Preparation method of hollow iron oxide (Fe₃O₄) particle reinforced magnesium matrix composite material

Abstract

A preparation method of a hollow magnetite particle-reinforced magnesium matrix composite material, which relates to a preparation method of a magnesium matrix composite material. The present invention aims to solve the technical problems of the relatively large density of current metal electromagnetic shielding bodies and the poor mechanical properties of conductive polymers and their composite materials. In the present invention, a water-based dispersant can effectively reduce the surface energy of particles. The use of multi-stage variable temperature difference speed high-shear dispersion + variable frequency ultrasound combined with multi-stage variable temperature magnetic stirring is beneficial to improving the dispersion of particles in the melt and enhancing the electromagnetic shielding ability. The use of hierarchical multi-step hot pressing rapid forming can reduce the casting defects in the composite material, significantly improving the strength and toughness of the magnesium matrix composite material. The magnesium matrix composite material prepared by the present invention can meet the civilian requirements, and the composite material finally realizes both good mechanical and electromagnetic shielding properties, successfully designing a structural-functional integrated magnesium matrix composite material.

Description

Technical Field

[0001] The present invention relates to a method for preparing a magnesium-based composite material. Background Art

[0002] With the development of modern science and technology, the use of more and more electronic devices brings great convenience to people's lives and work. At the same time, the electromagnetic waves generated by various electronic devices fill people's living space, thus forming a new type of pollution (electromagnetic radiation) following water pollution, air pollution, and noise pollution. Currently, the main electromagnetic shielding materials used are metal materials such as metallic copper, aluminum, and permalloy, as well as conductive polymers and their composites. Traditional metal materials have a large density, which limits their application in a wider range. Conductive polymers and their composites have problems such as poor mechanical properties or shielding effects. Therefore, developing functional structure integrated lightweight materials with good mechanical and electromagnetic shielding properties has become one of the important research directions in the field of electromagnetic protection. Hollow magnetite particles have the advantages of strong magnetism, large saturation magnetization intensity, good oxidation resistance, and small density, and can greatly improve the electromagnetic shielding performance of electromagnetic materials. They are an ideal reinforcing material. Summary of the Invention

[0003] The present invention aims to solve the technical problems of the relatively large density of current metal electromagnetic shields and the poor mechanical properties of conductive polymers and their composites, and provides a method for preparing a hollow magnetite particle-reinforced magnesium-based composite material.

[0004] The method for preparing the hollow magnetite particle-reinforced magnesium-based composite material of the present invention is carried out according to the following steps:

[0005] I. Preparing a hollow magnetite / ethanol suspension by using multi-stage variable temperature differential speed high shear + variable frequency ultrasonic combined with multi-stage variable temperature magnetic stirring: Adding magnetite hollow spheres and an aqueous dispersant into a beaker filled with absolute ethanol, performing multi-stage variable temperature differential speed high shear for the first dispersion for 1 h to 1.5 h. After the first dispersion is completed, seal the beaker with aluminum foil and let it stand for 10 min to 15 min; then perform variable frequency ultrasonic combined with multi-stage variable temperature magnetic stirring for the second dispersion for 1 h to 1.5 h. After the second dispersion is completed, seal the beaker with aluminum foil, put the beaker into a drying oven for drying, and grind it into powder to obtain hollow magnetite powder;

[0006] The mass ratio of the aqueous dispersant to the hollow magnetite particles is 1:(16 - 17);

[0007] The mass ratio of the hollow magnetite particles to the volume of absolute ethanol is 1 g:(50 mL - 63 mL);

[0008] The steps of the multi-stage variable temperature differential speed high-shear are as follows: Set the temperature to 30°C to 35°C, then place the high-shear disperser into a beaker, and conduct the first-stage dispersion at a temperature of 30°C to 35°C, set the speed to 120 r / min to 130 r / min, and the time to 30 min to 35 min; then set the temperature to 40°C to 45°C for the second-stage dispersion, set the speed to 240 r / min to 250 r / min, and the time to 30 min to 35 min.

[0009] The steps of the variable-frequency ultrasonic combined with multi-stage variable temperature magnetic stirring are as follows: Conduct the first-stage ultrasonic and magnetic stirring simultaneously for 30 min to 35 min under the conditions of an ultrasonic power of 800 W to 1000 W, a magnetic stirring speed of 60 r / min to 120 r / min, and a temperature of 25°C to 30°C; then conduct the second-stage ultrasonic and magnetic stirring simultaneously for 30 min to 35 min under the conditions of an ultrasonic power of 1000 W to 1200 W, a magnetic stirring speed of 130 r / min to 240 r / min, and a temperature of 30°C to 35°C.

