Al-mg-si series aluminum alloy for new energy automobile body and preparation method thereof

Abstract

The application discloses an Al-Mg-Si series aluminum alloy for a new energy automobile body and a preparation method thereof. The chemical components of the aluminum alloy are as follows in terms of percentage by mass based on the total weight of the aluminum alloy: Mg: 4.2-6.3 wt.%, Si: 1.9-2.9 wt.%, Mn: 0.55-0.95 wt.%, Ti: 0.12-0.28 wt.%, Zr: 0.08-0.18 wt.%, Cr: 0.05-0.25 wt.%, Re: 0.05-0.20 wt.%, Fe: <=0.25 wt.%, total content of inevitable impurity elements <=0.10 wt.%, and the balance being Al; wherein the mass ratio of Mg to Si is (1.8-2.2):1. The preparation method mainly comprises the following six steps: raw material preparation, smelting, refining and degassing, casting, homogenization treatment and forming processing, and no solid solution and aging heat treatment is needed throughout the process. The aluminum alloy can fully meet the use requirements of the new energy automobile body structural parts, and has the advantages of simple preparation process, low cost, high efficiency, significant technical advantages and industrial application value.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy material technology, specifically relating to an Al-Mg-Si aluminum alloy for new energy vehicle bodies and its preparation method. It is particularly suitable for the large-scale production of new energy vehicle body structural components, and can achieve a dual improvement in vehicle body lightweighting and structural strength, meeting the development needs of the automotive industry for "dual carbon" and energy conservation and emission reduction. Background Technology

[0002] With the rapid development of the new energy vehicle industry, lightweighting of vehicle bodies has become a core technological path to reduce overall vehicle energy consumption and increase driving range. Aluminum alloys, due to their advantages such as low density, high specific strength, corrosion resistance, and good recyclability, have become the preferred lightweight material for new energy vehicle bodies. Among them, Al-Mg-Si aluminum alloys are most widely used in the field of automotive body structural components due to their good cold / hot formability, weldability, and heat-treatable strengthening properties.

[0003] Currently, most Al-Mg-Si series aluminum alloys used in car bodies require heat treatment processes such as solution treatment and artificial aging (T6) to achieve the strength requirements of car body structural components. However, this heat treatment process has many technical drawbacks: First, the solution treatment and aging processes consume a large amount of electrical energy, prolonging the production cycle and significantly increasing production costs, which is inconsistent with the national "dual carbon" policy. Second, aluminum alloy components are prone to thermal deformation, surface oxidation, and abnormal grain growth during heat treatment, reducing the dimensional accuracy and surface quality of the components. This necessitates additional processing steps such as subsequent shaping and grinding, further increasing production difficulty and costs. Third, heat-treated aluminum alloy components suffer from stress concentration, which can easily lead to microcracks during subsequent assembly and use, affecting structural safety.

[0004] To address the aforementioned issues, some existing research attempts to develop heat-treatable Al-Mg-Si aluminum alloys, primarily by adjusting the alloy composition ratio to improve strength. However, these efforts generally suffer from a technical bottleneck where strength and toughness are difficult to balance: some alloys exhibit good plasticity but low strength, with tensile strength below 300 MPa, failing to meet the stringent impact and deformation resistance requirements of new energy vehicle bodies; others show a significant decrease in elongation after strength enhancement, potentially leading to brittle fracture of body components during collisions, posing safety hazards. Furthermore, existing heat-treatable Al-Mg-Si aluminum alloys are highly sensitive to impurities such as Fe, which readily form hard and brittle phases like Al-Fe-Si with the matrix, severely deteriorating the alloy's mechanical properties and formability. This necessitates extremely high raw material purity, further increasing raw material costs. In addition, the manufacturing processes for some heat-treatable aluminum alloys are complex, involving special modification treatments and multi-stage deformation processes, making industrial-scale production difficult and limiting their widespread application in the new energy vehicle body sector.

[0005] For example, an Al-Mg-Si series heat-free aluminum alloy disclosed in the prior art has a tensile strength of only 315MPa, a yield strength of 215MPa, and an elongation of 8%, which is significantly lower than that of 6016 wrought aluminum alloy sheet for automobiles (yield strength 280MPa). It is likely to become a performance bottleneck when used as a connection for body structural components. Another heat-free die-cast aluminum alloy has good casting performance, but it belongs to the Al-Si series alloy, and it is difficult to achieve both strength and toughness at the same time. In addition, it has poor weldability and cannot meet the integrated assembly requirements of body structural components.

