among the first metal layer 11 and the second metal layer 12 is 1:(0.8-1.2). The greater the thermal expansion coefficient of the metal, the greater the deformation of the metal when the temperature rises. Therefore, when the connecting layer is metal, the present application controls the thermal expansion coefficient of the connecting layer to be close to the thermal expansion coefficient of the metal layer with larger thermal expansion coefficient among the first metal layer and the second metal layer, so as to minimize the difference in deformation between the connecting layer and the first metal layer and the second metal layer when heated, improve the deformation coordination between the heterogeneous metals, and make the connecting layer better combined with the first metal layer and the second metal layer during the preparation of the composite metal, so that the phenomenon of peeling or cracking between the layers of the composite metal due to too large difference in thermal expansion coefficient does not occur. In some specific embodiments, the ratio of the thermal expansion coefficient of the connecting layer to the thermal expansion coefficient of the metal layer with larger thermal expansion coefficient among the first metal layer and the second metal layer can be, for example, 1:0.8, 1:0.9, 1:1, 1:1.1, or 1:1.2, etc. In an embodiment of the present application, the first metal layer is titanium alloy, the second metal layer is aluminum alloy, and the thermal expansion coefficient of the connecting layer is 2×10 -5 / K-2.7×10 -5 / K. Specifically, the thermal expansion coefficient of the connecting layer can be, but is not limited to, 2×10 -5 / K, 2.1×10 -5 / K, 2.2×10 -5 / K, 2.3×10 -5 / K, 2.4×10 -5 / K, 2.5×10 -5 / K, 2.6×10 -5 / K, or 2.7×10 -5 / K, etc.

[0395] In the embodiments of the present application, the connecting layer 21 and the first metal layer 11 and the second metal layer 12 are different metal layers, i.e., the connecting layer and the first metal layer are different metal layers and the connecting layer and the second metal layer are different metal layers. In some embodiments of the present application, at least one of the following is satisfied: the connecting layer and the first metal layer are different types of metal alloys, and the second metal layer 12 is a different type of metal alloy. In other embodiments of the present application, at least one of the following is satisfied: the connecting layer 21 and the first metal layer 11 are the same type but different models of metal alloys, and the second metal layer is the same type but different models of metal alloys. Since the connecting layer and the first metal layer and the second metal layer are different metal layers, there is a micron-level intermetallic diffusion bonding layer formed by intermolecular thermal motion at the interface between the connecting layer and the first metal layer and the second metal layer, which includes the connecting metal in the connecting layer and the first metal in the first metal layer or the second metal in the second metal layer, i.e., the elements of the connecting metal and the elements of the first metal can be measured simultaneously at each point in the intermetallic diffusion layer between the connecting layer and the first metal layer by EDS (Energy Dispersive Spectroscopy), and the elements of the connecting metal and the elements of the second metal can be measured simultaneously at each point in the intermetallic diffusion layer between the connecting layer and the second metal layer. The thickness of the intermetallic diffusion layer corresponds to the intermetallic diffusion depth, which is the depth in the thickness direction of the composite metal. In an embodiment of the present application, the intermetallic diffusion depth is 1-10 μm. Controlling the intermetallic diffusion depth between the connecting layer and the first metal layer and the second metal layer to a smaller range can make the heterogeneous metal interface bonding performance better, thereby improving the bonding force between the heterogeneous metals and improving the comprehensive mechanical properties of the composite metal, which can improve the forming limit of the R angle during stamping forming, thereby forming a nearly right angle structure, and also making the organization at the R angle uniform, obtaining a color-uniform product during subsequent anodic oxidation coloring, and improving the appearance of the product. Specifically, the intermetallic diffusion depth may, for example, be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm.

[0396] In an embodiment of the present application, the shear strength between the first metal layer 11 and the second metal layer 12 is greater than or equal to 100 MPa. By using the connecting layer and setting the concave-convex structure at the interface bonding between the first metal layer and the connecting layer and between the second metal layer and the connecting layer, the present application can significantly improve the bonding strength between the first metal layer and the second metal layer, and further improve the comprehensive mechanical properties of the composite metal, facilitate subsequent forming processing and prolong the service life of the composite metal. Specifically, the bonding strength between the first metal layer and the second metal layer can be, but is not limited to, 100 MPa, 105 MPa, 110 MPa, 120 MPa, 130 MPa, 150 MPa, 180 MPa or 200 MPa, etc. In some embodiments, the shear strength between the first metal layer and the connecting layer is greater than or equal to 100 MPa. In some embodiments, the shear strength between the second metal layer and the connecting layer is greater than or equal to 100 MPa.

[0397] In an embodiment of the present application, the first metal layer 11 comprises at least one of magnesium and its alloys, aluminum and its alloys, copper and its alloys, iron and its alloys, zirconium and its alloys, titanium and its alloys, manganese and its alloys, chromium and its alloys, and zinc and its alloys; and the second metal layer 12 comprises at least one of magnesium and its alloys, aluminum and its alloys, copper and its alloys, iron and its alloys, zirconium and its alloys, titanium and its alloys, manganese and its alloys, chromium and its alloys, and zinc and its alloys.

[0398] In an embodiment of the present application, the first metal layer 11 can be used as an outer metal layer 301 of the shell, i.e., as an outer surface metal layer exposed outside the shell. In some specific embodiments, the first metal layer 11 comprises at least one of iron and its alloys, zirconium and its alloys, and titanium and its alloys. In some specific embodiments, the iron alloy comprises a steel, i.e., an iron-carbon alloy. In some specific embodiments, the elastic modulus of the first metal layer is 30 GPa-300 GPa, and the elastic modulus of the first metal layer is greater than the elastic modulus of the second metal layer. In some specific embodiments, the yield strength of the first metal layer is 100 MPa-1000 MPa, and the yield strength of the first metal layer is greater than the yield strength of the second metal layer. When the first metal layer is used as an outer surface metal layer exposed outside, controlling its elastic modulus and strength within a suitable range can provide better mechanical properties for the shell to cope with the impact when the shell encounters sharp objects or falls.

[0399] In an embodiment of the present application, the second metal layer 12 can be used as an inner metal layer 302 of the shell, i.e., as an inner surface metal layer not exposed outside the shell. In some specific embodiments, the second metal layer comprises at least one of magnesium and its alloys, aluminum and its alloys, copper and its alloys, and zinc and its alloys. In some embodiments, the second metal layer has a thermal conductivity of 10 W·m -1 ·k -1 -1000 W·m-1 ·k -1 , and the thermal conductivity of the second metal layer is greater than the thermal conductivity of the first metal layer. In some embodiments, the density of the second metal layer is greater than or equal to 1.2 g / cm 3 , and the density of the second metal layer is less than the density of the first metal layer. When the shell is an electronic device shell, the second metal layer serves as an inner surface metal layer close to the interior of the electronic device. By controlling the thermal conductivity and density of the second metal layer within a suitable range, better heat dissipation performance can be provided and the weight of the entire shell can be reduced.

[0400] In an embodiment of the present application, the first metal layer 11 comprises titanium alloy, the second metal layer 12 comprises 6013 aluminum alloy, and the connecting layer 21 comprises A380 aluminum alloy. Titanium alloy has good mechanical properties. If the first metal layer is made of titanium alloy, the resulting composite metal can be used as a device shell to effectively protect the device inside the shell. Titanium alloy also has good wear resistance and corrosion resistance, which can improve the service life of the composite metal. Aluminum alloy has good thermal conductivity and low density. If the second metal layer is made of aluminum alloy, the resulting composite metal can be used as a device shell to effectively dissipate heat and reduce the overall mass of the shell. A380 aluminum alloy has a hardness similar to that of 6013 aluminum alloy. Using A380 aluminum alloy as a connecting layer between the first metal layer of titanium alloy and the second metal layer of 6013 aluminum alloy can improve the bonding force between the first metal layer and the second metal layer.

[0401] In an embodiment of the present application, the thickness of the first metal layer 11 is greater than or equal to 0.2 mm; the thickness of the second metal layer 12 is greater than or equal to 0.2 mm; and the thickness of the connecting layer 21 is greater than or equal to 0.05 mm. The composite metal provided by the present application can control the minimum thickness of the first metal layer and the second metal layer to 0.2 mm. Controlling the thickness of each layer of the composite metal within a suitable range can improve the bonding performance between the layers of the composite metal and facilitate subsequent processing.

[0402] The present application also provides a preparation method of a composite metal. Referring to FIG. 26, the present application provides a flow chart of a preparation method of a composite metal, which comprises the following steps:

[0403] S301, roughening the surfaces to be combined of the first metal and the second metal to form a plurality of concave-convex structures on the surfaces to be combined of the first metal and the second metal;

[0404] S302, placing the surfaces with the concave-convex structures of the first metal and the second metal opposite each other, and compounding a connecting layer between the first metal and the second metal by a solid-liquid bonding method; and obtaining a composite metal.

[0405] The preparation method provided in the application can significantly improve the bonding force between the first metal layer and the second metal layer of the obtained composite metal and improve the comprehensive mechanical properties thereof by means of solid-liquid combination of the connecting layer on the surface of the first metal and the second metal having the concave-convex structure, so that subsequent processing and forming can be facilitated. Moreover, the preparation method is novel, the process is simple, and industrial production is facilitated.

[0406] In step S301, the surface roughening treatment includes at least one of milling and laser engraving. In an embodiment of the application, the micron-level concave-convex structure is obtained on the surface of the first metal and the second metal to be combined by means of milling or laser engraving, and the shape and size of the required concave-convex structure can be obtained by adjusting the parameters of milling or laser engraving. In an embodiment of the application, the surface roughening treatment includes laser engraving. In some specific embodiments, the power of laser engraving can be 50W-200W, the frequency of laser engraving can be 70Hz-160Hz, the speed of laser engraving can be 200mm / s-700mm / s, and the number of times of laser engraving can be 1-3 times.

