A high strength specific Mg-Y-Zn-Si-Li-Al alloy and a preparation method thereof

Abstract

The application discloses a high-strength and high-plasticity Mg-Y-Zn-Si-Li-Al alloy and a preparation method thereof, and relates to the technical field of light alloy processing. 97.5 Y1Zn 0.5 In the Mg 97.5 Y1Zn 0.5 Si1base alloy, the Si element is combined with the Y element to form a YSi hard and brittle phase, which is easy to hinder the elongation of the alloy; the addition of the Li element plays a grain refining role on the one hand, effectively improves the strength of the alloy, and optimizes the second phase form on the other hand, promotes the transformation of the second phase to the nanometer level, provides more slip paths for dislocation movement, and avoids plasticity deterioration; the Al element is further combined with the Y element to form a high-strength Al2Y strengthening phase, which not only reduces the precipitation of the hard and brittle phase, but also stabilizes the organizational structure through the pinning effect at the grain boundary.

Description

Technical Field

[0001] This application belongs to the field of light alloy processing technology, and in particular relates to a high strength-ductility-product Mg-Y-Zn-Si-Li-Al alloy and its preparation method. Background Technology

[0002] Strength-ductility product is a core indicator for measuring the balance between strength and ductility in a material. The higher the value, the stronger the material's resistance to fracture and impact under load, and the better its service safety and reliability. Magnesium alloys, as lightweight engineering materials, are increasingly in demand in the industrial field. However, traditional commercial magnesium alloys generally suffer from low strength-ductility product, making them prone to brittle fracture during service and unable to meet the stringent requirements of high-end equipment for a good balance of strength and toughness.

[0003] In existing technologies, although researchers have improved the absolute strength of magnesium alloys through alloying and processing optimization, with the tensile strength of some high-performance magnesium alloys exceeding 500 MPa, most suffer from a poor balance between strength and ductility—ductility decreases significantly with increasing strength, and the strength-ductility product remains at a low level. This greatly limits the application of magnesium alloys in high-end load-bearing structural components. To improve the strength-toughness balance of magnesium alloys, adding rare earth elements to Mg-RE-Zn alloys to form long-period stacked ordered phases (LPSO phases) has become an important technical direction. While magnesium rare earth alloys containing LPSO phases can achieve some improvement in strength and ductility, the modification effect of single rare earth alloying is limited, and the increase in strength-ductility product still cannot meet industrial demands.

[0004] Building upon this foundation, researchers have attempted to modify magnesium alloys through alloying with elements such as Si, Li, and Al. They discovered that Si can form a high-strength second phase and improve melt fluidity, Li can regulate the electron concentration in the matrix, refine grains, and improve plasticity, while Al can form a strengthening phase with rare earth elements, promote dynamic recrystallization, and increase alloy elongation. However, existing technologies mostly involve the simple addition of single or two elements, and a systematic alloying scheme with stepwise composite addition of Si, Li, and Al has not yet been developed. Furthermore, a hot extrusion process that maximizes the strength-ductility product has not been developed to match the compositional characteristics of multi-element composite alloying. A systematic technical solution for preparing high-strength-ductility-product magnesium alloys through synergistic modification via multi-element alloying combined with precise process control is lacking.

[0005] Meanwhile, hot extrusion forming is a key processing method for improving the mechanical properties of magnesium alloys. Process parameters such as extrusion temperature, extrusion ratio, and extrusion speed have a significant impact on the alloy grain size, second-phase distribution, and degree of dynamic recrystallization. If the process parameters are not properly matched, it will lead to a loss of alloy strength or plasticity, and the optimal improvement of the strength-ductility product cannot be achieved. Summary of the Invention

[0006] To address some or all of the technical problems existing in the prior art, this application provides a high-strength, high-ductility Mg-Y-Zn-Si-Li-Al alloy and its preparation method.

[0007] This application provides a high-strength, high-ductility Mg-Y-Zn-Si-Li-Al alloy, with magnesium as the matrix. Its chemical composition, by atomic percentage, includes: Y: 1 at.%, Zn: 0.5 at.%, Si: 1 at.%, with the balance being Mg and unavoidable impurities. The microstructure of the alloy contains long-period stacked ordered phases and intermetallic compound phases containing yttrium and silicon.

