High-formability 6xxx aluminum alloy plate capable of being anodized and preparation method of high-formability 6xxx aluminum alloy plate

Abstract

The invention relates to a high-formability anodizing 6xxx aluminum alloy plate and a preparation method thereof. The aluminum material is composed of the following components in percentage by mass: 0.2-0.6% of Si; 0.6%-1.1% of Mg; 0.01% to 0.04% of Ti; according to the preparation method disclosed by the invention, by regulating and controlling semi-continuous casting, hot rolling and cold rolling processes, the grain size of the finished aluminum alloy plate is uniform and fine, the average grain size is 20-60 microns, the surface roughness of the plate strip is 0.25-0.45 microns, the glossiness is 350-420 GU, the tensile strength is 70-90 MPa, the yield strength is 30-50 MPa, the elongation is 30-45%, and the hardness HV is 25-45; and after the plate is subjected to subsequent room-temperature stamping forming, the surface quality is excellent, the defects of scratches, orange peels, cracks and the like are avoided, and the technical requirements of high-end products on appearance decoration surfaces are met.

Description

Technical Field

[0001] The present invention belongs to the technical field of aluminum alloy materials, and in particular to a 6xxx series aluminum alloy plate with high formability and suitable for anodizing treatment and a preparation method thereof. Background Art

[0002] With the sustained and rapid development of the national economy, people not only pay attention to the internal quality of products, but also put forward higher requirements for the appearance and touch of products. In the civilian consumer market, aluminum alloy materials have become one of the materials with the largest usage and the most coverage, mainly because of its many advantages such as high strength, good plasticity and toughness, smooth and bright surface, and anodizing treatment. After anodizing treatment, a layer of oxide film with both wear resistance and corrosion resistance will be formed on the surface of aluminum. After coloring treatment, the surface of aluminum presents a variety of colors, which can enhance the artistic and technological sense of the product, and become the best choice for 3C materials, shells and other surface materials.

[0003] However, in the prior art, the aluminum material for the housing is prone to surface defects such as pitting, lines, and cracks during deep drawing, which affects the forming accuracy and appearance quality of the product. In addition, during the anodizing process, due to the non-uniformity of the surface microstructure of the aluminum alloy material, it is easy to cause uneven color of the oxide film, usually with mottled and dark colors on the surface, which affects the decorativeness and corrosion resistance of the product, and also greatly affects the surface quality of the product, resulting in scrapping, which seriously restricts the application and development of aluminum alloy in the field of surface materials. Summary of the invention

[0004] The technical purpose of the present invention is to prepare a finished aluminum alloy sheet with uniform and fine grain size, surface roughness of 0.25-0.45 μm, tensile strength of 70-90 MPa, yield strength of 30-50 MPa, elongation of 30-45%, hardness of HV25-45 and excellent comprehensive performance through adjusting the composition and ratio of alloy elements and fine control of specific operation steps and methods of semi-continuous casting, hot rolling and cold rolling in the preparation method. After subsequent room temperature stamping and anodizing treatment, the aluminum alloy sheet has uniform surface color and excellent quality without defects such as scratches, orange peel and cracks, and can better meet the technical requirements of high-end products for the appearance of decorative aluminum alloy surfaces.

[0005] To achieve the above object, the technical solution adopted by the present invention is: a method for preparing a high-formable anodized 6xxx aluminum alloy plate, comprising a smelting and semi-continuous casting step, a homogenization step, a hot rolling step, a cold rolling step and a finished product annealing step in sequence, in which the semi-continuous casting temperature is 685-705°C, the stable production speed of the ingot is 43-53 mm / min, the crystallizer cooling water temperature is 20-28°C, and the flow rate is 135-147 m / min.3 / h; in the hot rolling step, the surface roughness Ra of the roll is 1.0-1.6 μm, and the maximum reduction of a single pass is greater than 30 mm; in the cold rolling step, the surface roughness Ra of the roll is ≤0.4 μm.

[0006] Furthermore, in the smelting and semi-continuous casting steps, the aluminum alloy plate raw material used is composed of the following components in mass percentage: Si is 0.2% to 0.6%; Mg is 0.6% to 1.1%; Ti is 0.01% to 0.04%; Fe is ≤0.06%, and the remainder is Al and unavoidable impurity elements, and the content of impurity elements is ≤0.02%.

[0007] Furthermore, in the smelting and semi-continuous casting steps, the smelting temperature is 740-760°C.

[0008] Furthermore, during the smelting and semi-continuous casting steps, the Ti is added online in the form of Al-Ti-B wires.

