Magnesium alloy modifier containing graphene / magnesium oxide double-phase particles and preparation method of magnesium alloy modifier

Abstract

The invention discloses a magnesium alloy modifier containing graphene / magnesium oxide double-phase particles and a preparation method thereof, and relates to the technical field of magnesium alloys. The problem that an existing magnesium alloy modifier is poor in grain refinement effect on Mg-Al alloy is solved. The novel composite modifier containing graphene and magnesium oxide nanoparticles at the same time is prepared through a gas-liquid in-situ reaction by utilizing a chemical reaction between CO2 / CO and active metal Mg. By regulating and controlling the ratio of CO2 to CO, the ratio of graphene to magnesium oxide particles in the optimal ratio combination is obtained, and the optimal grain refinement effect and mechanical property can be ensured to be obtained. The grain refinement efficiency of the magnesium alloy modifier to Mg-Al alloy can reach 80% or above. And under the conventional casting process conditions, the grain size of the Mg-Al alloy can be reduced to be less than 50 microns, and a very remarkable grain refinement effect is achieved. The magnesium alloy modifier method has the remarkable advantages of being low in cost, simple, efficient, clean, environmentally friendly and the like, and is suitable for large-scale production.

Description

Technical Field

[0001] The present invention relates to the technical field of magnesium alloys, and particularly relates to a magnesium alloy modifier containing graphene and magnesium oxide biphasic particles and a preparation method thereof. Background Art

[0002] Due to excellent specific strength and specific stiffness, significant low-density advantages, and good forming properties, alloys are widely used in the fields of aerospace, national defense, and digital communication, and have become the most potential lightweight metal materials at present. At present, the casting forming technology is the main processing method for magnesium alloy products. In particular, casting alloys represented by the Mg-Al system, such as AZ91 and AZ61, have been widely used in products such as aero engines and automobile wheels. However, due to the non-uniform diffusion of solute atoms and the rapid growth of the second phase during the casting process, the magnesium alloy products formed by casting often face problems such as coarse microstructure and poor mechanical properties, which seriously limit the application and development of magnesium alloys.

[0003] Grain refinement is the most effective method to improve the microstructure of alloys and enhance the strength and plasticity of castings. By adding a modifier to the magnesium alloy melt, the microstructure of the alloy can be effectively refined, and casting defects such as shrinkage and shrinkage can be eliminated, significantly improving the metallurgical quality of the casting. This method has become a commonly used refinement method in the field of magnesium alloys because of its simplicity, high efficiency, and easy operation. At present, magnesium alloy modifiers are usually mainly based on the addition of intermediate alloys containing Zr elements. However, for Mg-Al alloys, since Zr elements easily react with Al elements to form a precipitate phase, the Mg-Al alloy cannot be refined, which is also called Zr poisoning phenomenon. For Mg-Al alloys, commonly used modifiers are mainly based on the addition of particles or compounds containing carbon elements, such as graphite particles, MgCO3, MnCO3, etc. However, due to the poor interface wettability between carbon elements and magnesium elements, it is difficult to disperse them evenly in the melt, resulting in low final grain refinement efficiency and unsatisfactory refinement effect. Therefore, there has been a lack of efficient modifiers for the most commonly used Mg-Al alloys, which has seriously hindered the industrialization process and development of magnesium alloys. Therefore, it is of great significance to promote the leapfrog development of magnesium alloys from the laboratory stage to industrial application by designing and developing new low-cost, green magnesium alloy modifiers. Patent CN109554573A and patent CN113265553 A disclose methods for preparing magnesium alloy modifiers using a single gas of CO or CO2. Both methods can achieve the grain refinement effect on Mg-Al alloys. However, the ratio of graphene to MgO particles in the modifier prepared by a single gas is fixed, and it is impossible to achieve the regulation of the ratio of the two. The ratio regulation of graphene to MgO particles is a key factor affecting its grain refinement effect. In the process of grain refinement of magnesium alloys using graphene / magnesium oxide composite modifiers, the ratio regulation between graphene / MgO particles affects its distribution morphology in the magnesium alloy melt and affects its final refinement effect. The content of MgO particles in the composite modifier prepared by CO gas is relatively low, resulting in an insignificant final refining effect; the content of MgO particles in the composite modifier synthesized by CO2 gas is relatively high, resulting in the agglomeration of MgO particles and weakening the refining effect. Summary of the invention

[0004] In order to solve the problem that the existing magnesium alloy modifier has poor grain refining effect on Mg-Al alloy, the present invention proposes a low-cost, high-efficiency, easy-to-disperse novel modifier and its preparation method. The main components of the magnesium alloy modifier of the present invention are dual-phase nanoparticles of graphene and magnesium oxide. During the preparation process, the ratio of CO to CO2 is controlled to prepare a novel composite modifier containing graphene and magnesium oxide particles.

