High bulk graphene reinforced magnesium matrix composite and method of making

Abstract

The application provides a high-density graphene reinforced magnesium-based composite material and a preparation method thereof, and relates to the technical field of composite materials.The composite material is formed by a composite melt containing a magnesium matrix, magnesium oxide nanoparticles and graphene.The content of the graphene in the composite melt is not less than 1.5 wt%.The graphene in the composite material is in a reticular distribution.The graphene reinforced magnesium-based material provided by the application has an excellent reinforcing effect because the graphene is in a reticular distribution, and the problem that the graphene is in a random distribution and the graphene layers are isolated from each other and cannot fully play the reinforcing effect of the graphene in the prior graphene reinforced magnesium-based composite material is overcome.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, and specifically relates to a high volumetric graphene-reinforced magnesium-based composite material and its preparation method. Background Technology

[0002] Magnesium alloys are widely used due to their lowest density among common structural metals, and are currently frequently used in aerospace, defense, and automotive fields to achieve lightweighting of various components. However, magnesium alloys have drawbacks such as low strength, low stiffness, and low thermal conductivity. Adding suitable reinforcements to create a magnesium matrix composite is one of the effective solutions to these problems.

[0003] In recent years, graphene has been considered an ideal choice for reinforcing metal materials due to its excellent properties of high strength, high electrical and thermal conductivity, and two-dimensional structure. It can effectively improve stress concentration at the interface of composite materials and enhance the overall mechanical, electrical, and thermal properties of the composites. However, in existing graphene-reinforced magnesium-based materials, graphene often exhibits a random distribution, and the isolated graphene sheets make it difficult to fully realize the reinforcing effect of graphene.

[0004] Therefore, there is an urgent need for a graphene-reinforced magnesium-based material with excellent reinforcing effect. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a high volumetric graphene-reinforced magnesium-based composite material and its preparation method. The graphene in the graphene-reinforced magnesium-based material provided by this invention is distributed in a network structure, which has excellent strengthening effect. This overcomes the problem that in existing graphene-reinforced magnesium-based composite materials, the graphene is randomly distributed and the graphene sheets are isolated from each other, making it difficult to fully exert the reinforcing effect of graphene.

[0006] In a first aspect, the present invention provides a high volumetric graphene-reinforced magnesium-based composite material, wherein the composite material is formed by molding a composite melt comprising a magnesium matrix, magnesium oxide nanoparticles and graphene; the graphene content in the composite melt is not less than 1.5 wt%; and the graphene in the composite material is distributed in a network.

[0007] Preferably, the composite melt comprises 89-93.5 wt% magnesium matrix, 5-8.5 wt% magnesium oxide nanoparticles, and 1.5-2.5 wt% graphene.

[0008] Preferably, the composite material comprises 74-88 wt% magnesium matrix, 2.8-6 wt% graphene, and 9-20 wt% magnesium oxide nanoparticles.

[0009] Preferably, the composite material contains 20-25 wt% graphene and 75-80 wt% magnesium oxide nanoparticles.

[0010] In a second aspect, the present invention provides a method for preparing the high-volume graphene-reinforced magnesium-based composite material described in the first aspect, the method comprising:

[0011] Carbon monoxide is introduced into pure magnesium melt, and a gas-liquid reaction is carried out to obtain a composite melt with thixotropic properties. The composite melt is then cooled and solidified to obtain a cast composite material.

[0012] The cast composite material is subjected to a first hot extrusion and a first vacuum evaporation to obtain a high volumetric graphene-reinforced magnesium-based composite material; the first vacuum evaporation is a stepped vacuum evaporation with a temperature gradient decreasing.

[0013] Preferably, the temperature of the gas-liquid reaction is 680–700°C; and / or

[0014] The temperature of the first hot extrusion is 300-400℃.

[0015] Preferably, the temperature of the first vacuum evaporation is 620–800°C; the vacuum degree of the first vacuum evaporation is not greater than 1000 Pa.

[0016] Preferably, a second vacuum evaporation step is included after the first vacuum evaporation;

[0017] Preferably, the temperature of the second vacuum evaporation is 800°C.

