A high-strength and high-elastic modulus magnesium-lithium alloy and its preparation method

Abstract

The present invention discloses a high-strength and high-elastic modulus casting magnesium-lithium alloy and a preparation method thereof; the casting magnesium-lithium alloy includes: Li 6-10%, Al 3-8%, Zn 2-7%, Ag 2-6%, Gd 0.5-4%, Y 1-4%, Si 1-6%, and the balance is Mg; its preparation method includes smelting and T6 heat treatment. The present invention addresses the problem that the strength and rigidity of the cast magnesium-lithium alloy are both low. By adding RE and Si elements, high-modulus RE-containing and Si-containing phases are generated, and the Mg-Zn-RE and Al-RE phases generated at the same time have a strong strengthening effect. At the same time, Al, Zn, and Ag solid solution strengthening elements are added to improve the modulus of the alloy α-Mg and β-Li matrix phases, and then the corresponding heat treatment process is optimized to give the alloy higher strength and elastic modulus. The present invention can obtain a casting magnesium-lithium alloy with a tensile strength of not less than 320MPa and an elastic modulus of not less than 60GPa.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal materials; relates to a magnesium-lithium alloy and a preparation method thereof, and in particular to a high-strength and high-elastic modulus magnesium-lithium alloy and a preparation method thereof. Background Art

[0002] As one of the lowest-density metal structural materials currently in practical application, magnesium-lithium alloy possesses many superior properties, making it an ideal choice for lightweight component products. It has high specific strength and specific stiffness, as well as good machinability, excellent electromagnetic shielding capabilities, and outstanding low-temperature plasticity and impact resistance. Therefore, it has broad application prospects in aerospace, weaponry, 3C electronics and other fields. However, there is currently a gap between the actual application of magnesium-lithium alloy and its potential. Among them, the low absolute stiffness and absolute strength are one of the main factors limiting its further development and application. Therefore, how to improve the strength and elastic modulus of magnesium-lithium alloy is a top priority in current research.

[0003] The law of mixing states that the elastic modulus of a multiphase alloy is determined by the elastic moduli and volume fractions of its constituent phases. Therefore, adding high-modulus second-phase particles to an alloy can significantly increase its elastic modulus. The main methods for adding high-modulus second-phase particles include external addition (forming a composite material) and reaction generation (alloying). While the external addition method can increase the elastic modulus of an alloy, the added particles have poor wettability with the alloy matrix, prone to interfacial reactions, and can severely impair the alloy's casting properties. The high-modulus second phase formed by the reaction generation method not only has good wettability but also exhibits excellent casting properties. Therefore, alloying and heat treatment are currently the most commonly used and effective methods for increasing the elastic modulus of alloys. Liu Wencai et al. published "A high-strength and high-elastic modulus cast magnesium-rare earth alloy and its preparation method" (authorization number CN104928549B). By adding Si, it reacts with Mg and rare earth elements to form high-modulus Mg2Si (120GPa), Gd5Si3 (168.4GPa), and YSi2 (136.4GPa) phases, significantly improving the elastic modulus of the magnesium-rare earth alloy. In addition, the addition of rare earth elements plays an important role in improving the mechanical properties of magnesium-lithium alloys. However, there is currently no effective alloying method for improving the elastic modulus and strength of magnesium-lithium alloys as lightweight structural materials.

[0004] Therefore, it is necessary to design the existing magnesium-lithium alloy components and develop a high-strength and high-elastic modulus cast magnesium-lithium alloy to meet the requirements of military and high-end civilian fields for lightweight materials with high strength and high stiffness. Summary of the Invention

[0005] To address the low strength and rigidity of cast magnesium-lithium alloys and the shortcomings of existing methods, the present invention aims to provide a high-strength, high-elastic modulus magnesium-lithium alloy composition design and preparation method. The present invention forms a rare earth-containing high-modulus strengthening phase by adding rare earth elements Gd and Y, which not only increases the alloy's elastic modulus but also improves its thermal stability and strength. The addition of Al, Zn, and Ag solid solution strengthening elements increases the modulus of the alloy's α-Mg and β-Li matrix phases. The addition of Si reacts with Mg and rare earth elements to form high-modulus Mg-Si and RE-Si phases, significantly increasing the alloy's elastic modulus. By optimizing the vacuum melting process, Li burnout is reduced, the yield of refractory elements such as RE and Si is increased, and the preparation cost is reduced. Furthermore, by optimizing the corresponding heat treatment process, a high-strength, high-elastic modulus cast magnesium-lithium alloy with a tensile strength of not less than 320 MPa and an elastic modulus of not less than 60 GPa is obtained.

