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 a use thereof. In the neodymium-iron-boron magnet, the content of heavy rare earths in a first easy-to-demagnetize area, the content of the heavy rare earths in a second easy-to-demagnetize area, the content of the heavy rare earths in a third easy-to-demagnetize area, and the content of the heavy rare earths in a fourth easy-to-demagnetize area are identical; the content of the heavy rare earths in a first transition area, the content of the heavy rare earths in a second transition area, the content of the heavy rare earths in a third transition area, and the content of the heavy rare earths in a fourth transition area are identical; the content of Dy in the first easy-to-demagnetize area, the content of Dy in the first transition area, and the content of Dy in an uneasy-to-demagnetize area are identical and are not 0; the content of Tb in the first transition area to the content of Tb in the first easy-to-demagnetize area is (0.8-1):1; the content of Tb in the uneasy-to-demagnetize area to the content of Tb in the first easy-to-demagnetize area is (0-0.9):1. When residual magnetism is ensured, the neodymium-iron-boron magnet of the present invention can reduce the attenuation of surface magnetism and magnetic flux of the neodymium-iron-boron magnet, and has good anti-demagnetization performance.

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 without changing the remanence. 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 diffusion weight gain 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 heavy rare earth 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 content ratio of Tb in the first transition zone to the first remanence zone is (0.8-1):1;

[0014] The content ratio of Tb in the non-remanence zone to the first remanence zone is (0-0.9):1.

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

[0018] In the present application, the "diffusion weight gain of heavy rare earth is the same" means that the type of heavy rare earth introduced by diffusion in each region is the same, and the diffusion weight gain of each type of heavy rare earth is the same.

[0019] In the present application, the diffusion weight gain of Dy in the first easy demagnetization zone, the first transition zone and the non-easy demagnetization zone can be 0.1wt%-1wt%, for example, 0.5wt%, 0.6wt% or 0.7wt%.

[0020] In the present application, the content of Dy in the first easy demagnetization zone, the first transition zone and the non-easy demagnetization zone can be 0.1-4wt%, for example, 0.5wt%, 0.6wt% or 0.7wt%.

[0021] In the present application, the diffusion weight gain ratio of Tb in the first transition zone and the first easy demagnetization zone can be (0.8-1):1, preferably (0.9-1):1, for example, 0.98:1 or 1:1.

[0022] In the present application, the content ratio of Tb in the first transition zone and the first easy demagnetization zone can be (0.9-1):1, for example, 0.98:1 or 1:1.

[0023] In the present application, the diffusion weight gain ratio of Tb in the non-easy demagnetization zone and the first easy demagnetization zone can be (0-0.05):1, for example, 0:1, 0.01:1, 0.02:1, 0.03:1 or 0.05:1.

[0024] In the present application, the content ratio of Tb in the non-easy demagnetization zone and the first easy demagnetization zone can be (0-0.9):1, preferably (0-0.2):1, for example, 0:1, 0.01:1, 0.02:1, 0.03:1 or 0.05:1.

[0025] In the present application, the diffusion weight gain of Tb in the first easy demagnetization zone can be 0.1wt%-1wt%, for example, 0.6wt% or 0.58wt%.

[0026] In the present application, the content of Tb in the first easy demagnetization zone is 0.1-2.5wt%, for example, 0.6wt% or 0.58wt%.

[0027] In the present application, the diffusion weight gain of Tb in the non-easy demagnetization zone can be 0.05wt% and below, for example, 0, 0.006wt%, 0.012wt%, 0.018wt% or 0.029wt%.

[0028] In the present application, the content of Tb in the non-easy demagnetization zone can be 0-1.6wt%, for example, 0, 0.006wt%, 0.012wt%, 0.018wt% or 0.029wt%.

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

[0030] In the present application, the content of Tb in the transition zone can be 0.1-2.5wt%, for example, 0.588wt%, 0.57wt% or 0.58wt%.

[0031] In the present application, the Nd-Fe-B 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.

[0032] In some embodiments, the M elements are all from the Nd-Fe-B base material.

[0033] In other embodiments, the M elements include diffusion-introduced M elements, wherein the diffusion-introduced M elements preferably account for 0wt%-0.4wt% of the mass percentage of the Nd-Fe-B magnet.

[0034] In the present application, there is an interface A between the transition zone and the easy demagnetization zone, which includes first interface A, second interface A, third interface A and fourth interface A corresponding to the first transition zone, the second transition zone, the third transition zone and the fourth transition zone, and the diffusion weight gain of Tb of the first interface A, the second interface A, the third interface A and the fourth interface A is the same.

[0035] Preferably, the diffusion weight gain of Tb of the first interface A to the first easy demagnetization zone is (0.95-1):1, for example, 0.96:1, 0.98:1, 0.99:1 or 1:1.

[0036] Preferably, the content of Tb of the first interface A to the first easy demagnetization zone is (0.9-1):1, for example, 0.96:1, 0.98:1, 0.99:1 or 1:1.

[0037] In the present application, there is an interface B between the transition zone and the non-easy demagnetization zone, which includes first interface B, second interface B, third interface B and fourth interface B corresponding to the first transition zone, the second transition zone, the third transition zone and the fourth transition zone, and the diffusion weight gain of Tb of the first interface B, the second interface B, the third interface B and the fourth interface B is the same.

