Middle frame, preparation method of middle frame and electronic equipment

Abstract

The invention relates to the technical field of electronic equipment, discloses a middle frame, a preparation method of the middle frame and electronic equipment, and aims to improve the structural strength and appearance quality of the middle frame on the premise of realizing lightweight design of the middle frame. The middle frame comprises a base body, an oxide layer, a base layer, a composite layer and a color layer, the oxide layer, the base layer, the composite layer and the color layer are sequentially stacked on the base body, and the base body is made of at least one of metal-based composite materials or alloy materials; the base layer is made of a reflective base material, the color layer is made of an appearance material, the composite layer is made of a mixed material, and the mixed material comprises all elements in the base material and all elements in the appearance material.

Description

Technical Field

[0001] This application relates to the field of electronic devices, and more particularly to a mid-frame, a method for manufacturing the mid-frame, and an electronic device. Background Technology

[0002] The mid-frame of an electronic device provides support for its components and structural framework. In some cases, it also serves as part of the device's housing, enhancing its mechanical strength and aesthetics. With the continuous development of electronic devices and the increasing demands of users, the industry has placed higher requirements on the structural strength and surface properties of mid-frames. Common mid-frame materials often have inherent problems, such as low strength, high density, or relatively poor appearance. Therefore, achieving a mid-frame that possesses both high structural strength and good aesthetics while maintaining a relatively lightweight design is a pressing technical challenge. Summary of the Invention

[0003] This application provides a mid-frame, a method for manufacturing the mid-frame, and an electronic device, so as to improve the structural strength and appearance quality of the mid-frame while achieving a lightweight design.

[0004] Firstly, this application provides a mid-frame comprising a substrate, an oxide layer, a base layer, a composite layer, and a color layer, wherein the oxide layer, base layer, composite layer, and color layer are sequentially stacked on the substrate. The substrate is made of at least one of metal-based composite materials or alloy materials, which have low density and relatively low cost. The oxide layer can be used to increase the hardness of the mid-frame, giving it high structural strength. The base layer is made of a reflective base material, which can create a high reflectivity effect on the surface of the mid-frame. The color layer is made of an appearance material, which can give the mid-frame a specific decorative color. The composite layer is made of a mixed material, which includes all elements of the base material and all elements of the appearance material. The composite layer can improve the bonding force between the base layer and the color layer, reduce the risk of the mid-frame peeling off due to impacts, and also alleviate the stress on the mid-frame during the color layer formation process, thereby reducing the impact on the structural strength of the mid-frame. Therefore, the mid-frame provided by this application not only achieves lightweight and low-cost design but also obtains high structural strength and aesthetic quality.

[0005] In some implementations, the hardness of the oxide layer is greater than or equal to 500 HV. The hardness of metal matrix composites or alloys is often less than 300 HV, but the surface hardness of the middle frame can be significantly improved by forming an oxide layer on its surface.

[0006] In some implementations, the surface roughness of the oxide layer is less than or equal to 0.8 μm. By controlling the surface roughness of the oxide layer to within 0.8 μm, the fabrication difficulty of subsequent base layers, composite layers, and color layers can be reduced, and the surface smoothness of the midframe can be improved.

[0007] In some implementations, the porosity of the oxide layer is less than or equal to 3%. Lower porosity can increase the density of the oxide layer, enabling it to achieve relatively high hardness.

[0008] In some implementations, the oxide layer can be a micro-arc oxide layer, an anodic oxide layer, or a hard anodic layer. The hardness of the micro-arc oxide layer can reach 800 HV or higher, while the hardness of the anodic oxide layer or the hard anodic layer can reach 500 HV or higher.

[0009] In some implementations, the base layer is a non-insulating layer, and the base material may include at least one of titanium, chromium, zirconium, copper, and gold. For example, the base material may be any one of titanium, chromium, zirconium, copper, and gold, or a mixture of at least two of titanium, chromium, zirconium, copper, and gold. Titanium, chromium, zirconium, copper, and gold all have a certain degree of reflectivity, thus enabling the formed base layer to have a reflective effect.

[0010] In some implementations, the color layer is an insulating layer, and the appearance material includes at least one of diamond-like carbon, tetrahedral amorphous carbon, chromium nitride, titanium nitride, titanium oxynitride, and tungsten carbide. These appearance materials can both give the color layer a specific color and ensure that the color layer has relatively high hardness.

[0011] For example, when the outer material is titanium nitride, the atomic percentage of nitrogen atoms to titanium atoms in titanium nitride is close to 1:1, and in the composite layer, the mass proportion of titanium nitride in the mixed material can be greater than 70% to ensure the insulation of the outermost color layer.

[0012] For example, when the outer material is chromium nitride, the atomic percentage of nitrogen atoms to chromium atoms in chromium nitride is close to 1:1, and in the composite layer, the mass ratio of chromium nitride in the mixed material can be greater than 60% to ensure the insulation of the outermost color layer.

[0013] In some implementations, the appearance material is diamond-like carbon, with an sp3 bond content greater than 30%, so that the hardness of the formed color layer is greater than or equal to 1800 HV.

[0014] In some implementations, the appearance material is tetrahedral amorphous carbon, with an sp3 bond content greater than 60%, so that the hardness of the formed color layer is greater than or equal to 3000 HV.

[0015] In some implementations, the color layer is a non-insulating layer, and the appearance material includes at least one of diamond-like carbon, copper, gold, copper or gold nitrocarbons, copper or gold oxynitrides, copper or gold carbides, and copper or gold nitrides. These appearance materials can both give the color layer a specific color and ensure that the color layer has relatively high hardness.

[0016] In some embodiments, when the color layer is not an insulating layer, the middle frame may further include a first transparent insulating layer disposed on the side of the color layer facing away from the composite layer. The first transparent insulating layer includes stacked multilayer oxide films. The first transparent insulating layer can improve the corrosion resistance of the middle frame on the one hand, and reduce the reflection and scattering of light on the surface of the middle frame on the other hand, thereby increasing the transparency of the surface of the middle frame and making the middle frame present a more vivid and bright color effect.

[0017] For example, the oxide film can have 2 to 20 layers, and each oxide film layer can be any one of silicon oxide, titanium oxide, tantalum oxide, silicon carbide, etc.

[0018] In some implementations, the base layer is an insulating layer. In this case, the base material used to form the base layer can be silicon, which has a certain degree of reflectivity, thus enabling the formed base layer to have a reflective effect.

[0019] In some implementations, the color layer is an insulating layer, and the appearance material includes at least one of a mixture of silicon nitride and silicon oxynitride, silicon nitride, and tungsten carbide. These appearance materials can both give the color layer a specific color and ensure that the color layer has relatively high hardness.

[0020] In some implementations, along the stacking direction of the base layer, the composite layer, and the color layer, the mass ratio of the elements of the appearance material in the composite layer to the elements of the base material gradually increases. This design allows the base layer to transition more reliably to the color layer via the composite layer, further alleviating the stress on the frame during the formation of subsequent color layers.

[0021] In some implementations, the matrix can be one or two of aluminum-based composites, magnesium-based composites, magnesium alloys, aluminum alloys, or composites of magnesium and aluminum alloys. Aluminum-based and magnesium-based composites have relatively high elastic modulus and yield strength, which can effectively improve the mechanical properties of the mid-frame. Furthermore, their low density is beneficial for lightweight design of electronic devices. Aluminum alloys, magnesium alloys, or composites of magnesium and aluminum alloys also have the advantage of low density; therefore, mid-frames using these as matrix materials are relatively lightweight, which is also beneficial for lightweight design of electronic devices.

[0022] In some implementations, the substrate is a composite of magnesium alloy and aluminum alloy. The substrate includes a first component and a second component. The first component is made of magnesium alloy and the second component is made of aluminum alloy. The first component and the second component are connected by friction stir welding. The residual stress caused by friction stir welding is relatively low, so the first component and the second component are not easily deformed. The substrate formed in this way can also maintain the shape of the middle frame well, which is beneficial to improving the yield of the middle frame.

[0023] In some implementations, the mid-frame is used in electronic devices. The mid-frame includes a mid-plate and a frame, with the frame surrounding the periphery of the mid-frame. One side of the mid-plate includes a protrusion, and the protruding surface of the protrusion and the outer surface of the frame can serve as the exterior surface of the electronic device. The base of the mid-plate is a first component, and the base of the frame is a second component. Based on the materials of the first and second components, both have relatively good machinability, thus providing feasibility for achieving the aforementioned appearance design of the mid-frame.

[0024] In some embodiments, the substrate is made of aluminum-based composite material or aluminum alloy, and the base material includes aluminum and alumina. In the portion of the base layer near the oxide layer, the base layer material can be a mixture of aluminum and alumina; in the portion of the base layer away from the oxide layer, the base layer material is alumina.

[0025] In some implementations, the mid-frame also includes a second transparent insulating layer disposed on the side surface of the color layer facing away from the composite layer. The second transparent insulating layer can improve the mid-frame's resistance to corrosion from acids, alkalis, and sweat, thereby further enhancing the mid-frame's corrosion resistance.

[0026] In some implementations, the mid-frame also includes an anti-fingerprint layer disposed on the side of the second transparent insulating layer opposite to the color layer. The anti-fingerprint layer can give the surface of the mid-frame good hydrophobicity and oleophobicity, giving the mid-frame waterproof, oil-proof, stain-proof, and fingerprint-proof functions, and improving the ease of cleaning the mid-frame.

[0027] Secondly, this application also provides a mid-frame, comprising a substrate, a base layer, a composite layer, and a color layer, wherein the base layer, composite layer, and color layer are sequentially stacked on the substrate. The substrate is made of at least one of metal-based composite materials or alloy materials, which have low density and relatively low cost. The base layer is made of a reflective base material, enabling the mid-frame surface to achieve a high reflectivity effect. The color layer is made of an appearance material, allowing the mid-frame to display a specific decorative color. The composite layer is made of a mixed material, comprising all elements of the base material and all elements of the appearance material. The composite layer can improve the bonding strength between the base layer and the color layer, reducing the risk of the mid-frame peeling off due to impacts. Furthermore, the composite layer can alleviate the stress on the mid-frame during the color layer formation process, thereby reducing the impact on the structural strength of the mid-frame. Therefore, the mid-frame provided by this application not only achieves lightweight and low-cost design but also obtains high aesthetic quality.

[0028] In some implementations, the base layer is a non-insulating layer, and the base material may include at least one of titanium, chromium, zirconium, copper, and gold. For example, the base material may be any one of titanium, chromium, zirconium, copper, and gold, or a mixture of at least two of titanium, chromium, zirconium, copper, and gold. Titanium, chromium, zirconium, copper, and gold all have a certain degree of reflectivity, thus enabling the formed base layer to have a reflective effect.

[0029] In some implementations, the color layer is an insulating layer, and the appearance material includes at least one of diamond-like carbon, tetrahedral amorphous carbon, chromium nitride, titanium nitride, titanium oxynitride, and tungsten carbide. These appearance materials can both give the color layer a specific color and ensure that the color layer has relatively high hardness.

[0030] In some implementations, the color layer is a non-insulating layer, and the appearance material includes at least one of diamond-like carbon, copper, gold, copper or gold nitrocarbons, copper or gold oxynitrides, copper or gold carbides, and copper or gold nitrides. These appearance materials can both give the color layer a specific color and ensure that the color layer has relatively high hardness.

