Neodymium iron boron magnets, their preparation methods and applications

Abstract

This invention discloses neodymium iron boron (NdFeB) magnets, their preparation methods, and applications. In the NdFeB magnets: the content of heavy rare earth elements (Tb) in the first, second, third, and fourth easily demagnetized regions is the same; the content of heavy rare earth elements in the first, second, third, and fourth transition regions is the same; the Tb content ratio of the non-easily demagnetized region to the first easily demagnetized region is (0-0.9):1; the Dy content ratio of the first easily demagnetized region to the non-easily demagnetized region is (0-0.9):1; and the Tb content ratio of the first transition region to the first easily demagnetized region is (0.8-1):1. The NdFeB magnets of this invention can reduce the attenuation of surface magnetism and magnetic flux while maintaining remanence, exhibiting good anti-demagnetization performance.

Description

Technical Field

[0001] This invention specifically relates to neodymium iron boron magnets, their preparation methods, and applications. Background Technology

[0002] Since its invention, neodymium iron boron (NdFeB) permanent magnet materials have been widely used in automobiles, wind power, home appliances, industrial robots, and other fields. Due to the different operating conditions in each field, the performance requirements for the magnets in these products also vary. In recent years, the booming development of new energy vehicles has led to a sharp increase in the demand for magnets in main drive motors. Since the normal operating temperature of main drive motors is mainly concentrated in the range of 120–180℃, NdFeB materials require higher coercivity and thermal stability. To improve the temperature resistance of NdFeB permanent magnet materials, large amounts of heavy rare earth elements (Dy and Tb) are typically added to increase the anisotropic field of the main phase magnetocrystalline structure. However, the scarcity and high price of heavy rare earth resources severely restrict the application of NdFeB magnets in various industries.

[0003] With the increasing demand for high-performance magnets, grain boundary diffusion technology is gradually becoming more widely known and accepted. Conventional grain boundary diffusion technology uses a physical vapor deposition method to deposit the diffusion source onto the magnet surface, then uses high temperature and pressure to allow the diffusion source to penetrate along the grain boundaries into the magnet's interior. The biggest advantage of this technology is that it significantly improves coercivity while maintaining almost no change in remanence using only a small amount of heavy rare earth elements. In terms of the effective utilization rate of heavy rare earth elements, traditional grain boundary diffusion products offer a substantial improvement over non-grain boundary diffusion products.

[0004] However, in the actual use of NdFeB magnets, the performance requirements for each part of the magnet are not the same. For example, in motors, the reverse magnetic field generated after the coil is energized is not a uniform magnetic field. Therefore, it is important to design a NdFeB magnet that meets the needs of different applications, ensuring coercivity and remanence while also having good anti-demagnetization ability. Summary of the Invention

[0005] The present invention aims to overcome the shortcomings of poor demagnetization resistance of neodymium iron boron magnets in the prior art, and provides neodymium iron boron magnets, their preparation methods and applications. The neodymium iron boron magnets of the present invention can reduce the attenuation of surface magnetism and magnetic flux of neodymium iron boron magnets while ensuring remanence, and have good demagnetization resistance.

[0006] In order to overcome the deficiencies in the prior art, the present invention provides a neodymium iron boron magnet, its preparation method and application.

[0007] The present invention mainly solves the above technical problems through the following technical solutions.

[0008] During the research of this invention, electromagnetic simulation using neodymium iron boron magnets under main drive motor conditions was used to identify easily demagnetized and non-easily demagnetized regions. We found that easily demagnetized regions all appeared near the rotor air gap corners, while demagnetization was less pronounced near the rotor and the middle area of ​​the magnets. To further improve the utilization rate of heavy rare earth elements and reduce unnecessary waste, and to achieve more precise evaluation of the diffusion area, for the easily demagnetized regions, a high-performance magnet with the same remanence was bonded to a lower-performance magnet with the same remanence in the non-easily demagnetized regions. This process prepared the required combined magnet, thus saving on the use of heavy rare earth elements in the non-easily demagnetized regions. Furthermore, based on the performance characteristics of each region, different heavy rare earth metal contents were designed to achieve a matching relationship in the coercivity of each region, ensuring both coercivity and remanence while improving anti-demagnetization performance.

[0009] The present invention provides a neodymium iron boron magnet, wherein the neodymium iron boron magnet is a cuboid, and a three-dimensional rectangular coordinate system is established with the center of the upper surface of the cuboid as the origin, wherein the orientation direction is the positive Z-axis, and the X-axis is parallel to one side of the upper surface;

[0010] The neodymium iron boron magnet includes a non-demagnetizing region, a transition region, and a demagnetizing region; the demagnetizing region includes a first demagnetizing region, a second demagnetizing region, a third demagnetizing region, and a fourth demagnetizing region respectively disposed at the four corners of the cuboid along the Z-axis direction and not in contact with each other;

[0011] The transition region is located at the boundary between the easily demagnetized region and the non-easily demagnetized region, and includes a first transition region, a second transition region, a third transition region, and a fourth transition region corresponding to the first easily demagnetized region, the second easily demagnetized region, the third easily demagnetized region, and the fourth easily demagnetized region, respectively.

[0012] The heavy rare earth elements in the first, second, third, and fourth easily demagnetized regions are the same.

[0013] The heavy rare earth elements in the first transition zone, the second transition zone, the third transition zone, and the fourth transition zone are the same.

[0014] The Tb content ratio of the non-demagnetizing region to the first demagnetizing region is (0-0.9):1;

[0015] The content ratio of Dy in the first easily demagnetized region to that in the non-easily demagnetized region is (0-0.9):1;

[0016] The Tb content ratio of the first transition region and the first easily demagnetized region is (0.8-1):1.

[0017] In this invention, the heavy rare earth elements may be derived from the substrate and / or diffusion process.

[0018] In this invention, the content of heavy rare earth elements refers to the percentage of the mass of heavy rare earth elements in a certain region relative to the total mass of the magnet in that region. For example, the content of Tb in the first easily demagnetized region means the percentage of the mass of Tb in the first easily demagnetized region relative to the total mass of the magnet in the first easily demagnetized region.

[0019] In this invention, the diffusion weight gain of heavy rare earth elements refers to the percentage of the mass of heavy rare earth elements introduced into a certain region by diffusion relative to the total mass of the magnet in that region. For example, the diffusion weight gain of Tb in the first easily demagnetized region refers to the percentage of the mass of Tb introduced into the first easily demagnetized region by diffusion relative to the total mass of the magnet in the first easily demagnetized region.

[0020] In this invention, "the diffusion weight gain of heavy rare earth elements is the same" means that the types of heavy rare earth elements introduced by diffusion in each region are the same, and the diffusion weight gain of each type of heavy rare earth element is the same.