[0038] The ratio of the coercivity of the first transition zone to the coercivity of the first easy demagnetization zone can be (0.95-1):1, for example 0.95:1, 0.97:1 or 0.98:1.

[0039] The ratio of the content of Tb of the first interface B to the content of Tb of the first easy demagnetization zone is (0.5-0.96):1.

[0040] In the present application, the coercivities of the first easy demagnetization zone, the second easy demagnetization zone, the third easy demagnetization zone and the fourth easy demagnetization zone are the same.

[0041] In the present application, the coercivities of the first transition zone, the second transition zone, the third transition zone and the fourth transition zone are the same.

[0042] In the present application, the coercivity of the first easy demagnetization zone is not lower than the coercivity of the first transition zone, and the coercivity of the first transition zone is not lower than the coercivity of the non-easy demagnetization zone.

[0043] In the present application, the ratio of the coercivity of the first transition zone to the coercivity of the first easy demagnetization zone can be (0.95-1):1, for example 0.95:1, 0.97:1 or 0.98:1.

[0044] In the present application, the difference between the coercivity of the first easy demagnetization zone and the coercivity of the non-easy demagnetization zone can be 0-10kOe, for example 2.6kOe, 3kOe, 3.2kOe, 3.5kOe or 3.9kOe.

[0045] In the present application, the ratio of the coercivity of the non-easy demagnetization zone to the coercivity of the first easy demagnetization zone can be (0.7-0.96):1, for example 0.85:1, 0.87:1, 0.88:1 or 0.9:1.

[0046] In the present application, the remanences of the first easy demagnetization zone, the second easy demagnetization zone, the third easy demagnetization zone and the fourth easy demagnetization zone are the same; the remanences of the first transition zone, the second transition zone, the third transition zone and the fourth transition zone are the same.

[0047] In the present application, the ratio of the remanence of the first easy demagnetization zone to the remanence of the non-easy demagnetization zone can be (0.99-1):1, for example 0.99:1 or 1:1.

[0048] In the present application, the ratio of the remanence of the first transition zone to the remanence of the non-easy demagnetization zone can be (0.99-1):1, for example 1:1.

[0049] In the present application, in any plane perpendicular to the orientation direction, the shapes of the first easy demagnetization zone, the second easy demagnetization zone, the third easy demagnetization zone and the fourth easy demagnetization zone are each independently selected from a rectangle, a sector or a triangle.

[0050] In some preferred embodiments, the first, second, third and fourth easy demagnetization regions are rectangular and have the same width, wherein the width of an easy demagnetization region refers to the distance extending along the X-axis or Y-axis from the edge of the Nd-Fe-B magnet.

[0051] In the present application, the first, second, third and fourth transition regions have the same width, wherein the width of the first transition region refers to the distance between the interface between the first transition region and the first easy demagnetization region and the interface between the first transition region and the non-easy demagnetization region along the X-axis or Y-axis.

[0052] In the present application, the width ratio of the first transition region to the Nd-Fe-B magnet can be (0-0.1):1, for example, 0.092:1, 0.093:1 or 0.094:1.

[0053] In the present application, the width ratio of the non-easy demagnetization region to the Nd-Fe-B magnet can be (0.2-0.7):1, for example, 0.527:1, wherein the width of the non-easy demagnetization region refers to the distance extending along the X-axis or Y-axis from the interface between the transition region and the non-easy demagnetization region or the edge of the Nd-Fe-B magnet.

[0054] In the present application, the width ratio of the first easy demagnetization region to the Nd-Fe-B magnet can be (0.05-0.4):1.

[0055] In the present application, the width of the first transition region can be 0-1 mm and not 0.

[0056] 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.

[0057] wherein 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 region is conventional in the art, i.e. a two-particle grain boundary region with Re>95%.

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

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

[0060] Preferably, the content of Tb in the main phase grain shell layer of the first easy demagnetization region is not less than the content of Tb in the main phase grain shell layer of the first transition region.

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

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

[0063] Preferably, the thicknesses of the main phase grain shell layers of the first easy demagnetization region, the second easy demagnetization region, the third easy demagnetization region and the fourth easy demagnetization region are the same.

[0064] Preferably, the thicknesses of the main phase grain shell layers of the first transition region, the second transition region, the third transition region and the fourth transition region are the same.

[0065] Preferably, the thicknesses of the Re-rich grain boundaries of the first easy demagnetization region, the second easy demagnetization region, the third easy demagnetization region and the fourth easy demagnetization region are the same.

[0066] Preferably, the thicknesses of the Re-rich grain boundaries of the first transition region, the second transition region, the third transition region and the fourth transition region are the same.

[0067] Preferably, the main phase grain inter-shell layer and the Re-rich grain boundary of the first easy demagnetization region contain a higher concentration of Dy and Tb, and the thickness is preferably 0-3 μm; the main phase grain inter-shell layer and the Re-rich grain boundary of the first transition region contain a higher concentration of Dy and Tb, and the thickness is preferably 0-3 μm; the main phase grain inter-shell layer and the Re-rich grain boundary of the non-easy demagnetization region contain a higher concentration of Dy, and the thickness is preferably 0-2 μm.