[0009] Furthermore, in the smelting and semi-continuous casting steps, the aluminum alloy ingot finally produced has a thickness of 400 to 600 mm and a width of 1000 to 1350 mm.

[0010] Furthermore, in the homogenization step, the furnace gas temperature is set at 550-580°C, and the ingot is placed after the furnace gas reaches the set temperature. When the temperature of the ingot is 510-530°C, the furnace gas temperature is adjusted to 530-550°C and kept warm for 7-9 hours.

[0011] Furthermore, in the hot rolling step, the starting rolling temperature is 510-520°C, the final rolling temperature is 390-400°C, and the thickness of the hot rolled plate is 9.9-10.1 mm; in the cold rolling step, the thickness of the plate obtained after cold rolling is 1.9-2.1 mm.

[0012] Furthermore, in the finished product annealing step, the whole coil of plate and strip obtained after cold rolling is placed in a heat treatment furnace, and the furnace gas temperature is first set to 535-580°C, and the temperature is increased to the set temperature at a heating rate of 220-250°C and then kept warm for 0.5-1h. Thereafter, the furnace gas temperature is set to 330-370°C, and the temperature is lowered to the set temperature and kept warm for 0.5-1h. Then, the plate and strip are taken out of the furnace for cooling, and the cooling rate is controlled to 15°C / h.

[0013] A high-formability anodizable 6xxx aluminum alloy sheet has an average grain size of 14 to 30 μm and a surface roughness of 0.25 to 0.45 μm. After being stamped at room temperature, the sheet has a smooth surface without scratches, orange peel and cracking defects.

[0014] Furthermore, the aluminum alloy plate has a tensile strength of 70-90 MPa, a yield strength of 30-50 MPa, an elongation of 30-45%, and a hardness HV of 25-45.

[0015] Beneficial effects of the present invention: 1. A high-formability anodized 6xxx aluminum alloy sheet of the present invention adjusts the alloy element composition and ratio, i.e. Si is 0.2% to 0.6%; Mg is 0.6% to 1.1%; Ti is 0.01% to 0.04%; Fe≤0.06%, and the balance is Al. Combined with uniquely regulated semi-continuous casting, hot rolling and cold rolling process operations, the size of the grains in the finished alloy is accurately controlled, so that the internal grain size of the finished aluminum alloy is uniform and small, and the surface quality is excellent. After subsequent room temperature stamping and anodizing treatment, the surface color is uniform, the texture is smooth, and there are no defects such as scratches, orange peel, and cracks. It can better meet the technical requirements of high-end products for the appearance of decorative aluminum alloy surfaces, thereby improving the yield rate of aluminum alloy sheets and strips.

[0016] 2. The preparation method of a highly formable anodized 6xxx aluminum alloy sheet of the present invention aims to solve the technical problem that the surface of the existing 6xxx aluminum alloy sheet and strip is prone to orange peel and cracking defects after room temperature stamping. The preparation process of the present invention controls the temperature of the semi-continuous casting to 685-705°C, the stable production speed of the ingot to 43-53mm / min, the crystallizer cooling water temperature to 20-28°C, and the flow rate to 135-147m / min by precisely adjusting the process parameters in the semi-continuous casting step. 3 / h. This is because: the structure of the aluminum alloy ingot obtained after smelting and semi-continuous casting directly affects the mechanical properties and surface quality of the finished plate, and the uniform and fine grain structure of the finished plate is of great significance to the quality of the product after subsequent stamping and anodizing. The present invention can effectively make the grain size formed in the aluminum alloy ingot smaller by adjusting the process parameters of semi-continuous casting, and can form more fine-structure recrystallized structures after subsequent rolling and annealing treatment, so that the finished aluminum alloy plate has fine grains and a large number of grain boundaries, thereby ensuring good deformation uniformity and consistency in the subsequent deep drawing process of the plate, and having excellent yield strength and elongation. At the same time, the fine grains inside the alloy also ensure that it will not show color unevenness due to different grain orientations after anodizing, thereby avoiding the generation of surface mottled defects, ensuring the quality of the finished product, and reducing the scrap rate.

