A method for preparing nano-silicon carbide particle reinforced magnesium matrix composite

Abstract

The application relates to a preparation method of a nano-SiC particle reinforced magnesium-based composite material and belongs to the technical field of alloy preparation. The preparation method comprises the following steps: 1) sequentially performing high-temperature treatment on nano-SiC particles at 600 DEG C-800 DEG C and 800 DEG C-1100 DEG C; 2) mixing the pretreated nano-SiC particles and micron aluminum powder and performing ball milling treatment; 3) heating a magnesium-based alloy to a semi-solid state under argon protection, and adding an intermediate alloy powder into the semi-solid magnesium-based alloy under stirring; 4) heating the mixed slurry to above a liquidus under argon protection; 5) performing ultrasonic treatment on the liquid mixed slurry under argon protection, and casting the slurry after the ultrasonic treatment to obtain the nano-SiC particle reinforced magnesium-based composite material. The method provided by the application can improve the dispersibility of nano-SiC in the magnesium-based alloy and change the wettability between the nano-SiC and the magnesium-based alloy matrix.

Description

Technical Field

[0001] This invention belongs to the field of alloy preparation technology, and particularly relates to a method for preparing a magnesium-based composite material reinforced with nano-SiC particles. Background Technology

[0002] Magnesium alloys possess high specific strength and specific stiffness, good thermal conductivity and damping properties, strong electromagnetic shielding capabilities, excellent machinability, and superior casting performance, earning them the reputation of "green engineering materials for the 21st century" and leading to their widespread application in transportation, aerospace, and electronics industries. However, magnesium alloys have relatively low absolute strength, and their strength decreases more significantly with increasing operating temperature. Furthermore, their poor wear resistance and corrosion resistance limit their widespread use as structural materials in many fields. With the deepening research into metal matrix composites, introducing high-modulus, high-strength ceramic phases into magnesium alloys as reinforcements to create magnesium-based composites can significantly improve the yield strength, hardness, wear resistance, and high-temperature creep resistance of magnesium alloys. These multifunctional materials, organically combining the plasticity of magnesium alloys with ceramic phases, greatly enhance their comprehensive mechanical properties and broaden their application areas.

[0003] Among various particulate reinforcements, SiC particles possess a series of advantages such as high strength, good thermal stability, good wear resistance, low expansion, and low density, making them an ideal reinforcement for composite material preparation. From the perspective of microscopic reinforcement mechanisms, the strength and plasticity of materials increase with the reduction of reinforcement particle size, especially when the reinforcement particle size reaches the nanoscale, the dislocation strengthening and Orowan dispersion strengthening effects on the matrix become increasingly significant. The uniform dispersion of nanoscale SiC in the matrix can refine grains, strengthen the matrix, and improve the comprehensive mechanical properties of magnesium alloys. However, the main problems encountered in using nanoscale SiC particles as reinforcements for the preparation of magnesium-based composites are: nanoscale SiC has a high specific surface energy and is prone to agglomeration, making it difficult to uniformly disperse in magnesium alloys, resulting in poor dispersion of nanoparticles in the matrix; simultaneously, the excessive surface tension of the magnesium alloy melt leads to poor wettability between nanoparticles and the magnesium alloy matrix. Furthermore, in traditional smelting processes, the interface between nanoparticles and the matrix is ​​prone to interfacial reactions under high-temperature conditions, resulting in a small volume fraction of particles in the matrix and an insignificant strengthening effect. Summary of the Invention

[0004] In view of this, the present invention provides a method for preparing a magnesium-based composite material reinforced with nano-SiC particles, the method of which can improve the dispersibility of nano-SiC in magnesium-based alloys and change the wettability between nano-SiC and the magnesium-based alloy matrix.

[0005] This invention provides a method for preparing a magnesium-based composite material reinforced with nano-SiC particles, comprising the following steps:

[0006] 1) The nano-SiC particles were subjected to high-temperature treatment at 600℃~800℃ and 800℃~1100℃ in sequence to obtain pretreated nano-SiC particles.

[0007] 2) The pretreated nano-SiC particles are mixed with micron-sized aluminum powder and ball-milled to obtain intermediate alloy powder;

[0008] 3) The magnesium-based alloy is heated to a semi-solid state under argon protection, and the intermediate alloy powder is added to the semi-solid magnesium-based alloy under stirring to obtain a mixed slurry;

[0009] 4) Under argon protection, the mixed slurry is heated to above the liquidus line to obtain a liquid mixed slurry;

[0010] 5) The liquid mixed slurry is ultrasonicated under argon protection, and the ultrasonicated slurry is cast to obtain a magnesium-based composite material reinforced with nano-SiC particles.

[0011] Preferably, in step 1), the temperature is independently treated for 60 min to 90 min in the ranges of 600℃~800℃ and 800℃~1100℃ respectively, and the heating rate is 15℃~25℃ / min during heating.

[0012] Preferably, the size of the nano-SiC particles is 60-200 nm; the volume ratio of the pretreated nano-SiC particles to the micron-sized aluminum powder is 1:3 to 1:6.

