Large-span grain size isomerism aluminum alloy material and preparation method thereof

Abstract

The invention relates to a large-span grain size isomerism aluminum alloy material and a preparation method thereof, the grain size of the designed aluminum alloy material is gradually increased from the surface to the core part of the material, and the grain size is distributed in a stepped structure. The preparation method comprises the following steps: firstly, carrying out remelting treatment on the surface of an aluminum alloy annealed plate by utilizing a millisecond laser beam, and forming a layer of small-size equiaxed grains on the surface of the material; then, the remelted aluminum alloy plate is subjected to rolling large deformation treatment in a low-temperature environment, so that the recrystallization temperature of the remelted aluminum alloy plate is lower than that of surface layer deformation grains; then, the surface and the interior of the aluminum alloy subjected to low-temperature rolling and large deformation are recrystallized through a critical annealing technology so as to achieve the purpose of grain refinement, and the mechanical property of the material is improved through grain refinement strengthening; and finally, small-deformation rolling is conducted on a sample subjected to critical annealing, dislocation is introduced into large-size recrystallization equiaxed grains in the material, the yield strength of the material is further improved, and the high-strength and high-plasticity design of the aluminum alloy is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of aluminum alloy material production, and particularly relates to an aluminum alloy material with a large-span grain size heterogeneity and a preparation method thereof. Background Art

[0002] Due to characteristics such as light weight, high strength, and excellent processing performance, aluminum alloys have been widely used in many industrial fields such as aerospace, frame pipelines, ship transportation, and automobile manufacturing. However, the relatively low yield strength of aluminum alloys severely restricts their use in high-strength components. Therefore, improving the yield strength of aluminum alloys has become an urgent problem to be solved.

[0003] Aluminum alloy strengthening methods such as solid solution strengthening, precipitation strengthening, and strain strengthening aim to improve the material strength by hindering or reducing the dislocation movement inside the material. However, mobile dislocations are necessary for the plastic deformation of the material. Therefore, while these strengthening methods improve the yield strength of aluminum alloys, they will inevitably cause a decrease in plasticity. To solve the strength-plasticity trade-off problem, researchers have prepared aluminum alloy heterogeneous materials through methods such as surface mechanical rolling, high-pressure torsion, equal-channel angular pressing, and accumulative pressing. Different from homogeneous materials, the microstructure and mechanical properties between different regions inside heterogeneous materials are significantly different. This difference may be caused by different grain sizes, crystal structures, or chemical compositions. It is precisely these differences that enable heterogeneous materials to have good elongation while having a high yield strength. However, the improvement effects of surface mechanical rolling and high-pressure torsion technologies on material properties are limited, and they are not suitable for materials with complex geometries; the production efficiency of equal-channel angular pressing and accumulative pressing technologies is low, and they can only process materials with the same cross-section as the extrusion die channel, which limits their application in industrial production. Therefore, developing heterogeneous aluminum alloy materials with high yield strength and good elongation, and a preparation process suitable for industrial production, is an important research direction. Summary of the Invention

[0004] In view of the problem that the strengthening means of aluminum alloy cause great loss of material plasticity, and the limitation that the existing preparation methods of heterogeneous aluminum alloy materials are not applicable to industrial production, the present invention innovatively proposes an aluminum alloy material with a large-span grain size heterogeneity and a preparation method thereof. Its tissue characteristic is that the grain size distribution range is 0.7 - 21 μm, and the grain size gradually increases from the surface to the core of the material, showing a stepped structure distribution. The surface fine grains are used to achieve fine grain strengthening to improve the yield strength and plasticity of the aluminum alloy, and the core coarse grains maintain good plasticity. At the same time, the back stress strengthening effect is introduced by using the heterogeneity characteristic between large and small grains to improve the mechanical properties of the aluminum alloy and achieve high strength and plasticity design. At the same time, the production process of the designed heterogeneous aluminum alloy material has low requirements for equipment, is easy to implement, and is convenient for industrial use. The present invention first uses a millisecond laser beam to perform surface remelting treatment on an aluminum alloy annealed plate, forming a layer of small-sized equiaxed grains on the material surface; subsequently, the remelted aluminum alloy plate is subjected to large deformation rolling treatment at a low temperature environment to generate a deformation gradient between the surface and the core (small deformation on the surface and large deformation on the core); then, the aluminum alloy material after large deformation is subjected to critical annealing treatment, so that the surface and the core obtain an equiaxed grain size heterogeneous structure due to different recrystallization temperatures; finally, the critically annealed sample is subjected to small deformation rolling to introduce dislocations into the large grains in the core, and further improve the yield strength of the material through strain strengthening, obtaining a high-strength and high-plastic aluminum alloy material with a large-span grain size heterogeneity.

