A high-strength, high-ductility, multi-scale hierarchical heterostructure magnesium alloy and its preparation method

Abstract

This invention relates to the field of magnesium alloy preparation technology, specifically to a high-strength, high-ductility, multi-scale hierarchical heterostructure magnesium alloy and its preparation method. The magnesium alloy, by weight percentage (100%), comprises the following components: Mg: 65-70%, Sc: 20-33%, with the balance being Gd. The preparation method includes: S1, weighing Mg, Sc, and Gd metals, and vacuum melting to obtain a magnesium alloy ingot; S2, solution treatment and aging to precipitate needle-like secondary α phase within the β phase; S3, high-temperature hot rolling to promote dynamic recrystallization; S4, heat treatment to adjust the biphase structure ratio of the magnesium alloy, promoting the precipitation of nano-B2-rich Sc particles and L12-rich Gd nano-precipitates, followed by cold quenching to room temperature to obtain a hierarchical heterostructure magnesium alloy. The hierarchical heterostructure prepared by this invention has a maximum tensile strength of 493 MPa, a maximum yield strength of 439 MPa, and a maximum elongation after fracture of 40.8%. This invention, through heat treatment process control and Gd alloying, produces a hierarchical heterostructure magnesium alloy with excellent comprehensive mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of magnesium alloy preparation technology, specifically to a high-strength, high-ductility, multi-scale hierarchical heterostructure magnesium alloy and its preparation method. Background Technology

[0002] Magnesium alloys possess advantages such as low density and high specific strength, making them ideal structural materials for lightweight applications in the automotive and aerospace industries. However, traditional α-type magnesium alloys have a hexagonal close-packed (HCP) matrix structure with a limited number of independent slip systems, resulting in generally low room-temperature plasticity and formability, which severely restricts their engineering applications. How to significantly improve plasticity while maintaining high strength, achieving synergistic optimization of comprehensive mechanical properties, has become a significant research challenge in the field of magnesium alloys. In recent years, by constructing heterogeneous structures with alternating soft and hard phases (regions) within the material, geometrically necessary dislocations can be generated during deformation, forming back stress and normal stress, thus achieving heterogeneous deformation-induced strengthening and achieving a better balance between strength and plasticity. However, existing heterogeneous magnesium alloy structures mostly rely on complex strong plastic deformation or multi-step thermo-mechanical composite processes, which are costly, have narrow process windows, and are difficult to precisely control the ratio and spatial distribution of soft and hard regions, hindering their engineering application.

[0003] Patent CN 118792561 A points out that using Zn as a third element can only achieve solid solution strengthening for grain refinement, but cannot form a coherent strengthening phase with the matrix, resulting in limited strengthening effect and limited performance upper limit (tensile strength ≤381MPa, elongation ≤25%). In addition, excessive addition of Zn will precipitate in the form of Zn-rich precipitates such as ScZn and ZnSc, which will deteriorate the mechanical properties of the alloy and make it difficult to meet the dual requirements of high strength and high toughness in the high-end lightweight field.

[0004] Therefore, there is an urgent need to develop a magnesium alloy with controllable process and excellent comprehensive performance, as well as its preparation method, in order to achieve a synergistic improvement in strength and plasticity and meet the high-performance requirements of lightweight materials in the automotive, aerospace and other fields. Summary of the Invention

[0005] In view of this, this invention proposes a high-strength, high-ductility, multi-scale hierarchical heterostructure magnesium alloy and its preparation method. By adding the alloying element Sc, a "soft β phase + hard α phase" two-phase heterostructure is obtained. Combined with aging process and the addition of the alloying element Gd, nano-needle-shaped secondary α phase / L12 Gd-rich nano-precipitate phase with hierarchical grain size distribution is generated within the soft β phase, simultaneously improving the strength and toughness of the plate. The technical solution of this invention is achieved as follows: In the first aspect, the present invention proposes a high-strength, high-ductility, multi-scale hierarchical heterostructure magnesium alloy, which, by weight percentage, comprises the following components: Mg 65~70%, Sc 20~33%, the total amount of Mg and Sc is not greater than 100%, and the balance is Gd.