[0068] Preferably, in the first easy demagnetization region, the first transition region and the non-easy demagnetization region, the thickness of the main phase grain shell layer preferably satisfies: first easy demagnetization region≥first transition region≥non-easy demagnetization region.

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

[0070] Preferably, the thickness of the main phase grain shell layer in the first easy demagnetization zone and the first transition zone is 0-4 μm, more preferably 0.5-1.5 μm.

[0071] Preferably, the thickness of the main phase grain shell layer in the non-easy demagnetization zone is 0-2 μm, more preferably 0.5-1 μm.

[0072] Preferably, the thickness of the Re-rich phase grain boundary in the first easy demagnetization zone, the first transition zone and the non-easy demagnetization zone is 0-1 μm, but not 0.

[0073] 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 zone, the first transition zone and the non-easy demagnetization zone is (0.5-1.5):(0-1), but not 0.

[0074] Preferably, the particle size of the main phase grain in the first easy demagnetization zone, the second easy demagnetization zone, the third easy demagnetization zone and the fourth easy demagnetization zone is the same; the particle size of the main phase grain in the first transition zone, the second transition zone, the third transition zone and the fourth transition zone is the same.

[0075] Preferably, the particle size of the main phase grain in 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.

[0076] Preferably, the particle size of the surface layer main phase grain in the first easy demagnetization zone is 1-1.5 times that of the surface layer main phase grain in the non-easy demagnetization zone.

[0077] Preferably, the particle size of the surface layer main phase grain in the first easy demagnetization zone and the first transition zone is 1-1.5 times that of the central main phase grain.

[0078] Preferably, the particle size of the surface layer main phase grain in the non-easy demagnetization zone is 1-1.3 times that of the central main phase grain.

[0079] Preferably, the thickness of the main phase grain shell layer in the first easy demagnetization zone and the first transition zone is 1-5 times that of the main phase grain shell layer in the non-easy demagnetization zone.

[0080] Preferably, the particle size of the surface layer main phase grain in the first easy demagnetization zone and the first transition zone is the same, preferably 1-12 μm.

[0081] Preferably, the particle size of the surface layer main phase grain in the non-easy demagnetization zone is 1-8 μm.

[0082] In the present application, the surface layer means a surface perpendicular to the orientation direction, and the center means a median plane along the orientation direction.

[0083] In the present application, the main phase grain shell layer of the easy demagnetization region comprises a first inner shell layer and a first outer shell layer, the main phase grain shell layer of the transition region comprises a second inner shell layer and a second outer shell layer; and the main phase grain shell layer of the non-easy demagnetization region comprises a third inner shell layer.

[0084] In the present application, 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 is 80% or more of the total content of Tb and Dy elements; and 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 is 80% or more of the total content of Tb and Dy elements.

[0085] In the present application, the Tb diffusion weight gain of the first outer shell layer and the second outer shell layer preferably satisfies: the first outer shell layer ≥ the second outer shell layer.

[0086] In the present application, the Tb diffusion weight gain of the first outer shell layer is preferably 0.1wt%-0.9wt%, for example, 0.6wt%.

[0087] In the present application, the content of Tb in the first outer shell layer is preferably 0.1wt%-2.4wt%, for example, 0.6wt%.

[0088] In the present application, the Tb diffusion weight gain of the second outer shell layer is preferably 0.1wt%-0.8wt%, for example, 0.6wt% or 0.58wt%.

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

[0090] In the present application, the Dy diffusion weight gain of the first inner shell layer, the second inner shell layer and the third inner shell layer preferably satisfies: the third inner shell layer ≥ the second inner shell layer ≥ the first inner shell layer.

[0091] In the present application, the Dy diffusion weight gain of the first inner shell layer is preferably 0.1wt%-0.9wt%, for example, 0.5wt%, 0.6wt% or 0.7wt%.

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

[0093] In the present application, the Dy diffusion weight gain of the second inner shell layer is preferably 0.1wt%-0.9wt%, for example, 0.5wt%, 0.6wt%, 0.69wt% or 0.7wt%.

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

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

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

[0097] 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.

[0098] The thicknesses of the first inner shell layer and the first outer shell layer preferably satisfy: first outer shell layer≤first inner shell layer.

[0099] The thicknesses of the second inner shell layer and the second outer shell layer preferably satisfy: second outer shell layer≤second inner shell layer.

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

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

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

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

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

[0105] In the present application, the main phase grain shell layer of the non-easy demagnetization region further comprises a third outer shell layer.

[0106] The Tb diffusion weight gain in the third outer shell layer of the main phase grain shell layer of the non-easy demagnetization region is preferably 0-0.05wt%.

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

[0108] Preferably, the first shell layer > the second shell layer > the third shell layer.

[0109] Preferably, the thickness of the first shell layer > the second shell layer > the third shell layer.

[0110] Preferably, the thickness of the third inner shell layer > the third outer shell layer.