[0010] II. Melt the magnesium alloy ingot, add the preheated particles when it reaches the semi-solid state, and after the melting is completed, pour the molten metal into the mold and rapidly form it under multi-stage step-by-step hot pressing: Put the hollow iron oxide powder prepared in Step 1 into a resistance furnace for preheating, the preheating temperature is 100°C to 110°C, and the time is 20 min to 30 min; Put the matrix magnesium alloy ingot into a crucible, evenly sprinkle a layer of covering agent on the surface, introduce a protective gas, heat to make the magnesium alloy ingot start to melt, and then skim off a layer of oxide slag on the surface of the melt; Then lower the temperature of the melt to 30°C to 40°C above the liquidus temperature, start the stirrer device, continue to lower the temperature of the melt until it reaches the semi-solid state, and add the preheated hollow iron oxide powder at a position 10 cm to 15 cm above the melt surface near the center of the stirring shaft, adjust the stirrer parameters to make the reinforcement evenly dispersed in the melt and avoid burning of the reinforcement, and turn off the stirrer; Set the preheating temperature of the ultrasonic rod to 640°C to 680°C, raise the temperature of the melt to 700°C to 720°C, put the preheated ultrasonic rod 2 cm to 3 cm below the melt surface for ultrasonic treatment, and the time, power, and frequency of the ultrasonic treatment are in turn: 10 min to 20 min, 1300 W to 2000 W, and 20 GHz to 21 GHz; After the ultrasonic treatment, skim off the slag, pour the melt into the preheated mold and rapidly form it under multi-stage step-by-step hot pressing, and the preheating temperature of the mold is 400°C to 450°C.

[0011] The mass of the preheated hollow iron oxide powder is 1% to 1.5% of the mass of the matrix magnesium alloy ingot.

[0012] The protective gas is a mixed gas of CO2 and SF6, and the volume ratio of CO2 to SF6 is (40 - 45):1;

[0013] The parameters set for the stirrer are as follows: rotation speed 30 r / min - 60 r / min, time 20 min - 25 min, where it rotates clockwise for 12 min - 15 min first, and then rotates counterclockwise for 8 min - 10 min;

[0014] The semi - solid range of the magnesium alloy is 540°C - 580°C;

[0015] The steps of the hierarchical multi - step hot pressing rapid prototyping are as follows:

[0016] First stage: First, set the pressure to 50 kN - 55 kN, the pressure - holding time to 5 s - 10 s, and the load application rate to 5 kN / s - 10 kN / s; then set the pressure to 100 kN - 110 kN, the pressure - holding time to 10 s - 15 s, and the load application rate to 10 kN / s - 15 kN / s;

[0017] Second stage: First, set the pressure to 150 kN - 155 kN, the pressure - holding time to 10 s - 15 s, and the load application rate to 15 kN / s - 20 kN / s; then set the pressure to 450 kN - 500 kN, the pressure - holding time to 60 s - 70 s, and the load application rate to 20 kN / s - 25 kN / s.

[0018] In step one of the present invention, the multi - stage variable - temperature differential - speed high - shear generates a strong shear force through the close cooperation of the stator and rotor of the machine - dispersing cutter head, causing the larger agglomerated particles that agglomerate together to split, break, and disperse to form smaller particles; the variable - frequency ultrasonic wave will have a strong impact of high - energy ultrasonic waves on the solution, and under the action of the multi - stage variable - temperature magnetic stirring, most of the smaller agglomerated particles in the solution are uniformly subjected to the impact of the high - energy ultrasonic waves, so that the smaller agglomerated particles split and break to form particles with even smaller sizes. At this time, the contact area between the particles and the aqueous dispersant in the solution increases. At this time, the flexible poly(propylene oxide) copolymer long chains in the aqueous dispersant form a hydration film to prevent particle aggregation. These hydration films will generate a high enough steric repulsion energy to overcome the attractive force of the van der Waals force between the particles, so that the particles are stably dispersed in the solution. At this time, the hydration film on the particle surface tends to orient the hydrophilic groups towards the aqueous phase and the hydrophobic groups away from the aqueous phase, that is, the hydrophobic groups are neatly arranged at positions far from the aqueous phase. The result of such an arrangement is the formation of a layer of hydrophobic groups. The hydrophobic groups mean that their surface energy is relatively low, thus reducing the particle surface energy.

[0019] In step two of the present invention, the matrix magnesium alloy is heated to a temperature between the solid-liquid two-phase region temperature (semi-solid temperature range), and then reinforcing phase particles are added. The metal melt undergoing the solidification process is vigorously stirred by a stirring device, so that the reinforcing particles enter the melt under the action of stirring. In addition, semi-solid stirring can greatly reduce the gas entrainment of the metal liquid during full-liquid stirring and the oxidation and burning loss of the magnesium alloy at high temperatures. Subsequently, the temperature is raised to the liquidus temperature for ultrasonic treatment. Under the impact of strong ultrasonic waves, the particles can be evenly dispersed in the metal melt, and finally the particles will be evenly dispersed in the material, and the slag and pore-like defects in the composite material are greatly reduced, which will significantly improve the mechanical properties and electromagnetic shielding properties of the composite material.

