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 magnet, the content of heavy rare earth elements 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 content of Dy in the first easily demagnetized region, first transition region, and non-easily demagnetized region is the same and not zero; the content ratio of Tb in the first transition region to the first easily demagnetized region is (0.8-1):1; and the content ratio of Tb in the non-easily demagnetized region to the first easily demagnetized region is (0-0.9):1. The NdFeB magnet 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] The present invention mainly solves the above technical problems through the following technical solutions.

[0007] 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;

[0008] 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;

[0009] 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.

[0010] The diffusion weight gain of heavy rare earth elements is the same in the first easily demagnetized region, the second easily demagnetized region, the third easily demagnetized region, and the fourth easily demagnetized region;

[0011] 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.

[0012] The Dy content in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region is the same and not zero;

[0013] The Tb content ratio of the first transition region to the first easily demagnetized region is (0.8-1):1;

[0014] The Tb content ratio between the non-demagnetizing region and the first demagnetizing region is (0-0.9):1.

[0015] In this invention, the heavy rare earth elements may be derived from the substrate and / or diffusion process.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] In this invention, the diffusion weight gain of Dy in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region can be 0.1wt%-1wt%, for example, 0.5wt%, 0.6wt%, or 0.7wt%.

[0020] In this invention, the content of Dy in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region can be 0.1-4 wt%, for example, 0.5 wt%, 0.6 wt%, or 0.7 wt%.

[0021] In this invention, the diffusion weight gain ratio of Tb in the first transition region to the first easily demagnetized region can be (0.8-1):1, preferably (0.9-1):1, for example 0.98:1 or 1:1.

[0022] In this invention, the Tb content ratio of the first transition region to the first easily demagnetized region can be (0.9-1):1, such as 0.98:1 or 1:1.

[0023] In this invention, the Tb diffusion weight gain ratio between the non-demagnetizing region and the first demagnetizing region can be (0-0.05):1, for example 0:1, 0.01:1, 0.02:1, 0.03:1 or 0.05:1.

[0024] In this invention, the Tb content ratio of the non-demagnetizing region to the first demagnetizing region can be (0-0.9):1, preferably (0-0.2):1, for example 0:1, 0.01:1, 0.02:1, 0.03:1 or 0.05:1.

[0025] In this invention, the diffusion weight gain of Tb in the first easily demagnetized region can be 0.1wt%-1wt%, for example, 0.6wt% or 0.58wt%.

[0026] In this invention, the Tb content in the first easily demagnetized region is 0.1-2.5 wt%, for example, 0.6 wt% or 0.58 wt%.

[0027] In this invention, the diffusion weight gain of Tb in the non-demagnetizing region can be 0.05 wt% or less, for example, 0, 0.006 wt%, 0.012 wt%, 0.018 wt%, or 0.029 wt%.

[0028] In this invention, the Tb content in the non-demagnetizing region can be 0-1.6 wt%, for example 0, 0.006 wt%, 0.012 wt%, 0.018 wt%, or 0.029 wt%.

[0029] In this invention, the diffusion weight gain of Tb in the transition region can be 0.1wt%-1wt%, for example 0.588wt%, 0.57wt%, or 0.58wt%.

[0030] In this invention, the Tb content in the transition region can be 0.1-2.5 wt%, for example 0.588 wt%, 0.57 wt%, or 0.58 wt%.

[0031] In this invention, the neodymium iron boron magnet can be represented by the chemical formula R1-R2-R3-TBM, wherein R1 includes one or more of Pr, Nd, Ce, Er, Tm, Y, Lu, Gd and Ho; R2 is Tb introduced by diffusion; R3 is Dy introduced by diffusion; 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.

[0032] In some implementations, the M element is entirely derived from a NdFeB substrate.

[0033] In other embodiments, the M element comprises a diffusion-introduced M element, wherein the diffusion-introduced M element accounts for a preferred mass percentage of 0 wt% to 0.4 wt% of the NdFeB magnet.

[0034] In this invention, 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 Tb at the first interface A, the second interface A, the third interface A, and the fourth interface A is the same.

[0035] The Tb diffusion weight gain ratio between the first interface A and the first easily demagnetized region is preferably (0.95-1):1, for example, 0.96:1, 0.98:1, 0.99:1 or 1:1.

[0036] The Tb content of the first interface A and the first easily demagnetized region is preferably (0.9-1):1, for example 0.96:1, 0.98:1, 0.99:1 or 1:1.

[0037] In this invention, there is an interface B between the transition region and the non-demagnetizing region. The interface includes 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. The diffusion weight gain of Tb is the same for the first interface B, the second interface B, the third interface B, and the fourth interface B.

[0038] Preferably, the Tb diffusion weight gain ratio between the first interface B and the non-demagnetizing region is 1:(0-0.1), for example, 1:0.02, 1:0.03, 1:0.04 or 1:0.05.

[0039] The content ratio of Tb at the first interface B to that at the first easily demagnetized region is (0.5-0.96):1.

[0040] In this invention, the coercivity of the first, second, third, and fourth easily demagnetized regions is the same.

[0041] In this invention, the coercivity of the first transition region, the second transition region, the third transition region, and the fourth transition region is the same.

[0042] 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.