[0006] Preferably, the dual-phase structure of the magnesium alloy includes a micron-sized α phase (hcp, P63 / mmc(194)) and a micron-sized β phase (bcc, Im-3m(229)), wherein the micron-sized β phase includes a nano-needle-shaped secondary α phase, nano-B2-rich Sc particles and L12-rich Gd nano-precipitate phase (fcc, Fm-3m(225)).

[0007] Preferably, the micron-sized α-phase grain size is 5μm~70μm, the micron-sized β-phase grain size is 5μm~50μm, the nano-needle-shaped secondary α-phase grain size is 20nm~200nm, the nano-B2-rich Sc particle grain size is 20nm~50nm, and the L12-rich Gd nano-precipitated grain size is 10nm~30nm.

[0008] More preferably, the α phase has a hexagonal close-packed crystal structure, the β phase has a body-centered cubic crystal structure, the needle-like secondary α phase has a hexagonal close-packed crystal structure, the B2-rich Sc particles have a body-centered cubic crystal structure, and the L12-rich Gd nanoprecipitate phase has a face-centered cubic crystal structure.

[0009] In this invention, the α-phase matrix has a hexagonal close-packed (HCP) structure, with only three principal basal plane slip systems activated at room temperature. The insufficient number of independent slip systems limits plasticity. The β-phase has a body-centered cubic (BCC) structure with 12 independent slip systems, providing ample plastic deformation capacity and significantly improving the room-temperature plasticity of the alloy. During deformation, the softer β-phase preferentially undergoes plastic deformation in the initial loading stage, while the surrounding harder α-phase region is constrained by differences in crystal structure, strength, and stacking fault energy. This results in a significant strength gradient between the β and α phases. This promotes the rapid accumulation of geometrically necessary dislocations (GNDs) at the phase boundaries, generating substantial back stress and effectively inhibiting further dislocation slip in the β-phase. Simultaneously, the acicular secondary α-phase within the β-phase hinders dislocation movement. As deformation intensifies, the acicular secondary α-phase is sheared and deformed, accompanied by changes in grain orientation. Therefore, while hindering dislocation movement, it does not cause stress concentration, greatly promoting continuous work hardening. The nanoscale B2-rich Sc particles and nanoscale L12-rich Gd precipitates coherent with the matrix within the β phase can act as effective barriers to dislocation movement. Dislocations interact with L12-rich Gd and B2-rich Sc nanoparticles through ring-shaped or cleaving precipitates, which helps to enhance the BCC matrix.

[0010] In a second aspect, the present invention provides a method for preparing a high-strength, high-ductility, multi-scale hierarchical heterostructure magnesium alloy as described in the first aspect, comprising the following steps: S1. Weigh out Mg, Sc and Gd metals and vacuum melt them to obtain magnesium alloy ingots; S2. The magnesium alloy ingot obtained in S1 is subjected to solution-aging treatment. S3. Hot rolling the ingot obtained in S2 to obtain magnesium alloy sheet; S4. The magnesium alloy sheet obtained in S3 is subjected to heat treatment and quenching to obtain the graded heterogeneous structure magnesium alloy.

[0011] In this invention, step S2 involves solution treatment and aging to precipitate needle-shaped secondary α phase inside the β phase; step S3 involves high-temperature hot rolling to obtain magnesium alloy sheet to promote dynamic recrystallization; step S4 involves heat treatment to eliminate stress concentration caused by large deformation, promote recovery recrystallization, regulate the two-phase structure and nano-precipitated phases, and then quench to room temperature to obtain a hierarchical heterostructure magnesium alloy.

[0012] Preferably, the purity of Mg, Sc, and Gd metals in step S1 is 99.99 at%, the vacuum melting temperature is 900℃~1000℃, the vacuum melting time is 10~15 min, and the vacuum degree is ≤1×10 -3 Pa, the atmosphere is argon.

[0013] Preferably, the solution temperature in step S2 is 630℃~700℃, the solution time is 0.5~8h, the aging temperature is 100℃~400℃, and the aging time is 1~6h.

[0014] Preferably, the hot rolling temperature in step S3 is 550℃~650℃, the single-pass reduction is less than 10%, and the total reduction is 70%~90%.

[0015] Preferably, the heat treatment temperature in step S4 is 550℃~650℃, and the holding time is 10min~120min.

