Neodymium-iron-boron magnet, and preparation method therefor and use thereof

Abstract

Disclosed in the present invention are a neodymium-iron-boron magnet, and a preparation method therefor and the use thereof. In the neodymium-iron-boron magnet, the contents of heavy rare earth in a first vulnerable-to-demagnetization region, a second vulnerable-to-demagnetization region, a third vulnerable-to-demagnetization region and a fourth vulnerable-to-demagnetization region are the same; the contents of Tb in a first transition region, a second transition region, a third transition region and a fourth transition region are the same; the contents of Dy in the first vulnerable-to-demagnetization region, the transition region and an invulnerable-to-demagnetization region are the same and are not 0; the ratio of the content of Tb in the invulnerable-to-demagnetization region to the content of Tb in the first vulnerable-to-demagnetization region is (0-0.9):1; and the ratio of the content of Tb in the first transition region to the content of Tb in the first vulnerable-to-demagnetization region is (0.5-0.96):1. On the premise that the residual magnetism of the neodymium-iron-boron magnet of the present invention is guaranteed, the attenuation of the surface magnetism and magnetic flux of the neodymium-iron-boron magnet can be reduced, and the magnet has good demagnetization resistance.

Description

Neodymium-iron-boron magnet, preparation method and application thereof TECHNICAL FIELD

[0001] The present application relates to a neodymium-iron-boron magnet, a preparation method and application thereof. BACKGROUND

[0002] Since the advent of neodymium-iron-boron permanent magnet, it has been widely used in the fields of automobile, wind power, household appliances, industrial robots, etc. Due to different working conditions in different fields, the performance of the magnetic steel in the field is also required to be different. In recent years, new energy vehicles have developed rapidly, and the demand for magnetic steel of main drive motor has increased dramatically. Since the normal working temperature of the main drive motor mainly concentrates in the range of 120-180℃, the neodymium-iron-boron material needs higher coercivity and thermal stability. In order to improve the temperature resistance of the neodymium-iron-boron permanent magnet, a large amount of heavy rare earth Dy and Tb is usually added to increase the anisotropic field of the main phase magnetic crystal. However, the resources of heavy rare earth are scarce and the price is high, which seriously restricts the application of neodymium-iron-boron magnet in various industries.

[0003] With the increasing demand for high-performance magnets, the grain boundary diffusion technology has gradually been known and accepted by everyone. The conventional grain boundary diffusion technology adopts a physical vapor deposition method to deposit a diffusion source on the surface of the magnet, and then penetrates the diffusion source into the magnet along the grain boundary under high temperature and certain pressure. The biggest advantage of this technology is that it can greatly improve the coercivity using a small amount of heavy rare earth while keeping the remanence almost unchanged. In terms of effective utilization rate of heavy rare earth, the traditional grain boundary diffusion product has been greatly improved compared with the non-grain boundary diffusion product.

[0004] However, in the actual use of neodymium-iron-boron, the performance requirements of each part of the magnet are not the same. For example, in the motor, since the reverse magnetic field generated after the coil is energized in the motor is not a uniform magnetic field, how to design a neodymium-iron-boron magnet according to the needs of different regions to meet the needs of different applications, while ensuring the coercivity and remanence, and also having good anti-demagnetization ability. SUMMARY

[0005] The present application mainly overcomes the defect of poor anti-demagnetization performance of the neodymium-iron-boron magnet in the prior art, and provides a neodymium-iron-boron magnet, a preparation method and application thereof. The neodymium-iron-boron magnet of the present application can reduce the decay of surface magnetic and magnetic flux of the neodymium-iron-boron magnet under the premise of ensuring the remanence, and has good anti-demagnetization performance.

[0006] The present application mainly solves the above technical problems through the following technical solutions.

[0007] The present application provides a neodymium-iron-boron magnet, which is a rectangular parallelepiped. A three-dimensional rectangular coordinate system is established with the center of the upper surface of the rectangular parallelepiped as the origin, wherein the orientation direction is the positive direction of the Z-axis, and the X-axis is parallel to one side of the upper surface.

[0008] The Nd-Fe-B magnet comprises a non-remanence zone, a transition zone and a remanence zone; the remanence zone comprises a first remanence zone, a second remanence zone, a third remanence zone and a fourth remanence zone arranged at four corners of the cuboid along the Z-axis direction respectively and not in contact with each other;

[0009] The transition zone is located at the junction of the remanence zone and the non-remanence zone and comprises a first transition zone, a second transition zone, a third transition zone and a fourth transition zone corresponding to the first remanence zone, the second remanence zone, the third remanence zone and the fourth remanence zone respectively;

[0010] The content of heavy rare earth in the first remanence zone, the second remanence zone, the third remanence zone and the fourth remanence zone is the same;

[0011] The content of Tb in the first transition zone, the second transition zone, the third transition zone and the fourth transition zone is the same;

[0012] The content of Dy in the first remanence zone, the first transition zone and the non-remanence zone is the same and not 0;

[0013] The ratio of the content of Tb in the non-remanence zone to the first remanence zone is (0-0.9):1;

[0014] The ratio of the content of Tb in the first transition zone to the first remanence zone is (0.5-0.96):1.

[0015] In the present application, the heavy rare earth element can be derived from a substrate and / or a diffusion process.

[0016] In the present application, the content of heavy rare earth refers to the percentage of the mass of heavy rare earth in a certain region to the total mass of the magnet in the region, for example, the content of Tb in the first remanence zone means the percentage of the mass of Tb in the first remanence zone to the total mass of the magnet in the first remanence zone.

[0017] In the present application, the "the diffusion weight gain of heavy rare earth is the same" means that the types of heavy rare earth introduced by diffusion in each region are the same, and the diffusion weight gain of each type of heavy rare earth is the same.

[0018] In the present application, the diffusion weight gain of heavy rare earth means the percentage of the mass of heavy rare earth introduced by diffusion in a certain region to the total mass of the magnet in the region, for example, the diffusion weight gain of Tb in the first remanence zone means the percentage of the mass of Tb introduced by diffusion in the first remanence zone to the total mass of the magnet in the first remanence zone.

[0019] In the present application, the specific position of the upper surface is not specifically limited, and those skilled in the art can generally understand that the upper surface refers to the surface opposite to the plane when the magnet is placed on the plane.

[0020] In the present application, the diffusion weight gain of Dy in the first easy demagnetization region, the first transition region and the non-easy demagnetization region can be 0.1wt%-1wt%, for example, 0.5wt%, 0.6wt% or 0.7wt%.

