Preparation method of mirror surface aluminum material, mirror surface aluminum material and application

Abstract

The invention provides a preparation method of a mirror surface aluminum material, the mirror surface aluminum material and application. The preparation method comprises the steps that an aluminum ingot is sequentially subjected to smelting, semi-continuous casting, homogenizing heat treatment, hot rolling, pre-annealing, cold rolling, mirror rolling and finished product annealing, and the mirror aluminum material is obtained. Wherein in the pre-annealing step, the annealing temperature is 270-290 DEG C, and the heat preservation time is 3-8 hours. According to the method, the three links of pre-annealing, cold rolling and mirror surface rolling are tightly connected, so that effective accumulation of cold deformation energy is achieved, and the distribution uniformity of the cubic texture in the mirror surface aluminum material is effectively improved. The mirror surface aluminum material prepared through the preparation method has high glossiness, high strength and good oxidation resistance, material lines are not likely to appear after anodic oxidation of the mirror surface aluminum material, and film cracking of an oxidation film obtained through anodic oxidation after electrophoresis can be effectively inhibited.

Description

Technical Field

[0001] This application relates to the field of aluminum alloy processing technology, and more specifically, to a method for preparing mirror aluminum material, the mirror aluminum material itself, and its applications. Background Technology

[0002] In modern automotive manufacturing, mirror-finish aluminum, due to its unique high gloss and excellent corrosion resistance, has become an indispensable material for high-end automotive interior and exterior components. Among them, 1-series mirror-finish aluminum is made from 1-series aluminum alloys (i.e., industrial pure aluminum, with an aluminum content ≥99%) as the base material, possessing good formability, weldability, and corrosion resistance. With the rapid development of the automotive industry, the demand for mirror-finish aluminum has increased dramatically, especially in the high-end automotive sector, where the quality requirements for mirror-finish aluminum are even more stringent.

[0003] However, existing manufacturing processes for 1-series mirror aluminum materials have several problems, making it difficult to meet the experimental standards for automotive mirror aluminum materials. First, anodizing is a common metal surface treatment process that improves the corrosion resistance and wear resistance of materials while giving products an aesthetically pleasing appearance. Existing mirror aluminum products often exhibit surface defects such as grain lines after anodizing, severely impacting the product's appearance and yield. Second, imported mirror aluminum materials can successfully produce oxide films with a thickness exceeding 13μm after anodizing and maintain film integrity after electrophoretic sealing. However, when the oxide film thickness of mirror aluminum materials exceeds 13μm, cracks easily appear in the oxide film after electrophoresis, which not only affects the material's appearance but also reduces its protective performance and service life.

[0004] In-depth research revealed that the formation of grain lines is closely related to the aggregation and distribution of cubic textures on the surface of mirror-finish aluminum materials. Cube texture is a specific crystal orientation; its uneven distribution on the alloy surface accelerates the corrosion rate in this area during anodizing, creating a roughness difference compared to the surrounding normal area, thus forming a visible color difference, the so-called grain line defect. Furthermore, the uneven distribution of cube texture also leads to uneven oxide film thickness in mirror-finish aluminum materials, resulting in uneven stress distribution. This uneven stress distribution causes stress concentration, which in turn induces cracks in the oxide film during electrophoresis. Therefore, controlling the uniform distribution of cube texture is crucial for improving the quality of finished mirror-finish aluminum materials after anodizing and electrophoresis.

[0005] Based on the above, how to further optimize the processing technology in the preparation of 1-series mirror aluminum materials, reduce the proportion of cube texture in mirror aluminum materials, achieve its discrete and uniform distribution on the material surface, and at the same time solve the problem that oxide films with a thickness of more than 13μm are prone to cracking after electrophoresis, so as to improve the finished product quality and overall performance of mirror aluminum materials after anodizing and electrophoresis treatment, and meet the growing high-quality demand of high-end automotive manufacturing for mirror aluminum materials, has become an urgent problem to be solved. Summary of the Invention

[0006] The main objective of this application is to provide a method for preparing mirror aluminum materials, mirror aluminum materials, and their applications, in order to solve the problems of high proportion and uneven distribution of cube texture in existing mirror aluminum materials, as well as the resulting problems of easy appearance of material marks on the oxide film after anodizing and easy film cracking after electrophoresis. The aim is to improve the finished product quality and overall performance of mirror aluminum materials after anodizing and electrophoresis, so as to meet the growing high-quality demand of the high-end automobile manufacturing industry for mirror aluminum materials.

[0007] To achieve the above objectives, this application provides a method for preparing mirror-finish aluminum material, which includes: sequentially performing melting and semi-continuous casting, homogenization heat treatment, hot rolling, pre-annealing, cold rolling, mirror rolling, and finished product annealing on aluminum ingots to obtain mirror-finish aluminum material; wherein the annealing temperature in the pre-annealing step is 270-290℃, and the holding time is 3-8h.

[0008] Furthermore, in the hot rolling step, the initial hot rolling temperature is 440–480°C, and the final hot rolling temperature is 250–270°C; preferably, the initial hot rolling temperature is 460–480°C, and the final hot rolling temperature is 250–260°C.

[0009] Furthermore, in the hot rolling step, the maximum deformation per pass is ≥50%, preferably 55-65%; the thickness of the hot-rolled plate obtained in the hot rolling step is 4-6 mm.