[0013] Preferably, in step 2), the ball milling is carried out using ZrO balls in a vacuum environment or under inert gas protection, and the ball milling speed is 300-360 rpm and the time is 300-600 min.

[0014] Preferably, the magnesium-based alloy in step 3) includes AZ, AM and rare earth magnesium alloys.

[0015] Preferably, in step 3), the intermediate alloy powder is added to the semi-solid magnesium-based alloy at a rate of 30-50 g / min; the stirring speed in step 3) is 500-800 rpm, and the stirring time is 2-8 min.

[0016] Preferably, in step 3), the amount of intermediate alloy powder added is determined by the amount of pretreated nano-SiC particles added, wherein the amount of pretreated nano-particles added is 0.5 to 2% of the mass of the magnesium-based alloy.

[0017] Preferably, the heating temperature for heating to a semi-solid state in step 3) is 585–610°C; after heating the magnesium-based alloy to a semi-solid state in step 3), the temperature is held for 15 minutes before adding the intermediate alloy powder.

[0018] Preferably, in step 4), the temperature is increased to 630-670°C at a rate of 1-2.5°C / min.

[0019] Preferably, in step 5), the ultrasonic power is 2-4 kW, the frequency is 15-30 kHz, and the duration is 15-30 min.

[0020] The preparation method of magnesium-based composite material reinforced with nano-SiC particles provided by this invention has achieved the following technical effects:

[0021] This invention improves the dispersibility of SiC nanoparticles in magnesium-based alloys by pretreating them, thus preventing agglomeration. It also alters the wettability between the nanoparticles and the magnesium-based alloy matrix, allowing for increased nanoparticle SiC content and effectively enhancing the strength of the magnesium-based composite material. The resulting magnesium-based composite material exhibits increased tensile strength by over 18% and yield strength by over 15%. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the microstructure of the nano-SiC reinforced magnesium matrix composite material in Example 1;

[0023] Figure 2 This is a schematic diagram of the microstructure of the nano-SiC reinforced magnesium matrix composite material in Example 2;

[0024] Figure 3 This is a schematic diagram of the microstructure of the nano-SiC reinforced magnesium matrix composite material in Example 3;

[0025] Figure 4 This is a schematic diagram of the microstructure of the nano-SiC reinforced magnesium matrix composite material in Example 4;

[0026] Figure 5 This is a schematic diagram of the microstructure of the nano-SiC reinforced magnesium matrix composite material in Comparative Example 1.

[0027] Figure 6 This is a diagram showing the smelting effect of Comparative Example 1;

[0028] Figure 7 This is a schematic diagram of the microstructure of the nano-SiC reinforced magnesium matrix composite material in Comparative Example 2.

[0029] Figure 8 This is a diagram showing the smelting effect of Comparative Example 2;

[0030] Figure 9 This is a diagram showing the smelting effect of Comparative Example 3;

[0031] Figure 10 This is a diagram showing the smelting effect of Comparative Example 4. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] This invention provides a method for preparing a magnesium-based composite material reinforced with nano-SiC particles, comprising the following steps:

[0034] 1) The nano-SiC particles were subjected to high-temperature treatment at 600℃~800℃ and 800℃~1100℃ in sequence to obtain pretreated nano-SiC particles.

[0035] 2) The pretreated nano-SiC particles are mixed with micron-sized aluminum powder and ball-milled to obtain intermediate alloy powder;

[0036] 3) Under argon protection, the magnesium-based alloy is heated to a semi-solid state and held for 15 minutes. The intermediate alloy powder is then added to the semi-solid magnesium-based alloy while stirring to obtain a mixed slurry.

[0037] 4) Under argon protection, the mixed slurry is heated to above the liquidus line to obtain a liquid mixed slurry;

[0038] 5) The liquid mixed slurry is ultrasonicated under argon protection, and the ultrasonicated slurry is cast to obtain a magnesium-based composite material reinforced with nano-SiC particles.

[0039] This invention involves sequentially subjecting nano-SiC particles to high-temperature treatment at 600℃~800℃ and 800℃~1100℃ to obtain pretreated nano-SiC particles. In this invention, the particle size of the nano-SiC particles is preferably 60~200 nm. In this invention, the high-temperature treatment time at 600℃~800℃ is preferably 60 min~90 min; the high-temperature treatment time at 800℃~1100℃ is preferably 60 min~90 min. In this invention, when heating during the high-temperature treatment, a heating rate of 15℃~25℃ / min is preferred, more preferably 20℃.

[0040] In this invention, nano-SiC particles are subjected to high-temperature treatment sequentially at 600℃~800℃ and 800℃~1100℃. This process serves two purposes: firstly, it dries the nano-SiC particles; secondly, it promotes thermal equilibrium between the nano-SiC particles and the melt, reducing the possibility of agglomeration and floating caused by temperature differences. Simultaneously, high-temperature oxidation occurs under these conditions, forming a dense SiO2 layer on the surface of the nano-SiC particles. The reaction between SiO2 and the matrix enhances wettability. This invention employs a two-stage high-temperature treatment. The segmented heating prevents agglomeration of the nano-SiC particles caused by rapid temperature increases. Furthermore, the primary purpose of the first stage of heating is to remove crystalline water and adsorbates from the surface of the nano-SiC particles, eliminating the possibility of void formation during SiO2 formation. This improves the interfacial bonding strength between the nano-SiC particles and SiO2, making them less prone to peeling and enhancing their wettability and viscosity with the magnesium alloy matrix.

