Neodymium iron boron magnets, their preparation methods and applications

Abstract

This invention discloses a neodymium iron boron (NdFeB) magnet, its preparation method, and its applications. The NdFeB magnet comprises a non-demagnetizing region, a transition region, and a demagnetizing region; the Tb content ratio of the transition region to the demagnetizing region is (0.5-0.96):1; the Tb content ratio of the transition region to the non-demagnetizing region is 1:(0-0.93); the Dy content ratio of the transition region to the demagnetizing region is 1:1; and the Dy content ratio of the transition region to the non-demagnetizing region is 1:1. This NdFeB magnet exhibits excellent demagnetization resistance.

Description

Technical Field

[0001] This invention relates to a neodymium iron boron magnet, its preparation method, and its application. 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 magnets require higher coercivity and thermal stability. To improve the temperature resistance of rare earth permanent magnets, 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 has gradually become known and accepted. Conventional grain boundary diffusion technology uses a physical vapor deposition method to deposit a diffusion source onto the magnet surface, and 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.

[0004] In terms of the effective utilization rate of heavy rare earth elements, traditional grain boundary diffusion products have significantly improved compared to non-grain boundary diffusion products. However, in order to further improve the utilization rate of heavy rare earth elements and reduce unnecessary waste, and to make the diffusion area more accurate and quantifiable, another objective of this invention is to use neodymium iron boron magnets to identify easily demagnetized and non-easily demagnetized regions under the operating conditions of a main drive motor. We found that easily demagnetized regions are all located near the corners of the rotor air gap, while demagnetization is not obvious in the area near the rotor and the middle of the magnets. Therefore, for easily demagnetized regions, high-performance magnets with the same remanence and low-performance magnets with the same remanence are bonded together to prepare the required combined magnets, thereby saving the use of heavy rare earth elements in the non-easily demagnetized regions.

[0005] In practical applications of NdFeB magnets, the performance requirements for each part of the magnet are not the same. For example, in a motor, because the reverse magnetic field generated after the coil is energized is not uniform, NdFeB magnets exhibit easily demagnetized areas, difficult-to-demagnetize areas, and transitional areas between these two regions. Due to the characteristics of these different regions, the coercivity of each region needs to be matched to ensure sufficient coercivity in the easily demagnetized and transitional areas, while preventing attenuation of surface magnetism and magnetic flux in the difficult-to-demagnetize areas. Simultaneously, the transitional and difficult-to-demagnetize areas should have the highest remanence, thus achieving the best cost-performance ratio for high-grade magnets such as 48UH. Summary of the Invention

[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, which has excellent anti-demagnetization ability.

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

[0008] This invention provides a neodymium iron boron magnet, which establishes a three-dimensional rectangular coordinate system, wherein the orientation direction is the positive Z-axis, the X-axis is parallel to the upper surface, and the origin of the three-dimensional rectangular coordinate system is located inside the neodymium iron boron magnet.

[0009] The neodymium iron boron magnet includes a non-demagnetizing region, a transition region, and a demagnetizing region; the demagnetizing region is an outer annular region located on the neodymium iron boron magnet along the Z-axis direction, the non-demagnetizing region is a central region located on the neodymium iron boron magnet along the Z-axis direction, and the transition region is the boundary region located between the demagnetizing region and the non-demagnetizing region;

[0010] The Tb content ratio of the transition region to the easily demagnetized region is (0.5-0.96):1;

[0011] The Tb content ratio of the transition region to the non-demagnetizing region is 1:(0-0.93);

[0012] The ratio of Dy content in the transition region to that in the easily demagnetized region is 1:1;

[0013] The ratio of Dy content in the transition region to that in the non-demagnetizing region is 1:1.

[0014] In this invention, the heavy rare earth elements may originate from the substrate and / or the diffusion process, preferably from the diffusion process.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] In this invention, preferably, the Tb content ratio of the transition region to the easily demagnetized region is (0.5-0.9):1, for example, 0.79:1 or 0.8:1.

[0019] In this invention, preferably, the diffusion weight gain ratio of Tb in the transition region to the easily demagnetized region is (0.5-0.9):1, more preferably (0.5-0.8):1, for example 0.79:1 or 0.8:1.