[0031] In some embodiments, when the color layer is not an insulating layer, the middle frame may further include a first transparent insulating layer disposed on the side of the color layer facing away from the composite layer. The first transparent insulating layer includes stacked multilayer oxide films. The first transparent insulating layer can improve the corrosion resistance of the middle frame on the one hand, and reduce the reflection and scattering of light on the surface of the middle frame on the other hand, thereby increasing the transparency of the surface of the middle frame and making the middle frame present a more vivid and bright color effect.

[0032] In some implementations, the base layer is an insulating layer. In this case, the base material used to form the base layer can be silicon, which has a certain degree of reflectivity, thus enabling the formed base layer to have a reflective effect.

[0033] In some implementations, the color layer is an insulating layer, and the appearance material includes at least one of a mixture of silicon nitride and silicon oxynitride, silicon nitride, and tungsten carbide. These appearance materials can both give the color layer a specific color and ensure that the color layer has relatively high hardness.

[0034] In some implementations, along the stacking direction of the base layer, the composite layer, and the color layer, the mass ratio of the elements of the appearance material in the composite layer to the elements of the base material gradually increases. This design allows the base layer to transition more reliably to the color layer via the composite layer, further alleviating the stress on the frame during the formation of subsequent color layers.

[0035] In some implementations, the substrate is a composite of magnesium alloy and aluminum alloy. The substrate includes a first component and a second component. The first component is made of magnesium alloy and the second component is made of aluminum alloy. The first component and the second component are connected by friction stir welding. The residual stress caused by friction stir welding is relatively low, so the first component and the second component are not easily deformed. The substrate formed in this way can also maintain the shape of the middle frame well, which is beneficial to improving the yield of the middle frame.

[0036] In some implementations, the mid-frame is used in electronic devices. The mid-frame includes a mid-plate and a frame, with the frame surrounding the periphery of the mid-frame. One side of the mid-plate includes a protrusion, and the protruding surface of the protrusion and the outer surface of the frame can serve as the exterior surface of the electronic device. The base of the mid-plate is a first component, and the base of the frame is a second component. Based on the materials of the first and second components, both have relatively good machinability, thus providing feasibility for achieving the aforementioned appearance design of the mid-frame.

[0037] Thirdly, this application also provides a method for preparing a middle frame, the method comprising:

[0038] An oxide layer is formed on the surface of the substrate, and the substrate material includes at least one of metal composite materials or alloy materials;

[0039] A base layer is formed on the surface of the oxide layer, and the base layer is made of a reflective base material.

[0040] A composite layer is formed on the surface of the base layer. The composite layer is made of a mixed material, which includes all elements of the base material and all elements of the appearance material.

[0041] A color layer is formed on the surface of the composite layer, and the material of the color layer is the aforementioned appearance material.

[0042] The mid-frame prepared using the above method has a relatively low substrate density and is relatively inexpensive. In the sequentially formed layers on the substrate, the oxide layer increases the frame's rigidity, the base layer creates a high-reflectivity surface, the composite layer enhances the adhesion between the base layer and the color layer and alleviates stress on the frame during subsequent color layer formation, and the color layer imparts a specific decorative color. Therefore, this mid-frame not only achieves lightweight and low-cost design but also achieves high structural strength and aesthetic quality.

[0043] In some embodiments, an oxide layer is formed on the surface of the substrate, including:

[0044] The substrate is immersed in a micro-arc oxidation solution, and an oxide layer is formed through the micro-arc oxidation process. The oxide layer obtained by the micro-arc oxidation process can significantly improve the surface hardness of the mid-frame.

[0045] In some embodiments, at least one of titanium dioxide nanoparticles, zirconium dioxide nanoparticles, yttrium oxide nanoparticles, and cerium oxide nanoparticles is added to the micro-arc oxidation solution. These additives can reduce the porosity of the oxide layer near the substrate and improve the salt spray resistance of the oxide layer.

[0046] In some implementations, after forming the oxide layer via micro-arc oxidation, the preparation method further includes:

[0047] The oxide layer is polished to a depth greater than or equal to 5 micrometers, resulting in a surface roughness of less than or equal to 0.8 μm. This lower surface roughness facilitates the fabrication of subsequent layers and improves the surface quality of the mid-frame.

[0048] In some embodiments, a composite layer is formed on the surface of the oxide layer, including:

[0049] A composite layer is obtained by simultaneously depositing base material and appearance material on the surface of the base layer using vapor deposition, resulting in a composite layer containing all elements of both the base material and the appearance material. The vapor deposition can be either physical vapor deposition or chemical vapor deposition.

[0050] In some embodiments, when the color layer is a non-insulating layer, after forming the color layer on the surface of the composite layer, the preparation method further includes:

[0051] Multiple oxide films are sequentially fabricated on the surface of the color layer to form the first transparent insulating layer. This first transparent insulating layer improves the corrosion resistance of the mid-frame, reduces light reflection and scattering on the mid-frame surface, increases the transparency of the mid-frame surface, and allows the mid-frame to exhibit a more vibrant and bright color effect.

[0052] Fourthly, this application also provides an electronic device including a display screen and a mid-frame as described in either the first or second aspect, with the display screen disposed on one side of the mid-frame. The mid-frame can serve as part of the housing of the electronic device to ensure its mechanical strength and appearance quality. Attached Figure Description

[0053] Figure 1 An exploded view of an electronic device provided in an embodiment of this application;

[0054] Figure 2 This is a schematic diagram of the structure of a middle frame provided in an embodiment of this application;

[0055] Figure 3 This is a schematic diagram of another mid-frame structure provided in an embodiment of this application;

[0056] Figure 4 This is a schematic diagram of a cross-sectional structure of a middle frame provided in an embodiment of this application;

[0057] Figure 5 for Figure 4 The fabrication process flow diagram of the middle frame is shown below;

[0058] Figure 6 Another fabrication flowchart of the middle frame provided in this application embodiment;

[0059] Figure 7 Another fabrication flowchart of the middle frame provided in this application embodiment;

[0060] Figure 8 Another fabrication flowchart of the middle frame provided in this application embodiment;

[0061] Figure 9 Another fabrication flowchart of the middle frame provided in this application embodiment;

[0062] Figure 10 Another fabrication flowchart of the middle frame provided in this application embodiment;

[0063] Figure 11 Another fabrication flowchart of the middle frame provided in this application embodiment;

[0064] Figure 12 Another fabrication flowchart of the middle frame provided in this application embodiment;

[0065] Figure 13 This is a schematic diagram of the cross-sectional structure of a middle frame provided in an embodiment of this application.

[0067] 1-Electronic device; 100-Display screen; 200-Back cover; 300-Middle frame; 310-Middle plate; 311-Protrusion; 320-Border;

[0068] 321 - Outer surface of the frame; 301 - Substrate; 302 - Oxidation layer; 303 - Base layer; 304 - Composite layer; 305 - Color layer;

[0069] 400 - Circuit board; 500 - Battery. Detailed Implementation

[0070] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in further detail below with reference to the accompanying drawings. However, the exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein. The same reference numerals in the figures denote the same or similar structures, and therefore repeated descriptions of them will be omitted. The terms expressing position and direction described in the embodiments of this application are illustrative based on the accompanying drawings, but changes can be made as needed, and all such changes are included within the scope of protection of this application. The accompanying drawings of the embodiments of this application are only for illustrating relative positional relationships and do not represent actual scale.

[0071] It should be noted that specific details are set forth in the following description to facilitate understanding of this application. However, the embodiments of this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the embodiments of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0072] The mid-frame provided in this application embodiment can be applied to various electronic devices such as mobile phones, foldable phones, tablets, and laptops, providing support for related electronic components and structural parts within the electronic device. Furthermore, the mid-frame can also serve as part of the electronic device's casing, ensuring its mechanical strength and aesthetic appearance. Additionally, in some embodiments, the mid-frame can provide heat dissipation channels for the electronic components, enabling the electronic device to have good heat dissipation capabilities.

[0073] refer to Figure 1 , Figure 1 This document illustrates an exploded view of an electronic device 1 according to an embodiment of this application, using a mobile phone as an example. The electronic device 1 includes a display screen 100, a back cover 200, and a mid-frame 300. The display screen 100 is disposed on one side of the mid-frame 300, and the back cover 200 is disposed on the other side of the mid-frame 300. The display screen 100, mid-frame 300, and back cover 200 together enclose the interior of the electronic device 1. The interior of the electronic device 1 can accommodate components such as a circuit board 400, a battery 500, a camera module, a receiver, and a microphone. It should be noted that... Figure 1 The image only shows some components of an electronic device as examples; the actual shape, size, location, and construction of these components are not subject to change. Figure 1 The limitation.

[0074] Figure 2 This is a schematic diagram of the structure of a middle frame 300 provided in an embodiment of this application. (Reference) Figure 2 As shown, this application embodiment uses a mid-frame 300 applied in a mobile phone as an example for description. The mid-frame 300 may include a mid-plate 310 and a frame 320. The mid-plate 310 can provide fixed support for components such as the mobile phone's circuit board and battery. The frame 320 surrounds the periphery of the mid-plate 310, and the outer side 321 of the frame 320 can serve as the appearance surface of the mobile phone. In addition, the shape of the mid-frame 300 can be designed according to the shape of the mobile phone. For example, in one example, the mobile phone has a flat rectangular structure, and the four corners of the mobile phone are rounded. Based on this, the frame 320 can be designed as a rectangular frame structure with rounded corners, and the outer contour of the mid-plate 310 can be designed as a rectangular plate structure with rounded corners.

[0075] Figure 3 This is a schematic diagram of another structure of the middle frame 300 provided in an embodiment of this application. (See reference...) Figure 3 As shown, this application embodiment also uses a mid-frame 300 applied in a mobile phone as an example for description. The mid-frame 300 may also include a mid-plate 310 and a frame 320, with the frame 320 surrounding the periphery of the mid-plate 310, and... Figure 2 Unlike the embodiment shown, in this embodiment, a portion of one side surface of the middle plate 310 has a protrusion 311, and the surface of the protrusion 311 and the outer side of the frame 320 both serve as the appearance surface of the mobile phone.

[0076] Depend on Figure 2 and Figure 3As can be seen, the design of the mid-frame 300 not only affects the structural reliability of electronic devices but also plays a crucial role in their appearance. With the continuous development of electronic devices and the increasing demands of users, the industry has placed higher requirements on the structural strength and surface performance of the mid-frame 300. Common materials for mid-frame 300 manufacturing include metal alloys and stainless steel. Taking aluminum alloy as an example, aluminum alloys have good plasticity and toughness, and advantages such as easy processing, engineering reliability, and low price. However, their disadvantage is lower strength, which cannot adequately guarantee the structural reliability of electronic devices. Furthermore, the appearance of aluminum alloys after anodizing is not easily recognizable, which is detrimental to improving the aesthetic quality of electronic devices. Compared to aluminum alloys, stainless steel has higher strength, and mid-frame 300 made from it can also achieve good structural performance. However, mid-frame 300 made from stainless steel is heavier, more difficult to process, and has higher material costs. In addition, stainless steel cannot achieve good surface performance through anodizing, which is not conducive to its widespread application.