[0041] After obtaining pretreated nano-SiC particles, the present invention mixes the pretreated nano-SiC particles with micron-sized aluminum powder and performs ball milling to obtain intermediate alloy powder. In the present invention, the particle size of the micron-sized aluminum powder is preferably 40–200 μm. In the present invention, the volume ratio of the pretreated nano-SiC particles to the micron-sized aluminum powder is preferably 1:3–1:6. In the present invention, the ball milling is preferably performed using ZrO2 balls under vacuum or inert gas protection, the ball milling speed is preferably 300–360 rpm, and the time is preferably 300–600 min. In the present invention, ZrO2 is used as the grinding media ball because ZrO2 has a high density and a smooth, hard surface, which can prevent contamination of SiC particles and Al powder due to its own wear during ball milling. Simultaneously, due to its chemical inertness, it will not react with SiC particles or Al powder during grinding, thus preventing the introduction of excess substances.

[0042] In this invention, pretreated nano-SiC particles are mixed with micron-sized aluminum powder and ball-milled. During the ball milling process, the micron-sized Al powder and nano-SiC particles collide under the action of the ball. Since the amount of micron-sized Al powder is much higher than that of nano-SiC, and the strength of Al powder is much lower than that of SiC particles, the Al particles deform during the collision, resulting in a decrease in internal stress and dislocation density. This dislocation movement creates a large number of supersaturated vacancies, thus reducing the surface energy of the composite particles. Simultaneously, under effective collision, the atomically clean surfaces of the Al powder and nano-SiC particles come into close contact, undergoing cold welding. Under mechanical alloying, multilayer composite particles are formed, resulting in micron-sized mixed alloy particles. This overcomes the problem of poor wettability caused by the nano-size effect. In this process, high-energy ball milling leads to strong dislocation movement and the formation of a large number of supersaturated vacancies, reducing the particle surface energy and facilitating the dispersion of the composite particles in the matrix. Furthermore, the reduced surface tension between the particles and the melt decreases the wetting angle between the micron-sized particles and the melt, increasing the wettability between the particles and the matrix.

[0043] After obtaining the intermediate alloy powder, the magnesium-based alloy is heated to a semi-solid state under argon protection. The intermediate alloy powder is then added to the semi-solid magnesium-based alloy while stirring to obtain a mixed slurry. In this invention, the magnesium-based alloy preferably includes AZ, AM, and rare earth magnesium alloys, and more preferably consists of the following components by weight percentage: Al: 7.5–11%, Zn: 0.5–1%, Mn: 0.1–0.5%, small amounts of Si, Cu, Ni, Fe, etc., with the remainder being Mg. In this invention, the amount of intermediate alloy powder added is determined by the amount of pretreated nano-SiC particles added, wherein the amount of pretreated nano-particles added is 0.5–2% of the mass of the magnesium-based alloy. In this invention, the semi-solid is a solid-liquid mixed slurry structure formed by vigorous stirring during the solidification process, resulting in a liquid metal mother liquor with a certain solid phase component uniformly suspended in it. This semi-solid slurry structure exhibits certain rheological properties, i.e., good fluidity. In this invention, the magnesium-based alloy is preferably heated to 585–610°C to obtain a semi-solid magnesium-based alloy. In this invention, after heating the magnesium-based alloy to a semi-solid state, it is preferable to hold the temperature for 15 minutes before adding the intermediate alloy powder. In this invention, holding the temperature ensures that the entire magnesium-based alloy melt remains in a semi-solid state. In this invention, adding the intermediate alloy powder while the magnesium-based alloy is in a semi-solid state allows for better support and backing of the nanoparticles due to the greater viscous resistance of the magnesium alloy slurry to the reinforcement under semi-solid conditions. Simultaneously, the reduced fluidity of the melt significantly restricts the reinforcement, effectively inhibiting its floating, sinking, or agglomeration.

[0044] In this invention, the intermediate alloy powder is preferably added to the semi-solid magnesium-based alloy at a rate of 30–50 g / min. The stirring speed is preferably 600–800 rpm / min, and the stirring time is preferably 3–8 min. By controlling the addition rate, the intermediate alloy powder can be added to the semi-solid magnesium-based alloy to avoid excessively rapid addition and poor dispersion. Simultaneously, under strong stirring, the intermediate alloy powder is uniformly dispersed into the magnesium alloy matrix by the vortex formed during stirring. A graphite crucible or a stainless steel crucible is preferably used to heat and melt the magnesium-based alloy. A blade-type stirring device is preferably used for stirring.

