As-cast graphene reinforced magnesium-based composite material and preparation method thereof

Abstract

The invention relates to an as-cast graphene reinforced magnesium-based composite material and a preparation method thereof.The preparation method comprises the following steps that a magnesium material is heated and melted in a heating device in the presence of shielding gas, then hydrocarbon gas is introduced, stirring is conducted for the first time, a refining agent is added after stirring is conducted for the first time, and then stirring is conducted for the second time; and after stirring is finished, the as-cast graphene reinforced magnesium-based composite material is obtained. The graphene and the magnesium material are well combined, the strengthening effect of the graphene is fully played, the interface is pure and free of oxide inclusion, the performance of the composite material is improved, the porosity is reduced, the production cost is low, and the equipment is simple and safe; the method is suitable for composite material preparation.

Description

Technical Field

[0001] This invention relates to the field of composite materials technology, and in particular to a cast graphene-reinforced magnesium-based composite material and its preparation method. Background Technology

[0002] Graphene is a single-layer, two-dimensional lattice structure composed of carbon atoms in sp² hybridization. It is considered one of the hardest, thinnest, and most electrically and thermally conductive materials known to date. Since its first successful preparation in 2004, graphene has rapidly attracted widespread attention in the field of materials science. These unique properties give it enormous application potential in various fields, especially in composite materials. Research shows that adding graphene to polymer, metal, or ceramic matrices can significantly improve the mechanical strength, stiffness, electrical conductivity, and thermal conductivity of composite materials.

[0003] Magnesium alloys, with their low density, high specific strength and specific stiffness, as well as excellent thermal conductivity and electromagnetic shielding properties, have become a hot topic in new materials research and application. Magnesium is one of the most abundant elements in the Earth's crust, with abundant reserves and relatively low price. Combined with its lightweight properties, magnesium alloys show great application potential in fields with high weight reduction requirements, especially in the aerospace and automotive industries, and also have broad application prospects in electronic equipment and biomedicine. Despite the many advantages of magnesium alloys, their application still faces some challenges, such as easy oxidation and corrosion, low-temperature brittleness, and processing difficulties, which limit their application in certain specific environments. To address these challenges, researchers are constantly exploring new alloy formulations and processing techniques, while also introducing reinforcements of different sizes and types (nanocarbon materials, ceramic particles, etc.) to prepare magnesium-based composite materials, thereby improving the performance and stability of the composites and expanding their application range. While traditional ceramic particle-reinforced magnesium-based composites offer significant improvements in strength and hardness, the reduction in plasticity is a considerable concern. Often, greater plasticity is sacrificed for increased strength, resulting in a strength-plasticity inversion. Although the addition of nano-carbon materials cannot perfectly solve this problem, it can effectively reduce the impact on plasticity, making it superior to traditional ceramic materials. Among nano-carbon materials, graphene's two-dimensional sheet structure makes it superior to carbon nanotubes and amorphous carbon in reinforcement. Its large-area sheets provide a higher specific surface area and more contact interfaces, significantly improving the mechanical properties and interfacial bonding of the composite material. Simultaneously, graphene possesses extremely high tensile strength and elastic modulus, far exceeding those of carbon nanotubes and amorphous carbon. This gives graphene-reinforced magnesium-based composites a significant advantage in improving mechanical properties, more effectively enhancing the material's tensile, compressive, and flexural strength. Furthermore, graphene has extremely high electrical and thermal conductivity, surpassing other nano-carbon materials. Its addition significantly improves the electrical and thermal conductivity of magnesium-based composites, making them superior in electronic devices and thermal management applications. These advantages give graphene enormous application potential and broad development prospects in the field of high-performance composite materials.