[0005] In order to achieve the above object, the present invention is realized by the following means:

[0006] The first aspect of the present invention provides a preparation method of an aluminum alloy material with a large-span grain size heterogeneity, including the following steps:

[0007] (1) Perform laser surface remelting treatment on an aluminum alloy annealed plate with a thickness of d. The laser pulse frequency used is 200 - 600 Hz, the pulse width is 10 - 80 ms, the spot diameter is 0.2 - 3 mm, the laser power is 200 - 1500 W, the overlap rate is 5 - 15%, the laser scanning speed is 50 - 250 mm / s, and the laser scanning times are 1 - 4 times;

[0008] (2) During the laser remelting treatment, use argon as the protective gas, fill argon into the treatment environment, and control the oxygen content in the environment at 150 - 470 PPm;

[0009] (3) Perform low-temperature rolling large deformation treatment on the workpiece after laser surface treatment. The deformation temperature is -196 - -30 °C, and the total deformation amount is 40 - 90%;

[0010] (4) The workpiece after large deformation by cold rolling is subjected to critical annealing treatment using a heat treatment furnace. The annealing temperature is 150 - 370 °C, the heating rate is 4 - 13 °C / min, and the isothermal time is (20 - 40)*d minutes;

[0011] (5) The workpiece after critical annealing is subjected to small deformation rolling treatment. The deformation temperature is 10 - 100 °C, and the total deformation is 3 - 15%.

[0012] Preferably, the aluminum alloy annealed plate in step (1) is a 5 - series aluminum alloy with the grade of 5182.

[0013] Preferably, in step (1), the pulse frequency is 300 - 500 Hz, the pulse width is 30 - 70 ms, the spot diameter is 1 - 2 mm, the laser power is 400 - 800 W, the overlap rate is 8 - 13%, the laser scanning speed is 100 - 200 mm / s, and the laser scanning times are 1 - 2 times.

[0014] Preferably, the thickness d of the aluminum alloy annealed plate in step (1) is 2 - 10 mm.

[0015] Preferably, the oxygen content in step (2) is controlled at 200 - 340 PPm.

[0016] Preferably, in step (3), the deformation temperature is - 196 - - 50 °C, and the total deformation is 50 - 80%.

[0017] Preferably, in step (4), the critical annealing temperature is 200 - 350 °C, the heating rate is 5 - 8 °C / min, and the isothermal time is 20*d minutes.

[0018] Preferably, in step (5), the deformation temperature is 20 - 40 °C, and the total deformation is 5 - 10%.

[0019] The second aspect of the present invention provides an aluminum alloy material with a large - span grain size heterogeneity, in which the grain size distribution range is 0.7 - 21 μm, and the grain size gradually increases from the surface to the core of the material, showing a stepped structure distribution.