[0020] In the present invention, the aqueous dispersant can effectively reduce the surface energy of the particles. Using multi-stage variable temperature differential speed high-shear dispersion + variable frequency ultrasonic combined with multi-stage variable temperature magnetic stirring is beneficial to improve the dispersion of the particles in the melt and enhance the electromagnetic shielding ability. Using hierarchical multi-step hot pressing and rapid forming can reduce the casting defects in the composite material, and significantly improve the strength and toughness of the magnesium matrix composite material.

[0021] The beneficial effects of the present invention:

[0022] In the present invention, in the first step, hollow magnetite / ethanol suspension is prepared by using multi-stage variable temperature differential speed high-shear + variable frequency ultrasonic combined with multi-stage variable temperature magnetic stirring. Using multi-stage variable temperature differential speed high-shear + variable frequency ultrasonic combined with multi-stage variable temperature magnetic stirring can significantly reduce the surface energy of the particles and reduce the agglomeration of the particles. The ultrasonic treatment and semi-solid stirring in step two can make the particles achieve a more uniform distribution in the melt, and can significantly improve the mechanical properties and electromagnetic shielding properties of the composite material. The hierarchical multi-step hot pressing and rapid forming in step two can greatly reduce the casting defects of the composite material and improve its mechanical properties. Under the action of multi-stage variable temperature differential speed high-shear + variable frequency ultrasonic combined with multi-stage variable temperature magnetic stirring and hierarchical multi-step hot pressing and rapid forming, the strength and toughness of the magnesium matrix composite material reinforced by hollow magnetite particles can be significantly improved. The tensile strength reaches more than 450 MPa, the yield strength reaches more than 390 MPa, and the elongation reaches more than 2%. When the thickness is only 1.5 mm, the electromagnetic shielding performance in the microwave band (8 GHz - 12 GHz) can reach up to more than 56 dB at most, and the average value reaches more than 52 dB. According to the evaluation standard of electromagnetic shielding performance, EMI performance ≥ 35 dB can meet the civilian requirements. From this, it can be seen that the magnesium matrix composite material prepared by the present invention can meet the civilian requirements, and the composite material finally realizes the integration of good mechanical and electromagnetic shielding properties, and successfully designs a structure-functional integrated magnesium matrix composite material. Brief Description of the Drawings

[0023] Figure 1It is the optical micrograph of the hollow Fe₃O₄ particle-reinforced magnesium matrix composite prepared in Experiment 1;

[0024] Figure 2 It is the optical micrograph of the extruded bar prepared in Experiment 1;

[0025] Figure 3 It is the optical micrograph of the extruded bar prepared in Experiment 2;

[0026] Figure 4 It is the optical micrograph of the extruded bar prepared in Experiment 3;

[0027] Figure 5 It is the engineering stress - engineering strain curve of the extruded bar prepared in Experiment 1;

[0028] Figure 6 It is the engineering stress - engineering strain curve of the extruded bar prepared in Experiment 2;

[0029] Figure 7 It is the engineering stress - engineering strain curve of the extruded bar prepared in Experiment 3;

[0030] Figure 8 It is the test chart of the electrical conductivity of the hollow Fe₃O₄ particle-reinforced magnesium matrix composite and magnesium alloy AZ91 prepared in Experiment 1;

[0031] Figure 9 It is the magnetic test chart of the hollow Fe₃O₄ particle-reinforced magnesium matrix composite prepared in Experiment 1;

[0032] Figure 10 It is the test chart of the electromagnetic shielding performance of the hollow Fe₃O₄ particle-reinforced magnesium matrix composite prepared in Experiment 1 in the microwave band. Specific implementation mode

[0033] Specific implementation mode 1: This implementation mode is a preparation method of a hollow Fe₃O₄ particle-reinforced magnesium matrix composite, and the specific steps are as follows:

[0034] 1. Prepare a hollow Fe₃O₄ / ethanol suspension by using multi-stage variable temperature differential high shear + variable frequency ultrasonic combined with multi-stage variable temperature magnetic stirring: Add hollow Fe₃O₄ spheres and a water-based dispersant into a beaker filled with anhydrous ethanol, perform multi-stage variable temperature differential high shear for the first dispersion for 1 h to 1.5 h. After the first dispersion is completed, seal the beaker with aluminum foil and let it stand for 10 min to 15 min; then perform variable frequency ultrasonic combined with multi-stage variable temperature magnetic stirring for the second dispersion for 1 h to 1.5 h. After the second dispersion is completed, seal the beaker with aluminum foil, put the beaker into a drying oven for drying, and grind it into powder to obtain hollow Fe₃O₄ powder;

