A high thermal stability nanocrystalline magnesium alloy and its preparation method

Abstract

This invention discloses a high thermal stability nanocrystalline magnesium alloy and its preparation method, belonging to the field of metal material preparation technology. This invention achieves a multimodal distribution of aluminum in a magnesium matrix through mechanical alloying and mechanical mixing, and obtains the high thermal stability nanocrystalline magnesium alloy using conventional pressing and extrusion forming. The three modal distribution forms of aluminum in the nanocrystalline magnesium alloy prepared by this invention include: solid solution in the magnesium matrix, segregation at magnesium grain boundaries, and dispersion in the magnesium matrix as an aluminum-rich phase. Under the coupled effects of dragging and pinning, the thermal stability of the nanocrystalline magnesium grains is significantly improved. This invention uses aluminum powder as a material to improve the thermal stability of the nanocrystalline magnesium matrix, which has low density and low cost; furthermore, the preparation process is simple, requires low equipment, and has high production efficiency, showing good industrialization prospects.

Description

Technical Field

[0001] This invention belongs to the field of metal material preparation technology, specifically relating to a high thermal stability nanocrystalline magnesium alloy and its preparation method. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] High strength in metallic materials is a persistent goal for materials researchers and a crucial way to improve specific strength. Nanocrystalline materials possess many superior properties, particularly demonstrating unparalleled advantages in enhancing material strength. The finer the grain size, the higher the strength; this principle holds true when the grain size exceeds a certain critical size (approximately 10–15 nm), becoming a major driving force for the development of ultrafine-grained materials. Currently, all ultra-high-strength magnesium alloy bulk materials reported in publicly available literature are nanocrystalline materials.

[0004] Thermal stability directly affects the application range and applicability of surface nanocrystalline samples. As temperature increases, nanostructures lose stability, and high-density grain boundaries significantly decrease. While the activation energy for grain growth in metallic magnesium is relatively low (92 kJ / mol for pure magnesium), the driving force for grain growth in nanocrystalline magnesium structures is extremely high. Theoretically, when the grain size doubles, the number of non-equilibrium boundary atoms in nanocrystalline structures will decrease by approximately 1000 times compared to micrometer-scale grains. Grain coarsening in nanocrystalline structures is much easier than in micrometer-scale structures, and grains grow readily even at relatively low temperatures. Therefore, improving the thermal stability of nanocrystalline magnesium matrices is essential.

[0005] Currently, published literature describes methods to improve the thermal stability of nanocrystalline magnesium matrices by adding rare earth elements or ceramic second-phase particles, utilizing the pinning effect of the precipitated / second-phase phase, the dragging effect of solid solution atoms, or a combination of both. However, the inventors have found the following shortcomings in these methods:

[0006] (1) Rare earth elements are expensive, which leads to increased material costs;

[0007] (2) Rare earth elements have a high specific gravity, and ideal thermal stability requires a large amount of rare earth elements to be added, which increases the material density and affects the lightweight properties of magnesium alloys.

[0008] (3) It is difficult to achieve the industrial-scale dispersion of nanoscale ceramic second-phase particles;

[0009] (4) Micron-sized ceramics contribute little to thermal stability and are prone to causing cracks in the magnesium matrix, affecting the strength and plasticity of the material. Summary of the Invention

[0010] To address the shortcomings of existing technologies, the present invention aims to provide a high thermal stability nanocrystalline magnesium alloy and its preparation method. The high thermal stability nanocrystalline magnesium alloy and its preparation method provided by the present invention are low in cost and simple in process, solving the problems of high cost and complex process in improving the thermal stability of nanocrystalline magnesium alloys.

[0011] To achieve the above objectives, the technical solution of the present invention is as follows:

[0012] In a first aspect, the present invention provides a method for preparing a high thermal stability nanocrystalline magnesium alloy, comprising the following steps:

[0013] (1) Pure aluminum powder and magnesium-based powder are mechanically alloyed to obtain nanocrystalline mixed powder A;

[0014] (2) The nanocrystalline mixed powder A is mixed with pure aluminum powder evenly to obtain mixed powder B;

[0015] (3) The mixed powder B is solidified under pressure to obtain a high thermal stability nanocrystalline magnesium alloy.