[0016] Preferably, the ultimate tensile strength of the graded heterostructure magnesium alloy in step S4 is 439.4 MPa to 493 MPa, the yield strength is 309.6 MPa to 439 MPa, and the elongation at break is 22.8% to 40.8%.

[0017] Thirdly, the present invention provides an application of the high-strength, high-ductility, multi-scale hierarchical heterostructure magnesium alloy as described in the first aspect in lightweight structural components for automobiles or aerospace.

[0018] Compared with the prior art, the advantages of the present invention are as follows: (1) The magnesium alloy of the present invention, based on the traditional micron-scale α / β dual-phase structure, constructs a hierarchical heterogeneous structure within the β phase, comprising nano-needle-shaped secondary α phase, nano-B2-rich Sc particles, and L12-rich Gd nano-precipitates with graded grain size distribution. During tensile testing, the soft-hard dual-phase interface induces GND accumulation and generates back stress strengthening; the nano-needle-shaped α phase hinders dislocation slip and provides continuous work hardening; the B2-rich Sc particles and Mg3Gd precipitates generate synergistic precipitation strengthening. The synergistic effect of the above multi-scale structures significantly improves the strength and plasticity of the material, achieving simultaneous enhancement of strength and plasticity.

[0019] (2) The hierarchical heterostructure preparation method provided by the present invention adds an aging treatment step between the ingot solution treatment and high-temperature rolling in the traditional magnesium alloy preparation process, which is used to pre-form needle-shaped secondary α phase and fine precipitates in the β matrix. This step can significantly enrich the types and quantities of precipitates with hierarchical grain size distribution, strengthen the initial strength of the β matrix, and lay the foundation for the formation of hierarchical heterostructures in the subsequent deformation process.

[0020] (3) The magnesium alloy prepared by the hierarchical heterostructure preparation method provided by the present invention can achieve a synergistic improvement in strength and plasticity. Its strength and plasticity are significantly better than those of pure magnesium, and significantly better than those of traditional heterostructure magnesium alloys and magnesium-scandium alloys. The alloy and preparation method provided by the present invention are simple to operate and easy to promote industrially, providing a new technical approach for the development of high-strength and high-toughness magnesium alloy plates, and further expanding the application prospects of magnesium alloys in the field of lightweighting. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention 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 some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 Comparison of the properties of magnesium alloys prepared in Examples 3, 6, 8 and Comparative Example 1; Figure 2 EBSD image of the magnesium alloy prepared in Example 6; Figure 3 The images shown are SEM and TEM images of the magnesium alloy prepared in Example 6. Detailed Implementation

[0023] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0024] Existing heterostructure magnesium alloys mostly rely on complex strong plastic deformation or multi-step thermo-mechanical composite processes, which are costly, have narrow process windows, and are difficult to precisely control the ratio and spatial distribution of soft and hard regions, hindering their engineering application. To address these issues, based on the stabilizing effect of Sc on the β (BCC) phase in the Mg-Sc phase diagram and the strong precipitation tendency of the Mg-Gd system for the Mg3Gd stable phase, this study selects Gd as the directional alloying element. It is expected that Gd will introduce high-density interface and microstructure regulation effects in the β matrix through the precipitation of nano-coherent Mg3Gd. Based on the Mg-Sc phase diagram, the β(BCC) phase undergoes a decomposition transformation from β to α(HCP) + B2 in the aging temperature range below approximately 481℃. Therefore, aging is introduced after melting to controllably precipitate needle-like α and B2 phases, constructing a hierarchical heterostructure. Combined with subsequent heat treatment processes, the proportions of the two-phase BCC / HCP heterostructure, smaller-scale nano-needle-like secondary α phase, and dispersed B2-rich Sc particles and L12-rich Gd nanoprecipitates can be precisely controlled, forming a multi-scale heterostructure with synergistic strengthening by the second phase. The resulting magnesium alloy exhibits a tensile strength of approximately 440 MPa and an elongation of approximately 40%, maintaining high strength while possessing excellent plasticity, which is expected to significantly expand the application range of magnesium-based materials in the automotive, aerospace, and other fields.

[0025] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0026] In this document, the terms “containing,” “comprising,” or “including” are open-ended expressions, meaning they include the contents specified in this invention but do not exclude other aspects.

[0027] In this document, the terms “optional,” “optionally,” or “optional” generally refer to an event or condition that may, but may not, occur, and the description includes both cases in which the event or condition occurs and cases in which the event or condition does not occur.