[0006] Therefore, developing an Al-Mg-Si aluminum alloy that can achieve high strength and toughness without solution aging heat treatment, has a simple preparation process, controllable cost, low impurity sensitivity, and is fully compatible with the needs of new energy vehicle body structural components has become an urgent technical challenge to be solved in this field. Summary of the Invention

[0007] To address the shortcomings of existing Al-Mg-Si aluminum alloys for vehicle bodies, such as the need for heat treatment, difficulty in balancing strength and toughness, high manufacturing costs, high sensitivity to impurities, and challenges in large-scale production, this invention aims to provide an Al-Mg-Si aluminum alloy for new energy vehicle bodies and its preparation method. This invention achieves high-strength, high-toughness aluminum alloy materials without solution aging heat treatment by precisely controlling the alloy's chemical composition and element ratios, introducing multi-element microalloying elements, and optimizing the preparation process. Simultaneously, it simplifies the preparation process, reduces production energy consumption and raw material costs, and improves production efficiency, thus meeting the needs of large-scale production of new energy vehicle body structural components.

[0008] The present invention achieves the above objectives using the following technical solution: An Al-Mg-Si aluminum alloy for new energy vehicle bodies, based on the total weight of the aluminum alloy, has the following chemical composition by mass percentage: Mg: 4.2~6.3wt.%, Si: 1.9~2.9wt.%, Mn: 0.55~0.95wt.%, Ti: 0.12~0.28wt.%, Zr: 0.08~0.18wt.%, Cr: 0.05~0.25wt.%, Re: 0.05~0.20wt.%, Fe: ≤0.25wt.%, unavoidable impurity elements total content ≤0.10wt.%, with the balance being Al; wherein, the mass ratio of Mg to Si is (1.8~2.2):1. This ratio is one of the core parameters for achieving high strength and toughness of the alloy without heat treatment, ensuring the formation of an appropriate amount of fine Mg2Si reinforcing phase in the alloy, achieving strength improvement without heat treatment, while avoiding the formation of a hard and brittle phase by excessive Si with the matrix, thus ensuring the plasticity and toughness of the alloy.

[0009] Preferably, Re is a mixture of La and Ce, wherein La: 0.02~0.08 wt.% and Ce: 0.03~0.12 wt.%.

[0010] Preferably, the unavoidable impurity elements include Cu, Zn, and Pb, wherein Cu ≤ 0.05 wt.%, Zn ≤ 0.05 wt.%, and Pb ≤ 0.01 wt.%. Strictly controlling the impurity content can prevent impurity elements from forming harmful phases with the matrix or main alloying elements, and prevent the alloy's strength, toughness, and corrosion resistance from decreasing.

[0011] The proportions of each alloying element in this invention are designed with clear technical considerations in mind. The roles of each element and the reasons for limiting their proportions are as follows: (1) Mg and Si: As the main alloying elements, the two form the Mg2Si strengthening phase, which is the core source of alloy strength. The Mg / Si ratio is controlled at 1.8~2.2:1, which ensures the full formation of the Mg2Si phase and avoids the presence of free Si, thus preventing the alloy toughness from deteriorating. If the Mg / Si ratio is too low, the free Si increases and the alloy plasticity decreases. If the Mg / Si ratio is too high, the excess Mg is prone to forming coarse intermetallic compounds, which reduces the alloy formability.

[0012] (2) Mn: It forms an Al-Mn dispersed phase with Al, which refines the grains and hinders dislocation movement, thereby improving the strength and corrosion resistance of the alloy. If the content is too low, the strengthening effect will be insufficient, and if it is too high, a coarse Al-Mn phase will be formed, which will reduce the plasticity of the alloy. Therefore, it is limited to 0.55~0.95wt.

[0013] (3) Ti and Zr: The two work together to significantly refine the as-cast grains of the alloy and improve the strength, toughness and formability of the alloy; Ti can also form Al-Ti nucleation cores to prevent grain growth during casting, and Zr can form Al-Zr dispersed phases to inhibit recrystallization during subsequent processing. The ratio of the two is limited to Ti 0.12~0.28wt.% and Zr 0.08~0.18wt.%, respectively.