[0407] In an embodiment of the application, at least one of the following is met: the surface roughening treatment further includes chemical etching after milling, and chemical etching after laser engraving. The nanometer secondary structure such as nanopores can be obtained on the surface of the micron-level concave-convex structure by chemical etching, and the chemical etching includes but is not limited to ordinary chemical etching and electrochemical etching. In an embodiment of the application, the aluminum alloy is subjected to electrochemical etching, the concentration of fluoride ions in the etching solution can be 10g / L-20g / L, the temperature of electrochemical etching is 25℃, the voltage of electrochemical etching is 15V-30V, and the time of electrochemical etching is 10min-30min.

[0408] In an embodiment of the application, the solid-liquid combination specifically refers to connecting and compounding the solid first metal and the solid second metal by using a liquid connecting layer material such as metal or resin, and then filling the liquid connecting layer material into the concave-convex structure of the first metal and the second metal, so as to obtain a connecting layer which is tightly nested and combined with the first metal layer and the second metal layer after solidification. In an embodiment of the application, the filling rate of the liquid connecting layer material in the concave-convex structure of the first metal and the second metal is greater than or equal to 96%. In the application, the filling rate of the liquid connecting layer material in the concave-convex structure of the first metal and the second metal is indirectly calculated by measuring the porosity of the interface between the connecting layer and the first metal and the second metal (filling rate+porosity=100%).

[0409] The application provides application of the metal-plastic composite structure or the metal composite structure in electronic equipment, vehicles and electrical appliances, so that the service life of the electronic equipment, the vehicles and the electrical appliances is prolonged, and the preparation cost of the electronic equipment, the vehicles and the electrical appliances is reduced.

[0410] The application further provides a structural member comprising the metal-plastic composite structure according to any one of the above embodiments or the metal-plastic composite structure prepared by the preparation method according to any one of the above embodiments or the metal composite structure prepared by the preparation method according to any one of the above embodiments. In an embodiment of the application, the structural member is an electronic equipment shell comprising a middle frame and a back cover. For example, the electronic equipment shell can be an electronic equipment middle frame, wherein the first metal layer of the metal-plastic composite structure can be used as an inner metal layer of the shell close to the inside of the electronic equipment, so as to provide good heat dissipation performance for the shell and reduce the weight of the whole shell; the second metal layer can provide good mechanical properties for the shell to cope with the impact of sharp objects or the impact when the shell falls; the first oxidation layer can improve the bonding strength of the first metal layer and the first plastic layer, and / or the second oxidation layer can improve the bonding strength of the second metal layer and the second plastic layer, so as to improve the structural stability and service life of the electronic equipment shell. In some embodiments, the electronic equipment middle frame and the electronic equipment back cover can be an integrated structure or a split structure.

[0411] In an embodiment of the application, the electronic equipment shell comprises four R corners, and each R corner is greater than or equal to 0.1 mm. The application uses the composite metal with good processability obtained by connecting the bonding surfaces of the first metal layer and the second metal layer through the connecting layer to prepare the electronic equipment shell 30, so that the R corner is approximately a right angle, and the minimum R corner can reach 0.1 mm.

[0412] In an embodiment of the application, the thickness of the first metal layer in the electronic equipment shell is greater than or equal to 0.2 mm; the thickness of the second metal layer is greater than or equal to 0.2 mm; and the thickness of the connecting layer is greater than or equal to 0.05 mm. The electronic equipment shell provided by the application can make the thickness of the first metal layer exposed on the outer surface as thin as 0.2 mm, so as to realize the light weight of the product, improve the material utilization, realize green development and improve the user experience while ensuring the mechanical properties of the shell.

[0413] At present, in order to make the electronic device shell have good mechanical properties and lighter quality, the method of compounding the metal with small density and the metal with good mechanical properties is usually adopted. However, the forming method of the electronic device shell at present is usually pressure casting, casting forming or adopting the method of powder metallurgy to form multiple times, and one product structure is divided into two or more parts for processing, and then the parts are combined into a whole. The heterogeneous composite metal has the advantage of one-piece forming, which can effectively improve the combination of the electronic product shell and shorten the process flow. However, there are still problems such as the difference in flowability of different metals in the stamping forming process of the electronic device shell, the irregular bonding line of the interface between the heterogeneous metals in the electronic device shell, the uneven grain structure of the composite metal, the poor comprehensive mechanical properties, and the limited range of R angle.

[0414] With the change of the design style of electronic products in recent years, the square right-angle frame design of the electronic device shell is more and more popular. There are usually two forming methods to realize the approximate right-angle frame, one is CNC machining, that is, computer numerical control precision machining, and the other is stamping forming. Due to the particularity of the heterogeneous composite metal, only the stamping forming method can be adopted, and the upsetting and extruding process is needed to form the approximate right-angle design. The metal flowability of different metal layers of the electronic device shell compounded by different metal materials is different, which will cause the problems such as the irregular bonding line of the interface between the heterogeneous metals in the cross section of the electronic device shell, the uneven grain structure of the composite metal, the poor comprehensive mechanical properties, and the limited range of R angle.

[0415] In view of the above problems, the electronic device shell, the preparation method thereof and the electronic device are provided. The R angle of the electronic device shell 30 is small, the approximate right-angle structure can be formed, the thickness of the outer metal layer 301 and the inner metal layer 302 is uniform, the straightness of the bonding line of the cross section is small, and the comprehensive mechanical properties of the electronic device shell 30 are excellent.

[0416] Referring to FIG. 31, a schematic diagram of a partial cross-sectional structure of an electronic device shell 30 is provided according to an embodiment of the present application. The electronic device shell 30 provided by the present application includes an outer metal layer 301 and an inner metal layer 302 arranged in a stack, and the outer metal layer 301 and the inner metal layer 302 are metal layers of different materials. In an embodiment of the present application, the electronic device shell 30 has at least one first R angle, and the first R angle is greater than or equal to 0.1 mm. Specifically, the size of the first R angle can be, for example, 0.1 mm, 0.15 mm, 0.2 mm, 0.25 mm, 0.3 mm, 0.5 mm, or 1 mm. The electronic device shell provided by the present application can minimize the size of the first R angle to 0.1 mm, and control it within an appropriate range to obtain a structure close to a right angle, thereby improving the aesthetics of the electronic device shell. In an embodiment of the present application, at the first R angle, the cross-sectional joint of the outer metal layer 301 and the inner metal layer 302 has a joint line, and the straightness of the joint line is less than 0.1 mm. Since the outer metal layer 301 and the inner metal layer 302 are metal layers of different materials, a joint line will be formed at the cross-sectional joint in the thickness direction. In the present application, the straightness of the joint line refers to the total amount of variation allowed by the joint line in the cross-sectional plane in the thickness direction of the electronic device shell, that is, the width of the tolerance band. The straightness of the joint line can be measured and calculated by the metallographic test method: a part of the sample is cut and polished along the thickness direction of the sample, and then the joint line of the outer metal layer and the inner metal layer is observed and measured by a metallographic microscope, and the range is recorded as the straightness of the joint line. The present application controls the straightness of the joint line at the cross-sectional joint of the outer metal layer and the inner metal layer within a smaller range, effectively solves the problem of poor flatness of the joint line between the heterogeneous metals in the current electronic device shell, and can be beneficial to make the thickness of the outer metal layer and the inner metal layer of the electronic device shell more uniform, thereby improving the uniformity of the overall performance of the electronic device shell and the uniformity of subsequent oxidation coloring, improving the mechanical properties and aesthetics of the electronic device, and controlling the straightness of the joint line within an appropriate range can also improve the bonding force between the outer metal layer and the inner metal layer, preventing the two heterogeneous metal layers from peeling or falling off during processing or use. Specifically, the straightness of the joint line can be, for example, 0.01 mm, 0.01 mm, 0.02 mm, 0.03 mm, 0.04 mm, 0.05 mm, etc.

[0417] In an embodiment of the present application, since the outer metal layer 301 and the inner metal layer 302 are metal layers of different materials, there is a micron-level intermetallic diffusion layer formed by intermolecular thermal motion at the interface between the outer metal layer 301 and the inner metal layer 302, which includes both the first metal in the outer metal layer and the second metal in the inner metal layer, i.e. the first metal element of the outer metal layer and the second metal element of the inner metal layer can be measured at each position in the intermetallic diffusion layer between the outer metal layer and the inner metal layer by EDS (Energy Dispersive Spectroscopy). The thickness of the intermetallic diffusion layer corresponds to the diffusion depth between the metals, and the diffusion depth between the metals is specifically the depth in the thickness direction of the electronic device shell. In an embodiment of the present application, the diffusion depth between the metals is 0.1-10 μm. Controlling the diffusion depth between the metals between the outer metal layer and the inner metal layer in a smaller range can make the heterogeneous metal interface bonding performance better, thereby improving the bonding force between the outer metal layer and the inner metal layer of the electronic device shell and improving the comprehensive mechanical properties of the electronic device shell, forming a nearly right-angle structure, effectively preventing the electronic device shell from warping, curling, poor flatness and other problems after forming due to the difference in thermal deformation performance of heterogeneous metals, and also making the R-angle structure uniform, obtaining a product with uniform color after subsequent anodic oxidation coloring, and improving the appearance of the product. Specifically, the diffusion depth between the metals can be, for example, 0.1 μm, 0.2 μm, 0.3 μm, 0.5 μm, 0.6 μm, 0.8 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm.