[0004] Graphene-reinforced magnesium-based composites, as an emerging high-performance composite material, have received widespread attention and research in the field of materials science in recent years. Researchers mainly prepare magnesium-based composites using the following methods: Mechanical alloying, which uses high-energy ball milling to uniformly disperse graphene into magnesium materials. While ball milling provides uniform dispersion and is simple, it may introduce impurities and consumes a large amount of energy, posing an explosion hazard. Stirred casting involves directly adding graphene to molten magnesium, followed by pre-dispersion and ultrasonic stirring to bond it with the magnesium material at high temperatures. This method is simple and easy to scale up, but high temperatures can damage the graphene structure, affecting the reinforcement effect. Additionally, graphene may aggregate at grain boundaries in the matrix, resulting in uneven dispersion. Powder metallurgy involves mixing graphene and magnesium powders, then pressing and sintering to form a composite material. This method allows for precise control of the graphene content, but sintering can easily create porosity, affecting material properties. Pressure infiltration involves injecting liquid metal into a preform of the reinforcing material using pressurized gas. This method can solve the problem of poor wettability between the reinforcing phase and the matrix, but it requires sophisticated equipment, making the process difficult to promote. Friction stirring softens the matrix and promotes the fusion of composite materials through the frictional heat of the stirring head. The resulting graphene has a fine grain size and is uniformly dispersed, but it is still in the exploratory stage, the process is not yet mature, and the size and shape of the material are limited.

[0005] In general, various methods have their own advantages and limitations in the preparation of graphene-reinforced magnesium matrix composites. Therefore, there is a need to develop a graphene-reinforced magnesium matrix composite with simple process, pure and tight interface between the reinforcement and the matrix, and strong plasticity matching. Summary of the Invention

[0006] The technical problem to be solved by this invention is that existing magnesium-based composite material preparations suffer from poor interfacial bonding, uneven dispersion, complex processes, oxidation and explosion hazards during smelting, and porosity during casting. To address the shortcomings of existing technologies, this invention provides a cast graphene-reinforced magnesium-based composite material and its preparation method.

[0007] To address the aforementioned technical problems, this invention provides a method for preparing a cast graphene-reinforced magnesium-based composite material. The method includes the following steps: heating and melting magnesium material in a heating device under the presence of a protective gas, then introducing hydrocarbon gas and performing a first stirring; after the first stirring is completed, adding a refining agent; then performing a second stirring; and finally obtaining the cast graphene-reinforced magnesium-based composite material after the stirring is completed.

[0008] In this invention, the first stirring can promote the pyrolysis reaction, and the addition of a refining agent after the first stirring can remove impurities and hydrogen. The second stirring can promote the dispersion of graphene and the densification of the material.

[0009] This invention provides a cast graphene-reinforced magnesium-based composite material. It utilizes a reaction system where hydrocarbon gases such as methane are catalytically cracked in molten magnesium to generate graphene. Stirring and ultrasonic dispersion ensure uniform dispersion of graphene within the molten magnesium. Finally, refining agents and die-casting are used to remove voids, followed by quenching and cooling to obtain the cast material. Firstly, regarding raw material selection, hydrocarbon gases such as methane (CH4) serve as a carbon source due to their simple molecular structure, high carbon content, and the fact that their cracking temperature matches the magnesium melting temperature, making them ideal for generating graphene under high-temperature conditions. Pure magnesium or magnesium alloys are used as the matrix material. Magnesium possesses low density, high specific strength, and good thermal conductivity, enabling it to form excellent composite materials with the generated graphene. The experimental principle is simple: methane is catalytically cracked in molten magnesium, releasing carbon atoms, which then rearrange to synthesize graphene. When methane gas is introduced into molten magnesium, it undergoes a cracking reaction at high temperature to generate carbon atoms, which gradually form graphene sheets on the surface or inside the molten magnesium. This process not only generates high-quality graphene but also enables it to bond well with magnesium materials, thus preparing graphene-reinforced magnesium-based composite materials. The chemical reaction equation is as follows: CH4→C+2H2. The experimental equipment can be modified from a traditional stirred casting device, saving casting costs and time. Therefore, methane is chosen as the carbon source, and magnesium or magnesium alloys are chosen as the reaction and catalytic matrix to prepare graphene-reinforced magnesium-based composite materials. This addresses the problems of poor wettability between graphene and the matrix under existing processes, which prevents effective interfacial bonding and results in limited dispersion and strengthening effects of the reinforcing graphene; complex composite material preparation processes with high equipment requirements; and the potential oxidation and explosion hazards of magnesium materials.

