Alkaline earth and rare earth element composite modified Mg-Al-Si magnesium alloy and preparation method thereof

Abstract

The present invention provides an alkaline earth and rare earth element composite modified Mg‑Al‑Si magnesium alloy and a preparation method thereof, which belong to the field of metal materials. The Mg‑Al‑Si magnesium alloy is composed of the following components in terms of mass percentage: Al: 2-9%, Si: 2-4%, Ca: 0.2-2%, Ce: 0.2-1.5%, Mn: 0.1-0.4%, inevitable impurities ≤0.05%, and the balance is magnesium. The preparation method includes: smelting, degassing and impurity removal, and casting. Compared with the prior art, the Mg2Si and CaMgSi phase sizes in the Mg‑Al‑Si magnesium alloy obtained by the present invention are significantly reduced, and the room temperature strength and plasticity of the alloy are significantly improved. Compared with the prior art, the alloy obtained by the present invention omits heat treatment or high-temperature homogenization treatment, so that the alloy simultaneously improves strength and plasticity, is suitable for the preparation of various load-bearing structural parts, and has great application value in the lightweighting of structural parts in the fields of automobiles, aerospace, etc.

Description

Technical Field

[0001] The present invention belongs to the field of metal materials, and in particular relates to an alkaline earth and rare earth element composite modified Mg-Al-Si magnesium alloy and a preparation method thereof. Background Art

[0002] Magnesium alloys have high specific strength, specific stiffness, good damping and electromagnetic shielding properties, and have significant lightweight advantages. Cast magnesium alloys have the advantages of high production efficiency, high precision, and high surface quality, and are widely used in transportation, electronics, mechanical equipment, and construction. Mg-Al-Si magnesium alloys have a series of advantages such as good casting performance, excellent high-temperature performance, and low cost, and are widely used in industries such as automobiles and aerospace. However, due to the addition of Si, coarse Mg2Si phases will be produced during the solidification process of magnesium alloys, which will seriously split the matrix and reduce the strength and plasticity of the alloy. Therefore, in industrial production, under the premise of controlling costs and not changing the production process as much as possible, developing a high-strength and plastic Mg-Al-Si magnesium alloy with fine Mg2Si and other precipitated phases with a simple, reliable and low-cost preparation process is a technical problem that the magnesium alloy industry urgently needs to solve. Summary of the Invention

[0003] In order to solve the above technical problems, the present invention also provides an alkaline earth and rare earth composite modified Mg-Al-Si magnesium alloy, wherein the components of the magnesium alloy are, by mass percentage, Al: 2-9%, Si: 2-4%, Ca: 0.2-2%, Ce: 0.2-1.5%, Mn: 0.1-0.4%, unavoidable impurities ≤ 0.05%, and the balance is magnesium; the preparation method of the magnesium alloy comprises the following steps:

[0004] (1) Under protective gas, pure magnesium, pure aluminum, and magnesium-silicon master alloy are added in sequence, heated to 680-780°C for melting, kept at this temperature for 30-150 minutes, and then cooled to 670-710°C for 5-30 minutes to obtain alloy liquid 1;

[0005] (2) adding magnesium-manganese master alloy, magnesium-cerium master alloy and magnesium-calcium master alloy to the alloy liquid 1 obtained in step (1) in sequence, stirring for 5-20 minutes after being completely melted, then blowing argon gas into the mixture and stirring for 5-20 minutes, and then keeping the mixture at 670-720°C to obtain alloy liquid 2;

[0006] (3) After the alloy liquid 2 obtained in step (2) is deslagging, a magnesium alloy is obtained by steel mold casting or sub-rapid solidification; the magnesium alloy has a tensile strength of 215 to 245 MPa and an elongation of 6.4 to 14%; and the Mg2Si phase size of the magnesium alloy is 5 to 20 μm.

[0007] Furthermore, the protective gas in step (1) is a mixed gas of SF6 and CO2 or one of SF6 and CO2 gases, and the volume ratio of SF6 and CO2 in the mixed gas is 1:10-1:5.

[0008] Compared with the prior art, the present invention has the following characteristics:

[0009] The present invention achieves the following effects by adjusting the alloy composition, proportion and synergistic effect of the process: first, heterogeneous nucleation points are generated to refine the Mg2Si phase; second, the shape and size of the CaMgSi phase are simultaneously changed. By shortening the growth time of the CaMgSi phase and hindering the diffusion of Si atoms, the growth of the CaMgSi phase is restricted, and the CaMgSi phase is transformed from a continuous fishbone or needle shape to a discontinuous, small, uniform short rod shape, thereby significantly refining the Mg2Si phase and the CaMgSi phase in the Mg-Al-Si magnesium alloy and improving the strength and plasticity of the alloy.