[0010] Furthermore, the homogenization heat treatment temperature is 500–530℃, and the holding time is 4–8 hours.

[0011] Furthermore, the annealing temperature in the finished product annealing step is 270–300℃, and the holding time is 6–8 hours.

[0012] Furthermore, the total deformation in the cold rolling step is 60-80%, preferably 60-70%.

[0013] Furthermore, the number of rolling passes in the mirror rolling step is 3 to 5, and the deformation amount in each pass is ≤10%.

[0014] Furthermore, by weight percentage, the aluminum ingot comprises: Al ≥ 99.5%, Mg ≤ 0.01%, Fe 0.08~0.13%, Cu ≤ 0.01%, Si 0.06~0.12%, and the total content of other impurity elements ≤ 0.04%.

[0015] To achieve the above objectives, another aspect of this application provides a mirror aluminum material, which is prepared using the preparation method of the mirror aluminum material provided in this application.

[0016] Furthermore, the average grain size of the mirror aluminum material is 100–140 μm; the area ratio of cubic texture in the cross-section of the mirror aluminum material is 0.2–5%.

[0017] Furthermore, the gloss of the mirror aluminum material is ≥700GU; the tensile strength of the mirror aluminum material is ≥120MPa, the yield strength is ≥80MPa, and the elongation is ≥16%.

[0018] Another aspect of this application provides an application of the above-mentioned mirror aluminum material, which is used in the field of automotive mirror aluminum.

[0019] The fourth aspect of this application also provides a mirror aluminum for automobiles, which is obtained by sequentially polishing, stamping, anodizing and electrophoresis of the aforementioned mirror aluminum material provided in this application.

[0020] Furthermore, the thickness of automotive mirror aluminum is 13–16 μm.

[0021] By applying the technical solution of this application, the three steps of pre-annealing, cold rolling, and mirror rolling are closely linked to achieve effective accumulation of cold deformation energy, thereby optimizing the distribution of cubic texture in mirror aluminum materials. Compared with the process of alternating cold rolling and annealing, this application performs a pre-annealing step after the hot rolling step. On the one hand, this releases the stress and deformation energy generated in the hot rolling step, making it easier to deform in the subsequent cold rolling step. On the other hand, the continuous cold working process after the pre-annealing step (cold rolling step and mirror rolling step) maximizes the accumulation of cold deformation energy, promoting the formation of a finer and more uniformly distributed cube texture and reducing the proportion of cube texture. The finished product annealing step after continuous cold working allows the finished product to be annealed at a lower temperature. This not only reduces energy consumption but also inhibits recrystallization inside the material to a certain extent, thereby further controlling the uniform distribution of cube texture and ensuring that the final product has high gloss, high strength, and good oxidation resistance.

[0022] The mirror aluminum material prepared by the above-mentioned preparation method of this application has a low proportion of cube texture, which can be evenly distributed on the surface of the mirror aluminum material. Furthermore, the prepared mirror aluminum material is not prone to material lines after anodizing, and can effectively inhibit the film cracking of the oxide film after electrophoresis, which significantly improves the aesthetics and durability of the mirror aluminum material and meets the stringent requirements of the automotive industry for high-performance mirror aluminum products. Attached Figure Description

[0023] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0024] Figure 1 The grain diagram of the mirror aluminum material obtained in Example 1 of this application is shown;

[0025] Figure 2 The diagram shows the cubic texture distribution in the mirror aluminum material obtained in Example 1 of this application;

[0026] Figure 3 The grain diagram of the mirror aluminum material prepared in Comparative Example 1 of this application is shown;

[0027] Figure 4 The cubic texture distribution in the mirror aluminum material prepared in Comparative Example 1 of this application is shown. Detailed Implementation

[0028] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0029] As described in the background section, existing mirror aluminum materials often exhibit surface defects such as grain lines after anodizing, severely impacting product aesthetics and yield. Furthermore, domestically produced mirror aluminum materials with oxide film thicknesses exceeding 13μm are prone to film cracking after electrophoresis, affecting not only aesthetics but also reducing protective performance and lifespan. These problems significantly hinder the further development of domestic automotive mirror aluminum. In-depth research has revealed that grain lines are closely related to the aggregation and distribution of cubic textures on the surface of mirror aluminum materials. Therefore, optimizing the processing technology in mirror aluminum material preparation to effectively reduce the proportion of cube textures, achieve their discrete and uniform distribution on the surface, and simultaneously solve the problem of film cracking after electrophoresis for oxide films thicker than 13μm, in order to meet the growing high-quality demands of the high-end automotive manufacturing industry for mirror aluminum materials, has become an urgent problem to be solved.

[0030] To address the aforementioned issues, this application provides a method for preparing mirror-finish aluminum material. The method includes: sequentially performing melting and semi-continuous casting, homogenization heat treatment, hot rolling, pre-annealing, cold rolling, mirror rolling, and finished product annealing on an aluminum ingot to obtain mirror-finish aluminum material; wherein the annealing temperature in the pre-annealing step is 270–290°C, and the holding time is 3–8 hours.

