High-entropy die-casting magnesium-based alloy and preparation method thereof

Abstract

The invention discloses a high-entropy die-casting magnesium-based alloy and a preparation method thereof, relates to the technical field of magnesium alloy materials, and solves the problems that in the prior art, magnesium alloy is poor in fluidity and is difficult to be suitable for production of large complex thin-wall die castings. The high-entropy die-casting magnesium-based alloy comprises, by mass, 18%-26% of Al, 8%-14% of Zn, 8%-16% of Cu, 6%-12% of Ni, 2%-6% of Mn and the balance Mg and inevitable impurities. The high-entropy die-casting magnesium alloy has ultrahigh fluidity, can perfectly fill a complex die cavity, and can produce a large die casting with thinner wall thickness and more complex structure.

Description

Technical Field

[0001] This invention relates to the field of magnesium alloy materials technology, specifically to a high-entropy die-cast magnesium-based alloy and its preparation method. Background Technology

[0002] Magnesium alloys, as the lightest metallic structural materials, have broad application prospects in aerospace, automotive, and 3C electronics industries. Die casting is the primary forming process for magnesium alloys, offering high production efficiency, near-net-shape forming, and the ability to manufacture complex thin-walled parts. However, traditional die-cast magnesium alloys (such as AZ91D and AM60B) have relatively limited fluidity. When filling large, complex, and thin-walled mold cavities, defects such as incomplete filling and cold shuts are prone to occur, limiting their application in high-requirement structural components. The fluidity of an alloy mainly depends on its solidification characteristics. Traditional magnesium alloys have a wide solidification temperature range, and during solidification, dendrite growth is rapid, and the viscosity of the molten slurry increases quickly, severely hindering the long-distance flow of the molten metal.

[0003] High-entropy alloys (HEAs) are a new type of alloy composed of five or more main elements. Their high-entropy effect can promote the formation of a single solid solution phase and inhibit the precipitation of intermetallic compounds, thus potentially endowing the alloy with unique properties. In recent years, researchers have begun to introduce the design concept of high-entropy alloys into magnesium alloy systems, developing a series of high-entropy magnesium-based alloys. However, these studies have mostly focused on the mechanical properties or corrosion resistance of the alloys, and there are few reports specifically on high-entropy magnesium-based alloys with high-entropy fluidity for die casting. Summary of the Invention

[0004] One objective of this invention is to provide a high-entropy die-casting magnesium-based alloy to solve the problem of poor fluidity in existing magnesium alloys, making them unsuitable for the production of large, complex, thin-walled die-cast parts. Another objective is to provide a method for preparing this high-entropy die-casting magnesium-based alloy. This invention's alloy, through a unique multi-component high-entropy formulation design, promotes uniform solidification, significantly narrows the alloy's solidification temperature range, inhibits dendrite formation in the early stages of solidification, and reduces the viscosity of the melt during the filling process, thereby achieving ultra-high fluidity far exceeding that of traditional magnesium alloys, making it particularly suitable for the production of large, complex, thin-walled die-cast parts.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, this application provides a high-entropy die-cast magnesium-based alloy, comprising, by mass percentage: Al 18%~26%, Zn 8%~14%, Cu 8%~16%, Ni 6%~12%, Mn 2%~6%, with the balance being Mg and unavoidable impurities.

[0006] In some possible implementations, Al is 20%~24%; In some possible implementations, Zn is 10%~12%; In some possible implementations, Cu is 10%~14%; In some possible implementations, Ni is 8%~10%; In some possible implementations, Mn is 3%~5%.

[0007] Secondly, this application provides a method for preparing a high-entropy die-cast magnesium-based alloy, comprising the following steps: S1. Melt the raw materials to obtain the first alloy melt; S2. Refine the first alloy melt to obtain the second alloy melt; S3. Cast the second alloy melt into an ingot to obtain a die-cast magnesium-based alloy.

[0008] In some possible implementations, S1 includes melting each raw material sequentially, stirring until homogeneous, and keeping it at a constant temperature to form a first alloy melt.

[0009] In some possible implementations, the step of sequentially melting the raw materials includes: first, melting magnesium ingots to obtain molten magnesium; then adding aluminum and zinc ingots to the molten magnesium and melting them; then adding copper and nickel plates to dissolve and diffuse them; and finally adding a magnesium-manganese master alloy to melt it. In some possible implementations, the step of mixing evenly includes: after all raw materials have been added, mixing at 730~750°C using a mechanical stirrer at a speed of 300~600 rpm for 10~15 minutes. In some possible implementations, the temperature for heat preservation and static setting is 735~745℃, and the time is 5~15min.

