High-elongation aluminum alloy plate for automobile and preparation method of high-elongation aluminum alloy plate

Abstract

The invention relates to the technical field of aluminum alloy processing and manufacturing, in particular to a high-elongation aluminum alloy plate for an automobile and a preparation method of the high-elongation aluminum alloy plate. The content of Fe is 0.08 to 0.23 percent; the content of Cu is 0 to 0.1 percent; the content of Mn is 0.12 to 0.18 percent; the content of Mg is 2.7 to 2.9 percent; the content of Cr is 0.06 to 0.1 percent; the content of Zn is 0-0.1%; the content of Ti is 0.015 to 0.025 percent; the content of V is 0-0.05%; the single content of other impurity elements is less than or equal to 0.05%; the total content of other impurity elements is less than or equal to 0.15%; the plate has the advantages of high elongation, high plastic strain ratio, high work hardening index and good stamping performance, and is suitable for being used as an automobile inner plate material.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloy processing and manufacturing, and in particular to an aluminum alloy plate for automobiles with high elongation and a preparation method thereof. Background Art

[0002] With the continuous development of industry, environmental protection and energy conservation are urgently needed. Fuel-powered vehicles need to reduce fuel consumption, emissions, and efficiency. New energy electric vehicles need to reduce power consumption and weight to increase range and enhance competitiveness. Vehicle lightweighting is the most direct and effective way to reduce pollution and energy consumption. Aluminum alloys and their processed materials have become the primary materials used by automakers to reduce vehicle weight due to their low density, high strength, excellent elasticity, impact resistance, corrosion resistance, recyclability, and excellent processability.

[0003] 5754 aluminum alloy has excellent corrosion resistance, good plasticity, and is easy to cold stamp and bend. It is suitable for manufacturing automobile engine hood inner panel reinforcements, door inner panel structural parts, etc. At present, most automobile companies have used 5 series alloys in automobile structural parts. As the structure of automobile structural parts becomes complex, the 5754 alloy manufactured by the current process is prone to obvious anisotropy at larger and deeper stamping positions during the subsequent stamping process, resulting in differences in flow resistance in different directions, aggravating material accumulation and forming wrinkles. The grain size of the fully annealed 5754 aluminum alloy is over 50μm, and the deformation ability of large grains varies significantly during deep drawing. Some grains protrude from the surface to form orange peel, and the material thinning rate is greater than 25%, causing cracking. Therefore, the stamping performance requirements of the 5 series alloy are relatively high.

[0004] Therefore, there is an urgent need to provide a high-elongation 5754 sheet for automobiles and a preparation method so that the sheet has excellent elongation and mechanical properties and excellent stamping performance. Summary of the Invention

[0005] The present invention aims to solve the technical problem of how to provide a 5754 sheet material for automobiles with high elongation and a preparation method thereof.

[0006] In order to achieve the above-mentioned object, the first aspect of the present invention provides a high-elongation aluminum alloy sheet for automobiles, wherein the components and their weight percentages in the sheet are as follows: Si content is 0-0.18%; Fe content is 0.08-0.23%; Cu content is 0-0.1%; Mn content is 0.12-0.18%; Mg content is 2.7-2.9%; Cr content is 0.06-0.1%; Zn content is 0-0.1%; Ti content is 0.015-0.025%; V content is 0-0.05%; The individual content of other impurity elements is ≤0.05%; The total content of other impurity elements is ≤0.15%; The balance is Al.

[0007] A second aspect of the present invention provides a method for preparing the above-mentioned high-elongation automotive aluminum alloy sheet, wherein the method comprises: Melting, sawing and milling, homogenization, hot rolling, cold rolling, annealing, straightening, pre-stretching, packaging; The conditions for the melting and casting include: a melting temperature of 700-750°C, a standing time of 35-45 minutes, and a refining temperature of 720-750°C; The homogenization treatment conditions include: the first stage temperature is 520-540°C for 4-10 hours, the second stage temperature is 460-500°C for 4-6 hours, the cooling method is air cooling, the cooling rate is 9-10°C / h, and the temperature is cooled to 460-500°C.

