High-strength and high-toughness Nb-containing heat-treatment-free aluminum-magnesium alloy for automobile thin-wall parts and preparation method thereof

Abstract

The application discloses a high-strength and high-toughness Nb-containing heat-treatment-free aluminum magnesium alloy for automobile thin-wall parts and a preparation method thereof. The content of Mg is 4.0%-6.5% of the total mass of the alloy, the content of Si is 1.6%-3.0%, the content of Mn is 0.3%-0.5%, the content of Ti is 0.05%-0.1%, the content of Nb is 0.05%-0.2%, the content of B is 0.01%-0.03%, the content of RE is not more than 0.15%, the content of Fe is less than or equal to 0.2%, the content of other uncontrollable impurity elements is less than or equal to 0.5%, and the balance is Al. The yield strength of the alloy in the high-pressure casting process can be up to 210.05 MPa, the tensile strength can be up to 370.22 MPa, and the elongation can be up to 12.18%. The application belongs to the technical field of aluminum alloys.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy technology, specifically relating to a high-strength, high-toughness Nb-containing aluminum-magnesium alloy for thin-walled automotive parts that does not require heat treatment, and its preparation method. Background Technology

[0002] In recent years, the application of aluminum alloys produced by integrated die casting technology in the automotive industry has gradually become a new trend, especially for thin-walled parts with complex structures. These structural parts not only require high strength but also high ductility. Therefore, developing high-strength, high-ductility aluminum alloys suitable for die casting is extremely important.

[0003] Heat treatment is one of the most effective ways to improve the strength and toughness of alloys. However, for structural parts with thin walls and complex features, heat treatment often leads to dimensional instability in die castings. This is mainly manifested in the easy formation of bubbles on the surface of the die castings, easy deformation of the structural parts, and resulting in an extremely high scrap rate.

[0004] Therefore, it is necessary to develop heat-free aluminum alloys with excellent comprehensive mechanical properties to broaden the practical application of aluminum alloys in thin-walled parts. Summary of the Invention

[0005] To address the problems of unstable dimensions in existing die-castings, which leads to easy formation of bubbles on the casting surface, easy deformation of structural parts, and high scrap rate, this invention provides a high-strength, high-toughness Nb-containing aluminum-magnesium alloy for thin-walled automotive parts that does not require heat treatment, and its preparation method.

[0006] The first aspect of this invention provides a high-strength, high-toughness, Nb-containing, heat-treatable aluminum-magnesium alloy for thin-walled automotive parts. Based on the total mass of the alloy, the alloy contains 4.0%–6.5% Mg, 1.6%–3.0% Si, 0.3%–0.5% Mn, 0.05%–0.1% Ti, 0.05%–0.2% Nb, 0.01%–0.03% B, no more than 0.15% RE, ≤0.2% Fe, ≤0.5% other uncontrollable impurity elements, and the balance being Al.

[0007] As an embodiment of the present invention, the RE element is one or more of La, Ce and Sc.

[0008] In one embodiment of the present invention, the elemental mass ratio of Mg to Si in the alloy is 2.0 to 2.5:1, the elemental mass ratio of Mn to Fe is 1.5 to 3.5:1, the elemental mass ratio of Nb to B is 5 to 9:1, and the elemental mass ratio of Nb to Ti is 1 to 1.5:1.

[0009] As an embodiment of the present invention, Nb element is added in the form of Al-Nb-B alloy, and Ti element is added in the form of Al-Ti alloy.

[0010] As an embodiment of the present invention, the other uncontrollable impurity elements include one or more of O, C and Na.

[0011] A second aspect of the present invention provides a method for preparing the alloy described in the first aspect, the method comprising:

[0012] S1: Batching and smelting: Si, Mn, Ti, and Al are batched according to their mass percentages and placed into a smelting furnace. The temperature is raised to 790℃~810℃ until the alloy is completely melted. The temperature is then lowered to 775℃~785℃, and Nb and B are added. After they are completely melted, the mixture is stirred for 30s~40s. The smelting temperature is further lowered to 730℃~735℃, and Mg and RE are added.

[0013] S2: Refining and casting. After degassing and refining for 30 to 35 minutes, remove the slag and let it stand for 15 to 20 minutes before casting. The casting temperature is 680℃ to 700℃.

[0014] As an embodiment of the present invention, the elements selected in step S1 are added in the following forms: Al-Si master alloy, Al-Ti master alloy, industrial pure aluminum with a purity of 99.9%, Al-Nb-B master alloy, industrial pure magnesium with a purity of 99.9%, and Al-RE master alloy.

[0015] In one embodiment of the present invention, the refining gas used in step S2 is argon, and the gas flow rate is 9L / min to 11L / min.