[0005] In the magnesium alloy modifier containing graphene / magnesium oxide biphasic particles of the present invention, the content of Si element is 0.1-2 wt.%, the content of graphene is 0.1-10 wt.%, the content of magnesium oxide is 0.1-20 wt.%, and the rest is Mg;

[0006] The preparation method of the magnesium alloy modifier containing graphene / magnesium oxide biphasic particles of the present invention is carried out according to the following steps:

[0007] 1. Weigh pure Mg ingots and Mg-Si master alloy as raw materials according to the contents of Si element and Mg element in the magnesium alloy modifier, and pretreat the raw materials;

[0008] 2. Mix CO and CO2, and pretreat the mixed gas;

[0009] The volume ratio of the CO to the CO2 is (1-5):(1-20); by regulating different gas ratios, the generation amounts of graphene and magnesium oxide particles in the magnesium alloy modifier can be effectively regulated;

[0010] The pretreatment process of the mixed gas is: cleaning the gas with sulfuric acid solution to effectively remove impurities such as water vapor contained in the gas;

[0011] 3. Preheat the raw materials treated in step 1, and then carry out melting under a protective atmosphere to obtain an alloy melt;

[0012] The gas of the protective atmosphere is a mixed gas of SF6 and CO2;

[0013] The melting process is: under a protective atmosphere, first melt the pure Mg ingots, then add the Mg-Si master alloy, stir the mixture after the master alloy is completely melted, and finally keep it static and heat-insulated to obtain a Mg-Si alloy melt;

[0014] The melting temperature of the pure Mg ingots is 700-760 °C;

[0015] 4. Pass the mixed gas treated in step 2 into the Mg-Si alloy melt obtained in step 3 for in-situ reaction, carry out mechanical stirring during the in-situ reaction process, and finally water-cool the alloy after the reaction is completed to obtain a magnesium alloy modifier containing graphene and magnesium oxide particles;

[0016] The temperature of the in-situ reaction is 680 °C to 750 °C, and the time is 20 min to 120 min;

[0017] The flow rate of the mixed gas is 0.2 L / min to 2 L / min.

[0018] The principle and beneficial technical effects of the present invention are as follows:

[0019] 1. The present invention utilizes the chemical reaction between CO2 / CO and active metal Mg to prepare a novel composite modifier containing both graphene and magnesium oxide nanoparticles through a gas-liquid in-situ reaction. The present invention obtains the optimal ratio of graphene and magnesium oxide particles by regulating the ratio of CO2 to CO, thereby ensuring the best grain refinement effect and mechanical property improvement.

[0020] Graphene mainly achieves the refinement effect by regulating the early nucleation stage of the grains, while MgO particles mainly achieve the refinement effect by hindering the grain growth process and modifying the graphene interface with MgO particles. The present invention significantly improves the wettability of the C-Mg interface by modifying the interface with MgO nanoparticles, that is, improves the uniformity of graphene dispersion in the melt, so that the prepared new modifier has a significant easy-to-disperse characteristic, and improves the refinement effect of the composite modifier. By regulating the ratio of different graphene / magnesium oxide, the whole process of crystal nucleation and growth process is regulated to obtain the best refinement effect. In addition, MgO particles can play a strengthening effect of pinning dislocations, and the strengthening effect provided by a small amount of MgO particles is not obvious. Excessive MgO particles will agglomerate in the melt and produce stress concentration, resulting in performance degradation. Therefore, only MgO particles with an appropriate content can obtain a significant mechanical property improvement effect. Too few MgO particles cannot provide sufficient strengthening effect, and too many MgO particles will cause clusters to form in the melt, resulting in stress concentration and microcracks, which will damage the mechanical properties of the alloy. Therefore, only by fully controlling the content of MgO particles can a significant improvement in mechanical properties be achieved.

