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

Abstract

Disclosed in the present invention are a neodymium-iron-boron magnet, and a preparation method therefor and an application thereof. The neodymium-iron-boron magnet in the present invention comprises a first demagnetization-prone region, a first transition region, a non-demagnetization-prone region, a second transition region and a second demagnetization-prone region, which are sequentially distributed in a direction perpendicular to an orientation direction, wherein the first demagnetization-prone region, the second demagnetization-prone region, the non-demagnetization-prone region, the first transition region and the second transition region are all rectangular. In the present invention, by means of controlling the cooperation of the contents of Tb and Dy introduced by means of diffusion in transition regions, demagnetization-prone regions and non-demagnetization-prone regions, cross-region inter-diffusion of Tb or Dy caused by a concentration gradient difference of Tb in the transition region can be reduced. Moreover, in the present invention, the demagnetization-prone regions, the non-demagnetization-prone regions and the transition regions are all configured to be rectangular, such that the demagnetization resistance of four corners and long edges of a neodymium-iron-boron magnet can be improved.

Description

A neodymium iron boron magnet and its preparation method and application Technical Field

[0001] The invention relates to a neodymium iron boron magnet and a preparation method and application thereof. Background Art

[0002] Since its introduction, neodymium iron boron (NdFeB) permanent magnets have been widely used in automotive, wind power, home appliances, industrial robotics, and other fields. Due to the varying operating conditions in each field, the performance requirements for magnetic steel used in these fields also vary. In recent years, with the booming development of new energy vehicles, the demand for magnetic steel in the main drive motors has increased dramatically. Since the normal operating temperature of main drive motors is primarily concentrated in the 120-180°C range, NdFeB requires higher coercivity and thermal stability. To improve the temperature resistance of rare earth permanent magnets, large amounts of heavy rare earths (Dy and Tb) are typically added to increase the main phase magnetocrystalline anisotropy field. However, the scarcity and high price of heavy rare earth resources have severely restricted the application of NdFeB magnets in various industries.

[0003] With the increasing demand for high-performance magnets, grain boundary diffusion (GBD) technology has gradually become well-known and accepted. Conventional GBD uses a physical vapor deposition method to deposit a diffusion source on the magnet surface. The source is then infiltrated into the magnet's interior along the grain boundaries under high temperature and pressure. The greatest advantage of this technique is that it significantly increases coercivity while maintaining virtually unchanged remanence, using only a small amount of heavy rare earth elements.

[0004] In terms of the effective utilization rate of heavy rare earths, traditional grain boundary diffusion products have been greatly improved compared with non-grain boundary diffusion products. However, in order to further improve the utilization rate of heavy rare earths, reduce unnecessary waste of heavy rare earths, and at the same time to make the diffusion area more accurate and evaluated, another purpose of the present invention is to use electromagnetic simulation of neodymium iron boron under the main drive motor working conditions to identify the easily demagnetized and non-easy demagnetization areas. We found that the easily demagnetized areas all appear near the corners of the rotor air gap, while the demagnetization is not obvious in the area near the rotor and the middle of the magnetic steel. Therefore, for the easily demagnetized areas, high-performance magnets with the same remanence are bonded with low-performance magnets with the same remanence in the non-easy demagnetization areas to prepare the required combined magnets, thereby saving the use of heavy rare earths in the non-easy demagnetization areas.

[0005] In the actual use of NdFeB magnets, the performance requirements for each part of the magnet vary. For example, in motors, the reverse magnetic field generated when the motor coil is energized is not uniform. Therefore, the NdFeB magnet will have an easily demagnetized region, a non-demagnetized region, and a transition region between the easy and non-demagnetized regions. Due to the performance characteristics of these regions, the coercivity of each region must be matched to ensure that the coercivity of the easily demagnetized and transition regions is high while the non-demagnetized region does not experience surface magnetism and flux attenuation. At the same time, the remanence in the transition and non-demagnetized regions is the highest.

[0006] Summary of the Invention

[0007] In order to solve the defects in the prior art, the present invention provides a neodymium iron boron material and its preparation method and application. The material can improve the anti-demagnetization ability of the neodymium iron boron magnet by coordinating the HRE content between the easy demagnetization zone, the transition zone and the non-demagnetization zone.