[0020] In this invention, preferably, the Tb content ratio of the transition region to the non-demagnetizing region is 1:(0-0.2), for example, 1:0.02, 1:0.04 or 1:0.05.

[0021] In this invention, preferably, the diffusion weight gain ratio of Tb in the transition region to that in the non-demagnetizing region is 1:(0-0.2), for example, 1:0.02 or 1:0.04.

[0022] In this invention, preferably, the Tb content ratio of the easily demagnetized region to the non-easily demagnetized region is 1:(0-0.9), more preferably 1:(0-0.5), even more preferably 1:(0-0.2), for example 1:0.02, 1:0.03 or 1:0.04.

[0023] In this invention, preferably, the diffusion weight gain ratio of Tb in the easily demagnetized region to that in the non-easily demagnetized region is 1:(0-0.9), more preferably 1:(0-0.5), and even more preferably 1:(0-0.2), for example 1:0.02, 1:0.03, or 1:0.04.

[0024] In this invention, preferably, the diffusion weight gain ratio of Dy in the easily demagnetized region to that in the non-easily demagnetized region is 1:1.

[0025] In this invention, preferably, the diffusion weight gain of Tb in the easily demagnetized region is distributed in a gradient along the X-axis.

[0026] In this invention, preferably, the diffusion weight gain of Tb in the transition region is distributed in a gradient along the X-axis.

[0027] In this invention, preferably, the diffusion weight gain of Tb in the non-demagnetizing region is distributed in a gradient along the X-axis.

[0028] In this invention, preferably, the Tb content in the easily demagnetized region is 0.1wt%-2.5wt%, more preferably 0.25wt%-1wt%, and even more preferably 0.25wt%-0.6wt%, for example 0.55wt%, 0.58wt%, or 0.6wt%.

[0029] In this invention, preferably, the diffusion weight gain of Tb in the easily demagnetized region is 0.1wt%-2.5wt%, more preferably 0.25wt%-1wt%, and even more preferably 0.25wt%-0.6wt%, for example 0.55wt%, 0.58wt%, or 0.6wt%.

[0030] In this invention, preferably, the Tb content in the non-demagnetizing region is 0-1.6 wt%, more preferably 0-0.5 wt%, and even more preferably 0-0.05 wt%, for example, 0.01 wt%, 0.02 wt%, or 0.022 wt%.

[0031] In this invention, preferably, the diffusion weight gain of Tb in the non-demagnetizing region is 0-1.6 wt%, more preferably 0-0.5 wt%, and even more preferably 0-0.05 wt%, for example 0.01 wt%, 0.02 wt%, or 0.022 wt%.

[0032] In this invention, preferably, the Tb content in the transition region is 0.1wt%-2.4wt%, more preferably 0.125wt%-1wt%, for example 0.24wt%, 0.36wt%, 0.38wt%, 0.44wt%, 0.46wt%, or 0.48wt%.

[0033] In this invention, preferably, the diffusion weight gain of Tb in the transition region is 0.1wt%-2.4wt%, more preferably 0.125wt%-1wt%, for example 0.24wt%, 0.36wt%, 0.38wt%, 0.44wt%, 0.46wt%, or 0.48wt%.

[0034] In this invention, preferably, the Dy content of the easily demagnetized region is 0.1wt%-4wt%, for example, 2.2wt%.

[0035] In this invention, preferably, the diffusion weight gain of Dy in the easily demagnetized region is 0-0.8 wt%, more preferably 0.2 wt%-0.6 wt%.

[0036] In this invention, preferably, the content of Dy in the non-demagnetizing region is 0.1wt%-4wt%, for example, 2.2wt%.

[0037] In this invention, preferably, the diffusion weight gain of Dy in the non-demagnetizing region is 0-0.8 wt%, more preferably 0.2 wt%-0.6 wt%.

[0038] In this invention, preferably, the Dy content in the transition region is 0.1wt%-4wt%, for example, [missing information]. 0.45wt% or 2.2wt%.

[0039] In this invention, preferably, the diffusion weight gain of Dy in the transition region is 0-0.8 wt%, for example, 0.6 wt%.

[0040] In this invention, the coercivity ratio between the easily demagnetized region and the non-easily demagnetized region is preferably 1:(0.7-0.96), more preferably 1:(0.8-0.97), for example 1:0.875, 1:0.946 or 1:0.907.

