Bulky nanotwin lightweight metal material and method for manufacturing the same

Abstract

Provided are a bulk nanobimodal lightweight metal material and a method for manufacturing the same. 【Solution means】The bulk nanobimodal lightweight metal material has a chemical composition formula of Mg-xN-yM, where x and y are mass fractions, 6 ≤ x ≤ 20, 0 < y ≤ 3, N is one or more of Zn, Li, Al, and Sc, and M is one or more of Ti, Cu, Mo, Si, Ni, Ce, and Zr. This bulk nanobimodal lightweight metal material is obtained by melting through pressure arc discharge, ball milling at low temperature and high energy, and sintering at high temperature and high pressure. 【Effect】The manufacturing method of the present invention is simple, the process is easy to control, the type of twin of the manufactured bulk nanobimodal lightweight metal material is a {10-11} compression twin, the volume fraction of the twin is up to 90% of the total volume of the material, the density is low, the specific strength is high, and it has the characteristics of excellent comprehensive mechanical properties, and can be used in multiple fields such as aerospace, new energy vehicles, biomedicine, and national defense military.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal material manufacturing, and relates to a bulk nano-twinned lightweight metal material and a manufacturing method thereof.

Background Art

[0002] Currently, the situation faced in achieving the goals of energy conservation and emission reduction remains serious. Therefore, widely popularizing the application of light alloy structural materials is an effective means to alleviate environmental stress, especially in the automotive industry. Magnesium alloys are one of the lightest metal structural materials, having high specific strength, good cutting performance, electromagnetic shielding performance, and damping capacity. However, the two technical bottlenecks that their strength is relatively low and it is difficult to perform deformation processing at room temperature severely limit their future as potential structural materials. In the past few decades, methods such as alloying, grain refinement, precipitation strengthening, and heat treatment have been widely used to improve the strength of magnesium alloys. The hexagonal close-packed (HCP) crystal structure has limited independent slip systems provided during the deformation process, so the deformability of magnesium alloys is closely related to the formation and growth of twins. Therefore, intensively studying the types of twins and their related deformation mechanisms in magnesium alloys is the key to improving their cold working performance and mechanical properties.

[0003] Twin grain boundaries, similar to crystal grain boundaries, play a crucial role in improving the mechanical performance of magnesium alloys with HCP structures that have a limited slip system, due to their interaction with dislocations. Furthermore, twin grain boundaries typically exhibit higher thermal and mechanical stability compared to conventional high-angle grain boundaries, especially at the nanoscale. Therefore, twinning strengthening is considered a possible strengthening mechanism in high-performance magnesium alloys, similar to grain refinement strengthening and precipitation strengthening. However, while the strengthening effect of twin grain boundaries is comparable to that of crystal grain boundaries in terms of quantity, its strengthening effect is not as pronounced compared to grain refinement strengthening when the twin grain boundary pitch is on the micron scale. The most common types of twinning in magnesium alloys are {10-11} compression twins and {10-12} tensile twins. Here, {10-12} tensile twins have poor interfacial stability, are prone to migration under force, and can potentially occupy entire grains during deformation; therefore, their width is usually maintained between a few microns and tens of microns. In contrast, {10-11} compression twins are typically smaller in size and more stable. Furthermore, the critical shear stress required to activate compression twins is usually much higher than that required for tensile twins. This indicates that during plastic deformation, a greater driving force (higher local stress) can trigger the nucleation of compression twins. However, conventional plastic deformation methods struggle to achieve such high stress levels. Therefore, how to produce high-density and stable {10-11} compression twins is a significant technological challenge in the current field of magnesium alloy processing.

[0004] The paper "Nature communications, 2021, 12(1):4616" describes a method for producing nanotwinned magnesium alloys. Specifically, hot-rolled AZ80 plates are cut into blocks, then solution-treated at 400°C for 24 hours, and quenched in cold water. After solution treatment, the sample is subjected to multidirectional compression 1, 3, 6, and 12 times, and a compression mode is used that cycles between low strain (3%) and high strain (6.5%) to obtain a high-performance nanotwinned magnesium alloy. The multidirectional compression method used in the paper was successfully used to produce a magnesium alloy with an average twin thickness of 200 nm. However, upon further research, it was found that all of the twins were of the {10-12} tensile twin type, and this type of twin has a limited strengthening effect on magnesium alloys (and therefore does not reach the nanoscale precipitate phase). Strategies for introducing a large amount of {10-12} tensile twins into magnesium alloys are widely applied and studied, so this method lacks originality.

