Aluminum alloy for high-strength vehicle body and preparation method of aluminum alloy

Abstract

The invention relates to the technical field of automobile alloys, and particularly discloses a high-strength aluminum alloy for an automobile body and a preparation method of the high-strength aluminum alloy. The invention discloses a high-strength aluminum alloy for a vehicle body. The aluminum alloy is prepared from the following raw materials in percentage by mass: 0.5-1.5% of magnesium; 1-2% of silicon; 0.4-1% of copper; 0.1 to 0.5 percent of tin; 0.01 to 0.05 percent of manganese; 0.05 to 0.1 percent of iron; 0.1 to 0.2 percent of boron; 0.3-1.5% of a rare earth element mixture; and the balance of aluminum. The rare earth element mixture is composed of niobium, scandium and cobalt, and the weight ratio of niobium to scandium to cobalt is 1: (3.4-4.4): (12-15). The preparation method comprises the following steps: under the protection of inert gas, melting aluminum, and then proportionally adding a mixture of magnesium, silicon, copper, tin, manganese, iron, boron and rare earth elements for mixed smelting to obtain a smelting solution; a refining agent is added into the smelting solution for refining treatment, and after deslagging and degassing treatment, casting is conducted to obtain an alloy semi-finished product; and the alloy semi-finished product is subjected to solution treatment and aging treatment. The high-strength aluminum alloy for the vehicle body is high in strength, excellent in ductility and good in overall quality.

Description

Technical Field

[0001] The present application relates to the technical field of automobile alloys, and more specifically, to a high-strength aluminum alloy for vehicle bodies and a preparation method thereof. Background Art

[0002] Aluminum alloy is an alloy made of aluminum as the main component and other metal elements through a specific process. It is a light metal material and plays a vital role in the industrial field. At the same time, due to the characteristics of aluminum alloy such as light weight, high strength and good formability, its application in automobile body structure is becoming more and more extensive, mainly used in body frames, doors, hoods, trunk lids and other parts, improving fuel economy and collision safety.

[0003] At present, in the automotive industry, Al-Mg-Si series aluminum alloys are widely used in body frame structures due to their low density, good formability and recycling value. However, with the continuous improvement of vehicle safety in the automotive industry, traditional Al-Mg-Si alloys are difficult to meet the needs of the new generation of high-performance body designs due to their low yield strength and tensile strength. In recent years, the strength of aluminum alloys has been improved by adding trace alloying elements such as Cu and Sn, or by heat treatment. However, although the above methods can improve strength to a certain extent, they often sacrifice ductility, resulting in the practical application of aluminum alloys in automobile bodies being limited.

[0004] Regarding the above-mentioned related technologies, high-strength aluminum alloy bodies can better absorb energy, thereby effectively resisting collisions and impacts and protecting the safety of passengers; high-ductility aluminum alloy bodies can better resist deformation and cracking and maintain the integrity of the body structure. When the ductility of aluminum alloy is poor, it also limits its application in the manufacture of complex shapes; therefore, how to maintain or even improve the ductility while improving the strength of aluminum alloy has become one of the problems that the industry urgently needs to break through. At present, it is urgent to propose a solution to solve the above technical problems. Summary of the invention

[0005] In order to improve the strength of aluminum alloy while ensuring excellent ductility of the aluminum alloy, the present application provides a high-strength aluminum alloy for vehicle body and a preparation method thereof.

[0006] In a first aspect, the present application provides a high-strength aluminum alloy for vehicle body, which adopts the following technical solution: A high-strength aluminum alloy for vehicle bodies, made of raw materials containing the following mass percentages: Magnesium 0.5-1.5%; Silicon 1-2%; Copper 0.4-1%; Tin 0.1-0.5%; Manganese 0.01-0.05%; Iron 0.05-0.1%; Boron 0.1-0.2%; Rare earth element mixture 0.3-1.5%; The balance is aluminum; The rare earth element mixture consists of niobium, scandium and cobalt, and the weight ratio of niobium, scandium and cobalt is 1:(3.4-4.4):(12-15).

