An ultra-light high-tenacity cast magnesium-lithium alloy and a method for preparing the same

Abstract

The application discloses an ultra-light high-strength and high-toughness cast magnesium-lithium alloy and a preparation method thereof, and belongs to the technical field of non-ferrous metal preparation. The chemical composition of the ultra-light high-strength and high-toughness cast magnesium-lithium alloy is as follows in terms of percentage by mass: Li 11-15%, Al 1-4%, Cu 0.5-1.5%, Zr 0.05-0.15%, and the balance of Mg and impurities. The application adopts a vacuum melting technology and adds trace low-cost Al, Cu and Zr alloy elements in the Mg-14Li alloy to form high-melting-point AlMgCu and Al3Zr precipitated phases and a large number of AlLi particles, so that the tensile strength and compressive strength of the as-cast magnesium-lithium alloy and the stability of the structure and mechanical properties are greatly improved, the preparation process is simple, and the alloy cost is low. The prepared material has an ultimate tensile strength of 200-235 MPa, a tensile yield strength of 180-190 MPa, an elongation of 5-7%, an ultimate compressive strength of 400-460 MPa, and a compressive yield strength of 225-235 MPa, the tensile and compressive strengths are much higher than those of other existing LA14 series cast magnesium-lithium alloys and even AZ series cast magnesium alloys, and the compressive yield strength is higher than the tensile yield strength, so that the use range of the high-performance magnesium-lithium alloy is greatly improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of non-ferrous metal preparation, and particularly relates to an ultralight high-toughness cast magnesium-lithium alloy and a preparation method thereof. BACKGROUND

[0002] The ultralight magnesium-lithium alloy is a metal structural material with the smallest density, and has the characteristics of low density (generally 1.35-1.65 g / cm 3 , high specific strength and specific stiffness, good biocompatibility, and the like, especially excellent damping and vibration reduction performance and electromagnetic shielding performance, and has a wide application prospect in the fields of aerospace, 3C electronic products, and biomedical science. The addition of lithium (Li) can reduce the density of the magnesium alloy, reduce the c / a axial ratio of the magnesium alloy, induce the phase transition of α-Mg (HCP)→β-Li (BCC), and significantly improve the plastic formability of the magnesium alloy. However, the magnesium-lithium alloy has the defects of low absolute strength (generally 150-200 MPa, and even lower in the cast state), poor corrosion resistance, unstable microstructure and performance, and the like, and is expensive, which greatly limits the application.

[0003] In the development of the β-Li single-phase magnesium-lithium alloy (Li≥10.3 wt.%), a typical LA141 (Mg-14Li-1Al) cast magnesium-lithium alloy has a density (ρ) of 1.35 g / cm 3, the tensile strength (UTS) is 130 MPa, the yield strength (YS) is 103 MPa, and the elongation (EL) is 12%. Liu Hongyu et al. (Materials Characterization, 2019, 157) prepared LA141 magnesium-lithium alloy by vacuum induction melting and homogenization treatment, and the UTS is 152 MPa, the EL is 6.3%, and after cryogenic rolling, the UTS is 223 MPa and the EL is 25.8%. Jiao Yunlei et al. (Light Alloy Fabrication Technology, 2021, 49) prepared Mg-14Li-3Al-1Y-0.4Zr-0.8Sc as-cast magnesium-lithium alloy by high vacuum electromagnetic induction melting, and the UTS is 153 MPa and the EL is 8.2%, and after homogenization treatment and 200℃ / 60% reduction hot rolling, the UTS is 235 MPa and the EL is 6.5%. Jin Siyuan et al. (Materials Science and Engineering A, 2020, 788: 139611) prepared as-cast LA141-0.1Yb alloy by vacuum induction melting, and the UTS is 197 MPa and the EL is 17.5%. Liu Bin et al. (Materials Science and Engineering: A, 2008, 487(1-2): 347-351) prepared LA141-0.6wt%Nd cast magnesium-lithium alloy by vacuum induction melting, and the UTS is 191.6 MPa. C.O. Muga et al. (Materials Science and Engineering A, 2017, 689: 195-202) prepared Mg-14Li-3Al-Ce cast alloy by vacuum induction melting, and the UTS is 104.3 MPa, the YS is 72.6 MPa, and the EL is 5.8%, and after 280℃×15h aging water cooling treatment, the UTS is 136.8 MPa, the YS is 105.5 MPa, and the EL is 19.2%. Zheng Haipeng et al. (Journal of Materials Engineering and Performance, 2022. 31, 6617-6625) prepared Mg-14Li-3Al-2Gd cast alloy by vacuum induction melting, and the UTS is 125.6 MPa, the YS is 73.2 MPa, and the EL is 38.2%, and after 4 cycles of large strain cumulative accumulative roll bonding (ARB4), the YS is 223.5±4.9 MPa, the UTS is 252.6±4.7 MPa, and the EL is 27.4±0.2%, but the tensile curves of the ARB alloy show serious strain softening and stress instability.