[0010] In some possible implementations, the temperature at which the magnesium ingot is melted is 710~730°C; In some possible implementations, the melting temperature of the added aluminum and zinc ingots is 710~730°C; In some possible implementations, the dissolution and diffusion temperature of the copper and nickel plates is 740~750°C; In some possible implementations, the temperature at which the magnesium-manganese master alloy is added to melt is 740~750°C; In some possible implementations, the mass percentage of Mn in the magnesium-manganese master alloy is 28-32%.

[0011] In some possible implementations, the raw materials are further pretreated before being melted. In some possible implementations, the step of melting the raw materials is carried out in a mixture of CO2 and SF6.

[0012] In some possible implementations, the pretreatment includes preheating the raw material to 150-200°C; In some possible implementations, the volume ratio of CO2 to SF6 in the mixed gas is (65~200):1.

[0013] In some possible implementations, S2 includes: adding a refining agent to the first alloy melt, reacting for a period of time, and then slag removal; keeping it at a constant temperature for a period of time to obtain the second alloy melt.

[0014] In some possible implementations, the refining agent is pressed into the first alloy melt to a depth of 1 / 2 to 2 / 3; In some possible implementations, the mixture is sludged after reacting for 5-8 minutes. In some possible implementations, in step S2, the temperature for heat preservation and static setting is 735~745℃, and the time is 10~15min; In some possible implementations, the refining agent is preheated to 280-320°C before being added to the first alloy melt.

[0015] The beneficial effects of this invention are: The high-entropy die-cast magnesium-based alloy of the present invention comprises, by mass percentage: Al 18%~26%, Zn 8%~14%, Cu 8%~16%, Ni 6%~12%, Mn 2%~6%, with the balance being Mg and unavoidable impurities.

[0016] This invention reveals that controlling the Al content to 18%–26% allows for the formation of a large number of low-melting-point eutectic networks, significantly reducing the liquidus temperature and providing a foundation for ultra-high fluidity, while simultaneously achieving significant solid solution strengthening. Controlling the Zn content to 8%–14% also allows for the formation of low-melting-point eutectic phases with Mg and Al, lowering the melting and solidification temperature range of the alloy, positively contributing to improved fluidity, and effectively strengthening the magnesium matrix. Controlling the Cu content to 8%–16%, in synergy with specific proportions of Al and Zn, forms a multi-element low-eutectic network, effectively suppressing the preferential precipitation of high-melting-point primary phases and reducing the free energy of the liquid system. This not only significantly lowers the alloy's melting point but also enhances strength while maintaining good toughness by suppressing coarse, brittle phases and promoting the formation of nanoscale high-entropy precipitates. Controlling the Ni content to 6%–12%, in conjunction with Cu, maximizes the high-entropy effect, forming a solid solution and a thermally stable strengthening phase, jointly optimizing the solidification process and mechanical properties. The Mn content is controlled at 2%~6%, which greatly improves the corrosion resistance of the alloy by capturing and eliminating harmful impurity elements such as iron, while refining the grains and playing a key role in optimizing the overall performance.

[0017] This invention introduces multiple alloying elements such as Zn, Cu, Ni, and Mn, which work synergistically with Al to form a melt with high mixing entropy. The high entropy effect significantly lowers the alloy's liquidus temperature and greatly narrows the solidification temperature range, making its solidification behavior approximate that of a eutectic alloy. The alloy melt hardly experiences a high-viscosity, pasty region during solidification, thus maintaining extremely low flow resistance for a long time during mold filling, achieving a flow distance far exceeding that of traditional alloys such as AZ91D. This ultra-high fluidity allows the alloy to perfectly fill complex mold cavities, producing large die-cast parts with thinner walls and more complex structures, eliminating incomplete filling and cold shut defects, and significantly improving the yield and design freedom of die-casting production. The solid solution strengthening of multiple elements and the dispersion strengthening of nanoscale precipitates enable this die-cast alloy to maintain good toughness while possessing high strength, with comprehensive mechanical properties superior to traditional die-cast magnesium alloys. The smelting and die-casting processes are compatible with existing magnesium alloy production processes, requiring no special equipment and facilitating industrial-scale promotion. Attached Figure Description

[0018] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 This is a photograph of the casting fluidity (700°C) test of Example 1 of the present invention. Detailed Implementation

[0020] The embodiments of the present invention will be described below with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention and not for limiting the scope of protection of the present invention.