[0010] The magnesium alloy obtained by the present invention has high strength and plasticity without the need for heat treatment or high-temperature homogenization treatment. At room temperature, the tensile strength of the cast alloy is 215-245 MPa and the elongation is 6.4-14%. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is the BSE diagram of the Mg-5Al-2Si magnesium alloy obtained by Bo Hu et al. in comparative example 4;

[0012] Figure 2 This is the BSE diagram of the Mg-4Al-2Si-0.5Ca-0.2Ce-0.1Mn magnesium alloy obtained in step (3) of Example 1. DETAILED DESCRIPTION

[0013] Example 1

[0014] Taking Mg-4Al-2Si-0.5Ca-0.2Ce-0.1Mn alloy as an example (composition by mass percentage: Al: 4%, Si: 2%, Ca: 0.5%, Mn: 0.1%, Ce: 0.2%, the total amount of unavoidable impurities ≤ 0.05%, the balance being magnesium), its preparation method is as follows:

[0015] (1) Under a protective gas atmosphere of SF6 and CO2 in a volume ratio of 1:5, raw materials were weighed according to the above alloy ratio, pure magnesium, pure aluminum, and magnesium-silicon master alloy were added in sequence, and the mixture was heated to 740°C for melting and then kept at this temperature for 90 minutes. The mixture was then cooled to 670°C and kept at this temperature for 10 minutes to obtain alloy liquid 1;

[0016] (2) adding magnesium-manganese master alloy, magnesium-calcium master alloy, and magnesium-cerium master alloy to the alloy liquid 1 obtained in step (1) in sequence, stirring for 15 minutes after being completely melted, then blowing argon gas into the alloy liquid and stirring for 12 minutes, and then keeping the mixture at 680°C to obtain alloy liquid 2;

[0017] (3) After the alloy liquid 2 obtained in step (2) is cleaned of slag, it is cast into an ingot by steel mold casting to obtain a Mg-4Al-2Si-0.5Ca-0.2Ce-0.1Mn alloy ingot.

[0018] Example 2

[0019] Taking Mg-4Al-2Si-1Ca-0.5Ce-0.1Mn alloy as an example (composition by mass percentage: Al: 4%, Si: 2%, Ca: 1%, Mn: 0.1%, Ce: 0.5%, the total amount of unavoidable impurities ≤ 0.05%, the balance being magnesium), its preparation method is as follows:

[0020] (1) Under a protective gas atmosphere of SF6 and CO2 in a volume ratio of 1:10, raw materials were weighed according to the above alloy ratio, pure magnesium, pure aluminum, and magnesium-silicon master alloy were added in sequence, and the mixture was heated to 725°C for melting, kept at this temperature for 65 minutes, and then cooled to 675°C for 15 minutes to obtain alloy liquid 1;

[0021] (2) adding magnesium-manganese master alloy, magnesium-calcium master alloy, and magnesium-cerium master alloy to the alloy liquid 1 obtained in step (1) in sequence, stirring for 10 minutes after being completely melted, then blowing argon gas into the mixture and stirring for 8 minutes, and then keeping the mixture at 685°C to obtain alloy liquid 2;

[0022] (3) After the alloy liquid 2 obtained in step (2) is deslagging, it is cast into an ingot by a sub-rapid casting method to obtain a Mg-4Al-2Si-1Ca-0.5Ce-0.1Mn alloy ingot.

[0023] Example 3

[0024] Taking Mg-6Al-2Si-1Ca-1Ce-0.3Mn alloy as an example (composition by mass percentage: Al: 6%, Si: 2%, Ca: 1%, Mn: 0.3%, Ce: 1%, the total amount of unavoidable impurities ≤ 0.05%, the balance being magnesium), its preparation method is as follows:

[0025] (1) Under a protective gas atmosphere of SF6 and CO2 in a volume ratio of 1:8, raw materials were weighed according to the above alloy ratio, pure magnesium, pure aluminum, and magnesium-silicon master alloy were added in sequence, and the mixture was heated to 765°C for melting, kept at this temperature for 120 minutes, and then cooled to 690°C for 20 minutes to obtain alloy liquid 1;

