Novel special high-temperature electrical-grade magnesium oxide powder and preparation method thereof

Abstract

The invention discloses novel special high-temperature electrical-grade magnesium oxide powder and a preparation method thereof, and relates to the technical field of metal processing.The preparation method comprises the following steps that 6.5 parts by weight of aluminum ingots are heated to 800 DEG C, 0.75 part by weight of zirconium powder and 0.4 part by weight of scandium powder are added, and then stirring is conducted; adding 0.3 part by weight of niobium powder and 0.15 part by weight of titanium powder, continuously stirring for 30 minutes to form an intermediate alloy melt, pouring the melt into a rotating copper roller, stirring for 30 minutes at the rotating speed of 3000rpm for solidification, adding 0.2 part by weight of calcium particles and 0.075 part by weight of strontium particles, and continuously stirring for 20 minutes at the rotating speed of 3000rpm; adding 0.25 part by weight of # imgabs0 # agent, refining for 2 hours, then standing for 10 minutes, skimming surface scum to obtain a magnesium powder melt, cooling the magnesium powder melt to 600 DEG C, and keeping the temperature for 10 minutes to form a solid-liquid two-phase coexistence state; then stirring is conducted for 30 min at the rotating speed of 300 rpm, semi-solid slurry is obtained, then the semi-solid slurry is injected into a mold preheated to 250-300 DEG C, the pressure casting pressure is 100 MPa, and the pressure maintaining time is 12 s; high strength and high corrosion resistance can be both considered.

Description

Technical Field

[0001] The invention relates to the technical field of metal processing, and more specifically to a novel special high-temperature electrical grade magnesium oxide powder and a preparation method thereof. Background Art

[0002] Magnesium powder is widely used in many fields due to its low density, high strength and good corrosion resistance. It has broad application prospects in aerospace, automobile manufacturing, electronic equipment and other fields. However, the magnesium-aluminum matrix easily reacts with water, oxygen, chloride ions and other substances in the environment to form a loose oxide film, which leads to local corrosion, such as pitting and galvanic corrosion. Therefore, it is necessary to improve the corrosion resistance of magnesium powder. Traditional magnesium powder relies on major elements (such as Al and Zn) for composition design, lacks the coordinated optimization of trace elements, and is difficult to take into account both high strength and high corrosion resistance. It is also easy to introduce microscopic defects such as pores, shrinkage, segregation, etc. These defects become the starting point of corrosion. Existing processes are difficult to effectively refine grains or optimize composite strengthening phases, resulting in sensitivity to intergranular corrosion. Summary of the invention

[0003] In order to solve the above problems, the present invention provides a method for preparing a novel special high-temperature electrical grade magnesium oxide powder.

[0004] The present invention provides a method for preparing a novel special high-temperature electrical grade magnesium oxide powder, comprising the following steps: Step 1: Heat 6.5 parts by weight of an aluminum ingot to 800° C., add 0.75 parts by weight of zirconium powder and 0.4 parts by weight of scandium powder, and then stir; Then, 0.3 parts by weight of niobium powder and 0.15 parts by weight of titanium powder were added, and stirring was continued for 30 minutes to form an intermediate alloy melt. The melt was poured into a rotating copper roller and stirred at 3000 rpm for 30 minutes for solidification. 0.2 parts by weight of calcium particles and 0.075 parts by weight of strontium particles were added, and stirring was continued at 3000 rpm for 20 minutes. Add 0.25 parts by weight agent, refining for 2 hours, then standing for 10 minutes, skimming the surface scum to obtain a magnesium-aluminum alloy melt; Step 2: Cooling the magnesium-aluminum alloy melt to 600°C and keeping it at this temperature for 10 minutes to form a solid-liquid two-phase coexistence state; Then, the mixture was stirred at a speed of 300 rpm for 30 min to obtain a semi-solid slurry, and then the semi-solid slurry was injected into a mold preheated to 250-300°C, with a die-casting pressure of 100 MPa and a holding time of 12 s. Finally, the mixture was cooled to room temperature to obtain a nearly formed casting. Step 3: Heat the nearly formed casting to 440°C, keep it warm for 12 hours, then water quench it to room temperature, and then air cool it at 180°C for 10 hours, and finally air cool it at 120°C for 24 hours to obtain a complete casting; Step 4: Immerse the complete casting in chemical degreasing solution at 550°C for 15 minutes. Then rinse with clean water until the degreaser remaining on the surface is removed; The cleaned complete casting is placed in a micro-arc oxidation tank, alkaline electrolyte is added to the micro-arc oxidation tank, the working voltage is set to 550V, the current density is 0.05 amperes per square decimeter, the processing time is 45 minutes, and the preparation is completed.

