Middle frame, preparation method thereof and electronic equipment

Abstract

The invention provides a middle frame, a preparation method thereof and electronic equipment. The middle frame comprises a middle plate and a frame arranged along the peripheral side of the middle plate, the middle plate is made of high-strength 7-series aluminum alloy, the frame comprises an appearance layer, and the appearance layer is made of 5-series aluminum alloy or 7-series aluminum alloy which can be anodized and has yield strength smaller than that of the middle plate, so that the strength and attractiveness of the middle frame of the electronic equipment are improved.

Description

Technical Field

[0001] The present application relates to the field of electronic equipment, and in particular to a middle frame and a preparation method thereof, and an electronic device. Background Art

[0002] Aluminum alloy materials are still the preferred material for the appearance and structure of electronic products such as mobile phones, tablet computers, and laptops due to their advantages of light weight, high specific strength, good heat dissipation, and bright color after surface oxidation treatment. Series 1 aluminum alloys, 3 series aluminum alloys, 5 series aluminum alloys, and 6 series aluminum alloys usually have low alloy element content, excellent machinability, corrosion resistance, weldability, and electroplating properties, are easy to polish, and have excellent anodizing effects. Compared with the generally higher strength 2 series aluminum alloys and 7 series aluminum alloys, 1 series aluminum alloys, 3 series aluminum alloys, 5 series aluminum alloys, and 6 series aluminum alloys have advantages in surface color after anodizing treatment. The 7 series aluminum alloys represented by 7055 and 7075 are ultra-high strength aluminum alloys (Al-Zn-Mg-Cu series), and their yield strength can reach more than 500MPa, which is about twice that of conventional 6 series aluminum alloys. Therefore, the effect of structural weight reduction is also far better than the lower strength 1 series aluminum alloys, 3 series aluminum alloys, 5 series aluminum alloys, and 6 series aluminum alloys. As the frame material of electronic products, 7 series aluminum alloy has the advantages of light weight and less prone to bending and deformation, which can effectively improve product reliability. However, 7 series aluminum alloy, especially ultra-high strength Al-Zn-Mg-Cu alloy, generally has a high content of alloy elements, and the components will inevitably be unevenly distributed to form segregation. At the same time, there are also large differences in the morphology, size, and distribution of the second phase particles. These will cause the appearance of 7 series aluminum alloy after anodizing and the reliability of the anodized film to be inferior to 6 series aluminum alloy.

[0003] The continuous upgrading and innovation of consumer electronic products have put forward higher requirements on the comprehensive performance of aluminum alloys. On the one hand, the middle frames of consumer electronic products such as smartphones, tablets, and laptops need to have high strength to effectively protect the glass panel; on the other hand, the products must meet the high standards of consumers in terms of appearance design, brightness, color, and many other aspects. However, strength and appearance are contradictory to a certain extent. If all high-strength 7-series aluminum alloys are used, the aesthetics of the product will be affected to a certain extent; if all 5-series aluminum alloys and 6-series aluminum alloys are used, the strength of the product will not meet the high-strength requirements. Therefore, there is currently a lack of a middle frame that has both high strength and high aesthetic performance. Summary of the invention

[0004] The present application provides a middle frame and a preparation method thereof and an electronic device, so as to improve the strength and aesthetics of the middle frame of the electronic device.

[0005] In a first aspect, the present application provides a middle frame of an electronic device. The middle frame includes a middle plate and a frame arranged along the periphery of the middle plate, the middle plate is a high-strength 7-series aluminum alloy, and the frame includes an appearance layer, the appearance layer is a 5-series aluminum alloy or an anodizable 7-series aluminum alloy whose yield strength is less than the yield strength of the middle plate.

[0006] The middle frame provided in the present application has a middle plate of 7 series aluminum alloy, which can provide high-strength support for the middle frame, and its strength can reach more than 600MPa. The appearance layer of the frame is 5 series aluminum alloy or 7 series aluminum alloy with an anodized strength less than the strength of the middle plate. Since the anodizing effect of 5 series aluminum alloy or 7 series aluminum alloy with an anodized strength less than the strength of the middle plate is better, therefore, using 5 series aluminum alloy or 7 series aluminum alloy with an anodized strength less than the strength of the middle plate as the appearance layer of the frame can provide the middle frame with an anodized layer with better appearance effects such as brightness and color.