[0008] The present invention mainly solves the above technical problems through the following technical solutions.

[0009] The present invention provides a neodymium iron boron magnet, comprising a first easily demagnetized region, a first transition region, a non-easily demagnetized region, a second transition region, and a second easily demagnetized region, which are sequentially distributed along a direction perpendicular to an orientation direction; the first easily demagnetized region, the second easily demagnetized region, the non-easily demagnetized region, the first transition region, and the second transition region are all rectangular;

[0010] The Tb diffusion weight gain of the first easily demagnetized region and the second easily demagnetized region is the same; the Dy diffusion weight gain of the first easily demagnetized region and the second easily demagnetized region is the same;

[0011] The Tb diffusion weight gain of the first transition zone and the second transition zone is the same; the Dy diffusion weight gain of the first transition zone and the second transition zone is the same;

[0012] The Tb diffusion weight gain ratio between the first transition region and the first easily demagnetized region is (0.8-1):1;

[0013] The Tb diffusion weight gain ratio between the center of the non-demagnetization-prone region and the first demagnetization-prone region is (0-0.05): (0.3-1);

[0014] The Dy diffusion weight gain ratio of the first easily demagnetized region to the non-easily demagnetized region is (0-0.05):(0.3-1).

[0015] In the present invention, the diffusion weight gain means the percentage of the mass of Tb or Dy introduced into a certain area by diffusion to the total mass of the magnet in that area. For example, the Tb diffusion weight gain in the first easily demagnetized zone means the percentage of the mass of Tb introduced into the first easily demagnetized zone by diffusion to the total mass of the magnet in the first easily demagnetized zone.

[0016] In the present invention, the center of the non-demagnetizable region is defined as: a central cross section of the non-demagnetizable region along the distribution direction of each region.

[0017] In the present invention, the Dy diffusion weight gain ratio of the first transition region to the non-demagnetizable region may be (0.05-0.9):1, preferably (0.14-0.90):1, for example 0.25:1.

[0018] In the present invention, the Dy diffusion weight gain ratio of the first transition region to the first easily demagnetized region may be (0-0.05):(0.05-0.9). Preferably, the Dy diffusion weight gain of the first transition region is 0.

[0019] In the present invention, the Dy diffusion weight gain in the first easily demagnetized region may be 0.05 wt % or less, for example, 0.

[0020] In the present invention, the Dy diffusion weight gain in the first transition zone may be 0.05wt%-0.9wt%, preferably 0.1wt%-0.45wt%.

[0021] In the present invention, the Dy diffusion weight gain in the non-demagnetizable region may be 0.1 wt%-1 wt%, preferably 0.4 wt%-0.7 wt%, for example 0.5 wt%.

[0022] In the present invention, the Tb diffusion weight gain in the first easily demagnetized region is preferably higher than the Tb diffusion weight gain in the first transition region.

[0023] In the present invention, the Tb diffusion weight gain in the first transition region is preferably higher than the Tb diffusion weight gain in the center of the non-demagnetizable region.

[0024] In the present invention, the Tb diffusion weight gain ratio between the first transition region and the first easily demagnetized region is preferably (0.9-1):1, for example, 0.68:0.7.

[0025] In the present invention, the Tb diffusion weight gain ratio between the center of the non-demagnetizable region and the first demagnetizable region is preferably 0:0.7.

[0026] In the present invention, the Tb diffusion weight gain in the first easily demagnetized region may be 0.1 wt%-1 wt%, preferably 0.3 wt%-0.7 wt%, for example 0.7 wt%.

[0027] In the present invention, the Tb diffusion weight gain in the center of the non-demagnetizable region may be 0.05 wt % or less, for example, 0.

[0028] In the present invention, the Tb diffusion weight gain in the first transition zone may be 0.1 wt%-1 wt%, preferably 0.24 wt%-0.7 wt%, for example 0.68 wt% or 0.7 wt%.

