High-strength corrosion-resistant aluminum alloy for automobile battery tray and preparation method of high-strength corrosion-resistant aluminum alloy

Abstract

The invention discloses a high-strength corrosion-resistant aluminum alloy for an automobile battery tray and a preparation method thereof.According to the high-strength corrosion-resistant aluminum alloy for the automobile battery tray and the preparation method thereof, by adding the La element in a specific proportion and regulating and controlling the content of Si and Mg, the corrosion resistance of the material is remarkably improved on the premise that the strength is not sacrificed, in addition, addition of the Cr element is avoided, meanwhile, the La element is introduced, the plastic deformation capacity of the alloy is effectively improved, and the service life of the alloy is prolonged. And an ultrasonic treatment process is combined to promote the uniformity of the melt, so that the complex-section profile is easier to extrude and form, the production efficiency is favorably improved, and the defects such as dragging and breaking are not easy to occur. The La element is added, the morphology of Si particles is converted from a continuous sheet shape to a discontinuous short rod shape, extension of corrosion along a grain boundary is effectively hindered, and the alloy has remarkable mechanical performance and corrosion resistance by combining the synergistic effect of a specific refining agent, components and the process.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy materials technology, and more specifically, to a high-strength corrosion-resistant aluminum alloy for automotive battery trays and its preparation method. Background Technology

[0002] Aluminum alloys possess advantages such as low density, high specific strength, and good corrosion resistance, leading to their increasingly widespread application in the new energy vehicle sector. Aluminum profiles are primarily used in critical components such as automotive crash beams, battery trays, and energy-absorbing boxes. As the power carrier of new energy vehicles, battery trays not only need to withstand certain loads but also possess sufficient corrosion resistance to prevent corrosion from electrolytes. Therefore, the market has placed new demands on the strength and corrosion resistance of aluminum profiles.

[0003] Currently, the commonly used aluminum profile for battery trays is 6061-T6. This aluminum alloy is generally considered to have relatively high strength, but relatively poor corrosion resistance. Reducing the content of alloying elements can effectively improve the material's corrosion resistance, but the material's strength will decrease rapidly. Furthermore, the aluminum profiles used for battery trays generally have complex structures, and the commonly used 6061 alloy composition range is often near the lower limit of national standards. It is difficult to maintain material strength while significantly improving corrosion resistance simply by adjusting the main alloying element composition. New alloying elements must be introduced, and the manufacturing process optimized, to achieve a balance between high strength and corrosion resistance. Summary of the Invention

[0004] In view of this, and in order to solve the above-mentioned technical problems, the present invention provides a high-strength corrosion-resistant aluminum alloy for automotive battery trays and its preparation method, the specific technical solution of which is as follows: A high-strength, corrosion-resistant aluminum alloy for automotive battery trays, the high-strength, corrosion-resistant aluminum alloy comprising the following components by weight percentage: Si: 0.45~0.65%, Mg: 0.45~0.65%, Cu: 0.15~0.4%, La: 0.1~0.2%, Fe≤0.2%, individual impurity mass content≤0.05%, total impurity content≤0.15%, balance is Al.

[0005] In addition, the present invention also provides a method for preparing a high-strength corrosion-resistant aluminum alloy for automotive battery trays, the method comprising the following steps: S1. Add the raw materials for preparing high-strength corrosion-resistant aluminum alloy to a melting furnace and melt them to obtain aluminum alloy melt; S2. Refine the aluminum alloy melt, then remove the slag and let it stand; S3. Ultrasonic treatment of the molten aluminum alloy; S4. Degas and filter the aluminum alloy melt; S5. The aluminum alloy melt is cast to obtain an aluminum alloy ingot; S6. Homogenize the aluminum alloy ingot; S7. The homogenized aluminum alloy ingot is extruded to obtain aluminum alloy profiles; S8. Perform solution treatment on aluminum alloy profiles; S9. Perform artificial aging treatment on the solution-treated aluminum alloy profiles.

[0006] Further, in step S1, the raw materials for preparation include: Al-20Cu alloy, Al-20Si alloy, Al-La alloy, aluminum ingot with a purity of 99.8%, and magnesium ingot with a purity of 99.9%.