[0008] Preferably, the alloy further comprises Li: 1 at.%, forming Mg 96.5 Y1Zn 0.5 The Si1Li1 alloy system; the addition of Li element causes the second phase in the alloy to transform to the nanoscale and refines the matrix grains.

[0009] Preferably, the alloy further comprises Al: 1 at.%, forming Mg 95.5 Y1Zn 0.5 The Si1Li1Al1 alloy system: Al combines with Y to form the Al2Y strengthening phase, which is distributed at the grain boundaries.

[0010] A method for preparing a high-strength, high-ductility Mg-Y-Zn-Si-Li-Al alloy includes the following steps: Step S1: Raw material pretreatment: Distribute materials according to the target composition, remove oxide scale from magnesium raw materials, seal and protect easily oxidized lithium and powdered silicon, and preheat all raw materials, covering agents and refining agents. Step S2: Melting into alloy ingots: Under inert gas protection, magnesium is melted first and a covering agent is added. Then magnesium-yttrium master alloy, zinc and sealed silicon are added in sequence. After complete melting, lithium and aluminum are added step by step according to the composition requirements. After refining and heat preservation, the ingots are cast. Step S3: Homogenization heat treatment: The ingot is heat-treated at a temperature of ≥500℃ to eliminate compositional segregation and refine the as-cast structure, and then cooled in the furnace. Step S4: Hot extrusion deformation: The processed ingot is processed into a sample. The mold and sample are preheated at a preset temperature. Then, the sample is hot extruded using an extrusion device at a set extrusion ratio and extrusion speed to obtain an extruded alloy with high strength-ductility product.

[0011] Preferably, in step S2, after adding silicon powder, it is necessary to stir thoroughly; after each addition, it is necessary to remove the slag and add a covering agent again for covering and protection.

[0012] Preferably, in step S4, the preset temperature for heat preservation and preheating is 360°C, the extrusion ratio is 25:1, the extrusion speed is 0.4mm / s, and the extrusion angle is 30°.

[0013] The high-strength, high-ductility Mg-Y-Zn-Si-Li-Al alloy and its preparation method presented in this application have the following advantages and positive effects: (1) A development scheme for high-strength, high-ductility magnesium alloys with compatible composition and process was constructed, achieving a significant step-by-step improvement in strength and ductility. Using Mg... 97.5 Y1Zn 0.5 Based on the Si1 alloy, a composite alloying strategy of adding Li and Al elements in stages was adopted to precisely control the alloy microstructure and properties: the initial strength-ductility product of the base alloy was 3.6 GPa·%, which was increased to 4.9 GPa·% after adding Li. After further adding Al, the strength-ductility product reached a maximum value of 6.57 GPa·%, forming a clear performance improvement gradient. This provides a new idea and feasible path for the composition design and performance optimization of high-performance magnesium alloys.

