A dual heterostructure Mg-Y-Ni alloy and a preparation method thereof

Abstract

This application discloses a dual heterostructure Mg-Y-Ni alloy and its preparation method, relating to the field of high-performance magnesium alloy preparation technology. The alloy uses Mg as the matrix element, with Y and Ni added as alloying elements, wherein the atomic ratio of Y to Ni is 0.5~1.5, and the balance is Mg and unavoidable trace impurities. This dual heterostructure Mg-Y-Ni alloy and its preparation method construct a dual heterostructure in the magnesium alloy, combining a two-phase structure of "high-hardness LPSO phase / high-toughness α-Mg magnesium matrix" with a mixed-grain structure of "unrecrystallized hard coarse-grained region / recrystallized soft fine-grained region." This structure can overcome the bottleneck of traditional magnesium alloys where "increased strength and modulus inevitably lead to decreased plasticity," by utilizing the strengthening effect generated by the synergistic deformation of the soft and hard regions. It achieves simultaneous optimization of alloy strength, plasticity, and elastic modulus, resulting in comprehensive mechanical properties superior to existing Mg-Y-Ni alloys with only a single heterostructure.

Description

Technical Field

[0001] This application belongs to the field of high-performance magnesium alloy preparation technology, and particularly relates to a dual heterostructure Mg-Y-Ni alloy and its preparation method. Background Technology

[0002] Magnesium alloys are currently the lowest density metallic structural materials used in industrial applications. With their outstanding lightweight advantages, they possess irreplaceable application value and broad industrial prospects in the fields of weight reduction and efficiency improvement for high-end equipment such as aerospace, rail transportation, and new energy vehicles. However, compared with maturely used aluminum and titanium alloys, commercially available magnesium alloys have inherent performance shortcomings that are difficult to overcome. Their absolute strength is relatively low, their room temperature plasticity is poor, and their elastic modulus is insufficient. Furthermore, there is a significant inverse relationship between strength and plasticity, and between strength and elastic modulus, making it impossible to achieve synergistic improvement among these three properties. This core technological bottleneck severely limits the large-scale application of magnesium alloys in key load-bearing components of equipment and has become an industry challenge restricting the development of high-performance magnesium alloy materials.

[0003] In recent years, heterostructure design has provided a novel technological path for overcoming the bottlenecks in the mechanical properties of metallic materials. By controlling composition and optimizing fabrication processes, heterogeneous regions are constructed within the matrix. Through the synergistic deformation of soft and hard regions and the strengthening mechanism induced by heterogeneous deformation, the strength of materials can be improved while maintaining or even enhancing plasticity, making it a cutting-edge research direction for the high-performance development of magnesium alloys. However, existing heterostructure-related technologies, such as the multi-step melting, solution treatment, extrusion, and rolling composite process for preparing magnesium alloy heterostructures, suffer from cumbersome fabrication processes, narrow process control windows, and high production costs, making them unsuitable for large-scale industrial production. Furthermore, the 3D printing-based heterostructure construction technology cannot be directly transferred to magnesium alloy systems and suffers from low production efficiency and high manufacturing costs, lacking feasibility for large-scale industrial application.

[0004] In magnesium alloy systems, alloying with rare earth and transition metal elements is a core approach to improving their mechanical properties. Among these, Mg-Y-Ni alloys can form an LPSO phase in the matrix with hardness and elastic modulus far exceeding that of the α-Mg matrix, constructing a two-phase heterostructure with a hard LPSO phase and a soft α-Mg matrix. This achieves a simultaneous improvement in alloy strength and elastic modulus, representing a core research system for overcoming the performance bottlenecks of traditional magnesium alloys. However, current research on Mg-Y-Ni alloys is limited to controlling the volume fraction of the LPSO phase through alloy element ratios, relying on a single two-phase heterostructure for performance optimization. This approach fails to overcome the industry challenge of synergistically improving strength, plasticity, and elastic modulus. Existing manufacturing processes often employ high-extrusion specific heat deformation schemes, which, while achieving LPSO phase fragmentation, easily lead to complete recrystallization of the alloy matrix. This prevents the construction of a mixed-crystal heterostructure with greater performance gains within the matrix, limiting the potential for performance improvement. Summary of the Invention

[0005] To address some or all of the technical problems existing in the prior art, this application provides a dual heterostructure Mg-Y-Ni alloy and its preparation method.

