A magnesium-lithium-aluminum-based lightweight medium-entropy alloy and a preparation method thereof

Abstract

This invention discloses a magnesium-lithium-aluminum-based lightweight medium-entropy alloy and its preparation method, belonging to the field of metallic materials and their preparation. The chemical formula of the magnesium-lithium-aluminum-based lightweight medium-entropy alloy proposed in this invention is Mg. a Li b Al c Zn d Ca e X f Where X is Nd, Gd, or Y; a, b, c, d, e, and f are the atomic percentages of each element, 30at.%≤a≤50at.%, 25at.%≤b≤40at.%, 5at.%≤c≤25at.%, 1at.%≤d≤5at.%, 1at.%≤e≤5at.%, 0.1at.%≤f≤5at.%, and a+b+c+d+e+f=100at.%. The magnesium-lithium-aluminum-based lightweight medium-entropy alloy prepared by this invention exhibits an excellent combination of strength and plasticity, and the preparation process is simple and stable, showing good prospects for industrial application.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials and their preparation technology, specifically relating to a magnesium-lithium-aluminum based lightweight medium-entropy alloy and its preparation method. Background Technology

[0002] Magnesium alloys are among the lightest metallic structural materials available today, characterized by their low density (approximately 1.74 g / cm³). 3 Magnesium alloys, with their high specific strength, high specific stiffness, excellent electromagnetic shielding, good damping performance, and recyclability, exhibit significant potential for lightweight applications in aerospace and transportation. Especially under the global trend of energy conservation and emission reduction, further reducing the weight of structural components has become a key way to improve energy efficiency. While traditional magnesium alloys are lightweight, their absolute strength is limited. In particular, when the density of magnesium alloys is further reduced by adding lithium, the strength often decreases, severely limiting their use in load-bearing structures.

[0003] In recent years, the high-entropy alloy design concept has provided new ideas for breakthroughs in the performance of metallic materials. As a novel alloy design concept, it focuses on "multi-principal element" composition design, breaking through the traditional alloy design paradigm based on a single element, and allowing exploration within a wider range of compositions. Early research on high-entropy alloys mainly focused on transition elements such as Fe, Mn, Cu, Cr, Co, and Ni. Although these alloys have excellent properties, they generally have high densities; therefore, the density of most high-entropy alloys exceeds 7 g / cm³. 3 However, this approach struggles to meet lightweight requirements. Therefore, within the framework of high-entropy alloys, reducing density and developing lightweight medium / high-entropy alloys with Mg, Li, Al, and Ti as the main lightweight elements has become a cutting-edge research area and an inevitable trend in this field. These alloys are expected to maintain low density while synergistically improving strength and plasticity, aiming to combine the superior performance of high-entropy alloys with the low-density advantages of lightweight materials to provide a new generation of ultra-lightweight, high-strength structural materials for aerospace and transportation.

[0004] However, lightweight elements are mostly main group elements with high electronegativity. Their large-scale introduction into the system often leads to complex alloy microstructures and a sharp decrease in plasticity, making it difficult to balance strength and ductility, severely limiting their engineering applications. Studies have shown that in lightweight high-entropy alloys, excessively high entropy values ​​are more likely to cause the alloy to exhibit brittleness. Summary of the Invention

[0005] To address the technical problems of low absolute strength in existing magnesium alloys and the extremely poor plasticity of medium / high entropy alloys with lightweight elements as the main component in the as-cast state, this invention provides a magnesium-lithium-aluminum-based lightweight medium-entropy alloy and its preparation method. This invention uses Mg, Li, and Al as the basic framework, introduces Zn, Ca, and Nd, Gd, or Y elements and controls their content to construct an alloy system with a composition within the medium-entropy alloy range. While meeting the lightweight requirement, it comprehensively controls the strength and plasticity of the alloy, and the preparation process is simple and stable, showing good prospects for industrial application.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows.

[0007] The first objective of this invention is to provide a magnesium-lithium-aluminum-based lightweight medium-entropy alloy, wherein the chemical formula of the magnesium-lithium-aluminum-based lightweight medium-entropy alloy is Mg. a Li b Al c Zn d Ca e X f Where X is Nd, Gd, or Y; a, b, c, d, e, and f are the atomic percentages of each element, 30at.%≤a≤50at.%, 25at.%≤b≤40at.%, 5at.%≤c≤25at.%, 1at.%≤d≤5at.%, 1at.%≤e≤5at.%, 0.1at.%≤f≤5at.%, and a+b+c+d+e+f=100at.%.