[0008] The beneficial effects of the present invention are: The present invention regulates alloy composition, adjusts the homogenization system, strictly controls hot rolling and cold rolling process parameters, and adjusts the pre-stretching system. The obtained aluminum alloy plate has high elongation, high plastic strain ratio, high work hardening index, good stamping performance, and is suitable for use as automobile inner panel material. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a process flow chart of the present invention; Figure 2 This is a grain size diagram of the plate of Example 1; Figure 3 This is the grain size diagram of the plate of Comparative Example 1. DETAILED DESCRIPTION

[0010] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0011] In the existing technology, the existing alloy composition and preparation process have been improved to reduce the production process, improve the surface quality of the alloy, and eliminate the defects of the Luders band, but have not been improved in combination with the various problems that arise in the final actual stamping use. It is difficult to prepare automotive aluminum alloy sheets with excellent mechanical strength and high elongation that are suitable for stamping complex-shaped automotive internal structural parts.

[0012] In the present invention, the inventors have discovered that by controlling the alloy composition and adjusting the processing technology, the performance of the aluminum alloy sheet can meet the requirements and have excellent mechanical strength and high elongation.

[0013] To achieve this goal, the inventors discovered that the above-mentioned purpose can be achieved through a specific composition of each component, a two-stage annealing process and other processes.

[0014] A first aspect of the present invention provides a high-elongation aluminum alloy sheet for automobiles, wherein the components and their weight percentages in the sheet are as follows: Si content is 0-0.18%; Fe content is 0.08-0.23%; Cu content is 0-0.1%; Mn content is 0.12-0.18%; Mg content is 2.7-2.9%; Cr content is 0.06-0.1%; Zn content is 0-0.1%; Ti content is 0.015-0.025%; V content is 0-0.05%; The individual content of other impurity elements is ≤0.05%; The total content of other impurity elements is ≤0.15%; The balance is Al.

[0015] In the present invention, reducing the Mg and Mn components on the basis of the 5754 alloy can improve the elongation of the plate.

[0016] A second aspect of the present invention provides a method for preparing the above-mentioned high-elongation automotive aluminum alloy sheet, wherein the method comprises: Melting, sawing and milling, homogenization, hot rolling, cold rolling, annealing, straightening, pre-stretching, packaging; The conditions for the melting and casting include: a melting temperature of 700-750°C, a standing time of 35-45 minutes, and a refining temperature of 720-750°C; The homogenization treatment conditions include: the first stage temperature is 520-540°C for 4-10 hours, the second stage temperature is 460-500°C for 4-6 hours, the cooling method is air cooling, the cooling rate is 9-10°C / h, and the temperature is cooled to 460-500°C.

[0017] In the present invention, raw materials are melted and cast to obtain ingots, the ingots are sawed and milled, the ingot starter at the start of casting and the gate at the end of casting are cut off, and the surface oxide scale and surface defects are milled off to obtain ingots with good surface quality, and then the ingots are homogenized and hot rolled to obtain intermediate billets, and then cold rolled to obtain blanks, which are annealed, straightened, pre-stretched, and then packaged to obtain plates.

[0018] According to the present invention, the hot rolling conditions include: rough rolling and finish rolling, wherein the rough rolling temperature is 460-500°C, the rough rolling rate is 36-66m / min, the rough rolling passes are 18-24 passes, the maximum reduction is 40-45mm, and the intermediate billet thickness is 34-36mm.

[0019] According to the present invention, the hot rolling is followed by rough rolling and finishing rolling is performed, with four finishing passes and reduction ratios of the four finishing passes being 30-35%, 38-42%, 35-39% and 32-36% respectively. The thickness of the billet after finishing rolling is 7.5-8.5 mm and the coiling temperature is 310-330°C.

[0020] In the present invention, a specific hot rolling process with high temperature and large deformation is used to lay a microstructural foundation for subsequent processes and produce a plate with high elongation and low anisotropy.

