An aluminum alloy material with heterogeneous inner and outer layers and its preparation method

Abstract

This invention relates to an aluminum alloy material with heterogeneous inner and outer layers and its preparation method. The designed aluminum alloy exhibits a wide-ranging grain size distribution, with submicron equiaxed crystals on the surface and micron-sized deformed internal structures. The preparation method is as follows: First, the workpiece undergoes high-frequency pulsed nanosecond laser remelting. Utilizing the extremely short duration and high instantaneous energy of the high-frequency pulsed nanosecond laser, submicron equiaxed crystals with a size of 350–550 nm are formed on the material surface. Then, the laser-melted workpiece undergoes heat treatment to reduce residual internal stress caused by recrystallization. Finally, the heat-treated workpiece undergoes low-temperature rolling deformation treatment, resulting in a banded structure within the material, constructing an aluminum alloy material with a surface of 350–550 nm submicron equiaxed crystals encapsulating an internal banded structure. While ensuring good plasticity, this invention significantly improves the yield strength of the material, solving the technical problem of balancing yield strength and plasticity in aluminum alloy materials.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy material processing technology, and specifically relates to an aluminum alloy material with heterogeneous inner and outer layers and its preparation method. Background Technology

[0002] Aluminum alloys are widely used in aerospace, transportation, and electronics industries due to their lightweight, high strength, good corrosion resistance, and good machinability. However, with the increasing pursuit of lightweight and high-performance structural designs, the relatively low yield strength of aluminum alloys makes it difficult to meet the requirements for high-strength components.

[0003] Currently, the following processes are commonly used to strengthen aluminum alloy materials: Solid solution strengthening, which strengthens the aluminum alloy by increasing the content of alloying elements. However, increasing the number of solute atoms can cause lattice irregularities and distortions, and solute atoms have a pinning effect on dislocation movement, increasing the resistance to dislocation movement and reducing mobile dislocations. While improving the yield strength of the aluminum alloy, it can also damage the plasticity of the aluminum alloy. Precipitation strengthening, which uses heat treatment and aging to precipitate alloying elements in the form of a second phase in the aluminum alloy. However, the distribution and size of the second phase particles are difficult to control. Coarse or unevenly distributed second phase particles can lead to local stress concentration and reduce the plasticity of the material. In particular, 5-series aluminum alloys are not suitable for precipitation strengthening because the precipitation phase is difficult, there are few nuclei, and the aging strengthening effect is poor. Deformation strengthening introduces high-density dislocations into the interior of the aluminum alloy material through plastic deformation. During the movement of dislocations, they intersect each other to form cleavage, reducing mobile dislocations and transforming the internal structure of the material into a hardened state, which can greatly improve the yield strength of the material. However, plastic deformation severely damages the plasticity of the material, and the equipment cost is high. Therefore, how to improve the yield strength of aluminum alloys while ensuring their good plasticity has become a key issue that urgently needs to be addressed in the development of aluminum alloys. Summary of the Invention

[0004] This invention addresses the problem that existing aluminum alloy strengthening methods, while improving yield strength, often lead to a decrease in plasticity. It innovatively proposes an aluminum alloy material with heterogeneous inner and outer layers and its preparation method. Compared to conventional laser processing methods, high-frequency pulsed nanosecond lasers (pulse frequency in the KHz range, pulse width in the ns range) have extremely short interaction times with the material surface and extremely fast cooling rates. This ultra-high cooling rate causes a significant temperature hysteresis in the crystallization nucleation process, effectively inhibiting grain growth and forming a layer of ultrafine equiaxed grains on the material surface. This fine-grain strengthening improves the material's plasticity and strength; simultaneously, the banded structure within the material further enhances its strength, achieving a high yield strength design. This invention first performs laser surface melting on a commercial aluminum alloy sheet, combined with a low-temperature pad and argon protection, to obtain submicron equiaxed crystals on the surface; then, the surface-melted aluminum alloy material is annealed to reduce or eliminate internal stress caused by crystallization; finally, the annealed aluminum alloy sheet is subjected to low-temperature rolling to introduce a banded structure into the material, resulting in an aluminum alloy material with an ultrafine equiaxed crystal with a submicron grain size of 350-550 nm encapsulating an internal banded structure.

