Preparation method for large-depth efficient grain boundary diffusion of neodymium-iron-boron magnet

Abstract

The invention discloses a preparation method for large-depth efficient grain boundary diffusion of a neodymium-iron-boron magnet, and belongs to the technical field of magnetic materials. The preparation method comprises the following steps: preparing a low-melting-point Re1-aTma alloy target material by adopting a vacuum induction melting technology, sputtering the low-melting-point Re1-aTma alloy target material on the surface of a square neodymium-iron-boron magnet in six directions, and then placing the magnet in cryogenic equipment for multiple circulating cryogenic treatment to obtain a magnet with a micro-crack area inside, the microscopic cracks can serve as effective channels of grain boundary diffusion, the grain boundary diffusion depth of heavy rare earth elements is greatly increased, the contact area between diffusions and magnets is greatly increased, then vacuum diffusion heat treatment is conducted, and the diffusion efficiency of the rare earth elements is improved. The method is simple in technological process, easy to operate and beneficial to application of the high-performance neodymium-iron-boron magnet in more permanent magnet devices so as to meet market requirements.

Description

Technical Field

[0001] The invention relates to the technical field of magnetic materials, and in particular to a method for preparing a NdFeB magnet by high-depth and efficient grain boundary diffusion. Background Art

[0002] Rare earth is a key raw material for high-tech industries and a non-renewable resource. How to fully and efficiently utilize rare earth materials is a common problem faced by many rare earth application companies. Rare earth high-performance magnetic materials are widely used in high-tech fields such as national defense and intelligent manufacturing. They have superior performance, but the cost is high due to the addition of rare earth elements (the cost of rare earth materials accounts for about 80% of the cost of raw materials). Grain boundary diffusion technology is a new process for improving the coercive force of sintered NdFeB. It mainly uses rare earth metal or compound powder as a diffusion source, performs diffusion heat treatment at a certain temperature, and optimizes the grain boundary phase and improves the anisotropy field of the main phase to improve the magnetic properties of NdFeB magnets.

[0003] Studies have shown that by depositing or coating a low melting point alloy on the surface and performing grain boundary diffusion on the magnet, the intrinsic coercivity of the magnet can be greatly improved under the premise of using a lower amount of heavy rare earth, while keeping the remanence basically unchanged. 1-a Tm a The alloy is sputtered on the surface of the block-shaped NdFeB magnet in six directions, and then the magnet is placed in a cryogenic device for cryogenic treatment to obtain a magnet with a microcrack area inside, which greatly increases the contact area between the diffuser and the magnet, and then a vacuum diffusion heat treatment is performed to improve the diffusion efficiency of the rare earth element. The present invention simplifies the process, is easy to operate, has low cost, and is suitable for large-scale batch production. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention aims to provide a method for preparing NdFeB magnets by high-efficiency deep grain boundary diffusion.

[0005] The method for preparing a NdFeB magnet by high-efficiency deep grain boundary diffusion of the present invention comprises the following steps: (1) Preparation of low melting point Re using vacuum induction melting technology 1-a Tm a Alloy ingot, wherein 0≤a≤0.6, Re is one or more of heavy rare earth Dy, Tb, Ho, Tm, Yb, Lu, Y, Tm is one or more of Cu, Ga, Al, Ti, Zr, Si, Sn, In, and then the alloy ingot is made into a sputtering target by grinding and cutting; (2) removing the oxide film on the surface of a square NdFeB magnet of a certain brand and size of 10×10×5 cm, wherein the brand of the NdFeB magnet is N42M, N45H, N40SH, N42UH or N42EH; (3) The low melting point Re obtained in step (1) 1-a Tm a The target material is uniformly sputtered on the surface of the square iron boron magnet obtained in step (2) in six directions in sequence, and the thickness of the surface sputtered layer is 10 to 500 μm; (4) placing the magnet obtained after sputtering in step (3) in a cryogenic device for cryogenic treatment to obtain a magnet having microcrack regions inside; (5) The magnet after deep cryogenic treatment in step (4) is subjected to vacuum diffusion heat treatment to obtain a final magnet.

[0006] Furthermore, the temperature of the cryogenic treatment in step (4) is -195 to -150°C, the cooling rate is 1 to 5°C / min, the holding time is 1 to 3 hours, and then the magnet is placed in the equipment to return to room temperature, and this step is repeated 2 to 4 times.