[0020] The yield strength of aluminum alloy can be effectively improved by constructing a heterogeneous structure. However, this method has high requirements for equipment and is limited by the size and shape of workpieces, so it has not been widely used. Therefore, how to improve the yield strength of aluminum alloy materials by constructing a heterogeneous structure has become an important research direction. In order to construct a heterogeneous structure aluminum alloy, the applicant uses a millisecond laser to remelt the material surface to form a layer of small-sized equiaxed grains, while maintaining the organizational structure of large-sized coarse grains inside. By utilizing the heterogeneous characteristics between large and small grains, the back stress strengthening effect is introduced to improve the mechanical properties of the material. Although a gradient heterogeneous structure aluminum alloy has been constructed through laser treatment, due to the large grain size inside the material, the yield strength of the material is low. In response, based on the fine grain strengthening theory, the applicant adopts large deformation rolling followed by critical annealing treatment to refine the grains. At the same time, due to the larger deformation degree of the internal large grains, they have a higher dislocation density than the small grains on the surface, making the recrystallization temperature of the internal large grains lower than that of the small grains on the surface. Therefore, when annealing at the same temperature, the internal grain size will be larger than the surface grain size, and gradient structure heterogeneous materials with grain sizes ranging from 0.7 to 21 μm can be successfully prepared by precisely controlling the heat treatment temperature. Further, in order to continue to improve the yield strength of the material, the applicant utilizes the deformation coordination characteristics of materials with different grain sizes and introduces a small deformation process to introduce dislocations only into the large grains in the core, thereby further improving the yield strength of the material and achieving high strength and high plasticity design.

[0021] The present invention has the following beneficial effects compared with the prior art:

[0022] (1) The present invention innovatively proposes a coupling process of millisecond laser surface melting - large deformation by low-temperature rolling - critical annealing - small deformation rolling. Through the coupling effect of multiple processes, the aluminum alloy forms a structure with submicron equiaxed grains on the surface and mixed grains inside, effectively solving the problem that the improvement of the strength of aluminum alloy will reduce its plasticity, and providing a new idea for the high-strength design of aluminum alloy.

[0023] (2) The present invention prepares an aluminum alloy material with a gradient structure heterogeneous grain size (0.7 - 21 μm). By using the surface fine grains to improve the yield strength of the material and the back stress strengthening effect of the heterogeneous structure, it is possible to ensure good plasticity while increasing the yield strength of the aluminum alloy, providing a new direction for the design of material organizational structure and a new method for the design of high-performance aluminum alloy.

[0024] (3) On the premise of ensuring a certain elongation rate, the yield strength of the aluminum alloy is effectively improved; at the same time, each process in the process designed in this application has the significant advantages of simple operation, low cost, and continuous production, providing a new technical means for the production of heterogeneous aluminum alloy materials. Detailed implementation manners

[0025] To make the objectives, technical solutions and effects of the present invention clearer and more definite, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0026] Example 1

[0027] An aluminum alloy with surface sub-micron equiaxed crystal inclusions and internal mixed crystals, and its preparation method includes the following steps:

[0028] (1) Gradually polish the 5182 aluminum alloy annealed plate with a thickness of 3 mm using SiC sandpaper to 2000-mesh sandpaper, and ultrasonically clean it in absolute ethanol;

[0029] (2) After cleaning, perform laser surface remelting treatment. The laser pulse frequency used is 300 Hz, the pulse width is 30 ms, the spot diameter is 1 mm, the laser power is 400 W, the overlap rate is 8%, the laser scanning speed is 100 mm / s, and the laser scanning times is 1 time;

[0030] (3) During the laser remelting treatment, use argon as the protective gas to make the oxygen content 200 PPm;

[0031] (4) After laser remelting, perform low-temperature rolling large deformation treatment. The deformation temperature is -50 °C, and the total deformation is 50%;

[0032] (5) Use a heat treatment furnace to perform critical annealing treatment on the workpiece after low-temperature rolling large deformation. The annealing temperature is 240 °C, the heating rate is 5 °C / min, and the isothermal time is 1 h;

[0033] (6) Perform small deformation rolling treatment on the workpiece after critical annealing. The deformation temperature is 25 °C, the total deformation is 5%, and an aluminum alloy with a large-span grain size heterogeneity of surface sub-micron equiaxed crystal inclusions and internal mixed crystals is obtained, where the grain size distribution range is 0.7 - 21 μm, and the grain size gradually increases from the surface to the core of the material, showing a stepped structure distribution.