[0007] In an optional implementation, the alloy composition of the 7-series aluminum alloy forming the middle plate includes, by weight percentage: Zn 8.5-10.5%, Mg 2.0-3.0%, Cu 1.0-2.2%, Ti 0-0.06, Zr 0.06-0.5%, Re0-0.2%, Fe≤0.05%, Si≤0.05%, inevitable impurities, the content of any one impurity ≤0.05%, the total amount of the impurities ≤0.15%, and the balance is Al. The 7-series aluminum alloy of this alloy composition has a relatively high yield strength, which can reach more than 600MPa, and can form a high-strength connection relationship with the 5-series aluminum alloy or 7-series aluminum alloy of the appearance layer, thereby improving the strength of the entire middle frame.

[0008] In an optional implementation, the yield strength of the middle plate is ≥600 MPa, and the elongation is ≥5%. The middle plate can be used to provide a high-strength middle frame.

[0009] In an optional implementation, the exterior layer is 5052 aluminum alloy or 7003 aluminum alloy. 5052 aluminum alloy or 7003 aluminum alloy can be more easily compounded with the above-mentioned 7 series aluminum alloy through extrusion compounding, and the processing technology of the two is more matched, so as to prevent the frame from not being able to obtain a good anodized layer due to the mismatch of the material process, so that the middle frame cannot meet the requirements of rigidity and high aesthetics.

[0010] In an optional implementation, the exterior layer is 5052 aluminum alloy. 5052 aluminum alloy can be more compatible with the heat treatment process of 7 series aluminum alloy. During the preparation process, the solution heat treatment temperature will not cause coarse second phase particles to appear in the 5052 aluminum alloy, thereby ensuring that the subsequent polishing and anodizing treatment effects will be better.

[0011] In an optional implementation, the frame further includes a substrate, and the appearance layer is disposed on the outer surface of the substrate. The frame may include a two-layer structure, one layer being the substrate and the other being the appearance layer. The substrate may be integrally formed with the middle plate using the same material, such as a 7 series aluminum alloy, to provide high-strength support for the frame and improve the anti-fall capability of the frame.

[0012] In an optional implementation, the substrate and the appearance layer are an integrally connected structure. The substrate and the appearance layer are integrally formed using different materials to form an integrally connected structure, which can further improve the strength of the frame, improve its drop resistance, and facilitate processing and manufacturing.

[0013] In an optional implementation, the thickness of the frame is 0.1 to 2.0 mm. If the frame is too thin, it will affect the polishing effect, and further affect the anodizing effect and appearance of the middle frame. If the frame is too thick, it will affect the size and refinement of the electronic device.

[0014] In an optional implementation, the difference between the maximum thickness value of the appearance layer and the minimum thickness value of the appearance layer is less than or equal to 0.1 mm, so as to ensure that the thickness of the appearance layer at various locations of the middle frame is relatively uniform.

[0015] In an optional implementation, the middle frame is provided with rounded corners at the edges, and the radius of the rounded corners is 1 to 20 mm.

[0016] The preparation method of the middle frame of the embodiment of the present application includes: placing an extruded billet in an extruder for reverse extrusion to obtain an aluminum alloy composite profile, performing solid solution and aging heat treatment on the aluminum alloy composite profile and then machining to obtain the middle frame; wherein the extruded billet includes an outer layer alloy and an inner layer alloy, and the strength of the outer layer alloy is less than the strength of the inner layer alloy; during the reverse extrusion process, the temperature of the extruded billet is 340-380°C, the extrusion temperature is 360-400°C, the extrusion speed is 0.5-3mm / min, and the extrusion ratio is 10-20.

[0017] In a second aspect, the present application provides a method for preparing a middle frame, the method comprising:

[0018] Placing an extruded billet in an extruder for reverse extrusion to obtain an aluminum alloy composite profile, wherein the extruded billet comprises an outer layer alloy and an inner layer alloy, the inner layer alloy is a 7 series aluminum alloy, and the outer layer alloy is a 5 series aluminum alloy or an anodizable 7 series aluminum alloy having a yield strength less than the yield strength of the middle plate;

[0019] The aluminum alloy composite profile is subjected to solution treatment and aging heat treatment and then machined to obtain the middle frame; the middle frame includes a middle plate and a frame arranged along the peripheral side of the middle plate, the inner layer alloy forms the matrix of the middle plate and the optional frame, and the outer layer alloy forms the appearance layer of the frame.