[0031] The method for preparing the mirror-finish aluminum material provided in this application includes a pre-annealing step after the hot rolling step and a mirror rolling step directly after the cold rolling step. This adjustment in the process sequence effectively accumulates the cold deformation energy of the mirror-finish aluminum material, thereby effectively reducing the content of cubic texture and optimizing its distribution. This results in a final mirror-finish aluminum material with high gloss, high strength, and good oxidation resistance, perfectly addressing the urgent need for high-performance mirror-finish aluminum products. Furthermore, the method exhibits high stability in practical applications, and the performance of the mirror-finish aluminum material is not prone to significant fluctuations due to different batches. The reasons for these excellent effects are speculated to include the following:

[0032] First, the process design of this application breaks through the limitations of traditional mirror aluminum preparation processes. A pre-annealing step is performed after the hot rolling step, followed by a cold rolling step and a mirror rolling step. This adjustment in the processing technology maximizes the cumulative cold deformation amount and effectively reduces the proportion of cube texture in the mirror aluminum material through continuous cold working processes (cold rolling and mirror rolling). In particular, compared with the conventional process of cold rolling followed by annealing and finally mirror rolling, the preparation process provided in this application adjusts the pre-annealing step to be performed before the cold rolling step, thereby concentrating the cold working processes (i.e., cold rolling and mirror rolling). This reduces the problem of waiting for intermediate annealing scheduling due to interruptions in the cold working process during actual production, significantly improving production efficiency. Simultaneously, it can better reduce the proportion of cube texture in the mirror aluminum material and further optimize the distribution of cube texture, resulting in better performance of the prepared mirror aluminum material.

[0033] Secondly, the pre-annealing step following the hot rolling step not only increases the accumulation of cold deformation before the finished product annealing step, but also avoids the work hardening problem caused by excessive stress in direct cold rolling. Although work hardening can improve the strength of mirror aluminum materials to some extent, it also makes subsequent rolling extremely difficult, and the increased accumulated elastic strain energy leads to a narrow annealing process window, which not only seriously affects the stability of production batches, but also prevents the stress from being fully released, thus inducing film cracking during subsequent electrophoresis. The pre-annealing step in this application can fully release the energy accumulated in the hot rolling step, so that the material obtained in the pre-annealing step is in the optimal state for cold rolling, which not only ensures the smooth progress of processing, but also accumulates sufficient cold deformation energy, creating favorable conditions for subsequent mirror rolling.

[0034] Furthermore, this application effectively accumulates the cold deformation energy of the material by closely linking the three stages of pre-annealing, cold rolling, and mirror rolling. This balances the release and accumulation of energy stored within the material, providing a foundation for subsequent finished product annealing. In addition, in conventional processes, cold-rolled materials need to be heated from room temperature to the annealing temperature for annealing, a process that consumes significant energy. However, the process design of this application selects to directly perform the pre-annealing step at the high temperature after hot rolling, greatly shortening the annealing heating time and achieving the goal of energy conservation and emission reduction. More importantly, performing the pre-annealing step after hot rolling allows the material to cool and soften to a certain extent, effectively releasing the stress and deformation energy generated during the hot rolling process, making it easier to deform in the subsequent cold rolling step. Performing the finished product annealing step after continuous cold working allows the annealing process to be carried out at a lower temperature, which not only reduces energy consumption but also inhibits recrystallization within the material to a certain extent. The result is that the cube texture in the mirror aluminum material is kept small and discretely distributed, which not only improves the gloss and mechanical properties of the material, but also significantly reduces the probability of texture marks appearing after anodizing.

[0035] Compared to other ranges, limiting the annealing temperature and holding time in the pre-annealing step to the above-mentioned specific range can fully release the energy accumulated in the hot rolling step, thereby allowing the material obtained in the pre-annealing step to be cold rolled in the best condition, which is convenient for subsequent preparation processes. At the same time, the pre-annealing temperature specified in this application is lower than the recrystallization temperature of the grains, which can effectively suppress the recrystallization of the material in the pre-annealing step, thereby reducing the proportion of cube texture, promoting the uniform distribution of cube texture, and thus improving the gloss and mechanical strength of the obtained mirror aluminum material.

[0036] In summary, this application achieves effective accumulation of cold deformation energy through the combination of pre-annealing and cold rolling, thereby optimizing the distribution of the cube texture. At the same time, by using a finished product annealing step below the recrystallization temperature, not only is energy consumption reduced, but the final product also has high gloss, high strength and good oxidation resistance. The above-mentioned mirror aluminum material is not prone to material lines after anodizing and can effectively inhibit the film cracking of the oxide film after electrophoresis, significantly improving the aesthetics and durability of the mirror aluminum material, and meeting the stringent requirements of the automotive industry for high-performance mirror aluminum products.

[0037] In a preferred embodiment, the initial hot rolling temperature is 440–480°C, and the final hot rolling temperature is 250–270°C. Compared to other ranges, limiting the initial and final hot rolling temperatures to these ranges helps to suppress dynamic recrystallization of the material during hot rolling, inhibits abnormal grain growth, and reduces the formation of cube texture, thereby improving the gloss and mechanical strength of the resulting mirror-finish aluminum material. It should be noted that the relatively low initial and final hot rolling temperatures in this application result in a higher accumulation of elastic strain energy in the hot-rolled sheet. Therefore, after the hot rolling step, a pre-annealing step is required at the specific temperatures specified in this application to fully release the stored energy. This allows the material obtained from the pre-annealing step to be cold-rolled in its optimal state, further reducing the proportion of cube texture, promoting a uniform distribution of cube texture, and improving the gloss and mechanical strength of the resulting mirror-finish aluminum material.