[0016] The design concept of the high thermal stability nanocrystalline magnesium alloy of this invention is:

[0017] Aluminum powder and magnesium-based powder are mixed by mechanical alloying and mechanical mixing to achieve a multimodal distribution of aluminum in a nanocrystalline magnesium matrix, including: aluminum atoms dissolved in the magnesium matrix and segregated at the magnesium grain boundaries, and aluminum-rich phase dispersed in the magnesium matrix. Under the coupling effect of dragging effect and pinning effect, the thermal stability of nanocrystalline magnesium grains is significantly improved.

[0018] In some embodiments of the present invention, in step (1), the magnesium-based powder is pure magnesium powder or magnesium alloy powder, and the average particle size of the magnesium-based powder is between 10 μm and 2 mm. For example, the average particle size of the magnesium-based powder can be 10 μm, 15 μm, 20 μm, 50 μm, 500 μm, 1 mm, 1.5 mm or 2 mm, etc.

[0019] The magnesium alloy powder can be selected from AZ31 magnesium alloy powder, AM50 magnesium alloy powder, AZ3IN magnesium alloy powder or AZ33M magnesium alloy powder, or other types of magnesium alloy powder.

[0020] In some embodiments of the present invention, in step (1), the purity of the pure aluminum powder is greater than 99.5 wt.%, and the average particle size of the pure aluminum powder is between 1 μm and 45 μm. For example, the average particle size of the pure aluminum powder can be 1 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm or 45 μm, etc.

[0021] The pure aluminum powder can be obtained by gas atomization or purchased externally.

[0022] In some embodiments of the present invention, in step (1), the mass fraction of pure aluminum powder in the nanocrystalline mixed powder A is 1-10%, for example, it can be 1%, 3%, 5%, 6%, 9%, 10%, etc.; the mass fraction of Al element in the nanocrystalline mixed powder A is ≥6%.

[0023] This invention provides a continuous supply of aluminum atoms to the grain boundaries of nanocrystalline magnesium during heat treatment by dispersing micron-sized pure aluminum phases within a magnesium matrix. This prevents the agglomerated aluminum atoms from dissolving within the magnesium grains, which would cause abnormal grain growth and unstable grain distribution. Therefore, in the nanocrystalline mixed powder A, insufficient Al content leads to insufficient thermal stability of the resulting nanocrystalline magnesium alloy.

[0024] In some embodiments of the present invention, in step (2), the purity of the pure aluminum powder is greater than 99.5 wt.%, and the average particle size of the pure aluminum powder is between 1 μm and 10 μm. For example, the average particle size of the pure aluminum powder can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, etc.

[0025] In some embodiments of the present invention, in step (2), the mass fraction of pure aluminum powder in the mixed powder B is 2 to 5%, for example, it can be 2%, 3%, 4% or 5%, etc.

[0026] In some embodiments of the present invention, the ball-to-material ratio for mechanical alloying is 58-62:1, preferably 60:1; the ball milling time is 15-20 hours, preferably 16 hours; and the ball milling speed is 250-350 rpm, preferably 300 rpm.

[0027] In some embodiments of the present invention, the mixed powder B is solidified by compression molding or extrusion molding.

[0028] In some embodiments of the present invention, the pressing pressure for the compression molding is 1.0 to 1.5 GPa, and the holding time is 3 to 8 min.

[0029] In some embodiments of the present invention, the extrusion ratio of the extrusion molding is 8 to 12:1, the extrusion temperature is 250 to 350°C, and the extrusion billet holding time is 0.8 to 1.2 hours.