[0007] By adopting the above technical solutions, magnesium can promote the grain refinement and deformation hardening of aluminum alloys, thereby improving the strength of aluminum alloys; silicon forms a solid solution with aluminum to enhance the crystal structure of aluminum, thereby improving the mechanical properties of the alloy; copper can strengthen the grain boundary strength and solid solution strength of aluminum alloys, thereby significantly improving the strength and hardness of aluminum alloys; the compound formed by tin and aluminum plays a role of dispersion strengthening in the alloy, thereby improving the strength and hardness of the aluminum alloy; the combination of magnesium, silicon, copper, tin and aluminum can form a relatively stable phase structure of aluminum alloy, which not only excels in strength, corrosion resistance and processing performance, but is also easy to accept and integrate other different elements.

[0008] An appropriate amount of manganese content can improve the corrosion resistance of aluminum alloys, while too high a manganese content will increase the brittleness of the aluminum alloy and reduce its hardness. An appropriate amount of iron in an aluminum alloy can improve the high-temperature fluidity of the alloy, reduce the shrinkage rate of the aluminum alloy, and improve the processing performance, while too high an iron content will reduce the plasticity, strength and hardness of the aluminum alloy. Therefore, manganese and iron in the above-mentioned dosage range can bring about the above-mentioned excellent effects while not easily producing the above-mentioned adverse effects, thereby ensuring the overall stability of the aluminum alloy.

[0009] The rare earth element mixture is composed of niobium, scandium and cobalt. Among them, niobium and cobalt can accelerate the dissolution and diffusion of rare elements in aluminum alloys, and scandium adjusts the grain size and distribution by controlling the growth rate of the lattice. The combination of the three can bring about a comprehensive improvement in the hardness and ductility of aluminum alloys. Boron mainly forms fine crystal nuclei with aluminum in aluminum alloys. These crystal nuclei exist stably in the aluminum liquid and become the starting point of grain growth, thereby significantly refining the grains in the aluminum liquid and improving the strength, plasticity and toughness of the aluminum alloy. At the same time, when the rare earth element mixture composed of niobium, scandium and cobalt is used, it can promote the formation of crystal nuclei and refine the grains after combining with boron, thereby improving the microstructure of the alloy. These fine particles that grow together are evenly distributed in the grain boundaries, and can also coordinate deformation through grain boundary sliding, thereby bringing about an improvement in the strength of excellent aluminum alloys and a significant improvement in the ductility of aluminum alloys.

[0010] Preferably, the weight ratio of niobium, scandium and cobalt is 1:4:14.

[0011] By adopting the above technical scheme, when a rare earth element mixture composed of niobium, scandium and cobalt in the above weight ratio is used, it can not only stably exert its own excellent effects, but also can cooperate with boron to exert excellent synergistic effects in aluminum alloys, not only forming stable hard phase particles, dispersion strengthening the aluminum alloy, bringing about a significant increase in strength, but also can bring about better grain boundary sliding coordinated deformation effect, thereby showing better ductility.

[0012] Preferably, the weight ratio of the boron and rare earth element mixture is 1:5.

[0013] By adopting the above technical scheme, when the boron and rare earth element mixtures in the above weight ratio are used in combination, the coordination system formed in the aluminum alloy is relatively uniform and the corresponding effect brought is better. It can improve the strength of the aluminum alloy while giving the aluminum alloy excellent ductility, and the overall performance is better.

[0014] Preferably, the mass percentages of magnesium, silicon, copper and tin are: Magnesium 0.8-1.2%; Silicon 1.2-1.8%; Copper 0.6-0.8%; Tin 0.2-0.4%.

[0015] By adopting the above technical scheme, when the above mass percentages of magnesium, silicon, copper and tin are mixed, the formation of the precipitation phase of the aluminum alloy after solution treatment can be more balanced, which is beneficial to the subsequent aging strengthening, and can make the boron and rare earth element mixtures easier to cooperate in the alloy system and exert better corresponding effects, thereby obtaining a high-strength aluminum alloy for car body with better quality.