[0418] In an embodiment of the present application, the average grain size deviation of the grain structure of the outer metal layer 301 in the electronic device shell 30 is less than or equal to 10%. The average grain size is a measure of the size of the metal grain structure, which is generally represented by the average area and average diameter of the grains, and is measured by a metallographic microscope. The average grain size deviation in the present application refers to the difference in the average grain size at two arbitrary positions, that is, the absolute value of the difference in the grain size at two arbitrary positions divided by the average grain size. In an embodiment of the present application, the measurement position of the average grain size can be any position of the outer metal layer 301 of the electronic device shell 30, specifically, the interior of the extruded region of the outer metal layer 301, the interior of the non-extruded region of the outer metal layer 301, or the extruded region of the outer metal layer 301 and the non-extruded region of the outer metal layer 301. The electronic device shell of the present application is obtained by stamping a heterogeneous composite metal, and the design of forming an approximately right-angle R corner also requires a process of upsetting and extruding. The average grain size deviation of the grain structure of the parts of the electronic device shell of the present application subjected to upsetting and extrusion and not subjected to upsetting and extrusion is less than or equal to 10%. The overall grain structure size of the electronic device shell of the present application is basically uniform, the size is uniform, and thus the uniformity of the mechanical properties of the electronic device shell can be improved, the mechanical strength and service life of the electronic device shell are improved; and when the electronic device shell is subjected to subsequent anodic oxidation coloring treatment, the corrosion degree of each part is similar, and thus a colored electronic device shell with uniform coloring can be obtained, and the aesthetic appearance of the electronic device shell is improved.

[0419] In an embodiment of the present application, the thickness of the outer metal layer is greater than or equal to 0.2 mm. The electronic device shell provided by the present application can control the minimum thickness of the outer metal layer to 0.2 mm. Specifically, the thickness of the outer metal layer can be, for example, 0.2 mm, 0.25 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.8 mm, or 1 mm. The electronic device shell provided by the present application can make the thickness of the outer metal layer exposed to the outside as thin as 0.2 mm, so as to realize the light weight of the product as much as possible while ensuring the mechanical properties of the electronic device shell, improve the material utilization rate, realize green development, and improve the user experience.

[0420] In an embodiment of the present application, the bonding strength between the outer metal layer and the inner metal layer is greater than or equal to 70 MPa. By controlling the bonding strength between the outer metal layer and the inner metal layer to be greater than or equal to 70 MPa, the comprehensive mechanical properties of the electronic device shell can be improved, the outer metal layer and the inner metal layer can be prevented from peeling off or falling off during use, and the service life of the electronic device shell can be prolonged. In an embodiment of the present application, the bonding strength between the outer metal layer and the inner metal layer can be measured by a shear test. Specifically, the bonding strength between the outer metal layer and the inner metal layer can be, but is not limited to, 70 MPa, 80 MPa, 90 MPa, 100 MPa, 105 MPa, 110 MPa, 120 MPa, 130 MPa, 150 MPa, 180 MPa, or 200 MPa, etc.

[0421] In an embodiment of the present application, the outer metal layer comprises at least one of magnesium and its alloys, aluminum and its alloys, copper and its alloys, iron and its alloys, zirconium and its alloys, titanium and its alloys, manganese and its alloys, chromium and its alloys, and zinc and its alloys; and the inner metal layer comprises at least one of magnesium and its alloys, aluminum and its alloys, copper and its alloys, iron and its alloys, zirconium and its alloys, titanium and its alloys, manganese and its alloys, chromium and its alloys, and zinc and its alloys.

[0422] In an embodiment of the present application, the outer metal layer can serve as an outer surface metal layer exposed outside the electronic device shell. When the electronic device shell is, for example, an electronic device middle frame, the outer metal layer faces the outside of the electronic device. In some specific embodiments, the outer metal layer comprises at least one of aluminum and its alloys, titanium and its alloys, iron and its alloys, and zirconium and its alloys. In some specific embodiments, the iron alloy comprises a steel, i.e., an iron-carbon alloy. In some embodiments, the elastic modulus of the outer metal layer is greater than or equal to 70 GPa, and the elastic modulus of the outer metal layer is greater than the elastic modulus of the inner metal layer. In some embodiments, the yield strength of the outer metal layer is greater than or equal to 150 MPa, and the strength of the outer metal layer is greater than the strength of the inner metal layer. When the outer metal layer serves as an outer surface metal layer exposed outside, controlling its elastic modulus and strength within a suitable range can provide the electronic device shell with better mechanical properties to cope with the impact when the electronic device shell encounters a sharp object or falls.

[0423] In an embodiment of the present application, the inner metal layer can serve as an inner surface metal layer not exposed outside the electronic device shell. When the electronic device shell is, for example, an electronic device middle frame, the inner metal layer faces the inside of the electronic device. In some specific embodiments, the inner metal layer comprises at least one of aluminum and its alloys, copper and its alloys, zinc and its alloys, and magnesium and its alloys. In some embodiments, the thermal conductivity of the inner metal layer is greater than or equal to 100 W·m -1 ·k -1, and the thermal conductivity of the inner metal layer is greater than the thermal conductivity of the outer metal layer. In some embodiments, the density of the inner metal layer is greater than or equal to 1.2 g / cm 3 , and the density of the inner metal layer is less than the density of the outer metal layer. Controlling the thermal conductivity and density of the inner metal layer within a suitable range can provide better heat dissipation performance and reduce the weight of the entire electronic device shell.

[0424] In an embodiment of the present application, the first metal layer comprises a titanium alloy, the second metal layer comprises an aluminum alloy, and the connecting layer comprises die-cast aluminum. The titanium alloy has good mechanical properties. Using the titanium alloy as the first metal layer of the composite metal used as the electronic device shell can effectively protect the internal devices of the electronic device shell. The titanium alloy has good wear resistance and corrosion resistance, which can improve the service life of the composite metal. The aluminum alloy has good thermal conductivity and a small density. Using the aluminum alloy as the second metal layer of the composite metal used as the electronic device shell can effectively dissipate heat and reduce the overall mass of the electronic device shell. The die-cast aluminum has a hardness similar to that of the aluminum alloy. Using the die-cast aluminum as the connecting layer between the first metal layer of the titanium alloy and the second metal layer of the aluminum alloy can improve the bonding force between the first metal layer and the second metal layer.

[0425] In an embodiment of the present application, the connecting layer is disposed between the outer metal layer and the inner metal layer. The connecting layer comprises, but is not limited to, a metal or a resin. In some specific embodiments, the metal can be at least one of magnesium and its alloys, aluminum and its alloys, zinc and its alloys, and copper and its alloys. The resin can be at least one of polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), polyamide (PA), polyphthalamide (PPA), polypropylene (PP), polycarbonate (PC), polyphenylene sulfone (PPSU), and polyether ether ketone (PEEK). Disposing the connecting layer between the outer metal layer and the inner metal layer can improve the bonding force between the outer metal layer and the inner metal layer.

[0426] The present application also provides a preparation method of an electronic device shell. Referring to FIG. 32, a flowchart of the preparation method of the electronic device shell according to an embodiment of the present application is provided, which comprises the following steps:

[0427] S401, providing a to-be-stamped composite metal, the to-be-stamped composite metal comprising a first metal layer and a second metal layer stacked and arranged; the first metal layer is used to form the outer metal layer, and the second metal layer is used to form the inner metal layer;

[0428] S402, placing the to-be-stamped composite metal in a stamping die for stamping treatment, and then performing heat treatment to obtain an electronic device shell blank;

[0429] S403, milling the electronic device shell blank to obtain an electronic device shell.

[0430] In step S401, referring to FIG. 33 and FIG. 34, a composite metal to be punched 300 provided by an embodiment of the present application is shown in FIG. 33, which is a planar top view of the composite metal to be punched 300, and FIG. 34 is an enlarged side view of the thickness direction of region A of the composite metal to be punched 300 in FIG. 33. In an embodiment of the present application, the composite metal to be punched 300 is a flat plate, and the composite metal to be punched 300 includes a first metal layer 11 and a second metal layer 12 stacked together, wherein the first metal layer 11 is used to form an outer metal layer 301 of an electronic device shell 30, and the second metal layer is used to form an inner metal layer of the electronic device shell 30.

[0431] As shown in FIG. 33, in an embodiment of the present application, the edge of the first metal layer 11 away from the second metal layer 12 has at least one second R angle, and the thickness of the first metal layer 11 is defined as t1, and the second R angle satisfies: 3t1≤second R angle≤6t1. Specifically, the size of the second R angle may, for example, be 3t1, 4t1, 5t1, 6t1. In an embodiment of the present application, the edge of the second metal layer 12 away from the first metal layer 11 has a third R angle at a position corresponding to the second R angle described above, and there is one third R angle corresponding to each second R angle in the composite metal to be punched. The thickness of the second metal layer 12 is defined as t2, and the third R angle satisfies: 7t2≤third R angle≤13t2. Specifically, the size of the third R angle may, for example, be 7t2, 8t2, 9t2, 10t2, 11t2, 12t2, 13t2. By specially designing the second R angle and the third R angle in the composite metal to be punched according to the thickness of the metal layer, the present application can obtain a smaller R angle that is approximately a right angle after the composite metal to be punched is punched and upset, and can ensure that the bonding line between the corresponding outer metal layer and inner metal layer has good flatness.

[0432] As can be seen from FIG. 34, the second R angle transitions to the third R angle corresponding to the position of the second R angle to form a slope, i.e., the part enclosed by the dashed line in FIG. 31. The thickness of the slope gradually decreases from the second metal layer to the first metal layer in the direction, and the top of the slope is located at the second R angle, and the bottom of the slope is located at the third R angle corresponding to the second R angle.

[0433] In an embodiment of the present application, the slope angle a of the slope is greater than or equal to 10° and less than or equal to 40°, and specifically, the slope angle a may, for example, be 10°, 15°, 20°, 25°, 30°, 35°, or 40°. The total thickness t of the composite metal to be punched is defined as t = t1 + t2, where t1 is the thickness of the first metal layer and t2 is the thickness of the second metal layer. In an embodiment of the present application, the distance L1 of the slope from the second R-angle vertex to the third R-angle vertex satisfies L1≥2t, and specifically, L1 may, for example, be 2t, 2.2t, 2.5t, 2.8t, 3t, 4t, or 5t. In an embodiment of the present application, the slope height h of the slope satisfies h≤t, and specifically, the slope height h may, for example, be 0.3t, 0.4t, 0.5t, 0.6t, 0.7t, 0.8t, 0.9t, or t. By designing the slope between the corresponding second R-angle and third R-angle of the composite metal to be punched and controlling the relevant parameters of the slope within a suitable range, the first R-angle of the composite metal to be punched after the punching and coining processes has an approximate right angle, and the bonding line between the outer metal layer and the inner metal layer has good flatness.