[0041] In some specific embodiments, on any plane perpendicular to the orientation direction, the shape of the easily demagnetized region is a rectangular outer ring region.

[0042] In some specific embodiments, the neodymium iron boron magnet is a cuboid.

[0043] In some specific embodiments, the non-demagnetizing region is rectangular in shape on any plane perpendicular to the orientation direction.

[0044] In this invention, the ratio of the length to the thickness of the neodymium iron boron magnet is preferably (3-25):1, more preferably (3.64-24.27):1, even more preferably (8.74-24.27):1, for example 12.85:1; 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.

[0045] In this invention, preferably, the thickness of the neodymium iron boron magnet is ≥5mm.

[0046] In this invention, preferably, the width of the easily demagnetized area is 0-6mm and not 0, more preferably 3-5mm; the width means the length covered by the easily demagnetized area along the direction perpendicular to the origin.

[0047] In this invention, the volume of the easily demagnetized region accounts for a percentage of the volume of the neodymium iron boron magnet that is preferably 20%-80%, more preferably 29%-70%, for example 54.6% or 42.48%.

[0048] In this invention, the volume of the transition region accounts for a more preferably 5%-15% of the volume of the neodymium iron boron magnet, more preferably 10%-15%, and even more preferably 10.6%-13.65%.

[0049] In this invention, the volume of the non-demagnetizing region accounts for a more preferably 20%-80% of the volume of the neodymium iron boron magnet, more preferably 24.18%-70.66%, and even more preferably 34.27%-57.5%.

[0050] 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.

[0051] In some implementations, the M element is entirely derived from a NdFeB substrate.

[0052] In other embodiments, the M element comprises a diffusion-introduced M element, wherein the diffusion-introduced M element preferably accounts for 0%-0.4% of the mass percentage of the NdFeB magnet.

[0053] In some preferred embodiments of the present invention, 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-phase grains comprise a core and a shell; the Re is Dy and / or Tb. The Re₂Fe 14 The shell of the B-phase grain has the conventional meaning in this field, namely (Nd, Re)₂Fe. 14 B hard magnetic layer; the meaning of the Re-rich phase grain boundary is the conventional meaning in the art, that is, a two-particle grain boundary region with Re>95%.

[0054] Preferably, the Re2Fe14B main phase grains in the easily demagnetized region include, from the inside out, a core layer, a first shell layer, and a second shell layer, wherein the first shell layer is a (Nd, Tb)2Fe14B hard magnetic layer, and the second shell layer is a (Nd, Dy)2Fe14B hard magnetic layer.

[0055] In this invention, the non-demagnetizing region, transition region, and demagnetizing region are preferably obtained by simulation cloud maps under operating conditions.

[0056] The present invention also provides a method for preparing the above-mentioned neodymium iron boron magnet, which includes the following steps: applying a first diffusion source on four non-oriented surfaces of a neodymium iron boron substrate, applying a second diffusion source on at least one oriented surface of the neodymium iron boron substrate, and performing grain boundary diffusion treatment on the neodymium iron boron substrate to which the diffusion sources are applied.

[0057] The orientation surface is the surface of the NdFeB substrate perpendicular to the orientation direction, and the non-orientation surface is the surface of the NdFeB substrate parallel to the orientation direction.

[0058] The first diffusion source contains Tb, and the second diffusion source contains Dy.

[0059] The preparation method of the present invention can apply a diffusion source to the oriented and non-oriented surfaces according to the operating conditions of some types of motors and the distribution of easily demagnetized areas, which enables the neodymium iron boron magnet to have excellent anti-demagnetization ability during use.

[0060] 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.

[0061] In some preferred embodiments of the invention, the second diffusion source is applied to two orientation surfaces of the NdFeB substrate.

[0062] In some preferred embodiments of the present invention, the first diffusion source does not contain Dy.

[0063] In some preferred embodiments of the present invention, the second diffusion source does not contain Tb.

[0064] In some specific embodiments of the present invention, the first diffusion source is elemental Tb.