[0005] Chinese invention patent application number 202110271202.X discloses a method for manufacturing an ultra-high-strength, high-toughness nano-gradient twinned magnesium alloy. In this invention, first, a magnesium alloy ingot after semi-continuous casting is subjected to homogenization annealing, and then the middle portion of the ingot is cut out and processed into a rod by hot extrusion technology. A disc-shaped sample is cut out from the obtained rod and subjected to solution treatment. Subsequently, under room temperature conditions, intense plastic deformation is achieved by high-pressure torsion processing, and further aging optimization treatment is performed to finally obtain a magnesium alloy with excellent overall mechanical performance. However, the high performance of this alloy is mainly due to intense plastic deformation processes such as high-pressure torsion (microcrystalline strengthening, texture strengthening, etc.), and the contribution of the twinned structure is relatively limited, resulting in a low twinned volume fraction. Furthermore, in this invention, a magnesium rare-earth alloy with a total rare-earth content of more than 10 wt.% is selected as the raw material, which results in high costs and makes it difficult to meet the needs of large-scale industrial production.

[0006] Chinese invention patent application number 202211414290.5 discloses a method for producing a TB8 titanium alloy having a nanotwin structure. In this invention, a TB8 titanium alloy having a nanotwin structure was successfully produced by modifying a single-phase TB8 titanium alloy after heat treatment by high-voltage electric pulse treatment. The microstructure of the obtained titanium alloy mainly consists of a β-titanium matrix and α-titanium precipitates containing nanotwins. The method provided in this invention has the remarkable advantages of low cost, ease of operation, and simple process flow, but the strengthening effect is limited due to the relatively low content of nanotwins in the produced alloy. Furthermore, although the density of twins improves with increasing pressure, the development of such a structure, accompanied by the coarsening phenomenon of twins, weakens the strengthening effect of the material to some extent and limits further improvement of mechanical performance.

[0007] In short, the main drawbacks of current lightweight metal materials are as follows: Firstly, the twinning type is a {10-12} tensile twin with poor strengthening effect and lacks innovation. Secondly, the manufacturing process is complex and unsuitable for large-scale production. Thirdly, twins have low density and poor overall mechanical performance, and while their strength improves, their plasticity decreases. [Overview of the project] [Problems that the invention aims to solve]

[0008] In view of the above technical problems, an object of the present invention is to provide a bulk nano-twinned lightweight metal material and a method for manufacturing the same. The chemical composition formula of this bulk nano-twinned lightweight metal material is Mg-xN-yM, where x and y are mass fractions, 6≦x≦20, 0<y≦3, N is one or more of Zn, Li, Al, Sc, and M is one or more of Ti, Cu, Mo, Si, Ni, Ce, Zr. This bulk nano-twinned lightweight metal material is obtained by melting through pressure arc discharge, ball milling at low temperature and high energy, and sintering at high temperature and high pressure. The manufacturing method of the present invention is simple, the process is easy to control, the type of twin of the manufactured bulk nano-twinned lightweight metal material is {10-11} compression twin, the volume fraction of the twin is up to 90% of the total volume of the material, the density is low, the specific strength is high, and it has the characteristics of excellent comprehensive mechanical properties, and can be used in multiple fields such as aerospace, new energy vehicles, biomedicine and national defense military.

Means for Solving the Problems

[0009] To achieve the above object, the present invention uses the following technical solutions.

[0010] A bulk nano-twinned lightweight metal material with a chemical composition formula of Mg-xN-yM, where x and y are mass fractions (wt.%), 6≦x≦20, 0<y≦3, N is one or more of Zn, Li, Al, Sc, and M is one or more of Ti, Cu, Mo, Si, Ni, Ce, Zr.

[0011] As a limitation of the present invention, the microstructure of the bulk nano-twinned lightweight metal material includes nano-twins and recrystallized grains. The nano-twins have stacking defects inside, an average thickness of 94~144nm, the recrystallized grains are equiaxed crystals, the average grain size is 109~153μm, and the volume fraction of the nano-twins occupies 58%~90% of the total volume of the material.

[0012] As another limitation of the present invention, the nano-twins are {10-11} compression twins.

[0013] According to the present invention, S1 is obtained by blending according to the alloy components, placing it in a vacuum melting furnace, and melting it under an argon gas atmosphere at 10 MPa and 300 rpm to obtain an as-cast Mg-xN-yM alloy, The aforementioned Mg-xN-yM as-cast alloy is placed in a quenched steel ball milling tank, 10 mL of n-hexane is added as a grinding aid, the ball milling tank is immersed in liquid nitrogen at -196°C for 20 minutes to pre-cool and ball mill the alloy, then it is dried in a vacuum drying oven, and finally the ball-milled powder is pressed into a cylindrical shape with a diameter of 30 mm and a height of 20 mm at a pressure of 5 MPa (S2). A method for producing a massive nanotwin lightweight metal material is provided, which involves the steps of S3, S4, S5, S6, S7, S8, S7, S8, S9

[0014] As a limitation of the manufacturing method of the present invention, in step S1, the melting process is as follows: first, melting with a current of 200A for 30s, then melting with a current of 600A for 120s, finally reducing the current to 400A and melting for 60s, reversing three times during the 60s of melting with a current of 400A, and after the melting is completed, extinguishing the arc and maintaining the pressure for 5 to 10 minutes.