[0005] To achieve the above objectives, the present invention is accomplished by the following means:

[0006] The first aspect of this invention provides an aluminum alloy material with heterogeneous inner and outer layers and a method for preparing the same, comprising the following steps:

[0007] (1) High-frequency pulsed nanosecond laser remelting was performed on the surface and bottom of an aluminum alloy plate with a thickness of d. The laser frequency was 120–330 kHz, the pulse width was 10–50 ns, the spot diameter was 15–120 μm, and the laser power density was 5–40 kW / cm². 2 The overlap rate is 5-15%, the scanning speed is 350-950 mm / s, the light-on delay is 30 μs, the light-off delay is 185 μs, the corner delay is 85 μs, the number of scans is 1-3, and the scanning path is a serpentine path.

[0008] (2) During the laser remelting process, a low-temperature pad is placed under the workpiece to accelerate the cooling speed and achieve ultra-fast cooling. The temperature of the low-temperature pad is -25 to -70℃.

[0009] (3) During the laser remelting process, argon gas is used to protect the molten pool and argon gas is introduced into the environment to make the oxygen content in the environment 170-340 ppm;

[0010] (4) The remelted workpiece is heat-preserved at a temperature of 110℃~270℃ for a time of (20~40)*d minutes and a heating rate of 5~15℃ / min. After heat preservation, the workpiece is removed.

[0011] (5) After the heat preservation is completed, the workpiece is subjected to low temperature rolling deformation treatment. The deformation temperature is -25 to -196℃, and the total deformation is 15% to 40%.

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

[0013] Preferably, the laser frequency in step (1) is 210–280 kHz, the pulse width is 25–35 ns, the spot diameter is 35–55 μm, and the laser power density is 10–30 kW / cm². 2 The overlap rate is 8-12%, the scanning speed is 350-850 mm / s, and the number of scans is 1-2.

[0014] Preferably, the thickness d of the aluminum alloy plate in step (1) is 3 to 15 mm.

[0015] Preferably, the temperature of the low-temperature pad in step (2) is -30 to -65°C.

[0016] Preferably, the oxygen content in step (3) is 200-280 ppm.

[0017] Preferably, the heat preservation temperature in step (4) is 150-200℃, the heat preservation time is (25-40)*d minutes, and the heating rate is 9-12℃ / min.

[0018] Preferably, the deformation temperature in step (5) is -50 to -196°C, and the total deformation is 15% to 25%.

[0019] The second aspect of the present invention provides an aluminum alloy material with an outer layer heterogeneity, consisting of submicron equiaxed crystals with a surface area of ​​350-550 nm enclosing an internal strip-like microstructure, prepared according to the above-described preparation method.

[0020] Strengthening methods for aluminum alloys, such as solid solution strengthening, precipitation strengthening, and deformation strengthening, can effectively improve the yield strength of aluminum alloys. However, these methods significantly impair the material's plasticity. Therefore, how to improve the yield strength while maintaining good plasticity is an important research direction. Based on the theory of fine-grained strengthening, the applicant proposes to remelt the material surface using a high-frequency pulsed nanosecond laser. Utilizing the laser's extremely short interaction time with the material surface, concentrated energy, and extremely rapid cooling rate, combined with a low-temperature pad at the bottom of the material to accelerate the cooling of the melt, ultra-fine equiaxed grains are formed on the material surface. This fine-grained strengthening improves both the yield strength and plasticity of the material. However, the internal stress generated by the recrystallization of the surface grains during laser remelting can damage the material's plasticity. To address this, this invention uses annealing to reduce or eliminate internal pressure, thereby mitigating the impact of internal stress on the material's plasticity. Considering that surface grain refinement has limited impact on improving the yield strength of materials, the applicant, based on strain hardening theory, introduced low-temperature rolling technology. By creating a low-temperature environment to reduce stacking fault energy and decrease resistance to dislocation movement, a higher dislocation density can be obtained after low-temperature rolling. Furthermore, during the rolling process, the internal large grains deform more than the surface fine grains, and the internal grains are elongated to introduce a banded structure into the material. This internal banded structure significantly improves the yield strength of the material. This invention, through the coupling effect of the above processes, constructs an inner and outer layer heterogeneous aluminum alloy material with a surface of fine equiaxed grains (350–550 nm submicron size) enclosing an internal banded structure. This significantly improves the yield strength of the aluminum alloy while maintaining its excellent plasticity.