[0077] Another type of material that can be used to manufacture the 300mm mid-frame is metal matrix composite (MMC). MMC is generally a composite material made by artificially combining a metal or alloy as the matrix with one or more metal or non-metal reinforcements. The reinforcements are mostly inorganic non-metals, such as ceramics, carbon, graphite, and boron, but can also be metals. The reinforcements can be fibrous, whisker-like, or granular. Varieties include self-reinforcing composites and laminated metal matrix composites, where the reinforcement reacts within the metal matrix. MMC retains the properties of the metal itself while also possessing the comprehensive properties of composite materials. Through optimized combinations of different matrix materials and reinforcements, various high-performance composite materials with various special properties and excellent overall performance can be obtained. MMC can be classified according to matrix type, including aluminum-based, magnesium-based, zinc-based, copper-based, and intermetallic compound-based composites.

[0078] Taking aluminum-based composite materials as an example, these materials use aluminum or aluminum alloys as the base material, with reinforcement typically consisting of ceramic materials (such as silicon carbide (SiC), alumina (Al2O3), boron carbide (B4C), titanium diboride (TiB2), etc.) or fiber materials. Aluminum-based composite materials not only possess the good plasticity and toughness inherent in aluminum or aluminum alloys, but also have advantages such as high mechanical strength and high elastic modulus. However, a drawback is that existing surface treatment methods, such as anodizing, magnesium alloy spraying, or micro-arc oxidation, cannot support the high-gloss finish of aluminum-based composite materials. Therefore, the appearance quality of the 300 mid-frame made from them needs further improvement.

[0079] In view of this, embodiments of this application provide a mid-frame 300 that combines high structural strength and good appearance quality, while also being lightweight and relatively low in cost. The mid-frame 300 provided in the embodiments of this application will now be described in further detail with reference to the accompanying drawings.

[0080] Figure 4 This is a schematic cross-sectional view of a middle frame 300 provided in an embodiment of this application. (Reference) Figure 4 As shown in this embodiment, the middle frame 300 includes a substrate 301 and an oxide layer 302, a base layer 303, a composite layer 304, and a color layer 305 sequentially stacked on the substrate 301. The substrate 301 can be fabricated into the shape of the middle frame, for example... Figure 2 or Figure 3 The shape of the mobile phone frame shown is similar to that of other electronic devices, including foldable phones, laptops, or tablets. The substrate 301 is made of at least one of a metal matrix composite material or an alloy material. For example, the substrate 301 may include one metal matrix composite material or one alloy material, or two or more metal matrix composite materials, or two or more alloy materials. The oxide layer 302 can be used to increase the hardness of the frame 300, giving it high structural strength. The base layer 303 is made of a reflective base material, which can create a high reflectivity effect on the surface of the frame 300. The color layer 305 can give the frame 300 a specific decorative color; the combination of the two helps to achieve a high aesthetic quality for the frame 300. The composite layer 304 between the base layer 303 and the color layer 305 is made of a mixed material, which includes all elements of the base material and all elements of the appearance material. The composite layer 304 can improve the bonding force between the base layer 303 and the color layer 305, reduce the risk of the middle frame 300 peeling off due to impact, and the composite layer 304 can also alleviate the stress on the middle frame 300 during the formation of the color layer 305, thereby reducing the impact on the structural strength of the middle frame 300.

[0081] Among them, the reflective base material can be understood as having a relatively good effect on reflecting light. For example, in this embodiment, the visible light reflectivity of the base material can be greater than or equal to 20%.

[0082] In some embodiments, the matrix 301 can be one or two of aluminum-based composite materials, magnesium-based composite materials, magnesium alloys, aluminum alloys, or composite materials of magnesium alloys and aluminum alloys. The aluminum-based composite material can be composed of 7-series aluminum alloys doped with silicon carbide, or 2-series aluminum alloys doped with silicon carbide. The magnesium-based composite material can be composed of magnesium alloys doped with silicon carbide. Aluminum-based and magnesium-based composite materials have relatively high elastic modulus and yield strength, which can effectively improve the mechanical properties of the mid-frame. Furthermore, aluminum-based and magnesium-based composite materials also have relatively strong thermal conductivity, which is beneficial for improving the overall heat dissipation performance. In addition, compared to stainless steel or titanium alloys, aluminum-based and magnesium-based composite materials have lower density, which is beneficial for lightweight design of electronic devices. Aluminum alloys, magnesium alloys, or composite materials of magnesium alloys and aluminum alloys also have the advantage of low density; therefore, the mid-frame 300 using these as matrix materials is relatively lightweight, which is beneficial for lightweight design of electronic devices.

[0083] In addition, when the substrate 301 is made of aluminum-based composite material or magnesium alloy, by sequentially forming an oxide layer 302, a base layer 303, a composite layer 304 and a color layer 305 on the surface of the substrate, the bonding force between the substrate 301 and each layer structure is ensured, and the problem that the existing technology cannot produce a high-gloss surface effect on the surface of aluminum-based composite material and magnesium alloy is also solved, thereby effectively improving the appearance quality of the mid-frame.

[0084] In some embodiments, the oxide layer 302 can be a micro-arc oxidation layer, a hard anodizing layer, or an anodizing layer. In other words, the oxide layer 302 can be formed by a micro-arc oxidation process, a hard anodizing process, or an anodizing process. Typically, the surface hardness of metal matrix composites and metal alloys is no greater than 300 HV (Vickers hardness), while the hardness of the oxide layer 302 formed after oxidation can reach more than 500 HV, thereby significantly improving the surface hardness of the middle frame 300.

[0085] In some embodiments, the thickness of the oxide layer 302 is greater than or equal to 5 μm and less than or equal to 30 μm. Exemplarily, the thickness of the oxide layer 302 can be 5 μm, 8 μm, 15 μm, 23 μm, 30 μm, etc. Due to the formation method of the oxide layer 302, its surface roughness is generally relatively large, which is not conducive to the formation of subsequent layers. Furthermore, during the formation of oxide layer 302, the porosity of the portion of oxide layer 302 near the surface of substrate 301 is relatively low (e.g., less than or equal to 2%), while the porosity of the other portion of oxide layer 302 away from the surface of substrate 301 is relatively high (e.g., greater than 2%). This results in the hardness of the portion of oxide layer 302 near the surface of substrate 301 being greater than the hardness of the other portion. Therefore, after the formation of oxide layer 302, the other portion of oxide layer 302 away from the surface of substrate 301 can be removed by polishing, reducing the thickness of oxide layer 302 to approximately 5µm-30µm, thereby obtaining a dense oxide layer 302 with higher hardness. The final formed oxide layer 302 has a porosity of less than or equal to 2% and a surface roughness of less than or equal to 0.8µm. Porosity can be understood as the proportion of a certain area (e.g., square centimeters or square millimeters) occupied by surface pores. For example, the porosity of the oxide layer 302 can be 2%, 1.8%, 1.2%, 1%, etc.; the surface roughness of the oxide layer can be 0.8um, 0.7um, 0.5um, 0.2um, etc.

[0086] As will be known to those skilled in the art, oxide layer 302 is generally an insulating layer. The insulation properties of the three layers above oxide layer 302—base layer 303, composite layer 304, and color layer 305—can be designed according to actual needs, and this application does not impose any restrictions on this. For example, the three layers may each be non-insulating layers, or each layer may be insulating layers, or a combination of insulating and non-insulating layers may be present in the three layers.

[0087] In one embodiment, the base layer 303 is a non-insulating layer, the color layer 305 is an insulating layer, and the composite layer 304 can be either a non-insulating layer or an insulating layer. In this case, the base material used for the base layer 303 can be a metal with high reflectivity. Exemplarily, the base material can include at least one of titanium (Ti), chromium (Cr), zirconium (Zr), copper (Cu), and gold (Au). Exemplarily, the base material can be any one of titanium, chromium, zirconium, copper, and gold, or a mixture of at least two of titanium, chromium, zirconium, copper, and gold. The appearance material used for the color layer 305 can include at least one of diamond-like carbon (DLC), tetrahedral amorphous carbon (TaC), chromium nitride (CrN), titanium nitride (TiN), titanium oxynitride (TiON), and tungsten carbide (WC). The composite layer 304 is a mixture of all elements in the base material and all elements in the appearance material, and the insulation of the composite layer 304 is determined by the mass ratio of the elements in its mixture.

[0088] It should be noted that when the outer material is diamond-like carbon (DLC), the DLC has relatively more sp2 bonds or relatively fewer doped metal elements to ensure the insulation of the outermost color layer 305. When the outer material is titanium nitride, the atomic percentage of nitrogen atoms to titanium atoms in titanium nitride is close to 1:1, and in the composite layer, the mass proportion of titanium nitride in the mixed material can be greater than 70% to ensure the insulation of the outermost color layer 305. When the outer material is chromium nitride, the atomic percentage of nitrogen atoms to chromium atoms in chromium nitride is close to 1:1, and in the composite layer, the mass proportion of chromium nitride in the mixed material can be greater than 60% to ensure the insulation of the outermost color layer 305.

[0089] In the example where the base layer 303 and composite layer 304 are non-insulating layers, when the substrate 301 is made of aluminum-based composite material or aluminum alloy, the base layer 303 can be made of aluminum (Al) and aluminum oxide (Al2O3). In the portion of the base layer 303 near the oxide layer 302, the base layer 303 can be a mixture of aluminum and aluminum oxide; in the portion of the base layer 303 away from the oxide layer 302, the base layer 303 is made of aluminum oxide. Depending on the thickness of the base layer 303, it can exhibit colors such as yellow, green, and blue.

[0090] In some embodiments, the base layer 303, composite layer 304, and color layer 305 can all be insulating layers. In this case, the base material used for the base layer 303 can be silicon (Si). The appearance material used for the color layer 305 can be silicon nitride (Si3N4) and silicon oxynitride (SiO2). x Oy N z The composite layer 304 is a mixture of at least one of the following: tungsten carbide (WC), diamond-like carbon, and tetrahedral amorphous carbon. The composite layer 304 is a mixture of all elements in the base material and all elements in the appearance material.

[0091] It should be noted that when the outer material is a mixture of silicon nitride and silicon oxynitride, since silicon is a semiconductor, it is not conductive. Therefore, silicon nitride and silicon oxynitride are also not conductive, thus ensuring the insulation of the outermost color layer 305.

[0092] In some embodiments, the base layer 303, composite layer 304, and color layer 305 can all be non-insulating layers. In this case, the base material used for the base layer 303 may include at least one of titanium, chromium, zirconium, copper, and gold. The appearance material used for the color layer 305 may include at least one of diamond-like carbon, copper, gold, copper or gold nitrides, copper or gold oxynitrides, copper or gold carbides, and copper or gold nitrides. The composite layer 304 is a mixture of all elements in the base material and all elements in the appearance material.

[0093] It should be noted that when the outer material is diamond-like carbon, the relatively few sp2 bonds in diamond-like carbon or the relatively large amount of doped metal elements can make the resulting color layer 305 a non-insulating layer.

[0094] In addition, when the color layer 305 is a non-insulating layer, the middle frame 300 may also include a first transparent insulating layer. The first transparent insulating layer is disposed on the side of the color layer 305 facing away from the composite layer. The first transparent insulating layer may include multiple layers of oxide films stacked together; it is easy to understand that each oxide film is also a transparent film. The first transparent insulating layer can improve the corrosion resistance of the middle frame 300 on the one hand, and reduce the reflection and scattering of light on the surface of the middle frame on the other hand, thereby increasing the transparency of the surface of the middle frame 300 and making the middle frame 300 present a more vivid and bright color effect.

