Method for preparing a graphene-containing modifying agent based on a carbon-containing gas and applications thereof

Abstract

The application relates to a method for preparing a graphene-containing modifier based on a carbon-containing gas and application, and belongs to the technical field of magnesium alloy. The application aims to solve the problems of high cost, poor refining effect, unstable refining effect, poor working environment, poor forming capacity and mechanical property of cast magnesium-aluminum alloy complex thin-wall components of existing magnesium-aluminum alloy modifiers. The graphene-containing modifier is prepared by feeding the carbon-containing gas into a magnesium melt, and the graphene in the modifier is well dispersed. The modifier is put into a magnesium-aluminum alloy melt, and after standing, the melt is fully mixed and reacted by stirring, and then is solidified at a certain cooling speed after standing, so that the magnesium-aluminum alloy is refined. The application has the advantages of low cost, simple operation, cleanness, stability and high efficiency of the modifier, and slow refining recession. The graphene-containing modifier prepared by the application is suitable for grain refinement of aluminum-magnesium alloy.

Description

Technical Field

[0001] This invention belongs to the field of magnesium alloy technology, specifically relating to a method and application for preparing graphene-containing modifiers based on carbon-containing gas. Background Technology

[0002] Magnesium alloys possess low density, high specific strength, good vibration damping performance, and excellent electromagnetic shielding capabilities, making them promising candidates for lightweight structural materials in aerospace, automotive lightweighting, rail transportation, and defense equipment. Compared to aluminum alloys and steel, magnesium alloys have a density only about two-thirds that of aluminum and one-quarter that of steel, offering significant advantages in reducing structural weight, lowering energy consumption, and improving equipment performance, especially suitable for weight-sensitive components. However, magnesium alloys also have significant limitations. Due to their hexagonal close-packed crystal structure at room temperature, the number of independent slip systems available for dislocation slip is relatively small, resulting in relatively insufficient room-temperature plasticity and overall mechanical properties, limiting their further application. Furthermore, during casting, magnesium alloy melts often suffer from uneven solute diffusion, rapid solidification rates, and significant dendrite growth, easily leading to casting defects such as coarse grains, uneven microstructure, shrinkage porosity, and gas pores, severely affecting the density and service reliability of castings. Therefore, how to improve the as-cast properties of magnesium alloys through reasonable microstructure control has become an important research direction, and grain refinement can precisely improve these defects.

[0003] Grain refinement can effectively improve material strength, enhance the balance between ductility and toughness, improve microstructure uniformity, and reduce the adverse effects of casting defects on performance. Generally, fine and uniform grain structures not only help increase the number of grain boundaries and hinder dislocation movement, thereby improving material strength, but also improve solute distribution during solidification, reduce local segregation, and lower the probability of shrinkage cavities and porosity formation. For non-Mg-Al magnesium alloys, Zr is currently one of the most mature and stable commercial grain refiners due to its excellent heterogeneous nucleation effect in magnesium melts, which significantly refines grains. However, for Mg-Al magnesium alloys, Zr reacts with Al, weakening or even completely eliminating its effective nucleation effect, thus limiting its refining effect. This has resulted in a long-standing lack of a universally applicable, cost-effective grain refiner with excellent refining properties for Mg-Al magnesium alloys.

[0004] Currently, common grain refinement methods for Mg-Al alloys include chlorides, ceramic particles, carbon-containing modifiers, and master alloys. Among these, carbon-containing modifiers have become a research hotspot in recent years due to their significant grain refinement effect, long duration of action, slow decay, and relatively low processing temperature. Carbonaceous refiners can not only provide effective heterogeneous nucleation sites in the melt but also generate carbon phases or composite phases with special structures through in-situ reactions, thereby further improving grain refinement efficiency. However, traditional carbonaceous refiners still have some significant drawbacks, such as complex preparation and introduction processes, poor wettability and dispersibility of the carbon phase in the melt, easy agglomeration, and harsh working environment during operation, affecting industrial applications. In addition, some refiners may also be accompanied by problems such as inclusion introduction, incomplete reaction, or insufficient stability, further limiting their widespread adoption.