[0021] The present invention has the following advantages over the prior art:

[0022] (1) This invention proposes an aluminum alloy material with a surface of 350-550nm submicron equiaxed crystals and an interior of banded grain structure. The surface fine grain strengthening improves the plasticity and yield strength of the aluminum alloy material, while the internal banded grain structure further improves the yield strength of the material. This solves the problem of the difficulty in achieving both yield strength and plasticity in aluminum alloys and provides a new idea for the design of high-performance aluminum alloys.

[0023] (2) This invention innovatively proposes a coupled process of laser remelting-heat treatment-low temperature rolling deformation, which realizes the fine control of aluminum alloy grains, provides a new direction for material microstructure design, and provides a new means for the design of high-performance aluminum alloys.

[0024] (3) While ensuring the good plasticity of aluminum alloy, the yield strength of aluminum alloy is significantly improved. At the same time, each step in the process designed in this invention is a common process in the field, which has the advantages of simple operation, low cost and easy large-scale production. Detailed Implementation

[0025] To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0026] Example 1

[0027] An aluminum alloy material with heterogeneous inner and outer layers and its preparation method, the preparation method comprising the following steps:

[0028] (1) Grind the 3mm thick 5182 aluminum alloy plate from 500 grit to 2000 grit using SiC sandpaper, and then clean it with ultrasonic in anhydrous ethanol.

[0029] (2) Laser remelting was performed on the top and bottom surfaces of the cleaned aluminum alloy plate. The laser frequency was 210 kHz, the pulse width was 25 ns, the scanning speed was 350 mm / s, the spot diameter was 35 μm, and the laser power density was 10 kW / cm². 2 The overlap rate is 8%, the light-on delay is 30μs, the light-off delay is 185μs, the corner delay is 85μs, a serpentine scanning path is used, and the number of scans is 1.

[0030] (3) During the laser remelting process, a low-temperature pad is placed under the workpiece, and the temperature of the low-temperature pad is set to -30℃;

[0031] (4) During the laser remelting process, argon is used as a protective gas and argon is introduced into the environment to ensure that the oxygen content is 200 ppm;

[0032] (5) After remelting, the workpiece is kept at 150℃ for 75 minutes with a heating rate of 9℃ / min. After the heat preservation is completed, it is taken out and air-cooled.

[0033] (6) The heat-treated workpiece is subjected to low-temperature rolling deformation treatment at a temperature of -50℃ and a total deformation of 18%, thereby preparing an aluminum alloy material with an inner and outer layer heterogeneity, in which the surface has a submicron equiaxed crystal structure of 350-550nm encapsulating the internal strip-like structure.

[0034] Example 2

[0035] An aluminum alloy material with heterogeneous inner and outer layers and its preparation method, the preparation method comprising the following steps:

[0036] (1) Grind the 7mm thick 5182 aluminum alloy plate from 500 grit to 2000 grit using SiC sandpaper, and then clean it with ultrasonic in anhydrous ethanol.

