450mpa grade low-cost high-tenacity heat deformation resistant magnesium alloy and preparation method thereof

Abstract

The application discloses a 450MPa-grade low-cost high-strength and high-toughness heat deformation magnesium alloy and a preparation method thereof, and belongs to the technical field of magnesium alloys.The 450MPa-grade low-cost high-strength and high-toughness heat deformation magnesium alloy is composed of the following chemical components: 6.5-8.0 wt.% Zn, 1.5-2.5 wt.% Y, 1.5-2.5 wt.% Nd, 0.3-0.5 wt.% Zr, 0.01-0.3 wt.% Ca, 0.01-0.2 wt.% Sr, Fe≤0.003 wt.%, Ni≤0.001 wt.%, Cu≤0.01 wt.%, Si≤0.04 wt.%, and the balance of Mg.Compared with existing deformation magnesium alloys of the same strength grade, the application does not need to add a large amount of valuable rare earth elements, the preparation process is simple and controllable, the raw material cost is low, and the application is suitable for industrialized production, can be widely applied to the fields of aerospace, rail transportation and the like, and has good application value.

Description

Technical Field

[0001] This invention relates to the field of magnesium alloy technology, and in particular to a low-cost, high-strength, high-toughness, heat-resistant deformable magnesium alloy of 450MPa grade and its preparation method. Background Technology

[0002] With the continuous acceleration of lightweighting in aerospace, rail transportation and other fields, end-use equipment is placing more stringent performance requirements on the load-bearing capacity and high-temperature service stability of structural components. Wrought magnesium alloys, due to their combination of room temperature strength and toughness, high-temperature softening resistance, low cost and ease of mass production, have become a core structural material urgently needed for development in the industry.

[0003] Currently, most commercially available wrought magnesium alloys struggle to simultaneously meet both performance and cost requirements. For example, rare-earth-free / low-rare-earth magnesium alloys, such as AZ31B and ZK60A, while having lower raw material costs and excellent plasticity, generally have tensile strengths below 350 MPa and significantly insufficient resistance to softening at high temperatures, limiting their application range. On the other hand, high-rare-earth heat-resistant magnesium alloys, such as WE43B and VW93M, offer stable high-temperature performance, but their high total rare-earth content increases casting difficulty and raw material costs. Furthermore, these high-rare-earth magnesium alloys exhibit greater resistance to plastic deformation, resulting in lower production efficiency and hindering large-scale application.

[0004] To address the aforementioned issues, the industry has conducted extensive research on Mg-Zn-RE rare earth magnesium alloys, aiming to improve the mechanical properties of materials through the combined precipitation strengthening effect of Zn and RE elements. However, existing technologies still have several limitations: some alloy systems continuously increase the proportion of rare earth elements in pursuit of high strength, making it difficult for alloys with low rare earth content to achieve a room temperature tensile strength of 400 MPa, and the precipitated phases exhibit poor thermal stability, resulting in significant strength degradation at high temperatures, making it difficult to simultaneously achieve the requirements of high strength, toughness, and heat resistance. Furthermore, most material system solutions rely on complex plastic deformation processes, cumbersome production processes, and heat treatment regimes, leading to low processing efficiency, high hidden costs, and difficulty in achieving stable production.

[0005] Based on the above situation, developing a low-cost, high-performance heat-resistant deformable magnesium alloy material that is cost-controllable, simple to process, and has both high strength and toughness as well as high heat resistance is of great engineering significance for breaking through the bottleneck of large-scale application of magnesium alloys and promoting the upgrading of lightweight material systems. Summary of the Invention

[0006] The purpose of this invention is to provide a low-cost, high-strength, high-toughness, and heat-resistant wrought magnesium alloy with a strength of 450MPa and its preparation method, thereby solving the aforementioned problems in the background art. Compared with existing wrought magnesium alloys of the same strength level, this invention does not require the addition of large amounts of precious rare earth elements, has a simple and controllable preparation process, lower raw material costs, is suitable for large-scale industrial production, and can be widely used in aerospace, rail transportation, and other fields, demonstrating significant application value.

