Composite metal, preparation method therefor, and use thereof

Abstract

The present application provides a composite metal, a preparation method therefor, and a use thereof. The composite metal comprises a first metal layer and a second metal layer which are stacked, and a connection layer provided between the first metal layer and the second metal layer; the first metal layer and the second metal layer are different metal layers; at least one of a surface where the first metal layer is connected to the connection layer and a surface where the second metal layer is connected to the connection layer is provided with a relief structure; and the relief structure comprises at least one of recess structures and protrusion structures.

Description

Composite metal and preparation method and application thereof

[0001] Cross-references to related documents

[0002] The present application claims priority to the Chinese patent application No. 202410718273.3, filed on June 04, 2024, and entitled "Composite metal and preparation method and application thereof", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

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

[0004] 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 and a metal with good mechanical properties is usually adopted. However, the current composite metal still has the problem of poor combination between the two heterogeneous metals. SUMMARY

[0005] In view of this, the present application provides a composite metal and a preparation method and application thereof. The composite metal is connected by setting a concave-convex structure on the surface of at least one of the first metal layer and the second metal layer and through a connecting layer, which effectively improves the combination between the first metal layer and the second metal layer of the composite metal, and further improves the performance of the processing and forming thereof, so as to meet the higher processing requirements.

[0006] In a first aspect, the present application provides a composite metal, which comprises a first metal layer and a second metal layer arranged in layers, and a connecting layer arranged between the first metal layer and the second metal layer, the first metal layer and the second metal layer are different metal layers, at least one of 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 is provided with a concave-convex structure, and the concave-convex structure comprises at least one of a pit structure and a protrusion structure.

[0007] In some embodiments, the concave-convex structure comprises a plurality of pit structures or a plurality of protrusion structures.

[0008] In some embodiments, the concave-convex structure comprises a plurality of pit structures and a plurality of protrusion structures.

[0009] In some embodiments, one protrusion structure is formed between every two adjacent pit structures; the distance between two adjacent pit structures is 0.1mm-0.5mm; the distance between two adjacent pit structures is 0.1mm-0.5mm.

[0010] In some embodiments, the depth of the pit structure is 100-500 μm, and the lateral dimension of the pit structure is 50-350 μm.

[0011] In some embodiments, the cross-sectional shape of each pit structure along the thickness direction of the composite metal is rectangular, trapezoidal, triangular, or T-shaped.

[0012] In some embodiments, the inner surface of at least one pit structure is provided with a first nano-substructure; the first nano-substructure comprises nanopores with a diameter of 50-500 nm.

[0013] In some embodiments, the outer surface of at least one protrusion structure is provided with a second nano-substructure; the second nano-substructure comprises nanopores with a diameter of 50-500 nm.

[0014] In some embodiments, the surface roughness of at least one of the pit structure and the protrusion structure is 10-25 μm.

[0015] In some embodiments, the connecting layer comprises a metal or a resin; the metal comprises at least one of magnesium and its alloys, aluminum and its alloys, zinc and its alloys, copper and its alloys; the resin comprises at least one of polybutylene terephthalate, polyphenylene sulfide, polyamide, polyphthalamide, polypropylene, polycarbonate, polyphenylene sulfone, polyether ether ketone.

[0016] 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).

[0017] In some embodiments, the coefficient of thermal expansion of the connecting layer is 2×10 -5 / K-2.7×10 -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).

[0018] In some embodiments, the connecting layer and the first metal layer are different metal layers, 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, the intermetallic diffusion depth at the interface between the connecting layer and the second metal layer is 1-10 μm.

[0019] In some embodiments, the shear strength between the first metal layer and the second metal layer is greater than or equal to 100 MPa.

[0020] 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, zinc and its alloys.

[0021] 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, zinc and its alloys.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] The composite metal provided in the present application effectively improves the bonding between the first metal layer and the second metal layer of the composite metal by providing a 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 after processing and forming, and meeting the higher processing requirements.

[0027] In a second aspect, the present application provides a preparation method of the composite metal provided in the first aspect, comprising:

[0028] Performing roughening treatment on the surfaces to be bonded of the first metal and the second metal to form a plurality of concave-convex structures on the surfaces to be bonded of the first metal and the second metal;

[0029] 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 bonding; to obtain a composite metal.