[0026] (2) adding magnesium-manganese master alloy, magnesium-calcium master alloy, and magnesium-cerium master alloy to the alloy liquid 1 obtained in step (1) in sequence, stirring for 5 minutes after being completely melted, then blowing argon gas into the mixture and stirring for 7 minutes, and then keeping the mixture at 690°C to obtain alloy liquid 2;

[0027] (3) After the alloy liquid 2 obtained in step (2) is deslagging, it is cast into an ingot by a sub-rapid casting method to obtain a Mg-6Al-2Si-1Ca-1Ce-0.3Mn alloy ingot.

[0028] Example 4

[0029] Taking Mg-9Al-2Si-0.5Ca-0.2Ce-0.2Mn alloy as an example (composition by mass percentage: Al: 9%, Si: 2%, Ca: 0.5%, Mn: 0.2%, Ce: 0.2%, the total amount of unavoidable impurities ≤ 0.05%, the balance being magnesium), its preparation method is as follows:

[0030] (1) Under a protective gas atmosphere of SF6 and CO2 in a volume ratio of 1:7, raw materials were weighed according to the above alloy ratio, pure magnesium, pure aluminum, and magnesium-silicon master alloy were added in sequence, and the mixture was heated to 715°C for melting, kept at this temperature for 150 minutes, and then cooled to 683°C for 6 minutes to obtain alloy liquid 1;

[0031] (2) adding magnesium-manganese master alloy, magnesium-calcium master alloy, and magnesium-cerium master alloy to the alloy liquid 1 obtained in step (1) in sequence, stirring for 5 minutes after being completely melted, then blowing argon gas into the mixture and stirring for 11 minutes, and then keeping the mixture at 700°C to obtain alloy liquid 2;

[0032] (3) After the alloy liquid 2 obtained in step (2) is cleaned of slag, it is cast into an ingot by steel mold casting to obtain a Mg-9Al-2Si-0.5Ca-0.2Ce-0.2Mn alloy ingot.

[0033] Example 5

[0034] Taking Mg-4Al-4Si-0.5Ca-1.2Ce-0.1Mn alloy as an example (composition by mass percentage: Al: 4%, Si: 4%, Ca: 0.5%, Mn: 0.1%, Ce: 1.2%, the total amount of unavoidable impurities ≤ 0.05%, the balance being magnesium), its preparation method is as follows:

[0035] (1) Under a protective gas atmosphere of SF6 and CO2 in a volume ratio of 1:8, raw materials were weighed according to the above alloy ratio, pure magnesium, pure aluminum, and magnesium-silicon master alloy were added in sequence, and the mixture was heated to 755°C for melting and then kept at this temperature for 95 minutes. The mixture was then cooled to 690°C for 15 minutes to obtain alloy liquid 1.

[0036] (2) adding magnesium-manganese master alloy, magnesium-calcium master alloy, and magnesium-cerium master alloy to the alloy liquid 1 obtained in step (1) in sequence, stirring for 10 minutes after being completely melted, then blowing argon gas into the mixture and stirring for 6 minutes, and then keeping the mixture at 690°C to obtain alloy liquid 2;

[0037] (3) After the alloy liquid 2 obtained in step (2) is cleaned of slag, it is cast into an ingot by steel mold casting to obtain a Mg-4Al-4Si-0.5Ca-1.2Ce-0.1Mn alloy ingot.

[0038] Comparative Example 1

[0039] Taking Mg-9Al-3Si-0.37Sr-0.78Y alloy as an example, Zhang Lianteng et al. from Nanchang Hangkong University published a master's thesis in 2020 on the influence of alloying and physical fields on the microstructure and mechanical properties of Mg-9Al-3Si alloy. The preparation method is as follows:

[0040] (1) Under a protective gas atmosphere of SF6 and CO2 in a volume ratio of 1:5, raw materials were weighed according to the above alloy ratio, pure magnesium, pure aluminum, and aluminum-silicon master alloy were added in sequence, and the mixture was heated to melt at 760°C, kept at this temperature for 10 minutes, and then cooled to 740°C to obtain alloy liquid 1;

[0041] (2) adding magnesium-strontium master alloy and magnesium-yttrium master alloy to the alloy liquid 1 obtained in step (1) in sequence, stirring after complete melting, and keeping the mixture at 740°C for 15 minutes to obtain alloy liquid 2;

[0042] (3) subjecting the alloy liquid 2 obtained in step (2) to ultrasonic treatment at an ultrasonic power of 700 W, an ultrasonic time of 60 s, and an ultrasonic temperature of 690° C. to obtain alloy liquid 3;

[0043] (4) After refining, degassing and slag removal, the alloy liquid 3 obtained in step (3) is cast into an ingot by steel mold casting to obtain a Mg-9Al-3Si-0.37Sr-0.78Y alloy ingot.

