Surface treatment method of metal part

Abstract

This disclosure provides a surface treatment method for a metal part. In this method, a micro-powder beading process is performed on the surface of the metal part to form a metallographic strengthening zone. The recrystallization temperature of this metallographic strengthening zone is lower than the recrystallization temperature of the internal structure of the metal part. The surface layer covers this internal structure. A heat treatment process is then performed on the metal part. The heat treatment temperature is equal to or greater than the recrystallization temperature of the metallographic strengthening zone but less than the recrystallization temperature of the internal structure.

Description

Technical Field

[0001] This disclosure relates to a surface treatment technology, and more particularly to a surface treatment method for metal parts. Prior Technology

[0002] Metal components, such as metal housings, play a crucial role in 3C products. They not only protect the internal electronic components but also contribute to the product's texture and aesthetic design. Common metal housing materials for 3C products include aluminum alloy, magnesium alloy, stainless steel, and titanium alloy.

[0003] Aluminum alloys are a common type of metallic material, characterized by their lightweight, high strength, good heat dissipation, and excellent texture. They are frequently used in 3C products such as mobile phones, tablets, and laptops. Magnesium alloys are relatively lightweight and possess good strength and corrosion resistance, commonly used in mobile phones and cameras. Stainless steel offers excellent corrosion resistance and durability, making it suitable for high-end mobile phones and watches. Titanium alloys are lightweight and high-strength, but also more expensive, and are often used in high-end mobile phones and smartwatches.

[0004] Combining high-gloss anodized aluminum alloy casings with frosted tempered glass creates a jarring overall appearance for 3C products, making it unsuitable for the mainstream 3C market. However, by undergoing complete recrystallization and coarse-graining heat treatment, the aluminum alloy casing typically exhibits a snowflake-like metallographic structure. Combining this snowflake-like aluminum alloy casing with frosted tempered glass results in a more harmonious product appearance, suitable for the mainstream 3C market.

[0005] However, existing metal alloy shells typically struggle to achieve a uniform coarse-grained recrystallized structure while maintaining good mechanical properties. Summary of the Invention

[0006] Therefore, one of the objectives of this disclosure is to provide a surface treatment method for metal parts that can impart a grain pattern appearance to the metal parts while maintaining the hardness and mechanical strength of the internal structure of the metal parts.

[0007] In accordance with the aforementioned objectives of this disclosure, a surface treatment method for metal parts is proposed. In this method, a micro-powder beading process is performed on the surface layer of the metal part to form a metallographic strengthening zone. The recrystallization temperature of this metallographic strengthening zone is lower than the recrystallization temperature of the internal structure of the metal part. The surface layer covers this internal structure. A heat treatment process is then performed on the metal part. The heat treatment temperature of this process is equal to or greater than the recrystallization temperature of the metallographic strengthening zone but less than the recrystallization temperature of the internal structure.

[0008] According to one embodiment of this disclosure, the above-described microparticle beading process includes continuously impacting the surface of a metal part with a plurality of microparticles. The material of these microparticles is alloy steel or ceramic, and the particle size of these microparticles is 0.01 mm to 0.5 mm.

[0009] According to one embodiment of this disclosure, the hardness of the above-mentioned micro powder is HV1000 to HV2700.

[0010] According to one embodiment of this disclosure, the above-described microparticle beading process includes applying pressure to the microparticles using a spray gun to cause them to impact the surface of the metal part. This pressure is between 2 and 6 bar.

[0011] According to one embodiment of this disclosure, the spray gun sprays micro-powder toward the surface at an incident angle of 20 to 85 degrees.

[0012] According to one embodiment of this disclosure, the depth of the metallographic strengthening region is 5 micrometers to 50 micrometers.

[0013] According to one embodiment of this disclosure, the material of the aforementioned metal part is aluminum alloy, magnesium alloy, stainless steel, titanium alloy, bearing steel, high-speed steel, or mold steel.

[0014] According to one embodiment of this disclosure, the heat treatment process includes transforming the metallographic strengthening region into a recrystallized equiaxed grain structure region.

[0015] According to one embodiment of this disclosure, the hardness of the recrystallized equiaxed grain structure region is HRC28 to HRC68.

[0016] According to one embodiment of this disclosure, the heat treatment temperature is 150 degrees to 650 degrees.