[0034] Example 2

[0035] An aluminum alloy with surface sub-micron equiaxed crystal inclusions and internal mixed crystals, and its preparation method includes the following steps:

[0036] (1) Gradually polish the 5182 aluminum alloy annealed plate with a thickness of 3 mm using SiC sandpaper to 2000-mesh sandpaper, and ultrasonically clean it in absolute ethanol;

[0037] (2) After cleaning, laser surface remelting treatment was performed, and the laser pulse frequency used was 400 Hz, the pulse width was 50 ms, the spot diameter was 2 mm, the laser power was 600 W, the overlap rate was 9%, the laser scanning speed was 150 mm / s, and the number of laser scanning times was 1;

[0038] (3) During the laser remelting process, argon was used as the protective gas, so that the oxygen content was 220 ppm;

[0039] (4) After laser remelting, low-temperature rolling and large deformation treatment are performed, with a deformation temperature of -50°C and a total deformation of 80%;

[0040] (5) using a heat treatment furnace to perform critical annealing on the workpiece after low-temperature rolling and large deformation, the annealing temperature is 240°C, the heating rate is 5°C / min, and the isothermal time is 1h;

[0041] (6) The workpiece after intercritical annealing is subjected to a small deformation rolling treatment, the deformation temperature is 25°C, the total deformation amount is 5%, and the grain size distribution range is 0.7 to 21 μm, and the grain size gradually increases from the surface to the core of the material, and the surface submicron equiaxed crystal inclusions are mixed with internal mixed crystals with a large span of grain size heterogeneity of the aluminum alloy in a stepped structure.

[0042] Example 3

[0043] An aluminum alloy with surface submicron equiaxed crystals and internal mixed crystals, wherein the preparation method comprises the following steps:

[0044] (1) A 3 mm thick 5182 aluminum alloy annealed plate was polished to 2000 grit using SiC sandpaper and then ultrasonically cleaned in anhydrous ethanol;

[0045] (2) After cleaning, laser surface remelting treatment was performed, and the laser pulse frequency used was 500 Hz, the pulse width was 70 ms, the spot diameter was 2 mm, the laser power was 800 W, the overlap rate was 13%, the laser scanning speed was 200 mm / s, and the laser scanning number was 1 time;

[0046] (3) During the laser remelting process, argon was used as the protective gas, so that the oxygen content was 300 ppm;

[0047] (4) After laser remelting, low-temperature rolling and large deformation treatment are performed, with a deformation temperature of -196°C and a total deformation of 50%;

[0048] (5) using a heat treatment furnace to perform critical annealing on the workpiece after low-temperature rolling and large deformation, the annealing temperature is 240°C, the heating rate is 8°C / min, and the isothermal time is 1h;

[0049] (6) The workpiece after critical annealing is subjected to small-deformation rolling treatment at a deformation temperature of 25°C and a total deformation of 10%, to obtain an aluminum alloy with a grain size distribution range of 0.7 - 21 μm, and the grain size gradually increases from the surface to the core of the material, presenting a stepped structure distribution of large-span grain size heterogeneity with surface submicron equiaxed crystal inclusions and internal mixed crystals.

[0050] Example 4

[0051] An aluminum alloy with surface submicron equiaxed crystal inclusions and internal mixed crystals, and its preparation method includes the following steps:

[0052] (1) The 5182 aluminum alloy annealed plate with a thickness of 3 mm is ground step by step with SiC sandpaper up to 2000-mesh sandpaper, and ultrasonically cleaned in absolute ethanol.