[0014] (2) The mechanism by which multi-element alloying synergistically enhances strength and plasticity was clarified, achieving a synergistic match between strength and plasticity. In Mg 97.5 Y1Zn 0.5 In Si1 base alloys, Si and Y combine to form the YSi hard and brittle phase, which acts as a stress concentration point and hinders the improvement of alloy elongation. The addition of Li plays a role in grain refinement, effectively improving the strength of the alloy. On the other hand, it optimizes the morphology of the second phase, promoting its transformation to the nanoscale, providing more slip paths for dislocation movement and avoiding plasticity deterioration. Al further combines with Y to form a high-strength Al2Y strengthening phase, which not only reduces the precipitation of the hard and brittle phase, but also stabilizes the microstructure through the pinning effect at grain boundaries, ultimately achieving a significant improvement in the strength-ductility product of the alloy. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for further understanding of the embodiments of this application and constitute a part of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 Tensile property curves of different types of extruded alloys of this application; Figure 2 Optical micrographs of different types of extruded alloys of this application; Figure 3 For the Mg of this application 97.5 Y1Zn0.5 EDS spectrum of Si1 extruded alloy; Figure 4 For the Mg of this application 95.5 Y1Zn 0.5 EDS spectrum of Si1Li1Al1 extruded alloy. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0017] This application provides a high-strength, high-ductility Mg-Y-Zn-Si-Li-Al alloy, with magnesium as the matrix. The core components, by atomic percentage, are Y: 1 at.%, Zn: 0.5 at.%, Si: 1 at.%, with the balance being Mg and unavoidable impurities. The alloy's microstructure naturally forms long-period stacked ordered phases and intermetallic compound phases containing yttrium and silicon, providing fundamental strength and toughness. Based on this, Li: 1 at.%, Al: 1 at.%, are added stepwise to form Mg... 97.5 Y1Zn 0.5 Si1, Mg 96.5 Y1Zn 0.5 Si1Li1, Mg 95.5 Y1Zn 0.5 In the Si1Li1Al1 alloy system, the addition of Li can transform the second phase in the alloy to the nanoscale and refine the matrix grains, thereby improving both strength and plasticity. Al combines with Y to form the Al2Y strengthening phase, which is distributed at the grain boundaries, reducing the precipitation of hard and brittle phases while pinning the grain boundaries, ultimately achieving a significant step-by-step increase in the strength-plasticity product of the alloy.

[0018] This embodiment focuses on the preparation and performance testing of the three alloy systems mentioned above. The composition design of the three alloys revolves around the morphological control of the second phase and the precise formation of the strengthening phase. Synergistic modification effects of each element are achieved through the stepwise addition of Li and Al elements, thereby realizing the gradient optimization of the strength-ductility product of the alloy. The high strength-ductility product Mg-Y-Zn-Si-Li-Al alloy of this application is prepared by the following method, and the alloy billet, extrusion, microstructure, and performance characteristics formed during the preparation process can be obtained through... Figures 1 to 4 Visual representation: Step S1: Raw material pretreatment Based on the target atomic percentages of the three alloys, the atomic ratios were converted into mass percentages to accurately calculate the amount of raw materials required. Magnesium ingots, zinc blocks, silicon powder, lithium blocks, and aluminum blocks with a purity ≥99.99 wt.%, as well as a magnesium-yttrium master alloy (Mg-30 wt.% Y), were selected as raw materials. High-purity raw materials can effectively avoid the adverse effects of impurity elements on the alloy structure and properties, ensuring the purity of the alloy melt and laying the foundation for the subsequent preparation of high-performance magnesium alloys. Compared with directly adding pure yttrium, the use of magnesium-yttrium master alloy makes it easier to achieve uniform dissolution of yttrium in the magnesium melt, avoiding the compositional segregation problem caused by the high melting point and slow dissolution of pure yttrium.

[0019] The magnesium ingot surface is thoroughly polished to remove adhering oxide scale and impurities, preventing these impurities from entering the melt during smelting and forming inclusions and other defects that affect alloy quality. Considering the characteristics of silicon powder (which is easily oxidized due to its powdery nature) and lithium blocks (which are chemically reactive and readily react with air), the silicon powder is tightly wrapped and sealed with tin foil, and the lithium blocks undergo a special anti-oxidation sealing treatment to prevent oxidation and failure of both before and during smelting. All the treated raw materials are placed in a drying oven for preheating. Preheating effectively removes adsorbed moisture from the raw material surface, preventing the reaction of moisture with the magnesium melt during smelting to produce hydrogen gas, which could lead to defects such as porosity and looseness in the alloy casting. Simultaneously, the smelting salt covering agent is ground into powder and placed in the drying oven for simultaneous preheating along with the refining agent. Furthermore, the crucible and tools used for smelting, slag removal, and stirring also need to be preheated to prevent a sudden drop in localized temperature of the melt when the low-temperature covering agent, refining agent, and tools come into contact with the high-temperature magnesium melt, thus affecting the melt's fluidity and the uniformity of alloy element dissolution.