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0029] All materials used in this invention were purchased commercially. Specifically, Mg, Sc, and Gd metals were sourced from Hunan Gaochuang Rare Earth New Materials Co., Ltd.

[0030] Example 1 This embodiment provides a method for preparing a high-strength, high-ductility, multi-scale hierarchical heterostructure magnesium alloy, wherein the composition of the magnesium alloy is: by weight percentage, Mg: 68.22%, Sc: 25.35%, Gd: 6.43%, and specifically includes the following steps: (1) Vacuum induction melting: Mg, Sc and Gd metals were weighed according to the alloy ratio and melted in a vacuum induction melting furnace to prepare magnesium alloy melt. The process parameters for vacuum melting were: argon atmosphere, temperature 1000℃, vacuum melting time 15min, and vacuum degree 1×10 -3 Pa.

[0031] (2) Solution treatment: The magnesium alloy ingot is placed in a muffle furnace for solution treatment. The solution temperature is 700 ℃, the solution time is 0.5h, the heating rate is 10℃ / min, and the solution is then quenched.

[0032] (3) Aging treatment: The magnesium alloy ingot after solution treatment is placed in a muffle furnace for aging treatment. The aging temperature is 400℃, the aging time is 3h, the heating rate is 10℃ / min, and the quenching treatment is performed after aging.

[0033] (4) High temperature rolling: The magnesium alloy ingot after aging treatment is rolled to obtain magnesium alloy sheet. The rolling temperature is 650℃, the reduction per pass is no more than 10%, and the total reduction is 90%.

[0034] (5) Heat treatment: The hot-rolled magnesium alloy sheet is placed in a muffle furnace for heat treatment. The heat treatment temperature is 550℃, the heat treatment holding time is 30min, the heating rate is 10℃ / min, and water quenching is performed after the heat treatment is completed.

[0035] The hierarchical heterostructure MgScGd alloy has a dual-phase structure of α and β phases. The α phase grain size is 17.6 μm and the volume fraction is 80.5%, while the β phase grain size is 14.2 μm and the volume fraction is 19.5%.

[0036] The mechanical properties of the obtained heterostructure magnesium alloy were tested according to the national standard GB / T228.1-2021. The results showed that its ultimate tensile strength was 452.0 MPa, its yield strength was 322.0 MPa, and its ultimate elongation was 22.8%.

[0037] Example 2 This embodiment provides a method for preparing a high-strength, high-ductility, multi-scale hierarchical heterostructure magnesium alloy, wherein the composition of the magnesium alloy is: by weight percentage, Mg: 68.22%, Sc: 25.35%, Gd: 6.43%, and specifically includes the following steps: (1) Vacuum induction melting: Mg, Sc and Gd metals were weighed according to the alloy ratio and melted in a vacuum induction melting furnace to prepare magnesium alloy melt. The process parameters for vacuum melting were: argon atmosphere, temperature 900℃, vacuum melting time 15min, and vacuum degree 1×10⁻⁶. -3 Pa.

[0038] (2) Solution treatment: The magnesium alloy ingot is placed in a muffle furnace for solution treatment. The solution temperature is 630℃, the solution time is 8h, the heating rate is 10℃ / min, and the quenching treatment is performed after solution treatment.

[0039] (3) Aging treatment: The solution-treated magnesium alloy ingot is placed in a muffle furnace for aging treatment. The aging temperature is 100℃, the aging time is 6h, and the heating rate is 10℃ / min. After aging, quenching treatment is performed.

[0040] (4) High-temperature rolling: The magnesium alloy ingot after aging treatment is rolled to obtain magnesium alloy sheet. The rolling temperature is 550℃, the reduction per pass is no more than 10%, and the total reduction is 70%.

[0041] (5) Heat treatment: The hot-rolled magnesium alloy sheet is placed in a muffle furnace for heat treatment. The heat treatment temperature is 550℃, the heat treatment holding time is 120min, the heating rate is 10℃ / min, and water quenching is performed after the heat treatment is completed.

[0042] The hierarchical heterostructure MgScGd alloy has a dual-phase structure of α and β phases. The α phase grain size is 19.8 μm and the volume fraction is 78.4%, while the β phase grain size is 16.3 μm and the volume fraction is 21.6%.