[0007] To achieve the above objectives, the present invention provides the following technical solution: One of the technical solutions of this invention is to provide a 450MPa grade low-cost, high-strength, tough, heat-resistant, and deformable magnesium alloy, which is composed of the following chemical components by mass percentage: 6.5~8.0 wt.% Zn, 1.5~2.5 wt.% Y, 1.5~2.5 wt.% Nd, 0.3~0.5 wt.% Zr, 0.01~0.3 wt.% Ca, 0.01~0.2 wt.% Sr, Fe≤0.003 wt.%, Ni≤0.001 wt.%, Cu≤0.01 wt.%, Si≤0.04 wt.%, and the balance is Mg.

[0008] Preferably, the 450MPa grade low-cost, high-strength, tough, heat-resistant deformable magnesium alloy is composed of the following chemical components by weight percentage: The composition is 6.8~7.8 wt.% Zn, 1.8~2.3 wt.% Y, 1.8~2.3 wt.% Nd, 0.37~0.47 wt.% Zr, 0.02~0.2 wt.% Ca, and 0.02~0.15 wt.% Sr, with strict control over impurity content: Fe≤0.003 wt.%, Ni≤0.001 wt.%, Cu≤0.01 wt.%, Si≤0.04 wt.%, with the balance being Mg.

[0009] The resulting wrought magnesium alloy has a room temperature tensile strength ≥450MPa, a yield strength ≥390MPa, and an elongation ≥9%; and the material can still maintain a high strength and toughness level at 200℃.

[0010] The second technical solution of this invention provides a method for preparing the above-mentioned 450MPa grade low-cost, high-strength, tough, heat-resistant deformable magnesium alloy, comprising the following steps: (1) The ingredients are prepared according to the chemical composition, then melted, refined and cast to obtain magnesium alloy rods; (2) The magnesium alloy casting rod is homogenized and cooled to obtain a homogeneous casting rod; (3) The homogeneous cast rod is subjected to hot extrusion treatment and cooled to obtain magnesium alloy extrusion products; (4) Heat treatment: After performing a two-stage solution heat treatment on the magnesium alloy extrusion product, a two-stage aging heat treatment is performed to obtain the 450MPa grade low-cost, high-strength, tough, heat-resistant deformable magnesium alloy.

[0011] Preferably, the homogenization temperature of the homogenization process is 450~480℃, and the homogenization time is 15~25h.

[0012] Preferably, the cooling method in step (2) is air cooling.

[0013] Preferably, the parameters of the hot extrusion treatment are as follows: extrusion ratio of 12~40, extrusion speed of 0.3~0.7mm / s, and extrusion cylinder temperature, extrusion die temperature and sample temperature of 320~380℃.

[0014] Preferably, the cooling method in step (3) is air cooling.

[0015] Preferably, the extruded product is in the shape of a round bar.

[0016] Preferably, the two-stage solution heat treatment includes the following steps: heating to 470°C at a heating rate of 185°C / h, then holding at 470°C for 8 hours, then heating to 490°C at a heating rate of 12.5°C / h, holding at 490°C for 4 hours, and then water cooling.

[0017] Preferably, the two-stage aging heat treatment includes the following steps: heating to 90°C at a heating rate of 65°C / h, then holding at 90°C for 4 hours, then heating to 200°C at a heating rate of 110°C / h, holding at 200°C for 20 hours, and then air cooling.

[0018] Preferably, the casting is a semi-continuous casting process, using a magnesium alloy casting rod machine for production, and the casting crystallizer is equipped with an electromagnetic stirrer with an electromagnetic oscillation frequency of 20Hz and a casting speed of 50mm / min.