[0017] 3. The present invention provides a method for preparing a highly formable anodized 6xxx aluminum alloy sheet, which is aimed at the technical problems in the prior art that the surface of the 6xxx aluminum alloy sheet is prone to material defects after room temperature stamping, and the surface of the product is obviously scratched after anodizing. The rolling process is regulated, that is, the roughness of the roller surface during hot rolling and cold rolling is accurately controlled, and the surface roughness Ra of the roller during hot rolling is controlled to be 1.0-1.6μm, and the maximum reduction of a single pass is greater than 30mm; during cold rolling, the surface roughness of the roller Ra≤0.4μm, achieving a surface roughness of 0.25-0.45μm for the finished aluminum alloy sheet, thereby eliminating defects such as surface scratches and meeting the technical requirements of high-end products for surface quality. This is because: in the hot rolling process, the use of a hot rolling process with a large reduction can better break up the relatively coarse cast structure of the ingot, including grains and intergranular compounds, and provide a better deformation structure guarantee for further cold rolling and recrystallization. Controlling the roughness of the hot-rolling roller surface can, on the one hand, prevent aluminum oxide and other adhesions from being pressed into the sheet due to aluminum sticking to the roller surface, which directly affects the surface roughness and glossiness of the sheet. On the other hand, it can better control the surface roughness of the sheet, obtain hot-rolled sheets with less roughness, and provide better surface quality of the slab for subsequent cold rolling. Similarly, controlling the roughness of the cold-rolling roller surface can better control the surface roughness of the finished sheet, thereby obtaining finished sheets with low roughness and high gloss. After stamping and anodizing, the product surface quality is good, without surface defects such as scratches and grains.

[0018] 4. The high-formability anodized 6xxx aluminum alloy sheet of the present invention, by limiting the composition of the alloy and the mass percentage ratio of each component, makes the various alloy components reasonably compatible, comprehensive, and mutually alloyed, thereby significantly improving the comprehensive performance of the 6xxx aluminum alloy material. The average grain size of the finished aluminum alloy sheet is 14-30um, the surface roughness is 0.25-0.45μm, the tensile strength is 70-90MPa, the yield strength is 30-50MPa, the elongation is 30-45%, the hardness is HV25-45, and the surface of the sheet is smooth after being stamped at room temperature, without defects such as scratches, orange peel and cracks, and has excellent comprehensive performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a grain photograph of the aluminum alloy ingot obtained after semi-continuous casting in Example 1; Figure 2 This is a metallographic coating photograph of the finished aluminum alloy plate obtained in Example 1; Figure 3 This is a product surface photograph of the finished aluminum alloy plate obtained in Example 1 after being stamped at room temperature; Figure 4 This is a grain photograph of the aluminum alloy ingot obtained after semi-continuous casting in Comparative Example 1; Figure 5 This is a metallographic coating photograph of the finished aluminum alloy plate obtained in Comparative Example 1; Figure 6 This is a photo of the product surface of the finished aluminum alloy sheet obtained in Comparative Example 1 after being stamped at room temperature. DETAILED DESCRIPTION

[0020] In order to make the technical means, creative features, objectives and beneficial effects achieved by the present invention easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0021] A high-formability anodizable 6xxx aluminum alloy plate material, wherein the raw materials of the aluminum alloy plate and strip material are composed of the following components in mass percentage: Si is 0.2% to 0.6%; Mg is 0.6% to 1.1%; Ti is 0.01% to 0.04%; Fe is ≤0.06%; other impurity elements are ≤0.02%, and the balance is Al; the average grain size of the aluminum alloy plate material is 14 to 30 μm, the surface roughness is 0.25 to 0.45 μm, the tensile strength is 70 to 90 MPa, the yield strength is 30 to 50 MPa, the elongation is 30 to 45%, the hardness HV is 25 to 45, and the plate material has excellent surface quality after being stamped at room temperature, and is free of defects such as scratches, orange peel and cracks.

[0022] A method for preparing a highly formable anodized 6xxx aluminum alloy sheet material comprises the following steps: Step 1: Melting and semi-continuous casting According to the above mass percentage ratio, high-purity aluminum ingots with a purity higher than 99%, pure magnesium ingots, and industrial silicon are weighed and added in proportion to melt into aluminum liquid. Ti is added online in the form of Al-Ti-B wire. The prepared alloy raw materials are added into a smelting furnace at 740~760℃. The temperature of semi-continuous casting is controlled at 685~705℃, the stable production speed of ingot casting is 43~53mm / min, and the cooling water flow rate of the crystallizer is 135~147m 3 / h, the cooling water temperature is 20~28℃, and finally an aluminum alloy ingot with a thickness of 400~600mm and a width of 1000~1350mm is produced.

[0023] Step 2: Homogenization The furnace gas temperature is set to 550-580°C. After the furnace gas reaches the set temperature, the aluminum alloy ingot obtained in step ① is placed in a homogenization treatment furnace. When the temperature of the ingot is 510-530°C, the furnace gas temperature is adjusted to 530-550°C and kept warm for 7-9 hours.