[0021] According to the present invention, the cold rolling conditions include: 3 cold rolling passes, a cold rolling rate of 60-70 m / min, a total processing deformation of 65-75%, a thickness after cold rolling of 2.4-2.5 mm, and reduction rates of the three cold rolling passes of 38-42%, 35-39% and 23-26% respectively.

[0022] In the present invention, the specific cold rolling significantly improves the strength, elongation and stamping performance of the material through high deformation and multiple rolling passes.

[0023] According to the present invention, the annealing conditions include: a tension of 1-2 MPa, heating to 395-405° C. in an air cushion furnace, holding for 9-11 seconds, then heating to 475-485° C., holding for 4-6 seconds, and a coiling process speed of 35-50 m / min; During annealing in the air cushion furnace, electromagnetic induction of 1-10 KHz is applied.

[0024] In the present invention, the coil running process rate is the conveying rate of the blank in the air cushion furnace.

[0025] In the present invention, a specific double-stage annealing and electromagnetic induction process is adopted.

[0026] According to the present invention, the pre-stretching conditions include: a deformation amount of 0.1-0.5%, a pre-stretching rate of 65-70 mm / min, maintained for 1-2 seconds, and then 25-30 mm / min, maintained for 4-5 seconds.

[0027] In the present invention, a two-stage pre-stretching process is adopted to perform two-stage variable speed pre-stretching, wherein the high-speed section eliminates the macroscopic Lüders band and the low-speed section releases the microscopic dislocation stress.

[0028] Test Method The test method for the composition of aluminum alloy plates is in accordance with GB / T7999-2015 Aluminum and Aluminum Alloy Photoelectric Direct Reading Emission Spectroscopy Analysis Method, and the testing equipment is ARL-3460 direct reading spectrometer.

[0029] The yield strength, tensile strength, elongation after fracture, uniform elongation (Ag), work hardening index (n value), and plastic strain ratio (r value) were tested using an AG-X 100KN electronic universal testing machine. The test standard is GB / T6892-2015, Aluminum and aluminum alloy extruded sheets for general industrial use, and the test method is GB / T16865-2013, Specimens and methods for tensile testing of deformed aluminum, magnesium, and their alloy products.

[0030] The specimen direction is 90.

[0031] The technical solution of the present invention is further described in detail below with reference to the accompanying drawings and embodiments. Obviously, the embodiments described herein are only some embodiments of the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments implemented by those of ordinary skill in the art without making creative improvements are within the scope of protection of the present invention.

[0032] Example 1 Ingredients: Calculate the amount of each aluminum alloy raw material and prepare the aluminum alloy raw materials according to the ratio: Si=0.054wt%; Fe=0.132wt%; Cu=0.008wt%; Mn=0.172wt%; Mg=2.886wt%; Cr=0.08wt%; Zn=0.006wt%; Ti=0.021wt%; V=0.116wt%. Other individual ≤0.05%, other total ≤0.15%, and the balance is Al.

[0033] Casting: The prepared aluminum alloy raw materials are added to a melting furnace and uniformly mixed with slag through electromagnetic stirring at a temperature of 732°C for 30 minutes to form a melt. The melt is then transferred from the converter to a holding furnace for refining at 720°C. The melt undergoes online degassing using a mixture of chlorine and inert gas to reduce the hydrogen content to less than 0.15ml / 100gAl. Impurities larger than 20μm in diameter are filtered out through a two-stage ceramic foam filtration system. DC direct cooling semi-continuous casting is employed at a casting temperature of 696°C and a casting speed of 59mm / min during the stable period. The molten aluminum enters the starter head to form a base and is cooled through the mold wall to form a V-shaped solidification zone. The mold is then lowered at a certain speed by a hydraulic cylinder or steel wire rope, and water is sprayed through the mold at a certain angle for secondary cooling. The mold wall is lubricated with oil or graphite to improve the surface quality of the flat ingot, ultimately forming an ingot.

[0034] Sawing and milling: sawing and milling the ingot, cutting off the ingot starter at the start of casting and the gate at the end of casting, and milling off the surface oxide scale and surface defects to obtain an ingot with good surface quality.