[0043] The mechanical properties of the obtained heterostructure magnesium alloy were tested according to the national standard GB / T228.1-2021. The results showed that its ultimate tensile strength was 439.4 MPa, its yield strength was 309.6 MPa, and its ultimate elongation was 24.0%.

[0044] Example 3 This embodiment provides a method for preparing a high-strength, high-ductility, multi-scale hierarchical heterostructure magnesium alloy, wherein the composition of the magnesium alloy is: by weight percentage, Mg: 68.22%, Sc: 25.35%, Gd: 6.43%, and specifically includes the following steps: (1) Vacuum induction melting: Mg, Sc and Gd metals were weighed according to the alloy ratio and melted in a vacuum induction melting furnace to prepare magnesium alloy melt. The process parameters for vacuum melting were: argon atmosphere, temperature 1000℃, vacuum melting time 10min, and vacuum degree 1×10⁻⁶. -3 Pa.

[0045] (2) Solution treatment: The magnesium alloy ingot is placed in a muffle furnace for solution treatment. The solution temperature is 700℃, the solution time is 2h, and the heating rate is 10℃ / min. After solution treatment, quenching treatment is performed.

[0046] (3) Aging treatment: The solution-treated magnesium alloy ingot is placed in a muffle furnace for aging treatment. The aging temperature is 300℃, the aging time is 1h, and the heating rate is 10℃ / min. After aging, quenching treatment is performed.

[0047] (4) High-temperature rolling: The magnesium alloy ingot after aging treatment is rolled to obtain magnesium alloy sheet. The rolling temperature is 650℃, the reduction per pass is no more than 10%, and the total reduction is 90%.

[0048] (5) Heat treatment: The hot-rolled magnesium alloy sheet is placed in a muffle furnace for heat treatment. The heat treatment temperature is 550℃, the heat treatment holding time is 10min, the heating rate is 10℃ / min, and water quenching is performed after the heat treatment is completed.

[0049] The hierarchical heterostructure MgScGd alloy has a dual-phase structure of α and β phases. The α phase grain size is 18.3 μm and the volume fraction is 82.6%, while the β phase grain size is 13.8 μm and the volume fraction is 17.4%.

[0050] The mechanical properties of the obtained heterostructure magnesium alloy were tested according to the national standard GB / T228.1-2021. The results showed that its ultimate tensile strength was 442.0 MPa, its yield strength was 320.0 MPa, and its ultimate elongation was 23.9%.

[0051] Example 4 This embodiment provides a method for preparing a high-strength, high-ductility, multi-scale hierarchical heterostructure magnesium alloy, wherein the composition of the magnesium alloy is: by weight percentage, Mg: 65.22%, Sc: 33.35%, Gd: 1.43%. The specific preparation method is the same as in Embodiment 1, except that the composition of the magnesium alloy is different.

[0052] The hierarchical heterostructure MgScGd alloy has a dual-phase structure of α and β phases. The α phase grain size is 19.6 μm and the volume fraction is 85.2%, while the β phase grain size is 15.4 μm and the volume fraction is 14.8%.

[0053] The mechanical properties of the obtained heterostructure magnesium alloy were tested according to the national standard GB / T228.1-2021. The results showed that its ultimate tensile strength was 448.2 MPa, its yield strength was 323.7 MPa, and its ultimate elongation was 24.1%.

[0054] Example 5 This embodiment provides a method for preparing a high-strength, high-ductility, multi-scale hierarchical heterostructure magnesium alloy, wherein the composition of the magnesium alloy is as follows (by weight percentage): Mg: 70.22%, Sc: 20.35%, Gd: 9.43%. The specific preparation method is the same as in Example 1, except that the composition of the magnesium alloy is different.

[0055] The hierarchical heterostructure MgScGd alloy has a dual-phase structure of α and β phases. The α phase grain size is 21.4 μm and the volume fraction is 69.4%, while the β phase grain size is 16.5 μm and the volume fraction is 30.6%.

[0056] The mechanical properties of the obtained heterostructure magnesium alloy were tested according to the national standard GB / T228.1-2021. The results showed that its ultimate tensile strength was 440.1 MPa, its yield strength was 321.3 MPa, and its ultimate elongation was 28.4%.