[0095] In practice, the number of oxide film layers can range from 2 to 20. Each oxide film layer can be any one of silicon oxide (SiO2), titanium oxide (TiO2), tantalum oxide (Ta2O5), silicon carbide, etc., and the thickness of each oxide film layer is greater than or equal to 0.15 μm and less than or equal to 0.2 μm. By reasonably setting the number of oxide film layers, material, and thickness, the transparency of the transparent insulating layer can reach more than 97%.

[0096] In one implementation, the thickness of the base layer 303 can be greater than or equal to 0.2 μm and less than or equal to 1.2 μm. Exemplarily, the thickness of the base layer 303 can be 0.2 μm, 0.3 μm, 0.6 μm, 1 μm, 1.2 μm, etc. The base layer 303 can be formed using physical vapor deposition (PVD) or chemical vapor deposition (CVD) processes. In particular, when the material of the base layer 303 includes multiple metals or non-metals, the base layer 303 can be formed by simultaneously depositing multiple metals or non-metals.

[0097] In one implementation, the thickness of the composite layer 304 can be greater than or equal to 0.2 μm and less than or equal to 4 μm. Exemplarily, the thickness of the composite layer 304 can be 0.2 μm, 0.5 μm, 1.8 μm, 3.2 μm, 4 μm, etc. The composite layer 304 can also be formed by physical vapor deposition or chemical vapor deposition processes, for example, by simultaneously depositing a base material and an appearance material to form a composite layer 304 comprising all elements of both the base material and the appearance material.

[0098] Along the stacking direction of the base layer 303, composite layer 304, and color layer 305, the mass ratio of the elements of the appearance material to the elements of the base material in the composite layer 304 gradually increases. That is, the closer to the color layer 305, the larger the weight proportion of the appearance material elements and the smaller the weight proportion of the base material elements in the composite layer 304; conversely, the closer to the base layer 303, the smaller the weight proportion of the appearance material elements and the larger the weight proportion of the base material elements. Through this design, the base layer 303 can more reliably transition to the color layer 305 via the composite layer 304, further alleviating the stress on the middle frame 300 during the subsequent formation of the color layer 305.

[0099] In one implementation, the thickness of the color layer 305 can be greater than or equal to 0.2 μm and less than or equal to 5 μm. Exemplarily, the thickness of the color layer 305 can be 0.2 μm, 0.8 μm, 1.5 μm, 3.5 μm, 4 μm, 5 μm, etc. The color layer 305 can be formed by physical vapor deposition or chemical vapor deposition processes.

[0100] In one example, the base layer 303 is made of at least one of titanium, chromium, zirconium, copper, and gold, and the color layer 305 is a diamond-like carbon (DLC) layer. In this case, by controlling the deposition thickness of the DLC, the color layer 305 can exhibit different colors, such as black or gray. Furthermore, the sp3 bond content in the color layer 305 can be greater than 30%, and the hardness of the color layer 305 can be greater than or equal to 1800 HV.

[0101] In one example, the base layer 303 is made of at least one of titanium, chromium, zirconium, copper, and gold, and the color layer 305 is a tetrahedral amorphous carbon layer. By controlling the deposition thickness of the tetrahedral amorphous carbon, the color layer 305 can exhibit different colors, such as black, blue, and green. Furthermore, the sp3 bond content in the color layer 305 can be greater than 60%, and the hardness of the color layer 305 can be greater than or equal to 3000 HV.

[0102] In one example, the base layer 303 is made of at least one of titanium, chromium, zirconium, copper, and gold, and the color layer 305 is a chromium nitride layer. In this case, the surface of the middle frame 300 can present a silver-white effect.

[0103] In one example, the base layer 303 is made of at least one of titanium, chromium, zirconium, copper, and gold, and the color layer 305 is a titanium nitride layer. In this case, the surface of the middle frame 300 can present a yellow effect.

[0104] In one example, the base layer 303 is made of at least one of titanium, chromium, zirconium, copper, and gold, and the color layer 305 is a titanium oxynitride layer. In this case, by controlling the deposition thickness of the titanium oxynitride, the color layer 305 can be made to present different colors, such as green, blue, etc.

[0105] In one example, the base layer 303 is made of at least one of titanium, chromium, zirconium, copper, and gold, and the color layer 305 is a tungsten carbide layer. In this case, the surface of the middle frame 300 can present a black or gray color effect.

[0106] In one example, the base layer 303 is made of at least one of titanium, chromium, zirconium, copper, and gold, and the color layer 305 is made of at least one of copper, gold, copper nitrides, copper oxides, copper nitrides, gold nitrides, gold oxides, and gold nitrides. In this case, the surface of the middle frame 300 can present a golden yellow, rose gold, or other golden effects.

[0107] In one example, the base layer 303 is made of at least one of titanium, chromium, zirconium, copper, and gold, and the color layer 305 is made of at least one of copper carbide or gold carbide. In this case, by controlling the ratio of copper (or gold) to carbon in the carbide, the color layer 305 can present different colors, such as black, gray, tarnish, etc.

[0108] In one example, the base layer 303 is made of silicon, and the color layer 305 is a mixture of silicon nitride and silicon oxynitride. In this case, by controlling the proportion of nitrogen, oxygen and silicon in silicon oxynitride, the color layer 305 can present different colors, such as gray, silver-white, yellow and so on.

[0109] In one example, the base layer 303 is made of silicon and the color layer 305 is a tungsten carbide layer. In this case, the surface of the middle frame 300 can present a black or gray color effect.

[0110] It is worth mentioning that the color layer 305 is located relatively close to the surface of the middle frame 300, so it has high requirements for its color and hardness. The color layer 305 formed by the above materials can not only make the middle frame 300 present a specific color, but also help to further increase the hardness of the middle frame 300.

[0111] In this embodiment, there are no strict boundaries between the layers of the middle frame 300, and adjacent layers can merge at the contact point. Therefore, each layer can contain elements or compounds from the adjacent layers.

[0112] Furthermore, in some embodiments, the middle frame 300 may also include a second transparent insulating layer. When the color layer 305 is an insulating layer, the second transparent insulating layer may be disposed on the surface of the color layer 305 facing away from the composite layer 304; when the color layer 305 is not an insulating layer, the second transparent insulating layer may be disposed on the surface of the first transparent insulating layer facing away from the color layer 305. The second transparent insulating layer can improve the middle frame's resistance to corrosion from acids, alkalis, and sweat, thereby further enhancing the corrosion resistance of the middle frame 300.

[0113] In some embodiments, the middle frame 300 may further include an anti-fingerprint coating (AFC) disposed on the outermost surface of the middle frame 300. For example, the anti-fingerprint coating may be disposed on the surface of the second transparent insulating layer opposite to the color layer 305. The anti-fingerprint coating can give the surface of the middle frame 300 good hydrophobicity and oleophobicity, enabling the middle frame 300 to have functions such as waterproofing, oil resistance, stain resistance, and fingerprint resistance, thereby improving the ease of cleaning of the middle frame 300. The main components of the anti-fingerprint coating may include organosilicon compounds, fluorine compounds, etc., and its thickness may be less than 30 nm.

[0114] refer to Figure 5 As shown, Figure 5 for Figure 4 The flowchart illustrates the fabrication process of a portion of the middle frame 300. In this embodiment, the fabrication method of the middle frame 300 includes the following steps:

[0115] An oxide layer 302 is formed on the surface of the substrate 301, wherein the material of the substrate 301 includes at least one of metal composite materials or alloy materials;

[0116] A base layer 303 is formed on the surface of the oxide layer 302, and the base layer 303 is made of a reflective base material;

[0117] A composite layer 304 is formed on the surface of the base layer 303. The composite layer 304 is made of a mixed material, which includes all elements of the base material and all elements of the appearance material.

[0118] A color layer 305 is formed on the surface of the composite layer 304, and the material of the color layer 305 is the aforementioned appearance material.

[0119] The mid-frame 300 prepared using the above method has a relatively low material density and low cost for its substrate 301. In the sequentially formed layers on the substrate 301, the oxide layer 302 enhances the hardness of the mid-frame, the base layer 303 creates a high-reflectivity surface on the mid-frame 300, the composite layer 304 improves the bonding between the base layer 303 and the color layer 305 and alleviates the stress on the mid-frame 300 during the subsequent formation of the color layer 305, and the color layer 305 gives the mid-frame 300 a specific decorative color. Therefore, this mid-frame 300 not only achieves lightweight and low-cost design but also obtains high structural strength and aesthetic quality.

[0120] In some embodiments, an oxide layer 302 is formed on the surface of the substrate 301, including:

[0121] The substrate 301 is immersed in a micro-arc oxidation solution, and an oxide layer 302 is formed through a micro-arc oxidation process. The resulting oxide layer 302 can significantly improve the surface hardness of the middle frame.

[0122] The micro-arc oxidation solution may contain one of the following: titanium dioxide (TiO2) nanoparticles, zirconium dioxide (ZrO2) nanoparticles, yttrium oxide (Y2O3) nanoparticles, cerium oxide (CeO2) nanoparticles, or alumina nanoparticles, added at an amount of 2.0 g / L to 8.0 g / L. This reduces the porosity of the oxide layer 302 near the substrate 301 and improves the salt spray resistance of the oxide layer 302. For example, by adding the above-mentioned substances to the micro-arc oxidation solution, the porosity of the oxide layer 302 near the substrate 301 can be reduced to below 1%.

[0123] In some embodiments, after forming the oxide layer 302 by a micro-arc oxidation process, the preparation method further includes:

[0124] The oxide layer 302 is polished to make the porosity of the polished oxide layer 302 less than or equal to 2%.

[0125] During the formation of oxide layer 302, the portion of oxide layer 302 near the substrate 301 has relatively low porosity, while the portion farther from the substrate 301 has relatively high porosity. This results in the portion of oxide layer 302 near the substrate 301 having a higher hardness than the portion farther from the substrate 301. Therefore, after the oxide layer 302 is formed, the portion farther from the substrate 301 can be removed by polishing, thereby obtaining a dense oxide layer 302 with higher hardness. For example, the removal depth of oxide layer 302 after polishing can be greater than or equal to 5 μm. In addition, the surface roughness of oxide layer 302 after polishing is less than or equal to 0.8 μm. The smaller surface roughness is beneficial to the fabrication of subsequent layers and can improve the surface quality of the middle frame 300.

[0126] In other embodiments, the removal depth of the oxide layer 302 after polishing can also be reduced according to the actual situation, so that the surface roughness of the oxide layer 302 is less than 1 μm.

[0127] In some embodiments, a base layer 303 is formed on the surface of the oxide layer 302, including:

[0128] A base layer 303 is formed on the surface of the oxide layer 302 by vapor deposition. In specific implementations, vapor deposition can be physical vapor deposition or chemical vapor deposition. Physical vapor deposition can include one or more of arc ion plating, high-power magnetron sputtering, and DC magnetron sputtering, while chemical vapor deposition can include thermochemical vapor deposition, plasma chemical vapor deposition, laser chemical vapor deposition, etc.

