A magnesium alloy with both high modulus and high plasticity and its preparation method

Abstract

This invention relates to a magnesium alloy possessing both high modulus and high plasticity, and its preparation method. The method includes: preparing a cast magnesium alloy containing graphene; subjecting the cast graphene-containing magnesium alloy to isochannel extrusion deformation to obtain an isochannel extruded material; the isochannel extrusion deformation speed is 40–60 mm / min, and the isochannel extrusion deformation temperature is 300–450 °C; and subjecting the isochannel extruded material to low-temperature extrusion deformation at 100–200 °C to obtain a magnesium alloy possessing both high modulus and high plasticity. This invention utilizes high-temperature isochannel extrusion and low-temperature extrusion deformation processes to control the microstructure of the magnesium alloy material, ultimately producing a magnesium alloy material with high modulus and ultra-high plasticity. The elongation of the magnesium alloy material can be stably maintained at 30–40%, achieving a significant improvement in plasticity compared to traditional magnesium alloy materials while maintaining a high modulus.

Description

Technical Field

[0001] This invention relates to the field of non-ferrous metal material preparation technology, specifically to a magnesium alloy with both high modulus and high plasticity and its preparation method. Background Technology

[0002] Magnesium and magnesium alloys are widely considered the most ideal green engineering materials of the 21st century due to their excellent properties such as extremely low density, high specific strength and stiffness, and good biocompatibility. However, their low modulus and low plasticity also greatly limit their applications. In particular, magnesium alloys suffer from narrow deformation temperature ranges, low product performance and safety factors, and high maintenance costs due to their low ductility, which severely restricts their application in various lightweighting fields. Therefore, improving the plasticity of magnesium alloys while increasing their modulus is an urgent problem to be solved. Simply adding alloying elements to metallic magnesium is no longer sufficient to prepare magnesium alloys with both high modulus and high plasticity, especially to achieve a synergistic improvement in both modulus and plasticity, which severely limits the application of magnesium alloys. Graphene is the first two-dimensional material discovered by mankind in nature, with a tensile strength and Young's modulus of over 130 GPa and 1.0 TPa, respectively. In addition, graphene also has high elasticity, capable of withstanding a maximum bending deformation of 25%. Therefore, introducing graphene into magnesium may be a new strategy for developing magnesium alloys that combine high modulus and high ductility.

[0003] Magnesium or magnesium alloys exhibit poor wettability with graphene, and graphene sheets are prone to agglomeration due to strong van der Waals forces. Existing technologies, such as CN109354012A, CN109207787A, CN109554573A, and CN113278840A, have proposed novel methods for combining graphene with magnesium or magnesium alloys, effectively solving the problem of reinforcement dispersion. However, in these existing technologies, while graphene can improve the strength and modulus of magnesium alloys, it also significantly reduces their plasticity, failing to overcome the technical challenge of developing magnesium alloys with both high modulus and high plasticity. Furthermore, many existing technologies have made numerous attempts, such as employing configurational design concepts to extend graphene "three-dimensional networks," "double interconnections" between the matrix alloy and the reinforcing phase, and biomimetic "micro-nano bricklaying" of nacreous shells; or using different methods to stimulate conical slip in the magnesium alloy substrate, especially by refining the grains to promote more [growth / agglomeration] in the magnesium matrix.<c+a> The activation of the slip system significantly enhances the mobility and multiplication of dislocations in the matrix, which is significant for improving the plasticity of magnesium alloys. While these methods have achieved some success, they still cannot overcome the inherent defects of interfacial stress concentration caused by lattice mismatch and elastic mismatch between graphene and the matrix in magnesium alloys. Therefore, the improvement in the plasticity of magnesium alloys is relatively limited, with the elongation only increasing by a maximum of about 20%. Thus, more rational methods are needed to alleviate the problem of interfacial stress concentration in alloy materials, utilizing the interaction between the reinforcing phase and the matrix phase to regulate the intrinsic deformation behavior of the magnesium matrix and significantly improve the material's plasticity.

[0004] In summary, it is essential to provide a magnesium alloy with both high modulus and high plasticity, and a method for its preparation. Summary of the Invention

[0005] To address one or more technical problems existing in the prior art, this invention provides a magnesium alloy with both high modulus and high plasticity, and a method for preparing the same.

[0006] The present invention provides a method for preparing a magnesium alloy with both high modulus and high ductility in a first aspect, the method comprising the following steps:

[0007] (1) Preparation of as-cast magnesium alloys containing graphene;

[0008] (2) The cast magnesium alloy containing graphene is subjected to equal channel extrusion deformation to obtain equal channel extruded material; the extrusion speed of the equal channel extrusion deformation is 40-60 mm / min, and the temperature of the equal channel extrusion deformation is 300-450℃.

[0009] (3) The equal channel extruded material is subjected to low temperature extrusion deformation at 100-200℃ to obtain a magnesium alloy with both high modulus and high plasticity.

[0010] Preferably, in step (2), 8 to 20 passes of equal channel extrusion deformation are performed, and in the first 4 passes, the temperature of equal channel extrusion deformation is 380 to 450°C. In subsequent passes, the temperature of equal channel extrusion deformation decreases at a rate of 2 to 5°C per pass. In the last pass, the temperature of equal channel extrusion deformation is 300 to 350°C.

[0011] Preferably, the equal channel extrusion deformation is equal channel diameter-angle extrusion deformation; the equal channel extrusion deformation is carried out using an equal channel extrusion die with a channel bending angle of 80-120° and a curvature angle of 30-40°; and / or before carrying out the equal channel extrusion deformation, the temperature of the equal channel extrusion die is preheated to 20°C or higher than the temperature of equal channel extrusion deformation and kept at that temperature for 0.5-1h.