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

[0112] The present application also provides a preparation method of the Nd-Fe-B magnet, comprising the following steps: applying diffusion source Dy on the upper and lower surfaces of the Nd-Fe-B substrate along the Z-axis direction, applying diffusion source Tb on the four corner regions, and performing grain boundary diffusion parallel to the orientation direction, so as to obtain the Nd-Fe-B magnet; wherein the four corner regions form the reversible demagnetization region after the grain boundary diffusion.

[0113] 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 the grain boundary diffusion, and the utilization rate is generally 85%-95%, so that more amount of Dy or Tb is generally applied in the actual preparation process.

[0114] 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 diffusion amount of Dy or Tb is achieved.

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

[0116] In other embodiments, the diffusion source is a Dy-M alloy, and 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.

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

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

[0119] In some embodiments, the diffusion source is a Tb-M alloy, M comprises one or more of Cu, Al, Co, Ga, Zr and Ti. In some embodiments, the mass percentage of M in the Tb-M alloy is 0-40%, and is not 0.

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

[0121] In the present application, the diffusion source can be applied by conventional methods, for example, by coating.

[0122] In some embodiments, the coating is preferably spraying or printing. In some embodiments, the spraying is preferably performed at a dewaxing temperature of 200-400℃, and the printing is preferably performed at a dewaxing temperature of 100-500℃.

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

[0124] In some embodiments, the solvent is water, alcohol, ketone or ester.

[0125] In the present application, the heat treatment temperature in the grain boundary diffusion is preferably 750-950℃, for example, 900℃.

[0126] In the present application, the heat treatment time in the grain boundary diffusion is preferably 5-30h, for example, 25h.

[0127] In the present application, the heat treatment in the grain boundary diffusion is generally followed by aging treatment.

[0128] In some embodiments, the aging treatment temperature is preferably 300-600℃, for example, 490℃.

[0129] In some embodiments, the aging treatment time is preferably 1-10h, for example, 6h.

[0130] The present application also provides a use of the above-mentioned Nd-Fe-B magnet in magnetic steel.

[0131] On the basis of common sense in the art, the above-mentioned preferred conditions can be combined in any manner to obtain preferred examples of the present application.

[0132] The reagents and raw materials used in the present application are commercially available.

[0133] The positive progress effect of the present application is that:

[0134] The Nd-Fe-B magnet described in the present application comprises a transition zone, and by controlling the Tb content introduced by diffusion in the transition zone, the easy demagnetization zone and the non-easy demagnetization zone, and the matching of the Dy content of all zones, the problem of the performance of the interface zone presenting a gradient decline and causing the anti-demagnetization effect to weaken due to the Tb cross-zone interdiffusion caused by the difference in the Tb concentration gradient of the transition zone can be reduced, the decay of the surface magnetism and the magnetic flux of the Nd-Fe-B magnet can be reduced under the premise of ensuring the remanence of the Nd-Fe-B magnet, and the anti-demagnetization capability of the Nd-Fe-B magnet can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0135] Fig. 1 is a structural schematic diagram of each zone of the Nd-Fe-B magnet.

[0136] Fig. 2 is a structural schematic diagram of the main phase grain core and shell layer in each zone of the Nd-Fe-B magnet.

[0137] Fig. 3 is a scanning electron microscope image of the Nd-Fe-B magnet of Example 1.

[0138] Fig. 4 is a line scan image of the Cu content of the grain shell layer of Fig. 3.

[0139] Fig. 5 is a line scan image of the Al content of the grain shell layer of Fig. 3.

[0140] Fig. 6 is a line scan image of the Dy content of the grain shell layer of Fig. 3.

[0141] Fig. 7 is a line scan image of the Tb content of the grain shell layer of Fig. 3.

[0142] Fig. 8 is a line scan image of the Nd content of the grain shell layer of Fig. 3.

[0143] Fig. 9 is a schematic diagram of the diffusion weight gain distribution of Tb of the Nd-Fe-B magnet of Example 1 along the test line 1 and the test line 2 shown in Fig. 1.

[0144] Fig. 10 is a schematic diagram of the diffusion weight gain distribution of Dy of the Nd-Fe-B magnet of Example 1 along the test line 1 and the test line 2 shown in Fig. 1.

[0145] Figure legend: 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

[0146] The present application will be further described in the following examples, but the present application is not limited in the scope of the examples. The experimental methods not specified in the following examples are selected according to the conventional methods and conditions, or according to the product instructions.

[0147] Examples 1-5 and Comparative Examples 1-2

[0148] Spraying Dy on both surfaces of the Nd-Fe-B substrate along the Z-axis direction in the whole area of the two surfaces, spraying Tb in the four-corner area, the dewaxing temperature of spraying is 300℃, and the grain boundary diffusion parallel to the orientation direction is performed, thereby obtaining the Nd-Fe-B magnet; wherein the utilization rate of Dy or Tb in the diffusion source is 85%-95%.

[0149] wherein the temperature of heat treatment in the grain boundary diffusion is 850℃, the time of heat treatment is 25h, and the aging treatment is further included after the heat treatment, the temperature of the aging treatment is 490℃, and the time of the aging treatment is 6h.

