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 (0.7-1):1; the Tb content ratio of the transition region to the non-demagnetizing region is 1:(0-0.9); the Dy content ratio of the transition region to the demagnetizing region is (0-1):(0-0.9); and the Dy content ratio of the transition region to the non-demagnetizing region is (0-0.98):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 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] 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.

[0006] The present invention mainly solves the above-mentioned technical problems through the following technical solutions.

[0007] 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.

[0008] 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;

[0009] The Tb content ratio of the transition region to the easily demagnetized region is (0.7-1):1;

[0010] The Tb content ratio between the transition region and the non-demagnetizing region is 1:(0-0.9);

[0011] The ratio of Dy content in the transition region to that in the easily demagnetized region is (0-1):(0-0.9);

[0012] The ratio of Dy content in the transition region to that in the non-demagnetizing region is (0-0.98):1.

[0013] In this invention, the heavy rare earth elements may originate from the substrate and / or the diffusion process, preferably from the diffusion process. The percentage of the mass of heavy rare earth elements introduced into a region by the diffusion process relative to the total mass of the magnet in that region is called the diffusion weight gain of the heavy rare earth elements.

[0014] 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.

[0015] 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.

[0016] In this invention, preferably, the Tb content ratio of the transition region to the easily demagnetized region is 0.71:1, 0.8:1, or 0.83:1.

[0017] In this invention, preferably, the diffusion weight gain ratio of Tb in the transition region to the easily demagnetized region is (0.7-1):1, more preferably 0.71:1, 0.8:1 or 0.83:1.

[0018] In this invention, preferably, the Tb content ratio of the transition region to the non-demagnetizing region is 1:(0-0.2), more preferably 1:(0-0.05), for example 1:0.02 or 1:0.05.

[0019] 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), more preferably 1:(0-0.05), for example 1:0.02 or 1:0.05.

[0020] In this invention, preferably, the ratio of Dy content in the transition region to that in the easily demagnetized region is (0.05-0.9):(0-0.05), more preferably 1:(0-0.9), and even more preferably 1:(0-0.8), for example 8:1, 37:5 or 23:5.

[0021] In this invention, preferably, the diffusion weight gain ratio of Dy in the transition region to that in the easily demagnetized region is (0.05-0.9):(0-0.05), more preferably 1:(0-0.9), even more preferably 1:(0-0.8), for example 8:1, 37:5 or 23:5.

[0022] In this invention, preferably, the ratio of Dy content in the transition region to that in the non-demagnetizing region is (0.05-0.9):1, more preferably 0.57:1, 0.58:1 or 0.67:1.

[0023] In this invention, preferably, the diffusion weight gain ratio of Dy in the transition region to that in the non-demagnetizing region is (0.05-0.9):1, more preferably 0.57:1, 0.58:1 or 0.67:1.

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

[0025] In this invention, preferably, the diffusion weight gain ratio of Tb in the non-demagnetizing region and the demagnetizing region is (0-0.05):1, more preferably (0-0.03):1, for example 0.01:1 or 0.02:1.

[0026] In this invention, preferably, the content ratio of Dy in the easily demagnetized region and the non-easily demagnetized region is (0-0.05):(0.3-1), and is not 0, more preferably (0-0.03):(0.3-0.7), and is not 0, for example, 0.07:1, 0.09:1 or 0.13:1.

[0027] In this invention, preferably, the diffusion weight gain ratio of Dy in the easily demagnetized region and the non-easily demagnetized region is (0-0.05):(0.3-1), and is not 0, more preferably (0-0.03):(0.3-0.7), and is not 0, for example, 0.07:1, 0.09:1 or 0.13:1.

[0028] In this invention, preferably, the Tb content in the easily demagnetized region is 0.1wt%-2.5wt%, for example, 0.4wt%, 0.55wt%, or 0.7wt%.

[0029] In this invention, preferably, the Tb content in the non-demagnetizing region is 0-1.6 wt%, for example, 0.015 wt% or 0.01 wt%.

[0030] In this invention, preferably, the Tb content in the transition region is 0.1wt%-2.5wt%, for example, 0.33wt%, 0.4wt%, or 0.5wt%.

[0031] In this invention, preferably, the Dy content of the easily demagnetized region is 0-3.1 wt%, for example, 0.05 wt%.

[0032] In this invention, preferably, the content of Dy in the non-demagnetizing region is 0.1wt%-4wt%, more preferably 0.4wt%-0.7wt%, for example 0.5wt% or 0.55wt%.

[0033] In this invention, preferably, the content of Dy in the transition region is 0.05wt%-3.9wt%, more preferably 0.05wt%-0.4wt%, for example 0.23wt% or 0.37wt%.

[0034] 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%.

[0035] In this invention, preferably, the diffusion weight gain of Tb at any two points in the non-demagnetizing region is equal.

[0036] In this invention, preferably, the diffusion weight gain of Dy at any two points in the non-demagnetizing region is equal.

[0037] In this invention, preferably, the Tb content at any two points in the easily demagnetized region is equal.

[0038] In this invention, preferably, the Dy content is equal at any two points in the non-demagnetizing region.

[0039] 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%-14%, and even more preferably 10.6%-13.65%.

[0040] In this invention, the volume of the non-demagnetizing region accounts for a more preferably 20%-75% of the volume of the neodymium iron boron magnet, more preferably 24.18%-70.66%, and even more preferably 34.27%-57.5%.

[0041] 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:(0.8-0.9), and for example 1:0.85.

[0042] 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.

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

[0044] In some specific embodiments, the neodymium iron boron magnet is a cuboid.

[0045] 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.

[0046] In this invention, preferably, the width of the easily demagnetized area is 0-5mm and not 0, more preferably 2-4mm; the width means the length covered by the easily demagnetized area along the direction perpendicular to the origin and the surrounding area.