[0053] (2) After cleaning, laser surface remelting treatment is carried out. The laser pulse frequency used is 400 Hz, the pulse width is 50 ms, the spot diameter is 2 mm, the laser power is 600 W, the overlap rate is 9%, the laser scanning speed is 150 mm / s, and the laser scanning times is 1 time.

[0054] (3) During the laser remelting treatment, argon is used as the protective gas to make the oxygen content 220 PPm.

[0055] (4) After laser remelting, low-temperature rolling large-deformation treatment is carried out at a deformation temperature of -196°C and a total deformation of 80%.

[0056] (5) The workpiece after low-temperature rolling large-deformation is subjected to critical annealing treatment in a heat treatment furnace at an annealing temperature of 240°C, a heating rate of 7°C / min, and an isothermal time of 1 h.

[0057] (6) The workpiece after critical annealing is subjected to small-deformation rolling treatment at a deformation temperature of 25°C and a total deformation of 7%, to obtain an aluminum alloy with a grain size distribution range of 0.7 - 21 μm, and the grain size gradually increases from the surface to the core of the material, presenting a stepped structure distribution of large-span grain size heterogeneity with surface submicron equiaxed crystal inclusions and internal mixed crystals.

[0058] In addition, in other embodiments of the present invention, the laser pulse frequency can also be set to 200 Hz, 600 Hz or other values, the pulse width can be set to 10 ms, 80 ms or other values, the spot diameter can be set to 0.2 mm, 3 mm or other values, the laser power can be set to 200 W, 1500 W or other values, the overlap rate can be set to 5%, 15% or other values, the laser scanning speed can be set to 50 mm / s, 250 mm / s or other values, the laser scanning times can be set to 2 times, 3 times or 4 times, and the oxygen content can be controlled at 150 PPm, 470 PPm or other values; moreover, during the low-temperature rolling large-deformation treatment, the deformation temperature can be set to -113 °C, -30 °C or other values, the total deformation amount can be set to 40%, 90% or other values, the critical annealing temperature can be set to 150 °C, 370 °C or other values, the heating rate can be set to 4 °C / min, 13 °C / min or other values, and the isothermal time can be set to 30*d minutes, 40*d minutes or other values; during the small-deformation rolling treatment, the deformation temperature can be set to 10 °C, 100 °C or other values, and the total deformation amount can be set to 3%, 15% or other values. And an aluminum alloy annealing plate with a thickness d of 2 mm, 6 mm, 10 mm or other thicknesses can also be used.

[0059] Comparative Example 1

[0060] A 5182 aluminum alloy, and its preparation method includes the following steps:

[0061] (1) Perform low-temperature rolling large-deformation treatment on an aluminum alloy annealing plate with a thickness of 3 mm, with a deformation temperature of -50 °C and a total deformation amount of 50%;

[0062] (2) Use a heat treatment furnace to perform critical annealing treatment on the workpiece after low-temperature rolling large-deformation, with an annealing temperature of 240 °C, a heating rate of 8 °C / min, and an isothermal time of 1 h;

[0063] (3) Perform rolling treatment on the workpiece after critical annealing, with a deformation temperature of 25 °C and a total deformation amount of 8%.

[0064] Comparative Example 2

[0065] A 5182 aluminum alloy, and its preparation method includes the following steps:

[0066] (1) Gradually polish an aluminum alloy annealing plate with a thickness of 3 mm using SiC sandpaper up to 2000-mesh sandpaper, and perform ultrasonic cleaning in absolute ethanol;

[0067] (2) After cleaning, laser surface remelting treatment is carried out. The laser pulse frequency used is 400 Hz, the pulse width is 50 ms, the spot diameter is 2 mm, the laser power is 600 W, the overlap rate is 9%, the laser scanning speed is 150 mm / s, and the laser scanning times is 1 time;

[0068] (3) During the laser remelting treatment, argon is used as the protective gas to make the oxygen content 220 PPm;

[0069] (4) After laser remelting, cold rolling with large deformation is carried out. The deformation temperature is -50 °C and the total deformation is 50%;

[0070] (5) The workpiece after cold rolling with large deformation is subjected to small deformation rolling treatment. The deformation temperature is 25 °C and the total deformation is 8%.