[0021] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0022] In a first aspect, this application provides a high-entropy die-cast magnesium-based alloy, comprising, by mass percentage: Al 18%~26%, Zn 8%~14%, Cu 8%~16%, Ni 6%~12%, Mn 2%~6%, with the balance being Mg and unavoidable impurities.

[0023] This invention reveals that controlling the Al content to 18%–26% allows for the formation of a large number of low-melting-point eutectic networks, significantly reducing the liquidus temperature and providing a foundation for ultra-high fluidity, while simultaneously achieving significant solid solution strengthening. Controlling the Zn content to 8%–14% also allows for the formation of low-melting-point eutectic phases with Mg and Al, lowering the melting and solidification temperature range of the alloy, positively contributing to improved fluidity, and effectively strengthening the magnesium matrix. Controlling the Cu content to 8%–16%, in synergy with specific proportions of Al and Zn, forms a multi-element low-eutectic network, effectively suppressing the preferential precipitation of high-melting-point primary phases and reducing the free energy of the liquid system. This not only significantly lowers the alloy's melting point but also enhances strength while maintaining good toughness by suppressing coarse, brittle phases and promoting the formation of nanoscale high-entropy precipitates. Controlling the Ni content to 6%–12%, in conjunction with Cu, maximizes the high-entropy effect, forming a solid solution and a thermally stable strengthening phase, jointly optimizing the solidification process and mechanical properties. The Mn content is controlled at 2%~6%, which greatly improves the corrosion resistance of the alloy by capturing and eliminating harmful impurity elements such as iron, while refining the grains and playing a key role in optimizing the overall performance.

[0024] This invention introduces multiple alloying elements such as Zn, Cu, Ni, and Mn, which work synergistically with Al to form a melt with high mixing entropy. The high entropy effect significantly lowers the alloy's liquidus temperature and greatly narrows the solidification temperature range, making its solidification behavior approximate that of a eutectic alloy. The alloy melt hardly experiences a high-viscosity, pasty region during solidification, thus maintaining extremely low flow resistance for a long time during mold filling, achieving a flow distance far exceeding that of traditional alloys such as AZ91D. This ultra-high fluidity allows the alloy to perfectly fill complex mold cavities, producing large die-cast parts with thinner walls and more complex structures, eliminating incomplete filling and cold shut defects, and significantly improving the yield and design freedom of die-casting production. The solid solution strengthening of multiple elements and the dispersion strengthening of nanoscale precipitates enable this die-cast alloy to maintain good toughness while possessing high strength, with comprehensive mechanical properties superior to traditional die-cast magnesium alloys. The smelting and die-casting processes are compatible with existing magnesium alloy production processes, requiring no special equipment and facilitating industrial-scale promotion.

[0025] In some possible implementations, Al is 20%~24%; In some possible implementations, Zn is 10%~12%; In some possible implementations, Cu is 10%~14%; In some possible implementations, Ni is 8%~10%; In some possible implementations, Mn is 3%~5%.

[0026] Secondly, this application provides a method for preparing the aforementioned high-entropy die-cast magnesium-based alloy, comprising the following steps: S1. Melt the raw materials to obtain the first alloy melt; S2. Refine the first alloy melt to obtain the second alloy melt; S3. Cast the second alloy melt into an ingot to obtain a die-cast magnesium-based alloy.

[0027] In some possible implementations, S1 includes melting each raw material sequentially, stirring evenly, and keeping it at a constant temperature to ensure that each component is fully melted and uniformly mixed to form a first alloy melt.

[0028] In some possible implementations, in S1, the step of sequentially melting each raw material includes: first, melting magnesium ingots to obtain magnesium liquid; then adding aluminum ingots and zinc ingots to the magnesium liquid and melting them; then adding copper plates and nickel plates to dissolve and diffuse them; and finally adding magnesium-manganese master alloy to melt it.

