A method for preparing anisotropic NdFeB alloy powder

Abstract

A method for preparing anisotropic NdFeB alloy powder comprises the following steps: S1: batching and smelting, wherein the alloy is batched according to the nominal composition of commercial NdFeB permanent magnet alloy, and then the raw materials in the furnace are heated by vacuum induction melting until the NdFeB alloy is completely melted and the vacuum degree is not less than 6×10 2 Pa, 1100℃-1400℃, keep warm when the liquid surface turns bright red, a method for preparing anisotropic NdFeB alloy powder has the following advantages: (1) the powder particles prepared by injection molding equipment have a smaller grain size than conventional NdFeB powder, which can significantly enhance the exchange coupling effect inside the alloy and significantly improve the maximum magnetic energy product and remanence.

Description

Technical Field

[0001] The invention relates to a method for preparing anisotropic NdFeB alloy powder. Background Art

[0002] Neodymium iron boron (NdFeB) permanent magnets, due to their excellent magnetic properties, are widely used in aerospace, wind power generation, energy-saving home appliances, electronic appliances, and new energy vehicles. Existing NdFeB permanent magnets are primarily categorized into sintered NdFeB and bonded NdFeB. The former is produced through rapid solidification, hydrogen pulverization, airflow milling, orientation molding, pressing, and sintering and tempering to produce a rough magnet. The latter is produced through smelting, rapid bonding, crushing, crystallization, and pressing or injection molding.

[0003] The core technology behind both types of NdFeB permanent magnets lies in the preparation of anisotropic alloy powders. However, existing processes and technologies make it difficult to produce fine-particle, anisotropic NdFeB alloy powders. Consequently, the magnetic properties along the magnetization direction of the magnets fail to meet the industry's practical application requirements, limiting the application and development of NdFeB permanent magnet alloys in high-tech fields. Summary of the Invention

[0004] The invention provides a method for preparing anisotropic NdFeB alloy powder.

[0005] The technical solution adopted by the present invention to solve the above technical problems is:

[0006] The following steps are involved:

[0007] S1: Batching and smelting: The alloy is batched according to the nominal composition of commercial NdFeB permanent magnet alloy. Then, vacuum induction melting is used to heat the raw materials in the mixing furnace until the NdFeB alloy is completely melted and the liquid surface turns bright red, and then the temperature is kept constant.

[0008] S2: Spray atomization: The alloy is sprayed and atomized. After the alloy solution is fully melted and evenly distributed, the alloy solution is controlled to flow downward through a flow control valve. At the same time, nitrogen or argon gas is added in the direction perpendicular to the liquid flow, so that the alloy solution forms atomized particles under impact, and then passes through a small aperture and is sprayed vertically downward.

[0009] S3: Particle differentiation: When the atomized particles hit the tip of the particle insulation plate during the downward spraying process, the atomized particles further differentiate into fine particles after hitting the tip and slide downward;

[0010] S4: Directional cooling, the droplets flow downward along the insulation plate and cool rapidly when they flow to the copper roller. After cooling, the alloy forms columnar crystals along the rotation direction of the copper roller, obtaining NdFeB permanent magnet alloy powder with small grains and high texture.

[0011] Preferably, the insulation board or its surface coating has a low friction coefficient and is made of high-temperature materials, such as refractory metals and rare earth metals.

[0012] Preferably, the vacuum degree in the mixing furnace is not less than 6×10 2 Pa, 1100℃-1400℃.

[0013] Preferably, the flow control valve controls the speed flow at 0~0.2m 3 / s.

[0014] Preferably, the spray pressure of nitrogen or argon gas applied is ≥2.0×10 5 Pa.

[0015] Preferably, the diameter of the injection hole is: 20 μm ≤ pore size ≤ 500 μm, and the distance between the pore size and the insulation board is controlled at 5-30 mm.

[0016] Preferably, the thickness of the tip of the insulation board is: 20 μm ≤ tip thickness ≤ 100 μm.

[0017] Preferably, the difference between the insulation temperature of the insulation plate and the temperature when the solution is completely melted is 0-60° C., and the alloy droplets form droplets with a particle size of 3-8 μm on the insulation plate.

[0018] Preferably, the rotation speed of the copper roller is controlled at 10-45 m / s.

[0019] Compared with the prior art, the method for preparing anisotropic NdFeB alloy powder of the present invention has the following advantages:

[0020] (1) The powder particles prepared by the injection molding equipment have a smaller grain size than conventional NdFeB powder, which can significantly enhance the exchange coupling effect inside the alloy and significantly improve the maximum magnetic energy product and remanence;

[0021] (2) Adding a particle differentiation and heat preservation device to the injection molding equipment can significantly refine the particle size, and form a strongly textured alloy powder after cooling by a copper roller, which significantly improves the coercive force;

[0022] (3) The process of the present invention is simple and the equipment requirements are relatively low. It can be completed by modifying the original sintered NdFeB production equipment and has the prospect of large-scale promotion and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the preparation process of the present invention.