[0065] In other embodiments of the present invention, the first diffusion source is a Tb-M alloy, wherein M comprises one or more of Cu, Al, Co, Ga, Zr, and Ti. Preferably, the mass percentage of M in the Tb-M alloy is 0-40%, and not 0.

[0066] In other embodiments of the present invention, the first diffusion source is a hydride of Tb or a fluoride of Tb.

[0067] In some specific embodiments of the present invention, the second diffusion source is elemental Dy.

[0068] In other embodiments of the present invention, the second diffusion source is a Dy-M alloy, wherein M comprises one or more of Cu, Al, Co, Ga, Zr, and Ti. Preferably, the mass percentage of M in the Dy-M alloy is 0-40%, and not 0.

[0069] In other embodiments of the present invention, the second diffusion source is a hydride of Dy or a fluoride of Dy.

[0070] In this invention, preferably, the mass percentage of Tb in the first diffusion source is 0.25%-0.75%, more preferably 0.3%-0.75%.

[0071] In this invention, preferably, the mass percentage of Dy in the second diffusion source is 0.25%-0.75%.

[0072] In this invention, the application can be performed using methods conventional in the art, such as coating.

[0073] In this invention, those skilled in the art generally understand 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, this invention does not limit the coating thickness, as long as the corresponding diffusion weight gain is achieved.

[0074] The coating method is preferably spraying or printing.

[0075] The dewaxing temperature of the spray coating is preferably 200-400℃.

[0076] The dewaxing temperature for the printing process is preferably 100-500℃.

[0077] In certain embodiments of the present invention, when the first diffusion source and the second diffusion source are applied by means of coating, the first diffusion source and the second diffusion source further include a solvent and a binder.

[0078] The solvent may be conventional in the art, such as water, alcohol, ketone or ester.

[0079] In this invention, preferably, the temperature of the grain boundary diffusion is 750-950°C, for example, 900°C.

[0080] In this invention, preferably, the grain boundary diffusion time is 5-30 hours, for example, 10 hours.

[0081] In this invention, preferably, an aging treatment is further included after the grain boundary diffusion.

[0082] The aging treatment temperature is preferably 300-600℃, for example, 500℃.

[0083] The time for the time-sensitive processing is preferably 1-10 hours, for example, 3 hours.

[0084] The present invention also provides a neodymium iron boron magnet prepared by the above-described method for preparing neodymium iron boron magnets.

[0085] The present invention also provides an application of the above-mentioned neodymium iron boron magnet in magnetic steel.

[0086] 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.

[0087] The reagents and raw materials used in this invention are all commercially available.

[0088] The positive and progressive effects of this invention are as follows:

[0089] The neodymium iron boron (NdFeB) magnet described in this invention includes a transition region. By controlling the Tb and Dy content introduced by diffusion in the transition region, the easily demagnetized region, and the non-easily demagnetized region, as well as the diffusion direction, the interdiffusion of Tb or Dy across regions caused by the Tb concentration gradient difference in the transition region can be reduced. This reduces the gradient decrease in the performance of the boundary region, resulting in a weakened anti-demagnetization effect. While maintaining the remanence of the NdFeB magnet, the attenuation of the surface magnetism and magnetic flux of the NdFeB magnet is reduced, thus improving the anti-demagnetization capability of the NdFeB magnet. Furthermore, this invention sets the easily demagnetized region, the non-easily demagnetized region, and the transition region to be rectangular, which improves the anti-demagnetization capability of the four long sides of the NdFeB magnet. Attached Figure Description

[0090] Figure 1 This is a schematic diagram of the structure of the neodymium iron boron magnet in Example 1.

[0091] Figure 2 This is a schematic diagram of the microstructure of the easily demagnetized region in Example 1.

[0092] The attached figures are labeled as follows:

[0093] 1-Non-demagnetizing region; 2-Transition region; 3-Demagnetizing region; 301-Core layer; 302-First shell layer; 303-Second shell layer. Detailed Implementation

[0094] 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.

[0095] Examples 1-3

[0096] The neodymium iron boron magnets provided in Examples 1-3 are cuboids, specifically as follows: Figure 1 As shown, a three-dimensional rectangular coordinate system is established, wherein the orientation direction is the positive Z-axis, the X-axis is parallel to one side of the upper surface, and the origin of the three-dimensional rectangular coordinate system is located inside the neodymium iron boron magnet.