[0012] Preferably, the extrusion ratio of the low-temperature extrusion deformation is (10-25):1.

[0013] Preferably, the as-cast graphene-containing magnesium alloy contains 0.6% to 2% graphene by mass.

[0014] Preferably, the preparation of the as-cast graphene-containing magnesium alloy includes the following sub-steps:

[0015] (a) Under mechanical stirring, carbon dioxide gas is introduced into a magnesium-based melt at 650–700 °C to carry out an in-situ reaction to obtain an alloy melt;

[0016] (b) High-energy ultrasound is introduced into the alloy melt to promote the dispersion of graphene, and then the melt is cooled and solidified with water to obtain a cast magnesium alloy containing graphene.

[0017] Preferably, the magnesium-based melt is one or more of pure magnesium melt, magnesium-calcium alloy melt, magnesium-manganese alloy melt, and magnesium-bismuth alloy melt.

[0018] Preferably, the magnesium alloy obtained in step (3) with both high modulus and high plasticity has an elastic modulus of not less than 50 GPa and an elongation of 35-40%.

[0019] The present invention provides, in a second aspect, a magnesium alloy having both high modulus and high ductility, prepared by the method described in the first aspect of the present invention.

[0020] Compared with the prior art, the present invention has at least the following beneficial effects:

[0021] (1) The method of the present invention has prepared a magnesium alloy material with both high modulus and ultra-high plasticity. The preparation method is efficient, simple and low cost, and can be applied to the industrial preparation of high-performance ultrafine-grained magnesium alloy materials. It solves the bottleneck problem of modulus-plasticity inversion in the existing technology of magnesium alloy materials.

[0022] (2) This invention prepares highly dispersed graphene-containing magnesium alloy materials through an in-situ self-generation method. The microstructure of the magnesium alloy materials is controlled by high-temperature isochannel extrusion and low-temperature extrusion deformation processes. Finally, graphene-reinforced magnesium alloy materials with high modulus and ultra-high plasticity are prepared. High-temperature isochannel extrusion provides a microstructure with uniform graphene dispersion, good interfacial bonding, low texture strength and high dislocation density for the subsequent low-temperature extrusion process. Low-temperature extrusion effectively compensates for the defects brought about by the previous process. The extruded magnesium alloy has the microstructure characteristics of small grain size and graphene distribution along the grain boundaries. The elongation of the finally prepared magnesium alloy material is stable at 30-40%, preferably 35-40%. Compared with traditional magnesium alloy materials, it has achieved a huge improvement in plasticity and maintains a high modulus. Attached Figure Description

[0023] Figure 1 These are dimensional measurement diagrams of the isochannel extruded material sample obtained by this invention at different angles.

[0024] Figure 2 These are dimensional measurement images of the magnesium alloy sample with high modulus and high plasticity obtained by this invention, taken from different angles.

[0025] Figure 3 These are high-magnification TEM images of the as-cast graphene-containing magnesium alloy prepared in Example 1 of this invention at different magnifications.

[0026] Figure 4 These are electron backscatter diffraction patterns of the isochannel extruded material and the magnesium alloy with both high modulus and high plasticity obtained in Example 1 of this invention; in the figure, (a) corresponds to the isochannel extruded material and (b) corresponds to the magnesium alloy with both high modulus and high plasticity.

[0027] Figure 5 These are SEM images of the as-cast graphene-containing magnesium alloy and the isochannel extruded material obtained in Example 2 of this invention; in the figures, (a) corresponds to the as-cast graphene-containing magnesium alloy, and (b) corresponds to the isochannel extruded material.

[0028] Figure 6 The figures show a TEM image of the magnesium alloy with high modulus and high plasticity obtained in Example 3 of this invention, as well as a schematic diagram of the grain, graphene, and dislocation relationships of the material. In the figures, (a) is a TEM image, where graphene represents graphene, and (b) is a schematic diagram of the grain, graphene, and dislocation relationships of the material.

[0029] Figure 7 This is a stress-strain curve of the mechanical properties of the magnesium alloy with high modulus and high plasticity obtained in Example 3 of the present invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0031] The present invention provides a method for preparing a magnesium alloy with both high modulus and high ductility in a first aspect, the method comprising the following steps:

[0032] (1) Preparation of as-cast magnesium alloy containing graphene; In this invention, the as-cast magnesium alloy containing graphene may also be referred to as as-cast graphene reinforced magnesium matrix composite material;

[0033] (2) The cast magnesium alloy containing graphene is subjected to equal channel extrusion deformation to obtain equal channel extruded material; the extrusion speed of the equal channel extrusion deformation is 40-60 mm / min (e.g., 40, 45, 50, 55 or 60 mm / min), and the temperature of the equal channel extrusion deformation is 300-450℃ (e.g., 300℃, 320℃, 350℃, 380℃, 400℃, 420℃ or 450℃); grain refinement can increase the number of movable slip systems in the material, and at the same time, it is conducive to intergranular deformation forms such as grain boundary slip and grain rotation, thereby establishing a new material micro-deformation behavior regulation mechanism. This invention found that by applying intense plastic deformation through equal channel extrusion and introducing large strain into the material, the grains can be refined and equiaxed, and the texture distribution is more uniform. Under the condition of good reinforcement dispersion, the introduction of equal channel extrusion technology is beneficial to improving the plasticity of the material;

[0034] (3) The isochannel extruded material is subjected to low-temperature extrusion deformation at 100-200℃ (e.g., 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃ or 200℃) to obtain a magnesium alloy with both high modulus and high plasticity. It should be noted that the magnesium alloy in this invention has a broad meaning, that is, it can be a magnesium alloy formed by graphene and pure magnesium, or a magnesium alloy formed by graphene and magnesium-calcium alloy, magnesium-manganese alloy or magnesium-bismuth alloy, etc. In this invention, the magnesium alloy with both high modulus and high plasticity obtained in step (3) can also be referred to as a graphene-reinforced magnesium-based material with both high modulus and high plasticity.