[0029] In the present invention, a first interface is formed between the first transition region and the first easily demagnetized region, and a second interface is formed between the second transition region and the second easily demagnetized region.

[0030] The Tb diffusion weight gain in the first interface and the second interface is the same, and the Tb diffusion weight gain ratio between the first interface and the first easily demagnetized region is preferably (0.9-1):1.

[0031] The Dy mass concentration in the first interface and the second interface is the same, and the Dy diffusion weight gain ratio between the first interface and the first easily demagnetized region is preferably 1:(0-0.05), more preferably 1:0.

[0032] In the present invention, a third interface is formed between the first transition region and the non-demagnetizable region, and a fourth interface is formed between the second transition region and the non-demagnetizable region.

[0033] The Dy diffusion weight gain in the third interface is the same as that in the fourth interface, and the Dy diffusion weight gain ratio between the third interface and the non-easily demagnetized region is preferably (0.3-1):1.

[0034] The Tb diffusion weight gain in the third interface is the same as that in the fourth interface, and the Tb diffusion weight gain ratio between the third interface and the center of the non-demagnetizable region is preferably 1:(0-0.05), more preferably 1:0.

[0035] In the present invention, the NdFeB magnet can be represented by the chemical formula R1-R2-TBM, wherein R1 includes one or more of Pr, Nd, Ce, Er, Tm, Y, Lu, Gd and Ho; R2 is Dy and / or Tb 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 the M element contains one or more of Cu, Al, Co, Ga, Zr and Ti.

[0036] In some embodiments, the M elements are all derived from a NdFeB matrix.

[0037] In other embodiments, the M element includes M element introduced by diffusion, wherein the mass percentage of the M element introduced by diffusion in the NdFeB magnet is preferably 0%-0.4%.

[0038] In some preferred embodiments, the coercive forces of the first easily demagnetized region and the second easily demagnetized region are the same, and the coercive forces of the first transition region and the second transition region are the same.

[0039] The coercive force of the first easily demagnetized region is greater than or equal to the coercive force of the first transition region and greater than or equal to the coercive force of the non-easily demagnetized region.

[0040] The coercive force ratio of the first transition region to the first easily demagnetized region is preferably (0.95-1):1, more preferably (0.98-1):1, for example 0.99:1.

[0041] The coercive force difference between the first easily demagnetized region and the non-easily demagnetized region is preferably 0-10 kOe, more preferably 2-5 kOe, for example, 2.5 kOe or 4 kOe.

[0042] The coercive force ratio of the non-easily demagnetized region to the first easily demagnetized region is preferably (0.7-0.96):1, more preferably (0.8-0.9):1, for example 0.85:1.

[0043] In some preferred embodiments, the remanence of the first easily demagnetized region is the same as the remanence of the second easily demagnetized region, and the remanence of the first transition region is the same as the remanence of the second transition region.

[0044] The remanence ratio of the first easily demagnetized region to the non-easily demagnetized region is preferably (0.99-1):1.

[0045] The remanence ratio of the first transition region to the non-demagnetizable region is preferably (0.99-1):1.

[0046] In some preferred embodiments, the width of the first easily demagnetized region is the same as the width of the second easily demagnetized region, and the width of the first transition region is the same as the width of the second transition region. The width refers to the length extending perpendicular to the orientation direction.

[0047] The width ratio of the first transition region to the NdFeB magnet is preferably (0-0.1):1, for example, 0.093:1.

[0048] The width ratio of the non-demagnetized region to the NdFeB magnet is preferably (0.2-0.7):1.

[0049] The width ratio of the first easily demagnetized region to the NdFeB magnet is preferably (0.05-0.4):1.

[0050] The width of the first transition zone and the second transition zone is preferably 0-1 mm, and is not 0.

[0051] In some preferred embodiments, the grain size of the main phase grains in the first easily demagnetized zone is the same as the grain size of the main phase grains in the second easily demagnetized zone; the grain size of the main phase grains in the first transition zone is the same as the grain size of the main phase grains in the second transition zone; wherein the ratio of the grain sizes of the main phase grains in the first easily demagnetized zone, the first transition zone and the non-easy demagnetized zone is preferably 1:1:1.