[0037] (2) Laser remelting was performed on the top and bottom surfaces of the cleaned aluminum alloy plate. The laser frequency was 250 kHz, the pulse width was 30 ns, the scanning speed was 550 mm / s, the spot diameter was 45 μm, and the laser power density was 20 kW / cm². 2 The overlap rate is 10%, the light-on delay is 30μs, the light-off delay is 185μs, the corner delay is 85μs, a serpentine scanning path is used, and the number of scans is 1.

[0038] (3) During the laser remelting process, a low-temperature pad is placed under the workpiece, and the temperature of the low-temperature pad is set to -50℃;

[0039] (4) During the laser remelting process, argon is used as a protective gas and argon is introduced into the environment to ensure that the oxygen content is 250 ppm;

[0040] (5) After remelting, the workpiece is kept at 170℃ for 210 min with a heating rate of 10℃ / min. After the heat preservation is completed, it is taken out and air-cooled.

[0041] (6) The heat-treated workpiece is subjected to low-temperature rolling deformation treatment with a deformation temperature of -100℃ and a total deformation of 20%, thereby preparing an aluminum alloy material with an inner and outer layer heterogeneity of submicron equiaxed crystals with a surface of 350-550nm encapsulating an internal strip-like microstructure.

[0042] Example 3

[0043] An aluminum alloy material with heterogeneous inner and outer layers and its preparation method, the preparation method comprising the following steps:

[0044] (1) Grind the 15mm thick 5182 aluminum alloy plate from 500 grit to 2000 grit using SiC sandpaper, and then clean it with ultrasonic in anhydrous ethanol.

[0045] (2) Laser remelting was performed on the top and bottom surfaces of the cleaned aluminum alloy plate. The laser frequency was 280 kHz, the pulse width was 35 ns, the scanning speed was 750 mm / s, the spot diameter was 55 μm, and the laser power density was 30 kW / cm². 2 The overlap rate is 12%, the light-on delay is 30μs, the light-off delay is 185μs, the corner delay is 85μs, a serpentine scanning path is used, and the number of scans is 1.

[0046] (3) During the laser remelting process, a low-temperature pad is placed under the workpiece, and the temperature of the low-temperature pad is set to -65℃;

[0047] (4) During the laser remelting process, argon is used as a protective gas and argon is introduced into the environment to ensure that the oxygen content is 280 ppm;

[0048] (5) After remelting, the workpiece is kept at 200℃ for 600 min with a heating rate of 12℃ / min. After the heat preservation is completed, it is taken out and air-cooled.

[0049] (6) The heat-treated workpiece is subjected to low-temperature rolling deformation treatment with a deformation temperature of -196℃ and a total deformation of 25%, thereby preparing an aluminum alloy material with an inner and outer layer heterogeneity, in which the surface has a submicron equiaxed crystal structure of 350-550nm encapsulating the internal strip-like structure.

[0050] Furthermore, in other embodiments of the present invention, the laser frequency can be set to 120 kHz, 330 kHz, or other values; the pulse width can be set to 10 ns, 50 ns, or other values; the scanning speed can be set to 850 mm / s, 950 mm / s, or other values; the spot diameter can be set to 15 μm, 120 μm, or other values; and the laser power density can be set to 5 kW / cm². 2 40kW / cm 2 Or other values, overlap rate set to 5%, 15% or other values, number of scans set to 2 or 3, temperature of low temperature pad set to -25℃, -70℃ or other values, oxygen content set to 170PPm, 340PPm or other values, heat preservation temperature set to 110℃, 270℃ or other values, heat preservation time set to 20*d minutes, 35*d minutes or other values, heating rate set to 5℃ / min, 15℃ / min or other values, deformation temperature set to -25℃, -110℃ or other values, total deformation set to 15%, 40% or other values.

[0051] Comparative Example 1

[0052] A 5182 aluminum alloy, the preparation method of which includes the following steps:

[0053] (1) The 5182 aluminum alloy plate is subjected to rolling deformation treatment at a temperature of -196℃ and a deformation amount of 20%.