[0024] Reference numerals:

[0025] 1-Mixing furnace, 2-Flow control valve, 3-Insulation board, 4-Copper roller. Implementation Method

[0026] The present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

[0027] As attached Figure 1 As shown, a method for preparing anisotropic NdFeB alloy powder of the present invention comprises the following steps:

[0028] Step 1: Prepare ingredients and smelt the alloy according to the nominal composition of commercial NdFeB permanent magnet alloy. Then, use vacuum induction melting to heat the raw materials in the mixing furnace 1 until the NdFeB alloy is completely melted and the vacuum degree is not less than 6×10 2 Pa, 1100 ℃-1400 ℃, the vacuum degree in this embodiment is 6×10 2 Pa, 1300 °C, keep warm when the liquid surface turns bright red;

[0029] Step 2: Spray atomize the alloy. After the alloy solution is fully melted and evenly distributed, the flow rate and speed of the alloy solution flowing downward are controlled by the flow control valve at 0~0.2 m 3 / s, in this embodiment the flow rate is 0.1 m 3 / s, and simultaneously apply high-pressure nitrogen or argon in the direction perpendicular to the liquid flow, with a spray pressure of ≥2.0×10 5 Pa, and in this embodiment, the injection pressure is: 2.0×10 5 Pa, so that the alloy solution forms atomized particles under high pressure impact, and then is sprayed vertically downward after passing through a small aperture (20 μm ≤ aperture size ≤ 500 μm). In this embodiment, the aperture size is 30 μm, and alloy droplets with a particle size of 30 μm are obtained. The distance between the aperture and the insulation plate 3 is controlled to be 5-30 mm. In this embodiment, the distance between the aperture and the insulation plate 3 is 20 mm;

[0030] Step 3: During the downward spraying process, the atomized particles collide with the tip of the particle insulation plate 3. The thickness of the tip of the insulation plate 3 is: 20 μm ≤ tip thickness ≤ 100 μm. After hitting the tip, the atomized particles further decompose into fine particles and slide downward (the insulation plate 3 or its surface coating is made of a low friction coefficient, high-temperature material, which may be CrAlN, Ti(C,N)-based metal ceramics, tungsten, molybdenum, tantalum, niobium, vanadium, chromium, titanium, zirconium and other refractory metals, as well as borides, carbides, nitrides, silicides, phosphides and sulfides of rare earth metals, etc.), wherein the difference between the insulation temperature of the insulation plate 3 and the temperature when the solution is completely melted is 0-60 ° C, and the alloy droplets form droplets with a particle size of 3-8 μm on the insulation plate 3. In this embodiment, the temperature is 20 ° C, and the alloy droplets form droplets with a particle size of 5 μm on the insulation plate 3. The droplets are atomized liquid particles;

[0031] Step 4: The droplets flow downward along the insulation plate 3 and cool rapidly when they flow to the copper roller 4. The rotation speed of the copper roller 4 is controlled at 10-45 m / s. In this embodiment, the rotation speed is 25 m / s. After cooling, the alloy powder forms columnar crystals along the rotation direction of the copper roller 4, thereby obtaining a NdFeB permanent magnet alloy powder with small grains and high texture.

[0032] The powders prepared by the above four steps are shown in Table 1:

[0033] Table 1 Properties of NdFeB alloy powder

[0034] sample Magnetocrystalline anisotropy field / kOe Maximum magnetic energy product / MGOe Remanence / kGs Coercive force / kOe Particle size / μm Wettability contact angle / ° Example 1 35.17 53.20 14.5 20.55 3-6 42 Example

[0035] The difference between Example 2 and Example 1 is that: the step (2) of forming atomized particles of the alloy solution under high pressure impact and spraying vertically downward after passing through a small aperture (10 μm ≤ aperture size ≤ 50 μm) is not adopted. Instead, the aperture size is set outside the parameter range. The nominal composition of the alloy and the remaining steps are the same. The properties of the NdFeB alloy powder prepared by Example 1 are shown in Table 2:

[0036] Table 2 Properties of NdFeB alloy powder

[0037] sample Magnetocrystalline anisotropy field / kOe Maximum magnetic energy product / MGOe Remanence / kGs Coercive force / kOe Particle size / μm Wettability contact angle / ° Comparative Example 1 28.42 48.30 13.6 17.38 1-10 65 Example

[0038] The difference between Example 3 and Example 1 is that the distance between the control hole and the insulation plate 3 is not 5-30 mm in step (2), but the distance between the fine hole and the insulation plate 3 is set outside the parameter range. The nominal composition of the alloy and the remaining steps are the same. The properties of the NdFeB alloy powder prepared by Example 1 are shown in Table 3:

[0039] Table 3 Properties of NdFeB alloy powder

[0040] sample Magnetocrystalline anisotropy field / kOe Maximum magnetic energy product / MGOe Remanence / kGs Coercive force / kOe Particle size / μm Wettability contact angle / ° Comparative Example 2 23.57 47.75 13.4 17.21 5-12 57 Example

[0041] The difference between Example 4 and Example 1 is that the temperature difference between the insulation temperature of the insulation plate 3 and the temperature when the solution is completely melted is not 0-60 ° C in step (3), but the distance between the fine hole and the insulation plate 3 is set outside the parameter range. The nominal composition of the alloy and the remaining steps are the same. The properties of the NdFeB alloy powder prepared by Example 1 are shown in Table 4:

[0042] Table 4 Properties of NdFeB alloy powder

[0043] sample Magnetocrystalline anisotropy field / kOe Maximum magnetic energy product / MGOe Remanence / kGs Coercive force / kOe Particle size / μm Wettability contact angle / ° Comparative Example 3 32.38 50.32 13.9 18.89 2-7 53

[0044] Compared with the prior art, the present invention has the following advantages:

[0045] (1) The powder particles prepared by the injection molding equipment have a smaller grain size than conventional NdFeB powder, which can significantly enhance the exchange coupling effect inside the alloy and significantly improve the maximum magnetic energy product and remanence;

[0046] (2) A particle differentiation and heat preservation device is added to the injection molding equipment to achieve significant refinement of the particle size, and after cooling through the copper roller 4, a strongly textured alloy powder is formed, which significantly improves the coercive force;

[0047] (3) The process of the present invention is simple and the equipment requirements are relatively low. It can be completed by modifying the original sintered NdFeB production equipment and has the prospect of large-scale promotion and use.

[0048] By vacuum melting the NdFeB alloy according to the nominal composition ratio, atomizing it with high-pressure gas jet, and then undergoing particle differentiation and directionally cooling, an alloy powder with a distinct texture is formed along the cooling direction, thereby obtaining a nanopowder with high magnetic anisotropy, laying a good foundation for the preparation of high-performance NdFeB permanent magnet materials.

[0049] Finally, it should be noted that the above embodiments only illustrate the technical solutions of the present invention and do not limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing anisotropic NdFeB alloy powder, characterized in that: The following steps are involved: S1: Batching and smelting: The alloy is batched according to the nominal composition of commercial NdFeB permanent magnet alloy. Then, vacuum induction melting is used to heat the raw materials in the mixing furnace until the NdFeB alloy is completely melted and the liquid surface turns bright red, and then the temperature is kept constant. S2: Spray atomization: The alloy is sprayed and atomized. After the alloy solution is fully melted and evenly distributed, the alloy solution is controlled to flow downward through a flow control valve. At the same time, nitrogen or argon gas is added in the direction perpendicular to the liquid flow, so that the alloy solution forms atomized particles under impact, and then passes through a small aperture and is sprayed vertically downward. S3: Particle differentiation: When the atomized particles hit the tip of the particle insulation plate during the downward spraying process, the atomized particles further differentiate into fine particles after hitting the tip and slide downward; S4: Directional cooling, the droplets flow downward along the insulation plate and cool rapidly when they flow to the copper roller. After cooling, the alloy forms columnar crystals along the rotation direction of the copper roller, obtaining NdFeB permanent magnet alloy powder with small grains and high texture.

2. A method for preparing anisotropic NdFeB alloy powder according to claim 1, characterized in that: The insulation board or its surface coating has a low friction coefficient and is made of high-temperature materials, such as refractory metals and rare earth metals.

3. A method for preparing anisotropic NdFeB alloy powder according to claim 1, characterized in that: The vacuum degree in the mixing furnace is not less than 6×10 2 Pa, 1100℃-1400℃.

4. A method for preparing anisotropic NdFeB alloy powder according to claim 1, characterized in that: The flow control valve controls the speed flow at 0~0.2m 3 / s.

5. A method for preparing anisotropic NdFeB alloy powder according to claim 1, characterized in that: The spray pressure of nitrogen or argon gas applied is ≥2.0×10 5 Pa.

6. A method for preparing anisotropic NdFeB alloy powder according to claim 1, characterized in that: The diameter of the fine pore is: 20μm≤pore size≤500μm, and the distance between the pore and the insulation board is controlled to be 5-30 mm.

7. A method for preparing anisotropic NdFeB alloy powder according to claim 1, characterized in that: The thickness of the tip of the insulation board is: 20μm≤tip thickness≤100μm.

8. A method for preparing anisotropic NdFeB alloy powder according to claim 1, characterized in that: The difference between the insulation temperature of the insulation plate and the temperature when the solution is completely melted is 0-60° C., and the alloy droplets form droplets with a particle size of 3-8 μm on the insulation plate.

9. A method for preparing anisotropic NdFeB alloy powder according to claim 1, characterized in that: The copper roller rotation speed is controlled at 10-45 m / s.

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