[0015] As another limitation of the manufacturing method of the present invention, in step S2, the ball milling process is to place hardened steel mill balls and material having a ball-to-material ratio of 20:1 into a hardened steel ball milling tank and to ball mill for only 4 to 6 cycles at 600 to 1000 rpm, each cycle consisting of 30 minutes of ball milling followed by 10 minutes of rest, during which the ball milling tank is immersed in liquid nitrogen at -196°C to maintain a low temperature.

[0016] The low-temperature, high-energy ball milling process of the present invention is extremely important and is used to produce precursor alloy powders rich in stacking fault structures. Twin formation is mainly due to the shear behavior of atoms in a specific crystal direction, which alters the atomic arrangement in the stacking fault region. Because it is in a high-energy state, the stacking fault is likely to become a nucleation site for twins.

[0017] As a third limitation of the manufacturing method of the present invention, in step S2, the drying is performed at a temperature of 25°C for a duration of 1 hour.

[0018] As a fourth limitation of the manufacturing method of the present invention, in step S3, the high-temperature, high-pressure sintering process involves raising the temperature from room temperature to 700-1100°C at a heating rate of 6°C / s at 6 GPa, and then holding the temperature and pressure for 1 hour.

[0019] In this invention, the temperature and pressure during high-temperature, high-pressure sintering affect the densification behavior of the material, the grain growth dynamics, and the stability of the twin structure. Sintering at a pressure of 6 GPa at 700-1100°C allows for sufficient dynamic recrystallization and twin nucleation, resulting in a dense and uniformly fine nano-twin structure. If the pressure is less than 6 GPa and the temperature is less than 700°C at this stage, plastic flow is insufficient and the diffusion rate is too low, leading to incomplete densification, insufficient twin formation, and a deterioration of mechanical performance. If the pressure exceeds 6 GPa and the temperature exceeds 1100°C at this stage, abnormal growth of crystal grains and nano-twin structures occurs, ultimately leading to the disappearance of twins, as well as softening of the material and a decrease in strength. Holding the heat and pressure for 1 hour is necessary to allow sufficient diffusion to proceed, eliminate internal stress, and stabilize the nano-twin structure.

[0020] As is well known, {10-12} tensile twins are activated and easily expand under low critical shear stresses of 2-8 MPa, and consequently occupy the entire grain during the deformation process. In contrast, {10-11} compression twins have a more stable interface, their critical shear stress is approximately 30-100 MPa, and they can effectively pin dislocation motion, resulting in a stronger strengthening effect. In this invention, we have succeeded in producing a lightweight metallic material having high-density {10-11} compression nanotwin crystals by combining a high-temperature, high-pressure sintering process with low-temperature, high-energy ball milling. The core of this invention lies in using high-melting-point metal atoms as mass points to induce stacking faults and producing a precursor alloy powder rich in stacking fault structures by a low-temperature, high-energy ball milling process. The formation of twins is mainly due to the shear behavior of atoms in a specific crystal direction, which changes the atomic arrangement in the stacking fault region, and because it is in a high-energy state, the stacking fault is likely to become a nucleation site for twins. Furthermore, the cubic press possesses hexagonal compression properties and can effectively suppress {10-12} tensile twinning caused by tension along the crystallographic c-axis. Therefore, after undergoing the high-temperature, high-pressure sintering process of the cubic press, a lightweight metallic material with high-density {10-11} compression nanotwinings is ultimately obtained.

[0021] The above technical means of the present invention, as a whole, involve closely related and influencing relationships between each step, which commonly determine the morphological characteristics and performance of the product. [Effects of the Invention]

[0022] The above technical means has the following advantages or beneficial effects. 1. In the bulk nanotwin lightweight metal material manufactured according to the present invention, the twinning type of the nanotwin is {10-11} compression twin, it has a high twinning density, and the volume fraction of nanotwin can account for up to 90% of the total material volume. 2. The bulk nanotwin lightweight metal material manufactured according to the present invention exhibits excellent mechanical properties, with a yield strength of up to 412 MPa and a tensile strength of up to 455 MPa. 3. The manufacturing method of the present invention is simple, easy to control the process, and suitable for large-scale industrial production.

[0023] The present invention is suitable for the manufacture of bulk nanobinary lightweight metal materials.

[0024] Hereinafter, the technical means of the present invention will be described in more detail with reference to the drawings and specific embodiments.

Brief Description of the Drawings

[0025] [Figure 1] It is an optical microscope view of the bulk nanobinary lightweight metal material manufactured in Example 1 of the present invention. [Figure 2] It is a transmission electron microscope view of the bulk nanobinary lightweight metal material manufactured in Example 2 of the present invention. [Figure 3] It is a graph showing the change in Vickers hardness of the bulk nanobinary lightweight metal material manufactured in Example 2 of the present invention. [Figure 4] It is a high-resolution view of the nanobinary structure of the bulk nanobinary lightweight metal material manufactured in Example 3 of the present invention, and the upper right corner in the figure is a fast Fourier transform (FFT) view.