[0018] Preferably, the process further includes a second hot extrusion step after the first vacuum evaporation; preferably, the temperature of the second hot extrusion is 300-400°C.

[0019] Preferably, the extrusion ratio of the first hot extrusion is less than that of the second hot extrusion; more preferably, the extrusion ratio of the first hot extrusion is (4-9):1; and the extrusion ratio of the second hot extrusion is greater than 25:1.

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

[0021] The graphene-reinforced magnesium-based composite material provided by this invention is obtained by molding a thixotropic composite melt containing a magnesium matrix, magnesium oxide nanoparticles, and graphene. The steric hindrance of the magnesium oxide particles modified on the graphene surface hinders the aggregation tendency of graphene, avoiding direct stacking of graphene sheets. Van der Waals forces, electrostatic adsorption, and π-π stacking between graphene layers induce the overlapping of graphene sheets in the melt, forming a non-random, relatively ordered spatial distribution and creating a relatively ordered network structure with inter-bonded graphene layers. The interaction between graphene sheets and the steric hindrance effect of magnesium oxide nanoparticles not only achieve the design and orderly arrangement of the network structure but also realize the synergistic design of the magnesium oxide nanoparticle reinforcement and the two-dimensional graphene reinforcement. This interrelation effectively enhances the interaction of the graphene network, transforming the reinforcing effect of isolated graphene sheets into a synergistic reinforcing effect of the graphene network, thereby significantly improving the strengthening effect of the composite material and effectively increasing its strength. In this invention, the graphene in the graphene-reinforced magnesium-based composite material is distributed in a network structure, which has an excellent strengthening effect. This overcomes the problem that in existing graphene-reinforced magnesium-based composite materials, the graphene is randomly distributed and the graphene sheets are isolated from each other, making it difficult to fully exert the reinforcing effect of graphene. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a physical image of a graphene-reinforced magnesium-based composite material provided by the present invention;

[0024] Figure 2 This is a physical image of another graphene-reinforced magnesium-based composite material provided by the present invention;

[0025] Figure 3 This is a microstructure diagram of the graphene-reinforced magnesium-based composite material provided by the present invention;

[0026] Figure 4 This is a micropillar compressive stress-strain curve of the graphene-reinforced magnesium-based composite material provided in Example 3 of the present invention;

[0027] Figure 5 This is a flowchart illustrating the preparation process of the graphene-reinforced magnesium-based composite material provided by the present invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0029] The first aspect of the present invention provides a high volumetric graphene-reinforced magnesium-based composite material, wherein the composite material is obtained by molding a composite melt comprising a magnesium matrix, magnesium oxide nanoparticles and graphene; the graphene content in the composite melt is not less than 1.5 wt%; and the graphene in the composite material is distributed in a network.

[0030] The graphene-reinforced magnesium-based composite material provided by this invention is formed by molding a thixotropic composite melt containing a magnesium matrix, magnesium oxide nanoparticles, and graphene. The steric hindrance of the magnesium oxide particles modified on the graphene surface hinders the aggregation tendency of graphene, avoiding direct stacking of graphene sheets. Van der Waals forces, electrostatic adsorption, and π-π stacking interactions between graphene layers induce the overlapping of graphene sheets in the melt, forming a non-random, relatively ordered spatial distribution. This results in a relatively ordered network structure with inter-bonded graphene layers. The interaction between graphene sheets and the steric hindrance effect of magnesium oxide nanoparticles not only achieve the design and ordered arrangement of the network structure but also realize the synergistic design of the magnesium oxide nanoparticle reinforcement and the two-dimensional graphene reinforcement. This interrelation effectively enhances the interaction of the graphene network, transforming the reinforcing effect of isolated graphene sheets into a synergistic reinforcing effect of the graphene network, thereby significantly improving the strengthening effect of the composite material and effectively increasing its strength.