[0038] In order to further suppress dynamic recrystallization of the material during hot rolling, suppress abnormal grain growth, further reduce the formation of cube texture, and thus further improve the gloss and mechanical strength of the obtained mirror aluminum material, preferably, the hot rolling start temperature is 460-480℃ and the hot rolling finish temperature is 250-260℃.

[0039] In order to promote grain refinement, further reduce the proportion of cube texture, promote uniform distribution of cube texture, and at the same time, in order to control the total deformation of the subsequent cold rolling step within a more suitable range and facilitate the finished product roll-out step, in a preferred embodiment, the maximum deformation per pass in the hot rolling step is ≥50%; the thickness of the hot-rolled plate obtained by the hot rolling step is 4-6 mm.

[0040] To further promote grain refinement, further reduce the proportion of cube texture, and promote its uniform distribution, and to control the total deformation of the subsequent cold rolling step within a more suitable range, preferably, the maximum deformation per pass in the hot rolling step is 55-65%.

[0041] In a preferred embodiment, the homogenization heat treatment temperature is 500–530°C, and the holding time is 4–8 hours. The temperature and time of the homogenization heat treatment include, but are not limited to, the above range. Limiting them to the above range is beneficial to promote the full diffusion of solute atoms in the aluminum ingot, eliminate the component segregation formed during the casting process, and thus improve the thermal stability and processing performance of the material.

[0042] In a preferred embodiment, the annealing temperature in the finished product annealing step is 270–300°C, and the holding time is 6–8 hours. Compared to other ranges, limiting the annealing temperature and holding time in the finished product annealing step to the above range is beneficial to promoting slight recrystallization of some grains and inhibiting excessive recrystallization. Extending the holding time is beneficial to fully releasing the deformation energy accumulated in the cold rolling and mirror rolling steps, thereby improving the uniformity of the cube texture distribution, improving the surface quality and mechanical strength of the obtained mirror aluminum material, and further helping to suppress the appearance of material marks on the mirror aluminum material after anodizing and suppressing the film cracking of the oxide film obtained by anodizing during electrophoresis.

[0043] In a preferred embodiment, the total deformation in the cold rolling step is 60-80%. The total deformation in the cold rolling step includes, but is not limited to, the above range. Limiting it to the above range helps to eliminate the cube texture formed by dynamic recrystallization in the hot rolling step, thereby reducing the proportion of cube texture and improving the uniformity of cube texture distribution, which in turn helps to improve the surface quality and mechanical strength of the obtained mirror aluminum material.

[0044] In order to further eliminate the cube texture formed by dynamic recrystallization in the hot rolling step, further reduce the proportion of cube texture, and improve the uniformity of cube texture distribution, thereby further improving the surface quality and mechanical strength of the obtained mirror aluminum material, preferably, the total deformation in the cold rolling step is 60-70%.

[0045] In a preferred embodiment, the mirror rolling step involves 3 to 5 rolling passes, with a deformation of ≤10% per pass. The number of rolling passes and the deformation per pass in the mirror rolling step include, but are not limited to, the above range. Limiting them to the above range is beneficial for improving the gloss and surface quality of the obtained mirror aluminum material.

[0046] In order to further improve the microstructure of mirror aluminum material and further enhance its gloss and mechanical strength, in a preferred embodiment, the aluminum ingot comprises, by weight percentage: Al≥99.5%, Mg≤0.01%, Fe 0.08~0.13%, Cu≤0.01%, Si 0.06~0.12%, and the total content of other impurity elements≤0.04%.

[0047] The second aspect of this application also provides a mirror-finish aluminum material, which is prepared using the method described above. The method described above effectively reduces the proportion of cube texture, promotes uniform distribution of cube texture, and results in a mirror-finish aluminum material with higher gloss, higher mechanical strength, and good oxidation resistance. Furthermore, the mirror-finish aluminum material provided above is less prone to surface marks after anodizing and effectively inhibits film cracking after electrophoresis, significantly improving the aesthetics and durability of the mirror-finish aluminum material and meeting the stringent requirements of the automotive industry for high-performance mirror-finish aluminum products. In addition, the above preparation method ensures stable performance of the prepared mirror-finish aluminum material during practical applications, preventing significant performance fluctuations due to batch differences.

[0048] It should be noted that, due to the special nature of mirror aluminum materials and the limitations of existing testing and characterization methods, it is difficult to comprehensively and quantitatively characterize the complex microstructure of the mirror aluminum materials obtained above. However, experiments show that the proportion of cube texture in the mirror aluminum materials prepared by the above-mentioned mirror aluminum preparation method provided in this application is low and it is evenly distributed on the surface of the mirror aluminum materials. This makes the mirror aluminum materials obtained above-mentioned in this application have higher gloss, higher mechanical strength, better plastic deformation ability and good oxidation resistance.

[0049] In a preferred embodiment, the average grain size of the mirror-finish aluminum material is 100–140 μm, and the area ratio of the cubic texture in the cross-section of the mirror-finish aluminum material is 0.2–5%. It should be noted that the average grain size of the mirror-finish aluminum material in this application refers to the average size of all grains in the microstructure of the mirror-finish aluminum material. Compared to other ranges, limiting the average grain size and the area ratio of the cubic texture of the mirror-finish aluminum material to the above ranges is beneficial to improving the surface quality and mechanical strength of the obtained mirror-finish aluminum material.

