A low-cost low-density high-modulus magnesium alloy and a method for producing the same

Abstract

The application provides a low-cost low-density high-modulus magnesium alloy and a preparation method thereof, the magnesium alloy contains the following elements in the following mass percentages: Al accounts for (2.5-5) wt%, Ca accounts for (2-4) wt%, Mn accounts for (0.2-0.6) wt%, SiC particles account for (3.5-6.5) wt%, and the rest is Mg and inevitable impurities; the preparation method comprises the following steps: mechanical stirring is performed on the melt, SiC particles are quickly added after the melt forms a stable vortex, the SiC particles are uniformly distributed in the melt after continuous stirring after the addition of the SiC particles is completed, secondary dispersion of the SiC particles in the melt is realized through ultrasonic treatment, the magnesium alloy ingot is obtained through the mode of air cooling first and then water cooling, three-up and three-down is performed after homogenization treatment, and extrusion deformation is performed. 3 The application meets the urgent demand of the lightweight field for low-density high-modulus materials and low-cost materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnesium alloy preparation, and in particular relates to a low-cost, low-density, high-modulus magnesium alloy and a preparation method thereof. Background Art

[0002] As a new generation of lightweight, green engineering structural materials, magnesium alloys offer the inherent advantages of low density and high specific strength, holding enormous potential for weight reduction in equipment design. However, the elastic modulus of conventional magnesium alloys is less than 45 GPa, resulting in insufficient resistance to elastic deformation. This shortcoming significantly limits their application in engineering. Therefore, developing a new generation of magnesium alloys with both high modulus and high strength and toughness is of great significance.

[0003] At present, the main methods for improving the elastic modulus of magnesium alloys are alloying and compounding. Traditional alloying methods have limited effect on improving the elastic modulus and toughness of magnesium alloys. Alloying methods are mainly used for rare earth magnesium alloys. Although adding a large amount of rare earth elements such as Gd, Y or Ce can improve the elastic modulus and toughness of the material, due to the high density of rare earth elements, the large amount of addition makes the density of magnesium alloys reach 2.0g / cm 3 The density of magnesium alloys is higher than that of aluminum alloys, which is contrary to the lightweight design concept of materials. At the same time, the addition of precious rare earth elements makes the preparation cost of materials remain high. In the prior art, the solution of document CN 114318093A increases the elastic modulus of magnesium alloys by adding Li elements. However, since the preparation of Mg-Li alloys requires specific vacuum melting equipment, the manufacturing cost is high, and the improvement of the elastic modulus of magnesium alloys by Li elements is limited. The elastic modulus of the prepared materials is lower than 60GPa. The solution of document CN 114686738A increases the elastic modulus of magnesium alloys by adding rare earth elements such as Ce. However, rare earth elements are not only expensive but also have high density, resulting in the density of the prepared magnesium alloy reaching (2.13~3.24) g / cm 3 , and even its density exceeds that of aluminum alloy, but its elastic modulus is far lower than that of aluminum alloy; in the solution of document CN109972009A, by adding one or more of the RE rare earth elements Gd, Y, Sm, Nd, Er, Eu, Ho, Tm, Lu, Dy, and Yb, the cost of preparing magnesium alloy is high, and the density of the material is greatly increased. Moreover, the elastic modulus of the prepared magnesium alloy is lower than 55 GPa.

[0004] In summary, magnesium alloys struggle to balance elastic modulus, density, and cost, hindering their potential for widespread, large-scale lightweight applications. The development of low-cost, low-density, high-modulus magnesium alloys has been a key research topic in recent years. Summary of the Invention

[0005] At least to solve the technical problems mentioned in the background art, the present application aims to provide a low-cost low-density high-modulus magnesium alloy and a preparation method thereof.

[0006] The present application adopts the following technical solutions.

[0007] A low-cost low-density high-modulus magnesium alloy, characterized in that the mass percentage of each element in the magnesium alloy is as follows:

[0008] Al accounts for (2.5-5) wt%, Ca accounts for (2-4) wt%, Mn accounts for (0.2-0.6) wt%, SiC particles account for (3.5-6.5) wt%, and the balance is Mg and inevitable impurities; wherein the SiC particles are composed of nano-SiC particles and micro-SiC particles, and the mass ratio of micro-SiC particles to nano-SiC particles is 6:1-4:1.