[0005] In our previous research (see Chinese patent applications CN109554573A and CN113265553A), we prepared uniformly dispersed graphene-containing modifiers using CO or CO2 and pure magnesium, which exhibited good grain refinement effects on Mg-Al alloys. However, further research revealed that the presence of oxygen in the gas easily generates a large amount of magnesium oxide during the preparation process, leading to a decrease in melt cleanliness and promoting the formation of defects such as oxide inclusions and porosity. This not only reduces the forming quality of castings but also adversely affects their mechanical properties, fatigue life, and corrosion resistance. Furthermore, magnesium oxide particles adsorb onto the surface of graphene, hindering the reaction between graphene and Al, thus preventing the optimal grain refinement effect. Therefore, further research is needed to improve the grain refinement efficiency of in-situ generated graphene modifiers and minimize the adverse effects of magnesium oxide. Summary of the Invention

[0006] The purpose of this invention is to address the problems of existing magnesium-aluminum alloy modifiers, such as high cost, poor refining effect, unstable refining effect, harsh working environment, and poor ability to improve the forming ability and mechanical properties of cast magnesium-aluminum alloy complex thin-walled components. The invention provides a method and application for preparing graphene-containing modifiers based on carbon-containing gas.

[0007] A method for preparing graphene-containing modifiers based on carbon-containing gases is carried out according to the following steps:

[0008] 1. Continuously blow SF6 / CO2 mixed gas into the crucible to prevent the magnesium melt from oxidizing and burning. Place the pure magnesium into the crucible heated to 680℃-900℃. After the pure magnesium melts, the pure magnesium melt is obtained.

[0009] 2. At a temperature of 670℃-870℃, carbon-containing gas is continuously introduced into pure magnesium melt while the pure magnesium melt is continuously stirred until graphene accounts for 0.1wt.%-5wt.% of the total mass of the melt. Then, the carbon-containing gas is stopped, stirring is stopped, the melt is allowed to stand, and then the melt is quenched to solidify, thus obtaining a graphene-containing modifier.

[0010] Application of graphene-containing modifiers in grain refinement of magnesium-aluminum alloy castings.

[0011] Compared with the prior art, the present invention has at least the following advantages:

[0012] I. This invention proposes to introduce carbon-containing gases such as methane and ethylene into magnesium melt to construct a gas-liquid reaction system for in-situ growth of graphene nanosheets, thereby achieving in-situ growth and efficient dispersion of graphene nanosheets in magnesium melt. An intermediate alloy containing graphene modifiers is developed, and using the intermediate alloy as a carrier, rapid and efficient dispersion of graphene modifiers in magnesium-aluminum alloys is achieved. This invention utilizes the unique nanoscale effect, interface effect, and morphology effect of graphene to regulate the microstructure of the Al-C phase formed by the reaction, thereby improving the heterogeneous nucleation effect of Al-C phase on magnesium alloys.

[0013] Second, carbon-containing gases such as methane are widely available, inexpensive, and highly pure. Compared to oxygen-containing gases such as CO and CO2, modifiers prepared from carbon-containing gases like methane do not introduce magnesium oxide. The increase in magnesium oxide often weakens melt fluidity, affecting the filling and feeding processes, and thus increasing the probability of oxide inclusions, porosity, and other casting defects. This not only reduces the forming quality of the casting but also adversely affects its mechanical properties, fatigue life, and corrosion resistance. Furthermore, magnesium oxide particles adsorb onto the surface of graphene, hindering the reaction between graphene and Al, preventing optimal refining. This invention utilizes carbon-containing gases such as methane to prepare graphene-containing modifiers, which can solve these problems to the greatest extent possible.