[0045] After obtaining the mixed slurry, the present invention heats the mixed slurry above the liquidus line under argon protection to obtain a liquid mixed slurry. In the present invention, it is preferable to heat to 630-670°C at a rate of 1-2.5°C / min. In the present invention, controlling the heating rate at 1-2.5°C / min can avoid changes in the dispersion state of nanoparticles in the melt.

[0046] After obtaining the liquid mixed slurry, the present invention sonicates the liquid mixed slurry under argon protection, and then casts the sonicated slurry to obtain a magnesium matrix composite material reinforced with nano-SiC particles. In the present invention, the ultrasonic power is preferably 2-4 kW, the frequency is preferably 15-30 kHz, and the time is preferably 15-30 min. In the present invention, sonicating the liquid mixed slurry has two advantages. First, during the high-energy ultrasonic treatment, the gas and impurities adsorbed on the n-SiCp surface are removed, and the surface energy of the particles increases. At the same time, the high-frequency vibration and radiation pressure of the ultrasound can generate effective agitation and flow in the melt. The cavitation bubble vibration generates strong jets and local micro-impacts on the surface of the nanoparticles, which can significantly reduce the surface tension and friction of the liquid, thereby reducing the contact angle between the nanoparticles and the melt and increasing the wettability. Second, the dispersion of nanoparticles in the melt by ultrasound is a synergistic effect of acoustic cavitation and acoustic flow. As a result, the acoustic cavitation effect generates numerous tiny cavitation bubbles on and around the end face of the amplitude transformer. At the moment these cavitation bubbles collapse, the nanoparticles are dispersed under the intense shock wave and simultaneously carried into the entire melt by the macroscopic stirring effect of the acoustic flow, thus achieving uniform dispersion of the nanoparticles. Simultaneously, under the action of ultrasonic cavitation, the gas in the melt rises along the edge of the amplitude transformer until it is successfully expelled from the melt. Ultrasonic treatment also removes adsorbed gas and inclusions from the surface of the nanoparticles, achieving degassing and slag removal, thereby achieving a good and tight bond between the nanoparticles and the melt. Traditional mechanical stirring, due to its intense vibration, entrains a large amount of gas during stirring, creating numerous bubbles and voids. However, during ultrasonic treatment, because the melt surface is not agitated, no gas is entrained.

[0047] In this invention, the preferred casting method is to pour the liquid slurry into a preheated metal mold (preheating temperature 300℃~350℃) when the temperature of the liquid slurry is raised to 700~710℃, and then remove it after cooling to obtain a nano-SiC particle reinforced magnesium matrix composite alloy ingot.

[0048] Example 1

[0049] A SiC / AZ31 magnesium-based composite material with a weight percentage of 0.5% (wt.%) of nano-SiC particles was prepared.

[0050] Pretreated nano-SiC particles with a particle size of 80 nm were treated at 600 °C for 1 h, and then heated to 850 °C for 1 h at a heating rate of 20 °C / min to obtain pretreated nano-SiC particles. The pretreated nano-SiC particles were mixed with aluminum powder with a particle size of 60 μm at a volume ratio of 1:3 and then transferred to a star ball mill. The mixture was ball-milled with ZrO2 balls at a speed of 300 rpm for 600 min to obtain intermediate alloy powder.

[0051] Magnesium-based alloy was placed in a graphite crucible and heated to 590°C under argon protection, causing it to become semi-solid. After holding at this temperature for 15 minutes, 350g of the aforementioned intermediate alloy powder was added to 20kg of the semi-solid magnesium-based alloy at a rate of 30g / min, while simultaneously stirring at 600rpm / min using a blade stirrer for 8 minutes to obtain a mixed slurry. Under argon protection, the mixed slurry was heated to 630°C at a heating rate of 2°C / min to obtain a liquid mixed slurry. The liquid mixed slurry was then subjected to ultrasonic treatment using a high-energy ultrasonic processor (output power 3kW, frequency 30kHz, treatment time 15min) under argon protection. After ultrasonication, the temperature was increased to 705°C at a heating rate of 2°C / min, and then poured into a preheated metal mold (preheating temperature 300°C). After cooling, the ingot was removed to obtain a nano-SiC reinforced magnesium-based composite alloy ingot.

[0052] The specific composition of AZ31 magnesium alloy is as follows: Al: 3.2%, Zn: 0.9%, Mn: 0.6%, Si: 0.04%, and the remainder is Mg.

[0053] The microstructure and mechanical properties of the obtained nano-SiC reinforced magnesium matrix composite were observed and tested. Specifically, as follows... Figure 1 As shown, from Figure 1 The tissue images show that the nano-SiC particles are relatively uniformly dispersed in the magnesium alloy matrix, without obvious agglomeration.

[0054] The mechanical properties of the obtained nano-SiC reinforced magnesium matrix composite were tested. The tensile properties of the obtained nano-SiC reinforced magnesium matrix composite sample (processed according to GB6397-86) were tested on a universal testing machine. The results showed that the tensile strength and yield strength of the obtained composite were 342 MPa and 313 MPa, respectively. Compared with the matrix magnesium alloy, the tensile strength of the obtained nano-SiC reinforced magnesium matrix composite was increased by 18% and the yield strength was increased by 15%.