Modes for Carrying Out the Invention

[0026] The following examples are only some examples of the present invention, not all examples. Therefore, the detailed description of the examples of the present invention provided below is not intended to limit the scope of the claimed invention, but only represents selected examples of the present invention. Based on the examples of the present invention, all other examples obtained on the premise that those skilled in the art do not perform creative labor belong to the protection scope of the present invention.

[0027] In the present invention, unless otherwise specified, all equipment, raw materials, etc. can all be purchased from the market or are commonly used in the industry. The methods in the following examples are all common methods in this field unless otherwise explained.

[0028] (Example 1) In this example, a Mg-6Li-1Cu massive nanotwin lightweight metal material (component mass percentage: Li: 6 wt.%, Cu: 1 wt.%, remainder Mg) is manufactured, and the manufacturing process and steps are as follows (S1-S3).

[0029] In S1, the alloy was mixed according to its composition, placed in a vacuum melting furnace, and melted under an argon gas atmosphere at 10 MPa and 300 rpm. First, it was melted for 30 seconds at a current of 200 A, then for 120 seconds at a current of 600 A, and finally the current was reduced to 400 A for 60 seconds. During the 60 seconds of melting at 400 A, the mixture was reversed three times (on average once every 20 seconds), and after the arc was extinguished, the pressure was maintained for 5 minutes to obtain the as-cast Mg-6Li-1Cu alloy.

[0030] In S2, the Mg-6Li-1Cu as-cast alloy was placed in a quenched steel ball milling tank, 10 mL of n-hexane was added as a grinding aid, and the ball milling tank was pre-cooled for 20 minutes by immersing it in liquid nitrogen at -196°C before ball milling. The quenched steel mill balls and material, with a ball-to-material ratio of 20:1, were placed in a quenched steel ball milling tank, and ball milling was performed for only four cycles at 800 rpm. Each cycle consisted of 30 minutes of ball milling followed by a 10-minute stop, during which the ball milling tank was immersed in liquid nitrogen at -196°C to maintain a low temperature. After that, it was dried at 25°C for 1 hour, and finally, the powder, which had been ball milled at 5 MPa under an argon gas atmosphere, was pressed into a cylindrical shape with a diameter of 30 mm and a height of 20 mm.

[0031] In S3, the prepress-formed sample was placed in a cubic press and heated from room temperature to 700°C at a heating rate of 6°C / s at 6 GPa, followed by holding pressure for 1 hour to obtain a massive nanotwin lightweight metal material. The massive nanotwin lightweight metal material had an average nanotwin thickness of 135 nm, an equiaxed average crystal grain size of 122 μm, and the nanotwin volume fraction accounted for 61% of the total material volume.

[0032] Mechanical performance tests were conducted on the bulk nanotwin lightweight metal material produced in this embodiment, and its tensile strength was 370 MPa, its yield strength was 322 MPa, and its fracture strain was 25%. In addition, the as-cast alloy produced in step S1 of this embodiment was used as a comparative example, and mechanical performance tests were conducted on it. The test results showed that the Mg-6Li-1Cu as-cast alloy melted by pressure arc discharge alone had a tensile strength of only 151 MPa and a yield strength of only 90 MPa.

[0033] Figure 1 is an optical microscope image of the massive nanotwin lightweight metal material produced in this embodiment. As can be seen from the figure, the crystal grains of the sample after high temperature and pressure were equiaxed.

[0034] (Example 2) In this example, a Mg-9Li-1.5Zr bulk nanotwin lightweight metal material (component mass percentage: Li: 9 wt.%, Zr: 1.5 wt.%, remainder Mg) is manufactured, and the manufacturing process and steps are as follows (S1-S3).

[0035] In S1, the alloy was mixed according to its composition, placed in a vacuum melting furnace, and melted under an argon gas atmosphere at 10 MPa and 300 rpm. First, it was melted for 30 seconds at a current of 200 A, then for 120 seconds at a current of 600 A, and finally the current was reduced to 400 A for 60 seconds. During the 60 seconds of melting at 400 A, the mixture was reversed three times (on average once every 20 seconds), and after the arc was extinguished, the pressure was maintained for 10 minutes to obtain the as-cast Mg-9Li-1.5Zr alloy.

[0036] In S2, the Mg-9Li-1.5Zr as-cast alloy was placed in a quenched steel ball milling tank, 10 mL of n-hexane was added as a grinding aid, and the ball milling tank was pre-cooled for 20 minutes by immersing it in liquid nitrogen at -196°C before ball milling. The quenched steel mill balls and material, with a ball-to-material ratio of 20:1, were placed in a quenched steel ball milling tank, and ball milling was performed for only 6 cycles at 1000 rpm. Each cycle consisted of 30 minutes of ball milling followed by a 10-minute stop, during which the ball milling tank was immersed in liquid nitrogen at -196°C to maintain a low temperature. After that, it was dried at 25°C for 1 hour, and finally, the powder, which had been ball milled at 5 MPa under an argon gas atmosphere, was pressed into a cylindrical shape with a diameter of 30 mm and a height of 20 mm.