[0004] The absolute strength of the above-mentioned β-Li single-phase cast magnesium-lithium alloy is still low even by adding alloy elements such as rare earth, Sc, Yb and the like, and the heat treatment and plastic deformation can improve the strength to a certain extent, but the preparation process is complex and the alloy cost is greatly increased. Therefore, it is particularly important to develop a new type of low-cost cast magnesium-lithium alloy with low density, high strength and meeting the application requirements of engineering structure. SUMMARY

[0005] In view of the problems of low absolute strength, complex preparation process and high cost of the current β-Li single-phase magnesium-lithium alloy, the application provides a low-cost ultra-light high-toughness β-Li single-phase cast magnesium-lithium alloy and a preparation method thereof.

[0006] In order to achieve the above-mentioned purpose, the following technical solutions are adopted in the application:

[0007] The application provides a low-cost ultra-light high-toughness cast magnesium-lithium alloy, and the mass percentage of each element in the low-cost ultra-light high-toughness cast magnesium-lithium alloy is Li 11-15%, Al 1-4%, Cu 0.5-1.5%, Zr 0.05-0.15%, and the balance is Mg and inevitable impurities; wherein: the content of Zr element cannot be 0.

[0008] Further, the total amount of Si, Fe, Ni and Ca in the impurities is less than 0.03wt.%.

[0009] Further, the mechanical properties of the low-cost ultra-light high-toughness cast magnesium-lithium alloy are as follows: the ultimate tensile strength is 200-235 MPa, the tensile yield strength is 180-190 MPa, and the elongation is 5-7%; the ultimate compressive strength is 400-460 MPa, and the compressive yield strength is 225-235 MPa.

[0010] A preparation method of a low-cost ultra-light high-toughness cast magnesium-lithium alloy, the preparation method comprises the following steps:

[0011] (1) Prepare Mg ingot, pure Li, Al-50Cu intermediate alloy and Al-5Zr intermediate alloy as raw materials, and the chemical composition of each raw material is controlled as follows: Li 11-15%, Al 1-4%, Cu 0.5-1.5%, Zr 0.05-0.15%, and the balance is Mg; wherein, the pure Li is wrapped with pure aluminum foil; all the raw materials except Li are preheated in a dry furnace;

[0012] (2) Preheat the crucible to 480℃, put the preheated Mg ingot into the graphite crucible, and place it in a vacuum induction heating furnace, and close the furnace cover; when the vacuum pressure gauge shows that the vacuum pressure reaches 5-10 Pa, close the vacuum pump; introduce argon protective gas and charge to 0.08-0.15 MPa; heat to completely melt the Mg ingot;

[0013] (3) melt temperature rises to 700-750℃, then add the preheated Al-50Cu intermediate alloy, Al-5Zr intermediate alloy above;

[0014] (4) when the intermediate alloy is completely melted, the melt temperature drops to 650-710℃, then add the pure Li above, and stir quickly for 5-10 minutes;

[0015] (5) pour the melt into a preheated mold, and take out the alloy ingot from the mold after waiting for 30 minutes.

[0016] Further, argon protection is adopted to prevent magnesium liquid from oxidizing and burning.

[0017] Compared with the prior art, the present application has the following advantages:

[0018] The mechanical properties of the super-light high-strength and high-toughness cast magnesium-lithium alloy of the present application are as follows: ultimate tensile strength is 200-235 MPa, tensile yield strength is 180-190 MPa, elongation is 5-7%, ultimate compressive strength is 400-460 MPa, and compressive yield strength is 225-235 MPa.

[0019] The tensile and compressive strengths of the magnesium-lithium alloy prepared by the present application are much higher than those of other existing LA14 series cast magnesium-lithium alloys or even AZ series cast magnesium alloys, and the compressive yield strength is higher than the tensile yield strength, thus overcoming the poor forming performance problem caused by the serious tensile-compressive asymmetry (the compressive yield strength is much lower than the tensile yield strength) of conventional AZ series magnesium alloys.

[0020] The present application uses the addition of trace amounts of low-cost Al, Cu and Zr alloy elements to form high-melting-point AlMgCu, Al3Zr precipitated phases and a large number of AlLi particles to greatly improve the tensile / compressive strength and the stability of the microstructure and mechanical properties of the as-cast magnesium-lithium alloy, and the preparation process is simple, the alloy cost is low, and the use range of high-performance magnesium-lithium alloys is greatly improved. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without any creative effort based on these drawings.