[0005] Preferably, the specific working steps of step 2 also include the following: A monitoring cycle is set in advance, and the temperature T of the magnesium-aluminum alloy melt is obtained every other cycle; The ambient temperature T1, ambient humidity RH, ambient air velocity V and ambient atmospheric pressure P are obtained every other cycle; Every other cycle according to the formula , the cooling rate D of the magnesium-aluminum alloy melt is calculated and obtained, and the unit of the cooling rate D is ℃ / min; Where A is the surface area of ​​the magnesium-aluminum alloy solution, in m², is the density of the aluminum-magnesium alloy solution, in kg / m³, c is the specific heat capacity of the magnesium-aluminum alloy solution, in J / (kg·K), and V is the volume of the magnesium-aluminum alloy solution, in m³; Where H is the effective heat transfer coefficient, T2 is the dew point temperature; Every other cycle, the power P of the cooling device used in the cooling process of the magnesium-aluminum alloy melt is calculated according to the cooling rate D of the magnesium-aluminum alloy melt, and the power P of the cooling device obtained by calculation is transmitted to the cooling device as a signal to adjust the power of the cooling device to P.

[0006] Preferably, the specific calculation steps of the effective heat transfer coefficient are as follows: According to the formula , calculate and obtain the effective heat transfer coefficient H.

[0007] Preferably, the specific steps of calculating the power P of the cooling equipment used in the process of cooling the magnesium-aluminum alloy melt according to the cooling rate D of the magnesium-aluminum alloy melt are as follows: The reference ambient temperature T3 when the magnesium-aluminum alloy melt is cooled is set in advance; According to the formula , calculate and obtain the power P of the adjusted cooling device, where is the difference between the current temperature T and the target temperature, obtained by subtracting the current temperature T from the target temperature. The target temperature is 600°C; Indicates the cumulative value of temperature deviation over time, that is, the sum of temperature deviations from the start of control to the current moment.

[0008] Preferably, the step 2 further comprises adjusting the rotation speed according to the ambient humidity to inhibit oxidation and ensure the rheological properties, and the specific steps of adjusting the rotation speed are as follows; Obtain a reference rotation speed N of the magnesium-aluminum alloy melt stirrer; Every other cycle, according to the formula

[0009] Calculate and obtain the adjusted agitator speed , and the obtained stirrer speed is calculated The signal is transmitted to the stirrer to adjust the speed of the cooling device to ; in is the current viscosity of the magnesium-aluminum alloy solution, is the target viscosity of the magnesium-aluminum alloy solution.

[0010] Preferably, the working step of step 2 further includes calculating the magnesium content loss of the magnesium-aluminum alloy solution in the process of becoming a near-molded casting according to the ambient pressure. , the specific steps are as follows: Every other cycle, the atmospheric pressure Pt of the current environment is obtained; According to the formula , where t1 is the exposure time of the magnesium-aluminum alloy under the current atmospheric pressure Pt, that is, the time of one cycle.

[0011] Preferably, the step three further comprises dynamically adjusting the solution holding time according to the initial state of the casting to ensure that the non-equilibrium phase is completely dissolved, and the specific steps are: Every other cycle, the initial residual stress M and initial density of the nearly formed casting are obtained. ; Every other cycle, according to the formula , the dynamically adjusted solution holding time V1 is calculated, where V is the holding time of the nearly formed casting, which is 12h. The target density of the near-shaped casting is set in advance.

[0012] Preferably, the specific steps of preparing the chemical degreasing liquid in step 4 include the following: The chemical degreasing liquid specifically includes the following components and mass concentrations: sodium hydroxide 30-50g / L; sodium carbonate 20-30g / L; trisodium phosphate 10-20g / L; sodium silicate 5-10g / L and the balance water; During the preparation process, add about 500 mL of water to a corrosion-resistant container, then add sodium hydroxide. When sodium hydroxide dissolves, it will release heat, so you need to wear protective gloves and glasses. Add sodium carbonate, trisodium phosphate and sodium silicate in turn, stir, and finally add the remaining water to complete the preparation.