[0029] The steps of sequentially melting each raw material follow the principle of "adding those with low melting point eutectic with magnesium first, and those with high melting point and easy oxidation later." Specifically, the order is as follows: First, add aluminum and zinc ingots. Al and Mg can form a low melting point eutectic, which helps the melting of subsequent elements. Zn has a low melting point and easily forms a low melting point phase with Mg and Al. Next, add copper and nickel plates. Since Cu and Ni have high melting points, the melt temperature needs to be appropriately increased to 740℃~750℃, and the mixture should be stirred thoroughly to accelerate dissolution and prevent the formation of refractory "hard lumps" that settle at the bottom of the crucible. Finally, add a magnesium-manganese master alloy. This is because Mn has high reactivity; directly adding pure Mn is difficult to dissolve and results in severe burn-off. Using a master alloy is the most effective way to introduce Mn. Optionally, the magnesium-manganese master alloy is Mg-30Mn master alloy.

[0030] In some possible implementations, in step S1, the step of uniform stirring includes: after all raw materials have been added, stirring at 730-750°C using a mechanical stirrer at a speed of 300-600 rpm for 10-15 minutes; the impeller penetrates deep into the lower part of the melt to ensure uniform composition of the upper and lower melt layers and accelerate the diffusion and dissolution of high-melting-point elements. For example, stirring at 730°C, 735°C, 740°C, 745°C, or 750°C using a mechanical stirrer at a speed of 300 rpm, 400 rpm, 500 rpm, or 600 rpm for 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, or 15 minutes.

[0031] In some possible implementations, in S1, the temperature for heat preservation and settling is 735~745℃, and the time is 5~15 min; heat preservation and settling allows the components to be further homogenized. For example, the temperature for heat preservation and settling is 735℃, 736℃, 737℃, 738℃, 739℃, 740℃, 741℃, 742℃, 743℃, 744℃, or 745℃, and the time is 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min, or 15 min.

[0032] In some possible implementations, in S1, the temperature at which the magnesium ingot is melted is 710~730°C; for example, it can be 710°C, 715°C, 720°C, 725°C or 730°C. In some possible implementations, in S1, the temperature at which the aluminum ingot and zinc ingot are added to melt is 710~730°C; for example, it can be 710°C, 715°C, 720°C, 725°C or 730°C. In some possible implementations, in S1, the temperature at which the copper and nickel plates dissolve and diffuse is 740~750°C; for example, it can be 740°C, 742°C, 745°C, 747°C or 750°C. In some possible implementations, in S1, the temperature at which the magnesium-manganese master alloy is added to melt is 740~750°C; for example, it can be 740°C, 742°C, 745°C, 747°C or 750°C. In some possible implementations, in S1, the mass percentage of Mn in the magnesium-manganese master alloy is 28-32%. For example, it could be 28%, 29%, 30%, 31%, or 32%.

[0033] In some possible implementations, S1 further includes a step of pre-treating the raw materials before melting them; In some possible implementations, in S1, the step of melting the raw materials is carried out in a mixture of CO2 and SF6; In some possible implementations, in S1, the pretreatment includes preheating the raw material to 150-200°C to remove surface moisture and prevent "splattering" accidents during melting. For example, preheating to 150°C, 160°C, 170°C, 180°C, 190°C, or 200°C.

[0034] The raw materials are melted using a graphite crucible or a steel crucible with a protective coating. After the raw materials are preheated, a mixture of CO2 and SF6 is introduced. The CO2 and SF6 react with the molten magnesium to form a dense protective film of MgO and MgF2 on the surface of the melt, which effectively prevents the magnesium from burning and oxidizing. The temperature is raised slowly so that the magnesium ingot is completely melted.

[0035] In some possible implementations, in S1, the volume ratio of CO2 to SF6 in the mixed gas is (65~200):1. Exemplary ratios could be 65:1, 70:1, 80:1, 90:1, 99:1, 100:1, 120:1, 140:1, 160:1, 180:1, or 200:1.

[0036] In some possible implementations, S2 includes: adding a refining agent to the first alloy melt, reacting for a period of time, and then slag removal; keeping it at a constant temperature for a period of time to obtain the second alloy melt.

[0037] For example, the refining agent could be RJ-2 refining agent specifically designed for magnesium alloys.

[0038] In some possible implementations, in S2, the refining agent is pressed into the first alloy melt to 1 / 2 to 2 / 3 of its depth (below the melt surface). In some possible implementations, in S2, after reacting for 5 to 8 minutes, the residue is removed; for example, the reaction time may be 5 minutes, 6 minutes, 7 minutes, or 8 minutes.