[0007] Furthermore, the vacuum diffusion heat treatment described in step (5) is divided into primary diffusion heat treatment and secondary diffusion heat treatment, the temperature of the primary diffusion heat treatment is 750-950°C, the heating rate is 1-3°C / min, the insulation time is 1-6h, and then it is rapidly cooled to room temperature; the temperature of the secondary diffusion heat treatment is 400-550°C, the heating rate is 1-3°C / min, the insulation time is 2-4h, and then it is rapidly cooled to room temperature.

[0008] Compared with the existing technology, the present invention has the following advantages and beneficial effects: the present invention prepares low melting point Re by vacuum induction melting technology 1-a Tm a Alloy target material is sputtered on the surface of the block-shaped NdFeB magnet in six directions, and then the magnet is placed in a cryogenic device for multiple cycles of cryogenic treatment to obtain a magnet with microcracks inside. These microcracks can be used as effective channels for grain boundary diffusion, greatly improving the depth of grain boundary diffusion of heavy rare earth elements, greatly increasing the contact area between the diffuser and the magnet, and then performing vacuum diffusion heat treatment to improve the diffusion efficiency of rare earth elements. The present invention breaks through the limitation that the traditional grain boundary diffusion process can only diffuse and treat magnets with smaller thickness, simplifies the process, is easy to operate, has low cost, and is suitable for large-scale batch production. DETAILED DESCRIPTION

[0009] The present invention will be further described in detail below with reference to the embodiments, but the present invention is not limited to the following embodiments.

[0010] Example 1 (1) Preparation of low melting point Dy by vacuum induction melting technology 0.2 Ho 0.2 Cu 0.4 Al 0.2 Alloy ingots are then ground and cut to form sputtering targets; (2) The surface oxide film of a square NdFeB magnet with a grade of N42M and a size of 10×10×5 cm is first removed; (3) The low melting point Dy obtained in step (1) 0.2 Ho 0.2 Cu 0.4 Al 0.2 The target material is uniformly sputtered on the surface of the block-shaped iron boron magnet obtained in step (2) in six directions in sequence, and the thickness of the surface sputtered layer is 100, 200, and 300 μm; (4) the magnet obtained after sputtering in step (3) is placed in a cryogenic device for cryogenic treatment, the cryogenic treatment temperature is -150°C, the cooling rate is 5°C / min, and the holding time is 1 hour. The magnet is then placed in the device to return to room temperature, and this step is repeated twice to obtain a magnet with a microcrack area inside; (5) The magnet after deep cryogenic treatment in step (4) is subjected to vacuum diffusion heat treatment, and the vacuum diffusion heat treatment is divided into primary diffusion heat treatment and secondary diffusion heat treatment. The temperature of the primary diffusion heat treatment is 750°C, the heating rate is 1°C / min, the holding time is 5h, and then it is rapidly cooled to room temperature; the temperature of the secondary diffusion heat treatment is 550°C, the heating rate is 1°C / min, the holding time is 2h, and then it is rapidly cooled to room temperature to obtain the final magnet.

[0011] The magnetic properties of the NdFeB magnet prepared by the present invention after grain boundary diffusion are measured, and the remanence is 13.2 kG, the coercive force is 16.6 kOe, and the magnetic energy product is 47.1 MGOe.

[0012] Example 2 (1) Preparation of low melting point Tb by vacuum induction melting technology 0.4 Yb 0.1 Ga 0.5 Alloy ingots are then ground and cut to form sputtering targets; (2) The surface oxide film of a square NdFeB magnet with a grade of N45H and a size of 10×10×5 cm is first removed; (3) The low melting point Tb obtained in step (1) 0.4 Yb 0.1 Ga 0.5The target material is uniformly sputtered on the surface of the block-shaped iron boron magnet obtained in step (2) in six directions, and the thickness of the surface sputtered layer is 100, 200, and 300 μm; (4) the magnet obtained after sputtering in step (3) is placed in a cryogenic device for cryogenic treatment, the cryogenic treatment temperature is -175°C, the cooling rate is 3°C / min, and the holding time is 2h. The magnet is then placed in the device to return to room temperature, and this step is repeated 3 times to obtain a magnet with a microcrack area inside; (5) The magnet after deep cryogenic treatment in step (4) is subjected to vacuum diffusion heat treatment, and the vacuum diffusion heat treatment is divided into primary diffusion heat treatment and secondary diffusion heat treatment. The temperature of the primary diffusion heat treatment is 825°C, the heating rate is 2°C / min, the holding time is 4h, and then it is rapidly cooled to room temperature; the temperature of the secondary diffusion heat treatment is 480°C, the heating rate is 2°C / min, the holding time is 3h, and then it is rapidly cooled to room temperature to obtain the final magnet.