[0022] Figure 1 is the microstructure diagram of the super-light high-strength and high-toughness cast magnesium-lithium alloy of the present application;

[0023] Figure 2 is the room temperature tensile curve of the super-light high-strength and high-toughness cast magnesium-lithium alloy of the present application;

[0024] Figure 3 is the room temperature compression curve of the ultra-light high-tenacity cast Mg-Li alloy of the embodiment of the present application. DETAILED DESCRIPTION

[0025] In order to make the purpose, process scheme and advantages of the present application clearer, the present application will be explained in detail in combination with the drawings and specific embodiments. It should be understood that the specific embodiments are only the explanation of some special aspects, specific nature and implementation scheme of the present application, and are not used to limit the present application.

[0026] Embodiment 1

[0027] (1) Prepare Mg ingot, pure Li, Al-50Cu intermediate alloy, Al-5Zr intermediate alloy as raw materials, and the chemical composition of each raw material is controlled as follows in percentage by mass: Li 14%, Al 2.59%, Cu 0.5%, Zr 0.11%, and the balance is Mg; wherein, the pure Li is wrapped with pure aluminum foil; all raw materials except Li are preheated in a dry furnace.

[0028] (2) Preheat the crucible to 480℃, put the preheated Mg ingot into the graphite crucible, and place it in the vacuum induction heating melting furnace, close the furnace cover; vacuumize to 7Pa as shown by the vacuum pressure gauge, then close the vacuum pump; introduce argon protective gas, and charge to 0.1MPa; heat to completely melt the Mg ingot.

[0029] (3) When the melt temperature rises to 720℃, sequentially add the preheated Al-50Cu intermediate alloy and Al-5Zr intermediate alloy;

[0030] (4) When the intermediate alloy is completely melted, and the melt temperature drops to 680℃, add the pure Li, and quickly stir for 5 minutes.

[0031] (5) Pour the melt into the preheated mold, and take out the alloy ingot from the mold after 30 minutes.

[0032] The microstructure of the obtained alloy is shown in Figure 1 The as-cast Mg-Li alloy is composed of β-Li matrix and a large number of fine and dispersed AlCuMg, Al3Zr and AlLi particle precipitated phases. Figure 2 The room temperature tensile properties are shown in Figure 3 The ultimate tensile strength of the as-cast Mg-Li alloy is 235MPa, the tensile yield strength is 189MPa, and the elongation is 5%. The room temperature compression properties are shown in

[0033] Embodiment 2

[0034] (1) Prepare Mg ingot, pure Li, Al-50Cu master alloy, Al-5Zr master alloy as raw materials, the chemical composition of each raw material is controlled as follows in mass percentage: Li 12%, Al 3.09%, Cu 1%, Zr 0.11%, and the balance is Mg; wherein, the pure Li is wrapped with pure aluminum foil; all raw materials except Li are preheated in a dry furnace.

[0035] (2) Preheat the crucible to 480℃, put the preheated Mg ingot into the graphite crucible, and place it in the vacuum induction heating melting furnace, close the furnace cover; vacuumize to 8Pa as shown by the vacuum pressure gauge, then close the vacuum pump; introduce argon protective gas until the pressure reaches 0.12MPa; heat to completely melt the Mg ingot.

[0036] (3) When the melt temperature rises to 750℃, sequentially add the preheated Al-50Cu master alloy and Al-5Zr master alloy;

[0037] (4) When the melt temperature drops to 700℃, add the pure Li after the master alloy is completely melted, and quickly stir for 8 minutes.

[0038] (5) Pour the melt into the preheated mold, and take out the alloy ingot from the mold after 30 minutes.

[0039] The mechanical properties of the obtained ultra-light high-strength and high-toughness cast magnesium-lithium alloy are as follows: ultimate tensile strength 210MPa, tensile yield strength 183MPa, elongation 6%; ultimate compressive strength 430MPa, compressive yield strength 227MPa.

[0040] Example 3

[0041] (1) Prepare Mg ingot, pure Li, Al-50Cu master alloy, Al-5Zr master alloy as raw materials, the chemical composition of each raw material is controlled as follows in mass percentage: Li 15%, Al 3.59%, Cu 1.5%, Zr 0.11%, and the balance is Mg; wherein, the pure Li is wrapped with pure aluminum foil; all raw materials except Li are preheated in a dry furnace.