[0020] The middle frame obtained by the preparation method of the present application can obtain the same characteristics as the middle frame of the first aspect of the present application, which will not be repeated here. Among them, the preparation method of the present application forms a composite profile by reverse extrusion. During the reverse extrusion process, the relative movement direction of the extrusion shaft is opposite to the flow direction of the alloy material. Since there is no relative movement and friction between the inner wall of the extrusion barrel and the extruded blank during reverse extrusion, the alloy material can be deformed more uniformly, so that the obtained aluminum alloy composite profile can have a coating layer with a more uniform thickness.

[0021] In an optional implementation, during the reverse extrusion process, the temperature of the extruded billet is 340-380°C, the extrusion temperature is 360-400°C, the extrusion speed is 0.5-3 mm / min, and the extrusion ratio is 10-20. If the temperature of the extruded billet and the extrusion temperature are too low, extrusion cannot be achieved; if they are too high, the grains of the extruded aluminum alloy composite profile will be coarsened, thereby reducing the strength of the aluminum alloy. If the extrusion speed is too slow, it is not conducive to improving efficiency; if the extrusion speed is too fast, it is easy to cause cracking at the corners of the aluminum alloy composite profile, thereby affecting the yield of the aluminum alloy composite profile and even making the extruded profile completely scrapped. If the extrusion ratio is too large, it is difficult to process and the surface of the aluminum alloy composite profile is prone to cracking. If the extrusion ratio is too small, the strength of the aluminum alloy is low and the bonding force between the inner and outer alloys of the composite profile is small, which is not conducive to improving the strength of the middle frame. Therefore, by adopting the above extrusion process, a stable connection interface can be formed between the outer alloy and the inner alloy, the connection strength between the outer alloy and the inner alloy can be improved, and at the same time, the grain size and metallographic structure of the obtained aluminum alloy composite profile meet the requirements, thereby achieving the purpose of improving the strength of the aluminum alloy composite profile. Therefore, the upper extrusion process of the present application can achieve the purpose of preventing the surface alloy from falling off, good alloy interface bonding, and high product yield rate.

[0022] In an optional implementation, the extruded billet includes a barrel formed by an outer layer alloy and a core column formed by an inner layer alloy, the barrel includes a barrel bottom and a barrel wall, the core column is inserted into the barrel and connected to the barrel wall of the barrel by interference fit, and the barrel bottom is arranged close to the extrusion shaft of the extruder. In the extruded billet, the core column and the barrel wall are completely abutted. The structure of the connection between the barrel and the core column can realize the uniform formation of the coating layer around the extruded profile during the reverse extrusion process, and the barrel bottom of the barrel needs to be fixedly connected to the barrel wall to ensure that an aluminum alloy composite profile with a complete coating layer can be formed.

[0023] In an optional implementation, the bottom of the cylinder is provided with an exhaust hole. By providing the exhaust hole, the pore defects in the aluminum alloy composite profile can be reduced and the molding quality of the aluminum alloy composite profile can be improved.

[0024] In an optional implementation, the barrel and the stem are assembled by heat-fitting, for example, the barrel is heated to 200-350° C. and then heat-fitted with the stem.

[0025] In a third aspect, the present application provides an electronic device, which includes the middle frame of the first aspect of the present application and various possible implementation methods.

[0026] The technical effects that can be achieved in the above-mentioned second aspect can be described with reference to the corresponding effects in the above-mentioned first aspect, and will not be repeated here.

[0027] Among them, the data in the above-mentioned possible implementation methods of the present application, such as the strength of the middle plate, the thickness of the frame and other data, when measuring, the values ​​within the scope of engineering measurement error should be understood to be within the scope specified in the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A schematic diagram of the structure of a middle frame in an embodiment;

[0029] Figure 2 A schematic structural diagram of a frame of an embodiment;

[0030] Figure 3 A schematic diagram of the structure of an extruded billet according to an embodiment;

[0031] Figure 4 A schematic diagram of the structure of an extrusion device according to an embodiment;

[0032] Figure 5 The figure is a schematic diagram of the structure of a composite sheet according to an embodiment.