[0014] (4) Cr: It forms an Al-Cr dispersed phase, which hinders the growth of recrystallized grains, refines the processing structure, and improves the strength and fatigue resistance of the alloy. If the content is too high, it will form a coarse and brittle phase, so it is limited to 0.05~0.25wt.%.

[0015] (5) Re (La+Ce): As a rare earth microalloying element, it can form a low-melting-point, plastic rare earth-Fe-Si phase with Fe impurities, replacing the hard and brittle Al-Fe-Si phase, reducing the alloy's sensitivity to Fe impurities. Even if the Fe content reaches 0.25 wt.%, the alloy's strength and toughness can still be guaranteed. Secondly, it can refine the grains and Mg2Si strengthening phase, improving the alloy's strength, toughness, and formability. Thirdly, it can improve the alloy's surface oxidation properties and enhance its corrosion resistance. Therefore, the total content is limited to 0.05~0.20 wt.%, and La and Ce are matched in proportion to achieve the best effect.

[0016] (6) Fe: As a major impurity element, although it cannot be completely avoided, the present invention can effectively suppress its harmful effects through the role of Re element. Therefore, its content is relaxed to ≤0.25wt.%, which broadens the source of raw materials and reduces the cost of raw materials.

[0017] The mechanical properties and corrosion resistance of this aluminum alloy are as follows: tensile strength 380~420MPa, yield strength 320~360MPa, elongation 12%~18%, and salt spray corrosion resistance time ≥1000h, which fully meets the requirements for use in new energy vehicle body structural components.

[0018] This invention also provides a method for preparing the above-mentioned Al-Mg-Si aluminum alloy. This method includes six steps: raw material preparation, smelting, refining and degassing, casting, homogenization treatment, and forming. No solution aging heat treatment is required throughout the entire process. The specific process is as follows: (1) Raw material preparation: Prepare pure Al, Al-Si master alloy, Al-Mg master alloy, Al-Mn master alloy, Al-Ti master alloy, Al-Zr master alloy, Al-Cr master alloy and Al-Re master alloy according to the above chemical composition ratio. The purity of all raw materials is ≥99.7%. Remove oxide scale and oil stains from the surface of the raw materials.

[0019] (2) Melting: Pure Al is put into the melting furnace and heated to 730~750℃ to melt. After the pure Al is completely melted, Al-Si master alloy, Al-Mg master alloy, Al-Mn master alloy, Al-Ti master alloy, Al-Zr master alloy, Al-Cr master alloy and Al-Re master alloy are added in order from low melting point to high melting point. Stirring is done while adding, and the stirring rate is 200~300r / min to ensure that each alloy element is uniformly dissolved. After all the master alloys are added, the temperature is raised to 740~760℃ and held for 15~30min. Protective gas is introduced throughout the melting process to allow the alloy elements to diffuse fully and obtain a uniform aluminum alloy melt.

[0020] (3) Refining and degassing: Add 0.15~0.30wt.% of Al-Ti-BC refining agent to the aluminum alloy melt, stir evenly and keep it at the temperature for 10~20min. This refining agent has multiple functions of refining, slag removal and grain refinement. Then, degassing is carried out by rotary blowing. The blowing gas is high-purity argon (purity ≥99.99%) and the blowing time is 8~12min. This allows the argon bubbles to fully contact the melt and remove hydrogen and inclusions from the melt. After degassing, let the melt stand for 5~10min to allow the remaining inclusions to float to the surface. Then, use a slag skimmer to remove the slag on the surface of the melt to obtain a high-purity aluminum alloy melt.

[0021] (4) Casting: The refined and degassed aluminum alloy melt is cooled to 710~730℃ and cast into ingots using a semi-continuous casting process at a casting speed of 80~120mm / min and a cooling rate of 150~300K / s. The required ingots are cast into ingots.

[0022] (5) Homogenization treatment: After removing the surface oxide scale, the ingot is placed in a homogenization furnace and a stepped homogenization process is adopted. First, it is held at 470~490℃ for 2~4h to fully dissolve the low melting point phase inside the ingot. Then, the temperature is raised to 545~555℃ and held for 3~7h to eliminate the component segregation inside the ingot, so that the alloy elements are evenly distributed and promote the precipitation of fine dispersed phases. After the holding is completed, it is cooled to room temperature with the furnace at a cooling rate ≤50℃ / h to obtain a homogenized ingot. This stepped homogenization process is the key to achieving heat treatment-free alloying and can replace the traditional solution aging heat treatment, which can improve the strength of the alloy while ensuring toughness.