[0008] In a preferred embodiment, the atomic percentages of each element in the magnesium-lithium-aluminum-based lightweight medium-entropy alloy are as follows: Mg content is 35 at.% to 50 at.%, Li content is 25 at.% to 35 at.%, Al content is 20 at.% to 25 at.%, Zn content is 1 at.% to 5 at.%, Ca content is 1 at.% to 5 at.%, and X content is 0.1 at.% to 5 at.%, totaling 100 at.%.

[0009] In a preferred embodiment, the magnesium-lithium-aluminum based lightweight medium-entropy alloy has a density of 1.63 g / cm³. 3 ~1.74g / cm 3 .

[0010] In a preferred embodiment, the room temperature compressive yield strength of the magnesium-lithium-aluminum-based lightweight medium-entropy alloy is 335 MPa to 470 MPa.

[0011] In a preferred embodiment, the compressive strain rate of the magnesium-lithium-aluminum-based lightweight medium-entropy alloy is 6.1% to 50%.

[0012] A second objective of this invention is to provide a method for preparing magnesium-lithium-aluminum based lightweight medium-entropy alloys, comprising the following steps: Magnesium blocks, aluminum granules, and zinc granules are used as raw materials. Mg-30Ca and Mg-30X master alloys are added, and the mixture is heated to 750℃~800℃ under vacuum conditions of <5Pa to obtain molten material.

[0013] The temperature is lowered to 670℃~720℃, lithium particles are added to the molten material, the temperature is maintained, and the mixture is cast and cooled to obtain a magnesium-lithium-aluminum-based lightweight medium-entropy alloy.

[0014] In the Mg-30X, X is Nd, Gd, or Y.

[0015] In a preferred embodiment, the melting time is 20 min to 30 min.

[0016] In a preferred embodiment, the cooling rate to 670℃~720℃ is 5℃ / min~10℃ / min, and the holding time after adding lithium particles is 10min~15min.

[0017] In a preferred embodiment, the purity of the magnesium block, lithium granules, aluminum granules, and zinc granules is greater than 99.99%; the purity of Mg-30Ca and Mg-30X is greater than 99.95%.

[0018] In a preferred embodiment, the lithium granules are wrapped in aluminum foil and placed in a secondary feeding hopper. The aluminum foil wrapping is used to isolate the lithium from air and slow down the feeding process, thereby reducing lithium oxidation loss, splashing, and volatilization loss, and improving the stability of the alloy composition and the uniformity of the microstructure.

[0019] Compared with the prior art, the present invention has the following beneficial effects: The magnesium-lithium-aluminum-based lightweight medium-entropy alloy provided by this invention is based on low-density elements Mg, Li, and Al, and incorporates Zn, Ca, and Nd / Gd / Y elements for multi-principal component design. This increases the alloy entropy value and regulates the presence and distribution of phases in the alloy, thereby comprehensively controlling the strength and plasticity of the alloy.

[0020] The magnesium-lithium-aluminum based lightweight medium-entropy alloy prepared by this invention has a density of 1.63 g / cm³. 3 ~1.74g / cm 3 This lightweight, medium-entropy alloy exhibits an excellent combination of strength and plasticity, with a room temperature compressive yield strength of 335 MPa to 470 MPa in the as-cast state and a compressive fracture strain exceeding 50%. Moreover, its preparation process is simple and stable, and it has good prospects for industrial application. Attached Figure Description

[0021] Figure 1This is the microstructure of the magnesium-lithium-aluminum-based lightweight medium-entropy alloy prepared in Example 1 of the present invention.

[0022] Figure 2 The mechanical properties of the magnesium-lithium-aluminum-based lightweight medium-entropy alloy prepared in Example 1 of this invention are shown.

[0023] Figure 3 This is the microstructure of the magnesium-lithium-aluminum-based lightweight medium-entropy alloy prepared in Example 2 of the present invention.

[0024] Figure 4 The mechanical properties of the magnesium-lithium-aluminum-based lightweight medium-entropy alloy prepared in Example 2 of this invention are shown.

[0025] Figure 5 This is the microstructure of the magnesium-lithium-aluminum-based lightweight medium-entropy alloy prepared in Example 3 of the present invention.

[0026] Figure 6 The mechanical properties of the magnesium-lithium-aluminum-based lightweight medium-entropy alloy prepared in Example 3 of this invention are shown.