[0006] The object of the present invention is achieved through the following technical solutions:

[0007] The invention relates to a high-strength and high-elastic modulus casting magnesium-lithium alloy. The casting magnesium-lithium alloy mainly consists of the following components in percentage by mass: Li 6-10%, Al 3-8%, Zn 2-7%, Ag 2-6%, Gd 0.5-4%, Y 1-4%, Si 1-6%, and the balance is Mg.

[0008] Furthermore, the cast magnesium-lithium alloy generates Mg-Zn-RE and Al-RE high-modulus rare-earth-containing phases. The addition of Gd and Y rare-earth elements to the magnesium-lithium alloy system of the present invention can generate Mg-Zn-RE and Al-RE high-modulus rare-earth-containing phases, which have a strong strengthening effect.

[0009] Furthermore, the cast magnesium-lithium alloy generates a high-modulus Si-containing phase, a Mg-Si phase, and a RE-Si phase. The addition of 1 to 6% Si by mass to the magnesium-lithium alloy system of the present invention can react with Mg and RE elements to generate a high-modulus Si-containing phase, a Mg-Si phase, and a RE-Si phase.

[0010] The present invention relates to a method for preparing a high-strength and high-elastic modulus magnesium-lithium alloy, comprising vacuum melting and T6 heat treatment. The specific steps are as follows:

[0011] S1. Ingredients: Ingredients are prepared according to the mass percentage of each component in the alloy;

[0012] S2. Melting and casting: Use a vacuum furnace to melt the alloy. Put the raw materials except Li into the crucible. First, pump the vacuum furnace to 0.5-1Pa, then pass 5-7×10 4Pa of argon, then electromagnetically heat the crucible until the raw materials are completely melted, keep the temperature at 750-770°C, mechanically stir for 15-25 minutes, and stir at a rate of 100-200 r / min, cool to 690-710°C, add pure Li wrapped in aluminum foil, heat to 710-730°C, keep the temperature, mechanically stir for 5-10 minutes, and stir at a rate of 100-200 r / min, then let it stand for 5-10 minutes and cool to 690-710°C to cast the ingot;

[0013] S3. Heat treatment: The ingot is placed in an argon atmosphere heat treatment furnace, and a two-stage solid solution heat treatment is adopted. After water quenching, a low-temperature aging heat treatment is performed in an oil bath furnace to obtain a high-strength and high-elastic modulus cast magnesium-lithium alloy.

[0014] In step S2, the magnesium alloy is smelted at a high temperature of 750-770°C and Li is added at a low temperature of 690-710°C, which greatly improves the yield of RE and Si and reduces the burning loss of Li at high temperature.

[0015] Specifically, in step (2), the magnesium alloy is smelted at a high temperature of 750-770°C, and Li is added at a low temperature of 690-710°C, which greatly improves the yield of RE and Si and reduces the burning loss of Li at high temperature.

[0016] As an embodiment, in step S1, the surface oxide scale of pure Mg, pure Al, pure Zn, pure Ag and Mg-RE master alloy is removed using an angle grinder.

[0017] As an embodiment, in step S2, pure Li is wrapped with aluminum foil and then placed into the feeding port.

[0018] As an embodiment, in step S3, in the double-stage solution heat treatment, the first-stage solution temperature is 310-380°C, the solution time is 2-8 hours, and the second-stage solution temperature is 400-470°C, the solution time is 1-4 hours.