[0006] This application provides a dual heterostructure Mg-Y-Ni alloy, wherein Mg is used as the base element, and Y and Ni are added as alloying elements, wherein the atomic ratio of Y to Ni is 0.5~1.5, and the balance is Mg and unavoidable trace impurities; the alloy has a dual heterostructure, the first heterostructure is a two-phase heterostructure composed of LPSO phase hard region and α-Mg matrix soft region; the second heterostructure is a mixed-crystal heterostructure composed of coarse non-recrystallization hard region and fine recrystallization soft region in the alloy matrix.

[0007] Preferably, the atomic ratio of Y to Ni in the alloy is 1.5, and the alloy composition is Mg. 92.5 Y 4.5 Ni3.

[0008] Preferably, the LPSO phase includes an 18R-type LPSO phase and a 14H-type LPSO phase, wherein the 18R-type LPSO phase is distributed in the α-Mg matrix to form a biphase heterostructure, and the 14H-type LPSO phase precipitates in the non-recrystallization region.

[0009] A method for preparing a Mg-Y-Ni alloy with a dual heterostructure includes the following steps: Step S1, Preparation of die-casting masterbatch: Through raw material pretreatment, step-by-step melting and die-casting under inert gas protection, an extrusion masterbatch with uniform composition and dense structure is prepared; Step S2, Hot Extrusion Deformation: After isothermal preheating of the extrusion base material and the extrusion die, hot extrusion deformation is carried out at an extrusion temperature of 420℃, an extrusion speed of 3mm / s, and an extrusion ratio of 4:1 to control the microstructure of the alloy to construct a dual heterostructure. After extrusion, the alloy is air-cooled to room temperature to obtain the target dual heterostructure Mg-Y-Ni alloy.

[0010] Preferably, the raw material pretreatment in step S1 specifically involves: weighing magnesium ingots, nickel sheets, and magnesium-yttrium master alloy according to the composition ratio of the target alloy; grinding to remove the oxide layer on the surface of the magnesium ingots; cutting the magnesium-yttrium master alloy into small pieces; cutting the nickel sheets into small-sized pieces and cleaning to remove surface oil and impurities; and placing all the treated raw materials, smelting auxiliary materials, and tooling that comes into contact with the alloy melt in a 200°C environment for drying and preheating before use.

[0011] Preferably, the step-by-step melting in step S1 is as follows: the melting process is carried out in a resistance furnace under continuous argon protection. Magnesium ingots, magnesium-yttrium master alloy and nickel sheets are added in steps using a gradient heating method. After each step of adding materials, the corresponding temperature is maintained until the raw materials are completely dissolved. During the melting process, the oxide slag on the surface of the melt is removed multiple times. A refining agent is added to stir the melt to achieve deep purification and impurity removal. Finally, after heating, holding and standing, a uniform alloy melt is obtained.

[0012] Preferably, the die casting process in step S1 specifically involves: preheating the die casting mold to 200°C and maintaining the temperature at a constant temperature; smoothly injecting the molten alloy obtained from smelting into the barrel of a horizontal die casting machine; and then die casting to obtain the extruded masterbatch.

[0013] Preferably, the isothermal preheating in step S2 specifically involves: preheating and holding the extrusion base material at 420°C for 1 hour, and preheating and holding the extrusion die at 420°C for 2 hours.