[0150] wherein the parameters of each area of the Nd-Fe-B magnet of Examples 1-5 and Comparative Examples 1-2 are listed in Table 1, Table 2 and Table 3 below, and the element content of the Nd-Fe-B substrate used in Examples 1-5 and Comparative Examples 1-2 is shown in Table 4. Since the content of heavy rare earth metal in the substrate is 0, the diffusion weight gain of heavy rare earth in Examples 1-5 and Comparative Examples 1-2 is equal to its content.

[0151] The structural schematic diagram of the Nd-Fe-B magnet of Examples 1-5 and Comparative Examples 1-2 is shown in Figure 1, wherein the first easy demagnetization area 1, the second easy demagnetization area 5, the third easy demagnetization area 6 and the fourth easy demagnetization area 9 are all rectangular; the shape of the first transition area 2, the second transition area 4, the third transition area 7 and the fourth transition area 8 is L-shaped, and the non-easy demagnetization area 3 is cross-shaped; the thickness of the Nd-Fe-B magnet is 3mm, and the ratio of the length to the thickness is 3. Wherein the direction of the arrow M represents the magnetizing 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 structural schematic diagram 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. It can be seen that the shell layer of the main phase grain of the easy demagnetization area and the transition area all contains the inner shell layer and the outer shell layer, and the main phase grain of the non-easy demagnetization area only contains the inner shell layer. Figure 9 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. Figure 10 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.

[0152] Table 1. The diffusion weight gain of Dy and Tb in each area of the Nd-Fe-B magnet prepared by Examples 1-5 and Comparative Examples 1-2 and the Tb content ratio in the main phase grain shell layer of each area

[0153] Table 1 (continued)

[0154] Table 2. Coercivity ratio, zone width ratio and grain size of the main phase of the Nd-Fe-B magnets prepared in Examples 1-5 and Comparative Examples 1-2

[0155] 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 1-5 and Comparative Examples 1-2

[0156] Table 4. Mass concentration of each element in the base material of Examples 1-5 and Comparative Examples 1-2

[0157] Effect Example 1

[0158] The Nd-Fe-B magnets of Examples 1-5 and Comparative Examples 1-2 were subjected to the following tests, and the results are shown in Table 5.

[0159] 1. Coercivity test: The samples of Examples 1-5 and Comparative Examples 1-2 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℃).

[0160] 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 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.

[0161] 3. Remanence test: The Nd-Fe-B magnets of Examples 1-5 and Comparative Examples 1-2 were placed in a PFM-14 pulse magnetic performance measuring instrument of China Institute of Metrology to measure the remanence.

[0162] 4. The test method and test instrument of line scanning are as follows: the surface of the selected region of the magnet was microphotographed under the equipment EMMA, the equipment model is JEOL 8530f, the shooting magnification is X3000, and the two main phase grains were pulled and line scanned to characterize the distribution of Cu, Al, Dy, Tb and Nd, etc.

[0163] Table 5. Coercivity and demagnetization resistance of each zone of the magnets of Examples 1-5 and Comparative Examples 1-2 Note: in all the above tables, ① "easy demagnetization zone" means the first, second, third or fourth easy demagnetization zone; ② "transition zone" means the first, second, third or fourth transition zone.

[0164] As shown in Table 5, the ratio of the coercivity of the first transition zone to the first easy demagnetization zone of the Nd-Fe-B magnets prepared in Examples 1-5 is between (0.95-1):1, the difference of the coercivity between the first easy demagnetization zone and the non-easy demagnetization zone is between 2.6-3.9 kOe, and the demagnetization rate of the Nd-Fe-B magnets prepared in Examples 1-5 at 130°C is only 2.5%-6.1%, which indicates that the remanence of Examples 1-5 is more and the anti-demagnetization ability is excellent.

[0165] Fig. 3 is a scanning electron microscope image of the Nd-Fe-B magnet prepared in Example 1, and Figs. 4-8 are line scanning images of the content of each element on the shell layer based on Fig. 3. It can be seen that the content of Dy is higher than that of Tb in the grain shell layer of the Nd-Fe-B magnet.

[0166] The ratio of the Tb diffusion weight gain of the first transition zone to the first easy demagnetization zone of Comparative Example 1 is 0.5:1, which affects the content of Tb in the main phase grain shell layer in the transition zone, the thickness of the outer shell layer and the width of the transition zone, and other aspects are the same as those of Example 1. The demagnetization rate of the Nd-Fe-B magnet prepared in Comparative Example 1 at 130°C is 18%, which is higher than that of Example 1, indicating that the anti-demagnetization ability of Comparative Example 1 is worse than that of Example 1.

[0167] In Comparative Example 2, no Dy diffusion is performed in the easy demagnetization zone, the transition zone and the non-easy demagnetization zone, and Tb diffusion is performed in the transition zone and the easy demagnetization zone. The demagnetization rate of the Nd-Fe-B magnet prepared in Comparative Example 2 at 130°C is as high as 26.9%, which is much higher than that of Examples 1-5, indicating that the anti-demagnetization ability of Comparative Example 2 is worse than that of Examples.