[0009] As a preferred solution, the average particle size of micro-SiC particles is 20 μm, and the average particle size of nano-SiC particles is 60 nm.

[0010] As one of the more preferred solutions, the mass percentage of each element in the magnesium alloy is as follows: Al accounts for 3.5 wt%, Ca accounts for 3 wt%, Mn accounts for 0.3 wt%, SiC particles account for 5.4 wt%, and the balance is Mg and inevitable impurities; wherein the mass ratio of micro-SiC particles to nano-SiC particles is 5:1. As another of the more preferred solutions, the mass percentage of each element in the magnesium alloy is as follows: Al accounts for 5 wt%, Ca accounts for 4 wt%, Mn accounts for 0.5 wt%, SiC particles account for 6.5 wt%, and the balance is Mg and inevitable impurities; wherein the mass ratio of micro-SiC particles to nano-SiC particles is 4:1. As a third of the more preferred solutions, the mass percentage of each element in the magnesium alloy is as follows: Al accounts for 3 wt%, Ca accounts for 2 wt%, Mn accounts for 0.6 wt%, SiC particles account for 3.5 wt%, and the balance is Mg and inevitable impurities; wherein the mass ratio of micro-SiC particles to nano-SiC particles is 6:1.

[0011] A preparation method of the aforementioned magnesium alloy, comprising the following steps:

[0012] Step 1, using pure magnesium, pure aluminum, magnesium-calcium intermediate alloy, magnesium-manganese intermediate alloy, and micro-SiC particles and nano-SiC particles as raw materials, and performing batching;

[0013] Step 2, uniformly mixing the micro-SiC particles and nano-SiC particles prepared in step 1 by mechanical stirring, then wrapping them with aluminum foil, and then preheating the SiC particles together with pure magnesium, pure aluminum, magnesium-calcium intermediate alloy, and magnesium-manganese intermediate alloy, the preheating temperature is 150-200℃, and the preheating time is 40-60 min.

[0014] Step 3, first heat the crucible to 350-400 DEG C, then add preheated pure magnesium, while the mixed gas of CO2 and SF6 is introduced into the interior of the crucible to protect the pure magnesium from oxidation, continue to heat to 700-720 DEG C, after the pure magnesium is completely melted, sequentially add pure aluminum, magnesium calcium intermediate alloy and magnesium manganese intermediate alloy, after complete melting, slowly stir the interior of the melt to homogenize the melt;

[0015] Step 4, the melt is placed and cooled to 580-600 DEG C, so that the melt is in a semi-solid state, and the impurities on the surface of the melt are cleaned, then the melt is mechanically stirred, after the melt forms a stable vortex, the SiC particles preheated in step 2 are quickly added, and the SiC particles are uniformly distributed in the melt after continued stirring;

[0016] Step 5, the melt is placed and quickly heated to 710-730 DEG C, and the SiC particles are subjected to secondary dispersion in the melt by ultrasonic treatment, and the treatment time is 15-20 min;

[0017] Step 6, the melt is placed for a period of time, then transferred to a metal mold preheated to 300-350 DEG C, and a magnesium alloy ingot is obtained by air cooling and then water cooling;

[0018] Step 7, the oxide skin of the magnesium alloy ingot is removed, and then homogenization treatment is carried out, the homogenization treatment temperature is 480-500 DEG C, and the holding time is 5-7 h;

[0019] Step 8, the ingot after homogenization treatment is subjected to three-up and three-down, and a blank is obtained, the upsetting length-diameter ratio is controlled to be 2-2.5, and the initial forging temperature of the ingot is 460-500 DEG C;

[0020] Step 9, the blank obtained in step 8 is subjected to extrusion deformation, the blank extrusion temperature is 380-420 DEG C, the extrusion ratio is greater than 10:1, and then air cooling to room temperature.