[0030] In a second aspect, the present invention provides a high thermal stability nanocrystalline magnesium alloy, which is prepared by the preparation method described in the first aspect;

[0031] The high thermal stability nanocrystalline magnesium alloy was subjected to vacuum isothermal heat treatment at a temperature of 450°C for 10 hours, resulting in an average grain size of less than 250 nm in the magnesium matrix.

[0032] The beneficial effects of this invention are as follows:

[0033] This invention provides a method for preparing a high thermal stability nanocrystalline magnesium alloy, comprising the following steps: (1) mechanically alloying pure aluminum powder with magnesium-based powder to obtain nanocrystalline mixed powder A; (2) uniformly mixing the nanocrystalline mixed powder A with pure aluminum powder to obtain mixed powder B; (3) solidifying the mixed powder B under pressure to obtain a high thermal stability nanocrystalline magnesium alloy. This invention achieves a three-modal distribution of aluminum in a nanocrystalline magnesium matrix based on mechanical alloying and mechanical mixing, introducing drag and pinning effects to improve the thermal stability of the nanocrystalline magnesium matrix. Aluminum is used as a stabilizing element to inhibit nanocrystalline coarsening, offering advantages such as low cost and low specific gravity. The material preparation process is simple, production efficiency is high, and product stability is good. This invention has a simple process flow, low equipment requirements, high production efficiency, good product stability, and low cost, showing good industrialization prospects.

[0034] This invention provides aluminum atoms to continuously supply aluminum elements to the grain boundaries of nanocrystalline magnesium during heat treatment by dispersing micron-sized pure aluminum phases in a magnesium matrix. This prevents the agglomerated aluminum atoms from solidifying inside the magnesium grains, which would cause abnormal growth of the magnesium grains and result in unstable grain distribution.

[0035] The nanocrystalline magnesium alloy obtained in this invention was subjected to vacuum isothermal heat treatment at 450°C for 10 hours. The magnesium alloy after heat treatment was observed using a transmission electron microscope. The average grain size of the magnesium matrix was between 180 and 230 nm, significantly lower than the average grain size of the comparative example (380 nm to 2 μm). Therefore, the nanocrystalline magnesium alloy prepared by this invention exhibits excellent thermal stability. Attached Figure Description

[0036] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0037] Figure 1 The images shown are scanning electron microscope images and X-ray diffraction patterns of the high thermal stability nanocrystalline magnesium alloy prepared in Example 1 of this invention.

[0038] Figure 2 This is a schematic diagram of the microstructure of the high thermal stability nanocrystalline magnesium alloy with a three-mode distribution of aluminum element prepared in Example 1 of the present invention;

[0039] Figure 3This is a transmission electron microscope image of the high thermal stability nanocrystalline magnesium alloy prepared in Example 1 of the present invention. Detailed Implementation

[0040] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0041] Example 1

[0042] A method for preparing a high thermal stability nanocrystalline magnesium alloy includes the following steps:

[0043] (1) Pure aluminum powder and magnesium-based powder are mechanically alloyed to obtain nanocrystalline mixed powder A.

[0044] The magnesium-based powder is pure magnesium powder with an average particle size of 10 μm; the pure aluminum powder has an average particle size of 45 μm and a content of 6 wt.%; the mechanical alloying ball-to-powder ratio is 60:1, the ball milling time is 16 h, and the ball milling speed is 300 rpm.

[0045] (2) The nanocrystalline mixed powder A and pure aluminum powder are uniformly mixed using a powder mixer to obtain mixed powder B.

[0046] The pure aluminum powder has an average particle size of 1 μm and a content of 3 wt.%.

[0047] (3) The mixed powder B was shaped by room temperature pressing to obtain nanocrystalline magnesium alloy.

[0048] The pressing pressure is 1.3 GPa, and the holding time is 5 min.

[0049] The nanocrystalline magnesium alloy obtained in step (3) of Example 1 was observed using a scanning electron microscope, and the results are as follows: Figure 1 As shown in (a), the aluminum-rich phase is uniformly distributed in the magnesium matrix and its size is less than 2 μm. The aluminum powder added in step (1) decomposes during mechanical alloying, dissolves in the magnesium matrix, and agglomerates at the magnesium grain boundaries. The aluminum powder added in step (2) is uniformly distributed in the magnesium matrix.