[0043] In this invention, the ratio of the coercivity of the first transition region to the first demagnetizing region can be (0.95-1):1, for example, 0.95:1, 0.97:1 or 0.98:1.

[0044] In this invention, the coercivity difference between the first easily demagnetized region and the non-easily demagnetized region can be 0-10 kOe, for example, 2.6 kOe, 3 kOe, 3.2 kOe, 3.5 kOe or 3.9 kOe.

[0045] 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, for example, 0.85:1, 0.87:1, 0.88:1 or 0.9:1.

[0046] In this invention, 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.

[0047] In this invention, the remanence ratio of the first easily demagnetized region to the non-easily demagnetized region can be (0.99-1):1, for example, 0.99:1 or 1:1.

[0048] In this invention, the remanence ratio of the first transition region to the non-demagnetizing region can be (0.99-1):1, for example, 1:1.

[0049] 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 from rectangles, sectors, or triangles.

[0050] In some preferred embodiments, the first, second, third, and fourth demagnetizing regions are all rectangular and have the same width. 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.

[0051] 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.

[0052] In this invention, the width ratio of the first transition region to the width of the neodymium iron boron magnet can be (0-0.1):1, for example, 0.092:1, 0.093:1 or 0.094:1.

[0053] In this invention, the width ratio of the non-demagnetizing region to the width of the NdFeB magnet can be (0.2-0.7):1, for example, 0.527:1. 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.

[0054] In this invention, the width ratio of the first easily demagnetized region to the width of the neodymium iron boron magnet can be (0.05-0.4):1.

[0055] In this invention, the width of the first transition zone can be 0-1mm, but is not 0.

[0056] 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 main phase grains contain a main phase grain shell; Re is one or more of Nd, Dy, and Tb.

[0057] The term "main phase grain shell" is conventional in the art, namely (Nd, Dy / Tb)2Fe. 14 B. Hard magnetic layer. The meaning of the Re-rich phase grain boundary region is unconventional in the art, that is, a two-particle grain boundary region with Re > 95%.

[0058] Preferably, the Tb content of the main phase grain shell in the first, second, third, and fourth easily demagnetized regions is the same.

[0059] Preferably, the Tb content of the main phase grain shells in the first transition region, second transition region, third transition region and fourth transition region is the same.

[0060] Preferably, the Tb content of the main phase grain shell in the first easily demagnetized region is not lower than the Tb content of the main phase grain shell in the first transition region.

[0061] Preferably, the ratio of Tb content in the non-demagnetizing region to the main phase grain shell of the first demagnetizing region is (0-0.05):(0.3-0.65), for example, 0:0.60, 0.01:0.59, 0.01:0.57, 0.02:0.69 or 0.03:0.58.

[0062] Preferably, the ratio of Tb content in the first transition region to the main phase grain shell of the first easily demagnetized region is (0.2-0.65):(0.2-0.65), for example, 0.59:0.60, 0.58:0.59, 0.57:0.57, 0.57:0.60 or 0.60:0.60.

[0063] Preferably, the thickness of the main phase grain shell in the first, second, third, and fourth easily demagnetized regions is the same.

[0064] Preferably, the thickness of the main phase grain shell in the first transition region, the second transition region, the third transition region, and the fourth transition region is the same.

[0065] Preferably, the Re-rich phase grain boundaries of the first, second, third, and fourth easily demagnetized regions have the same thickness.

[0066] 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.

[0067] Preferably, the shell layer between the main phase grains and the Re-rich grain boundaries in the first easily demagnetized region contain a high concentration of Dy and Tb, and the thickness is preferably 0-3 μm; the shell layer between the main phase grains and the Re-rich grain boundaries in the first transition region contain a high concentration of Dy and Tb, and the thickness is preferably 0-3 μm; the shell layer between the main phase grains and the Re-rich grain boundaries in the non-easily demagnetized region contain a high concentration of Dy, and the thickness is preferably 0-2 μm.

[0068] Preferably, the thickness of the main phase grain shell in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region preferably satisfies the following condition: first easily demagnetized region ≥ first transition region ≥ non-easily demagnetized region.

[0069] Preferably, in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region, the thickness of the Re-rich grain boundary of the main phase grain preferably satisfies: first easily demagnetized region ≥ first transition region ≥ non-easily demagnetized region.

[0070] Preferably, in both the first demagnetizing region and the first transition region, the thickness of the main phase grain shell is 0-4 μm, more preferably 0.5-1.5 μm.

[0071] Preferably, in the non-demagnetizing region, the thickness of the main phase grain shell is 0-2 μm, more preferably 0.5-1 μm;

[0072] 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 0-1 μm, but not 0.

[0073] Preferably, 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 (0.5-1.5):(0-1), but not 0.

[0074] Preferably, the main phase grains in the first, second, third, and fourth easily demagnetized regions have the same grain size; the main phase grains in the first, second, third, and fourth transition regions have the same grain size.

[0075] Preferably, the grain size of the main phase grains in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region satisfies the following condition: first easily demagnetized region ≥ first transition region ≥ non-easily demagnetized region.

[0076] Preferably, the grain size of the main phase grains on the surface of the first easily demagnetized region is 1-1.5 times the grain size of the main phase grains on the surface of the non-easily demagnetized region.