[0042] (2) Preheat the crucible to 480℃, put the preheated Mg ingot into the graphite crucible, and place it in the vacuum induction heating melting furnace, close the furnace cover; vacuumize to 6Pa as shown by the vacuum pressure gauge, then close the vacuum pump; introduce argon protective gas until the pressure reaches 0.15MPa; heat to completely melt the Mg ingot.

[0043] (3) When the melt temperature rises to 730℃, sequentially add the preheated Al-50Cu master alloy and Al-5Zr master alloy;

[0044] (4) When the intermediate alloy is completely melted, the melt temperature is reduced to 690℃, and the pure Li is added, and stirred rapidly for 10 minutes.

[0045] (5) The melt is cast into a preheated mold, and the alloy ingot is taken out from the mold after 30 minutes.

[0046] The mechanical properties of the obtained ultra-light high-strength and high-toughness cast Mg-Li alloy are: ultimate tensile strength 220 MPa, tensile yield strength 185 MPa, elongation 7%; ultimate compressive strength 445 MPa, compressive yield strength 232 MPa.

[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. It is also to be understood that the use of "comprise", "comprising", "comprises", "include", "including", "includes", "have", "has", "having", or variants thereof is to be construed as open-ended, i.e., to mean including, but not limited to.

[0048] The content not described in detail in the specification of the present application is the prior art known to those skilled in the art. Although the above describes the specific embodiments of the present application in order to facilitate the understanding of the present application by those skilled in the art, it should be clear that the present application is not limited to the scope of the specific embodiments, and for the numerical range in the present application, it should be understood that each intermediate value between the upper limit and the lower limit of the range is also specifically disclosed. Each smaller range between any stated value or intermediate value within the range and any other stated value or intermediate value within the range is also included in the present application. The upper limit and the lower limit of these smaller ranges can be independently included or excluded from the range, which is obvious to those skilled in the art. As long as various modifications, equivalent replacements and improvements of the technical solutions of the present application within the spirit and scope of the present application defined and determined by the appended claims are made, these changes are obvious, and all the inventions made by using the concept of the present application are within the scope of protection.

Claims

1. A low-cost, ultra-lightweight, high-strength, and high-toughness cast magnesium-lithium alloy, characterized in that: The mass percentage of each element in the low-cost, ultra-light, high-strength and tough cast magnesium-lithium alloy is Li 11-15%, Al 1-4%, Cu 0.5-1.5%, Zr 0.05-0.15%, with the balance being Mg and unavoidable impurities; The mechanical properties of the low-cost, ultra-light, high-strength, and tough cast magnesium-lithium alloy are as follows: ultimate tensile strength of 200–235 MPa, tensile yield strength of 180–190 MPa, and elongation of 5–7%; ultimate compressive strength of 400–460 MPa and compressive yield strength of 225–235 MPa.

2. The low-cost, ultra-lightweight, high-strength, and tough cast magnesium-lithium alloy according to claim 1, characterized in that: The total amount of Si, Fe, Ni and Ca in the impurities is less than 0.03 wt.%.

3. A method for preparing a low-cost, ultra-lightweight, high-strength, and tough cast magnesium-lithium alloy according to any one of claims 1 to 2, characterized in that: The preparation method includes the following steps: (1) Prepare Mg ingots, pure Li, Al-50Cu master alloy, and Al-5Zr master alloy as raw materials. The chemical composition of each raw material is controlled by mass percentage as follows: Li 11-15%, Al 1-4%, Cu 0.5-1.5%, Zr 0.05-0.15%, with the balance being Mg. Pure Li is wrapped in pure aluminum foil. All raw materials except Li are preheated in a drying furnace. (2) Preheat the crucible to 480°C, put the preheated Mg ingot into the graphite crucible, place it in the vacuum induction heating melting furnace, and close the furnace lid; evacuate until the vacuum pressure gauge shows 5-10 Pa, then turn off the vacuum pump; introduce argon protective gas until it reaches 0.08-0.15 MPa; heat until the Mg ingot is completely melted; (3) When the melt temperature rises to 700-750℃, add the preheated Al-50Cu master alloy and Al-5Zr master alloy in sequence. (4) When the intermediate alloy is completely melted and the melt temperature drops to 650-710℃, add the above-mentioned pure Li and stir quickly for 5-10 minutes. (5) Pour the molten liquid into a preheated mold and wait 30 minutes before removing the alloy ingot from the mold.

4. The method for preparing low-cost, ultralight, high-strength, and tough cast magnesium-lithium alloy according to claim 3, characterized in that: Argon gas is used for protection to prevent the magnesium liquid from oxidizing and burning.

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