[0016] In a second aspect, the present application provides a method for preparing a high-strength aluminum alloy for a vehicle body, using the following technical solution: A method for preparing a high-strength aluminum alloy for a vehicle body comprises the following steps: (1) preparing raw materials including magnesium, silicon, copper, tin, manganese, iron, boron, rare earth element mixture and aluminum according to the proportion; (2) Under the protection of an inert gas, the aluminum in step (1) is melted, and then magnesium, silicon, copper, tin, manganese, iron, boron, and a rare earth element mixture are added in proportion to perform mixed smelting to obtain a molten liquid; (3) adding a refining agent to the molten liquid obtained in step (2) for refining, removing slag and degassing, and then casting to obtain an alloy semi-finished product; (4) The semi-finished alloy product obtained in step (3) is first subjected to a solution treatment, then subjected to an aging treatment, and then cooled to obtain a high-strength aluminum alloy for vehicle bodies.

[0017] By adopting the above technical solution, the above preparation steps are few, the process is simple, and it is convenient for large-scale industrial production. At the same time, aluminum is first melted and then mixed with other raw materials for smelting, which can ensure that the raw materials can fully cooperate and play an excellent corresponding effect; and after the raw materials are mixed and smelted, the refining treatment, solution treatment and aging treatment can also ensure that the high-strength aluminum alloy for the car body with excellent quality and stability is obtained.

[0018] Preferably, in step (2), the smelting temperature is 700-800°C and the smelting time is 2-3h.

[0019] By adopting the above technical solution, the above smelting temperature and smelting time can ensure the full mixing of the various raw materials, making it difficult for the alloy elements to be burned, which is conducive to finally obtaining an aluminum alloy with excellent and stable quality.

[0020] Preferably, in step (3), the refining temperature is 820-860°C and the refining time is 30-40 min.

[0021] By adopting the above technical solution, refining is carried out by adding a refining agent to the molten liquid to perform degassing and slag removal treatment. The above refining temperature and refining time are conducive to the dissolution of alloy elements and the discharge of gases and inclusions, thereby making the final aluminum alloy have excellent quality.

[0022] Preferably, in step (3), the amount of the refining agent used is 0.1-0.2% of the mass of the smelting liquid, and the refining agent is any one of sodium chloride, potassium chloride, sodium fluoride and calcium fluoride, or a combination of several of them.

[0023] By adopting the above technical scheme, the refining agent composed of the above raw materials has strong impurity removal and degassing capabilities, which can not only improve the uniformity of the aluminum alloy, but also play a role in modifying and refining the aluminum alloy structure, and improve the melt properties of the aluminum alloy such as fluidity, wettability and solidification shrinkage, thereby improving the casting performance and forming performance of the aluminum alloy, which is conducive to ensuring the high-strength aluminum alloy for car body with excellent and stable quality.

[0024] Preferably, in step (4), the temperature of the solution treatment is 520-540° C., and the holding time is 3-4 h.

[0025] By adopting the above technical scheme, the solution treatment can optimize the microstructure of the aluminum alloy, reduce the microstructure heterogeneity, and thus improve the overall performance of the aluminum alloy; and the combination of the above solution treatment temperature and solution time can bring about better corresponding effects, and ultimately obtain a high-strength aluminum alloy for car body with excellent and stable quality.

[0026] Preferably, in step (4), the aging treatment temperature is 160-180° C. and the holding time is 3-4 h.

[0027] By adopting the above technical solution, the aging treatment can significantly improve the strength and hardness of the aluminum alloy by precipitating the strengthening phase, and the processing performance is significantly improved. A dense oxide film will be formed on the surface of the aluminum material, which can effectively improve the corrosion resistance of the aluminum material. The combination of the above aging treatment temperature and time can bring about better corresponding effects, and finally obtain a high-strength aluminum alloy for car body with excellent and stable quality.