[0047] In this invention, there is an interface A between the transition region and the corresponding demagnetizing region, and the interface A is annular.

[0048] The content of Tb at interface A is preferably 0.1wt%-2.5wt%, for example 0.35wt%, 0.4wt%, 0.5wt% or 0.55wt%.

[0049] The diffusion weight gain of Tb at interface A is preferably 0.1wt%-2.5wt%, for example, 0.35wt%, 0.4wt%, 0.5wt%, or 0.55wt%.

[0050] The preferred ratio of the content of Tb at the interface A to that in the easily demagnetized region is (0.9-1):1.

[0051] The diffusion weight gain ratio of the interface A to the Tb of the easily demagnetized region is preferably (0.9-1):1.

[0052] The content of Dy at interface A is preferably 0.01wt%-3.5wt%, for example, 0.05wt%.

[0053] The diffusion weight gain of Dy at interface A is preferably 0.01wt%-3.5wt%, for example, 0.05wt%.

[0054] The content of the interface A and the Dy in the easily demagnetized region is preferably (0.02-0.2):(0-0.05), more preferably 1:(0.8-1), for example 1:1.

[0055] The diffusion weight gain ratio of the interface A to the easily demagnetized region Dy is preferably (0.02-0.2):(0-0.05), more preferably 1:(0.8-1), for example 1:1.

[0056] In this invention, there is an interface B between the transition region and the corresponding non-demagnetizing region, and the interface B is annular.

[0057] The content of Tb at the interface B is preferably 0.05wt%-2.4wt%, for example, 0.22wt% or 0.23wt%.

[0058] The diffusion weight gain of Tb at the interface B is preferably 0.05wt%-2.4wt%, for example, 0.22wt% or 0.23wt%.

[0059] The ratio of the content of Tb at the interface B to that in the non-demagnetizing region is preferably 1:(0-0.94), more preferably 1:(0-0.05), for example 1:0.04 or 1:0.045.

[0060] The ratio of the content of Tb at the interface B to that in the non-demagnetizing region is preferably 1:(0-0.94), more preferably 1:(0-0.2), and even more preferably 1:(0-0.05), for example 1:0.04 or 1:0.045.

[0061] The diffusion weight gain ratio of the interface B to the Tb in the non-demagnetizing region is preferably 1:(0-0.94), more preferably 1:(0-0.2), and even more preferably 1:(0-0.05), for example 1:0.04 or 1:0.045.

[0062] The content of Dy at interface B is preferably 0.08wt%-4wt%, for example, 0.37wt% or 0.23wt%.

[0063] The diffusion weight gain of Dy at interface B is 0.05wt%-1wt%, for example, 0.37wt%.

[0064] The content of the interface B and the Dy in the non-demagnetizing region is preferably (0.5-1):1, for example, 0.57:1, 0.67:1 or 0.58:1.

[0065] The diffusion weight gain ratio of the interface B to the non-demagnetizing region Dy is preferably (0.1-0.7):1, for example, 0.13:1, 0.14:1, 0.22:1 or 0.4:1.

[0066] 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.

[0067] In some implementations, the M element is entirely derived from a NdFeB substrate.

[0068] In other embodiments, the M element comprises diffusion-introduced M element, wherein the diffusion-introduced M element accounts for a preferred mass percentage of 0%-0.4% of the NdFeB magnet.

[0069] 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%.

[0070] In certain specific embodiments of the present invention, the Re2Fe in the easily demagnetized region 14 The shell of the B-phase main grains includes (Nd, Tb)₂Fe. 14 B. Hard magnetic layer.

[0071] In certain specific embodiments of the present invention, the Re2Fe in the non-demagnetizing region 14The shell of the B-phase main grains includes (Nd, Dy)2Fe. 14 B. Hard magnetic layer.

[0072] In certain specific embodiments of the present invention, Re2Fe at any two locations in the easily demagnetized region 14 The difference in grain size between the B main phase grains does not exceed 1-8 μm.

[0073] In certain specific embodiments of the present invention, Re2Fe at any two points in the transition region 14 The difference in grain size between the B main phase grains does not exceed 1-8 μm.

[0074] In some specific embodiments of the present invention, the surface Re2Fe of the easily demagnetized region, the transition region, and the non-easily demagnetized region is... 14 The B main phase grains have equal grain size, and the surface layer refers to the surface perpendicular to the orientation direction.

[0075] In some specific embodiments of the present invention, the Re2Fe in the easily demagnetized region, the transition region, and the non-easily demagnetized region are described. 14 The B-phase grains are all of equal size, and the center refers to the mid-plane along the orientation direction.

[0076] In this invention, the grain size refers to the average grain size of all grains in a certain region. For example, the grain size of the main phase grain in the easily demagnetized region means the average grain size of all grains in the easily demagnetized region.

[0077] In certain preferred embodiments of the present invention, the Re2Fe in the easily demagnetized region, the transition region, and the non-easily demagnetized region 14 The core layer of the B main phase grains and the Re2Fe 14 The shell of the B main phase grain satisfies the following conditions: the R1 content in the core layer is greater than or equal to the R1 content in the shell layer; the R2 content in the core layer is less than the R2 content in the shell layer; wherein, R1 includes one or more of Pr, Nd, Ce, Er, Tm, Y, Lu, Gd and Ho; and R2 is Dy and / or Tb.

[0078] In certain specific embodiments of the present invention, in the easily demagnetized region, on the surface equidistant from the interface between the transition region and the easily demagnetized region, the Re2Fe 14 The shell thickness of the B-phase grains is equal. Here, "equal distance" means that the perpendicular distance from any point in the easily demagnetized region to the interface is equal, and "equal thickness" means that the Re2Fe at any two points on the surface is equal. 14 The difference in shell thickness between the B main phase grains is less than 0.1 μm.