[0055] Example 2

[0056] Prepare SiC / AZ31 magnesium-based composite material with a weight percentage of 1% (wt.%) of nano-SiC particles.

[0057] SiC particles with a particle size of 120 nm were treated at 800 °C for 1 h, and then heated to 1100 °C for 1 h at a heating rate of 25 °C / min to obtain pretreated nano-SiC particles. The pretreated nano-SiC particles were mixed with aluminum powder with a particle size of 150 μm at a volume ratio of 1:3 and then transferred to a star ball mill. The mixture was ball-milled with ZrO2 balls at a speed of 360 rpm for 400 min to obtain intermediate alloy powder.

[0058] Magnesium-based alloys were placed in a graphite crucible and heated to 595°C under argon protection, causing them to become semi-solid. After holding at this temperature for 15 minutes, 920 g of the aforementioned intermediate alloy powder was added to 20 kg of the semi-solid magnesium-based alloy at a rate of 40 g / min, while simultaneously stirring at 800 rpm for 3 minutes using a blade stirrer to obtain a mixed slurry. Under argon protection, the mixed slurry was heated to 640°C at a heating rate of 2°C / min to obtain a liquid mixed slurry. The liquid mixed slurry was then subjected to ultrasonic treatment using a high-energy ultrasonic processor (output power 3 kW, frequency 30 kHz, treatment time 15 minutes) under argon protection. After ultrasonic treatment, the temperature was increased to 705°C at a heating rate of 2°C / min, and then poured into a preheated metal mold (preheating temperature 300°C). After cooling, the ingot was removed to obtain a nano-SiC reinforced magnesium-based composite alloy ingot.

[0059] The specific composition of AZ31 magnesium alloy is as follows: Al: 3.2%, Zn: 0.9%, Mn: 0.6%, Si: 0.04%, and the remainder is Mg.

[0060] The microstructure and mechanical properties of the obtained nano-SiC reinforced magnesium matrix composite were observed and tested. Specifically, as follows... Figure 2 As shown, from Figure 2 The tissue images show that the nano-SiC particles are relatively uniformly dispersed in the magnesium alloy matrix, without obvious agglomeration.

[0061] The mechanical properties of the obtained nano-SiC reinforced magnesium matrix composite were tested. The results showed that the tensile strength and yield strength of the obtained composite were 363 MPa and 333 MPa, respectively. Compared with the matrix magnesium alloy, the tensile strength of the obtained nano-SiC reinforced magnesium matrix composite was increased by 25.1% and the yield strength was increased by 22.5%.

[0062] Example 3

[0063] A SiC / AZ91 magnesium-based composite material with a weight percentage of 1.5% (wt.%) of nano-SiC particles was prepared.

[0064] SiC particles with a particle size of 150 nm were treated at 700 °C for 90 min, and then heated to 1000 °C for 1 h at a heating rate of 15 °C / min to obtain pretreated nano-SiC particles. The pretreated nano-SiC particles were mixed with aluminum powder with a particle size of 180 μm at a volume ratio of 1:5 and then transferred to a star ball mill. The mixture was ball-milled with ZrO2 balls at a speed of 360 rpm for 300 min to obtain intermediate alloy powder.

[0065] Magnesium-based alloys were placed in a graphite crucible and heated to 600°C under argon protection, causing them to become semi-solid. After holding at this temperature for 15 minutes, 1555 g of the aforementioned intermediate alloy powder was added to the semi-solid magnesium-based alloy at a rate of 50 g / min, while simultaneously stirring at 700 rpm for 5 minutes using a blade stirrer to obtain a mixed slurry. Under argon protection, the mixed slurry was heated to above the liquidus line (640°C) at a heating rate of 2.5°C / min to obtain a liquid mixed slurry. The liquid mixed slurry was then subjected to ultrasonic treatment using a high-energy ultrasonic processor (output power 2 kW, frequency 15 kHz, treatment time 30 minutes) under argon protection. After ultrasonication, the temperature was increased to 705°C at a heating rate of 2.5°C / min, and then poured into a preheated metal mold (preheating temperature 350°C). After cooling, the ingot was removed to obtain a nano-SiC reinforced magnesium-based composite alloy ingot.

[0066] The specific composition of AZ91 magnesium alloy is as follows: wt.%: Al: 9.2%, Zn: 0.51%, Mn: 0.28%, Si: 0.08%, with small amounts of Fe, Cu, and Ni, and the remainder being Mg.

[0067] The microstructure and mechanical properties of the obtained nano-SiC reinforced magnesium matrix composite were observed and tested. Specifically, as follows... Figure 3 As shown, from Figure 3 The tissue images show that the nano-SiC particles are relatively uniformly dispersed in the magnesium alloy matrix, without obvious agglomeration.

[0068] The mechanical properties of the obtained nano-SiC reinforced magnesium matrix composite were tested. The results showed that the tensile strength and yield strength of the composite were 346 MPa and 319 MPa, respectively. Compared with the matrix magnesium alloy, the tensile strength of the obtained nano-SiC reinforced magnesium matrix composite was increased by 19.3% and the yield strength was increased by 17.2%.

