Strengthening method of 5-series aluminum alloy

Abstract

The invention provides a method for strengthening a 5-series aluminum alloy with surface submicron equiaxed crystals and an internal banded structure, which comprises the following steps of: firstly, carrying out calendering treatment on a 5-series aluminum alloy plate to obtain the banded structure and improve the yield strength of the material; afterwards, surface remelting treatment is conducted through nanosecond laser, surface remelting treatment is conducted on the material through the characteristics that the nanosecond laser is short in acting time and high in instantaneous energy, the material surface is rapidly solidified after being melted, grain growth is effectively restrained through the ultra-high cooling rate, the surface grain size is kept to be 200-400 nm, and the surface grain size is kept to be 200-400 nm; the surface fine grains improve the plasticity and corrosion resistance of the material; and finally, the aluminum alloy material with the submicron equiaxed crystals with the surface being 200-400 nm and the strip-shaped hardened structure inside is formed, the yield strength of the aluminum alloy is remarkably improved, the excellent corrosion resistance of the aluminum alloy is also considered, and the technical problem that the yield strength and the corrosion resistance of the aluminum alloy are difficult to balance is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of aluminum alloy strengthening production, and particularly relates to a strengthening method for 5 series aluminum alloy. Background Art

[0002] The main alloying elements in 5 series aluminum alloys are aluminum and magnesium. With the characteristics of light weight, high strength and good processing performance, they have been widely used in many fields such as marine ships, frame pipes and automobile manufacturing. However, 5 series aluminum alloys are non-heat-treatable aluminum alloys, which means that the material strength cannot be improved through precipitation strengthening mechanism. Therefore, the mechanical properties of 5 series aluminum alloys are limited by chemical composition and internal organizational structure, and their strength improvement mainly depends on solid solution strengthening, deformation strengthening and fine grain strengthening.

[0003] Solid solution strengthening, by increasing the solid solubility of magnesium in aluminum, thereby improving the yield strength of 5 series aluminum alloys. However, the solid solubility of magnesium in aluminum is limited, and when the magnesium content is too high, it will increase the sensitivity of the alloy to intergranular corrosion and stress corrosion; deformation strengthening, by introducing high-density dislocations into the material through rolling treatment, the internal structure is transformed into a deformed structure, which greatly improves the yield strength of the material, but rolling destroys the original passivation film structure on the surface of the material, resulting in a decrease in the corrosion resistance of the material; grain refinement strengthening, first subjecting the material to large plastic deformation and then annealing to form small grains, and improving the mechanical properties of aluminum alloys through grain refinement, but this method has high requirements for equipment and high energy consumption, and due to large plastic deformation, it has great restrictions on the production of thick steel plates. Therefore, there is an urgent need for an economical and effective method that can enhance the yield strength of aluminum alloys while maintaining their good corrosion resistance. Summary of the invention

[0004] Aiming at the problem that the deformation strengthening method improves the yield strength of 5-series aluminum alloy while causing the corrosion resistance of the material to decrease, the present invention proposes a new method for preparing 5-series aluminum alloy with high strength, high plasticity and high corrosion resistance. The structural characteristics of the aluminum alloy prepared by the method are: the surface is submicron equiaxed crystals, and the interior is a heterogeneous structure of banded hardened structure. This structural heterogeneity can make full use of the surface submicron grain fine grain strengthening to improve the plasticity of the material, while using the internal banded structure to improve the yield strength of the material, and the surface is remelted by high-frequency nanosecond laser to produce internal defect-free equiaxed grains, which can ensure the excellent corrosion resistance of the material, and achieve the improvement of the yield strength of the material without reducing the corrosion resistance. The present invention firstly performs a rolling deformation treatment on the 5-series aluminum alloy plate to obtain a banded hardened structure; then, the surface of the material is remelted by a nanosecond laser beam, and a layer of uniform ultrafine equiaxed grains is formed on the surface of the material by using the characteristics of rapid solidification and rapid cooling of the nanosecond laser, while the material maintains a banded hardened structure inside, so as to construct an aluminum alloy material with equiaxed crystals of 200-400nm on the surface and a banded hardened structure inside. By utilizing the surface submicron equiaxed crystal structure, the plasticity and corrosion resistance of the aluminum alloy are enhanced, and with the help of the internal strip-like hardened structure, its yield strength is further improved, thus achieving the goal of ensuring good corrosion resistance while improving the yield strength.