[0039] In some possible implementations, in step S2, the temperature for heat preservation and static setting is 735~745℃, and the time is 10~15 minutes. For example, the temperature for heat preservation and static setting is 735℃, 736℃, 737℃, 738℃, 739℃, 740℃, 741℃, 742℃, 743℃, 744℃, or 745℃, and the time is 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, or 15 minutes.

[0040] In some possible implementations, step S2, before adding the refining agent to the first alloy melt, further includes a step of preheating the refining agent to 280-320°C. Exemplarily, the temperature can be preheated to 280°C, 290°C, 300°C, 310°C, or 320°C.

[0041] In some possible implementations, the refining agent is placed inside a bell jar and preheated to approximately 280-320°C. At 735-745°C, the refining agent is slowly pressed into the melt to a depth of approximately 1 / 2 to 2 / 3 using the bell jar, and the bell jar is slowly moved within the molten pool for 5-8 minutes. During this time, the refining agent reacts with the melt, producing tiny bubbles. Gases and inclusions in the melt are adsorbed onto the surface of these bubbles and rise to the surface of the melt, forming scum. After refining, the melt is allowed to stand for 10-15 minutes, and then the scum on the surface of the melt is thoroughly and cleanly skimmed off until a smooth, mirror-like finish is achieved.

[0042] Example 1 This embodiment provides a high-entropy die-cast magnesium-based alloy, which, by mass percentage, includes the following components: Al 22%, Zn 11%, Cu 12%, Ni 9%, Mn 4%, unavoidable impurity elements, and the balance Mg.

[0043] The preparation method of the ultra-high fluidity high-entropy die-cast magnesium-based alloy in this embodiment includes the following steps: S1. Prepare raw materials according to the composition ratio, select magnesium ingots, aluminum ingots, zinc ingots, copper plates, nickel plates and Mg-30Mn master alloy with a purity of ≥99.9% (i.e., Mn element mass percentage is 30%), and preheat all raw materials to 180℃.

[0044] S2. After preheating the dried magnesium ingot in a graphite crucible, a CO2 and SF6 mixture with a volume ratio of 99:1 is introduced, and the temperature is slowly raised to 720°C to completely melt the magnesium ingot. Then, aluminum and zinc ingots are added and completely melted. The melt temperature is increased to 745°C, and copper and nickel plates are added to completely dissolve and diffuse. Finally, Mg-30Mn master alloy is added and completely melted. At 740°C, the mixture is stirred at 450 rpm for 12 minutes using a mechanical stirrer, and then held at that temperature for 10 minutes to ensure that all components are fully melted and uniformly mixed, thus obtaining the first alloy melt.

[0045] S3. Place the magnesium alloy RJ-2 refining agent into the bell jar and preheat it to about 300°C. At 740°C, use the bell jar to slowly press the refining agent into the melt to about 2 / 3 of its depth. Slowly move the bell jar in the molten pool for 6 minutes. Skim off the slag on the surface of the melt until it has a smooth mirror finish. Let the melt stand for 12 minutes to obtain a second alloy melt with the required composition.

[0046] S4. The second alloy melt is cast into an ingot to obtain a high-entropy die-cast magnesium-based alloy with ultra-high fluidity.

[0047] Example 2 This embodiment provides a high-entropy die-cast magnesium-based alloy, which, by mass percentage, includes the following components: Al 20%, Zn 12%, Cu 10%, Ni 10%, Mn 3%, unavoidable impurity elements, and the balance Mg.

[0048] The preparation method of the high-entropy die-cast magnesium-based alloy in this embodiment includes the following steps: S1. Prepare raw materials according to the composition ratio, select magnesium ingots, aluminum ingots, zinc ingots, copper plates, nickel plates and Mg-30Mn master alloy with a purity of ≥99.9% (i.e., Mn element mass percentage is 30%), and preheat all raw materials to 150℃.

[0049] S2. After preheating the dried magnesium ingot in a graphite crucible, a CO2 and SF6 mixed gas with a volume ratio of 199:1 is introduced, and the temperature is slowly raised to 710℃ to completely melt the magnesium ingot. Then, aluminum and zinc ingots are added and completely melted. The melt temperature is increased to 740℃, and then copper and nickel plates are added and completely dissolved and diffused. Finally, Mg-30Mn master alloy is added and completely melted. At 730℃, the mixture is stirred at 600 rpm for 10 minutes using a mechanical stirrer, and then held at that temperature for 15 minutes to ensure that all components are fully melted and uniformly mixed to obtain the first alloy melt.