[0168] The above-described examples are only better examples of the present application, which facilitate the 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 examples without creative labor and apply them to other examples. Therefore, the present application is not limited to the above-described examples, 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 the 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 heavy rare earth 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 first transition area and the first easy demagnetization area is (0.8-1):1; The content ratio of Tb in the non-easy demagnetization area and the first easy demagnetization area is (0-0.9):

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 (0.8-1):1, preferably (0.9-1):1, for example, 0.98:1 or 1:1; And / or, the content ratio of Tb in the first transition area and the first easy demagnetization area is (0.9-1):1, for example, 0.98:1 or 1:1; 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):1, for example, 0:1, 0.01:1, 0.02:1, 0.03:1 or 0.05:1; And / or, the content ratio of Tb in the non-easy demagnetization area and the first easy demagnetization area is (0-0.9):1, preferably (0-0.2):1, for example, 0:1, 0.01:1, 0.02:1, 0.03:1 or 0.05:1; And / or, the diffusion weight gain of Tb in the first easy demagnetization area is 0.1wt%-1wt%, for example, 0.6wt% or 0.58wt%; And / or, the content of Tb in the first easy demagnetization area is 0.1-2.5wt%, for example, 0.6wt% or 0.58wt%. and / or, the diffusion weight gain of Tb in the non-freely demagnetized region is 0.05wt% and below, such as 0, 0.006wt%, 0.012wt%, 0.018wt% or 0.029wt%; and / or, the content of Tb in the non-freely demagnetized region is 0-1.6wt%, such as 0, 0.006wt%, 0.012wt%, 0.018wt% or 0.029wt%; and / or, the diffusion weight gain of Tb in the transition region is 0.1wt%-1wt%, such as 0.588wt%, 0.57wt% or 0.58wt%; and / or, the content of Tb in the transition region is 0.1-2.5wt%, such as 0.588wt%, 0.57wt% or 0.58wt%; and / or, there is an interface A between the transition region and the freely demagnetized region, the interface A comprising first interface A, second interface A, third interface A and fourth interface A corresponding to the first transition region, the second transition region, the third transition region and the fourth transition region, the diffusion weight gain of Tb in the first interface A, the second interface A, the third interface A and the fourth interface A being the same; wherein the ratio of the diffusion weight gain of Tb in the first interface A to the first freely demagnetized region is preferably (0.95-1):1, such as 0.96:1, 0.98:1, 0.99:1 or 1:1; wherein the ratio of the content of Tb in the first interface A to the first freely demagnetized region is preferably (0.9-1):1, such as 0.96:1, 0.98:1, 0.99:1 or 1:1; and / or, there is an interface B between the transition region and the non-freely demagnetized region, the interface B comprising first interface B, second interface B, third interface B and fourth interface B corresponding to the first transition region, the second transition region, the third transition region and the fourth transition region, the diffusion weight gain of Tb in the first interface B, the second interface B, the third interface B and the fourth interface B being the same; wherein the ratio of the diffusion weight gain of Tb in the first interface B to the non-freely demagnetized region is preferably 1:(0-0.1), such as 1:0.02, 1:0.03, 1:0.04 or 1:0.05; wherein the ratio of the content of Tb in the first interface B to the first freely demagnetized region is (0.5-0.96):

1.

3. The neodymium-iron-boron magnet of claim 1, wherein, the coercivity of the first freely demagnetized region, the second freely demagnetized region, the third freely demagnetized region and the fourth freely demagnetized region is the same; and / or, the coercivity of the first transition region, the second transition region, the third transition region and the fourth transition region is the same; and / or, the coercivity of the first freely demagnetized region is not lower than the coercivity of the first transition region, and the coercivity of the first transition region is not lower than the coercivity of the non-freely demagnetized region; and / or, the ratio of the coercivity of the first transition region to the first freely demagnetized region is (0.95-1):1, such as 0.95:1, 0.97:1 or 0.98:1; and / or, the coercivity difference between the first demagnetization easy zone and the non-demagnetization easy zone is 0-10 kOe, for example, 2.6 kOe, 3 kOe, 3.2 kOe, 3.5 kOe or 3.9 kOe; and / or, the ratio of the coercivity of the non-demagnetization easy zone to the first demagnetization easy zone is (0.7-0.96):1, for example, 0.85:1, 0.87:1, 0.88:1 or 0.9:1; and / or, the remanence of the first demagnetization easy zone, the second demagnetization easy zone, the third demagnetization easy zone and the fourth demagnetization easy zone is the same; the remanence of the first transition zone, the second transition zone, the third transition zone and the fourth transition zone is the same; and / or, the ratio of the remanence of the first demagnetization easy zone to the non-demagnetization easy zone is (0.99-1):1, for example, 0.99:1 or 1:1; and / or, the ratio of the remanence of the first transition zone to the non-demagnetization easy zone is (0.99-1):1, for example, 1:1; and / or, in any plane perpendicular to the orientation direction, the shape of the first demagnetization easy zone, the second demagnetization easy zone, the third demagnetization easy zone and the fourth demagnetization easy zone is independently selected from a rectangle, a sector or a triangle; Preferably, the first demagnetization easy zone, the second demagnetization easy zone, the third demagnetization easy zone and the fourth demagnetization easy zone are all rectangles and have the same width; the width of the demagnetization easy zone refers to the distance extending along the X-axis or Y-axis from the edge of the Nd-Fe-B magnet; and / or, the width of the first transition zone, the second transition zone, the third transition zone and the fourth transition zone is the same; the width of the first transition zone refers to the distance between the interface of the first transition zone and the first demagnetization easy zone and the interface of the first transition zone and the non-demagnetization easy zone along the X-axis or Y-axis direction; and / or, the width ratio of the first transition zone to the Nd-Fe-B magnet is preferably (0-0.1):1, for example, 0.092:1, 0.093:1 or 0.094:1; and / or, the width ratio of the non-demagnetization easy zone to the Nd-Fe-B magnet is preferably (0.2-0.7):1, for example, 0.527:1; the width of the non-demagnetization easy zone refers to the distance extending along the X-axis or Y-axis from the interface of the transition zone and the non-demagnetization easy zone or the edge of the Nd-Fe-B magnet; and / or, the width ratio of the first demagnetization easy zone to the Nd-Fe-B magnet is preferably (0.05-0.4):1; and / or, the width of the first transition zone is preferably 0-1 mm and is not 0.