[0069] Example 4

[0070] Prepare a SiC / AZ91 magnesium-based composite material with a weight percentage of 2% (wt.%) of nano-SiC particles.

[0071] SiC particles with a particle size of 200 nm were treated at 750 °C for 1 h, and then heated to 1100 °C for 1 h at a heating rate of 20 °C / min to obtain pretreated nano-SiC particles. The pretreated nano-SiC particles were mixed with aluminum powder with a particle size of 200 μm at a volume ratio of 1:6 and then transferred to a star ball mill. The mixture was ball-milled with ZrO2 balls at a speed of 360 rpm for 300 min to obtain intermediate alloy powder.

[0072] Magnesium-based alloys were placed in a graphite crucible and heated to 605°C under argon protection, causing them to become semi-solid. After holding at this temperature for 15 minutes, 2410 g of the aforementioned intermediate alloy powder was added to the semi-solid magnesium-based alloy at a rate of 50 g / min, while simultaneously stirring at 700 rpm for 5 minutes using a blade stirrer to obtain a slurry. Under argon protection, the slurry was heated to 650°C at a heating rate of 2.5°C / min to obtain a liquid slurry. The liquid slurry was then subjected to ultrasonic treatment using a high-energy ultrasonic processor (output power 3 kW, frequency 30 kHz, treatment time 15 minutes) under argon protection. After ultrasonication, the temperature was increased to 705°C at a heating rate of 2.5°C / min, and the mixture was poured into a preheated metal mold (preheating temperature 350°C). After cooling, the ingot was removed to obtain a nano-SiC reinforced magnesium-based composite alloy ingot.

[0073] The specific composition of AZ91 magnesium alloy is as follows: wt.%: Al: 9.2%, Zn: 0.51%, Mn: 0.28%, Si: 0.08%, with small amounts of Fe, Cu, and Ni, and the remainder being Mg.

[0074] The microstructure and mechanical properties of the obtained nano-SiC reinforced magnesium matrix composite were observed and tested. Specifically, as follows... Figure 4 As shown, from Figure 4 The tissue images show that as the amount of nano-SiC particles added increases, a small amount of agglomeration occurs in some local areas, but the overall distribution is relatively uniform, which strengthens the matrix.

[0075] The mechanical properties of the obtained nano-SiC reinforced magnesium matrix composite were tested. The results showed that the tensile strength and yield strength of the composite were 342 MPa and 317 MPa, respectively. Compared with the matrix magnesium alloy, the tensile strength of the obtained nano-SiC reinforced magnesium matrix composite was increased by 18.1% and the yield strength was increased by 16.5%.

[0076] Comparative Example 1

[0077] The difference from Example 1 is that the nano-SiC particles were not subjected to high-temperature treatment and were directly used for subsequent experimental verification. The specific operation is as follows:

[0078] After drying 80nm SiC nanoparticles at 150℃, they were mixed with aluminum powder with a particle size of 60μm at a volume ratio of 1:3 and then transferred into a star ball mill. The mixture was ball-milled with ZrO2 balls at a speed of 300rpm for 600min to obtain intermediate alloy powder.

[0079] Magnesium-based alloy was placed in a graphite crucible and heated to 590°C under argon protection, causing it to become semi-solid. After holding at this temperature for 15 minutes, 350g of the aforementioned intermediate alloy powder was added to 20kg of the semi-solid magnesium-based alloy at a rate of 30g / min, while simultaneously stirring at 600rpm / min for 8 minutes using a blade-type stirrer to obtain a mixed slurry. Under argon protection, the mixed slurry was heated to 630°C at a heating rate of 2°C / min to obtain a liquid mixed slurry. The liquid mixed slurry was then subjected to ultrasonic treatment using a high-energy ultrasonic processor (output power 3kW, frequency 30kHz, treatment time 15min) under argon protection. After ultrasonic treatment, a large number of floating nano-SiC particles covered the surface of the melt. After slag removal, the temperature was increased to 705°C at a heating rate of 2°C, and then poured into a preheated metal mold (preheating temperature 300°C). After cooling, the ingot was obtained as a composite alloy ingot. The specific composition of AZ31 magnesium alloy is as follows: Al: 3.2%, Zn: 0.9%, Mn: 0.6%, Si: 0.04%, and the remainder is Mg.

[0080] The microstructure and mechanical properties of the obtained composite material were observed and tested, specifically as follows: Figure 5 and 6 As shown, by Figure 6It is evident that without high-temperature oxidation treatment, a considerable number of nano-SiC particles float on the surface of the melt. This is mainly because the nanoparticles were not subjected to high-temperature oxidation treatment. Therefore, during the ball milling of SiC and Al powder, the SiC particles exhibited significant agglomeration on the surface of the Al powder. Consequently, the wettability between the composite powder and the matrix was poor during the subsequent smelting process, and the SiC particles failed to penetrate well into the magnesium alloy matrix, resulting in a noticeable floating phenomenon on the surface of the melt. This phenomenon did not provide an effective strengthening effect on the matrix.