[0020] Step S2: Melt into alloy ingots The preheated crucible is placed in a box-type resistance furnace, the furnace temperature is set to 500℃ and the heating program is started. After the temperature is reached, the preheated magnesium ingot is added to the crucible. Then, a layer of preheated salt covering agent is evenly sprinkled on the surface of the magnesium ingot. After closing the furnace lid, high-purity argon gas is immediately introduced into the furnace. Through the composite protection method of "salt covering agent + high-purity argon gas", a double protection is formed from two dimensions: the surface of the melt and the atmosphere of the furnace, which completely prevents the oxidation and combustion of the high-temperature magnesium melt and ensures the purity of the magnesium melt.

[0021] The resistance furnace temperature was then raised to 720℃ and held for 20 minutes. This temperature and holding time ensured that the magnesium ingot melted smoothly and completely, preventing splashing of the molten magnesium due to rapid heating, and ensuring uniform temperature of the melt without local overheating or incomplete melting. After the magnesium ingot was completely melted, a special slag removal tool was used to remove impurities such as slag and oxide slag from the surface of the melt. Then, the preheated magnesium-yttrium master alloy and zinc block were added to the magnesium melt. The furnace temperature was raised to 750℃ and held for 10 minutes. This temperature is the optimal melting temperature for the magnesium-yttrium master alloy and zinc block. The 10-minute holding time ensured that the two were fully melted and uniformly mixed with the magnesium melt, effectively preventing component segregation.

[0022] After the heat preservation is completed, slag removal is performed again to remove impurities that precipitate in the melt due to temperature changes. Then, silicon powder wrapped and sealed with tin foil is added, and the mixture is stirred thoroughly in the same direction with a graphite stirring rod until the silicon powder is completely melted, so that the silicon element is uniformly mixed with the melt. After stirring, a covering agent is spread on the surface of the melt again, the furnace temperature is reduced to 650℃ and held for 10 minutes to provide suitable thermodynamic conditions for the silicon element to combine with yttrium element to form an intermetallic compound phase containing yttrium and silicon.

[0023] For Mg that requires the addition of Li 96.5 Y1Zn 0.5 Si1Li1 alloy and Mg 95.5 Y1Zn 0.5 For the Si1Li1Al1 alloy, after the silicon powder is melted and held at a certain temperature, slag is removed again. Sealed lithium blocks are then added to the melt, and a covering agent is evenly sprinkled in. The furnace temperature is then raised to 750℃ and held for 10 minutes to ensure the lithium blocks are fully melted and uniformly mixed with the melt. For Mg alloys requiring Al addition... 95.5 Y1Zn 0.5 After the lithium block melts and is kept at a constant temperature, the slag is skimmed off, pure aluminum blocks are added and a covering agent is sprinkled on them. The furnace temperature is maintained at 750℃ and held for 10 minutes to ensure that the aluminum blocks are fully melted and react with yttrium to form the Al2Y phase.

[0024] After all alloying elements were added, the furnace temperature was lowered to 730℃ for refining. A preheated refining agent was evenly sprinkled onto the surface of the melt to degas and remove impurities, further improving the purity of the magnesium alloy melt. After refining, the furnace temperature was raised to 750℃ and held for 20 minutes to further homogenize the melt composition and allow gases and impurities to rise to the surface. The melt was then poured into a metal mold and cooled to obtain an alloy ingot. All the above smelting steps were carried out in a box-type resistance furnace under an argon atmosphere, with an inert atmosphere protection throughout to prevent secondary oxidation of the melt. After each addition of alloying elements, slag was removed and a covering agent was added again to ensure the melt remained under protective conditions throughout the process.

[0025] Step S3: Homogenization heat treatment The three alloy ingots obtained from casting were placed in a heat treatment furnace and heated to 500℃ for homogenization heat treatment. After holding at this temperature for 10 hours, they were cooled with the furnace. The heat treatment temperature of 500℃ is the optimal homogenization temperature for the Mg-Y-Zn-Si-Li-Al alloy system. This temperature can effectively eliminate the compositional segregation and microstructure inhomogeneity problems that occur during the casting process, and also avoid grain coarsening caused by excessively high temperatures. The 10-hour holding time ensures that the composition of the ingot is homogenized from the surface to the core, allowing the second phase to fully dissolve and distribute evenly. At the same time, it refines the as-cast grains, improves the plastic deformation capacity of the ingot, and lays a good microstructure foundation for subsequent hot extrusion forming, avoiding forming defects such as cracks and peeling during the extrusion process.