[0129] In some embodiments, a composite layer 304 is formed on the surface of the base layer 303, including:

[0130] A composite layer 304 is formed by simultaneously depositing a base material and an appearance material on the surface of the base layer 303 using vapor deposition. Similarly, the deposition method used to form the composite layer 304 can also be physical vapor deposition or chemical vapor deposition, which will not be repeated here. In one implementation, the deposition method of the composite layer 304 is the same as that of the base layer 303 to simplify the fabrication process of the middle frame 300.

[0131] In some embodiments, a color layer 305 is formed on the surface of the composite layer 304, including:

[0132] A color layer 305 is formed on the surface of the composite layer 304 using vapor deposition. Similarly, the deposition method used to form the color layer 305 can also be physical vapor deposition or chemical vapor deposition, which will not be repeated here. In one implementation, the three layers of color layer 305, composite layer 304, and base layer 303 can be formed using the same deposition method to further simplify the fabrication process of the middle frame 300.

[0133] In some embodiments, when the color layer 305 is an insulating layer, after the color layer is formed on the surface of the composite layer 304, the preparation method may further include:

[0134] An anti-fingerprint layer is formed on the surface of the color layer 305. The anti-fingerprint layer can be formed by physical coating or chemical coating.

[0135] In some embodiments, when the color layer 305 is a non-insulating layer, after forming the color layer on the surface of the composite layer, the preparation method may further include:

[0136] Multiple oxide films are sequentially fabricated on the surface of the color layer to form the first transparent insulating layer. Each oxide film can be formed by chemical vapor deposition or magnetron sputtering.

[0137] After understanding the structure and basic fabrication method of the mid-frame 300, several specific design schemes of the mid-frame 300 will be illustrated below. It is worth mentioning that the mid-frames in the following embodiments mainly differ in the substrate, oxide layer, base layer, composite layer, and color layer. The designs of the transparent insulating layer and anti-fingerprint layer are roughly the same, so the formation steps of the transparent insulating layer and anti-fingerprint layer will not be described in detail below.

[0138] Please refer to this again first. Figure 5 In this embodiment, the method for preparing the middle frame 300 specifically includes:

[0139] Step 1: Fabricate the aluminum-based composite material into the shape of the mid-frame 300, forming the matrix 301. This aluminum-based composite material can be composed of 7-series aluminum alloy doped with silicon carbide. Furthermore, the shape of the mid-frame 300 can be designed according to the electronic device to which the mid-frame is applied; for example, the electronic device can be a mobile phone, a foldable phone, a tablet computer, a laptop computer, etc.

[0140] Step 2: The substrate 301 is placed in a micro-arc oxidation solution to form an oxide layer 302 through a micro-arc oxidation process. The mass ratio of sodium hydroxide (NaOH) to sodium metasilicate (Na2SiO3) in the micro-arc oxidation solution is 1:9, and the pH is in the range of 8.5-13. The thickness of the generated oxide layer 302 is approximately 25µm-48µm. The main body of the micro-arc oxidation layer 302 is composed of α-Al2O3 and γ-Al2O3. Along the thickness direction of the oxide layer 302, the portion closer to the substrate 301 has more α-Al2O3, while the portion farther away from the substrate 301 has more γ-Al2O3. Furthermore, the porosity of the oxide layer 302 closer to the substrate 301 is relatively low (greater than 2%), while the porosity of the other portion of the oxide layer 302 farther away from the surface of the substrate 301 is relatively high (less than or equal to 2%).

[0141] Step 3: Polish the oxide layer 302 to reduce its thickness to approximately 10µm-30µm to obtain a dense oxide layer 302. The polishing process may include rough polishing, medium polishing, and fine polishing. The final oxide layer 302 has a porosity of less than or equal to 2% and a surface roughness of less than or equal to 0.8µm.

[0142] Step 4: Deposit a base material on the surface of oxide layer 302 using physical vapor deposition to form base layer 303. The base material can be one or more of titanium, chromium, zirconium, copper, and gold. The equipment used for physical vapor deposition can consist of a multi-arc target and a magnetron sputtering target. The thickness of the base layer 303 formed is 0.3µm-1µm.

[0143] Step 5: Deposit all elements of the base material and all elements of the appearance material on the surface of the base layer 303 using physical vapor deposition to obtain a composite layer 304 composed of a mixture of the aforementioned elements. The base material can be one or more of titanium, chromium, zirconium, copper, and gold, and the appearance material is diamond-like carbon. The thickness of the composite layer 304 is within 0.3µm-3µm. In the composite layer 304, along the stacking direction of the base layer 303, composite layer 304, and color layer 305, or in other words, along the direction from the base layer 303 to the color layer 305, the mass ratio of the appearance material elements to the base material elements in the composite layer 304 gradually increases. This allows the base layer 303 to transition more reliably to the color layer 305 through the composite layer 304, further alleviating the stress on the middle frame 300 during the subsequent formation of the color layer 305.

[0144] Step Six: Deposit an appearance material onto the surface of composite layer 304 using physical vapor deposition to form color layer 305. As described in Step Five, the appearance material is diamond-like carbon (DLC), therefore the formed color layer is a DLC layer. The thickness of color layer 305 can be 0.3µm-5µm. Furthermore, by controlling the deposition thickness of the DLC, color layer 305 can exhibit different colors, such as black or gray. Additionally, the sp3 bond content in color layer 305 can be greater than 30%, and the hardness of color layer 305 can be greater than or equal to 1800 HV, thereby giving the middle frame 300 a high-hardness surface and improving the structural strength of the middle frame 300.

[0145] Taking titanium as the material and base material of the base layer 303 as an example, the middle frame 300 in this embodiment includes an aluminum-based composite material matrix 301 and a micro-arc oxidation layer, a titanium layer, a composite layer of titanium and diamond-like material, and a diamond-like layer formed sequentially on the matrix 301. The final surface color of the middle frame 300 is black or gray.

[0146] refer to Figure 6 As shown, Figure 6 This is a flowchart illustrating the fabrication process of another middle frame 300 provided in this embodiment. In this embodiment, the fabrication method of the middle frame 300 specifically includes:

[0147] Step 1: Fabricate the aluminum-based composite material into the shape of the mid-frame 300 to form the matrix 301. This aluminum-based composite material can be composed of 6-series aluminum alloy doped with silicon carbide. Furthermore, the shape of the mid-frame 300 can be designed according to the electronic device to which it is applied; for example, the electronic device can be a mobile phone, a foldable phone, a tablet computer, a laptop computer, etc.

[0148] Step 2: The substrate 301 is placed in a micro-arc oxidation solution to form an oxide layer 302 through a micro-arc oxidation process. The mass ratio of sodium hydroxide to sodium metasilicate in the micro-arc oxidation solution is 1:9, and the pH is between 8.5 and 13. The thickness of the generated oxide layer 302 is approximately 20µm-40µm. The oxide layer 302 is mainly composed of α-Al₂O₃ and γ-Al₂O₃. Along the thickness direction of the oxide layer 302, the portion closer to the substrate 301 has more α-Al₂O₃, while the portion farther away from the substrate 301 has more γ-Al₂O₃. Furthermore, the porosity of the oxide layer 302 closer to the substrate 301 is relatively low (greater than 2%), while the porosity of the other portion of the oxide layer 302 farther away from the substrate 301 surface is relatively high (less than or equal to 2%).

[0149] Step 3: Polish the oxide layer 302 to reduce its thickness to approximately 5µm-20µm, resulting in a dense oxide layer 302. The polishing process may include rough polishing, medium polishing, and fine polishing. The final oxide layer 302 should have a porosity of less than or equal to 2% and a surface roughness of less than or equal to 0.6µm.

[0150] Step 4: Deposit a base material on the surface of oxide layer 302 using physical vapor deposition to form base layer 303. The base material can be one or more of titanium, chromium, zirconium, copper, and gold. The equipment used for physical vapor deposition can consist of a magnetically filtered multi-arc target and a magnetron sputtering target. The thickness of the base layer 303 formed is 0.2µm-1.2µm.

[0151] Step 5: Deposit all elements of the base material and all elements of the appearance material on the surface of the base layer 303 using physical vapor deposition to obtain a composite layer 304 composed of a mixture of the aforementioned elements. The base material can be one or more of titanium, chromium, zirconium, copper, and gold, and the appearance material is tetrahedral amorphous carbon. The thickness of the composite layer 304 is within 0.2µm-4µm. In the composite layer 304, along the stacking direction of the base layer 303, composite layer 304, and color layer 305, or in other words, along the direction from the base layer 303 to the color layer 305, the mass ratio of the appearance material elements to the base material elements in the composite layer 304 gradually increases. This allows the base layer 303 to transition more reliably to the color layer 305 through the composite layer 304, further alleviating the stress on the middle frame 300 during the subsequent formation of the color layer 305.

[0152] Step Six: Deposit an appearance material onto the surface of composite layer 304 using physical vapor deposition to form color layer 305. As described in Step Five, the appearance material is tetrahedral amorphous carbon, therefore the formed color layer 305 is a tetrahedral amorphous carbon layer. The thickness of color layer 305 can be within the range of 0.2µm-5µm. Furthermore, by controlling the deposition thickness of the tetrahedral amorphous carbon, color layer 305 can exhibit different colors, such as black, blue, green, etc. The sp3 bond content in color layer 305 can be greater than 60%, and the hardness of color layer 305 is greater than or equal to 3000 HV, thereby giving the middle frame 300 a high-hardness surface and improving the structural strength of the middle frame 300.

[0153] Taking chromium as the material and base material of the base layer 303 as an example, the middle frame 300 in this embodiment includes an aluminum-based composite material matrix 301 and a micro-arc oxidation layer, a chromium layer, a composite layer of chromium and tetrahedral amorphous carbon mixed material, and a tetrahedral amorphous carbon layer formed sequentially on the matrix 301. The final surface color of the middle frame 300 is black, blue, or green.

[0154] It is worth mentioning that, Figure 6 In the illustrated embodiment, the material of the substrate 301 can also be replaced with 7-series aluminum alloy, where the hardness of the 7-series aluminum alloy is greater than or equal to 130 HV. In this case, the middle frame consists of a 7-series aluminum alloy substrate 301, a micro-arc oxidation layer, a chromium layer, a composite layer of chromium and tetrahedral amorphous carbon, and a tetrahedral amorphous carbon layer. Correspondingly, step one can be modified to: fabricating the 7-series aluminum alloy into the shape of the middle frame 300 to form the substrate 301; the remaining steps are the same as... Figure 6 The embodiments shown are the same, and will not be described again here.

[0155] refer to Figure 7 As shown, Figure 7 This is a flowchart illustrating the fabrication process of another middle frame 300 provided in this embodiment. In this embodiment, the fabrication method of the middle frame 300 specifically includes:

[0156] Step 1: Fabricate the aluminum-based composite material into the shape of the mid-frame 300 to form the matrix 301. This aluminum-based composite material can be composed of a 2-series aluminum alloy doped with silicon carbide. Furthermore, the shape of the mid-frame 300 can be designed according to the electronic device to which it is applied; for example, the electronic device can be a mobile phone, a foldable phone, a tablet computer, a laptop computer, etc.