[0050] The nanocrystalline magnesium alloy obtained in step (3) of Example 1 was characterized using X-ray diffraction, and the results are as follows: Figure 1 As shown in (b), the magnesium alloy is composed of Mg, Al, and Mg 17 Al 12 Phase composition was determined, and the average grain size of the magnesium matrix was found to be 72 nm, reaching the nanocrystalline level.

[0051] The nanocrystalline magnesium alloy obtained in step (3) of Example 1 was tested using a Vickers hardness tester, and the material hardness was 156HV.

[0052] Further, a schematic diagram of the microstructure of the nanocrystalline magnesium alloy obtained in step (3) of Example 1 is shown below. Figure 2 As shown, a magnesium alloy with a three-mode Al distribution was obtained through mechanical alloying and mechanical mixing.

[0053] Furthermore, the nanocrystalline magnesium alloy obtained in step (3) of Example 1 was subjected to vacuum isothermal heat treatment at a temperature of 450°C for 10 hours. The magnesium alloy after heat treatment was observed using a transmission electron microscope, and the results are as follows: Figure 3 As shown, the magnesium matrix grain size ranges from 113 nm to 500 nm, with an average grain size of 180 nm. The hardness of the heat-treated material was tested using a Vickers hardness tester, and the hardness was 110 HV. Therefore, the nanocrystalline magnesium alloy prepared in Example 1 exhibits excellent thermal stability.

[0054] Example 2

[0055] A method for preparing a high thermal stability nanocrystalline magnesium alloy includes the following steps:

[0056] (1) Pure aluminum powder and magnesium-based powder are mechanically alloyed to obtain nanocrystalline mixed powder A.

[0057] The magnesium-based powder is AZ31 magnesium alloy powder with an average particle size of 2 mm; the pure aluminum powder has an average particle size of 1 μm and a content of 3 wt.%; the mechanical alloying ball-to-powder ratio is 60:1, the ball milling time is 16 h, and the ball milling speed is 300 rpm.

[0058] (2) The nanocrystalline mixed powder A and pure aluminum powder are uniformly mixed using a powder mixer to obtain mixed powder B.

[0059] The pure aluminum powder has an average particle size of 10 μm and a content of 3 wt.%.

[0060] (3) The mixed powder B was shaped by room temperature pressing to obtain nanocrystalline magnesium alloy.

[0061] The pressing pressure is 1.3 GPa, and the holding time is 5 min.

[0062] Furthermore, the microstructure of the nanocrystalline magnesium alloy obtained in step (3) of Example 2 was observed, and the average grain size of the magnesium grains was 68 nm.

[0063] The nanocrystalline magnesium alloy obtained in step (3) of Example 2 was tested using a Vickers hardness tester, and the material hardness was 135HV.

[0064] Furthermore, the nanocrystalline magnesium alloy obtained in step (3) of Example 2 was subjected to vacuum isothermal heat treatment at a temperature of 450°C for 10 hours. The average grain size of the magnesium matrix was measured to be 220 nm. The hardness of the heat-treated material was tested using a Vickers hardness tester, and the hardness was 106 HV.

[0065] Example 3

[0066] A method for preparing a high thermal stability nanocrystalline magnesium alloy includes the following steps:

[0067] (1) Pure aluminum powder and magnesium-based powder are mechanically alloyed to obtain nanocrystalline mixed powder A.

[0068] The magnesium-based powder is pure magnesium powder with an average particle size of 45 μm; the pure aluminum powder has an average particle size of 45 μm and a content of 9 wt.%; the mechanical alloying ball-to-powder ratio is 60:1, the ball milling time is 16 h, and the ball milling speed is 300 rpm.

[0069] (2) The nanocrystalline mixed powder A and pure aluminum powder are uniformly mixed using a powder mixer to obtain mixed powder B.