[0035] This invention utilizes the in-situ autogenous reaction of carbon dioxide (CO2) with magnesium or magnesium alloys to prepare magnesium alloy materials containing graphene functional phases. After obtaining the as-cast magnesium alloy containing graphene, a plastic deformation process involving equal channel extrusion and secondary low-temperature extrusion is used to prepare magnesium alloy materials that possess both ultra-high plasticity and maintain high modulus. Compared with ordinary magnesium alloy materials, while maintaining high modulus, plasticity is also significantly improved, which broadens the service range of magnesium alloy materials in various lightweight application fields.

[0036] The performance advantages of this invention are as follows: This invention obtains cast magnesium alloy materials through an in-situ self-generated method, and then further processes them through equal-channel extrusion and secondary extrusion deformation to produce magnesium alloys with ultra-high plasticity while maintaining high strength and high modulus. The elongation of the material can be stably maintained at 30-40%, more preferably 35%-40%, and even more preferably 37-40%, representing a significant improvement compared to traditional magnesium alloy materials. This invention is expected to overcome the barrier of difficulty in coordinating modulus and plasticity in magnesium alloy materials. In particular, the matrix alloy systems selected in this invention are pure magnesium, magnesium-calcium, magnesium-manganese, and magnesium-bismuth systems, which have poor intrinsic plastic deformation. The microstructure and properties can be controlled by adjusting the dislocation density within the material and the relationship between graphene and the alloy matrix. For aging alloy systems such as magnesium-zinc systems, the overall performance of the material can be improved simply through solution aging. Furthermore, the dimensional stability can be maintained over a wider range during the preparation process, largely avoiding the generation of defects and cracks, greatly expanding the service range of magnesium alloy materials in various application fields, and promoting the healthy development of lightweight magnesium alloy materials.

[0037] The advantages of this invention in terms of process are as follows:

[0038] First, during the in-situ spontaneous reaction process, the sheet-like graphene can be well dispersed in the magnesium matrix under mechanical stirring, acting as a reinforcing agent and significantly refining the grains. At the same time, nano-magnesium oxide is generated on the graphene surface to modify the interface, which promotes the effective transfer of stress from the matrix to the magnesium matrix through the interface region, thus giving full play to the performance of graphene.

[0039] Secondly, isochannel extrusion is one of the core steps in the preparation method of this invention. The cross-sectional dimensions of the material remain unchanged throughout the extrusion process. Simple shear strain can be introduced at the intersection of the two channels. Repeated extrusion leads to a very large accumulation of shear strain, which refines the material grains to 5–8 micrometers and results in a uniform equiaxed morphology. This equiaxed morphology is beneficial for the excitation of the substrate cone-slip system and exhibits uniform properties and texture distribution across all orientations. This also provides favorable microstructural conditions for subsequent secondary deformation (low-temperature deformation). The accumulated strain generates extremely high-density dislocations, providing a carrier for cone-slip. Simultaneously, isochannel extrusion eliminates voids in the material, densifies it, and breaks down the large graphene sheets in the preceding process, forming a more uniformly dispersed structural system, allowing graphene to truly disperse throughout the microstructure. It should be noted that the microstructure achieved through parameter-optimized isochannel extrusion possesses excellent low-temperature formability, perfectly matching the subsequent low-temperature extrusion process. The good matching of the two processes is a key step in achieving ultra-high plasticity. The parameter design of equal channel extrusion is also particularly important for matching the formation of the extruded microstructure. First, high-temperature processing is necessary to maintain the material's good formability. Second, the bend angle should be selected as 80-120° and the curvature angle as 30-40° to ensure that the shear zone is as narrow as possible and the friction between the material and the die wall is as small as possible. The extrusion speed should be kept stable at 40-60 mm / min to ensure that the material does not crack macroscopically. In order to further control the microstructure, the previous equal channel extrusion passes need to maintain a high temperature. As the number of extrusion passes increases, the extrusion temperature decreases successively. The reciprocating control of equal channel extrusion provides a better microstructure preparation for low-temperature extrusion, enabling the extrusion process to be carried out stably and efficiently.