[0434] In step S402, referring to FIG. 35, a partial cross-sectional structure of the punching die 31 in the preparation method provided in an embodiment of the present application is shown. The punching die 31 includes an upper die 312 and a lower die 311. The lower die 311 includes a groove for placing the composite metal to be punched. A convex portion is arranged around the position where the inner wall bottom of the groove is connected to the side wall. During the punching process, the first metal layer of the composite metal to be punched is in contact with the groove of the lower die. In the embodiment of the present application, the convex portion protrudes to the side of the groove opening.

[0435] In the embodiments of the present application, the convex part includes a horizontal boss, which is a convex part portion with a consistent height in the horizontal direction, i.e., the side surface of the horizontal boss facing the groove opening is a plane. For the convenience of description, the direction along the groove side wall to the center of the groove is defined as the first direction. In the embodiments of the present application, the width L2 of the horizontal boss is the length of the horizontal boss in the first direction, and the width L2 of the horizontal boss satisfies T2≥t2, and specifically, the width L2 of the horizontal boss may, for example, be t2, 1.2t2, 1.5t2, 1.8t2, 2t2, 3t2, or 4t2. In the embodiments of the present application, the height D of the horizontal boss is the vertical straight line distance from the side surface of the horizontal boss facing the groove opening to the part of the groove inner wall bottom without the convex part, and the height D of the horizontal boss satisfies 1 / 4t1≤D≤t1, and specifically, the height D of the horizontal boss may, for example, be 1 / 4t1, 0.3t1, 0.4t1, 0.5t1, 0.6t1, 0.7t1, 0.8t1, 0.9t1, or t1. In some embodiments of the present application, the convex part further includes a first transition part connecting the horizontal boss and the groove side wall, the side surface of the first transition part facing the groove opening in the first direction is an arc-shaped curved surface or an inclined surface, and / or a second transition part connecting the horizontal boss and the part of the groove bottom without the convex part, the side surface of the second transition part facing the groove opening is an arc-shaped curved surface or an inclined surface. In the present application, through the special convex part structure design of the lower die of the stamping die and the cooperation with the specially designed composite metal to be stamped, the first R angle of approximately 90° of the composite metal to be stamped after the stamping and upsetting and extruding treatment can be obtained, and the first metal layer 11 of the composite metal to be stamped 300 is obtained after stamping to obtain the outer metal layer precursor 201, and the second metal layer 12 of the composite metal to be stamped 300 is obtained after stamping to obtain the inner metal layer precursor 202.

[0436] The minimum value of the melting point of the outer metal layer and the melting point of the inner metal layer is defined as T m , the material and the melting point of the first metal layer 11, the outer metal layer precursor 201, and the outer metal layer 301 are the same, and the material and the melting point of the second metal layer 12, the inner metal layer precursor 202, and the inner metal layer 302 are the same. In an embodiment of the present application, the stamping temperature T1 of the stamping treatment satisfies 1 / 4T m <T1<T m , and specifically, the stamping temperature may, for example, be 1 / 4T m , 0.3T m , 0.4T m , 0.5T m , 0.6T m , 0.7T m , 0.8T m , 0.9T m , or T mIn an embodiment of the present application, the stamping time of the stamping process is 3s-15s, and the holding time of the stamping process is 30s-60s. Specifically, the stamping time of the stamping process may, for example, be 3s, 4s, 5s, 6s, 8s, 9s, 10s, 12s, 14s, 15s, and the holding time of the stamping process may, for example, be 30s, 35s, 40s, 45s, 50s, 55s, 60s. Controlling the relevant parameters of the stamping process within a suitable range can facilitate the stamping and integration of the electronic device shell, and obtain an electronic device shell with a suitable R angle and good heterogeneous metal interfacial bonding.

[0437] In an embodiment of the present application, the temperature T2 of the heat treatment satisfies: T2≤1 / 3T m , and specifically, the temperature T2 of the heat treatment may, for example, be 0.1T m , 0.15T m , 0.2T m , 0.25T m , 0.3T m , 1 / 3T m In an embodiment of the present application, the time of the heat treatment is 30min-120min, and specifically, the heat treatment may, for example, be 30min, 40min, 50min, 60min, 80min, 100min, 110min, 120min. Since the upsetting and extruding in the stamping process can cause different metals at the deformed position and the undeformed position to deform incoordination, resulting in uneven distribution of grain structure and color difference on the surface of the electronic device shell after subsequent anodic oxidation coloring treatment, the present application can effectively improve the appearance quality of the electronic device shell without affecting the heterogeneous metal interfacial bonding force and deformation performance of the electronic device shell by reasonably designing the parameters of the heat treatment.

[0438] In an embodiment of the present application, the milling is followed by injection molding. In an embodiment of the present application, the material of the injection molding includes plastic and glass fiber, and the plastic may, but is not limited to, include at least one of polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), acrylonitrile-styrene-butadiene copolymer (ABS), polyamide (PA), polyphthalamide (PPA), polypropylene (PP), polyethylene terephthalate (PET), polycarbonate (PC), polyphenylene sulfone resin (PPSU), polyaryletherketone (PEAK), and polyether ether ketone (PEEK). In an embodiment of the present application, the material of the injection molding may be polybutylene terephthalate (PBT).

[0439] In an embodiment of the present application, the mass percentage of the glass fiber in the material for injection molding is less than or equal to 55%. Specifically, the mass percentage of the glass fiber can be, but is not limited to, less than or equal to 55%, less than or equal to 50%, less than or equal to 45%, less than or equal to 40%, less than or equal to 35%, less than or equal to 30%, or less than or equal to 20%, etc. In an embodiment of the present application, the mass percentage of the glass fiber can be 40%.

[0440] The method for manufacturing the electronic device shell provided by the present application adopts an integrated molding process, has low manufacturing cost and short manufacturing period, and through special design of the to-be-stamped composite metal, the stamping die, and the parameters of stamping and heat treatment, the thickness of the outer metal layer and the inner metal layer of the electronic device shell is uniform, the straightness of the bonding line at the interface bonding position is small, the comprehensive mechanical properties of the electronic device shell are excellent, the grain structure of the electronic device shell is uniform, uniform coloring is facilitated, and the problems of warping, edge curling, poor flatness, etc. of the electronic device shell after molding due to the difference in thermal deformation performance of heterogeneous metals are effectively solved.

[0441] The present application also provides an electronic device shell, which is used in an electronic device middle frame and is an integrated structure with an electronic device back cover.

[0442] The present application also provides an electronic device, which comprises the structural member or the electronic device shell according to any one of the embodiments described above, and the electronic device can be, for example, a mobile phone, a tablet computer, a notebook computer, a wearable device (watch, bracelet), a digital camera, etc.

[0443] The structural member or the electronic device shell provided by the present application has excellent mechanical properties and heat dissipation performance and is low in density and light in weight, and has good mechanical properties at the same time, so that the user has good experience and a long service life.

[0444] The effects of the technical solutions of the present application are further described below through specific examples.

[0445] Example 1-1

[0446] The to-be-injection-combined metal material (the first metal layer is TA18 titanium alloy and the second metal layer is 6013 aluminum alloy) is pretreated (oil removal, water washing, neutralization, water washing, alkali etching, water washing, acid etching, water washing, ash removal, water washing, and ultrasonic water washing), oil removal is performed by using a NaOH solution with a concentration of 40 g / L and adding a surfactant with a mass ratio of 1%, the oil removal temperature is 50°C, and the oil removal time is 10 min, neutralization is performed by using nitric acid with a concentration of 100 g / L, alkali etching is performed by using a NaOH solution with a concentration of 80 g / L, the alkali etching temperature is 50°C, acid etching is performed by using a mixed solution of phosphoric acid and sulfuric acid with a mass ratio of 4:1, the acid etching temperature is 95°C, and the acid etching time is 20 s;

[0447] The seventh metal layer of the to-be-injection-combined metal material is subjected to first etching on the surface not connected to the eighth metal layer to obtain a fifth metal layer, the first etching solution is a mixed solution of acetic acid, sodium citrate, phosphoric acid, and sodium fluoride with a concentration of 20 g / L, the mass ratio of acetic acid, sodium citrate, phosphoric acid, and sodium fluoride is 1:1:1:3, the first etching temperature is 28°C, and the first etching time is 1800 s;

[0448] The eighth metal layer of the to-be-injection-combined metal material is subjected to second etching on the surface not connected to the seventh metal layer to obtain a sixth metal layer, the second etching solution is a mixed solution of hydrochloric acid and ferric chloride with a concentration of 300 g / L, the mass ratio of hydrochloric acid and ferric chloride is 5:1, the second etching temperature is 28°C, and the second etching time is 180 s;

[0449] After the etched to-be-injection-combined metal material is washed with water, first anodic oxidation treatment and second anodic oxidation treatment are sequentially performed, the first electrolyte is a mixed solution of sulfuric acid, phosphoric acid, and ammonium hydrogen fluoride with a concentration of 40 g / L, the mass ratio of sulfuric acid, phosphoric acid, and ammonium hydrogen fluoride is 1:3:1, the first anodic oxidation treatment temperature is 30°C, the first anodic oxidation treatment voltage is 20 V, the first anodic oxidation treatment current is less than 40 A, the first anodic oxidation treatment time is 300 s, the second electrolyte is a mixed solution of oxalic acid and hydrofluoric acid with a concentration of 20 g / L, the mass ratio of oxalic acid and hydrofluoric acid is 5:1, the second anodic oxidation treatment temperature is 28°C, the second anodic oxidation treatment voltage is 20 V, the second anodic oxidation treatment current is less than 30 A, and the second anodic oxidation treatment time is 300 s.