[0024] Step 3: Hot rolling The aluminum alloy ingot after the homogenization treatment in step ② is directly hot rolled, and the surface roughness Ra of the roller is controlled to be 1.0-1.6 μm during hot rolling, the starting rolling temperature is 510-520°C, the final rolling temperature is 390-400°C, and the hot rolling adopts large reduction rolling, the maximum reduction of a single pass is greater than 30 mm, and the thickness of the final hot-rolled plate is 9.9-10.1 mm.

[0025] Step ④: Cold rolling The hot-rolled plate obtained in step ③ is continuously cold-rolled, and the surface roughness of the roller during cold rolling is controlled to be Ra≤0.4 μm, and finally rolled into a plate with a thickness of 1.9 to 2.1 mm.

[0026] Step ⑤: Finished product annealing The whole coil of plate and strip obtained after cold rolling is put into a heat treatment furnace, and the furnace gas temperature is first set to 535-580°C, and the temperature is increased to the set temperature at a heating rate of 220-250°C and then kept warm for 0.5-1h. Thereafter, the furnace gas temperature is set to 330-370°C, and the temperature is lowered to the set temperature and kept warm for 0.5-1h. Then, it is taken out of the furnace to cool, and the cooling rate is controlled at 15°C / h to finally obtain a finished aluminum alloy plate.

[0027] The present invention provides a method for preparing a high-formability anodized 6xxx aluminum alloy plate. By regulating the semi-continuous casting, hot rolling and cold rolling processes (roller surface roughness) in the preparation process, the finished aluminum alloy plate has a uniform and fine grain size, an average grain size of 20-60um, a plate and strip surface roughness of 0.25-0.45μm, a tensile strength of 70-90MPa, a yield strength of 30-50MPa, an elongation of 30-45%, and a hardness of HV25-45. After subsequent room temperature stamping, the plate has excellent surface quality without defects such as scratches, orange peel, and cracks, meeting the technical requirements of high-end products for the appearance decorative surface.

[0028] Example 1 A high-formability anodizable 6xxx aluminum alloy plate of the present embodiment has the following alloy components in percentage by mass: Si=0.58%, Fe=0.05%, Mg=0.85%, Ti=0.023%, and the remainder of Al and unavoidable impurities.

[0029] The preparation method of the aluminum alloy plate specifically comprises the following steps: S1. Melting and semi-continuous casting: High-purity aluminum ingots with a purity higher than 99%, pure magnesium ingots, and industrial silicon are added in proportion to melt into aluminum liquid. Ti is added online in the form of Al-Ti-B wire. The final preparation specification is an aluminum alloy ingot with a thickness of 580 mm and a width of 1150 mm. The melting temperature is 758°C, the semi-continuous casting temperature is 695°C, the ingot stable production speed is 50 mm / min, and the crystallizer cooling water flow rate is 142 m3 / h, cooling water temperature 23℃.

[0030] S2. Homogenization treatment: Set the furnace gas temperature to 560°C. After the furnace gas reaches the set temperature, place the aluminum alloy ingot obtained in step ① into the homogenization treatment furnace. When the temperature of the ingot is 520°C, adjust the furnace gas temperature to 540°C and keep it warm for 8 hours.

[0031] S3. Hot rolling: The ingot after homogenization treatment is directly hot rolled, the surface roughness Ra of the roller is 1.1μm, the starting rolling temperature is 510℃, the final rolling temperature is 390℃, the thickness of the hot rolled plate is 9.95mm; the maximum reduction of a single pass during the rolling process is 42mm.

[0032] S4, cold rolling: the surface roughness of the working roll during finished product rolling is Ra = 0.3μm, and the thickness of the finished plate is 1.95mm.

[0033] S5. Finished product annealing: add the whole coil of plate and strip into the heat treatment furnace, set the furnace gas temperature to 580℃, keep it warm for 0.5h, and heat up at a rate of 220℃ / h. Then set the temperature to 330℃, keep it warm for 0.5h, and then take it out of the furnace for cooling at a cooling rate of 15℃ / h to obtain the finished aluminum alloy plate.

[0034] Figure 1 is a grain photograph of the aluminum alloy ingot obtained after semi-continuous casting in this embodiment; Figure 2 This is a metallographic coating photograph of the finished aluminum alloy plate obtained in this embodiment; Figure 3 This is a photo of the product surface of the finished aluminum alloy plate obtained in this embodiment after being stamped at room temperature.