[0050] The mirror-finish aluminum material provided in this application has higher gloss, tensile strength, yield strength, and elongation, which can meet the higher standards of use required in the field. In a preferred embodiment, the gloss of the mirror-finish aluminum material is ≥700 GU; the tensile strength of the mirror-finish aluminum material is ≥120 MPa, the yield strength is ≥80 MPa, and the elongation is ≥16%.

[0051] It should be noted that the gloss of the above-mentioned mirror aluminum material was measured using a gloss meter according to the method described in ASTM D523 "Standard Test Method for Specular Gloss"; the tensile strength, yield strength and elongation were measured using a tensile testing machine with a maximum load of 10T according to the method described in the national standard GB / T 228.1-2021 "Metallic Materials - Tensile Testing - Part 1: Test Method at Room Temperature".

[0052] A third aspect of this application also provides an application of the aforementioned mirror aluminum material, specifically its use in the automotive mirror aluminum field. The mirror aluminum material provided in this application exhibits a low proportion of cube texture, which is uniformly distributed across its surface. Furthermore, the mirror aluminum material is less prone to surface defects after anodizing and effectively inhibits film cracking after electrophoresis, thereby significantly improving its aesthetics and durability. Applying it to the automotive mirror aluminum field meets the stringent requirements of the automotive industry for high-performance mirror aluminum products.

[0053] The fourth aspect of this application also provides a mirror aluminum for automobiles, which is obtained by sequentially polishing, stamping, anodizing, and electrophoresis of the mirror aluminum material provided in this application; preferably, the thickness of the mirror aluminum for automobiles is 13-16 μm. The mirror aluminum material provided in this application has a low proportion of cube texture and is uniformly distributed on the surface of the mirror aluminum material. Furthermore, the mirror aluminum material is not prone to material lines after anodizing and can effectively suppress film cracking of the oxide film obtained by anodizing after electrophoresis. It is very suitable for preparing mirror aluminum for automobiles with a thickness exceeding 13 μm. Even if the thickness of the mirror aluminum for automobiles exceeds 13 μm, cracking will not occur, effectively improving the flatness, gloss, and mechanical strength of the mirror aluminum for automobiles. The resulting mirror aluminum for automobiles is suitable for application scenarios with higher standards.

[0054] It should be noted that when preparing the above-mentioned automotive mirror aluminum of this application, the process parameters for polishing, stamping, anodizing and electrophoresis steps can be selected from commonly used process parameters in the field, and all can achieve the above-mentioned technical effects of this application.

[0055] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0056] Example 1

[0057] A method for preparing mirror-finish aluminum material specifically includes the following steps:

[0058] (1) Smelting and semi-continuous casting: The aluminum ingot is smelted and semi-continuously cast in sequence to obtain an ingot with a thickness of 460 mm; the smelting temperature is 800℃, the semi-continuous casting temperature is 750℃, and the casting speed is controlled between 45 and 55 mm / min; by weight percentage, the aluminum ingot includes: Al 99.708 wt%, Mg 0.001 wt%, Fe 0.13 wt%, Cu 0.001 wt%, Si 0.12 wt%, and the total content of other impurity elements is 0.04 wt%;

[0059] (2) Homogenization heat treatment: The ingot obtained in step (1) is subjected to homogenization heat treatment at a temperature of 530℃ and a holding time of 4h to obtain heat-treated plate.

[0060] (3) Hot rolling step: The heat-treated plate obtained in step (2) is hot rolled to obtain a hot-rolled plate with a thickness of 4 mm; wherein, the initial hot rolling temperature is 440℃, the final hot rolling temperature is 250℃, and the maximum deformation per pass is 65%;

[0061] (4) Pre-annealing step: The hot-rolled plate obtained in step (3) is pre-annealed at a temperature of 270°C and a holding time of 8h to obtain the annealed material;

[0062] (5) Cold rolling step: The annealed material obtained in step (4) is cold rolled to obtain a cold-rolled plate with a thickness of 1.2 mm. The total deformation of the cold rolling step is 60%.

[0063] (6) Mirror rolling step: The cold-rolled sheet obtained in step (5) is mirror rolled, with 3 rolling passes and 9% deformation per pass, to obtain the mirror-rolled sheet.

[0064] (7) Finished product annealing step: The mirror-finished rolled sheet obtained in step (6) is subjected to finished product annealing. The temperature of finished product annealing is 270℃ and the holding time is 6h to obtain mirror-finished aluminum material.

[0065] Figure 1 The grain pattern of the mirror-finish aluminum material prepared in Example 1 is shown, obtained using a scanning electron microscope; from Figure 1 It can be seen that the mirror aluminum material includes large-sized grains and small-sized grains. The large-sized grains are formed by the elongation of large-sized grains inherited from the hot-rolled plate after cold rolling and finished product annealing. The small-sized grains are recrystallized grains generated during the finished product annealing process. The small-sized grains are the main source of the cube texture in the mirror aluminum material. The above-mentioned grain distribution can effectively reduce the recrystallization structure caused by excessively high hot rolling temperature, and inhibit the cube texture generated during the hot rolling process from becoming a continuously distributed large-sized cube texture after finished product annealing. This suppresses the appearance of material marks after anodizing of the mirror aluminum material and improves the quality of the finished product.