[0030] In some embodiments, the surface roughening treatment comprises milling processing and / or laser engraving.

[0031] In some embodiments, the surface roughening treatment further comprises chemical etching, and the chemical etching is performed after the milling processing and / or laser engraving treatment.

[0032] The preparation method of the composite metal provided in the application is novel, the preparation process is simple, and the heterogeneous intermetallic bonding performance of the composite metal is excellent.

[0033] In a third aspect, the application provides a structural member, which comprises the composite metal provided in the first aspect or prepared by the preparation method provided in the second aspect.

[0034] In some embodiments, the structural member is an electronic device shell, which comprises four R corners, and each R corner is greater than or equal to 0.1 mm.

[0035] The structural member provided in the application has lighter mass and better mechanical properties, and can better meet the subsequent processing requirements.

[0036] In a fourth aspect, the application provides an electronic device, which comprises the structural member provided in the third aspect.

[0037] The electronic device provided in the application has excellent mechanical properties and low density, and has good mechanical properties, good user experience and long service life. BRIEF DESCRIPTION OF DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the 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 application, and are not used to limit the application.

[0039] FIG. 1 is a schematic diagram of the cross-sectional structure of the composite metal provided in an embodiment of the application;

[0040] FIG. 2 is a schematic diagram of the concave-convex structure of the composite metal provided in an embodiment of the application;

[0041] FIG. 3 is a metallographic characterization diagram of the cross-sectional morphology of the concave structure of some embodiments of the application along the thickness direction of the composite metal;

[0042] FIG. 4 is a flowchart of the preparation method of the composite metal provided in an embodiment of the application;

[0043] FIG. 5 is an SEM (Scanning Electron Microscope) characterization diagram of the nano secondary structure of the concave-convex structure surface of the first metal TC4 titanium alloy of Embodiment 1 of the application;

[0044] FIG. 6 is a metallographic characterization diagram of the concave-convex structure of the first metal TC4 titanium alloy of Embodiment 1 of the application;

[0045] Fig. 7 is a metallographic characterization diagram of the cross-section structure of the composite metal along the thickness direction according to the embodiment 1 of the present application;

[0046] Fig. 8(a) is a metallographic characterization diagram of the interface bonding between the first metal TC4 titanium alloy and the connecting metal A380 aluminum alloy according to the embodiment 1 of the present application; and Fig. 8(b) is an EDS (Energy Dispersive Spectroscopy) characterization result of the interface bonding.

[0047] Fig. 100, composite metal; 11, first metal layer; 12, second metal layer; 13, connecting layer. DETAILED DESCRIPTION

[0048] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0049] At present, in order to make the electronic product shell have good mechanical properties and lighter quality, a method of compounding a metal with small density such as 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 enhanced compared with aluminum alloy. Although these composite metals have the advantage of one-piece forming, due to the difference in metal fluidity between the two different metals, when a large area is used for one-piece forming such as die casting or casting to prepare products, the deformation of the product is large, the interface bonding 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, which further leads to poor bonding between the heterogeneous metal layers, it is difficult to meet the mechanical property requirements of subsequent processing and is easy to separate and fall off during use; it also leads to uneven mechanical properties of the obtained composite metal as a whole, the range of R angle obtained by stamping forming is limited, and local deformation is easy to occur during use; it also leads to uneven color of the final product obtained during anodic oxidation coloring of the composite metal due to uneven distribution of the heterogeneous metal layer, affecting the appearance of the product.

[0050] In view of the above problems, the present application provides a composite metal, which effectively improves the bonding between the first metal layer and the second metal layer of the composite metal by setting a concave-convex structure on the surface of the first metal layer and the second metal layer and connecting through a connecting layer, thereby improving the performance of processing and forming, and meeting the higher processing requirements.

[0051] Referring to FIG. 1, a schematic diagram of a cross-sectional structure of a composite metal 100 according to an embodiment of the present application is shown. The composite metal 100 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 13 arranged between the first metal layer 11 and the second metal layer 12.

