A method for preparing high-coercivity neodymium-iron-boron magnets by grain boundary diffusion

Abstract

The application discloses a preparation method of a high-coercivity neodymium-iron-boron magnet prepared through grain boundary diffusion, and belongs to the technical field of magnetic materials. 70 Zn 20 Ga 10 low-melting-point alloy powder, and immersing a neodymium-iron-boron magnet of a certain grade in the paste liquid of the low-melting-point alloy powder, and then performing subsequent in-situ grain boundary diffusion high-pressure torsion heat treatment to obtain a final magnet. The application has a simple process and is easy to operate, and is favorable for application of the high-coercivity neodymium-iron-boron magnet in more permanent magnet devices, so as to meet market demands.

Description

Technical Field

[0001] This invention relates to the field of magnetic materials technology, and in particular to a method for preparing high coercivity NdFeB magnets by grain boundary diffusion. Background Technology

[0002] With the rapid increase in demand for NdFeB magnets, scarce rare earth elements such as Nd, Pr, Dy, and Tb are being consumed in large quantities, while abundant rare earth elements such as La, Ce, and Y, despite their high reserves in the Earth's crust, have long been rarely used in the field of rare earth permanent magnets. As sintered NdFeB materials are widely used in modern industry and electronic technology, especially in new energy vehicles, industrial robots, and mobile intelligence, there is a growing demand for NdFeB products to be lighter, thinner, smaller, and higher energy, placing increasingly higher demands on the magnet's energy product, coercivity, and thermal stability. However, under traditional manufacturing processes, there has always been a trade-off between high coercivity and high energy product in sintered NdFeB magnets. Grain boundary diffusion technology, developed in recent years, is a technique that can effectively improve the magnetic properties of sintered NdFeB magnets. It mainly uses rare earth metal or compound powders as a diffusion source, and performs diffusion heat treatment at a certain temperature to enhance the magnetic properties of NdFeB magnets.

[0003] This invention prepares submicron-sized Tb using melt rapid quenching and high-energy ball milling techniques. 70 Zn 20 Ga 10 Low-melting-point alloy powder is prepared into a paste-like liquid of a certain viscosity for later use. The oxide film on the surface of a blocky NdFeB magnet of a specific grade is first removed, and then the NdFeB magnet is immersed in the paste-like liquid. Subsequent in-situ grain boundary diffusion high-pressure torsion heat treatment fundamentally changes the limitation of the diffusion magnet depth, allowing the grain growth process and the heavy rare earth diffusion process to occur simultaneously. This helps to lower the grain boundary diffusion temperature and improve the diffusion efficiency of rare earth elements. This invention simplifies the process, is easy to operate, has low cost, and is suitable for large-scale mass production. Summary of the Invention

[0004] To address the problems existing in the prior art, the present invention aims to provide a method for preparing high coercivity NdFeB magnets by grain boundary diffusion.

[0005] The method for preparing high-coercivity NdFeB magnets by grain boundary diffusion according to the present invention includes the following steps:

[0006] (1) Tb containing heavy rare earth elements in atomic percentage was prepared by melt quenching method. 70 Zn 20 Ga 10 Low-melting-point alloy rapid quenching strip, copper roller speed 10-30 m / s; then Tb 70 Zn 20 Ga10 The rapidly quenched belt was ball-milled in a high-energy ball mill for 10–40 min to obtain submicron-sized low-melting-point alloy powder with an average particle size of 0.4–0.7 μm;

[0007] (2) The submicron-sized Tb obtained in step (1) 70 Zn 20 Ga 10 Low-melting-point alloy powder is mixed with anhydrous ethanol to form a paste-like liquid with a viscosity of 400-800 mmPa·s;

[0008] (3) Remove the oxide film on the surface of a 5×5×5cm block-shaped NdFeB magnet of a certain grade first, and then immerse the NdFeB magnet in the paste liquid obtained in step (2) for 1 to 6 hours.