[0450] After the to-be-injection-combined metal material subjected to anodic oxidation treatment is subjected to hot air cutting and baking, a metal-plastic combined structure is obtained by injection molding, the cutting temperature is 40°C, the baking temperature is 80°C, the baking time is 300 s, the material for injection molding is polycarbonate (PC) and glass fiber, the mass percentage of glass fiber is 40%, the injection molding temperature is 260°C, and the injection molding pressure is 120 MPa.

[0451] Example 1-2

[0452] The difference from Example 1-1 is that the second etching time is 300 s.

[0453] Example 1-3

[0454] The difference from Example 1-1 is that the first metal layer is SUS304, the first etching solution is a mixed solution of ammonium hydrogen fluoride and ferric chloride with a concentration of 80 g / L, the mass ratio of ammonium hydrogen fluoride to ferric chloride is 1:10, and the first etching time is 300 s.

[0455] Example 1-4

[0456] The difference from Example 1-1 is that the first etching is not performed.

[0457] Example 1-5

[0458] The difference from Example 1-1 is that the second etching is not performed.

[0459] Example 1-6

[0460] The difference from Example 1-1 is that in the second electrolyte, the mass ratio of oxalic acid to hydrofluoric acid is 3:1.

[0461] Example 1-7

[0462] The difference from Example 1-1 is that in the second electrolyte, the mass ratio of oxalic acid to hydrofluoric acid is 7:1.

[0463] Example 1-8

[0464] The difference from Example 1-1 is that in the second anodization treatment, the voltage of the second anodization treatment is 40 V, the current of the second anodization treatment is 30 A, and the time of the second anodization treatment is 500 s.

[0465] Comparative Example 1-1

[0466] The difference from Example 1-1 is that the first anodization treatment is not performed.

[0467] Comparative Example 1-2

[0468] The difference from Example 1-1 is that the second anodization treatment is not performed.

[0469] Performance Test

[0470] The metal-plastic composite structure prepared in the above Examples 1-1 to 1-8 and Comparative Examples 1-1 to 1-2 was tested for the total area ratio of nanopores in the porous oxide film layer and the transition oxide film layer and the thickness of the porous oxide film layer and the transition oxide film layer by using a scanning electron microscope. The testing process was as follows: the surface of the metal-plastic composite structure not subjected to injection molding was placed in the scanning electron microscope, and the nanopore image in the porous oxide film layer was taken, and the pores with a pore size less than or equal to 100 nm were identified, and then the proportion of the identified area to the whole taken area was calculated by using image recognition software to obtain the total area ratio of nanopores; the porous oxide film layer was removed by using ion sputtering, and the exposed transition oxide film layer was placed in the scanning electron microscope, and the nanopore image in the transition oxide film layer was taken, and the nanopore area was identified, and then the proportion of the identified area to the whole taken area was calculated by using image recognition software to obtain the total area ratio of nanopores. The results are shown in Tables 1 and 2.

[0471] The metal-plastic composite structure prepared in the above Examples 1-1 to 1-8 and Comparative Examples 1-1 to 1-2 was tested for the thickness of the porous oxide film layer and the transition oxide film layer by using a scanning electron microscope. The testing process was as follows: the metal-plastic composite structure was cut along the thickness direction by using FIB to obtain the cross section of the metal-plastic composite structure, and the cross section was placed in the scanning electron microscope to obtain the thickness of the porous oxide film layer and the dense oxide film layer. The results are shown in Tables 1 and 2.

[0472] FIG. 6 is a scanning electron microscope image of the surface of the first porous oxide film layer close to the first plastic layer side provided in Example 1-1, FIG. 7 is a scanning electron microscope image of the first nanopore provided in Example 1-1, and FIG. 8 is a cross-sectional scanning electron microscope image of the first transition oxide film layer and the first porous oxide film layer provided in Example 1-1; FIG. 9 is a scanning electron microscope image of the surface of the second porous oxide film layer close to the second plastic layer side provided in Example 1-1, FIG. 10 is a scanning electron microscope image of the second nanopore provided in Example 1-1, and FIG. 11 is a cross-sectional scanning electron microscope image of the second transition oxide film layer and the second porous oxide film layer provided in Example 1-1. As can be seen, the first micropore and the first nanopore appear in the first porous oxide film layer, the pore size of the first micropore is 1-5 μm, the pore size of the first nanopore is 40-100 nm, the thickness of the first porous oxide film layer is 50-80 nm, and the thickness of the first transition oxide film layer is 80-150 nm; the second micropore and the second nanopore appear in the second porous oxide film layer, the pore size of the second micropore is 2-10 μm, the pore size of the second nanopore is 20-40 nm, the thickness of the second porous oxide film layer is 80-150 nm, and the thickness of the second transition oxide film layer is 100-300 nm.

[0473] The metal-plastic composite structure prepared in the above examples 1-1 to 1-8 and comparative examples 1-1 to 1-2 was subjected to shear strength test, and the test process was as follows: the metal-plastic composite structure was processed into a sample with a size of 50 mm x 30 mm x 4 mm, the plastic layer side was pushed, the maximum force in the pushing process was recorded, the maximum stress was calculated as the shear strength between the metal layer and the plastic layer, and after the shear strength test, the residual area of the plastic layer was recorded. The residual area of the plastic layer was tested by the following process: the whole bonding condition of the metal-plastic composite structure was photographed by an optical microscope, the unbonding was marked, and then the proportion of the bonding area in the whole photographed area was calculated by using image recognition software, and finally the proportion of the residual layer area was obtained. The results are shown in Table 3.

[0474] Fig. 12 is a schematic diagram of the bonding of the first plastic layer after the shear strength test provided by example 1-1 of the present application, and Fig. 13 is a schematic diagram of the bonding of the second plastic layer after the shear strength test provided by example 1-1 of the present application. It can be seen that the first plastic layer and the second plastic layer both appear bonding phenomenon on the surface of the first metal layer and the second metal layer after the shear test, which indicates that the bonding force between the first metal layer and the first plastic layer and between the second metal layer and the second plastic layer is strong.

[0475] Table 1: Performance test results

[0476] Table 2: Performance test results

[0477] Table 3: Mechanical property test results

[0478] According to examples 1-1 to 1-8 and comparative examples 1-1 to 1-2, it can be seen that the metal-plastic composite structure provided by the present application has a transition oxide film layer and a porous oxide film layer, which enhances the bonding force between the metal layer and the plastic layer and improves the reliability of the metal-plastic composite structure. According to examples 1-1 and 1-2 to 1-8, it can be seen that suitable etching conditions can improve the bonding force between the metal layer and the plastic layer, increase the residual area of the plastic layer, and improve the reliability of the metal-plastic composite structure. According to examples 1-1 and comparative examples 1-1 to 1-2, it can be seen that two anodizing treatments can promote the formation of the porous oxide film layer and the transition oxide film layer in the metal-plastic composite structure, which is beneficial to enhancing the strength and reliability of the metal-plastic composite structure.

[0479] Example 2-1

[0480] A composite metal material (the first metal layer is TA4 titanium alloy and the second metal layer is 6013 aluminum alloy) with a size of 40 mm x 12 mm x 3 mm to be injection molded was pretreated (degreasing, alkali etching, sanding, chemical polishing, neutralization treatment and ultrasonic cleaning);

[0481] The composite metal material to be injection molded is used as an anode to perform an anodization treatment to obtain an oxidized composite metal material to be injection molded. The anodization treatment temperature is 40℃, the voltage is 30V, and the oxidation time is 15min. The electrolyte composition for the anodization treatment is fluoride (10g / L of potassium fluoride, fluoride ion concentration 3.3g / L), corrosion inhibitor (20g / L of potassium permanganate), pH buffer (100g / L of phosphoric acid), and the solvent is water;

[0482] After the anodization treatment of the composite metal material to be injection molded, post-treatment (ultrasonic cleaning, drying) is performed, and then PBT resin and glass fiber are used for injection molding, wherein the mass percentage of the glass fiber is 40%, the injection molding temperature is 265℃, and the mold temperature is 150℃. After the injection molding, a metal-plastic composite structure can be obtained.

[0483] Example 2-2

[0484] The difference from Example 2-1 is that the electrolyte is fluoride (5g / L of potassium fluoride, fluoride ion concentration 1.6g / L), 50g / L of potassium sodium tartrate, corrosion inhibitor (1g / L of sodium dodecyl benzene sulfonate), the solvent is water and ethylene glycol with a mass ratio of 3:1, the anodization treatment temperature is 35℃, the anodization treatment voltage is 15V, and the anodization treatment time is 15min.

[0485] Example 2-3

[0486] The difference from Example 2-1 is that the first metal layer is TC4 titanium alloy, and the second metal layer is 6063 aluminum alloy.

[0487] Example 2-4

[0488] The difference from Example 2-2 is that the first metal layer is TC4 titanium alloy, and the second metal layer is 6063 aluminum alloy.

[0489] Comparative Example 2-1

[0490] The difference from Example 2-1 is that the electrolyte does not contain fluoride.

[0491] Performance detection

[0492] The metal-plastic composite structures obtained in Examples 2-1 to 2-4 and Comparative Example 2-1 are characterized by a scanning electron microscope to characterize the pore size, pore depth, and spacing of adjacent pores of the nanopores in the first oxide film layer and the second oxide film layer. The results are shown in Table 4.

[0493] Figure 19 is a scanning electron microscope image of the first oxide film layer of the metal-plastic composite structure prepared in Example 2-1 of the present application; Figure 20 is a cross-sectional scanning electron microscope image of the first oxide film layer of the metal-plastic composite structure prepared in Example 2-1 of the present application; Figure 21 is a scanning electron microscope image of the second oxide film layer of the metal-plastic composite structure prepared in Example 2-1 of the present application; Figure 22 is a cross-sectional scanning electron microscope image of the second oxide film layer of the metal-plastic composite structure prepared in Example 2-1 of the present application. As can be seen from Figures 19-22, the first oxide film layer and the second oxide film layer comprise a plurality of nano-pores, the third nano-pores have a pore size of 50-70 nm, the average pore size is 59 nm, the thickness of the first oxide film layer is about 700 nm, the fourth nano-pores have a pore size of 25-45 nm, the average pore size is 34 nm, and the thickness of the second oxide film layer is about 1350 nm.