[0014] Third, the method of this invention can be directly integrated with existing stirred casting equipment. It only requires the introduction of reactive gas into the existing gas refining system, which has good industrial compatibility and scale-up potential. At the same time, the stirring effect helps to improve the dispersion uniformity of the product and avoid the problem of poor refining effect caused by the agglomeration of nucleation particles. In addition, compared with directly introducing gas into the melt for modification treatment, this method first prepares an intermediate alloy containing graphene modifier. This method has lower equipment requirements and is more suitable for industrial production. The carbon content in the prepared intermediate alloy is easier to control, the dispersion is more uniform, and the refining effect of the modifier is more stable. Compared with traditional solid carbon modifiers, it can avoid the problem of solid carbon modifiers easily carrying oxides or moisture, reducing the risk of impurity introduction from the source. Moreover, the preparation of traditional graphene or carbon nanomaterials is complicated and expensive, and they are prone to agglomeration during the addition of them to the melt, resulting in unsatisfactory refining effect. Attached Figure Description

[0015] Figure 1 XRD pattern of carbon products in the graphene-containing modifier prepared in Example 1;

[0016] Figure 2 Raman spectroscopy of carbon products in the graphene-containing modifier prepared in Example 1;

[0017] Figure 3 The figures show metallographic images of ZM5 before and after modification treatment. In the figures, a is ZM5 alloy and b is a ZM5-10wt.% modifier casting prepared using Example 1.

[0018] Figure 4 The images show scans of ZM5 before and after modification treatment. In the images, a is the ZM5 alloy and b is the ZM5-10wt.% modifier casting prepared using Example 1.

[0019] Figure 5 The hardness of the ZM5 alloy before and after modification treatment. Detailed Implementation

[0020] The following embodiments further illustrate the content of the present invention, but should not be construed as limiting the present invention. Any modifications and substitutions made to the methods, steps, or conditions of the present invention without departing from the essence of the invention are within the scope of the present invention.

[0021] Specific Implementation Method 1: This implementation method is a method for preparing graphene-containing modifiers based on carbon-containing gas, specifically completed according to the following steps:

[0022] 1. Continuously blow SF6 / CO2 mixed gas into the crucible to prevent the magnesium melt from oxidizing and burning. Place the pure magnesium into the crucible heated to 680℃-900℃. After the pure magnesium melts, the pure magnesium melt is obtained.

[0023] 2. At a temperature of 670℃-870℃, carbon-containing gas is continuously introduced into pure magnesium melt while the pure magnesium melt is continuously stirred until graphene accounts for 0.1wt.%-5wt.% of the total mass of the melt. Then, the carbon-containing gas is stopped, stirring is stopped, the melt is allowed to stand, and then the melt is quenched to solidify, thus obtaining a graphene-containing modifier.

[0024] Furthermore, by adjusting the graphene content in the melt to 0.1 wt.%-4 wt.% of the total melt mass, the content of nucleation sites in the modifier may be altered, thereby further affecting the refining effect of the modifier on the magnesium-aluminum alloy.

[0025] Furthermore, in step two, carbon-containing gas is continuously introduced into the pure magnesium melt at a temperature of 670℃-800℃; by changing the melt reaction temperature and stirring temperature, the effects of reaction temperature and stirring temperature on the degree of reaction and the graphene formation efficiency are analyzed, thereby affecting the relative content of graphene and pure magnesium in the modifier.

[0026] Furthermore, in step two, carbon-containing gas is continuously introduced into the pure magnesium melt at a temperature of 700℃-800℃. By changing the reaction temperature, the degree of reaction during the deterioration process may be affected, thereby affecting the number and quality of nucleated particles in the melt.

[0027] The advantages of this embodiment are low cost, simple operation, cleanliness and environmental friendliness, stable and efficient grain refinement effect of the modifier, and slow grain refinement degradation. The graphene-containing modifier prepared in this embodiment is suitable for grain refinement of aluminum-magnesium alloys.