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

[0006] The first aspect of the present invention provides a 5-series aluminum alloy strengthening method by nanosecond laser surface remelting, comprising the following steps:

[0007] (1) The 5 series aluminum alloy plate is subjected to rolling deformation treatment, the deformation temperature is 10 to 70° C., and the total deformation amount is 10 to 30%;

[0008] (2) After calendering deformation, it is subjected to laser melting treatment, with the laser pulse frequency of 100-400KHz, pulse width of 10-30ns, spot diameter of 10-100μm, and laser power density of 10-90kW / cm 2 , overlap rate 5-15%, laser scanning speed 300-800mm / s, light on delay 20μs, light off delay 180μs, corner delay 80μs, laser scanning times 1-3 times;

[0009] (3) During the laser melting process, argon gas is used to protect the molten pool so that the oxygen content in the environment is 150-330 ppm;

[0010] (4) During the laser melting process, a low-temperature pad is placed at the bottom of the material to accelerate the cooling rate of the molten pool and achieve ultra-fast cooling. The temperature of the low-temperature pad is -90 to -196 °C.

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

[0012] Preferably, the deformation temperature in step (1) is 20-55° C., and the total deformation amount is 10-20%.

[0013] Preferably, the pulse frequency in step (2) is 200-350 KHz, the pulse width is 15-20 ns, the spot diameter is 30-50 μm, and the laser power density is 15-75 kW / cm 2 The overlap rate is 8-10%, the laser scanning speed is 500mm / s-600mm / s, and the laser scanning times are 1-2 times.

[0014] Preferably, the oxygen content in step (3) is 180-300 ppm.

[0015] Preferably, the temperature of the low-temperature pad in step (4) is -110 to -196°C.

[0016] The second aspect of the present invention provides an aluminum alloy material prepared according to the above strengthening method, which has submicron equiaxed crystals of 200 to 400 nm on the surface and a strip-shaped hardened structure inside.

[0017] Existing 5 series aluminum alloy strengthening methods, such as solid solution strengthening and deformation strengthening, often reduce the corrosion resistance of the material while increasing the yield strength of the aluminum alloy. In this regard, exploring ways to increase the yield strength of 5 series aluminum alloys while ensuring their good corrosion resistance is an important scientific research direction. Based on the theory of deformation strengthening, the applicant proposed to use the rolling process to transform the interior of the aluminum alloy into a strip-like hardened state structure, and significantly improve the yield strength of the aluminum alloy material by reducing the number of movable dislocations inside the material. However, the rolling process will damage the plasticity and corrosion resistance of the material. In this regard, the applicant proposes to introduce submicron equiaxed crystals to the surface of the material to improve the plasticity and corrosion resistance of the material. In order to obtain submicron equiaxed crystals on the surface while maintaining a high-strength hardened state structure inside the material, the applicant uses nanosecond laser surface remelting technology, taking advantage of the characteristics of concentrated nanosecond laser energy density, small heat-affected zone, and fast cooling rate. While the surface of the material is melted by the laser beam, the internal structure of the material will not change due to the heat effect. Combined with a low-temperature pad, ultra-fast cooling of the surface molten pool is achieved. The ultra-fast cooling rate forms submicron equiaxed crystals with a size of 200 to 400nm on the surface of the material, and the plasticity of the aluminum alloy is improved by fine grain strengthening. The defect-free submicron equiaxed grains on the surface can ensure good corrosion resistance. The aluminum alloy material with 200 to 400nm submicron equiaxed crystals on the surface and internal strip-shaped hardened state structure constructed by the present invention can improve the yield strength while also ensuring the good corrosion resistance of the material through the coupling of multiple processes.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) The present invention proposes an aluminum alloy with submicron equiaxed crystals of 200 to 400 nm on the surface and a strip-like hardened heterogeneous structure inside. The surface fine grain strengthening and defect-free submicron equiaxed crystals improve the plasticity and corrosion resistance of the material. At the same time, the internal deformed structure improves the yield strength of the material, thereby solving the problem that the corrosion resistance of high-strength aluminum alloys is difficult to ensure, and providing a new idea for the design of high-performance aluminum alloys.