[0081] Mechanical property testing of the composite material under these conditions revealed a tensile strength of 318.4 MPa and a yield strength of 297 MPa. Compared to the matrix magnesium alloy, the tensile strength of the obtained nano-SiC reinforced magnesium matrix composite material increased by 9.8%, and the yield strength increased by 9.1%. Although the mechanical properties of the composite material were improved compared to the matrix magnesium alloy, these properties still do not meet the requirements of aerospace and naval products for material mechanical properties.

[0082] Comparative Example 2

[0083] The difference from Example 1 is that the high-temperature treatment of the nano-SiC particles uses a one-step heating method, and the specific operation is as follows:

[0084] SiC particles with a particle size of 80 nm were treated at 820 °C for 2 h to obtain pretreated nano-SiC particles. The pretreated nano-SiC particles were mixed with aluminum powder with a particle size of 60 μm at a volume ratio of 1:3 and then transferred into a star ball mill. The mixture was ball-milled with ZrO2 balls at a speed of 300 rpm for 600 min to obtain intermediate alloy powder.

[0085] Magnesium-based alloy was placed in a graphite crucible and heated to 590°C under argon protection, causing it to become semi-solid. After holding at this temperature for 15 minutes, 350g of the aforementioned intermediate alloy powder was added to 20kg of the semi-solid magnesium-based alloy at a rate of 30g / min, while simultaneously stirring at 600rpm / min using a blade stirrer for 8 minutes to obtain a mixed slurry. Under argon protection, the mixed slurry was heated to above the liquidus line (630°C) at a heating rate of 2°C / min to obtain a liquid mixed slurry. The liquid mixed slurry was then subjected to ultrasonic treatment using a high-energy ultrasonic processor (output power 3kW, frequency 30kHz, treatment time 15 minutes) under argon protection. After ultrasonication, the temperature was increased to 705°C at a heating rate of 2°C / min, and then poured into a preheated metal mold (preheating temperature 300°C). After cooling, the ingot was removed to obtain a nano-SiC reinforced magnesium-based composite alloy ingot.

[0086] The specific composition of AZ31 magnesium alloy is as follows: Al: 3.2%, Zn: 0.9%, Mn: 0.6%, Si: 0.04%, and the remainder is Mg.

[0087] Figure 7 and 8 The images show the melt state and microstructure of the composite material under these conditions. It can be seen from the images that a certain number of nano-SiC particles still float on the melt surface. The microstructure images also reveal obvious particle aggregation in the composite material without stepwise high-temperature oxidation treatment of the nanoparticles.

[0088] The mechanical properties of the obtained nano-SiC reinforced magnesium matrix composite material were tested and found that the tensile strength of the composite material was 322 MPa and the yield strength was 304 MPa. Compared with the matrix magnesium alloy, the tensile strength of the obtained nano-SiC reinforced magnesium matrix composite material was increased by 11% and the yield strength was increased by 11.7%. Although the performance was improved compared with the matrix magnesium alloy, it still cannot meet the requirements of aerospace and naval products for material mechanical properties, and there is still a certain gap from the composite target.

[0089] Comparative Example 3

[0090] The difference from Example 1 is that no ball milling treatment was performed. The specific operation is as follows:

[0091] Pretreated nano-SiC particles with a particle size of 80 nm were treated at 600 °C for 1 h, and then heated to 850 °C for 1 h at a heating rate of 20 °C / min to obtain pretreated nano-SiC particles.

[0092] Magnesium-based alloy was placed in a graphite crucible and heated to 590°C under argon protection, causing it to become semi-solid. After holding at this temperature for 15 minutes, 100g of the high-temperature oxidized nano-SiC particles were added to 20kg of the semi-solid magnesium-based alloy at a rate of 30g / min, while simultaneously stirring at 600rpm / min using a blade stirrer to obtain a slurry. The slurry was then heated to 630°C under argon protection at a rate of 2°C / min to obtain a liquid slurry. The liquid slurry was then subjected to ultrasonic treatment using a high-energy ultrasonic processor (output power 3kW, frequency 30kHz, treatment time 15min) under argon protection. After ultrasonic treatment, the temperature was increased to 705°C at a rate of 2°C / min, and the mixture was poured into a preheated metal mold (preheating temperature 300°C). After cooling, the ingot was obtained as a nano-SiC reinforced magnesium-based composite alloy.

[0093] The specific composition of AZ31 magnesium alloy is as follows: Al: 3.2%, Zn: 0.9%, Mn: 0.6%, Si: 0.04%, and the remainder is Mg.

[0094] During the smelting process, it can be observed that although SiC particles, without ball milling, form SiO2 with good bonding to the matrix after high-temperature oxidation treatment, their particle size remains nanoscale. Due to the influence of the nanoscale particle size effect, the specific surface area is large, increasing the surface tension in the matrix. Therefore, it is difficult to form good wettability with the magnesium alloy matrix. Consequently, during mechanical stirring and subsequent high-energy ultrasonic treatment, nano-SiC particles gradually float from the melt to the melt surface (e.g., ...). Figure 9 As shown in the figure, the number of nano-SiC particles immersed in the matrix is ​​very small, so the reinforcing effect of the particles on the matrix is ​​negligible. Under these melting conditions, it is not necessary to continue with the subsequent microstructure and performance testing.