[0010] Preferably, the magnesium material is elemental magnesium or a magnesium alloy.

[0011] In this invention, the magnesium material can be pure magnesium or a magnesium alloy, and the magnesium alloy can be a magnesium-zinc alloy, a magnesium-calcium alloy, or a magnesium-copper alloy.

[0012] Preferably, the protective gas is a mixture of sulfur hexafluoride and carbon dioxide, and the gas flow rate of the protective gas is 200~700 mL / min, for example, it can be 200 mL / min, 300 mL / min, 400 mL / min, 500 mL / min, 600 mL / min or 700 mL / min, etc. The mixture of sulfur hexafluoride and carbon dioxide of the present invention can prevent magnesium materials from being oxidized.

[0013] Preferably, the heating and melting temperature is 100-200°C higher than the melting point of magnesium, for example, it can be 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, or 200°C. In this invention, the heating and melting temperature and the heating rate can be set to 15°C / min.

[0014] Preferably, the heating device includes an air inlet, a vent pipe, and a gas collection device. The hydrocarbon gas is introduced into the heating device through the air inlet. The vent pipe extends into the lower middle part of the molten magnesium material. The gas collection device is located 40-60 mm above the surface of the molten magnesium material.

[0015] In this invention, the lowest point of the vent pipe is approximately 10 mm from the bottom of the heating device. In the reaction apparatus, magnesium is in excess, and the introduction of hydrocarbon gases is slow, but the overall reaction process is incomplete. The collection device is mainly used to handle the hydrogen and methane and other hydrocarbon gases that overflow from the reaction.

[0016] Preferably, the hydrocarbon gas includes any one or a combination of at least two of methane, ethane, ethylene, acetylene, propane, or butane; the rate of introduction of the hydrocarbon gas is 100~9000 mL / min.

[0017] Preferably, the rate at which the hydrocarbon gas is introduced is 100~9000 mL / min, for example, it can be 100 mL / min, 200 mL / min, 300 mL / min, 400 mL / min, 500 mL / min, 600 mL / min, 700 mL / min, 800 mL / min, 900 mL / min, 1000 mL / min, 2000 mL / min, 3000 mL / min, 4000 mL / min, 5000 mL / min, 6000 mL / min, 7000 mL / min, 8000 mL / min, or 9000 mL / min.

[0018] In this invention, the magnesium material should be in a fully molten state when hydrocarbon gas is introduced.

[0019] Preferably, the stirring temperature for the first stirring is 680~980℃, for example, 680℃, 700℃, 800℃, 850℃, 900℃ or 980℃, etc., the stirring speed is 100~10000r / min, for example, 100r / min, 800 r / min, 1000 r / min, 2000 r / min, 2500 r / min, 3000 r / min, 4000r / min, 5000r / min, 6000r / min, 7000r / min, 8000r / min, 9000r / min or 10000r / min, etc., and the stirring time is 30~600min, for example, 30min, 100min, 200min, 300min, 400min, 500min or 600min, etc.

[0020] This invention accelerates the pyrolysis reaction by stirring, keeping the entire reaction device uniform and stable, and promoting the pyrolysis of methane to generate graphene and the uniform dispersion of graphene in the magnesium melt.

[0021] Preferably, the refining agent is a mixture of chloride salts, fluoride salts, and hexachloroethane. In this invention, the chloride salt can be magnesium chloride, potassium chloride, or calcium chloride, etc., and the fluoride salt can be sodium fluoride, etc.