[0033] Reference numerals:

[0034] 10-middle frame; 11-middle plate; 12-frame; 121-base; 122-appearance layer; 14-extruded blank;

[0035] 141-outer alloy; 142-inner alloy; 21-extrusion cylinder; 22-extrusion die; 23-extrusion shaft;

[0036] 24-die hole; 31-composite sheet; 32-sheet outer layer; 33-sheet inner layer. DETAILED DESCRIPTION

[0037] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings.

[0038] The terms used in the following embodiments are only for the purpose of describing specific embodiments and are not intended to be limiting of the present application. As used in the specification and appended claims of the present application, the singular expressions "a", "an", "above", "the" and "this" are intended to also include expressions such as "one or more", unless there is a clear contrary indication in the context.

[0039] References to "one embodiment" or "some embodiments" etc. described in this specification mean that a particular feature, structure or characteristic described in conjunction with the embodiment is included in one or more embodiments of the present application. Thus, the phrases "in one embodiment", "in some embodiments", "in some other embodiments", "in some other embodiments", etc. that appear at different places in this specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "including", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized in other ways.

[0040] Electronic devices, such as mobile phones, usually have packaging components including a display screen, a back cover, and a middle frame. The middle frame is located between the display screen and the back cover and plays a role in packaging and protection. Figure 1 FIG. 1 is a schematic diagram of the structure of a middle frame in an embodiment. Figure 1 As shown, the middle frame 10 of this embodiment includes a middle plate 11 and a frame 12. The middle plate 11 and the frame 12 of the middle frame 10 are explained below.

[0041] like Figure 1 As shown, the middle plate 11 may be a quadrilateral structure, and rounded corners may be provided at the edges and corners. The radius of the rounded corners may be 1 to 20 mm. The middle plate 11 is located inside the electronic device and is used to carry electronic components such as chips, receivers, and cameras. The middle plate 11 plays a major load-bearing role in the structure of the middle frame 10 and needs to have high strength. The middle plate 11 may be prepared and formed of a 7 series aluminum alloy. Among them, the yield strength of the middle plate 11 is ≥600MPa, and the elongation is ≥5%.

[0042] Wherein, in terms of weight percentage, the alloy composition of the 7 series aluminum alloy forming the middle plate includes: Zn 8.5-10.5%, Mg 2.0-3.0%, Cu 1.0-2.2%, Ti 0-0.06, Zr 0.06-0.5%, Re 0-0.2%, Fe≤0.05%, Si≤0.05%, inevitable impurities, the content of any one impurity is ≤0.05%, the total amount of the impurities is ≤0.15%, and the balance is Al. Wherein, the weight percentage of Zn can be, for example, 8.5%, 9%, 9.5%, 10%, or 10.5% or a value between any two of the above values. The weight percentage of Mg can be, for example, 2%, 2.2%, 2.4%, 2.6%, 2.8%, or 3% or a value between any two of the above values. The weight percentage of Cu can be, for example, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, or 2.2%, or a value between any two of the above values. The weight percentage of Ti can be, for example, 0, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, or 0.06%, or a value between any two of the above values. The weight percentage of Zr can be, for example, 0.06%, 0.1%, 0.15%, 0.3%, or 0.5%, or a value between any two of the above values. The weight percentage of Re can be, for example, 0, 0.01%, 0.04%, 0.06%, 0.08%, 0.10%, 0.12%, 0.14%, 0.16%, 0.18%, or 0.2%, or a value between any two of the above values. The weight percentage of Fe may be, for example, 0, 0.01%, 0.02%, 0.03%, 0.04%, or 0.05%, or any value between the above two values. The weight percentage of Si≤ may be, for example, 0, 0.01%, 0.02%, 0.03%, 0.04%, or 0.05%, or any value between the above two values.