[0040] Finally, low-temperature extrusion effectively improved the defects caused by the isochannel extrusion process, further refining the grains to achieve a grain size of 2–4 micrometers or even submicrometer 0.8–2 micrometers. Simultaneously, it released a high level of stored energy within the material, improving its dimensional stability. While isochannel extrusion resulted in good graphene sheet dispersion, the graphene dispersed within the grains did not fully realize its intrinsic properties. After a second low-temperature extrusion at a suitable temperature, the broken nano-graphene sheets became more dispersed, increasing the graphene distribution density. Most of the graphene was distributed at the grain boundaries, with only a small amount remaining within the grains, exhibiting a distinct banded characteristic. The graphene at the grain boundaries demonstrated excellent effects in grain boundary pinning and load transfer, thus contributing to grain refinement and material strengthening and toughening. It should be noted that the requirements for low-temperature deformation processes of general materials are quite stringent. Direct extrusion is likely to cause crack propagation and material breakage and failure. The microstructure preparation provided by equal-channel extrusion is essential. The low-temperature extrusion of this invention at a suitable temperature of 100-200℃ achieves ultra-high plasticity by further optimizing and improving the preceding microstructure. If the low-temperature extrusion deformation temperature is too low, the formability of the material will be poor. In the entire process, equal-channel extrusion and low-temperature extrusion complement each other. The former provides a good microstructure preparation for the latter, and the latter compensates for the deficiencies of the former at the microscopic level, ultimately achieving ultra-high plasticity of the material, with an elongation of 30-40%, and even reaching 35%. With an elongation of 40%, this invention offers a significant advantage in the field of magnesium alloys. Directly subjecting general materials to low-temperature deformation processes can easily lead to crack propagation and material breakage and failure. This is why low-temperature extrusion processes are not commonly used in existing technologies. However, this invention creatively discovers that performing equal channel extrusion followed by low-temperature extrusion can effectively prevent crack formation. It is precisely because equal channel extrusion and low-temperature extrusion complement each other in this invention that magnesium alloys with both high modulus and high plasticity can be produced. This maintains the high modulus while significantly improving plasticity, achieving an elongation of 30-40%, or even 35-40%, compared to the highest elongation of approximately 20% for magnesium alloys in existing technologies.

[0041] According to some preferred embodiments, in step (2), isochannel extrusion deformation is performed for 8 to 20 passes (e.g., 8, 12, 16, or 20 passes). In the first four passes, the isochannel extrusion deformation temperature is 380–450°C (e.g., 380°C, 390°C, 400°C, 410°C, 420°C, 430°C, 440°C, or 450°C). In subsequent passes, the isochannel extrusion deformation temperature decreases at a rate of 2–5°C per pass (e.g., 2, 3, 4, or 5°C per pass). In the final pass, the isochannel extrusion deformation temperature is 300–350°C (e.g., 300°C, 310°C, 320°C, 330°C, 340°C, or 350°C). In this invention, using this suitable gradient cooling method for isochannel extrusion can further regulate the microstructure. This invention allows for finer grains and better grain refinement in the material. Furthermore, by maintaining a high temperature in the initial equal-channel extrusion passes and gradually decreasing the extrusion temperature with each pass, this reciprocating control of equal-channel extrusion provides better microstructure preparation for low-temperature extrusion, enabling stable and efficient extrusion processes and improving the plasticity of magnesium alloys. This invention also reveals that if the temperature of the equal-channel extrusion deformation in the final pass is below 300°C, the low-temperature formability of the microstructure will be relatively poor, adversely affecting subsequent low-temperature extrusion and consequently impacting the performance of the magnesium alloy. In this invention, the gradual temperature decrease gradient should not be too large; an excessively large deceleration rate will hinder formability control during equal-channel extrusion, and a large temperature gradient may lead to crack initiation and propagation in the equal-channel extruded material.

[0042] According to some preferred embodiments, the equal channel extrusion deformation is equal channel radial angle extrusion (ECAP) deformation; the equal channel extrusion deformation is carried out using an equal channel extrusion die with a channel bending angle of 80-120° (e.g., 80°, 85°, 90°, 95°, 100°, 110° or 120°) and a curvature angle of 30-40° (e.g., 30°, 35° or 40°); before carrying out the equal channel extrusion deformation, the temperature of the equal channel extrusion die is preheated to 20°C (e.g., 20°C, 25°C, 30°C, 35°C or 40°C) higher than the temperature of equal channel extrusion deformation and held at that temperature for 0.5-1 hour (e.g., 0.5 or 1 hour).

[0043] According to some preferred embodiments, the extrusion ratio of the low-temperature extrusion deformation is (10-25):1 (e.g., 10:1, 15:1, 20:1 or 25:1).

[0044] According to some preferred embodiments, the as-cast graphene-containing magnesium alloy contains 0.6% to 2% graphene by mass (e.g., 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2%).

[0045] According to some preferred embodiments, the preparation of the as-cast graphene-containing magnesium alloy includes the following sub-steps:

[0046] (a) Under mechanical stirring, carbon dioxide gas is introduced into a magnesium-based melt at 650–700°C (e.g., 650°C, 660°C, 670°C, 680°C, 690°C or 700°C) to carry out an in-situ reaction to obtain an alloy melt.

[0047] (b) High-energy ultrasound is introduced into the alloy melt to promote the dispersion of graphene, and then the melt is cooled and solidified with water to obtain a cast magnesium alloy containing graphene. The present invention does not specify the conditions for mechanical stirring, high-energy ultrasound, and cooling and solidification, which are conventional techniques in the field.

[0048] According to some preferred embodiments, the magnesium-based melt is one or more of pure magnesium melt, magnesium-calcium alloy melt, magnesium-manganese alloy melt, and magnesium-bismuth alloy melt.