[0035] The average grain size of the finished aluminum alloy sheet prepared in this embodiment is measured to be 14.6um, the surface roughness Ra=0.27μm, the tensile strength is 91MPa, the yield strength is 50MPa, the elongation is 42%, and the hardness HV is 33.6. As can be seen from the figure, there is no pitting defect on the surface of the plate and strip after stamping, and the surface color of the product after anodizing is uniform without defects such as spots.

[0036] Example 2 A high-formability anodizable 6xxx aluminum alloy plate of the present embodiment has the following alloy components in percentage by mass: Si=0.35%, Fe=0.06%, Mg=0.78%, Ti=0.016%, and the remainder of Al and unavoidable impurities.

[0037] The preparation method of the aluminum alloy plate specifically comprises the following steps: S1. Melting and semi-continuous casting: High-purity aluminum ingots with a purity higher than 99%, pure magnesium ingots, and industrial silicon are added in proportion to melt into aluminum liquid. Ti is added online in the form of Al-Ti-B wire. The final preparation specification is an aluminum alloy ingot with a thickness of 580 mm and a width of 1150 mm. The melting temperature is 750°C, the semi-continuous casting temperature is 700°C, the ingot stable production speed is 45 mm / min, and the crystallizer cooling water flow rate is 138 m 3 / h, cooling water temperature 21℃.

[0038] S2. Homogenization treatment: Set the furnace gas temperature to 550°C. After the furnace gas reaches the set temperature, place the aluminum alloy ingot obtained in step ① into the homogenization treatment furnace. When the temperature of the ingot is 530°C, adjust the furnace gas temperature to 540°C and keep it warm for 7 hours.

[0039] S3. Hot rolling: The ingot after homogenization treatment is directly hot rolled, the surface roughness Ra of the roller is 1.6μm, the starting rolling temperature is 515℃, the final rolling temperature is 395℃, the thickness of the hot rolled plate is 10.05mm; the maximum reduction of a single pass during rolling is 38mm.

[0040] S4, cold rolling: the surface roughness of the finished rolling work roll is Ra = 0.33μm, and the thickness of the finished plate is 2.05mm.

[0041] S5. Finished product annealing: add the whole coil of plate and strip into the heat treatment furnace, set the furnace gas temperature to 535℃, keep warm for 1h, and heat up at a rate of 250℃ / h. Then set the temperature to 350℃, keep warm for 1h, and then take it out of the furnace for cooling at a cooling rate of 15℃ / h to obtain the finished aluminum alloy plate.

[0042] The average grain size of the finished aluminum alloy sheet prepared in this embodiment is measured to be 19.3um, the surface roughness Ra=0.31μm, the tensile strength is 77MPa, the yield strength is 47MPa, the elongation is 41%, and the hardness HV is 29.7. The plate and strip have no pitting defects on the surface after stamping, and the surface color of the product is uniform after anodizing treatment, without defects such as spots.

[0043] Example 3 A high-formability anodizable 6xxx aluminum alloy plate of the present embodiment has the following alloy components in percentage by mass: Si=0.49%, Fe=0.06%, Mg=0.98%, Ti=0.033%, and the remainder of Al and unavoidable impurities.

[0044] The preparation method of the aluminum alloy plate specifically comprises the following steps: S1. Melting and semi-continuous casting: High-purity aluminum ingots with a purity higher than 99%, pure magnesium ingots, and industrial silicon are added in proportion to melt into aluminum liquid. Ti is added online in the form of Al-Ti-B wire. The final preparation specification is an aluminum alloy ingot with a thickness of 580 mm and a width of 1150 mm. The melting temperature is 760°C, the semi-continuous casting temperature is 688°C, the ingot stable production speed is 51 mm / min, and the crystallizer cooling water flow rate is 147 m 3 / h, cooling water temperature 27℃.

[0045] S2. Homogenization treatment: Set the furnace gas temperature to 560°C. After the furnace gas reaches the set temperature, place the aluminum alloy ingot obtained in step ① into the homogenization treatment furnace. When the temperature of the ingot is 530°C, adjust the furnace gas temperature to 550°C and keep it warm for 7 hours.

[0046] S3. Hot rolling: The ingot after homogenization treatment is directly hot rolled, the surface roughness Ra of the roller is 1.3μm, the starting rolling temperature is 510℃, the final rolling temperature is 390℃, the thickness of the hot rolled plate is 9.95mm; the maximum reduction of a single pass during the rolling process is 35mm.

[0047] S4, cold rolling: the surface roughness of the finished rolling work roll is Ra = 0.37μm, and the thickness of the finished plate is 1.95mm.