[0021] In the prior art, a single gas is used to react in situ with a pure Mg melt, and a graphene powder is obtained, but the graphene has many defects and a small area. The present invention uses a mixed gas to react in situ with a Mg-Si alloy. By adding Si elements to the melt, the activation energy of graphene nucleation can be significantly reduced, so that the graphene nuclei are more evenly distributed, and the grain boundary defects caused by uneven nucleation are reduced. In addition, Si atoms have a strong chemical affinity for oxygen atoms. Compared with C elements, Si elements preferentially react with oxygen atoms mixed in the magnesium melt to generate SiO2, reducing the destruction of the sp2 bond of graphene by oxygen elements, thereby reducing oxygen-containing defects and microscopic holes, realizing the catalysis and regulation of in-situ generated graphene, significantly reducing the lattice defects and microscopic holes of graphene, so that the prepared graphene has significant advantages such as few defects, thin layers, and large area, thereby greatly improving the quality of graphene.

[0022] The grain refinement efficiency of the magnesium alloy modifier containing graphene / magnesium oxide composite particles of the present invention for Mg-Al series alloys can reach more than 80%. Under the conditions of conventional casting process, the grain size of Mg-Al alloy can be reduced to less than 50 μm, showing a very significant grain refinement effect.

[0023] 2. In the present invention, the graphene and magnesium oxide particles prepared by the in-situ gas-liquid reaction technology are of nanoscale. Compared with the traditional micron-scale magnesium alloy modifiers, the nanoscale modifiers have a more efficient refinement effect and a more significant improvement in the mechanical properties of magnesium alloys. Therefore, the nanoscale magnesium alloy modifier prepared by the present invention has more excellent refinement efficacy and performance improvement ability. The development of this magnesium alloy modifier can meet the strategic needs of national key engineering fields such as precision components in national defense and military industries, and the chassis of new energy vehicles for material lightweighting, and promote the industrial application process of magnesium alloys.

[0024] 3. The method of the magnesium alloy modifier of the present invention has significant advantages such as low cost, simple and efficient, clean and environmentally friendly, and is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 XRD pattern of graphene in the magnesium alloy modifier prepared in Example 1;

[0026] Figure 2 Raman characterization pattern of graphene in the magnesium alloy modifier prepared in Example 1;

[0027] Figure 3 Transmission electron microscopy image of the microstructure of graphene in the magnesium alloy modifier prepared in Example 1;

[0028] Figure 4 Transmission electron microscopy image (high magnification) of the microstructure of graphene in the magnesium alloy modifier prepared in Example 1;

[0029] Figure 5 Scanning electron microscopy image of the morphology of the distribution of graphene / magnesium oxide in the magnesium alloy modifier prepared in Example 1;

[0030] Figure 6 Comparative analysis diagram of the grain refinement of AZ91 alloy by the magnesium alloy modifier prepared in Example 1;

[0031] Figure 7 Tensile engineering stress-engineering strain curves of AZ91 alloy before and after grain refinement by the magnesium alloy modifier prepared in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0032] The technical solution of the present invention is not limited to the specific embodiments listed below, and also includes any reasonable combination between the specific embodiments.

[0033] Embodiment 1: In the magnesium alloy modifier containing graphene / magnesium oxide biphasic particles of this embodiment, the content of Si element is 0.1 - 2 wt.%, the content of graphene is 0.1 - 10 wt.%, the content of magnesium oxide is 0.1 - 20 wt.%, and the rest is Mg.

[0034] This embodiment has the following beneficial effects:

[0035] 1. The composite modifier prepared in this embodiment contains both graphene and magnesium oxide nanoparticles, thus ensuring that the best grain refinement effect and mechanical property improvement can be obtained.

