A magnesium alloy with good organizational thermal stability and a preparation method and application thereof

Abstract

The application belongs to the technical field of magnesium alloy materials, and more particularly relates to a magnesium alloy with good microstructure thermal stability and a preparation method and application thereof. The magnesium alloy provided by the application comprises the following components in percentage by mass: Al: 2% to 4%, Zn: 0.5% to 1.5%, Ca: 0.5% to 1.5%, Mn: 0.1% to 0.5%, and the balance is Mg. The magnesium alloy ingot with the above components is subjected to hot extrusion at 200 DEG C to 225 DEG C and annealing treatment at 340 DEG C to 360 DEG C, a multi-scale second phase system composed of micron Al-Ca phases and nano Al2Ca precipitated phases is constructed in the alloy through the synergistic alloying effect of Ca and Al elements, and a typical bimodal microstructure structure is maintained, so that the magnesium alloy with high microstructure thermal stability and excellent mechanical properties can be prepared, and is suitable for lightweight structural parts in transportation and aerospace equipment.

Description

Technical Field

[0001] This application belongs to the field of aluminum alloy technology, and more specifically, relates to a magnesium alloy with good thermal stability and its preparation method and application. Background Technology

[0002] Magnesium alloys are widely used in transportation, electronics, and lightweight structures due to their low density and high specific strength. However, the mechanical properties of traditional Mg-Al-Zn magnesium alloys need improvement, and they are prone to rapid static recrystallization (SRX) and grain coarsening under medium- and high-temperature conditions (300℃~350℃), which leads to a decrease in microstructure stability and mechanical properties, limiting their application in structural components with high service temperatures or requiring heat treatment.

[0003] Existing research indicates that alloying with rare earth elements can improve the thermal stability of magnesium alloys, but the high cost of rare earth elements hinders large-scale industrial applications.

[0004] Therefore, it is necessary to provide a magnesium alloy that has low material cost and excellent microstructural stability in the medium and high temperature range. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this application is to provide a magnesium alloy with good microstructure and thermal stability, its preparation method and application, and to solve the problems of poor microstructure and thermal stability of traditional Mg-Al-Zn magnesium alloys, high production cost of high thermal stability magnesium alloys made by adding rare earth elements, and unsuitability for industrial application.

[0006] To achieve the above objectives, in a first aspect, this application provides a magnesium alloy with good thermal stability, comprising the following components by mass percentage: Al: 2%~4%, Zn: 0.5%~1.5%, Ca: 0.5%~1.5%, Mn: 0.1%~0.5%, with the balance being Mg; The alloy microstructure of the aforementioned magnesium alloy includes deformed grains and recrystallized grains, as well as micron-sized Al-Ca compounds distributed in a lamellar pattern along the extrusion direction and lamellar nano-sized Al2Ca precipitates dispersed within the grains.

[0007] Preferably, the average grain size of the deformed grains is 15μm to 30μm.

[0008] Preferably, the average grain size of the recrystallized grains is 1 μm to 5 μm.

[0009] Preferably, the thickness of the above-mentioned micron-sized Al-Ca compound is 1 μm to 3 μm.

[0010] Preferably, the thickness of the above-mentioned nanoscale Al2Ca precipitate is 2nm~8nm.

[0011] Preferably, the magnesium alloy has a room temperature tensile strength ≥420MPa and a room temperature elongation ≥8%.

[0012] Secondly, this application provides a method for preparing the above-mentioned magnesium alloy, comprising the following steps: S1. Prepare the raw materials according to the above-mentioned magnesium alloy composition, then melt the prepared raw materials under a protective atmosphere. After all the raw materials have melted, pour them into a preheated mold and cool them to obtain a magnesium alloy ingot. S2. The above magnesium alloy ingot is homogenized and annealed, and then hot extruded to obtain an extruded magnesium alloy. S3. Anneal the extruded magnesium alloy to obtain the magnesium alloy.

[0013] Preferably, in step S1, the protective atmosphere gas is one or more of nitrogen, carbon dioxide, sulfur hexafluoride, and an inert gas with a purity of not less than 99.99%.

[0014] Preferably, in step S1, the melting temperature is 700℃~760℃ and the melting time is 10min~30min.

[0015] Preferably, in step S1, the preheating temperature of the mold is 150℃~250℃.