[0020] (2) The present invention innovatively proposes a coupling process of rolling deformation-nanosecond laser surface remelting, through which the microstructure of aluminum alloy can be regulated, providing a new method for regulating the microstructure of aluminum alloy materials.

[0021] (3) The present invention effectively improves the yield strength of aluminum alloy without damaging its corrosion resistance; at the same time, each link of the process is easy to operate, cost-effective, and suitable for continuous production, providing a new means for the production of aluminum alloy. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical scheme and effect of the present invention clearer and more specific, the present invention is further described in detail with reference to the following 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.

[0023] Example 1

[0024] A method for strengthening a 5 series aluminum alloy comprises the following steps:

[0025] (1) A 5182 aluminum alloy plate with a thickness of 3 mm was subjected to a rolling process with a deformation temperature of 25°C and a total deformation of 20%;

[0026] (2) The deformed workpiece was polished step by step using SiC sandpaper to 2000 grit sandpaper, and then ultrasonically cleaned in anhydrous ethanol;

[0027] (3) The polished workpiece was subjected to laser melting treatment. The laser pulse frequency used was 220 KHz, the pulse width was 15 ns, the spot diameter was 30 μm, and the laser power density was 15 kW / cm 2 , overlap rate 8%, laser scanning speed 500mm / s, light on delay 20μs, light off delay 180μs, corner delay 80μs, laser scanning times 1;

[0028] (4) During the laser melting process, argon gas is used to protect the molten pool so that the oxygen content in the environment is 180 ppm;

[0029] (5) During the laser melting process, a low-temperature pad is set at the bottom of the material to accelerate the cooling rate of the molten pool and achieve ultra-fast cooling. The temperature of the low-temperature pad is -196°C.

[0030] The strengthening method can prepare an aluminum alloy material with submicron equiaxed crystals of 200 to 400 nm on the surface and a strip-shaped hardened structure inside.

[0031] Example 2

[0032] A method for strengthening a 5 series aluminum alloy comprises the following steps:

[0033] (1) A 5182 aluminum alloy plate with a thickness of 3 mm was subjected to rolling treatment, with a deformation temperature of 25°C and a total deformation of 15%;

[0034] (2) The deformed workpiece was polished step by step using SiC sandpaper to 2000 grit sandpaper, and then ultrasonically cleaned in anhydrous ethanol;

[0035] (3) The polished workpiece was subjected to laser melting treatment. The laser pulse frequency used was 280 kHz, the pulse width was 20 ns, the spot diameter was 45 μm, and the laser power density was 54 kW / cm 2 , overlap rate 9%, laser scanning speed 550mm / s, light on delay 17μs, light off delay 180μs, corner delay 80μs, laser scanning times 1;

[0036] (4) During the laser melting process, argon gas is used to protect the molten pool so that the oxygen content in the environment is 240 ppm;

[0037] (5) During the laser melting process, a low-temperature pad is set at the bottom of the material to accelerate the cooling rate of the molten pool and achieve ultra-fast cooling. The temperature of the low-temperature pad is -150°C.

[0038] The strengthening method can prepare an aluminum alloy material with submicron equiaxed crystals of 200 to 400 nm on the surface and a strip-shaped hardened structure inside.

[0039] Example 3

[0040] A method for strengthening a 5 series aluminum alloy comprises the following steps:

[0041] (1) A 5182 aluminum alloy plate with a thickness of 3 mm was subjected to rolling treatment, with a deformation temperature of 25°C and a total deformation of 10%;

[0042] (2) The deformed workpiece was polished step by step using SiC sandpaper to 2000 grit sandpaper, and then ultrasonically cleaned in anhydrous ethanol;

[0043] (3) The polished workpiece was subjected to laser melting treatment. The laser pulse frequency used was 330 KHz, the pulse width was 20 ns, the spot diameter was 50 μm, and the laser power density was 75 kW / cm 2 , overlap rate 10%, laser scanning speed 600mm / s, light on delay 20μs, light off delay 180μs, corner delay 80μs, laser scanning times 1;

[0044] (4) During the laser melting process, argon gas is used to protect the molten pool so that the oxygen content in the environment is 240 ppm;

[0045] (5) During the laser melting process, a low-temperature pad is set at the bottom of the material to accelerate the cooling rate of the molten pool and achieve ultra-fast cooling. The temperature of the low-temperature pad is -110°C.