[0019] The technical principle of this invention is as follows: This invention uses the conventional element Zn as the core strengthening element. On the one hand, it can improve the intrinsic strength of the matrix through solid solution; on the other hand, it can provide a compositional basis for aging precipitation. Based on this, by adding light and heavy rare earth elements Nd and Y, relying on the synergistic effect of multi-element alloying, the room temperature strength and toughness and high temperature heat resistance of the alloy are simultaneously optimized, improving the stability of the microstructure under high temperature environments. Zr acts as the main grain refiner, refining the α-Mg matrix grains through heterogeneous nucleation, achieving a simultaneous improvement in strength and plasticity through the grain refinement strengthening effect. Trace amounts of Ca and Sr can assist in refining the microstructure, optimizing the morphology and distribution of the grain boundary second phase, inhibiting the formation of continuous brittle network phases, and pinning grain boundaries to suppress grain coarsening and phase aggregation at high temperatures, further synergistically improving the alloy's strength, toughness, and the thermal stability of the matrix microstructure. Hot extrusion plastic deformation breaks up the coarse as-cast microstructure, eliminates casting defects, induces dynamic recrystallization, and achieves microstructure refinement and homogenization. Based on the above elemental formulation design, this invention employs a two-stage solid solution + two-stage aging heat treatment process to solve the problem of balancing diffusion sufficiency and microstructure stability in single-stage processes. This is mainly because the Mg-Zn phase in the material system of this invention has a lower melting point than the Mg-RE phase. In the two-stage solid solution stage, the low-melting-point phase is dissolved at a low temperature to avoid overburning, and then the temperature is increased to promote the re-dissolution of rare earth phases, maximizing the solid solution solute. Furthermore, the Zr and Ca / Sr synergistic pinning inhibits grain coarsening, reserving solute for aging. In the two-stage aging stage, the high-density metastable phase nucleation is induced at a low temperature, and then the uniform growth of the nano-precipitated phase is promoted at a high temperature, ensuring precipitation strengthening effect, optimizing grain boundary phase morphology, and synergistically improving the material's strength, toughness, and high-temperature thermal stability.

[0020] The beneficial technical effects of the present invention are as follows: This invention provides a low-cost, high-strength, high-toughness, and heat-resistant deformable magnesium alloy with a strength of 450 MPa and its preparation method. The total rare earth content is controlled to be <5 wt%, lower than that of commercial high rare earth magnesium alloys, resulting in a significant cost advantage. The obtained product exhibits excellent strength and toughness and is suitable for large-scale production. Through synergistic alloying design of Zn with light and heavy rare earth elements, combined with traditional hot extrusion and special heat treatment processes, a composite strengthening mechanism is constructed. The magnesium alloy achieves a room temperature tensile strength of 450 MPa and also possesses both room temperature toughness and high-temperature softening resistance, making it suitable for medium- and high-temperature service scenarios. 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 embodiments 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 This is a process flow diagram of the present invention.

[0023] Figure 2 This is a schematic diagram of the temperature control process for the two-stage solution heat treatment in Embodiment 1 of the present invention.

[0024] Figure 3 This is a schematic diagram of the temperature control process for the two-stage aging heat treatment in Embodiment 1 of the present invention. Detailed Implementation

[0025] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0026] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0027] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. It should be noted that any aspects of this invention not described in detail are conventional practices in the art and are not the focus of this invention.

[0028] The terms “comprising,” “including,” “having,” “containing,” etc., used in this invention are all open-ended terms, meaning that they include but are not limited to.

[0029] This invention discloses a 450MPa grade, low-cost, high-strength, tough, and heat-resistant deformable magnesium alloy, which is composed of the following chemical components by mass percentage: 6.5~8.0 wt.% Zn, 1.5~2.5 wt.% Y, 1.5~2.5 wt.% Nd, 0.3~0.5 wt.% Zr, 0.01~0.3 wt.% Ca, 0.01~0.2 wt.% Sr, Fe≤0.003 wt.%, Ni≤0.001 wt.%, Cu≤0.01 wt.%, Si≤0.04 wt.%, and the balance is Mg.