[0021] In this invention, the specific location of the upper surface is not specifically limited. Those skilled in the art will generally understand that the upper surface refers to the surface opposite to a plane when the magnet is placed on a plane.

[0022] In this invention, the Tb content ratio between the non-demagnetizing region and the first demagnetizing region can be (0-0.2):1, for example, 0.03:1, 0.05:1 or 0.02:1.

[0023] In this invention, the diffusion weight gain ratio of Tb in the non-demagnetizing region to the first demagnetizing region can be (0-0.05):(0.50-0.70), for example 0.02:0.60, 0.03:0.60, 0.01:0.55, 0.01:0.50 or 0.01:0.60.

[0024] In this invention, the content ratio of Dy in the first easily demagnetized region to that in the non-easily demagnetized region can be (0-0.8):1, for example 0:1, 0.02:1 or 0.04:1.

[0025] In this invention, the diffusion weight gain ratio of Dy in the first easily demagnetized region to that in the non-easily demagnetized region can be (0-0.05):(0.5-0.7), for example, 0:0.3, 0.01:0.5, 0.03:0.7 or 0:0.5.

[0026] In this invention, the Tb content ratio of the first transition region and the first easily demagnetized region can be (0.9-1):1, for example 0.97:1, 0.98:1 or 1:1.

[0027] In this invention, the diffusion weight gain ratio of Tb in the first transition region and the first easily demagnetized region can be (0.9-1):1, for example 0.97:1, 0.98:1 or 1:1.

[0028] In this invention, the diffusion weight gain ratio of Dy in the first transition region and the first easily demagnetized region can be (0.05-0.6):(0-0.05), for example 0.1:0, 0.32:0.01, 0.1:0.03 or 0.1:0.01.

[0029] In this invention, the diffusion weight gain ratio of Dy in the first transition region to the non-demagnetizing region can be (0.05-0.9):1, preferably (0.14-0.90):1, for example 0.33:1, 0.14:1 or 0.20:1.

[0030] In this invention, the diffusion weight gain of Tb in the first easily demagnetized region can be 0.1wt%-1wt%, for example, 0.50wt%, 0.55wt%, or 0.60wt%.

[0031] In this invention, the Tb content in the first easily demagnetized region can be 0.1wt%-2.5wt%, for example, 0.50wt%, 0.55wt%, or 0.60wt%.

[0032] In this invention, the diffusion weight gain of Dy in the first easily demagnetized region can be 0.05 wt% or less, for example, 0, 0.01 wt%, 0.02 wt%, or 0.03 wt%.

[0033] In this invention, the content of Dy in the first easily demagnetized region can be 0wt%-3.1wt%, for example, 0, 0.01wt%, 0.02wt% or 0.03wt%.

[0034] In this invention, the diffusion weight gain of Tb in the first transition region can be 0.1wt%-1wt%, preferably 0.3wt%-0.7wt%, for example 0.49wt%, 0.55wt%, 0.58wt% or 0.59wt%.

[0035] In this invention, the Tb content in the first transition region can be 0.1wt%-2.5wt%, for example 0.49wt%, 0.55wt%, 0.58wt%, or 0.59wt%.

[0036] In this invention, the diffusion weight gain of Dy in the first transition region can be 0.05wt%-0.9wt%, preferably 0.1wt%-0.5wt%, for example 0.1wt% or 0.32wt%.

[0037] In this invention, the content of Dy in the first transition region can be 0.05wt%-3.9wt%, for example 0.1wt% or 0.32wt%.

[0038] In this invention, the diffusion weight gain of Tb in the non-demagnetizing region can be 0.05 wt% or less, for example, 0.01 wt%, 0.02 wt%, or 0.03 wt%.

[0039] In this invention, the Tb content in the non-demagnetizing region can be 0wt%-1.6wt%, for example, 0.01wt%, 0.02wt%, or 0.03wt%.

[0040] In this invention, the diffusion weight gain of Dy in the non-demagnetizing region can be 0.1wt%-1wt%, preferably 0.2wt%-0.7wt%, for example 0.3wt%, 0.5wt% or 0.7wt%.

[0041] In this invention, the content of Dy in the non-demagnetizing region is 0.1wt%-4wt%, for example, 0.3wt%, 0.5wt% or 0.7wt%.

[0042] In some specific implementations, the Tb diffusion gain in the first demagnetizing region is greater than the Tb diffusion gain in the first transition region.

[0043] In some specific implementations, the Tb diffusion weight gain in the first transition region is higher than that in the non-demagnetizing region.

[0044] In some specific implementations, the diffusion weight gain of Dy in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region increases sequentially.

[0045] In this invention, an interface A exists between the transition region and the easily demagnetized region. Interface A includes a first interface A, a second interface A, a third interface A, and a fourth interface A corresponding to the first transition region, the second transition region, the third transition region, and the fourth transition region. The diffusion weight gain of heavy rare earth elements is the same for the first interface A, the second interface A, the third interface A, and the fourth interface A. In this invention, the first interface A refers to the interface between the first easily demagnetized region and the first transition region; the second interface A refers to the interface between the second easily demagnetized region and the second transition region; the third interface A refers to the interface between the third easily demagnetized region and the third transition region; and the fourth interface A refers to the interface between the fourth easily demagnetized region and the fourth transition region.

[0046] The Tb diffusion weight gain ratio between the first interface A and the first easily demagnetized region is preferably (0.9-1):1, for example, 0.98:1 or 1:1.

[0047] The Tb content of the first interface A and the first easily demagnetized region is preferably (0.9-1):1, for example 0.98:1 or 1:1.

[0048] The preferred ratio of the diffusion weight gain of the first interface A and the first easily demagnetized region is (0.02-0.2):(0-0.05), for example, 0.03:0, 0.1:0.01, 0.03:0.03, 0.02:0.03 or 0.03:0.01.

[0049] The content of Dy at the first interface A and the first easily demagnetized region is preferably 1:(0.8-1), for example 1:0.1 or 1:1.

[0050] In this invention, an interface B exists between the transition region and the non-demagnetizing region. This interface B includes a first interface B, a second interface B, a third interface B, and a fourth interface B corresponding to the first, second, third, and fourth transition regions, respectively. The diffusion weight gain of heavy rare earth elements is the same for all four interfaces. Specifically, the first interface B refers to the interface between the first transition region and the non-demagnetizing region; the second interface B refers to the interface between the second transition region and the non-demagnetizing region; the third interface B refers to the interface between the third transition region and the non-demagnetizing region; and the fourth interface B refers to the interface between the fourth transition region and the non-demagnetizing region.

[0051] Preferably, the Tb diffusion weight gain ratio between the first interface B and the non-demagnetizing region is (0.5-0.9):(0-0.05), for example, 0.47:0.02, 0.48:0.03, 0.46:0.01, 0.4:0.01, 0.52:0.01 or 0.47:0.03.