[0021] Beneficial effects: the application alloys the Mg matrix by low-cost and low-density Al, Ca and other non-rare earth alloying elements, generates Al2Ca phase (elastic modulus is about 110 GPa) in situ, and adds specific SiC particles (elastic modulus is about 450 GPa) with low density and high modulus, so that the elastic modulus of the magnesium alloy can be improved to more than 60 GPa, and the material density can be controlled to 1.9 g / cm 3The following meets the urgent demand of low-density high-modulus materials in the field of lightweight; the application uses specific proportion of micro-nano double-scale SiC particles to match and strengthen magnesium alloy, cooperatively improves the strength and toughness and elastic modulus of the magnesium alloy, and disperses the aforementioned specific micro-nano double-scale SiC particles through a three-stage dispersion method of "semi-solid mechanical stirring + high-energy ultrasonic treatment + strong plastic deformation", effectively avoiding the agglomeration of SiC particles in the matrix alloy; the application directly completes twice plastic deformation of the magnesium alloy through one-time homogenization heating treatment, avoids the performance loss of the magnesium alloy caused by repeated heating, and through cheap raw materials and optimized strong plastic deformation process, not only reduces the production cost, but also significantly improves the elastic modulus and strength and toughness of the alloy. DETAILED DESCRIPTION

[0022] The technical solutions in the application will be described below in a clear and complete manner. Obviously, the described embodiments are only some of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the application.

[0023] Embodiment 1

[0024] A low-cost low-density high-modulus magnesium alloy (0.9nSiCp-4.5mSiCp / Mg-3.5Al-3Ca-0.3Mn) has the following mass percentages of elements: 3.5wt% of Al, 3wt% of Ca, 0.3wt% of Mn, 5.4wt% of SiC particles, and the balance of Mg and unavoidable impurities; wherein the mass ratio of micro-SiC particles to nano-SiC particles is 5:1.

[0025] The preparation method of the magnesium alloy in the embodiment is as follows:

[0026] Step 1: using pure magnesium, pure aluminum, magnesium-calcium intermediate alloy, magnesium-manganese intermediate alloy, and micro and nano SiC particles as raw materials, according to the aforementioned proportioning, considering the burning loss of each alloy element;

[0027] Step 2: mix the micro and nano SiC particles prepared in step 1 uniformly through mechanical stirring, then wrap them with aluminum foil, and then preheat the SiC particles together with pure magnesium, pure aluminum, magnesium-calcium intermediate alloy and magnesium-manganese intermediate alloy, the preheating temperature is 160℃, and the time is 60min;

[0028] Step 3, first heat the crucible to 380℃, then add preheated pure magnesium, at the same time, introduce the mixed gas of CO2 and SF6 into the crucible to protect the pure magnesium from oxidation, continue to heat to 710℃, after the pure magnesium is completely melted, add pure aluminum, magnesium-calcium intermediate alloy and magnesium-manganese intermediate alloy in sequence, after completely melted, use a strainer to slowly stir the melt inside, so that the melt is homogenized;

[0029] Step 4, let the melt stand and cool to 590℃ to make the melt in a semi-solid state, clean the impurities on the surface of the melt, then mechanically stir the melt, after the melt forms a stable vortex, quickly add the SiC particles preheated in step 2, continue to mechanically stir in one direction for 15min, then stir in the opposite direction for 15min, so that the SiC particles are preliminarily uniformly distributed in the melt;

[0030] Step 5, let the melt stand and quickly heat to 720℃, use high-energy ultrasonic equipment to treat the melt, through the cavitation and acoustic streaming effect generated by the ultrasonic wave, the SiC particles are further dispersed in the melt, the ultrasonic frequency is 20kHz, the power is 30kW, and the treatment time is 20min;

[0031] Step 6, let the melt stand for 10min, then transfer to a metal mold preheated to 320℃, and get a low-density magnesium alloy ingot by air cooling and then water cooling;

[0032] Step 7, remove the oxide skin on the surface of the ingot, then perform homogenization treatment, through adjusting the morphology and distribution of the second phase inside the ingot, the plastic deformation ability of the alloy is improved, the homogenization treatment temperature is 480℃, and the holding time is 6h;

[0033] Step 8, directly perform three-up and three-down on the ingot in step 7, the upsetting length-diameter ratio is 2, and the initial forging temperature of the ingot is 470℃;

[0034] Step 9, directly perform extrusion deformation on the blank obtained in step 8, to perform tertiary dispersion of the micro-nano scale SiC particles inside the alloy, at the same time, the alloy organization is refined, and the morphology and distribution of the strengthening phase in the alloy are further improved, the extrusion temperature of the blank is 400℃, the extrusion ratio is 12:1, and the blank is air cooled to room temperature.