[0071] Comparative Example 3

[0072] A 5182 aluminum alloy, and its preparation method includes the following steps:

[0073] (1) The aluminum alloy annealed plate with a thickness of 3 mm is polished step by step with SiC sandpaper to 2000 - mesh sandpaper and ultrasonically cleaned in absolute ethanol;

[0074] (2) After cleaning, laser surface remelting treatment is carried out. The laser pulse frequency used is 400 Hz, the pulse width is 50 ms, the spot diameter is 2 mm, the laser power is 600 W, the overlap rate is 9%, the laser scanning speed is 150 mm / s, and the laser scanning times is 1 time;

[0075] (3) During the laser remelting treatment, argon is used as the protective gas to make the oxygen content 220 PPm;

[0076] (4) The workpiece after laser remelting is subjected to small deformation rolling treatment. The deformation temperature is 25 °C and the total deformation is 8%.

[0077] Comparative Example 4

[0078] A 5182 aluminum alloy, and its preparation method includes the following steps:

[0079] (1) The aluminum alloy annealed plate with a thickness of 3 mm is polished step by step with SiC sandpaper to 2000 - mesh sandpaper and ultrasonically cleaned in absolute ethanol;

[0080] (2) After cleaning, laser surface remelting treatment is carried out. The laser pulse frequency used is 400 Hz, the pulse width is 50 ms, the spot diameter is 2 mm, the laser power is 600 W, the overlap rate is 9%, the laser scanning speed is 150 mm / s, and the laser scanning times is 1 time;

[0081] (3) During the laser remelting process, argon is used as the protective gas, resulting in an oxygen content of 220 ppm.

[0082] (4) After laser remelting, low-temperature rolling with large deformation is carried out. The deformation temperature is -50°C, and the total deformation is 50%.

[0083] (5) The workpiece after low-temperature rolling with large deformation is subjected to critical annealing treatment in a heat treatment furnace. The annealing temperature is 240°C, the heating rate is 8°C / min, and the isothermal time is 1 h.

[0084] Verification Example 1

[0085] Aluminum alloy annealing plates of 5182 aluminum alloy, aluminum alloys obtained in Examples 1-4 and Comparative Examples 1-4 are respectively taken, and their microstructures, yield strengths and uniform elongation rates are detected by conventional technical methods in the art. The specific detection results are shown in Table 1 below.

[0086] Table 1 Detection results of 5182 aluminum alloy annealing plates, Examples 1-4 and Comparative Examples 1-4

[0087]

[0088] By comparing the properties of the aluminum alloys in Examples 1-4 and the 5182 aluminum alloy annealing plate, it is found that preparing aluminum alloy materials with a gradient structure heterogeneity of grain size from 0.7 to 21 μm can ensure good uniform elongation while improving the yield strength.

[0089] By comparing and analyzing the results of Examples 1-4 and Comparative Examples 1-4, the following conclusions can be obtained:

[0090] (1) Comparing the control examples with the comparative examples, it can be seen that preparing aluminum alloy materials with a gradient structure heterogeneity of grain size from 0.7 to 21 μm can effectively improve the yield strength of the 5182 aluminum alloy annealing plate and ensure good elongation.