[0077] Preferably, the grain size of the surface main phase grains in the first easily demagnetized region and the first transition region is 1-1.5 times the grain size of the central main phase grains;

[0078] Preferably, the grain size of the surface main phase grains in the non-demagnetizing region is 1-1.3 times the grain size of the central main phase grains.

[0079] Preferably, the thickness of the main phase grain shell in the first easily demagnetized region and the first transition region is 1-5 times the thickness of the main phase grain shell in the non-easily demagnetized region.

[0080] Preferably, the surface main phase grains of the first demagnetizing region and the first transition region have the same grain size, preferably 1-12 μm.

[0081] Preferably, the grain size of the main phase grains on the surface of the non-demagnetizing region is 1-8 μm.

[0082] In this invention, the term "surface" refers to a surface perpendicular to the orientation direction, and the term "center" refers to a mid-plane along the orientation direction.

[0083] In this invention, the main phase grain shell layer of the easily demagnetized region includes a first inner shell layer and a first outer shell layer; the main phase grain shell layer of the transition region includes a second inner shell layer and a second outer shell layer; and the main phase grain shell layer of the non-easily demagnetized region includes a third inner shell layer.

[0084] The inner shell refers to the region where the Dy content in the main phase grain shell accounts for 80% or more of the sum of the total Tb and Dy element content; the outer shell refers to the region where the Tb content in the main phase grain shell accounts for 80% or more of the sum of the total Tb and Dy element content.

[0085] Preferably, the Tb diffusion weight gain of the first outer shell layer and the second outer shell layer satisfies the condition that the first outer shell layer ≥ the second outer shell layer.

[0086] Preferably, the Tb diffusion weight gain in the first outer shell layer is 0.1wt%-0.9wt%, for example, 0.6wt%.

[0087] Preferably, the Tb content in the first outer shell layer is 0.1wt%-2.4wt%, for example, 0.6wt%.

[0088] Preferably, the Tb diffusion weight gain in the second outer shell layer is 0.1wt%-0.8wt%, for example, 0.6wt% or 0.58wt%.

[0089] The Tb content in the second outer shell layer is preferably 0.1wt%-2.3wt%, for example, 0.6wt% or 0.58wt%.

[0090] The Dy diffusion weight gain of the first inner shell, the second inner shell, and the third inner shell preferably satisfies the following condition: third inner shell ≥ second inner shell ≥ first inner shell.

[0091] Preferably, the Dy diffusion weight gain in the first inner shell is 0.1wt%-0.9wt%, for example, 0.5wt%, 0.6wt%, or 0.7wt%.

[0092] The content of Dy in the first inner shell is preferably 0.1-3.9 wt%, for example 0.5 wt%, 0.6 wt%, or 0.7 wt%.

[0093] The Dy diffusion weight gain in the second inner shell is preferably 0.1wt%-0.9wt%, for example 0.5wt%, 0.6wt%, 0.69wt% or 0.7wt%.

[0094] The content of Dy in the second inner shell is preferably 0.1-3.9 wt%, for example 0.5 wt%, 0.6 wt%, 0.69 wt%, or 0.7 wt%.

[0095] The Dy diffusion weight gain in the third inner shell is preferably 0.1wt%-0.9wt%, for example, 0.5wt%, 0.6wt%, or 0.7wt%.

[0096] The content of Dy in the third inner shell is preferably 0.1-3.9 wt%, for example 0.5 wt%, 0.6 wt%, or 0.7 wt%.

[0097] Preferably, the thicknesses of the first inner shell layer, the second inner shell layer, and the third inner shell layer satisfy the following condition: third inner shell layer ≥ second inner shell layer ≥ first inner shell layer.

[0098] Preferably, the thicknesses of the first inner shell layer and the first outer shell layer satisfy the following condition: the thickness of the first outer shell layer is less than or equal to the thickness of the first inner shell layer.

[0099] Preferably, the thicknesses of the second inner shell layer and the second outer shell layer satisfy the following condition: the thickness of the second outer shell layer is less than or equal to that of the second inner shell layer.

[0100] The thickness of the first inner shell layer is preferably 0-2 μm, for example, 1.8 μm, 1.9 μm or 2 μm.

[0101] Preferably, the thickness of the first outer shell layer is 0-2 μm, for example, 1.7 μm, 1.8 μm, or... 1.9μm.

[0102] The thickness of the second inner shell layer is preferably 0-2 μm, for example 1.8 μm, 1.9 μm or 2 μm.

[0103] The thickness of the second outer shell layer is preferably 0-2 μm, for example, 1.8 μm, 1.7 μm or 2 μm.

[0104] The thickness of the third inner shell layer is preferably 0-2 μm, for example, 1.8 μm, 1.9 μm or 2 μm.

[0105] In this invention, the main phase grain shell layer of the non-demagnetizing region further includes a third outer shell layer.

[0106] Preferably, the Tb diffusion weight gain in the third outer shell of the main phase grain shell in the non-demagnetizing region is 0-0.05 wt%.

[0107] The content of Tb in the third outer shell of the main phase grain shell in the non-demagnetizing region is preferably 0wt%-1.6wt%.