[0021] In the present application, the content of Dy in the first easy demagnetization region, the first transition region and the non-easy demagnetization region can be 0.1-4wt%, for example, 0.5wt%, 0.6wt% or 0.7wt%.

[0022] In the present application, the diffusion weight gain ratio of Tb in the first transition region to the first easy demagnetization region can be (0.5-0.9):1, preferably (0.6-0.9):1, for example, 0.7:1, 0.8:1, 0.86:1, 0.9:1.

[0023] In the present application, the content ratio of Tb in the first transition region to the first easy demagnetization region can be (0.6-0.9):1, for example, 0.7:1, 0.8:1, 0.86:1, 0.9:1.

[0024] In the present application, the diffusion weight gain ratio of Tb in the non-easy demagnetization region to the first easy demagnetization region can be (0-0.05):(0.3-1), for example, 0.02:0.6, 0.05:0.7, 0.01:0.7 or 0.05:0.65.

[0025] In the present application, the content ratio of Tb in the non-easy demagnetization region to the first easy demagnetization region can be (0-0.2):1, for example, 0.03:1, 0.07:1, 0.01:1 or 0.08:1.

[0026] In the present application, the diffusion weight gain of Tb in the first easy demagnetization region can be 0.1wt%-1wt%, for example, 0.6wt%, 0.65wt% or 0.7wt%.

[0027] In the present application, the content of Tb in the first easy demagnetization region can be 0.1wt%-2.5wt%, for example, 0.6wt%, 0.65wt% or 0.7wt%.

[0028] In the present application, the diffusion weight gain of Tb in the non-easy demagnetization region can be 0.05wt% and below, for example, 0.01wt% or 0.05wt%.

[0029] In the present application, the content of Tb in the non-freely demagnetized region can be 0wt%-1.6wt%, for example, 0.01wt% or 0.05wt%.

[0030] In the present application, the diffusion weight gain of Tb in the first transition region can be 0.05-0.9wt%, preferably 0.2-0.5wt%, for example, 0.35wt%.

[0031] In the present application, the content of Tb in the transition region can be 0.1wt%-2.4wt%, for example, 0.6wt% or 0.62wt%.

[0032] In some specific embodiments, the diffusion weight gain of Tb in the first transition region is 0.6wt% or 0.62wt%.

[0033] In the present application, in any plane perpendicular to the orientation direction, the ratio of the diffusion weight gain of Tb in the first freely demagnetized region to the non-freely demagnetized region can be 1:(1 / L-1), wherein L is the interval between the sampling regions, and the value of L is >1.

[0034] In the present application, the diffusion weight gain of Tb in the first freely demagnetized region is preferably higher than that in the non-freely demagnetized region.

[0035] In the present application, the neodymium-iron-boron magnet can be represented by the chemical formula R1-R2-R3-T-B-M, wherein R1 includes one or more of Pr, Nd, Ce, Er, Tm, Y, Lu, Gd and Ho; R2 is Tb introduced by diffusion; R3 is Dy introduced by diffusion; T contains 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 elements include one or more of Cu, Al, Co, Ga, Zr and Ti.

[0036] In some embodiments, the M elements are all from the neodymium-iron-boron base material.

[0037] In other embodiments, the M elements include diffusion-introduced M elements, and the mass percentage of the diffusion-introduced M elements in the neodymium-iron-boron magnet is preferably 0wt%-0.4wt%.

[0038] In the present application, the coercivities of the first, second, third and fourth freely demagnetized regions are the same.

[0039] In the present application, the coercivities of the first, second, third and fourth transition regions are the same.

[0040] In the present application, the coercivity of the first easy demagnetization region is not lower than the coercivity of the first transition region, and the coercivity of the first transition region is not lower than the coercivity of the non-easy demagnetization region.

[0041] In the present application, the ratio of the coercivity of the first transition region to the coercivity of the first easy demagnetization region is (0.8-1):1, for example, 0.9:1, 0.96:1, 0.98:1, 0.99:1 or 1:1.

[0042] In the present application, the difference between the coercivity of the first easy demagnetization region and the coercivity of the non-easy demagnetization region is 0-10kOe, for example, 2.6kOe, 3.5kOe, 3.9kOe, 2.8kOe, 3kOe or 3.2kOe.

[0043] In the present application, the ratio of the coercivity of the non-easy demagnetization region to the coercivity of the first easy demagnetization region is (0.7-0.96):1, for example, 0.85:1, 0.87:1, 0.88:1, 0.89:1 or 0.9:1.

[0044] In the present application, the remanence of the first easy demagnetization region, the second easy demagnetization region, the third easy demagnetization region and the fourth easy demagnetization region is the same.

[0045] In the present application, the remanence of the first transition region, the second transition region, the third transition region and the fourth transition region is the same.

[0046] In the present application, the ratio of the remanence of the first easy demagnetization region to the remanence of the non-easy demagnetization region is (0.99-1):1, for example, 1:1.

[0047] In the present application, the ratio of the remanence of the first transition region to the remanence of the non-easy demagnetization region is (0.99-1):1, for example, 1:1.

[0048] In the present application, in any plane perpendicular to the orientation direction, the shape of the first easy demagnetization region, the second easy demagnetization region, the third easy demagnetization region and the fourth easy demagnetization region is independently selected from a rectangle, a sector or a triangle; preferably, the first easy demagnetization region, the second easy demagnetization region, the third easy demagnetization region and the fourth easy demagnetization region are all rectangles and have the same width. The width of the easy demagnetization region refers to the distance extending along the X-axis or Y-axis from the edge of the neodymium-iron-boron magnet.

[0049] In the present application, the width of the first transition region, the second transition region, the third transition region and the fourth transition region is the same; the width of the first transition region refers to the distance between the interface of the first transition region and the first easy demagnetization region and the interface of the first transition region and the non-easy demagnetization region along the X-axis or Y-axis direction.

[0050] In the present application, the ratio of the width of the first transition region to the width of the neodymium-iron-boron magnet is (0-0.1):1, for example, 0.09:1.

[0051] In the present application, the width of the first transition zone is preferably 0-1 mm and is not 0;

[0052] In the present application, the width ratio of the non-reversible magnetic zone to the Nd-Fe-B magnet is (0.2-0.7):1, for example, 0.527:1. The width of the non-reversible magnetic zone refers to the distance along the X-axis or Y-axis that the interface of the transition zone and non-reversible magnetic zone or the edge of the Nd-Fe-B magnet extends.