[0030] Compared with existing wrought magnesium alloys of the same strength level (such as VW93M, VW84M, WN54M and other magnesium alloys involved in "GB / T 38715-2020 High Strength Magnesium Alloy Rods"), this invention does not require the addition of a large amount of precious rare earth elements, the preparation process is simple and controllable, the raw material cost is low, it is suitable for large-scale industrial production, and can be widely used in aerospace, rail transportation and other fields, and has great application value.

[0031] This invention also discloses a method for preparing the above-mentioned 450MPa grade low-cost, high-strength, tough, and heat-resistant deformable magnesium alloy, comprising the following steps: (1) Semi-continuous casting of rods: Magnesium ingots are put into a melting crucible and after they melt, Zn ingots, MgY30 master alloy, MgNd30 master alloy, metallic Sr, MgZr30 master alloy and MgCa15 master alloy are added in sequence to alloy the magnesium liquid. The magnesium liquid is refined by using 2 wt.% RJ-5 flux. During the melting process, SF6+N2 mixed gas is used to protect the magnesium liquid. After the composition is qualified, the magnesium alloy rod casting machine is used to produce rods. The casting crystallizer is equipped with electromagnetic stirring. The electromagnetic oscillation frequency is 20~30Hz and the casting speed is 45-65mm / min. The generated electromagnetic force strengthens the movement of magnesium alloy liquid in the liquid phase cavity, improves the solidification structure and composition segregation of magnesium rods, ensures product quality, and obtains magnesium alloy semi-continuous casting rods. (2) Homogenization treatment of cast rod: The magnesium alloy semi-continuous cast rod prepared in step (1) is placed in a heat treatment furnace for homogenization treatment. The homogenization temperature is 450~480℃, the homogenization time is 15~25h, and the cooling method is room temperature air cooling. This eliminates the segregation of the as-cast components, improves the hot extrusion performance, and obtains a homogenized cast rod. (3) Hot extrusion: The homogeneous cast rod obtained in step (2) is hot extruded. The extruded product is a round rod with an extrusion ratio of 12 to 40 and an extrusion speed of 0.3 to 0.7 mm / s. The temperature of the extrusion cylinder, the temperature of the extrusion die and the temperature of the sample are 320 to 380℃. Then, it is air-cooled to room temperature. The coarse matrix structure of the cast is broken by plastic deformation to obtain an extruded rod with fine grains and uniform structure. (4) Heat treatment: The magnesium alloy round bar obtained in step (3) is placed in a heat treatment furnace for heat treatment (first a two-stage solution heat treatment, then a two-stage aging heat treatment); wherein, the temperature control process of the two-stage solution heat treatment is: heating to 470°C at a heating rate of 185°C / h, then holding at 470°C for 8h, then heating to 490°C at a heating rate of 12.5°C / h, holding at 490°C for 4h, and then water cooling at room temperature to obtain the solution product; the temperature control process of the two-stage aging heat treatment is: heating to 90°C at a heating rate of 65°C / h, then holding at 90°C for 4h, then heating to 200°C at a heating rate of 110°C / h, holding at 200°C for 20h, and then air cooling at room temperature to obtain the final product.

[0032] Unless otherwise specified, "room temperature" in this invention refers to 25±5℃.

[0033] All raw materials used in the following embodiments and comparative examples of the present invention are commercially available products.

[0034] Figure 1 This is a process flow diagram of the present invention.

[0035] The technical solution of the present invention will be further illustrated by the following embodiments.

[0036] Example 1 A low-cost, high-strength, high-toughness, heat-resistant deformable magnesium alloy with a strength of 450 MPa is composed of the following chemical components by mass percentage: 6.86 wt.% Zn, 1.95 wt.% Y, 2.13 wt.% Nd, 0.39 wt.% Zr, 0.02 wt.% Ca, 0.03 wt.% Sr, with impurities of 0.002 wt.% Fe, 0.0002 wt.% Ni, 0.0026 wt.% Cu, 0.0103 wt.% Si, and the balance being Mg.