[0027] Figure 7 The mechanical properties of the magnesium-lithium-aluminum-based lightweight medium-entropy alloy prepared in Comparative Example 1 of this invention are shown in the figure. Detailed Implementation

[0028] To enable those skilled in the art to better understand and implement the technical solutions of this invention, the invention is further described below with reference to specific embodiments. However, the embodiments are not intended to limit the invention. Unless otherwise specified, the following test methods and detection methods are conventional methods; unless otherwise specified, the reagents and raw materials are commercially available.

[0029] As research on high-entropy alloys deepens, their application fields continue to expand. However, early research on high-entropy alloys mainly focused on transition elements such as Fe, Mn, Cu, Cr, Co, and Ni. While these alloys exhibit excellent properties, they generally have high densities; therefore, the density of most high-entropy alloys exceeds 7 g / cm³. 3 However, this approach struggles to meet lightweight requirements. Therefore, reducing density within the framework of high-entropy alloys and developing lightweight medium / high-entropy alloys with Mg, Li, Al, and Ti as the main lightweight elements has become a cutting-edge research area and an inevitable trend in this field. These alloys are expected to maintain low density while synergistically improving strength and plasticity, aiming to combine the superior properties of high-entropy alloys with the low-density advantages of lightweight materials, providing a new generation of ultra-lightweight, high-strength structural materials for aerospace, transportation, and other fields.

[0030] However, lightweight elements are mostly main group elements with high electronegativity. Their large-scale introduction into the system often leads to complex alloy microstructure and a sharp decrease in plasticity, making it difficult to balance strength and plasticity, severely limiting their engineering application prospects. Based on the above problems, this invention provides a magnesium-lithium-aluminum based lightweight medium-entropy alloy and its preparation method.

[0031] The technical solution of the present invention will be analyzed in detail below.

[0032] This invention provides a magnesium-lithium-aluminum-based lightweight medium-entropy alloy, wherein the chemical formula of the magnesium-lithium-aluminum-based lightweight medium-entropy alloy is Mg. a Li b Al c Zn d Ca e X f Where X is Nd, Gd, or Y; a, b, c, d, e, and f are the atomic percentages of each element, 30at.%≤a≤50at.%, 25at.%≤b≤40at.%, 5at.%≤c≤25at.%, 1at.%≤d≤5at.%, 1at.%≤e≤5at.%, 0.1at.%≤f≤5at.%, and a+b+c+d+e+f=100at.%.

[0033] In the above technical solution, this invention uses Mg, Li, and Al as the basic framework, introduces Zn, Ca, Nd or Gd or Y elements and controls their content to construct an alloy system with a composition in the medium entropy alloy range. By comprehensively controlling the strength and plasticity of the alloy, a density of 1.63 g / cm³ is obtained. 3 ~1.74g / cm 3 This lightweight, medium-entropy alloy exhibits an excellent combination of strength and plasticity, with a room temperature compressive yield strength of 335 MPa to 470 MPa in the as-cast state and a compressive fracture strain exceeding 50%. Moreover, its preparation process is simple and stable, and it has good prospects for industrial application.

[0034] The technical solution of the present invention will be further illustrated below through the following embodiments and comparative examples.

[0035] Example 1 A magnesium-lithium-aluminum based lightweight medium-entropy alloy Mg 47 Li 25 Al 25 The preparation method of Zn1Ca1Nd1 includes the following steps: Weigh out magnesium blocks, aluminum granules, zinc granules, Mg-30Ca, and Mg-30Nd according to atomic percentages (at.%): Mg: 47%, Li: 25%, Al: 25%, Zn: 1%, Ca: 1%, Nd: 1%. Place the raw materials (excluding lithium granules) into the crucible in order of increasing melting point to improve melting efficiency and compositional stability, reduce unmelted particles and segregation, shorten high-temperature residence time, reduce volatilization and burn-off losses, and obtain a more uniform microstructure and more stable mechanical properties. Wrap the lithium granules in aluminum foil and place them in the secondary feeding bin. Place the crucible containing the raw materials in a vacuum melting furnace, close the furnace lid, and evacuate until the pressure inside the melting furnace is <5Pa. Turn on the melting power, heat to 770℃, and hold until the raw materials in the crucible are completely melted. Then lower the temperature to 720℃, add the aluminum foil-wrapped lithium granules to the melt, and hold for 15 minutes. Turn off the smelting power supply and pour the uniformly smelted alloy liquid into a mold to obtain a magnesium-lithium-aluminum based lightweight medium-entropy alloy, denoted as Mg. 47 Li 25 Al 25 Zn1Ca1Nd1, theoretical density is 1.74 g / cm³. 3 .