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 content of Tb in the main phase grain shell layer of the first demagnetization easy zone, the second demagnetization easy zone, the third demagnetization easy zone and the fourth demagnetization easy zone is the same; Preferably, the content of Tb in the main phase grain shell layer of the first transition zone, the second transition zone, the third transition zone and the fourth transition zone is the same; Preferably, the content of Tb in the main phase grain shell layer of the first demagnetization easy zone is not less than the content of Tb in the main phase grain shell layer of the first transition zone. Preferably, the ratio of the content of Tb in the main phase grain shell of the first transition zone to the content of Tb in the main phase grain shell of the first easy magnetization reversal zone is preferably (0.2-0.65):(0.2-0.65), for example 0.59:0.60, 0.58:0.59, 0.57:0.57, 0.57:0.60 or 0.60:0.60; Preferably, the ratio of the content of Tb in the main phase grain shell of the first transition zone to the content of Tb in the main phase grain shell of the first easy magnetization reversal zone is preferably (0.2-0.65):(0.2-0.65), for example 0.59:0.60, 0.58:0.59, 0.57:0.57, 0.57:0.60 or 0.60:0.60; Preferably, the thicknesses of the main phase grain shells of the first easy magnetization reversal zone, the second easy magnetization reversal zone, the third easy magnetization reversal zone and the fourth easy magnetization reversal zone are the same; Preferably, the thicknesses of the main phase grain shells of the first transition zone, the second transition zone, the third transition zone and the fourth transition zone are the same; Preferably, the thicknesses of the Re-rich grain boundaries of the first easy magnetization reversal zone, the second easy magnetization reversal zone, the third easy magnetization reversal zone and the fourth easy magnetization reversal zone are the same; Preferably, the thicknesses of the Re-rich grain boundaries of the first transition zone, the second transition zone, the third transition zone and the fourth transition zone are the same; Preferably, in the first easy magnetization reversal zone, the first transition zone and the non-easy magnetization reversal zone, the thicknesses of the main phase grain shells preferably satisfy: first easy magnetization reversal zone≥first transition zone≥non-easy magnetization reversal zone; Preferably, in the first easy magnetization reversal zone, the first transition zone and the non-easy magnetization reversal zone, the thicknesses of the Re-rich grain boundaries preferably satisfy: first easy magnetization reversal zone≥first transition zone≥non-easy magnetization reversal zone; Preferably, in the first easy magnetization reversal zone and the first transition zone, the thicknesses of the main phase grain shells are 0-4 μm, more preferably 0.5-1.5 μm; Preferably, in the non-easy magnetization reversal zone, the thickness of the main phase grain shell is 0-2 μm, more preferably 0.5-1 μm; Preferably, in the first easy magnetization reversal zone, the first transition zone and the non-easy magnetization reversal zone, the thicknesses of the Re-rich grain boundaries are all 0-1 μm, but not 0; Preferably, in the first easy magnetization reversal zone, the first transition zone and the non-easy magnetization reversal zone, the ratio of the thickness of the main phase grain shell to the thickness of the Re-rich grain boundary is (0.5-1.5):(0-1), but not 0.

5. The neodymium-iron-boron magnet of claim 4, wherein, The grain sizes of the main phase grains of the first easy magnetization reversal zone, the second easy magnetization reversal zone, the third easy magnetization reversal zone and the fourth easy magnetization reversal zone are the same; the grain sizes of the main phase grains of the first transition zone, the second transition zone, the third transition zone and the fourth transition zone are the same; And / or, the grain sizes of the main phase grains of the first easy magnetization reversal zone, the first transition zone and the non-easy magnetization reversal zone satisfy: first easy magnetization reversal zone≥first transition zone≥non-easy magnetization reversal zone; And / or, the grain size of the surface layer main phase grain of the first easy magnetization reversal zone is 1-1.5 times the grain size of the surface layer main phase grain of the non-easy magnetization reversal zone; And / or, the grain size of the surface layer main phase grain of the first easy magnetization reversal zone and the first transition zone is 1-1.5 times the grain size of the center main phase grain. And / or, the grain size of the surface layer main phase grain of the non-freely demagnetized region is 1-1.3 times of the grain size of the center main phase grain; And / or, the grain size of the surface layer main phase grain of the first freely demagnetized region and the first transition region is the same, preferably 1-12 μm; And / or, the grain size of the surface layer main phase grain of the non-freely demagnetized region is 1-8 μm.