[0031] In this invention, the graphene in the graphene-reinforced magnesium-based composite material is distributed in a network structure, which has an excellent strengthening effect. This overcomes the problem that in existing graphene-reinforced magnesium-based composite materials, the graphene is randomly distributed and the graphene sheets are isolated from each other, making it difficult to fully exert the reinforcing effect of graphene.

[0032] According to some preferred embodiments, the composite melt comprises 89–93.5 wt% magnesium matrix (e.g., 89 wt%, 89.6 wt%, 90.5 wt%, 90.9 wt%, 91.3 wt%, 91.5 wt%, 91.8 wt%, 92 wt%, 92.2 wt%, 92.6 wt%, 93.1 wt%, or 93.5 wt%) and 5–8.5 wt% magnesium oxide nanoparticles (e.g., 5 wt%, 5.3 wt%, 5.6 wt%). 5.8wt%, 6wt%, 6.3wt%, 6.5wt%, 6.6wt%, 7wt%, 7.3wt%, 7.6wt%, 8wt%, 8.3wt%, or 8.5wt%) and 1.5 to 2.5wt% of graphene (e.g., 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, 2wt%, 2.1wt%, 2.2wt%, 2.3wt%, 2.4wt%, or 2.5wt%).

[0033] According to some preferred embodiments, the composite material comprises 74-88 wt% magnesium matrix (e.g., 74 wt%, 74.5 wt%, 75 wt%, 75.5 wt%, 76 wt%, 76.5 wt%, 77 wt%, 77.5 wt%, 78 wt%, 78.5 wt%, 79 wt%, 79.5 wt%, 80 wt%, 80.5 wt%, 81 wt%, 81.5 wt%, 82 wt%, 82.5 wt%, 83 wt%, 83.5 wt%, 84 wt%, 84.5 wt%, 85 wt%, 85.5 wt%, 86 wt%, 86.5 wt%, 87 wt%, 87.5 wt%, or 88 wt%) and 2.8-6 wt% graphene (e.g., 2.8 wt%, 3 wt%, 3 wt%). 0.2wt%, 3.5wt%, 3.8wt%, 4wt%, 4.2wt%, 4.5wt%, 4.8wt%, 5wt%, 5.2wt%, 5.5wt%, 5.8wt%, or 6wt%) and 9–20wt% magnesium oxide nanoparticles (e.g., 9wt%, 9.3wt%, 10.6wt%, 11wt%, 11.6wt%, 12wt%, 12.6wt%, 13%, 13.3wt%, 13.6wt%, 14wt%, 14.5wt%, 15wt%, 156wt%, 16wt%, 16.6wt%, 17wt%, 17.3wt%, 17.6wt%, 18wt%, 18.3wt%, 18.6wt%, 19wt%, 19.6wt%, or 20wt%). In this invention, graphene is uniformly dispersed in a network structure in a graphene-reinforced magnesium-based composite material, achieving a high graphene content (not less than 2.8 wt%) and a graphene volume fraction of not less than 2.2 vol.

[0034] According to some preferred embodiments, the composite material comprises 20-25 wt% graphene (e.g., 20 wt%, 20.5 wt%, 21 wt%, 21.5 wt%, 22 wt%, 22.5 wt%, 23 wt%, 23.5 wt%, 24 wt%, 24.5 wt%, or 25 wt%) and 75-80 wt% magnesium oxide nanoparticles (e.g., 75 wt%, 75.5 wt%, 76 wt%, 77 wt%, 77.5 wt%, 78 wt%, 78.5 wt%, 79 wt%, 9.5 wt%, or 80 wt%).

[0035] like Figure 5 As shown, a second aspect of the present invention provides a method for preparing the high-volume graphene-reinforced magnesium-based composite material described in the first aspect, the method comprising:

[0036] Carbon monoxide is introduced into pure magnesium melt, and a gas-liquid reaction is carried out to obtain a composite melt with thixotropic properties. The composite melt is then cooled and solidified to obtain a cast composite material.

[0037] The cast composite material is subjected to a first hot extrusion and a first vacuum evaporation to obtain a high volumetric graphene-reinforced magnesium-based composite material; the first vacuum evaporation is a stepped vacuum evaporation with a temperature gradient decreasing.

