Aluminum alloy strengthening method combining cross rolling and nanosecond laser surface remelting

Abstract

The present invention relates to a method for strengthening an aluminum alloy by combining cross-rolling with nanosecond laser surface remelting. The designed aluminum alloy has the characteristics of equiaxed crystal-wrapped deformed structure. The strengthening method is as follows: first, a commercial aluminum alloy plate is rolled using a cross-rolling technique. After the cross-deformation, the dislocation density of the grains increases, and the internal texture is weakened, which helps to improve the yield strength of the material; then, a high-frequency pulse nanosecond laser is used to remelt the surface of the material. Due to the short action time and high instantaneous energy of the high-frequency pulse nanosecond laser, the material surface melts and then solidifies rapidly. The ultra-fast cooling rate effectively inhibits grain growth, forming an aluminum alloy material with submicron equiaxed crystals of 320 to 560 nm on the surface and a banded hardened structure inside. This not only significantly improves the yield strength of the aluminum alloy, but also takes into account its good corrosion resistance, solving the technical problem of the difficult balance between the yield strength and corrosion resistance of the aluminum alloy.

Description

Technical Field

[0001] The present invention belongs to the technical field of aluminum alloy material production, and in particular relates to an aluminum alloy strengthening method combining cross rolling with nanosecond laser surface remelting. Background Art

[0002] Aluminum alloys, due to their low density, high specific strength, and excellent processing properties, are the material of choice for lightweight design and are widely used in a variety of fields, including marine vessels, pipe frameworks, and automotive manufacturing. However, their low yield strength limits their application in high-strength components. Commonly used methods for strengthening aluminum alloys include solid solution strengthening, precipitation strengthening, and deformation strengthening.

[0003] Solid solution strengthening involves dissolving alloying elements into the aluminum matrix, causing lattice distortion and pinning of solute atoms, increasing resistance to dislocation movement and improving the material's strength. However, the dissolved elements combine with the aluminum matrix to form compounds that precipitate at grain boundaries, increasing the material's susceptibility to intergranular corrosion. Precipitation strengthening involves heat treatment to form fine, evenly distributed precipitates in aluminum alloys to improve their mechanical properties. However, controlling the distribution and size of these precipitates is difficult, and coarse or uneven precipitates can form microgalvanic corrosion with the matrix, reducing the material's corrosion resistance. Furthermore, precipitation strengthening cannot improve the material's strength in non-heat-treatable aluminum alloys, such as the 5-series aluminum alloy. Deformation strengthening involves introducing a high density of dislocations into the material through plastic deformation, reducing the number of mobile dislocations and transforming the internal structure into a hardened state. This can significantly increase the material's yield strength, but plastic deformation destroys the original passive film structure on the material's surface, reducing the material's corrosion resistance. Therefore, how to improve the yield strength of aluminum alloys while maintaining good corrosion resistance has become a key issue that needs to be addressed in the development of aluminum alloys. Summary of the Invention

[0004] To address the problem that existing aluminum alloy strengthening methods struggle to simultaneously improve yield strength and corrosion resistance, this present invention proposes an aluminum alloy strengthening method that combines cross-rolling with nanosecond laser surface remelting. Submicron equiaxed grains are produced on the surface of a banded hardened structure using a nanosecond laser. This surface refinement improves the material's plasticity, while the internal banded hardened structure significantly enhances the material's yield strength. Furthermore, the defect-free equiaxed grains on the surface ensure excellent corrosion resistance. The present invention first subjects commercial aluminum alloy sheets to a rolling deformation treatment to produce a banded hardened structure. Subsequently, the surface is remelted using a high-frequency pulsed nanosecond laser beam, forming a layer of uniform, ultrafine equiaxed grains with a size of 320 to 560 nm. This results in an aluminum alloy material with a surface size of 320 to 560 nm and an internal banded hardened structure. The surface submicron equiaxed grains enhance the aluminum alloy's plasticity and corrosion resistance, while the internal banded hardened structure further enhances yield strength, achieving both improved yield strength and a comprehensive improvement in corrosion resistance.