[0035] Test the density, elastic modulus and room temperature tensile properties of the extruded magnesium alloy, and the results are shown in Table 1.

[0036] Table 1 Density, elastic modulus and room temperature tensile properties of magnesium alloy

[0037] Density g / cm 3 ]] Elastic modulus GPa Tensile strength MPa Yield strength MPa Elongation at break % 1.82 65 406 375 8.5

[0038] The scheme realizes the improvement of the elastic modulus of the magnesium alloy to 65 GPa while controlling the material density at 1.9 g / cm 3 Below, while rare earth elements are omitted, the magnesium alloy is reasonably considered in terms of high elastic modulus, low density and low cost.

[0039] Embodiment 2

[0040] A low-cost low-density high-modulus magnesium alloy (1.3nSiCp-5.2mSiCp / Mg-5Al-4Ca-0.5Mn), the mass percentage of each element is: Al accounts for 5wt%, Ca accounts for 4wt%, Mn accounts for 0.5wt%, SiC particles account for 6.5wt%, and the balance is Mg and inevitable impurities; wherein the mass ratio of micron SiC particles to nano SiC particles is 4:1.

[0041] The preparation method of the magnesium alloy in this embodiment is as follows:

[0042] Step 1, using pure magnesium, pure aluminum, magnesium-calcium intermediate alloy, magnesium-manganese intermediate alloy, and micron and nano SiC particles as raw materials, according to the above-mentioned proportioning, considering the burning loss of each alloy element;

[0043] Step 2, mix the micron SiC particles and nano SiC particles prepared in step 1 uniformly by mechanical stirring, then wrap them with aluminum foil, and then preheat the SiC particles with pure magnesium, pure aluminum, magnesium-calcium intermediate alloy and magnesium-manganese intermediate alloy, the preheating temperature is 180℃, and the time is 60min;

[0044] Step 3, first heat the crucible to 390℃, then add the preheated pure magnesium, at the same time, introduce the mixed gas of CO2 and SF6 into the inside of the crucible to protect the pure magnesium from oxidation, continue to heat to 715℃, after the pure magnesium is completely melted, add pure aluminum, magnesium-calcium intermediate alloy and magnesium-manganese intermediate alloy in turn, after completely melted, use a strainer to slowly stir the inside of the melt, so that the melt is homogenized;

[0045] Step 4, let the melt stand and cool down to 595℃ to make the melt in a semi-solid state, clean the impurities on the surface of the melt, then mechanically stir the melt, after the melt forms a stable vortex, quickly add the preheated SiC particles in step 2, continue to mechanically stir in one direction for 15min after the addition of SiC particles is completed, and then stir in the opposite direction for 15min, so that the SiC particles get a primary uniform distribution in the melt;

[0046] Step 5, the melt is quickly warmed to 715℃, and the melt is treated by high-energy ultrasonic equipment. The SiC particles are further dispersed in the melt by cavitation and acoustic streaming effects generated by ultrasonic waves. The ultrasonic frequency is 20 kHz, the power is 25 kW, and the treatment time is 20 min.

[0047] Step 6, the melt is left for 10 min, and then transferred to a metal mold preheated to 330℃. A low-density magnesium alloy ingot is obtained by air cooling followed by water cooling.

[0048] Step 7, the oxide skin on the surface of the ingot is removed, and then homogenization treatment is performed. The morphology and distribution of the second phase in the ingot are controlled to improve the plastic deformation ability of the alloy. The homogenization treatment temperature is 490℃, and the holding time is 6 h.

[0049] Step 8, the ingot in step 7 is directly subjected to three-up and three-down, and the upsetting length-diameter ratio is 2.2. The initial forging temperature of the ingot is 465℃.

[0050] Step 9, the billet obtained in step 8 is directly subjected to extrusion deformation. The micro-nano dual-scale SiC particles in the alloy are subjected to tertiary dispersion, and the alloy structure is refined, further improving the morphology and distribution of the strengthening phase in the alloy. The extrusion temperature of the billet is 410℃, the extrusion ratio is 20:1, and the billet is air-cooled to room temperature.

[0051] The density, elastic modulus, and room temperature tensile properties of the extruded magnesium alloy are tested, and the results are shown in Table 2.