[0017] In summary, the embodiments disclosed herein first subject the metal part to a micro-powder beading process to lower the recrystallization temperature of the metal part's surface layer, creating a temperature difference between the recrystallization temperatures of the surface layer and the internal structure. Then, a heat treatment process is performed on the metal part at a temperature equal to or higher than the recrystallization temperature of the surface layer, but lower than the recrystallization temperature of the internal structure. Therefore, during the heat treatment process, recrystallization and grain growth only occur on the surface layer of the metal part, while the microstructure and grain size of the internal structure are maintained. Thus, the surface treatment method disclosed herein can effectively improve the applicability of the metal part by forming a uniform coarse-grained recrystallized microstructure on the surface layer while maintaining the mechanical properties of the internal structure. Simple Explanation of the Diagram

[0018] A better understanding of the features disclosed herein can be obtained from the following detailed description taken in conjunction with the accompanying drawings. It should be noted that, according to industry standard practice, the features are not drawn to scale. In fact, the dimensions of the features can be arbitrarily increased or decreased for clarity of discussion. [Figure 1] is a schematic flowchart illustrating a surface treatment method for a metal part according to one embodiment of the present disclosure. Figures 2 through 4 are schematic diagrams illustrating the material structure of a metal part at various stages of surface treatment according to one embodiment of the present disclosure. Implementation

[0019] The embodiments of this disclosure are discussed in detail below. However, it will be understood that the embodiments provide many applicable concepts that can be implemented in a wide variety of specific situations. The embodiments discussed and disclosed are for illustrative purposes only and are not intended to limit the scope of this disclosure. All embodiments of this disclosure disclose a variety of different features, but these features can be implemented individually or in combination as needed.

[0020] Furthermore, the terms "first," "second," etc., used in this article do not specifically refer to order or sequence; they are merely used to distinguish elements or operations described using the same technical terms.

[0021] The spatial relationship between the two components described in this disclosure applies not only to the orientation shown in the diagrams, but also to orientations not shown in the diagrams, such as inverted orientations. Furthermore, the terms "connection," "electrical connection," or similar expressions used in this disclosure to refer to the two components are not limited to a direct or electrical connection, but may also include indirect or electrical connections as needed.

[0022] The inventors discovered that the bottleneck in achieving both mechanical properties and a uniform coarse-grained recrystallized structure in metal parts lies in the fact that, to give metal parts a grain pattern, heat treatment is typically used to control the grain size. However, during the heat treatment process that causes the surface grains to grow, the internal grains of the metal part also grow simultaneously. This results in a decrease in the hardness and mechanical strength of the internal material, making the metal part easily deformed by external forces, thus hindering its application in the casings of 3C electronic products.

[0023] In view of this, this disclosure proposes a surface treatment method for metal parts, which can make the surface and interior of the metal parts have different grain structure and mechanical properties, so that the metal parts can have the appearance of grain pattern characteristics while taking into account mechanical strength and material hardness, thereby improving the applicability of the metal parts.

[0024] Please refer to Figures 1 to 4, where Figure 1 is a flowchart illustrating a surface treatment method 100 for a metal part 200 according to one embodiment of the present disclosure, and Figures 2 to 4 are schematic diagrams illustrating the material structure of the metal part 200 at each stage of the surface treatment process according to one embodiment of the present disclosure. When surface treating the metal part 200 using the surface treatment method 100, step 110 can be performed to provide the metal part 200 and to perform a micro-powder beading treatment process on the surface layer 210 of the metal part 200. As shown in Figure 2, the metal part 200 may include a surface layer 210 and an internal structure 220, wherein the surface layer 210 covers the internal structure 220. For example, the metal part 200 may be a metal shell and can be used in 3C electronic products. Thus, the metal part 200 not only protects the internal electronic components of the 3C electronic product but also gives the 3C electronic product a metallic appearance. For example, the material of the metal part 200 may be aluminum alloy, magnesium alloy, stainless steel, titanium alloy, bearing steel, high-speed steel, or mold steel.

[0025] When performing a micro-powder beading process on the surface layer 210 of the metal part 200, numerous micro-powder particles continuously bombard the surface layer 210 of the metal part 200. This micro-powder beading process can be performed at room temperature. As shown in Figure 3, the continuous bombardment of the micro-powder on the surface layer 210 of the metal part 200 generates significant plastic deformation, dislocation, and high residual compressive stress, resulting in the formation of a dense and compressed metallographic strengthening region 212 on the surface layer 210 of the metal part 200. In this case, the grain structure within the metallographic strengthening region 212 exhibits a non-equiaxed structure. In some embodiments, the depth D of the formed metallographic strengthening region 212 can be controlled between 5 micrometers and 50 micrometers during the micro-powder beading process.

