Aluminum alloy material with heterogeneous inner layer and outer layer and preparation method of aluminum alloy material

Abstract

The invention relates to an aluminum alloy material with heterogeneous inner and outer layers and a preparation method thereof. The grain size of the designed aluminum alloy is in large-span distribution, the surface is submicron equiaxed crystals, and the interior is a micron-sized deformed structure. The preparation method comprises the following steps that firstly, a workpiece is subjected to high-frequency pulse nanosecond laser remelting treatment, and submicron isometric crystals with the size ranging from 350 nm to 550 nm are formed on the surface of a material by means of the characteristics that high-frequency pulse nanosecond laser is extremely short in acting time and high in instantaneous acting energy; then the workpiece subjected to laser melting is subjected to heat treatment, and residual internal stress generated by recrystallization is reduced; and finally, the workpiece subjected to heat treatment is subjected to low-temperature rolling deformation treatment, a banded structure is obtained in the material, and the aluminum alloy material with the internal banded structure wrapped by submicron equiaxed crystals with the surface ranging from 350 nm to 550 nm is constructed. On the premise that good plasticity of the material is guaranteed, the yield strength of the material is remarkably improved, and the technical problem that the yield strength and plasticity of the aluminum alloy material are difficult to achieve at the same time is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of aluminum alloy material processing, and particularly relates to an aluminum alloy material with heterogeneous inner and outer layers and a preparation method thereof. Background Art

[0002] Aluminum alloys are widely used in aerospace, transportation, electronics and other industries due to their light weight, high strength, good corrosion resistance and good machinability. However, with the continuous pursuit of lightweight and high-performance design structures, the low yield strength of aluminum alloys makes it difficult to meet the requirements of high-strength components.

[0003] At present, the following process methods are commonly used to strengthen aluminum alloy materials: solid solution strengthening, which strengthens aluminum alloys by increasing the content of alloying elements in aluminum alloys. However, the increase of solute atoms will cause irregularity and distortion of the lattice and the solute atoms have a pinning effect on dislocation movement, increase the resistance to dislocation movement, and reduce movable dislocations. While improving the yield strength of aluminum alloys, it will damage the plasticity of aluminum alloys; precipitation strengthening, which precipitates alloying elements in aluminum alloys in the form of a second phase by heat treatment-aging, but the distribution and size of the second phase particles are difficult to control. Coarse or unevenly distributed second phase particles will cause local stress concentration and reduce the plasticity of the material. In particular, 5 series aluminum alloys are not suitable for precipitation strengthening due to the difficulty of precipitating phases, few cores, and poor aging strengthening effects; deformation strengthening, which introduces high-density dislocations into the material by plastic deformation of aluminum alloy materials. Dislocations will intersect with each other to form steps during movement, reducing movable dislocations, and converting the internal structure of the material into a hardened structure, which can greatly improve the yield strength of the material. However, plastic deformation seriously damages the plasticity of the material and the equipment cost is relatively high. Therefore, how to improve the yield strength of aluminum alloys while ensuring their good plasticity has become a key issue that needs to be overcome in the development of aluminum alloys. Summary of the invention

[0004] In view of the problem that the existing aluminum alloy strengthening methods increase the yield strength of aluminum alloys while causing the plasticity of aluminum alloys to decrease, the present invention innovatively proposes an aluminum alloy material with heterogeneous inner and outer layers and a preparation method thereof. Compared with ordinary laser processing methods, high-frequency pulse nanosecond laser (pulse frequency is at the KHz level, pulse width is at the ns level) has the characteristics of extremely short action time on the material surface and extremely fast cooling rate. The ultra-high cooling rate causes a large temperature hysteresis phenomenon in the crystallization nucleation process, effectively inhibits grain growth, and forms a layer of ultra-fine equiaxed grains on the material surface, thereby improving the plasticity and strength of the material through fine grain strengthening; at the same time, the material strength is further improved through the banded structure inside the material, realizing a high yield strength design. The present invention first performs laser surface melting treatment on a commercial aluminum alloy plate, cooperates with a bottom low-temperature pad and argon protection to obtain submicron equiaxed crystals on the surface; then, the aluminum alloy material after surface melting is annealed to reduce or eliminate the internal stress caused by crystallization; finally, the annealed aluminum alloy plate is subjected to low-temperature rolling treatment to introduce a strip-shaped structure into the material, and an aluminum alloy material with a surface having a submicron grain size of 350 to 550 nm and an internal strip-shaped structure wrapped in ultrafine equiaxed crystals.