[0044] Comparative Example 2

[0045] Taking the Mg-6Al-1Zn-0.7Si-0.4Sb alloy as an example, Yang Mingbo et al. published "Effect of Sb Modification on Heat Treatment Microstructure and Mechanical Properties of Mg-6Al-1Zn-0.7Si Magnesium Alloy" in the Journal of Nonferrous Metals, Vol. 17, No. 12, December 2007. The alloy addition content is higher than that in Example 1, and the added rare earth content is also much higher than that in Example 1. In addition, Comparative Example 1 also adds high-temperature, long-term solution and aging treatments that are not used in the present invention. However, the performance and plasticity of the alloy in Example 1 of the present invention are higher than the results disclosed in Comparative Example 2 (according to the composition mass percentages: Al: 6%, Si: 0.7%, Zn: 1%, Sb: 0.4%, the total of unavoidable impurities ≤ 0.05%, and the balance is magnesium). The preparation method is as follows:

[0046] (1) Under a protective gas atmosphere of SF6 and CO2 in a volume ratio of 1:10, raw materials were weighed according to the above alloy ratio, pure magnesium, pure aluminum, and pure zinc master alloy were added in sequence, and the mixture was heated to melt at 780°C and kept warm for 20 minutes to obtain alloy liquid 1;

[0047] (2) adding aluminum-silicon master alloy and pure antimony to the alloy liquid obtained in step (1) in sequence, stirring for 20 minutes after complete melting, then blowing argon gas into the mixture and stirring for 5 minutes, and keeping the mixture at 740°C for 20 minutes to obtain alloy liquid 2;

[0048] (3) After the alloy liquid 2 obtained in step (2) is deslagging, it is cast into an ingot through a steel mold to obtain a Mg-6Al-1Zn-0.7Si-0.4Sb alloy ingot.

[0049] (4) The as-cast Mg-6Al-1Zn-0.7Si-0.4Sb alloy obtained in step (3) was solution treated at 420°C for 16 h, water quenched to room temperature, then aged at 200°C for 12 h, and air-cooled to room temperature.

[0050] Comparative Example 3

[0051] Taking Mg-10Al-1.5Si-0.15Ca-0.1Ce-0.05Mn alloy as an example (the composition by mass percentage is: Al: 10%, Si: 1.5%, Ca: 0.15%, Mn: 0.05%, Ce: 0.1%, the total amount of unavoidable impurities ≤ 0.05%, and the balance is magnesium), its preparation method is as follows:

[0052] (1) Under SF6 protective gas, raw materials were weighed according to the above alloy ratio, pure magnesium was heated to melt at 720°C, kept warm for 30 minutes, and then heated to 780°C to obtain alloy liquid 1;

[0053] (2) adding magnesium-cerium master alloy, pure aluminum, and pure silicon powder to the alloy liquid 1 obtained in step (1) in sequence, and keeping the mixture at 780° C. for 40 minutes after the mixture is completely melted to obtain alloy liquid 2;

[0054] (3) After degassing and clearing the slag from the alloy liquid 2 obtained in step (2), the alloy liquid 2 is cast into an ingot by a steel mold casting method to obtain a Mg-10Al-1.5Si-0.15Ca-0.1Ce-0.05Mn alloy ingot.

[0055] Comparative Example 4

[0056] Attachment Figure 1 The size of the Mg2Si phase in the Mg-5Al-2Si alloy disclosed in "Effects of Ce content on the modification of Mg2Si phase in Mg-5Al-2Si alloy" by BOHu et al. in Journal of Magnesium and alloys, October 2021, doi: 10.1016, is approximately 60 to 100 μm.