[0019] As an embodiment, in step S3, the aging temperature of the low-temperature aging heat treatment is 50-100° C., and the aging time is 2-15 hours.

[0020] The present invention adds Si to the Mg-Li-Al-Zn alloy to form a high elastic modulus Si-containing strengthening phase, thereby significantly improving the rigidity of the alloy. At the same time, rare earth elements Gd and Y are added to react with Si to generate a high modulus RE-Si phase, and can also react with Al and Zn elements in the alloy to generate Mg-Zn-RE and Al-RE strengthening phases, thereby improving the strength of the alloy. The addition of Al, Zn, and Ag solid solution strengthening elements improves the modulus of the alloy's α-Mg and β-Li matrix phases. Furthermore, by optimizing the vacuum melting and T6 heat treatment processes of the alloy, the alloy has higher room temperature strength and elastic modulus while reducing the preparation cost, and has a very broad application prospect.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1) The present invention designs a high-strength and high-elastic modulus magnesium-lithium alloy, which adds Al, Zn, and Ag solid solution strengthening elements to increase the modulus of the alloy's α-Mg and β-Li matrix phases, thereby improving the strength and modulus of the alloy; adding 1 to 6% by mass of Si elements can react with Mg and RE elements to form high-modulus Si-containing phases, Mg-Si phases, and RE-Si phases; adding Gd and Y rare earth elements can generate Mg-Zn-RE and Al-RE high-modulus rare earth-containing phases, which have a strong strengthening effect and simultaneously improve the strength and stiffness of the alloy.

[0023] 2) The present invention adopts a vacuum melting method to prepare the high-strength and high-modulus magnesium-lithium alloy. The magnesium alloy is melted at a high temperature of 750-770°C and Li is added at a low temperature of 690-710°C. While significantly improving the yield of RE and Si, it also reduces the burnout of Li at high temperatures, reduces the preparation cost, and reduces the inclusions in the alloy melt, ensuring the high quality and high performance of the prepared alloy.

[0024] 3) The present invention systematically studies the solid solution and aging behaviors of the high-strength and high elastic modulus magnesium-lithium alloy at different temperatures, and obtains optimized process parameters for solid solution and aging treatment, so that the magnesium-lithium alloy can fully exert its solid solution strengthening effect under optimized heat treatment process conditions, and achieve the purpose of improving stiffness by precipitating high modulus phase through aging.

[0025] 4) The high-strength and high-elastic modulus magnesium-lithium alloy prepared by the present invention can meet the demand for manufacturing lightweight materials or parts with a tensile strength of more than 320 MPa and an elastic modulus of more than 60 GPa at room temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0027] Figure 1 This is a metallographic micrograph of the high-strength and high-elastic modulus cast magnesium-lithium alloy described in Example 1;

[0028] Figure 2 This is a metallographic microscope image of the Si-free magnesium-lithium alloy described in Comparative Example 2. DETAILED DESCRIPTION

[0029] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, several variations and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0030] Example 1

[0031] A high-strength and high-elastic modulus cast magnesium-lithium alloy mainly consists of the following components in percentage by mass: 7.5% Li, 5% Al, 4% Zn, 3% Ag, 1% Gd, 2% Y, 3% Si, and the balance is Mg.

[0032] The method for preparing the high-strength and high-elastic modulus magnesium-lithium alloy includes vacuum melting and T6 heat treatment. The specific steps are as follows:

[0033] (1) Ingredients: The ingredients are prepared according to the mass percentage of each component in the alloy, and the alloy is smelted in a vacuum furnace. Pure Mg, pure Al, pure Zn, pure Ag and Mg-RE master alloy need to be removed from the surface oxide scale using an angle grinder. The raw materials except Li are placed in a crucible, and pure Li is wrapped with aluminum foil and placed in the feeding port;

[0034] (2) Melting and casting: First, the vacuum of the vacuum furnace was pumped to 0.7 Pa, and then 6×10 4 Pa of argon, then electromagnetically heat the crucible until the raw materials are completely melted, keep the temperature at 760 ° C, mechanically stir for 20 minutes, and stir at a rate of 150 r / min, cool to 700 ° C, add Li, heat to 720 ° C, keep the temperature, mechanically stir for 8 minutes, and stir at a rate of 150 r / min, then let it stand for 8 minutes and cool to 700 ° C to cast the ingot;