[0014] The dual heterostructure Mg-Y-Ni alloy and its preparation method of this application have the following advantages and positive effects: (1) A dual heterostructure combining a two-phase structure of “high-hardness LPSO phase / high-toughness α-Mg magnesium matrix” and a mixed-crystal structure of “unrecrystallized hard coarse grain region / recrystallized soft fine grain region” was constructed in magnesium alloy. This structure can overcome the bottleneck of “increased strength and modulus will inevitably lead to decreased plasticity” in traditional magnesium alloys by leveraging the strengthening effect generated by the synergistic deformation of soft and hard regions. It can achieve simultaneous optimization of alloy strength, plasticity and elastic modulus, and the comprehensive mechanical properties are significantly better than those of existing Mg-Y-Ni alloys with only a single heterostructure. (2) The composite process of “die casting + 4:1 small extrusion specific heat extrusion” is adopted, which abandons the cumbersome route of existing complex heat treatment and large deformation processing. The target heterostructure can be constructed stably and controllably. The process flow is simple and the parameters are controllable. By adjusting the Y / Ni atomic ratio to the optimal range of 0.5~1.5, the compositional basis for the construction of heterostructure is laid, while avoiding problems such as brittle phase precipitation and compositional segregation. 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 It is a schematic diagram of an extrusion die and Mg 92.5 Y 4.5 Photo of Ni3 alloy; Figure 2 The microstructure of the extruded Mg-Y-Ni alloy is shown by SEM (extrusion ratio 16:1). Figure 3 The microstructure of the extruded Mg-Y-Ni alloy is shown by SEM (extrusion ratio 4:1). Figure 4 This is a statistical chart of the modulus of extruded Mg-Y-Ni alloys; Figure 5 It is the stress-strain curve of the extruded Mg-Y-Ni 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 several embodiments, all of which are based on the alloy composition design and composite preparation process described in this application. Each alloy composition includes two parallel extrusion processes with a 16:1 large extrusion ratio and a 4:1 small extrusion ratio to verify the control law of alloy composition and extrusion process on microstructure and mechanical properties. Unless otherwise specified, all raw material specifications, equipment parameters, and operational details in all embodiments are performed according to conventional techniques in the fields of magnesium alloy smelting, die casting, and hot extrusion.

[0018] Example 1: Mg 95.5 Y 1.5 Preparation of Ni3 alloy In this embodiment, the Y / Ni atomic ratio is 0.5, and the alloy composition is Mg. 95.5 Y 1.5 Ni3 (atomic ratio), the actual chemical composition is controlled as follows: Y element 1~2 at.%, Ni element 2.5~3.5 at.%, with the balance being Mg and unavoidable trace impurities. The specific preparation steps of this embodiment are as follows: 1. Preparation of die-casting base material (1) Raw material preparation and pretreatment Based on the atomic ratio of the target alloy, the mass proportion of each raw material was calculated, and the raw materials were prepared using magnesium ingots with a purity of 99.99 wt.%, nickel sheets with a purity of 99.99 wt.%, and Mg-30 wt.% Y master alloy. The oxide layer on the surface of the magnesium ingots was removed by grinding with an angle grinder. The Mg-30Y master alloy was cut into small pieces, and the nickel sheets were cut into 5×5mm square pieces and cleaned with alcohol to remove surface oil and impurities. All raw materials, covering agents, refining agents, and smelting equipment were placed together in a 200℃ drying oven for preheating and preparation.

[0019] (2) Smelting under protective atmosphere The entire smelting process was carried out in a box-type resistance furnace under argon atmosphere protection. The specific steps were as follows: the crucible was placed in the furnace and heated to 500°C. Preheated magnesium ingots were added and evenly covered with powdered covering agent. Argon gas was introduced to establish a protective atmosphere. The temperature was raised to 710°C and held for 10 minutes. The temperature was then raised to 720°C and held for 10 minutes to completely melt the magnesium ingots. After removing the slag from the surface of the melt, preheated Mg-Y master alloy was added. After spreading the covering agent, the temperature was raised to 750°C and held for 10 minutes until the master alloy was completely dissolved. After removing the slag again, preheated nickel sheets were added and stirred thoroughly to evenly disperse the nickel sheets in the melt. After spreading the covering agent, the temperature was raised to 750°C and held for 20 minutes. The temperature was lowered to 730°C and the slag was removed again. A refining agent was added and stirred thoroughly to purify the melt. Finally, the temperature was raised to 750°C and held for 20 minutes to complete the smelting.

[0020] (3) Die casting The die-casting mold of the horizontal die-casting machine is preheated to 200°C and kept at that temperature. The molten alloy is then slowly injected into the die-casting machine barrel, and the die-casting process produces the extruded masterbatch.

[0021] 2. Hot extrusion deformation Cylindrical specimens of Ø40×35mm were machined at the gate position of the die-casting base material using a wire EDM machine. The surface oxide layer was removed by grinding. The specimens were divided into two groups for hot extrusion experiments. The extrusion temperature was fixed at 420℃ and the extrusion speed was fixed at 3mm / s. The extrusion sleeve, die, and other dies were preheated at 420℃ for 2 hours, as detailed below: Sample #1 (Extrusion Ratio 16:1): Preheat the sample in a 420℃ heat treatment furnace for 1 hour, then quickly assemble it into the preheated extrusion die. Hot extrusion is completed at an extrusion ratio of 16:1. After extrusion, air cool to room temperature. The microstructure of this sample corresponds to the information in the attached instruction manual. Figure 2 As shown in (a) and (b), the stress-strain curves correspond to those in the appendix of the instruction manual. Figure 5 As shown in (a), the elastic modulus data corresponds to the data in the appendix of the instruction manual. Figure 4 As shown.