[0037] A process flow for preparing a 450MPa grade, low-cost, high-strength, tough, and heat-resistant deformable magnesium alloy is shown below. Figure 1 The specific steps are as follows: (1) Semi-continuous casting of rods: Magnesium ingots are put into a melting crucible and after they melt, Zn ingots, MgY30 master alloy, MgNd30 master alloy, metallic Sr, MgZr30 master alloy and MgCa15 master alloy are added in sequence to alloy the magnesium liquid. The magnesium liquid is refined by using 2 wt.% RJ-5 flux. During the melting process, SF6+N2 mixed gas (volume ratio of the two is 1:99) is used to protect the magnesium liquid. After the composition is qualified, the magnesium alloy rod casting machine is used to produce rods. The casting crystallizer is equipped with electromagnetic stirring, the electromagnetic oscillation frequency is 20Hz and the casting speed is 50mm / min to obtain magnesium alloy semi-continuous rods.

[0038] (2) Homogenization treatment of cast rod: The magnesium alloy semi-continuous cast rod prepared in step (1) is placed in a heat treatment furnace for homogenization treatment. The homogenization temperature is 460℃, the homogenization time is 18h, and the cooling method is room temperature air cooling to obtain a homogenized cast rod.

[0039] (3) Hot extrusion: The homogeneous cast rod obtained in step (2) is hot extruded. The extruded product is a round rod with an extrusion ratio of 35 and an extrusion speed of 0.5 mm / s. The temperature of the extrusion cylinder, the temperature of the extrusion die and the temperature of the magnesium rod are all 340℃. Then, it is air-cooled to room temperature to obtain a magnesium alloy round rod.

[0040] (4) Heat treatment: The magnesium alloy round bar obtained in step (3) is placed in a heat treatment furnace for heat treatment (first, a two-stage solution heat treatment is performed, followed by a two-stage aging heat treatment). The temperature control process for the two-stage solution heat treatment is described in [link to relevant documentation]. Figure 2 (Heat to 470℃ at a heating rate of 185℃ / h, then hold at 470℃ for 8 hours, then heat to 490℃ at a heating rate of 12.5℃ / h, hold at 490℃ for 4 hours, then cool with water at room temperature) to obtain the solid solution product; the temperature control process for the two-stage aging heat treatment is described in [link to relevant documentation]. Figure 3 (Heating to 90℃ at a heating rate of 65℃ / h, then holding at 90℃ for 4h, then heating to 200℃ at a heating rate of 110℃ / h, holding at 200℃ for 20h, and then air cooling at room temperature) The solute elements are fully dissolved by step heating and solid solution, and the distribution of the precipitated phase is controlled by two-stage aging to obtain the final product.

[0041] Through the above four steps of semi-continuous casting, casting homogenization, hot extrusion, and heat treatment, a low-cost, high-strength, tough, and heat-resistant deformable magnesium alloy with a strength of 450MPa is finally obtained.

[0042] Figure 2 This is a schematic diagram of the temperature control process for the two-stage solution heat treatment in Embodiment 1 of the present invention.

[0043] Figure 3 This is a schematic diagram of the temperature control process for the two-stage aging heat treatment in Embodiment 1 of the present invention.

[0044] Example 2 A low-cost, high-strength, high-toughness, heat-resistant deformable magnesium alloy with a strength of 450 MPa is composed of the following chemical composition by mass percentage: 7.3 wt.% Zn, 2.23 wt.% Y, 2.25 wt.% Nd, 0.42 wt.% Zr, 0.03 wt.% Ca, 0.04 wt.% Sr, with impurities of 0.0018 wt.% Fe, 0.0002 wt.% Ni, 0.0019 wt.% Cu, 0.0152 wt.% Si, and the balance being Mg. The specific steps are as follows: (1) Semi-continuous casting of rods: Magnesium ingots are put into a melting crucible and after they melt, Zn ingots, MgY30 master alloy, MgNd30 master alloy, metallic Sr, MgZr30 master alloy and MgCa15 master alloy are added in sequence to alloy the magnesium liquid to obtain magnesium liquid. The magnesium liquid is refined by using 2 wt.% RJ-5 flux. During the melting process, SF6+N2 mixed gas is used to protect the magnesium liquid. After the composition is qualified, magnesium alloy rod casting machine is used to produce rods. The casting crystallizer is equipped with electromagnetic stirring. The electromagnetic oscillation frequency is 25Hz and the casting speed is 48mm / min to obtain magnesium alloy semi-continuous rods.