[0079] In certain specific embodiments of the present invention, in the easily demagnetized region, on the surface equidistant from the interface between the transition region and the easily demagnetized region, the Re-rich phase grain boundaries have equal thicknesses. Here, "equidistant" means that the perpendicular distance from any point in the easily demagnetized region to the interface is equal, and "equidistant thickness" means that the Re2Fe content at any two points on the surface is equal. 14 The difference in shell thickness between the B main phase grains is less than 0.1 μm.

[0080] In certain specific embodiments of the present invention, in the transition region, on the surface equidistant from the interface between the transition region and the easily demagnetized region, the Re2Fe 14 The shell thickness of the B-phase grains is equal. Here, "equal distance" means that the perpendicular distance from any point in the transition region to the interface is equal, and "equal thickness" means that the Re2Fe at any two points on the surface is equal. 14 The difference in shell thickness between the B main phase grains is less than 0.1 μm.

[0081] In certain specific embodiments of the present invention, in the transition region, on the surface equidistant from the interface between the transition region and the easily demagnetized region, the thickness of the Re-rich phase grain boundary is equal. Here, "equidistant" means that the perpendicular distance from any point in the transition region to the interface is equal, and "equidistant thickness" means that the Re2Fe at any two points on the surface is equal. 14 The difference in shell thickness between the B main phase grains is less than 0.1 μm.

[0082] In a specific embodiment of the present invention, the Re2Fe in the easily demagnetized region, the transition region, and the non-easily demagnetized region are described. 14 The grain size ratio of the B main phase is 1:1:1.

[0083] Preferably, in the easily demagnetized region, the transition region, and the non-easily demagnetized region, the surface Re2Fe... 14 The grain size of the B main phase is the central Re2Fe. 14 The grain size of the B main phase is 1 to 1.5 times that of the main phase grains.

[0084] Preferably, the surface Re2Fe of the easily demagnetized region, the transition region, and the non-easily demagnetized region... 14 The grain size of the B main phase is 1-12 μm.

[0085] Wherein, when R2 is Tb, the content of R2 in the easily demagnetized region, the transition region and the non-easily demagnetized region satisfies the following condition: easily demagnetized region ≥ transition region > non-easily demagnetized region.

[0086] Wherein, when R2 is Dy, the content of R2 in the easily demagnetized region, the transition region and the non-easily demagnetized region satisfies the following condition: non-easily demagnetized region ≥ transition region > easily demagnetized region.

[0087] Preferably, the Re-rich grain boundaries and Re2Fe in the easily demagnetized region are... 14 The shell thickness ratio of the B main phase grains is (0-1):(0.5-1.5), and is not 0.

[0088] The thickness of the shell layer of the main phase grains in the easily demagnetized region is preferably 0-4 μm, more preferably 0-2 μm, and even more preferably 0.5-1.5 μm.

[0089] Preferably, the thickness of the Re-rich phase grain boundary in the easily demagnetized region is 0-1 μm and not 0.

[0090] In a specific embodiment of the present invention, the Re2Fe in the easily demagnetized region 14 The shell thickness of the B main phase grain is 1 μm, and the thickness of the Re-rich phase grain boundary in the easily demagnetized region is 0.3 μm.

[0091] Wherein, the Re2Fe in the transition region 14 The thickness of the shell of the B main phase grains and the Re-rich phase grain boundaries is preferably (0-2.5):(0-1), and Re2Fe 14 The thickness of both the shell of the B principal phase grains and the grain boundary of the Re-rich phase is not zero.

[0092] Wherein, the Re2Fe in the transition region 14 The thickness of the shell layer of the B main phase grain is preferably 0-4 μm, and more preferably 0-2.5 μm.

[0093] Preferably, the thickness of the Re-rich phase grain boundary in the transition region is 0-1 μm and not 0.

[0094] In a specific embodiment of the present invention, the Re2Fe in the transition region 14 The shell thickness of the B main phase grain is 1 μm, and the thickness of the Re-rich phase grain boundary in the transition region is 0.4 μm.

[0095] Preferably, the Re-rich grain boundaries and Re2Fe in the non-demagnetizing region are... 14 The shell thickness ratio of the B main phase grains is (0-1):(0.5-1.5), and is not 0.

[0096] Among them, the Re2Fe in the non-demagnetizing region 14 The thickness of the shell layer of the B main phase grain is preferably 0-4 μm, more preferably 0-2 μm, and even more preferably 0.5-1 μm.

[0097] Preferably, the thickness of the Re-rich phase grain boundary in the non-demagnetizing region is 0-1 μm and not 0.

[0098] In a specific embodiment of the present invention, the Re2Fe in the non-demagnetizing region 14 The shell thickness of the B main phase grain is 1 μm, and the thickness of the Re-rich phase grain boundary in the non-demagnetizing region is 0.2 μm.

[0099] In this invention, the non-demagnetizing region, transition region, and demagnetizing region are preferably obtained by simulation cloud maps under operating conditions.

[0100] The present invention also provides a method for preparing the above-mentioned neodymium iron boron magnet, which includes the following steps: on a neodymium iron boron substrate, a first diffusion source, a second diffusion source, and a third diffusion source are applied to the annular edges of the upper surface and / or the lower surface perpendicular to the orientation direction and diffused towards the center, respectively, and grain boundary diffusion is performed to form a demagnetizing region, a transition region, and a non-demagnetizing region; the first diffusion source, the second diffusion source, and the third diffusion source each independently contain Dy and / or Tb.

[0101] 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.