[0053] In the present application, the width ratio of the first reversible magnetic zone to the Nd-Fe-B magnet is (0.05-0.4):1.

[0054] In the present application, the grain boundary structure of the Nd-Fe-B magnet comprises Re2Fe 14 B main phase grains and Re-rich phase grain boundaries; the Re2Fe 14 B main phase grains comprise a main phase grain shell layer; the Re is one or more of Nd, Dy and Tb.

[0055] In the present application, the meaning of the main phase grain shell layer is conventional in the art, i.e. (Nd, Dy / Tb)2Fe 14 B hard magnetic layer. The meaning of the Re-rich phase grain boundary zone is conventional in the art, i.e. a two-particle grain boundary zone with Re>95%.

[0056] In some preferred embodiments, the content of Tb in the main phase grain shell layer of the first reversible magnetic zone, second reversible magnetic zone, third reversible magnetic zone and fourth reversible magnetic zone is the same.

[0057] In some preferred embodiments, the content of Tb in the main phase grain shell layer of the first transition zone, second transition zone, third transition zone and fourth transition zone is the same.

[0058] In some preferred embodiments, the ratio of the content of Tb in the main phase grain shell layer of the first reversible magnetic zone to the first reversible magnetic zone is (0-0.05):(0.3-0.65), for example, 0.05:0.7, 0.01:0.7 or 0.04:0.65.

[0059] In some preferred embodiments, the thickness of the main phase grain shell layer of the first reversible magnetic zone, second reversible magnetic zone, third reversible magnetic zone and fourth reversible magnetic zone is the same.

[0060] In some preferred embodiments, the thickness of the main phase grain shell layer of the first transition zone, second transition zone, third transition zone and fourth transition zone is the same.

[0061] In some preferred embodiments, the thickness of the Re-rich grain boundary in the first, second, third and fourth easy demagnetization regions is the same.

[0062] In some preferred embodiments, the thickness of the Re-rich grain boundary in the first, second, third and fourth transition regions is the same.

[0063] Preferably, the thickness of the main phase grain shell in the first easy demagnetization region, the first transition region and the non-easy demagnetization region preferably satisfies: first easy demagnetization region≥first transition region≥non-easy demagnetization region.

[0064] Preferably, the thickness of the Re-rich grain boundary gradually decreases from the easy demagnetization region to the non-easy demagnetization region in any plane perpendicular to the orientation direction.

[0065] Preferably, the thickness of the Re-rich grain boundary in the first easy demagnetization region, the first transition region and the non-easy demagnetization region preferably satisfies: first easy demagnetization region≥first transition region≥non-easy demagnetization region.

[0066] Preferably, the thickness of the main phase grain shell in the first easy demagnetization region and the first transition region is 0-4 μm, more preferably 0.5-1.5 μm.

[0067] Preferably, the thickness of the main phase grain shell in the non-easy demagnetization region is 0-2 μm, more preferably 0.5-1 μm.

[0068] Preferably, the thickness of the Re-rich grain boundary in the first easy demagnetization region, the first transition region and the non-easy demagnetization region is 0-1 μm, but not 0.

[0069] Preferably, the ratio of the thickness of the main phase grain shell to the thickness of the Re-rich grain boundary in the first easy demagnetization region, the first transition region and the non-easy demagnetization region is (0.5-1.5):(0-1), but not 0.

[0070] In some preferred embodiments, the particle size of the main phase grain in the first, second, third and fourth easy demagnetization regions is the same.

[0071] The surface layer means a surface perpendicular to the orientation direction, and the center means a median plane along the orientation direction.

[0072] The particle size of the main phase grain in the non-easy demagnetization region is 1-8 μm.

[0073] The particle size of the main phase grain in the first, second, third and fourth transition regions is the same.

[0074] In some preferred embodiments, the grain size of the main phase grains of the first easy demagnetization zone, the first transition zone and the non-easy demagnetization zone satisfies: first easy demagnetization zone ≥ first transition zone ≥ non-easy demagnetization zone.

[0075] In some preferred embodiments, the grain size of the surface layer main phase grains of the first easy demagnetization zone is 1-1.5 times that of the surface layer main phase grains of the non-easy demagnetization zone.

[0076] In some preferred embodiments, the grain size of the surface layer main phase grains of the first easy demagnetization zone and the first transition zone is 1-1.5 times that of the center main phase grains.

[0077] In some preferred embodiments, the grain size of the surface layer main phase grains of the non-easy demagnetization zone is 1-1.3 times that of the center main phase grains.

[0078] In some preferred embodiments, the grain size of the surface layer main phase grains of the first easy demagnetization zone and the first transition zone is 1-12 μm.

[0079] In some preferred embodiments, the main phase grain shell layer of the easy demagnetization zone comprises a first inner shell layer and a first outer shell layer, the main phase grain shell layer of the transition zone comprises a second inner shell layer and a second outer shell layer, and the main phase grain shell layer of the non-easy demagnetization zone comprises a third inner shell layer.

[0080] Wherein, the meaning of the inner shell layer is a region in which the content of Dy in the main phase grain shell layer of each region accounts for 80% or more of the total content of Tb and Dy elements; the meaning of the outer shell layer is a region in which the content of Tb in the main phase grain shell layer of each region accounts for 80% or more of the total content of Tb and Dy elements.

[0081] Wherein, the Tb diffusion weight gain of the first outer shell layer and the second outer shell layer preferably satisfies: first outer shell layer ≥ second outer shell layer.

[0082] Wherein, the Tb diffusion weight gain in the first outer shell layer is preferably 0.1wt%-0.9wt%, for example, 0.6wt%;

[0083] Wherein, the content of Tb in the first outer shell layer is preferably 0.1wt%-2.4wt%, for example, 0.6wt%.

[0084] Wherein, the Tb diffusion weight gain in the second outer shell layer is preferably 0.1wt%-0.8wt%, for example, 0.6wt%.

[0085] Wherein, the content of Tb in the second outer shell layer is preferably 0.1wt%-2.3wt%, for example, 0.6wt%.

[0086] Preferably, the Dy diffusion weight gain of the first inner shell layer, the second inner shell layer and the third inner shell layer satisfies: the third inner shell layer ≥ the second inner shell layer ≥ the first inner shell layer.

[0087] Preferably, the Dy diffusion weight gain of the first inner shell layer is 0.1wt%-0.9wt%, for example, 0.5wt%, 0.6wt% or 0.7wt%.