[0054] Comparative Example 2

[0055] A laser strengthening method for aluminum alloy surfaces includes the following steps:

[0056] (1) Grind the 3mm thick 5182 aluminum alloy plate from 500 grit to 2000 grit using SiC sandpaper, and then clean it with ultrasonic in anhydrous ethanol.

[0057] (2) Laser remelting was performed on the top and bottom surfaces of the cleaned aluminum alloy plate. The laser frequency was 240 kHz, the pulse width was 25 ns, the scanning speed was 550 mm / s, the spot diameter was 40 μm, and the laser power density was 12.5 kW / cm². 2 The overlap rate is 10%, the light-on delay is 30μs, the light-off delay is 185μs, the corner delay is 85μs, a serpentine scanning path is used, and the number of scans is 1.

[0058] (3) During the laser remelting process, a low-temperature pad is placed under the workpiece, and the temperature of the low-temperature pad is set to -40℃;

[0059] (4) During the laser remelting process, argon is used as a protective gas and argon is introduced into the environment to ensure that the oxygen content is 250 ppm;

[0060] (5) After remelting, the workpiece is kept at 100℃ for 1 hour with a heating rate of 10℃ / min. After the heat preservation is completed, the workpiece is taken out and air-cooled.

[0061] Comparative Example 3

[0062] A millisecond laser strengthening method for aluminum alloy surfaces, comprising the following steps:

[0063] (1) Grind the 3mm thick 5182 aluminum alloy plate from 500 grit to 2000 grit using SiC sandpaper, and then clean it with ultrasonic in anhydrous ethanol.

[0064] (2) Laser remelting is performed on the top and bottom surfaces of the cleaned aluminum alloy plate. The laser frequency is 400Hz, the pulse width is 50ms, the scanning speed is 150mm / s, the spot diameter is 1mm, the overlap rate is 10%, a serpentine scanning path is used, and the number of scans is 1.

[0065] (3) During the laser remelting process, a low-temperature pad is placed under the workpiece, and the temperature of the low-temperature pad is set to -40℃;

[0066] (4) During the laser remelting process, argon is used as a protective gas and argon is introduced into the environment to ensure that the oxygen content is 250 ppm;

[0067] (5) After remelting, the workpiece is kept at 100℃ for 1 hour with a heating rate of 10℃ / min. After the heat preservation is completed, it is taken out and air-cooled.

[0068] (6) The heat-treated workpiece is subjected to low-temperature rolling deformation treatment at a temperature of -196℃ and a total deformation of 20%.

[0069] Verification Example 1

[0070] 5182 aluminum alloy plates, aluminum alloys prepared in Examples 1-3 and Comparative Examples 1-3 were taken respectively, and their microstructure, yield strength and uniform elongation were tested using conventional techniques in the art. The specific test results are shown in Table 1 below.

[0071] Table 1. Test results of 5182 aluminum alloy sheet, Examples 1-3 and Comparative Examples 1-3

[0072]

[0073] By comparing the performance of aluminum alloys in Examples 1-3 and 5182 aluminum alloy plates, it was found that the submicron grain size structure can significantly improve the yield strength of aluminum alloys while ensuring plasticity.

[0074] By comparing and analyzing the results of Examples 1-3 and Comparative Examples 1-3, the following conclusions can be drawn:

[0075] (1) As can be seen from the comparative examples and comparative examples, the construction of submicron grain size structure can effectively improve the yield strength of 5182 aluminum alloy plate.