[0016] Preferably, in step S2, the temperature of the homogenization treatment is 400℃~450℃, and the holding time of the homogenization treatment is 24h~36h.

[0017] Preferably, in step S2, the temperature of the hot extrusion is 200℃~225℃, the extrusion ratio of the hot extrusion is (3~10):1, and the hot extrusion speed is 0.1mm / s~0.3mm / s.

[0018] Preferably, before hot extrusion in step S2, the extrusion die and the homogenized annealed magnesium alloy ingot are preheated.

[0019] More preferably, the preheating temperature of the extrusion die is 180℃~250℃, and the preheating temperature of the magnesium alloy ingot after homogenization annealing is 180℃~240℃.

[0020] Preferably, in step S3, the annealing temperature is 340℃~360℃ and the annealing time is 1min~30min.

[0021] Thirdly, this application protects the application of the above-mentioned magnesium alloy in the manufacture of lightweight structural components for transportation vehicles or aerospace equipment.

[0022] In summary, the technical solutions conceived in this application have the following main technical advantages compared with the prior art: (1) The magnesium alloy with good thermal stability provided in this application is constructed by designing the element types and ratios of the magnesium alloy and utilizing the synergistic alloying effect of Ca and Al elements to construct a multi-scale second-phase system of micron-sized Al-Ca phase and nano-sized Al2Ca precipitate. Among them, the micron-sized Al-Ca phase is distributed in a lamellar shape along the extrusion direction, forming a spatial separation effect between deformed grains and recrystallized grains in the bimodal structure; the nano-sized Al2Ca precipitate is uniformly dispersed in a lamellar shape inside the deformed grains and recrystallized grains, forming high-density pinning points within the grains. The synergistic effect of the two effectively suppresses grain boundary migration and static recrystallization coarsening under medium and high temperature conditions, so that the alloy structure maintains a stable bimodal structure, achieving excellent matching in tensile strength and elongation, and maintaining high strength while achieving good plasticity. Compared with existing magnesium alloys, this magnesium alloy avoids the high cost brought by rare earth elements, and at the same time exhibits excellent structural stability and mechanical property matching in the medium and high temperature range, effectively solving the problem of poor thermal stability of traditional Mg-Al-Zn alloys.

[0023] (2) The preparation method provided in this application, by precisely controlling the hot extrusion temperature and annealing process, introduces high-density dislocations and small-angle grain boundaries during the hot extrusion stage to provide nucleation sites for subsequent precipitation. During the annealing stage, it induces the nanosheet-like Al2Ca precipitates to grow controllably from about 1 nm to 2~8 nm. At the same time, the small-angle grain boundaries migrate and are strongly pinned by the thickened precipitates, so that the bimodal structure remains highly stable after annealing, and the recrystallization volume fraction remains stable at 45%~60%. Through the synergistic regulation of hot extrusion and annealing, the dynamic thickening of the nano-Al2Ca precipitates and the synergistic regulation of the grain boundary state are achieved.

[0024] (3) The elements used in the preparation method provided in this application are all low-cost, readily available industrial pure metals and intermediate alloys, and there is no need to add rare earth elements; the extrusion temperature range is wide (200℃~225℃), the extrusion ratio is moderate (3~10), and there is no need for large-scale special equipment; the annealing time is short (1~30min), the energy consumption is low, and near-net-shape products such as bars and profiles can be obtained directly. It has significant advantages such as a wide process window, strong operability, and suitability for industrial production, and is suitable for the manufacture of lightweight structural parts in the fields of transportation and electronic communication. Attached Figure Description