[0052] In some preferred embodiments, the particle sizes of the surface main phase grains in the first easily demagnetized zone, the first transition zone and the non-easy demagnetized zone are the same; the particle sizes of the central main phase grains in the first easily demagnetized zone, the first transition zone and the non-easy demagnetized zone are the same; wherein, in the first easily demagnetized zone, the first transition zone and the non-easy demagnetized zone, the particle sizes of the surface main phase grains are preferably 1-1.5 times the particle sizes of the central main phase grains.

[0053] The surface layer means the surface perpendicular to the orientation direction, and the center means the median plane along the orientation direction.

[0054] The particle size of the main phase grains in the surface layer of the first easily demagnetized region is preferably 1-12 μm.

[0055] The particle size of the main phase grains in the surface layer of the first transition zone is preferably 1-12 μm.

[0056] The particle size of the main phase grains in the surface layer of the non-easily demagnetized region is preferably 1-12 μm.

[0057] In some preferred embodiments, in the first easily demagnetized zone, the first transition zone and the non-easily demagnetized zone, the main phase grain core and the main phase grain shell meet the following conditions: the R1 content in the main phase grain core is greater than or equal to the R1 content in the main phase grain shell; the R2 content in the main phase grain core is less than the R2 content in the main phase grain shell.

[0058] The R2 content in the main phase grain shells of the first easily demagnetized region, the first transition region, and the non-easily demagnetized region preferably satisfies the following conditions:

[0059] When R2 is Tb, the first easily demagnetized region ≥ the first transition region > the non-easily demagnetized region.

[0060] When R2 is Dy, the non-demagnetization region ≥ the first transition region > the first demagnetization region.

[0061] In the present invention, the grain boundary structure of the magnet includes Re2Fe 14 B main phase grains and Re-rich phase grain boundaries; the Re2Fe 14 The B main phase grains include a main phase grain shell; and the Re is Dy and / or Tb.

[0062] The main phase grain shell has the same meaning as that 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, ie, the grain boundary region between two particles with Re>95%.

[0063] In some preferred embodiments, the thickness of the main phase grain shell of the first easily demagnetized zone is the same as the thickness of the main phase grain shell of the second easily demagnetized zone; the thickness of the main phase grain shell of the first transition zone is the same as the thickness of the main phase grain shell of the second transition zone; the thickness of the Re-rich grain boundary of the first easily demagnetized zone is the same as the thickness of the Re-rich grain boundary of the second easily demagnetized zone; the thickness of the Re-rich grain boundary of the first transition zone is the same as the thickness of the Re-rich grain boundary of the second transition zone.

[0064] In the first easily demagnetized region, the thickness of the main phase grain shell is preferably 0-4 μm, more preferably 0-2 μm; the thickness of the Re grain boundary is preferably 0-1 μm, but not 0; and the ratio of the thickness of the main phase grain shell to the thickness of the Re-rich grain boundary is preferably (0-2.0):(0-1), but not 0. For example, when the thickness of the main phase grain shell in the first easily demagnetized region is 1 μm, the thickness of the Re-rich grain boundary may be 0.2 μm.

[0065] In the first transition zone, the thickness of the main phase grain shell is preferably 0-4 μm, more preferably 0-2 μm; the thickness of the Re-rich grain boundary is preferably 0-1 μm, but not 0; and the ratio of the thickness of the main phase grain shell to the thickness of the Re-rich grain boundary is preferably (0-2.0):(0-1), but not 0. For example, when the thickness of the main phase grain shell in the first transition zone is 1 μm, the thickness of the Re-rich grain boundary may be 0.2 μm.

[0066] In the non-easily demagnetized region, the thickness of the main phase grain shell is preferably 0-4 μm, more preferably 0-2 μm; the thickness of the Re-rich grain boundary is preferably 0-1 μm, but not 0; and the ratio of the thickness of the main phase grain shell to the thickness of the Re-rich grain boundary is preferably (0-2.0):(0-1), but not 0. For example, when the thickness of the main phase grain shell in the non-easily demagnetized region is 1 μm, the thickness of the Re-rich grain boundary can be 0.2 μm.