[0037] In S3, the pre-pressed sample was placed in a cubic press and heated from room temperature to 900°C at a heating rate of 6°C / s at 6 GPa, followed by 1 hour of heat and pressure holding to obtain a massive nanotwin lightweight metal material. The massive nanotwin lightweight metal material had an average nanotwin thickness of 94 nm, an average equiaxed crystal grain size of 109 μm, and the nanotwin volume fraction accounted for 90% of the total material volume.

[0038] Mechanical performance tests were conducted on the bulk nanotwin lightweight metal material produced in this embodiment, and its tensile strength was 455 MPa, its yield strength was 412 MPa, and its fracture strain was 16%. Furthermore, the as-cast alloy produced in step S1 of this embodiment was used as a comparative example, and mechanical performance tests were conducted on it. The test results showed that the Mg-9Li-1.5Zr as-cast alloy, melted solely by pressure arc discharge, had a tensile strength of only 132 MPa and a yield strength of only 85 MPa.

[0039] Figure 2 is a transmission electron microscope image of the bulk nanotwin lightweight metal material produced in this embodiment. As can be seen from the figure, after high-temperature, high-pressure sintering, high-density nanotwin crystals are formed inside the crystal grains of the bulk nanotwin lightweight metal material. This indicates that low-temperature, high-energy ball milling can be combined with a high-temperature, high-pressure sintering process to effectively produce bulk alloys with high-density nanotwin crystals.

[0040] Figure 3 is a graph showing the Vickers hardness change of the massive nanotwin lightweight metal material produced in this embodiment. As can be seen from the figure, after undergoing a series of high-temperature, high-pressure process treatments, the Vickers hardness of the alloy significantly improved compared to the as-cast state, reaching a peak value under conditions of 6 GPa and 900°C. This demonstrates that combining low-temperature, high-energy ball milling with a high-temperature, high-pressure sintering process can significantly improve the mechanical properties of the alloy.

[0041] (Example 3) In this example, a Mg-10Sc-1Ti massive nanotwin lightweight metal material (component mass percentage: Sc: 10 wt.%, Ti: 1 wt.%, remainder Mg) is manufactured, and the manufacturing process and steps are as follows (S1-S3).

[0042] In S1, the alloy was mixed according to its composition, placed in a vacuum melting furnace, and melted under an argon gas atmosphere at 10 MPa and 300 rpm. First, it was melted for 30 seconds at a current of 200 A, then for 120 seconds at a current of 600 A, and finally the current was reduced to 400 A for 60 seconds. During the 60 seconds of melting at 400 A, the mixture was reversed three times (on average once every 20 seconds), and after the arc was extinguished, the pressure was maintained for 7 minutes to obtain the as-cast Mg-10Sc-1Ti alloy.

[0043] In S2, as-cast Mg-10Sc-1Ti alloy was placed in a quenched steel ball milling tank, 10 mL of n-hexane was added as a grinding aid, and the ball milling tank was pre-cooled for 20 minutes by immersing it in liquid nitrogen at -196°C before ball milling. The quenched steel mill balls and material, with a ball-to-material ratio of 20:1, were placed in a quenched steel ball milling tank, and ball milling was performed for only 5 cycles at 900 rpm. Each cycle consisted of 30 minutes of ball milling followed by a 10-minute stop, during which the ball milling tank was immersed in liquid nitrogen at -196°C to maintain a low temperature. After that, it was dried at 25°C for 1 hour, and finally, the powder, which had been ball milled at a pressure of 5 MPa under an argon gas atmosphere, was pressed into a cylindrical shape with a diameter of 30 mm and a height of 20 mm.

[0044] In S3, the pre-pressed sample was placed in a cubic press and heated from room temperature to 1100°C at a heating rate of 6°C / s at 6 GPa, followed by 1 hour of holding pressure to obtain a massive nanotwin lightweight metal material. The massive nanotwin lightweight metal material had an average nanotwin thickness of 122 nm, an average equiaxed crystal grain size of approximately 140 μm, and the nanotwin volume fraction accounted for 77% of the total material volume.

[0045] Mechanical performance tests were conducted on the bulk nanotwin lightweight metal material produced in this embodiment, and its tensile strength was 408 MPa, its yield strength was 364 MPa, and its fracture strain was 20%. Furthermore, the as-cast alloy produced in step S1 of this embodiment was used as a comparative example, and mechanical performance tests were conducted on it. The test results showed that the Mg-10Sc-1Ti as-cast alloy, melted by pressure arc discharge alone, had a tensile strength of only 218 MPa and a yield strength of only 147 MPa.