[0052] The preferred ratio of Tb content at the first interface B to that at the first easily demagnetized region is (0.5-0.96):1.

[0053] The preferred ratio of the diffusion weight gain of the first interface B to the Dy diffusion weight gain of the non-demagnetizing region is (0.3-1):1, for example, 0.67:1, 0.86:1, 0.43:1, 0.44:1 or 0.50:1.

[0054] The preferred ratio of the content of Dy at the first interface B to that at the first easily demagnetized region is (0.5-1):1.

[0055] In this invention, the neodymium iron boron magnet can be represented by the chemical formula R1-R2-TBM, wherein R1 includes one or more of Pr, Nd, Ce, Er, Tm, Y, Lu, Gd and Ho; R2 is Dy and / or Tb; T includes one or more of Zn, Si, V, Cr, Mn, Ni, Ge, Ti, Nb, Mo, Pd, Ag, Cd, Sb, Hf, Ta, W, O, C, N, S, F and P; and M includes one or more of Cu, Al, Co, Ga, Zr and Ti.

[0056] In some implementations, the M element is entirely derived from a NdFeB substrate.

[0057] In other embodiments, the M element comprises diffusion-introduced M element, wherein the diffusion-introduced M element accounts for a preferred mass percentage of 0%-0.4% of the NdFeB magnet.

[0058] In this invention, on any plane perpendicular to the orientation direction, the shapes of the first, second, third, and fourth easily demagnetized regions are each independently selected as rectangular, sector-shaped, or triangular. The shapes of the transition region and the non-easily demagnetized region correspond to the shapes of the easily demagnetized regions.

[0059] When the first, second, third, and fourth easily demagnetized regions are all rectangular, the first, second, third, and fourth transition regions are all L-shaped, and the non-easily demagnetized region is cross-shaped.

[0060] In some preferred embodiments, the first, second, third, and fourth demagnetizing regions have the same width, and the width of the demagnetizing region refers to the distance extending from the edge of the NdFeB magnet along the X-axis or Y-axis; the ratio of the width of the first demagnetizing region to the total width of the NdFeB magnet is preferably (0.05-0.4):1.

[0061] In this invention, the first transition region, the second transition region, the third transition region, and the fourth transition region have the same width. The width of the first transition region refers to the distance between the interface between the first transition region and the first easily demagnetized region and the interface between the first transition region and the non-easily demagnetized region along the X-axis or Y-axis direction. The ratio of the width of the first transition region to the total width of the NdFeB magnet is preferably (0-0.1):1, for example, 0.078:1.

[0062] In this invention, the ratio of the width of the non-demagnetizing region to the total width of the NdFeB magnet is (0.2-1):1, for example, 0.522:1, 0.7:1 or 1:1. The width of the non-demagnetizing region refers to the distance along the X-axis or Y-axis extending from the interface between the transition region and the non-demagnetizing region or the edge of the NdFeB magnet.

[0063] In some specific embodiments, the width of the first transition region is preferably 0-1 mm and not 0.

[0064] In this invention, the ratio of the length to the thickness of the neodymium iron boron magnet is ≥3, and preferably, the thickness of the neodymium iron boron magnet is 0.5-5mm; the length refers to the distance of one side of the upper surface extending along the positive X-axis; the thickness refers to the distance of the cuboid extending from the upper surface along the positive Z-axis.

[0065] In this invention, the ratio of the coercivity of the non-demagnetizing region to the first demagnetizing region can be (0.7-0.96):1, more preferably (0.8-0.9):1, for example 0.85:1.

[0066] In this invention, the coercivity difference between the first easily demagnetized region and the non-easily demagnetized region can be 0-10 kOe, more preferably 2-5 kOe, for example 2.5 kOe or 4 kOe.

[0067] In this invention, the ratio of the coercivity of the first transition region to the first demagnetizing region can be (0.95-1):1, more preferably (0.98-1):1, for example 0.99:1.

[0068] In this invention, the coercivity of the first, second, third, and fourth easily demagnetized regions can be the same.

[0069] In this invention, the coercivity of the first transition region, the second transition region, the third transition region, and the fourth transition region can be the same.

[0070] In this invention, the coercivity of the first easily demagnetized region is not lower than that of the first transition region, and the coercivity of the first transition region is not lower than that of the non-easily demagnetized region.

[0071] In this invention, the residual magnetism of the first, second, third, and fourth easily demagnetized regions can be the same.

[0072] In this invention, the residual magnetism of the first transition region, the second transition region, the third transition region, and the fourth transition region can be the same.

[0073] In this invention, the remanence ratio of the first easily demagnetized region to the non-easily demagnetized region can be (0.99-1):1.

[0074] In this invention, the remanence ratio of the first transition region to the non-demagnetizing region can be (0.99-1):1.

[0075] In this invention, the grain boundary structure of the NdFeB magnet includes Re2Fe. 14 B-phase grains and Re-rich phase grain boundaries; the Re2Fe 14 The B principal phase grains comprise a core layer and a shell layer; the Re is Dy and / or Tb.

[0076] Preferably, the thickness of the main phase grain shell in the first, second, third, and fourth easily demagnetized regions is the same.

[0077] Preferably, the thickness of the principal phase grain shell in the first transition region, the second transition region, the third transition region, and the fourth transition region is the same.

[0078] Preferably, the Re-rich phase grain boundaries in the first, second, third, and fourth easily demagnetized regions have the same thickness.

[0079] Preferably, the Re-rich phase grain boundaries of the first transition region, the second transition region, the third transition region, and the fourth transition region have the same thickness.

[0080] Preferably, in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region, the thickness of the main phase grain shell is preferably 0-4 μm, and more preferably 0-2 μm.

[0081] Preferably, in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region, the thickness of the Re-rich phase grain boundary is preferably 0-1 μm, but not 0.

[0082] Preferably, in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region, the ratio of the thickness of the shell layer of the main phase grain to the thickness of the Re-rich phase grain boundary is preferably (0-2.0):(0-1), but not 0.

[0083] Preferably, the main phase grains in the first, second, third, and fourth easily demagnetized regions have the same grain size.

[0084] Preferably, the main phase grains in the first transition region, second transition region, third transition region and fourth transition region have the same grain size.

[0085] Preferably, the grain size ratio of the main phase grains in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region is 1:1:1.

[0086] Preferably, the surface main phase grains of the first easily demagnetized region, the first transition region, and the non-easily demagnetized region have the same grain size, preferably 1-12 μm.

[0087] Preferably, the grain size of the surface main phase grains in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region is 1-1.5 times the grain size of the central main phase grains.