[0097] The neodymium iron boron magnet includes a non-demagnetizing region 1, a transition region 2, and a demagnetizing region 3; the demagnetizing region is an outer annular region located on the neodymium iron boron magnet along the Z-axis direction, and the non-demagnetizing region is a central region located on the neodymium iron boron magnet along the Z-axis direction; the transition region is the boundary region located between the demagnetizing region and the non-demagnetizing region.

[0098] Among them, Re2Fe in the easily demagnetized region 14 The structure of the B main phase grains is as follows: Figure 2It consists of a core layer 301, a first shell layer 302, and a second shell layer 303, from the inside out. The first shell layer is (Nd, Tb)2Fe. 14 B is a hard magnetic layer, and the second shell is (Nd, Dy)2Fe. 14 B hard magnetic layer;

[0099] The diffusion weight gain of each region is listed in Table 1. The Tb content in the substrate is 0, so the Tb content of Examples 1-3 is equal to its diffusion weight gain. The Dy content of each region is listed in Table 1 (continued). The volume percentage of each region is listed in Table 2.

[0100] Table 1

[0101]

[0102]

[0103] Continued from Table 1

[0104]

[0105] Table 2

[0106]

[0107] Table 3

[0108]

[0109] The preparation methods of Examples 1-3 are as follows: a first diffusion source is applied to four non-oriented surfaces of a NdFeB substrate, and a second diffusion source is applied to two oriented surfaces of the NdFeB substrate. The NdFeB substrate with the applied diffusion sources is subjected to grain boundary diffusion treatment. The oriented surfaces are the surfaces of the NdFeB substrate perpendicular to the orientation direction, and the non-oriented surfaces are the surfaces of the NdFeB substrate parallel to the orientation direction. The first diffusion source contains elemental Tb but not Dy, and the second diffusion source contains elemental Dy but not Tb. The elemental mass content of the NdFeB substrates used in Examples 1-3 is listed in Table 3.

[0110] The temperature for grain boundary diffusion is 900°C; the time for grain boundary diffusion is 10 hours; after grain boundary diffusion, an aging treatment is further included; wherein the temperature for the aging treatment is 500°C; wherein the time for the aging treatment is 3 hours; the application method is, for example, coating; wherein the coating method is spraying, and the dewaxing temperature for spraying is 200°C.

[0111] Example 1

[0112] The neodymium iron boron magnets of Examples 1-3 were subjected to the following tests:

[0113] 1. Coercivity test: Samples from Examples 1-3 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.

[0114] 2. Demagnetization Rate Test: Using electromagnetic simulation software, Ansys Workbench, with an input speed of 13000 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.

[0115] 3. 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 phases to characterize the distribution of elements such as Dy / Nd.

[0116] The technical effects of Examples 1-3 are listed in Table 4 below:

[0117] Table 4

[0118]

[0119] As shown in Table 4 above, the coercivity ratio between the easily demagnetized region and the transition region of the NdFeB magnets prepared in Examples 1-3 is between 1:(0.93-0.98), and the coercivity difference between the easily demagnetized region and the non-easily demagnetized region is between 0-3.5kOe, indicating excellent anti-demagnetization ability. The demagnetization rate of the NdFeB magnets in Examples 1-3 at 160℃ is only 0.9%-2.5%.

[0120] 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, A three-dimensional rectangular coordinate system is established, wherein the orientation direction is the positive Z-axis, the X-axis is parallel to the upper surface, and the origin of the three-dimensional rectangular coordinate system is located inside the neodymium iron boron magnet. The neodymium iron boron magnet includes a non-demagnetizing region, a transition region, and a demagnetizing region; the demagnetizing region is an outer annular region located on the neodymium iron boron magnet along the Z-axis direction, the non-demagnetizing region is a central region located on the neodymium iron boron magnet along the Z-axis direction, and the transition region is the boundary region located between the demagnetizing region and the non-demagnetizing region; The Tb content ratio of the transition region to the easily demagnetized region is (0.79-0.96):1; The Tb content ratio of the transition region to the non-demagnetizing region is 1:(0-0.93). The ratio of Dy content in the transition region to that in the easily demagnetized region is 1:1; The ratio of Dy content in the transition region to that in the non-demagnetizing region is 1:1; The diffusion weight gain ratio of Tb in the transition region to that in the easily demagnetized region is (0.79-0.9):1; The diffusion weight gain ratio of Dy in the easily demagnetized region to that in the non-easily demagnetized region is 1:1; The volume of the transition region accounts for 5%-15% of the volume of the neodymium iron boron magnet.