[0035] The mass ratio of the aqueous dispersant to the hollow iron oxide particles is 1:(16 - 17);

[0036] The mass ratio of the hollow iron oxide particles to the volume of absolute ethanol is 1g:(50mL - 63mL);

[0037] The steps of multi-stage variable temperature differential speed high-shear are as follows: Set the temperature to 30°C - 35°C, then place the high-shear disperser into a beaker, and conduct the first-stage dispersion at a temperature of 30°C - 35°C, set the speed to 120r / min - 130r / min, and the time to 30min - 35min; then set the temperature to 40°C - 45°C for the second-stage dispersion, set the speed to 240r / min - 250r / min, and the time to 30min - 35min;

[0038] The steps of variable-frequency ultrasonic combined with multi-stage variable-temperature magnetic stirring are as follows: Conduct the first-stage ultrasonic and magnetic stirring simultaneously for 30min - 35min under the conditions of ultrasonic power of 800W - 1000W, magnetic stirring speed of 60r / min - 120r / min, and temperature of 25°C - 30°C; then conduct the second-stage ultrasonic and magnetic stirring simultaneously for 30min - 35min under the conditions of ultrasonic power of 1000W - 1200W, magnetic stirring speed of 130r / min - 240r / min, and temperature of 30°C - 35°C;

[0039] II. Melt the magnesium alloy ingot. When it reaches the semi-solid state, add the preheated particles. After the melting is completed, pour the molten metal into the mold and perform rapid prototyping under graded multi-step hot pressing: Put the hollow iron oxide powder prepared in Step 1 into a resistance furnace for preheating. The preheating temperature is 100°C to 110°C, and the time is 20 min to 30 min; put the matrix magnesium alloy ingot into a crucible, evenly sprinkle a layer of covering agent on the surface, introduce a protective gas, heat to make the magnesium alloy ingot start to melt, and then skim off a layer of oxide slag on the surface of the melt; then lower the temperature of the melt to 30°C to 40°C above the liquidus temperature, start the stirrer device, continue to lower the temperature of the melt until it reaches the semi-solid state, and add the preheated hollow iron oxide powder at a position 10 cm to 15 cm above the melt surface near the center of the stirring shaft. Adjust the parameters of the stirrer to make the reinforcement evenly dispersed in the melt and avoid burning of the reinforcement, and then turn off the stirrer; set the preheating temperature of the ultrasonic rod to 640°C to 680°C, raise the temperature of the melt to 700°C to 720°C, put the preheated ultrasonic rod 2 cm to 3 cm below the melt surface for ultrasonic treatment. The time, power, and frequency of the ultrasonic treatment are 10 min to 20 min, 1300 W to 2000 W, and 20 GHz to 21 GHz in sequence; after the ultrasonic treatment, skim the slag, pour the melt into the preheated mold and perform rapid prototyping under graded multi-step hot pressing. The preheating temperature of the mold is 400°C to 450°C;

[0040] The mass of the preheated hollow iron oxide powder is 1% to 1.5% of the mass of the matrix magnesium alloy ingot;

[0041] The protective gas is a mixed gas of CO2 and SF6, and the volume ratio of CO2 to SF6 is (40 - 45):1;

[0042] The parameters set for the stirrer are: rotation speed 30 r / min to 60 r / min, time 20 min to 25 min, where it rotates clockwise for 12 min to 15 min first, and then rotates counterclockwise for 8 min to 10 min;

[0043] The steps of the graded multi-step hot pressing rapid prototyping are as follows:

[0044] First stage: First, set the pressure to 50 kN to 55 kN, the pressure holding time to 5 s to 10 s, and the load application rate to 5 kN / s to 10 kN / s; then set the pressure to 100 kN to 110 kN, the pressure holding time to 10 s to 15 s, and the load application rate to 10 kN / s to 15 kN / s;

[0045] Second level: First, set the pressure to 150 kN to 155 kN, the pressure holding time to 10 s to 15 s, and the load application rate to 15 kN / s to 20 kN / s; then set the pressure to 450 kN to 500 kN, the pressure holding time to 60 s to 70 s, and the load application rate to 20 kN / s to 25 kN / s.

[0046] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that: the drying temperature in Step 1 is 90°C to 110°C, and the time is 3 days to 5 days. Others are the same as Specific Embodiment 1.