[0494] The metal-plastic composite structures prepared in Examples 2-1 to 2-4 and Comparative Example 2-1 were tested for the bonding force between the first metal layer and the first oxide film layer using a universal material testing machine, and the results are shown in Table 5.

[0495] The metal-plastic composite structures prepared in Examples 2-1 to 2-4 and Comparative Example 2-1 were tested for the bonding force between the second metal layer and the second oxide film layer using a universal material testing machine, and the results are shown in Table 5.

[0496] Table 4: Performance test results

[0497] Table 5: Mechanical property test results

[0498] As can be seen from Examples 2-1 to 2-4 and Comparative Example 2-1, the metal-plastic composite structure provided by the present application has good bonding force between the metal layer and the plastic layer, and high reliability. As can be seen from Examples 2-1 and 2-2, appropriate preparation parameters can improve the bonding capacity between the metal layer and the plastic layer. As can be seen from Examples 2-1 and 2-3, 2-4, the anodization treatment method provided by the present application can be used with a variety of titanium alloys and a variety of aluminum alloys, and has a wide range of applications. As can be seen from Examples 2-1 and Comparative Example 2-1, the use of an electrolyte containing fluorine can etch nano-pores on the surfaces of metals with different properties at the same time, and maintain the bonding capacity of the first metal layer and the first plastic layer, and the bonding capacity of the second metal layer and the second plastic layer within an appropriate range, which is conducive to improving the reliability of the metal-plastic composite structure.

[0499] Example 3-1

[0500] The first metal TC4 titanium alloy edge bar with a thickness of 3 mm is bent into a "U" type structure, and then the "U" type TC4 titanium alloy edge bar and the surface to be combined of the second metal 6013 aluminum alloy middle plate with a thickness of 7 mm are subjected to surface concave-convex structure manufacturing in a laser engraving manner. The laser engraving parameters used are: power 100 W, frequency 120 Hz, speed 300 mm / s, and number of times 2. After laser engraving, the first metal TC4 titanium alloy is subjected to chemical etching by using a ammonium bifluoride solution. The concentration of the ammonium bifluoride solution is 18 g / L, and the temperature is 25℃. The obtained nano-pores are shown in FIG. 27, and the diameter of the nano-pores is 230 nm. The second metal 6013 aluminum alloy is subjected to electrochemical etching by using an anodic oxidation process. The etching voltage is 20 V, the etching time is 20 min, and the etching temperature is 25℃. The diameter of the obtained nano-pores is 170 nm.

[0501] The concave-convex structure of the surface of the first metal TC4 titanium alloy subjected to surface roughening is shown in FIG. 28. The shape of the concave pit structure is rectangular, the pitch of two adjacent concave pit structures is 250 μm, the depth of the concave pit structure is 330 μm, the lateral dimension of the concave pit structure is 180 μm, and the surface roughness of the concave-convex structure of the first metal TC4 titanium alloy is 14 μm.

[0502] The shape of the concave pit structure of the surface of the second metal 6013 aluminum alloy is rectangular, the pitch of two adjacent concave pit structures is 350 μm, the depth of the concave pit structure is 200 μm, the lateral dimension of the concave pit structure is 350 μm, and the surface roughness of the second metal 6013 aluminum alloy is 19 μm.

[0503] Then, the first metal TC4 titanium alloy and the second metal 6013 aluminum alloy are placed in a mold for die casting treatment, wherein the surfaces with the concave-convex structure of the first metal TC4 titanium alloy and the second metal 6013 aluminum alloy are placed opposite to each other. The die casting process parameters are: pressure 65 MPa, pressurization time 6 s, filling speed 0.2 m / s, and the connecting metal die cast aluminum is A380 aluminum alloy. After the mold is cooled, a composite metal of the first metal layer TC4 titanium alloy and the second metal layer 6013 aluminum alloy connected by the connecting layer A380 aluminum alloy is obtained. Finally, the composite metal is subjected to CNC milling to obtain the final electronic device middle frame.

[0504] The interface bonding between the first metal layer TC4 titanium alloy and the connecting layer A380 aluminum alloy and the interface bonding between the second metal layer 6013 aluminum alloy and the connecting metal A380 aluminum alloy of the prepared composite metal were observed by intercepting, and the results are shown in FIG. 29. It can be observed that the connecting metal (A380 aluminum alloy) of the connecting layer has fully entered the micro-pore structure of the connected substances (the first metal TC4 titanium alloy and the second metal 6013 aluminum alloy), and the immersion depth is about 360 μm, so that effective and close connection is formed between the heterogeneous metal layers. The hardness of the first metal layer TC4 titanium alloy, the connecting layer A380 aluminum alloy and the second metal layer 6013 aluminum alloy was tested, and it was found that the hardness of the connecting metal A380 aluminum alloy is close to that of the second metal 6013 aluminum alloy, so that the hardness difference is not too large, and the deformation is not coordinated.

[0505] The elements at the interface bonding between the connecting metal A380 aluminum alloy and the first metal TC4 titanium alloy were detected by EDS (Energy Dispersive Spectroscopy), and the positions of the aluminum element and the titanium element were measured, that is, the intermetallic diffusion layer. The thickness of the intermetallic diffusion layer corresponds to the intermetallic diffusion depth, and the intermetallic diffusion depth is the depth in the thickness direction of the composite metal. The results are shown in FIG. 30. FIG. 30(a) is a metallographic characterization diagram of the interface bonding between the first metal TC4 titanium alloy and the connecting metal A380 aluminum alloy of Example 3-1, and the EDS (Energy Dispersive Spectroscopy) test position is indicated by an arrow in FIG. 30(a). FIG. 30(b) is the EDS characterization result of the interface bonding at the position indicated by the arrow in FIG. 30(a). As shown in FIG. 30, the intermetallic diffusion depth between the first metal layer and the connecting layer of the composite metal of Example 3-1 is about 2.5 μm.

[0506] Example 3-2

[0507] The difference from Example 3-1 is that the connecting layer is a polyphenylene sulfone (PPSU) resin, which further comprises 35% by mass of glass fibers.

[0508] Example 3-3

[0509] The difference from Example 3-1 is that the first metal layer is TA4 titanium alloy, and the second metal layer is 7075 aluminum alloy.

[0510] Example 3-4

[0511] The difference from Example 3-1 is that the shape of the pit structure on the surface of the first metal and the second metal is T-shaped.

[0512] Example 3-5

[0513] The difference from Example 3-1 is that the pitch of the adjacent two pit structures of the surface-roughened first metal TC4 titanium alloy surface is 300 pm, the depth of the pit structure is 450 pm, and the lateral dimension of the pit structure is 270 pm.

[0514] Example 3-6

[0515] The difference from Example 3-1 is that the pitch of the adjacent two pit structures of the surface-roughened second metal 6013 aluminum alloy surface is 330 pm, the depth of the pit structure is 260 pm, and the lateral dimension of the pit structure is 230 pm.

[0516] Example 3-7

[0517] The difference from Example 3-1 is that no chemical etching is performed, and the first metal and the second metal have no nano secondary structure on the relief structure surface.

[0518] Comparative Example 3-1

[0519] The difference from Example 3-1 is that the first metal and the second metal surface are not roughened, and have no relief structure.

[0520] Comparative Example 3-2

[0521] The difference from Example 3-1 is that after the first metal and the second metal are roughened, direct pressing is performed without a connecting layer.

[0522] Performance detection

[0523] Performance tests are performed on Examples 3-1 to 3-7 and Comparative Examples 3-1 to 3-2, and the results are shown in Table 6.

[0524] Surface roughness: the surfaces of the composite metals prepared in Examples 3-1 to 3-7 and Comparative Examples 3-1 to 3-2 are cleaned, and then the measured surface is placed on the measurement table of the roughness measuring instrument. The surface position is adjusted to make it contact with the measurement head. The measurement head needs to be kept perpendicular to the measured surface during the measurement. The surface roughness of the measured surface is measured.

[0525] Intermetallic diffusion depth: the composite metals prepared in Examples 3-1 to 3-7 and Comparative Examples 3-1 to 3-2 are cut along the thickness direction using a wire electrical discharge machine. The interface bonding morphology of the heterogeneous metal layer is observed using a field emission scanning electron microscope. The distribution of each element near the interface is analyzed using an energy dispersive spectrometer EDS. The element diffusion rule and composition change rule are inferred by measuring the content of each element in the diffusion layer at the interface position, and then the intermetallic diffusion depth is obtained.

[0526] Bonding strength: the composite metal prepared from Example 3-1 to Example 3-7 and Comparative Example 3-1 to Comparative Example 3-2 was placed in a shear mold with the interface to be tested facing down to perform a shear test, the shear groove of the shear mold was processed into a size of 7.2 mm x 5.6 mm x 10 mm, a cuboid groove, with a length, width and height allowance, which can ensure that the shear sample is only subjected to shear force, the maximum pressure borne by the sample when the interface to be tested is peeled off is measured, and the ratio of the effective area of the diffusion bonding surface of the sample is obtained, and the shear bonding strength of the interface is obtained.

[0527] Table 6 Performance test results

[0528] As can be seen from Table 6, compared with Comparative Example 3-1 in which the first metal layer and the second metal layer are not roughened and Comparative Example 3-2 in which no connecting layer is provided, the bonding strength between the first metal layer and the second metal layer of the composite metal prepared in Example 3-1 to Example 3-7 is significantly improved, and the depth of the intermetallic diffusion layer between the first metal layer and the second metal layer with the concave-convex structure obtained by roughening and the connecting layer is significantly deepened, further improving the bonding force between the first metal layer and the second metal layer.