[0070] The pure aluminum powder has an average particle size of 1 μm and a content of 2 wt.%.

[0071] (3) The mixed powder B is shaped by extrusion to obtain nanocrystalline magnesium alloy.

[0072] The extrusion ratio was 10:1, the extrusion temperature was 300℃, and the extruded billet was kept warm for 1 hour.

[0073] Furthermore, the microstructure of the nanocrystalline magnesium alloy obtained in step (3) of Example 3 was observed, and the average grain size of the magnesium grains was 90 nm.

[0074] Furthermore, the mechanical properties of the nanocrystalline magnesium alloy obtained in step (3) of Example 3 were tested. The compressive yield strength of the material was 492 MPa and the compressive fracture strain was 7%, indicating that the material has excellent strength and plasticity.

[0075] Furthermore, the nanocrystalline magnesium alloy obtained in step (3) of Example 3 was subjected to vacuum isothermal heat treatment at a temperature of 450°C for 10 hours. The average grain size of the magnesium alloy was found to be 230 nm.

[0076] Comparative Example 1

[0077] This comparative example is basically the same as the method in Example 1, except that pure aluminum powder is not added in step (2) of this comparative example. The specific steps are as follows:

[0078] (1) Pure aluminum powder and magnesium-based powder are mechanically alloyed to obtain nanocrystalline mixed powder A.

[0079] The magnesium-based powder is pure magnesium powder with an average particle size of 10 μm; the pure aluminum powder has an average particle size of 45 μm and a content of 6 wt.%; the mechanical alloying ball-to-powder ratio is 60:1, the ball milling time is 16 h, and the ball milling speed is 300 rpm.

[0080] (2) The nanocrystalline mixed powder A is mixed using a powder mixer to obtain mixed powder B.

[0081] (3) The mixed powder B was shaped by room temperature pressing to obtain nanocrystalline magnesium alloy.

[0082] The pressing pressure is 1.3 GPa, and the holding time is 5 min.

[0083] Furthermore, Comparative Example 1 yielded a two-mode distribution nanocrystalline magnesium alloy in which aluminum elements are dissolved in the magnesium matrix and segregated at the magnesium grain boundaries.

[0084] Furthermore, the microstructure of the nanocrystalline magnesium alloy obtained in step (3) of Comparative Example 1 was observed, and the average grain size of the magnesium grains was 72 nm.

[0085] The nanocrystalline magnesium alloy obtained in step (3) of Comparative Example 1 was tested using a Vickers hardness tester, and the material hardness was 150 HV.

[0086] Furthermore, the nanocrystalline magnesium alloy obtained in step (3) of Comparative Example 1 was subjected to vacuum isothermal heat treatment at a temperature of 450℃ for 10 hours, resulting in an average grain size of 380nm. The hardness of the heat-treated material was tested using a Vickers hardness tester, and the hardness was 95HV.

[0087] Comparative Example 2

[0088] Comparative Example 2 is basically the same as Example 1 in terms of method, except that pure aluminum powder is not added in steps (1) and (2) of Comparative Example 2, and the mass fraction of Al element in step (1) is 0, which is less than 6%. The specific steps are as follows:

[0089] (1) Magnesium-based powder is mechanically alloyed to obtain nanocrystalline mixed powder A.

[0090] The magnesium-based powder is pure magnesium powder with an average particle size of 10μm; the mechanical alloying ball-to-powder ratio is 60:1, the ball milling time is 16h, and the ball milling speed is 300rpm.

[0091] (2) The nanocrystalline mixed powder A was mixed using a powder mixer to obtain powder B.

[0092] (3) Powder B was shaped by room temperature pressing to obtain nanocrystalline magnesium alloy.

[0093] The pressing pressure is 1.3 GPa, and the holding time is 5 min.

[0094] Furthermore, Comparative Example 2 yielded nanocrystalline pure magnesium.

[0095] Furthermore, the microstructure of the nanocrystalline pure magnesium obtained in step (3) of Comparative Example 2 was observed, and the average grain size of the magnesium grains was 98 nm.