[0028] In summary, this application has the following beneficial effects: The present application uses a rare earth element mixture consisting of niobium, scandium and cobalt, and cooperates with boron to not only improve the microstructure of the alloy, but also can evenly distribute the grown fine particles in the grain boundaries to bring about the effect of coordinated deformation of grain boundary sliding, thereby improving the strength of the aluminum alloy while ensuring excellent ductility of the aluminum alloy. DETAILED DESCRIPTION

[0029] The present application is further described in detail below with reference to the embodiments.

[0030] Example 1 A high-strength aluminum alloy for vehicle body, the raw materials and their corresponding percentages are shown in Table 1, and are prepared by the following steps: (1) preparing raw materials including magnesium, silicon, copper, tin, manganese, iron, boron, rare earth element mixture and aluminum according to the proportion; (2) Under the protection of an inert gas, the aluminum in step (1) is melted, and then magnesium, silicon, copper, tin, manganese, iron, boron, and a rare earth element mixture are added in proportion to perform mixed smelting to obtain a molten liquid; (3) adding a refining agent to the molten liquid obtained in step (2) for refining, removing slag and degassing, and then casting to obtain an alloy semi-finished product; (4) The semi-finished alloy product obtained in step (3) is first subjected to a solution treatment, then subjected to an aging treatment, and then cooled to obtain a high-strength aluminum alloy for vehicle bodies.

[0031] Note: In the above operation, the rare earth element mixture consists of niobium, scandium and cobalt, and the weight ratio of niobium, scandium and cobalt is 1:4:14. In step (2), the smelting temperature is 750°C and the smelting time is 2.5h. In step (3), the refining temperature is 840°C, the refining time is 35min, the amount of refining agent is 0.15% of the mass of the smelting liquid, and the refining agent is composed of sodium chloride, potassium chloride and calcium fluoride in a weight ratio of 11:7:8. In step (4), the temperature of the solution treatment is 530°C and the holding time is 3.5h; the temperature of the aging treatment is 170°C and the holding time is 3.5h.

[0032] Example 2-3 A high-strength aluminum alloy for vehicle body, which is different from Example 1 in that the raw materials and their corresponding weights are shown in Table 1.

[0033] Table 1 Raw materials and their corresponding mass percentages (%) of Examples 1-3 raw material Example 1 Example 2 Example 3 magnesium 1 0.5 1.5 silicon 1.5 1 2 copper 0.7 0.4 1 tin 0.3 0.1 0.5 manganese 0.03 0.01 0.05 iron 0.075 0.05 0.1 boron 0.15 0.1 0.2 Rare earth element mixture 0.9 0.3 1.5 aluminum 95.345 97.54 93.15

[0034] Example 4 A high-strength aluminum alloy for vehicle body, which is different from Example 1 in that the rare earth element mixture consists of niobium, scandium and cobalt, and the weight ratio of niobium, scandium and cobalt is 1:3.9:13.5.

[0035] Example 5 A high-strength aluminum alloy for vehicle body, which is different from Example 1 in that the rare earth element mixture consists of niobium, scandium and cobalt, and the weight ratio of niobium, scandium and cobalt is 1:3.4:12.

[0036] Example 6 A high-strength aluminum alloy for vehicle body, which is different from Example 1 in that the rare earth element mixture consists of niobium, scandium and cobalt, and the weight ratio of niobium, scandium and cobalt is 1:4.4:15.

[0037] Example 7 A high-strength aluminum alloy for vehicle body, which is different from Example 1 in that the total amount of boron and rare earth element mixture remains unchanged, and the weight ratio of the two is adjusted to 1:5.

[0038] Embodiment 8-11 A high-strength aluminum alloy for vehicle body, which is different from Example 1 in that the raw materials and their corresponding weights are shown in Table 2.

[0039] Table 2 Examples 8-11 Raw materials and their corresponding mass percentages (%) raw material Example 8 Example 9 Example 10 Embodiment 11 magnesium 0.8 1.2 0.7 1.3 silicon 1.2 1.8 1.1 1.9 copper 0.6 0.8 0.5 0.9 tin 0.2 0.4 0.1 0.5 manganese 0.03 0.03 0.03 0.03 iron 0.075 0.075 0.075 0.075 boron 0.15 0.15 0.15 0.15 Rare earth element mixture 0.9 0.9 0.9 0.9 aluminum 96.045 94.645 96.445 94.245

[0040] Example 12 A high-strength aluminum alloy for vehicle body, which is different from Example 1 in that, in step (2), the melting temperature is 700° C. and the melting time is 3 hours.

