High-resistivity hot-pressed samarium-cobalt permanent magnet and preparation method thereof

Abstract

The invention relates to a high-resistivity hot-pressed samarium-cobalt permanent magnet and a preparation method thereof. The magnet is composed of samarium-cobalt-based alloy and an inorganic nano insulating material coating main phase grains of the magnet. The samarium cobalt-based alloy is one of SmCo5, Sm2Co17 and Sm2 (Co1-a-b-cFeaCubZrc) 17, a is equal to 0.08-0.16, b is equal to 0.01-0.02, c is equal to 0.05-0.07, the nano inorganic insulating material is two or more of four fluorides of CaF2, SmF3, DyF3 and NdF3, and the content of the fluorides accounts for 3%-11% of the total mass of the magnet. The magnet has the characteristics of high density, high corrosion resistance and high resistivity.

Description

Technical Field

[0002] The present invention belongs to the field of rare earth permanent magnet materials, and relates to a high-resistivity samarium cobalt permanent magnet material and a preparation method thereof. Background Art

[0003] Samarium cobalt permanent magnet materials are widely used in wind power generation, rail transit, aerospace, and military fields due to their excellent corrosion resistance, high temperature stability, and high coercivity. However, as an alloy, samarium cobalt permanent magnet materials inherently have good electrical conductivity. When samarium cobalt permanent magnet materials are applied to motors, eddy current losses will occur, causing the temperature to rise, the magnetic properties to decline, and irreversible demagnetization in severe cases.

[0004] To address the above problems, there are usually two solutions. One is to optimize the structure of the motor to improve the overall temperature resistance of the motor. Research shows that by improving the magnetic circuit structure, pole-slot matching, stator winding arrangement, and changing the shape and size of the magnet, eddy current losses can be reduced to a certain extent, but the effect is not ideal, and it places high requirements on motor designers. The other is to insulate and coat the main phase grains by adding high-resistivity organic polymers or inorganic substances to the magnet to reduce the electron transport efficiency inside the magnet, thereby increasing the resistivity of the permanent magnet. However, the incorporation of organic polymers will significantly reduce the density of the permanent magnet, resulting in a decline in magnetic properties, and most of their melting points are relatively low. The continuously rising temperature during the operation of the motor will soften them, affecting the working efficiency of the motor. Inorganic nano-insulating materials avoid this problem and can maintain high temperature resistance while increasing the resistivity of the permanent magnet.

[0005] Therefore, it is an urgent problem to be solved to provide a preparation method for a high-resistivity hot-pressed samarium cobalt composite magnet to reduce eddy current losses generated during the operation of the motor. Summary of the Invention

[0006] Samarium cobalt permanent magnet materials are widely used in wind power generation, rail transit, aerospace, and military fields due to their excellent corrosion resistance, high temperature stability, and high coercivity. However, as an alloy, samarium cobalt permanent magnet materials inherently have good electrical conductivity. When samarium cobalt permanent magnet materials are applied to motors, eddy current losses will occur, causing the temperature to rise, the magnetic properties to decline, and irreversible demagnetization in severe cases.

[0007] For the above problems, there are usually two solutions. One is to optimize the structure of the motor to improve the overall temperature resistance of the motor. Research shows that by improving the magnetic circuit structure, pole-slot matching, stator winding arrangement, and changing the shape and size of the magnet, eddy current loss can be reduced to a certain extent, but the effect is not ideal, and it poses high requirements for motor designers. The other is to insulate and coat the main-phase grains by adding high-resistivity organic polymers or inorganic substances to the magnet, reducing the electron transport efficiency inside the magnet, thereby increasing the resistivity of the permanent magnet. However, the incorporation of organic polymers will significantly reduce the density of the permanent magnet, leading to a decline in magnetic properties, and most of their melting points are relatively low. The continuously rising temperature during motor operation will soften them, affecting the working efficiency of the motor. Inorganic nano-insulating materials avoid this problem and can maintain high temperature resistance while increasing the resistivity of the permanent magnet.