[0157] Step 2: The substrate 301 is placed in a micro-arc oxidation solution to form an oxide layer 302 through a micro-arc oxidation process. The mass ratio of sodium hydroxide to sodium metasilicate in the micro-arc oxidation solution is 1:9, and the pH is between 8.5 and 13. The thickness of the generated oxide layer 302 is approximately 15µm-40µm. The main body of the micro-arc oxidation layer 302 is composed of α-Al₂O₃ and γ-Al₂O₃. Along the thickness direction of the oxide layer 302, the portion closer to the substrate 301 has more α-Al₂O₃, while the portion farther away from the substrate 301 has more γ-Al₂O₃. Furthermore, the porosity of the oxide layer 302 closer to the substrate 301 is relatively low (greater than 2%), while the porosity of the other portion of the oxide layer 302 farther away from the surface of the substrate 301 is relatively high (less than or equal to 2%).

[0158] Step 3: Polish the oxide layer 302 to reduce its thickness to approximately 5µm-25µm to obtain a dense oxide layer 302. The polishing process may include rough polishing, medium polishing, and fine polishing. The final oxide layer 302 should have a porosity of less than or equal to 2% and a surface roughness of less than or equal to 0.4µm.

[0159] Step 4: Deposit a base material on the surface of oxide layer 302 using physical vapor deposition to form base layer 303. The base material can be one or more of titanium, chromium, zirconium, copper, and gold. The equipment used for physical vapor deposition can consist of a magnetically filtered multi-arc target and a magnetron sputtering target. The thickness of the base layer 303 formed is 0.2µm-1.2µm.

[0160] Step 5: Deposit all elements of the base material and all elements of the appearance material on the surface of the base layer 303 using physical vapor deposition to obtain a composite layer 304 composed of a mixture of the aforementioned elements. The base material can be one or more of titanium, chromium, zirconium, copper, and gold, and the appearance material is chromium nitride. The thickness of the composite layer 304 is within 0.2µm-4µm. In the composite layer 304, along the stacking direction of the base layer 303, composite layer 304, and color layer 305, or in other words, along the direction from the base layer 303 to the color layer 305, the mass ratio of the appearance material elements to the base material elements in the composite layer 304 gradually increases. This allows the base layer 303 to transition more reliably to the color layer 305 through the composite layer 304, further alleviating the stress on the middle frame 300 during the subsequent formation of the color layer 305.

[0161] Step Six: Deposit an appearance material, color layer 305, onto the surface of composite layer 304 using physical vapor deposition. As described in Step Five, the appearance material is chromium nitride, therefore the formed color layer 305 is a chromium nitride layer. The thickness of color layer 305 is 0.2µm-5µm. Color layer 305 can exhibit a silver-white color effect.

[0162] Taking chromium as the material and base material of the base layer 303 as an example, the middle frame 300 in this embodiment includes an aluminum-based composite material matrix 301 and a micro-arc oxidation layer, a chromium layer, a composite layer of chromium and chromium nitride mixed material, and a chromium nitride layer formed sequentially on the matrix 301. The final surface color of the middle frame 300 is silver-white.

[0163] refer to Figure 8 As shown, Figure 8 This is a flowchart illustrating the fabrication process of another middle frame 300 provided in this embodiment. In this embodiment, the fabrication method of the middle frame 300 specifically includes:

[0164] Step 1: Fabricate the aluminum-based composite material into the shape of the mid-frame 300 to form the matrix 301. This aluminum-based composite material can be composed of 7-series aluminum alloy doped with silicon carbide. Furthermore, the shape of the mid-frame 300 can be designed according to the electronic device to which it is applied; for example, the electronic device can be a mobile phone, a foldable phone, a tablet computer, a laptop computer, etc.

[0165] Step 2: The substrate 301 is placed in a micro-arc oxidation solution to form an oxide layer 302 through a micro-arc oxidation process. The mass ratio of sodium hydroxide to sodium metasilicate in the micro-arc oxidation solution is 1:9, and the pH is in the range of 8.5-13. The thickness of the generated oxide layer 302 is approximately 25µm-48µm. The oxide layer 302 is mainly composed of α-Al₂O₃ and γ-Al₂O₃. Along the thickness direction of the oxide layer 302, the portion closer to the substrate 301 has more α-Al₂O₃, while the portion farther away from the substrate 301 has more γ-Al₂O₃. Furthermore, the porosity of the oxide layer 302 closer to the substrate 301 is relatively low (greater than 2%), while the porosity of the other portion of the oxide layer 302 farther away from the surface of the substrate 301 is relatively high (less than or equal to 2%).

[0166] Step 3: Polish the oxide layer 302 to reduce its thickness to approximately 10µm-30µm to obtain a dense oxide layer 302. The polishing process may include rough polishing, medium polishing, and fine polishing. The final oxide layer 302 has a porosity of less than or equal to 2% and a surface roughness of less than or equal to 0.8µm.

[0167] Step 4: Deposit a base material on the surface of oxide layer 302 using physical vapor deposition to form base layer 303. The base material can be one or more of titanium, chromium, zirconium, copper, and gold. The equipment used for physical vapor deposition can consist of a multi-arc target and a magnetron sputtering target, and the thickness of the formed base layer 303 is 0.3µm-1µm.

[0168] Step 5: Deposit all elements of the base material and all elements of the appearance material on the surface of the base layer 303 using physical vapor deposition to obtain a composite layer 304 composed of a mixture of the aforementioned elements. The base material can be one or more of titanium, chromium, zirconium, copper, and gold, and the appearance material is titanium oxynitride. The thickness of the composite layer 304 is within 0.3µm-3µm. In the composite layer 304, along the stacking direction of the base layer 303, composite layer 304, and color layer 305, or in other words, along the direction from the base layer 303 to the color layer 305, the mass ratio of the appearance material elements to the base material elements in the composite layer 304 gradually increases. This allows the base layer 303 to transition more reliably to the color layer 305 through the composite layer 304, further alleviating the stress on the middle frame 300 during the subsequent formation of the color layer 305.

[0169] Step Six: Deposit an appearance material onto the surface of composite layer 304 using physical vapor deposition to form color layer 305. As described in Step Five, the appearance material is titanium oxynitride, therefore the formed color layer 305 is a titanium oxynitride layer. The thickness of color layer 305 is 0.3µm-5µm. By controlling the deposition thickness of titanium oxynitride, color layer 305 can exhibit different colors, such as green and blue.

[0170] Taking titanium as the material and base material of the base layer 303 as an example, the middle frame 300 in this embodiment includes an aluminum-based composite material matrix 301 and a micro-arc oxidation layer, a titanium layer, a composite layer of titanium and titanium oxynitride mixed material, and a titanium oxynitride layer formed sequentially on the matrix 301. The final surface color of the middle frame 300 is green or blue, etc.

[0171] refer to Figure 9 As shown, Figure 9 This is a flowchart illustrating the fabrication process of another middle frame 300 provided in this embodiment. In this embodiment, the fabrication method of the middle frame 300 specifically includes:

[0172] Step 1: The magnesium alloy material is fabricated into the shape of the middle frame 300 to form the substrate 301. The yield strength of this magnesium alloy material is greater than or equal to 230 MPa, and the hardness is greater than or equal to 100 HV. The shape of the middle frame 300 can be designed according to the electronic device to which the middle frame 300 is applied. For example, the electronic device can be a mobile phone, a foldable phone, a tablet computer, a laptop computer, etc.

[0173] Step 2: The substrate 301 is placed in a micro-arc oxidation solution to form an oxide layer 302 through a micro-arc oxidation process. The mass ratio of sodium hydroxide (NaOH), sodium hexametaphosphate ((NaPO3)6), and sodium fluoride (NaF) in the micro-arc oxidation solution is 50:1:1. The thickness of the generated oxide layer 302 is approximately 25µm-45µm. The main body of the oxide layer 302 is composed of magnesium fluoride (MgF) and magnesium triphosphate (Mg3(PO4)2). Along the thickness direction of the oxide layer 302, the part of the oxide layer 302 closer to the substrate 301 has a relatively low porosity (greater than 3%), while the other part of the oxide layer 302 farther away from the surface of the substrate 301 has a relatively high porosity (less than or equal to 2%).

[0174] Step 3: Polish the oxide layer 302 to reduce its thickness to approximately 10µm-30µm to obtain a dense oxide layer 302. The polishing process may include rough polishing, medium polishing, and fine polishing. The final oxide layer 302 should have a porosity of less than or equal to 2% and a surface roughness of less than or equal to 0.5µm.

[0175] Step 4: Deposit a base material on the surface of oxide layer 302 using physical vapor deposition to form base layer 303. The base layer 303 is made of one or more of titanium, chromium, zirconium, copper, and gold. The equipment used for physical vapor deposition can consist of a multi-arc target and a magnetron sputtering target. The thickness of the base layer 303 is 0.3µm-1µm.

[0176] Step 5: Deposit all elements of the base material and all elements of the appearance material on the surface of the base layer 303 using physical vapor deposition to obtain a composite layer 304 composed of a mixture of the aforementioned elements. The base material can be one or more of titanium, chromium, zirconium, copper, and gold, and the appearance material is diamond-like carbon. The thickness of the composite layer 304 is within 0.3µm-3µm. In the composite layer 304, along the stacking direction of the base layer 303, composite layer 304, and color layer 305, or in other words, along the direction from the base layer 303 to the color layer 305, the mass ratio of the appearance material elements to the base material elements in the composite layer 304 gradually increases. This allows the base layer 303 to transition more reliably to the color layer 305 through the composite layer 304, further alleviating the stress on the middle frame 300 during the subsequent formation of the color layer 305.

[0177] Step Six: Deposit an appearance material onto the surface of composite layer 304 using physical vapor deposition to form color layer 305. As described in Step Five, the appearance material is diamond-like carbon (DLC), therefore the formed color layer 305 is a DLC layer. The thickness of color layer 305 is 0.3µm-5µm. By controlling the deposition thickness of the DLC, color layer 305 can exhibit different colors, such as black or gray. Furthermore, the sp3 bond content in color layer 305 can be greater than 30%, and the hardness of color layer 305 can be greater than or equal to 1800 HV, thereby giving the middle frame 300 a high-hardness surface and improving the structural strength of the middle frame 300.

[0178] Taking titanium as the material and base material of the base layer 303 as an example, the middle frame 300 in this embodiment includes a magnesium alloy substrate 301 and a micro-arc oxidation layer, a titanium layer, a composite layer of titanium and diamond-like material, and a diamond-like layer formed sequentially on the substrate 301. The final surface color of the middle frame 300 is black or gray.

[0179] refer to Figure 10 As shown, Figure 10 This is a flowchart illustrating the fabrication process of another middle frame 300 provided in this embodiment. In this embodiment, the fabrication method of the middle frame 300 specifically includes:

[0180] Step 1: The composite of aluminum alloy and magnesium alloy is fabricated into the shape of a mid-frame 300, forming a matrix 301. In this composite material, the yield strength of the magnesium alloy is greater than or equal to 230 MPa, and the hardness is greater than or equal to 100 HV. The shape of the mid-frame 300 can be designed according to the electronic device to which the mid-frame 300 is applied. For example, the electronic device can be a mobile phone, a foldable phone, a tablet computer, a laptop computer, etc.

[0181] In one implementation, the substrate 301 includes a first component and a second component, the first component being made of magnesium alloy and the second component being made of aluminum alloy. When the substrate 301 corresponding to the portion of the mid-frame 300 that serves as the external surface of the electronic device includes at least a portion of both the first component and the second component, the first and second components can be connected by friction stir welding. Friction stir welding results in relatively low residual stress, thus the first and second components are less prone to deformation. This allows the substrate 301, synthesized from both, to maintain the shape of the mid-frame 300 well, which is beneficial for improving the yield rate of the mid-frame 300. For example, in... Figure 3 The middle frame shown includes a middle plate and a frame. The surface of the protrusion of the middle plate and the outer side of the frame both serve as the appearance surface of the mobile phone. The first component can be the base of the middle plate, and the second component can be the base of the frame.