[0036] Graphene mainly realizes the refinement effect by regulating the nucleation stage of grains in the early stage, while MgO particles mainly play a refinement effect by hindering the grain growth process and using MgO particles to modify the graphene interface. In this embodiment, through the modification of the interface by MgO nanoparticles, the wettability of the C-Mg interface is significantly improved, that is, the dispersion uniformity of graphene in the melt is improved, making the prepared new modifier have a significant easy-dispersion characteristic and improving the refinement effect of the composite modifier. By regulating the ratio of different graphene / magnesium oxide, the whole process of crystal nucleation and growth can be regulated, so as to obtain the best refinement effect. In addition, MgO particles can play a strengthening effect of pinning dislocations. The strengthening effect provided by a small amount of MgO particles is not obvious, and excessive MgO particles will agglomerate in the melt and cause stress concentration, resulting in performance degradation. Therefore, only an appropriate content of MgO particles can obtain a significant improvement in mechanical properties. Too few MgO particles cannot provide sufficient strengthening effect, and too many MgO particles will form clusters in the melt, resulting in stress concentration and generating microcracks, which will damage the mechanical properties of the alloy. Therefore, only by fully regulating the content of MgO particles can a significant improvement in mechanical properties be achieved.

[0037] The grain refinement efficiency of the magnesium alloy modifier containing graphene / magnesium oxide composite particles of this embodiment for Mg-Al alloys can reach more than 80%. Under the conditions of conventional casting process, the grain size of Mg-Al alloy can be reduced to less than 50 μm, with a very significant grain refinement effect.

[0038] 2. In this embodiment, graphene and magnesium oxide particles are of nano-size. Compared with traditional micron-sized magnesium alloy modifiers, nano-sized modifiers have a more efficient refinement effect and a more significant improvement in the mechanical properties of magnesium alloys. Therefore, the nano-sized magnesium alloy modifier prepared in this embodiment has more excellent refinement efficacy and performance improvement ability. The development of this magnesium alloy modifier can meet the strategic needs of material lightweighting in key national engineering fields such as precision components in national defense and military industries and the chassis of new energy vehicles, and promote the industrial application process of magnesium alloys.

[0039] 3. The method of the magnesium alloy modifier in this embodiment has significant advantages such as low cost, simplicity, high efficiency, cleanliness, and environmental protection, and is suitable for large-scale production.

[0040] Specific Embodiment 2: The preparation method of the magnesium alloy modifier containing graphene / magnesium oxide biphasic particles in this embodiment is carried out according to the following steps:

[0041] I. Weigh pure Mg ingots and Mg-Si master alloy as raw materials according to the contents of Si element and Mg element in the magnesium alloy modifier, and perform pretreatment on the raw materials;

[0042] II. Mix CO and CO2, and perform pretreatment on the mixed gas;

[0043] The volume ratio of CO to CO2 is (1 - 5):(1 - 20); by regulating different gas ratios, the generation amounts of graphene and magnesium oxide particles in the magnesium alloy modifier can be effectively regulated;

[0044] The pretreatment process of the mixed gas is: cleaning the gas with sulfuric acid solution to effectively remove impurities such as water vapor contained in the gas;

[0045] III. Preheat the raw materials processed in step I, and then carry out melting under a protective atmosphere to obtain an alloy melt;

[0046] The gas of the protective atmosphere is a mixed gas of SF6 and CO2;

[0047] The melting process is: under the protective atmosphere, first melt the pure Mg ingots, then add the Mg-Si master alloy, stir after the master alloy is completely melted, and finally keep it static and heat-insulated to obtain the Mg-Si alloy melt;

[0048] The melting temperature of the pure Mg ingots is 700 - 760 °C;

[0049] IV. Introduce the mixed gas processed in Step II into the Mg-Si alloy melt obtained in Step III for in-situ reaction. During the in-situ reaction, mechanical stirring is carried out. Finally, the alloy after the reaction is water-cooled to obtain a magnesium alloy modifier containing graphene and magnesium oxide particles;

[0050] The temperature of the in-situ reaction is 680°C to 750°C, and the time is 20 min to 120 min;

[0051] The flow rate of the mixed gas is 0.2 L / min to 2 L / min.

[0052] 1. This embodiment utilizes the chemical reaction between CO2 / CO and the active metal Mg, and through gas-liquid in-situ reaction, a new type of composite modifier containing both graphene and magnesium oxide nanoparticles is prepared. In this embodiment, by adjusting the ratio of CO2 to CO, the optimal ratio combination of graphene and magnesium oxide particles is obtained, so as to ensure the best grain refinement effect and mechanical property improvement.