[0050] S3. Place the magnesium alloy RJ-2 refining agent into the bell jar and preheat it to about 280°C. At 740°C, use the bell jar to slowly press the refining agent into the melt to about 1 / 2 of its depth. Slowly move the bell jar in the molten pool for 5 minutes. Skim off the slag on the surface of the melt until it has a smooth mirror finish. Let the melt stand for 15 minutes to obtain a second alloy melt with the required composition.

[0051] S4. The second alloy melt is cast into an ingot to obtain a high-entropy die-cast magnesium-based alloy with ultra-high fluidity.

[0052] Example 3 This embodiment provides a high-entropy die-cast magnesium-based alloy, which, by mass percentage, comprises the following components: Al 24%, Zn 10%, Cu 14%, Ni 8%, Mn 5%, unavoidable impurity elements, and the balance Mg.

[0053] The preparation method of the high-entropy die-cast magnesium-based alloy in this embodiment includes the following steps: S1. Prepare raw materials according to the composition ratio, select magnesium ingots, aluminum ingots, zinc ingots, copper plates, nickel plates and Mg-30Mn master alloy with a purity of ≥99.9% (i.e., Mn element mass percentage is 30%), and preheat all raw materials to 200℃.

[0054] S2. After preheating the dried magnesium ingot in a graphite crucible, a CO2 and SF6 mixed gas with a volume ratio of 66:1 is introduced, and the temperature is slowly raised to 730℃ to completely melt the magnesium ingot. Then, aluminum and zinc ingots are added and completely melted. The melt temperature is increased to 750℃, and then copper and nickel plates are added and completely dissolved and diffused. Finally, Mg-30Mn master alloy is added and completely melted. At 750℃, the mixture is stirred at 300 rpm for 15 minutes using a mechanical stirrer, and then held at that temperature for 5 minutes to ensure that all components are fully melted and uniformly mixed to obtain the first alloy melt.

[0055] S3. Place the magnesium alloy RJ-2 refining agent into the bell jar and preheat it to about 320°C. At 740°C, use the bell jar to slowly press the refining agent into the melt to a depth of about 2 / 3. Slowly move the bell jar in the molten pool for 8 minutes. Skim off the slag on the surface of the melt until it has a smooth mirror finish. After the melt has stood for 10 minutes, a second alloy melt with the required composition is obtained.

[0056] S4. The second alloy melt is cast into an ingot to obtain a high-entropy die-cast magnesium-based alloy with ultra-high fluidity.

[0057] Example 4 This embodiment provides a high-entropy die-cast magnesium-based alloy, which, by mass percentage, comprises the following components: Al 18%, Zn 14%, Cu 8%, Ni 12%, Mn 2%, unavoidable impurity elements, and the balance Mg.

[0058] The preparation method of the high-entropy die-cast magnesium-based alloy in this embodiment is the same as that in Example 1.

[0059] Example 5 This embodiment provides a high-entropy die-cast magnesium-based alloy, which, by mass percentage, comprises the following components: Al 26%, Zn 8%, Cu 16%, Ni 6%, Mn 6%, unavoidable impurity elements, and the balance Mg.

[0060] The preparation method of the ultra-high fluidity high-entropy die-cast magnesium-based alloy in this embodiment is the same as that in Example 1.

[0061] Example 6 This embodiment provides a high-entropy die-cast magnesium-based alloy with the same composition as in Example 1.

[0062] The preparation method of the ultra-high fluidity high-entropy die-cast magnesium-based alloy in this embodiment includes the following steps: S1. Prepare raw materials according to the composition ratio, select magnesium ingots, aluminum ingots, zinc ingots, copper plates, nickel plates and Mg-30Mn master alloy with a purity of ≥99.9% (i.e., Mn element mass percentage is 30%), and preheat all raw materials to 180℃.