[0102] In this invention, preferably, the first diffusion source is a Tb-containing diffusion source, and more preferably, the third diffusion source is a Dy-containing diffusion source. In this invention, the first diffusion source is a Tb-containing diffusion source, and the third diffusion source is a Dy-containing diffusion source. After diffusion, a small amount of Tb from the applied first diffusion source may diffuse into the non-demagnetizing region.

[0103] In some specific embodiments of the present invention, the first diffusion source, the second diffusion source and the third diffusion source are each independently elemental Dy.

[0104] In other embodiments of the present invention, the first diffusion source, the second diffusion source, and the third diffusion source are each independently 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.

[0105] In other embodiments of the present invention, the first diffusion source, the second diffusion source and the third diffusion source are each independently a hydride of Dy or a fluoride of Dy.

[0106] In some specific embodiments of the present invention, the first diffusion source, the second diffusion source and the third diffusion source are each independently elemental Tb.

[0107] In other embodiments of the present invention, the first diffusion source, the second diffusion source, and the third diffusion source are each independently 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.

[0108] In other embodiments of the present invention, the first diffusion source, the second diffusion source and the third diffusion source are each independently a hydride of Tb or a fluoride of Tb.

[0109] In this invention, the application can be performed using methods conventional in the art, such as coating.

[0110] 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 content is achieved.

[0111] The coating method is preferably spraying or printing.

[0112] The dewaxing temperature of the spray coating is preferably 200-400℃.

[0113] The dewaxing temperature for the printing process is preferably 100-500℃.

[0114] In certain specific embodiments of the present invention, when the first diffusion source, the second diffusion source, and the third diffusion source are applied by means of coating, the first diffusion source, the second diffusion source, and the third diffusion source further include a solvent and a binder.

[0115] The solvent may be conventional in the art, such as water, alcohol, ketone or ester.

[0116] In this invention, preferably, the Dy of the third diffusion source accounts for 0.3%-1.2% of the mass percentage of the third diffusion source, the Tb of the first diffusion source accounts for 0.3%-1.2% of the mass percentage of the first diffusion source, the Tb of the second diffusion source accounts for 0.3%-1.2% of the mass percentage of the second diffusion source, and the Dy of the second diffusion source accounts for 0.3%-1% of the mass percentage of the second diffusion source.

[0117] In this invention, preferably, the temperature of the grain boundary diffusion is 750-950°C, for example, 900°C.

[0118] In this invention, preferably, the grain boundary diffusion time is 5-30 hours, for example, 10 hours.

[0119] In this invention, preferably, an aging treatment is further included after the grain boundary diffusion.

[0120] The aging treatment temperature is preferably 300-600℃, for example, 500℃.

[0121] The time for the time-sensitive processing is preferably 1-10 hours, for example, 3 hours.

[0122] The present invention also provides a neodymium iron boron magnet prepared by the above-described method for preparing neodymium iron boron magnets.

[0123] 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.

[0124] The reagents and raw materials used in this invention are all commercially available.

[0125] The positive and progressive effects of this invention are as follows:

[0126] This invention, by setting an annular easily demagnetized region, a transition region, and a non-easily demagnetized region and controlling the Tb and Dy content introduced by diffusion in the above three regions, can reduce the problem of gradient decrease in the performance of the boundary region caused by the cross-diffusion of Tb or Dy due to the Tb concentration gradient difference in the transition region, thus weakening the anti-demagnetization effect. It can reduce the attenuation of the surface magnetism and magnetic flux of NdFeB magnets while ensuring the remanence of NdFeB magnets, thereby improving the anti-demagnetization ability of NdFeB magnets. Attached Figure Description

[0127] Figure 1 The diagram shows the structure of the neodymium iron boron magnets in Examples 1-3 and Comparative Examples 1-2.

[0128] The attached figures are labeled as follows:

[0129] 1-Non-demagnetizing region; 2-Transition region; 3-Demagnetizing region. Detailed Implementation

[0130] 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.

[0131] Examples 1-3 and Comparative Example 1

[0132] The neodymium iron boron magnets provided in Examples 1-3 and Comparative Example 1 are cuboids, and their structural schematic diagrams are shown below. Figure 1As shown, 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.

[0133] The neodymium iron boron magnet includes a non-demagnetizing region, a transition region, and a demagnetizing region. The demagnetizing region is a rectangular annular area along the Z-axis on the neodymium iron boron magnet. The non-demagnetizing region is a rectangular central region along the Z-axis on the neodymium iron boron magnet. The transition region is the boundary region between the demagnetizing region and the non-demagnetizing region. The content of heavy rare earth elements in each region is listed in Table 2. Since the content of heavy rare earth metals in the substrate is 0, the content of heavy rare earth elements in Examples 1-3 and Comparative Example 1 is equal to their diffusion weight gain.

[0134] The percentage of the volume of the easily demagnetized region, the transition region, and the non-easily demagnetized region relative to the total volume of the NdFeB magnet, as well as the coercivity ratio between the easily demagnetized region and the non-easily demagnetized region, are listed in Table 3.

[0135] In Examples 1-3 and Comparative Example 1, there is an interface A between the transition region and the corresponding easily demagnetized region, and interface A is annular; there is an interface B between the transition region and the corresponding non-easily demagnetized region, and interface B is annular. The content ratios of interfaces A, B, and the easily demagnetized region are listed in Table 4.

[0136] The mass concentrations of each element in the substrates of Examples 1-3 and Comparative Example 1 are the same, as shown in Table 5.