[0026] The extensive plastic deformation, differential arrangement, and high residual compressive stress generated in the surface layer 210 of the metal part 200 cause the recrystallization temperature of the surface layer 210 to decrease. However, the internal structure 220, shielded by the surface layer 210, is not bombarded by the microparticles, thus its recrystallization temperature remains at its original level. Therefore, the recrystallization temperature of the metallographic strengthening region 212 is lower than the recrystallization temperature of the internal structure 220 of the metal part 200.

[0027] For example, the recrystallization temperature of the metallographic strengthening region 212 can be 50°C to 200°C lower than the recrystallization temperature of the internal structure 220. In some embodiments, the recrystallization temperature of the metallographic strengthening region 212 is 50°C to 100°C lower than the recrystallization temperature of the internal structure 220. A recrystallization temperature 50°C or more lower than the recrystallization temperature of the internal structure 220 allows for a larger process window for subsequent heat treatment processes, which is beneficial for the heat treatment process.

[0028] In some embodiments, the material of the micropowder is alloy steel or ceramic, i.e., the micropowder is alloy steel micropowder or ceramic micropowder. Furthermore, the micropowder is micron-sized. For example, the particle size of the micropowder can be from 0.01 mm to 0.5 mm. Moreover, the hardness of the micropowder can be from HV1000 to HV2700. In some embodiments, a spray gun is used to perform a micropowder beading process on the metal part 200. Specifically, the spray gun can be fluidly connected to a high-pressure gas source, and pressure is applied to the micropowder through the high-pressure gas provided by the high-pressure gas source. By spraying the micropowder towards the metal part 200 through the spray gun, the micropowder impacts the surface 210 of the metal part 200. For example, the pressure applied to the micropowder by the spray gun can be from 2 bar to 6 bar, causing the micropowder to impact the metal part 200 at high speed. In some embodiments, the spray gun sprays these micropowders towards the surface 210 of the metal part 200 at an incident angle. This incident angle can be, for example, from 20 degrees to 85 degrees. In some embodiments, the incident angle is 20 to 60 degrees.

[0029] After the micronized beading treatment of the surface layer 210 of the metal part 200 is completed, step 120 can be performed to conduct a heat treatment process on the metal part 200. For example, the metal part 200 after micronized beading treatment can be placed in a heat treatment furnace to conduct a heat treatment process. The heat treatment temperature is controlled to be equal to or greater than the recrystallization temperature of the metallographic strengthening zone 212 and less than the recrystallization temperature of the internal structure 220. In some embodiments, the heat treatment temperature is 150 degrees to 650 degrees. The heat treatment temperature can be adjusted according to the material of the metal part 200, which is not limited to this disclosure. During the heat treatment process, since the heat treatment temperature exceeds the recrystallization temperature of the grains in the metallographic strengthening zone 212, the grains in the metallographic strengthening zone 212 will recrystallize and grow. Therefore, this heat treatment process can also be called the recrystallization treatment process of the metallographic strengthening zone 212 of the metal part 200.

[0030] On the other hand, since the heat treatment temperature is lower than the recrystallization temperature of the internal structure 220, the grains in the internal structure 220 will not recrystallize or grow, and the material structure and grain size of the internal structure 220 will not be affected by the heat treatment process. Thus, after the heat treatment process, the internal structure 220 of the metal part 200 can maintain its original material hardness and mechanical strength. Therefore, the application of surface treatment method 100 allows the surface layer 210 and the internal structure 220 of the metal part 200 to possess different grain structure morphologies and mechanical properties.

[0031] As shown in Figure 4, in some embodiments, during the heat treatment process, the grains in the metallographic strengthening region 212 undergo recrystallization and growth, transforming the metallographic strengthening region 212 into a recrystallized equiaxed grain structure region 214. As can be seen from Figure 4, the grain structure in the recrystallized equiaxed grain structure region 214 exhibits a substantially equiaxed structure, i.e., a near-circular structure. In some embodiments, the hardness of the recrystallized equiaxed grain structure region 214 is HRC28 to HRC68.

[0032] During the heat treatment process, the grain size in the surface layer 210 can be adjusted by controlling the heat treatment temperature and time. As the heat treatment temperature increases, the grain size in the surface layer 210 increases. In addition, as the heat treatment time increases, the grain size in the surface layer 210 also increases.

[0033] After the heat treatment process, the surface of the metal part 200 can be ground or polished first, and then the surface of the metal part 200 can be etched to make the surface of the metal part 200 exhibit grain pattern characteristics.