[0038] This invention involves introducing carbon monoxide into pure magnesium melt to initiate a gas-liquid reaction. Utilizing the agglomeration tendency of graphene and the steric hindrance of magnesium oxide nanoparticles, graphene sheets interlock within the melt to form a network structure, increasing the melt viscosity. This results in a high-viscosity composite melt with thixotropic properties that does not flow under no external force. The composite melt is then cooled and solidified to obtain a cast composite material with a graphene network structure. Hot extrusion of the cast composite material densifies it and adjusts the graphene orientation. The hot-extruded cast composite material is then subjected to stepped vacuum evaporation at a gradually decreasing temperature to further increase the content of the reinforcing phase (total graphene and magnesium oxide content), resulting in a high-graphene-content magnesium-based composite material while maintaining the original graphene network structure. By adjusting the hot extrusion and vacuum evaporation process parameters before and after the vacuum evaporation process, the orientation of graphene is controlled, thereby regulating the anisotropy of the composite material's mechanical and electrothermal properties.

[0039] During the gas-liquid reaction of carbon monoxide in pure magnesium melt, the graphene concentration gradually increases. Simultaneously, due to graphene's high aspect ratio and strong interlayer van der Waals forces, there is a significant tendency for graphene sheets to aggregate. The steric hindrance effect of MgO nanoparticles on the graphene surface hinders this tendency. Under the combined effects of aggregation and steric hindrance, as the graphene concentration further increases (reaching 1.5 wt%), the graphene sheets overlap and form a network structure in the melt. This network structure significantly increases the viscosity of the composite melt, preventing flow under no external force and forming a high-viscosity fluid with thixotropic properties. In this invention, carbon monoxide is introduced into pure magnesium melt to initiate a gas-liquid reaction until the melt surface shows no significant change. A counterweight is then placed stably on the melt surface. If the counterweight does not settle, it indicates that graphene in the melt has cross-linked to form a network structure, resulting in a composite melt with thixotropic properties. At this point, the graphene content in the composite melt is not less than 1.5 wt%. If the graphene content in the composite melt is less than 1.5 wt%, the graphene cannot cross-link to form a network structure.

[0040] Furthermore, since defects such as shrinkage cavities and porosity are easily generated during the process of composite melt cooling and solidifying to form cast composite materials, hot extrusion is used to densify the composite material and adjust the orientation of graphene in the composite material.

[0041] Furthermore, to increase the content of the reinforcing phase in the composite material, the hot-extruded composite material is subjected to vacuum evaporation. Simultaneously, due to the high specific surface area of ​​graphene, the capillary forces generated during vacuum evaporation are more significant. To avoid damage to the graphene network structure caused by capillary forces and to ensure successful vacuum evaporation, this invention employs a stepped vacuum evaporation method with a gradually decreasing temperature. This increases the content of the reinforcing phases (graphene and magnesium oxide) in the composite material without destroying the original graphene network structure. In the initial stage of the first vacuum evaporation process, a higher evaporation temperature and a relatively higher vacuum degree are used to reduce the viscosity of the composite melt, simultaneously achieving the evaporation of the magnesium matrix and the shrinkage of the composite melt. In the later stages of the first vacuum evaporation process, a lower evaporation temperature and a lower vacuum degree are used to strengthen the composite melt and prevent damage to the graphene structure caused by capillary forces during vacuum evaporation. Meanwhile, due to the thixotropic properties of the composite melt, it can be directly vacuum evaporated without container constraints. During the vacuum evaporation process, the high surface area of ​​the reinforcing phase due to the high graphene content and the improved interfacial wettability brought about by the magnesium oxide modified on the graphene surface result in significant capillary forces that can fill the pores caused by the evaporation of the magnesium matrix, ensuring the density of the composite material during the evaporation process.

[0042] According to some preferred embodiments, the temperature of the gas-liquid reaction is 680–700°C (e.g., 680°C, 685°C, 690°C, 695°C, or 700°C); it should be noted that the gas-liquid reaction of the present invention is carried out under the condition of a mixture of CO2 and SF6 as a protective gas; and / or

[0043] The temperature of the first hot extrusion is 300-400°C (for example, it can be 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C or 400°C).