[0047] Specific Embodiment 3: The difference between this embodiment and Specific Embodiment 1 or 2 is that: the steps of multi-stage variable temperature and high-shear are as follows: Set the temperature to 30°C, then put the high-shear disperser into the beaker, and perform the first-stage dispersion at 30°C, set the speed to 120 r / min, and the time to 30 min; then set the temperature to 40°C for the second-stage dispersion, set the speed to 240 r / min, and the time to 30 min. Others are the same as Specific Embodiment 1 or 2.

[0048] Specific Embodiment 4: The difference between this embodiment and any one of Specific Embodiments 1 to 3 is that: the steps of variable-frequency ultrasonic combined with multi-stage variable-temperature magnetic stirring are as follows: Perform the first-stage ultrasonic and magnetic stirring simultaneously for 30 min under the conditions of ultrasonic power of 800 W to 1000 W, magnetic stirring speed of 60 r / min to 120 r / min, and temperature of 25°C to 30°C; then perform the second-stage ultrasonic and magnetic stirring simultaneously for 30 min under the conditions of ultrasonic power of 1000 W to 1200 W, magnetic stirring speed of 130 r / min to 240 r / min, and temperature of 30°C to 35°C. Others are the same as any one of Specific Embodiments 1 to 3.

[0049] Specific Embodiment 5: The difference between this embodiment and Specific Embodiment 4 is that: the mass of the preheated hollow iron oxide powder in Step 2 is 1% of the mass of the matrix magnesium alloy ingot. Others are the same as Specific Embodiment 4.

[0050] Specific Embodiment 6: The difference between this embodiment and Specific Embodiment 5 is that: the steps of hierarchical multi-step hot pressing and rapid prototyping are as follows:

[0051] First level: First, set the pressure to 50 kN, the pressure holding time to 5 s, and the load application rate to 5 kN / s; then set the pressure to 100 kN, the pressure holding time to 10 s, and the load application rate to 10 kN / s;

[0052] Second level: First, set the pressure to 150 kN, the pressure holding time to 10 s, and the load application rate to 15 kN / s; then set the pressure to 450 kN, the pressure holding time to 60 s, and the load application rate to 20 kN / s. Others are the same as in the fifth specific implementation manner.

[0053] The present invention is verified by the following tests:

[0054] Test 1: This test is a preparation method of a hollow iron oxide (Fe₃O₄) particle-reinforced magnesium matrix composite material, and specifically, it is carried out according to the following steps:

[0055] I. Prepare a hollow iron oxide (Fe₃O₄) / ethanol suspension by using multi-stage variable temperature differential speed high shear + variable frequency ultrasonic combined with multi-stage variable temperature magnetic stirring: Add iron oxide (Fe₃O₄) hollow spheres and an aqueous dispersant into a beaker filled with anhydrous ethanol, and perform the first dispersion by multi-stage variable temperature differential speed high shear for 1 h. After the first dispersion is completed, seal the beaker with aluminum foil and let it stand for 10 min; then perform the second dispersion by variable frequency ultrasonic combined with multi-stage variable temperature magnetic stirring for 1 h. After the second dispersion is completed, seal the beaker with aluminum foil, put the beaker into a drying oven for drying, and grind it into powder to obtain hollow iron oxide (Fe₃O₄) powder; the drying temperature is 90 °C and the time is 3 days;

[0056] The particle size of the iron oxide (Fe₃O₄) hollow spheres is 0.4 μm to 0.5 μm, and the shell thickness is 100 nm;

[0057] The aqueous dispersant is HH2017 of Guangzhou Houhuan Chemical Auxiliary Co., Ltd., and the mass is 0.5 g (liquid);

[0058] The mass of the hollow iron oxide (Fe₃O₄) particles is 8 g;

[0059] The volume ratio of the anhydrous ethanol is 400 mL;

[0060] The steps of the multi-stage variable temperature differential speed high shear are as follows: Set the temperature to 30 °C, then put the high shear disperser into the beaker, and perform the first-stage dispersion at 30 °C, set the speed to 120 r / min, and the time to 30 min; then set the temperature to 40 °C for the second-stage dispersion, set the speed to 240 r / min, and the time to 30 min;

[0061] The steps of the variable-frequency ultrasound combined with multi-stage variable-temperature magnetic stirring are as follows: Place the beaker at the center of the tray of the magnetic stirrer, and then insert the ultrasonic rod into the liquid surface. Perform the first-stage ultrasound and magnetic stirring simultaneously for 30 min under the conditions of an ultrasonic power of 800 W, a rotational speed of the magnetic stirring of 100 r / min, and a temperature of 25 °C. Then perform the second-stage ultrasound and magnetic stirring simultaneously for 30 min under the conditions of an ultrasonic power of 1000 W, a rotational speed of the magnetic stirring of 130 r / min, and a temperature of 30 °C.