[0088] Preferably, the core layer and shell layer of the main phase grain in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region satisfy the following conditions: the R1 content in the core layer is greater than or equal to the R1 content in the shell layer; the R2 content in the core layer is less than the R2 content in the shell layer; wherein R1 includes one or more of Pr, Nd, Ce, Er, Tm, Y, Lu, Gd, and Ho; and R2 is Dy and / or Tb.

[0089] Preferably, the R2 content in the main phase grain shell of the first easily demagnetized region, the first transition region, and the non-easily demagnetized region satisfies the following condition:

[0090] When R2 is Tb, the first easily demagnetized region ≥ the first transition region > the non-easily demagnetized region;

[0091] When R2 is Dy, the non-demagnetizing region ≥ the first transition region > the first demagnetizing region.

[0092] The present invention also provides a method for preparing the above-mentioned neodymium iron boron magnet, which includes the following steps: applying a diffusion source Tb to the four corner regions and a diffusion source Dy to the non-corner regions on the upper and lower surfaces of the neodymium iron boron substrate along the Z-axis, and performing grain boundary diffusion parallel to the orientation direction to obtain the neodymium iron boron magnet; wherein, the four corner regions form easily demagnetized regions through grain boundary diffusion; and the non-corner regions form non-easily demagnetized regions and transition regions.

[0093] In this invention, the Tb content in the NdFeB substrate can be conventional in the art, preferably 0-1.5 wt%.

[0094] In this invention, the Dy content in the NdFeB substrate can be conventional in the art, preferably 0-3 wt%.

[0095] As is known to those skilled in the art in this invention, during grain boundary diffusion, the Dy or Tb in the diffusion source does not completely diffuse into the magnet, and its utilization rate is generally 85%-95%. Therefore, in the actual preparation process, a larger amount of Dy or Tb is usually applied.

[0096] In some implementations, the diffusion source is pure Dy.

[0097] In other embodiments, the diffusion source is a Dy-M alloy, where M comprises one or more of Cu, Al, Co, Ga, Zr, and Ti. The mass percentage of M in the Dy-M alloy is 0-40%, and not zero.

[0098] In other embodiments, the diffusion source is a Dy hydride or a Dy fluoride.

[0099] In some implementations, the diffusion source is pure Tb.

[0100] In other embodiments, the diffusion source is a Tb-M alloy, where M comprises one or more of Cu, Al, Co, Ga, Zr, and Ti. The mass percentage of M in the Tb-M alloy is 0-40%, and not zero.

[0101] In other embodiments, the diffusion source is a Tb hydride or a Tb fluoride.

[0102] In some implementations, the diffusion source is pure Tb.

[0103] In other embodiments, the diffusion source is a Tb-M alloy, where M comprises one or more of Cu, Al, Co, Ga, Zr, and Ti. The mass percentage of M in the Tb-M alloy is 0-40%, and not zero.

[0104] In other embodiments, the diffusion source is a Tb hydride or a Tb fluoride.

[0105] In this invention, the diffusion source can be applied using methods conventional in the art, such as coating. Those skilled in the art know that different grain boundary diffusion methods will result in different coating thicknesses when diffusing the same amount of Dy or Tb into the magnet. Therefore, in the actual fabrication process, the coating thickness is not limited; it is sufficient to achieve the corresponding amount of Dy or Tb diffusion.

[0106] The coating method is preferably spraying or printing; the dewaxing temperature for spraying is preferably 200-400°C; and the dewaxing temperature for printing is preferably 100-500°C.

[0107] When the diffusion source is applied by the coating method, the diffusion source, solvent and binder are generally mixed in a certain proportion to form a slurry.

[0108] The solvent may be conventional in the art, such as water, alcohol, ketone or ester.

[0109] In some preferred embodiments, the diffusion source is applied by coating. In the diffusion source used in the non-demagnetizing region, the mass concentration of Dy is preferably 0.3%-1%; in the diffusion source used in the demagnetizing region, the mass concentration of Tb is preferably 0.3%-1.2%; in the diffusion source used in the first transition region, the mass concentration of Tb is preferably 0.3%-1.2%; and the mass concentration of Dy is preferably 0.3%-1%, where the percentage is the mass percentage of Dy or Tb in the diffusion source.

[0110] In this invention, the temperature of the heat treatment during grain boundary diffusion is 750–950°C, for example, 900°C;

[0111] In this invention, the heat treatment time for grain boundary diffusion is 5 to 30 hours, for example, 10 hours;

[0112] In this invention, the heat treatment in the grain boundary diffusion generally includes aging treatment.

[0113] In this invention, the aging treatment temperature is preferably 300–600°C, for example, 500°C;

[0114] In this invention, the aging process is preferably carried out for 1 to 10 hours, for example, 3 hours;

[0115] In some preferred embodiments, the method for preparing the neodymium iron boron magnet includes the following steps: applying a Tb diffusion source to the upper surface of the easily demagnetized region and a Dy diffusion source to the upper surface of the non-easily demagnetized region, and performing grain boundary diffusion parallel to the orientation direction to obtain the neodymium iron boron magnet.

[0116] In the preferred embodiment described above, during the diffusion process, a Tb diffusion source is applied only to the surface of the easily demagnetized region, while no Tb diffusion source is applied to the non-easily demagnetized region. However, after diffusion, a small amount of Tb applied to the easily demagnetized region may diffuse towards the center of the non-easily demagnetized region. The diffused Tb is mainly distributed at the boundary between the easily demagnetized region and the non-easily demagnetized region, and the Tb content in the center of the non-easily demagnetized region is relatively low.

[0117] The present invention also provides an application of the above-mentioned neodymium iron boron magnet in magnetic steel.

[0118] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0119] The reagents and raw materials used in this invention are all commercially available.

[0120] The positive and progressive effects of this invention are as follows:

[0121] The neodymium iron boron magnet described in this invention comprises a demagnetizing region, a non-demagnetizing region, and a transition region. By controlling the diffusion weight gain ratio of Tb and Dy introduced by diffusion in the transition region, the demagnetizing region, and the non-demagnetizing region, the problem of the gradient decrease in performance at the interface region, which leads to poor demagnetization resistance, is improved. Under the premise of ensuring the remanence of the neodymium iron boron magnet, the attenuation of the surface magnetism and magnetic flux of the neodymium iron boron magnet is reduced, thereby improving the demagnetization resistance of the neodymium iron boron magnet. Attached Figure Description

[0122] Figure 1 This is a schematic diagram of the structure of each region of a neodymium iron boron magnet.

[0123] Figure 2 This is a schematic diagram of the structure of the main phase grain nuclei and shells in each region of a neodymium iron boron magnet.

[0124] Figure 3 The neodymium iron boron magnet of Example 1 Figure 1 The diagram shows the diffusion weight gain distribution of Tb for test lines 1 and 2.

[0125] Figure 4 The neodymium iron boron magnet of Example 1 Figure 1 The diagram shows the diffusion weight gain distribution of Dy for test lines 1 and 2.