[0008] Therefore, it is an urgent problem to be solved to provide a method for preparing a high-resistivity hot-pressed samarium cobalt composite magnet to reduce the eddy current loss generated during motor operation. Specific Embodiments

[0009] Weigh metallic samarium and metallic cobalt according to the molar ratio of 1:5, and add 5% more metallic samarium to make up for the volatilization of samarium element during melting, and carry out melting in a vacuum induction arc furnace; put the obtained ingot into a tubular furnace, evacuate the tubular furnace to a vacuum state, introduce argon into it, heat it to 900 °C at a heating rate of 10 °C / min, then hold for 60 min, and finally cool it to room temperature in the furnace and take it out; put the annealed ingot into a grinding jar to break and grind it, and pass through an 80-mesh sieve to obtain SmCo5 raw powder with a particle size of 8 - 100 μm; put four kinds of powders of CaF2, SmF3, DyF3, and NdF3 into anhydrous ethanol and argon for ball milling for 0 - 3 h, with a ball-to-material ratio of 7:1, and select the optimal particle size of each of the four kinds of powders: wet mill DyF3 for 0.5 h, wet mill NdF3 for 1 h, wet mill SmF3 for 3 h, and dry mill CaF2 for 1 h. Examples

[0010] The DyF3 wet-milled for 0.5 h and the NdF3 wet-milled for 1 h were mixed in a mass ratio of 1:1 and then incorporated into the samarium-cobalt powder for high-energy ball milling. The doping amount accounted for 5% of the total mass of the ball-milled powder. The ball-milling medium was n-heptane, the ball-to-material ratio was 10:1, and the ball-milling time was as long as 3 h. The ball-milled powder was placed in a drying oven and dried for 5 h. The inside of the drying oven was in a vacuum environment to avoid powder oxidation. Finally, a high-resistivity SmCo5 magnet was prepared by hot pressing technology. The hot pressing temperature was 550 °C and the pressure was 904 MPa. The magnetoelectric properties of the high-resistivity samarium-cobalt permanent magnet prepared in this example are shown in Table 1: remanence 5.95 kGs, coercivity 9.35 kOe, and maximum energy product 7.02 MGOe. The resistivity increased by 82 μΩ·cm compared with 81 μΩ·cm of Comparative Example 1 in Table 1. Example

[0011] The DyF3 wet-milled for 0.5 h and the NdF3 wet-milled for 1 h were mixed in a mass ratio of 1:2 and then incorporated into the samarium-cobalt powder for high-energy ball milling. The doping amount accounted for 5% of the total mass of the ball-milled powder. The ball-milling medium was n-heptane, the ball-to-material ratio was 10:1, and the ball-milling time was as long as 3 h. The ball-milled powder was placed in a drying oven and dried for 5 h. The inside of the drying oven was in a vacuum environment to avoid powder oxidation. Finally, a high-resistivity SmCo5 magnet was prepared by hot pressing technology. The hot pressing temperature was 550 °C and the pressure was 904 MPa. The magnetoelectric properties of the high-resistivity samarium-cobalt permanent magnet prepared in this example are shown in Table 1: remanence 9.02 kGs, coercivity 5.90 kOe, and maximum energy product 7.46 MGOe. The resistivity increased by 134 μΩ·cm compared with 81 μΩ·cm of Comparative Example 1 in Table 1. Example

[0012] The DyF3 wet-milled for 0.5 h and the NdF3 wet-milled for 1 h were mixed in a mass ratio of 2:1 and then incorporated into the samarium-cobalt powder for high-energy ball milling. The doping amount accounted for 5% of the total mass of the ball-milled powder. The ball-milling medium was n-heptane, the ball-to-material ratio was 10:1, and the ball-milling time was as long as 3 h. The ball-milled powder was placed in a drying oven and dried for 5 h. The inside of the drying oven was in a vacuum environment to avoid powder oxidation. Finally, a high-resistivity SmCo5 magnet was prepared by hot pressing technology. The hot pressing temperature was 550 °C and the pressure was 904 MPa. The magnetoelectric properties of the high-resistivity samarium-cobalt permanent magnet prepared in this example are shown in Table 1: remanence 5.74 kGs, coercivity 8.91 kOe, and maximum energy product 6.81 MGOe. The resistivity increased by 92 μΩ·cm compared with 81 μΩ·cm of Comparative Example 1 in Table 1.