[0023] (6) Forming and processing: The homogenized ingot is hot rolled or extruded to obtain the plates, profiles or forgings required for the body structure of new energy vehicles; the finished products after forming and processing can be directly used for the assembly of body structure of new energy vehicles after surface cleaning, without the need for subsequent heat treatment.

[0024] Preferably, the protective gas in step (2) is a mixture of carbon dioxide and sulfur hexafluoride, wherein the volume ratio of carbon dioxide to sulfur hexafluoride is 7:1 to 10:1; or the protective gas is argon.

[0025] Preferably, the Al-Mn master alloy mentioned in step (2) is an Al-10Mn master alloy, the Al-Cr master alloy is an Al-10Cr master alloy, the Al-Zr master alloy is an Al-5Zr master alloy, the Al-Ti master alloy is an Al-5Ti master alloy, and the Al-Re master alloy is an Al-10Re master alloy (a mixture of La and Ce). Selecting the above master alloys can ensure the uniform addition of alloying elements and avoid the segregation problem caused by directly adding pure metals.

[0026] Preferably, the spraying pressure of the rotary spraying method in step (3) is 0.15~0.25MPa, and the rotation speed of the rotary nozzle is 400~500r / min.

[0027] Preferably, a water-cooled crystallizer is used in the casting process in step (4) to control uniform cooling and avoid casting defects such as shrinkage porosity, air holes, and cracks in the ingot, and the surface finish of the ingot is ≤Ra3.2μm.

[0028] Preferably, the cooling rate of the furnace to room temperature in step (5) is ≤50℃ / h.

[0029] Preferably, the hot rolling process parameters in step (6) are: hot rolling temperature 480~520℃, total reduction 65~75%, reduction per pass 10~15%, and final rolling temperature ≥350℃; the extrusion process parameters are: extrusion temperature 460~500℃, extrusion speed 10~20mm / s, and extrusion ratio 15~25:1.

[0030] Compared with the prior art, the present invention has the following beneficial effects: (1) No heat treatment required and excellent strength and toughness: This invention achieves solution-free aging heat treatment of aluminum alloy by precisely controlling the Mg / Si ratio and introducing Mn, Ti, Zr, Cr and Re multi-element microalloying elements, combined with a step-by-step homogenization process, and significantly improves mechanical properties - tensile strength 380~420MPa, yield strength 320~360MPa, elongation 12~18%. The strength and toughness indicators are significantly better than existing heat-free Al-Mg-Si aluminum alloys, which can fully meet the impact resistance and deformation resistance requirements of new energy vehicle body structural parts, while avoiding problems such as energy consumption, component deformation and stress concentration caused by heat treatment.

[0031] (2) Low impurity sensitivity and low raw material cost: This invention uses the micro-alloying effect of Re element (La+Ce) to form a plastic rare earth - Fe-Si phase with Fe impurities, replacing the hard and brittle Al-Fe-Si phase, effectively suppressing the harmful effects of Fe impurities, relaxing the Fe content to ≤0.25wt.%, greatly reducing the requirements for raw material purity, broadening the source of raw materials, and reducing the cost of raw material procurement.

[0032] (3) The preparation process is simple and the production efficiency is high: The preparation method of the present invention includes only six steps: raw material preparation, smelting, refining and degassing, casting, homogenization treatment and forming processing. It does not require complicated heat treatment process and subsequent shaping and polishing process. The production cycle is shortened by more than 30% compared with the existing heat treatment process and the production efficiency is increased by more than 30%. Moreover, the process parameters are mild and no special equipment is required. It is easy to realize industrial-scale production. There is no harmful gas emission during the preparation process, which meets the requirements of green production.

[0033] (4) Excellent comprehensive performance and strong adaptability: The aluminum alloy of the present invention not only has excellent strength and toughness, but also has good corrosion resistance (salt spray corrosion resistance ≥1000h), formability and weldability. It can be prepared into various forms such as plates, profiles and forgings by hot rolling, extrusion and other methods. It is suitable for various structural parts such as longitudinal beams, cross beams, battery trays and door inner panels of new energy vehicle bodies. Its mechanical properties are highly compatible with commonly used body deformable aluminum alloys such as 6061 and 6016. It has good welding compatibility and can be directly used for assembly on existing body production lines without the need to modify the production line. It has broad prospects for promotion and application.