[0049] According to some specific embodiments, the preparation of the magnesium alloy with both high modulus and high plasticity described in this invention includes the following steps:

[0050] ① Under mechanical stirring, CO2 gas is introduced into a magnesium-based melt at 680℃ for in-situ reaction. After the reaction, high-energy ultrasound is introduced into the alloy melt to promote the dispersion of graphene. The melt is then cooled and solidified to obtain a cast magnesium alloy containing 0.6-2 wt.% graphene (i.e., the mass fraction of graphene in the cast magnesium alloy containing graphene is 0.6-2%). The magnesium-based melt is a magnesium melt and / or a magnesium alloy melt. The magnesium alloy melt is an alloy system with a large difference between the critical shear stress of basal slip and conical slip, such as magnesium-calcium, magnesium-manganese, or magnesium-bismuth. Of course, in this invention, carbon monoxide (CO) gas can be used to replace CO2 gas for in-situ autogenous reaction to generate a cast magnesium alloy containing graphene. The CO gas is, for example, CO gas with a purity of 99.9%.

[0051] ② Select an equal-channel extrusion die with a channel bending angle of 80-120° and a curvature angle of 30-40°, and fully lubricate the inner wall of the die. This will minimize the friction between the subsequent material and the die wall, and preheat the die to a temperature 20-40°C higher than the equal-channel extrusion temperature, and hold it at that temperature for 0.5-1 hour. The lubrication operation is not specifically limited in this invention and is a conventional technique in the field.

[0052] ③ The cast graphene-containing magnesium alloy is milled into a square ingot of 50mm (length) × 50mm (width) × 100mm (height). The ingot is subjected to 16 passes of equal channel diameter-angle extrusion deformation at 350-420℃ and the extrusion speed is 40-60mm / min. The temperature of the first four passes of equal channel diameter-angle extrusion deformation is kept at around 400℃. The subsequent extrusion temperature gradually decreases with the increase of the number of passes, and finally drops to 350℃ to obtain the equal channel extruded material.

[0053] ④ Cut the isochannel extruded material into round ingots suitable for low-temperature extrusion dies. For example, round ingots with a diameter of 50mm and a height of 20mm can be cut, i.e., round ingots with dimensions of Φ50×20mm can be cut. The material is then subjected to low-temperature extrusion at a temperature of 100~200℃ and an extrusion ratio of (10~25):1 to prepare the extruded material, i.e., to prepare a magnesium alloy with both high modulus and high plasticity.

[0054] According to some preferred embodiments, the magnesium alloy with high modulus and high plasticity obtained in step (3) has an elastic modulus of not less than 50 GPa and an elongation of 35-40%.

[0055] The present invention provides, in a second aspect, a magnesium alloy having both high modulus and high ductility, prepared by the method described in the first aspect of the present invention.

[0056] The present invention will be further described below by way of examples, but the scope of protection of the present invention is not limited to these embodiments.

[0057] Example 1

[0058] ① Pure magnesium was heated and melted in a crucible under a protective atmosphere of carbon dioxide and sulfur hexafluoride (SF6) at a heating temperature of 680℃, with a volume ratio of CO2 to SF6 of 40:1. Under mechanical stirring (stirring speed of 1500 r / min), CO2 gas at a flow rate of 0.9 L / min was introduced into the 680℃ pure magnesium melt for in-situ reaction for 80 min to obtain an alloy melt with an outlet pore diameter of 1.5 mm. After the reaction, high-energy ultrasound was introduced into the alloy melt to promote the dispersion of graphene, and then the melt was cooled and solidified with water to obtain a cast magnesium alloy containing 1 wt.% graphene.

[0059] ② Select an equal-channel extrusion die with a channel bending angle of 90° and a curvature angle of 40°, fully lubricate the inner wall of the die, and preheat the die to 420°C and keep it at that temperature for 0.5 hours.

[0060] ③ The cast graphene-containing magnesium alloy is milled into a square ingot of 50mm (length) × 50mm (width) × 100mm (height). A 16-pass equal channel diameter-angle extrusion deformation is applied at 350–380℃ with an extrusion speed of 40mm / min. The temperature of the first four passes of equal channel diameter-angle extrusion deformation is maintained at 380℃. The subsequent extrusion temperature gradually decreases with each pass, at a rate of 2.5℃ / pass, eventually dropping to 350℃, yielding the equal channel extruded material. Specifically, the temperatures of the 16 passes of equal channel diameter-angle extrusion deformation are, in sequence: 380℃, 380℃, 380℃, 380℃, 377.5℃, 375℃, 372.5℃, 370℃, 367.5℃, 365℃, 362.5℃, 360℃, 357.5℃, 355℃, 352.5℃, and 350℃.

[0061] ④ Cut the isochannel extruded material into round ingots with a size of Φ50×20mm. Extrude the round ingots at a temperature of 200℃ and an extrusion ratio of 25:1 to prepare the extruded material, that is, to prepare a magnesium alloy with both high modulus and high plasticity.

[0062] The isochannel extruded material and the magnesium alloy with both high modulus and high plasticity prepared in this embodiment are, for example, as shown below. Figure 1 and Figure 2 As shown, high-magnification TEM images of the as-cast graphene-containing magnesium alloy obtained in step ① of this embodiment at different magnifications are shown below. Figure 3 As shown, from Figure 3 It can be seen that MgO nanoparticles are synchronously distributed on the graphene surface. Under the action of this interface structure, stress can be effectively transferred from the matrix to the graphene through the interface region.

[0063] The electron backscattering diffraction patterns of the isochannel extruded material and the magnesium alloy with both high modulus and high plasticity obtained in this embodiment are as follows: Figure 4 As shown, from Figure 4 It can be seen that the extruded material after low-temperature extrusion has a significantly finer grain size than the isochannel extruded material, and the grain morphology is significantly improved. The grain size of the isochannel extruded material obtained in this embodiment is 5-8 μm, and the grain size of the magnesium alloy with both high modulus and high plasticity obtained in this embodiment is 2-3 μm.