[0057] Example 6 This embodiment provides a method for preparing a high-strength, high-ductility, multi-scale hierarchical heterostructure magnesium alloy, wherein the composition of the magnesium alloy is as follows: by weight percentage, Mg: 68.22%, Sc: 25.35%, Gd: 6.43%. The specific preparation method is the same as in Embodiment 1, except that the heat treatment temperature in step (5) is 600℃.

[0058] The EBSD morphology of hierarchical heterostructure MgScGd alloys is as follows Figure 2 As shown, a dual-phase structure of α and β phases exists. The α phase grain size is 17.6 μm with a volume fraction of 44.8%, and the β phase grain size is 25.6 μm with a volume fraction of 55.2%. Figure 3 Further TEM morphology analysis revealed the presence of nanoneedle-shaped secondary α particles with sizes ranging from 20 nm to 200 nm in the β phase, as well as high-density dispersed B2-rich Sc nanoparticles with sizes ranging from 20 nm to 50 nm and L12-rich Gd nanoprecipitates with sizes ranging from 10 nm to 30 nm.

[0059] The mechanical properties of the obtained heterostructure magnesium alloy were tested, and the results showed that its ultimate tensile strength was 453.0 MPa, its yield strength was 409.0 MPa, and its ultimate elongation was 32%.

[0060] Example 7 This embodiment provides a method for preparing a high-strength, high-ductility, multi-scale hierarchical heterostructure magnesium alloy, wherein the composition of the magnesium alloy is as follows: by weight percentage, Mg: 68.22%, Sc: 25.35%, Gd: 6.43%. The specific preparation method is the same as in Embodiment 1, except that the heat treatment temperature in step (5) is 620℃.

[0061] The hierarchical heterostructure MgScGd alloy has a dual-phase structure of α and β phases. The α phase grain size is 15.8 μm and the volume fraction is 30.2%, while the β phase grain size is 26.1 μm and the volume fraction is 69.8%.

[0062] The mechanical properties of the obtained heterostructure magnesium alloy were tested, and the results showed that its ultimate tensile strength was 493 MPa, its yield strength was 439 MPa, and its ultimate elongation was 38.2%.

[0063] Example 8 This embodiment provides a method for preparing a high-strength, high-ductility, multi-scale hierarchical heterostructure magnesium alloy, wherein the composition of the magnesium alloy is as follows: by weight percentage, Mg: 68.22%, Sc: 25.35%, Gd: 6.43%. The specific preparation method is the same as in Embodiment 1, except that the heat treatment temperature in step (5) is 650℃.

[0064] The hierarchical heterostructure MgScGd alloy has a dual-phase structure of α and β phases. The α phase grain size is 8.67 μm and the volume fraction is 5.5%, while the β phase grain size is 38.8 μm and the volume fraction is 94.5%.

[0065] The mechanical properties of the obtained heterostructure magnesium alloy were tested, and the results showed that its ultimate tensile strength was 439.7 MPa, its yield strength was 387.7 MPa, and its ultimate elongation was 40.8%.

[0066] Comparative Example 1 This comparative example provides a method for preparing a dual-phase heterostructure magnesium alloy, wherein the composition of the magnesium alloy is: Mg: 69.46% and Sc: 30.5% by weight percentage, specifically including the following steps: (1) Vacuum induction melting: Mg and Sc metals were weighed according to the alloy ratio and melted in a vacuum induction melting furnace to prepare magnesium alloy melt. The process parameters for vacuum melting were: 800℃ under argon atmosphere, 15min vacuum melting time, and 1×10⁻⁶ vacuum degree. -3 Pa.

[0067] (2) High temperature rolling: Magnesium alloy ingots are rolled to obtain magnesium alloy plates. The rolling temperature is 650℃, the reduction per pass is no more than 10%, and the total reduction is 90%.

[0068] (3) Heat treatment: The hot-rolled magnesium alloy sheet is placed in a muffle furnace for heat treatment. The heat treatment temperature is 600℃, the heat treatment holding time is 30min, the heating rate is 10℃ / min, and water quenching is performed after the heat treatment is completed.

[0069] The microstructure of the dual-phase heterostructure MgSc alloy prepared in this comparative example is consistent with that of the traditional dual-phase magnesium-scandium alloy. It does not have a size-graded nano-precipitated phase and consists only of α phase and β dual phase.