[0034] (5) Green and environmentally friendly with good recyclability: The aluminum alloy of the present invention has no harmful elements added and the recycling rate is ≥95%, which is in line with the development concept of "green, environmentally friendly and sustainable" new energy vehicles; the preparation process has low energy consumption and low pollutant emissions, which meets the national "dual carbon" policy and the energy-saving and consumption-reducing development needs of the automobile industry. Attached Figure Description

[0035] Figure 1 Micrograph of the aluminum alloy product prepared in Example 2 of this invention.

[0036] Figure 2 Comparison of the tensile properties of aluminum alloys prepared in Example 2 of this invention and those prepared in the comparative example.

[0037] Figure 3 SEM image of intergranular corrosion of the aluminum alloy prepared in Example 2 of this invention.

[0038] Figure 4 SEM images of intergranular corrosion of the aluminum alloy prepared in the comparative example. Detailed Implementation

[0039] Example 1 A heat-treatable Al-Mg-Si high-strength and high-toughness aluminum alloy for new energy vehicle bodies has the following chemical composition by mass percentage: Mg: 4.2 wt.%, Si: 2.3 wt.% (Mg:Si=1.83:1), Mn: 0.55 wt.%, Ti: 0.12 wt.%, Zr: 0.08 wt.%, Cr: 0.05 wt.%, Re: 0.05 wt.% (La: 0.02 wt.%, Ce: 0.03 wt.%), Fe: 0.15 wt.%, unavoidable impurities (Cu: 0.03 wt.%, Zn: 0.02 wt.%, Pb: 0.005 wt.%) totaling 0.055 wt.%, with the balance being Al.

[0040] Its preparation method includes the following steps: (1) Raw material preparation: According to the above chemical composition ratio, prepare pure Al (purity 99.8%), Al-Si master alloy (Si content 20wt.%), Al-Mg master alloy (Mg content 30wt.%), Al-10Mn master alloy, Al-5Ti master alloy, Al-5Zr master alloy, Al-10Cr master alloy, Al-10Re master alloy (La and Ce mixture), remove oxide scale by mechanical grinding, clean the surface oil stains with anhydrous ethanol, and dry for later use.

[0041] (2) Melting: Pure Al is put into a graphite crucible melting furnace and heated to 730°C until it is completely melted. Then, each intermediate alloy is added in sequence and stirred evenly at 200r / min. The temperature is raised to 740°C and held for 15min. Argon gas is introduced throughout the process to obtain aluminum alloy melt.

[0042] (3) Refining and degassing: Add 0.15wt.% Al-Ti-BC refining agent to the melt, stir evenly and keep warm for 10min; use rotary blowing method to blow high-purity argon gas at 0.15MPa pressure for 8min, with nozzle speed of 400r / min, and let stand for 5min after degassing to remove scum.

[0043] (4) Casting: The melt is cooled to 710℃ and a semi-continuous casting process is adopted. The casting speed is 80mm / min and the cooling rate is 150K / s to cast ingots with a diameter of 120mm.

[0044] (5) Homogenization treatment: After removing the oxide scale from the surface of the ingot, it is placed in a homogenization furnace, kept at 470℃ for 2 hours, then heated to 545℃ and kept at 3 hours, and then cooled to room temperature with the furnace at a cooling rate of 40℃ / h.

[0045] (6) Forming and processing: The homogenized ingot is hot rolled at a temperature of 480°C, with a total reduction of 65%, a reduction per pass of 10%, and a final rolling temperature of 360°C to form a 2mm thick sheet metal for the car body.

[0046] The performance of the finished product of this embodiment was tested according to the national standards GB / T 228.1-2021 (tensile test of metallic materials) and GB / T 10125-2021 (artificial atmosphere corrosion test, salt spray test). The results are as follows: tensile strength 380MPa, yield strength 320MPa, elongation 18%, salt spray corrosion resistance time 1200h, and intergranular corrosion depth 259μm.