2. The neodymium iron boron magnet as described in claim 1, characterized in that, The Tb content ratio of the transition region to the easily demagnetized region is (0.79-0.9):1; And / or, the diffusion weight gain ratio of Tb in the transition region to that in the easily demagnetized region is 0.79:1 or 0.8:1; And / or, the Tb content ratio of the transition region to the non-demagnetizing region is 1:(0-0.2). And / or, the diffusion weight gain ratio of Tb in the transition region to that in the non-demagnetizing region is 1:(0-0.2). And / or, the Tb content ratio of the easily demagnetized region to the non-easily demagnetized region is 1:(0-0.9). And / or, the diffusion weight gain ratio of Tb in the easily demagnetized region to that in the non-easily demagnetized region is 1:(0-0.9). And / or, the diffusion weight gain of Tb in the easily demagnetized region is distributed in a gradient along the X-axis; And / or, the diffusion weight gain of Tb in the transition region is distributed in a gradient along the X-axis; And / or, the diffusion weight gain of Tb in the non-demagnetizing region is gradient-distributed along the X-axis.

3. The neodymium iron boron magnet as described in claim 2, characterized in that, The Tb content ratio of the transition region to the easily demagnetized region is 0.79:1 or 0.8:1; And / or, the Tb content ratio of the transition region to the non-demagnetizing region is 1:0.02, 1:0.04, or 1:0.05; And / or, the diffusion weight gain ratio of Tb in the transition region to that in the non-demagnetizing region is 1:0.02 or 1:0.04; And / or, the Tb content ratio of the easily demagnetized region to the non-easily demagnetized region is 1:(0-0.5). And / or, the diffusion weight gain ratio of Tb in the easily demagnetized region to that in the non-easily demagnetized region is 1:(0-0.5).

4. The neodymium iron boron magnet as described in claim 3, characterized in that, The Tb content ratio of the easily demagnetized region to the non-easily demagnetized region is 1:(0-0.2). And / or, the diffusion weight gain ratio of Tb in the easily demagnetized region to that in the non-easily demagnetized region is 1:(0-0.2).

5. The neodymium iron boron magnet as described in claim 4, characterized in that, The Tb content ratio of the easily demagnetized region to the non-easily demagnetized region is 1:0.02, 1:0.03, or 1:0.04; And / or, the diffusion weight gain ratio of Tb in the easily demagnetized region to that in the non-easily demagnetized region is 1:0.02, 1:0.03, or 1:0.

04.

6. The neodymium iron boron magnet as described in claim 1, characterized in that, The Tb content in the easily demagnetized region is 0.1wt%-2.5wt%; And / or, the diffusion weight gain of Tb in the easily demagnetized region is 0.1wt%-2.5wt%; 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 non-demagnetizing region is 0-1.6 wt%; And / or, the Tb content in the transition region is 0.1wt%-2.4wt%; And / or, the diffusion weight gain of Tb in the transition region is 0.1wt%-2.4wt%; And / or, the Dy content in the easily demagnetized region is 0.1wt%-4wt%; And / or, the diffusion weight gain of Dy in the easily demagnetized region is 0-0.8 wt%; And / or, the Dy content in the non-demagnetizing region is 0.1wt%-4wt%; And / or, the diffusion weight gain of Dy in the non-demagnetizing region is 0-0.8 wt%; And / or, the Dy content in the transition region is 0.1wt%-4wt%; And / or, the diffusion weight gain of Dy in the transition region is 0-0.8 wt%.