[0052] Table 2 Density, elastic modulus, and room temperature tensile properties of magnesium alloy

[0053] Density g / cm 3 ]] Elastic modulus GPa Tensile strength MPa Yield strength MPa Elongation at break % 1.87 68 415 392 9.0

[0054] This scheme realizes the improvement of the elastic modulus of the magnesium alloy to 68 GPa while controlling the density of the material to 1.9 g / cm 3 The rare earth elements are omitted, and the effects of high elastic modulus, low density, and low cost of the magnesium alloy are reasonably considered.

[0055] Example 3

[0056] A low-cost, low-density, and high-modulus magnesium alloy (0.5nSiCp-3mSiCp / Mg-3Al-2Ca-0.6Mn) is provided. The mass percentage of each element is as follows: Al accounts for 3wt%, Ca accounts for 2wt%, Mn accounts for 0.6wt%, SiC particles account for 3.5wt%, and the balance is Mg and unavoidable impurities. The mass ratio of micron SiC particles to nano SiC particles is 6:1.

[0057] The preparation method of the magnesium alloy in this example is as follows:

[0058] Step 1, using pure magnesium, pure aluminum, magnesium calcium intermediate alloy, magnesium manganese intermediate alloy, and micron and nano SiC particles as raw materials, according to the above-mentioned proportioning, considering the burning loss of each alloy element;

[0059] Step 2, mix the micron SiC particles and nano SiC particles prepared in step 1 uniformly by mechanical stirring, then wrap them with aluminum foil, and then preheat the SiC particles with pure magnesium, pure aluminum, magnesium calcium intermediate alloy and magnesium manganese intermediate alloy, the preheating temperature is 150℃, and the time is 50min;

[0060] Step 3, first heat the crucible to 360℃, then add the preheated pure magnesium, at the same time, introduce a mixed gas of CO2 and SF6 into the inside of the crucible to protect the pure magnesium from oxidation, continue to heat to 720℃, after the pure magnesium is completely melted, add pure aluminum, magnesium calcium intermediate alloy and magnesium manganese intermediate alloy in turn, after completely melted, use a strainer to slowly stir the inside of the melt, so that the melt is homogenized;

[0061] Step 4, let the melt stand and cool down to 585℃ to make the melt in a semi-solid state, clean the impurities on the surface of the melt, then mechanically stir the melt, after the melt forms a stable vortex, quickly add the preheated SiC particles in step 2, continue to mechanically stir in one direction for 13min, and then stir in the opposite direction for 13min, so that the SiC particles are preliminarily uniformly distributed in the melt;

[0062] Step 5, let the melt stand and quickly heat to 730℃, use high-energy ultrasonic equipment to treat the melt, through the cavitation and acoustic streaming effect generated by ultrasonic waves, the SiC particles are further dispersed in the melt, the ultrasonic frequency is 20kHz, the power is 25kW, and the treatment time is 15min;

[0063] Step 6, let the melt stand for 10min, then transfer it to a metal mold preheated to 300℃, and get a low-density magnesium alloy ingot by air cooling and then water cooling;

[0064] Step 7, remove the oxide skin on the surface of the ingot, then perform homogenization treatment, control the morphology and distribution of the second phase in the ingot, and improve the plastic deformation ability of the alloy, the homogenization treatment temperature is 480℃, and the holding time is 7h;

[0065] Step 8, directly perform three-up and three-down on the ingot in step 7, the upsetting length-diameter ratio is 2.5, and the initial forging temperature of the ingot is 470℃;

[0066] Step 9, the billet obtained in step 8 is directly extruded to disperse the micro-nano scale SiC particles in the alloy, refine the structure of the alloy, and further improve the morphology and distribution of the strengthening phase in the alloy, the extrusion temperature of the billet is 390℃, the extrusion ratio is 15:1, and the billet is air-cooled to room temperature.

[0067] The density, elastic modulus and room temperature tensile properties of the extruded magnesium alloy are tested, and the results are shown in Table 3.

[0068] Table 3 Density, elastic modulus and room temperature tensile properties of the magnesium alloy

[0069] Density g / cm 3 ]] Elastic modulus GPa Tensile strength MPa Yield strength MPa Elongation at break % Elastic modulus GPa Tensile strength MPa Yield strength MPa Elongation at break % 1.79 63 398 370 10.5

[0070] The scheme realizes the improvement of the elastic modulus of the magnesium alloy to 63 GPa while the density of the material is controlled to 1.8 g / cm 3 The rare earth element is omitted at the same time, and the effects of high elastic modulus, low density and low cost of the magnesium alloy are reasonably considered.