[0007] Furthermore, in step S3, the power of the ultrasonic treatment is 160~180W, and the vibration time is 10~15min.

[0008] Further, in step S4, the degassing and filtration process includes: passing the molten aluminum alloy through a rotating system with a rotation speed of 200-300 r / min and an argon flow rate of 4-5 m³ / min. 3 The air is removed from the degassing chamber at a rate of / h, and then passed through a double-layer foam ceramic filter plate with a porosity of 40ppi+60ppi.

[0009] Furthermore, in step S5, the casting temperature is 720~740℃, the speed is 80~90mm / min, and the cooling water pressure is 0.1~0.2MPa.

[0010] Furthermore, in step S6, the homogenization treatment is carried out at a temperature of 550~570℃ for 8~10 hours.

[0011] Further, in step S7, the extrusion process is as follows: the aluminum alloy ingot heating temperature is 460~480℃, the die temperature is 460~480℃, the extrusion cylinder temperature is 400~420℃, and the extrusion speed is 1.5~2.5mm / s.

[0012] Furthermore, in step S8, the solution treatment temperature is 520~540℃, the time is 40~60min, and the solution is immediately water-quenched after treatment.

[0013] Furthermore, in step S9, the aging treatment temperature is 170~190℃ and the time is 7~9h.

[0014] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention significantly improves the corrosion resistance of materials without sacrificing strength by adding a specific proportion of La and controlling the content of Si and Mg. Specifically, the aluminum alloy of this invention has a tensile strength ≥355 MPa, a yield strength ≥298 MPa, and an elongation after fracture ≥11.2%. After salt spray testing, there are no obvious corrosion marks on the surface, showing excellent corrosion resistance and stability.

[0015] 2. This invention effectively improves the plastic deformation capacity of the alloy by reducing the content of Si and Mg elements and avoiding the addition of Cr element, while introducing La element. Combined with ultrasonic treatment process to promote melt uniformity, it makes it easier to extrude and form complex cross-section profiles, which helps to improve production efficiency and reduces the occurrence of defects such as "drag and tear".

[0016] 3. The addition of La in this invention transforms the morphology of Si particles from continuous lamellar to discontinuous short rod-shaped, effectively hindering the spread of corrosion along grain boundaries. La enriches on the surface of Mg2Si particles, delaying their corrosion process, thereby improving the alloy's resistance to intergranular corrosion and exfoliation corrosion. The synergistic effect of composition and process results in an alloy with significant mechanical properties and corrosion resistance.

[0017] 4. This invention prepares a specific refining agent by using lanthanum oxide and boron nitride, which can not only effectively prevent component segregation formed between coarse dendrites, making the composition and structure more uniform, but also appropriately supplement the La loss during alloy smelting, ensuring the designed La content in the formula, thereby stabilizing the Si phase morphology to improve corrosion resistance, and further balancing the mechanical properties and corrosion resistance of aluminum alloys, making them more suitable for use in the preparation of automotive battery trays. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the microstructure of the high-strength corrosion-resistant aluminum alloy prepared in Example 1 of the present invention; Figure 2 This is a schematic diagram of the microstructure of the high-strength corrosion-resistant aluminum alloy prepared in Example 1 of the present invention after undergoing an intergranular corrosion test. Figure 3 This is a schematic diagram of the high-strength corrosion-resistant aluminum alloy sample prepared in Example 1 of the present invention after undergoing an anti-stripping corrosion test. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to its embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the scope of protection of the invention.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0021] A high-strength, corrosion-resistant aluminum alloy for automotive battery trays, as described in one embodiment of the present invention, comprises the following components by mass percentage: Si: 0.45~0.65%, Mg: 0.45~0.65%, Cu: 0.15~0.4%, La: 0.1~0.2%, Fe≤0.2%, individual impurity mass content≤0.05%, total impurity content≤0.15%, balance is Al.