[0063] S2. After preheating the dried magnesium ingot in a graphite crucible, a CO2 and SF6 mixture with a volume ratio of 99:1 is introduced, and the temperature is slowly raised to 720°C to completely melt the magnesium ingot. The melt temperature is then increased to 745°C, and copper and nickel plates are added to completely dissolve and diffuse them. The melt temperature is then lowered to 720°C, and aluminum and zinc ingots are added to completely melt them. Finally, the melt temperature is increased to 745°C, and Mg-30Mn master alloy is added to completely melt it. At 740°C, the mixture is stirred at 450 rpm for 12 minutes using a mechanical stirrer, and then held at that temperature for 10 minutes to ensure that all components are fully melted and uniformly mixed, thus obtaining the first alloy melt.

[0064] S3. Place the magnesium alloy RJ-2 refining agent into the bell jar and preheat it to about 300°C. At 740°C, use the bell jar to slowly press the refining agent into the melt to about 2 / 3 of its depth. Slowly move the bell jar in the molten pool for 6 minutes. Skim off the slag on the surface of the melt until it has a smooth mirror finish. Let the melt stand for 12 minutes to obtain a second alloy melt with the required composition.

[0065] S4. The second alloy melt is cast into an ingot to obtain a high-entropy die-cast magnesium-based alloy with ultra-high fluidity.

[0066] Comparative Example 1 This comparative example provides a conventional commercial die-cast magnesium alloy AZ91D, which, by mass percentage, comprises the following chemical composition: Al 9.1%, Zn 0.6%, Mn 0.3%, Be 0.002%, unavoidable impurity elements, and the balance Mg.

[0067] The traditional method for preparing the commercially available die-cast magnesium alloy AZ91D includes the following steps: S1. Prepare materials according to the formula composition, select magnesium ingots, aluminum ingots, zinc ingots with a purity of ≥99.9%, as well as Mg-30Mn master alloy (i.e., Mn element mass percentage of 30%) and Mg-5Be master alloy (i.e., Be element mass percentage of 5%), and preheat all raw materials to 180℃.

[0068] S2. After preheating the dried magnesium ingot in a graphite crucible, a CO2 and SF6 mixture with a volume ratio of 99:1 is introduced, and the temperature is slowly raised to 720°C to completely melt the magnesium ingot. Then, aluminum and zinc ingots are added and completely melted. Finally, the melt temperature is increased to 745°C, and Mg-30Mn and Mg-5Be master alloys are added and completely melted. At 740°C, the mixture is stirred at 450 rpm for 12 minutes using a mechanical stirrer, and then held at that temperature for 10 minutes to ensure that all components are fully melted and uniformly mixed, thus obtaining the first alloy melt.

[0069] S3. Place the magnesium alloy RJ-2 refining agent into the bell jar and preheat it to about 300°C. At 740°C, use the bell jar to slowly press the refining agent into the melt to about 2 / 3 of its depth. Slowly move the bell jar in the molten pool for 6 minutes. Skim off the slag on the surface of the melt until it has a smooth mirror finish. Let the melt stand for 12 minutes to obtain a second alloy melt with the required composition.

[0070] S4. The second alloy melt is cast into an ingot to obtain the conventional commercial die-cast magnesium alloy AZ91D.

[0071] Comparative Example 2 This comparative example provides a magnesium-based alloy comprising, by mass percentage: Al 17%, Zn 15%, Cu 7%, Ni 13%, Mn 1%, unavoidable impurity elements, and the balance Mg.

[0072] The preparation method of this comparative magnesium-based alloy is the same as that in Example 1.

[0073] Comparative Example 3 This comparative example provides a magnesium-based alloy comprising, by mass percentage: Al 27%, Zn 7%, Cu 17%, Ni 5%, Mn 6%, unavoidable impurity elements, and the balance Mg.

[0074] The preparation method of this comparative magnesium-based alloy is the same as that in Example 1.

[0075] Test case The casting fluidity of the ultra-high fluidity high-entropy die-cast magnesium-based alloys prepared in Examples 1-6, the conventional commercial die-cast magnesium alloy AZ91D prepared in Comparative Example 1, and the magnesium-based alloys prepared in Comparative Examples 2 and 3 were compared and tested. The test method was based on the spiral mold recognized in the industry and the test method was based on the provisions of "Casting Handbook Volume 3 Casting Nonferrous Alloys". The test results are shown in Table 1.

[0076] The test results are shown in Table 1 and Figure 1 .