[0053] Graphene mainly realizes the refinement effect by regulating the nucleation stage of grains in the early stage, while MgO particles mainly play a refinement effect by hindering the grain growth process and modifying the graphene interface with MgO particles. In this embodiment, through the modification of the interface by MgO nanoparticles, the wettability of the C-Mg interface is significantly improved, that is, the dispersion uniformity of graphene in the melt is improved, making the prepared new modifier have a significant easy-dispersion characteristic and improving the refinement effect of the composite modifier. By adjusting the ratio of different graphene / magnesium oxide, the whole process of crystal nucleation and growth is regulated, so as to obtain the best refinement effect. In addition, MgO particles can play a strengthening effect of pinning dislocations. The strengthening effect provided by a small amount of MgO particles is not obvious, and excessive MgO particles will agglomerate in the melt and cause stress concentration, resulting in performance degradation. Therefore, only an appropriate content of MgO particles can achieve a significant improvement in mechanical properties. Too few MgO particles cannot provide sufficient strengthening effect, and too many MgO particles will form clusters in the melt, resulting in stress concentration and generating microcracks, which will damage the mechanical properties of the alloy. Therefore, only by fully regulating the content of MgO particles can a significant improvement in mechanical properties be achieved.

[0054] In the prior art, a single gas is used to react in situ with a pure Mg melt, and graphene powder is obtained. The graphene has many defects and a small area. The present embodiment uses a mixed gas to react in situ with a Mg-Si alloy. By adding Si elements to the melt, the activation energy of graphene nucleation can be significantly reduced, so that the graphene nuclei are more evenly distributed, and the grain boundary defects caused by uneven nucleation are reduced. In addition, Si atoms have a strong chemical affinity for oxygen atoms. Compared with C elements, Si elements preferentially react with oxygen atoms mixed in the magnesium melt to generate SiO2, reducing the destruction of the sp2 bond of graphene by oxygen elements, thereby reducing oxygen-containing defects and microscopic holes, realizing the catalysis and regulation of in-situ generated graphene, significantly reducing the lattice defects and microscopic holes of graphene, so that the prepared graphene has significant advantages such as few defects, thin layers, and large area, thereby greatly improving the quality of graphene.

[0055] The magnesium alloy modifier containing graphene / magnesium oxide composite particles of this embodiment can achieve a grain refining efficiency of Mg-Al alloy of more than 80%. Under conventional casting process conditions, the grain size of Mg-Al alloy can be reduced to less than 50 μm, which has a very significant grain refining effect.

[0056] 2. In this embodiment, the graphene and magnesium oxide particles prepared by the in-situ gas-liquid reaction technology are nano-sized. Compared with the traditional micron-sized magnesium alloy modifier, the nano-sized modifier has a more efficient refinement effect and a more significant improvement in the mechanical properties of the magnesium alloy. Therefore, the nano-sized magnesium alloy modifier prepared in this embodiment has a more excellent refinement effect and performance improvement ability. The development of this magnesium alloy modifier can meet the strategic needs of national key engineering fields such as precision components of national defense and military industry, chassis of new energy vehicles, etc. for lightweight materials, and promote the industrial application process of magnesium alloys.

[0057] 3. The magnesium alloy modifier method of this embodiment has significant advantages such as low cost, simplicity, high efficiency, cleanliness and environmental protection, and is suitable for large-scale production.

[0058] Specific implementation method three: This implementation method is different from specific implementation method two in that: the raw material pretreatment process described in step one is: grinding the raw material with coarse sandpaper to remove surface oxide scale and impurities.

[0059] Specific embodiment 4: This embodiment differs from specific embodiment 2 in that: in the magnesium alloy modifier described in step 1, the content of Si element is 0.1-2wt.%, the content of graphene is 0.1-5wt.%, the content of magnesium oxide is 0.1-20wt.%, and the rest is Mg.

[0060] Specific Embodiment 5: The difference between this embodiment and Specific Embodiment 2 is that: the concentration of the sulfuric acid solution described in Step 2 is 0.5 mol / L.

[0061] Specific Embodiment 6: The difference between this embodiment and Specific Embodiment 2 is that: the preheating treatment temperature described in Step 3 is 200°C to 350°C.