[0022] Preferably, the second stirring is performed at a temperature 10-50°C higher than the first stirring, and the stirring time is 10-30 minutes. This second, continuous stirring improves the uniformity and flowability of the material, and allows for the continuous introduction of protective gas. After stirring, the mixture can be quenched and cooled to obtain a cast graphene-reinforced magnesium-based composite material.

[0023] On the other hand, the present invention also provides a cast graphene-reinforced magnesium-based composite material prepared by the preparation method described above.

[0024] Preferably, the cast graphene-reinforced magnesium matrix composite material is an extruded graphene-reinforced magnesium matrix composite material obtained by hot extrusion.

[0025] The cast graphene-reinforced magnesium matrix composite material provided by this invention has a pure and tightly bonded interface between the reinforcement and the matrix, exhibiting strong plasticity matching. Furthermore, to meet different performance and testing requirements, this invention can also subject the cast material to heat treatment and deformation processing, repeating the previous steps to reduce heat loss and ensure continuous graphene generation and dispersion, thus achieving continuous and efficient preparation of the graphene-reinforced magnesium matrix composite material.

[0026] Implementing this invention has the following beneficial effects: This invention provides a method for preparing graphene-reinforced magnesium matrix composites via the cracking reaction of methane in molten magnesium. This method overcomes the problems inherent in traditional magnesium matrix composite preparation methods, such as poor wettability between the added reinforcement and the matrix, resulting in ineffective interfacial bonding and limited dispersion and strengthening effects of the graphene reinforcement; complex production processes with high equipment requirements; high casting porosity; and the potential for oxidation and explosion hazards. In this invention, graphene and magnesium materials bond well, fully utilizing the reinforcing effect of graphene. The interface is pure and free of oxide inclusions, which is beneficial for improving composite material performance, reducing porosity, and reducing production costs while requiring simple and safe equipment. Furthermore, based on the principle of synthesizing graphene through the cracking reaction of methane and other hydrocarbon gases, and the preparation of composite materials using stirred casting, this method is applicable to the field of composite material preparation. Attached Figure Description

[0027] Figure 1 This is the cast graphene-reinforced magnesium-based composite material prepared in Example 1 of this invention.

[0028] Figure 2 This is an XRD pattern of carbon products in the cast graphene-reinforced magnesium-based composite material prepared in Example 1 of this invention.

[0029] Figure 3 This is a Raman spectral image of the carbon products of the cast graphene-reinforced magnesium-based composite material prepared in Example 1 of this invention.

[0030] Figure 4 This is an atomic force micrograph of the carbon products of the cast graphene-reinforced magnesium-based composite material prepared in Example 1 of this invention.

[0031] Figure 5 This is an atomic force microscopy image of the carbon products of the cast graphene-reinforced magnesium-based composite material prepared in Example 1 of this invention.

[0032] Figure 6 This is a scanning electron microscope (SEM) image of the carbon products of the cast graphene-reinforced magnesium-based composite material prepared in Example 1 of this invention.

[0033] Figure 7A This is a scanning electron microscope image of the microstructure of the cast graphene-reinforced magnesium-based composite material prepared in Example 1 of this invention.

[0034] Figure 7B This is the magnesium element energy spectrum of the cast graphene-reinforced magnesium-based composite material prepared in Example 1 of this invention.

[0035] Figure 7C This is the zinc element energy spectrum of the cast graphene-reinforced magnesium-based composite material prepared in Example 1 of this invention.

[0036] Figure 7D This is the carbon element energy spectrum of the cast graphene-reinforced magnesium-based composite material prepared in Example 1 of this invention.

[0037] Figure 8A This is a scanning electron microscope image of the microstructure of the extruded graphene-reinforced magnesium-based composite material prepared in Example 1 of this invention.

[0038] Figure 8B This is the magnesium element energy spectrum of the extruded graphene-reinforced magnesium-based composite material prepared in Example 1 of this invention.

[0039] Figure 8C This is the zinc element energy spectrum of the extruded graphene-reinforced magnesium-based composite material prepared in Example 1 of this invention.