[0064] Example 2

[0065] ① Pure magnesium was heated and melted in a crucible under a protective atmosphere of carbon dioxide and sulfur hexafluoride (SF6) at a heating temperature of 680℃, with a volume ratio of CO2 to SF6 of 40:1. Under mechanical stirring (stirring speed of 1500 r / min), CO2 gas at a flow rate of 0.9 L / min was introduced into the 680℃ pure magnesium melt for in-situ reaction for 80 min to obtain an alloy melt with an outlet pore diameter of 1.5 mm. After the reaction, high-energy ultrasound was introduced into the alloy melt to promote the dispersion of graphene, and then the melt was cooled and solidified with water to obtain a cast magnesium alloy containing 1 wt.% graphene.

[0066] ② Select an equal-channel extrusion die with a channel bending angle of 120° and a curvature angle of 40°, fully lubricate the inner wall of the die, and preheat the die to 420°C and keep it at that temperature for 0.5 hours.

[0067] ③ The cast graphene-containing magnesium alloy is milled into a square ingot of 50mm (length) × 50mm (width) × 100mm (height). A 16-pass equal channel diameter-angle extrusion deformation is applied at 352–400℃ with an extrusion speed of 40mm / min. The temperature of the first four passes of equal channel diameter-angle extrusion deformation is maintained at 400℃. The subsequent extrusion temperature gradually decreases with each pass, at a rate of 4℃ / pass, eventually dropping to 352℃, yielding the equal channel extruded material. Specifically, the temperatures of the 16 passes of equal channel diameter-angle extrusion deformation are 400℃, 400℃, 400℃, 400℃, 396℃, 392℃, 388℃, 384℃, 380℃, 376℃, 372℃, 368℃, 364℃, 360℃, 356℃, and 352℃, respectively.

[0068] ④ Cut the isochannel extruded material into round ingots with a size of Φ50×20mm. Extrude the round ingots at a temperature of 200℃ and an extrusion ratio of 25:1 to prepare the extruded material, that is, to prepare a magnesium alloy with both high modulus and high plasticity.

[0069] TEM images of the as-cast graphene-containing magnesium alloy and the isochannel extruded material obtained in this embodiment are shown below. Figure 5 As shown, Figure 5 (a) It can be seen that graphene is relatively uniformly distributed in the magnesium matrix, but there are many large clusters. After isochannel compression, the clusters are significantly broken up, and the graphene becomes smaller and more dispersed, which is beneficial to the improvement of performance, such as... Figure 5 As shown in (b).

[0070] Example 3

[0071] ① Pure magnesium was heated and melted in a crucible under a protective atmosphere of carbon dioxide and sulfur hexafluoride (SF6) at a heating temperature of 680℃, with a volume ratio of CO2 to SF6 of 40:1. Under mechanical stirring (stirring speed of 1500 r / min), CO2 gas at a flow rate of 0.9 L / min was introduced into the 680℃ pure magnesium melt for in-situ reaction for 80 min to obtain an alloy melt with an outlet pore diameter of 1.5 mm. After the reaction, high-energy ultrasound was introduced into the alloy melt to promote the dispersion of graphene, and then the melt was cooled and solidified with water to obtain a cast magnesium alloy containing 1 wt.% graphene.

[0072] ② Select an equal-channel extrusion die with a channel bending angle of 90° and a curvature angle of 40°, fully lubricate the inner wall of the die, and preheat the die to 420°C and keep it at that temperature for 0.5 hours.

[0073] ③ The cast graphene-containing magnesium alloy is milled into a square ingot of 50mm (length) × 50mm (width) × 100mm (height). A 16-pass equal channel diameter-angle extrusion deformation is applied at 350–380℃ with an extrusion speed of 40mm / min. The temperature of the first four passes of equal channel diameter-angle extrusion deformation is maintained at 380℃. The subsequent extrusion temperature gradually decreases with each pass, at a rate of 2.5℃ / pass, eventually dropping to 350℃, yielding the equal channel extruded material. Specifically, the temperatures of the 16 passes of equal channel diameter-angle extrusion deformation are, in sequence: 380℃, 380℃, 380℃, 380℃, 377.5℃, 375℃, 372.5℃, 370℃, 367.5℃, 365℃, 362.5℃, 360℃, 357.5℃, 355℃, 352.5℃, and 350℃.

[0074] ④ Cut the isochannel extruded material into round ingots with a size of Φ50×20mm. Extrude the round ingots at a temperature of 130℃ and an extrusion ratio of 25:1 to prepare the extruded material, that is, to prepare a magnesium alloy with both high modulus and high plasticity.

[0075] The TEM image of the magnesium alloy with both high modulus and high ductility obtained in this embodiment is shown below. Figure 6 As shown in (a), from Figure 6 (a) It can be seen that the extruded material obtained by low-temperature extrusion at 130℃ has finer grains than that obtained by low-temperature extrusion at 200℃, with a grain size of 0.8–2 μm, reaching the submicron level. This indicates that within a suitable low-temperature extrusion temperature range, lowering the extrusion temperature is beneficial for reducing grain size. Simultaneously, a higher graphene content near the grain boundaries is observed, which is beneficial for grain boundary pinning and load transfer. Compared to other magnesium alloy materials commonly found in the prior art, the magnesium alloy material in this invention has a significantly finer grain size.