[0044] According to some preferred embodiments, the temperature of the first vacuum evaporation is 620-800°C (for example, it can be 620°C, 630°C, 640°C, 650°C, 660°C, 670°C, 680°C, 690°C, 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, 760°C, 770°C, 780°C, 790°C or 800°C); the vacuum degree of the first vacuum evaporation is not greater than 1000 Pa.

[0045] In some preferred embodiments, the vacuum evaporation is divided into four stages: the first stage: temperature 800°C, vacuum degree not greater than 1000Pa, time 0.5h; the second stage: temperature 760°C, vacuum degree not greater than 700Pa, time 1h; the third stage: temperature 720°C, vacuum degree not greater than 400Pa, time 2h; and the fourth stage: temperature 680°C, vacuum degree not greater than 100Pa, time 4h.

[0046] According to some preferred embodiments, a second vacuum evaporation step is included after the first vacuum evaporation; preferably, the temperature of the second vacuum evaporation is 800°C.

[0047] After the composite material is basically shaped by the first vacuum evaporation, a second vacuum evaporation (isothermal vacuum evaporation) is performed to completely evaporate the magnesium matrix in the composite material. This maintains the microstructure (network structure) of graphene in the composite material without damage, resulting in a graphene-reinforced magnesium matrix composite material with a network structure (magnesium oxide-reinforced graphene dry gel). This graphene-reinforced magnesium matrix composite material contains only graphene and magnesium oxide nanoparticles. Preferably, the graphene-reinforced magnesium matrix composite material contains 20-25 wt% graphene and 75-80 wt% magnesium oxide nanoparticles.

[0048] According to some preferred embodiments, a second hot extrusion step is further included after the first vacuum evaporation; preferably, the temperature of the second hot extrusion is 300-400°C (for example, it can be 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C or 400°C).

[0049] This invention further involves a second hot extrusion of the composite material after the first vacuum evaporation. Since the evaporation of the magnesium matrix after the first vacuum evaporation introduces porosity, the hot extrusion improves the density and strength of the composite material. This graphene-reinforced magnesium-based composite material contains only a magnesium matrix, graphene, and magnesium oxide nanoparticles. Preferably, the graphene-reinforced magnesium-based composite material contains 74–88 wt% magnesium matrix, 2.8–6 wt% graphene (corresponding to a volume fraction of 2.2–5.1 vol%), and 9–20 wt% magnesium oxide nanoparticles.

[0050] According to some preferred embodiments, the extrusion ratio of the first hot extrusion is less than that of the second hot extrusion; preferably, the extrusion ratio of the first hot extrusion is (4-9):1 (for example, it can be 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1 or 9:1); and the extrusion ratio of the second hot extrusion is greater than 25:1.

[0051] It should be noted that the extrusion ratio in this invention refers to the ratio of the cross-sectional area of ​​the composite material before and after hot extrusion.

[0052] Because defects such as shrinkage cavities and porosity are easily generated during the cooling process of cast composite materials, the cast composite materials are first densified by hot extrusion with a small amount of deformation. After vacuum evaporation, the evaporation of the magnesium matrix will bring pores. The density and strength of the composite material are improved by hot extrusion with a larger amount of deformation.

[0053] To more clearly illustrate the technical solution and advantages of the present invention, the present invention will be further described below in conjunction with embodiments.

[0054] The materials and reagents used in this invention can be purchased directly from the market or synthesized in-house, and there are no restrictions on the specific models.

[0055] Example 1

[0056] (1) Pure magnesium is melted to obtain pure magnesium melt, and the temperature of pure magnesium melt is adjusted to 680-700℃. Carbon monoxide is introduced into it to obtain composite melt. Then the composite melt is cooled and solidified to obtain a cast magnesium-based composite material with a graphene content of 2.2wt%.