[0040] Figure 8D This is the carbon element energy spectrum of the extruded graphene-reinforced magnesium-based composite material prepared in Example 1 of this invention.

[0041] Figure 9This is a comparison diagram of the tensile mechanical properties of the cast graphene-reinforced magnesium matrix composite material prepared in Example 1 of this invention and the Mg6Zn alloy. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] Example 1 (1) 700g of pure magnesium is heated and melted in a reaction apparatus. During the melting process, SF6 / CO2 mixed protective gas is continuously blown over the surface of the magnesium material to prevent the magnesium material from being oxidized. The gas flow rate is set to 200ml / min, the melting temperature is set to 750℃, and the heating rate is set to 15℃ / min. (2) During the melting of magnesium material, a gas inlet pipe, gas flow meter, control valve, and gas inlet device are installed. The top of the reaction device is connected to the gas inlet device and the gas collection device. The gas inlet device is responsible for introducing CH4. The gas inlet pipe is placed aside for standby. The gas collection device is located 50 mm above the surface of the magnesium melt. Although the magnesium material is in excess and the introduction of methane is slow, the reaction is still incomplete. The gas outlet is used to treat the hydrogen and CH4 that have dissolved in the magnesium material during the reaction. (3) After the magnesium material has completely melted, first insert the stirring paddle into the magnesium melt, about 5 mm from the bottom of the crucible, and then insert the gas pipe into the magnesium melt, about 10 mm from the bottom of the crucible. The selected liquid stirring temperature is 700℃, and the stirring speed is 700 r / min. The CH4 gas is introduced at a rate of 200 ml / min. The CH4 gas is slowly and continuously added to the melt and mechanically stirred for 60 min. Stirring accelerates the cracking reaction, keeps the entire reaction device uniform and stable, and promotes the cracking of methane to generate graphene and the uniform dispersion of graphene in the magnesium melt. (4) After the aeration and stirring are completed, turn off the stirring device, add refining agent to remove hydrogen and impurities, then heat to 750℃ and stir for 10 minutes to improve the uniformity and surface fluidity of the material, and continue to blow in protective gas. (5) After the stirring is completed, quench and cool to obtain the cast graphene-reinforced magnesium-based composite material, the specific product of which is as follows: Figure 1 As shown.

[0044] A 25g sample of the composite material obtained in this embodiment was soaked in a 1g / ml dilute acid. Since the magnesium material and related products except carbon in this embodiment are soluble in acid, after the sample was completely dissolved, the solution was poured into an extraction device for extraction. After the extraction was completed, the filter paper layer was removed, and the extracted carbon product was attached to it. The obtained carbon product was placed in a vacuum drying oven and dried for 2 hours. After drying, the carbon product was weighed, and the mass was 0.032g, and the mass fraction of the carbon product was 0.1%, which initially proved the feasibility.

[0045] The obtained carbon product was subjected to XRD analysis, and the test results are shown in the figure below. Figure 2 As shown, a characteristic peak of graphene appears at around 26.3°, which matches the (002) peak of graphene. It can be determined that the carbon product generated in this embodiment has a graphene structure.

[0046] A portion of the obtained carbon product was subjected to Raman spectroscopy, and the results are as follows: Figure 3 As shown, obvious G peak, D peak, 2D peak of graphene can be observed. The ratio of D peak to G peak can characterize the degree of microscopic defects in graphene, and the ratio of 2D peak to G peak can characterize the number of graphene layers. Therefore, it can be further concluded that the graphene nanosheet generated in this embodiment is complete and has multiple stacked layers.

[0047] To further verify that the generated carbon product is a multilayered stacked graphene nanosheet, atomic force (AFM) testing was performed on the generated carbon product, and the results are as follows: Figure 4 , Figure 5 As shown, the generated graphene nanosheets are indeed stacked, with a thickness between 3nm and 4nm. The thickness of a single graphene nanosheet is 0.335nm. Therefore, the number of graphene nanosheets generated in this embodiment is about 8-11 layers, which is relatively thin, rather than carbon nanotubes or carbon nanoparticles.