[0022] Sample #2 (Extrusion Ratio 4:1): Preheat the sample in a 420℃ heat treatment furnace for 1 hour, then quickly assemble it into the preheated extrusion die. Hot extrusion is completed at an extrusion ratio of 4:1. After extrusion, air cool to room temperature. The microstructure of this sample corresponds to the information in the attached instruction manual. Figure 3 As shown in (a) and (b), the stress-strain curves correspond to those in the appendix of the instruction manual. Figure 5 As shown in (b), the elastic modulus data corresponds to the data in the appendix of the instruction manual. Figure 4 As shown.

[0023] In this embodiment, the Y / Ni atomic ratio of the alloy is 0.5, with a relative excess of Ni, resulting in a low volume fraction of the LPSO phase in the alloy matrix. In sample #1 with a 16:1 extrusion ratio, the LPSO phase is distributed in a fragmented island-like pattern within the α-Mg matrix, with relatively large interphase spacing. The matrix is ​​dominated by a fully recrystallized fine-grained structure, without forming a significant mixed-crystalline heterostructure. In sample #2 with a 4:1 extrusion ratio, the LPSO phase size is slightly increased, and a small number of non-recrystallized regions appear in the matrix, but a stable mixed-crystalline heterostructure has still not formed. (See attached specification). Figure 3 Microscopic morphology of (a) and (b).

[0024] Specimen #1 (16:1 extrusion ratio) had a yield strength of 278.8 MPa, a tensile strength of 322.7 MPa, an elongation of 8.3%, and an elastic modulus of 48.42 GPa; Specimen #2 (4:1 extrusion ratio) had a yield strength of 283.6 MPa, a tensile strength of 339.6 MPa, an elongation of 5.8%, and an elastic modulus of 48.67 GPa. Compared to the specimen with the larger extrusion ratio, the specimen with the smaller extrusion ratio showed a slight improvement in strength and elastic modulus. However, due to the insufficient volume fraction of the LPSO phase, the dual heterogeneous structure described in this application was not formed, resulting in a limited improvement in overall performance.

[0025] Example 2: Mg 94 Preparation of Y3Ni3 alloy In this embodiment, the Y / Ni atomic ratio is 1, and the alloy composition is Mg. 94 Y3Ni3 (atomic ratio), the actual chemical composition is controlled as follows: Y element 2.5~3.5 at.%, Ni element 2.5~3.5 at.%, with the balance being Mg and unavoidable trace impurities. The specific preparation steps of this embodiment are as follows: 1. Preparation of die-casting base material The raw material pretreatment, protective atmosphere melting, and die casting process parameters and operating procedures in this embodiment are exactly the same as in Example 1, except that they follow the same procedure as in Example 1. 94 By adjusting the atomic ratio of Y3Ni3 alloy and the weighing ratio of each raw material, a uniformly composed extruded masterbatch is prepared.

[0026] 2. Hot extrusion deformation The basic processes, such as sample preparation, mold preheating, extrusion temperature, and extrusion speed, were completely consistent with those in Example 1. The hot extrusion experiments were conducted in two groups: Sample #1 (Extrusion Ratio 16:1): Hot extrusion was performed at an extrusion ratio of 16:1, followed by air cooling to room temperature. The microstructure of this sample corresponds to the information provided in the instruction manual. Figure 2 As shown in (c) and (d), the stress-strain curves correspond to those in the appendix of the instruction manual. Figure 5 As shown in (a), the elastic modulus data corresponds to the data in the appendix of the instruction manual. Figure 4 As shown.

[0027] Sample #2 (Extrusion Ratio 4:1): Hot extrusion was performed at a 4:1 ratio, followed by air cooling to room temperature. The microstructure of this sample corresponds to the information provided in the instruction manual. Figure 3 As shown in (c) and (d), the stress-strain curves correspond to those in the appendix of the instruction manual. Figure 5 As shown in (b), the elastic modulus data corresponds to the data in the appendix of the instruction manual. Figure 4 As shown.