[0057] (2) The cast composite material is heated to 300°C and hot extruded. The opening of the extrusion cup is round and the extrusion ratio is 9:1 to obtain a cylindrical extruded magnesium-based composite material.

[0058] (3) The extruded magnesium-based composite material was placed in a tube furnace and filled with argon gas for 5 minutes to replace the air in the tube furnace. Then, a vacuum was drawn, and the vacuum degree should not exceed 1000 Pa. Then, step heat vacuum evaporation was carried out. The first stage was 800℃ with a vacuum degree of 1000 Pa and held for 0.5 h. The second stage was 760℃ with a vacuum degree of 700 Pa and held for 1 h. The third stage was step heat treatment at 680℃ with a vacuum degree of 400 Pa and held for 4 h. The fourth stage was step heat treatment at 680℃ with a vacuum degree of 100 Pa and held for 8 h. After the initial vacuum evaporation, the mass of the composite material was reduced by about 80%.

[0059] (4) The composite material that was initially vacuum evaporated was then vacuumed again with a vacuum degree of 0.1 Pa. The heat preservation temperature was raised to 800℃ and the heat preservation time was 12h. The final step of vacuum evaporation was carried out. The mass of the composite material was reduced to 92% of that before evaporation. The magnesium matrix in the composite material was completely evaporated, leaving only graphene and nano-magnesium oxide for reinforcement. A graphene-reinforced magnesium matrix composite material (MgO particle-reinforced graphene dry gel) with a graphene content of 23wt% was obtained.

[0060] In this embodiment, the graphene-reinforced magnesium matrix composite material (MgO particle-reinforced graphene dry gel, such as...) Figure 1 In the composite material, the microstructure (network structure) of graphene is not destroyed, and it contains only graphene and magnesium oxide particles. The magnesium oxide particles on the graphene surface can effectively improve the overall strength of the graphene dry gel.

[0061] Example 2

[0062] (1) Pure magnesium is melted to obtain pure magnesium melt, and the temperature of pure magnesium melt is adjusted to 680-700℃. Carbon monoxide is introduced into it to obtain composite melt. Then the composite melt is cooled and solidified to obtain a cast magnesium-based composite material with a graphene content of 2.2wt%.

[0063] (2) The cast composite material is heated to 300°C and hot extruded. The opening of the extrusion cup is round and the extrusion ratio is 9:1 to obtain a cylindrical extruded magnesium-based composite material.

[0064] (3) Place the extruded magnesium-based composite material in a tube furnace, fill it with argon gas for 5 minutes to replace the air in the tube furnace, then evacuate it. The vacuum degree should not exceed 1000 Pa. Then perform stepped thermal vacuum evaporation. First stage: 800℃, vacuum degree of 1000 Pa, hold for 0.5 h; second stage: 760℃, vacuum degree of 700 Pa, hold for 1 h; third stage: 680℃ stepped heat treatment, vacuum degree of 400 Pa, hold for 4 h; fourth stage: 680℃ stepped heat treatment, vacuum degree of 100 Pa, hold for 8 h.

[0065] (4) The composite material that has been vacuum evaporated is heated to 300°C and hot extruded. The extrusion temperature is 300°C and the extrusion ratio is 45:1 to obtain a graphene-reinforced magnesium-based composite material with a graphene content of 5.5wt%.

[0066] The magnesium-based composite material in this embodiment is as follows: Figure 2 As shown, the microstructure diagram of the composite material is as follows. Figure 3 As shown, graphene interlocks with each other in the magnesium matrix to form a network structure, which improves the stress-strain distribution of the composite material during deformation, resulting in more significant strengthening of the reinforcing phase. The graphene content in the composite material is significantly increased to 5.5 wt% (corresponding to a volume fraction of 4.6 vol%), while the total volume fraction of graphene and magnesium oxide reinforcing phase is 23.8 wt%.