[0070] The mechanical properties of the obtained heterostructure magnesium alloy were tested, and the results showed that its ultimate tensile strength was 331.2 MPa, its yield strength was 274.1 MPa, and its ultimate elongation was 18.8%.

[0071] Comparative Example 2 This comparative example provides a method for preparing a multi-scale hierarchical heterostructure magnesium alloy. The difference from Example 1 is that steps (2) and (3) are omitted, that is, the solution aging treatment is not performed. The rest is the same as Example 1.

[0072] Comparative Example 3 This comparative example provides a method for preparing a multi-scale hierarchical heterostructure magnesium alloy, wherein the composition of the magnesium alloy is: by weight percentage, Mg: 69.46%, Sc: 30.5%. The difference from Example 1 is that only the composition of the magnesium alloy is different, while the rest is the same as in Example 1.

[0073] Comparative Example 4 This comparative example provides a method for preparing a dual-phase heterostructure magnesium alloy, wherein the composition of the magnesium alloy is as follows (by weight percentage): Mg: 60.82%, Sc: 30.7%, Gd: 8.48%. The specific preparation method is the same as in Example 1, except that the composition of the magnesium alloy is different.

[0074] Comparative Example 5 This comparative example provides a method for preparing a dual-phase heterostructure magnesium alloy, wherein the composition of the magnesium alloy is: by weight percentage, Mg: 75.22%, Sc: 15.7%, Gd: 9.08%, and the specific preparation method is the same as in Example 1, except that the composition of the magnesium alloy is different.

[0075] Comparative Example 6 This comparative example provides a method for preparing a multi-scale hierarchical heterostructure magnesium alloy. The difference from Example 1 is that the aging temperature is 450℃, while the rest is the same as Example 1.

[0076] Comparative Example 7 This comparative example provides a method for preparing a multi-scale hierarchical heterostructure magnesium alloy. The difference from Example 1 is that the aging temperature is 80℃, while the rest is the same as Example 1.

[0077] The mechanical properties of the obtained heterostructured magnesium alloy were tested, and the results are shown in Table 1.

[0078] Table 1. Test table of alloy mechanical properties obtained in the embodiments and comparative examples of the present invention.

[0079] As shown in Table 1, the hierarchical heterostructure magnesium alloy prepared in the embodiments of the present invention maintains both high strength and good plasticity. The key to the improved plasticity lies in the back stress strengthening caused by the hierarchical heterostructure and the interaction between the nano-precipitated phase and dislocations. These factors promote the synergistic effect of multiple deformation mechanisms, enabling the material to maintain continuous work hardening capacity during tensile testing. The alloy and preparation method provided by the present invention not only achieve a synergistic improvement in strength and plasticity but also further expand the development potential of magnesium alloys in the field of lightweight applications.

[0080] Comparative Examples 1, 2, and 3 demonstrate the effects of Gd doping and solution aging. Gd doping significantly influences the microstructure of the alloy, particularly in the preparation of hierarchical heterostructures. Gd can form nano-coherent Mg3Gd precipitates in the alloy, which possess strong strengthening properties, contributing to increased strength and hardness. By controlling the amount of Gd doping, the hierarchical structure of the heterostructure can be enriched, thereby regulating the mechanical properties of the material. Furthermore, the formation of Mg3Gd precipitates effectively hinders dislocation movement and prevents dislocation pile-up, improving the alloy's plasticity and toughness.

[0081] The purpose of solution aging is to promote the homogenization of alloy ingots, resulting in a more uniform distribution of elements and optimizing the alloy's microstructure. During the aging process, secondary acicular α phase and nano-B2 phase in the β phase gradually precipitate, thereby strengthening the alloy. By controlling parameters such as temperature and time during the aging process, the transformation of the β phase can be effectively regulated, allowing the alloy to obtain the desired heterogeneous structural characteristics.