[0062] Specific Embodiment 7: The difference between this embodiment and Specific Embodiment 2 is that: in the mixed gas of SF6 and CO2 described in Step 3, the volume of SF6 is 1% to 5%, and the balance is CO2.

[0063] Specific Embodiment 8: The difference between this embodiment and Specific Embodiment 2 is that: the stirring treatment time described in Step 3 is 10 to 40 s.

[0064] Specific Embodiment 9: The difference between this embodiment and Specific Embodiment 2 is that: the standing and heat preservation time described in Step 3 is 10 to 20 min.

[0065] Specific Embodiment 10: The difference between this embodiment and Specific Embodiment 2 is that: the mechanical stirring speed described in Step 4 is 500 r / min to 2000 r / min.

[0066] Example 1

[0067] The preparation method of the magnesium alloy modifier containing graphene / magnesium oxide biphasic particles in this example is carried out according to the following steps:

[0068] I. Weigh pure Mg ingots and Mg-20Si master alloy as raw materials according to the contents of Si element and Mg element in the magnesium alloy modifier, and perform pretreatment on the raw materials;

[0069] The raw material pretreatment process is: use coarse sandpaper to polish the raw materials to remove the surface oxide scale and impurities;

[0070] In the magnesium alloy modifier, the content of Si element is 0.5 wt.%, the content of graphene is 0.5 wt.%, the content of magnesium oxide is 3 wt.%, and the rest is Mg;

[0071] II. Mix CO and CO2, and perform pretreatment on the mixed gas;

[0072] The volume ratio of CO to CO2 is 1:1; by adjusting different gas ratios, the generation amounts of graphene and magnesium oxide particles in the magnesium alloy modifier can be effectively regulated;

[0073] The pretreatment process of the mixed gas is: wash the gas with sulfuric acid solution to effectively remove impurities such as water vapor contained in the gas; the concentration of the sulfuric acid solution is 0.5 mol / L;

[0074] III. Preheat the raw materials processed in Step I, and then carry out smelting under a protective atmosphere to obtain an alloy melt;

[0075] The temperature of the preheating treatment is 250 °C;

[0076] The gas of the protective atmosphere is a mixed gas of SF6 and CO2. The volume of SF6 in the mixed gas is 3%, and the balance is CO2;

[0077] The process of the smelting is as follows: Under a protective atmosphere, first melt the pure Mg ingot, then add the Mg-Si master alloy. After the master alloy is completely melted, carry out stirring treatment, and finally keep it static and heat-insulated to obtain a Mg-Si alloy melt;

[0078] The melting temperature of the pure Mg ingot is 700 °C;

[0079] The time of the stirring treatment is 25 s;

[0080] The time of the static heat-insulation is 15 min;

[0081] IV. Pass the mixed gas processed in Step II into the Mg-Si alloy melt obtained in Step III for in-situ reaction. During the in-situ reaction process, carry out mechanical stirring. Finally, water-cool the alloy after the reaction is completed. The water-cooling temperature is 25 °C to obtain a magnesium alloy modifier containing graphene and magnesium oxide particles.

[0082] The temperature of the in-situ reaction is 700 °C, and the time is 80 min;

[0083] The flow rate of the mixed gas is 996 L / min;

[0084] The mechanical stirring speed is 1000 r / min;

[0085] In this example, through gas-liquid in-situ reaction, the prepared graphene has the characteristics of less defect content, high C atom crystallization degree, fewer graphene layers and large sheet diameter, which is significantly better than the quality of graphene synthesized by the current in-situ preparation method. This is because the addition of Si atoms significantly optimizes the crystallization of C atoms and reduces the energy barrier of intermolecular binding force, thereby promoting the improvement of graphene quality. In addition, through the mixing of CO and CO in a specific ratio, compared with the composite modifier synthesized by a single CO or CO2 gas, through the optimization of the ratio, the regulation of the ratio of graphene and magnesium oxide particles in the matrix is realized, thereby optimizing the regulation effect of the composite modifier on the grain nucleation and growth process, reducing the content of magnesium oxide particles in the melt, and enhancing the strengthening effect on the mechanical properties of the material.