[0036] Example 2 A magnesium-lithium-aluminum based lightweight medium-entropy alloy Mg 40 Li 35 Al 20 The preparation method of Zn2Ca2Gd1 includes the following steps: Weigh out magnesium blocks, aluminum granules, zinc granules, Mg-30Ca, and Mg-30Gd according to atomic percentages (at.%): Mg: 40%, Li: 35%, Al: 20%, Zn: 2%, Ca: 2%, Gd: 1%. Place the raw materials (excluding lithium granules) into a crucible in order of increasing melting point. Wrap the lithium granules in aluminum foil and place them in a secondary feeding bin. Place the crucible containing the raw materials in a vacuum melting furnace, close the furnace lid, and evacuate the furnace until the pressure inside the furnace is <5 Pa. Turn on the melting power and heat to 750℃, holding until the raw materials in the crucible are completely melted. Then lower the temperature to 700℃, add the aluminum foil-wrapped lithium granules to the melt, and hold for 10 minutes. Turn off the melting power and pour the uniformly melted alloy into a mold to obtain a magnesium-lithium-aluminum based lightweight medium-entropy alloy, denoted as Mg. 40 Li 35 Al 20 Zn₂Ca₂Gd₁ has a theoretical density of 1.63 g / cm³. 3 .

[0037] Example 3 A magnesium-lithium-aluminum based lightweight medium-entropy alloy Mg 39 Li 30 Al 20 The preparation method of Zn5Ca5Y1 includes the following steps: Weigh out magnesium blocks, aluminum granules, zinc granules, Mg-30Ca, and Mg-30Y according to atomic percentages (at.%): Mg: 39%, Li: 30%, Al: 20%, Zn: 5%, Ca: 5%, Y: 1%. Place the raw materials (excluding lithium granules) into a crucible in order of increasing melting point. Wrap the lithium granules in aluminum foil and place them in a secondary feeding bin. Place the crucible containing the raw materials in a vacuum melting furnace, close the furnace lid, and evacuate until the pressure inside the melting furnace is <5 Pa. Turn on the melting power and heat to 750℃, holding until the raw materials in the crucible are completely melted. Then lower the temperature to 700℃, add the aluminum foil-wrapped lithium granules to the melt, and hold for 10 minutes. Turn off the melting power and pour the uniformly melted alloy into a mold to obtain a magnesium-lithium-aluminum based lightweight medium-entropy alloy, denoted as Mg. 39 Li 30 Al 20 Zn5Ca5Y1 has a theoretical density of 1.74 g / cm³. 3 .

[0038] To further illustrate the technical effects of the present invention, a comparative example is also provided, as follows.

[0039] Comparative Example 1 A magnesium-lithium-aluminum based lightweight medium-entropy alloy Mg 39 Li 30 Al 20 The preparation method of Zn5Ca5Y1-2 includes the following steps: Weigh out magnesium blocks, aluminum granules, zinc granules, Mg-30Ca, and Mg-30Y according to atomic percentages (at.%): Mg: 39%, Li: 30%, Al: 20%, Zn: 5%, Ca: 5%, Y: 1%. Place the raw materials (except lithium granules) into a crucible in order of increasing melting point. Wrap the lithium granules in aluminum foil and place them in a secondary feeding bin. Place the crucible containing the raw materials in a vacuum melting furnace, close the furnace lid, and evacuate until the pressure inside the furnace is <5 Pa. Turn on the melting power and heat to 800℃, holding until the raw materials in the crucible are completely melted. Then lower the temperature to 740℃, add the aluminum foil-wrapped lithium granules to the melt, and hold for 15 minutes. Turn off the melting power and pour the uniformly melted alloy into a mold to obtain a magnesium-lithium-aluminum based lightweight medium-entropy alloy, denoted as Mg. 39 Li 30 Al 20 Zn5Ca5Y1-2.

[0040] The compressive stress-strain curve of the magnesium-lithium-aluminum-based lightweight medium-entropy alloy prepared in Example 1 of this invention is shown below. Figure 2 As shown, its room temperature compressive yield strength is 470 MPa and its compressive strain is 6.1%.

[0041] The compressive stress-strain curve of the magnesium-lithium-aluminum-based lightweight medium-entropy alloy prepared in Example 2 of this invention is shown below. Figure 4 As shown, its room temperature compressive yield strength is 335 MPa and its compressive strain is 14.9%.

[0042] The compressive stress-strain curve of the magnesium-lithium-aluminum-based lightweight medium-entropy alloy prepared in Example 3 of this invention is shown below. Figure 6 As shown, its room temperature compressive yield strength is 350 MPa, and its compressive strain is >50%.