[0028] In this embodiment, the Y / Ni atomic ratio of the alloy is 1, which is more conducive to the stable formation of the LPSO phase, and the volume fraction of the LPSO phase in the alloy matrix is ​​significantly increased. In sample #1 with a 16:1 extrusion ratio, the LPSO phase is fragmented by large deformation and distributed in strips in the α-Mg matrix. The matrix undergoes complete recrystallization, and only a single LPSO / α-Mg dual-phase heterostructure can be formed, as shown in the attached specification. Figure 2 Microstructures of samples (c) and (d); In sample #2 with a 4:1 extrusion ratio, the LPSO phase exhibits a continuous network distribution with significantly reduced interphase spacing. The matrix contains both coarse non-recrystallized regions and fine recrystallized regions, initially forming the "two-phase isomerism + mixed-crystallization isomerism" dual heterostructure described in this application. However, in addition to the 18R LPSO phase, a large amount of Mg2Ni phase precipitates along the extrusion direction under this composition, and a "pure" two-phase isomerism is not obtained. (See attached specification). Figure 3 Microscopic morphology of (c) and (d).

[0029] Sample #1 (16:1 extrusion ratio) exhibited a yield strength of 253.3 MPa, a tensile strength of 341.2 MPa, an elongation of 4.2%, and an elastic modulus of 48.55 GPa; Sample #2 (4:1 extrusion ratio) showed a yield strength of 351.4 MPa, a tensile strength of 430.4 MPa, an elongation of 7.1%, and an elastic modulus of 50.80 GPa. Compared to the high extrusion ratio sample, the low extrusion ratio sample, through the construction of a dual heterogeneous structure, achieved a simultaneous and significant improvement in strength, plasticity, and elastic modulus, demonstrating the synergistic optimization effect of the low extrusion ratio process of this invention on alloy properties.

[0030] Example 3: Mg 92.5 Y 4.5Preparation of Ni3 alloy In this embodiment, the Y / Ni atomic ratio is 1.5, and the alloy composition is Mg. 92.5 Y 4.5 Ni3 (atomic ratio), the actual chemical composition is controlled as follows: 4~5 at.% Y, 2.5~3.5 at.% Ni, with the balance being Mg and unavoidable trace impurities. The specific preparation steps in this embodiment are as follows: 1. Preparation of die-casting base material The raw material pretreatment, protective atmosphere melting, and die casting process parameters and operating procedures in this embodiment are exactly the same as in Example 1, except that they follow the same procedure as in Example 1. 92.5 Y 4.5 By adjusting the atomic ratio of Ni3 alloy and the weighing ratio of each raw material, a uniformly composed extruded masterbatch is prepared.

[0031] 2. Hot extrusion deformation The basic processes, such as sample preparation, mold preheating, extrusion temperature, and extrusion speed, were completely consistent with those in Example 1. The hot extrusion experiments were conducted in two groups: Sample #1 (Extrusion Ratio 16:1): Hot extrusion was performed at an extrusion ratio of 16:1, followed by air cooling to room temperature. The microstructure of this sample corresponds to the information provided in the instruction manual. Figure 2 As shown in (e) and (f), the stress-strain curves correspond to those in the appendix of the instruction manual. Figure 5 As shown in (a), the elastic modulus data corresponds to the data in the appendix of the instruction manual. Figure 4 As shown.

[0032] Sample #2 (Extrusion Ratio 4:1): Hot extrusion was performed at an extrusion ratio of 4:1, followed by air cooling to room temperature. This sample is the optimal sample for this invention; the microstructure corresponds to the appendix to the specification. Figure 3 As shown in (e) and (f), the stress-strain curves correspond to those in the appendix of the instruction manual. Figure 5 As shown in (b), the elastic modulus data corresponds to the data in the appendix of the instruction manual. Figure 4 As shown, the instruction manual corresponds to both the mold and the actual sample. Figure 1 As shown in (b) and (d) in the middle.