[0137] The microstructures of Examples 1-3 and Comparative Example 1 are listed in Table 1:

[0138] Table 1

[0139]

[0140] Table 2

[0141]

[0142]

[0143] Table 3

[0144]

[0145] Table 4

[0146]

[0147] Table 5

[0148]

[0149] The preparation methods of Examples 1-3 and Comparative Example 1 include the following steps: on a neodymium iron boron substrate, a first diffusion source, a second diffusion source, and a third diffusion source are coated on the annular edge of the upper surface perpendicular to the orientation direction towards the center, and grain boundary diffusion is performed to form an easily demagnetized region, a transition region, and a non-easily demagnetized region; the first diffusion source, the second diffusion source, and the third diffusion source are each independently elemental Dy and elemental Tb;

[0150] The grain boundary diffusion temperature is 900℃; the grain boundary diffusion time is 10h; after grain boundary diffusion, there is also an aging treatment; the aging treatment temperature is 500℃; the aging treatment time is 3h; the coating method is spraying; the dewaxing temperature of the spraying is 300℃.

[0151] Example 1

[0152] The neodymium iron boron magnets of Examples 1-3 and Comparative Example 1 were subjected to the following tests:

[0153] 1. Coercivity test: Samples of Examples 1-3 and Comparative Example 1 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.

[0154] 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.

[0155] 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.

[0156] The technical effects of Examples 1-3 and Comparative Example 1 are listed in Table 6 below:

[0157] Table 6

[0158]

[0159]

[0160] As shown in Table 6 above, the coercivity ratio between the transition region and the easily demagnetized region of the NdFeB magnets prepared in Examples 1-3 is between (0.94-0.99):1, and the coercivity difference between the easily demagnetized region and the non-easily demagnetized region is between 2.0-5 kOe, exhibiting excellent demagnetization resistance. The demagnetization rate of the NdFeB magnets in Examples 1-3 at 130℃ is only 2.0%-5.2%.

[0161] The Tb content in the easily demagnetized region of Comparative Example 1 was too low, while the Dy content in the non-easily demagnetized region was slightly higher, specifically 4:1. The coercivity ratio of the easily demagnetized region to the non-easily demagnetized region of the NdFeB magnet in Comparative Example 1 was approximately 0.96:1, and the difference in coercivity between the easily demagnetized region and the non-easily demagnetized region was -1kOe. The NdFeB magnet prepared in Comparative Example 1 had poor demagnetization resistance, with a demagnetization rate of 8.1% at 130°C, which was higher than that of Examples 1-3.

[0162] 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 (0.7-1):1; The Tb content ratio of the transition region to the non-demagnetizing region is 1:(0-0.9). The ratio of Dy content in the transition region to that in the easily demagnetized region is (0-1):(0-0.9). The ratio of Dy content in the transition region to that in the non-demagnetizing region is (0.05-0.9):1; The diffusion weight gain ratio of Tb in the transition region to that in the easily demagnetized region is (0.7-1):1; The diffusion weight gain ratio of Dy in the transition region to that in the non-demagnetizing region is (0.05-0.9):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 0.71:1, 0.8:1, or 0.83:1; And / or, the diffusion weight gain ratio of Tb in the transition region to that in the easily demagnetized region is 0.71:1, 0.8:1, or 0.83:1; 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 ratio of Dy content in the transition region to that in the easily demagnetized region is (0.05-0.9):(0-0.05); And / or, the diffusion weight gain ratio of Dy in the transition region to that in the easily demagnetized region is (0.05-0.9):(0-0.05); And / or, the ratio of Dy content in the transition region to that in the non-demagnetizing region is 0.57:1, 0.58:1, or 0.67:1; And / or, the diffusion weight gain ratio of Dy in the transition region to that in the non-demagnetizing region is 0.57:1, 0.58:1, or 0.67:1; And / or, the Tb content ratio of the non-demagnetizing region to the demagnetizing region is (0-0.05):1; And / or, the diffusion weight gain ratio of Tb in the non-demagnetizing region and the demagnetizing region is (0-0.05):1; And / or, the ratio of Dy content in the easily demagnetized region to that in the non-easily demagnetized region is (0-0.05):(0.3-1), and is not 0; And / or, the diffusion weight gain ratio of Dy in the easily demagnetized region and the non-easily demagnetized region is (0-0.05):(0.3-1), and is not 0; And / or, the Tb content 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 Tb content in the transition region is 0.1wt%-2.5wt%; And / or, the Dy content of the easily demagnetized region is 0-3.1 wt%; And / or, the Dy content in the non-demagnetizing region is 0.1wt%-4wt%; And / or, the Dy content in the transition region is 0.05wt%-3.9wt%; And / or, the volume of the easily demagnetized region accounts for 20%-80% of the volume of the NdFeB magnet; And / or, the Tb content at any two points in the easily demagnetized region is equal; And / or, the diffusion weight gain of Tb at any two points in the non-demagnetizing region is equal; And / or, the Dy content is equal at any two points in the non-demagnetizing region; And / or, the diffusion weight gain of Dy at any two points in the non-demagnetizing region is equal.

3. The neodymium iron boron magnet as described in claim 2, characterized in that, The Tb content ratio of the transition region to the non-demagnetizing region is 1:(0-0.05). And / or, the diffusion weight gain ratio of Tb in the transition region to that in the non-demagnetizing region is 1:(0-0.05). And / or, the ratio of Dy content in the transition region to that in the easily demagnetized region is 1:(0-0.9). And / or, the diffusion weight gain ratio of Dy in the transition region to that in the easily demagnetized region is 1:(0-0.9). And / or, the Tb content ratio of the non-demagnetizing region to the demagnetizing region is (0-0.03):1; And / or, the diffusion weight gain ratio of Tb in the non-demagnetizing region and the demagnetizing region is (0-0.03):1; And / or, the ratio of Dy content in the easily demagnetized region to that in the non-easily demagnetized region is (0-0.03):(0.3-0.7), and is not 0; And / or, the diffusion weight gain ratio of Dy in the easily demagnetized region and the non-easily demagnetized region is (0-0.03):(0.3-0.7), and is not 0; And / or, the Tb content in the easily demagnetized region is 0.4 wt%, 0.55 wt%, or 0.7 wt%; And / or, the Tb content in the non-demagnetizing region is 0.015 wt% or 0.01 wt%; And / or, the Tb content in the transition region is 0.33wt%, 0.4wt%, or 0.5wt%; And / or, the Dy content of the easily demagnetized region is 0.05 wt%; And / or, the Dy content in the non-demagnetizing region is 0.4wt%-0.7wt%; And / or, the Dy content in the transition region is 0.05wt%-0.4wt%; And / or, the volume of the easily demagnetized region accounts for 29%-70% of the volume of the neodymium iron boron magnet.