[0013] The magnetic properties of the NdFeB magnet prepared by the present invention after grain boundary diffusion are measured, and the remanence is 13.9 kG, the coercive force is 21.3 kOe, and the magnetic energy product is 48.2 MGOe.

[0014] Example 3 (1) Preparation of low melting point Dy by vacuum induction melting technology 0.3 Tb 0.2 Ti 0.1 Cu 0.4 Alloy ingots are then ground and cut to form sputtering targets; (2) The surface oxide film of a square NdFeB magnet with a grade of N40SH and a size of 10×10×5 cm is first removed; (3) The low melting point Dy obtained in step (1) 0.3 Tb 0.2 Ti 0.1 Cu 0.4 The target material is uniformly sputtered on the surface of the block-shaped iron boron magnet obtained in step (2) in six directions in sequence, and the thickness of the surface sputtered layer is 100, 200, and 300 μm; (4) the magnet obtained after sputtering in step (3) is placed in a cryogenic device for cryogenic treatment, the cryogenic treatment temperature is -190°C, the cooling rate is 1°C / min, and the holding time is 3 hours. The magnet is then placed in the device to return to room temperature, and this step is repeated 4 times to obtain a magnet with a microcrack area inside; (5) The magnet after deep cryogenic treatment in step (4) is subjected to vacuum diffusion heat treatment, and the vacuum diffusion heat treatment is divided into primary diffusion heat treatment and secondary diffusion heat treatment. The temperature of the primary diffusion heat treatment is 910°C, the heating rate is 3°C / min, the holding time is 3h, and then it is rapidly cooled to room temperature; the temperature of the secondary diffusion heat treatment is 420°C, the heating rate is 3°C / min, the holding time is 4h, and then it is rapidly cooled to room temperature to obtain the final magnet.

[0015] The magnetic properties of the NdFeB magnet prepared by the present invention after grain boundary diffusion are measured, and the remanence is 12.7 kG, the coercive force is 25.7 kOe, and the magnetic energy product is 44.9 MGOe.

Claims

1. A method for preparing NdFeB magnets by high-efficiency deep grain boundary diffusion, characterized in that The steps include: (1) Preparation of low melting point Re using vacuum induction melting technology 1-a Tm a Alloy ingot, wherein 0≤a≤0.6, Re is one or more of heavy rare earth Dy, Tb, Ho, Tm, Yb, Lu, Y, Tm is one or more of Cu, Ga, Al, Ti, Zr, Si, Sn, In, and then the alloy ingot is made into a sputtering target by grinding and cutting; (2) removing the oxide film on the surface of a square NdFeB magnet of a certain brand and size of 10×10×5 cm, wherein the brand of the NdFeB magnet is N42M, N45H, N40SH, N42UH or N42EH; (3) The low melting point Re obtained in step (1) 1-a Tm a The target material is uniformly sputtered on the surface of the square iron boron magnet obtained in step (2) in six directions in sequence, and the thickness of the surface sputtered layer is 10 to 500 μm; (4) placing the magnet obtained after sputtering in step (3) in a cryogenic device for cryogenic treatment to obtain a magnet having microcrack regions inside; (5) The magnet after deep cryogenic treatment in step (4) is subjected to vacuum diffusion heat treatment to obtain a final magnet.

2. The method for preparing a NdFeB magnet by high-efficiency deep grain boundary diffusion according to claim 1, characterized in that: The temperature of the cryogenic treatment in step (4) is -195 to -150°C, the cooling rate is 1 to 5°C / min, and the holding time is 1 to 3 hours. The magnet is then placed in the equipment to return to room temperature, and this step is repeated 2 to 4 times.

3. The method for preparing NdFeB magnets by high-efficiency deep grain boundary diffusion according to claim 1, characterized in that: The vacuum diffusion heat treatment described in step (5) is divided into primary diffusion heat treatment and secondary diffusion heat treatment. The temperature of the primary diffusion heat treatment is 750-950°C, the heating rate is 1-3°C / min, the insulation time is 1-6h, and then it is rapidly cooled to room temperature; the temperature of the secondary diffusion heat treatment is 400-550°C, the heating rate is 1-3°C / min, the insulation time is 2-4h, and then it is rapidly cooled to room temperature.