[0035] (3) Heat treatment: The ingot was placed in an argon atmosphere heat treatment furnace and subjected to a two-stage solution heat treatment. The first stage solution temperature was 350 °C and the solution time was 4 h. The second stage solution temperature was 430 °C and the solution time was 2 h. After water quenching, low-temperature aging heat treatment was performed in an oil bath furnace at a temperature of 75 °C and an aging time of 8 h.

[0036] The metallographic microstructure photo of the high strength and high elastic modulus magnesium-lithium alloy T6 is as follows: Figure 1As shown in the figure, there are a large number of black second phases, which are high modulus Mg-Si phase and RE-Si phase. There are fine white second phases inside some black second phases and in the matrix, which are strengthening phases Mg-Zn-RE phase and Al-RE phase. The room temperature mechanical properties of the alloy T6 state are:

[0037] Tensile strength: 325 MPa, elastic modulus: 60.5 GPa. The tensile test specimens and methods are based on the national standard GB / T228.1-2010, and the elastic modulus test specimens and methods are based on the national standard GB / T22315-2008. The same applies below.

[0038] The actual alloy composition mass fractions obtained by ICP testing in this embodiment are:

[0039] Li 7.4%, Al 5.0%, Zn 4.1%, Ag 3.1%, Gd 1.1%, Y 2.1%, Si 3.3%, and the balance is Mg.

[0040] Example 2

[0041] A high-strength and high-elastic modulus cast magnesium-lithium alloy is mainly composed of the following components in percentage by mass: 10% Li, 6% Al, 2% Zn, 4% Ag, 0.5% Gd, 3% Y, 4% Si, and the balance is Mg.

[0042] The preparation method of the high-strength and high-elastic modulus magnesium-lithium alloy includes vacuum melting and T6 heat treatment, and the specific steps are as follows:

[0043] (1) Ingredients: The ingredients are prepared according to the mass percentage of each component in the alloy, and the alloy is smelted in a vacuum furnace. Pure Mg, pure Al, pure Zn, pure Ag and Mg-RE master alloy need to be removed from the surface oxide scale using an angle grinder. The raw materials except Li are placed in a crucible, and pure Li is wrapped with aluminum foil and placed in the feeding port;

[0044] (2) Melting and casting: First, the vacuum of the vacuum furnace was pumped to 0.5Pa, and then 7×10 4 Pa of argon, then electromagnetically heat the crucible until the raw materials are completely melted, keep the temperature at 770 ° C, mechanically stir for 25 minutes, stirring at a rate of 200 r / min, cool to 710 ° C, add Li, heat to 730 ° C, keep the temperature, mechanically stir for 10 minutes, stirring at a rate of 200 r / min, then let it stand for 10 minutes and cool to 710 ° C to cast the ingot;

[0045] (3) Heat treatment: The ingot was placed in an argon atmosphere heat treatment furnace and subjected to a two-stage solution heat treatment. The first stage solution temperature was 310 °C and the solution time was 8 h. The second stage solution temperature was 460 °C and the solution time was 1 h. After water quenching, low-temperature aging heat treatment was carried out in an oil bath furnace at a temperature of 100 °C and an aging time of 2 h.

[0046] The room temperature mechanical properties of the high-strength and high-elastic modulus magnesium-lithium alloy in the T6 state are:

[0047] Tensile strength: 320MPa, elastic modulus: 62GPa.

[0048] Example 3

[0049] A high-strength and high-elastic modulus cast magnesium-lithium alloy mainly consists of the following components in percentage by mass: 6% Li, 3% Al, 5% Zn, 5% Ag, 2% Gd, 1% Y, 2% Si, and the balance is Mg.