[0028] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the volume fraction of SF6 in the SF6 / CO2 mixed gas mentioned in step one is 2.4%. The other steps are the same as in Specific Implementation Method One.

[0029] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that steps one and two are both carried out under the protection of an SF6 / CO2 mixed gas to prevent the magnesium melt from oxidizing and burning. The other steps are the same as in Specific Implementation Method One or Two.

[0030] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that: the stirring speed in step two is 200 r / min-1000 r / min; the settling time in step two is 10 min-30 min. Other steps are the same as in Specific Implementation Methods One to Three.

[0031] Furthermore, the stirring speed mentioned in step two is 200 r / min-600 r / min. By changing the stirring speed of the overly reacted melt, it may affect the growth efficiency and dispersion of graphene, thereby affecting the distribution and growth morphology of graphene in the modifier.

[0032] Furthermore, the settling time mentioned in step two is 10-20 minutes; changing the settling and heat preservation time before deterioration may affect the uniformity of the internal temperature of the melt, thereby affecting the reaction efficiency and refining effect after the deteriorating agent is added.

[0033] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the carbon-containing gas mentioned in step two is methane, ethane, propane, butane, ethylene, or acetylene. The other steps are the same as in Specific Implementation Methods One to Four.

[0034] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that: in step two, the carbon-containing gas is continuously introduced into the pure magnesium melt at a flow rate of 100 mL / min to 1000 mL / min. The other steps are the same as in Specific Implementation Methods One to Five.

[0035] Furthermore, in step two, carbon-containing gas is continuously introduced into the pure magnesium melt at a flow rate of 100 mL / min-500 mL / min. By changing the gas introduction rate, the extent of the reaction and the graphene formation rate may be affected, thereby affecting the preparation speed of the graphene-containing modifier. At the same time, the gas flow rate affects the bubble size, which in turn affects the growth morphology and dispersion degree of graphene in the modifier.

[0036] Specific Implementation Method Seven: This implementation method is prepared by any one of Specific Implementation Methods One to Six.

[0037] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that it involves the application of the graphene-containing modifier in refining the grain size and improving the mechanical properties of magnesium-aluminum alloy castings. The other steps are the same as in Specific Implementation Methods One to Seven.

[0038] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the application of the graphene-containing modifier in refining the grain size and improving the mechanical properties of magnesium-aluminum alloy castings is specifically accomplished according to the following steps:

[0039] 1. Place the magnesium-aluminum alloy into a crucible heated to 680℃-900℃ to melt it. Continuously blow a mixture of SF6 / CO2 gas into the crucible opening to prevent the melt from oxidizing and burning. After the magnesium-aluminum alloy melts, adjust the temperature to 700℃-850℃ and hold it at that temperature. After holding, add the graphene-containing modifier preheated to 100℃-200℃ into the magnesium-aluminum alloy melt. Let it stand until it melts completely, then stir it to ensure that the graphene-containing modifier is evenly dispersed and reacts fully.

[0040] 2. After stirring, adjust the melt temperature to 700℃-800℃ and hold it at that temperature. After holding, remove the slag and pour the melt into a preheated mold. After pouring, let it stand to allow it to solidify completely, and finally demold it to obtain a casting with refined grains and improved mechanical properties. Other steps are the same as in specific implementation methods one to eight.

[0041] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in the following ways: Steps One and Two are both carried out under the protection of an SF6 / CO2 mixed gas to prevent oxidation and combustion of the magnesium melt; the holding time in Step One is 5-40 minutes; the amount of graphene-containing modifier added in Step One is 1%-20% of the mass of the magnesium-aluminum alloy; the settling time in Step One is 5-30 minutes; the stirring time in Step One is 10-40 minutes; the volume fraction of SF6 in the SF6 / CO2 mixed gas is 2.4%; the holding time in Step Two is 5-120 minutes; the temperature of the mold in Step Two is 200℃-400℃; the settling time in Step Two is 20-30 minutes. Other steps are the same as in Specific Implementation Methods One to Eight.