[0046] Figure 4 is a high-resolution view of the nanotwin structure of the massive nanotwin lightweight metal material manufactured in this embodiment. The upper right corner of the figure is the Fast Fourier Transform (FFT) diagram. As can be seen from the analysis, the (0001) plane of the matrix and the twin are mirror-symmetric with respect to the (10-11) twin plane, and the (10-10) plane also exhibits similar symmetry. Therefore, it can be determined that the twin type belongs to {10-11} compression twinning.

[0047] (Example 4) In this example, a Mg-10Sc-1Si bulk nanotwin lightweight metal material (component mass percentage: Sc: 10 wt.%, Si: 1 wt.%, remainder Mg) is manufactured, and the manufacturing process and steps are as follows (S1-S3).

[0048] In S1, the alloy was mixed according to its composition, placed in a vacuum melting furnace, and melted under an argon gas atmosphere at 10 MPa and 300 rpm. First, it was melted for 30 seconds at a current of 200 A, then for 120 seconds at a current of 600 A, and finally the current was reduced to 400 A for 60 seconds. During the 60 seconds of melting at 400 A, the mixture was reversed three times (on average once every 20 seconds), and after the arc was extinguished, the pressure was maintained for 7 minutes to obtain the as-cast Mg-10Sc-1Si alloy.

[0049] In S2, the as-cast Mg-10Sc-1Si alloy was placed in a quenched steel ball milling tank, 10 mL of n-hexane was added as a grinding aid, and the ball milling tank was pre-cooled for 20 minutes by immersing it in liquid nitrogen at -196°C before ball milling. The quenched steel mill balls and material, with a ball-to-material ratio of 20:1, were placed in the quenched steel ball milling tank, and ball milling was performed for only 5 cycles at 900 rpm. Each cycle consisted of 30 minutes of ball milling followed by a 10-minute stop, during which the ball milling tank was immersed in liquid nitrogen at -196°C to maintain a low temperature. After that, it was dried at 25°C for 1 hour, and finally, the powder, which had been ball milled at a pressure of 5 MPa under an argon gas atmosphere, was pressed into a cylindrical shape with a diameter of 30 mm and a height of 20 mm.

[0050] In S3, the pre-pressed sample was placed in a cubic press and heated from room temperature to 1100°C at a heating rate of 6°C / s at 6 GPa, followed by holding pressure for 1 hour to obtain a massive nanotwin lightweight metal material. The massive nanotwin lightweight metal material had an average nanotwin thickness of 130 nm, an equiaxed average crystal grain size of 134 μm, and the nanotwin volume fraction accounted for 72% of the total material volume.

[0051] Mechanical performance tests were conducted on the bulk nanotwin lightweight metal material produced in this embodiment, and its tensile strength was 391 MPa, its yield strength was 354 MPa, and its fracture strain was 22%. In addition, the as-cast alloy produced in step S1 of this embodiment was used as a comparative example, and mechanical performance tests were conducted on it. The test results showed that the tensile strength of the Mg-10Sc-1Si as-cast alloy melted by pressure arc discharge alone was only 202 MPa, and its yield strength was only 142 MPa.

[0052] (Example 5) In this example, a Mg-9Al-2Ce-1Ni massive nanotwin lightweight metal material (component mass percentages: Al: 9 wt.%, Ce: 2 wt.%, Ni: 1 wt.%, remainder Mg) is produced, and the production process and steps are as follows (S1-S3).

[0053] In S1, the alloy was mixed according to its composition, placed in a vacuum melting furnace, and melted under an argon gas atmosphere at 10 MPa and 300 rpm. First, it was melted for 30 seconds at a current of 200 A, then for 120 seconds at a current of 600 A, and finally the current was reduced to 400 A for 60 seconds. During the 60 seconds of melting at 400 A, the furnace was reversed three times (on average once every 20 seconds), and after the arc was extinguished, the pressure was maintained for 5 minutes to obtain the as-cast Mg-9Al-2Ce-1Ni alloy.

[0054] In S2, the as-cast Mg-9Al-2Ce-1Ni alloy was placed in a quenched steel ball milling tank, 10 mL of n-hexane was added as a grinding aid, and the ball milling tank was pre-cooled for 20 minutes by immersing it in liquid nitrogen at -196°C before ball milling. The quenched steel mill balls and material, with a ball-to-material ratio of 20:1, were placed in a quenched steel ball milling tank, and ball milling was performed for only four cycles at 800 rpm. Each cycle consisted of 30 minutes of ball milling followed by a 10-minute stop, during which the ball milling tank was immersed in liquid nitrogen at -196°C to maintain a low temperature. After that, it was dried at 25°C for 1 hour, and finally, the powder, which had been ball milled at a pressure of 5 MPa under an argon gas atmosphere, was pressed into a cylindrical shape with a diameter of 30 mm and a height of 20 mm.