[0067] The present invention also provides a method for preparing the NdFeB magnet, which comprises the following steps: applying a diffusion source on the upper surface of the first easily demagnetized region, the first transition region, the non-easily demagnetized region, the second transition region, and the second easily demagnetized region distributed perpendicular to the orientation direction of the NdFeB substrate, and performing grain boundary diffusion parallel to the orientation direction to obtain the NdFeB magnet; the diffusion source contains Dy and / or Tb.

[0068] In the present invention, those skilled in the art know that during grain boundary diffusion, Dy or Tb in the diffusion source is not completely diffused into the magnet, and its utilization rate is generally 85%-95%. Therefore, in the actual preparation process, a larger amount of Dy or Tb is generally applied.

[0069] In some preferred embodiments, the preparation method of the NdFeB magnet preferably includes the following steps: applying a Tb diffusion source on the upper surface of the first easily demagnetized region and the second easily demagnetized region, applying a Dy diffusion source on the upper surface of the non-easily demagnetized region, and performing grain boundary diffusion parallel to the orientation direction to obtain the NdFeB magnet.

[0070] In the above preferred embodiment, during the diffusion process, a Tb diffusion source is applied only to the upper surfaces of the first easily demagnetized region and the second easily demagnetized region, and no Tb diffusion source is applied to the non-easy demagnetized region. However, after diffusion, a small amount of Tb applied to the first easily demagnetized region and the second easily demagnetized region may diffuse toward the center of the non-easy demagnetized region. After diffusion, the Tb is mainly distributed at the junction of the easily demagnetized region and the non-easy demagnetized region, and the Tb content in the center of the non-easy demagnetized region is relatively low.

[0071] In the present invention, it is known to those skilled in the art that different grain boundary diffusion methods will result in different coating thicknesses when diffusing the same amount of Dy or Tb into the magnet. Therefore, in the actual preparation process, the coating thickness is not limited as long as the corresponding Dy or Tb diffusion amount is achieved.

[0072] In some embodiments, the diffusion source is pure Dy.

[0073] In other embodiments, the diffusion source is a Dy-M alloy, where M comprises one or more of Cu, Al, Co, Ga, Zr, and Ti, wherein the mass percentage of M in the Dy-M is 0-40% and is not 0.

[0074] In other embodiments, the diffusion source is Dy hydride or Dy fluoride.

[0075] In some embodiments, the diffusion source is pure Tb.

[0076] In other embodiments, the diffusion source is a Tb-M alloy, where M comprises one or more of Cu, Al, Co, Ga, Zr, and Ti, wherein the mass percentage of M in the Tb-M is 0-40% and is not 0.

[0077] In other embodiments, the diffusion source is Tb hydride or Tb fluoride.

[0078] In some embodiments, the diffusion source is pure Tb.

[0079] In other embodiments, the diffusion source is a Tb-M alloy, where M comprises one or more of Cu, Al, Co, Ga, Zr, and Ti, wherein the mass percentage of M in the Tb-M is 0-40% and is not 0.

[0080] In other embodiments, the diffusion source is Tb hydride or Tb fluoride.

[0081] In the present invention, the diffusion source can be applied by conventional methods in the art, such as coating.

[0082] The coating method 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.

[0083] When the diffusion source is applied in the coating manner, the diffusion source is generally mixed with a solvent and a binder in a certain proportion to form a slurry.

[0084] The solvent is, for example, water, alcohol, ketone or ester.

[0085] In a preferred embodiment of the present invention, the diffusion source is applied by coating. The mass concentration of Dy in the diffusion source used in the non-demagnetized region is preferably 0.3%-1%; the mass concentration of Tb in the diffusion source used in the easily demagnetized region is preferably 0.3%-1.2%; the mass concentration of Tb in the diffusion source used in the first transition region is preferably 0.3%-1.2%; and the mass concentration of Dy is preferably 0.3%-1%. The percentages are the mass percentages of Dy or Tb in the diffusion source.

[0086] In the present invention, the temperature of the heat treatment during the grain boundary diffusion is preferably 750-950°C, for example, 900°C.