[0025] Figure 1 This is a schematic flowchart of the preparation method of the magnesium alloy with good thermal stability provided in this application; Figure 2 These are microscopic morphology images of the extruded magnesium alloy obtained in Example 1 of this application; wherein the scale bar of content (a) is 100 nm and the scale bar of content (b) is 5 nm; Figure 3 This is a TEM image of the microstructure of the high thermal stability magnesium alloy obtained in Example 1 of this application; Figure 4 This is an EBSD microstructure diagram of the extruded magnesium alloy obtained in Example 1 of this application; wherein content (a) is a PF orientation distribution diagram and content (b) is a grain distribution diagram; Figure 5 This is an EBSD microstructure diagram of the high thermal stability magnesium alloy obtained in Example 1 of this application; wherein content (a) is a PF orientation distribution diagram and content (b) is a grain distribution diagram; Figure 6 This is an EBSD microstructure diagram of the high thermal stability magnesium alloy obtained in Example 2 of this application; wherein content (a) is a PF orientation distribution diagram and content (b) is a grain distribution diagram; Figure 7 This is an EBSD microstructure diagram of the high thermal stability magnesium alloy obtained in Example 3 of this application; wherein content (a) is a PF orientation distribution diagram and content (b) is a grain distribution diagram; Figure 8 This is an EBSD microstructure diagram of the high thermal stability magnesium alloy obtained in Example 4 of this application; wherein content (a) is a PF orientation distribution diagram and content (b) is a grain distribution diagram; Figure 9 The figures show the recrystallization volume kinetics curves of the magnesium alloys obtained in Examples 1-4 of this application. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0027] In the description of this application, it should be understood that the term "and / or" describes a relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. The symbol " / " in this document indicates that the related objects are in an "or" relationship; for example, A / B means A or B.

[0028] In the description of the embodiments in this application, the words "exemplary" or "for example" are used to indicate that they are examples, illustrations, or descriptions. Any embodiment or design that is described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design options. Specifically, the use of the words "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0029] In the description of the embodiments in this application, unless otherwise stated, "multiple" means two or more.

[0030] This application provides a magnesium alloy with good thermal stability, comprising the following components by mass percentage: Al: 2%~4%, Zn: 0.5%~1.5%, Ca: 0.5%~1.5%, Mn: 0.1%~0.5%, with the balance being Mg; The alloy microstructure of the aforementioned magnesium alloy includes deformed grains and recrystallized grains, as well as micron-sized Al-Ca compounds distributed in a lamellar pattern along the extrusion direction and lamellar nano-sized Al2Ca precipitates dispersed within the grains.

[0031] In some embodiments, the magnesium alloy comprises the following components and their mass percentages: Al: 3%, Zn: 1%, Ca: 1%, Mn: 0.3%, with the balance being Mg.

[0032] In some embodiments, the average grain size of the deformed grains is 15 μm to 30 μm, and the average grain size of the recrystallized grains is 1 μm to 5 μm. In some embodiments, the volume fraction of the recrystallized grains is 45% to 60%.

[0033] In some embodiments, the thickness of the above-mentioned micron-sized Al-Ca compound is 1 μm to 3 μm, and the thickness of the above-mentioned nano-sized Al2Ca precipitate is 2 nm to 8 nm.

[0034] In some embodiments, the magnesium alloy has a room temperature tensile strength ≥420MPa and a room temperature elongation ≥8%, exhibiting excellent mechanical properties and toughness, and is suitable for various lightweight structural components.

[0035] In some embodiments, after the above-mentioned magnesium alloy is heat-treated at 300°C for 30 minutes, its tensile strength is still ≥400MPa and its elongation is ≥10%. It has excellent thermal stability and good mechanical properties, and is suitable for lightweight structural parts used in medium and high temperature environments (such as 300°C~350°C).

[0036] On the other hand, such as Figure 1 As shown, this application also provides a method for preparing the above-mentioned magnesium alloy, comprising the following steps: S1. Prepare the raw materials according to the above-mentioned magnesium alloy composition, then melt the prepared raw materials under a protective atmosphere. After all the raw materials have melted, pour them into a preheated mold and cool them to obtain a magnesium alloy ingot. S2. The above magnesium alloy ingot is homogenized and then hot extruded to obtain an extruded magnesium alloy. S3. Anneal the extruded magnesium alloy to obtain the magnesium alloy.

[0037] In some embodiments, the raw materials used in the above-prepared formulation include aluminum-containing raw materials, zinc-containing raw materials, calcium-containing raw materials, manganese-containing raw materials, and magnesium-containing raw materials. It is understood that this application does not limit the form of the above raw materials; they can be alloys or pure metals containing the above elements, as long as the composition of the magnesium alloy obtained after melting the added raw materials is within the range defined in this application. In some embodiments, the above raw materials may include pure Al or Al alloys, pure Zn or Zn alloys, pure Ca or Ca alloys, pure Mn or Mn alloys, and pure Mg or Mg alloys. In some specific embodiments of this application, the above raw materials include pure Al, pure Zn, pure Mg, magnesium-manganese alloys, and magnesium-calcium alloys.