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

[0006] A first aspect of the present invention provides an aluminum alloy strengthening method by cross-rolling combined with nanosecond laser surface remelting, comprising the following steps:

[0007] (1) A cross-rolling deformation treatment is performed on an aluminum alloy plate with a thickness of d. After each rolling pass, the aluminum alloy plate is rotated 90° before the next rolling pass. The deformation temperature is 0-70°C and the total deformation is 10-25%;

[0008] (2) The surface of the deformed workpiece is subjected to laser melting treatment. The laser pulse frequency used is 170-340 kHz, the pulse width is 8-25 ns, the spot diameter is 30-80 μm, and the laser power density is 5-60 kW / cm 2 , overlap rate 4~13%, laser scanning speed 350~850mm / s, light on delay 20μs, light off delay 180μs, corner delay 80μs, laser scanning times 1 time;

[0009] (3) During the laser melting process, argon is used as the protective gas. By filling the processing environment with argon, the oxygen content in the environment is controlled within the range of 170-370 ppm;

[0010] (4) During the laser melting process, a low-temperature pad is set at the bottom of the material to accelerate heat dissipation and achieve ultra-fast cooling of the molten pool. The temperature of the low-temperature pad is -40 to -150°C.

[0011] Preferably, the aluminum alloy plate in step (1) is a 5 series aluminum alloy with a grade of 5182.

[0012] Preferably, the deformation temperature in step (1) is 15-50° C., and the total deformation amount is 10-20%.

[0013] Preferably, the thickness d of the aluminum alloy plate in step (1) is 3 to 15 mm.

[0014] Preferably, the pulse frequency in step (2) is 220-310 KHz, the pulse width is 12-21 ns, the spot diameter is 40-60 μm, and the laser power density is 10-40 kW / cm 2 , overlap rate is 6-9%, and laser scanning speed is 450mm / s-700mm / s.

[0015] Preferably, the oxygen content in step (3) is controlled within the range of 200 to 300 ppm.

[0016] Preferably, the temperature of the low-temperature pad in step (4) is -70 to -110°C.

[0017] The second aspect of the present invention provides an aluminum alloy material prepared according to the above-mentioned aluminum alloy strengthening method, which has submicron equiaxed crystals of 320 to 560 nm on the surface and a strip-shaped hardened structure inside.

[0018] While aluminum alloy strengthening methods such as solid solution strengthening, precipitation strengthening, and deformation strengthening increase the yield strength of the material, they inevitably lead to a decrease in the material's corrosion resistance. Therefore, exploring how to improve the yield strength of aluminum alloys without compromising their corrosion resistance is an important research topic. Based on the theory of deformation strengthening, the applicant uses cross-rolling to deform the material in different directions. The entanglement of dislocations in different directions, combined with the weakening of the matrix texture by cross-rolling, significantly improves the material's strength. However, the plasticity and corrosion resistance of the material are greatly damaged after cross-rolling. Therefore, the applicant proposes to use high-frequency pulsed nanosecond laser remelting to transform the deformed structure of the material surface into submicron equiaxed crystals, and improve the plasticity and corrosion resistance of the material through fine grain strengthening. Compared with ordinary millisecond lasers, high-frequency pulsed nanosecond lasers have concentrated energy, small heat-affected zone and small molten pool during processing. The smaller heat-affected zone can avoid the internal deformed structure from being affected by heat during laser processing. The small molten pool has a fast cooling rate of the internal melt, and the low-temperature pad can achieve ultra-fast cooling of the molten pool. Therefore, high-frequency pulsed nanosecond laser can form submicron equiaxed crystals with a size of 320 to 560 nm on the surface of the material while ensuring that the material has a deformed structure inside. Through the above process, an aluminum alloy material with submicron equiaxed crystals of 320 to 560 nm on the surface and deformed structure inside is constructed. Through the coupling effect of multiple processes, the yield strength is improved while also ensuring good corrosion resistance of the material.

[0019] The present invention has the following beneficial effects compared to the prior art:

[0020] (1) The present invention proposes an aluminum alloy material with submicron equiaxed crystals of 320 to 560 nm on the surface and a deformed structure inside. The plasticity of the material is improved by surface fine grain strengthening, while the yield strength of the material is improved by the deformed structure inside. In addition, the defect-free submicron equiaxed crystals on the surface can ensure the excellent corrosion resistance of the material, solving the problem that the corrosion resistance of high-strength aluminum alloys is difficult to ensure, and providing new ideas for the design of high-performance aluminum alloys.

[0021] (2) The present invention innovatively proposes a coupling process of cross-rolling deformation-high-frequency pulse nanosecond laser surface remelting. Through this process, the microstructure of aluminum alloy grains can be regulated and structures with different grain sizes and morphologies can be constructed, providing a new method for regulating the microstructure of aluminum alloy materials.

[0022] (3) The present invention effectively improves the yield strength of aluminum alloy without damaging the corrosion resistance of aluminum alloy; at the same time, all processes in this application have the advantages of simple operation, low cost, and continuous production, providing a new means for the production of aluminum alloy. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail with reference to the following examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0024] Example 1

[0025] A method for strengthening aluminum alloy by cross-rolling combined with nanosecond laser surface treatment, comprising the following steps:

[0026] (1) A 5182 aluminum alloy plate with a thickness of 3 mm was cross-rolled. After each rolling pass, the aluminum alloy plate was rotated 90° before the next rolling pass. The deformation temperature was 24°C and the total deformation was 20%.