[0057] Compared with the comparative examples, the present invention reduces the high-temperature solid solution or aging treatment process, among which the mechanical properties of Example 1 are the lowest of all the examples. The alloy addition amount used in this example is less than the alloy addition amount of the comparative examples, but the tensile strength and elongation are higher than all the comparative examples. The specific analysis is as follows: Compared with Example 1, Comparative Example 1 also uses a combination of ultrasound and high temperature; Comparative Example 2 uses a higher amount of alloy component addition and also adds a process combining solid solution and aging. As a result, the strength and plasticity of the alloy obtained are lower than the alloy obtained in Example 1; Compared with the present invention, the alloy addition amount of Comparative Example 3 is higher and the casting process is also different from that of this example. The melting temperature is higher than that of the present invention. As a result, the strength and plasticity obtained in Comparative Example 3 are indeed lower than the performance and plasticity of the alloy obtained in the present invention.

[0058] Compared with the prior art, the alloy obtained by the present invention significantly refines the Mg2Si phase. The size of the Mg2Si phase in the Mg-4Al-2Si-0.5Ca-0.2Ce-0.1Mn alloy obtained in Example 1 of the present invention is about 5 to 20 μm, while the size of the Mg2Si phase in the Mg-5Al-2Si magnesium alloy obtained by BOHu et al. in Comparative Example 4 is about 60 to 100 μm, and its strength and plasticity are lower than the minimum performance and plasticity of the embodiment of the present invention. Figure 2 It can be seen that the CaMgSi phase transforms into discontinuous, uniform, small short rods, which ultimately significantly refines the Mg2Si phase and CaMgSi phase in the Mg-Al-Si magnesium alloy, and simultaneously improves the strength and plasticity of the alloy.

[0059] In summary: the components, proportions and preparation processes used in the embodiments of the present invention are all different, among which the alloy strength and plasticity of Example 3 are the highest among all the embodiments, but the alloy component content and the total alloy addition amount are not the highest among all the embodiments; in addition, compared with the comparative example, the components and processes used in the present invention are significantly different. When the rare earth content used in the embodiments of the present invention is less than that in the comparative example, and when the high-temperature and long-term heat treatment process is reduced, the alloy strength and plasticity obtained are higher than those obtained in the comparative example; in summary, compared with the prior art, the present invention saves raw materials, the addition amount of rare earth and simplifies the process, but achieves significant technical effects. This shows that the optimal excellent performance of the alloy obtained by the present invention is achieved by the interaction of alloy components, proportions and synergistic effects of processes.

[0060] Table 1 summarizes the strength and plasticity properties of Examples 1-5 and Comparative Examples 1-4

[0061] Tensile strength (MPa) Elongation (%) Example 1 215 8.7 Example 2 238 12.4 Example 3 245 14 Example 4 227 7.7 Example 5 233 6.4 Comparative Example 1 180 4 Comparative Example 2 209 5.8 Comparative Example 3 191 3.9 Comparative Example 4 92 1.6

[0062] Table 1.

Claims

1. An alkaline earth and rare earth element composite modified Mg-Al-Si magnesium alloy, characterized by: The alloy comprises, by mass percentage, 2-9% Al, 2-4% Si, 0.2-2% Ca, 0.2-1.5% Ce, and 0.1-0.4% Mn, with unavoidable impurities ≤ 0.05% and the balance being magnesium. The preparation method of the magnesium alloy comprises the following steps: (1) Under protective gas, pure magnesium, pure aluminum, and magnesium-silicon master alloy are added in sequence, heated to 680-780°C for melting, kept warm for 30-150 minutes, and then kept warm at 670-710°C for 5-30 minutes to obtain alloy liquid 1; (2) adding magnesium-manganese master alloy, magnesium-cerium master alloy and magnesium-calcium master alloy to the alloy liquid 1 obtained in step (1) in sequence, stirring for 5-20 minutes after being completely melted, then blowing argon gas into the mixture and stirring for 5-20 minutes, and then keeping the mixture at 670-720°C to obtain alloy liquid 2; (3) After the alloy liquid 2 obtained in step (2) is deslagging, a magnesium alloy is obtained by steel mold casting or sub-rapid solidification; the magnesium alloy has a tensile strength of 215 to 245 MPa and an elongation of 6.4 to 14%; and the Mg2Si phase size of the magnesium alloy is 5 to 20 μm.

2. The Mg-Al-Si magnesium alloy modified by alkaline earth and rare earth elements according to claim 1, characterized in that: The protective gas described in step (1) is a mixed gas of SF6 and CO2 or one of SF6 and CO2 gases, and the volume ratio of SF6 and CO2 in the mixed gas is 1:10-1:5.

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