4. The neodymium iron boron magnet as described in claim 3, characterized in that, The Tb content ratio between the transition region and the non-demagnetizing region is 1:0.02 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 1:0.05; And / or, the ratio of Dy content in the transition region to that in the easily demagnetized region is 1:(0-0.8). And / or, the diffusion weight gain ratio of Dy in the transition region to that in the easily demagnetized region is 1:(0-0.8). And / or, the Tb content ratio of the non-demagnetizing region to the demagnetizing region is 0.01:1 or 0.02:1; And / or, the diffusion weight gain ratio of Tb in the non-demagnetizing region and the demagnetizing region is 0.01:1 or 0.02:1; And / or, the content ratio of Dy in the easily demagnetized region to the non-easily demagnetized region is 0.07:1, 0.09:1, or 0.13:1; And / or, the diffusion weight gain ratio of Dy in the easily demagnetized region and the non-easily demagnetized region is 0.07:1, 0.09:1, or 0.13:1; And / or, the Dy content in the non-demagnetizing region is 0.5 wt% or 0.55 wt%; And / or, the Dy content in the transition region is 0.23wt% or 0.37wt%; And / or, the volume of the easily demagnetized region accounts for 54.6% or 42.48% of the volume of the NdFeB magnet.

5. The neodymium iron boron magnet as described in claim 4, characterized in that, The ratio of Dy content in the transition zone to that in the easily demagnetized zone is 8:1, 37:5, or 23:5; And / or, the diffusion weight gain ratio of the transition region to the easily demagnetized region Dy is 8:1, 37:5, or 23:

5.

6. The neodymium iron boron magnet as described in claim 1, characterized in that, The width of the easily demagnetized zone is 0-5mm 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 transition region accounts for 10%-14% of the volume of the NdFeB magnet; And / or, the volume of the non-demagnetizing region accounts for 20%-75% of the volume of the NdFeB magnet; And / or, the coercivity ratio of the easily demagnetized region to 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, on any plane perpendicular to the orientation direction, the non-demagnetizing region is rectangular in shape; And / or, the neodymium iron boron magnet is a cuboid; 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.

7. The neodymium iron boron magnet as described in claim 6, characterized in that, The width of the easily demagnetized zone is 2-4 mm; 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; And / or, the coercivity ratio of the easily demagnetized region to the non-easily demagnetized region is 1:(0.8-0.9). And / or, the length-to-thickness ratio of the neodymium iron boron magnet is (3.64-24.27):

1.

8. The neodymium iron boron magnet as described in claim 7, characterized in that, The volume of the non-demagnetizing region accounts for 34.27%-57.5% of the volume of the NdFeB magnet; And / or, the coercivity ratio of the easily demagnetized region to the non-easily demagnetized region is 1:0.85; And / or, the length-to-thickness ratio of the neodymium iron boron magnet is (8.74-24.27):

1.

9. The neodymium iron boron magnet as described in claim 8, characterized in that, The length-to-thickness ratio of the neodymium iron boron magnet is 12.85:

1.

10. The neodymium iron boron magnet as described in claim 1, characterized in that, An interface A exists between the transition region and the easily demagnetized region, and the interface A is annular. And / or, there is an interface B between the transition region and the corresponding non-demagnetizing region, and the interface B is annular.

11. The neodymium iron boron magnet as described in claim 10, characterized in that, The Tb content at interface A is 0.1wt%-2.5wt%; And / or, the diffusion weight gain of Tb at interface A is 0.1wt%-2.5wt%; And / or, the content ratio of the interface A to the Tb content in the easily demagnetized region is (0.9-1):1; And / or, the diffusion weight gain ratio of the interface A to the Tb of the easily demagnetized region is (0.9-1):1; And / or, the content of Dy at interface A is 0.01wt%-3.5wt%; And / or, the diffusion weight gain of Dy at interface A is 0.01wt%-3.5wt%; And / or, the content ratio of the interface A to the Dy content of the easily demagnetized region is (0.02-0.2):(0-0.05); And / or, the diffusion weight gain ratio of the interface A to the easily demagnetized region Dy is (0.02-0.2):(0-0.05).

12. The neodymium iron boron magnet as described in claim 11, characterized in that, The Tb content at interface A is 0.35 wt%, 0.4 wt%, 0.5 wt%, or 0.55 wt%. And / or, the diffusion weight gain of Tb at interface A is 0.35wt%, 0.4wt%, 0.5wt%, or 0.55wt%; And / or, the content of Dy at interface A is 0.05 wt%; And / or, the diffusion weight gain of Dy at interface A is 0.05 wt%; And / or, the content ratio of the interface A to the Dy content of the easily demagnetized region is 1:(0.8-1). And / or, the diffusion weight gain ratio of the interface A to the easily demagnetized region Dy is 1:(0.8-1).

13. The neodymium iron boron magnet as described in claim 12, characterized in that, The content ratio of interface A to Dy in the easily demagnetized region is 1:1; And / or, the diffusion weight gain ratio of the interface A to the easily demagnetized region Dy is 1:

1.