[0041] Example 13 A high-strength aluminum alloy for vehicle body, which is different from Example 1 in that, in step (2), the melting temperature is 800° C. and the melting time is 2 h.

[0042] Embodiment 14 A high-strength aluminum alloy for vehicle body, which is different from Example 1 in that, in step (3), the refining temperature is 820° C. and the refining time is 40 min.

[0043] Embodiment 15 A high-strength aluminum alloy for vehicle body, which is different from Example 1 in that, in step (3), the refining temperature is 860° C. and the refining time is 30 min.

[0044] Example 16 A high-strength aluminum alloy for vehicle body, which is different from Example 1 in that, in step (3), the amount of refining agent used is 0.2% of the mass of the smelting liquid.

[0045] Embodiment 17 A high-strength aluminum alloy for vehicle body, which is different from Example 1 in that, in step (3), the amount of refining agent used is 0.1% of the mass of the smelting liquid.

[0046] Embodiment 18 A high-strength aluminum alloy for vehicle body, which is different from Example 1 in that, in step (4), the temperature of the solution treatment is 520° C. and the holding time is 4 hours.

[0047] Embodiment 19 A high-strength aluminum alloy for vehicle body, which is different from Example 1 in that, in step (4), the temperature of the solution treatment is 540° C. and the holding time is 3 h.

[0048] Embodiment 20 A high-strength aluminum alloy for vehicle body, which is different from Example 1 in that, in step (4), the aging treatment temperature is 160° C. and the holding time is 4 h.

[0049] Embodiment 21 A high-strength aluminum alloy for vehicle body, which is different from Example 1 in that, in step (4), the aging treatment temperature is 180° C. and the holding time is 3 h.

[0050] Comparative Example 1 A high-strength aluminum alloy for vehicle body, which is different from Example 1 in that the mass of boron and other components in the raw material is replaced by aluminum.

[0051] Comparative Example 2 A high-strength aluminum alloy for vehicle body, which is different from Example 1 in that the mass of the rare earth element mixture in the raw material is replaced by aluminum.

[0052] Comparative Example 3 A high-strength aluminum alloy for vehicle body, which is different from Example 1 in that the mass of the boron and rare earth element mixture in the raw materials is replaced by aluminum.

[0053] Comparative Example 4 A high-strength aluminum alloy for vehicle body, which is different from Example 1 in that niobium and cobalt are not used in the rare earth element mixture.

[0054] Comparative Example 5 A high-strength aluminum alloy for vehicle body, which is different from Example 1 in that scandium and cobalt are not used in the rare earth element mixture.

[0055] Comparative Example 6 A high-strength aluminum alloy for vehicle body, which is different from Example 1 in that niobium and scandium are not used in the rare earth element mixture.

[0056] Comparative Example 7 A high-strength aluminum alloy for vehicle body, which is different from Example 1 in that niobium is not used in the rare earth element mixture.

[0057] Comparative Example 8 A high-strength aluminum alloy for vehicle body, which is different from Example 1 in that scandium is not used in the rare earth element mixture.

[0058] Comparative Example 9 A high-strength aluminum alloy for vehicle body, which is different from Example 1 in that cobalt is not used in the rare earth element mixture.

[0059] Performance testing Test samples: The high-strength aluminum alloy for vehicle body obtained in Examples 1-21 was used as test sample 1-21, and the high-strength aluminum alloy for vehicle body obtained in Comparative Examples 1-9 was used as control sample 1-9.