[0013] Preferably, the specific preparation steps of the alkaline electrolyte include the following: The alkaline electrolyte specifically includes the following components and mass concentrations: sodium silicate: 20 g / L, sodium hydroxide: 15 g / L, potassium fluoride: 3 g / L, sodium citrate: 1 g / L, triethanolamine: 3 mL / L, and the balance is deionized water; During the preparation process, sodium silicate, sodium hydroxide, potassium fluoride, and sodium citrate were dissolved in appropriate amounts of deionized water, and then 3 mL / L of triethanolamine was added and stirred continuously. The mixed electrolyte was allowed to stand for 1 hour to complete the preparation.

[0014] Preferably, the electrolyte temperature will rise during the micro-arc oxidation process in step 4, and a cooling system is required to control the overall temperature. The specific working steps include: Install a circulating cooling system in the micro-arc oxidation tank, including a cooling water circulation device and a heat exchanger; Before starting micro-arc oxidation, the electrolyte was precooled to 35 °C to reduce initial temperature fluctuations; Install a temperature sensor in the electrolyte tank to monitor the current temperature of the electrolyte; Every other cycle, the cooling power of the cooling system is automatically adjusted according to the current temperature of the electrolyte to ensure that the electrolyte temperature does not exceed 40°C; The steps to adjust the cooling power of the cooling system are as follows: Obtain the temperature rise rate X1 of the electrolyte in the current cycle relative to the previous cycle, and obtain the difference X2 between the target temperature of the electrolyte and the current temperature; According to the formula , calculate the cooling power of the adjusted cooling system , and according to the cooling power of the adjusted cooling system Adjust the power of the cooling system; in is the total heat of the electrolyte.

[0015] Beneficial effects: By adding zirconium, scandium, niobium, titanium and other alloy elements, a multi-element alloy strengthening phase is formed, which greatly improves the high temperature resistance of magnesium oxide and enables the material to maintain excellent thermal stability at a high temperature of 2000°C. By dynamically controlling the cooling rate and stirring parameters, adjusting the cooling power and stirring speed in real time, the melt viscosity fluctuation is stabilized, solving the problem of unstable performance caused by fluctuations in environmental parameters in traditional processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0017] Application scenarios: In actual use, traditional magnesium-aluminum alloys rely on major elements (such as Al and Zn) for composition design, lack the coordinated optimization of trace elements, and are difficult to take into account both high strength and high corrosion resistance. They are also prone to introduce microscopic defects such as pores, shrinkage, segregation, etc. These defects become the starting point of corrosion. Existing processes are difficult to effectively refine grains or optimize composite strengthening phases, resulting in sensitivity to grain boundary corrosion.

[0018] like Figure 1 As shown: A method for preparing a new type of special high-temperature electrical grade magnesium oxide powder, comprising the following steps: Step 1: Heat 6.5 parts by weight of an aluminum ingot to 800° C., add 0.75 parts by weight of zirconium powder and 0.4 parts by weight of scandium powder, and then stir; Then, 0.3 parts by weight of niobium powder and 0.15 parts by weight of titanium powder were added, and stirring was continued for 30 minutes to form an intermediate alloy melt. The melt was poured into a rotating copper roller and stirred at 3000 rpm for 30 minutes for solidification. 0.2 parts by weight of calcium particles and 0.075 parts by weight of strontium particles were added, and stirring was continued at 3000 rpm for 20 minutes. Add 0.25 parts by weight agent, refined for 2 hours, then allowed to stand for 10 minutes, and the surface scum was skimmed off to obtain a magnesium-aluminum alloy melt; it should be noted that before the preparation, high-purity magnesium ingots (≥99.98%) and high-purity aluminum ingots (≥99.95%) were prepared, the surface of the magnesium ingots was polished to remove the oxide layer, the aluminum ingots were preheated to 200°C to remove surface moisture, the magnesium ingots and aluminum ingots were placed in a vacuum furnace, heated to 400°C (magnesium) and 600°C (aluminum), and kept warm for 1 hour to remove the adsorbed gas; Step 2: Cooling the magnesium-aluminum alloy melt to 600°C and keeping it warm for 10 minutes to form a solid-liquid coexistence state; it should be noted that the solid phase ratio is 30-40%; Then, the mixture was stirred at a speed of 300 rpm for 30 min to obtain a semi-solid slurry, and then the semi-solid slurry was injected into a mold preheated to 250-300°C, with a die-casting pressure of 100 MPa and a holding time of 12 s. Finally, the mixture was cooled to room temperature to obtain a nearly formed casting. Step 3: Heat the nearly formed casting to 440°C, keep it warm for 12 hours, then water quench it to room temperature, and then air cool it at 180°C for 10 hours, and finally air cool it at 120°C for 24 hours to obtain a complete casting; Step 4: Immerse the complete casting in chemical degreasing solution at 550°C for 15 minutes. Then rinse with clean water until the degreaser remaining on the surface is removed; The cleaned complete casting is placed in a micro-arc oxidation tank, alkaline electrolyte is added to the micro-arc oxidation tank, the working voltage is set to 550V, the current density is 0.05 amperes per square decimeter, the processing time is 45 minutes, and the preparation is completed.