[0052] In the embodiments 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 surfaces of the first metal layer 11 and the connecting layer 13 and / or the surfaces of the second metal layer 12 and the connecting layer 13 is provided with at least one concave-convex structure, wherein the concave-convex structure includes at least one concave structure and / or at least one convex structure.

[0053] The composite metal according to the present application includes a first metal layer and a second metal layer made of different materials, so that the composite metal has both 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 surfaces of the first metal layer and the connecting layer and the surfaces of the second metal layer and the connecting layer are each provided with a plurality of concave-convex structures, so that the concave-convex structure portions in the connecting layer are 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 to form a firmly combined composite metal whole, which significantly improves the bonding force between the first metal layer and the second metal layer, prolongs the service life of the composite metal, and is more conducive to meeting the demand for mechanical properties in 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 further provided with concave-convex structures on the bonding 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 lines at the bonding 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 and widening its application scenarios, for example, improving the forming limit of the R angle during stamping forming, thereby forming a nearly right-angle structure.

[0054] 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 and the second metal layer 12 can be regular shapes or irregular shapes, and the first metal layer 11 can be a layer structure with equal thickness or unequal thickness at different positions, and the second metal layer 12 can be a layer structure with equal thickness or unequal thickness at different positions.

[0055] 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).

[0056] Referring to FIG. 2, FIG. 2 is a schematic diagram of the concave-convex structure of the bonding surface of the connecting layer 13 and the first metal layer 11, and / or the connecting layer 13 and the second metal layer 12 in the composite metal 100 provided by the present application, which includes at least one concave structure and / or 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.

[0057] 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. The distribution of the suitable 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.

[0058] 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.

[0059] 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. 3, 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. 3. The rectangle can be a rectangle, as shown in (b) of FIG. 3, or a square. In an embodiment of the present application, as shown in (c) of FIG. 3, 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. 3, 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.

[0060] 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.

[0061] In an embodiment of the present application, the surface roughness of the concave-convex structure is 10 μm-25 μm, i.e., the surface roughness of the concave structure and / or 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.

[0062] In an embodiment of the present application, the connection layer 13 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, the connection layer, the first metal layer, and / or the second metal layer are different metal layers. 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), and polyether ether ketone (PEEK).

[0063] In an embodiment of the present application, the connecting layer 13 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.

[0064] In an embodiment of the present application, the ratio of the thermal expansion coefficient of the connecting layer 13 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 caused by 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.

[0065] In the embodiments of the present application, the connecting layer 13, 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, the connecting layer and the first metal layer and / or the second metal layer are different types of metal alloys. In other embodiments of the present application, the connecting layer and the first metal layer and / or the second metal layer are the same type but different models of metal alloys. Since the connecting layer, 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. That is, the elements of the connecting metal and the elements of the first metal can be simultaneously measured at each position 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 simultaneously measured at each position 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 microstructure uniform at the R angle, obtaining a color-uniform product during subsequent anodizing coloring, and improving the appearance of the product. Specifically, the intermetallic diffusion depth can be, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm.

[0066] 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 of 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.

[0067] 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.

[0068] In an embodiment of the present application, the first metal layer 11 can be used as an outer metal layer of the shell, i.e., as an outer surface metal layer exposed outside the shell. In some specific embodiments, the first metal layer 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.

[0069] In an embodiment of the present application, the second metal layer 12 can be used as an inner metal layer 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.

[0070] 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 13 comprises A380 aluminum alloy. Titanium alloy has good mechanical properties. By selecting titanium alloy as the first metal layer, the resulting composite metal can be used as a device shell, which can effectively protect the device inside the shell. Titanium alloy has good wear resistance and corrosion resistance, which can improve the service life of the composite metal. Aluminum alloy has good thermal conductivity and small density. By selecting aluminum alloy as the second metal layer, the resulting composite metal can be used as a device shell, which can effectively dissipate heat and reduce the overall mass of the shell. A380 aluminum alloy has a hardness similar to that of 6013 aluminum alloy. By using A380 aluminum alloy as the connecting layer between the titanium alloy first metal layer and the 6013 aluminum alloy second metal layer, the bonding force between the first metal layer and the second metal layer can be improved.

[0071] 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 13 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.