[0035] Homogenization: The ingot is homogenized at a heating rate of 85°C / h, heated to 536°C and kept for 8.2h, then cooled to 493°C and kept for 5h. The cooling method is air cooling at a cooling rate of 10°C / h to 493°C.

[0036] Hot rolling: Rough hot rolling was carried out at 465°C using a 1+5 mill, with a rolling speed of 2.6 m / s, 17 roughing passes, a maximum reduction of 35 mm, and an intermediate billet thickness of 35 mm. Four continuous finishing passes were then carried out, with reductions of 33%, 40%, 37%, and 34% respectively, to obtain a hot-rolled coil with a thickness of 8.2 mm. The coiling temperature was 327°C.

[0037] Cold rolling: The hot rolled coil is subjected to three passes with a total processing deformation of 70% to a finished thickness of 2.45 mm. The rolling speed is 67 m / min, and the reductions of the three passes are 38%, 35%, and 26% respectively.

[0038] Annealing: The finished cold-rolled coil with a thickness of 2.45mm is subjected to two-stage air cushion annealing. Before annealing, the tension is reduced to 2Mpa to prevent large fluctuations in the tension. The temperature needs to be rapidly increased in the air cushion furnace with an electromagnetic induction of 5KHz. The temperature is raised to 400℃ in the air cushion furnace and kept warm for 10s. The temperature is then raised to 480℃ and kept warm for 5s. The coil running process speed is 48m / min, and then the temperature is lowered to room temperature.

[0039] Straightening and pre-stretching: The annealed 5754 alloy is straightened in a straightening machine through the combined action of a tension roller and a bending roller. The straightened 5754 alloy is then subjected to a two-stage speed change, first at 70 mm / min, maintained for 1 second, and then at 30 mm / min, maintained for 4 seconds for pre-stretching, with a deformation of 0.3%.

[0040] An aluminum alloy plate A1 was obtained.

[0041] Example 2 An aluminum alloy plate was prepared according to the processing method of Example 1, except that the aluminum alloy composition was Si=0%; Fe=0.08wt%; Cu=0wt%; Mn=0.12wt%; Mg=2.7wt%; Cr=0.06wt%; Zn=0wt%; Ti=0.015wt%; and V=0.001wt%.

[0042] An aluminum alloy plate A2 was obtained.

[0043] Example 3 An aluminum alloy plate was prepared according to the processing method of Example 1, except that the aluminum alloy composition was Si=0.18wt%; Fe=0.23wt%; Cu=0.1wt%; Mn=0.18wt%; Mg=2.9wt%; Cr=0.1wt%; Zn=0.1wt%; Ti=0.025wt%; and V=0.046wt%.

[0044] An aluminum alloy plate A3 was obtained.

[0045] Example 4 An aluminum alloy plate was prepared according to the processing method of Example 1, except that the ingot was homogenized at 520° C. for 4 h in the first stage and at 480° C. for 4 h in the second stage.

[0046] An aluminum alloy plate A4 is obtained.

[0047] Example 5 The aluminum alloy plate was prepared according to the processing method of Example 1, except that the ingot was homogenized at 540° C. for 10 h in the first stage and 500° C. for 6 h in the second stage.

[0048] An aluminum alloy plate A5 was obtained.

[0049] Example 6 An aluminum alloy plate was prepared according to the processing method of Example 1, except that the rough rolling temperature was 460°C, the rough rolling rate was 37 m / min, the rough rolling passes were 18 passes, the maximum reduction was 40 mm, the intermediate billet thickness was 34 mm, the reduction rates of the four finishing rolling passes were 30%, 38%, 35% and 32% respectively, the billet thickness after finishing rolling was 7.5 mm, and the coiling temperature was 310°C.

[0050] Aluminum alloy plate A6 was obtained.

[0051] Example 7 An aluminum alloy plate was prepared according to the processing method of Example 1, except that the rough rolling temperature was 500°C, the rough rolling rate was 65 m / min, the rough rolling passes were 23, the maximum reduction was 45 mm, the intermediate billet thickness was 35 mm, the reduction rates of the four finishing rolling passes were 35%, 42%, 39% and 36% respectively, the billet thickness after finishing rolling was 8.5 mm, and the coiling temperature was 330°C.