[0095] Comparative Example 4

[0096] The difference from Example 1 is that no ultrasonic treatment was performed. The specific operation is as follows:

[0097] Pretreated nano-SiC particles with a particle size of 80 nm were treated at 600 °C for 1 h, and then heated to 850 °C for 1 h at a heating rate of 20 °C / min to obtain pretreated nano-SiC particles. The pretreated nano-SiC particles were mixed with aluminum powder with a particle size of 60 μm at a volume ratio of 1:3 and then transferred to a star ball mill. The mixture was ball-milled with ZrO balls at a speed of 300 rpm for 600 min to obtain intermediate alloy powder.

[0098] Magnesium-based alloy was placed in a graphite crucible and heated to 590°C under argon protection, causing it to become semi-solid. After holding at this temperature for 15 minutes, 350 g of the aforementioned intermediate alloy powder was added to 20 kg of the semi-solid magnesium-based alloy at a rate of 30 g / min, while simultaneously stirring at 600 rpm for 8 minutes using a blade stirrer to obtain a slurry. The slurry was then heated to 630°C under argon protection at a heating rate of 2°C / min to obtain a liquid slurry. This liquid slurry was then heated to 705°C at a heating rate of 2°C / min and poured into a preheated metal mold (preheated to 300°C). After cooling, the ingot was removed to obtain a nano-SiC reinforced magnesium-based composite alloy ingot.

[0099] The specific composition of AZ31 magnesium alloy is as follows: Al: 3.2%, Zn: 0.9%, Mn: 0.6%, Si: 0.04%, and the remainder is Mg.

[0100] Figure 10The image shows the melting effect under these conditions. It can be seen that in the semi-solid state without ultrasonic treatment of the mixed slurry, a large number of SiC particles float on the surface of the melt, and there is also obvious particle agglomeration. Therefore, under these melting conditions, it is unnecessary to continue with further microstructure and property testing, because only a small number of SiC particles penetrate into the matrix, resulting in a very poor strengthening effect of nano-SiC on the magnesium alloy matrix.

[0101] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a magnesium-based composite material reinforced with nano-SiC particles, characterized in that, Includes the following steps: 1) The nano-SiC particles were subjected to high-temperature treatment at 600℃~800℃ and 800℃~1100℃ in sequence to obtain pretreated nano-SiC particles. 2) The pretreated nano-SiC particles are mixed with micron-sized aluminum powder and ball-milled to obtain intermediate alloy powder; 3) The magnesium-based alloy is heated to a semi-solid state under argon protection, and the intermediate alloy powder is added to the semi-solid magnesium-based alloy under stirring to obtain a mixed slurry; 4) Under argon protection, the mixed slurry is heated above the liquidus line to obtain a liquid mixed slurry; 5) The liquid mixed slurry is ultrasonicated under argon protection, and the ultrasonicated slurry is cast to obtain a magnesium-based composite material reinforced with nano-SiC particles. In step 1), the samples were independently treated for 60 min to 90 min in the ranges of 600℃~800℃ and 800℃~1100℃ respectively, and the heating rate was 15℃~25℃ / min during the heating process. The size of the nano-SiC particles is 60~200nm; the particle size of the micron-sized aluminum powder is 40~200μm; the volume ratio of the pretreated nano-SiC particles to the micron-sized aluminum powder is 1:3~1:

6.

2. The preparation method according to claim 1, characterized in that, In step 2), the ball milling is carried out using ZrO balls in a vacuum environment or under inert gas protection. The ball milling speed is 300~360 rpm and the time is 300 min~600 min.

3. The preparation method according to claim 1, characterized in that, The magnesium-based alloys mentioned in step 3) include AZ, AM and rare earth magnesium alloys.

4. The preparation method according to claim 1, characterized in that, In step 3), the intermediate alloy powder is added to the semi-solid magnesium-based alloy at a rate of 30-50 g / min; the stirring speed in step 3) is 500-800 rpm, and the stirring time is 2-8 min.

5. The preparation method according to claim 1, characterized in that, In step 3), the amount of intermediate alloy powder added is determined by the amount of pretreated nano-SiC particles added, wherein the amount of pretreated nano-particles added is 0.5~2% of the mass of magnesium-based alloy.

6. The preparation method according to claim 1, characterized in that, The heating temperature for heating to a semi-solid state in step 3) is 585~610℃; after heating the magnesium-based alloy to a semi-solid state in step 3), the temperature is held for 15 minutes before adding the intermediate alloy powder.

7. The preparation method according to claim 1, characterized in that, In step 4), the temperature is increased to 630-670℃ at a rate of 1-2.5℃ / min.

8. The preparation method according to claim 1, characterized in that, In step 5), the ultrasonic power is 2~4kw, the frequency is 15~30kHz, and the time is 15~30min.

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