[0072] The present application also provides a preparation method of a composite metal. Referring to FIG. 4, the present application provides a flow chart of a preparation method of a composite metal, which comprises:

[0073] S101, 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;

[0074] S102, placing the surfaces with the concave-convex structures of the first metal and the second metal opposite to each other, and compounding a connecting layer between the first metal and the second metal by a solid-liquid bonding method; obtaining a composite metal.

[0075] 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. The preparation method is novel, the process is simple, and industrial production is facilitated.

[0076] In step S101, the surface roughening treatment includes milling and / or 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 laser engraving can be 1-3 times.

[0077] In an embodiment of the application, the surface roughening treatment further includes chemical etching after milling and / or 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.

[0078] 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%).

[0079] The application also provides a structural member comprising the composite metal provided in the foregoing or prepared by the preparation method provided in the foregoing. In an embodiment of the application, the structural member is an electronic device shell, which can be, for example, an electronic device middle frame, wherein the first metal layer of the composite metal serves as an exposed outer surface metal layer, providing the shell with better mechanical properties to cope with impacts when the shell encounters sharp objects or falls; the second metal layer can serve as an inner side metal layer close to the inside of the electronic device, providing the shell with good heat dissipation performance and reducing the weight of the entire shell. Moreover, when a functional through hole is subsequently processed according to actual needs, the composite metal is specially designed at the through hole position, effectively alleviating the phenomenon of galvanic corrosion, and the corrosion resistance of the shell can be improved.

[0080] In an embodiment of the application, the electronic device shell comprises four R corners, each of which is greater than or equal to 0.1 mm. The composite metal with good processability is obtained by specially designing the bonding surface of the first metal layer and the second metal layer and connecting them through the connecting layer. The electronic device shell prepared from the composite metal can obtain an R corner close to a right angle, and the minimum R corner can reach 0.1 mm.

[0081] In an embodiment of the application, the thickness of the first metal layer in the electronic device 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 device shell provided in the application can make the thickness of the exposed outer surface metal layer, the first metal layer, as thin as 0.2 mm, so as to realize the light weight of the product as much as possible, improve the material utilization rate, realize green development, and improve the user experience while ensuring the mechanical properties of the shell.

[0082] The application also provides an electronic device comprising the structural member provided in the foregoing, which can be, for example, a mobile phone, a tablet computer, a notebook computer, a wearable device (watch, bracelet), a digital camera, etc.

[0083] The effects of the technical solutions of the application are described below through specific examples.

[0084] Example 1

[0085] 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 DEG C. The obtained nano-pores have a diameter of 230 nm as shown in FIG. 5. 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 DEG C. The obtained nano-pores have a diameter of 170 nm.

[0086] The concave-convex structure of the surface of the first metal TC4 titanium alloy after surface roughening is shown in FIG. 6. The shape of the concave pit structure is rectangular, the pitch of the adjacent two 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.

[0087] The shape of the concave pit structure of the surface of the second metal 6013 aluminum alloy is rectangular, the pitch of the adjacent two 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.

[0088] Then, the first metal TC4 titanium alloy and the second metal 6013 aluminum alloy are placed together in a mold for die casting treatment. The surfaces of the first metal TC4 titanium alloy and the second metal 6013 aluminum alloy having the concave-convex structure 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.

[0089] 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 are observed, and the results are shown in FIG. 7. 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 substance (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 is tested, and it is found that the hardness of the connecting metal A380 aluminum alloy is close to the hardness of the second metal 6013 aluminum alloy, so that the hardness difference is not too large, and the deformation is not coordinated.

[0090] The elements at the interface bonding between the connecting metal A380 aluminum alloy and the first metal TC4 titanium alloy are detected by EDS (Energy Dispersive Spectroscopy), and the positions of the aluminum element and the titanium element are 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. 8. FIG. 8(a) is a metallographic representation of the interface bonding between the first metal TC4 titanium alloy and the connecting metal A380 aluminum alloy of Example 1, and the EDS (Energy Dispersive Spectroscopy) test position is indicated by an arrow in FIG. 8(a). FIG. 8(b) is the EDS representation of the interface bonding at the position indicated by the arrow in FIG. 8(a). As shown in FIG. 8, the intermetallic diffusion depth between the first metal layer and the connecting layer of the composite metal of Example 1 is about 2.5 μm.