[0052] An aluminum alloy plate A7 was obtained.

[0053] Example 8 An aluminum alloy plate was prepared according to the processing method of Example 1, except that the cold rolling rate was 60 m / min, the total processing deformation was 70%, the thickness after cold rolling was 2.4 mm, and the reduction rates of the three cold rolling passes were 38%, 35% and 23%, respectively.

[0054] An aluminum alloy plate A8 was obtained.

[0055] Example 9 An aluminum alloy plate was prepared according to the processing method of Example 1, except that the cold rolling rate was 70 m / min, the total processing deformation was 75%, the thickness after cold rolling was 2.5 mm, and the reduction rates of the three cold rolling passes were 42%, 39% and 26%, respectively.

[0056] An aluminum alloy plate A9 was obtained.

[0057] Example 10 An aluminum alloy plate was prepared according to the processing method of Example 1, except that the tension was 1 MPa, the temperature was raised to 395°C in an air cushion furnace, kept warm for 9 seconds, then raised to 475°C, kept warm for 4 seconds, the process speed was 35 m / min, and the electromagnetic induction was 1 kHz.

[0058] Aluminum alloy plate A10 was obtained.

[0059] Example 11 An aluminum alloy plate was prepared according to the processing method of Example 1, except that the tension was 2 MPa, the temperature was raised to 404°C in an air cushion furnace, kept warm for 11 seconds, then raised to 483°C, kept warm for 6 seconds, the process speed was 50 m / min, and the electromagnetic induction was 10 kHz.

[0060] An aluminum alloy plate A11 was produced.

[0061] Example 12 An aluminum alloy plate was prepared according to the processing method of Example 1, except that the deformation was 0.1%, the pre-stretching rate was 65 mm / min, maintained for 1 s, and then 25 mm / min, maintained for 4 s.

[0062] Aluminum alloy sheet A12 was obtained.

[0063] Example 13 An aluminum alloy plate was prepared according to the processing method of Example 1, except that the deformation was 0.5%, the pre-stretching rate was 70 mm / min, maintained for 2 s, and then 30 mm / min, maintained for 5 s.

[0064] Aluminum alloy plate A13 was obtained.

[0065] Comparative Example 1 Preparation of conventional 5754 aluminum alloy sheets Ingredients: Calculate the amount of each aluminum alloy raw material and prepare the aluminum alloy raw materials according to the ratio: Si=0.012wt%; Fe=0.19wt%; Cu=0.012wt%; Mn=0.432wt%; Mg=3.274wt%; Cr=0.013wt%; Zn=0.007wt%; Ti=0.008wt%; V=0.0113wt%. Other individual ≤0.05%, other total ≤0.15%, and the balance is Al.

[0066] Casting: The prepared aluminum alloy raw materials are added to a melting furnace and uniformly mixed with slag through electromagnetic stirring at a temperature range of 720°C for 30 minutes to form a melt. The melt is then transferred from the converter to a holding furnace for refining at 710°C. The melt undergoes online degassing using a mixture of chlorine and inert gas to reduce the hydrogen content to less than 0.15ml / 100gAl. Impurities larger than 20μm in diameter are filtered out through a two-stage ceramic foam filtration system. DC direct cooling semi-continuous casting is employed at a casting temperature of 682°C and a casting speed of 57mm / min during the stable period. The molten aluminum enters the starter head to form a base and is cooled through the mold wall to form a V-shaped solidification zone. The mold is then lowered at a certain speed by a hydraulic cylinder or steel wire rope, and water is sprayed through the mold at a certain angle for secondary cooling. The inner wall of the mold is lubricated with oil or graphite to improve the surface quality of the flat ingot, ultimately forming an ingot.

[0067] Sawing and milling: sawing and milling the ingot, cutting off the ingot starter at the start of casting and the gate at the end of casting, and milling off the surface oxide scale and surface defects to obtain an ingot with good surface quality.