[0088] Preferably, the content of Dy in the first inner shell layer is 0.1wt%-3.9wt%, for example, 0.5wt%, 0.6wt% or 0.7wt%.

[0089] Preferably, the Dy diffusion weight gain of the second inner shell layer is 0.1wt%-0.9wt%, for example, 0.5wt%, 0.6wt% or 0.7wt%.

[0090] Preferably, the content of Dy in the second inner shell layer is 0.1wt%-3.9wt%, for example, 0.5wt%, 0.6wt% or 0.7wt%.

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

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

[0093] Preferably, the thickness of the first inner shell layer, the second inner shell layer and the third inner shell layer satisfies: the third inner shell layer ≥ the second inner shell layer ≥ the first inner shell layer.

[0094] Preferably, the thickness of the first inner shell layer and the first outer shell layer satisfies: the first outer shell layer ≤ the first inner shell layer.

[0095] Preferably, the thickness of the second inner shell layer and the second outer shell layer satisfies: the second outer shell layer ≤ the second inner shell layer.

[0096] Preferably, the thickness of the first inner shell layer is 0-2μm, for example, 1.8μm, 1.9μm or 2μm.

[0097] Preferably, the thickness of the first outer shell layer is 0-2μm, for example, 1.7μm, 1.8μm or 1.9μm.

[0098] Preferably, the thickness of the second inner shell layer is 0-2μm, for example, 1.8μm, 1.9μm or 2μm.

[0099] The thickness of the second outer shell layer is preferably 0-2 μm, for example 1.8 μm or 1.7 μm.

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

[0101] In some preferred embodiments, the main phase grain shell layer of the non-freely demagnetized region further comprises a third outer shell layer.

[0102] The Tb diffusion weight gain in the third outer shell layer of the main phase grain shell layer of the non-freely demagnetized region is preferably 0-0.05 wt%.

[0103] The Tb content in the third outer shell layer of the main phase grain shell layer of the non-freely demagnetized region is preferably 0 wt%-1.6 wt%.

[0104] The Tb diffusion weight gain in the first outer shell layer, the second outer shell layer and the third outer shell layer preferably satisfies: first outer shell layer > second outer shell layer > third outer shell layer.

[0105] The thickness of the first outer shell layer, the second outer shell layer and the third outer shell layer preferably satisfies: first outer shell layer > second outer shell layer > third outer shell layer.

[0106] The thickness of the third inner shell layer and the third outer shell layer in the main phase grain shell layer of the non-freely demagnetized region preferably satisfies: third inner shell layer > third outer shell layer.

[0107] The thickness of the third outer shell layer of the main phase grain shell layer of the non-freely demagnetized region is preferably 0-0.5 μm.

[0108] The present application also provides a preparation method of the above-mentioned Nd-Fe-B magnet, which comprises the following steps: applying a diffusion source Dy on the entire area of the upper surface and the lower surface of an Nd-Fe-B substrate, and applying a diffusion source Tb on the four side surfaces perpendicular to the upper surface, corresponding to the four corner regions of the upper surface, and allowing the diffusion source Tb to perform grain boundary diffusion perpendicular to the orientation direction, thereby obtaining the Nd-Fe-B magnet; wherein the four corner regions form a freely demagnetized region after grain boundary diffusion; and the non-four corner regions form a non-freely demagnetized region and a transition region. In the present application, it is known to those skilled in the art that the Dy or Tb in the diffusion source is not completely diffused into the magnet during grain boundary diffusion, and the utilization rate is generally 85%-95%, so that a larger amount of Dy or Tb is generally applied in the actual preparation process.

[0109] In the present application, it is known to those skilled in the art that different grain boundary diffusion methods will have different coating thicknesses when the same amount of Dy or Tb is diffused into the magnet, so that the coating thickness is not limited in the actual preparation process, as long as the corresponding amount of Dy or Tb diffusion is achieved.

[0110] In some embodiments, the diffusion source is pure Dy.

[0111] In some other embodiments, the diffusion source is a Dy-M alloy, M comprises one or more of Cu, Al, Co, Ga, Zr and Ti. Wherein, the mass percentage of M in the Dy-M is 0-40%, and is not 0.

[0112] In some other embodiments, the diffusion source is a Tb-M alloy, M comprises one or more of Cu, Al, Co, Ga, Zr and Ti. Wherein, the mass percentage of M in the Tb-M is 0-40%, and is not 0.

[0113] In some embodiments, the diffusion source is pure Tb.

[0114] In some other embodiments, the diffusion source is a Tb-M alloy, M comprises one or more of Cu, Al, Co, Ga, Zr and Ti. Wherein, the mass percentage of M in the Tb-M is 0-40%, and is not 0.

[0115] In some other embodiments, the diffusion source is a Tb-M alloy, M comprises one or more of Cu, Al, Co, Ga, Zr and Ti. Wherein, the mass percentage of M in the Tb-M is 0-40%, and is not 0.

[0116] In the present application, the diffusion source can be applied by conventional methods in the art, for example, by coating.

[0117] Preferably, the coating method is spraying or printing. Preferably, the spraying temperature is 200-400℃, and the printing temperature is 100-500℃.

[0118] When the diffusion source is applied by coating, the diffusion source is generally mixed with solvent and binder in a certain proportion to form a slurry.

[0119] The solvent is, for example, water, alcohol, ketone or ester.

[0120] In the present application, the heat treatment temperature in the grain boundary diffusion is preferably 750-950℃, for example, 900℃.

[0121] In the present application, the heat treatment time in the grain boundary diffusion is preferably 5-30h, for example, 25h.

[0122] In the present application, the heat treatment in the grain boundary diffusion is generally followed by aging treatment.

[0123] Preferably, the aging treatment temperature is 300-600℃, for example, 490℃.

[0124] Preferably, the aging treatment time is 1-10h, for example, 6h.

[0125] The application further provides application of the above neodymium-iron-boron magnet in a magnetic steel.

[0126] On the basis of common knowledge in the art, the above-mentioned preferred conditions can be combined arbitrarily, thereby obtaining preferred examples of the application.

[0127] The reagents and raw materials used in the application are commercially available.

[0128] The positive progress effect of the application is that:

[0129] The application matches the demagnetization edge angle of the magnetic steel by controlling the Tb content introduced by diffusion in the easy demagnetization zone and the non-easy demagnetization zone and the matching of the Dy content in all zones, adopts a non-oriented diffusion mode to match the easy demagnetization characteristics of the center and the non-easy demagnetization characteristics of the edge, can reduce the surface magnetic and magnetic flux decay of the neodymium-iron-boron magnet under the premise of ensuring the remanence of the neodymium-iron-boron magnet, and improves the anti-demagnetization ability of the neodymium-iron-boron magnet. BRIEF DESCRIPTION OF DRAWINGS

[0130] Fig. 1 is a structural schematic diagram of each zone of a neodymium-iron-boron magnet.