[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 an aluminum alloy material with heterogeneous inner and outer layers and a preparation method thereof, comprising the following steps:

[0007] (1) The surface and bottom of the aluminum alloy plate with a thickness of d were remelted by high-frequency pulse nanosecond laser. 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 / cm 2 , overlap rate is 5-15%, scanning speed is 350-950mm / s, light-on delay is 30μs, light-off delay is 185μs, corner delay is 85μs, scanning times is 1-3 times, and scanning path is 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°C;

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

[0010] (4) The remelted workpiece is subjected to heat preservation treatment at a temperature of 110°C to 270°C for a time of (20 to 40)*d minutes and a heating rate of 5 to 15°C / min. After the heat preservation is completed, the workpiece is taken out;

[0011] (5) After the insulation is completed, the workpiece is subjected to low-temperature rolling deformation treatment, the deformation temperature is -25 to -196°C, and the total deformation amount is 15% to 40%.

[0012] Preferably, the aluminum alloy plate in step (1) is a 5 series aluminum alloy with a grade of 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 / cm 2 The overlap rate is 8-12%, the scanning speed is 350-850 mm / s, and the number of scans is 1-2 times.

[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 insulation temperature in step (4) is 150-200° C., the insulation time is (25-40)*d minutes, and the heating rate is 9-12° C. / min.

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

[0019] The second aspect of the present invention provides an aluminum alloy material prepared according to the above preparation method, which has an outer layer heterogeneous structure and an inner strip-shaped structure wrapped with submicron equiaxed crystals with a surface diameter of 350 to 550 nm.

[0020] The yield strength of aluminum alloys can be effectively improved by aluminum alloy strengthening methods such as solid solution strengthening, precipitation strengthening and deformation strengthening, but these methods greatly damage the plasticity of the material. In this regard, how to ensure good plasticity while improving the yield strength of the material is an important research direction. Based on the theory of fine grain strengthening, the applicant proposed to remelt the surface of the material by high-frequency pulse nanosecond laser, taking advantage of its extremely short action time with the material surface, concentrated energy, and extremely fast cooling rate, and cooperating with the low-temperature pad at the bottom of the material to accelerate the cooling of the melt, so that ultrafine equiaxed grains are formed on the surface of the material, and the yield strength and plasticity of the material are improved by fine grain strengthening. However, the internal stress generated by the recrystallization of the surface grains of the material during the laser remelting process will destroy the plasticity of the material. In this regard, the present invention reduces or eliminates the internal pressure through annealing treatment to reduce the influence of internal stress on the plasticity of the material. Considering that the improvement of the yield strength of the material by a single surface fine grain is limited, the applicant introduced low-temperature rolling technology based on the deformation strengthening theory, and reduced the stacking fault energy and the resistance to dislocation movement by creating a low-temperature environment. After low-temperature rolling, a higher dislocation density can be obtained; and during the rolling process, the internal large grains are deformed to a greater extent than the surface fine grains, and the internal grains are elongated to achieve the introduction of banded structure into the material. The internal banded structure greatly improves the yield strength of the material. The present invention constructs an inner and outer layer heterogeneous aluminum alloy material with a surface of 350-550nm submicron grain size fine equiaxed crystals wrapped in an internal banded structure through the coupling effect of the above processes, which significantly improves its yield strength while ensuring the excellent plasticity of the aluminum alloy.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The present invention proposes an aluminum alloy material with submicron equiaxed crystals of 350 to 550 nm on the surface and a banded grain structure inside. The surface fine grain strengthening is used to improve the plasticity and yield strength of the aluminum alloy material. At the same time, the banded grain structure inside the material is used to further improve the yield strength of the material. This solves the problem of the difficulty in balancing the yield strength and plasticity of aluminum alloys and provides a new idea for the design of high-performance aluminum alloys.

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

[0024] (3) Under the premise of ensuring good plasticity of aluminum alloy, the yield strength of aluminum alloy is significantly improved. At the same time, each link in the process designed by the present invention is a common process in the field, which has the advantages of simple operation, low cost and easy large-scale production. DETAILED DESCRIPTION

[0025] 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.