[0062] II. Melting the magnesium alloy ingot and adding the preheated particles when it reaches the semi-solid state. After the melting is completed, pour the molten metal into the mold and rapidly form it under multi-stage stepwise hot pressing: Put the prepared hollow iron oxide powder in the resistance furnace for preheating, with a preheating temperature of 100 °C and a time of 20 min. Place the matrix magnesium alloy ingot in the crucible, evenly sprinkle a layer of covering agent on the surface, introduce the protective gas, heat to make the magnesium alloy ingot start to melt, and then skim off a layer of oxide slag on the surface of the melt. Then, when the temperature of the melt is reduced to 30 °C above the liquidus temperature, start the stirrer device. Continue to reduce the temperature of the melt until it reaches the semi-solid state, and add the preheated hollow iron oxide powder at a position 10 cm above the melt surface and close to the center of the stirring shaft. Adjust the parameters of the stirrer to make the reinforcement evenly dispersed in the melt and avoid burning of the reinforcement, and then turn off the stirrer. Set the preheating temperature of the ultrasonic rod to 640 °C, raise the temperature of the melt to 700 °C, and place the preheated ultrasonic rod 2 cm below the melt surface for ultrasonic treatment. The time, power, and frequency of the ultrasonic treatment are 10 min, 1300 W, and 20 GHz in sequence. After the ultrasonic treatment, skim off the slag, pour the melt into the preheated mold and rapidly form it under multi-stage stepwise hot pressing to obtain the hollow iron oxide particle-reinforced magnesium matrix composite material. The preheating temperature of the mold is 400 °C.

[0063] The semi-solid range of the magnesium alloy is 540 - 580 °C.

[0064] The covering agent is flux No. 6 for magnesium alloy (RJ-6), with a mass of 16 g.

[0065] The matrix magnesium alloy ingot is AZ91, which is composed of 9% Al element, 1% Zn element, and 90% Mg element by mass fraction, and the mass of the magnesium alloy ingot is 830 g.

[0066] The mass of the preheated hollow iron oxide powder is 1% of the mass of the matrix magnesium alloy ingot.

[0067] The protective gas is a mixed gas of CO2 and SF6, and the volume ratio of CO2 to SF6 is 40:1.

[0068] The parameters set for the agitator are: rotation speed 30 r / min, time 20 min, where it rotates clockwise for 12 min first and then counterclockwise for 8 min;

[0069] The steps of the hierarchical multi-step hot pressing rapid prototyping are as follows:

[0070] First stage: First, set the pressure to 50 kN, the pressure holding time to 5 s, and the load application rate to 5 kN / s; then set the pressure to 100 kN, the pressure holding time to 10 s, and the load application rate to 10 kN / s;

[0071] Second stage: First, set the pressure to 150 kN, the pressure holding time to 10 s, and the load application rate to 15 kN / s; then set the pressure to 450 kN, the pressure holding time to 60 s, and the load application rate to 20 kN / s.

[0072] The hollow Fe₃O₄ particle-reinforced magnesium matrix composite obtained from Experiment 1 was cut into 20×50 mm blocks and solution-treated at 415 °C for 24 h. After the solution treatment was completed, the surfaces of the blocks were polished clean and wrapped with aluminum foil; first, the hot extrusion die was preheated in the furnace. After the die temperature reached 200 °C, the aluminum foil-wrapped blocks were placed in the furnace, preheated at 200 °C for 30 min and then taken out, and placed in the hot extrusion die for hot pressing to obtain an extrusion bar with a diameter of 10 mm.

[0073] Figure 1 It is the optical micrograph of the hollow Fe₃O₄ particle-reinforced magnesium matrix composite prepared in Experiment 1. It can be seen from the figure that its grain size is large, the second phase is distributed along the grain boundaries, and its plasticity and strength are poor.

[0074] Experiment 2: The difference between this experiment and Experiment 1 is that the hollow Fe₃O₄ particle-reinforced magnesium matrix composite obtained from Experiment 1 was cut into 20×50 mm blocks and solution-treated at 415 °C for 24 h. After the solution treatment was completed, the surfaces of the blocks were polished clean and wrapped with aluminum foil; first, the hot extrusion die was preheated in the furnace. After the die temperature reached 250 °C, the aluminum foil-wrapped blocks were placed in the furnace, preheated at 250 °C for 30 min and then taken out, and placed in the hot extrusion die for hot pressing to obtain an extrusion bar with a diameter of 10 mm.