[0066] Figure 2 The cubic texture distribution in the mirror-finished aluminum material prepared in Example 1 is shown, obtained using a scanning electron microscope; Figure 2 It can be seen that the proportion of Cube texture in the mirror aluminum material prepared in Example 1 is relatively low and the distribution is relatively uniform.

[0067] Example 2

[0068] The difference from Example 1 is that in step (4), the pre-annealing temperature is 290°C and the holding time is 3h; the remaining steps are the same as in Example 1.

[0069] Example 3

[0070] The difference from Example 1 is that in step (3), the hot rolling temperature is 480°C, the hot rolling temperature is 270°C, the maximum deformation per pass is 55%, and the thickness of the hot-rolled plate is 6mm; the remaining steps are the same as in Example 1.

[0071] Example 4

[0072] The difference from Example 1 is that in step (3), the hot rolling temperature is 500°C and the hot rolling temperature is 300°C, and the thickness of the hot rolled plate is 6mm; the remaining steps are the same as in Example 1.

[0073] Example 5

[0074] The difference from Example 1 is that in step (3), the maximum deformation per pass in the hot rolling step is 40%, and the thickness of the hot rolled plate is 6 mm; the remaining steps are the same as in Example 1.

[0075] Example 6

[0076] The difference from Example 1 is that in step (5), the total deformation of cold rolling is 80%, and the thickness of the cold-rolled plate is 0.6 mm; the remaining steps are the same as in Example 1.

[0077] Example 7

[0078] The difference from Example 1 is that in step (5), the total deformation of cold rolling is 50%, and the thickness of the cold-rolled plate is 1.5 mm; the remaining steps are the same as in Example 1.

[0079] Example 8

[0080] The difference from Example 1 is that in step (7), the annealing temperature of the finished product is 300°C and the holding time is 8h; the remaining steps are the same as in Example 1.

[0081] Example 9

[0082] The difference from Example 1 is that in step (7), the annealing time of the finished product is 4 hours; the other steps are the same as in Example 1.

[0083] Example 10

[0084] The difference from Example 1 is that in step (7), the annealing temperature of the finished product is 320°C; the remaining steps are the same as in Example 1.

[0085] Example 11

[0086] The difference from Example 1 is that in step (2), the homogenization heat treatment temperature is 500°C and the holding time is 8h; the remaining steps are the same as in Example 1.

[0087] Example 12

[0088] The difference from Example 1 is that in step (6), the mirror rolling step has 5 rolling passes and the deformation amount of each pass is 10%; the remaining steps are the same as in Example 1.

[0089] Comparative Example 1

[0090] The difference from Example 1 is that step (4) is omitted, and the hot-rolled plate obtained in step (3) is directly cold-rolled, and then intermediate annealing is carried out at 320°C for 2 hours. After intermediate annealing, mirror rolling is carried out; the remaining steps are the same as in Example 1.

[0091] Figure 3 The grain pattern of the mirror-finished aluminum material prepared in Comparative Example 1 is shown, obtained using a scanning electron microscope; from Figure 3 It can be seen that due to the large amount of recrystallization generated during the intermediate annealing process in Comparative Example 1, these grains were elongated in the subsequent cold rolling, forming uniformly distributed long fibrous crystals. Furthermore, the cube texture generated during the intermediate annealing process was inherited and continuously elongated and grew in the subsequent preparation process, forming a continuously distributed large-size cube texture. This resulted in a decrease in the gloss of the mirror aluminum material, a large number of material marks after anodizing, and because the oxide film structure generated by the cube texture is loose, it is more likely to crack after electrophoresis.

[0092] Figure 4 The cubic texture distribution in the mirror-finished aluminum material prepared in Comparative Example 1 is shown, obtained using a scanning electron microscope; Figure 4 It can be seen that the mirror aluminum material prepared in Comparative Example 1 has a large content of cube texture and is clustered, which will cause the mirror aluminum material to have texture lines after subsequent anodizing and will cause the oxide film to crack during electrophoresis.

[0093] Comparative Example 2

[0094] The difference from Example 1 is that in step (4), the pre-annealing temperature is 250°C; the remaining steps are the same as in Example 1.

[0095] Comparative Example 3

[0096] The difference from Example 1 is that in step (4), the pre-annealing temperature is 330°C; the remaining steps are the same as in Example 1.

[0097] Comparative Example 4

[0098] The difference from Example 1 is that in step (4), the heat preservation time for pre-annealing is 1 hour; the remaining steps are the same as in Example 1.

[0099] Comparative Example 5

[0100] The difference from Example 1 is that in step (4), the pre-annealing temperature is 290°C and the holding time is 10h; the remaining steps are the same as in Example 1.

[0101] Application Examples

[0102] A mirror-finish aluminum for automotive applications is prepared by the following method: the mirror-finish aluminum material is sequentially polished, stamped, anodized, and electrophoretically coated to obtain a mirror-finish aluminum for automotive applications with a thickness of 13 μm; wherein, the mirror-finish aluminum material is the mirror-finish aluminum material prepared in Examples 1 to 12 and Comparative Examples 1 to 5 of this application; the anodizing conditions are: at 15°C, using 180 g / L H2SO4 as the electrolyte, and using a constant voltage of 15 V for anodizing; the electrophoresis conditions are: using black cathode epoxy electrophoresis, the solid content of the electrophoresis solution is 10 wt%, the electrophoresis temperature is 28°C, the voltage is 100 V, the time is 2 min, the curing temperature is 180°C, and the holding time is 30 min.