[0019] It should be noted that the first stage is 180°C × 10h, which is used to form a high-density nano-precipitation phase, and the second stage is 120°C × 24h, which further refines the precipitation phase and improves strength and corrosion resistance.

[0020] As an optional embodiment: the specific working steps of step 2 also include the following: It should be noted that the magnesium-aluminum alloy melt needs to be accurately cooled from the liquid state (750-800°C) to the semi-solid range (580-600°C), and the temperature fluctuation needs to be controlled within ±5°C, otherwise the solid phase ratio (30-40%) is difficult to stabilize. Therefore, in actual use, it is necessary to adjust the subsequent parameters in real time according to the temperature of the magnesium-aluminum alloy melt; A monitoring cycle is set in advance, and the temperature T of the magnesium-aluminum alloy melt is obtained every other cycle; It should be noted that the monitoring period is a pre-set time interval, which is expressed in seconds in this embodiment. The monitoring period in this embodiment is 60 seconds; It should also be noted that the temperature of the magnesium-aluminum alloy melt can be obtained by temperature monitoring equipment, specifically a high-precision thermocouple: inserted into the melt, real-time temperature measurement and infrared thermometer; The ambient temperature T1, ambient humidity RH, ambient air velocity V and ambient atmospheric pressure P are obtained every other cycle; it should be noted that the above parameters are parameters under the preparation environment, which are specifically obtained by installing corresponding sensors in the workshop for detection; Every other cycle according to the formula , the cooling rate D of the magnesium-aluminum alloy melt is calculated and obtained, and the unit of the cooling rate D is ℃ / min; Where A is the surface area of ​​the magnesium-aluminum alloy solution, in m², is the density of the aluminum-magnesium alloy solution, in kg / m³, c is the specific heat capacity of the magnesium-aluminum alloy solution, in J / (kg·K), and V is the volume of the magnesium-aluminum alloy solution, in m³; it should be noted that the above parameters are obtained by measuring the magnesium-aluminum alloy melt after forming, wherein the typical value of the density of the magnesium-aluminum alloy is 1800 kg / m³, and the typical value of the specific heat capacity of the magnesium-aluminum alloy is 1000 J / (kg·K); Where H is the effective heat transfer coefficient, and T2 is the dew point temperature. It should be noted that the dew point temperature is closely related to the ambient humidity. The higher the humidity, the closer the dew point temperature is to the ambient temperature. During the melt cooling process, if the melt temperature is close to or lower than the dew point temperature, water vapor in the air will condense on the melt surface, intensifying the oxidation reaction and releasing heat, thereby affecting the cooling rate. It should also be noted that the dew point temperature T2 can be calculated from the ambient temperature T1 and the ambient humidity RH according to the formula Calculate and obtain; Every other cycle, the power P of the cooling device used in the cooling process of the magnesium-aluminum alloy melt is calculated according to the cooling rate D of the magnesium-aluminum alloy melt, and the power P of the cooling device obtained by calculation is transmitted to the cooling device as a signal to adjust the power of the cooling device to P.

[0021] It should be noted that in the actual semi-solid forming process of magnesium-aluminum alloy, environmental parameters (such as air flow rate, humidity, etc.) have a significant impact on the melt cooling process. This embodiment introduces specific environmental parameters so that the melt can be accurately cooled to 580-600°C and the solid phase fraction can be stabilized at 30-40% under ambient temperature fluctuations.