[0096] The nanocrystalline magnesium alloy obtained in step (3) of Comparative Example 2 was tested using a Vickers hardness tester, and the material hardness was 123 HV.

[0097] Furthermore, the nanocrystalline pure magnesium obtained in step (3) of Comparative Example 2 was subjected to vacuum isothermal heat treatment at a temperature of 450℃ for 10 hours, resulting in an average grain size of 2μm for the magnesium alloy. The hardness of the heat-treated material was tested using a Vickers hardness tester, and the hardness was 76HV.

[0098] Comparative Example 3

[0099] The method of Comparative Example 3 is basically the same as that of Example 2, except that pure aluminum powder is not added in step (2) of Comparative Example 3. The specific steps are as follows:

[0100] (1) Pure aluminum powder and magnesium-based powder are mechanically alloyed to obtain nanocrystalline mixed powder A.

[0101] The magnesium-based powder is AZ31 magnesium alloy powder with an average particle size of 2 mm; the pure aluminum powder has an average particle size of 1 μm and a content of 3 wt.%; the mechanical alloying ball-to-powder ratio is 60:1, the ball milling time is 16 h, and the ball milling speed is 300 rpm.

[0102] (2) The nanocrystalline mixed powder A was mixed using a powder mixer to obtain powder B.

[0103] (3) Powder B was shaped by room temperature pressing to obtain nanocrystalline magnesium alloy.

[0104] The pressing pressure is 1.3 GPa, and the holding time is 5 min.

[0105] Furthermore, Comparative Example 3 yielded a two-mode distribution nanocrystalline magnesium alloy in which aluminum elements are dissolved in the magnesium matrix and segregated at the magnesium grain boundaries.

[0106] Furthermore, the microstructure of the nanocrystalline magnesium alloy obtained in step (3) of Comparative Example 3 was observed, and the average grain size of magnesium grains was 68 nm.

[0107] Furthermore, the nanocrystalline magnesium alloy obtained in step (3) of Comparative Example 3 was subjected to vacuum isothermal heat treatment at a temperature of 450°C for 10 hours, and the average grain size of the magnesium alloy was 450 nm.

[0108] Comparative Example 4

[0109] Comparative Example 4 is basically the same as Example 2 in terms of method, except that pure aluminum powder is not added in steps (1) and (2) of Comparative Example 4, and the mass fraction of Al element in step (1) is 3%, which is less than 6%. The specific steps are as follows:

[0110] (1) Magnesium-based powder is mechanically alloyed to obtain nanocrystalline mixed powder A.

[0111] The magnesium-based powder is AZ31 magnesium alloy powder with an average particle size of 2 mm; the mechanical alloying ball-to-powder ratio is 60:1, the ball milling time is 16 h, and the ball milling speed is 300 rpm.

[0112] (2) The nanocrystalline mixed powder A was mixed using a powder mixer to obtain powder B.

[0113] (3) Powder B was shaped by room temperature pressing to obtain nanocrystalline magnesium alloy.

[0114] The pressing pressure is 1.3 GPa, and the holding time is 5 min.

[0115] Furthermore, the microstructure of the nanocrystalline magnesium alloy obtained in step (3) of Comparative Example 4 was observed, and the average grain size of the magnesium grains was 82 nm.

[0116] Furthermore, the nanocrystalline magnesium alloy obtained in step (3) of Comparative Example 4 was subjected to vacuum isothermal heat treatment at a temperature of 450°C for 10 hours. The average grain size of the magnesium alloy was 820 nm, and some grains reached 2 μm.

[0117] Comparative Example 5

[0118] Comparative Example 5 is basically the same as Example 3 in method, except that the amount of aluminum powder added in steps (1) and (2) is different in Comparative Example 5. In step (1), the mass fraction of Al element is 3%, which is less than 6%. The specific steps are as follows:

[0119] (1) Pure aluminum powder and magnesium-based powder are mechanically alloyed to obtain nanocrystalline mixed powder A.