[0086] The specific process of using the magnesium alloy modifier prepared in this example to refine the grains of AZ91 alloy is as follows: First, melt the AZ91 alloy at 720 °C and hold for 20 min. Then add the prepared magnesium alloy modifier to the AZ91 alloy melt, with an addition content of 3 wt.%, hold for 5 min, stir counterclockwise with a metal stirrer for 30 s, and hold for 20 min. Finally, pour the melt after modification treatment into a mold to obtain AZ91 specimens.

[0087] The magnesium alloy modifier prepared in this example can reduce the grain size of AZ91 alloy from 245 μm to 21 μm, and the grain refinement efficiency reaches 91%. The grain refinement efficiency is calculated as follows:

[0088]

[0089] In the formula, α represents the grain refinement efficiency, d before refinement represents the average grain size of the alloy without refinement treatment, and d after refinement represents the average grain size of the alloy after grain refinement treatment.

[0090] At the same time, the yield strength of the refined AZ91 alloy can be increased from 68 MPa to 109 MPa, and the elongation is also significantly improved. The grain refinement ability is significantly better than that of most magnesium alloy modifiers.

[0091] Figure 1 For the microstructure analysis of the graphene prepared in Example 1, as Figure 1 and Figure 2 shown, XRD and Raman analyses show that the graphene prepared by in-situ reaction has high crystal crystallinity, low graphene defect content, and thin layer thickness and other significant characteristics. Figure 3 is the transmission electron microscope image of the microstructure of graphene in the magnesium alloy modifier prepared in Example 1; Figure 4 is the transmission electron microscope image (high magnification) of the microstructure of graphene in the magnesium alloy modifier prepared in Example 1; it is found that the microstructure of the graphene prepared in Example 1 is relatively complete, the graphene sheet diameter size is large, and the number of layers is small. Figure 5 is the scanning electron microscope image of the morphology of the graphene / magnesium oxide distribution in the magnesium alloy modifier prepared in Example 1; it can be found that the distribution of graphene and magnesium oxide particles in the composite modifier prepared in Example 1 is relatively uniform, and no obvious agglomeration occurs. Figure 6 is the comparative analysis diagram of the grain refinement of AZ91 alloy by the magnesium alloy modifier prepared in Example 1; it shows that the composite modifier prepared in Example 1 has a significant grain refinement effect. Figure 5 is the mechanical property test analysis of AZ91 alloy before and after grain refinement by the composite modifier prepared in Example 1, Figure 7The tensile engineering stress-engineering strain curves of the AZ91 alloy before and after grain refinement by the magnesium alloy modifier prepared in Example 1 show that the mechanical properties of the AZ91 alloy after grain refinement are greatly improved.

[0092] Example 2

[0093] The difference between this example and Example 1 is that the volume ratio of CO to CO2 is 2:1; in the prepared magnesium alloy modifier, the content of Si element is 0.5 wt.%, the content of graphene is 0.5 wt.%, the content of magnesium oxide is 2.5 wt.%, and the rest is Mg;

[0094] The magnesium alloy modifier prepared in this example can reduce the grain size of the AZ91 alloy from 252 μm to 35 μm, and the grain refinement efficiency reaches 86%. The yield strength of the AZ91 alloy after refinement can be increased from 68 MPa to 92 MPa, and the elongation is increased by 5%.

[0095] Example 3

[0096] The difference between this example and Example 1 is that the volume ratio of CO to CO2 is 4:1; in the prepared magnesium alloy modifier, the content of Si element is 0.5 wt.%, the content of graphene is 0.5 wt.%, the content of magnesium oxide is 2 wt.%, and the rest is Mg;

[0097] The magnesium alloy modifier prepared in this example can reduce the grain size of the AZ91 alloy from 253 μm to 43 μm, and the grain refinement efficiency reaches 87%. The yield strength of the AZ91 alloy after refinement can be increased from 68 MPa to 89 MPa, and the elongation is increased by 8%.