[0048] S5. Finished product annealing: add the whole coil of plate and strip into the heat treatment furnace, set the furnace gas temperature to 560℃, keep it warm for 0.5h, and heat up at a rate of 230℃ / h. Then set the temperature to 370℃, keep it warm for 1h, and then take it out of the furnace for cooling at a cooling rate of 15℃ / h to obtain the finished aluminum alloy plate.

[0049] The average grain size of the finished aluminum alloy sheet prepared in this embodiment is measured to be 26.6um, the surface roughness Ra is 0.35μm, the tensile strength is 91MPa, the yield strength is 34MPa, the elongation is 39%, and the hardness HV is 30.2. The plate and strip have no pitting defects on the surface after stamping, and the surface color of the product is uniform after anodizing treatment, without defects such as spots.

[0050] Example 4 A high-formability anodizable 6xxx aluminum alloy plate of the present embodiment has the following alloy components in percentage by mass: Si=0.20%, Fe=0.04%, Mg=1.1%, Ti=0.025%, and the remainder of Al and unavoidable impurities.

[0051] The preparation method of the aluminum alloy plate specifically comprises the following steps: S1. Melting and semi-continuous casting: High-purity aluminum ingots with a purity higher than 99%, pure magnesium ingots, and industrial silicon are added in proportion to melt into aluminum liquid. Ti is added online in the form of Al-Ti-B wire. The final preparation specification is an aluminum alloy ingot with a thickness of 580 mm and a width of 1150 mm. The melting temperature is 740°C, the semi-continuous casting temperature is 705°C, the ingot stable production speed is 53 mm / min, and the crystallizer cooling water flow rate is 141 m 3 / h, cooling water temperature 28℃.

[0052] S2. Homogenization treatment: Set the furnace gas temperature to 580°C. After the furnace gas reaches the set temperature, place the aluminum alloy ingot obtained in step ① into the homogenization treatment furnace. When the temperature of the ingot is 510°C, adjust the furnace gas temperature to 530°C and keep it warm for 9 hours.

[0053] S3. Hot rolling: The ingot after homogenization treatment is directly hot rolled, the surface roughness Ra of the roller is 1.0μm, the starting rolling temperature is 515℃, the final rolling temperature is 400℃, and the thickness of the hot rolled plate is 9.90mm; the maximum reduction of a single pass during the rolling process is 37mm.

[0054] S4, cold rolling: the surface roughness of the finished rolling work roll is Ra = 0.32μm, and the thickness of the finished plate is 2.1mm.

[0055] S5. Finished product annealing: add the whole coil of plate and strip into the heat treatment furnace, set the furnace gas temperature to 540℃, keep it warm for 0.8h, and heat up at a rate of 240℃ / h. Then set the temperature to 340℃, keep it warm for 1h, and then take it out of the furnace for cooling at a cooling rate of 15℃ / h to obtain the finished aluminum alloy plate.

[0056] The average grain size of the finished aluminum alloy sheet prepared in this embodiment is measured to be 27.4 μm, the surface roughness Ra is 0.27 μm, the tensile strength is 71 MPa, the yield strength is 31 MPa, the elongation is 50%, and the hardness HV is 44.6. The plate and strip have no pitting defects on the surface after stamping, and the surface color of the product is uniform after anodizing treatment, without defects such as spots.

[0057] Example 5 A high-formability anodizable 6xxx aluminum alloy plate of the present embodiment has the following alloy components in percentage by mass: Si=0.43%, Fe=0.03%, Mg=0.60%, Ti=0.040%, and the remainder of Al and unavoidable impurities.

[0058] The preparation method of the aluminum alloy plate specifically comprises the following steps: S1. Melting and semi-continuous casting: High-purity aluminum ingots with a purity higher than 99%, pure magnesium ingots, and industrial silicon are added in proportion to melt into aluminum liquid. Ti is added online in the form of Al-Ti-B wire. The final preparation specification is an aluminum alloy ingot with a thickness of 580 mm and a width of 1150 mm. The melting temperature is 755°C, the semi-continuous casting temperature is 685°C, the ingot stable production speed is 43 mm / min, and the crystallizer cooling water flow rate is 135 m 3 / h, cooling water temperature 20℃.

[0059] S2. Homogenization treatment: Set the furnace gas temperature to 570°C. After the furnace gas reaches the set temperature, place the aluminum alloy ingot obtained in step ① into the homogenization treatment furnace. When the temperature of the ingot is 520°C, adjust the furnace gas temperature to 530°C and keep it warm for 8 hours.