[0048] The generated graphene nanosheets were tested using scanning electron microscopy (SEM), such as... Figure 6 As shown, the generated graphene nanosheets exhibit uniform shape and size, with a diameter between 1 and 3 μm, and good integrity.

[0049] SEM and EDS were performed on both as-cast and extruded composite material samples. Figure 7A , Figure 7B , Figure 7C and Figure 7D ,as well as Figure 8A , Figure 8B , Figure 8C and Figure 8DAs shown, a network of Mg6Zn phases was observed in the cast sample, but no significant enrichment of carbon was observed. This is because the graphene content was low and the thickness was thin, resulting in low contrast under scanning electron microscopy. In the extruded sample, the Mg6Zn phase was found to become banded after deformation, and some of it broke into granules. Similarly, no carbon distribution was observed. This further demonstrates that the microstructure is uniformly distributed without significant agglomeration in both cast and extruded states.

[0050] The composite material prepared in this embodiment was subjected to an extrusion deformation process with an extrusion ratio of 28:1, an extrusion temperature of 350℃, and a holding time of 1 hour. The resulting extruded bar was cut into tensile specimens for tensile mechanical property testing. Simultaneously, the Mg6Zn alloy was subjected to the same deformation process for tensile mechanical property testing, and the mechanical properties were obtained as follows: Figure 9 As shown, the yield strength of the Mg6Zn alloy is 182.9 MPa, the tensile strength is 285.5 MPa, and the elongation is 16.5%; while the yield strength of the 0.01 wt.% Gr / Mg-6Zn composite material is 264.2 MPa, the tensile strength is 323.4 MPa, and the elongation is 5.2%. The yield strength increased by 44.5%, the tensile strength increased by 13.3%, and the elongation decreased by 68.5%, proving that graphene nanosheets played a significant reinforcing role.

[0051] Example 2 The difference between this embodiment and Embodiment 1 is that the melting temperature in step (1) is changed to be 50-300℃ higher than the melting point. The result is that moderately increasing the melting temperature will have a beneficial effect on the initial system of magnesium melt and the energy storage of the system, thereby improving the pyrolysis efficiency of CH4 and the graphene generation efficiency, and thus affecting the dispersion and morphology of the reinforcement of the material.

[0052] Example 3 The difference between this embodiment and Embodiment 1 is that a magnesium-zinc alloy is selected as the matrix. The result is that it has a further catalytic effect on CH4 cracking and graphene formation, improves the formation and dispersion efficiency of the reinforcement and various properties of the composite material, and the alloy composition can improve the mechanical properties of the material.

[0053] Example 4 The difference between this embodiment and Embodiment 1 is that the stirring temperature in step (3) is changed to 680℃. The result is that by selecting a suitable stirring temperature, the continuous cracking efficiency of CH4 and the graphene generation efficiency are improved, the content and dispersion of the reinforcing body are changed, and the mechanical properties of the material are further improved.

[0054] Example 5 The difference between this embodiment and Embodiment 1 is that the stirring speed in step (3) is 8000 r / min. The result is that selecting a suitable stirring speed improves the continuous pyrolysis efficiency of CH4 and the final dispersion state of graphene, thereby further improving the structural function and mechanical properties of the material.

[0055] Example 6 The difference between this embodiment and Embodiment 1 is that the stirring time in step (3) is 600 min. The result is that by selecting a suitable stirring time, the optimal graphene content is obtained, and the mechanical properties of the material are improved.

[0056] Example 7 The difference between this embodiment and Embodiment 1 is that the CH4 gas introduction rate in step (3) is 2000 ml / min. The result is that by selecting an appropriate CH4 introduction rate, the shape and size of the CH4 bubbles in the melt are changed, affecting the microscopic surface quality of graphene and its macroscopic distribution in the melt, thereby further improving the mechanical properties of the material.