[0026] Step S4: Hot extrusion deformation The three alloy ingots after homogenization heat treatment were respectively processed into cylindrical specimens with a height of 25 mm and a diameter of 38.5 mm. The specimens of this size are highly matched with the subsequent extrusion process parameters, which can ensure that the alloys obtain sufficient plastic deformation during extrusion and avoid problems such as excessive extrusion pressure or uneven deformation caused by unreasonable specimen size. Then, the surface of the specimens was polished with sandpaper to remove the oxide scale and burrs on the surface to prevent surface defects from causing problems such as peeling and cracking in the extruded parts during extrusion.

[0027] This extrusion process employed a vertical extrusion press, equipped with an extrusion die, extrusion gasket, extrusion rod, and extrusion sleeve. An extrusion die with an extrusion ratio of 25:1 was selected. The working surface of the die was smoothed with sandpaper to reduce frictional resistance between the die and the sample during extrusion, ensuring the surface quality of the extruded part. The smoothed die was placed in the sleeve and heated to 360℃ for 2 hours to ensure uniform die temperature. This prevented a sudden drop in sample surface temperature due to temperature differences between the die and the sample during extrusion, which could affect extrusion formability and surface quality. Simultaneously, the cylindrical sample was placed in a heat treatment furnace and heated to 360℃ for 1 hour. This preheating temperature, consistent with the extrusion temperature, ensured uniform internal sample temperature, preventing uneven plastic deformation due to temperature differences between the inside and outside of the sample during extrusion. Furthermore, 360℃ is the optimal hot extrusion temperature for this alloy series. At this temperature, the alloy exhibits strong dynamic recrystallization ability, moderate resistance to plastic deformation, and is less prone to extrusion cracks. The 1-hour preheating time ensured that the sample reached the preset temperature from the surface to the core, guaranteeing good temperature uniformity.

[0028] After preheating the mold and sample, the sample is quickly placed into the extrusion mold and hot-extruded at an extrusion speed of 0.4 mm / s and an extrusion angle of 30°. The low extrusion speed of 0.4 mm / s ensures that the alloy has sufficient time for dynamic recrystallization during the extrusion process, refining the grains and optimizing the distribution of the second phase, while avoiding stress concentration caused by excessive extrusion speed. The 30° extrusion angle optimizes the flow direction of the metal and further improves the uniformity of the microstructure of the extruded part. After extrusion, a circular extruded bar with a diameter of 5.2 mm is obtained directly. The extruded bar is then naturally cooled to room temperature and sealed for storage to prevent surface oxidation.

[0029] After extrusion, the extruded alloy bars are visually inspected. Figure 1 The tensile property curves of the different extruded alloys in this application clearly show that after the above-mentioned hot extrusion process, all three alloys produced round extruded bars with regular dimensions and smooth surfaces, free from forming defects such as cracks, peeling, dents, and uneven deformation. This indicates that the composition system designed in this application is highly matched with the hot extrusion process parameters of 360℃ extrusion temperature and 25:1 extrusion ratio. The alloys have excellent extrusion formability and good process stability, and can produce extruded parts with excellent surface quality. At the same time, the stress-strain curves in the figure clearly show the changes in the tensile properties of the three alloys. With the stepwise addition of Li and Al elements, the plasticity of the alloys shows a significant upward trend, while the strength remains at a reasonable level, achieving a synergistic match between strength and plasticity, laying a performance foundation for improving the strength-plasticity product.