7. The neodymium iron boron magnet as described in claim 6, characterized in that, The Tb content in the easily demagnetized region is 0.25wt%-1wt%; And / or, the diffusion weight gain of Tb in the easily demagnetized region is 0.25wt%-1wt%; And / or, the Tb content in the non-demagnetizing region is 0-0.5 wt%; And / or, the diffusion weight gain of Tb in the non-demagnetizing region is 0-0.5 wt%; And / or, the Tb content in the transition region is 0.125wt%-1wt%; And / or, the diffusion weight gain of Tb in the transition region is 0.125wt%-1wt%; And / or, the Dy content of the easily demagnetized region is 2.2 wt%; And / or, the diffusion weight gain of Dy in the easily demagnetized region is 0.2wt%-0.6wt%; And / or, the Dy content of the non-demagnetizing region is 2.2 wt%; And / or, the diffusion weight gain of Dy in the non-demagnetizing region is 0.2wt%-0.6wt%; And / or, the Dy content in the transition region is 0.45 wt% or 2.2 wt%; And / or, the diffusion weight gain of Dy in the transition region is 0.6 wt%.

8. The neodymium iron boron magnet as described in claim 7, characterized in that, The Tb content in the easily demagnetized region is 0.25wt%-0.6wt%; And / or, the diffusion weight gain of Tb in the easily demagnetized region is 0.25wt%-0.6wt%; And / or, the Tb content in the non-demagnetizing region is 0-0.05 wt%; And / or, the diffusion weight gain of Tb in the non-demagnetizing region is 0-0.05 wt%; And / or, the Tb content in the transition region is 0.24wt%, 0.36wt%, 0.38wt%, 0.44wt%, 0.46wt%, or 0.48wt%; And / or, the diffusion weight gain of Tb in the transition region is 0.24wt%, 0.36wt%, 0.38wt%, 0.44wt%, 0.46wt%, or 0.48wt%.

9. The neodymium iron boron magnet as described in claim 8, characterized in that, The Tb content in the easily demagnetized region is 0.55wt%, 0.58wt%, or 0.6wt%. And / or, the diffusion weight gain of Tb in the easily demagnetized region is 0.55wt%, 0.58wt%, or 0.6wt%; And / or, the Tb content in the non-demagnetizing region is 0.01wt%, 0.02wt%, or 0.022wt%; And / or, the diffusion weight gain of Tb in the non-demagnetizing region is 0.01wt%, 0.02wt%, or 0.022wt%.

10. The neodymium iron boron magnet as described in claim 1, characterized in that, The coercivity ratio between the easily demagnetized region and the non-easily demagnetized region is 1:(0.7-0.96). And / or, on any plane perpendicular to the orientation direction, the shape of the easily demagnetized region is a rectangular outer ring region; And / or, the neodymium iron boron magnet is a cuboid; And / or, on any plane perpendicular to the orientation direction, the non-demagnetizing region is rectangular in shape; And / or, the ratio of the length to the thickness of the neodymium iron boron magnet is (3-25):1; 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. And / or, the thickness of the neodymium iron boron magnet is ≥5mm.

11. The neodymium iron boron magnet as described in claim 10, characterized in that, The coercivity ratio of the easily demagnetized region to the non-easily demagnetized region is 1:(0.8-0.97). And / or, the length-to-thickness ratio of the neodymium iron boron magnet is (3.64-24.27):

1.

12. The neodymium iron boron magnet as described in claim 11, characterized in that, The coercivity ratio between the easily demagnetized region and the non-easily demagnetized region is 1:0.875, 1:0.946, or 1:0.907; And / or, the length-to-thickness ratio of the neodymium iron boron magnet is (8.74-24.27):

1.

13. The neodymium iron boron magnet as described in claim 12, characterized in that, The length-to-thickness ratio of the neodymium iron boron magnet is 12.85:

1.

14. The neodymium iron boron magnet as described in claim 1, characterized in that, The width of the easily demagnetized zone is 0-6mm and not 0; the width means the length covered by the easily demagnetized zone along the direction perpendicular to the origin. And / or, the volume of the easily demagnetized region accounts for 20%-80% of the volume of the NdFeB magnet; And / or, the volume of the transition region accounts for 10%-15% of the volume of the NdFeB magnet; And / or, the volume of the non-demagnetizing region accounts for 20%-80% of the volume of the NdFeB magnet.