[0068] Homogenization: The ingot was homogenized at a heating rate of 82°C / h, heated to 532°C for 8.6h, and cooled to 470°C.

[0069] Hot rolling: Rough hot rolling was carried out at 465°C using a 1+5 mill, with a rolling speed of 2.7m / s, 17 roughing passes, a maximum reduction of 35mm, and an intermediate billet thickness of 35mm. Four continuous finishing passes were then carried out, with reductions of 33%, 40%, 37% and 34% respectively, to obtain a hot-rolled coil with a thickness of 8.2mm. The coiling temperature was 322°C.

[0070] Cold rolling: The hot rolled coil is subjected to three passes with a total processing deformation of 70% to a finished thickness of 2.45 mm. The rolling speed is 67 m / min, and the reductions of the three passes are 38%, 35%, and 26% respectively.

[0071] Annealing: The finished cold-rolled coil with a thickness of 2.45mm is subjected to box annealing, nitrogen is filled to the oxygen content ≤ 0.3%, the furnace temperature is raised to 300℃ in 180min, and then to 380℃ in 300min, so that the material temperature is 300℃, kept at 300℃ for 240min, cooled to 200℃ and taken out of the furnace, and then cooled to room temperature.

[0072] Straightening and pre-stretching: After annealing, the 5754 alloy needs to be stretched, with a deformation of 0.5% and a pre-stretching speed of 56mm / min.

[0073] An aluminum alloy plate DA1 was produced.

[0074] Comparative Example 2 An aluminum alloy plate was prepared according to the processing method of Example 1, except that the aluminum alloy composition was Si=0%; Fe=0.04wt%; Cu=0wt%; Mn=0.35wt%; Mg=2.95wt%; Cr=0.001wt%; Zn=0wt%; Ti=0.001wt%; and V=0.002wt%.

[0075] An aluminum alloy plate DA2 was produced.

[0076] Comparative Example 3 An aluminum alloy plate was prepared according to the processing method of Example 1, except that the aluminum alloy composition was Si=0.21wt%; Fe=0.25wt%; Cu=0.08wt%; Mn=0.49wt%; Mg=3.42wt%; Cr=0.06wt%; Zn=0.06wt%; Ti=0.033wt%; and V=0.037wt%.

[0077] An aluminum alloy plate DA3 was produced.

[0078] Comparative Example 4 An aluminum alloy plate was prepared according to the processing method of Example 1, except that the ingot was homogenized in the following manner: 515° C.×3 h in the first stage and 450° C.×3 h in the second stage.

[0079] Aluminum alloy sheet DA4 was produced.

[0080] Comparative Example 5 An aluminum alloy plate was prepared according to the processing method of Example 1, except that the ingot was homogenized in the following manner: the first stage was 550° C. for 11 h; the second stage was 505° C. for 7 h.

[0081] Aluminum alloy sheet DA5 was produced.

[0082] Comparative Example 6 An aluminum alloy plate was prepared according to the processing method of Example 1, except that the rough rolling temperature was 450°C, the rough rolling rate was 35 m / min, the rough rolling passes were 16, the maximum reduction was 38 mm, the intermediate billet thickness was 33 mm, the reduction rates of the four finishing rolling passes were 28%, 37%, 33% and 30% respectively, the billet thickness after finishing rolling was 72 mm, and the coiling temperature was 305°C.

[0083] Aluminum alloy sheet DA6 was produced.

[0084] Comparative Example 7 An aluminum alloy plate was prepared according to the processing method of Example 1, except that the rough rolling temperature was 510°C, the rough rolling rate was 68 m / min, the rough rolling passes were 26, the maximum reduction was 46 mm, the intermediate billet thickness was 37 mm, the reduction rates of the four finishing rolling passes were 36%, 43%, 40% and 38% respectively, the billet thickness after finishing rolling was 88 mm, and the coiling temperature was 340°C.

[0085] Aluminum alloy sheet DA7 was produced.