[0042] Furthermore, the amount of graphene-containing modifier added in step one is 5%-20% of the mass of the magnesium-aluminum alloy; the effects of adding different amounts of modifier on the refining effect of the magnesium-aluminum alloy and the limits of the refining effect of the modifier are analyzed.

[0043] Furthermore, the settling time mentioned in step one is 10-30 minutes; changing the settling time after adding the modifier may affect the degree of melting of the modifier and the number of nucleated particles in the melt, thereby affecting the refining effect after adding the modifier.

[0044] Furthermore, the stirring time mentioned in step one is 20-40 minutes; by changing the stirring time, the degree of reaction of the modifier and the degree of dispersion of nucleated particles may be affected, thereby affecting the refining efficiency of the modifier.

[0045] Furthermore, after stirring is completed in step two, the melt temperature is adjusted to 720℃-800℃. Changing the pouring temperature may affect the feeding and cooling rate of the melt during the pouring process, thereby affecting the integrity and grain size of the casting.

[0046] Furthermore, the heat preservation time mentioned in step two is 10 min to 120 min; changing the heat preservation time may affect the subsequent grain growth.

[0047] Furthermore, the temperature of the mold mentioned in step two is 200℃-300℃; changing the mold temperature may affect the cooling rate of the melt during the pouring process, which in turn affects the precipitation of the second phase during the cooling process, the shrinkage of the melt, and the grain size in the casting after solidification.

[0048] The beneficial effects of the present invention are verified using the following embodiments:

[0049] Example 1: A method for preparing graphene-containing modifiers based on carbon-containing gas, specifically carried out according to the following steps:

[0050] 1. Continuously blow SF6 / CO2 mixed gas into the crucible to prevent the magnesium melt from oxidizing and burning. Place pure magnesium into the crucible heated to 750°C. After the pure magnesium melts, pure magnesium melt is obtained.

[0051] 2. At a temperature of 700℃, methane is continuously introduced into pure magnesium melt at a flow rate of 150 mL / min, and the melt is continuously stirred at a speed of 600 r / min until graphene accounts for 1 wt.% of the total mass of the melt. Then, the gas supply and stirring are stopped, the melt is allowed to stand for 10 min, and then the melt is quenched to solidify, thus obtaining a graphene-containing modifier.

[0052] Both steps one and two are carried out under the protection of SF6 / CO2 mixed gas to prevent the magnesium melt from oxidizing and burning; the volume fraction of SF6 in the SF6 / CO2 mixed gas is 2.4%.

[0053] Take 40g of the graphene-containing modifier prepared in Example 1 and soak it in a 5% dilute acid solution. Since all substances in the modifier except the carbon product are soluble in acid, after the sample is completely dissolved, filter the solution and dry the obtained solid to obtain the carbon product. Perform XRD test on the obtained carbon product and find that a strong diffraction peak appears near 26°. Consult the PDF card and find that the diffraction peak corresponds to the (002) crystal plane of graphene. Two weaker diffraction peaks appear near 42° and 54°, which correspond to the (101) and (004) crystal planes of graphene, respectively. This indicates that the carbon product generated in the modifier is graphene and has a high degree of crystallinity.

[0054] The obtained carbon product was further subjected to Raman spectroscopy, see [link / reference]. Figure 2 As shown;

[0055] Figure 2 Raman spectroscopy of carbon products in the graphene-containing modifier prepared in Example 1;

[0056] from Figure 2 Distinct G, D, and 2D peaks of graphene can be observed. Typically, the D peak in Raman analysis represents structural defects in graphene, the G peak is a typical characteristic peak reflecting the degree of crystallinity, and the 2D peak is usually more sensitive to the number of graphene layers. The relative ratio of the D peak to the G peak (Ig) can be used to analyze the graphene structure. D / I G The ratio of the 2D peak to the G peak (I) is used to represent the defect content contained in graphene. 2D / I G ) characterizes the layer thickness of graphene, I D / IG The smaller the value, the more complete the graphene structure and the fewer defects it contains; 2D / I G The larger the value, the fewer layers the graphene contains, further indicating that the carbon product in the modifier prepared in this embodiment is a graphene nanosheet with a complete structure and multiple stacked layers.