[0091] Example 2

[0092] The difference from Example 1 is that the connecting layer is a polyphenylene sulfone (PPSU) resin, and the glass fiber accounts for 35% of the mass percentage.

[0093] Example 3

[0094] The difference from Example 1 is that the first metal layer is TA4 titanium alloy, and the second metal layer is 7075 aluminum alloy.

[0095] Example 4

[0096] The difference from Example 1 is that the shape of the pit structure on the surface of the first metal and the second metal is T-shaped.

[0097] Example 5

[0098] The difference from Example 1 is that the pitch of the adjacent two pit structures of the surface-roughened first metal TC4 titanium alloy surface is 300 μm, the depth of the pit structure is 450 μm, and the lateral dimension of the pit structure is 270 μm.

[0099] Example 6

[0100] The difference from Example 1 is that the pitch of the adjacent two pit structures of the surface-roughened second metal 6013 aluminum alloy surface is 330 μm, the depth of the pit structure is 260 μm, and the lateral dimension of the pit structure is 230 μm.

[0101] Example 7

[0102] The difference from Example 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.

[0103] Comparative Example 1

[0104] The difference from Example 1 is that the first metal and the second metal surface are not roughened, and have no relief structure.

[0105] Comparative Example 2

[0106] The difference from Example 1 is that after the first metal and the second metal are roughened, direct pressing is performed without a connecting layer.

[0107] Performance detection

[0108] Examples 1-7 and Comparative Examples 1-2 are subjected to performance testing, and the results are shown in Table 1.

[0109] Surface roughness: the surface of the composite metal prepared in Examples 1-7 and Comparative Examples 1-2 is 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.

[0110] Intermetallic diffusion depth: the composite metal prepared in Examples 1-7 and Comparative Examples 1-2 is cut along the thickness direction by a wire electrical discharge machine. The interface bonding morphology of the heterogeneous metal layer is observed by a field emission scanning electron microscope. The distribution of each element near the interface is analyzed by an energy dispersive spectrometer. 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.

[0111] Bonding strength: the composite metal prepared in Examples 1-7 and Comparative Examples 1-2 was placed into a shear mold with the surface to be tested facing down, and a shear test was performed. The shear groove of the shear mold was processed to have a size of 7.2 mm x 5.6 mm x 10 mm, and was a cuboid groove with a length, width, and height with a margin, so as to ensure that the shear sample was only subjected to a shear force. The maximum pressure borne by the sample when the interface was peeled apart was measured, and the ratio of the effective area of the diffusion bonding surface of the sample was obtained, to obtain the shear bonding strength of the interface.

[0112] Table 1

[0113] As can be seen from Table 1, the bonding strength between the first metal layer and the second metal layer of the composite metal prepared in Examples 1-7 is significantly improved, compared to Comparative Example 1 in which the first metal layer and the second metal layer are not subjected to roughening treatment, and Comparative Example 2 in which no connecting layer is provided. The depth of the intermetallic diffusion layer between the first metal layer and the second metal layer having the concave-convex structure obtained by roughening treatment and the connecting layer is significantly deepened, and the bonding force between the first metal layer and the second metal layer is improved.

[0114] The above describes preferred embodiments of the present application, but should not be construed as limiting the scope of the present application. It should be noted that, for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements are also considered to be within the scope of protection of the present application.

Claims

1. A composite metal, characterized by, The composite metal comprises: A first metal layer (11): A second metal layer (12): A connecting layer (13), the first metal layer (11) and the second metal layer (12) are different metal layers, the first metal layer (11), the connecting layer (13) and the second metal layer (12) are sequentially stacked. A concave-convex structure, the concave-convex structure comprises at least one of a concave structure and a convex structure, at least one of the surface of the first metal layer (11) combined with the connecting layer (13) and the surface of the second metal layer (12) combined with the connecting layer (13) is provided with the concave-convex structure.

2. The composite metal of claim 1, wherein, The concave-convex structure comprises a plurality of concave structures or a plurality of convex structures.

3. The composite metal of claim 1, wherein, The concave-convex structure comprises a plurality of concave structures and a plurality of convex structures.

4. The composite metal of claim 3, wherein, Each adjacent two concave structures form a convex structure; the distance between adjacent two concave structures is 0.1mm-0.5mm.