[0076] (2) Comparative Example 1 did not include a laser remelting process; Comparative Example 2 did not include a low-temperature rolling process; Comparative Example 3 used a millisecond laser surface remelting process. Comparative Example 1 did not significantly alter the existing microstructure of the aluminum alloy and did not achieve an aluminum alloy structure with submicron equiaxed crystals enclosing internal banded structures. Although Comparative Example 2 improved the strength and plasticity of the material through surface grain refinement, it lacked internal banded structures, thus limiting the improvement in the yield strength of the aluminum alloy. Due to the large diameter of the millisecond laser spot, the large heat-affected zone, the large molten pool, and the slow cooling rate of the molten pool in Comparative Example 3, the grains were coarse after surface remelting, which greatly reduced the yield strength of the material compared to the material treated with nanosecond laser. The above analysis reveals that high-frequency pulsed nanosecond laser remelting, heat treatment, and low-temperature rolling deformation treatment are all essential conditions for this design. The absence of any one of these processes would prevent the 5182 aluminum alloy from achieving optimal performance.

[0077] Furthermore, the preparation method described in this invention can be applied not only to 5-series aluminum alloys, but also to other aluminum alloys, and is equally applicable to other grades of 5-series aluminum alloys.

[0078] The above detailed embodiments provide a specific description of the analytical methods involved in this invention. It should be noted that the above description is only intended to help those skilled in the art better understand the methods and ideas of this invention, and is not intended to limit the scope of the invention. Without departing from the principles of this invention, those skilled in the art can make appropriate adjustments or modifications to this invention, and such adjustments and modifications should also fall within the protection scope of this invention.

Claims

1. A method for preparing an aluminum alloy material with heterogeneous inner and outer layers, characterized in that, Includes the following steps: (1) High-frequency pulsed nanosecond laser remelting is performed on the surface and bottom of an aluminum alloy plate with a thickness of d. The laser frequency used is 120~330KHz, the pulse width is 10~70ns, the spot diameter is 10~120µm, and the laser power density is 5~50kW / cm². 2 The overlap rate is 5~25%, the scanning speed is 350~950mm / s, the light-on delay is 30µs, the light-off delay is 185µs, the corner delay is 85µs, the number of scans is 1~3, and the scanning path is a serpentine path; the aluminum alloy plate is a 5-series aluminum alloy with grade 5182. (2) During the laser remelting process, a low-temperature pad is placed under the workpiece to accelerate the cooling speed of the workpiece and achieve ultra-fast cooling. The temperature of the low-temperature pad is -25~-70℃. (3) During the laser remelting process, argon gas is used to protect the molten pool and argon gas is introduced into the environment to make the oxygen content in the environment 170~340 ppm; (4) The remelted workpiece is heat-preserved at a temperature of 110℃~270℃ for a duration of (20~40)*d minutes and a heating rate of 5~15℃ / min. The workpiece is then removed after the heat preservation is completed. (5) After the heat preservation is completed, the workpiece is subjected to low temperature rolling deformation treatment. The deformation temperature is -25~-196℃ and the total deformation is 15%~40%.

2. The preparation method according to claim 1, characterized in that, The laser frequency in step (1) is 210~280KHz, the pulse width is 10~55ns, the spot diameter is 10~100µm, and the laser power density is 5~45kW / cm². 2 The overlap rate is 5-20%, the scanning speed is 350-850 mm / s, and the number of scans is 1-2.

3. The preparation method according to claim 1, characterized in that, The thickness d of the aluminum alloy plate mentioned in step (1) is 3~15mm.

4. The preparation method according to claim 1, characterized in that, The temperature of the low-temperature pad mentioned in step (2) is -30~-65℃.

5. The preparation method according to claim 1, characterized in that, The oxygen content mentioned in step (3) is 200~280 ppm.

6. The preparation method according to claim 1, characterized in that, The heat preservation temperature in step (4) is 150~200℃, the heat preservation time is (25~40)*d minutes, and the heating rate is 9~12℃ / min.

7. The preparation method according to claim 1, characterized in that, The deformation temperature in step (5) is -50 to -196°C, and the total deformation is 15% to 25%.

8. An aluminum alloy material with an inner and outer layer heterogeneity, in which the surface has a submicron equiaxed crystal structure of 350~550nm encapsulates an internal strip-like microstructure, is prepared by the preparation method according to any one of claims 1-7.

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