[0131] Fig. 2 is a structural schematic diagram of the main phase grain core and shell layer in each zone of a neodymium-iron-boron magnet.

[0132] Fig. 3 is a schematic diagram of the diffusion weight gain distribution of Tb of the neodymium-iron-boron magnet of Example 1 along the test line 1 and the test line 2 shown in Fig. 1.

[0133] Fig. 4 is a schematic diagram of the diffusion weight gain distribution of Dy of the neodymium-iron-boron magnet of Example 1 along the test line 1 and the test line 2 shown in Fig. 1.

[0134] Reference signs: 1-first easy demagnetization zone, 2-first transition zone, 3-non-easy demagnetization zone, 4-second transition zone, 5-second easy demagnetization zone, 6-third easy demagnetization zone, 7-third transition zone, 8-fourth transition zone, 9-fourth easy demagnetization zone, 10-main phase grain shell layer, 11-main phase grain core layer, 12-first inner shell layer, 13-first outer shell layer, 14-second inner shell layer, 15-second outer shell layer, 16-third inner shell layer. DETAILED DESCRIPTION

[0135] The application will be further described by way of examples below, but the application is not limited in the scope of the examples. The experimental methods in the following examples are not specified, and are selected according to conventional methods and conditions, or according to the instructions of the goods.

[0136] Examples 1-4 and Comparative Examples 1-3

[0137] The diffusion source Dy is applied on the upper surface and the lower surface of the Nd-Fe-B substrate, and the diffusion source Tb is applied on the four sides perpendicular to the upper surface, corresponding to the four corner regions of the upper surface, and the diffusion source Tb is subjected to grain boundary diffusion perpendicular to the orientation direction, thereby obtaining the Nd-Fe-B magnet; wherein the four corner regions form the easy demagnetization regions through grain boundary diffusion; and the non-four corner regions form the non-easy demagnetization regions and the transition regions. The utilization rate of Dy or Tb in the diffusion source is 85%-95%.

[0138] The temperature of the heat treatment in the grain boundary diffusion is 900°C, the time of the heat treatment is 25h, and the aging treatment is further included after the heat treatment, the temperature of the aging treatment is 490°C, and the time of the aging treatment is 6h.

[0139] The parameters of the Nd-Fe-B magnets of Examples 1-4 and Comparative Examples 1-3 are listed in Tables 1, 2 and 3, and the element contents of the Nd-Fe-B substrates used in Examples 1-4 and Comparative Examples 1-3 are shown in Table 4. Since the content of the heavy rare earth metal in the substrate is 0, the diffusion weight gain of the heavy rare earth metal in Examples 1-4 and Comparative Examples 1-3 is equal to the content thereof.

[0140] The structural schematic diagram of the Nd-Fe-B magnets of Examples 1-4 and Comparative Examples 1-3 is shown in Figure 1, wherein the first easy demagnetization region 1, the second easy demagnetization region 5, the third easy demagnetization region 6 and the fourth easy demagnetization region 9 are all rectangular; the first transition region 2, the second transition region 4, the third transition region 7 and the fourth transition region 8 are all L-shaped, and the non-easy demagnetization region 3 is cross-shaped; the thickness of the Nd-Fe-B magnet is 3mm, and the ratio of the length to the thickness is 2.5. The direction of the arrow M represents the magnetization direction of the Nd-Fe-B magnet, and the direction of the arrow P represents the orientation direction of the Nd-Fe-B magnet; the A surface represents the surface layer of the Nd-Fe-B magnet, and the B surface represents the middle layer of the Nd-Fe-B magnet. The structure of the main phase grain core and the shell layer is shown in Figure 2, wherein 10 is the main phase grain shell layer, 11 is the main phase grain core, 12 is the first inner shell layer, 13 is the first outer shell layer, 14 is the second inner shell layer, 15 is the second outer shell layer, and 16 is the third inner shell layer. Figure 3 is the diffusion weight gain distribution diagram of Tb of the Nd-Fe-B magnet of Example 1 along the test line 1 and the test line 2 shown in Figure 1. It can be seen that along the test line 1, from the first easy demagnetization region to the non-easy demagnetization region, the distribution of Tb is close to a linear function distribution. Figure 4 is the diffusion weight gain distribution diagram of Dy of the Nd-Fe-B magnet of Example 1 along the test line 1 and the test line 2 shown in Figure 1.

[0141] Table 1. The diffusion weight gain of Dy and Tb in each region of the Nd-Fe-B magnet prepared in Examples 1-4 and Comparative Examples 1-3 and the ratio of the content of Tb in the main phase grain shell layer in each region

[0142] Table 2. Coercivity ratio, zone width ratio and grain size of the main phase of the Nd-Fe-B magnets prepared in Examples 1-4 and Comparative Examples 1-3

[0143] Table 3. Thickness of the inner and outer shell layers of the main phase grains and the diffusion weight gain of Dy and Tb of the Nd-Fe-B magnets prepared in Examples 1-2 and Comparative Examples 1-2

[0144] Table 4. Mass concentration of each element in the base material of Examples 1-4 and Comparative Examples 1-3

[0145] Effect Example 1

[0146] The Nd-Fe-B magnets of Examples 1-4 and Comparative Examples 1-3 were subjected to the following tests, and the results are shown in Table 5.

[0147] 1. Coercivity test: The samples of Examples 1-4 and Comparative Examples 1-3 were prepared with a size of W2-3±0.1*L19±0.1*T4±0.1 mm, two pieces were stacked and tested, a coil with a size of W3*L19-20*T2.7 mm was used to test the magnets in a permanent magnet precision measurement system NIM-62000 at room temperature (temperature ≤200℃).

[0148] 2. Demagnetization rate test: An electromagnetic simulation software, Ansys Workbench, was used to input a rotation speed of 1300 rpm, and then the temperature was adjusted to the corresponding temperature working condition. The back electromotive force data of the motor and the magnetic steel cloud map changes were collected under the same time to identify whether the magnetic steel was demagnetized. The calculation formula of the demagnetization rate is: demagnetization rate = (high-temperature back electromotive force - room-temperature back electromotive force) / room-temperature back electromotive force.