[0082] Comparative Examples 4 and 5 demonstrate the influence of the MgSc ratio on the hierarchical heterostructure. Adjusting the Mg / Sc ratio significantly affects the phase transformation behavior and the formation of the hierarchical heterostructure. An excessively high or low MgSc ratio leads to compression of the α+β two-phase temperature range. Specifically, excessively high Sc content may cause over-stabilization of the β phase, making it difficult to form fine precipitates in the low-temperature aging region, thus affecting the control of the hierarchical heterostructure. Conversely, an excessively low MgSc ratio results in excessively high α-phase content, making it difficult for the hierarchical structure to form stably during aging. Therefore, a suitable MgSc ratio is crucial for achieving the preparation of a hierarchical heterostructure; an unreasonable ratio makes the control of the hierarchical heterostructure difficult, affecting the overall performance of the alloy.

[0083] Comparative Examples 6 and 7 demonstrate the influence of aging temperature; the choice of aging temperature plays a crucial role in the precipitation behavior and structural evolution of the alloy. When the aging temperature is too high, the β phase undergoes a rapid phase transformation, which may lead to coarsening of the secondary α phase, or even complete transformation into the α phase. This results in a decrease in the alloy's strength and affects the microstructural stability of the material. Furthermore, excessively high aging temperatures may also lead to excessively large and inhomogeneous precipitates in the alloy, thus affecting the overall performance of the alloy.

[0084] When the aging temperature is too low, the precipitation of the secondary needle-like α phase becomes very slow, and in this case, a long aging time is required to complete the precipitation. Prolonged aging processes may lead to increased energy dissipation and potentially cause instability in the material's microstructure. For example, under prolonged low-temperature aging, some precipitated phases may undergo reverse dissolution or redissolution, affecting the final mechanical properties.

[0085] The embodiments described above are some, but not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A high strength-to-plasticity multi-scale hierarchical heterogeneous structured magnesium alloy, characterized in that, The magnesium alloy comprises the following components by weight percentage: Mg 65~70%, Sc 20~33%, the total amount of Mg and Sc is not greater than 100%, and the balance is Gd.

2. The high strength to ductility multiscale hierarchical structured magnesium alloy of claim 1, wherein, The dual-phase structure of the magnesium alloy includes a micron-sized α phase and a micron-sized β phase, wherein the micron-sized β phase includes a nano-needle-shaped secondary α phase, nano-B2-rich Sc particles, and L12-rich Gd nano-precipitates.

3. The high strength plastic multi-scale hierarchical structure magnesium alloy of claim 2, wherein, The micron-scale α-phase grain size is 5μm~70μm, the micron-scale β-phase grain size is 5μm~50μm, the nano-needle-shaped secondary α-phase grain size is 20nm~200nm, the nano-B2-rich Sc particle grain size is 20nm~50nm, and the L12-rich Gd nano-precipitated grain size is 10nm~30nm.

4. The method for preparing high strength and ductility multi-scale hierarchical structure magnesium alloy according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Weigh out Mg, Sc and Gd metals and vacuum melt them to obtain magnesium alloy ingots; S2. The magnesium alloy ingot obtained in S1 is subjected to solution-aging treatment. S3. Hot rolling the ingot obtained in S2 to obtain magnesium alloy sheet; S4. The magnesium alloy sheet obtained in S3 is subjected to heat treatment and quenching to obtain the graded heterogeneous structure magnesium alloy.

5. The production method according to claim 4, wherein The purity of the Mg, Sc and Gd metals in step S1 is 99.99 at%, the temperature of vacuum smelting is 900-1000°C, the vacuum smelting time is 10-15 min, the vacuum degree is ≤1×10 - 3 Pa, and the atmosphere is an argon atmosphere.

6. The production method according to claim 4, wherein The solution temperature in step S2 is 630℃~700℃, the solution time is 0.5~8h, the aging temperature is 100℃~400℃, and the aging time is 1~6h.

7. The production method according to claim 4, wherein The hot rolling temperature in step S3 is 550℃~650℃, the single-pass reduction is less than 10%, and the total reduction is 70%~90%.

8. The production method according to claim 4, wherein The heat treatment temperature in step S4 is 550℃~650℃, and the holding time is 10min~120min.

9. The production method according to claim 4, wherein The ultimate tensile strength of the graded heterostructure magnesium alloy described in step S4 is 439.4 MPa to 493 MPa, the yield strength is 309.6 MPa to 439 MPa, and the elongation at break is 22.8% to 40.8%.

10. The application of a high-strength, high-ductility, multi-scale hierarchical heterostructure magnesium alloy as described in any one of claims 1 to 3 in lightweight structural components for automobiles or aerospace.

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