[0043] like Figure 1 As shown, the frame 12 is arranged along the circumference of the middle plate 11 to form a closed frame. In the electronic device, the frame 12 forms a part of the outer circumference of the electronic device. The frame 12 connects the display screen and the back cover, and the display screen, the frame 12 and the back cover form a space for accommodating the middle plate 11, the chip, the earpiece, the camera and other components.

[0044] Since the frame constitutes part of the appearance surface of the electronic device, in addition to having a certain strength, the frame must also have good anodization properties to reduce appearance defects and improve aesthetics. The frame 12 of the embodiment of the present application includes an appearance layer 122, and the appearance layer 122 is made of a 5-series aluminum alloy or a medium-strength 7-series aluminum alloy that can be anodized. In an optional embodiment, the appearance layer 122 is made of 5052 aluminum alloy. The 5052 aluminum alloy can be better combined with the 7-series aluminum alloy. During the preparation process, it will not be affected by the processing temperature of the 7-series aluminum alloy, avoiding the formation of defects on its surface. In addition, when the appearance layer is a 7-series aluminum alloy, a 7003 aluminum alloy can be used. The 7003 aluminum alloy can form a high-strength connection relationship with the 7-series aluminum alloy of the middle plate.

[0045] Figure 2 FIG. 1 is a schematic diagram of the structure of a frame of an embodiment. Figure 2 As shown, in one embodiment, the frame 12 may include a substrate 121 and an appearance layer 122. The substrate 121 is connected to the middle plate 11. The appearance layer 122 is provided on the appearance surface of the substrate 121 to form the appearance surface of the frame 12. The substrate 121 mainly provides bearing capacity, which can be prepared and formed by a 7 series aluminum alloy, and can be an integrally connected structure with the middle plate 11. The appearance layer 122 can be a 5 series aluminum alloy or a medium-strength 7 series aluminum alloy that can be anodized to form an appearance surface with higher aesthetics. The appearance layer 122 can be integrally processed and formed with the substrate 121 to form an integrally connected structure.

[0046] The thickness of the appearance layer 122 is 0.1-2.0 mm, and the difference between the maximum thickness of the appearance layer 122 and the minimum thickness of the appearance layer 122 is less than or equal to 0.1 mm.

[0047] like Figure 1 As shown, the middle frame 10 is provided with rounded corners at the edges, and the radius of the rounded corners is 1 to 20 mm, which can be set specifically according to the design size of the electronic device.

[0048] The middle frame of the embodiment of the present application can be prepared by the following method.

[0049] Step S11, providing extrusion blank, Figure 3 Figure 1 is a schematic diagram of the structure of an extruded billet. Figure 3As shown. The extruded billet 14 includes an outer alloy 141 and an inner alloy 142, wherein the outer alloy 141 is a cylinder, and the inner alloy 142 is a core column filled in the cylinder, such as a cylinder. The outer alloy is formed by a 5-series aluminum alloy or a 7-series aluminum alloy that can be anodized and has a yield strength less than the yield strength of the middle plate. The inner alloy is formed by a 7-series aluminum alloy. When both the outer alloy and the inner alloy are 7-series aluminum alloys, the yield strength of the outer alloy is less than the yield strength of the inner alloy. The cylinder includes a cylinder bottom and a cylinder wall, which can be welded or riveted. The cylinder can be an extruded tube or formed by rolling an aluminum plate. The cylinder and the cylinder are connected by interference fit. The wall thickness of the cylinder is 3 to 5% of the diameter of the cylinder. Several small circular holes are provided at the bottom of the cylinder as exhaust holes to ensure that the gas can be discharged during assembly. During assembly, the cylinder can be hot-fitted with the cylinder after being heated to 200 to 350°C.

[0050] Step S12: reverse extrusion to obtain a composite aluminum alloy profile. Figure 4 FIG. 2 is a schematic diagram of the structure of an extruder according to an embodiment of the present invention. Figure 4 As shown, the extrusion blank 14 is placed in the extrusion barrel 21 of the extruder. During the extrusion process, since there is no friction between the extrusion blank 14 and the extrusion barrel 21, the outer alloy and the inner alloy of the extrusion blank 14 can be ensured to flow relatively synchronously. One end of the barrel bottom of the extrusion blank 14 is close to the extrusion die 22; the extrusion shaft 23 adopts a flat die structure, and the shape of the die hole 24 of the extrusion die 22 is determined according to the cross-sectional shape of the extruded product. The main extrusion process parameters are: billet temperature 340~380℃, extrusion die and extrusion barrel 21 temperature 360~400℃, extrusion speed 0.5~3mm / min, extrusion ratio 10~20.