[0182] Step 2: The substrate 301 is placed in a micro-arc oxidation solution to form an oxide layer 302 through a micro-arc oxidation process. The mass ratio of sodium hydroxide (NaOH), sodium hexametaphosphate ((NaPO3)6), and sodium fluoride (NaF) in the micro-arc oxidation solution is 40:1:1. The thickness of the generated oxide layer 302 is approximately 20µm-50µm. The oxide layer 302 formed on the aluminum alloy surface is mainly composed of α-Al2O3 and γ-Al2O3, while the oxide layer 302 formed on the magnesium alloy surface is mainly composed of magnesium fluoride and trimagnesium phosphate. The oxide layer 302 formed at the weld between the aluminum and magnesium alloys is a mixture of the micro-arc oxidation of the aluminum and magnesium alloys. Along the thickness direction of the oxide layer 302, the portion of the oxide layer 302 closer to the substrate 301 has a relatively low porosity (greater than 3%), while the portion of the oxide layer 302 farther from the surface of the substrate 301 has a relatively high porosity (less than or equal to 3%).

[0183] Step 3: Polish the oxide layer 302 to reduce its thickness to approximately 10µm-30µm to obtain a dense oxide layer 302. The polishing process may include rough polishing, medium polishing, and fine polishing. The final oxide layer 302 should have a porosity of less than or equal to 3% and a surface roughness of less than or equal to 0.5µm.

[0184] Step 4: Deposit a base material on the surface of oxide layer 302 using physical vapor deposition to form base layer 303. The base material can be one or more of titanium, chromium, zirconium, copper, and gold. The equipment used for physical vapor deposition can consist of a magnetically filtered multi-arc target and a magnetron sputtering target, and the thickness of the formed base layer 303 is 0.2µm-1.2µm.

[0185] Step 5: Deposit all elements of the base material and all elements of the appearance material on the surface of the base layer 303 using physical vapor deposition to obtain a composite layer 304 composed of a mixture of the aforementioned elements. The base material can be one or more of titanium, chromium, zirconium, copper, and gold, and the appearance material is tetrahedral amorphous carbon. The thickness of the composite layer 304 is within 0.2µm-4µm. In the composite layer 304, along the stacking direction of the base layer 303, composite layer 304, and color layer 305, or in other words, along the direction from the base layer 303 to the color layer 305, the mass ratio of the appearance material elements to the base material elements in the composite layer 304 gradually increases. This allows the base layer 303 to transition more reliably to the color layer 305 through the composite layer 304, further alleviating the stress on the middle frame 300 during the subsequent formation of the color layer 305.

[0186] Step Six: Deposit an appearance material onto the surface of composite layer 304 using physical vapor deposition to form color layer 305. As described in Step Five, the appearance material is tetrahedral amorphous carbon, therefore the formed color layer 305 is a tetrahedral amorphous carbon layer. The thickness of color layer 305 can be within 0.2µm-5µm. Furthermore, by controlling the deposition thickness of the tetrahedral amorphous carbon, the formed color layer 305 can exhibit different colors, such as black, blue, green, etc. The sp3 bond content in color layer 305 can be greater than 60%, and the hardness of color layer 305 is greater than or equal to 3000 HV, thereby giving the middle frame 300 a high-hardness surface and improving the structural strength of the middle frame 300.

[0187] Taking chromium as the material and base material of the base layer 303 as an example, the middle frame 300 in this embodiment includes a substrate 301 composed of a composite of aluminum alloy and magnesium alloy, and a micro-arc oxidation layer, a chromium layer, a composite layer of chromium and tetrahedral amorphous carbon mixed material, and a tetrahedral amorphous carbon layer formed sequentially on the substrate 301. The final surface color of the middle frame 300 is black, blue or green, etc.

[0188] refer to Figure 11 As shown, Figure 11 This is a flowchart illustrating the fabrication process of another middle frame 300 provided in this embodiment. In this embodiment, the fabrication method of the middle frame 300 specifically includes:

[0189] Step 1: The composite of aluminum alloy and magnesium alloy is fabricated into the shape of a mid-frame 300, forming a matrix 301. In this composite material, the yield strength of the magnesium alloy is greater than or equal to 230 MPa, and the hardness is greater than or equal to 100 HV. The shape of the mid-frame 300 can be designed according to the electronic device to which the mid-frame 300 is applied. For example, the electronic device can be a mobile phone, a foldable phone, a tablet computer, a laptop computer, etc.

[0190] In one implementation, the portion of the substrate 301 made of aluminum alloy is the first component, and the portion of the substrate 301 made of magnesium alloy is the second component. When the portion of the middle frame 300 that serves as the exterior surface of the electronic device corresponds to the substrate 301 (such as a frame) that includes at least a portion of both the first component and at least a portion of the second component, the first component and the second component can be connected by friction stir welding.

[0191] Step 2: The substrate 301 is placed in a micro-arc oxidation solution to form an oxide layer 302 through a micro-arc oxidation process. The mass ratio of sodium hydroxide, sodium hexametaphosphate, and sodium fluoride in the micro-arc oxidation solution is 40:1:1. The thickness of the generated oxide layer 302 is approximately 20µm-50µm. The oxide layer 302 formed on the aluminum alloy surface is mainly composed of α-Al₂O₃ and γ-Al₂O₃, while the oxide layer 302 formed on the magnesium alloy surface is mainly composed of magnesium fluoride and trimagnesium phosphate. The oxide layer 302 formed at the weld between the aluminum and magnesium alloys is mainly a mixture produced by the micro-arc oxidation of the aluminum and magnesium alloys. Along the thickness direction of the oxide layer 302, the portion of the oxide layer 302 closer to the substrate 301 has a relatively low porosity (greater than 3%), while the portion of the oxide layer 302 farther from the surface of the substrate 301 has a relatively high porosity (less than or equal to 3%).

[0192] Step 3: Polish the oxide layer 302 to reduce its thickness to approximately 10µm-30µm to obtain a dense oxide layer 302. The polishing process may include rough polishing, medium polishing, and fine polishing. The final oxide layer 302 should have a porosity of less than or equal to 3% and a surface roughness of less than or equal to 0.5µm.

[0193] Step 4: Deposit a base material on the surface of oxide layer 302 using physical vapor deposition to form base layer 303. The base material is titanium, zirconium, or a composite material of titanium and zirconium. The equipment used for physical vapor deposition can consist of a magnetically filtered multi-arc target and a magnetron sputtering target. The thickness of the formed base layer 303 is 0.2µm-1.2µm.

[0194] Step 5: Deposit all elements of the base material and all elements of the appearance material on the surface of the base layer 303 using physical vapor deposition to obtain a composite layer 304 containing the aforementioned elements. The base material can be titanium, zirconium, or a composite material of titanium and zirconium, and the appearance material is titanium nitride. The thickness of the composite layer 304 is within 0.2µm-4µm. In the composite layer 304, along the stacking direction of the base layer 303, composite layer 304, and color layer 305, or in other words, along the direction from the base layer 303 to the color layer 305, the mass ratio of the appearance material elements to the base material elements in the composite layer 304 gradually increases. This allows the base layer 303 to transition more reliably to the color layer 305 through the composite layer 304, further alleviating the stress on the middle frame 300 during the subsequent formation of the color layer 305.

[0195] Step Six: Deposit an appearance material onto the surface of composite layer 304 using physical vapor deposition to form color layer 305. As described in Step Five, the appearance material is titanium nitride, therefore the formed color layer 305 is a titanium nitride layer. The thickness of color layer 305 is 0.2µm-5µm. Color layer 305 can exhibit a yellowish color effect.

[0196] Taking titanium as an example of the material and base material of the base layer 303, the middle frame 300 in this embodiment includes a substrate 301 composed of a composite of aluminum alloy and magnesium alloy, and a micro-arc oxidation layer, a titanium layer, a composite layer of titanium and titanium nitride mixed material, and a titanium nitride layer formed sequentially on the substrate 301. The final surface color of the middle frame 300 is yellow.

[0197] refer to Figure 12 As shown, Figure 12 This is a flowchart illustrating the fabrication process of another middle frame 300 provided in this embodiment. In this embodiment, the fabrication method of the middle frame 300 specifically includes:

[0198] Step 1: Fabricate the aluminum-based composite material into the shape of the mid-frame 300 to form the matrix 301. This aluminum-based composite material can be composed of 6-series aluminum alloy doped with silicon carbide. Furthermore, the shape of the mid-frame 300 can be designed according to the electronic device to which it is applied; for example, the electronic device can be a mobile phone, a foldable phone, a tablet computer, a laptop computer, etc.

[0199] Step 2: The substrate 301 is placed in a micro-arc oxidation solution to form an oxide layer 302 through a micro-arc oxidation process. The mass ratio of sodium hydroxide to sodium metasilicate in the micro-arc oxidation solution is 1:9, and the pH is between 8.5 and 13. The thickness of the generated oxide layer 302 is approximately 20µm-40µm. The oxide layer 302 is mainly composed of α-Al₂O₃ and γ-Al₂O₃. Along the thickness direction of the oxide layer 302, the portion closer to the substrate 301 has more α-Al₂O₃, while the portion farther away from the substrate 301 has more γ-Al₂O₃. Furthermore, the porosity of the oxide layer 302 closer to the substrate 301 is relatively low (greater than 2%), while the porosity of the other portion of the oxide layer 302 farther away from the substrate 301 surface is relatively high (less than or equal to 2%).

[0200] In one implementation, titanium dioxide (TiO2) nanoparticles or alumina nanoparticles can be added to the micro-arc oxidation solution at an amount of 2.0 g / L to 8.0 g / L. This increases the porosity of the oxide layer 302 near the substrate 301, thereby improving the salt spray resistance of the oxide layer. For example, by adding the above-mentioned substances to the micro-arc oxidation solution, the porosity of the oxide layer 302 near the substrate 301 can be reduced to below 1%.

[0201] Step 3: Polish the oxide layer 302 to reduce its thickness to approximately 5µm-20µm, resulting in a dense oxide layer 302. The polishing process may include rough polishing, medium polishing, and fine polishing. The final oxide layer 302 should have a porosity of less than or equal to 2% and a surface roughness of less than or equal to 0.6µm.

[0202] Step 4: Deposit a base material, silicon, on the surface of oxide layer 302 using physical vapor deposition to form base layer 303. The equipment used for physical vapor deposition can consist of a magnetically filtered multi-arc target and a magnetron sputtering target. The thickness of the base layer 303 formed is 0.2µm-1.2µm.

[0203] Step 5: Deposit all elements of the base material and all elements of the appearance material on the surface of the base layer 303 using physical vapor deposition to obtain a composite layer 304 containing the aforementioned elements. The base material is silicon, and the appearance material is diamond-like carbon. The thickness of the composite layer 304 is within 0.2µm-4µm. In the composite layer 304, along the stacking direction of the base layer 303, composite layer 304, and color layer 305, or in other words, along the direction from the base layer 303 to the color layer 305, the mass ratio of the appearance material elements to the base material elements gradually increases. This allows the base layer 303 to transition more reliably to the color layer 305 through the composite layer 304, further alleviating the stress on the middle frame 300 during the subsequent formation of the color layer 305.