[0075] Experiment 3: The difference between this experiment and Experiment 1 is as follows: The hollow Fe₃O₄ particle-reinforced magnesium matrix composite obtained in Experiment 1 was cut into blocks with dimensions of 20×50 mm, and solution treatment was carried out at 415 °C for 24 h. After the solution treatment was completed, the surface of the blocks was polished clean and wrapped with aluminum foil. First, the hot extrusion die was preheated in the furnace. After the die temperature reached 300 °C, the aluminum foil-wrapped blocks were placed in the furnace, preheated at 300 °C for 30 min, then taken out and placed in the hot extrusion die for hot pressing to obtain an extruded bar with a diameter of 10 mm.

[0076] Figure 2 、 Figure 3 and Figure 4 are the optical micrographs of the extruded bars prepared in Experiment 1, Experiment 2, and Experiment 3, respectively. It can be seen from the figures that the grains of the composite material prepared in Experiment 1 are elongated along the extrusion direction, and the second phase is distributed along the extrusion direction, with the highest strength.

[0077] The mechanical properties of the extruded bars were tested at room temperature to obtain the engineering stress-engineering strain curve. Figure 5 is for Experiment 1, Figure 6 is for Experiment 2, Figure 7 is for Experiment 3. It can be seen that the tensile strength of the extruded bar prepared in Experiment 1 is 454.6 MPa, the yield strength is 394.67 MPa, and the elongation is 2%; the tensile strength of the extruded bar prepared in Experiment 2 is 359.4 MPa, the yield strength is 303.45 MPa, and the elongation is 3.92%; the tensile strength of the extruded bar prepared in Experiment 3 is 299.04 MPa, the yield strength is 232.04 MPa, and the elongation is 5.10%.

[0078] The electrical conductivity of the hollow Fe₃O₄ particle-reinforced magnesium matrix composite prepared in Experiment 1 and magnesium alloy AZ91 was tested at room temperature. The electrical conductivity of the materials was obtained as Figure 8 shown. It can be seen that the electrical conductivity of magnesium alloy AZ91 is 6.4 MS / m, and the electrical conductivity of the composite material is 6.18 MS / m.

[0079] The magnetic properties of the hollow Fe₃O₄ particle-reinforced magnesium matrix composite prepared in Experiment 1 were tested at room temperature, as Figure 9 shown. The saturation magnetization of the composite material is 0.42 emu / g, and the remanent magnetization is 0.04 emu / g.

[0080] The electromagnetic shielding performance of the hollow Fe₃O₄ particle-reinforced magnesium matrix composite prepared in Experiment 1 was tested in the microwave band at room temperature, as Figure 10 shown. The highest EMI performance of the composite material at a frequency of 8 - 12 GHz is above 56 dB, and the average value is above 52 dB.