[0022] As an optional embodiment: the specific calculation steps of the effective heat transfer coefficient are as follows: According to the formula , calculate and obtain the effective heat transfer coefficient H.

[0023] As an optional embodiment: the specific steps of calculating the power P of the cooling device used in the process of cooling the magnesium-aluminum alloy melt according to the cooling rate D of the magnesium-aluminum alloy melt are as follows: The reference ambient temperature T3 of the magnesium-aluminum alloy melt when the temperature is reduced is set in advance; it should be noted that the reference ambient temperature T3 is the ideal state temperature of the magnesium-aluminum alloy melt when the temperature is reduced, and in this embodiment, it is 25° C.; According to the formula , calculate and obtain the power P of the adjusted cooling device, where is the difference between the current temperature T and the target temperature, obtained by subtracting the current temperature T from the target temperature. The target temperature is 600°C; Indicates the cumulative value of temperature deviation over time, that is, the sum of temperature deviations from the start of control to the current moment.

[0024] As an optional embodiment: the step of step 2 further includes adjusting the rotation speed according to the ambient humidity to inhibit oxidation and ensure the rheological properties. The specific steps of adjusting the rotation speed are as follows: The reference speed N of the magnesium-aluminum alloy melt stirrer is obtained; it should be noted that, in this embodiment, the reference speed N is 300 rpm; Every other cycle, according to the formula

[0025] Calculate and obtain the adjusted agitator speed , and the obtained stirrer speed is calculated The signal is transmitted to the stirrer to adjust the speed of the cooling device to ; in is the current viscosity of the magnesium-aluminum alloy solution, is the target viscosity of the magnesium-aluminum alloy solution.

[0026] It should be noted that the current viscosity is obtained by monitoring the monitoring equipment, and the target viscosity is the melt viscosity corresponding to the target solid phase ratio (30-40%).

[0027] As an optional embodiment: the working step of step 2 also includes calculating the magnesium content loss of the magnesium-aluminum alloy solution in the process of becoming a near-molded casting according to the ambient pressure. , the specific steps are as follows: It should be noted that in low pressure (such as in plateau areas), the volatilization of Mg elements will intensify, causing the composition of magnesium-aluminum alloy to deviate from the design value. This technical solution can calculate the addition of magnesium ingots at the end of smelting according to the current atmospheric pressure of the environment when the atmospheric pressure of the environment changes; Every other cycle, the atmospheric pressure Pt of the current environment is obtained; it should be noted that the atmospheric pressure Pt of the current environment is obtained through the corresponding sensor; According to the formula , where t1 is the exposure time of the magnesium-aluminum alloy under the current atmospheric pressure Pt, that is, the time of one cycle.

[0028] As an optional embodiment: the step three also includes dynamically adjusting the solution holding time according to the initial state of the casting to ensure that the non-equilibrium phase is completely dissolved, and the specific steps are: Every other cycle, the initial residual stress M and initial density of the nearly formed casting are obtained. ; It should be noted that the initial density of the casting can be obtained by non-destructive testing technology (such as ultrasonic testing, X-ray testing, etc.) or physical measurement methods (such as density measurement), and the initial residual stress of the casting can be obtained by residual stress measurement technology (such as X-ray diffraction method, blind hole method, etc.); Every other cycle, according to the formula , the dynamically adjusted solution holding time V1 is calculated, where V is the holding time of the nearly formed casting, which is 12h. It is the target density of the near-shaped casting set in advance. It should be noted that in this embodiment, the target density is 98%.

[0029] As an optional embodiment: the specific preparation steps of the chemical degreasing liquid in step 4 include the following: The chemical degreasing liquid specifically includes the following components and mass concentrations: sodium hydroxide 30-50g / L; sodium carbonate 20-30g / L; trisodium phosphate 10-20g / L; sodium silicate 5-10g / L and the balance water; During the preparation process, add about 500 mL of water to a corrosion-resistant container, then add sodium hydroxide. When sodium hydroxide dissolves, it will release heat, so you need to wear protective gloves and glasses. Add sodium carbonate, trisodium phosphate and sodium silicate in turn, stir, and finally add the remaining water to complete the preparation.