[0047] Example 2 A heat-treatable Al-Mg-Si high-strength and high-toughness aluminum alloy for new energy vehicle bodies has the following chemical composition by mass percentage: Mg: 5.2 wt.%, Si: 2.5 wt.% (Mg:Si=2.08:1), Mn: 0.75 wt.%, Ti: 0.20 wt.%, Zr: 0.13 wt.%, Cr: 0.15 wt.%, Re: 0.12 wt.% (La: 0.05 wt.%, Ce: 0.07 wt.%), Fe: 0.20 wt.%, unavoidable impurities (Cu: 0.04 wt.%, Zn: 0.03 wt.%, Pb: 0.008 wt.%) totaling 0.078 wt.%, with the balance being Al.

[0048] Its preparation method includes the following steps: (1) Raw material preparation: Same as in Example 1, all raw materials have a purity of ≥99.7%, and are used after removing oxide scale and oil stains.

[0049] (2) Smelting: Pure Al is put into the smelting furnace and heated to 740°C until it is completely melted. Then, each intermediate alloy is added in sequence and stirred evenly at 250 r / min. The temperature is raised to 750°C and held for 22 min. A mixture of carbon dioxide and sulfur hexafluoride protective gas (volume ratio 8:1) is introduced throughout the process to obtain aluminum alloy melt.

[0050] (3) Refining and degassing: Add 0.22wt.% Al-Ti-BC refining agent to the melt, stir evenly and keep warm for 15min; use rotary blowing method to blow high-purity argon gas at 0.20MPa pressure for 10min, with nozzle speed of 450r / min, and let stand for 8min after degassing to remove scum.

[0051] (4) Casting: Cool the melt to 720℃ and use a semi-continuous casting process with a casting speed of 100mm / min and a cooling rate of 220K / s to cast ingots with a diameter of 150mm.

[0052] (5) Homogenization treatment: After removing the oxide scale from the surface of the ingot, it is placed in a homogenization furnace, kept at 480℃ for 3 hours, then heated to 550℃ and kept at 5 hours, and then cooled to room temperature with the furnace at a cooling rate of 45℃ / h.

[0053] (6) Forming process: The homogenized ingot is extruded at a temperature of 480℃, an extrusion speed of 15mm / s, and an extrusion ratio of 20:1 to form a rectangular profile for the car body (section specification 50×10mm).

[0054] The performance of the finished product of this embodiment was tested using the same method as in Example 1. The results are as follows: tensile strength 400MPa, yield strength 340MPa, elongation 15%, salt spray corrosion resistance time 1100h, and intergranular corrosion depth 205μm.

[0055] Example 3 A heat-free Al-Mg-Si high-strength and high-toughness aluminum alloy for new energy vehicle bodies has the following chemical composition by mass percentage: Mg: 6.3 wt.%, Si: 2.9 wt.% (Mg:Si=2.17:1), Mn: 0.95 wt.%, Ti: 0.28 wt.%, Zr: 0.18 wt.%, Cr: 0.25 wt.%, Re: 0.20 wt.% (La: 0.08 wt.%, Ce: 0.12 wt.%), Fe: 0.25 wt.%, unavoidable impurities (Cu: 0.05 wt.%, Zn: 0.05 wt.%, Pb: 0.01 wt.%) totaling 0.10 wt.%, with the balance being Al.

[0056] Its preparation method includes the following steps: (1) Raw material preparation: Same as in Example 1, all raw materials have a purity of ≥99.7%, and are used after removing oxide scale and oil stains.

[0057] (2) Smelting: Pure Al is put into the smelting furnace and heated to 750°C until it is completely melted. Then, each intermediate alloy is added in sequence and stirred evenly at 300r / min. The temperature is raised to 760°C and held for 30min. A mixture of carbon dioxide and sulfur hexafluoride protective gas (volume ratio 10:1) is introduced throughout the process to obtain aluminum alloy melt.

[0058] (3) Refining and degassing: Add 0.30wt.% Al-Ti-BC refining agent to the melt, stir evenly and keep warm for 20min; use rotary blowing method to blow high-purity argon gas at 0.25MPa pressure for 12min, with nozzle speed of 500r / min, and let stand for 10min after degassing to remove scum.

[0059] (4) Casting: The melt is cooled to 730℃ and a semi-continuous casting process is adopted. The casting speed is 120mm / min and the cooling rate is 300K / s to cast ingots with a diameter of 200mm.