[0016] In this invention, the Mg element mainly improves the yield strength and tensile strength of the alloy by generating the Mg2Si strengthening phase and by solid solution strengthening in the α-Al matrix. The role of the Si element is to synergistically optimize the volume fraction, size, and distribution of the Mg2Si phase to balance the relationship between strength and ductility. The roles of the Nb and Ti elements are to achieve the best grain refinement effect through coordinated optimization, resist the "Si poisoning" effect, and disperse the Mg2Si phase and other second phases. The role of the Mn element is to optimize the large-size primary lamellar β-Fe phase in the alloy, improve the film adhesion of the alloy, and increase the mold life. The role of the RE element is to refine the grains by inhibiting the growth of the second phase, thereby optimizing its size, shape, and distribution, and precipitating strengthening phases such as Al3Sc, AlCeSi, and LaSi.

[0017] The alloy in this invention has a yield strength of up to 210.05 MPa, a tensile strength of up to 370.22 MPa, and an elongation of up to 12.18% in the as-cast state during high-pressure casting. Detailed Implementation

[0018] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with specific embodiments.

[0019] Example 1

[0020] In this example, the mass percentages of the components of the Nb-containing heat-free aluminum-magnesium alloy used in thin-walled automotive parts are as follows: 5.0% Mg; 2.1% Si; 0.5% Mn; 0.08% Ti; 0.1% Nb; 0.03% B; 0.12% RE; 0.20% Fe, with the balance being Al.

[0021] In this embodiment, a heat-free aluminum-magnesium alloy is prepared according to the following steps:

[0022] Material preparation: According to the alloy composition ratio, elements such as Mg, Si, Mn, Ti, Nb, B, RE, and Al are added in the form of 99.9% pure industrial magnesium, Al-Si master alloy, Al-Mn master alloy, Al-Ti master alloy, Al-Nb-B master alloy, Al-RE master alloy, and 99.9% pure industrial aluminum, respectively.

[0023] Melting: Al-Si master alloy, Al-Mn master alloy, Al-Ti master alloy, and 99.9% pure industrial aluminum are placed in a resistance melting furnace and heated to 800℃ until the alloy is completely melted; then the temperature is lowered to 780℃, and Al-Nb-B master alloy is added. After it is completely melted, the mixture is stirred for 30 seconds; the furnace temperature is further lowered to 730℃, and 99.9% pure industrial magnesium and Al-RE master alloy are added. To prevent oxidation and burn-off, the magnesium ingots are wrapped in aluminum foil and pressed into the molten aluminum using a graphite bell jar.

[0024] Refining: Argon gas is used for degassing and refining at a flow rate of 10 L / min. After degassing for 30 min, the slag is removed and the mixture is allowed to stand for 15 min.

[0025] Pouring: The hydrogen content of the melt is measured using a hydrogen analyzer, and the pinholes are no greater than grade 1 as specified in GB / T7946.3 for pinholes of cast aluminum alloys. After passing the test, pouring is carried out at a temperature of 700℃.

[0026] Casting: The molten aluminum is transferred to high-pressure casting equipment for die casting.

[0027] Example 2

[0028] In this example, the mass percentages of the components of the Nb-containing heat-free aluminum-magnesium alloy used in thin-walled automotive parts are as follows: 5.3% Mg; 2.0% Si; 0.48% Mn; 0.06% Ti; 0.1% Nb; 0.03% B; 0.12% RE; 0.20% Fe, with the balance being Al.

[0029] The preparation method of the Nb-containing heat-free aluminum-magnesium alloy for thin-walled automotive parts in this embodiment is the same as that in Example 1.

[0030] Example 3

[0031] In this example, the mass percentages of the components in the Nb-containing heat-free aluminum-magnesium alloy used for thin-walled automotive parts are as follows: 5.1% Mg; 2.1% Si; 0.49% Mn; 0.05% Ti; 0.1% Nb; 0.03% B; 0.12% RE; 0.20% Fe, with the balance being Al.

[0032] The preparation method of Nb-containing heat-free aluminum-magnesium alloy for thin-walled automotive parts in Example 3 is the same as that in Example 1.

[0033] Comparative Example 1

[0034] This comparative example provides an Al5Mg2SiMn aluminum-magnesium alloy with the following mass percentages of components: 6.1% Mg; 2.2% Si; 0.65% Mn; 0.05% Ti; 0.01% Sr; 0.18% Fe, with the balance being Al.

[0035] In this embodiment, a heat-free aluminum-magnesium alloy is prepared according to the following steps:

[0036] Material preparation: According to the alloy composition ratio, elements such as Mg, Si, Mn, Ti, B, and Al are added in the form of 99.9% pure industrial magnesium, Al-Si master alloy, Al-Mn master alloy, Al-Ti-B master alloy, Al-RE master alloy, and 99.9% pure industrial aluminum, respectively.