[0055] In S3, the prepress-formed sample was placed in a cubic press and heated from room temperature to 1100°C at a heating rate of 6°C / s at 6 GPa, followed by 1 hour of heat and pressure holding to obtain a massive nanotwin lightweight metal material. The massive nanotwin lightweight metal material had an average nanotwin thickness of 121 nm, an average equiaxed crystal grain size of approximately 162 μm, and the nanotwin volume fraction accounted for 65% of the total material volume.

[0056] Mechanical performance tests were conducted on the bulk nanotwin lightweight metal material produced in this embodiment, and its tensile strength was 382 MPa, its yield strength was 334 MPa, and its fracture strain was 25%. In addition, the as-cast alloy produced in step S1 of this embodiment was used as a comparative example, and mechanical performance tests were conducted on it. The test results showed that the Mg-9Al-2Ce-1Ni as-cast alloy, melted by pressure arc discharge alone, had a tensile strength of only 188 MPa and a yield strength of only 137 MPa.

[0057] (Example 6) In this example, a Mg-20Zn-3Mo bulk nanotwin lightweight metal material (component mass percentages: Zn: 20 wt.%, Mo: 3 wt.%, remainder Mg) is manufactured, and the manufacturing process and steps are as follows (S1-S3).

[0058] In S1, the alloy was mixed according to its composition, placed in a vacuum melting furnace, and melted under an argon gas atmosphere at 10 MPa and 300 rpm. First, it was melted for 30 seconds at a current of 200 A, then for 120 seconds at a current of 600 A, and finally the current was reduced to 400 A for 60 seconds. During the 60 seconds of melting at 400 A, the mixture was reversed three times (on average once every 20 seconds), and after the arc was extinguished, the pressure was maintained for 10 minutes to obtain the as-cast Mg-20Zn-3Mo alloy.

[0059] In S2, the as-cast Mg-20Zn-3Mo alloy was placed in a quenched steel ball milling tank, 10 mL of n-hexane was added as a grinding aid, and the ball milling tank was pre-cooled for 20 minutes by immersing it in liquid nitrogen at -196°C before ball milling. The quenched steel mill balls and material, with a ball-to-material ratio of 20:1, were placed in the quenched steel ball milling tank, and ball milling was performed for only 6 cycles at 600 rpm. Each cycle consisted of 30 minutes of ball milling followed by a 10-minute stop, during which the ball milling tank was immersed in liquid nitrogen at -196°C to maintain a low temperature. After that, it was dried at 25°C for 1 hour, and finally, the powder, which had been ball milled at a pressure of 5 MPa under an argon gas atmosphere, was pressed into a cylindrical shape with a diameter of 30 mm and a height of 20 mm.

[0060] In S3, the prepress-formed sample was placed in a cubic press and heated from room temperature to 900°C at a heating rate of 6°C / s at 6 GPa, followed by 1 hour of holding pressure to obtain a massive nanotwin lightweight metal material. The massive nanotwin lightweight metal material had an average nanotwin thickness of 144 nm, an average equiaxed crystal grain size of 153 μm, and the nanotwin volume fraction accounted for 58% of the total material volume.

[0061] Mechanical performance tests were conducted on the bulk nanotwin lightweight metal material manufactured in this embodiment, and its tensile strength was 362 MPa, its yield strength was 308 MPa, and its fracture strain was 20%. In addition, the as-cast alloy manufactured in step S1 of this embodiment was used as a comparative example, and mechanical performance tests were conducted on it. The test results showed that the as-cast Mg-20Zn-3Mo alloy melted by pressure arc discharge alone had a tensile strength of only 177 MPa and a yield strength of only 124 MPa.

[0062] (Comparative example) To explore the influence of different manufacturing processes and different parameters used in the manufacturing process of the present invention on the performance of the product of the present invention, the following comparative experiments were conducted. In the comparative examples below, different metal materials were manufactured, specifically as follows.

[0063] (Comparative Example 1) In this comparative example, a metal material is manufactured, and the manufacturing process is similar to that of Example 1, but it differs in that step S2 is omitted; that is, after manufacturing the as-cast alloy in step S1, high-temperature, high-pressure sintering in step S3 is performed directly.

[0064] Mechanical performance tests were conducted on the metal material produced in this comparative example, and its tensile strength was 301 MPa, yield strength was 277 MPa, and fracture strain was 28%. Because ball milling at low temperature and high energy was not performed, there were few stacking fault structures inside the as-cast alloy, and therefore high-density nanotwin crystals were not formed after high-temperature and high-pressure treatment, resulting in relatively poor mechanical performance.

[0065] (Comparative Example 2) In this comparative example, a metal material is manufactured, and the manufacturing process is similar to that of Example 1, but differs in that the high-temperature, high-pressure sintering in step S3 is omitted.