[0149] 3. Remanence test: The Nd-Fe-B magnets of Examples 1-4 and Comparative Examples 1-2 were placed in a PFM-14 pulse magnetic performance measuring instrument of the China Institute of Metrology to measure the remanence.

[0150] 4. The test method and test instrument of the line scan map are: the surface of the selected area of the magnet is microphotographed under the equipment EMMA, the equipment model is JEOL 8530f, the shooting magnification is X3000, and the two main phase grains are pulled and scanned, which represents the distribution of Cu, Al, Dy, Tb and Nd elements.

[0151] Table 5. Coercivity and demagnetization resistance of each zone of the magnets of Examples 1-4 and Comparative Examples 1-3 Note: In the above Tables 1-3 and 5, ① the meaning of "easy demagnetization zone" is the first, second, third or fourth easy demagnetization zone; ② the meaning of "transition zone" is the first, second, third or fourth transition zone.

[0152] As shown in Table 5, the remanence of the Nd-Fe-B magnets prepared in Examples 1-4 is maintained at 14.30 kGs and above, while the demagnetization rate at 130℃ is only 2.5%-7.2%, indicating that the Nd-Fe-B magnets of the present application can maintain a high remanence while having excellent demagnetization resistance. In addition, the different regions designed according to application requirements have different coercivities, greatly saving costs.

[0153] In Comparative Example 1, the Tb diffusion weight gain ratio of the transition zone to the easy demagnetization zone is not within the scope of the present application, in which the Tb diffusion weight gain ratio of the transition zone is too small, and the demagnetization rate of the Nd-Fe-B magnet prepared therein at 130℃ is 20.3%, higher than that of the examples, indicating that the demagnetization resistance of Comparative Example 1 is poorer than that of the examples.

[0154] In Comparative Example 2, no Dy diffusion is performed, and Tb diffusion is performed in the easy demagnetization zone. The demagnetization rate of the Nd-Fe-B magnet prepared in Comparative Example 2 at 130℃ is as high as 31.9%, much higher than that of the examples, indicating that the demagnetization resistance of Comparative Example 2 is poorer than that of the examples.

[0155] In Comparative Example 3, the Tb diffusion weight gain ratio of the transition zone to the easy demagnetization zone is 1:1, which is not within the scope of the present application, in which the Tb diffusion weight gain ratio of the transition zone is too large, and the demagnetization rate of the Nd-Fe-B magnet prepared therein at 130℃ is 21.2%, much higher than that of the examples, indicating that the demagnetization resistance of Comparative Example 1 is poorer than that of the examples.

[0156] The above-described examples are only better embodiments of the present application, facilitating understanding and use of the present application by those skilled in the art. Obviously, any skilled person in the art can make slight modifications or changes to the present embodiments without inventive labor and apply them to other embodiments. Therefore, the present application is not limited to the above-described embodiments, and any equivalent changes, simple modifications and modifications within the scope of the present application still fall within the scope of the present application.

Claims

1. A neodymium-iron-boron magnet, characterized in that The neodymium-iron-boron magnet is a cuboid, and a three-dimensional rectangular coordinate system is established with the center of the upper surface of the cuboid as the origin, wherein the orientation direction is the positive direction of the Z axis, and the X axis is parallel to one side of the upper surface; The neodymium-iron-boron magnet comprises a non-easy demagnetization area, a transition area and an easy demagnetization area; the easy demagnetization area comprises a first easy demagnetization area, a second easy demagnetization area, a third easy demagnetization area and a fourth easy demagnetization area respectively arranged at four corners of the cuboid along the Z axis direction and not in contact with each other; The transition area is located at the junction of the easy demagnetization area and the non-easy demagnetization area, and comprises a first transition area, a second transition area, a third transition area and a fourth transition area corresponding to the first easy demagnetization area, the second easy demagnetization area, the third easy demagnetization area and the fourth easy demagnetization area respectively; The content of heavy rare earth in the first easy demagnetization area, the second easy demagnetization area, the third easy demagnetization area and the fourth easy demagnetization area is the same; The content of Tb in the first transition area, the second transition area, the third transition area and the fourth transition area is the same; The content of Dy in the first easy demagnetization area, the first transition area and the non-easy demagnetization area is the same and is not 0; The content ratio of Tb in the non-easy demagnetization area and the first easy demagnetization area is (0-0.9):1; The content ratio of Tb in the first transition area and the first easy demagnetization area is (0.5-0.96):

1.

2. The neodymium-iron-boron magnet according to claim 1, characterized in that The diffusion weight gain of Dy in the first easy demagnetization area, the first transition area and the non-easy demagnetization area is 0.1wt%-1wt%, for example, 0.5wt%, 0.6wt% or 0.7wt%; And / or, the content of Dy in the first easy demagnetization area, the first transition area and the non-easy demagnetization area is 0.1-4wt%, for example, 0.5wt%, 0.6wt% or 0.7wt%; And / or, the diffusion weight gain ratio of Tb in the first transition area and the first easy demagnetization area is (0.5-0.9):1, preferably (0.6-0.9):1, for example, 0.7:1, 0.8:1, 0.86:1, 0.9:1; And / or, the content ratio of Tb in the first transition area and the first easy demagnetization area is (0.6-0.9):1, for example, 0.7:1, 0.8:1, 0.86:1, 0.9:1; And / or, the diffusion weight gain ratio of Tb in the non-easy demagnetization area and the first easy demagnetization area is (0-0.05):(0.3-1), for example, 0.02:0.6, 0.05:0.7, 0.01:0.7 or 0.05:0.65; And / or, the content ratio of Tb in the non-easy demagnetization area and the first easy demagnetization area is (0-0.2):1, for example, 0.03:1, 0.07:1, 0.01:1 or 0.08:1; And / or, the diffusion weight gain of Tb in the first easy demagnetization area is 0.1wt%-1wt%, for example, 0.6wt%, 0.65wt% or 0.7wt%; And / or, the content of Tb in the first easy demagnetization area is 0.1wt%-2.5wt%, for example, 0.6wt%, 0.65wt% or 0.7wt%. and / or, the diffusion weight gain of Tb in the non-consequent demagnetization region is 0.05wt% and below, for example 0.01wt% or 0.05wt%; and / or, the content of Tb in the non-consequent demagnetization region is 0wt%-1.6wt%, for example 0.01wt% or 0.05wt%; and / or, the diffusion weight gain of Tb in the first transition region is 0.05wt%-0.9wt%, for example 0.6wt% or 0.62wt%; and / or, the content of Tb in the transition region is 0.1wt%-2.4wt%, for example 0.6wt% or 0.62wt%; and / or, the ratio of the diffusion weight gain of Tb in the first consequent demagnetization region to the non-consequent demagnetization region is 1:(1 / L-1) in any plane perpendicular to the orientation direction, wherein L is the distance between the sampling regions, and the value of L is >1.