[0026] Example 1

[0027] An aluminum alloy material with heterogeneous inner and outer layers and a preparation method thereof, wherein the preparation method comprises the following steps:

[0028] (1) A 5182 aluminum alloy plate with a thickness of 3 mm was polished using SiC sandpaper from 500 mesh to 2000 mesh, and then ultrasonically cleaned in anhydrous ethanol;

[0029] (2) The top and bottom surfaces of the cleaned aluminum alloy plate were laser remelted with a laser frequency of 210 KHz, a pulse width of 25 ns, a scanning speed of 350 mm / s, a spot diameter of 35 μm, and a laser power density of 10 kW / cm 2 , the overlap rate is 8%, the light-on delay is 30μs, the light-off delay is 185μs, the corner delay is 85μs, the serpentine scanning path is adopted, 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°C;

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

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

[0033] (6) The workpiece after heat treatment is subjected to low-temperature rolling deformation treatment, the deformation temperature is -50°C, and the total deformation amount is 18%, thereby preparing an aluminum alloy material with inner and outer layers heterogeneous with a submicron equiaxed crystal with a surface thickness of 350 to 550 nm and an internal strip-shaped microstructure wrapped therein.

[0034] Example 2

[0035] An aluminum alloy material with heterogeneous inner and outer layers and a preparation method thereof, wherein the preparation method comprises the following steps:

[0036] (1) A 5182 aluminum alloy plate with a thickness of 7 mm was polished using SiC sandpaper from 500 mesh to 2000 mesh, and then ultrasonically cleaned in anhydrous ethanol;

[0037] (2) The top and bottom surfaces of the cleaned aluminum alloy plate were laser remelted with a laser frequency of 250 KHz, a pulse width of 30 ns, a scanning speed of 550 mm / s, a spot diameter of 45 μm, and a laser power density of 20 kW / cm 2 , the overlap rate is 10%, the light-on delay is 30μs, the light-off delay is 185μs, the corner delay is 85μs, the serpentine scanning path is adopted, 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°C;

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

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

[0041] (6) The workpiece after the heat treatment is subjected to low-temperature rolling deformation treatment, the deformation temperature is -100°C, and the total deformation amount is 20%, thereby preparing an aluminum alloy material with inner and outer layers heterogeneous with a submicron equiaxed crystal with a surface diameter of 350 to 550 nm and an internal strip-shaped microstructure wrapped therein.

[0042] Example 3

[0043] An aluminum alloy material with heterogeneous inner and outer layers and a preparation method thereof, wherein the preparation method comprises the following steps:

[0044] (1) A 5182 aluminum alloy plate with a thickness of 15 mm was polished using SiC sandpaper from 500 mesh to 2000 mesh, and then ultrasonically cleaned in anhydrous ethanol;

[0045] (2) The top and bottom surfaces of the cleaned aluminum alloy plate were laser remelted with a laser frequency of 280 KHz, a pulse width of 35 ns, a scanning speed of 750 mm / s, a spot diameter of 55 μm, and a laser power density of 30 kW / cm 2 , the overlap rate is 12%, the light-on delay is 30μs, the light-off delay is 185μs, the corner delay is 85μs, the serpentine scanning path is adopted, 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°C;

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

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

[0049] (6) The workpiece after heat treatment is subjected to low-temperature rolling deformation treatment, the deformation temperature is -196°C, and the total deformation amount is 25%, thereby preparing an aluminum alloy material with inner and outer layers heterogeneous with a submicron equiaxed crystal with a surface size of 350 to 550 nm and an internal strip-shaped microstructure wrapped therein.

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

[0051] Comparative Example 1

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

[0053] (1) A 5182 aluminum alloy plate was subjected to rolling deformation treatment, with a deformation temperature of -196°C and a deformation amount of 20%.

[0054] Comparative Example 2

[0055] A method for laser strengthening the surface of an aluminum alloy, the preparation method comprising the following steps:

[0056] (1) A 5182 aluminum alloy plate with a thickness of 3 mm was polished using SiC sandpaper from 500 mesh to 2000 mesh, and then ultrasonically cleaned in anhydrous ethanol;

[0057] (2) The top and bottom surfaces of the cleaned aluminum alloy plate were laser remelted with a laser frequency of 240 kHz, a pulse width of 25 ns, a scanning speed of 550 mm / s, a spot diameter of 40 μm, and a laser power density of 12.5 kW / cm 2 , the overlap rate is 10%, the light-on delay is 30μs, the light-off delay is 185μs, the corner delay is 85μs, the serpentine scanning path is adopted, 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°C;

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

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

[0061] Comparative Example 3

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

[0063] (1) A 5182 aluminum alloy plate with a thickness of 3 mm was polished using SiC sandpaper from 500 mesh to 2000 mesh, and then ultrasonically cleaned in anhydrous ethanol;

[0064] (2) The top and bottom surfaces of the cleaned aluminum alloy plate were laser remelted with a laser frequency of 400 Hz, a pulse width of 50 ms, a scanning speed of 150 mm / s, a spot diameter of 1 mm, an overlap rate of 10%, a serpentine scanning path, and a scanning number of 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°C;

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

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

[0068] (6) The workpiece after heat treatment is subjected to low-temperature rolling deformation treatment, the deformation temperature is -196°C, and the total deformation amount is 20%.