[0108] The Tb diffusion weight gain of the first outer shell layer, the second outer shell layer, and the third outer shell layer preferably satisfies the following order: first outer shell layer > second outer shell layer > third outer shell layer.

[0109] Preferably, the thicknesses of the first outer shell layer, the second outer shell layer, and the third outer shell layer satisfy the following order: first outer shell layer > second outer shell layer > third outer shell layer.

[0110] Preferably, the thicknesses of the third inner shell and the third outer shell in the main phase grain shell of the non-demagnetizing region satisfy the following condition: the thickness of the third inner shell is greater than that of the third outer shell.

[0111] Preferably, the thickness of the third outer shell layer of the main phase grain shell layer in the non-demagnetizing region is 0-0.5 μm.

[0112] 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 Dy to the entire area of ​​the upper and lower surfaces along the Z-axis on the upper and lower surfaces of the neodymium iron boron substrate, and applying a diffusion source Tb to the four corner areas, and performing grain boundary diffusion parallel to the orientation direction to obtain the neodymium iron boron magnet; wherein, the four corner areas form easily demagnetized regions through grain boundary diffusion.

[0113] In this invention, as is known to those skilled in the art, during grain boundary diffusion, Dy or Tb from the diffusion source does not completely diffuse into the magnet, and its utilization rate is generally 85%-95%. Therefore, in the actual preparation process, one Generally, more Dy or Tb will be applied.

[0114] In this invention, 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 preparation process, the coating thickness is not limited, as long as the corresponding amount of Dy or Tb diffusion is achieved.

[0115] In some implementations, the diffusion source is pure Dy.

[0116] 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.

[0117] In other embodiments, the diffusion source is a Dy hydride or a Dy fluoride.

[0118] In some implementations, the diffusion source is pure Tb.

[0119] 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.

[0120] In other embodiments, the diffusion source is a Tb hydride or a Tb fluoride.

[0121] In this invention, the diffusion source can be applied using methods conventional in the art, such as coating.

[0122] 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.

[0123] When the diffusion source is applied by the coating method, the diffusion source is generally mixed with solvent and binder in a certain proportion to form a slurry.

[0124] The solvent may be, for example, water, alcohol, ketone or ester.

[0125] In this invention, the temperature of the heat treatment during grain boundary diffusion is preferably 750–950°C, for example, 900°C.

[0126] In this invention, the heat treatment time during grain boundary diffusion is preferably 5 to 30 hours, for example, 25 hours.

[0127] In this invention, the heat treatment in the grain boundary diffusion generally includes an aging treatment.

[0128] The aging treatment temperature is preferably 300–600°C, for example, 490°C.

[0129] The aging process is preferably carried out over a period of 1 to 10 hours, for example, 6 hours.

[0130] The present invention also provides an application of the above-mentioned neodymium iron boron magnet in magnetic steel.

[0131] 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.

[0132] The reagents and raw materials used in this invention are all commercially available.

[0133] The positive and progressive effects of this invention are as follows:

[0134] The neodymium iron boron magnet described in this invention includes a transition region. By controlling the Tb content introduced by diffusion in the transition region, the easily demagnetized region, and the non-easily demagnetized region, as well as the Dy content in all regions, the problem of Tb interdiffusion across regions caused by the Tb concentration gradient difference in the transition region, which leads to a gradient decrease in the performance of the boundary region and a weakening of the anti-demagnetization effect, can be reduced. 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 can be reduced, thereby improving the anti-demagnetization ability of the neodymium iron boron magnet. Attached Figure Description

[0135] Figure 1 This is a schematic diagram of the structure of each region of a neodymium iron boron magnet.

[0136] 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.

[0137] Figure 3 This is a scanning electron microscope image of the neodymium iron boron magnet in Example 1.

[0138] Figure 4 for Figure 3 Line scan of Cu content in the grain shell.

[0139] Figure 5 for Figure 3 Line scan of Al content in the grain shell.

[0140] Figure 6 for Figure 3 Line scan of the Dy content in the grain shell.

[0141] Figure 7 for Figure 3 Line scan of Tb content in the grain shell.

[0142] Figure 8 for Figure 3 Line scan of Nd content in the grain shell.

[0143] Figure 9 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.

[0144] Figure 10 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.

[0145] Possession Mark:

[0146] 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, 12-First inner shell, 13-First outer shell, 14-Second inner shell, 15-Second outer shell, 16-Third inner shell. Detailed Implementation

[0147] 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.

[0148] Examples 1-5 and Comparative Examples 1-2

[0149] On the upper and lower surfaces of the neodymium iron boron substrate along the Z-axis, Dy is sprayed over the entire area of ​​both surfaces, and Tb is sprayed over the four 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 in the diffusion source is 85%-95%.

[0150] The heat treatment during grain boundary diffusion is carried out at a temperature of 850℃ for 25 hours. After the heat treatment, an aging treatment is also included, which is carried out at a temperature of 490℃ for 6 hours.

[0151] The parameters of each region of the NdFeB magnets in Examples 1-5 and Comparative Examples 1-2 are listed in Tables 1, 2, and 3 below. The elemental content of the NdFeB substrates used in Examples 1-5 and Comparative Examples 1-2 is shown in Table 4. Since the content of heavy rare earth metals in the substrate is 0, the diffusion weight gain of heavy rare earths in Examples 1-5 and Comparative Examples 1-2 is equal to their content.