[0045] (2) Homogenization treatment of cast rod: The magnesium alloy semi-continuous cast rod prepared in step (1) is placed in a heat treatment furnace for homogenization treatment. The homogenization temperature is 450℃, the homogenization time is 20h, and the cooling method is room temperature air cooling.

[0046] (3) Hot extrusion: The homogeneous cast rod obtained in step (2) is hot extruded. The extruded product is a round rod with an extrusion ratio of 30 and an extrusion speed of 0.6 mm / s. The temperature of the extrusion cylinder, the temperature of the extrusion die and the temperature of the magnesium rod are all 330℃. Then, it is air-cooled to room temperature to obtain a magnesium alloy round rod.

[0047] (4) Heat treatment: The magnesium alloy round bar obtained in step (3) is placed in a heat treatment furnace for heat treatment (first, a two-stage solution heat treatment is performed, followed by a two-stage aging heat treatment). The temperature control process for the two-stage solution heat treatment is described in [link to relevant documentation]. Figure 2 (Heat to 470℃ at a heating rate of 185℃ / h, then hold at 470℃ for 8 hours, then heat to 490℃ at a heating rate of 12.5℃ / h, hold at 490℃ for 4 hours, then cool with water at room temperature) to obtain the solid solution product; the temperature control process for the two-stage aging heat treatment is described in [link to relevant documentation]. Figure 3 (Heat to 90℃ at a heating rate of 65℃ / h, then hold at 90℃ for 4h, then heat to 200℃ at a heating rate of 110℃ / h, hold at 200℃ for 20h, and then air cool at room temperature) to obtain the final product.

[0048] Through the above four steps of semi-continuous casting, casting homogenization, hot extrusion, and heat treatment, a low-cost, high-strength, tough, and heat-resistant deformable magnesium alloy with a strength of 450MPa is finally obtained.

[0049] Example 3 A low-cost, high-strength, high-toughness, heat-resistant deformable magnesium alloy with a strength of 450 MPa, comprising the following chemical composition by mass percentage: 7.8 wt.% Zn, 2.28 wt.% Y, 2.24 wt.% Nd, 0.45 wt.% Zr, 0.05 wt.% Ca, 0.06 wt.% Sr, with impurities of 0.0024 wt.% Fe, 0.00018 wt.% Ni, 0.0033 wt.% Cu, 0.0144 wt.% Si, and the balance being Mg. The specific steps are as follows: (1) Semi-continuous casting of rods: Magnesium ingots are put into a melting crucible and after they melt, Zn ingots, MgY30 master alloy, MgNd30 master alloy, metallic Sr, MgZr30 master alloy and MgCa15 master alloy are added in sequence to alloy the magnesium liquid to obtain magnesium liquid. The magnesium liquid is refined by using 2 wt.% RJ-5 flux. During the melting process, SF6+N2 mixed gas is used to protect the magnesium liquid. After the composition is qualified, magnesium alloy rod casting machine is used to produce rods. The casting crystallizer is equipped with electromagnetic stirring. The electromagnetic oscillation frequency is 28Hz and the casting speed is 55mm / min to obtain magnesium alloy semi-continuous rods.

[0050] (2) Homogenization treatment of cast rod: The magnesium alloy semi-continuous cast rod prepared in step (1) is placed in a heat treatment furnace for homogenization treatment. The homogenization temperature is 470℃, the homogenization time is 22h, and the cooling method is room temperature air cooling.