[0067] Comparative Example 1

[0068] 397g of magnesium powder and 3g of graphene were added to 1000mL of ethanol and then placed in a water bath ultrasonic tank for ultrasonic dispersion of the graphene, while simultaneously stirring with a mechanical stirrer. The duration of ultrasonication and stirring was 1 hour. Subsequently, the ethanol-graphene-magnesium powder suspension was heated to 100℃ under ultrasonic stirring until the mixture was completely dry. After that, ultrasonication and mechanical stirring were stopped to obtain graphene-magnesium composite powder. The obtained composite powder was pressed into a compact using a mold, with a pressing pressure greater than 20MPa. The pressed block was then placed into a graphite mold and subsequently placed in a vacuum hot press furnace for vacuuming, with a vacuum degree less than 1×10⁻⁶. -5 After the vacuum level is reached, heating begins, with an initial temperature setting of 300℃. Once the sintering temperature reaches 300℃, it is increased to 600℃ at a rate of 10℃ / min. Pressure is applied within the range of 300–600℃, with the pressure increasing linearly with temperature, specifically 0 MPa at 300℃ and 20 MPa at 600℃. When the heating temperature reaches 600℃ and the pressure is 20 MPa, the pressure is maintained for 30 minutes. After this period, the pressure is released, the heating unit is shut off, and heating is stopped. The GNPs / Mg composite material is obtained once the vacuum hot press furnace has cooled to room temperature.

[0069] Table 1. Room temperature compression performance data of Example 2, Comparative Examples 1-2 and pure magnesium

[0070]

[0071]

[0072] It should be noted that the room temperature compression performance data of this invention are based on the GB / T 7314-2017 standard. As shown in Table 1, the composite material of Example 2 has a higher graphene content and superior mechanical properties. The compressive yield strength of the composite material of Example 2 is 10 times higher than that of pure magnesium and 7.1 times higher than that of the composite material prepared by powder metallurgy in Comparative Example 1. The compressive strength of the composite material is 4.1 times higher than that of pure magnesium and 2.7 times higher than that of the composite material prepared by powder metallurgy in Comparative Example 1. It is evident that the rigid framework formed by the interlocking high-content graphene and the network structure of graphene significantly enhance the performance of the composite material.

[0073] Example 3

[0074] (1) Pure magnesium is melted to obtain pure magnesium melt, and the temperature of pure magnesium melt is adjusted to 680-700℃. Carbon monoxide is introduced into it to obtain composite melt. Then the composite melt is cooled and solidified to obtain a cast magnesium-based composite material with a graphene content of 1.5wt%.

[0075] (2) The cast composite material is heated to 300°C and hot extruded. The opening of the extrusion cup is round and the extrusion ratio is 9:1 to obtain a cylindrical extruded magnesium-based composite material.

[0076] (3) Place the extruded magnesium-based composite material in a tube furnace, fill it with argon gas for 5 minutes to replace the air in the tube furnace, and then evacuate it. The vacuum degree should not be greater than 1000 Pa. Then carry out step heat vacuum evaporation with both temperature and vacuum degree decreasing in a gradient. First stage: 800℃, vacuum degree of 1000 Pa, hold for 0.5 h; second stage: 760℃, vacuum degree of 700 Pa, hold for 1 h; third stage: 680℃ step heat treatment, vacuum degree of 400 Pa, hold for 4 h; fourth stage: 680℃ step heat treatment, vacuum degree of 100 Pa, hold for 8 h.

[0077] (4) The composite material after vacuum evaporation is heated to 300°C and hot extruded. The extrusion temperature is 300°C and the extrusion ratio is 45:1 to obtain a graphene-reinforced magnesium-based composite material with a graphene content of 3wt% (corresponding to a volume fraction of 2.4vol%).

[0078] The micropillar compressive stress-strain curve of the magnesium-based composite material used in this embodiment is shown in the figure below. Figure 4 As shown, the overall performance of the composite material is significantly improved.

[0079] Comparative Example 2

[0080] (1) Pure magnesium is melted to obtain pure magnesium melt, and the temperature of pure magnesium melt is adjusted to 680-700℃. Carbon monoxide is introduced into it to obtain composite melt. Then the composite melt is cooled and solidified to obtain a cast magnesium-based composite material with a graphene content of 1.5wt%.