[0060] (5) Homogenization treatment: After removing the oxide scale from the surface of the ingot, it is placed in a homogenization furnace, kept at 490℃ for 4 hours, then heated to 555℃ and kept for 7 hours, and then cooled to room temperature with the furnace at a cooling rate of 50℃ / h.

[0061] (6) Forming and processing: The homogenized ingot is hot rolled at a temperature of 520°C, with a total reduction of 75%, a reduction per pass of 15%, and a final rolling temperature of 380°C to form a 3mm thick sheet metal for the car body.

[0062] The performance of the finished product of this embodiment was tested using the same method as in Example 1. The results are as follows: tensile strength 420MPa, yield strength 360MPa, elongation 12%, salt spray corrosion resistance time 1000h, and intergranular corrosion depth 296μm.

[0063] Comparative Example The conventional heat-free Al-Mg-Si aluminum alloy used in the prior art has the following chemical composition by mass percentage: Mg: 3.8 wt.%, Si: 2.5 wt.%, Mn: 0.4 wt.%, Ti: 0.1 wt.%, Fe: 0.20 wt.%, unavoidable impurities total 0.12 wt.%, and the balance is Al. The preparation method adopts conventional melting, casting, and single-temperature homogenization process (holding at 520℃ for 4 hours), without the addition of Re, Zr, and Cr elements, and without optimizing the Mg to Si ratio. The forming process adopts the same extrusion process as in Example 2.

[0064] The performance of the comparative sample was tested using the same method as in Example 1. The results are as follows: tensile strength 298 MPa, yield strength 210 MPa, elongation 6.8%, salt spray corrosion resistance time 800 h, and intergranular corrosion depth 396 μm.

[0065] at the same time, Figure 1 The microstructure of the aluminum alloy of the present invention is shown to be fine equiaxed crystals with uniformly distributed fine dispersed phases and no coarse, hard, or brittle phases; such as Figure 2 As shown, the tensile strength and yield strength of the aluminum alloy of the present invention are significantly higher than those of the comparative example; Figure 3 and Figure 4 The comparison shows that the intergranular corrosion depth of the aluminum alloy of the present invention after salt spray corrosion is significantly shallower than that of the comparative example.

[0066] Comparing the performance indicators of Examples 1-3 with those of the comparative examples, it can be seen that the aluminum alloy of the present invention is significantly superior to existing conventional heat-free Al-Mg-Si aluminum alloys in terms of tensile strength, yield strength, elongation, and corrosion resistance. The core reason is as follows: (1) The present invention precisely controls the Mg / Si ratio to 1.8~2.2:1, ensuring the formation of an appropriate amount of Mg2Si strengthening phase, which lays the foundation for strength improvement; while in the comparative example, the Mg / Si ratio is unbalanced, the Mg2Si phase is insufficiently formed, and the strength is low.

[0067] (2) The present invention introduces Mn, Ti, Zr, Cr and Re as multi-element microalloying elements. The synergistic effect of each element achieves multiple effects such as grain refinement, dispersion strengthening and suppression of the harmful effects of impurities. In contrast, the comparative example only added a small amount of Mn and Ti, without Zr, Cr and Re elements, resulting in coarse grains and Fe impurities forming a hard and brittle phase, which deteriorated the strength, toughness and corrosion resistance.

[0068] (3) The present invention adopts a step-by-step homogenization process, which effectively eliminates component segregation and promotes the precipitation of fine dispersed phases, replacing the traditional solid solution and aging heat treatment; while the comparative example adopts a single temperature homogenization process, which does not sufficiently eliminate component segregation and results in poor alloy uniformity.

[0069] In summary, the heat-toughened Al-Mg-Si series high-strength and high-toughness aluminum alloy for new energy vehicle bodies of the present invention exhibits excellent strength and toughness, good corrosion resistance, and low impurity sensitivity. Its preparation process is simple, low-cost, and highly efficient. It can be directly used for the large-scale production of structural components such as longitudinal beams, cross beams, battery trays, and door inner panels of new energy vehicle bodies without solution treatment or aging heat treatment. Furthermore, it has good formability and weldability, and can be adapted to the assembly requirements of existing automotive body production lines without requiring modifications to the production lines. It possesses significant industrial practicality and broad market prospects.