[0152] Schematic diagrams of the neodymium iron boron magnets in Examples 1-5 and Comparative Examples 1-2 are shown below. Figure 1 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. A schematic diagram of the main phase grain nucleus and shell structure is shown below. Figure 2As shown, 10 is the shell of the main phase grain, 11 is the core of the main phase grain, 12 is the first inner shell, 13 is the first outer shell, 14 is the second inner shell, 15 is the second outer shell, and 16 is the third inner shell. It can be seen that the shells of the main phase grains in the easily demagnetized region and the transition region both contain inner and outer shells, while the main phase grains in the non-easily demagnetized region only contain an inner shell. Figure 9 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 10 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.

[0153] Table 1. Diffusion weight gain of Dy and Tb in each region of the NdFeB magnets prepared in Examples 1-5 and Comparative Examples 1-2, and the ratio of Tb content in the main phase grain shell of each region.

[0154]

[0155] Continued from Table 1

[0156]

[0157]

[0158] Table 2. Coercivity ratios, width ratios, and main phase grain sizes of NdFeB magnets prepared in Examples 1-5 and Comparative Examples 1-2

[0159]

[0160] Table 3. Inner and outer shell layer thicknesses of the main phase grains in each region of the NdFeB magnets prepared in Examples 1-5 and Comparative Examples 1-2, as well as the diffusion weight gain of Dy and Tb.

[0161]

[0162] Table 4. Mass concentration of each element in the substrates of Examples 1-5 and Comparative Examples 1-2

[0163] Pr Nd Dy Gd Co Ho Cu Al Ga B Zr Ti Fe Total rare earth content 3 27 0 0 0.5 0 0.2 0.1 0.3 0.98 0 0.2 margin 30

[0164] Example 1

[0165] The neodymium iron boron magnets of Examples 1-5 and Comparative Examples 1-2 were tested as follows, and the results are listed in Table 5.

[0166] 1. Coercivity test: Samples of Examples 1-5 and Comparative Examples 1-2 were prepared with a sample size of W2~3±0.1*L19±0.1*T4±0.1mm. Two samples were stacked and tested at room temperature (temperature ≤200℃) using a coil with a size of W3*L19~20*T2.7mm on a permanent magnet precision measurement system NIM-62000.

[0167] 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 condition, 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.

[0168] 3. Remanence test: The neodymium iron boron magnets of Examples 1-5 and Comparative Examples 1-2 were placed in the PFM-14 pulse magnetic property measuring instrument of the National Institute of Metrology of China to measure the remanence.

[0169] 4. The test method and instrument for line scan images are as follows: The selected area of ​​the magnet surface is microscopically photographed under the EMMA equipment. The equipment model is JEOL 8530f, and the magnification is X3000. Line scans are performed on the two main phase grains to characterize the distribution of elements such as Cu, Al, Dy, Tb and Nd.

[0170] Table 5. Coercivity and demagnetization resistance of different regions in the magnets of Examples 1-5 and Comparative Examples 1-2.

[0171]

[0172] Note: In all the tables above, ① "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 "Transition zone" means the first transition zone, the second transition zone, the third transition zone, or the fourth transition zone.

[0173] As shown in Table 5, the coercivity ratio between the first transition region and the first easily demagnetized region of the NdFeB magnets prepared in Examples 1-5 is between (0.95-1):1, and the coercivity difference between the first easily demagnetized region and the non-easily demagnetized region is between 2.6-3.9 kOe. The demagnetization rate of the NdFeB magnets in Examples 1-5 at 130℃ is only 2.5%-6.1%, indicating that Examples 1-5 have more remanence and excellent anti-demagnetization ability.

[0174] Figure 3 This is a scanning electron microscope image of the neodymium iron boron magnet prepared in Example 1. Figure 4-8 In order to be in Figure 3Based on this, line scans of the elemental content in the grain shell of the neodymium iron boron magnet were obtained. It can be seen that in the grain shell of the neodymium iron boron magnet, the content of Dy is higher than that of Tb.

[0175] The Tb diffusion weight gain ratio of the first transition region to the first easily demagnetized region in Comparative Example 1 is 0.5:1, which affects the Tb content in the main phase grain shell, the thickness of the shell, and the width of the transition region. Everything else is the same as in Example 1. The demagnetization rate of the NdFeB magnet prepared in Comparative Example 1 at 130°C is 18%, which is higher than that in Example 1, indicating that the demagnetization resistance of Comparative Example 1 is worse than that in Example 1.

[0176] In Comparative Example 2, Dy diffusion was not performed in the easily demagnetized region, the transition region, and the non-easily demagnetized region, but Tb diffusion was performed in the transition region and the easily demagnetized region. The resulting NdFeB magnet had a demagnetization rate of up to 26.9% at 130°C, which was much higher than that of Examples 1-5, indicating that the demagnetization resistance of Comparative Example 2 was worse than that of the Examples.

[0177] 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 Dy content in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region is the same and not zero; The Tb content ratio of the first transition region to the first easily demagnetized region is (0.9-1):1; The Tb content ratio of the non-demagnetizing region to the first demagnetizing region is (0-0.9):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 first easily demagnetized region, the first transition region, and the non-easily demagnetized 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 width of the neodymium iron boron magnet is (0-0.1):

1.