[0098] Example 4

[0099] The difference between this example and Example 1 is that the volume ratio of CO to CO2 is 6:1; in the prepared magnesium alloy modifier, the content of Si element is 0.5 wt.%, the content of graphene is 0.5 wt.%, the content of magnesium oxide is 1.5 wt.%, and the rest is Mg;

[0100] The magnesium alloy modifier prepared in this example can reduce the grain size of the AZ91 alloy from 256 μm to 50 μm, and the grain refinement efficiency reaches 85%. The yield strength of the AZ91 alloy after refinement can be increased from 68 MPa to 79 MPa, and the elongation is increased by 10%.

Claims

1. A magnesium alloy modifier containing graphene / magnesium oxide dual-phase particles, characterized in that: In the magnesium alloy modifier containing graphene / magnesium oxide dual-phase particles, the content of Si element is 0.1-2wt.%, the content of graphene is 0.1-10wt.%, the content of magnesium oxide is 0.1-20wt.%, and the rest is Mg.

2. The method for preparing a magnesium alloy modifier containing graphene / magnesium oxide dual-phase particles according to claim 1, characterized in that: The preparation method of the magnesium alloy modifier containing graphene / magnesium oxide dual-phase particles is carried out according to the following steps:

1. According to the content of Si element and Mg element in the magnesium alloy modifier, pure Mg ingot and Mg-Si master alloy are weighed as raw materials, and the raw materials are pretreated; 2. Mix CO and CO2 and pre-treat the mixed gas; The volume ratio of CO to CO2 is (1-5):(1-20); The pretreatment process of the mixed gas is: cleaning the gas with a sulfuric acid solution; 3. Preheating the raw materials after the treatment in step 1, and then smelting them under a protective atmosphere to obtain an alloy melt; The protective atmosphere gas is a mixture of SF6 and CO2; The smelting process is as follows: firstly, a pure Mg ingot is melted in a protective atmosphere, then a Mg-Si master alloy is added, and after the master alloy is completely melted, a stirring process is performed, and finally, the Mg-Si alloy melt is kept at a static temperature to obtain a Mg-Si alloy melt; The melting temperature of the pure Mg ingot is 700-760°C; Fourth, the mixed gas treated in step 2 is introduced into the Mg-Si alloy melt obtained in step 3 for in-situ reaction, mechanical stirring is performed during the in-situ reaction, and finally the alloy after the reaction is completed is water-cooled to obtain a magnesium alloy modifier containing graphene and magnesium oxide particles; The temperature of the in-situ reaction is 680°C to 750°C, and the time is 20min to 120min; The flow rate of the mixed gas is 0.2L / min to 2L / min.

3. The method for preparing a magnesium alloy modifier containing graphene / magnesium oxide dual-phase particles according to claim 2, characterized in that: The raw material pretreatment process described in step 1 is: grinding the raw material with coarse sandpaper to remove surface oxide scale and impurities.

4. The method for preparing a magnesium alloy modifier containing graphene / magnesium oxide dual-phase particles according to claim 2, characterized in that: In the magnesium alloy modifier of step 1, the content of Si element is 0.1-2wt.%, the content of graphene is 0.1-5wt.%, the content of magnesium oxide is 0.1-20wt.%, and the rest is Mg.

5. The method for preparing a magnesium alloy modifier containing graphene / magnesium oxide dual-phase particles according to claim 2, characterized in that: The concentration of the sulfuric acid solution in step 2 is 0.5 mol / L.

6. The method for preparing a magnesium alloy modifier containing graphene / magnesium oxide dual-phase particles according to claim 2, characterized in that: The preheating temperature in step 3 is 200°C to 350°C.

7. The method for preparing a magnesium alloy modifier containing graphene / magnesium oxide dual-phase particles according to claim 2, characterized in that: In step 3, the volume of SF6 in the mixed gas of SF6 and CO2 is 1% to 5%, and the remainder is CO2.

8. The method for preparing a magnesium alloy modifier containing graphene / magnesium oxide dual-phase particles according to claim 2, characterized in that: The stirring time in step 3 is 10 to 40 seconds.

9. The method for preparing a magnesium alloy modifier containing graphene / magnesium oxide dual-phase particles according to claim 2, characterized in that: The time of standing and keeping warm in step 3 is 10 to 20 minutes.

10. The method for preparing a magnesium alloy modifier containing graphene / magnesium oxide dual-phase particles according to claim 2, characterized in that: The mechanical stirring speed described in step 4 is 500r / min~2000r / min.

Images