[0057] Example 8 The difference between this embodiment and embodiment one is that the height of the stirring paddle is changed to 10 mm in step (3). The result is that by selecting a suitable stirring paddle height, the stirring force field and flow field of the melt are changed, which affects the morphology of graphene formation and improves the graphene formation efficiency.

[0058] Example 9 The difference between this embodiment and Embodiment 1 is that the total amount of CH4 introduced and the feeding ratio of magnesium material are changed in step (3). The result is that selecting a suitable feeding ratio affects the CH4 cracking efficiency, thereby improving the utilization rate of CH4 raw materials while avoiding excessive waste.

[0059] Example 10 The difference between this embodiment and Embodiment 1 is that the composition of the molten gas introduced into the crucible is changed in step (3). This is achieved by changing the type and composition of the introduced gas, including but not limited to CO, CO2, C2H2, and other carbon hydrocarbon gases. The result is that changing the type of carbon source changes the type of carbon products generated, and may also introduce byproducts, further affecting the microstructure and mechanical properties of the material.

[0060] Example 11 The difference between this embodiment and Embodiment 1 is that an ultrasonic oscillation device is added in step (3). The result is that the addition of the ultrasonic oscillation device improves the CH4 cracking rate and the graphene generation efficiency.

[0061] Example 12 The difference between this embodiment and Embodiment 1 is that an ultrasonic oscillation device is added in step (3) to change the ultrasonic frequency from 20kHz to 40kHz, thereby further regulating the CH4 pyrolysis rate and the graphene formation efficiency. This is beneficial to improving the mechanical properties of the composite material.

[0062] Example 13 The difference between this embodiment and Embodiment 1 is that in step (1), a CO2 / SF2 mixed gas was introduced to prevent the magnesium melt surface from being oxidized, but instead, an Ar protective gas was introduced. The different types of protective gases will lead to differences in the surface quality and microstructure of the melt.

[0063] 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 cast graphene-reinforced magnesium-based composite material, characterized in that: The preparation method includes the following steps: heating and melting magnesium material in a heating device in the presence of a protective gas, then introducing hydrocarbon gas and stirring for the first time, adding a refining agent after the first stirring, and then stirring for the second time, and obtaining the cast graphene-reinforced magnesium-based composite material after stirring.

2. The preparation method according to claim 1, characterized in that: The magnesium material is elemental magnesium or a magnesium alloy.

3. The preparation method according to claim 1, characterized in that: The protective gas is a mixture of sulfur hexafluoride and carbon dioxide, and the gas flow rate of the protective gas is 200~700 mL / min.

4. The preparation method according to claim 1, characterized in that: The heating and melting temperature is 100-200°C higher than the melting point of magnesium.

5. The preparation method according to claim 1, characterized in that: The heating device includes an air inlet, a vent pipe, and a gas collection device. The hydrocarbon gas is introduced into the heating device through the air inlet. The vent pipe extends into the lower middle part of the molten magnesium material. The gas collection device is located 40-60 mm above the surface of the molten magnesium material.

6. The preparation method according to claim 1, characterized in that: The hydrocarbon gas includes any one or a combination of at least two of methane, ethane, ethylene, acetylene, propane, or butane; the rate of introduction of the hydrocarbon gas is 100~9000 mL / min.

7. The preparation method according to claim 1, characterized in that: The stirring temperature for the first stirring is 680~980℃, the stirring speed is 100~10000r / min, and the stirring time is 30~600min.

8. The preparation method according to claim 1, characterized in that: The refining agent is a mixture of chloride salts, fluoride salts and hexachloroethane.

9. The preparation method according to claim 1, characterized in that: The second stirring is carried out at a temperature 10-50°C higher than that of the first stirring, and the stirring time is 10-30 minutes.

10. The cast graphene-reinforced magnesium-based composite material prepared by the method according to claim 1; The cast graphene-reinforced magnesium matrix composite material is obtained by hot extrusion of the extruded graphene-reinforced magnesium matrix composite material.

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