[0126] Figure label:

[0127] 1-First easily demagnetized region, 2-First transition region, 3-Non-easily demagnetized region, 4-Second transition region, 5-Second easily demagnetized region, 6-Third easily demagnetized region, 7-Third transition region, 8-Fourth transition region, 9-Fourth easily demagnetized region, 10-Main phase grain shell, 11-Main phase grain nucleus. Detailed Implementation

[0128] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0129] Examples 1-7 and Comparative Examples 1-5

[0130] On the upper and lower surfaces of a neodymium iron boron substrate along the Z-axis, Tb is sprayed in the four corner areas and Dy is sprayed in the non-corner areas. The dewaxing temperature of the spraying is 300°C, and grain boundary diffusion parallel to the orientation direction is carried out to obtain the neodymium iron boron magnet. The utilization rate of Dy or Tb is 85%-95%.

[0131] The heat treatment during grain boundary diffusion is carried out at a temperature of 900℃ for 10 hours. After the heat treatment, an aging treatment is also included, which is carried out at a temperature of 500℃ for 3 hours.

[0132] The parameters of each region of the neodymium iron boron magnets in Examples 1-7 and Comparative Examples 1-5 are listed in Tables 1-2 below. The elemental content of the neodymium iron boron substrates used in Examples 1-7 and Comparative Examples 1-5 is shown in Table 3. Since the content of heavy rare earth metals in the substrate is 0, the diffusion weight gain of heavy rare earths in Examples 1-7 and Comparative Examples 1-5 is equal to their content.

[0133] Schematic diagrams of the neodymium iron boron magnets in Examples 1-7 and Comparative Examples 1-5 are shown below. Figure 1 As shown, the first easily demagnetized region 1, the second easily demagnetized region 5, the third easily demagnetized region 6, and the fourth easily demagnetized region 9 are all rectangular; the first transition region 2, the second transition region 4, the third transition region 7, and the fourth transition region 8 are all L-shaped, and the non-easily demagnetized region 3 is cross-shaped; the thickness of the NdFeB magnet is 3 mm, and the length-to-thickness ratio is 3. Arrow M represents the magnetization direction of the NdFeB magnet, and arrow P represents the orientation direction of the NdFeB magnet; surface A represents the surface layer of the NdFeB magnet, and surface B represents the middle layer of the NdFeB magnet. The grain structure is as follows... Figure 2 As shown, 10 is the main phase grain shell and 11 is the main phase grain nucleus. Figure 3 The neodymium iron boron magnet of Example 1 Figure 1 The diagram shows the diffusion weight gain distribution of Tb for test lines 1 and 2. Figure 4 The neodymium iron boron magnet of Example 1 Figure 1 The diagram shows the diffusion weight gain distribution of Dy for test lines 1 and 2.

[0134] Table 1. Diffusion weight gain of Dy and Tb in each region of Examples 1-7 and Comparative Examples 1-5.

[0135]

[0136]

[0137] Continued from Table 1

[0138]

[0139] Table 2 shows the coercivity ratios and the width ratio of the transition zone to the NdFeB magnet for each region in Examples 1-7 and Comparative Examples 1-5.

[0140]

[0141]

[0142] Table 3. Mass concentration (wt%) of each element in the substrates of Examples 1-7 and Comparative Examples 1-5

[0143] Pr Nd Co Cu Al Ga B Ti Fe 3 27 0.5 0.2 0.1 0.3 0.98 0.2 margin

[0144] Example 1

[0145] The neodymium iron boron magnets of Examples 1-7 and Comparative Examples 1-5 were subjected to the following tests:

[0146] 1. Coercivity and Remanence Testing: Samples of Examples 1-7 and Comparative Examples 1-5 were prepared with a sample size of W2~3±0.1*L15±0.1*T5.6±0.1mm. Single-piece testing was conducted using a coil with a size of W3*L15~16*T2.7mm and a permanent magnet precision measurement system NIM-62000 at room temperature (temperature ≤200℃).

[0147] 2. Demagnetization Rate Test: Using electromagnetic simulation software, Ansys Workbench, with an input speed of 1300 rpm, and the temperature adjusted to the corresponding operating conditions, back EMF data of the motor was collected over the same time period, and changes in the magnet contour plot were observed to determine whether demagnetization had occurred. The formula for calculating the demagnetization rate is: Demagnetization Rate = (High-Temperature Back EMF - Room-Temperature Back EMF) / Room-Temperature Back EMF.

[0148] The technical effects of Examples 1-7 and Comparative Examples 1-5 are listed in Table 4 below:

[0149] Table 4 shows the coercivity and demagnetization resistance of different regions in the magnets of Examples 1-7 and Comparative Examples 1-5.

[0150]

[0151] Note: ① In Tables 1, 2, and 4, "easy demagnetizing zone" means the first easy demagnetizing zone, the second easy demagnetizing zone, the third easy demagnetizing zone, or the fourth easy demagnetizing zone; ② In the tables, "transition zone" means the first transition zone, the second transition zone, the third transition zone, or the fourth transition zone.

[0152] As shown in the table above, the remanence of the neodymium iron boron magnets prepared in Examples 1-7 in the easily demagnetized region, transition region and non-easily demagnetized region is maintained above 14.30 kGs, and at the same time, they have excellent anti-demagnetization ability. The demagnetization rate of the neodymium iron boron magnets in Examples 1-7 at 130°C is only 2.5%-9.1%.

[0153] The Tb diffusion weight gain ratio of the first transition region to the first easily demagnetized region in Comparative Example 1 was too low, specifically 0.17:1. The demagnetization resistance of the neodymium iron boron magnet prepared in Comparative Example 1 was poor, and its demagnetization rate at 130°C was 10.5%, which was higher than that of Examples 1-7, indicating poor demagnetization resistance.

[0154] The Tb diffusion weight gain ratio of the first transition region to the first easily demagnetized region in Comparative Example 2 was too low, specifically 0.6:1, and the Dy diffusion weight gain in both the transition region and the non-easily demagnetized region was 0. As a result, the demagnetized NdFeB magnets prepared by this method had poor demagnetization resistance, and their demagnetization rate at 130°C was as high as 39.2%, which was much higher than that of Examples 1-7.

[0155] The Tb diffusion weight gain ratio of the first transition region and the first easily demagnetized region in Comparative Example 3 is within the range of the present invention, but the diffusion weight gain of Dy in both the transition region and the non-easily demagnetized region is 0, and its anti-demagnetization rate at 130°C is as high as 36.5%, which is poor anti-demagnetization performance.

[0156] The diffusion weight gain ratio of Tb in the non-demagnetizing region and the demagnetizing region in Comparative Example 4 is not within the scope of this invention, specifically 1:1; its demagnetization resistance rate at 130°C is as high as 24.2%, indicating poor demagnetization resistance.