[0051] Step S13: performing solution and aging heat treatment on the aluminum alloy composite profile, with the solution temperature being 420-480° C. and the solution time being 4-8 hours, and the aging temperature being 100-140° C. and the aging time being 20-30 hours.

[0052] Step S14: machining. First, the composite aluminum alloy profile is sliced ​​to obtain a composite sheet with a cladding structure on all sides, such as Figure 5 As shown. The composite sheet 31 includes an outer sheet layer 32 and an inner sheet layer 33. Figure 5 The composite sheet is subjected to numerical control (CNC) processing, polishing and other treatments, wherein the middle portion of the inner layer 33 of the sheet is thinned, and the circumferential edge of the inner layer 33 of the sheet is processed to form a receiving groove, the bottom of the receiving groove forms the middle plate 11, and the groove wall of the receiving groove forms the matrix of the frame. Thus, the inner layer 33 of the sheet can form the matrix 121 of the middle plate 11 and the frame 12, and the outer layer 32 of the sheet can be used to form the appearance layer 122. After the treatment, Figure 1 The middle frame 10 is shown.

[0053] The following is a detailed description of the specific processing process of the middle frame using the composite of 7 series aluminum alloy and 5 series aluminum alloy as an example.

[0054] Example 1

[0055] This embodiment is a middle frame, and its preparation process includes the following steps:

[0056] Step S11: Extrusion blank preparation

[0057] The outer alloy is a 5052 aluminum alloy extruded tube, and the inner alloy is a 7 series aluminum alloy round cast rod. The composition of the 7 series aluminum alloy used is: Al-8.8Zn-2.4Mg-2Cu-0.03Ti-0.13Zr, each impurity element is less than 0.05wt.%, and the total amount is less than 0.15wt.%. The wall thickness of the 5052 aluminum alloy cylinder is 20mm, and one end of the cylinder is sealed with a 5052 plate by riveting. The thickness of the sealing plate is 50mm, and 4 exhaust holes with a diameter of 5mm are opened on the plate. The cylinder is cleaned to remove surface oil stains. The diameter of the 7 series aluminum alloy round cast rod is 400mm after turning to remove the casting segregation layer. The inner diameter of the 5052 aluminum alloy cylinder is 2mm smaller than the diameter of the 7 series aluminum alloy round cast rod. The aluminum alloy cylinder is heated to 300°C and then taken out, and hot-loaded with the round cast rod maintained at room temperature to complete the blanking. The overall blank length is 800-1000mm.

[0058] Step S12: extrusion and heat treatment

[0059] The four-sided clad composite aluminum alloy profile was prepared by reverse extrusion process. The cross-sectional size of the composite aluminum alloy profile is 170mm×80mm. The aluminum alloy composite sheet was heat treated and aged. After heat treatment, the core alloy had a tensile strength of 680MPa, a yield strength of 630MPa, and an elongation of 8%.

[0060] Step S13: middle frame processing

[0061] A sheet with a thickness of 10 mm was sawed along the cross section of the composite aluminum alloy profile to obtain a four-sided clad aluminum alloy composite sheet with a size of 170 mm × 80 mm × 10 mm. Figure 5 The middle frame blank can be obtained by CNC processing using a plate of 170mm×80mm×10mm. The frame of the middle frame consists of a matrix and an appearance layer. The matrix and the middle plate are made of the same material, which is a 7 series high-strength aluminum alloy. The appearance layer is 5052 aluminum alloy, and the middle plate is a 7 series high-strength aluminum alloy. The appearance layer of the frame is polished and anodized to obtain the final middle frame structure.

[0062] Example 2

[0063] This embodiment is a middle frame, which is different from the first embodiment in that the alloy composition of the 7-series aluminum alloy forming the middle plate and the frame matrix is ​​different. The 7-series aluminum alloy composition of this embodiment is Al-9.8Zn-2.6Mg-1.6Cu-0.10Zr, and each impurity element is less than 0.05wt.%, and the total amount is less than 0.15wt.%.