[0022] In addition, the present invention also provides a method for preparing a high-strength corrosion-resistant aluminum alloy for automotive battery trays, the method comprising the following steps: S1. Add the raw materials for preparing high-strength corrosion-resistant aluminum alloy to a melting furnace and melt them to obtain aluminum alloy melt; S2. Refine the aluminum alloy melt, then remove the slag and let it stand; S3. Ultrasonic treatment of the molten aluminum alloy; S4. Degas and filter the aluminum alloy melt; S5. The aluminum alloy melt is cast to obtain an aluminum alloy ingot; S6. Homogenize the aluminum alloy ingot; S7. The homogenized aluminum alloy ingot is extruded to obtain aluminum alloy profiles; S8. Perform solution treatment on aluminum alloy profiles; S9. Perform artificial aging treatment on the solution-treated aluminum alloy profiles.

[0023] In one embodiment, in step S1, the raw materials for preparation include: Al-20Cu alloy, Al-20Si alloy, Al-La alloy, aluminum ingot with a purity of 99.8%, and magnesium ingot with a purity of 99.9%.

[0024] In one embodiment, in step S1, the melting temperature is 720~760°C.

[0025] In one embodiment, the refining process is as follows: in an argon atmosphere, a refining agent of 0.1-3% by mass of the aluminum alloy melt is added, and the refining process is carried out for 15-20 minutes.

[0026] In one embodiment, the refining agent is obtained by mixing and modifying lanthanum oxide and boron nitride in a mass ratio of (1~5):(2~7).

[0027] In one embodiment, the lanthanum oxide has a purity ≥ 99.9% and a particle size D50 ≤ 5 μm.

[0028] In one embodiment, the boron nitride has a purity ≥ 99% and a particle size D50 ≤ 1 μm.

[0029] In one embodiment, the refining agent is prepared by mixing lanthanum oxide and boron nitride, drying at 150-200°C for 3-5 hours, then ball milling at 300-500 r / min for 1-5 hours, heating to 600-1000°C, holding at that temperature for 1-2 hours, cooling, grinding, and sieving to obtain a refining agent with an average particle size of 5-30 μm. This invention introduces a specific refining agent with extremely low lattice mismatch with α-Al in the aluminum melt. Compared to traditional refining agents, this invention's refining agent can induce stronger heterogeneous nucleation, effectively reducing the size of the as-cast equiaxed crystals in the aluminum alloy. The fine equiaxed crystal structure effectively prevents compositional segregation formed between coarse dendrites, resulting in a more uniform composition and microstructure. Furthermore, it can appropriately supplement La element, ensuring the La element content in the formulation design, indirectly stabilizing the Si phase morphology to improve the corrosion resistance of the aluminum alloy.

[0030] In one embodiment, in step S3, the power of the ultrasonic treatment is 160~180W, and the vibration time is 10~15min.

[0031] In one embodiment, step S4, the degassing and filtration process includes: passing the molten aluminum alloy through a rotating system with a rotation speed of 200-300 r / min and an argon flow rate of 4-5 m³ / min. 3 The air is removed from the degassing chamber at a rate of / h, and then passed through a double-layer foam ceramic filter plate with a porosity of 40ppi+60ppi.

[0032] In one embodiment, in step S5, the casting process is carried out at a temperature of 720~740℃, a speed of 80~90mm / min, and a cooling water pressure of 0.1~0.2MPa.

[0033] In one embodiment, in step S6, the homogenization process is carried out at a temperature of 550~570°C for 8~10 hours.

[0034] In one embodiment, in step S7, the extrusion process is as follows: the aluminum alloy ingot heating temperature is 460~480℃, the die temperature is 460~480℃, the extrusion cylinder temperature is 400~420℃, and the extrusion speed is 1.5~2.5mm / s.

[0035] In one embodiment, in step S8, the solution treatment temperature is 520~540℃, the time is 40~60min, and the treatment is immediately followed by water quenching.

[0036] In one embodiment, in step S9, the aging treatment is carried out at a temperature of 170~190℃ for 7~9 hours.

[0037] The implementation schemes of the present invention will now be described in detail with reference to specific embodiments.

[0038] Examples 1-3: The chemical composition of the high-strength corrosion-resistant aluminum alloys used in automotive battery trays in Examples 1-3 is shown in Table 1. The refining agent in Examples 1-3 was prepared by mixing lanthanum oxide and boron nitride in a mass ratio of 3:7, drying at 150°C for 4 hours, ball milling at 300 r / min for 3 hours, heating to 800°C, holding at that temperature for 2 hours, cooling, grinding and sieving to obtain a refining agent with an average particle size of 25 μm.