3. The neodymium-iron-boron magnet of claim 1, wherein, the coercivity of the first consequent demagnetization region, the second consequent demagnetization region, the third consequent demagnetization region and the fourth consequent demagnetization region are the same; and / or, the coercivity of the first transition region, the second transition region, the third transition region and the fourth transition region are the same; and / or, the coercivity of the first consequent demagnetization region is not lower than the coercivity of the first transition region, and the coercivity of the first transition region is not lower than the coercivity of the non-consequent demagnetization region; and / or, the ratio of the coercivity of the first transition region to the first consequent demagnetization region is (0.8-1):1, for example 0.9:1, 0.96:1, 0.98:1, 0.99:1 or 1:1; and / or, the difference of the coercivity of the first consequent demagnetization region and the non-consequent demagnetization region is 0-10kOe, for example 2.6kOe, 3.5kOe, 3.9kOe, 2.8kOe, 3kOe or 3.2kOe; and / or, the ratio of the coercivity of the non-consequent demagnetization region to the first consequent demagnetization region is (0.7-0.96):1, for example 0.85:1, 0.87:1, 0.88:1, 0.89:1 or 0.9:1; and / or, the remanence of the first consequent demagnetization region, the second consequent demagnetization region, the third consequent demagnetization region and the fourth consequent demagnetization region are the same; the remanence of the first transition region, the second transition region, the third transition region and the fourth transition region are the same; and / or, the ratio of the remanence of the first consequent demagnetization region to the non-consequent demagnetization region is (0.99-1):1, for example 1:1; and / or, the ratio of the remanence of the first transition region to the non-consequent demagnetization region is (0.99-1):1, for example 1:1; and / or, in any plane perpendicular to the orientation direction, the shape of the first consequent demagnetization region, the second consequent demagnetization region, the third consequent demagnetization region and the fourth consequent demagnetization region are independently selected from a rectangle, a sector or a triangle; Preferably, the first consequent demagnetization region, the second consequent demagnetization region, the third consequent demagnetization region and the fourth consequent demagnetization region are all rectangles and have the same width; the width of the consequent demagnetization region refers to the distance extending along the X-axis or the Y-axis from the edge of the Nd-Fe-B magnet. And / or, the first transition zone, the second transition zone, the third transition zone and the fourth transition zone have the same width; the width of the first transition zone refers to the distance between the interface between the first transition zone and the first easy demagnetization zone and the interface between the first transition zone and the non-easy demagnetization zone along the X-axis or Y-axis direction; And / or, the width ratio of the first transition zone to the neodymium-iron-boron magnet is (0-0.1):1, for example, 0.09:1; And / or, the width ratio of the non-easy demagnetization zone to the neodymium-iron-boron magnet is (0.2-1):1, for example, 0.527:1; the width of the non-easy demagnetization zone refers to the distance along the X-axis or Y-axis direction that the interface between the transition zone and the non-easy demagnetization zone or the edge of the neodymium-iron-boron magnet extends; And / or, the width ratio of the first easy demagnetization zone to the neodymium-iron-boron magnet is (0.05-0.4):

1.

4. The neodymium-iron-boron magnet of claim 1, wherein, The grain boundary structure of the neodymium-iron-boron magnet comprises Re2Fe 14 B main phase grains and Re-rich phase grain boundaries; the Re2Fe 14 The B main phase grains comprise a main phase grain shell layer; the Re is one or more of Nd, Dy, and Tb Preferably, the first easy demagnetization zone, the second easy demagnetization zone, the third easy demagnetization zone and the fourth easy demagnetization zone have the same content of Tb in the main phase grain shell layer; Preferably, the first transition zone, the second transition zone, the third transition zone and the fourth transition zone have the same content of Tb in the main phase grain shell layer; Preferably, the content ratio of Tb in the main phase grain shell layer of the first easy demagnetization zone to the first easy demagnetization zone is (0-0.05):(0.3-0.65), for example, 0.05:0.7, 0.01:0.7 or 0.04:0.65; Preferably, the first easy demagnetization zone, the second easy demagnetization zone, the third easy demagnetization zone and the fourth easy demagnetization zone have the same thickness of the main phase grain shell layer; Preferably, the first transition zone, the second transition zone, the third transition zone and the fourth transition zone have the same thickness of the main phase grain shell layer; Preferably, the first easy demagnetization zone, the second easy demagnetization zone, the third easy demagnetization zone and the fourth easy demagnetization zone have the same thickness of the Re-rich phase grain boundary; Preferably, the first transition zone, the second transition zone, the third transition zone and the fourth transition zone have the same thickness of the Re-rich phase grain boundary; Preferably, in the first easy demagnetization zone, the first transition zone and the non-easy demagnetization zone, the thickness of the main phase grain shell layer preferably satisfies: first easy demagnetization zone≥first transition zone≥non-easy demagnetization zone; in any vertical orientation direction, from the easy demagnetization zone to the non-easy demagnetization zone, the thickness of the Re-rich phase grain boundary gradually decreases; Preferably, in the first easy demagnetization zone, the first transition zone and the non-easy demagnetization zone, the thickness of the main phase grain Re-rich phase grain boundary preferably satisfies: first easy demagnetization zone≥first transition zone≥non-easy demagnetization zone; Preferably, in the first easy demagnetization zone and the first transition zone, the thickness of the main phase grain shell layer is 0-4μm, more preferably 0.5-1.5μm; Preferably, in the non-easy demagnetization zone, the thickness of the main phase grain shell layer is 0-2μm, more preferably 0.5-1μm; Preferably, in the first easy demagnetization zone, the first transition zone and the non-easy demagnetization zone, the thickness of the Re-rich phase grain boundary is 0-1μm, but not 0. Preferably, the ratio of the thickness of the main phase grain shell layer to the thickness of the Re-rich phase grain boundary in the first easy demagnetization region, the first transition region and the non-easy demagnetization region is (0.5-1.5):(0-1), but not 0.