[0046] The strengthening method can prepare an aluminum alloy material with submicron equiaxed crystals of 200 to 400 nm on the surface and a strip-shaped hardened structure inside.

[0047] In addition, in other embodiments of the present invention, the deformation temperature can be set to 10°C, 70°C or other values, the total deformation amount can be set to 10%, 30% or other values, the laser pulse frequency can be set to 100KHz, 400KHz or other values, the pulse width can be set to 10ns, 30ns or other values, the spot diameter can be set to 10μm, 100μm or other values, and the laser power density can be set to 10kW / cm 2 、90kW / cm 2 or other values, the overlap rate is set to 5%, 15% or other values, the laser scanning speed is set to 300mm / s, 800mm / s or other values, the laser scanning times are set to 2 or 3 times, the oxygen content is controlled to 150PPm, 330PPm or other values, the low temperature pad temperature is set to -90℃, -143℃ or other values. In addition, in addition to the 5182 aluminum alloy, other aluminum alloys can also be used for the 5 series aluminum alloy.

[0048] Comparative Example 1

[0049] A method for improving the corrosion resistance of aluminum alloy by laser surface melting, the preparation method of which comprises the following steps:

[0050] (1) Use SiC sandpaper to polish the sample surface step by step to 1200 mesh sandpaper, use alcohol ultrasonic cleaning to keep the sample surface clean, and evenly coat a layer of carbon black on the sample surface to improve the laser absorption rate of aluminum alloy;

[0051] (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;

[0052] (3) Laser surface melting of aluminum alloy is performed, and the waveform of the laser light source is modulated into a square wave; wherein the parameters of the square wave are: peak power: 8000 W, pulse frequency: 100 Hz, duty cycle: 0.5. After the laser melting is completed, a molten layer is formed on the surface of the 5182 aluminum alloy.

[0053] Comparative Example 2

[0054] A 5182 aluminum alloy, the preparation method of which comprises the following steps:

[0055] (1) Laser melting treatment of 5182 aluminum alloy plate was performed with a laser pulse frequency of 220 KHz, a pulse width of 20 ns, a spot diameter of 30 μm, and a laser power density of 8 kW / cm 2 , overlap rate 8%, laser scanning speed 500mm / s, light on delay 20μs, light off delay 180μs, corner delay 80μs, laser scanning times 1;

[0056] (2) During the laser melting process, argon gas is used to protect the molten pool so that the oxygen content in the environment is 240 ppm;

[0057] (3) During the laser melting process, a low-temperature pad is set at the bottom of the material to accelerate the cooling rate of the molten pool and achieve ultra-fast cooling. The temperature of the low-temperature pad is -150°C.

[0058] Comparative Example 3

[0059] A 5182 aluminum alloy, the preparation method of which comprises the following steps:

[0060] (1) A 5182 aluminum alloy plate with a thickness of 3 mm was subjected to rolling treatment, the deformation temperature was 25°C, and the total deformation was 20%.

[0061] Comparative Example 4

[0062] A 5182 aluminum alloy millisecond laser surface melting method, the preparation method comprising the following steps:

[0063] (1) The aluminum alloy plate was laser remelted 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 one scanning time;

[0064] (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.

[0065] Verification Example 1

[0066] The 5182 aluminum alloy plate, the aluminum alloys prepared in Examples 1-3 and Comparative Examples 1-4 were respectively taken, and their organizational structure, yield strength and corrosion current density were tested using conventional technical methods in the art. The specific test results are shown in Table 1 below.