[0027] (2) The deformed workpiece was polished step by step using SiC sandpaper to 2000 grit sandpaper and then ultrasonically cleaned in anhydrous ethanol;

[0028] (3) The surface of the workpiece is subjected to laser melting treatment. The laser pulse frequency used is 220KHz, the pulse width is 12ns, the spot diameter is 40μm, and the laser power density is 10kW / cm 2 , overlap rate is 6%, laser scanning speed is 450mm / s, light on delay is 20μs, light off delay is 180μs, corner delay is 80μs, serpentine scanning path is used, laser scanning times is 1;

[0029] (4) During the laser melting process, argon is used as the protective gas. By filling the processing environment with argon, the oxygen content in the environment is controlled at 240 ppm;

[0030] (5) During the laser melting process, a low-temperature pad is set at the bottom of the material to accelerate heat dissipation and achieve ultra-fast cooling of the molten pool. The temperature of the low-temperature pad is -110℃.

[0031] The aluminum alloy strengthening method can produce an aluminum alloy material with submicron equiaxed crystals of 320 to 560 nm on the surface and a strip-shaped hardened structure inside.

[0032] Example 2

[0033] A method for strengthening aluminum alloy by cross-rolling combined with nanosecond laser surface remelting, comprising the following steps:

[0034] (1) A 5182 aluminum alloy plate with a thickness of 3 mm was cross-rolled. After each rolling pass, the aluminum alloy plate was rotated 90° before the next rolling pass. The deformation temperature was 30°C and the total deformation was 15%.

[0035] (2) The deformed workpiece was polished step by step using SiC sandpaper to 2000 grit sandpaper and then ultrasonically cleaned in anhydrous ethanol;

[0036] (3) The surface of the workpiece is subjected to laser melting treatment. The laser pulse frequency used is 290KHz, the pulse width is 15ns, the spot diameter is 55μm, and the laser power density is 17.9kW / cm 2 , overlap rate is 7%, laser scanning speed is 550mm / s, light on delay is 20μs, light off delay is 180μs, corner delay is 80μs, serpentine scanning path is adopted, laser scanning times is 1;

[0037] (4) During the laser melting process, argon is used as the protective gas. By filling the processing environment with argon, the oxygen content in the environment is controlled at 240 ppm;

[0038] (5) During the laser melting process, a low-temperature pad is set at the bottom of the material to accelerate heat dissipation and achieve ultra-fast cooling of the molten pool. The temperature of the low-temperature pad is -90°C.

[0039] The aluminum alloy strengthening method can produce an aluminum alloy material with submicron equiaxed crystals of 320 to 560 nm on the surface and a strip-shaped hardened structure inside.

[0040] Example 3

[0041] A method for strengthening aluminum alloy by cross-rolling combined with nanosecond laser surface remelting, comprising the following steps:

[0042] (1) A 5182 aluminum alloy plate with a thickness of 3 mm was cross-rolled. After each rolling pass, the aluminum alloy plate was rotated 90° before the next rolling pass. The deformation temperature was 50°C and the total deformation was 10%.

[0043] (2) The deformed workpiece was polished step by step using SiC sandpaper to 2000 grit sandpaper and then ultrasonically cleaned in anhydrous ethanol;

[0044] (3) The surface of the workpiece is subjected to laser melting treatment. The laser pulse frequency used is 310KHz, the pulse width is 21ns, the spot diameter is 60μm, and the laser power density is 40kW / cm 2 , overlap rate 9%, laser scanning speed 700mm / s, light on delay 20μs, light off delay 180μs, corner delay 80μs, serpentine scanning path, laser scanning times 1;

[0045] (4) During the laser melting process, argon is used as the protective gas. By filling the processing environment with argon, the oxygen content in the environment is controlled at 240 ppm;

[0046] (5) During the laser melting process, a low-temperature pad is set at the bottom of the material to accelerate heat dissipation and achieve ultra-fast cooling of the molten pool. The temperature of the low-temperature pad is -70°C.

[0047] The aluminum alloy strengthening method can produce an aluminum alloy material with submicron equiaxed crystals of 320 to 560 nm on the surface and a strip-shaped hardened structure inside.