[0057] Application Example 1: The application of the graphene-containing modifier prepared in Example 1 in refining the grain size and improving the mechanical properties of magnesium-aluminum alloy castings is specifically carried out according to the following steps:

[0058] 1. Continuously blow SF6 / CO2 mixed gas into the crucible to prevent the melt from oxidizing and burning. Place the ZM5 alloy into the crucible heated to 750℃ to melt it. After the magnesium-aluminum alloy melts, adjust the temperature to 720℃ and hold it for 10 minutes. After holding, add the graphene-containing modifier preheated to 200℃ into the magnesium-aluminum alloy melt. Let it stand for 20 minutes to melt it completely, and then stir for 10 minutes to make the graphene-containing modifier evenly dispersed and fully react.

[0059] The amount of graphene-containing modifier added in step one is 10% of the mass of the magnesium-aluminum alloy;

[0060] 2. After stirring, adjust the melt temperature to 760℃ and hold for 10 minutes. After holding, remove the slag and pour the melt into a mold preheated to 200℃. After pouring, let it stand for 20 minutes to allow it to solidify completely. Finally, demold to obtain ZM5-10wt.% modifier casting with refined grains and improved mechanical properties.

[0061] Both steps one and two are carried out under the protection of SF6 / CO2 mixed gas to prevent the magnesium melt from oxidizing and burning; the volume fraction of SF6 in the SF6 / CO2 mixed gas is 2.4%.

[0062] To ensure clear grain boundaries, ZM5 and ZM5 with added modifiers underwent solution treatment. After solution treatment, etching and metallographic observation were performed. Figure 3 As shown;

[0063] Figure 3 The figures show metallographic images of ZM5 before and after modification treatment. In the figures, a is ZM5 alloy and b is a ZM5-10wt.% modifier casting prepared using Example 1.

[0064] from Figure 3It can be observed that after adding the graphene-containing modifier prepared in Example 1, the grain size of the alloy is significantly reduced, with the average grain size decreasing from about 380 μm to about 140 μm, and the refining efficiency reaching 63%. Furthermore, the grain size after modification is more uniform, indicating that the modifier has good refining ability.

[0065] Scanning tests were performed on ZM5 samples before and after the deterioration treatment. See Figure 4 As shown;

[0066] Figure 4 The images show scans of ZM5 before and after modification treatment. In the images, a is the ZM5 alloy and b is the ZM5-10wt.% modifier casting prepared using Example 1.

[0067] from Figure 4 It can be observed that the second phase in the sample after the addition of the modifier is significantly refined, and changes from a relatively continuous long strip to a short rod shape. The results show that the graphene-containing modifier prepared in Example 1 has a good tissue refinement effect on ZM5.

[0068] Hardness tests were performed on ZM5 and ZM5 with added modifiers, see [link / reference]. Figure 5 As shown;

[0069] Figure 5 The hardness of the ZM5 alloy before and after modification treatment;

[0070] from Figure 5 It can be observed that the hardness value of ZM5 before modification is 54.1 HV. After adding the graphene-containing modifier prepared in Example 1, the hardness of the casting prepared with ZM5-10wt.% modifier in Example 1 increases to 63.2 HV, which is an increase of 9.1 HV. This indicates that the modification treatment effectively improves the mechanical properties of the material.