[0067] Table 1 Test results of 5182 aluminum alloy plate, Examples 1-3 and Comparative Examples 1-3

[0068]

[0069]

[0070] By comparing the performance of the aluminum alloys of Examples 1-3 and 5182 aluminum alloy plates, it was found that the aluminum alloy material with submicron equiaxed crystals of 200 to 400 nm on the surface and a strip-like hardened structure inside can effectively improve the yield strength of commercial 5182 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) By comparing the examples and comparative examples, it can be seen that the submicron equiaxed crystals of 200 to 400 nm and the structure of the internal band-like hardened state organization can effectively improve the yield strength of the commercial 5182 aluminum alloy while ensuring 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. Comparative Example 1 is a low-frequency laser melting technology with low frequency and large spot diameter, resulting in a large heat-affected zone, a large molten pool, and a slow cooling rate of the molten pool. Although a molten layer is formed on the surface of the material to improve the corrosion resistance of the material, due to the slow cooling rate, no submicron equiaxed crystals are formed on the surface of the material, and the internal structure of the material grows up due to the heat during the laser treatment process, which reduces the yield strength of the material; although submicron equiaxed crystals are formed on the surface of the comparative example 2 by laser surface remelting, the effect of improving the yield strength of the aluminum alloy is limited due to the lack of strip-shaped hardened state structure inside; although the yield strength of the aluminum alloy is improved by introducing a large number of dislocations, the corrosion resistance of the aluminum alloy is seriously reduced; comparative example 4 is due to the slow processing speed of the millisecond laser, the large heat-affected zone, the large molten pool, and the slow cooling rate of the molten pool. Therefore, the grains are coarse after the surface remelting of the material, 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 rolling deformation and nanosecond laser treatment are both essential conditions for this design, and the lack of any process cannot make the 5182 aluminum alloy obtain the best performance.

[0074] The above specific implementation method part specifically introduces the analytical 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 ideas of the present invention, rather than limiting the relevant content. Without departing from the principle of the present invention, those skilled in the art may also make appropriate adjustments or modifications to the present invention, and the above adjustments and modifications shall also fall within the scope of protection of the present invention.

Claims

1. A method for strengthening a 5 series aluminum alloy, characterized in that: The steps include: (1) The 5 series aluminum alloy plate is subjected to rolling deformation treatment, the deformation temperature is 10 to 70° C., and the total deformation amount is 10 to 30%; (2) After calendering deformation, the surface is subjected to laser melting treatment, and the laser pulse frequency used is 100-400KHz, the pulse width is 10-30ns, the spot diameter is 10-100μm, and the laser power density is 10-90kW / cm 2 , overlap rate 5-15%, laser scanning speed 300-800mm / s, light on delay 20μs, light off delay 180μs, corner delay 80μs, laser scanning times 1-3 times; (3) During the laser melting process, argon gas is used to protect the molten pool so that the oxygen content in the environment is 150-330 ppm; (4) During the laser melting process, a low-temperature pad is placed at the bottom of the material to accelerate the cooling rate of the molten pool and achieve ultra-fast cooling. The temperature of the low-temperature pad is -90 to -196 °C.

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

3. The strengthening method according to claim 1, characterized in that: The deformation temperature in step (1) is 20-55° C., and the total deformation amount is 10-20%.

4. The strengthening method according to claim 1, characterized in that: The pulse frequency in step (2) is 200-350KHz, the pulse width is 15-20ns, the spot diameter is 30-50μm, and the laser power density is 15-75kW / cm 2 The overlap rate is 8-10%, the laser scanning speed is 500mm / s-600mm / s, and the laser scanning times are 1-2 times.

5. The strengthening method according to claim 1, characterized in that: The oxygen content in step (3) is 180-300 ppm.

6. The strengthening method according to claim 1, characterized in that: The temperature of the low-temperature pad in step (4) is -110 to -196°C.

7. The strengthening method according to any one of claims 1 to 6, characterized in that: An aluminum alloy material having a submicron equiaxed crystal of 200 to 400 nm on the surface and a strip-shaped hardened state structure inside is prepared by the aluminum alloy strengthening method using nanosecond laser surface remelting.

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