[0060] Test method: (1) The aluminum alloy hardness of test samples 1-21 and control samples 1-9 was measured according to the content of YS / T 420-2023 "Test method for Webster hardness of aluminum alloy"; (2) Test the yield strength of test samples 1-21 and control samples 1-9 according to ASTM E8 / E8M; (3) The tensile strength of test samples 1-21 and control samples 1-9 was tested according to ASTM E8 / E8M; (4) Elongation refers to the percentage of the total elongation of the material after it breaks after stretching to the original gauge length. If the length of the material changes by ΔL before and after stretching, and the original length is L0, then the elongation can be calculated by the formula: Elongation = ΔL / L0 × 100%.

[0061] After completing the above tests on test samples 1-21 and control samples 1-9 in sequence, the corresponding results are recorded in Table 3.

[0062] Table 3 Test results of test samples 1-21 and control samples 1-9 sample Hardness (HV) Yield strength (MPa) Tensile strength (MPa) Elongation (%) Test sample 1 165.5 309.1 386.8 16.7 Test sample 2 163.2 306.8 384.5 14.4 Test sample 3 163.1 306.7 384.4 14.3 Test sample 4 164.1 307.7 385.4 15.3 Test sample 5 163.9 307.5 385.2 15.1 Test sample 6 164.3 307.9 385.6 15.5 Test sample 7 165.3 308.9 386.6 16.5 Test sample 8 165.1 308.7 386.4 16.3 Test sample 9 164.9 308.5 386.2 16.1 Test sample 10 163.5 307.1 384.8 14.7 Test sample 11 163.7 307.3 385.0 14.9 Test sample 12 164.5 308.1 385.8 15.7 Test sample 13 164.7 308.3 386.0 15.9 Test sample 14 164.0 307.6 385.3 15.2 Test sample 15 164.2 307.8 385.5 15.4 Test sample 16 164.8 308.4 386.1 16.0 Test sample 17 163.9 307.5 385.2 15.1 Test sample 18 164.4 308.0 385.7 15.6 Test sample 19 165.0 308.6 386.3 16.2 Test sample 20 164.6 308.2 385.9 15.8 Test sample 21 165.2 308.8 386.5 16.4 Control sample 1 150.8 294.4 372.1 13.1 Control sample 2 148.4 292.1 369.7 12.8 Control sample 3 141.1 284.7 362.4 11.2 Control sample 4 151.8 295.4 373.1 13.3 Control sample 5 152.7 296.3 374.0 13.5 Control sample 6 152.1 295.7 373.4 13.4 Control sample 7 155.5 299.1 376.8 13.7 Control sample 8 156.4 300.0 377.6 13.9 Control sample 9 156.1 299.7 377.4 13.8 Combining Example 1 and Comparative Examples 1-3 and Table 3, it can be seen that the present application uses a rare earth element mixture composed of niobium, scandium and cobalt, and cooperates with boron to achieve good ductility of aluminum alloy under high hardness, yield strength and high tensile strength. The hardness, yield strength, high tensile strength and ductility values ​​obtained by the above test can be significantly improved; if boron or rare earth element mixture is applied to the aluminum alloy system alone, although it can bring about the improvement of the corresponding effect, the improvement is limited, far less than the excellent effect brought by the combination of the two. It can be seen that the combination of boron and rare earth element mixture can bring about a significant improvement effect of 1+1>2. Combining Comparative Examples 4-9 and Table 3, it can be seen that in the rare earth element mixture, if only one or two of niobium, scandium and cobalt are used, the corresponding effects brought are limited, and the effects are only simply superimposed on each other. Only when the three are used in combination can a more prominent and significant corresponding effect be brought, thereby improving the overall strength of the aluminum alloy while making the aluminum alloy take into account excellent ductility.

[0063] Combining Example 1 and Examples 4-6 with Table 3, it can be seen that when the weight ratio of niobium, scandium and cobalt in the rare earth element mixture is 1: (3.4-4.4): (12-15), a stable and better application effect can be exerted. Among them, when the weight ratio of niobium, scandium and cobalt is 1: 4: 14, the application effect of the rare earth element mixture is better. Combining Example 7 with Table 3, it can be seen that when the weight ratio of boron and the rare earth element mixture is 1: 5, the coordination system formed by the two performs better in the aluminum alloy, and thus the obtained high-strength aluminum alloy for car body performs better in hardness, yield strength, high tensile strength and ductility.