[0038] In some embodiments, the order in which the above-mentioned raw materials are added can be selected according to actual needs. In some embodiments, in step S1, the order in which the raw materials are added is as follows: S11. Pure Mg is heated and melted at 700℃~760℃ (specifically 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, 760℃, etc.) to obtain magnesium melt; S12. Pure Al, pure Zn, magnesium-manganese alloy, and magnesium-calcium alloy are added to magnesium melt under a protective atmosphere for smelting. After complete melting, the oxide slag on the surface of the melt is removed to obtain magnesium alloy melt.

[0039] In some embodiments, the protective atmosphere is one or more of nitrogen (N2), carbon dioxide (CO2), sulfur hexafluoride (SF6), and an inert gas with a purity of not less than 99.99%, to prevent the magnesium melt from oxidizing and burning, and to reduce the entry of oxide inclusions into the ingot, thereby affecting the mechanical properties and thermal stability of the magnesium alloy.

[0040] In some embodiments, the melting temperature is 700℃~760℃ and the melting time is 10min~30min to ensure that all raw materials are fully melted and a magnesium alloy melt with uniform composition is obtained, which provides a basis for obtaining a stable as-cast structure and subsequent controllable precipitation behavior.

[0041] In some embodiments, in step S1, the preheating temperature of the mold is 150°C to 250°C, and the casting process should be as stable as possible to avoid secondary oxidation and air entrapment.

[0042] In some embodiments, in step S2, the temperature of the homogenization treatment is 400℃~450℃, and the holding time of the homogenization treatment is 24h~36h. This can reduce as-cast segregation, promote the diffusion of non-uniform components between dendrites, eliminate some residual internal stress, and provide a uniform microstructure starting point for the reasonable crushing, distribution and dynamic recrystallization behavior of the second phase during subsequent hot extrusion.

[0043] In some embodiments, in step S2, the hot extrusion temperature is 200℃~225℃, the extrusion ratio is (3~10):1, and the extrusion speed is 0.1mm / s~0.3mm / s. This allows for the introduction of a large amount of plastic deformation energy storage, inducing the coexistence of dynamic recrystallization and non-recrystallized deformed grains, forming a bimodal microstructure composed of coarse deformed grains and fine dynamically recrystallized grains. Simultaneously, it promotes the distribution of micron-sized Al-Ca phases and nano-Al2Ca precipitates along the extrusion direction. The formed micron-sized Al-Ca phase can also spatially separate the recrystallization region, thereby creating a microstructure within the grain that is conducive to the subsequent evolution of the nano-Al2Ca precipitate, subsequently forming a synergistic stabilizing effect with the nano-Al2Ca precipitate. Furthermore, it can retain a high density of small-angle grain boundaries and dislocation structures, creating conditions for utilizing grain boundary-precipitate interactions during subsequent annealing.

[0044] The inventors discovered through experiments that when the hot extrusion temperature is too high, the alloy microstructure of the extruded bar undergoes sufficient recrystallization, forming coarse recrystallized grains and failing to form a bimodal microstructure. This affects the tensile strength of the alloy, resulting in the inability to meet the strength requirements of the structural components. When the extrusion temperature is too low, it is impossible to obtain shaped magnesium alloy bars or profiles through the extrusion operation.

[0045] In some embodiments, before hot extrusion in step S2, the extrusion die and the homogenized annealed magnesium alloy ingot are preheated. In some embodiments, the preheating temperature of the extrusion die is 180℃~250℃, and the holding time is 1h~2h; the preheating temperature of the magnesium alloy ingot is 180℃~240℃, which can effectively reduce the extrusion deformation resistance, prevent defects such as cracking and hot spots caused by excessive temperature difference in the early stage of extrusion, ensure a more stable hot extrusion process, and create conditions for obtaining the expected bimodal microstructure with coarse deformed grains and fine dynamic recrystallized grains.

[0046] In some embodiments, in step S3, the annealing temperature is 340℃~360℃ and the annealing time is 1min~30min. This can induce and promote the thickening of the nano-Al2Ca precipitate, causing the migration and mismatch angle evolution of low-angle grain boundaries. Through the interaction between the precipitate and the small-angle grain boundaries, further static recrystallization is inhibited, so that the bimodal structure can still maintain high stability after annealing.