[0076] The mechanical property curves of the magnesium alloy with both high modulus and high plasticity obtained in this embodiment are shown in the figure. Figure 7 As shown, after mechanical property testing, the magnesium alloy prepared in this embodiment, which combines high modulus and high plasticity, has an elastic modulus of 52.5 GPa, a yield strength of 110.2 MPa, a tensile strength of 146.0 MPa, and an elongation of 40%. Compared with traditional magnesium alloy materials, this represents a significant improvement, with a remarkable advantage in plasticity. This indicates that the process in this invention produces a magnesium alloy material with ultra-high plasticity and high modulus.

[0077] Example 4

[0078] ① Pure magnesium was heated and melted in a crucible under a protective atmosphere of carbon dioxide and sulfur hexafluoride (SF6) at a heating temperature of 680℃, with a volume ratio of CO2 to SF6 of 40:1. Under mechanical stirring (stirring speed of 1500 r / min), CO2 gas at a flow rate of 0.9 L / min was introduced into the 680℃ pure magnesium melt for in-situ reaction for 80 min to obtain an alloy melt with an outlet pore diameter of 1.5 mm. After the reaction, high-energy ultrasound was introduced into the alloy melt to promote the dispersion of graphene, and then the melt was cooled and solidified with water to obtain a cast magnesium alloy containing 1 wt.% graphene.

[0079] ② Select an equal-channel extrusion die with a channel bending angle of 90° and a curvature angle of 40°, fully lubricate the inner wall of the die, and preheat the die to 420°C and keep it at that temperature for 0.5 hours.

[0080] ③ The cast graphene-containing magnesium alloy is milled into a square ingot of 50mm (length) × 50mm (width) × 100mm (height). A 12-pass equal channel diameter-angle extrusion deformation is applied at 348–380℃ with an extrusion speed of 40mm / min. The temperature of the first four passes of equal channel diameter-angle extrusion deformation is maintained at 380℃. The subsequent extrusion temperature gradually decreases with each pass, at a rate of 4℃ / pass, eventually dropping to 348℃, yielding the equal channel extruded material. Specifically, the temperatures of the 12 passes of equal channel diameter-angle extrusion deformation are 380℃, 380℃, 380℃, 380℃, 376℃, 372℃, 368℃, 364℃, 360℃, 356℃, 352℃, and 348℃, respectively.

[0081] ④ Cut the isochannel extruded material into round ingots with a size of Φ50×20mm. Extrude the round ingots at a temperature of 130℃ and an extrusion ratio of 25:1 to prepare the extruded material, that is, to prepare a magnesium alloy with both high modulus and high plasticity.

[0082] Example 5

[0083] Example 5 is basically the same as Example 3, except that:

[0084] ③ The cast magnesium alloy containing graphene is milled into a square ingot of 50mm (length) × 50mm (width) × 100mm (height). The ingot is subjected to 16 passes of equal channel diameter-angle extrusion deformation at 380℃. The temperature of each of the 16 passes of equal channel diameter-angle extrusion deformation is 380℃, and the extrusion speed is 40mm / min, to obtain the equal channel extruded material.

[0085] The grain size of the isochannel extruded material obtained in this embodiment is 7-10 μm, and the grain size of the magnesium alloy with both high modulus and high plasticity obtained in this embodiment is 2.5-4 μm.

[0086] Example 6

[0087] Example 6 is basically the same as Example 3, except that:

[0088] ② Select an equal-channel extrusion die with a channel bending angle of 90° and a curvature angle of 40°, fully lubricate the inner wall of the die, and preheat the die to 480°C and keep it at that temperature for 0.5 hours.

[0089] ③ The cast graphene-containing magnesium alloy is milled into a square ingot of 50mm (length) × 50mm (width) × 100mm (height). A 16-pass equal channel diameter-angle extrusion deformation is applied at 300–450℃ with an extrusion speed of 40mm / min. The temperature of the first four passes of equal channel diameter-angle extrusion deformation is maintained at 450℃. The subsequent extrusion temperature gradually decreases with each pass, at a rate of 12.5℃ / pass, eventually dropping to 300℃, yielding the equal channel extruded material. Specifically, the temperatures of the 16 passes of equal channel diameter-angle extrusion deformation are 450℃, 450℃, 450℃, 450℃, 437.5℃, 425℃, 412.5℃, 400℃, 387.5℃, 375℃, 362.5℃, 350℃, 337.5℃, 325℃, 312.5℃, and 300℃.

[0090] The grain size of the isochannel extruded material obtained in this embodiment is 10-12 μm, and the grain size of the magnesium alloy with both high modulus and high plasticity obtained in this embodiment is 5-8 μm.

[0091] Example 7

[0092] Example 7 is basically the same as Example 3, except that:

[0093] ① A magnesium-bismuth alloy (Mg-5Bi magnesium-bismuth alloy, containing 5 wt% bismuth) was heated and melted in a crucible under a mixed atmosphere of carbon dioxide and sulfur hexafluoride (SF6) at a temperature of 680℃, with a CO2 to SF6 volume ratio of 40:1. Under mechanical stirring (stirring speed of 1500 r / min), CO2 gas at a flow rate of 0.9 L / min was introduced into the 680℃ magnesium-bismuth alloy melt for in-situ reaction for 80 min, with an outlet pore diameter of 1.5 mm. After in-situ reaction for 80 min, high-energy ultrasound was introduced into the alloy melt to promote the dispersion of graphene, followed by water cooling and solidification to obtain a cast magnesium-bismuth alloy containing 1 wt.% graphene. This magnesium-bismuth alloy was then used for subsequent steps ②, ③, and ④.