[0030] The prepared extruded alloy rods were subjected to metallographic sample preparation and microstructure characterization. Figure 2 As can be seen from the optical microstructure photographs of different types of extruded alloys in this application, the images correspond sequentially to Mg. 97.5 Y1Zn 0.5 Si1, Mg 96.5 Y1Zn 0.5 Si1Li1, Mg 95.5 Y1Zn 0.5 The microstructure of Si1Li1Al1 alloy, Mg without added Li and Al 97.5 Y1Zn 0.5 The Si1 alloy has a relatively large grain size and contains some hard and brittle phase aggregates. After adding Li, the alloy grains are significantly refined, and the second phase is uniformly distributed in the matrix at the nanoscale. After further adding Al, the alloy grains are further refined, and obvious Al2Y reinforcing phase pinning is visible at the grain boundaries. The uniformity of the structure is greatly improved, which proves that the stepwise addition of Li and Al can effectively achieve grain refinement and second phase control. This is the core microstructure reason for the improvement of the strength-ductility product of the alloy.

[0031] For Mg 97.5 Y1Zn0.5 EDS surface scan analysis was performed on the extruded microstructure of Si1 alloy, from... Figure 3 Mg in this application 97.5 Y1Zn 0.5 The EDS spectrum of the Si1 extruded alloy shows that magnesium, yttrium, zinc, and silicon are uniformly distributed in the alloy structure. Yttrium and silicon are enriched in specific regions, forming obvious intermetallic compound phases containing yttrium and silicon. This verifies that the hard and brittle phase is the main second phase of the basic alloy system. It also proves that the smelting and extrusion process of this application can ensure the uniform distribution of alloy elements and that there is no obvious compositional segregation.

[0032] For Mg 95.5 Y1Zn 0.5 EDS surface scan analysis was performed on the extruded microstructure of the Si1Li1Al1 alloy. Figure 4 Mg in this application 95.5 Y1Zn 0.5 The EDS spectrum of the Si1Li1Al1 extruded alloy shows that aluminum and yttrium are co-enriched at the grain boundaries to form the Al2Y strengthening phase, while lithium is uniformly distributed in the magnesium matrix, which refines the matrix grains. At the same time, the enrichment areas of silicon and yttrium are significantly reduced, and the precipitation of hard and brittle phases is effectively suppressed. This proves that the addition of Al can effectively combine with Y to form a strengthening phase, reduce the precipitation of hard and brittle phases, and thus achieve a significant improvement in the plasticity of the alloy. It also verifies the scientific nature of the composition design and the effectiveness of the synergistic modification of each element in this application.

[0033] Mechanical properties of three extruded alloy bars were tested, and the results showed that Mg 97.5 Y1Zn 0.5 The Si1 alloy has a tensile strength of 212 MPa, a yield strength of 180 MPa, an elongation of 17%, and a strength-ductility product of 3.6 GPa·s. The addition of Li to Mg... 96.5 Y1Zn 0.5 The tensile strength of the Si1Li1 alloy is increased to 245 MPa, the yield strength to 189 MPa, the elongation to 20%, and the strength-ductility product to 4.9 GPa·s. Further addition of Al to Mg... 95.5 Y1Zn 0.5 The Si1Li1Al1 alloy exhibits a significant increase in elongation to 28.7%, while maintaining a tensile strength of 229 MPa and a yield strength of 139 MPa. The strength-ductility product reaches a peak of 6.57 GPa·%, representing a substantial, stepwise increase in strength-ductility product. These test results are highly consistent with the microstructure characterization results, demonstrating that the stepwise addition of Li and Al achieves a synergistic modification effect among the elements, significantly improving ductility while maintaining alloy strength, ultimately resulting in a high-strength-ductility-product Mg-Y-Zn-Si-Li-Al alloy.

[0034] In summary, this application, based on the Mg-Y-Zn-Si system, successfully developed a Mg-Y-Zn-Si-Li-Al alloy with both high strength and high plasticity through a stepwise composite addition of Li and Al, combined with a preparation process of "inert atmosphere melting - homogenization heat treatment - adaptable hot extrusion," achieving a significant improvement in the strength-plasticity product. This technical solution effectively controls the alloy's microstructure, refines grains, and optimizes the second-phase morphology by leveraging the synergistic modification effect of each element. Simultaneously, the preparation process is stable and controllable, without cumbersome procedures or special equipment requirements, making it suitable for large-scale industrial production. This provides a novel approach and technical route for the development and application of high-performance magnesium alloys.