[0047] Compared to existing preparation methods, this application precisely controls the hot extrusion temperature, introducing high-density dislocations and small-angle grain boundaries during the hot extrusion stage to provide nucleation sites for subsequent precipitation. The extruded magnesium alloy obtained after hot extrusion is then annealed, with the annealing temperature and time controlled to induce a controllable growth of the nano-plate-like Al2Ca precipitate from approximately 1 nm to 2–8 nm. Simultaneously, the small-angle grain boundaries migrate and are strongly pinned by the thickened precipitate, ensuring the bimodal microstructure remains highly stable after annealing, with the recrystallization volume fraction remaining stable at 45%–60%. This achieves synergistic control of the dynamic thickening of the nano-Al2Ca precipitate and the grain boundary state, resulting in a magnesium alloy with excellent microstructural stability and mechanical properties in the mid-to-high temperature range, suitable for lightweight structural components. Based on this, this application also provides the application of the aforementioned magnesium alloy in the manufacture of lightweight structural components for transportation vehicles or aerospace equipment.

[0048] It should be understood that materials of the same or similar type, model, quality, properties, or function as those used in the following embodiments can be used to implement this application. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods. Unless otherwise specified, the materials, reagents, etc., used in the following embodiments are commercially available.

[0049] The following are examples and comparative examples: Example 1 The method for preparing a magnesium alloy with good thermal stability provided in this embodiment includes the following steps: (1) Preparation of magnesium alloy ingots The magnesium alloy designed in this embodiment has the following composition by mass percentage: Al: 3%, Zn: 1%, Ca: 1%, Mn: 0.3%, with the balance being Mg. Raw materials were prepared according to the designed magnesium alloy composition, including pure Mg ingots, pure Al ingots, pure Zn ingots, Mg-Mn master alloy, and Mg-Ca master alloy. The surface oxide layer was removed by grinding. Pure Mg ingots were added to a crucible and heated to 720°C in a resistance melting furnace for melting. After complete melting, pure Al ingots, pure Zn ingots, Mg-Mn master alloy, and Mg-Ca master alloy were added sequentially for smelting. Argon gas was introduced during the smelting process to prevent oxidation and combustion of the magnesium liquid. After the raw materials were completely melted, the oxide slag on the surface of the melt was removed to reduce inclusions entering the ingot, resulting in a magnesium alloy melt. The magnesium alloy melt was then cast into a mold preheated to 200°C and allowed to cool naturally to room temperature in air, yielding a cylindrical magnesium alloy ingot with a diameter of approximately 35 mm.

[0050] (2) Preparation of extruded magnesium alloys The aforementioned magnesium alloy ingots were placed in a box-type resistance furnace for homogenization treatment at a heating rate of 5℃ / min, a homogenization temperature of 450℃, and a homogenization time of 24 hours. The ingots were then removed and cooled to room temperature in air. Based on the dimensions of the extrusion equipment, the homogenized ingots were processed into billets of suitable size, which were then placed in a heating furnace for preheating at 210℃ and held for 1 hour. Simultaneously, the extrusion die was preheated to 200℃. Subsequently, hot extrusion was performed using a hydraulic extrusion press at a temperature of 210℃, an extrusion ratio of 4.5:1, and a hot extrusion speed of 0.1 mm / s, yielding extruded magnesium alloy bars with a diameter of approximately 8 mm.

[0051] (3) Preparation of magnesium alloys with good microstructure and thermal stability The extruded magnesium alloy rods were placed in an electric resistance furnace for annealing at a temperature of 350°C for 2 minutes. After annealing, the samples were removed and cooled to room temperature in air to obtain a high thermal stability magnesium alloy.

[0052] The microstructure of the extruded magnesium alloy and the high thermal stability magnesium alloy were characterized by microscopy.

[0053] Figure 2 The microstructure (TEM image) of the extruded magnesium alloy is shown. Figure 2 Content (a) shows that the extruded magnesium alloy has micron-sized banded Al-Ca compounds distributed along the extrusion direction, with a thickness of approximately 2 μm; Figure 2 As can be seen from content (b), the extruded magnesium alloy has nanoscale lamellar Al2Ca precipitates distributed along the extrusion direction, with a thickness of about 1 mm.