2. The neodymium iron boron magnet as described in claim 1, characterized in that, The diffusion weight gain of Dy in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region is 0.5 wt%, 0.6 wt%, or 0.7 wt%, respectively. And / or, the content of Dy in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region is 0.1-4 wt%; And / or, the diffusion weight gain ratio of Tb in the first transition region to that in the first easily demagnetized region is (0.8-1):1; And / or, the Tb content ratio of the first transition region to the first easily demagnetized region is 0.98:1 or 1:1; And / or, the Tb diffusion weight gain ratio of the non-demagnetizing region to the first demagnetizing region is (0-0.05):1; And / or, 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 of Tb in the first easily demagnetized region is 0.6 wt% or 0.58 wt%; And / or, the Tb content in the first easily demagnetized region is 0.1-2.5 wt%; 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 0-1.6 wt%; And / or, the diffusion weight gain of Tb in the transition region is 0.1wt%-1wt%; And / or, the Tb content in the transition region is 0.1-2.5 wt%; And / or, 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, and the diffusion weight gain of Tb of the first interface A, the second interface A, the third interface A and the fourth interface A is the same; And / or, there is an interface B between the transition region and the non-demagnetizing region, and the interface includes 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 Tb of the first interface B, the second interface B, the third interface B and the fourth interface B is the same. The ratio of Tb content in the first interface B to that in the first easily demagnetized region is (0.5-0.96):

1.

3. The neodymium iron boron magnet as described in claim 2, characterized in that, The Dy content in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region is 0.5 wt%, 0.6 wt%, or 0.7 wt%, respectively. And / or, the diffusion weight gain ratio of Tb in the first transition region to that in the first easily demagnetized region is (0.9-1):1; And / or, the Tb diffusion weight gain ratio of the non-demagnetizing region to the first demagnetizing region is 0:1, 0.01:1, 0.02:1, 0.03:1 or 0.05:1; And / or, the Tb content ratio of the non-demagnetizing region to the first demagnetizing region is 0:1, 0.01:1, 0.02:1, 0.03:1 or 0.05:1; And / or, the Tb content in the first easily demagnetized region is 0.6 wt% or 0.58 wt%; And / or, the diffusion weight gain of Tb in the non-demagnetizing region is 0, 0.006 wt%, 0.012 wt%, 0.018 wt%, or 0.029 wt%; And / or, the Tb content in the non-demagnetizing region is 0, 0.006 wt%, 0.012 wt%, 0.018 wt%, or 0.029 wt%; And / or, the diffusion weight gain of Tb in the transition region is 0.588 wt%, 0.57 wt%, or 0.58 wt%; And / or, the Tb content in the transition region is 0.588 wt%, 0.57 wt%, or 0.58 wt%; And / or, the Tb diffusion weight gain ratio of the first interface A to the first easily demagnetized region is (0.95-1):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 Tb diffusion weight gain ratio of the first interface B to the non-demagnetizing region is 1:(0-0.1).

4. The neodymium iron boron magnet as described in claim 3, characterized in that, The diffusion weight gain ratio of Tb in the first transition region to that in the first easily demagnetized region is 0.98:1 or 1:1; And / or, the Tb diffusion weight gain ratio between the first interface A and the first easily demagnetized region is 0.96:1, 0.98:1, 0.99:1 or 1:1; And / or, the content ratio of Tb at the first interface A to that at the first easily demagnetized region is 0.96:1, 0.98:1, 0.99:1, or 1:1; And / or, the Tb diffusion weight gain ratio between the first interface B and the non-demagnetizing region is 1:0.02, 1:0.03, 1:0.04 or 1:0.

05.

5. 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; And / or, the coercivity of the first transition zone, the second transition zone, the third transition zone, and the fourth transition zone is the same; 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 ratio of the coercivity of the first transition region to the first easily demagnetized region is (0.95-1):1; And / or, the coercivity difference between the first easily demagnetized region and the non-easily demagnetized region is 0-10 kOe; And / or, the ratio of the coercivity of the non-demagnetizing region to the first demagnetizing region is (0.7-0.96):1; And / or, the remanence 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 remanence of the first transition region, the second transition region, the third transition region, and the fourth transition region is the same; 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; And / or, on any plane perpendicular to the orientation direction, the shapes of the first easily demagnetized region, the second easily demagnetized region, the third easily demagnetized region and the fourth easily demagnetized region are each independently selected from rectangles, sectors or triangles; And / or, the width ratio of the first transition region to the NdFeB magnet is 0.092:1, 0.093:1, or 0.094:1; And / or, the width of the non-demagnetizing region and the width of the NdFeB magnet are preferably (0.2-0.7):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 width ratio of the first easily demagnetized region to the width of the neodymium iron boron magnet is (0.05-0.4):1; And / or, the width of the first transition region is preferably 0-1 mm, and not 0.