[0051] (3) Hot extrusion: The homogeneous cast rod obtained in step (2) is hot extruded. The extruded product is a round rod with an extrusion ratio of 32 and an extrusion speed of 0.7 mm / s. The temperature of the extrusion cylinder, the temperature of the extrusion die and the temperature of the magnesium rod are all 350°C. Then, the rod is air-cooled to room temperature to obtain a magnesium alloy round rod.

[0052] (4) Heat treatment: The magnesium alloy round bar obtained in step (3) is placed in a heat treatment furnace for heat treatment (first, a two-stage solution heat treatment is performed, followed by a two-stage aging heat treatment). The temperature control process for the two-stage solution heat treatment is described in [link to relevant documentation]. Figure 2 (Heat to 470℃ at a heating rate of 185℃ / h, then hold at 470℃ for 8 hours, then heat to 490℃ at a heating rate of 12.5℃ / h, hold at 490℃ for 4 hours, then cool with water at room temperature) to obtain the solid solution product; the temperature control process for the two-stage aging heat treatment is described in [link to relevant documentation]. Figure 3(Heat to 90℃ at a heating rate of 65℃ / h, then hold at 90℃ for 4h, then heat to 200℃ at a heating rate of 110℃ / h, hold at 200℃ for 20h, and then air cool at room temperature) to obtain the final product.

[0053] Through the above four steps of semi-continuous casting, casting homogenization, hot extrusion, and heat treatment, a low-cost, high-strength, tough, and heat-resistant deformable magnesium alloy with a strength of 450MPa is finally obtained.

[0054] Comparative Example 1 The VW93M magnesium alloy extruded bars used in this comparative example were purchased from Shanxi Ruige Metal New Material Co., Ltd. Their composition conforms to GB / T 38715-2020 High-strength Magnesium Alloy Bars. The extrusion ratio was 36, the extrusion speed was 0.5 mm / s, and the extrusion barrel temperature, extrusion die temperature, and magnesium bar temperature were all 400℃. The bars were then air-cooled to room temperature. The extruded product was a round bar, and heat treatment was performed according to GB / T38715-2020 High-strength Magnesium Alloy Bars.

[0055] Comparative Example 2 The VW84M magnesium alloy extruded bars used in this comparative example were purchased from Shanxi Ruige Metal New Material Co., Ltd. Their composition conforms to GB / T 5153-2016 "Wrought Magnesium and Magnesium Alloys - Grades and Chemical Composition". The extrusion ratio was 36, the extrusion speed was 0.6 mm / s, and the extrusion barrel temperature, extrusion die temperature, and magnesium bar temperature were all 400℃. The bars were then air-cooled to room temperature. The extruded product was a round bar, and heat-treated according to GB / T 38715-2020 "High-Strength Magnesium Alloy Bars".

[0056] Comparative Example 3 The ZK61M magnesium alloy extruded bar used in this comparative example was purchased from Shanxi Ruige Metal New Material Co., Ltd. Its composition conforms to GB / T 5153-2016 "Wrought Magnesium and Magnesium Alloys - Grades and Chemical Composition". The extrusion ratio was 36, the extrusion speed was 0.5 mm / s, and the extrusion barrel temperature, extrusion die temperature, and magnesium bar temperature were all 380℃. The bar was then air-cooled to room temperature. The extruded product was a round bar, and heat-treated according to GB / T 38715-2020 "High-Strength Magnesium Alloy Bars".

[0057] Comparative Example 4 The AZ80A magnesium alloy extruded bar used in this comparative example was purchased from Shanxi Ruige Metal New Material Co., Ltd. Its composition conforms to GB / T 5153-2016 "Wrought Magnesium and Magnesium Alloy Grades and Chemical Composition". The extrusion ratio was 36, the extrusion speed was 0.5 mm / s, and the extrusion barrel temperature, extrusion die temperature, and magnesium bar temperature were all 390℃. It was then air-cooled to room temperature. The extruded product was a round bar, and heat-treated according to GB / T 5155-2013 "Hot Extruded Magnesium Alloy Bars".