[0054] Figure 3 The microstructure (TEM image) of the high thermal stability magnesium alloy shows that the thickness of the nanoscale lamellar Al2Ca precipitate is about 2.5~4 mm, indicating that the thickness of the nanoscale lamellar Al2Ca precipitate is significantly increased after the extruded magnesium alloy is annealed at 350℃ for 2 min.

[0055] Example 2 The method for preparing a high thermal stability magnesium alloy provided in this embodiment includes the following steps: (1) A magnesium alloy ingot was prepared according to the method provided in step (1) of Example 1.

[0056] (2) An extruded magnesium alloy was prepared according to the method provided in step (2) of Example 1.

[0057] (3) The above extruded magnesium alloy was placed in a resistance furnace at 350°C and kept at that temperature for 5 minutes for annealing. After annealing, the sample was taken out and cooled to room temperature in air to obtain a high thermal stability magnesium alloy.

[0058] Example 3 The method for preparing a high thermal stability magnesium alloy provided in this embodiment includes the following steps: (1) A magnesium alloy ingot was prepared according to the method provided in step (1) of Example 1.

[0059] (2) An extruded magnesium alloy was prepared according to the method provided in step (2) of Example 1.

[0060] (3) The above extruded magnesium alloy was placed in a resistance furnace at 350°C and kept at 350°C for 15 minutes for annealing. After annealing, the sample was taken out and cooled to room temperature in air to obtain a high thermal stability magnesium alloy.

[0061] Example 4 The method for preparing a high thermal stability magnesium alloy provided in this embodiment includes the following steps: (1) A magnesium alloy ingot was prepared according to the method provided in step (1) of Example 1.

[0062] (2) An extruded magnesium alloy was prepared according to the method provided in step (2) of Example 1.

[0063] (3) The above extruded magnesium alloy was placed in a resistance furnace at 350°C and kept at that temperature for 30 minutes for annealing. After annealing, the sample was taken out and cooled to room temperature in air to obtain a high thermal stability magnesium alloy.

[0064] Figure 4 The image shows the EBSD microstructure of the extruded magnesium alloy obtained in Example 1, wherein... Figure 4 Content (a) is an IPF orientation distribution map. Figure 4 Content (b) is a grain distribution diagram (scale bar is 10 μm, red represents deformed grains, and blue represents recrystallized grains). It can be seen that a bimodal structure with both deformed and recrystallized grains is formed in the extruded magnesium alloy.

[0065] Figure 5 , Figure 6 , Figure 7 , Figure 8 The images show the EBSD microstructures of the high thermal stability magnesium alloys from Examples 1 to 4. Content (a) shows the IPF orientation distribution of the magnesium alloys obtained in Examples 1 to 4, and content (b) shows the grain distribution of the magnesium alloys obtained in Examples 1 to 4 (scale bar is 10 μm, red represents deformed grains, and blue represents recrystallized grains). It can be seen that the average grain size of the deformed grains is 15 to 30 μm, and the average grain size of the recrystallized grains is 1 to 5 μm. Moreover, with the increase of annealing time, the deformed grains did not undergo significant recrystallization, and the annealed magnesium alloys still have a bimodal microstructure composed of deformed grains and recrystallized grains.

[0066] Figure 9 The figures show recrystallization volume kinetics curves of the magnesium alloys obtained in Examples 1-4. It can be seen that, compared with extruded magnesium alloys, annealing extruded magnesium alloys can increase the recrystallization volume fraction in magnesium alloys. As the annealing time increases, the recrystallization volume fraction shows a trend of first increasing and then leveling off, and the recrystallization volume fraction stabilizes at about 60%.

[0067] Example 5 The method for preparing a high thermal stability magnesium alloy provided in this embodiment includes the following steps: (1) A magnesium alloy ingot was prepared according to the method provided in step (1) of Example 1.

[0068] (2) An extruded magnesium alloy was prepared according to the method provided in step (2) of Example 1, except that the hot extrusion temperature was 225°C, the extrusion ratio was 6:1, and the extrusion speed was 0.1 mm / s.

[0069] (3) The above extruded magnesium alloy was placed in a resistance furnace at 350°C and kept at that temperature for 30 minutes for annealing. After annealing, the sample was taken out and cooled to room temperature in air to obtain a high thermal stability magnesium alloy.

[0070] The microstructure of the aforementioned high thermal stability magnesium alloy was characterized by microstructure analysis. Transmission electron microscopy revealed that the thickness of the nanoscale lamellar Al₂Ca precipitates was approximately 5–6.4 nm. Electron backscatter diffraction (EBSD) analysis showed that the recrystallization volume fraction in the magnesium alloy prepared in this embodiment was consistently around 60%.