[0157] In Comparative Example 5, no transition zone was set, and the diffusion weight gain ratio of Dy in its first easily demagnetized region to that in the non-easily demagnetized region was 0.1:0.5. The diffusion weight gain of Dy in the easily demagnetized region was relatively high, and the neodymium iron boron magnet prepared thereby had a demagnetization resistance rate as high as 13.2% at 130°C, indicating poor demagnetization resistance.

[0158] The embodiments described above are merely preferred embodiments of the present invention, enabling those skilled in the art to understand and use the invention. Obviously, anyone skilled in the art can make slight modifications or variations to these embodiments without creative effort and apply them to other embodiments. Therefore, the present invention is not limited to the above embodiments, and any equivalent changes, simple modifications, and alterations made within the scope of the present invention still fall within its coverage.

Claims

1. A neodymium iron boron magnet, characterized in that, The neodymium iron boron magnet is a cuboid. A three-dimensional rectangular coordinate system is established with the center of the upper surface of the cuboid as the origin, wherein the orientation direction is the positive Z-axis and the X-axis is parallel to one side of the upper surface. The neodymium iron boron magnet includes a non-demagnetizing region, a transition region, and a demagnetizing region; the demagnetizing region includes a first demagnetizing region, a second demagnetizing region, a third demagnetizing region, and a fourth demagnetizing region respectively disposed at the four corners of the cuboid along the Z-axis direction and not in contact with each other; The transition region is located at the boundary between the easily demagnetized region and the non-easily demagnetized region, and includes a first transition region, a second transition region, a third transition region, and a fourth transition region corresponding to the first easily demagnetized region, the second easily demagnetized region, the third easily demagnetized region, and the fourth easily demagnetized region, respectively. The heavy rare earth elements in the first, second, third, and fourth easily demagnetized regions are the same. The heavy rare earth elements in the first transition zone, the second transition zone, the third transition zone, and the fourth transition zone are the same. The Tb content ratio of the non-demagnetizing region to the first demagnetizing region is (0-0.9):1; The ratio of Dy content in the first easily demagnetized region to that in the non-easily demagnetized region is (0-0.9):1; The Tb content ratio of the first transition region to the first easily demagnetized region is (0.9-1):1; The diffusion weight gain of Tb in the first easily demagnetized region is 0.1wt%-0.6wt%; The diffusion weight gain of Dy in the non-demagnetizing region is 0.1wt%-0.7wt%; The first transition region, the second transition region, the third transition region, and the fourth transition region have the same width; the ratio of the width of the first transition region to the total width of the NdFeB magnet is (0-0.1):1; the width of the first transition region refers to the distance between the interface between the first transition region and the first easily demagnetized region and the interface between the first transition region and the non-easily demagnetized region along the X-axis or Y-axis direction.

2. The neodymium iron boron magnet as described in claim 1, characterized in that, The Tb content ratio of the non-demagnetizing region to the first demagnetizing region is (0-0.2):1; And / or, the diffusion weight gain ratio of Tb in the non-demagnetizing region to that in the first demagnetizing region is (0-0.05):(0.3-1); And / or, the content ratio of Dy in the first easily demagnetized region to that in the non-easily demagnetized region is (0-0.8):1; And / or, the diffusion weight gain ratio of Dy in the first easily demagnetized region to that in the non-easily demagnetized region is (0-0.05):(0.3-1); And / or, the Tb content ratio of the first transition region to the first easily demagnetized region is 0.97:1, 0.98:1, or 1:1; And / or, the diffusion weight gain ratio of Tb in the first transition region and the first easily demagnetized region is (0.8-1):1; And / or, the diffusion weight gain ratio of Dy in the first transition region and the first easily demagnetized region is (0.05-0.6):(0-0.05); And / or, the diffusion weight gain ratio of Dy in the first transition region to that in the non-demagnetizing region is (0.05-0.9):1; And / or, the diffusion weight gain of Tb in the first easily demagnetized region is 0.50 wt%, 0.55 wt%, or 0.60 wt%; And / or, the Tb content in the first easily demagnetized region is 0.1wt%-2.5wt%; And / or, the diffusion weight gain of Dy in the first easily demagnetized region is 0.05 wt% or less; And / or, the Dy content in the first easily demagnetized region is 0wt%-3.1wt%; And / or, the diffusion weight gain of Tb in the first transition region is 0.1wt%-1wt%; And / or, the Tb content in the first transition region is 0.1wt%-2.5wt%; And / or, the diffusion weight gain of Dy in the first transition region is 0.05wt%-0.9wt%; And / or, the Dy content in the first transition region is 0.05wt%-3.9wt%; And / or, the diffusion weight gain of Tb in the non-demagnetizing region is 0.05 wt% or less; And / or, the Tb content in the non-demagnetizing region is 0wt%-1.6wt%; And / or, the diffusion weight gain of Dy in the non-demagnetizing region is 0.2 wt%-0.7 wt%; And / or, the Dy content in the non-demagnetizing region is 0.1wt%-4wt%; And / or, the Tb diffusion weight gain in the first easily demagnetized region is higher than the Tb diffusion weight gain in the first transition region; And / or, the Tb diffusion weight gain in the first transition region is higher than the Tb diffusion weight gain in the non-demagnetizing region; And / or, the diffusion weight gain of Dy in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region increases sequentially.

3. The neodymium iron boron magnet as described in claim 2, characterized in that, The Tb content ratio between the non-demagnetizing region and the first demagnetizing region is 0.03:1, 0.05:1, or 0.02:1; And / or, the diffusion weight gain ratio of Tb in the non-demagnetizing region to that in the first demagnetizing region is (0-0.05):(0.50-0.70). And / or, the ratio of Dy content in the first easily demagnetized region to that in the non-easily demagnetized region is 0:1, 0.02:1, or 0.04:1; And / or, the diffusion weight gain ratio of Dy in the first easily demagnetized region to that in the non-easily demagnetized region is (0-0.05):(0.5-0.7). And / or, the diffusion weight gain ratio of Tb in the first transition region and the first easily demagnetized region is (0.9-1):1; And / or, the diffusion weight gain ratio of Dy in the first transition region and the first easily demagnetized region is 0.1:0, 0.32:0.01, 0.1:0.03, or 0.1:0.01; And / or, the diffusion weight gain ratio of Dy in the first transition region to that in the non-demagnetizing region is (0.14-0.90):1; And / or, the Tb content in the first easily demagnetized region is 0.50 wt%, 0.55 wt%, or 0.60 wt%; And / or, the diffusion weight gain of Dy in the first easily demagnetized region is 0, 0.01 wt%, 0.02 wt%, or 0.03 wt%; And / or, the Dy content in the first easily demagnetized region is 0, 0.01wt%, 0.02wt%, or 0.03wt%; And / or, the diffusion weight gain of Tb in the first transition region is 0.3wt%-0.7wt%; And / or, the Tb content in the first transition region is 0.49 wt%, 0.55 wt%, 0.58 wt%, or 0.59 wt%; And / or, the diffusion weight gain of Dy in the first transition region is 0.1wt%-0.5wt%; And / or, the content of Dy in the first transition region is 0.1 wt% or 0.32 wt%; And / or, the diffusion weight gain of Tb in the non-demagnetizing region is 0.01 wt%, 0.02 wt%, or 0.03 wt%; And / or, the Tb content in the non-demagnetizing region is 0.01 wt%, 0.02 wt%, or 0.03 wt%; And / or, the diffusion weight gain of Dy in the non-demagnetizing region is 0.3 wt%, 0.5 wt%, or 0.7 wt%; And / or, the content of Dy in the non-demagnetizing region is 0.3 wt%, 0.5 wt%, or 0.7 wt%.