6. The neodymium iron boron magnet as described in claim 5, characterized in that, The ratio of the coercivity of the first transition region to the first easily demagnetized region is 0.95:1, 0.97:1, or 0.98:1; And / or, the coercivity difference between the first easily demagnetized region and the non-easily demagnetized region is 2.6 kOe, 3 kOe, 3.2 kOe, 3.5 kOe or 3.9 kOe; And / or, the ratio of the coercivity of the non-demagnetizing region to the first demagnetizing region is 0.85:1, 0.87:1, 0.88:1, or 0.9:1; And / or, the remanence ratio of the first easily demagnetized region to the non-easily demagnetized region is 0.99:1 or 1:1; And / or, the remanence ratio of the first transition region to the non-demagnetizing region is 1:1; And / or, 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 width ratio of the non-demagnetizing region to the width of the neodymium iron boron magnet is 0.527:

1.

7. 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 The B main phase grains contain a main phase grain shell; Re is one or more of Nd, Dy, and Tb.

8. The neodymium iron boron magnet as described in claim 7, characterized in that, The Tb content of the main phase grain shells in the first, second, third, and fourth easily demagnetized regions is the same; And / or, the Tb content of the main phase grain shells in the first transition region, the second transition region, the third transition region, and the fourth transition region is the same; And / or, the Tb content of the main phase grain shell in the first easily demagnetized region is not lower than the Tb content of the main phase grain shell in the first transition region; And / or, the ratio of Tb content in the non-demagnetizing region to the main phase grain shell of the first demagnetizing region is (0-0.05):(0.3-0.65); And / or, the ratio of Tb content in the first transition region to the main phase grain shell of the first easily demagnetized region is (0.2-0.65):(0.2-0.65); And / or, the thickness of the principal phase grain shell in the first, second, third, and fourth easily demagnetized regions is the same; And / or, 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; And / or, the Re-rich phase grain boundaries of the first, second, third, and fourth easily demagnetized regions have the same thickness; And / or, 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; And / or, in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region, the thickness of the main phase grain shell layer satisfies: the first easily demagnetized region ≥ the first transition region ≥ the non-easily demagnetized region; And / or, in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region, the thickness of the Re-rich grain boundary of the main phase grain satisfies: first easily demagnetized region ≥ first transition region ≥ non-easily demagnetized region; And / or, in the first easily demagnetized region and the first transition region, the thickness of the main phase grain shell is 0-4 μm; And / or, in the non-demagnetizing region, the thickness of the main phase grain shell is 0-2 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 (0.5-1.5):(0-1), but not 0.

9. The neodymium iron boron magnet as described in claim 8, characterized in that, The ratio of Tb content in the non-demagnetizing region to the main phase grain shell of the first demagnetizing region is 0:0.60, 0.01:0.59, 0.01:0.57, 0.02:0.69 or 0.03:0.

58. And / or, the ratio of Tb content in the first transition region to the main phase grain shell of the first easily demagnetized region is 0.59:0.60, 0.58:0.59, 0.57:0.57, 0.57:0.60 or 0.60:0.60; And / or, in both the first easily demagnetized region and the first transition region, the thickness of the main phase grain shell is 0.5-1.5 μm; And / or, in the non-demagnetizing region, the thickness of the main phase grain shell is 0.5-1 μm.

10. The neodymium iron boron magnet as described in claim 7, characterized in that, The main phase grains in the first, second, third, and fourth easily demagnetized regions have the same grain size; the main phase grains in the first, second, third, and fourth transition regions have the same grain size. And / or, the grain size of the main phase grains in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region satisfies: the first easily demagnetized region ≥ the first transition region ≥ the non-easily demagnetized region; And / or, the grain size of the main phase grains on the surface of the first easily demagnetized region is 1-1.5 times the grain size of the main phase grains on the surface of the non-easily demagnetized region; And / or, the grain size of the surface main phase grains in the first easily demagnetized region and the first transition region is 1-1.5 times the grain size of the central main phase grains; And / or, the grain size of the surface main phase grains in the non-demagnetizing region is 1-1.3 times the grain size of the central main phase grains; And / or, the surface main phase grains of the first easily demagnetized region and the first transition region have the same grain size, preferably 1-12 μm; And / or, the grain size of the main phase grains on the surface of the non-demagnetizing region is 1-8 μm.

11. The neodymium iron boron magnet as described in claim 10, characterized in that, The surface main phase grains of the first easily demagnetized region and the first transition region have a grain size of 1-12 μm.

12. The neodymium iron boron magnet as claimed in claim 1, characterized in that, The main phase grain shell of the easily demagnetized region includes a first inner shell and a first outer shell; the main phase grain shell of the transition region includes a second inner shell and a second outer shell; and the main phase grain shell of the non-easily demagnetized region includes a third inner shell.