[0071] Comparative Example 1 The method for preparing the magnesium alloy provided in this comparative example includes the following steps: (1) A magnesium alloy ingot was prepared according to the method provided in step (1) of Example 1.

[0072] (2) The magnesium alloy ingot was homogenized according to the method provided in step (2) of Example 1 and processed into a billet of suitable size. Then it was placed in a heating furnace for preheating at a temperature of 180°C and held for 1 hour. At the same time, the extrusion die was preheated to 180°C. Subsequently, a hydraulic extrusion press was used for hot extrusion processing at a temperature of 180°C, an extrusion ratio of 4.5:1, and a hot extrusion speed of 0.1 mm / s.

[0073] During the experiment, it was found that at this extrusion temperature, the billet broke in the extrusion die, and extruded magnesium alloy bars could not be obtained.

[0074] Comparative Example 2 The method for preparing the magnesium alloy provided in this comparative example includes the following steps: (1) A magnesium alloy ingot was prepared according to the method provided in step (1) of Example 1.

[0075] (2) The magnesium alloy ingot was homogenized according to the method provided in step (2) of Example 1 and processed into a billet of suitable size. Then it was placed in a heating furnace for preheating at a temperature of 180°C and held for 1 hour, while the extrusion die was preheated to 180°C. Subsequently, a hydraulic extrusion press was used for hot extrusion processing at a temperature of 350°C, an extrusion ratio of 4.5:1, and a hot extrusion speed of 0.1 mm / s to obtain an extruded magnesium alloy rod with a diameter of about 8 mm.

[0076] (3) The extruded magnesium alloy rod was annealed according to the method provided in step (3) of Example 1 to obtain magnesium alloy.

[0077] Microstructural characterization of the magnesium alloy revealed the formation of coarse recrystallized grains with a diameter of approximately 15–20 μm, without a bimodal grain structure.

[0078] Comparative Example 3 The method for preparing the magnesium alloy provided in this comparative example includes the following steps: (1) A magnesium alloy ingot was prepared according to the method provided in step (1) of Example 1.

[0079] (2) An extruded magnesium alloy was prepared according to the method provided in step (2) of Example 1.

[0080] (3) The above extruded magnesium alloy was placed in a resistance furnace at 250°C and kept at that temperature for 30 minutes for annealing. After annealing, the sample was taken out and cooled to room temperature in air to obtain the magnesium alloy.

[0081] Microstructural characterization of the magnesium alloy revealed that the thickness of the nanolayered Al2Ca precipitates in the alloy was not significant (approximately 1 nm).

[0082] Comparative Example 4 The method for preparing the magnesium alloy provided in this comparative example includes the following steps: (1) A magnesium alloy ingot was prepared according to the method provided in step (1) of Example 1.

[0083] (2) An extruded magnesium alloy was prepared according to the method provided in step (2) of Example 1.

[0084] (3) The above extruded magnesium alloy was placed in a resistance furnace at 400°C and kept at that temperature for 30 minutes for annealing. After annealing, the sample was taken out and cooled to room temperature in air to obtain the magnesium alloy.

[0085] Microstructural characterization of the magnesium alloy prepared in this comparative example revealed that coarse recrystallized grains with a grain size of approximately 25-30 μm were formed in the alloy structure, and there was no bimodal grain structure. The volume fraction of recrystallized grains was 85%.

[0086] The tensile properties of the magnesium alloys prepared in Examples 1-5 and Comparative Examples 2-4 were tested using a universal testing machine, and the elongation of the magnesium alloys was tested using an extensometer. The results are shown in Table 1.

[0087]

[0088] As can be seen from Table 1, the high thermal stability magnesium alloy prepared in the embodiments of this application has excellent tensile properties and good toughness, with a room temperature tensile strength ≥420MPa and a room temperature elongation ≥8%, which meets the requirements of lightweight structural components for strong mechanical properties and high toughness.