[0030] As an optional embodiment: the specific preparation steps of the alkaline electrolyte include the following: The alkaline electrolyte specifically includes the following components and mass concentrations: sodium silicate: 20 g / L, sodium hydroxide: 15 g / L, potassium fluoride: 3 g / L, sodium citrate: 1 g / L, triethanolamine: 3 mL / L, and the balance is deionized water; During the preparation process, sodium silicate, sodium hydroxide, potassium fluoride, and sodium citrate were dissolved in appropriate amounts of deionized water, and then 3 mL / L of triethanolamine was added and stirred continuously. The mixed electrolyte was allowed to stand for 1 hour to complete the preparation.

[0031] As an optional embodiment: In the micro-arc oxidation process in step 4, the temperature of the electrolyte will rise, and a cooling system is required to control the overall temperature. The specific working steps include: Install a circulating cooling system in the micro-arc oxidation tank, including a cooling water circulation device and a heat exchanger; Before starting micro-arc oxidation, the electrolyte was precooled to 35 °C to reduce initial temperature fluctuations; Install a temperature sensor in the electrolyte tank to monitor the current temperature of the electrolyte; Every other cycle, the cooling power of the cooling system is automatically adjusted according to the current temperature of the electrolyte to ensure that the electrolyte temperature does not exceed 40°C; The steps to adjust the cooling power of the cooling system are as follows: Obtain the temperature rise rate X1 of the electrolyte in the current cycle relative to the previous cycle, and obtain the difference X2 between the target temperature of the electrolyte and the current temperature; According to the formula , calculate the cooling power of the adjusted cooling system , and according to the cooling power of the adjusted cooling system Adjust the power of the cooling system; in It should be noted that, through the above method, the temperature and cooling rate of the electrolyte can be effectively controlled, thereby ensuring the stability of the micro-arc oxidation process and the quality of the film layer.

[0032] Working principle: Step 1: Heat 6.5 parts by weight of an aluminum ingot to 800° C., add 0.75 parts by weight of zirconium powder and 0.4 parts by weight of scandium powder, and then stir; Then, 0.3 parts by weight of niobium powder and 0.15 parts by weight of titanium powder were added, and stirring was continued for 30 minutes to form an intermediate alloy melt. The melt was poured into a rotating copper roller and stirred at 3000 rpm for 30 minutes for solidification. 0.2 parts by weight of calcium particles and 0.075 parts by weight of strontium particles were added, and stirring was continued at 3000 rpm for 20 minutes. Add 0.25 parts by weight agent, refined for 2 hours, then allowed to stand for 10 minutes, and the surface scum was skimmed off to obtain a magnesium-aluminum alloy melt; it should be noted that before the preparation, high-purity magnesium ingots (≥99.98%) and high-purity aluminum ingots (≥99.95%) were prepared, the surface of the magnesium ingots was polished to remove the oxide layer, the aluminum ingots were preheated to 200°C to remove surface moisture, the magnesium ingots and aluminum ingots were placed in a vacuum furnace, heated to 400°C (magnesium) and 600°C (aluminum), and kept warm for 1 hour to remove the adsorbed gas; Step 2: Cooling the magnesium-aluminum alloy melt to 600°C and keeping it warm for 10 minutes to form a solid-liquid coexistence state; it should be noted that the solid phase ratio is 30-40%; Then, the mixture was stirred at a speed of 300 rpm for 30 min to obtain a semi-solid slurry, and then the semi-solid slurry was injected into a mold preheated to 250-300°C, with a die-casting pressure of 100 MPa and a holding time of 12 s. Finally, the mixture was cooled to room temperature to obtain a nearly formed casting. Step 3: Heat the nearly formed casting to 440°C, keep it warm for 12 hours, then water quench it to room temperature, and then air cool it at 180°C for 10 hours, and finally air cool it at 120°C for 24 hours to obtain a complete casting; Step 4: Immerse the complete casting in chemical degreasing solution at 550°C for 15 minutes. Then rinse with clean water until the degreaser remaining on the surface is removed; The cleaned complete casting is placed in a micro-arc oxidation tank, alkaline electrolyte is added to the micro-arc oxidation tank, the working voltage is set to 550V, the current density is 0.05 amperes per square decimeter, the processing time is 45 minutes, and the preparation is completed.

[0033] The above are only preferred implementations of the present invention. The protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technical staff in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of this template.