[0066] Mechanical performance tests were conducted on the metal material produced in this comparative example, and its tensile strength was 263 MPa, yield strength was 226 MPa, and fracture strain was 17%. High-temperature, high-pressure sintering can promote sufficient dynamic recrystallization and twin nucleation, giving the material a dense and uniformly fine nanotwin structure. However, after ball milling at low temperature and high energy, only a large number of stacking fault structures exist inside the material, and there is a lack of effective strengthening mechanisms, resulting in relatively poor mechanical performance.

[0067] (Comparative Example 3) In this comparative example, a metal material is manufactured, and the manufacturing process is similar to that of Example 1, but differs in that the sintering temperature in step S3 is 1200°C.

[0068] Mechanical performance tests were conducted on the metal material produced in this comparative example, and its tensile strength was 342 MPa, its yield strength was 301 MPa, and its fracture strain was 24.5%. When the temperature exceeds 1100°C, abnormal growth of crystal grains and nanotwin crystals occurs, leading to the disappearance of twin crystals, and further to softening of the material and a decrease in strength.

[0069] (Comparative Example 4) In this comparative example, a metal material is manufactured, and the manufacturing process is similar to that of Example 1, but differs in that the sintering pressure in step S3 is 4 GPa.

[0070] Mechanical performance tests were conducted on the metallic material produced in this comparative example, and its tensile strength was 341 MPa, its yield strength was 298 MPa, and its fracture strain was 18%. When the pressure is less than 6 GPa, plastic flow is insufficient, resulting in incomplete densification and insufficient twinning, thus leading to relatively poor mechanical performance.

[0071] The above description is merely a preferred embodiment of the present invention and does not limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can still modify the technical means described in the above embodiments or substitute equivalents for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are all included in the claims of the present invention.

Claims

1. The chemical formula is Mg-xN-yM, where x and y are mass fractions, 6 ≤ x ≤ 20, 0 < y ≤ 3, N is one or more of Zn, Li, Al, Sc, and M is one or more of Ti, Cu, Mo, Si, Ni, Ce, Zr. The microstructure includes nanotwin crystals and recrystallized grains. The aforementioned nanotwin crystals have stacking faults inside and have an average thickness of 94 to 144 nm. The aforementioned recrystallized grains are equiaxed, and have an average grain size of 10⁹ to 153 μm. The aforementioned nanotwin crystals account for 58% to 90% of the total volume of the material. A bulky, nanotwinned, lightweight metallic material characterized by these features.

2. The aforementioned nanotwin is a {10-11} compression twin. The bulk nanotwin lightweight metal material according to feature 1.

3. A method for producing a massive nanotwin lightweight metal material according to claim 1 or 2, Step S1 involves blending the alloy components according to their composition, placing them in a vacuum melting furnace, and melting them under an argon gas atmosphere at 10 MPa and 300 rpm to obtain an as-cast Mg-xN-yM alloy. Step S2 involves placing the aforementioned Mg-xN-yM as-cast alloy into a quenched steel ball milling tank, adding 10 mL of n-hexane as a grinding aid, pre-cooling the ball milling tank by immersing it in liquid nitrogen at -196°C for 20 mins, then ball milling, drying in a vacuum drying oven, and finally pressing the ball-milled powder into a cylindrical shape with a diameter of 30 mm and a height of 20 mm under an argon gas atmosphere at a pressure of 5 MPa. The steps are performed sequentially, starting with step S3, in which a pre-pressed sample is placed in a cubic press and subjected to high-temperature, high-pressure sintering to obtain a massive nanotwin lightweight metal material. A method for producing a massive nanotwin lightweight metal material, characterized by the following:

4. In step S1, the melting process involves first melting with a current of 200A for 30 seconds, then melting with a current of 600A for 120 seconds, and finally reducing the current to 400A for 60 seconds. During the 60 seconds of melting at 400A, the process is reversed three times, and after the melting is complete, the arc is extinguished and the pressure is maintained for 5 to 10 minutes. A method for producing a massive nanotwin lightweight metal material according to feature 3.

5. In step S2, the ball milling involves placing hardened steel mill balls, in a ball-to-material ratio of 20:1, and the material into a hardened steel ball milling tank, and performing ball milling for 4 to 6 cycles at 600 to 1000 rpm. One of the cycles involves ball milling for 30 mins, stopping for 10 mins, and maintaining a low temperature by immersing the ball milling tank in liquid nitrogen at -196°C during the stopping process. A method for producing a massive nanotwin lightweight metal material according to feature 3.

6. In step S2, the drying is performed at a temperature of 25°C for a duration of 1 hour. A method for producing a massive nanotwin lightweight metal material according to feature 3.

7. In step S3, the high-temperature, high-pressure sintering involves raising the temperature from room temperature to 700-1100°C at a heating rate of 6°C / s at 6 GPa, and then maintaining the temperature and pressure for 1 hour. A method for producing a massive nanotwin lightweight metal material according to feature 3.

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