[0086] Comparative Example 8 An aluminum alloy plate was prepared according to the processing method of Example 1, except that the cold rolling rate was 58 m / min, the total processing deformation was 62%, the thickness after cold rolling was 2.3 mm, and the reduction rates of the three cold rolling passes were 36%, 32% and 21%, respectively.

[0087] Aluminum alloy sheet DA8 was produced.

[0088] Comparative Example 9 An aluminum alloy plate was prepared according to the processing method of Example 1, except that the cold rolling rate was 72 m / min, the total processing deformation was 76%, the thickness after cold rolling was 2.6 mm, and the reduction rates of the three cold rolling passes were 44%, 40%, and 28%, respectively.

[0089] Aluminum alloy sheet DA9 was produced.

[0090] Comparative Example 10 An aluminum alloy plate was prepared according to the processing method of Example 1, except that the tension was 0.5 MPa, the temperature was raised to 380°C in an air cushion furnace, kept warm for 8 seconds, then raised to 470°C, kept warm for 3 seconds, the process speed was 32 m / min, and the electromagnetic induction was 0.5 kHz.

[0091] Aluminum alloy sheet DA10 was produced.

[0092] Comparative Example 11 An aluminum alloy plate was prepared according to the processing method of Example 1, except that the tension was 3 MPa, the temperature was raised to 410°C in an air cushion furnace, kept warm for 12 seconds, then raised to 490°C, kept warm for 7 seconds, the process speed was 55 m / min, and the electromagnetic induction was 12 kHz.

[0093] Aluminum alloy sheet DA11 was produced.

[0094] Comparative Example 12 An aluminum alloy plate was prepared according to the processing method of Example 1, except that the deformation was 0.05%, the pre-stretching rate was 60 mm / min, maintained for 0.5 s, and then 23 mm / min, maintained for 6 s.

[0095] Aluminum alloy sheet DA12 was produced.

[0096] Comparative Example 13 An aluminum alloy plate was prepared according to the processing method of Example 1, except that the deformation was 0.6%, the pre-stretching rate was 72 mm / min, maintained for 3 s, and then 35 mm / min, maintained for 6 s.

[0097] Aluminum alloy sheet DA13 was produced.

[0098] Comparative Example 14 An aluminum alloy plate was prepared according to the processing method of Example 1, except that the double-stage annealing and electromagnetic induction process were not used.

[0099] Aluminum alloy sheet DA14 was produced.

[0100] Comparative Example 15 The aluminum alloy plate was prepared according to the processing method of Example 1, except that the two-stage pre-stretching process was not adopted.

[0101] Aluminum alloy sheet DA15 was produced.

[0102] Performance tests were conducted on A1-A13 and DA1-DA15, as shown in Table 1. Table 1 By comparing the embodiments with the comparative examples, it can be seen that the present invention reduces the percentage of Mg and Mn elements in the aluminum matrix through component design, reduces the main strengthening phase Mg2Al3 formed by the eutectic reaction of Al and Mg and the dispersed strengthening phase MnAL6 produced by the solid solution and precipitation of Al and Mn, and increases the Cr content. The microstructure affected by the rolling reduction and the (Mn+Cr) element content will reduce the average grain size of the material. Cr forms a fine Al7Cr phase to pin dislocations and grain boundaries, compensate for the strength loss due to the reduction of Mg and Mn, and improve its strength and elongation. In the finished product annealing process, two-stage annealing is adopted, and Cr increases the recrystallization temperature, making the high-temperature stage of the two-stage annealing more controllable. First, the primary annealing is completed above the recrystallization temperature. Mg atoms diffuse to form nano-scale β' phase Mg2Al3, providing nucleation sites for subsequent precipitation, causing phase transformation of the internal structure of the alloy to obtain uniform equiaxed grains. The secondary annealing is completed by rapidly heating to eliminate the internal stress generated during the first stage annealing process. The high temperature promotes recrystallization, forming fine equiaxed crystals (grain size ≤ 20μm), thereby improving plasticity. The Al7Cr phase of Cr pins the grain boundaries to prevent abnormal grain growth. Residual Mg and Cr work together to form a thermally stable nano-precipitated phase (β+Al7Cr), maintaining the stable structure and properties of the alloy. Electromagnetic induction is added to the two-stage annealing process. During the air cushion furnace annealing, a medium-frequency electromagnetic field with a frequency of 1-10kHz is superimposed. Electromagnetic induction produces eddy current thermal effects inside the plate, which shortens the holding time in the 480°C high-temperature section, accelerates the diffusion of Cr elements, and promotes the Al7Cr phase to pin the grain boundaries, which more effectively inhibits grain growth. The pre-stretching is implemented in two stages with variable speed. The high-speed section eliminates the macro-Lüders band, and the low-speed section releases the micro-dislocation stress. The elongation can be further increased by 3-5%, obtaining a 5754 aluminum alloy with excellent comprehensive performance.