[0529] Example 4-1

[0530] (1) A composite metal to be punched was provided, which included a first metal layer and a second metal layer stacked, the first metal layer was 6013 aluminum alloy, the thickness t1 of the first metal layer was 2.25 mm, and the R angle R1 of the first metal layer was 10 mm; the second metal layer was AZ31 magnesium alloy, the thickness t2 of the second metal layer was 3.55 mm, and the R angle R2 of the second metal layer was 35 mm; the composite metal to be punched included a second R angle for forming a first R angle, the thickness of the second R angle along the center of the composite metal to be punched in the direction of the second R angle was gradually reduced to form a slope, the slope angle was 20°, the slope length L1 of the slope was 12 mm, and the slope height h of the slope was 3.5 mm;

[0531] (2) The composite metal to be punched was placed in a punching mold for punching treatment, the lower mold of the punching mold included a groove, a convex portion was arranged around the position where the bottom of the groove was connected with the side wall, the width L2 of the convex portion was 4.5 mm, and the height D of the convex portion was 1.4 mm; the mold was subjected to heating treatment, the heating time was 30 min, and the heating temperature was 200℃; after the mold was heated, the punching treatment was performed, the punching temperature of the punching treatment was 200℃, the punching time was 5 s, and the pressure holding time was 60 s;

[0532] (3) continuing to heat treat the material obtained after the stamping, the temperature of the heat treatment is 180°C, the time of the heat treatment is 90 min, and the heat treated material is naturally cooled to room temperature to obtain the electronic device shell blank;

[0533] (4) milling the prepared electronic device shell blank, milling and removing the remaining part of the outer metal layer precursor obtained after stamping the first metal layer except the part forming the frame body outer metal layer to form an aluminum alloy outer surface, and milling and removing the remaining part of the inner metal layer precursor obtained after stamping the second metal layer except the part forming the frame body inner metal layer to form a magnesium alloy inner cavity, to obtain an electronic device shell, the thickness of the inner metal layer of the electronic device shell is greater than or equal to 0.4 mm, and the thickness of the outer metal layer is 0.3 mm.

[0534] By cutting the prepared electronic device shell along the thickness direction, the interface bonding of the outer metal layer and the inner metal layer at the first R corner of the electronic device shell is observed by a metallographic microscope, and the obtained result is shown in FIG. 36. The straightness of the bonding line measured and calculated is 0.02 mm.

[0535] The grain structure of the extruded area of the outer metal layer and the non-extruded area of the outer metal layer of the prepared electronic device shell is observed by a metallographic microscope, and the obtained result is shown in FIG. 37. The average grain size of the extruded area and the average grain size of the non-extruded area are respectively measured and calculated, and the average grain size deviation of the extruded area and the non-extruded area is calculated. The calculated result is ≤10%, and the structure types of the extruded area and the non-extruded area of the outer metal layer are consistent. As can be seen from FIG. 37, the grain structure types of the two areas are both matrix and precipitated phase, and the precipitated phase is uniformly distributed on the matrix.

[0536] The elements at the interface bonding of the outer metal layer and the inner metal layer are detected by EDS (Energy Dispersive Spectroscopy), and the positions of the magnesium element and the aluminum element are measured at the same time, that is, the intermetallic diffusion layer. The thickness of the intermetallic diffusion layer corresponds to the intermetallic diffusion depth, and the intermetallic diffusion depth is specifically the depth along the thickness direction of the composite metal. The measured result is shown in FIG. 38. As can be seen from FIG. 38, the intermetallic diffusion depth between the outer metal layer and the inner metal layer in the electronic device shell of Example 4-1 is about 5 μm.

[0537] Example 4-2

[0538] The difference from Example 4-1 is that the first metal layer is TC4 titanium alloy.

[0539] Example 4-3

[0540] The only difference from Example 4-1 is that the second metal layer is 316L stainless steel.

[0541] Example 4-4

[0542] The only difference from Example 4-1 is that the heat treatment temperature is 210°C and the heat treatment time is 60 min.

[0543] Examples 4-5

[0544] The only difference from Example 4-1 is that the heat treatment temperature is 150°C and the heat treatment time is 80 min.

[0545] Examples 4-6

[0546] The only difference from Example 4-1 is that the thickness t1 of the first metal layer is 2.5 mm, the radius R1 of the first metal layer is 8 mm, the thickness t2 of the second metal layer is 4 mm, and the radius R2 of the second metal layer is 30 mm.

[0547] Examples 4-7

[0548] The only difference from Example 4-1 is that the slope angle is 30°, the slope length L1 is 15mm, and the slope height h is 5mm.

[0549] Examples 4-8

[0550] The only difference from Example 4-1 is that the width L2 of the protrusion is 4mm and the height D of the protrusion is 1mm.

[0551] Examples 4-9

[0552] The only difference from Example 4-1 is that the stamping temperature is 250°C, the stamping time is 8s, and the holding time is 30s.

[0553] Comparative Example 4-1

[0554] The only difference from Example 4-1 is that no design is made for the incoming material, which is a sheet of equal thickness.

[0555] Comparative Example 4-2

[0556] The only difference from Example 4-1 is that no mold is designed, and the lower mold has a flat structure.

[0557] Comparative Example 4-3

[0558] The only difference from Example 4-1 is that the material obtained after stamping is not heat-treated.

[0559] Performance testing

[0560] The following relevant performance tests were conducted on Examples 4-1 to 4-9 and Comparative Examples 4-1 to 4-3, and the results are shown in Table 7.

[0561] First R angle: The electronic device housings prepared from Examples 4-1 to 4-9 and Comparative Examples 4-1 to 4-3 were placed in the projection area of a projector, and light strips with precise structures were projected onto the surface of the electronic device housings using the light source of the projector. These line patterns can be used to measure and calculate the first R angle of the electronic device housings.

[0562] Straightness and average grain size deviation: The electronic device housings prepared from Examples 4-1 to 4-9 and Comparative Examples 4-1 to 4-3 were cut open along the thickness direction using a wire electrical discharge machine, and the cross section was used as the observation surface. The observation surface was ground using 200, 400, 600, 800, 1000, 1500, 2000, and 3000 grit sandpaper to remove surface wire cutting marks and ensure the observation surface was flat. After polishing, the observation surface was observed using a metallographic microscope, and the straightness and average grain size deviation were measured and calculated.

[0563] Intermetallic diffusion depth: The electronic device housings prepared from Examples 4-1 to 4-9 and Comparative Examples 4-1 to 4-3 were cut open along the thickness direction using a wire electrical discharge machine. The interface bonding morphology of the heterogeneous metal layer was observed using a field emission scanning electron microscope, and the distribution of each element near the interface was analyzed using an energy dispersive spectrometer (EDS). By measuring the content of each element in the diffusion layer at the interface position, the element diffusion rule and composition change rule were inferred, and the intermetallic diffusion depth was obtained.

[0564] Table 7 Performance test results

[0565] As can be seen from Table 7, the straightness of the bonding line formed at the interface between the outer metal layer and the inner metal layer at the first R angle of the electronic device housings of Examples 4-1 to 4-9, which were specially designed in terms of the incoming material and mold and the heat treatment process, was significantly smaller than that of Comparative Examples 4-1 and 4-2, under the same R angle.

[0566] Compared to Comparative Example 4-3, which was not subjected to heat treatment, the average grain size deviation in the outer metal layer was significantly reduced by heat treatment and controlling the parameters within a suitable range in Examples 4-1 to 4-9.

[0567] The above describes the preferred embodiments of the present application, but should not be construed as limiting the scope of the present application. It should be pointed out that, for those skilled in the art, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements are also considered within the scope of protection of the present application.

Claims

1. A metal-plastic composite structure (100), characterized in that, The first metal layer (11) and the second metal layer (12) are connected to each other, and at least one of the following conditions is met: a first transition oxide film layer (13), a first porous oxide film layer (14), and a first plastic layer (15) are sequentially stacked on the surface of the first metal layer (11) not connected to the second metal layer (12); and a second transition oxide film layer (16), a second porous oxide film layer (17), and a second plastic layer (18) are sequentially stacked on the surface of the second metal layer (12) not connected to the first metal layer (11); Wherein, the first metal layer (11) and the second metal layer (12) are metal layers of different materials; The first transition oxide film layer (13) contains a first metal oxide, the first porous oxide film layer (14) contains a second metal oxide, at least one metal element in the first metal oxide, the second metal oxide and the first metal layer (11) is the same, and the porosity of the first transition oxide film layer (13) is less than the porosity of the first porous oxide film layer (14); The second transition oxide film layer (16) contains a third metal oxide, the second porous oxide film layer (17) contains a fourth metal oxide, at least one metal element in the third metal oxide, the fourth metal oxide and the second metal layer (12) is the same, and the porosity of the second transition oxide film layer (16) is less than the porosity of the second porous oxide film layer (17).

2. The metal-plastic composite structure (100) according to claim 1, wherein, The first metal oxide and the second metal oxide are oxides of the metal material of the first metal layer (11); The third metal oxide and the fourth metal oxide are oxides of the metal material of the second metal layer (12).

3. The metal-plastic composite structure (100) according to claim 1 or 2, wherein The first metal layer (11) has a first surface and a second surface arranged opposite to each other, the second metal layer (12) has a third surface and a fourth surface arranged opposite to each other, the second surface and the third surface are connected to each other in a pasting manner, the first surface has a first transition oxide film layer (13), a first porous oxide film layer (14) and a first plastic layer (15) stacked thereon, and the fourth surface has a second transition oxide film layer (16), a second porous oxide film layer (17) and a second plastic layer (18) stacked thereon.

4. The metal-plastic composite structure (100) according to any one of claims 1 to 3, characterized in that The side surface of the first metal layer (11) is sequentially stacked with a first transition oxide film layer (13), a first porous oxide film layer (14) and a first plastic layer (15), and the side surface of the second metal layer (12) is sequentially stacked with a second transition oxide film layer (16), a second porous oxide film layer (17) and a second plastic layer (18).