[0033] In this embodiment, the Y / Ni atomic ratio of the alloy is 1.5, further increasing the formation of the LPSO phase. In sample #1 with a 16:1 extrusion ratio, the LPSO phase is finely fragmented by large deformation, exhibiting a dispersed granular and short strip distribution. The matrix undergoes complete recrystallization, resulting in only a single LPSO / α-Mg dual-phase heterostructure, as per the attached specification. Figure 2Microstructures of (e) and (f); In sample #2 with a 4:1 extrusion ratio, a continuous network of 18R-type LPSO phase with high volume fraction and low interphase spacing was formed, constructing a stable LPSO hard zone / α-Mg soft zone two-phase heterostructure. Simultaneously, a 14H-type LPSO phase precipitated in the coarse non-recrystallization region of the matrix, forming a stable mixed-crystal heterostructure with the fine recrystallization region. Ultimately, the synergistic construction of the "two-phase heterostructure + mixed-crystal heterostructure" described in this application was achieved. (See attached specification). Figure 3 The microstructures of (e) and (f) are shown; at the same time, less Mg2Ni phase is precipitated in this alloy composition, which is closer to a two-phase structure compared with the other two compositions.

[0034] Specimen #1 (16:1 extrusion ratio) exhibited a yield strength of 315.7 MPa, a tensile strength of 368.1 MPa, an elongation of 4.2%, and an elastic modulus of 49.70 GPa. Specimen #2 (4:1 extrusion ratio) showed a yield strength of 406.7 MPa, a tensile strength of 479.5 MPa, an elongation of 6.4%, and an elastic modulus of 50.80 GPa. Compared to the specimen with the larger extrusion ratio, the optimal specimen with the smaller extrusion ratio showed a 30.2% increase in tensile strength and an increase in elongation from 4.2% to 6.4%, while simultaneously improving the elastic modulus. This demonstrates a synergistic improvement in strength, plasticity, and elastic modulus, fully confirming the optimization effect of the dual heterogeneous structure design of this application on the comprehensive mechanical properties of magnesium alloys.

[0035] A comparison of the three sets of embodiments above clearly shows that: as the Y / Ni atomic ratio increases, the volume fraction of the LPSO phase in the alloy gradually increases, laying the compositional foundation for the construction of the dual heterostructure; compared with the large extrusion ratio of 16:1, the 4:1 small extrusion ratio process adopted in this invention can avoid complete recrystallization of the matrix, successfully constructing a dual heterostructure of "LPSO / α-Mg dual-phase isomerism + recrystallized / non-recrystallized mixed crystal isomerism" in the alloy, ultimately achieving a synergistic improvement in the alloy's strength, plasticity, and elastic modulus, wherein Mg 92.5 Y 4.5 The Ni3 alloy exhibits the best overall performance at an extrusion ratio of 4:1.

[0036] Figure 1 The diagram shows two extrusion die structures for the hot extrusion process of this invention, as well as the preferred embodiment Mg. 92.5 Y 4.5The figures show physical images of extrusion specimens of N3 alloy corresponding to the process. In the figures, A is the specimen, B is the mold, (a) and (c) are the mold structures and corresponding extrusion specimens of the 16:1 large extrusion ratio used in the parallel control test of the embodiment, and (b) and (d) are the mold structures and corresponding extrusion specimens of the 4:1 small extrusion ratio used in the process scheme of this application. The figures not only intuitively present the difference in mold cavity size corresponding to the two extrusion ratios, clearly reflecting the mold design basis of the two sets of parallel extrusion processes in the embodiment, but also fully demonstrate that the alloy specimens under the two extrusion processes have excellent forming quality. The specimen corresponding to the 4:1 small extrusion ratio is the target product with the best comprehensive mechanical properties and the successful construction of a dual heterogeneous structure in this application. It provides intuitive structural and physical evidence for the feasibility of the extrusion process in the embodiment and the control law of process parameters on the alloy microstructure and properties.

[0037] This application constructs a dual heterostructure in magnesium alloys, combining a two-phase structure of "high-hardness LPSO phase / high-toughness α-Mg magnesium matrix" with a mixed-grain structure of "unrecrystallized hard coarse-grained region / recrystallized soft fine-grained region". This structure, through the strengthening effect generated by the synergistic deformation of the hard and soft regions, overcomes the bottleneck of traditional magnesium alloys where "increased strength and modulus inevitably lead to decreased plasticity", achieving simultaneous optimization of alloy strength, plasticity, and elastic modulus. Its comprehensive mechanical properties are significantly superior to existing Mg-Y-Ni alloys with only a single heterostructure. Employing a composite process of "die casting and 4:1 small-extrusion specific heat extrusion", it abandons the cumbersome routes of existing complex heat treatment and large deformation processing, enabling stable and controllable construction of the target heterostructure. The process flow is simple and parameters are controllable. By adjusting the Y / Ni atomic ratio to the optimal range of 0.5~1.5, a compositional basis for heterostructure construction is laid, while avoiding problems such as brittle phase precipitation and compositional segregation.