[0060] S3. Hot rolling: The ingot after homogenization treatment is directly hot rolled, the surface roughness Ra of the roller is 1.4μm, the starting rolling temperature is 520℃, the final rolling temperature is 395℃, the thickness of the hot rolled plate is 10.1mm; the maximum reduction of a single pass during the rolling process is 43mm.

[0061] S4, cold rolling: the surface roughness of the working roll during finished product rolling is Ra = 0.4μm, and the thickness of the finished plate is 1.9mm.

[0062] S5. Finished product annealing: add the whole coil of plate and strip into the heat treatment furnace, set the furnace gas temperature to 560℃, keep it warm for 0.5h, and heat up at a rate of 230℃ / h. Then set the temperature to 350℃ and keep it warm for 1h. Then take it out of the furnace and cool it at a cooling rate of 15℃ / h to obtain the finished aluminum alloy plate.

[0063] The average grain size of the finished aluminum alloy sheet prepared in this embodiment is measured to be 17.1um, the surface roughness Ra is 0.31μm, the tensile strength is 83MPa, the yield strength is 50MPa, the elongation is 32%, and the hardness HV is 38.9. The plate and strip have no pitting defects on the surface after stamping, and the surface color of the product is uniform after anodizing treatment, without defects such as spots.

[0064] Comparative Example 1 The alloy composition and preparation process of this embodiment are the same as those of embodiment 1. Only in the semi-continuous casting process, the casting temperature is set to 710°C, the ingot stable production speed is 40mm / min, and the crystallizer cooling water flow rate is 126m 3 / h, and other preparation process parameters are the same as those in Example 1.

[0065] Figure 3 is a grain photograph of the aluminum alloy ingot obtained after semi-continuous casting in this embodiment; Figure 4 This is a metallographic coating photograph of the finished aluminum alloy plate obtained in this embodiment; Figure 5This is a photo of the product surface of the finished aluminum alloy plate obtained in this embodiment after being stamped at room temperature.

[0066] It was determined that the average grain size of the finished aluminum alloy plate prepared in this embodiment was 74.2 μm, the surface roughness Ra = 0.67 μm, the tensile strength was 54 MPa, the yield strength was 21 MPa, the elongation was 20%, and the hardness HV was 49.7.

[0067] As can be seen from the figure, after stamping, scratch defects appear on the surface of the plate and strip. After anodizing treatment, not only scratches appear on the surface of the product, but also cracks occur at the deformed parts.

[0068] This is because: the structure of aluminum alloy ingot directly affects the mechanical properties and surface quality of the finished plate. The uniform and fine grain structure of the finished plate is of great significance to the quality of the subsequent products after stamping and anodizing. The aluminum alloy ingot prepared by this process has coarse grains and coarse grains of more than 300um. These coarse grains cannot be completely broken by rolling, and the complete recrystallization structure cannot be obtained by annealing. The coarse grains of the finished plate and the reduced number of grain boundaries not only directly deteriorate the strength and elongation of the plate, but also lead to reduced deformation uniformity and consistency during stamping, resulting in micropores at the grain boundaries, which appear as orange peel at the deformation, and even cracking, resulting in product scrapping; after anodizing, the coarse grains will show color difference due to the reflection of their respective grain orientations, showing surface mottled defects, all of which directly affect the final product surface quality.

[0069] Comparative Example 2 The alloy composition and preparation process of this embodiment are the same as those of embodiment 1. Only in the hot rolling process, the surface roughness of the hot rolling roller is controlled to be Ra=2.2μm, and the maximum reduction of a single hot rolling pass is 23mm; in the cold rolling process, the surface roughness of the cold rolling roller is controlled to be Ra=0.8μm, and other preparation process parameters are the same as those of embodiment 1.

[0070] The finished plate of this embodiment has material grain defects on its surface after stamping, and after anodizing, the surface of the product is obviously scratched.

[0071] This is because: the hot rolling process with a large reduction can better break up the relatively coarse cast structure of the ingot, including grains and intergranular compounds, and provide a better deformation structure guarantee for further cold rolling and recrystallization. Controlling the roughness of the hot rolling roller surface can, on the one hand, avoid pressing aluminum oxide and other adhesions into the plate due to aluminum sticking to the roller surface, which directly affects the surface roughness and glossiness of the plate. On the other hand, it can better control the surface roughness of the plate, obtain hot-rolled plates with smaller roughness, and provide better surface quality of the slab for subsequent cold rolling. Similarly, controlling the roughness of the cold rolling roller surface can better control the surface roughness of the finished plate, thereby obtaining a finished plate with low roughness and high gloss. After stamping and anodizing, the product surface quality is good, without scratches, material lines and other surface defects.