[0103] The mirror-finished aluminum materials obtained from all the above embodiments and comparative examples of this application were subjected to the following performance tests:

[0104] (1) Average grain size: measured according to the method described in the national standard GB / T 6394-2017 "Method for determination of average grain size of metals";

[0105] (2) Cube texture area ratio: The area ratio of the cube texture to the cross-section of the mirror aluminum material was statistically analyzed using scanning electron microscopy;

[0106] (3) Gloss: The gloss was measured using a gloss meter according to the method described in ASTM D523, "Standard Test Method for Specular Gloss".

[0107] (4) Tensile strength, yield strength and elongation: measured using a tensile testing machine with a maximum load of 10T, in accordance with the method described in the national standard GB / T 228.1-2021 "Metallic materials, tensile testing - Part 1: Test method at room temperature";

[0108] Observe all the above embodiments and comparative examples of this application during the preparation of automotive mirror aluminum, whether the mirror aluminum shows material lines after anodizing, and whether film cracks appear after electrophoresis.

[0109] The test results are shown in Table 1. It should be noted that Comparative Examples 2 and 4 have poor plastic deformation ability due to their low elongation, which makes them unable to be stamped in subsequent processes, and thus unable to undergo anodizing and electrophoresis processes.

[0110] Table 1

[0111]

[0112] As can be seen from the above description, the embodiments of this application achieve the following technical effects:

[0113] Comparing Examples 1 and 2 with Comparative Example 1, and referring to Table 1, it can be seen that the area ratio of the Cube texture in the mirror aluminum material prepared in Comparative Example 1 is relatively high, which leads to a significant decrease in its gloss and mechanical properties. At the same time, due to the uneven distribution of the Cube texture on the surface of the mirror aluminum material, it exhibits material lines after anodizing and film cracks after electrophoresis. Therefore, compared with the traditional manufacturing process of alternating cold rolling and annealing, this application performs a pre-annealing step after the hot rolling step. On the one hand, this releases the stress and deformation energy generated in the hot rolling step, making it easier to deform in the subsequent cold rolling step. On the other hand, the continuous cold working process (cold rolling step and mirror rolling step) after the pre-annealing step maximizes the accumulation of cold deformation energy, promoting the formation of a finer and more uniformly distributed cube texture, and reducing the area ratio of the cube texture. The mirror aluminum material prepared by the above-mentioned manufacturing method of this application has a lower proportion of cube texture and can be uniformly distributed on the surface of the mirror aluminum material, thereby effectively suppressing the appearance of material marks after anodizing and effectively suppressing the film cracking of the oxide film after electrophoresis, thus significantly improving the aesthetics and durability of the mirror aluminum material.

[0114] Comparing Examples 1 and 2 with Comparative Examples 2 to 5, and referring to Table 1, it can be seen that the mirror aluminum materials prepared in Examples 1 and 2 all have a low cube texture ratio, high gloss, mechanical strength, and plastic deformation capacity. No material marks appeared after anodizing, and no film cracks appeared after electrophoresis. In Comparative Example 2, due to the lower pre-annealing temperature (which is outside the range defined above in this application), the formation of cube texture was suppressed to some extent, resulting in a lower cube texture ratio in the prepared mirror aluminum material and a certain degree of improvement in the mechanical strength of the mirror aluminum material. However, the elongation of Comparative Example 2 was only 12%, indicating that the plastic deformation capacity of this mirror aluminum material was very poor, and it was prone to cracking during subsequent stamping and forming processes, rendering it unusable. Comparative Example 3, due to its excessively high pre-annealing temperature (outside the limits of the aforementioned application), promoted local recrystallization of the material during pre-annealing. This resulted in a continuous distribution of large-sized cube textures after annealing, leading to a high proportion of cube textures and a significant decrease in gloss and mechanical strength. Furthermore, the uneven distribution of cube textures on the surface of the mirror aluminum material caused grain lines after anodizing, severely impacting the quality of the finished product. Comparative Example 4, due to its excessively short pre-annealing time (outside the limits of the aforementioned application), did not provide sufficient time for grain growth. While this reduced the proportion of cube textures to some extent, it resulted in a smaller average grain size in the mirror aluminum material, significantly reducing its plastic deformation capacity. Consequently, the mirror aluminum material was highly susceptible to cracking during subsequent stamping processes, rendering it unusable. In Comparative Example 5, the pre-annealing temperature is lower than the recrystallization temperature. This prevents the formation of a cube texture during the pre-annealing process and promotes the transformation of the grain structure of the mirror aluminum material towards an increase in large-sized grains and a decrease in small-sized grains. Therefore, the proportion of cube texture in Comparative Example 5 is reduced. However, due to the excessively long pre-annealing time of Comparative Example 5 (its holding time is outside the limits of the above-mentioned application), abnormal growth of large-sized grains occurs, resulting in an excessively large average grain size. Consequently, the gloss and mechanical strength of the mirror aluminum material decrease significantly. As can be seen from the above analysis, compared with other ranges, limiting the annealing temperature and holding time in the pre-annealing step to the specific range mentioned above in this application can fully release the energy accumulated in the hot rolling step, so that the material obtained in the pre-annealing step can be cold rolled in the best state, which is convenient for subsequent preparation processes. At the same time, it can also inhibit the recrystallization of the material in the pre-annealing step, thereby reducing the proportion of cube texture, promoting the uniform distribution of cube texture, and thus improving the gloss and mechanical strength of the obtained mirror aluminum material, suppressing the appearance of material lines after anodizing, and suppressing the appearance of cracks after electrophoresis.