[0038] 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 Mg-Y-Ni alloy with a dual heterostructure, characterized in that, The alloy uses Mg as the base element and adds Y and Ni as alloying elements, wherein the atomic ratio of Y to Ni is 0.5~1.5, and the balance is Mg and unavoidable trace impurities; the alloy has a dual heterostructure. The first heterostructure is a two-phase heterostructure composed of LPSO phase hard regions and α-Mg matrix soft regions; the second heterostructure is a mixed-crystal heterostructure composed of coarse non-recrystallized hard regions and fine recrystallized soft regions in the alloy matrix.

2. The Mg-Y-Ni alloy with a dual heterostructure according to claim 1, characterized in that, The alloy has an atomic ratio of Y to Ni of 1.5, and its composition is Mg. 92.5 Y 4.5 Ni3.

3. The Mg-Y-Ni alloy with a dual heterostructure according to claim 1, characterized in that, The LPSO phase includes an 18R-type LPSO phase and a 14H-type LPSO phase, wherein the 18R-type LPSO phase is distributed in the α-Mg matrix to form a biphase heterostructure, and the 14H-type LPSO phase precipitates in the non-recrystallization region.

4. A method for preparing a dual heterostructure Mg-Y-Ni alloy as described in any one of claims 1 to 3, characterized in that, Includes the following steps: Step S1, Preparation of die-casting masterbatch: Through raw material pretreatment, step-by-step melting and die-casting under inert gas protection, an extrusion masterbatch with uniform composition and dense structure is prepared; Step S2, Hot Extrusion Deformation: After isothermal preheating of the extrusion base material and the extrusion die, hot extrusion deformation is carried out at an extrusion temperature of 420℃, an extrusion speed of 3mm / s, and an extrusion ratio of 4:1 to control the microstructure of the alloy to construct a dual heterostructure. After extrusion, the alloy is air-cooled to room temperature to obtain the target dual heterostructure Mg-Y-Ni alloy.

5. The method for preparing the dual heterostructure Mg-Y-Ni alloy according to claim 4, characterized in that, The raw material pretreatment in step S1 is as follows: weigh magnesium ingots, nickel sheets and magnesium-yttrium master alloy according to the composition ratio of the target alloy, grind to remove the oxide layer on the surface of magnesium ingots, cut the magnesium-yttrium master alloy into small pieces, cut the nickel sheets into small-sized pieces and clean to remove surface oil and impurities, and place all processed raw materials, smelting auxiliary materials and tooling in contact with the alloy melt in a 200°C environment for drying and preheating for later use.

6. The method for preparing the dual heterostructure Mg-Y-Ni alloy according to claim 4, characterized in that, The step-by-step melting process in step S1 is as follows: the melting process is carried out in a resistance furnace under continuous argon protection. Magnesium ingots, magnesium yttrium master alloy and nickel sheets are added in steps using a gradient heating method. After each step of adding materials, the corresponding temperature is maintained until the raw materials are completely dissolved. During the melting process, the oxide slag on the surface of the melt is removed multiple times. A refining agent is added to stir the melt to achieve deep purification and impurity removal. Finally, after heating, holding and standing, a uniform alloy melt is obtained.

7. The method for preparing the dual heterostructure Mg-Y-Ni alloy according to claim 4, characterized in that, The die casting process in step S1 specifically involves: preheating the die casting mold to 200°C and maintaining the temperature, then steadily injecting the molten alloy obtained from the melting process into the barrel of a horizontal die casting machine, and finally die casting to obtain the extruded master material.

8. The method for preparing the dual heterostructure Mg-Y-Ni alloy according to claim 4, characterized in that, The isothermal preheating in step S2 specifically involves preheating the extrusion base material at 420°C for 1 hour and preheating the extrusion die at 420°C for 2 hours.

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