15. The neodymium iron boron magnet as described in claim 14, characterized in that, The width of the easily demagnetized area is 3-5mm; And / or, the volume of the easily demagnetized region accounts for 29%-70% of the volume of the NdFeB magnet; And / or, the volume of the transition region accounts for 10.6%-13.65% of the volume of the NdFeB magnet; And / or, the volume of the non-demagnetizing region accounts for 24.18%-70.66% of the volume of the NdFeB magnet.

16. The neodymium iron boron magnet as described in claim 15, characterized in that, The volume of the easily demagnetized region accounts for 54.6% or 42.48% of the volume of the neodymium iron boron magnet; And / or, the volume of the non-demagnetizing region accounts for 34.27%-57.5% of the volume of the NdFeB magnet.

17. The neodymium iron boron magnet as claimed 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 principal phase grains comprise a core layer and a shell layer; the Re is Dy and / or Tb.

18. The neodymium iron boron magnet as described in claim 17, characterized in that, The Re2Fe in the easily demagnetized region 14 The B-phase grains, from the inside out, consist of a core layer, a first shell layer, and a second shell layer. The first shell layer is (Nd, Tb)₂Fe. 14 B is a hard magnetic layer, and the second shell is (Nd,Dy)2Fe. 14 B. Hard magnetic layer.

19. A method for preparing a neodymium iron boron magnet as described in any one of claims 1-18, characterized in that, It includes the following steps: A first diffusion source is applied to four non-oriented surfaces of a NdFeB substrate, and a second diffusion source is applied to at least one oriented surface of the NdFeB substrate. The NdFeB substrate with the applied diffusion sources is subjected to grain boundary diffusion treatment. The orientation surface is the surface of the NdFeB substrate perpendicular to the orientation direction, and the non-orientation surface is the surface of the NdFeB substrate parallel to the orientation direction. The first diffusion source contains Tb, and the second diffusion source contains Dy.

20. The method for preparing a neodymium iron boron magnet as described in claim 19, characterized in that, The second diffusion source is applied to two orientation surfaces of the NdFeB substrate; And / or, the first diffusion source does not contain Dy; And / or, the second diffusion source does not contain Tb; And / or, the first diffusion source is elemental Tb; And / or, the first diffusion source is a Tb-M alloy, where M comprises one or more of Cu, Al, Co, Ga, Zr, and Ti; And / or, the first diffusion source is a hydride of Tb or a fluoride of Tb; And / or, the second diffusion source is elemental Dy; And / or, the second diffusion source is a Dy-M alloy, where M comprises one or more of Cu, Al, Co, Ga, Zr, and Ti; And / or, the second diffusion source is a hydride of Dy or a fluoride of Dy; And / or, the mass percentage of Tb in the first diffusion source is 0.25%-0.75%; And / or, the mass percentage of Dy in the second diffusion source is 0.25%-0.75%; And / or, the temperature of the grain boundary diffusion is 750-950°C; And / or, the time for grain boundary diffusion is 5-30 hours; And / or, after the grain boundary diffusion, an aging treatment is also included; And / or, the method of application is coating.

21. The method for preparing a neodymium iron boron magnet as described in claim 20, characterized in that, The first diffusion source is a Tb-M alloy, wherein the mass percentage of M in the Tb-M is 0-40%, and not 0; And / or, the second diffusion source is a Dy-M alloy, wherein the mass percentage of M in the Dy-M is 0-40%, and not 0; And / or, the mass percentage of Tb in the first diffusion source is 0.3%-0.75%; And / or, the temperature at which the grain boundary diffuses is 900°C; And / or, the grain boundary diffusion time is 10 hours; And / or, the aging treatment temperature is 300-600℃; And / or, the time for the aging process is 1-10 hours; And / or, the coating method is spraying or printing; And / or, the first diffusion source and the second diffusion source further include solvents and binders.

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 time for the aging process is 3 hours.

23. The method for preparing a neodymium iron boron magnet as described in claim 21, characterized in that, The dewaxing temperature for the spraying is 200-400℃; And / or, the dewaxing temperature of the printing is 100-500℃.

24. The method for preparing a neodymium iron boron magnet as described in claim 21, characterized in that, The solvent is water, alcohol, ketone or ester.

25. A neodymium iron boron magnet prepared by any one of the methods described in claims 19-24.

26. An application of a neodymium iron boron magnet as described in any one of claims 1-18 and 25 in magnetic steel.

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