5. The neodymium-iron-boron magnet of claim 4, wherein, The grain size of the main phase grains in the first easy demagnetization region, the second easy demagnetization region, the third easy demagnetization region and the fourth easy demagnetization region is the same; the grain size of the main phase grains in the first transition region, the second transition region, the third transition region and the fourth transition region is the same; And / or, the grain size of the main phase grains in the first easy demagnetization region, the first transition region and the non-easy demagnetization region satisfies: first easy demagnetization region≥first transition region≥non-easy demagnetization region; And / or, the grain size of the surface layer main phase grains in the first easy demagnetization region is 1-1.5 times that of the surface layer main phase grains in the non-easy demagnetization region; And / or, the grain size of the surface layer main phase grains in the first easy demagnetization region and the first transition region is 1-1.5 times that of the center main phase grains; And / or, the grain size of the surface layer main phase grains in the non-easy demagnetization region is 1-1.3 times that of the center main phase grains; And / or, the grain size of the surface layer main phase grains in the first easy demagnetization region and the first transition region is 1-12 μm; And / or, the grain size of the surface layer main phase grains in the non-easy demagnetization region is 1-8 μm.

6. The neodymium-iron-boron magnet of claim 1, wherein, The main phase grain shell layer of the easy demagnetization region includes a first inner shell layer and a first outer shell layer, the main phase grain shell layer of the transition region includes a second inner shell layer and a second outer shell layer, and the main phase grain shell layer of the non-easy demagnetization region includes a third inner shell layer; Preferably, the Tb diffusion weight gain of the first outer shell layer and the second outer shell layer satisfies: first outer shell layer≥second outer shell layer; Preferably, the Tb diffusion weight gain in the first outer shell layer is 0.1wt%-0.9wt%, for example, 0.6wt%; Preferably, the content of Tb in the first outer shell layer is 0.1wt%-2.4wt%, for example, 0.6wt%; Preferably, the Tb diffusion weight gain in the second outer shell layer is 0.1wt%-0.8wt%, for example, 0.6wt%; Preferably, the content of Tb in the second outer shell layer is 0.1wt%-2.3wt%, for example, 0.6wt%; Preferably, the Dy diffusion weight gain of the first inner shell layer, the second inner shell layer and the third inner shell layer satisfies: third inner shell layer≥second inner shell layer≥first inner shell layer; Preferably, the Dy diffusion weight gain in the first inner shell layer is 0.1wt%-0.9wt%, for example, 0.5wt%, 0.6wt% or 0.7wt%; Preferably, the content of Dy in the first inner shell layer is 0.1wt%-3.9wt%, for example, 0.5wt%, 0.6wt% or 0.7wt%; Preferably, the Dy diffusion weight gain in the second inner shell layer is 0.1wt%-0.9wt%, for example, 0.5wt%, 0.6wt% or 0.7wt%; Preferably, the content of Dy in the second inner shell layer is 0.1wt%-3.9wt%, for example, 0.5wt%, 0.6wt% or 0.7wt%. The third inner shell layer preferably has a Dy diffusion weight gain of 0.1wt%-0.9wt%, for example 0.5wt%, 0.6wt% or 0.7wt%; The third inner shell layer preferably has a Dy content of 0.1wt%-3.9wt%, for example 0.5wt%, 0.6wt% or 0.7wt%; The thicknesses of the first inner shell layer, the second inner shell layer and the third inner shell layer preferably satisfy: third inner shell layer≥second inner shell layer≥first inner shell layer; The thicknesses of the first inner shell layer and the first outer shell layer preferably satisfy: first outer shell layer≤first inner shell layer; The thicknesses of the second inner shell layer and the second outer shell layer preferably satisfy: second outer shell layer≤second inner shell layer; The first inner shell layer preferably has a thickness of 0-2μm, for example 1.8μm, 1.9μm or 2μm; The first outer shell layer preferably has a thickness of 0-2μm, for example 1.7μm, 1.8μm or 1.9μm; The second inner shell layer preferably has a thickness of 0-2μm, for example 1.8μm, 1.9μm or 2μm; The second outer shell layer preferably has a thickness of 0-2μm, for example 1.8μm or 1.7μm; The third inner shell layer preferably has a thickness of 0-2μm, for example 1.8μm, 1.9μm or 2μm.

7. The neodymium-iron-boron magnet of claim 6, wherein, The third outer shell layer of the main phase grain shell of the non-freely demagnetized region preferably has a Tb diffusion weight gain of 0-0.05wt%; The third outer shell layer of the main phase grain shell of the non-freely demagnetized region preferably has a Tb content of 0wt%-1.6wt%; The first outer shell layer, the second outer shell layer and the third outer shell layer preferably satisfy: first outer shell layer>second outer shell layer>third outer shell layer in terms of Tb diffusion weight gain; The thicknesses of the first outer shell layer, the second outer shell layer and the third outer shell layer preferably satisfy: first outer shell layer>second outer shell layer>third outer shell layer; The thicknesses of the third inner shell layer and the third outer shell layer of the main phase grain shell of the non-freely demagnetized region preferably satisfy: third inner shell layer>third outer shell layer; The third outer shell layer of the main phase grain shell of the non-freely demagnetized region preferably has a thickness of 0-0.5μm.

8. The method of producing a neodymium-iron-boron magnet according to any one of claims 1 to 7, characterized by, It comprises the following steps: applying diffusion source Dy on the entire area of the upper surface and the lower surface of the neodymium iron boron substrate, and applying diffusion source Tb on the portions corresponding to the four corner regions of the upper surface on the four side surfaces perpendicular to the upper surface, so that the diffusion source Tb performs grain boundary diffusion perpendicular to the orientation direction, thereby obtaining the neodymium iron boron magnet; wherein the four corner regions form a freely demagnetized region after grain boundary diffusion; and the non-four corner regions form a non-freely demagnetized region and a transition region.

9. The method of producing a neodymium-iron-boron magnet according to claim 8, wherein The diffusion source is applied by coating; The coating is preferably spraying or printing; the dewaxing temperature of the spraying is preferably 200-400°C; and the dewaxing temperature of the printing is preferably 100-500°C; and / or the temperature of the heat treatment in the grain boundary diffusion is 750-950 °C, such as 900 °C; and / or the time of the heat treatment in the grain boundary diffusion is 5-30 h, such as 10 h; and / or the heat treatment in the grain boundary diffusion is generally followed by an aging treatment; wherein the temperature of the aging treatment is preferably 300-600 °C, such as 500 °C; wherein the time of the aging treatment is preferably 1-10 h, such as 3 h.

10. Use of a neodymium-iron-boron magnet according to any one of claims 1-7 in a magnetic steel.

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