[0087] In the present invention, the heat treatment time in the grain boundary diffusion is preferably 5 to 30 hours, for example, 10 hours.

[0088] In the present invention, the heat treatment in the grain boundary diffusion process generally includes an aging treatment.

[0089] The aging treatment temperature is preferably 300-600°C, for example 500°C.

[0090] The aging treatment time is preferably 1 to 10 hours, for example, 3 hours.

[0091] The present invention also provides a NdFeB magnet produced by the above-mentioned NdFeB magnet production method.

[0092] The present invention also provides an application of the above-mentioned NdFeB magnet in magnetic steel.

[0093] On the basis of conforming to the common sense in this field, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0094] The reagents and raw materials used in the present invention are commercially available.

[0095] The positive progress effect of the present invention is:

[0096] The NdFeB magnet described in the present invention includes a transition zone, and by controlling the coordination of the Tb and Dy contents introduced by diffusion in the transition zone, the easily demagnetized zone, and the non-easy demagnetized zone, it is possible to reduce the cross-zone mutual diffusion of Tb or Dy caused by the Tb concentration gradient difference in the transition zone, thereby reducing the gradient drop in the performance of the interface zone and the weakening of the anti-demagnetization effect. While ensuring the remanence of the NdFeB magnet, it is possible to reduce the attenuation of the surface magnetism and magnetic flux of the NdFeB magnet, thereby improving the anti-demagnetization ability of the NdFeB magnet. In addition, the present invention sets the easily demagnetized zone, the non-easy demagnetized zone, and the transition zone to be rectangular, which can improve the anti-demagnetization ability of the four corners and long sides of the NdFeB magnet. BRIEF DESCRIPTION OF THE DRAWINGS

[0097] Figure 1 is a schematic diagram of the structure of each area of ​​the NdFeB magnet.

[0098] FIG2 is a schematic diagram of the structure of the core and shell of the main phase grains in each region of the NdFeB magnet.

[0099] FIG3 is a scanning electron microscope image of the easily demagnetized region of NdFeB in Example 3.

[0100] FIG. 4 is a line scan diagram of the Dy content in the grain shell of FIG. 3 .

[0101] FIG. 5 is a line scan diagram of the Tb content in the grain shell of FIG. 3 .

[0102] FIG. 6 is a line scan diagram of the Nd content in the grain shell of FIG. 3 .

[0103] FIG7 is a scanning electron microscope image of the non-demagnetized area of ​​NdFeB in Example 3.

[0104] FIG. 8 is a line scan diagram of the Dy content in the grain shell of FIG. 7 .

[0105] FIG. 9 is a line scan diagram of the Tb content in the grain shell of FIG. 7 .

[0106] FIG. 10 is a line scan diagram of the Nd content in the grain shell of FIG. 7 .

[0107] FIG11 is a scanning electron microscope image of the NdFeB transition region of Example 3.

[0108] FIG. 12 is a line scan diagram of the Dy content in the grain shell of FIG. 11 .

[0109] FIG. 13 is a line scan diagram of the Tb content in the grain shell of FIG. 11 .

[0110] FIG. 14 is a line scan diagram of the Nd content in the grain shell of FIG. 11 .

[0111] Reference numerals: 1 - first easily demagnetized region, 2 - first transition region, 3 - non-easily demagnetized region, 4 - second transition region, 5 - second easily demagnetized region, 6 - main phase grain shell, 7 - main phase grain core. DETAILED DESCRIPTION

[0112] The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the examples. Experimental methods in the following examples where specific conditions are not specified were performed according to conventional methods and conditions, or selected according to the product specifications.

[0113] Examples 1-3 and Comparative Examples 1-2

[0114] A diffusion source is applied to a first easily demagnetized region, a first transition region, a non-easily demagnetized region, a second transition region, and a second easily demagnetized region of a neodymium iron boron substrate, which are distributed perpendicular to the orientation direction, and grain boundary diffusion is performed parallel to the orientation direction to obtain the neodymium iron boron magnet; the diffusion source contains Dy and / or Tb; wherein the utilization rate of Dy or Tb in the diffusion source is 85%-95%.