[0089] The magnesium alloys prepared in Comparative Examples 2-4 showed significantly lower performance than those in Example 1. The reasons for this may be that when the hot extrusion temperature was too high (Comparative Example 2), the alloy underwent sufficient dynamic recrystallization, which prevented the formation of a bimodal structure and resulted in the growth of recrystallized grains, leading to a decrease in the alloy's strength. When the annealing temperature was too low (Comparative Example 3), the thickness of the precipitated phase was not significant, and static recrystallization could not be effectively prevented during the annealing process, causing the deformed grains to transform into recrystallized grains and destroying the bimodal structure. When the annealing temperature was too high (Comparative Example 4), static recrystallization was fully developed, and the recrystallized grains grew, increasing the overall grain size and thus destroying the bimodal structure, resulting in a rapid deterioration of the alloy's mechanical properties.

[0090] Furthermore, the magnesium alloy prepared in the embodiments of this application was heat-treated at 300°C for 30 min. Then, its microstructure was observed and its tensile properties were tested. It was found that the magnesium alloy after heat treatment in a medium-high temperature environment still has a typical bimodal grain structure, as well as micron-sized Al-Ca compounds distributed in a lamellar shape along the extrusion direction and lamellar nano-sized Al2Ca precipitates dispersed inside the grains. At the same time, its tensile strength is still ≥400MPa and its elongation is ≥10%. This indicates that the magnesium alloy prepared in the embodiments of this application has excellent thermal stability of microstructure and maintains excellent mechanical properties in the medium-high temperature range (such as 300°C~350°C), and is suitable for various lightweight structural parts used in medium-high temperature environments.

[0091] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A magnesium alloy with good thermal stability, characterized in that, It comprises the following components by mass percentage: Al: 2%~4%, Zn: 0.5%~1.5%, Ca: 0.5%~1.5%, Mn: 0.1%~0.5%, with the balance being Mg; The alloy microstructure of the magnesium alloy includes deformed grains and recrystallized grains, as well as micron-sized Al-Ca compounds distributed in a lamellar pattern along the extrusion direction and lamellar nano-sized Al2Ca precipitates dispersed within the grains.

2. The magnesium alloy according to claim 1, characterized in that, The average grain size of the deformed grains is 15μm~30μm; The average grain size of the recrystallized grains is 1μm~5μm; The thickness of the micron-sized Al-Ca compound is 1 μm to 3 μm; The thickness of the nanoscale Al2Ca precipitate is 2nm~8nm.

3. The magnesium alloy according to claim 1, characterized in that, The magnesium alloy has a room temperature tensile strength ≥420MPa and a room temperature elongation ≥8%.

4. A method for preparing a magnesium alloy as described in any one of claims 1 to 3, characterized in that, Includes the following steps: S1. Prepare the raw materials according to the composition of the magnesium alloy, then melt the prepared raw materials under a protective atmosphere, and after they are completely melted, pour them into a preheated mold and cool them to obtain a magnesium alloy ingot. S2. The magnesium alloy ingot is homogenized and annealed, and then hot extruded to obtain an extruded magnesium alloy. S3. Anneal the extruded magnesium alloy to obtain the magnesium alloy.

5. The preparation method according to claim 4, characterized in that, In step S1, the protective atmosphere is one or more of nitrogen, carbon dioxide, sulfur hexafluoride, and an inert gas with a purity of not less than 99.99%; and / or, The melting temperature is 700℃~760℃, and the melting time is 10min~30min; and / or, The preheating temperature of the mold is 150℃~250℃.

6. The preparation method according to claim 4, characterized in that, In step S2, the homogenization treatment temperature is 400℃~450℃, and the homogenization treatment holding time is 24h~36h.

7. The preparation method according to claim 4, characterized in that, In step S2, the temperature of the hot extrusion is 200℃~225℃, the extrusion ratio of the hot extrusion is (3~10):1, and the speed of the hot extrusion is 0.1mm / s~0.3mm / s.

8. The preparation method according to claim 7, characterized in that, Before hot extrusion in step S2, the extrusion die and the homogenized annealed magnesium alloy ingot are preheated. Preferably, the preheating temperature of the extrusion die is 180℃~250℃, and the preheating temperature of the magnesium alloy ingot after homogenization annealing is 180℃~240℃.

9. The preparation method according to claim 4, characterized in that, In step S3, the annealing temperature is 340℃~360℃, and the annealing time is 1min~30min.

10. The application of a magnesium alloy as described in any one of claims 1 to 3 in the manufacture of lightweight structural components for transportation vehicles or aerospace equipment.

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