[0039] A method for preparing a high-strength, corrosion-resistant aluminum alloy for automotive battery trays, as described in Examples 1-3, includes the following steps: S1. Al-20Cu alloy, Al-20Si alloy, Al-La alloy, aluminum ingot with a purity of 99.8% and magnesium ingot with a purity of 99.9% are added to a melting furnace and melted at 740℃ to obtain an aluminum alloy melt. S2. In an argon atmosphere, add a refining agent accounting for 1% of the mass of the aluminum alloy melt, refine for 20 minutes, then remove slag and let stand for 0 minutes; S3. The aluminum alloy melt is subjected to ultrasonic treatment with a power of 175W and a vibration time of 12min. S4. The aluminum alloy molten material is flowed through a rotating system with a rotation speed of 300 r / min and an argon gas flow rate of 5 m³ / min. 3 The air is degassed by a degassing chamber of / h, and then passed through a double-layer foam ceramic filter plate with a porosity of 40ppi+60ppi. S5. The aluminum alloy melt is cast at a temperature of 720℃, a speed of 85mm / min, and a cooling water pressure of 0.2MPa to obtain an aluminum alloy ingot. S6. The aluminum alloy ingot is homogenized at a temperature of 560℃ for 9 hours. S7. The homogenized aluminum alloy ingot is heated to 465℃, the die temperature is 480℃, the extrusion cylinder temperature is 420℃, and the extrusion speed is 2.2mm / s to obtain an aluminum alloy profile. S8. The aluminum alloy profile is solution treated at 525℃ for 50 minutes; S9. The aluminum alloy profile after solution treatment is subjected to artificial aging treatment at a temperature of 185℃ for 8 hours.

[0040] Comparative Examples 1-3: The difference between Comparative Examples 1-3 and Example 3 is that the chemical composition and component ratio of the high-strength corrosion-resistant aluminum alloys in Comparative Examples 1-3 are different, as shown in Table 1. The other aspects are the same as in Example 3.

[0041] Comparative Example 4: The difference between Comparative Example 4 and Example 3 is that Cr is used to replace La in Comparative Example 4, while the rest is the same as Example 3.

[0042] Comparative Example 5: The difference between Comparative Example 5 and Example 3 is that Comparative Example 5 was not subjected to ultrasonic treatment, but otherwise it was the same as Example 3.

[0043] Comparative Example 6: The difference between Comparative Example 6 and Example 3 is that the aging process in Comparative Example 6 is different. Comparative Example 6 uses natural aging and is placed at room temperature for 96 hours. Otherwise, it is the same as Example 3.

[0044] Comparative Example 7: The difference between Comparative Example 7 and Example 3 is that Comparative Example 7 uses boron nitride as a single refining agent, while the rest is the same as Example 3.

[0045] Comparative Example 8: The difference between Comparative Example 8 and Example 3 is that Comparative Example 8 uses a conventional refining agent, such as sodium chloride, while the rest is the same as Example 3.

[0046] It should be noted that the individual mass content of aluminum alloy impurities in Examples 1-3 and Comparative Examples 1-8 is ≤0.05%, and the total amount of impurities is ≤0.15%.

[0047] Table 1: Chemical composition of aluminum alloys in Examples 1-3 and Comparative Examples 1-3

[0048] The high-strength corrosion-resistant aluminum alloy samples from Examples 1-3 and the comparative aluminum alloy samples from Comparative Examples 1-8 were subjected to mechanical property tests, with the mechanical properties conforming to GB / T16865-2023. The results are shown in Table 2 below.