[0050] The preparation method of the high-strength and high-elastic modulus magnesium-lithium alloy includes vacuum melting and T6 heat treatment, and the specific steps are as follows:

[0051] (1) Ingredients: The ingredients are prepared according to the mass percentage of each component in the alloy, and the alloy is smelted in a vacuum furnace. Pure Mg, pure Al, pure Zn, pure Ag and Mg-RE master alloy need to be removed from the surface oxide scale using an angle grinder. The raw materials except Li are placed in a crucible, and pure Li is wrapped with aluminum foil and placed in the feeding port;

[0052] (2) Melting and casting: First, the vacuum of the vacuum furnace was reduced to 1Pa, and then 5×10 4 Pa of argon, then electromagnetically heat the crucible until the raw materials are completely melted, keep the temperature at 750 ° C, mechanically stir for 15 minutes, stir at a rate of 100 r / min, cool to 690 ° C, add Li, heat to 710 ° C, keep the temperature, mechanically stir for 5 minutes, stir at a rate of 100 r / min, then stand for 5 minutes and cool to 690 ° C to cast the ingot;

[0053] (3) Heat treatment: The ingot was placed in an argon atmosphere heat treatment furnace and subjected to a two-stage solution heat treatment. The first stage solution temperature was 380 °C, the solution time was 2 h, and the second stage solution temperature was 400 °C, the solution time was 4 h. After water quenching, low-temperature aging heat treatment was carried out in an oil bath furnace at a temperature of 50 °C and an aging time of 15 h.

[0054] The room temperature mechanical properties of the high-strength and high-elastic modulus magnesium-lithium alloy in the T6 state are:

[0055] Tensile strength: 330MPa, elastic modulus: 60GPa.

[0056] Comparative Example 1

[0057] The magnesium-lithium alloy and its preparation method described in this comparative example 1 are comparative examples of Example 1. The difference from the magnesium-lithium alloy described in Example 1 is that it contains neither Gd, Y rare earth elements nor Si element, and the proportions of other components are the same.

[0058] The preparation method of the magnesium-lithium alloy described in Comparative Example 1 is the same as that of Example 1, using the same vacuum melting and heat treatment processes; the room temperature mechanical properties of the magnesium-lithium alloy in the T6 state are:

[0059] Tensile strength: 250MPa, elastic modulus: 45GPa.

[0060] Comparative Example 2

[0061] The magnesium-lithium alloy and its preparation method described in Comparative Example 2 are comparative examples of Example 1. The difference from the magnesium-lithium alloy described in Example 1 is that the alloy does not contain Si element, and the proportions of other components are the same.

[0062] The preparation method of the magnesium-lithium alloy in Comparative Example 2 is the same as that in Example 1, using the same vacuum melting and heat treatment process; the metallographic microstructure photo of the high-strength and high-elastic modulus magnesium-lithium alloy in T6 state is as follows: Figure 2 As shown, compared with the microstructure of Example 1, there is no black second phase, that is, there is no high modulus Mg-Si phase and RE-Si phase, and the room temperature mechanical properties of the magnesium-lithium alloy in the T6 state are:

[0063] Tensile strength: 300MPa, elastic modulus: 47GPa.

[0064] Comparative Example 3

[0065] The magnesium-lithium alloy and the preparation method thereof described in Comparative Example 3 are comparative examples of Example 1. The difference from the magnesium-lithium alloy described in Example 1 is that the mass percentage of the Si component is 0.5%.

[0066] The preparation method of the magnesium-lithium alloy described in Comparative Example 3 is the same as that of Example 1, using the same vacuum melting and heat treatment processes; the room temperature mechanical properties of the magnesium-lithium alloy in the T6 state are:

[0067] Tensile strength: 305MPa, elastic modulus: 48GPa.

[0068] Comparative Example 4

[0069] The magnesium-lithium alloy and its preparation method described in Comparative Example 3 are comparative examples of Example 1. The difference between them is that the mass percentage of Si component is 7%.

[0070] The preparation method of the magnesium-lithium alloy described in Comparative Example 3 is the same as that of Example 1, using the same vacuum melting and heat treatment processes; the room temperature mechanical properties of the magnesium-lithium alloy in the T6 state are:

[0071] Tensile strength: 220MPa, elastic modulus: 55GPa.