[0091] (2) In Comparative Example 1, the laser surface treatment process was not set; in Comparative Example 2, the critical annealing process was not set; in Comparative Example 3, the low-temperature rolling large deformation process was not set; in Comparative Example 4, the small deformation rolling treatment was not set. In Comparative Example 1, the existing structure of the 5182 aluminum alloy annealed plate was not changed much, and a heterogeneous structure with a grain size gradient distribution was not obtained; in Comparative Example 2, a relatively high yield strength was obtained through low-temperature rolling, but due to the lack of an annealing process, the high-density dislocations inside the material seriously damaged the plasticity; in Comparative Example 3, due to the lack of large deformation rolling treatment, although a grain size heterogeneous aluminum alloy material was formed, the internal grain size was too large, and the improvement of the yield strength of the material was limited; in Comparative Example 4, due to the lack of small deformation rolling treatment, no defects were introduced into the large grains inside, so the material strength was low and the strengthening effect was limited. The above analysis reveals that laser surface melting, low-temperature rolling large deformation, critical annealing treatment, and small deformation rolling are all essential conditions for this design. Without any one of the processes, the 5182 aluminum alloy cannot obtain the best performance.

[0092] In addition, the preparation method described in the present invention can be applied not only to 5-series aluminum alloys but also to aluminum alloys of other series, and is also applicable to other grades of 5-series aluminum alloys.

[0093] The above specific implementation part specifically introduces the analysis method involved in the present invention. It should be noted that the above introduction is only to help those skilled in the art better understand the method and idea of the present invention, rather than a limitation on the relevant content. Without departing from the principle of the present invention, those skilled in the art can also make appropriate adjustments or modifications to the present invention, and the above adjustments and modifications should also fall within the protection scope of the present invention.

Claims

1. A method for preparing an aluminum alloy material with large-span grain size heterogeneity, characterized in that: The steps include: (1) A laser surface remelting treatment is performed on an aluminum alloy annealed plate with a thickness of d, wherein the laser pulse frequency used is 200-600 Hz, the pulse width is 10-80 ms, the spot diameter is 0.2-3 mm, the laser power is 200-1500 W, the overlap rate is 5-15%, the laser scanning speed is 50-250 mm / s, and the number of laser scanning times is 1-4 times; (2) During the laser remelting process, argon is used as the protective gas, and argon is filled into the processing environment to control the oxygen content in the environment to 150-470 ppm; (3) The workpiece after laser surface treatment is subjected to low temperature rolling large deformation treatment, the deformation temperature is -196 to -30°C, and the total deformation is 40 to 90%; (4) using a heat treatment furnace to perform critical annealing treatment on the workpiece after low-temperature rolling and large deformation, the annealing temperature is 150-370°C, the heating rate is 4-13°C / min, and the isothermal time is (20-40)*d minutes; (5) The workpiece after critical annealing is subjected to small deformation rolling treatment, the deformation temperature is 10 to 100° C., and the total deformation is 3 to 15%.

2. The preparation method according to claim 1, characterized in that: The aluminum alloy annealing plate described in step (1) is a 5 series aluminum alloy with a grade of 5182.

3. The preparation method according to claim 1, characterized in that: The pulse frequency in step (1) is 300-500 Hz, the pulse width is 30-70 ms, the spot diameter is 1-2 mm, the laser power is 400-800 W, the overlap rate is 8-13%, the laser scanning speed is 100-200 mm / s, and the number of laser scanning times is 1-2 times.

4. The preparation method according to claim 1, characterized in that: The thickness d of the aluminum alloy annealing plate in step (1) is 2 to 10 mm.

5. The preparation method according to claim 1, characterized in that: The oxygen content in step (2) is controlled at 200-340 ppm.

6. The preparation method according to claim 1, characterized in that: The deformation temperature in step (3) is -196 to -50°C, and the total deformation amount is 50 to 80%.

7. The preparation method according to claim 1, characterized in that: The critical annealing temperature in step (4) is 200-350° C., the heating rate is 5-8° C. / min, and the isothermal time is 20*d minutes.

8. The preparation method according to claim 1, characterized in that: The deformation temperature in step (5) is 20-40° C., and the total deformation amount is 5-10%.

9. The preparation method according to any one of claims 1 to 8 prepares an aluminum alloy material with a grain size distribution range of 0.7 to 21 μm, and the grain size gradually increases from the surface to the core of the material, with a large-span grain size heterogeneity distributed in a stepped structure.

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