[0049] Table 2: Mechanical Performance Test Results

[0050] Analysis of the data in Table 1 shows that, through optimization of composition, component ratio, and process, this invention can achieve an aluminum alloy with significantly improved strength and corrosion resistance. In Comparative Example 1, the La content was too low; a small amount of La was insufficient to completely transform the eutectic Si phase from continuous, sharp plates into discontinuous short rods, and the overall grain refinement effect was weakened, leading to a decrease in mechanical properties. In Comparative Example 2, the La content was too high, which did refine the grains, but it easily formed coarse and brittle phases with other alloying elements, reducing corrosion resistance. In Comparative Example 3, no La was added, and the Si / Mg ratio was too high, resulting in a compositional imbalance. Without the refining effect of La, the grains were coarse, leading to a decrease in mechanical properties. In Comparative Example 4, Cr replaced La. Cr in 6xxx series alloys typically exists as a dispersed Al7Cr phase, hindering grain growth and achieving a grain refinement effect. Meanwhile, these precipitates pin the grain boundaries, hindering grain boundary movement and preventing grain growth, ultimately improving mechanical properties. In this formulation, the aluminum alloy melt in Comparative Example 5 was not ultrasonically treated, resulting in slightly poorer microstructure uniformity and insufficient removal of gases and inclusions, leading to a decrease in strength and elongation. Comparative Example 6 used natural aging, which failed to achieve peak aging, resulting in the material's strength not meeting usage requirements. Comparative Example 7 used boron nitride as a single refining agent; its mechanical properties were inferior to Example 3 but superior to Comparative Example 8, indicating that boron nitride alone has a better refining effect than conventional sodium chloride, but it cannot supplement La, thus affecting the mechanical properties of the aluminum alloy. Comparative Example 8 used conventional sodium chloride as a refining agent, achieving a certain purification effect, such as degassing. However, it failed to achieve a more effective refining effect, resulting in the aluminum alloy's mechanical properties being inferior to Example 3.

[0051] The high-strength corrosion-resistant aluminum alloy samples of Examples 1-3 and the comparative aluminum alloy samples of Comparative Examples 1-8 were subjected to corrosion resistance tests. The intergranular corrosion test was performed in accordance with GB / T 7998-2023, the exfoliation corrosion resistance test was performed in accordance with GB / T22639-2008, and the 168h CASS test was performed in accordance with GB / T10125-2021. The results are shown in Table 3 below.

[0052] Table 3: Corrosion Resistance Test Results

[0053] As can be seen from the data analysis in Table 3, the aluminum alloy of the present invention, after composition optimization and process optimization, not only has excellent mechanical properties, but also significant corrosion resistance.

[0054] In Comparative Example 1, the La content was too low, insufficient to refine the Si phase and effectively inhibit the corrosion of the Mg2Si phase. The lamellar Si phase formed continuous weak channels at the grain boundaries, leading to a significant decrease in its corrosion resistance. In Comparative Example 2, the La content was too high. Excessive La would form coarse Al-La or Al-Si-La preferred corrosion points with Al or other elements, thus affecting its corrosion resistance. In Comparative Example 3, no La was added, and the Si and Mg contents were too high. The higher Si and Mg contents generated more network-like Mg2Si phases, which together formed well-developed grain boundary corrosion channels. Furthermore, the coarse lamellar Si and continuous Mg2Si phases themselves were stress concentration points. Without La, the corrosion resistance of the aluminum alloy would be significantly affected. In Comparative Example 4, Cr was used to replace La. Although this improved the mechanical properties, it showed poor corrosion resistance. Cr in 6xxx series aluminum alloys usually forms fine dispersed phases, such as Al. 12 Mg2Cr and other phases can pin grain boundaries and dislocations, accelerating the corrosion of the anodic phase at grain boundaries, thus affecting the overall corrosion resistance of the aluminum alloy. In Comparative Example 5, the aluminum alloy melt was not ultrasonically treated, resulting in slightly poor microstructure uniformity and insufficient removal of gases and inclusions, leading to more corrosion sites and a decrease in corrosion resistance. In Comparative Example 6, natural aging was used, resulting in fewer precipitates within the grains and at grain boundaries, thus improving resistance to intergranular corrosion. However, this sacrifices strength, making it difficult to balance the strength and corrosion resistance of the aluminum alloy, thus affecting its application. In Comparative Example 7, boron nitride was used as a single refining agent, but the grain refinement effect was not as good as in Example 3. Its modification effect on the Si phase and its corrosion inhibition effect on the Mg2Si phase were weakened, and the Si phase could not be completely transformed into the ideal short rod shape, resulting in a decrease in corrosion resistance. Comparative Example 8 used sodium chloride as a conventional refining agent, which failed to achieve the desired grain refinement effect. The coarse dendritic structure meant more severe component segregation and a more continuous grain boundary network, resulting in poor corrosion resistance. Therefore, this application can effectively balance mechanical properties and corrosion resistance by optimizing the composition and component ratio, thus meeting the application requirements.