[0204] Step Six: Deposit an appearance material onto the surface of composite layer 304 using physical vapor deposition to form color layer 305. As described in Step Five, if the appearance material is diamond-like carbon, then the formed color layer 305 is a diamond-like carbon layer. The thickness of color layer 305 can be 0.3µm-5µm. Color layer 305 can exhibit a black or gray color effect. Furthermore, the sp3 bond content in color layer 305 can be greater than 30%, and the hardness of color layer 305 is greater than or equal to 1800 HV, thereby giving the middle frame 300 a high-hardness surface and improving the structural strength of the middle frame 300.

[0205] In this embodiment, the middle frame 300 includes an aluminum-based composite material matrix 301 and a micro-arc oxidation layer, a silicon layer, and a composite layer of a silicon and diamond-like carbon material sequentially formed on the matrix 301. The final surface color of the middle frame 300 is black or gray. Furthermore, in this embodiment, apart from the matrix 301, all other layers of the middle frame 300 are insulating layers, thus contributing to improved corrosion resistance.

[0206] In addition, Figure 12 In the illustrated embodiment, the outer material can also be replaced with tetrahedral amorphous carbon, tungsten carbide, or a mixture of silicon nitride and silicon oxynitride. None of these materials are conductive; therefore, all layers in the middle frame 300 except the substrate 301 are insulating layers, which helps improve the corrosion resistance of the middle frame 300. Furthermore, the material of the substrate 301 can also be replaced with aluminum alloy, magnesium-based composite material, magnesium alloy, etc., which will not be elaborated here.

[0207] It is worth mentioning that, Figures 5 to 12 In step three of the embodiments shown, the removal depth of the oxide layer 302 by polishing can also be appropriately reduced so that the surface roughness of the oxide layer 302 after polishing is less than 1 μm.

[0208] In addition, in step two of the above embodiments, an oxide layer can be formed on the substrate surface through an anodizing process, and the formed oxide layer is the anodized layer. Along the direction away from the substrate, the anodized layer includes a bottom dense layer, an intermediate porous layer, and a surface sealing layer. After the anodized layer is formed, the intermediate porous layer and the surface sealing layer can be removed by polishing, retaining the bottom dense layer, and the base layer, composite layer, and color layer are prepared on the basis of the bottom dense layer.

[0209] In other embodiments, an oxide layer can be formed on the substrate surface using a hard anodizing process; the resulting oxide layer is the hard anodizing layer. The hard anodizing layer includes a bottom dense layer, an intermediate porous layer, and a surface sealing layer. After the hard anodizing layer is formed, the intermediate porous layer and the surface sealing layer can be removed by polishing, leaving the bottom dense layer. Based on the bottom dense layer, a base layer, a composite layer, and a color layer are then prepared.

[0210] Figure 13 This is a schematic cross-sectional view of another middle frame provided in an embodiment of this application. (See reference...) Figure 13 As shown in this embodiment, the middle frame 300 includes a base 301 and a base layer 303, a composite layer 304, and a color layer 305 sequentially stacked on the base 301. The base 301 can be fabricated into the shape of the middle frame, for example... Figure 2 or Figure 3 The shape of the mobile phone frame shown is similar to that of other electronic devices, including foldable phones, laptops, or tablets. The substrate 301 is made of at least one of a metal matrix composite material or an alloy material. For example, the substrate 301 may include one metal matrix composite material or one alloy material, or two or more metal matrix composite materials, or two or more alloy materials. The base layer 303 is made of a reflective base material, which can create a high reflectivity effect on the surface of the frame 300. The color layer 305 can give the frame 300 a specific decorative color; the combination of the two helps to achieve a high aesthetic quality for the frame 300. The composite layer 304 between the base layer 303 and the color layer 305 is a mixed material, which includes all elements of the base material and all elements of the appearance material. The composite layer 304 can improve the bonding strength between the base layer 303 and the color layer 305, reduce the risk of the frame 300 peeling off due to impacts, and also alleviate the stress on the frame 300 during the formation of the color layer 305, thereby reducing the impact on the structural strength of the frame 300.

[0211] In this embodiment, the specific materials, forming process, thickness, and other parameters of the substrate 301, base layer 303, composite layer 304, and color layer 305 can be designed with reference to the aforementioned embodiments, and will not be repeated here. Furthermore, in this embodiment, when the color layer 305 is a non-insulating layer, the middle frame 300 may also include a first transparent insulating layer. The first transparent insulating layer is disposed on the surface of the color layer 305 facing away from the composite layer 304 to improve the corrosion resistance of the middle frame 300 and to give the middle frame 300 a more vibrant and bright color effect. Additionally, the middle frame 300 may also include a second transparent insulating layer and an anti-fingerprint layer. The second transparent insulating layer can further improve the corrosion resistance of the middle frame 300, while the anti-fingerprint layer can give the middle frame 300 waterproof, oil-proof, stain-proof, and fingerprint-resistant functions, improving the ease of cleaning the middle frame 300.

[0212] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A middle frame, characterized in that, The material includes a substrate and an oxide layer, a base layer, a composite layer, and a color layer stacked sequentially on the substrate. The substrate is made of at least one of a metal matrix composite material or an alloy material. The base layer is made of a reflective base material. The color layer is made of the appearance material. The composite layer is made of a mixed material, which includes all elements of the base material and all elements of the appearance material.

2. The middle frame as described in claim 1, characterized in that, The hardness of the oxide layer is greater than or equal to 300 HV.

3. The middle frame as described in claim 1 or 2, characterized in that, The surface roughness of the oxide layer is less than or equal to 0.8 μm.

4. The middle frame as described in any one of claims 1-3, characterized in that, The porosity of the oxide layer is less than or equal to 3%.

5. The middle frame as described in any one of claims 1-4, characterized in that, The oxide layer is a micro-arc oxide layer, an anodic oxide layer, or a hard anodic layer.

6. The middle frame as described in any one of claims 1-5, characterized in that, The base layer is a non-insulating layer, and the base material includes at least one of titanium, chromium, zirconium, copper, and gold.

7. The middle frame as described in claim 6, characterized in that, The color layer is an insulating layer, and the appearance material includes at least one of diamond-like carbon, tetrahedral amorphous carbon, chromium nitride, titanium nitride, titanium oxynitride, and tungsten carbide.

8. The middle frame as described in claim 7, characterized in that, The outer material is diamond-like carbon, wherein the content of sp3 bonds in the diamond-like carbon is greater than 30%, and the hardness of the color layer is greater than or equal to 1800 HV; or... The exterior material is tetrahedral amorphous carbon, the content of sp3 bonds in the tetrahedral amorphous carbon is greater than 60%, and the hardness of the color layer is greater than or equal to 3000 HV.

9. The middle frame as described in claim 6, characterized in that, The color layer is a non-insulating layer, and the appearance material includes at least one of diamond-like carbon, copper, gold, copper or gold nitrogen-carbon compounds, copper or gold nitrogen-oxygen compounds, copper or gold carbides, and copper or gold nitrides.

10. The middle frame as described in claim 9, characterized in that, The middle frame further includes a first transparent insulating layer disposed on the side surface of the color layer facing away from the composite layer, the first transparent insulating layer comprising stacked multilayer oxide films.

11. The middle frame as described in any one of claims 1-5, characterized in that, The base layer is an insulating layer, and the base material is silicon.

12. The middle frame as described in claim 11, characterized in that, The color layer is an insulating layer, and the appearance material includes at least one of silicon nitride and silicon oxynitride, silicon nitride, and tungsten carbide.

13. The middle frame as described in any one of claims 1-12, characterized in that, Along the stacking direction of the base layer, the composite layer, and the color layer, the mass ratio of the elements of the appearance material in the composite layer to the elements of the base material gradually increases.

14. The middle frame as described in any one of claims 1-13, characterized in that, The matrix is ​​made of one or two of the following materials: aluminum-based composite material, magnesium-based composite material, magnesium alloy, aluminum alloy, or a composite of magnesium alloy and aluminum alloy.

15. The middle frame as described in claim 14, characterized in that, The substrate is a composite of magnesium alloy and aluminum alloy. The substrate includes a first component and a second component. The first component is made of magnesium alloy and the second component is made of aluminum alloy. The first component and the second component are connected by friction stir welding.

16. The middle frame as described in claim 15, characterized in that, The middle frame is used in an electronic device. The middle frame includes a middle plate and a frame. The frame surrounds the periphery of the middle plate. One side of the middle plate includes a protrusion. The protruding surface of the protrusion and the outer surface of the frame are the exterior surface of the electronic device. The base of the middle plate is the first component, and the base of the frame is the second component.

17. The middle frame as described in any one of claims 1-5, characterized in that, The substrate is made of aluminum-based composite material or aluminum alloy, and the base material includes aluminum and aluminum oxide.

18. A middle frame, characterized in that, The material includes a substrate and a base layer, a composite layer, and a color layer sequentially stacked on the substrate. The substrate is made of at least one of a metal matrix composite material or an alloy material. The base layer is made of a reflective base material. The color layer is made of a colored appearance material. The composite layer is made of a mixed material, which includes all elements of the base material and all elements of the appearance material.

19. The middle frame as described in any one of claims 1-18, characterized in that, The middle frame also includes a second transparent insulating layer disposed on the side surface of the color layer facing away from the composite layer, and the material of the second transparent insulating layer is tetrahedral amorphous carbon.

20. The middle frame as described in claim 19, characterized in that, The mid-frame also includes an anti-fingerprint layer disposed on the side surface of the second transparent insulating layer facing away from the color layer.

21. A method for preparing a middle frame, characterized in that, include: An oxide layer is formed on the surface of a substrate, wherein the substrate is made of at least one of a metal matrix composite material or an alloy material; A base layer is formed on the surface of the oxide layer, and the base layer is made of a reflective base material. A composite layer is formed on the surface of the base layer. The composite layer is made of a mixed material, which includes all elements of the base material and all elements of the appearance material. A color layer is formed on the surface of the composite layer, and the material of the color layer is the appearance material.

22. The preparation method according to claim 21, characterized in that, The formation of an oxide layer on the surface of the substrate includes: The substrate is placed in a micro-arc oxidation solution, and an oxide layer is formed through the micro-arc oxidation process.

23. The preparation method according to claim 22, characterized in that, The micro-arc oxidation solution contains at least one of titanium dioxide nanoparticles, zirconium dioxide nanoparticles, yttrium oxide nanoparticles, and cerium oxide nanoparticles.

24. The preparation method according to claim 22 or 23, characterized in that, After the oxide layer is formed by the micro-arc oxidation process, the preparation method further includes: The oxide layer is polished to a depth greater than or equal to 5 micrometers, so that the surface roughness of the polished oxide layer is less than or equal to 0.8 μm.

25. The preparation method according to any one of claims 21-24, characterized in that, The formation of a composite layer on the surface of the base layer includes: The base material and the appearance material are simultaneously deposited on the surface of the base layer using vapor deposition to form the composite layer.

26. An electronic device, characterized in that, It includes a display screen and a mid-frame as described in any one of claims 1-20, wherein the display screen is disposed on one side of the mid-frame.

Images