[0081] (2) The cast composite material is heated to 300°C and hot extruded. The extrusion cup opening is round and the extrusion ratio is 9:1 to obtain a cylindrical extruded magnesium-based composite material.

[0082] (3) The cast composite material is heated to 300°C and hot extruded. The extrusion cup opening is round and the extrusion ratio is 45:1 to obtain a cylindrical extruded magnesium-based composite material.

[0083] Table 2. Room temperature tensile properties of Example 3, Comparative Example 2, and pure magnesium

[0084]

[0085] It should be noted that the room temperature compression performance data of this invention are based on the GB / T228.1-2010 standard. As shown in Table 2, the composite material of Example 3 has a higher graphene content. The elastic modulus of the composite material is 8.33 GPa / wt% higher than that of pure magnesium and 11.33 GPa / wt% higher than that of the composite material of Comparative Example 2 without vacuum evaporation. The yield strength of the composite material is 3.3 times higher than that of pure magnesium and 58.7% higher than that of the composite material of Comparative Example 2 without vacuum evaporation. The tensile strength of the composite material is 1.33 times higher than that of pure magnesium and 36% higher than that of the composite material of Comparative Example 2 without vacuum evaporation. The nonlinear growth trend of the elastic modulus of the composite material indicates that the rigid skeleton formed by the interlocking graphene and the network structure of the graphene significantly enhance the performance of the composite material.

[0086] 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 they can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for 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 high-volume graphene-reinforced magnesium-based composite material, characterized in that, The composite material is formed from a composite melt comprising a magnesium matrix, magnesium oxide nanoparticles, and graphene; the graphene content in the composite melt is not less than 1.5 wt%; the graphene in the composite material is distributed in a network; the composite material comprises 74-88 wt% magnesium matrix, 2.8-6 wt% graphene, and 9-20 wt% magnesium oxide nanoparticles. The method for preparing the composite material includes: Carbon monoxide is introduced into pure magnesium melt, and a gas-liquid reaction is carried out to obtain a composite melt with thixotropic properties. The composite melt is then cooled and solidified to obtain a cast composite material. The cast composite material is subjected to a first hot extrusion and a first vacuum evaporation to obtain a high volumetric graphene-reinforced magnesium-based composite material; the first vacuum evaporation is a stepped vacuum evaporation with a temperature gradient decreasing; the temperature of the first vacuum evaporation is 620~800℃; the vacuum degree of the first vacuum evaporation is not greater than 1000Pa; after the first vacuum evaporation, a second hot extrusion step is also included; the temperature of the second hot extrusion is 300~400℃.

2. The composite material according to claim 1, characterized in that, The composite melt comprises 89-93.5 wt% magnesium matrix, 5-8.5 wt% magnesium oxide nanoparticles, and 1.5-2.5 wt% graphene.

3. A method for preparing the high-volume graphene-reinforced magnesium-based composite material according to claim 1, characterized in that, The preparation method includes: Carbon monoxide is introduced into pure magnesium melt, and a gas-liquid reaction is carried out to obtain a composite melt with thixotropic properties. The composite melt is then cooled and solidified to obtain a cast composite material. The cast composite material is subjected to a first hot extrusion and a first vacuum evaporation to obtain a high volumetric graphene-reinforced magnesium-based composite material; the first vacuum evaporation is a stepped vacuum evaporation with a temperature gradient decreasing; the temperature of the first vacuum evaporation is 620~800℃; the vacuum degree of the first vacuum evaporation is not greater than 1000Pa; after the first vacuum evaporation, a second hot extrusion step is also included; the temperature of the second hot extrusion is 300~400℃.

4. The preparation method according to claim 3, characterized in that, The temperature of the gas-liquid reaction is 680~700℃; and / or The temperature of the first hot extrusion is 300~400℃.

5. The preparation method according to claim 3, characterized in that, The extrusion ratio of the first hot extrusion is less than that of the second hot extrusion; the extrusion ratio of the first hot extrusion is (4~9):1; the extrusion ratio of the second hot extrusion is greater than 25:1.

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