Claims

1. A method for preparing a low-cost, low-density, high-modulus magnesium alloy, characterized in that: The mass percentages of the elements in the magnesium alloy are as follows: Al accounts for (2.5-5) wt%, Ca accounts for (2-4) wt%, Mn accounts for (0.2-0.6) wt%, SiC particles account for (3.5-6.5) wt%, and the balance is Mg and unavoidable impurities; wherein the SiC particles are composed of nano-SiC particles and micron-SiC particles, and the mass ratio of micron-SiC particles to nano-SiC particles is 4:1-6:1; the average particle size of the micron-SiC particles is 20 μm, and the average particle size of the nano-SiC particles is 60 nm; The preparation method comprises the following steps: Step 1: using pure magnesium, pure aluminum, magnesium-calcium master alloy, magnesium-manganese master alloy, and micron SiC particles and nano SiC particles as raw materials to prepare ingredients; Step 2: The micron SiC particles and nano SiC particles prepared in step 1 are mixed uniformly by mechanical stirring, and then wrapped with aluminum foil. The SiC particles are then preheated with pure magnesium, pure aluminum, magnesium-calcium master alloy, and magnesium-manganese master alloy at a preheating temperature of 150-200° C. for 40-60 minutes. Step 3: first heat the crucible to 350-400°C, then add preheated pure magnesium, and at the same time, introduce a mixed gas of CO2 and SF6 into the crucible to protect the pure magnesium from oxidation, continue to heat it to 700-720°C, and after the pure magnesium is completely melted, add pure aluminum, magnesium-calcium master alloy and magnesium-manganese master alloy in sequence. After all are melted, slowly stir the melt to homogenize the melt composition; Step 4: Cooling the melt to 580-600° C. to make it semi-solid, cleaning impurities on the surface of the melt, and then mechanically stirring the melt. After the melt forms a stable vortex, the SiC particles preheated in step 2 are quickly added. After the SiC particles are added, stirring is continued to ensure that the SiC particles are evenly distributed in the melt. Step 5: The melt is allowed to stand, and the temperature is rapidly raised to 710-730° C., and an ultrasonic treatment is performed to cause the SiC particles to be secondary dispersed in the melt. The treatment time is 15-20 minutes. Step 6: The melt is allowed to stand for a period of time, and then transferred to a metal mold preheated to 300-350° C., and cooled by air first and then by water to obtain a magnesium alloy ingot; Step 7, removing the oxide scale of the magnesium alloy ingot, and then performing a homogenization treatment, the homogenization treatment temperature is 480-500° C., and the holding time is 5-7 hours; Step 8: The homogenized ingot is subjected to three upsetting and three drawing to obtain a billet, wherein the upsetting aspect ratio is controlled at 2 to 2.5, and the initial forging temperature of the ingot is 460 to 500° C. Step 9: Extrusion deform the billet obtained in step 8 at a billet extrusion temperature of 380-420° C. and an extrusion ratio greater than 10:1, and then air-cooling to room temperature.

2. The method for preparing a magnesium alloy according to claim 1, wherein: The mass percentages of the elements in the magnesium alloy are: Al accounts for 3.5wt%, Ca accounts for 3wt%, Mn accounts for 0.3wt%, SiC particles account for 5.4wt%, and the balance is Mg and unavoidable impurities; wherein the mass ratio of micron SiC particles to nano SiC particles is 5:

1.

3. The method for preparing a magnesium alloy according to claim 1, wherein: The mass percentages of the elements in the magnesium alloy are: Al accounts for 5wt%, Ca accounts for 4wt%, Mn accounts for 0.5wt%, SiC particles account for 6.5wt%, and the balance is Mg and inevitable impurities; wherein the mass ratio of micron SiC particles to nano SiC particles is 4:

1.

4. The method for preparing a magnesium alloy according to claim 1, wherein: The mass percentages of the elements in the magnesium alloy are: Al accounts for 3wt%, Ca accounts for 2wt%, Mn accounts for 0.6wt%, SiC particles account for 3.5wt%, and the remainder is Mg and inevitable impurities; wherein the mass ratio of micron SiC particles to nano SiC particles is 6:1.