[0069] Verification Example 1

[0070] The 5182 aluminum alloy plate, the aluminum alloys prepared in Examples 1-3 and Comparative Examples 1-3 were respectively taken, and their organizational structure, yield strength and uniform elongation were tested using conventional technical methods in the field. The specific test results are shown in Table 1 below.

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

[0072]

[0073] By comparing the performance of the aluminum alloys of Examples 1-3 and the 5182 aluminum alloy plate, it was found that the submicron grain size structure can significantly improve the yield strength of the aluminum alloy 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) By comparing the examples with the comparative examples, it can be seen that the construction of the submicron grain size structure can effectively improve the yield strength of the 5182 aluminum alloy plate.

[0076] (2) Comparative Example 1 does not have a laser remelting process; Comparative Example 2 does not have a low-temperature rolling process; Comparative Example 3 uses a millisecond laser surface remelting process. Comparative Example 1 does not change the existing structure of the aluminum alloy much, and does not obtain an aluminum alloy structure in which the surface submicron equiaxed crystals wrap the internal banded structure; although Comparative Example 2 improves the strength and plasticity of the material by surface fine grain strengthening, it lacks the internal banded structure, so the improvement of the yield strength of the aluminum alloy is limited; Comparative Example 3 has a large millisecond laser spot diameter, a large heat-affected zone, a large molten pool, and a slow cooling rate of the molten pool, so the grains of the material after surface remelting are coarse, which greatly reduces the yield strength of the material compared with the material after nanosecond laser treatment; The above analysis reveals that high-frequency pulse nanosecond laser remelting, heat treatment, and low-temperature rolling deformation treatment are all essential conditions for this design, and the lack of any process cannot make the 5182 aluminum alloy obtain the best performance.

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

[0078] 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 preparing an aluminum alloy material with heterogeneous inner and outer layers, characterized in that: The steps include: (1) The surface and bottom of the aluminum alloy plate with a thickness of d were remelted by high-frequency pulse nanosecond laser. The laser frequency used was 120-330 kHz, the pulse width was 10-70 ns, the spot diameter was 10-120 μm, and the laser power density was 5-50 kW / cm 2 , overlap rate is 5-25%, scanning speed is 350-950mm / s, light-on delay is 30μs, light-off delay is 185μs, corner delay is 85μs, scanning times is 1-3 times, and scanning path is serpentine path; (2) During the laser remelting process, a low-temperature pad is placed under the workpiece to accelerate the cooling of the workpiece and achieve ultra-fast cooling. The temperature of the low-temperature pad is -25 to -70°C; (3) During the laser remelting process, argon gas is used to protect the molten pool, and argon gas is filled into the environment to make the oxygen content in the environment 170-340 ppm; (4) The remelted workpiece is subjected to heat preservation treatment at a temperature of 110°C to 270°C for a time of (20 to 40)*d minutes and a heating rate of 5 to 15°C / min. After the heat preservation is completed, the workpiece is taken out; (5) After the insulation is completed, the workpiece is subjected to low-temperature rolling deformation treatment, the deformation temperature is -25 to -196°C, and the total deformation amount is 15% to 40%.

2. The preparation method according to claim 1, characterized in that: The aluminum alloy 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 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 / cm 2 , the overlap rate is 5-20%, the scanning speed is 350-850 mm / s, and the number of scans is 1-2 times.

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

5. The preparation method according to claim 1, characterized in that: The temperature of the low-temperature pad in step (2) is -30 to -65°C.

6. The preparation method according to claim 1, characterized in that: The oxygen content in step (3) is 200-280 ppm.

7. The preparation method according to claim 1, characterized in that: The insulation temperature in step (4) is 150-200° C., the insulation time is (25-40)*d minutes, and the heating rate is 9-12° C. / min.

8. 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 amount is 15% to 25%.

9. The preparation method according to any one of claims 1 to 8 prepares an aluminum alloy material with inner and outer heterogeneous layers and an inner strip-shaped microstructure wrapped with submicron equiaxed crystals with a surface diameter of 350 to 550 nm.

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