[0120] The magnesium-based powder is pure magnesium powder with an average particle size of 45 μm; the pure aluminum powder has an average particle size of 45 μm and a content of 3 wt.%; the mechanical alloying ball-to-powder ratio is 60:1, the ball milling time is 16 h, and the ball milling speed is 300 rpm.

[0121] (2) The nanocrystalline mixed powder A is mixed using a powder mixer to obtain mixed powder B.

[0122] (3) The mixed powder B is shaped by extrusion to obtain nanocrystalline magnesium alloy.

[0123] The extrusion ratio was 10:1, the extrusion temperature was 300℃, and the extruded billet was kept warm for 1 hour.

[0124] Furthermore, the microstructure of the nanocrystalline magnesium alloy obtained in step (3) of Comparative Example 5 was observed, and the average grain size of the magnesium grains was 800 nm.

[0125] This invention achieves a three-modal distribution of aluminum in a nanocrystalline magnesium matrix through mechanical alloying and mechanical mixing. By utilizing the drag and pinning effects, the thermal stability of the nanocrystalline magnesium matrix is ​​significantly improved. Aluminum powder is used as the material to improve the thermal stability of the nanocrystalline magnesium matrix, which has low density and low cost. The preparation process is simple, the production efficiency is high, and it has the potential for large-scale application.

[0126] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a high thermal stability nanocrystalline magnesium alloy, characterized in that, Includes the following steps: (1) Pure aluminum powder and magnesium-based powder are mechanically alloyed to obtain nanocrystalline mixed powder A; (2) The nanocrystalline mixed powder A is mixed evenly with pure aluminum powder to obtain mixed powder B; (3) The mixed powder B is solidified under pressure to obtain a high thermal stability nanocrystalline magnesium alloy; In step (1), the magnesium-based powder is pure magnesium powder or magnesium alloy powder, and the average particle size of the magnesium-based powder is between 10 μm and 2 mm; in the nanocrystalline mixed powder A, the mass fraction of pure aluminum powder is 1 to 10%; in the nanocrystalline mixed powder A, the mass fraction of Al element is ≥6%; and the average particle size of pure aluminum powder is between 1 μm and 45 μm. In step (2), the mass fraction of pure aluminum powder in the mixed powder B is 2-5%; the average particle size of the pure aluminum powder is between 1 μm and 10 μm.

2. The preparation method according to claim 1, characterized in that, In step (1), the purity of the pure aluminum powder is greater than 99.5 wt.%.

3. The preparation method according to claim 1, characterized in that, In step (2), the purity of the pure aluminum powder is greater than 99.5 wt.%.

4. The preparation method according to claim 1, characterized in that, The ball-to-material ratio for mechanical alloying is 58-62:1, the ball milling time is 15-20 h, and the ball milling speed is 250-350 rpm.

5. The preparation method according to claim 4, characterized in that, The ball-to-material ratio for mechanical alloying is 60:

1.

6. The preparation method according to claim 4, characterized in that, The ball milling time was 16 hours.

7. The preparation method according to claim 4, characterized in that, The ball mill speed is 300 rpm.

8. The preparation method according to claim 1, characterized in that, The mixed powder B is solidified and formed by compression molding or extrusion molding.

9. The preparation method according to claim 8, characterized in that, The pressing pressure for the pressing molding is 1.0~1.5GPa, and the holding time is 3~8 min; Alternatively, the extrusion ratio of the extrusion molding is 8~12:1, the extrusion temperature is 250~350℃, and the extrusion billet holding time is 0.8~1.2 h.

10. A high thermal stability nanocrystalline magnesium alloy, characterized in that, Prepared by the preparation method according to any one of claims 1 to 9; The high thermal stability nanocrystalline magnesium alloy was subjected to vacuum isothermal heat treatment at a temperature of 450°C for 10 hours, resulting in an average grain size of less than 250 nm in the magnesium matrix.

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