Claims

1. A method for preparing a novel special high-temperature electrical grade magnesium oxide powder, characterized in that: The following steps are involved: Step 1: Heat 6.5 parts by weight of an aluminum ingot to 800° C., add 0.75 parts by weight of zirconium powder and 0.4 parts by weight of scandium powder, and then stir; Then, 0.3 parts by weight of niobium powder and 0.15 parts by weight of titanium powder were added, and stirring was continued for 30 minutes to form an intermediate alloy melt. The melt was poured into a rotating copper roller and stirred at 3000 rpm for 30 minutes for solidification. 0.2 parts by weight of calcium particles and 0.075 parts by weight of strontium particles were added, and stirring was continued at 3000 rpm for 20 minutes. Add 0.25 parts by weight agent, refining for 2 hours, then standing for 10 minutes, skimming the surface scum to obtain a magnesium-aluminum alloy melt; Step 2: Cooling the magnesium-aluminum alloy melt to 600°C and keeping it at this temperature for 10 minutes to form a solid-liquid two-phase coexistence state; Then, the mixture was stirred at a speed of 300 rpm for 30 min to obtain a semi-solid slurry, and then the semi-solid slurry was injected into a mold preheated to 250-300°C, with a die-casting pressure of 100 MPa and a holding time of 12 s. Finally, the mixture was cooled to room temperature to obtain a nearly formed casting. Step 3: Heat the nearly formed casting to 440°C, keep it warm for 12 hours, then water quench it to room temperature, and then air cool it at 180°C for 10 hours, and finally air cool it at 120°C for 24 hours to obtain a complete casting; Step 4: Immerse the complete casting in chemical degreasing solution at 550°C for 15 minutes. Then rinse with clean water until the degreaser remaining on the surface is removed; The cleaned complete casting is placed in a micro-arc oxidation tank, alkaline electrolyte is added to the micro-arc oxidation tank, the working voltage is set to 550V, the current density is 0.05 amperes per square decimeter, the processing time is 45 minutes, and the preparation is completed.

2. The method for preparing a novel special high temperature electrical grade magnesium oxide powder according to claim 1, characterized in that: The specific working steps of step 2 also include the following: A monitoring cycle is set in advance, and the temperature T of the magnesium-aluminum alloy melt is obtained every other cycle; The ambient temperature T1, ambient humidity RH, ambient air velocity V and ambient atmospheric pressure P are obtained every other cycle; Every other cycle according to the formula , the cooling rate D of the magnesium-aluminum alloy melt is calculated and obtained, and the unit of the cooling rate D is ℃ / min; Where A is the surface area of ​​the magnesium-aluminum alloy solution, in m², is the density of the aluminum-magnesium alloy solution, in kg / m³, c is the specific heat capacity of the magnesium-aluminum alloy solution, in J / (kg·K), and V is the volume of the magnesium-aluminum alloy solution, in m³; Where H is the effective heat transfer coefficient, T2 is the dew point temperature; Every other cycle, the power P of the cooling device used in the cooling process of the magnesium-aluminum alloy melt is calculated according to the cooling rate D of the magnesium-aluminum alloy melt, and the power P of the cooling device obtained by calculation is transmitted to the cooling device as a signal to adjust the power of the cooling device to P.

3. The method for preparing a novel special high temperature electrical grade magnesium oxide powder according to claim 2, characterized in that: The specific calculation steps of the effective heat transfer coefficient are as follows: According to the formula , calculate and obtain the effective heat transfer coefficient H.

4. The method for preparing a novel special high temperature electrical grade magnesium oxide powder according to claim 2, characterized in that: The specific steps of calculating the power P of the cooling device used in the process of cooling the magnesium-aluminum alloy melt according to the cooling rate D of the magnesium-aluminum alloy melt are as follows: The reference ambient temperature T3 when the magnesium-aluminum alloy melt is cooled is set in advance; According to the formula , calculate and obtain the power P of the adjusted cooling device, where is the difference between the current temperature T and the target temperature, obtained by subtracting the current temperature T from the target temperature. The target temperature is 600°C; Indicates the cumulative value of temperature deviation over time, that is, the sum of temperature deviations from the start of control to the current moment.