[0094] Comparative Example 1

[0095] Comparative Example 1 is basically the same as Example 3, except that:

[0096] ③ The cast magnesium alloy containing graphene is milled into a square ingot of 50mm (length) × 50mm (width) × 100mm (height). The ingot is subjected to 16 passes of equal channel diameter-angle extrusion deformation at 250℃. The temperature of each of the 16 passes of equal channel diameter-angle extrusion deformation is 250℃, and the extrusion speed is 40mm / min, to obtain the equal channel extruded material.

[0097] In this comparative example, the temperature of the equal channel extrusion deformation is below 300℃, only 250℃, which results in relatively poor low-temperature deformation and formability of the microstructure and low product elongation.

[0098] Comparative Example 2

[0099] Comparative Example 2 is basically the same as Example 3, except that:

[0100] ④ Cut the isochannel extruded material into round ingots with a size of Φ50×20mm, and hot extrude the round ingots at a temperature of 300℃ and an extrusion ratio of 25:1 to prepare the extruded material.

[0101] Comparative Example 3

[0102] Comparative Example 3 is basically the same as Example 3, except that:

[0103] ④ The equal channel extruded material is subjected to 6 passes of rolling deformation at a rolling temperature of 150℃, a reduction of 30%, and a rolling speed of 15m / min to prepare the rolled magnesium alloy material.

[0104] Comparative Example 4

[0105] Comparative Example 4 is basically the same as Example 3, except that:

[0106] ②The as-cast magnesium alloy containing graphene is first dissolved at 350℃ for 24 hours, and then hot-extruded at 300℃ with an extrusion ratio of 25:1 to prepare the extruded material.

[0107] ③ Select an equal-channel extrusion die with a channel bending angle of 90° and a curvature angle of 40°, fully lubricate the inner wall of the die, and preheat the die to 420°C and keep it at that temperature for 0.5 hours.

[0108] ④ The extruded material obtained in step ② is milled into a square ingot of 50mm (length) × 50mm (width) × 100mm (height). It is subjected to 16 passes of equal channel diameter-angle extrusion deformation at 380℃. The temperature of each of the 16 passes of equal channel diameter-angle extrusion deformation is 380℃, and the extrusion speed is 40mm / min, to obtain magnesium alloy material after equal channel extrusion deformation.

[0109] Comparative Example 5

[0110] Comparative Example 5 is basically the same as Example 3, except that:

[0111] Excluding step ④, after step ③, an equal channel extruded material is obtained, that is, a magnesium alloy material deformed by equal channel extrusion.

[0112] The present invention provides the grain size and elongation results of several common conventional magnesium alloy materials, as shown in Table 1.

[0113] Table 1

[0114]

[0115] The present invention tested the properties of the magnesium alloys with high modulus and high plasticity obtained in each embodiment and the magnesium alloy materials finally obtained in each comparative example. The results are shown in Table 2. Among them, the elastic modulus and elongation were determined with reference to the test standard ASTM E8 / E8M.

[0116] Table 2

[0117]

[0118]

[0119] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0120] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a magnesium alloy possessing both high modulus and high plasticity, characterized in that, The method includes the following steps: (1) Preparation of as-cast magnesium alloys containing graphene; (2) The cast magnesium alloy containing graphene is subjected to equal channel extrusion deformation to obtain equal channel extruded material; the extrusion speed of the equal channel extrusion deformation is 40~60mm / min; in step (2), 8~20 passes of equal channel extrusion deformation are performed, and in the first 4 passes, the temperature of equal channel extrusion deformation is 380~450℃, in the subsequent passes, the temperature of equal channel extrusion deformation decreases, the rate of decrease is 2~5℃ / pass, and in the last pass, the temperature of equal channel extrusion deformation is 300~350℃; (3) The isochannel extruded material is subjected to low-temperature extrusion deformation at 100~200℃ to obtain a magnesium alloy with both high modulus and high plasticity; the extrusion ratio of the low-temperature extrusion deformation is (10~25):1; The magnesium alloy obtained in step (3) has both high modulus and high plasticity, with an elastic modulus of not less than 50 GPa and an elongation of 35~40%.

2. The preparation method according to claim 1, characterized in that: The equal channel extrusion deformation is equal channel diameter-angle extrusion deformation.

3. The preparation method according to claim 1, characterized in that: The equal channel extrusion deformation is performed using an equal channel extrusion die with a channel bending angle of 80~120° and a curvature angle of 30~40°; and / or Before performing the equal channel extrusion deformation, the temperature of the equal channel extrusion die is preheated to 20°C above the temperature of equal channel extrusion deformation and kept at that temperature for 0.5~1h.

4. The preparation method according to claim 1, characterized in that: The cast-state graphene-containing magnesium alloy contains 0.6-2% graphene by mass.

5. The preparation method according to any one of claims 1 to 4, characterized in that, The preparation of the as-cast graphene-containing magnesium alloy includes the following sub-steps: (a) Under mechanical stirring, carbon dioxide gas is introduced into a magnesium-based melt at 650~700℃ to carry out an in-situ reaction to obtain an alloy melt; (b) High-energy ultrasound is introduced into the alloy melt to promote the dispersion of graphene, and then the melt is cooled and solidified with water to obtain a cast magnesium alloy containing graphene.

6. The preparation method according to claim 5, characterized in that: The magnesium-based melt is one or more of the following: pure magnesium melt, magnesium-calcium alloy melt, magnesium-manganese alloy melt, and magnesium-bismuth alloy melt.

7. A magnesium alloy with both high modulus and high plasticity prepared by the preparation method according to any one of claims 1 to 6.

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