[0034] Surface treatment method 100 utilizes a combination of micro-powder beading treatment and heat treatment to effectively control the grain structure pattern of the surface layer 210 of the metal part 200 and the mechanical properties of the material in the internal structure 220. This improves the applicability of the metal part 200 in 3C electronic products. Furthermore, both the micro-powder beading treatment and heat treatment processes can be applied to complex curved and planar workpieces, thus surface treatment method 100 has excellent applicability.

[0035] After undergoing the micro-powder beading treatment, the surface energy of the metal part 200 is improved, thereby enhancing the adhesion of the coating on the metal part 200. This is beneficial for the coating of the antibacterial film. Furthermore, the micro-powder beading treatment can release tensile stress on the surface of the metal part 200 and impart compressive residual stress, thereby inhibiting the formation of stress corrosion cracks in the metal part 200.

[0036] As can be seen from the above embodiments, the embodiments disclosed herein first subject the metal part to a micro-powder beading process to lower the recrystallization temperature of the surface layer of the metal part, thereby creating a temperature difference between the recrystallization temperature of the surface layer and the internal structure of the metal part. Then, a heat treatment process is performed on the metal part at a heat treatment temperature equal to or higher than the recrystallization temperature of the surface layer, but lower than the recrystallization temperature of the internal structure. Therefore, during the heat treatment process, recrystallization and grain growth only occur on the surface layer of the metal part, while the microstructure and grain size of the internal structure of the metal part are maintained. Thus, the surface treatment method disclosed herein can form a uniform coarse-grained recrystallized microstructure on the surface of the metal part while taking into account the mechanical properties of the internal structure, thereby significantly improving the applicability of the metal part.

[0037] Although this disclosure has been shown above by way of embodiments, it is not intended to limit this disclosure. Anyone with ordinary knowledge in this art can make various modifications and refinements without departing from the spirit and scope of this disclosure. Therefore, the scope of protection of this disclosure shall be determined by the appended claims.

[0038] 100: Surface treatment methods 110: Steps 120: Steps 200: Metal parts 210: Surface 212: Metallographic reinforcement zone 214: Recrystallized equiaxed grain structure region 220: Internal Structure D: Depth

[0039] Domestic storage information (please note in order of storage institution, date, and number) none Overseas storage information (please note in the order of storage country, institution, date, and number) none

Claims

1. A surface treatment method for a metal part, comprising: performing a micro-powder beading process on a surface layer of a metal part to form a metallographic strengthening region on the surface layer of the metal part, wherein the recrystallization temperature of the metallographic strengthening region is lower than the recrystallization temperature of an internal structure of the metal part, and the surface layer covers the internal structure; and performing a heat treatment process on the metal part, wherein the heat treatment temperature of the heat treatment process is equal to or greater than the recrystallization temperature of the metallographic strengthening region and less than the recrystallization temperature of the internal structure.

2. The surface treatment method for a metal part as described in claim 1, wherein the micro-powder beading process comprises continuously impacting the surface layer of the metal part with a plurality of micro-powders, the micro-powders being made of alloy steel or ceramic and having a particle size of 0.01 mm to 0.5 mm.

3. The surface treatment method for metal parts as described in claim 2, wherein one of the micro powders has a hardness of HV1000 to HV2700.

4. The surface treatment method for a metal part as described in claim 2, wherein performing the micropowder beading process includes applying pressure to the micropowder using a spray gun to cause the micropowder to impact the surface of the metal part, the pressure being 2 bar to 6 bar.

5. The surface treatment method for a metal part as described in claim 4, wherein the spray gun sprays the fine powder toward the surface at an incident angle of 20 to 85 degrees.

6. The surface treatment method for a metal part as described in claim 4, wherein the depth of one of the metallographic strengthening zones is 5 micrometers to 50 micrometers.

7. The surface treatment method for a metal part as described in claim 1, wherein the material of the metal part is aluminum alloy, magnesium alloy, stainless steel, titanium alloy, bearing steel, high-speed steel, or mold steel.

8. A surface treatment method for a metal part as described in claim 1, wherein the heat treatment process includes transforming the metallographic strengthening zone into a recrystallized equiaxed grain structure zone.

9. The surface treatment method for a metal part as described in claim 8, wherein the hardness of one of the recrystallized equiaxed grain structure regions is HRC28 to HRC68.

10. A surface treatment method for a metal part as described in claim 1, wherein the heat treatment temperature is between 150 degrees and 650 degrees.

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