[0009] (4) The magnet obtained in step (3) after soaking is subjected to in-situ grain boundary diffusion high pressure torsion heat treatment to obtain the final magnet.

[0010] Furthermore, the neodymium iron boron magnets mentioned in step (3) are graded as N33SH, N38H, N42M or N30UH.

[0011] Furthermore, the in-situ heat treatment temperature of the in-situ grain boundary diffusion high-pressure torsion heat treatment in step (4) is 650-950℃, the heat treatment time is 45-120min, the pressure is 100-400MPa, the number of torsion turns is 1-3 turns, and the torsion rate is 8° / min.

[0012] Compared with existing technologies, the present invention has the following advantages and beneficial effects: The present invention prepares submicron-sized Tb using melt rapid quenching and high-energy ball milling technology. 70 Zn 20 Ga 10 Low-melting-point alloy powder is used, and a specific grade of NdFeB magnet is immersed in a paste-like liquid of the low-melting-point alloy powder. Subsequent in-situ high-pressure torsional heat treatment with grain boundary diffusion is then performed. During the high-pressure torsional deformation process, the magnet generates a high density of defects (such as vacancies, dislocations, and stacking faults), and the microstructure undergoes evolution including lattice rotation, grain boundary migration, dynamic recrystallization, and grain fragmentation. By designing a low-melting-point exogenous grain boundary phase and using a plastic deformation field and temperature field, the growth of the main crystal phase, the evolution of the grain boundary phase, and the diffusion behavior of heavy rare earth elements in the NdFeB magnet are controlled, thereby improving the diffusion efficiency of rare earth elements. This invention simplifies the process, is easy to operate, has low cost, and is suitable for large-scale mass production. Detailed Implementation

[0013] 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.

[0014] Example 1.

[0015] (1) Tb containing heavy rare earth elements in atomic percentage was prepared by melt quenching method. 70 Zn 20 Ga 10 Low-melting-point alloy rapid quenching strip, copper roller rotation speed 10m / s; then Tb 70 Zn 20 Ga 10 The rapidly quenched belt was ball-milled in a high-energy ball mill for 10 minutes to obtain submicron-sized low-melting-point alloy powder with an average particle size of 0.7 μm;

[0016] (2) The submicron-sized Tb obtained in step (1) 70 Zn 20 Ga 10 Low-melting-point alloy powder was mixed with anhydrous ethanol to form a paste-like liquid with a viscosity of 400 mmPa·s;

[0017] (3) Remove the oxide film on the surface of the N33SH block-shaped NdFeB magnet with a size of 5×5×5cm. Then immerse the NdFeB magnet in the paste liquid obtained in step (2) for 2 hours.

[0018] (4) The magnet obtained after soaking in step (3) is subjected to in-situ grain boundary diffusion high pressure torsion heat treatment. The in-situ heat treatment temperature is 750℃, the heat treatment time is 45min, the pressure is 200MPa, the number of torsion turns is 1 turn, and the torsion rate is 8° / min to obtain the final magnet.

[0019] The NdFeB magnet prepared using this invention has the following magnetic properties measured: remanence of 12.7 kG, coercivity of 25.6 kOe, and energy product of 35.7 MGOe.

[0020] Example 2

[0021] (1) Tb containing heavy rare earth elements in atomic percentage was prepared by melt quenching method. 70 Zn 20 Ga 10 Low-melting-point alloy rapid quenching strip, copper roller rotation speed 20m / s; then Tb 70 Zn 20 Ga 10 The rapidly quenched belt was ball-milled in a high-energy ball mill for 25 minutes to obtain submicron-sized low-melting-point alloy powder with an average particle size of 0.6 μm;

[0022] (2) The submicron-sized Tb obtained in step (1) 70 Zn 20 Ga 10Low-melting-point alloy powder was mixed with anhydrous ethanol to form a paste-like liquid with a viscosity of 600 mmPa·s;

[0023] (3) Remove the oxide film on the surface of the N38H block-shaped NdFeB magnet with a size of 5×5×5cm. Then immerse the NdFeB magnet in the paste liquid obtained in step (2) for 4 hours.