5. The metal-plastic composite structure (100) according to any one of claims 1 to 4, wherein The first metal layer (11) has a first surface and a second surface arranged opposite to each other, the second metal layer (12) has a third surface and a fourth surface arranged opposite to each other, the second surface and the third surface are connected to each other in a pasting manner; And at least one of the following conditions is met: The first surface has a first transition oxide film layer (13), a first porous oxide film layer (14) and a first plastic layer (15) arranged in layers; and the fourth surface has a second transition oxide film layer (16), a second porous oxide film layer (17) and a second plastic layer (18) arranged in layers.

6. The metal-plastic composite structure (100) according to any one of claims 1 to 5, wherein The material of the first metal layer (11) is titanium, magnesium, titanium alloy, magnesium alloy or stainless steel, and the material of the second metal layer (12) is aluminum or aluminum alloy.

7. The metal-plastic composite structure (100) according to any one of claims 1 to 6, wherein The total area ratio of nano-pores on the surface of the first transition oxide film layer (13) close to the first plastic layer (15) is less than or equal to 1%, and the total area ratio of nano-pores on the surface of the first porous oxide film layer (14) close to the first transition oxide film layer (13) is 40%-80%. The area ratio of nano-pores on the surface of the second transition oxide film layer (16) close to the second plastic layer (18) is less than or equal to 1%, and the total area ratio of nano-pores on the surface of the second porous oxide film layer (17) close to the second transition oxide film layer (16) is 45%-70%.

8. The metal-plastic composite structure (100) according to any one of claims 1 to 7, wherein The thickness ratio of the first porous oxide film layer (14) to the first transition oxide film layer (13) is (0.2-2.5):1, and the thickness ratio of the second porous oxide film layer (17) to the second transition oxide film layer (16) is (0.2-2.5):

1.

9. The metal-plastic composite structure (100) according to any one of claims 1 to 8, wherein The thickness of the first transition oxide film layer (13) is 24nm-3.5μm, and the thickness of the first porous oxide film layer (14) is 60nm-700nm. The thickness of the second transition oxide film layer (16) is 24nm-3.5μm, and the thickness of the second porous oxide film layer (17) is 60nm-700nm.

10. The metal-plastic composite structure (100) according to any one of claims 1 to 9, wherein The surface roughness Ra of the side of the first porous oxide film layer (14) close to the first plastic layer (15) is greater than or equal to 1μm. The surface roughness Ra of the side of the second porous oxide film layer (17) close to the second plastic layer (18) is greater than or equal to 2μm.

11. The metal-plastic composite structure (100) according to any one of claims 1 to 10, wherein The first porous oxide film layer (14) comprises a plurality of first nano-pores, and the pore size of the first nano-pores is 20nm-100nm. The second porous oxide film layer (17) comprises a plurality of second nano-pores, and the pore size of the second nano-pores is 20nm-40nm.

12. The metal-plastic composite structure (100) according to any one of claims 1 to 11, wherein At least part of the first nano-pores are filled with plastic material, and at least part of the second nano-pores are filled with plastic material.

13. The metal-plastic composite structure (100) according to any one of claims 1 to 12, wherein The shear strength between the first plastic layer (15) and the first metal layer (11) is greater than or equal to 20MPa. The shear strength between the second plastic layer (18) and the second metal layer (12) is greater than or equal to 25MPa.

14. The metal-plastic composite structure (100) according to any one of claims 1 to 13, characterized in that The first metal layer (11) and the second metal layer (12) further comprise a connecting layer (21).

15. The metal-plastic composite structure (100) according to claim 14, wherein, The connecting layer (21) comprises metal or resin.

16. The metal-plastic composite structure (100) according to claim 14 or 15, characterized in that The thickness of the connecting layer (21) is greater than or equal to 0.05mm.

17. The method of manufacturing a metal-plastic composite structure (100) according to any one of claims 1 to 16, characterized in that Provided is a to-be-injection-molded composite metal material comprising a third metal layer and a fourth metal layer connected to each other; Provided is a to-be-injection-molded composite metal material comprising a third metal layer and a fourth metal layer connected to each other; satisfying at least one of the following: performing first etching on a surface of the third metal layer not connected with the fourth metal layer to form a fifth metal layer; and performing second etching on a surface of the fourth metal layer not connected with the third metal layer to form a sixth metal layer, to obtain an etched-to-be-injection-combined metal material; performing first anodic oxidation treatment and second anodic oxidation treatment on the etched-to-be-injection-combined metal material in sequence, satisfying at least one of the following: forming a first porous oxide film layer (14) and a first transition oxide film layer (13) from outside to inside on a surface layer of the fifth metal layer not connected with the sixth metal layer; and forming a second porous oxide film layer (17) and a second transition oxide film layer (16) from outside to inside on a surface layer of the sixth metal layer not connected with the fifth metal layer, to obtain an oxidized-to-be-injection-combined metal material; performing injection molding on the oxidized-to-be-injection-combined metal material, satisfying at least one of the following: forming a first plastic layer (15) on a surface of the first porous oxide film layer (14); and forming a second plastic layer (18) on a surface of the second porous oxide film layer (17), to obtain a metal-plastic combined structure (100).

18. The production method according to claim 17, wherein The material of the third metal layer is titanium, magnesium, titanium alloy, magnesium alloy or stainless steel, and the material of the fourth metal layer is aluminum or aluminum alloy.

19. The production method according to claim 17 or 18, wherein The first etching adopts a first etching solution, and the first etching solution comprises at least one of hydrofluoric acid, acetic acid, carbonic acid, hypochlorous acid, phosphoric acid, sodium fluoride, calcium fluoride, ammonium hydrogen fluoride, sodium citrate, sodium chloride and ferric chloride. The concentration of the first etching solution is 5 g / L-30 g / L, the pH value of the first etching solution is 2-5, and the conductivity of the first etching solution is 100 mS / cm-500 mS / cm.

20. The production method according to any one of claims 17 to 19, wherein The second etching adopts a second etching solution, and the second etching solution comprises at least one of nitric acid, sulfuric acid, hydrochloric acid, potassium chloride, ferric chloride, ferrous chloride, copper chloride, magnesium chloride and sodium chloride. The concentration of the second etching solution is 100 g / L-300 g / L, the pH value of the second etching solution is less than or equal to 2, and the conductivity of the second etching solution is 400 mS / cm-1000 mS / cm.

21. The method of any one of claims 17 to 20, wherein the method further comprises the step of: The first anodic oxidation treatment adopts a first electrolyte, and the first electrolyte comprises at least one of potassium dichromate, hydrogen peroxide, hydrofluoric acid, sulfuric acid, phosphoric acid, sodium fluoride, ammonium hydrogen fluoride and sodium sulfate. The concentration of the first electrolyte is 3 g / L-20 g / L, and the pH value of the first electrolyte is 3-6. The temperature of the first anodic oxidation treatment is 10°C-60°C, the voltage of the first anodic oxidation treatment is 5V-100V, and the current of the first anodic oxidation treatment is 1A-50A.

22. The method of any one of claims 17 to 21, wherein the method further comprises the step of: The second anodic oxidation treatment adopts a second electrolyte, and the second electrolyte comprises at least one of oxalic acid, citric acid, sodium citrate, sodium sulfate, acetic acid and phosphoric acid. The concentration of the second electrolyte is 15 g / L-25 g / L, and the pH value of the second electrolyte is 1-4. The second anodization treatment has a temperature of 20-40℃, a voltage of 15-50V, and a current of 15-50A.

23. The method of any one of claims 17 to 22, wherein the method further comprises the step of: 5 The injection molding has a temperature of 230-320℃ and a pressure of 80-120MPa.

24. A method of making a metal composite structure, characterized by, Comprising: Providing a composite metal material comprising a third metal layer and a fourth metal layer connected to each other; At least one of the following is satisfied: a first etching is performed on a surface of the third metal layer not connected to the fourth metal layer to form a fifth metal layer; and a second etching is performed on a surface of the fourth metal layer not connected to the third metal layer to form a sixth metal layer, obtaining an etched composite metal material; The etched composite metal material is sequentially subjected to a first anodization treatment and a second anodization treatment, at least one of the following is satisfied: a surface layer of the fifth metal layer not connected to the sixth metal layer is sequentially formed from outside to inside as a first porous oxide film layer (14) and a first transition oxide film layer (13); and a surface layer of the sixth metal layer not connected to the fifth metal layer is sequentially formed from outside to inside as a second transition oxide film layer (16) and a second porous oxide film layer (17), obtaining a metal composite structure; the first transition oxide film layer (13) comprises a first metal oxide, the first porous oxide film layer (14) comprises a second metal oxide, at least one metal element in the first metal oxide, the second metal oxide and the first metal layer (11) is the same, the porosity of the first transition oxide film layer (13) is less than the porosity of the first porous oxide film layer (14); the second transition oxide film layer (16) comprises a third metal oxide, the second porous oxide film layer (17) comprises a fourth metal oxide, at least one metal element in the third metal oxide, the fourth metal oxide and the second metal layer (12) is the same, the porosity of the second transition oxide film layer (16) is less than the porosity of the second porous oxide film layer (17).

25. Use of the metal-plastic composite structure (100) according to any one of claims 1-16 or the metal-plastic composite structure (100) prepared by the method according to any one of claims 17-23 or the metal composite structure according to claim 24 in electronic devices, vehicles and electrical appliances.

26. A structural member, characterized by The structural member comprises the metal-plastic composite structure (100) according to any one of claims 1-16 or the metal-plastic composite structure (100) prepared by the method according to any one of claims 17-23 or the metal composite structure prepared by the method according to claim 24.

27. The structural member of claim 26, wherein The structural member comprises an electronic device housing.

28. An electronic device, comprising: The electronic device comprises the structural member according to any one of claims 26-27. The electronic device comprises the structural member according to any one of claims 26-27.

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