Claims

1. A method for preparing graphene-containing modifiers based on carbon-containing gas, characterized in that... The method is specifically implemented according to the following steps:

1. Continuously blow SF6 / CO2 mixed gas into the crucible to prevent the magnesium melt from oxidizing and burning. Place the pure magnesium into the crucible heated to 680℃-900℃. After the pure magnesium melts, the pure magnesium melt is obtained.

2. At a temperature of 670℃-870℃, carbon-containing gas is continuously introduced into pure magnesium melt while the pure magnesium melt is continuously stirred until graphene accounts for 0.1wt.%-5wt.% of the total mass of the melt. Then, the carbon-containing gas is stopped, stirring is stopped, the melt is allowed to stand, and then the melt is quenched to solidify, thus obtaining a graphene-containing modifier.

2. The method for preparing graphene-containing modifiers based on carbon-containing gas according to claim 1, characterized in that... The volume fraction of SF6 in the SF6 / CO2 mixed gas mentioned in step one is 2.4%.

3. The method for preparing graphene-containing modifiers based on carbon-containing gas according to claim 1, characterized in that... Both steps one and two are carried out under the protection of SF6 / CO2 mixed gas to prevent the magnesium melt from oxidizing and burning.

4. The method for preparing graphene-containing modifiers based on carbon-containing gas according to claim 1, characterized in that... The stirring speed in step two is 200 r / min-1000 r / min; the settling time in step two is 10 min-30 min.

5. The method for preparing graphene-containing modifiers based on carbon-containing gas according to claim 1, characterized in that... The carbon-containing gas mentioned in step two is methane, ethane, propane, butane, ethylene, or acetylene.

6. The method for preparing graphene-containing modifiers based on carbon-containing gas according to claim 1, characterized in that... In step two, carbon-containing gas is continuously introduced into the pure magnesium melt at a flow rate of 100 mL / min to 1000 mL / min.

7. A method for preparing graphene-containing modifiers based on carbon-containing gas, characterized in that... It is prepared by the method described in any one of claims 1 to 6.

8. The application of the graphene-containing modifier prepared by the method according to any one of claims 1 to 6, characterized in that... The application of the graphene-containing modifier in refining the grain size and improving the mechanical properties of magnesium-aluminum alloy castings.

9. The application of the graphene-containing modifier according to claim 8, characterized in that... The application of the graphene-containing modifier in refining the grain size and improving the mechanical properties of magnesium-aluminum alloy castings is specifically accomplished through the following steps:

1. Continuously blow SF6 / CO2 mixed gas into the crucible to prevent the melt from oxidizing and burning. Place the magnesium-aluminum alloy into the crucible heated to 680℃-900℃ to melt it. After the magnesium-aluminum alloy melts, adjust the temperature to 700℃-850℃ and hold it at that temperature. After holding at that temperature, add the graphene-containing modifier preheated to 100℃-200℃ into the magnesium-aluminum alloy melt. Let it stand until it melts completely, then stir it to make the graphene-containing modifier evenly dispersed and fully reacted.

2. After stirring, adjust the melt temperature to 700℃-800℃ and keep it at that temperature. After keeping it at that temperature, remove the slag and then pour the melt into a preheated mold. After pouring, let it stand to allow it to solidify completely. Finally, demold the mold to obtain a casting with refined grains and improved mechanical properties.

10. The application of the graphene-containing modifier according to claim 8, characterized in that... Both steps one and two are carried out under the protection of SF6 / CO2 mixed gas to prevent the magnesium melt from oxidizing and burning; the holding time in step one is 5 min-40 min; the amount of graphene modifier added in step one is 1%-20% of the mass of the magnesium-aluminum alloy; the settling time in step one is 5 min-30 min; the stirring time in step one is 10 min-40 min; the volume fraction of SF6 in the SF6 / CO2 mixed gas is 2.4%; the holding time in step two is 5 min-120 min; the temperature of the mold in step two is 200℃-400℃; the settling time in step two is 20 min-30 min.

Images