[0055] in addition, Figure 1 This is a schematic diagram of the microstructure of the high-strength corrosion-resistant aluminum alloy prepared in Example 1 of the present invention. Figure 2 This is a schematic diagram of the microstructure of the high-strength, corrosion-resistant aluminum alloy prepared in Example 1 of the present invention after undergoing an intergranular corrosion test. Figure 1 as well as Figure 2 As can be seen, the high-strength corrosion-resistant aluminum alloy prepared in Example 1 has no obvious intergranular corrosion characteristics and has significant corrosion resistance. Figure 3 This is a schematic diagram of the high-strength, corrosion-resistant aluminum alloy sample prepared in Example 1 of this invention after undergoing an anti-exfoliation corrosion test. Figure 3 As can be seen, the experimental surface showed no obvious corrosion marks, indicating excellent corrosion resistance.

[0056] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0057] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A high-strength, corrosion-resistant aluminum alloy for automotive battery trays, characterized in that, The high-strength, corrosion-resistant aluminum alloy comprises the following components by mass percentage: Si: 0.45~0.65%, Mg: 0.45~0.65%, Cu: 0.15~0.4%, La: 0.1~0.2%, Fe≤0.2%, individual impurity mass content≤0.05%, total impurity content≤0.15%, balance is Al.

2. A method for preparing a high-strength, corrosion-resistant aluminum alloy for automotive battery trays, characterized in that, The preparation method is used to prepare the high-strength, corrosion-resistant aluminum alloy for automotive battery trays as described in claim 1, and the preparation method includes the following steps: S1. Add the raw materials for preparing high-strength corrosion-resistant aluminum alloy to a melting furnace and melt them to obtain aluminum alloy melt; S2. Refine the aluminum alloy melt, then remove the slag and let it stand; S3. Ultrasonic treatment of the molten aluminum alloy; S4. Degas and filter the aluminum alloy melt; S5. The aluminum alloy melt is cast to obtain an aluminum alloy ingot; S6. Homogenize the aluminum alloy ingot; S7. The homogenized aluminum alloy ingot is extruded to obtain aluminum alloy profiles; S8. Perform solution treatment on aluminum alloy profiles; S9. Perform artificial aging treatment on the solution-treated aluminum alloy profiles.

3. The preparation method according to claim 2, characterized in that, In step S1, the raw materials for preparation include: Al-20Cu alloy, Al-20Si alloy, Al-La alloy, aluminum ingot with a purity of 99.8%, and magnesium ingot with a purity of 99.9%.

4. The preparation method according to claim 2, characterized in that, In step S3, the power of the ultrasonic treatment is 160~180W, and the vibration time is 10~15min.

5. The preparation method according to claim 2, characterized in that, In step S4, the degassing and filtration process includes: passing the molten aluminum alloy through a rotating system with a rotation speed of 200-300 r / min and an argon flow rate of 4-5 m³ / min. 3 The air is removed from the degassing chamber at a rate of / h, and then passed through a double-layer foam ceramic filter plate with a porosity of 40ppi+60ppi.

6. The preparation method according to claim 2, characterized in that, In step S5, the casting temperature is 720~740℃, the speed is 80~90mm / min, and the cooling water pressure is 0.1~0.2MPa.

7. The preparation method according to claim 2, characterized in that, In step S6, the homogenization treatment is carried out at a temperature of 550~570℃ for 8~10 hours.

8. The preparation method according to claim 2, characterized in that, In step S7, the extrusion process is as follows: the aluminum alloy ingot heating temperature is 460~480℃, the die temperature is 460~480℃, the extrusion cylinder temperature is 400~420℃, and the extrusion speed is 1.5~2.5mm / s.

9. The preparation method according to claim 2, characterized in that, In step S8, the solution treatment temperature is 520~540℃ and the time is 40~60min, followed by immediate water quenching.

10. The preparation method according to claim 2, characterized in that, In step S9, the aging treatment is carried out at a temperature of 170~190℃ for 7~9 hours.

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