[0064] From Example 1 and Examples 8-11 and Table 3, it can be seen that when the mass percentages of magnesium, silicon, copper and tin are: 0.8-1.2% for magnesium, 1.2-1.8% for silicon, 0.6-0.8% for copper and 0.2-0.4% for tin, the formation of the precipitation phase of the aluminum alloy after solution treatment can be more balanced, which is beneficial to the subsequent aging strengthening, and can make the boron and rare earth element mixtures more easily cooperate in the alloy system, so that a high-strength aluminum alloy for vehicle body with better quality can be finally obtained.

[0065] It can be seen from Example 1 and Examples 12-21 and Table 3 that in the preparation of the high-strength aluminum alloy for vehicle body of the present application, the selection and coordination of parameters in each operation can ensure that the raw materials can fully cooperate, exert excellent corresponding effects, and ultimately obtain high-strength aluminum alloy for vehicle body with excellent and stable quality.

[0066] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A high-strength aluminum alloy for vehicle body, characterized in that: It is made of raw materials containing the following mass percentages: Magnesium 0.5-1.5%; Silicon 1-2%; Copper 0.4-1%; Tin 0.1-0.5%; Manganese 0.01-0.05%; Iron 0.05-0.1%; Boron 0.1-0.2%; Rare earth element mixture 0.3-1.5%; The balance is aluminum; The rare earth element mixture consists of niobium, scandium and cobalt, and the weight ratio of niobium, scandium and cobalt is 1:(3.4-4.4):(12-15).

2. The high-strength aluminum alloy for vehicle body according to claim 1, characterized in that: The weight ratio of niobium, scandium and cobalt is 1:4:

14.

3. The high-strength aluminum alloy for vehicle body according to claim 1, characterized in that: The weight ratio of the boron and rare earth element mixture is 1:

5.

4. The high-strength aluminum alloy for vehicle body according to claim 1, characterized in that: The mass percentages of magnesium, silicon, copper and tin are: Magnesium 0.8-1.2%; Silicon 1.2-1.8%; Copper 0.6-0.8%; Tin 0.2-0.4%.

5. The method for preparing the high-strength aluminum alloy for vehicle body according to claim 1, characterized in that: The following steps are involved: (1) preparing raw materials including magnesium, silicon, copper, tin, manganese, iron, boron, rare earth element mixture and aluminum according to the proportion; (2) Under the protection of an inert gas, the aluminum in step (1) is melted, and then magnesium, silicon, copper, tin, manganese, iron, boron, and a rare earth element mixture are added in proportion to perform mixed smelting to obtain a molten liquid; (3) adding a refining agent to the molten liquid obtained in step (2) for refining, removing slag and degassing, and then casting to obtain an alloy semi-finished product; (4) The semi-finished alloy product obtained in step (3) is first subjected to a solution treatment, then subjected to an aging treatment, and then cooled to obtain a high-strength aluminum alloy for vehicle bodies.

6. The method for preparing a high-strength aluminum alloy for vehicle body according to claim 5, characterized in that: In step (2), the smelting temperature is 700-800°C and the smelting time is 2-3h.

7. The method for preparing a high-strength aluminum alloy for vehicle body according to claim 5, characterized in that: In step (3), the refining temperature is 820-860°C and the refining time is 30-40 minutes.

8. The method for preparing a high-strength aluminum alloy for vehicle body according to claim 5, characterized in that: In step (3), the amount of the refining agent used is 0.1-0.2% of the mass of the smelting liquid, and the refining agent is any one or a combination of several of sodium chloride, potassium chloride, sodium fluoride and calcium fluoride.

9. The method for preparing a high-strength aluminum alloy for vehicle body according to claim 5, characterized in that: In step (4), the temperature of the solution treatment is 520-540°C and the holding time is 3-4h.

10. The method for preparing a high-strength aluminum alloy for vehicle body according to claim 5, characterized in that: In step (4), the aging treatment temperature is 160-180°C and the insulation time is 3-4h.