[0037] Melting: Al-Si master alloy, Al-Mn master alloy, Al-Ti master alloy, and 99.9% pure industrial aluminum are placed in a resistance melting furnace and heated to 800℃ until the alloy is completely melted; then the temperature is lowered to 780℃, and Al-Ti-B master alloy is added. After it is completely melted, it is stirred for 30 seconds; the furnace temperature is further lowered to 730℃, and 99.9% pure industrial magnesium and Al-RE master alloy are added. To prevent oxidation and burn-off, the magnesium ingots are wrapped in aluminum foil and pressed into the molten aluminum using a graphite bell jar.

[0038] Refining: Argon gas is used for degassing and refining at a flow rate of 10 L / min. After degassing for 30 min, the slag is removed and the mixture is allowed to stand for 15 min.

[0039] Pouring: The hydrogen content of the melt is measured using a hydrogen analyzer, and the pinholes are no greater than grade 1 as specified in GB / T7946.3 for pinholes of cast aluminum alloys. After passing the test, pouring is carried out at a temperature of 700℃.

[0040] Casting: The molten aluminum is transferred to high-pressure casting equipment for die casting.

[0041] Comparative Example 2

[0042] This comparative example provides a commonly used aluminum alloy in C611 automobile production, with the following mass percentages of each component: 0.22% Mg; 6.0% Si; 0.45% Mn; 0.1% Ti; 0.02% B; 0.012% Sr; 0.15% Fe, with the balance being Al.

[0043] The preparation method of the C611 alloy in this comparative example is the same as that in comparative example 1.

[0044] The tensile strength, yield strength, and elongation after fracture of the die-cast alloys of the examples and comparative examples were compared, and the results are shown in Table 1.

[0045] Table 1. Performance testing of aluminum alloys prepared in the examples and comparative examples.

[0046]

[0047] As shown in Table 1, the alloy provided by this invention outperforms other similar aluminum-magnesium alloys (Al5Mg2SiMn) in various performance aspects during high-pressure casting. Compared to the most mature heat-treated C611 alloy, the alloy exhibits significantly improved yield strength and tensile strength with a slight decrease in elongation, demonstrating its excellent strengthening properties.

[0048] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A high-strength, high-toughness, Nb-containing, heat-treatable-free aluminum-magnesium alloy for thin-walled automotive parts, characterized in that... Based on the total mass of the alloy, the content of Mg is 4.0%–6.5%, the content of Si is 1.6%–3.0%, the content of Mn is 0.3%–0.5%, the content of Ti is 0.05%–0.1%, the content of Nb is 0.05%–0.2%, the content of B is 0.01%–0.03%, the content of RE is not more than 0.15%, the content of Fe is ≤0.2%, the content of other uncontrollable impurity elements is ≤0.5%, and the balance is Al; RE elements are one or more of La, Ce, and Sc; The mass ratio of Mg to Si in the alloy is 2.0 to 2.5:1, the mass ratio of Mn to Fe is 1.5 to 3.5:1, the mass ratio of Nb to B is 5 to 9:1, and the mass ratio of Nb to Ti is 1 to 1.5:

1. Nb is added in the form of an Al-Nb-B alloy, and Ti is added in the form of an Al-Ti alloy. The method for preparing the alloy includes: S1: Batching and smelting: Si, Mn, Ti, and Al are batched according to their mass percentages and placed into a smelting furnace. The temperature is raised to 790℃~810℃ until the alloy is completely melted. The temperature is then lowered to 775℃~785℃, and Nb and B are added. After they are completely melted, the mixture is stirred for 30s~40s. The smelting temperature is further lowered to 730℃~735℃, and Mg and RE are added. S2: Refining and casting. After degassing and refining for 30 to 35 minutes, remove the slag and let it stand for 15 to 20 minutes before casting. The casting temperature is 680℃ to 700℃.

2. The alloy according to claim 1, characterized in that, The other uncontrollable impurity elements include one or more of O, C and Na.

3. A method for preparing the alloy according to any one of claims 1 to 2, characterized in that, The method includes: S1: Batching and smelting: Si, Mn, Ti, and Al are batched according to their mass percentages and placed into a smelting furnace. The temperature is raised to 790℃~810℃ until the alloy is completely melted. The temperature is then lowered to 775℃~785℃, and Nb and B are added. After they are completely melted, the mixture is stirred for 30s~40s. The smelting temperature is further lowered to 730℃~735℃, and Mg and RE are added. S2: Refining and casting. After degassing and refining for 30 to 35 minutes, remove the slag and let it stand for 15 to 20 minutes before casting. The casting temperature is 680℃ to 700℃.

4. The method according to claim 3, characterized in that, The elements selected in step S1 are added in the following forms: Al-Si master alloy, Al-Ti master alloy, industrial pure aluminum with a purity of 99.9%, Al-Nb-B master alloy, industrial pure magnesium with a purity of 99.9%, and Al-RE master alloy.

5. The method according to claim 3, characterized in that, The refining gas used in step S2 is argon, and the gas flow rate is 9 L / min to 11 L / min.

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