5. The method for preparing a novel special high temperature electrical grade magnesium oxide powder according to claim 2, characterized in that: The step 2 further includes adjusting the rotation speed according to the ambient humidity to inhibit oxidation and ensure the rheological properties. The specific steps of adjusting the rotation speed are as follows: Obtain a reference rotation speed N of the magnesium-aluminum alloy melt stirrer; Every other cycle, according to the formula ; Calculate and obtain the adjusted agitator speed , and the obtained stirrer speed is calculated The signal is transmitted to the stirrer to adjust the speed of the cooling device to ; in is the current viscosity of the magnesium-aluminum alloy solution, is the target viscosity of the magnesium-aluminum alloy solution.

6. The method for preparing a novel special high temperature electrical grade magnesium oxide powder according to claim 2, characterized in that: The working step of step 2 also includes calculating the magnesium content loss of the magnesium-aluminum alloy solution in the process of becoming a near-molded casting according to the ambient air pressure. , the specific steps are as follows: Every other cycle, the atmospheric pressure Pt of the current environment is obtained; According to the formula , where t1 is the exposure time of the magnesium-aluminum alloy under the current atmospheric pressure Pt, that is, the time of one cycle.

7. The method for preparing a novel special high temperature electrical grade magnesium oxide powder according to claim 1, characterized in that: The step three also includes dynamically adjusting the solution holding time according to the initial state of the casting to ensure that the non-equilibrium phase is completely dissolved. The specific steps are: Every other cycle, the initial residual stress M and initial density of the nearly formed casting are obtained. ; Every other cycle, according to the formula , the dynamically adjusted solution holding time V1 is calculated, where V is the holding time of the nearly formed casting, which is 12h. The target density of the near-shaped casting is set in advance.

8. The method for preparing a novel special high temperature electrical grade magnesium oxide powder according to claim 1, characterized in that: The specific preparation steps of the chemical degreasing liquid in step 4 include the following: The chemical degreasing liquid specifically includes the following components and mass concentrations: sodium hydroxide 30-50g / L; sodium carbonate 20-30g / L; trisodium phosphate 10-20g / L; sodium silicate 5-10g / L and the balance water; During the preparation process, add about 500 mL of water to a corrosion-resistant container, then add sodium hydroxide, then add sodium carbonate, trisodium phosphate and sodium silicate in sequence, stir, and finally add the remaining amount of water to complete the preparation.

9. The method for preparing a novel special high temperature electrical grade magnesium oxide powder according to claim 1, characterized in that: The specific preparation steps of the alkaline electrolyte include the following: The alkaline electrolyte specifically includes the following components and mass concentrations: sodium silicate: 20 g / L, sodium hydroxide: 15 g / L, potassium fluoride: 3 g / L, sodium citrate: 1 g / L, triethanolamine: 3 mL / L, and the balance is deionized water; During the preparation process, sodium silicate, sodium hydroxide, potassium fluoride, and sodium citrate were dissolved in an appropriate amount of deionized water, and then 3 mL / L of triethanolamine was added and stirred continuously. The mixed electrolyte was allowed to stand for 1 hour to complete the preparation; In the process of micro-arc oxidation in step 4, the temperature of the electrolyte will increase, and a cooling system is required to control the overall temperature. The specific working steps include: Install a circulating cooling system in the micro-arc oxidation tank, including a cooling water circulation device and a heat exchanger; Before starting micro-arc oxidation, the electrolyte was precooled to 35 °C to reduce initial temperature fluctuations; Install a temperature sensor in the electrolyte tank to monitor the current temperature of the electrolyte; Every other cycle, the cooling power of the cooling system is automatically adjusted according to the current temperature of the electrolyte to ensure that the electrolyte temperature does not exceed 40°C; The steps to adjust the cooling power of the cooling system are as follows: Obtain the temperature rise rate X1 of the electrolyte in the current cycle relative to the previous cycle, and obtain the difference X2 between the target temperature of the electrolyte and the current temperature; According to the formula , calculate the cooling power of the adjusted cooling system , and according to the cooling power of the adjusted cooling system Adjust the power of the cooling system; in is the total heat of the electrolyte.

10. A new type of special high temperature electrical grade magnesium oxide powder, characterized in that: The novel special high-temperature electrical grade magnesium oxide powder is prepared by the preparation method of the novel special high-temperature electrical grade magnesium oxide powder according to any one of claims 1 to 9.

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