14. The neodymium iron boron magnet as described in claim 10, characterized in that, The Tb content at interface B is 0.05wt%-2.4wt%; And / or, the diffusion weight gain of Tb at interface B is 0.05wt%-2.4wt%; And / or, the content ratio of the interface B to the Tb content in the non-demagnetizing region is 1:(0-0.94). And / or, the diffusion weight gain ratio of the interface B to the Tb of the non-demagnetizing region is 1:(0-0.94). And / or, the Dy content of interface B is 0.08wt%-4wt%; And / or, the diffusion weight gain of Dy at interface B is 0.05wt%-1wt%; And / or, the content ratio of the interface B to the Dy content of the non-demagnetizing region is (0.5-1):1; And / or, the diffusion weight gain ratio of the interface B to the non-demagnetizing region Dy is (0.1-0.7):

1.

15. The neodymium iron boron magnet as described in claim 14, characterized in that, The Tb content at interface B is 0.22 wt% or 0.23 wt%. And / or, the diffusion weight gain of Tb at interface B is 0.22 wt% or 0.23 wt%; And / or, the content ratio of the interface B to the Tb content in the non-demagnetizing region is 1:(0-0.2). And / or, the diffusion weight gain ratio of the interface B to the Tb of the non-demagnetizing region is 1:(0-0.2). And / or, the content of Dy at interface B is 0.37wt% or 0.23wt%; And / or, the diffusion weight gain of Dy at interface B is 0.37 wt%; And / or, the content ratio of the interface B to the Dy in the non-demagnetizing region is 0.57:1, 0.67:1, or 0.58:1; And / or, the diffusion weight gain ratio of the interface B to the non-demagnetizing region Dy is 0.13:1, 0.14:1, 0.22:1 or 0.4:

1.

16. The neodymium iron boron magnet as described in claim 15, characterized in that, The content ratio of the interface B to the Tb content in the non-demagnetizing region is 1:(0-0.05). And / or, the diffusion weight gain ratio of the interface B to the Tb of the non-demagnetizing region is 1:(0-0.05).

17. The neodymium iron boron magnet as described in claim 16, characterized in that, The content ratio of the interface B to the Tb in the non-demagnetizing region is 1:0.04 or 1:0.045; And / or, the diffusion weight gain ratio of the interface B to the Tb of the non-demagnetizing region is 1:0.04 or 1:0.

045.

18. 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.

19. The neodymium iron boron magnet as described in claim 18, characterized in that, The Re2Fe in the easily demagnetized region 14 The shell of the B-phase grains includes (Nd, Tb)₂Fe. 14 B hard magnetic layer; And / or, the Re2Fe in the non-demagnetizing region 14 The shell of the B-phase main grains includes (Nd, Dy)2Fe 14 B hard magnetic layer; And / or, Re2Fe at any two points in the easily demagnetized region 14 The difference in grain size between the B main phase grains does not exceed 1-8 μm; And / or, Re2Fe at any two points in the transition region 14 The difference in grain size between the B main phase grains does not exceed 1-8 μm; And / or, the surface Re2Fe of the easily demagnetized region, the transition region, and the non-easily demagnetized region. 14 The B main phase grains have equal grain size, and the surface layer refers to the surface perpendicular to the orientation direction; And / or, the central Re2Fe of the easily demagnetized region, the transition region, and the non-easily demagnetized region. 14 The B principal phase grains have equal grain size, where the center refers to the mid-plane along the orientation direction; And / or, the Re2Fe in the easily demagnetized region, the transition region, and the non-easily demagnetized region 14 The core layer of the B main phase grains and the Re2Fe 14 The shell of the B-phase grain satisfies the following conditions: the R1 content in the core layer is greater than or equal to the R1 content in the shell layer; the R2 content in the core layer is less than the R2 content in the shell layer; wherein, R1 includes one or more of Pr, Nd, Ce, Er, Tm, Y, Lu, Gd and Ho; and R2 is Dy and / or Tb. And / or, in the easily demagnetized region, on the surface equidistant from the interface between the transition region and the easily demagnetized region, the Re2Fe 14 The shells of the B principal phase grains have equal thickness; And / or, in the easily demagnetized region, on the surface equidistant from the interface between the transition region and the easily demagnetized region, the thickness of the Re-rich phase grain boundary is equal; And / or, in the transition region, on the surface equidistant from the interface between the transition region and the easily demagnetized region, the Re2Fe 14 The shells of the B principal phase grains have equal thickness; And / or, in the transition region, on surfaces equidistant from the interface between the transition region and the easily demagnetized region, the thickness of the Re-rich phase grain boundaries is equal.

20. The neodymium iron boron magnet as described in claim 19, characterized in that, The easily demagnetized region, the transition region, and the non-easily demagnetized region of Re2Fe 14 The grain size ratio of the B main phase is 1:1:1; And / or, in the easily demagnetized region, the transition region, and the non-easily demagnetized region, the surface Re2Fe 14 The grain size of the B main phase is the central Re2Fe. 14 The grain size of the B main phase is 1-1.5 times that of the main phase grains; And / or, the surface Re2Fe of the easily demagnetized region, the transition region, and the non-easily demagnetized region. 14 The grain size of the B main phase is 1-12 μm; And / or, when R2 is Tb, the content of R2 in the easily demagnetized region, the transition region and the non-easily demagnetized region satisfies the following condition: easily demagnetized region ≥ transition region > non-easily demagnetized region; And / or, when R2 is Dy, the content of R2 in the easily demagnetized region, the transition region and the non-easily demagnetized region satisfies the following condition: non-easily demagnetized region ≥ transition region > easily demagnetized region.