[0064] Example 3

[0065] This embodiment is a middle frame, which is different from the first embodiment in that the alloy composition of the 7-series aluminum alloy forming the middle plate and the frame matrix is ​​different. The 7-series aluminum alloy composition of this embodiment is Al-8.8Zn-2.0Mg-2.1Cu-0.08Zr-0.12Re, and each impurity element is less than 0.05wt.%, and the total amount is less than 0.15wt.%.

[0066] Example 4

[0067] This embodiment is a middle frame, which is different from the first embodiment in that the alloy composition of the 7 series aluminum alloy forming the middle plate and the frame matrix is ​​different. The 7 series aluminum alloy of this embodiment is the existing 7075 aluminum alloy, with a specific composition of Al-5.9Zn-2.2Mg-1.8Cu-0.21Cr, each impurity element is less than 0.05wt.%, and the total amount is less than 0.15wt.%.

[0068] Example 5

[0069] This embodiment is a middle frame, which is different from the first embodiment in that the alloy composition of the 7 series aluminum alloy forming the middle plate and the frame matrix is ​​different. The 7 series aluminum alloy of this embodiment is the existing 7055 aluminum alloy, with a specific composition of Al-7.8Zn-2.0Mg-2.5Cu-0.12Zr, and each impurity element is less than 0.05wt.%, and the total amount is less than 0.15wt.%.

[0070] Comparative Example 1

[0071] This comparative example is a middle frame, which differs from Example 1 in that the aluminum alloy forming the appearance layer is 1070 aluminum alloy, and the specific composition is Al-0.18Si-0.21Fe-0.02Cu-0.03V, and each impurity element is less than 0.03wt.%.

[0072] Comparative Example 2

[0073] This comparative example is a middle frame, which differs from Example 1 in that the aluminum alloy forming the appearance layer is 3004 aluminum alloy, and the specific composition is Al-1.2Mn-1.0Mg-0.2Si-0.4Fe, each impurity element is less than 0.05wt.%, and the total amount is less than 0.15wt.%.

[0074] Comparative Example 3

[0075] This comparative example is a middle frame, which differs from Example 1 in that the aluminum alloy forming the appearance layer is 6061 aluminum alloy, and the specific composition is Al-0.5Si-0.98Mg-0.26Cu-0.2Cr-0.14Fe-0.09Mn-0.05Zn, each impurity element is less than 0.05wt.%, and the total amount is less than 0.15wt.%.

[0076] The yield strength of the middle frame of each embodiment and comparative example was tested respectively, and the appearance of each sample was detected. The observation test results are listed in Table 1.

[0077] Table 1

[0078]

[0079] Appearance OK means that the number of appearance defects such as black spots and pitting is less than or equal to 2, and the area of ​​each defect is less than 0.05mm 2 .

[0080] Appearance NG means that the number of appearance defects such as black spots and pitting is greater than 2, or the size of any defect is greater than 0.05mm 2 .

[0081] The test method for scratch resistance is to use steel wool to apply a load of 1kgf on the surface of the sample. The test head area is 2cm*2cm. The sample is rubbed back and forth 1000 times within a stroke of 40mm at a speed of 40 reciprocating / min. If there is no scratch on the surface after the test, it is OK, otherwise it is NG.

[0082] It can be seen from the data in Table 1 that the yield strength and appearance performance of the middle frame corresponding to Examples 1-5 are better than those of Comparative Examples 1-3. From the comparison data of Examples 1-3 and 4-5, it can be seen that when the 7-series aluminum alloy adopts the composition of the 7-series aluminum alloy defined in the present application, its yield strength is better than that of the middle frame of Examples 4-5. It can be seen that the use of the 7-series aluminum alloy of the present application can effectively improve the strength of the middle frame. From the comparison of Example 1 and Comparative Examples 1-2, it can be seen that when the aluminum alloy of the appearance layer is a 1-series aluminum alloy or a 3-series aluminum alloy, the hardness of the appearance layer of the middle frame is low and cannot meet the requirements. From the comparison data of Example 1 and Comparative Example 3, it can be seen that when the aluminum alloy of the appearance layer is a 6-series aluminum alloy, the anodized film of the appearance layer of the middle frame is prone to defects such as pitting and black spots.