[0103] Attached to the instruction manual Figure 2 and attached Figure 3 It can be seen that compared with ordinary 5754 aluminum alloy, the plate produced by the present invention has a finer and more uniform grain size, better forming performance, and is more suitable for stamping automotive interior structural parts with complex shapes.

[0104] The above description is only a preferred specific implementation method of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, can make equivalent replacements or changes based on the technical solutions and inventive concepts of the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A high elongation aluminum alloy sheet for automobiles, characterized in that: The components and their weight percentages in the plate are: Si content is 0-0.18%; Fe content is 0.08-0.23%; Cu content is 0-0.1%; Mn content is 0.12-0.18%; Mg content is 2.7-2.9%; Cr content is 0.06-0.1%; Zn content is 0-0.1%; Ti content is 0.015-0.025%; V content is 0-0.05%; The content of other impurity elements is ≤0.05%; The total content of other impurity elements is ≤0.15%; The balance is Al.

2. A method for preparing the high-elongation automotive aluminum alloy sheet according to claim 1, characterized in that: The method comprises: Melting, sawing and milling, homogenization, hot rolling, cold rolling, annealing, straightening, pre-stretching, packaging; The conditions for the melting and casting include: a melting temperature of 700-750°C, a standing time of 35-45 minutes, and a refining temperature of 720-750°C; The homogenization treatment conditions include: the first stage temperature is 520-540°C for 4-10 hours, the second stage temperature is 460-500°C for 4-6 hours, the cooling method is air cooling, the cooling rate is 9-10°C / h, and the temperature is cooled to 460-500°C.

3. The method according to claim 2, characterized in that The hot rolling conditions include: rough rolling and finish rolling, wherein the rough rolling temperature is 460-500° C., the rough rolling rate is 36-66 m / min, the rough rolling passes are 18-24, the maximum reduction is 40-45 mm, and the intermediate billet thickness is 34-36 mm.

4. The method according to claim 3, characterized in that After the hot rolling rough rolling, the finishing rolling is carried out, and the finishing rolling passes are 4. The reduction rates of the 4 finishing rolling passes are 30-35%, 38-42%, 35-39% and 32-36% respectively. The thickness of the billet after finishing rolling is 7.5-8.5 mm, and the coiling temperature is 310-330°C.

5. The method according to claim 2, characterized in that The cold rolling conditions include: 3 cold rolling passes, a cold rolling rate of 60-70 m / min, a total processing deformation of 65-75%, a thickness after cold rolling of 2.4-2.5 mm, and reduction ratios of the three cold rolling passes of 38-42%, 35-39% and 23-26% respectively.

6. The method according to claim 2, characterized in that The annealing conditions include: a tension of 1-2 MPa, heating to 395-405°C in an air cushion furnace, holding for 9-11 seconds, then heating to 475-485°C, holding for 4-6 seconds, and a coiling process speed of 35-50 m / min; During annealing in the air cushion furnace, electromagnetic induction of 1-10 KHz is applied.

7. The method according to claim 2, characterized in that The pre-stretching conditions include: a deformation amount of 0.1-0.5%, a pre-stretching rate of 65-70 mm / min, maintained for 1-2 seconds, and then 25-30 mm / min, maintained for 4-5 seconds.

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