[0048] In addition, in other embodiments of the present invention, the deformation temperature can be set to 0°C, 15°C, 70°C or other values, the total deformation can be set to 10%, 25% or other values, the laser pulse frequency can be set to 170KHz, 340KHz or other values, the pulse width can be set to 8ns, 25ns or other values, the spot diameter can be set to 30μm, 80μm or other values, and the laser power density can be set to 5kW / cm 2 、60kW / cm 2 or other values, the overlap ratio is set to 4%, 13%, or other values, the laser scanning speed is set to 350 mm / s, 850 mm / s, or other values, the oxygen content is controlled at 170 ppm, 200 ppm, 300 ppm, 370 ppm, or other values, and the temperature of the low-temperature pad is set to -40°C, -150°C, or other values. Furthermore, the aluminum alloy plate may have a thickness d of 9 mm, 15 mm, or other thicknesses.

[0049] Comparative Example 1

[0050] A method for improving the corrosion resistance of aluminum alloy by laser surface melting comprises the following steps:

[0051] (1) Use SiC sandpaper to polish the sample surface step by step until it reaches 1200 mesh sandpaper, and use alcohol ultrasonic cleaning to keep the sample surface clean. In order to improve the absorption rate of aluminum alloy to laser, a layer of carbon black is evenly coated on the sample surface;

[0052] (2) Preliminary optimization of laser surface melting process parameters was performed to obtain a preliminary laser surface melting process window. The optimized parameters were: laser wavelength 1.06 μm, average laser power 800 W, scanning speed 8 mm / s, overlap rate 50%, spot diameter 2 mm, and carrier gas flow rate 10 L / min.

[0053] (3) Laser surface melting of aluminum alloy was performed, and the waveform of the laser light source was modulated into a square wave; wherein, the parameters of the square wave were: peak power: 8000W, pulse frequency: 100HZ, duty cycle: 0.5. After the laser melting was completed, a molten layer was formed on the surface of the 5182 aluminum alloy.

[0054] Comparative Example 2

[0055] A 5182 aluminum alloy, the preparation method of which comprises the following steps:

[0056] (1) Laser melting treatment of 5182 aluminum alloy plate was performed. The laser pulse frequency used was 230KHz, the pulse width was 15ns, the spot diameter was 45μm, and the laser power density was 17.9kW / cm 2 , overlap rate is 5%, laser scanning speed is 450mm / s, light on delay is 20μs, light off delay is 180μs, corner delay is 80μs, serpentine scanning path is adopted, laser scanning times is 1;

[0057] (2) During the laser melting process, argon is used as the protective gas. By filling the processing environment with argon, the oxygen content in the environment is controlled at 200 ppm;

[0058] (3) During the laser melting process, a low-temperature pad is set at the bottom of the material to accelerate heat dissipation and achieve ultra-fast cooling of the molten pool. The temperature of the low-temperature pad is -90°C.

[0059] Comparative Example 3

[0060] A 5182 aluminum alloy, the preparation method of which comprises the following steps:

[0061] (1) A 5182 aluminum alloy plate with a thickness of 3 mm was cross-rolled at a deformation temperature of 24°C and a total deformation of 20%.

[0062] Comparative Example 4

[0063] A 5182 aluminum alloy millisecond laser surface melting method, the preparation method comprising the following steps:

[0064] (1) Laser remelting of 5182 aluminum alloy plate was performed with a laser frequency of 400 Hz, a pulse width of 50 ms, a scanning speed of 120 mm / s, a spot diameter of 1 mm, an overlap rate of 10%, a serpentine scanning path, and 1 scan number;

[0065] (2) During the laser treatment process, argon is used as a protective gas and is filled into the environment so that the oxygen content is 210 ppm.

[0066] Verification Example 1

[0067] The microstructure, yield strength and corrosion current density of the 5182 aluminum alloy plate, the aluminum alloys prepared in Examples 1-3 and Comparative Examples 1-4 were tested using conventional technical methods in the art. The specific test results are shown in Table 1 below.

[0068] Table 1 Test results of 5182 aluminum alloy plate, Examples 1-3 and Comparative Examples 1-4

[0069]

[0070] By comparing the performance of the aluminum alloys of Examples 1-3 with the 5182 aluminum alloy, it was found that the aluminum alloy material with submicron equiaxed crystals of 320 to 560 nm on the surface and a strip-like hardened structure inside can effectively improve the yield strength of the 5182 commercial aluminum alloy.

[0071] By comparing and analyzing the results of Examples 1-3 and Comparative Examples 1-4, the following conclusions can be drawn:

[0072] (1) As can be seen from the comparative examples and comparative examples, the submicron equiaxed crystals of 320 to 560 nm and the internal strip-shaped hardened structure can significantly improve the yield strength of the 5182 commercial aluminum alloy while still maintaining good corrosion resistance.