6. The neodymium-iron-boron magnet of claim 1, wherein, The shell layer of the main phase grain of the freely demagnetized region includes a first inner shell layer and a first outer shell layer, the shell layer of the main phase grain of the transition region includes a second inner shell layer and a second outer shell layer; the shell layer of the main phase grain of the non-freely demagnetized region includes a third inner shell layer; 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; Wherein, the Tb diffusion weight gain in the first outer shell layer is preferably 0.1wt%-0.9wt%, for example 0.6wt%; Wherein, the content of Tb in the first outer shell layer is preferably 0.1wt%-2.4wt%, for example 0.6wt%; Wherein, the Tb diffusion weight gain in the second outer shell layer is preferably 0.1wt%-0.8wt%, for example 0.6wt% or 0.58wt%; Wherein, the content of Tb in the second outer shell layer is preferably 0.1wt%-2.3wt%, for example 0.6wt% or 0.58wt%; Wherein, the Dy diffusion weight gain of the first inner shell layer, the second inner shell layer and the third inner shell layer preferably satisfies: third inner shell layer≥second inner shell layer≥first inner shell layer; Wherein, the Dy diffusion weight gain in the first inner shell layer is preferably 0.1wt%-0.9wt%, for example 0.5wt%, 0.6wt% or 0.7wt%; Wherein, the content of Dy in the first inner shell layer is preferably 0.1-3.9wt%, for example 0.5wt%, 0.6wt% or 0.7wt%; Wherein, the Dy diffusion weight gain in the second inner shell layer is preferably 0.1wt%-0.9wt%, for example 0.5wt%, 0.6wt%, 0.69wt% or 0.7wt%; Wherein, the content of Dy in the second inner shell layer is preferably 0.1-3.9wt%, for example 0.5wt%, 0.6wt%, 0.69wt% or 0.7wt%; Wherein, the Dy diffusion weight gain in the third inner shell layer is preferably 0.1wt%-0.9wt%, for example 0.5wt%, 0.6wt% or 0.7wt%; Wherein, the content of Dy in the third inner shell layer is preferably 0.1-3.9wt%, for example 0.5wt%, 0.6wt% or 0.7wt%; Wherein, the thickness of the first inner shell layer, the second inner shell layer and the third inner shell layer preferably satisfies: third inner shell layer≥second inner shell layer≥first inner shell layer; Wherein, the thickness of the first inner shell layer and the first outer shell layer preferably satisfies: first outer shell layer≤first inner shell layer; Wherein, the thickness of the second inner shell layer and the second outer shell layer preferably satisfies: second outer shell layer≤second inner shell layer; The first inner shell layer preferably has a thickness of 0-2 μm, for example 1.8 μm, 1.9 μm or 2 μm; The first outer shell layer preferably has a thickness of 0-2 μm, for example 1.7 μm, 1.8 μm or 1.9 μm; The second inner shell layer preferably has a thickness of 0-2 μm, for example 1.8 μm, 1.9 μm or 2 μm; The second outer shell layer preferably has a thickness of 0-2 μm, for example 1.8 μm, 1.7 μm or 2 μm; The third inner shell layer preferably has a thickness of 0-2 μm, for example 1.8 μm, 1.9 μm or 2 μm.

7. The neodymium-iron-boron magnet of claim 6, wherein, The main phase grain shell of the non-freely demagnetized region further comprises a third outer shell layer; 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 0-0.05 wt%; The third outer shell layer of the main phase grain shell of the non-freely demagnetized region preferably has a Tb content of 0 wt%-1.6 wt%; 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 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 thickness; 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 in terms of thickness; The third outer shell layer of the main phase grain shell of the non-freely demagnetized region preferably has a thickness of 0-0.5 μm.

8. A method of producing a neodymium-iron-boron magnet as claimed in any one of claims 1 to 7, characterized in that It comprises the following steps: applying diffusion source Dy on both upper and lower surfaces of the Nd-Fe-B substrate along the Z-axis direction, applying diffusion source Tb on the four corner regions, and performing grain boundary diffusion parallel 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.

9. The method of producing a neodymium-iron-boron magnet according to claim 8, characterized by, 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; the dewaxing temperature of the printing is preferably 100-500 °C; The heat treatment in the grain boundary diffusion has a temperature of 750-950 °C, for example 900 °C; The heat treatment in the grain boundary diffusion has a time of 5-30 h, for example 10 h; The heat treatment in the grain boundary diffusion is generally followed by aging treatment; The aging treatment has a temperature of 300-600 °C, for example 500 °C; The aging treatment has a time of 1-10 h, for example 3 h.

10. Use of the Nd-Fe-B magnet according to any one of claims 1-7 in a magnetic steel.

Images