[0077] Table 1

[0078] As shown in Table 1, the ultra-high fluidity high-entropy die-casting magnesium-based alloy obtained by this invention exhibits excellent casting fluidity. This is attributed to the synergistic effect of alloying elements Zn, Cu, Ni, and Mn with Al, which forms a melt with high mixing entropy. This significantly reduces the alloy's liquidus temperature, greatly narrows the solidification temperature range, and substantially reduces the melt viscosity. The flow distance (i.e., the length of the flow sample) is significantly higher than that of the comparative conventional commercial die-casting magnesium alloy AZ91D. The ultra-high fluidity high-entropy die-casting magnesium-based alloy can achieve a filling distance at 700°C that is more than twice that of the conventional AZ91 die-casting magnesium alloy.

[0079] The above embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention.

Claims

1. A high-entropy die-cast magnesium-based alloy, characterized in that, By mass percentage, it includes: Al 18%~26%, Zn 8%~14%, Cu 8%~16%, Ni 6%~12%, Mn 2%~6%, with the balance being Mg and unavoidable impurities.

2. The high-entropy die-cast magnesium-based alloy according to claim 1, characterized in that, At least one of the following conditions must be met: （1）Al 20%~24%； (2) Zn 10%~12%; (3) Cu 10%~14%; (4) Ni 8%~10%; (5) Mn 3%~5%.

3. A method for preparing the high-entropy die-cast magnesium-based alloy according to claim 1 or 2, characterized in that, Includes the following steps: S1. Melt the raw materials to obtain the first alloy melt; S2. Refine the first alloy melt to obtain the second alloy melt; S3. Cast the second alloy melt into an ingot to obtain a die-cast magnesium-based alloy.

4. The method for preparing high-entropy die-cast magnesium-based alloy according to claim 3, characterized in that, S1 includes melting each raw material sequentially, stirring evenly, keeping it at a constant temperature, and forming a first alloy melt.

5. The method for preparing high-entropy die-cast magnesium-based alloy according to claim 4, characterized in that, At least one of the following conditions must be met: (1) The step of melting each raw material in sequence includes: first, melting magnesium ingots to obtain magnesium liquid; then adding aluminum ingots and zinc ingots to the magnesium liquid and melting them; then adding copper plates and nickel plates to dissolve and diffuse them; and finally adding magnesium-manganese master alloy to melt it. (2) The step of mixing evenly includes: after all raw materials are added, stirring at 730~750℃ using a mechanical stirrer at a speed of 300~600rpm for 10~15min; (3) The temperature for heat preservation and static setting is 735~745℃ and the time is 5~15min.

6. The method for preparing high-entropy die-cast magnesium-based alloy according to claim 5, characterized in that, At least one of the following conditions must be met: (1) The temperature at which the magnesium ingot is melted is 710~730℃; (2) The melting temperature of aluminum ingots and zinc ingots is 710~730℃; (3) The dissolution and diffusion temperature of the copper and nickel plates is 740~750℃; (4) The melting temperature of the magnesium-manganese master alloy is 740~750℃; (5) The mass percentage of Mn in the magnesium-manganese master alloy is 28-32%.

7. The method for preparing high-entropy die-cast magnesium-based alloy according to any one of claims 3-6, characterized in that, Before melting the raw materials, the process also includes a pretreatment step for the raw materials; And / or, the step of melting the raw materials is carried out in a mixture of CO2 and SF6.

8. The method for preparing high-entropy die-cast magnesium-based alloy according to claim 7, characterized in that, The pretreatment includes preheating the raw material to 150~200°C; And / or, the volume ratio of CO2 to SF6 in the mixed gas is (65~200):

1.

9. The method for preparing high-entropy die-cast magnesium-based alloy according to any one of claims 3-6, characterized in that, S2 includes: adding a refining agent to the first alloy melt, reacting for a period of time, and then removing slag; keeping it at a constant temperature for a period of time to obtain the second alloy melt.

10. The method for preparing high-entropy die-cast magnesium-based alloy according to claim 9, characterized in that, At least one of the following conditions must be met: (1) Press the refining agent into the first alloy melt to a depth of 1 / 2 to 2 / 3; (2) After reacting for 5-8 minutes, remove the residue; (3) In S2, the temperature for heat preservation and static setting is 735~745℃ and the time is 10~15min; (4) Before adding the refining agent to the first alloy melt, the step of preheating the refining agent to 280~320°C is also included.

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