4. The neodymium iron boron magnet as described in claim 3, characterized in that, The diffusion weight gain ratio of Tb in the non-demagnetizing region to that in the first demagnetizing region is 0.02:0.60, 0.03:0.60, 0.01:0.55, 0.01:0.50, or 0.01:0.60; And / or, the diffusion weight gain ratio of Dy in the first easily demagnetized region to that in the non-easily demagnetized region is 0:0.3, 0.01:0.5, 0.03:0.7, or 0:0.5; And / or, the diffusion weight gain ratio of Tb in the first transition region and the first easily demagnetized region is 0.97:1, 0.98:1 or 1:1; And / or, the diffusion weight gain ratio of the first transition region to the non-demagnetizing region Dy is 0.33:1, 0.14:1, or 0.20:1; And / or, the diffusion weight gain of Tb in the first transition region is 0.49 wt%, 0.55 wt%, 0.58 wt%, or 0.59 wt%; And / or, the diffusion weight gain of Dy in the first transition region is 0.1 wt% or 0.32 wt%.

5. The neodymium iron boron magnet as described in claim 1, characterized in that, There is an interface A between the transition region and the easily demagnetized region. The interface A includes a first interface A, a second interface A, a third interface A, and a fourth interface A corresponding to the first transition region, the second transition region, the third transition region, and the fourth transition region. The diffusion weight gain of heavy rare earth elements is the same for the first interface A, the second interface A, the third interface A, and the fourth interface A. And / or, there is an interface B between the transition region and the non-demagnetizing region, the interface B including a first interface B, a second interface B, a third interface B and a fourth interface B corresponding to the first transition region, the second transition region, the third transition region and the fourth transition region, and the diffusion weight gain of heavy rare earth elements in the first interface B, the second interface B, the third interface B and the fourth interface B is the same.

6. The neodymium iron boron magnet as described in claim 5, characterized in that, The Tb diffusion weight gain ratio between the first interface A and the first easily demagnetized region is (0.9-1):1; And / or, the content ratio of Tb at the first interface A to that at the first easily demagnetized region is (0.9-1):1; And / or, the diffusion weight gain ratio of the first interface A to the first easily demagnetized region is (0.02-0.2):(0-0.05); And / or, the content ratio of the first interface A to the Dy content of the first easily demagnetized region is 1:(0.8-1); And / or, the Tb diffusion weight gain ratio between the first interface B and the non-demagnetizing region is (0.5-0.9):(0-0.05); And / or, the content ratio of Tb at the first interface B to that at the first easily demagnetized region is (0.5-0.96):1; And / or, the diffusion weight gain ratio of the first interface B to the Dy diffusion weight gain ratio of the non-demagnetizing region is (0.3-1):1; And / or, the content ratio of the first interface B to the Dy content of the first easily demagnetized region is (0.5-1):

1.

7. The neodymium iron boron magnet as described in claim 6, characterized in that, The Tb diffusion weight gain ratio between the first interface A and the first easily demagnetized region is 0.98:1 or 1:1; And / or, the content ratio of Tb at the first interface A to that at the first easily demagnetized region is 0.98:1 or 1:1; And / or, the diffusion weight gain ratio of the first interface A to the first easily demagnetized region is 0.03:0, 0.1:0.01, 0.03:0.03, 0.02:0.03 or 0.03:0.01; And / or, the content ratio of the first interface A to the Dy content of the first easily demagnetized region is 1:0.1 or 1:1; And / or, the Tb diffusion weight gain ratio between the first interface B and the non-demagnetizing region is 0.47:0.02, 0.48:0.03, 0.46:0.01, 0.4:0.01, 0.52:0.01 or 0.47:0.03; And / or, the diffusion weight gain ratio of the first interface B to the Dy diffusion weight gain ratio of the non-demagnetizing region is 0.67:1, 0.86:1, 0.43:1, 0.44:1 or 0.50:

1.

8. The neodymium iron boron magnet as described in claim 1, characterized in that, On any plane perpendicular to the orientation direction, the shapes of the first, second, third, and fourth easily demagnetized regions are each independently selected from rectangles, sectors, or triangles. And / or, the ratio of the width of the first easily demagnetized region to the total width of the NdFeB magnet is (0.05-0.4):1; And / or, the ratio of the width of the non-demagnetizing region to the total width of the NdFeB magnet is (0.2-1):1; the width of the non-demagnetizing region refers to the distance along the X-axis or Y-axis of the interface between the transition region and the non-demagnetizing region or the edge of the NdFeB magnet. And / or, the ratio of the width of the first transition region to the total width of the NdFeB magnet is 0.078:1; And / or, the width of the first transition zone is 0-1mm and not 0; And / or, the ratio of the length to the thickness of the neodymium iron boron magnet is ≥3, where the length refers to the distance of one side of the upper surface extending along the positive X-axis; and the thickness refers to the distance of the cuboid extending from the upper surface along the positive Z-axis.

9. The neodymium iron boron magnet as described in claim 8, characterized in that, The first, second, third, and fourth easily demagnetized regions are all rectangular and have the same width; the width of the easily demagnetized region refers to the distance extended from the edge of the NdFeB magnet along the X-axis or Y-axis; And / or, the ratio of the width of the first easily demagnetized region to the total width of the NdFeB magnet is 0.20:1; And / or, the ratio of the width of the non-demagnetizing region to the total width of the NdFeB magnet is 0.522:1, 0.7:1, or 1:1; And / or, the thickness of the neodymium iron boron magnet is 0.5-5mm, where the thickness refers to the distance the cuboid extends from its upper surface along the positive Z-axis.