5. The composite metal according to any one of claims 2 to 4, wherein The depth of the concave structure is 100μm-500μm, and the lateral dimension of the concave structure is 50μm-350μm.

6. The composite metal of any one of claims 2-4, wherein, The cross-sectional shape of each concave structure along the thickness direction of the composite metal is rectangular, trapezoidal, triangular or T-shaped.

7. The composite metal according to any one of claims 1 to 6, wherein The inner surface of at least one concave structure is provided with a first nano secondary structure; the first nano secondary structure comprises nano holes, and the diameter of the nano holes is 50nm-500nm.

8. The composite metal of any one of claims 1-7, wherein, The outer surface of at least one convex structure is provided with a second nano secondary structure; the second nano secondary structure comprises nano holes, and the diameter of the nano holes is 50nm-500nm.

9. The composite metal of claim 7 or 8, wherein, The surface roughness of at least one of the concave structure and the convex structure is 10μm-25μm.

10. The composite metal of any one of claims 1-9, wherein, The connecting layer (13) 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; the resin comprises at least one of polybutylene terephthalate, polyphenylene sulfide, polyamide, polyphthalamide, polypropylene, polycarbonate, polyphenylene sulfone, polyether ether ketone.

11. The composite metal of any one of claims 1-10, wherein, The connecting layer (13) comprises metal, and the ratio of the hardness of the connecting layer (13) to the hardness of the metal with smaller hardness in the first metal layer (11) and the second metal layer (12) is 1:(0.8-1.2).

12. The composite metal of any one of claims 1-11, wherein, The connecting layer (13) comprises metal, the coefficient of thermal expansion of the connecting layer (13) is 2x10 -5 / K-2.7x10 -5 / K; the ratio of the coefficient of thermal expansion of the connecting layer (13) to the coefficient of thermal expansion of the larger one of the first metal layer (11) and the second metal layer (12) is 1:(0.8-1.2).

13. The composite metal of claim 11 or 12, wherein, The connecting layer (13) and the first metal layer (11) are different metal layers, the interfacial bonding between the connecting layer (13) and the first metal layer (11) has an intermetallic diffusion depth of 1μm-10μm; the connecting layer (13) and the second metal layer (12) are different metal layers, the interfacial bonding between the connecting layer (13) and the second metal layer (12) has an intermetallic diffusion depth of 1μm-10μm.

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

15. The composite metal of any one of claims 1-14, wherein, 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, zinc and its alloys; 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, zinc and its alloys.

16. The composite metal of claim 15, wherein, The first metal layer (11) comprises at least one of iron and its alloys, zirconium and its alloys, and titanium and its alloys; the second metal layer (12) comprises at least one of magnesium and its alloys, aluminum and its alloys, copper and its alloys, and zinc and its alloys.

17. The composite metal of claim 16, wherein, The first metal layer (11) comprises a titanium alloy, the second metal layer (12) comprises a 6013 aluminum alloy, and the connecting layer (13) comprises an A380 aluminum alloy.

18. The composite metal of any one of claims 1-17, wherein, 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 (13) is greater than or equal to 0.05 mm.

19. A method of manufacture for producing a composite metal as claimed in any one of claims 1 to 18, characterised by, Comprising: 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; Placing the surfaces of the first metal and the second metal with the concave-convex structures opposite to each other, and compounding a connecting layer (13) between the first metal and the second metal by solid-liquid combination; obtaining a composite metal.

20. The production method according to claim 19, wherein The surface roughening treatment comprises at least one of milling processing and laser engraving.

21. The production method according to claim 20, wherein The surface roughening treatment further comprises chemical etching, which is performed after at least one of the milling processing and the laser engraving.

22. A structural member, characterized by The structural member comprises the composite metal of any one of claims 1-18 or the composite metal prepared by the preparation method of any one of claims 19-21.

23. The structural member of claim 22, wherein The structural member is an electronic device shell, and the electronic device shell comprises four R-angles, each of which is greater than or equal to 0.1 mm.

24. An electronic device, comprising: The electronic device comprises the structural member of claim 22 or 23. The electronic device comprises the structural member of claim 22 or 23.

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