Claims

1. An Al-Mg-Si aluminum alloy for new energy vehicle bodies, characterized in that, Based on the total weight of the aluminum alloy, the chemical composition by mass percentage is as follows: Mg: 4.2~6.3wt.%, Si: 1.9~2.9wt.%, Mn: 0.55~0.95wt.%, Ti: 0.12~0.28wt.%, Zr: 0.08~0.18wt.%, Cr: 0.05~0.25wt.%, Re: 0.05~0.20wt.%, Fe: ≤0.25wt.%, total content of unavoidable impurity elements ≤0.10wt.%, balance Al; The mass ratio of Mg to Si is (1.8~2.2):

1.

2. The aluminum alloy according to claim 1, characterized in that, The Re is a mixture of La and Ce, wherein La: 0.02~0.08 wt.% and Ce: 0.03~0.12 wt.%.

3. The aluminum alloy according to claim 1, characterized in that, The unavoidable impurity elements include Cu, Zn, and Pb, wherein Cu ≤ 0.05 wt.%, Zn ≤ 0.05 wt.%, and Pb ≤ 0.01 wt.%.

4. The aluminum alloy according to any one of claims 1-3, characterized in that, The mechanical properties of this aluminum alloy are: tensile strength 380~420MPa, yield strength 320~360MPa, elongation 12%~18%, and salt spray corrosion resistance time ≥1000h.

5. A method for preparing an Al-Mg-Si aluminum alloy for new energy vehicle bodies according to any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Raw material preparation: Prepare pure Al, Al-Si master alloy, Al-Mg master alloy, Al-Mn master alloy, Al-Ti master alloy, Al-Zr master alloy, Al-Cr master alloy and Al-Re master alloy according to the chemical composition ratio described in claim 1. The purity of all raw materials is ≥99.7%. Remove oxide scale and oil stains from the surface of the raw materials. (2) Melting: Pure Al is put into the melting furnace and heated to 730~750℃ to melt. Then, each intermediate alloy is added in sequence and stirred evenly. The temperature is raised to 740~760℃ and held for 15~30 minutes. Protective gas is introduced throughout the melting process to obtain a uniform aluminum alloy melt. (3) Refining and degassing: Add 0.15~0.30wt.% of Al-Ti-BC refining agent to the aluminum alloy melt, keep it at the temperature for 10~20min, then use the rotary blowing method to blow argon gas for 8~12min to degas, let it stand for 5~10min after degassing, remove the slag on the surface of the melt, and obtain the aluminum alloy melt; (4) Casting: The refined and degassed aluminum alloy melt is cooled to 710~730℃ and cast into ingots using a semi-continuous casting process at a casting speed of 80~120mm / min and a cooling rate of 150~300K / s. (5) Homogenization treatment: The ingot is placed in a homogenization furnace and a step-type homogenization process is adopted. First, it is kept at 470~490℃ for 2~4h, then the temperature is raised to 545~555℃ and kept for 3~7h. Then it is cooled to room temperature with the furnace to obtain a homogenized ingot. (6) Forming and processing: The homogenized ingot is hot rolled or extruded to obtain the finished products required for the body structure of new energy vehicles.

6. The method according to claim 5, characterized in that, The protective gas in step (2) is a mixture of carbon dioxide and sulfur hexafluoride, wherein the volume ratio of carbon dioxide to sulfur hexafluoride is 7:1 to 10:1; or the protective gas is argon.

7. The method according to claim 5, characterized in that, The Al-Mn master alloy mentioned in step (2) is Al-10Mn master alloy, the Al-Cr master alloy is Al-10Cr master alloy, the Al-Zr master alloy is Al-5Zr master alloy, the Al-Ti master alloy is Al-5Ti master alloy, and the Al-Re master alloy is Al-10Re master alloy.

8. The method according to claim 5, characterized in that, The blowing pressure of the rotary jetting method in step (3) is 0.15~0.25MPa, and the rotation speed of the rotary nozzle is 400~500r / min.

9. The method according to claim 5, characterized in that, In step (4), a water-cooled crystallizer is used during the casting process; in step (5), the cooling rate of the furnace cooling is ≤50℃ / h.

10. The method according to claim 5, characterized in that, The hot rolling process parameters in step (6) are: hot rolling temperature 480~520℃, total reduction 65~75%; the extrusion process parameters are: extrusion temperature 460~500℃, extrusion speed 10~20mm / s.

Images