[0043] The compressive stress-strain curve of the magnesium-lithium-aluminum-based lightweight medium-entropy alloy prepared in Comparative Example 1 of this invention is shown below. Figure 7 As shown, its room temperature compressive yield strength is 350 MPa, and its compressive strain is 25.5%. Compared with Example 3, Comparative Example 1 has the same room temperature compressive yield strength, but its compressive strain is significantly reduced. This is because higher melting temperatures and higher lithium addition temperatures make it easier for lithium to be lost, leading to compositional deviation and changes in the matrix phase composition, which in turn results in a significant decrease in compressive fracture strain.

[0044] In summary, through the design and optimization of the alloy composition in this invention, the prepared magnesium-lithium-aluminum based lightweight medium-entropy alloy has a density of 1.74 g / cm³. 3 The room temperature compressive yield strength is 350 MPa, exceeding 50% of the compressive fracture strain, demonstrating excellent comprehensive performance of high strength and ductility at low density. This verifies that the magnesium-lithium-aluminum-based lightweight medium-entropy alloy prepared in this invention can achieve a synergistic improvement in strength and ductility at low density, providing a feasible material for the lightweight and high-performance requirements of aerospace and transportation fields.

[0045] It should be noted that when numerical ranges are involved in this invention, it should be understood that the two endpoints of each numerical range, as well as any value between the two endpoints, can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described in this invention to avoid redundancy. Although preferred embodiments of this invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments, and all such changes and modifications fall within the scope of this invention.

[0046] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. If these modifications and variations fall within the scope of equivalents of this invention, then this invention also intends to include these modifications and variations.

Claims

1. A magnesium-lithium-aluminum based lightweight medium-entropy alloy, characterized in that, The chemical formula of the magnesium-lithium-aluminum-based lightweight medium-entropy alloy is Mg. a Li b Al c Zn d Ca e X f Where X is Nd, Gd, or Y; a, b, c, d, e, and f are the atomic percentages of each element, 30at.%≤a≤50at.%, 25at.%≤b≤40at.%, 5at.%≤c≤25at.%, 1at.%≤d≤5at.%, 1at.%≤e≤5at.%, 0.1at.%≤f≤5at.%, and a+b+c+d+e+f=100at.%.

2. The magnesium-lithium-aluminum based lightweight medium-entropy alloy according to claim 1, characterized in that, The atomic percentages of each element in the magnesium-lithium-aluminum-based lightweight medium-entropy alloy are as follows: Mg content is 35 at.% to 50 at.%, Li content is 25 at.% to 35 at.%, Al content is 20 at.% to 25 at.%, Zn content is 1 at.% to 5 at.%, Ca content is 1 at.% to 5 at.%, and X content is 0.1 at.% to 5 at.%, totaling 100 at.%.

3. The magnesium-lithium-aluminum based lightweight medium-entropy alloy according to claim 1, characterized in that, The density of the magnesium-lithium-aluminum based lightweight medium-entropy alloy is 1.63 g / cm³. 3 ~1.74g / cm 3 .

4. The magnesium-lithium-aluminum based lightweight medium-entropy alloy according to claim 1, characterized in that, The room temperature compressive yield strength of the magnesium-lithium-aluminum-based lightweight medium-entropy alloy is 335 MPa to 470 MPa.

5. The magnesium-lithium-aluminum based lightweight medium-entropy alloy according to claim 1, characterized in that, The compressive strain rate of the magnesium-lithium-aluminum-based lightweight medium-entropy alloy is 6.1% to 50%.

6. The method for preparing a magnesium-lithium-aluminum based lightweight medium-entropy alloy according to any one of claims 1 to 5, characterized in that, Includes the following steps: Magnesium blocks, aluminum granules, and zinc granules were used as raw materials. Mg-30Ca and Mg-30X master alloys were added, and the mixture was heated to 750℃~800℃ under vacuum conditions of <5Pa to obtain molten material. The temperature was lowered to 670℃~720℃, lithium particles were added to the molten material, the temperature was maintained, and the mixture was cast and cooled to obtain a magnesium-lithium-aluminum-based lightweight medium-entropy alloy. In the Mg-30X, X is Nd, Gd, or Y.

7. The method for preparing a magnesium-lithium-aluminum based lightweight medium-entropy alloy according to claim 6, characterized in that, The melting time is 20 to 30 minutes.

8. The method for preparing a magnesium-lithium-aluminum based lightweight medium-entropy alloy according to claim 6, characterized in that, The cooling rate to 670℃~720℃ is 5℃ / min~10℃ / min, and the holding time after adding lithium particles is 10min~15min.

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