[0035] It should be noted that, unless otherwise expressly specified and limited, the term "connection" or its synonyms should be interpreted broadly in this document. For example, "connection" can be a fixed connection or a detachable connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal communication of two elements or the interaction between two elements. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances. Furthermore, expressions such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. At the same time, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. In addition, the terms "front," "rear," "left," "right," "upper," and "lower" in this document refer to the placement states shown in the accompanying drawings.

[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A high-strength, high-ductility Mg-Y-Zn-Si-Li-Al alloy, characterized in that, With magnesium as the matrix, its chemical composition by atomic percentage includes: Y: 1 at.%, Zn: 0.5 at.%, Si: 1 at.%, Li: 1 at.%, Al: 1 at.%, with the balance being Mg and unavoidable impurities; the microstructure of the alloy contains long-period stacked ordered phases and intermetallic compound phases containing yttrium and silicon; Al element combines with Y to form Al2Y reinforcing phase, which is distributed at the grain boundaries.

2. A method for preparing the high-strength, high-ductility Mg-Y-Zn-Si-Li-Al alloy according to claim 1, characterized in that, Includes the following steps: Step S1: Raw material pretreatment: Distribute materials according to the target composition. Based on the target atomic percentage of the alloy, convert the atomic ratio to the mass percentage and accurately calculate the amount of raw materials to be used. Select magnesium ingots, zinc blocks, silicon powder, lithium blocks, aluminum blocks, and magnesium-yttrium master alloy with a purity ≥99.99wt.% as raw materials. Remove the oxide scale from the magnesium raw materials. Seal and protect the easily oxidized lithium and powdered silicon. Tightly wrap and seal the silicon powder with tin foil. Perform special anti-oxidation sealing treatment on the lithium blocks. Place all raw materials in a drying oven for preheating. At the same time, grind the smelting salt covering agent into powder and place it in the drying oven together with the refining agent for synchronous preheating. Step S2: Melting into alloy ingots: Under the protection of high-purity argon gas, magnesium is melted in a resistance furnace at 500℃, and a salt covering agent is added. The furnace temperature is then raised to 720℃ and held for 20 minutes. This temperature and holding time ensure that the magnesium ingot melts smoothly and completely. Magnesium-yttrium master alloy and zinc blocks are then added sequentially, and the furnace temperature is raised to 750℃ and held for 10 minutes. Sealed silicon is added, and after complete melting, lithium and aluminum are added in steps according to the composition requirements. After refining and holding, the mixture is cast into ingots. After adding silicon powder, it is necessary to use a graphite stirring rod to stir thoroughly in the same direction until the silicon powder is completely melted, so that the silicon element is uniformly mixed with the melt. After each addition, slag must be removed and a salt covering agent must be added again for protection. After stirring with silicon powder, a covering agent is applied again to the surface of the melt, and the furnace temperature is lowered to 650℃ and held for 10 minutes. Step S3: Homogenization heat treatment: The ingot is heat-treated at a temperature of ≥500℃ to eliminate compositional segregation and refine the as-cast structure. After holding at the temperature for 10 hours, it is cooled with the furnace. Step S4: Hot extrusion deformation: The treated ingot is processed into a sample, and the surface of the sample is polished with sandpaper until smooth to remove the oxide scale and burrs. An extrusion die with an extrusion ratio of 25:1 was selected, and the working surface of the die was polished smooth with sandpaper. The polished extrusion die was placed in a sleeve, heated to 360℃ and held for 2 hours to ensure that the die temperature was completely uniform. At the same time, the sample was placed in a heat treatment furnace, heated to 360℃ and held for 1 hour. After the extrusion die and the sample were preheated, the sample was quickly placed into the extrusion die, and then hot extrusion was performed using an extrusion device at an extrusion speed of 0.4 mm / s and an extrusion angle of 30°. After natural cooling at room temperature, the sample was sealed and stored to prevent surface oxidation, thus obtaining an extruded alloy with high strength-ductility product.

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