[0115] Comparing Examples 1, 3 to 5, and referring to Table 1, it can be seen that, compared to other ranges, limiting the hot rolling temperature, the hot finishing rolling temperature, and the maximum deformation per pass in the hot rolling process to the above-mentioned preferred ranges in this application is beneficial to suppressing dynamic recrystallization of the material during hot rolling, suppressing abnormal grain growth, thereby reducing the formation of cube texture, and further improving the gloss and mechanical strength of the obtained mirror aluminum material.

[0116] Comparing Examples 1, 6, and 7, and referring to Table 1, it can be seen that, compared to other ranges, limiting the total deformation in the cold rolling step to the above-mentioned preferred range of this application is beneficial to eliminating the cube texture formed by dynamic recrystallization in the hot rolling step, thereby reducing the proportion of cube texture, improving the uniformity of cube texture distribution, and further improving the surface quality and mechanical strength of the obtained mirror aluminum material.

[0117] Comparing Examples 1, 8 to 10, Example 9, due to its shorter annealing time (its holding time is outside the range defined above in this application), lacks sufficient time to induce recrystallization, resulting in a lower proportion of Cube texture. However, this also leads to a significant decrease in the plastic deformation capacity of the mirror aluminum material. Therefore, compared to other ranges, limiting the annealing temperature and holding time to the preferred range defined above in this application is beneficial for promoting slight recrystallization of some grains and inhibiting excessive recrystallization. Extending the holding time helps to fully release the deformation energy accumulated in the cold rolling and mirror rolling steps, thereby improving the uniformity of Cube texture distribution, enhancing the surface quality and mechanical strength of the obtained mirror aluminum material, and further suppressing the appearance of material marks after anodizing and preventing film cracking of the oxide film obtained from anodizing during electrophoresis.

[0118] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented, for example, in a sequence other than those described herein.

[0119] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing mirror-finish aluminum material, characterized in that, The preparation method includes: sequentially performing melting and semi-continuous casting, homogenization heat treatment, hot rolling, pre-annealing, cold rolling, mirror rolling, and finished product annealing on aluminum ingots to obtain the mirror aluminum material; The annealing temperature in the pre-annealing step is 270–290°C, and the holding time is 3–8 hours.

2. The method for preparing mirror-finish aluminum material according to claim 1, characterized in that, In the hot rolling step, the initial hot rolling temperature is 440–480°C, and the final hot rolling temperature is 250–270°C. Preferably, in the hot rolling step, the initial hot rolling temperature is 460–480°C, and the final hot rolling temperature is 250–260°C. Preferably, in the hot rolling step, the maximum deformation per pass is ≥50%; the thickness of the hot-rolled plate obtained by the hot rolling step is 4-6 mm; More preferably, in the hot rolling step, the maximum deformation per pass is 55-65%.

3. The method for preparing mirror-finish aluminum material according to claim 1 or 2, characterized in that, The homogenization heat treatment is performed at a temperature of 500–530°C for 4–8 hours. Preferably, the annealing temperature in the finished product annealing step is 270–300°C, and the holding time is 6–8 hours.

4. The method for preparing mirror-finish aluminum material according to any one of claims 1 to 3, characterized in that, The total deformation in the cold rolling step is 60-80%; Preferably, the total deformation in the cold rolling step is 60-70%.

5. The method for preparing mirror-finish aluminum material according to any one of claims 1 to 4, characterized in that, The mirror rolling process involves 3 to 5 rolling passes, with each pass having a deformation amount of ≤10%.

6. The method for preparing mirror-finish aluminum material according to claim 1, characterized in that, The aluminum ingot, by weight percentage, comprises: Al ≥ 99.5%, Mg ≤ 0.01%, Fe 0.08~0.13%, Cu ≤ 0.01%, Si 0.06~0.12%, and the total content of other impurity elements ≤ 0.04%.

7. A mirror-finish aluminum material, characterized in that, The mirror aluminum material is prepared by the method for preparing mirror aluminum material according to any one of claims 1 to 6.

8. The mirror-finish aluminum material according to claim 7, characterized in that, The average grain size of the mirror-finish aluminum material is 100–140 μm; the area ratio of cubic texture in the cross-section of the mirror-finish aluminum material is 0.2–5%. Preferably, the gloss of the mirror-finished aluminum material is ≥700 GU; Preferably, the mirror aluminum material has a tensile strength ≥120MPa, a yield strength ≥80MPa, and an elongation ≥16%.

9. An application of the mirror-finish aluminum material according to claim 7 or 8, characterized in that, The aforementioned mirror aluminum material is used in the field of automotive mirror aluminum.

10. A type of mirror-finish aluminum for automobiles, characterized in that, The automotive mirror aluminum is obtained by sequentially polishing, stamping, anodizing and electrophoresis of the mirror aluminum material described in claim 7 or 8. Preferably, the thickness of the automotive mirror aluminum is 13–16 μm.

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