[0013] Table 1 Magnetic properties and resistivity data of magnets prepared in examples and comparative examples <![CDATA[B r (KGs)]]> <![CDATA[H cj (KOe)]]> <![CDATA[(BH)]]> max (MGOe)]]> Resistivity (μΩ·cm) Comparative Example 1 6.366 14.25 9.006 81 Example 1 5.95 9.35 7.02 163 Example 2 5.90 9.02 7.46 215 Example 3 5.74 8.91 6.81 173

Claims

1. A high-resistivity hot-pressed samarium cobalt magnet, characterized in that: The high resistivity composite magnet is composed of a samarium-cobalt-based alloy and a nanometer inorganic insulating material. The samarium-cobalt-based alloy is SmCo5, Sm2Co 17 、Sm2(Co 1-a-b-c Fe a Cu b Zr c ) 17 One of the above, wherein a=0.08-0.16, b=0.01-0.02, c=0.05-0.

07. The insulating material is located at the grain boundary of the composite magnet and uniformly covers the main phase grains. The nano inorganic insulating material is two or more of the four materials of CaF2, SmF3, DyF3, and NdF3, and the content of the doped nano inorganic insulating material accounts for 3%-11% of the total mass of the composite magnet.

2. The high-resistivity hot-pressed samarium cobalt composite magnet according to claim 1, characterized in that: The preparation method of the composite magnet comprises the following steps: (1) Metal Sm is mixed with metal Co, Fe, Cu, and Zr according to the corresponding material ratios, and 2% to 8% more metal Sm is added to compensate for the volatilization of the Sm element during the smelting process; (2)Repeatedly melt at a vacuum degree higher than 5×10 -3 Pa for 7 to 8 times to make the melting more sufficient and uniform, and obtain a samarium-cobalt-based alloy ingot; (3) annealing the alloy ingot in vacuum; (4) crushing the annealed ingot and grinding it in a grinding jar, and passing it through a 80-mesh sieve to obtain a powder of a samarium-cobalt-based alloy; (5) High-energy ball milling of the four fluorides was performed at 0 to 3 h to screen out the optimal particle size of the four fluorides; (6) mixing the samarium-cobalt alloy powder and the two-doped fluoride into a ball mill and performing ball milling; (7) Drying the ball-milled powder in a vacuum drying oven; (8) Place the dried powder into a hot pressing mold and perform hot pressing under the protection of an inert gas.

3. The preparation method according to claim 2, characterized in that: The alloy ingot prepared in step (2) is one of SmCo5, Sm2Co 17 , Sm2(Co 1-a-b-c Fe a Cu b Zr c ) 17 ).

4. The preparation method according to claim 2, characterized in that: In step (3), the annealing temperature is 800-1000° C. and the holding time is 30-180 min.

5. The preparation method according to claim 2, characterized in that: The particle size of the samarium-cobalt-based alloy powder after sieving in step (4) is 1 to 100 μm.

6. The preparation method according to claim 2, characterized in that: The four fluorides in step (5) were purchased from professional reagent product research and development companies such as Shanghai Aladdin Biochemical Technology Co., Ltd., Shanghai MacLean Biochemical Technology Co., Ltd., and Beijing Zhongjinyan New Material Technology Co., Ltd.

7. The preparation method according to claim 2, characterized in that: The particle size of the fluoride after ball milling in step (5) is 1 to 100 nm, the ball milling medium is one of ethanol, heptane, acetone and argon, and the ball-to-material ratio is 5:1 to 20:

1.

8. The preparation method according to claim 2, characterized in that: The fluoride in step (6) is two or more of CaF2, SmF3, DyF3, and NdF3, the mixing ratio is 0:10 to 10:0, and the doping amount is 3% to 11% of the total mass of the ball-milled powder.

9. The preparation method according to claim 2, characterized in that: In step (6), the ball milling time is 1 to 5 hours, the ball milling medium is one of ethanol, heptane, acetone and argon, and the ball-to-material ratio is 5:1 to 20:

1.

10. The preparation method according to claim 2, characterized in that: In step (8), the hot pressing temperature is 500-700° C. and the pressure is 350-950 MPa.