21. The neodymium iron boron magnet as described in claim 18 or 19, characterized in that, The Re-rich grain boundaries and Re2Fe in the easily demagnetized region 14 The shell thickness ratio of the B main phase grains is (0-1):(0.5-1.5), and is not 0; And / or, the Re2Fe in the easily demagnetized region 14 The shell thickness of the B main phase grains is 0-4 μm; And / or, the thickness of the Re-rich phase grain boundary in the easily demagnetized region is 0-1 μm and not 0; And / or, the Re2Fe in the easily demagnetized region 14 The shell thickness of the B main phase grain is 1 μm, and the thickness of the Re-rich phase grain boundary in the easily demagnetized region is 0.3 μm. And / or, the Re2Fe of the transition region 14 The thickness ratio of the shell layer of the B main phase grains to the Re-rich phase grain boundaries is (0-2.5):(0-1), and Re2Fe 14 The thickness of the shell of the B main phase grain and the thickness of the Re-rich phase grain boundary are both non-zero; And / or, the Re2Fe of the transition region 14 The shell thickness of the B main phase grains is 0-4 μm; And / or, the thickness of the Re-rich phase grain boundaries in the transition region is 0-1 μm and not 0; And / or, the Re2Fe of the transition region 14 The shell thickness of the B main phase grain is 1 μm, and the thickness of the Re-rich phase grain boundary in the transition region is 0.4 μm. And / or, the Re-rich grain boundaries and Re2Fe in the non-demagnetizing region 14 The shell thickness ratio of the B main phase grains is (0-1):(0.5-1.5), and is not 0; And / or, the Re2Fe in the non-demagnetizing region 14 The shell thickness of the B main phase grains is 0-4 μm; And / or, the thickness of the Re-rich phase grain boundary in the non-demagnetizing region is 0-1 μm and not 0; And / or, the Re2Fe in the non-demagnetizing region 14 The shell thickness of the B main phase grain is 1 μm, and the thickness of the Re-rich phase grain boundary in the non-demagnetizing region is 0.2 μm.

22. The neodymium iron boron magnet as described in claim 21, characterized in that, The Re2Fe in the easily demagnetized region 14 The shell thickness of the B main phase grains is 0-2 μm; And / or, the Re2Fe of the transition region 14 The shell thickness of the B main phase grains is 0-2.5 μm; And / or, the Re2Fe in the non-demagnetizing region 14 The shell thickness of the B main phase grains is 0-2 μm.

23. The neodymium iron boron magnet as described in claim 22, characterized in that, The Re2Fe in the easily demagnetized region 14 The shell thickness of the B main phase grains is 0.5-1.5 μm; And / or, the Re2Fe in the non-demagnetizing region 14 The shell thickness of the B main phase grains is 0.5-1 μm.

24. A method for preparing a neodymium iron boron magnet as described in any one of claims 1-23, characterized in that, It includes the following steps: on a NdFeB substrate, a first diffusion source, a second diffusion source, and a third diffusion source are applied to the periphery of the upper surface and / or the lower surface perpendicular to the orientation direction and diffused towards the center to form a demagnetizing region, a transition region, and a non-demagnetizing region; the first diffusion source, the second diffusion source, and the third diffusion source each independently contain Dy and / or Tb.

25. The method for preparing a neodymium iron boron magnet as described in claim 24, characterized in that, The first diffusion source is a Tb-containing diffusion source; And / or, the first diffusion source, the second diffusion source, and the third diffusion source are each independently elemental Dy; And / or, the first diffusion source, the second diffusion source and the third diffusion source are each independently a Dy-M alloy, where M comprises one or more of Cu, Al, Co, Ga, Zr and Ti; And / or, the first diffusion source, the second diffusion source and the third diffusion source are each independently a hydride of Dy or a fluoride of Dy; And / or, the first diffusion source, the second diffusion source, and the third diffusion source are each independently elemental Tb; And / or, the first diffusion source, the second diffusion source and the third diffusion source are each independently a Tb-M alloy, where M comprises one or more of Cu, Al, Co, Ga, Zr and Ti; And / or, the first diffusion source, the second diffusion source and the third diffusion source are each independently a hydride of Tb or a fluoride of Tb; And / or, the Dy of the third diffusion source accounts for 0.3%-1.2% of the mass percentage of the third diffusion source, the Tb of the first diffusion source accounts for 0.3%-1.2% of the mass percentage of the first diffusion source, the Tb of the second diffusion source accounts for 0.3%-1.2% of the mass percentage of the second diffusion source, and the Dy of the second diffusion source accounts for 0.3%-1% of the mass percentage of the second diffusion source; 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.

26. The method for preparing a neodymium iron boron magnet as described in claim 25, characterized in that, The third diffusion source is a diffusion source containing Dy; And / or, the first diffusion source, the second diffusion source and the third diffusion source are each independently a Dy-M alloy, wherein M accounts for 0-40% of the mass percentage of the Dy-M, and is not 0; And / or, the first diffusion source, the second diffusion source and the third diffusion source are each independently a Tb-M alloy, wherein the mass percentage of M in the Tb-M is 0-40% and not 0; 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 aging process takes 1-10 hours.

27. The method for preparing a neodymium iron boron magnet as described in claim 26, characterized in that, The aging treatment temperature is 500℃; And / or, the time for the aging process is 3 hours.

28. The method for preparing a neodymium iron boron magnet as described in claim 25, characterized in that, The coating method is spraying or printing; And / or, the first diffusion source, the second diffusion source and the third diffusion source further include solvents and binders.

29. The method for preparing a neodymium iron boron magnet as described in claim 28, characterized in that, The dewaxing temperature for the spraying is 200-400℃; And / or, the dewaxing temperature of the printing is 100-500℃; And / or, the solvent is water, alcohol, ketone or ester.

30. A neodymium iron boron magnet prepared by the method described in any one of claims 24-29.

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