[0072] The addition of excessive Si content will significantly reduce the fluidity and formability of the alloy, leading to the generation of structural defects such as pores, reducing the density of the alloy, adversely affecting the alloy modulus, and seriously damaging the strength and plasticity of the alloy.

[0073] Comparative Example 5

[0074] The magnesium-lithium alloy and its preparation method described in Comparative Example 5 are comparative examples of Example 1. The difference from the magnesium-lithium alloy described in Example 1 is that it does not contain Gd and Y rare earth elements, and the proportions of other components are the same.

[0075] The preparation method of the magnesium-lithium alloy described in Comparative Example 5 is the same as that of Example 1, using the same vacuum melting and heat treatment processes; the room temperature mechanical properties of the magnesium-lithium alloy in the T6 state are:

[0076] Tensile strength: 280MPa, elastic modulus: 51GPa.

[0077] Comparative Example 6

[0078] The magnesium-lithium alloy and its preparation method described in Comparative Example 6 are comparative examples of Example 1. The difference from the magnesium-lithium alloy described in Example 1 is that the mass percentages of the components Gd and Y rare earth elements are 0.3% and 0.5% respectively.

[0079] The preparation method of the magnesium-lithium alloy described in Comparative Example 6 is the same as that of Example 1, using the same vacuum melting and heat treatment processes; the room temperature mechanical properties of the magnesium-lithium alloy in the T6 state are:

[0080] Tensile strength: 295MPa, elastic modulus: 52GPa.

[0081] Comparative Example 7

[0082] The magnesium-lithium alloy and preparation method thereof described in Comparative Example 7 are comparative examples of Example 1. The difference from the magnesium-lithium alloy described in Example 1 is that the mass percentages of the components Gd and Y rare earth elements are 4.5% and 5% respectively.

[0083] The preparation method of the magnesium-lithium alloy described in Comparative Example 7 is the same as that of Example 1, using the same vacuum melting and heat treatment processes; the room temperature mechanical properties of the magnesium-lithium alloy in the T6 state are:

[0084] Tensile strength: 260MPa, elastic modulus: 54GPa.

[0085] Excessive addition of rare earth elements will generate excessive Mg-Zn-RE phase and Al-RE phase, consume Al and Zn elements in the alloy, resulting in a weakening of the solid solution strengthening effect of Al and Zn elements and a reduction in the strength and modulus of the alloy.

[0086] Comparative Example 8

[0087] The magnesium-lithium alloy and the preparation method thereof described in Comparative Example 8 are comparative examples of Example 1, and have the same composition ratio as the magnesium-lithium alloy described in Example 1.

[0088] The vacuum melting method of the magnesium-lithium alloy described in Comparative Example 8 is different from that in Example 1, and the specific steps are as follows:

[0089] (1) Ingredients: The ingredients are prepared according to the mass percentage of each component in the alloy. The ingredients are the same as those in Example 1. A vacuum furnace is used for alloy smelting. Pure Mg, pure Al, pure Zn, pure Ag and Mg-RE master alloy need to be removed from the surface oxide scale using an angle grinder. Pure Li is wrapped with aluminum foil. All raw materials are placed in a crucible;

[0090] (2) Melting and casting: First, the vacuum of the vacuum furnace was pumped to 0.5Pa, and then 7×10 4 Pa of argon, then electromagnetically heat the crucible until the raw materials are completely melted, keep the temperature at 740 ° C, mechanically stir for 20 minutes, and stir at a rate of 150 r / min, then let it stand for 10 minutes and cool to 710 ° C to cast the ingot;

[0091] The heat treatment process of the magnesium-lithium alloy in Comparative Example 8 is the same as that in Example 1. The room temperature mechanical properties of the magnesium-lithium alloy in T6 state are as follows:

[0092] Tensile strength: 310MPa, elastic modulus: 55GPa.