[0024] (4) The magnet obtained after soaking in step (3) is subjected to in-situ grain boundary diffusion high pressure torsion heat treatment. The in-situ heat treatment temperature is 850℃, the heat treatment time is 90min, the pressure is 300MPa, the number of torsion turns is 2 turns, and the torsion rate is 8° / min to obtain the final magnet.

[0025] The NdFeB magnet prepared using this invention has the following magnetic properties measured: remanence is 13.2 kG, coercivity is 23.5 kOe, and energy product is 41.4 MGOe.

[0026] Example 3

[0027] (1) Tb containing heavy rare earth elements in atomic percentage was prepared by melt quenching method. 70 Zn 20 Ga 10 Low-melting-point alloy rapid quenching strip, copper roller rotation speed 30m / s; then Tb 70 Zn 20 Ga 10 The rapidly quenched belt was ball-milled in a high-energy ball mill for 40 min to obtain submicron-sized low-melting-point alloy powder with an average particle size of 0.4 μm;

[0028] (2) The submicron-sized Tb obtained in step (1) 70 Zn 20 Ga 10 Low-melting-point alloy powder is mixed with anhydrous ethanol to form a paste-like liquid with a viscosity of 800 mmPa·s;

[0029] (3) Remove the oxide film on the surface of the N42M block-shaped NdFeB magnet with a size of 5×5×5cm. Then immerse the NdFeB magnet in the paste liquid obtained in step (2) for 6 hours.

[0030] (4) The magnet obtained after soaking in step (3) is subjected to in-situ grain boundary diffusion high pressure torsion heat treatment. The in-situ heat treatment temperature is 950℃, the heat treatment time is 120min, the pressure is 400MPa, the number of torsion turns is 3 turns, and the torsion rate is 8° / min to obtain the final magnet.

[0031] The NdFeB magnet prepared using this invention has the following magnetic properties measured: remanence of 13.6 kG, coercivity of 22.9 kOe, and energy product of 46.5 MGOe.

Claims

1. A method for preparing high coercivity NdFeB magnets by grain boundary diffusion, characterized in that... Includes the following steps: (1) Tb containing heavy rare earth elements in atomic percentage was prepared by melt quenching method. 70 Zn 20 Ga 10 Low-melting-point alloy rapid quenching strip, copper roller speed 10-30 m / s; then Tb 70 Zn 20 Ga 10 The rapidly quenched belt was ball-milled in a high-energy ball mill for 10–40 min to obtain submicron-sized low-melting-point alloy powder with an average particle size of 0.4–0.7 μm; (2) The submicron-sized Tb obtained in step (1) 70 Zn 20 Ga 10 Low-melting-point alloy powder is mixed with anhydrous ethanol to form a paste-like liquid with a viscosity of 400-800 mmPa·s; (3) Remove the oxide film on the surface of a 5×5×5cm block-shaped NdFeB magnet of a certain grade first, and then immerse the NdFeB magnet in the paste liquid obtained in step (2) for 1 to 6 hours. (4) The magnet obtained after soaking in step (3) is subjected to in-situ grain boundary diffusion high-pressure torsion heat treatment. The final magnet is obtained.

2. The method for preparing a high-coercivity NdFeB magnet by grain boundary diffusion according to claim 1, characterized in that: The neodymium iron boron magnets mentioned in step (3) are graded N33SH, N38H, N42M or N30UH.

3. The method for preparing a high-coercivity NdFeB magnet by grain boundary diffusion according to claim 1, characterized in that: The in-situ heat treatment in step (4) is performed at a temperature of 650–950°C, a heat treatment time of 45–120 min, a pressure of 100–400 MPa, a number of torsion turns of 1–3, and a torsion rate of 8° / min.