13. The neodymium iron boron magnet as described in claim 12, characterized in that, The Tb diffusion weight gain of the first outer shell layer and the second outer shell layer satisfies: the first outer shell layer ≥ the second outer shell layer; And / or, the Tb diffusion weight gain in the first outer shell layer is 0.1wt%-0.9wt%; And / or, the Tb content in the first outer shell layer is 0.1wt%-2.4wt%; And / or, the Tb diffusion weight gain in the second outer shell layer is 0.1wt%-0.8wt%; And / or, the Tb content in the second outer shell layer is 0.1wt%-2.3wt%; And / or, the Dy diffusion weight gain of the first inner shell, the second inner shell, and the third inner shell satisfies: the third inner shell ≥ the second inner shell ≥ the first inner shell; And / or, the Dy diffusion weight gain in the first inner shell is 0.1wt%-0.9wt%; And / or, the content of Dy in the first inner shell is 0.1-3.9 wt%; And / or, the Dy diffusion weight gain in the second inner shell is 0.1wt%-0.9wt%; And / or, the content of Dy in the second inner shell is 0.1-3.9 wt%; And / or, the Dy diffusion weight gain in the third inner shell is 0.1wt%-0.9wt%. And / or, the content of Dy in the third inner shell is 0.1-3.9 wt%; And / or, the thicknesses of the first inner shell, the second inner shell, and the third inner shell satisfy the following: the third inner shell ≥ the second inner shell ≥ the first inner shell; And / or, the thicknesses of the first inner shell layer and the first outer shell layer satisfy: the thickness of the first outer shell layer ≤ the thickness of the first inner shell layer; And / or, the thicknesses of the second inner shell layer and the second outer shell layer satisfy: the thickness of the second outer shell layer ≤ the thickness of the second inner shell layer; And / or, the thickness of the first inner shell layer is 0-2 μm; And / or, the thickness of the first outer shell layer is 0-2 μm; And / or, the thickness of the second inner shell layer is 0-2 μm; And / or, the thickness of the second outer shell layer is 0-2 μm; And / or, the thickness of the third inner shell layer is 0-2 μm.

14. The neodymium iron boron magnet as described in claim 13, characterized in that, The Tb diffusion weight gain in the first outer shell layer is 0.6 wt%; And / or, the Tb content in the first outer shell layer is 0.6 wt%; And / or, the Tb diffusion weight gain in the second outer shell layer is 0.6 wt% or 0.58 wt%; And / or, the Tb content in the second outer shell layer is 0.6 wt% or 0.58 wt%; And / or, the Dy diffusion weight gain in the first inner shell is 0.5wt%, 0.6wt%, or 0.7wt%; And / or, the content of Dy in the first inner shell is 0.5wt%, 0.6wt%, or 0.7wt%; And / or, the Dy diffusion weight gain in the second inner shell is 0.5 wt%, 0.6 wt%, 0.69 wt%, or 0.7 wt%; And / or, the content of Dy in the second inner shell is 0.5 wt%, 0.6 wt%, 0.69 wt%, or 0.7 wt%; And / or, the Dy diffusion weight gain in the third inner shell is 0.5wt%, 0.6wt%, or 0.7wt%; And / or, the content of Dy in the third inner shell is 0.5wt%, 0.6wt%, or 0.7wt%; And / or, the thickness of the first inner shell layer is 1.8 μm, 1.9 μm, or 2 μm; And / or, the thickness of the first outer shell layer is 1.7 μm, 1.8 μm, or 1.9 μm; And / or, the thickness of the second inner shell is 1.8 μm, 1.9 μm, or 2 μm; And / or, the thickness of the second outer shell layer is 1.8 μm, 1.7 μm, or 2 μm; And / or, the thickness of the third inner shell layer is 1.8 μm, 1.9 μm, or 2 μm.

15. The neodymium iron boron magnet as described in claim 12, characterized in that, The main phase grain shell of the non-demagnetizing region also includes a third outer shell layer.

16. The neodymium iron boron magnet as described in claim 15, characterized in that, The Tb diffusion weight gain in the third outer shell of the main phase grain shell in the non-demagnetizing region is 0-0.05 wt%. And / or, the Tb content in the third outer shell of the main phase grain shell in the non-demagnetizing region is 0wt%-1.6wt%; And / or, the Tb diffusion weight gain of the first outer shell layer, the second outer shell layer, and the third outer shell layer satisfies: first outer shell layer > second outer shell layer > third outer shell layer; And / or, the thicknesses of the first outer shell layer, the second outer shell layer, and the third outer shell layer satisfy the following condition: first outer shell layer > second outer shell layer > third outer shell layer; And / or, the thicknesses of the third inner shell and the third outer shell in the principal phase grain shell of the non-demagnetizing region satisfy the following: the thickness of the third inner shell is greater than that of the third outer shell. And / or, the thickness of the third outer shell layer of the main phase grain shell layer in the non-demagnetizing region is 0-0.5 μm.

17. A method for preparing a neodymium iron boron magnet as described in any one of claims 1-16, characterized in that, It includes the following steps: on the upper and lower surfaces of the neodymium iron boron substrate along the Z-axis, a diffusion source Dy is applied to the entire area of ​​the upper and lower surfaces, and a diffusion source Tb is applied to the four corner areas to carry out grain boundary diffusion parallel to the orientation direction, thereby obtaining the neodymium iron boron magnet; wherein, the four corner areas form easily demagnetized regions through grain boundary diffusion.

18. The method for preparing a neodymium iron boron magnet as described in claim 17, 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.

19. The method for preparing a neodymium iron boron magnet as described in claim 18, 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.

20. The method for preparing a neodymium iron boron magnet as described in claim 19, characterized in that, The aging treatment temperature is 500℃; And / or, the aging process takes 3 hours.

21. An application of a neodymium iron boron magnet as described in any one of claims 1-16 in magnetic steel.

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