[0058] Comparative Example 5 The only difference from Example 1 is that the alloy composition is modified as follows: no Zr, Ca, or Sr alloying elements are added, and 7.26 wt.% Zn, 2.31 wt.% Y, and 2.36 wt.% Nd are prepared, with impurities of 0.0019 wt.% Fe, 0.00017 wt.% Ni, 0.0021 wt.% Cu, and 0.0112 wt.% Si, with the balance being Mg, to obtain Mg-Zn-Y-Nd alloy rods.

[0059] Effect verification The mechanical properties of the deformed magnesium alloys prepared in each embodiment and comparative example were tested at room temperature and 200°C. The test results are shown in Table 1.

[0060] Table 1 Mechanical properties of the deformed magnesium alloys in Examples 1-3 and Comparative Examples 1-5 As can be seen from Table 1, the 450MPa grade low-cost high-strength and high-toughness heat-resistant deformable magnesium alloys prepared in the various embodiments of the present invention have a room temperature tensile strength ≥450MPa, a yield strength ≥390MPa, and an elongation ≥9%. At 200℃, the tensile strength ≥339MPa, the yield strength ≥250MPa, and the elongation ≥16%, which combines room temperature strength and toughness with high temperature resistance to softening.

[0061] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A low-cost, high-strength, tough, heat-resistant deformable magnesium alloy with a strength of 450 MPa, characterized in that, It consists of the following chemical components by mass percentage: 6.5~8.0 wt.% Zn, 1.5~2.5 wt.% Y, 1.5~2.5 wt.% Nd, 0.3~0.5 wt.% Zr, 0.01~0.3wt.% Ca, 0.01~0.2 wt.% Sr, Fe≤0.003 wt.%, Ni≤0.001 wt.%, Cu≤0.01 wt.%, Si≤0.04wt.%, the balance is Mg.

2. A method for preparing the 450MPa grade, low-cost, high-strength, tough, heat-resistant deformable magnesium alloy as described in claim 1, characterized in that, Includes the following steps: (1) The ingredients are prepared according to the chemical composition, then melted, refined and cast to obtain magnesium alloy rods; (2) The magnesium alloy casting rod is homogenized and cooled to obtain a homogeneous casting rod; (3) The homogeneous cast rod is subjected to hot extrusion treatment and cooled to obtain magnesium alloy extrusion products; (4) Heat treatment: After performing a two-stage solution heat treatment on the magnesium alloy extrusion product, a two-stage aging heat treatment is performed to obtain the 450MPa grade low-cost, high-strength, tough, heat-resistant deformable magnesium alloy.

3. The preparation method according to claim 2, characterized in that, The homogenization temperature for the homogenization process is 450~480℃, and the homogenization time is 15~25h.

4. The preparation method according to claim 2, characterized in that, The cooling method described in step (2) is air cooling.

5. The preparation method according to claim 2, characterized in that, The parameters for the hot extrusion treatment are as follows: extrusion ratio of 12~40, extrusion speed of 0.3~0.7 mm / s, and extrusion cylinder temperature, extrusion die temperature and sample temperature of 320~380℃.

6. The preparation method according to claim 2, characterized in that, The cooling method described in step (3) is air cooling.

7. The preparation method according to claim 2, characterized in that, The two-stage solution heat treatment includes the following steps: Heat to 470℃ at a heating rate of 185℃ / h, then hold at 470℃ for 8 hours, then heat to 490℃ at a heating rate of 12.5℃ / h, hold at 490℃ for 4 hours, and then water cool.

8. The preparation method according to claim 2, characterized in that, The two-stage aging heat treatment includes the following steps: Heat to 90℃ at a heating rate of 65℃ / h, then hold at 90℃ for 4 hours, then heat to 200℃ at a heating rate of 110℃ / h, hold at 200℃ for 20 hours, and then air cool.

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