Claims

1. A preparation method of a hollow iron oxide (Fe₃O₄) particle-reinforced magnesium matrix composite material, characterized in that The preparation method of the hollow iron oxide (Fe₃O₄) particle-reinforced magnesium matrix composite material is carried out according to the following steps: I. Preparation of the hollow iron oxide (Fe₃O₄) / ethanol suspension by using multi-stage variable temperature differential speed high-shear + variable frequency ultrasonic combined with multi-stage variable temperature magnetic stirring: Add the hollow iron oxide (Fe₃O₄) spheres and the aqueous dispersant into a beaker filled with anhydrous ethanol, and conduct the first dispersion by multi-stage variable temperature differential speed high-shear for 1 h to 1.5 h. After the first dispersion is completed, seal the beaker with aluminum foil and let it stand for 10 min to 15 min; then conduct the second dispersion by variable frequency ultrasonic combined with multi-stage variable temperature magnetic stirring for 1 h to 1.5 h. After the second dispersion is completed, seal the beaker with aluminum foil, put the beaker into a drying oven for drying, and grind it into powder to obtain the hollow iron oxide (Fe₃O₄) powder; The mass ratio of the aqueous dispersant to the hollow iron oxide (Fe₃O₄) particles is 1:(16 - 17); The mass ratio of the hollow iron oxide (Fe₃O₄) particles to the volume of anhydrous ethanol is 1 g:(50 mL - 63 mL); The steps of the multi-stage variable temperature differential speed high-shear are as follows: Set the temperature to 30°C to 35°C, then put the high-shear disperser into the beaker, and conduct the first-stage dispersion at a temperature of 30°C to 35°C, set the speed to 120 r / min to ​ II. Melting the magnesium alloy ingot, adding the preheated particles when it reaches the semi-solid state, and after the melting is completed, pouring the molten metal into the mold and rapidly forming it under multi-step hierarchical hot pressing: Put the hollow Fe₃O₄ powder prepared in Step 1 into a resistance furnace for preheating. The preheating temperature is 100°C to 110°C, and the time is 20 min to 30 min; Put the matrix magnesium alloy ingot into a crucible, evenly sprinkle a layer of covering agent on the surface, introduce a protective gas, heat to make the magnesium alloy ingot start to melt, and then skim off a layer of oxide slag on the surface of the melt; Then lower the temperature of the melt to 30°C to 40°C above the liquidus temperature, start the stirrer device, continue to lower the temperature of the melt until it reaches the semi-solid state, and add the preheated hollow Fe₃O₄ powder at a position 10 cm to 15 cm above the melt surface near the center of the stirrer shaft. Adjust the parameters of the stirrer to make the reinforcement evenly dispersed in the melt and avoid burning of the reinforcement, and then turn off the stirrer; Set the preheating temperature of the ultrasonic rod to 640°C to 680°C, raise the temperature of the melt to 700°C to 720°C, put the preheated ultrasonic rod 2 cm to 3 cm below the melt surface for ultrasonic treatment. The time, power, and frequency of the ultrasonic treatment are successively: 10 min to 20 min, 1300 W to 2000 W, and 20 GHz to 21 GHz; After the ultrasonic treatment, skim the slag, pour the melt into the preheated mold and rapidly form it under multi-step hierarchical hot pressing. The preheating temperature of the mold is 400°C to 450°C; The mass of the preheated hollow Fe₃O₄ powder is 1% to 1.5% of the mass of the matrix magnesium alloy ingot; 2. The preparation method of a hollow iron oxide (Fe₃O₄) particle-reinforced magnesium matrix composite according to claim 1, wherein The protective gas is a mixed gas of CO₂ and SF₆, and the volume ratio of CO₂ to SF₆ is (40 - 45):1; The parameters set for the stirrer are: rotation speed 30 r / min to 60 r / min, time 20 min to 25 min, where it rotates clockwise for 12 min to 15 min first, and then rotates counterclockwise for 8 min to 10 min; The steps of multi-step hierarchical hot pressing rapid forming are as follows: First stage: First, set the pressure to 50 kN to 55 kN, the pressure holding time to 5 s to 10 s, and the load application rate to 5 kN / s to 10 kN / s; then set the pressure to 100 kN to 110 kN, the pressure holding time to 10 s to 15 s, and the load application rate to 10 kN / s to 15 kN / s; Second stage: First, set the pressure to 150 kN to 155 kN, the pressure holding time to 10 s to 15 s, and the load application rate to 15 kN / s to 20 kN / s; then set the pressure to 450 kN to 500 kN, the pressure holding time to 60 s to 70 s, and the load application rate to 20 kN / s to 25 kN / s. The drying temperature in Step 1 is 90°C to 110°C, and the time is 3 days to 5 days.

3. The preparation method of a hollow iron oxide (Fe₃O₄) particle-reinforced magnesium matrix composite material according to claim 1, wherein The steps of multi-stage variable temperature differential speed high-shear in Step 1 are as follows: Set the temperature to 30 °C, then place the high-shear disperser into a beaker and conduct the first-stage dispersion at 30 °C, set the speed to 120 r / min, and the time to 30 min; then set the temperature to 40 °C for the second-stage dispersion, set the speed to 240 r / min, and the time to 30 min.

4. The preparation method of a hollow iron oxide (Fe₃O₄) particle-reinforced magnesium matrix composite material according to claim 1, wherein The steps of variable-frequency ultrasonic combined with multi-stage variable temperature magnetic stirring in Step 1 are as follows: Conduct the first-stage ultrasonic and magnetic stirring simultaneously for 30 min under the conditions of ultrasonic power of 800 W - 1000 W, magnetic stirring speed of 60 r / min - 120 r / min, and temperature of 25 °C - 30 °C; then conduct the second-stage ultrasonic and magnetic stirring simultaneously for 30 min under the conditions of ultrasonic power of 1000 W - 1200 W, magnetic stirring speed of 130 r / min - 240 r / min, and temperature of 30 °C - 35 °C.

5. The preparation method of a hollow iron oxide (Fe₃O₄) particle-reinforced magnesium matrix composite material according to claim 1, characterized in that The mass of the preheated hollow iron oxide powder described in Step 2 is 1% of the mass of the matrix magnesium alloy ingot.

6. The preparation method of a hollow iron oxide (Fe₃O₄) particle-reinforced magnesium matrix composite material according to claim 1, characterized in that The steps of hierarchical multi-step hot pressing rapid prototyping described in Step 2 are as follows: The first stage: First, set the pressure to 50 kN, the pressure holding time to 5 s, and the load application rate to 5 kN / s; then set the pressure to 100 kN, the pressure holding time to 10 s, and the load application rate to 10 kN / s; The second stage: First, set the pressure to 150 kN, the pressure holding time to 10 s, and the load application rate to 15 kN / s; then set the pressure to 450 kN, the pressure holding time to 60 s, and the load application rate to 20 kN / s.

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