[0093] Comparative Example 8 was tested by ICP, and the actual alloy component mass fractions obtained were:

[0094] Li 6.3%, Al 5.1%, Zn 3.8%, Ag 2.5%, Gd 0.5%, Y 0.5%, Si 1.5%, and the balance is Mg.

[0095] Using the ordinary magnesium-lithium alloy vacuum melting process, the yield of high-melting-point RE and Si is reduced, the Li element is severely burned, and the strength and stiffness of the alloy are reduced.

[0096] Comparative Example 9

[0097] The magnesium-lithium alloy and preparation method described in Comparative Example 9 are comparative examples of Example 1 and have the same composition ratios as the magnesium-lithium alloy described in Example 1. The difference from Example 1 lies in the heat treatment process, which uses a single-stage solution heat treatment at a solution temperature of 350°C for 6 hours. After water quenching, low-temperature aging heat treatment is performed in an oil bath furnace at a temperature of 75°C for 8 hours.

[0098] The room temperature mechanical properties of the magnesium-lithium alloy in T6 state are:

[0099] Tensile strength: 290MPa, elastic modulus: 52GPa.

[0100] The single-stage solid solution temperature is low, the solid solution is insufficient, the solid solution strengthening effect is not obvious, and the high modulus phase precipitated during aging is small, which reduces the strength and stiffness of the alloy.

[0101] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various variations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A high-strength and high-elastic modulus cast magnesium-lithium alloy, characterized in that: The cast magnesium-lithium alloy mainly consists of the following components in percentage by mass: Composition: Li 6-10%, Al 3-8%, Zn 2-7%, Ag 2-6%, Gd 0.5-4%, Y 1-4%, Si 1-6%, with the balance being Mg; the cast magnesium-lithium alloy generates Mg-Zn-RE and Al-RE high-modulus rare earth-containing phases, as well as high-modulus Mg-Si and high-modulus RE-Si phases; the added Al, Zn, and Ag solid solution strengthening elements increase the modulus of the α-Mg and β-Li matrix phases in the cast magnesium-lithium alloy; and the cast magnesium-lithium alloy has a tensile strength of not less than 320 MPa and an elastic modulus of not less than 60 GPa. The preparation method of the high-strength and high-elastic modulus magnesium-lithium alloy includes vacuum melting and T6 heat treatment; specifically includes the following steps: S1. Batching: Batching is carried out according to the mass percentage of each component in the alloy; S2. Melting and casting: Use a vacuum furnace to melt the alloy. Put the raw materials except Li into the crucible. First, pump the vacuum furnace to 0.5~1 Pa, then pass 5~7×10 4 Pa of argon, then electromagnetically heat the crucible until the raw materials are completely melted, keep the temperature at 750~770℃, mechanically stir for 15~25 min, and stir at a rate of 100~200 r / min, cool to 690~710℃, add pure Li wrapped in aluminum foil, heat to 710~730℃, keep the temperature, mechanically stir for 5~10 min, and stir at a rate of 100~200 r / min, then let it stand for 5~10 minutes and cool to 690~710℃ to cast the ingot; S3. Heat treatment: placing the ingot in an argon atmosphere heat treatment furnace, adopting a two-stage solid solution heat treatment, and performing low-temperature aging heat treatment in an oil bath furnace after water quenching to obtain a high-strength and high-elastic modulus cast magnesium-lithium alloy; in the two-stage solid solution heat treatment, the first stage solid solution temperature is 310-380°C, the solid solution time is 2-8 hours, and the second stage solid solution temperature is 400-470°C, and the solid solution time is 1-4 hours; the aging temperature of the low-temperature aging heat treatment is 50-100°C, and the aging time is 2-15 hours.

2. The high-strength and high-elastic modulus cast magnesium-lithium alloy according to claim 1, characterized in that: In step S1, the surface oxide scale of pure Mg, pure Al, pure Zn, pure Ag and Mg-RE master alloy is removed by using an angle grinder.

3. The high-strength and high-elastic modulus cast magnesium-lithium alloy according to claim 1, characterized in that: In step S2, pure Li is wrapped in aluminum foil and placed into the feed port.

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