[0072] In the above description, the statistical method of average grain size: refer to the standard "GB / T 6394-2017 Metal Average Grain Size Test Method" to conduct grain size analysis.

[0073] Testing and analysis standards for the surface roughness of aluminum alloy plates: Refer to the standard "GB / T3191-2010 Aluminum Alloy Material Comprehensive Product Standard" for roughness analysis.

[0074] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Those skilled in the art should understand that the specific implementation modes of the present invention may be modified or replaced by equivalents with reference to the above embodiments. Any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention are within the scope of protection of the pending claims.

Claims

1. A method for preparing a highly formable anodizable 6xxx aluminum alloy sheet, comprising a smelting and semi-continuous casting step, a homogenization step, a hot rolling step, a cold rolling step and a finished product annealing step, characterized in that: In the smelting and semi-continuous casting steps, the semi-continuous casting temperature is 685-705°C, the stable production speed of the ingot is 43-53 mm / min, the crystallizer cooling water temperature is 20-28°C, and the flow rate is 135-147 m 3 / h; in the hot rolling step, the surface roughness Ra of the roll is 1.0-1.6 μm, and the maximum reduction of a single pass is greater than 30 mm; in the cold rolling step, the surface roughness Ra of the roll is ≤0.4 μm.

2. The method for preparing a highly formable anodized 6xxx aluminum alloy sheet according to claim 1, wherein: In the smelting and semi-continuous casting steps, the aluminum alloy plate raw material used is composed of the following components in mass percentage: Si is 0.2% to 0.6%; Mg is 0.6% to 1.1%; Ti is 0.01% to 0.04%; Fe is ≤0.06%, and the balance is Al and unavoidable impurity elements, and the content of impurity elements is ≤0.02%.

3. The method for preparing a highly formable anodized 6xxx aluminum alloy sheet according to claim 1, wherein: In the melting and semi-continuous casting steps, the melting temperature is 740-760°C.

4. The method for preparing a highly formable anodized 6xxx aluminum alloy sheet according to claim 1, wherein: During the melting and semi-continuous casting steps, the Ti is added online in the form of Al-Ti-B wires.

5. The method for preparing a highly formable anodized 6xxx aluminum alloy sheet according to claim 1, wherein: In the smelting and semi-continuous casting steps, the aluminum alloy ingot finally produced has a thickness of 400 to 600 mm and a width of 1000 to 1350 mm.

6. The method for preparing a highly formable anodized 6xxx aluminum alloy sheet according to claim 1, wherein: In the homogenization step, the furnace gas temperature is set at 550-580°C, and the ingot is placed after the furnace gas reaches the set temperature. When the temperature of the ingot is 510-530°C, the furnace gas temperature is adjusted to 530-550°C and kept warm for 7-9 hours.

7. The method for preparing a highly formable anodized 6xxx aluminum alloy sheet according to claim 1, wherein: In the hot rolling step, the starting rolling temperature is 510-520°C, the final rolling temperature is 390-400°C, and the thickness of the hot rolled plate is 9.9-10.1 mm; in the cold rolling step, the thickness of the plate obtained after cold rolling is 1.9-2.1 mm.

8. The method for preparing a highly formable anodizable 6xxx aluminum alloy sheet according to claim 1, wherein: In the finished product annealing step, the whole coil of plate and strip obtained after cold rolling is placed in a heat treatment furnace, and the furnace gas temperature is first set to 535-580°C, and the temperature is increased to the set temperature at a heating rate of 220-250°C and then kept warm for 0.5-1h. Thereafter, the furnace gas temperature is set to 330-370°C, and the temperature is lowered to the set temperature and kept warm for 0.5-1h. Then, the plate and strip are taken out of the furnace and cooled, and the cooling rate is controlled to 15°C / h.

9. A highly formable anodizable 6xxx aluminum alloy sheet prepared according to the method of any one of claims 1 to 8, characterized in that: The average grain size of the aluminum alloy plate is 14-30 μm, the surface roughness is 0.25-0.45 μm, and the surface of the plate is smooth after being stamped at room temperature without scratches, orange peel and cracking defects.

10. The highly formable anodizable 6xxx aluminum alloy sheet of claim 9, wherein: The aluminum alloy plate has a tensile strength of 70 to 90 MPa, a yield strength of 30 to 50 MPa, an elongation of 30 to 45%, and a hardness HV of 25 to 45.

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