10. The neodymium iron boron magnet as described in claim 1, characterized in that, The coercivity of the first, second, third, and fourth easily demagnetized regions is the same; the coercivity of the first, second, third, and fourth transition regions is the same. And / or, the residual magnetism of the first easily demagnetized region, the second easily demagnetized region, the third easily demagnetized region, and the fourth easily demagnetized region is the same; the residual magnetism of the first transition region, the second transition region, the third transition region, and the fourth transition region is the same.

11. The neodymium iron boron magnet as described in claim 10, characterized in that, The ratio of the coercivity of the non-demagnetizing region to the first demagnetizing region is (0.7-0.96):1; and / or, the difference in coercivity between the first demagnetizing region and the non-demagnetizing region is 0-10 kOe; And / or, the ratio of the coercivity of the first transition region to the first easily demagnetized region is (0.95-1):1; And / or, the coercivity of the first easily demagnetized region is not lower than the coercivity of the first transition region, and the coercivity of the first transition region is not lower than the coercivity of the non-easily demagnetized region; And / or, the remanence ratio of the first easily demagnetized region to the non-easily demagnetized region is (0.99-1):1; And / or, the remanence ratio of the first transition region to the non-demagnetizing region is (0.99-1):

1.

12. The neodymium iron boron magnet as described in claim 11, characterized in that, The ratio of the coercivity of the non-demagnetizing region to the first demagnetizing region is 0.79:1, 0.85:1, 0.89:1, 0.92:1, 0.92:1, or 0.94:1; And / or, the coercivity difference between the first easily demagnetized region and the non-easily demagnetized region is 1-5 kOe. And / or, the ratio of the coercivity of the first transition region to the first easily demagnetized region is (0.98-1):1; And / or, the remanence ratio of the first easily demagnetized region to the non-easily demagnetized region is 1:1; And / or, the remanence ratio of the first transition region to the non-demagnetizing region is 1:

1.

13. The neodymium iron boron magnet as described in claim 12, characterized in that, The coercivity difference between the first easily demagnetized region and the non-easily demagnetized region is 1.5 kOe, 2.1 kOe, 2.6 kOe, 2.8 kOe, 4 kOe or 5.5 kOe; And / or, the ratio of the coercivity of the first transition region to the first demagnetizing region is 0.99:1 or 0.98:

1.

14. The neodymium iron boron magnet as described in claim 1, characterized in that, The grain boundary structure of the neodymium iron boron magnet includes Re2Fe 14 B-phase grains and Re-rich phase grain boundaries; the Re2Fe 14 B main phase grains contain a main phase grain shell; Re is Dy and / or Tb; The thickness of the main phase grain shells in the first, second, third, and fourth easily demagnetized regions is the same; the thickness of the main phase grain shells in the first, second, third, and fourth transition regions is the same. The Re-rich phase grain boundaries in the first, second, third, and fourth easily demagnetized regions have the same thickness; the Re-rich phase grain boundaries in the first, second, third, and fourth transition regions have the same thickness.

15. The neodymium iron boron magnet as described in claim 14, characterized in that, In the first easily demagnetized region, the first transition region, and the non-easily demagnetized region, the thickness of the shell layer of the main phase grain is 0-4 μm; And / or, in the first easily demagnetized region, the first transition region and the non-easily demagnetized region, the thickness of the Re-rich phase grain boundary is 0-1 μm, but not 0; And / or, in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region, the ratio of the thickness of the main phase grain shell to the thickness of the Re-rich phase grain boundary is (0-2.0):(0-1), but not 0.

16. The neodymium iron boron magnet as described in claim 15, characterized in that, In the first easily demagnetized region, the first transition region, and the non-easily demagnetized region, the thickness of the shell layer of the main phase grain is 0-2 μm.

17. The neodymium iron boron magnet as described in claim 14, characterized in that, The main phase grains in the first, second, third, and fourth easily demagnetized regions have the same grain size. And / or, the main phase grains in the first transition region, the second transition region, the third transition region, and the fourth transition region have the same grain size; And / or, the grain size ratio of the main phase grains in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region is 1:1:1; And / or, the surface main phase grains of the first easily demagnetized region, the first transition region, and the non-easily demagnetized region have the same grain size; And / or, the grain size of the surface main phase grains in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region is 1-1.5 times the grain size of the central main phase grain; And / or, the core layer and shell layer of the main phase grain in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region satisfy the following conditions: the R1 content in the core layer is greater than or equal to the R1 content in the shell layer; the R2 content in the core layer is less than the R2 content in the shell layer; wherein, R1 includes one or more of Pr, Nd, Ce, Er, Tm, Y, Lu, Gd, and Ho; and R2 is Dy and / or Tb; And / or, the R2 content in the main phase grain shell of the first easily demagnetized region, the first transition region, and the non-easily demagnetized region satisfies the following condition: When R2 is Tb, the first easily demagnetized region ≥ the first transition region > the non-easily demagnetized region; When R2 is Dy, the non-demagnetizing region ≥ the first transition region > the first demagnetizing region.

18. The neodymium iron boron magnet as described in claim 17, characterized in that, The surface main phase grains of the first easily demagnetized region, the first transition region, and the non-easily demagnetized region have a grain size of 1-12 μm.

19. A method for preparing a neodymium iron boron magnet as described in any one of claims 1-18, characterized in that, The process includes the following steps: applying a diffusion source Tb to the four corner regions and a diffusion source Dy to the non-corner regions on the upper and lower surfaces of a neodymium iron boron substrate along the Z-axis, and performing grain boundary diffusion parallel to the orientation direction to obtain the neodymium iron boron magnet; wherein, the four corner regions form easily demagnetized regions through grain boundary diffusion; and the non-corner regions form non-easily demagnetized regions and transition regions.

20. The method for preparing a neodymium iron boron magnet as described in claim 19, characterized in that, The diffusion source is applied by coating; And / or, the temperature of the heat treatment in the grain boundary diffusion is 750~950℃; And / or, the heat treatment time in the grain boundary diffusion is 5~30h; And / or, the heat treatment in the grain boundary diffusion is followed by an aging treatment; And / or, the Tb content in the NdFeB substrate is 0-1.5 wt%; And / or, the Dy content in the NdFeB substrate is 0-3wt%.

21. The method for preparing a neodymium iron boron magnet as described in claim 20, characterized in that, The coating method is spraying or printing; And / or, the dewaxing temperature of the spray coating is 200~400℃; And / or, the dewaxing temperature of the printing is 100~500℃; And / or, the temperature of the heat treatment in the grain boundary diffusion is 900°C; And / or, the heat treatment time in the grain boundary diffusion is 10 h; And / or, the aging treatment temperature is 300~600℃; And / or, the aging process takes 1 to 10 hours.

22. The method for preparing a neodymium iron boron magnet as described in claim 21, characterized in that, The aging treatment temperature is 500℃; And / or, the aging process takes 3 hours.

23. The application of a neodymium iron boron magnet as described in any one of claims 1-18 in magnetic steel.

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