[0073] (2) Comparative Example 1 is a method for improving the corrosion resistance of aluminum alloy by low-frequency laser surface melting; Comparative Example 2 does not have a rolling deformation process; Comparative Example 3 does not have a laser surface strengthening process; Comparative Example 4 is a millisecond laser melting process. In comparative example 1, carbon black needs to be applied on the surface of the material before processing, and the process is complicated. At the same time, the low-frequency laser melting technology has a low frequency, slow scanning speed, and large spot diameter, resulting in a large heat-affected zone and a long laser beam action time. Although a molten layer is formed on the surface of the material to improve the corrosion resistance of the material, the slow cooling rate makes the grains on the surface of the material coarse, and the internal structure of the material also grows due to the heat, which reduces the yield strength of the material; in comparative example 2, submicron equiaxed crystals are formed on the surface of the material through high-frequency pulse nanosecond laser surface remelting, while the interior lacks a strip-like hardened state structure. Although good corrosion resistance is guaranteed, the effect of improving the yield strength of the aluminum alloy is limited; in comparative example 3, a large number of dislocations are introduced through rolling, which improves the yield strength of the aluminum alloy, but seriously reduces the corrosion resistance of the aluminum alloy; in comparative example 4, due to the slow millisecond laser processing speed, large heat-affected zone, large molten pool, and slow molten pool cooling rate, the grains of the material surface are coarse after remelting, and the surface state is extremely poor, resulting in a decrease in the yield strength and corrosion resistance of the material. The above analysis reveals that cross-rolling deformation and high-frequency pulsed nanosecond laser treatment are both indispensable conditions for this design. Without any one of the processes, the 5182 aluminum alloy cannot achieve optimal performance.

[0074] In addition, the strengthening method of the present invention can be applied not only to 5 series aluminum alloys, but also to other series aluminum alloys, and is also applicable to other grades of 5 series aluminum alloys.

[0075] The above detailed description of the analytical methods involved in the present invention provides a detailed introduction. It should be noted that the above description is intended solely to help those skilled in the art better understand the methods and concepts of the present invention, and is not intended to limit the relevant content. Without departing from the principles of the present invention, those skilled in the art may make appropriate adjustments or modifications to the present invention, and such adjustments and modifications shall also fall within the scope of protection of the present invention.

Claims

1. A method for strengthening aluminum alloy by cross rolling combined with nanosecond laser surface remelting, characterized in that: The steps include: (1) The aluminum alloy plate with a thickness of d is subjected to cross-rolling deformation treatment. After each rolling pass, the aluminum alloy plate is rotated 90° before the next rolling pass. The deformation temperature is 0~70℃, and the total deformation is 10~25%. The aluminum alloy plate is 5 series aluminum alloy with a grade of 5182. (2) The surface of the deformed workpiece is subjected to laser melting treatment. The laser pulse frequency used is 170~340KHz, the pulse width is 8~25ns, the spot diameter is 30~80µm, and the laser power density is 5~60kW / cm 2 , overlap rate 4~13%, laser scanning speed 350~850mm / s, light on delay 20µs, light off delay 180µs, corner delay 80µs, laser scanning times 1; (3) During the laser melting process, argon is used as the protective gas. By filling the processing environment with argon, the oxygen content in the environment is controlled within the range of 170~370PPm; (4) During the laser melting process, a low-temperature pad is set at the bottom of the material to accelerate heat dissipation and achieve ultra-fast cooling of the molten pool. The temperature of the low-temperature pad is -40~-150℃.

2. The aluminum alloy strengthening method according to claim 1, characterized in that: The deformation temperature in step (1) is 15-50°C, and the total deformation is 10-20%.

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

4. The aluminum alloy strengthening method according to claim 1, characterized in that: The pulse frequency in step (2) is 220~310KHz, the pulse width is 12~21ns, the spot diameter is 40~60µm, and the laser power density is 10~40kW / cm 2 , overlap rate 6~9%, laser scanning speed is 450mm / s~700mm / s.

5. The aluminum alloy strengthening method according to claim 1, characterized in that: The oxygen content in step (3) is controlled within the range of 200-300 ppm.

6. The aluminum alloy strengthening method according to claim 1, characterized in that: The temperature of the low-temperature pad in step (4) is -70~-110℃.

7. An aluminum alloy material, prepared according to the aluminum alloy strengthening method according to any one of claims 1 to 6, characterized in that: The surface of the material is 320~560nm submicron equiaxed crystals and the interior is a striped hardened structure.

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