[0083] Based on the same technical purpose, the present application also provides an electronic device. The electronic device may be, for example, a mobile terminal device such as a mobile phone, a tablet computer, a watch, etc. The electronic device may include a display screen, a rear cover plate, and a middle frame of the embodiment of the present application. The display screen, the rear cover plate, and the frame of the middle frame may form a receiving cavity, and the electronic components of the electronic device, such as a handset, a camera, a chip, a battery, etc., are arranged in the above-mentioned receiving cavity.

[0084] The above are only specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A middle frame, characterized in that: It includes a middle plate and a frame arranged along the circumference of the middle plate, the middle plate is a 7 series aluminum alloy, the frame includes an appearance layer, the appearance layer is a 5 series aluminum alloy or an anodizable 7 series aluminum alloy with a yield strength less than that of the middle plate.

2. The middle frame according to claim 1, characterized in that: The exterior layer is made of 5052 aluminum alloy or 7003 aluminum alloy.

3. The middle frame according to claim 1 or 2, characterized in that: In terms of weight percentage, the alloy composition of the 7 series aluminum alloy forming the middle plate includes: Zn 8.5-10.5%, Mg 2.0-3.0%, Cu 1.0-2.2%, Ti 0-0.06, Zr0.06-0.5%, Re 0-0.2%, Fe≤0.05%, Si≤0.05%, inevitable impurities, the content of any one impurity is ≤0.05%, the total amount of the impurities is ≤0.15%, and the balance is Al.

4. The middle frame according to any one of claims 1 to 3, characterized in that: The frame also includes a substrate, and the appearance layer is arranged on the outer surface of the substrate.

5. The middle frame according to claim 4, characterized in that: The base and the middle plate are made of the same material and are an integrally processed structure.

6. The middle frame according to claim 4 or 5, characterized in that: The substrate and the appearance layer are an integrally connected structure.

7. The middle frame according to any one of claims 1 to 6, characterized in that: The yield strength of the middle plate is ≥600MPa, and the elongation is ≥5%.

8. The middle frame according to any one of claims 1 to 7, characterized in that: The thickness of the frame is 0.1-2.0 mm.

9. The middle frame according to claim 8, characterized in that: The difference between the maximum thickness value of the appearance layer and the minimum thickness value of the appearance layer is less than or equal to 0.1 mm.

10. A method for preparing a middle frame, characterized in that: include: Placing an extruded billet in an extruder for reverse extrusion to obtain an aluminum alloy composite profile, wherein the extruded billet comprises an outer layer alloy and an inner layer alloy, the inner layer alloy is a 7 series aluminum alloy, and the outer layer alloy is a 5 series aluminum alloy or an anodizable 7 series aluminum alloy having a yield strength less than the yield strength of the middle plate; The aluminum alloy composite profile is subjected to solution treatment and aging heat treatment and then machined to obtain the middle frame; the middle frame includes a middle plate and a frame arranged along the peripheral side of the middle plate, the inner layer alloy forms the middle plate, and the outer layer alloy forms the appearance layer of the frame.

11. The preparation method according to claim 10, characterized in that: During the reverse extrusion process, the temperature of the extruded billet is 340-380° C., the extrusion temperature is 360-400° C., the extrusion speed is 0.5-3 mm / min, and the extrusion ratio is 10-20.

12. The preparation method according to claim 10 or 11, characterized in that: The extruded billet includes a cylinder formed by an outer layer alloy and a core column formed by an inner layer alloy, the cylinder includes a cylinder wall and a cylinder bottom at one end, the cylinder bottom is fixedly connected to the cylinder wall, the core column is inserted into the cylinder and is interference fit with the cylinder wall of the cylinder, and the cylinder bottom is arranged close to one side of the extrusion shaft of the extruder.

13. An electronic device, characterized in that: It comprises the middle frame as described in any one of claims 1 to 9 or the middle frame obtained by the preparation method as described in any one of claims 10 to 12.

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