[0115] The heat treatment temperature in the grain boundary diffusion is 900° C., and the heat treatment time is 10 h. After the heat treatment, an aging treatment is also included. The aging treatment temperature is 500° C., and the aging treatment time is 3 h.

[0116] The parameters of each region of the NdFeB magnets of Examples 1-3 and Comparative Examples 1-2 are listed in Tables 1-2 below, and the element contents of the NdFeB substrates used in Examples 1-3 and Comparative Examples 1-2 are shown in Table 3.

[0117] The structural schematic diagrams of the NdFeB magnets of Examples 1-3 and Comparative Examples 1-2 are shown in Figures 1 and 2, wherein the direction of the arrow M represents the magnetization direction of the NdFeB magnet, and the direction of the arrow P represents the orientation direction of the NdFeB magnet; the A surface represents the surface layer of the NdFeB magnet, and the B surface represents the middle layer of the NdFeB magnet.

[0118] Table 1 Dy and Tb diffusion weight gain in each area of ​​Examples 1-3 and Comparative Examples 1-2

[0119] Table 2 Coercive force ratio of each region and width ratio of transition region to NdFeB magnet of Examples 1-3 and Comparative Examples 1-2

[0120] Table 3 Mass concentration of each element in the substrate of Examples 1-3 and Comparative Examples 1-2

[0121] Effect Example 1

[0122] The following tests were performed on the NdFeB magnets of Examples 1-3 and Comparative Examples 1-3:

[0123] 1. Coercive force test: Samples of Examples 1-3 and Comparative Examples 1-3 were prepared with sample specifications of W2~3±0.1*L19±0.1*T4±0.1mm. Two samples were stacked for testing. Coils with dimensions of W3*L19~20*T2.7mm were used in a permanent magnet precision measurement system NIM-62000 for room temperature testing (temperature ≤200°C).

[0124] 2. Demagnetization Rate Test: Using electromagnetic simulation software (Ansys Workbench), we set the motor speed to 1300 rpm and then adjusted the temperature to the corresponding operating temperature. We then collected back-EMF data and observed changes in the magnet cloud over the same period of time to determine if the magnet was demagnetized. The demagnetization rate is calculated using the formula: Demagnetization Rate = (High-Temperature Back-EMF - Room-Temperature Back-EMF) / Room-Temperature Back-EMF.

[0125] 3. The testing method and instrument for line scan images are as follows: the surface of the magnet in the selected area is microscopically photographed under the EMMA equipment. The equipment model is JEOL 8530f, and the shooting magnification is X3000. The two main phases are subjected to line scanning to characterize the distribution of elements such as Dy / Nd.

[0126] The technical effects of Examples 1-3 and Comparative Examples 1-2 are listed in Table 4 below:

[0127] Table 4 Coercive force and anti-demagnetization ability of each region in the magnets of Examples 1-3 and Comparative Examples 1-2 Note: ① “First demagnetization zone / second easy demagnetization zone” in the table means the first easy demagnetization zone or the second easy demagnetization zone; ② “First transition zone / second transition zone” in the table means the first transition zone or the second transition zone.

[0128] As can be seen from the above table, the coercive force ratio of the first transition zone to the first easily demagnetized zone of the NdFeB magnets prepared in Examples 1-3 is between (0.97-0.99):1, and the coercive force difference between the first easily demagnetized zone and the non-easily demagnetized zone is between 2.5-5 kOe, which shows excellent anti-demagnetization ability. The demagnetization rate of the NdFeB magnets of Examples 1-3 at 130°C is only 4.3%-8.1%.

[0129] Figures 3-6 show that the Tb content is higher than the Dy content in the main phase grain shells and Re-rich grain boundaries in the easily demagnetized region of Example 3. Figures 7-10 show that the Dy content is higher than the Tb content in the main phase grain shells and Re-rich grain boundaries in the non-easily demagnetized region of Example 3. Figures 11-14 show that the main phase grain shells and Re-rich grain boundaries in the transition region of Example 3 contain both Dy and Tb.

[0130] The Tb diffusion weight gain ratio of the first transition zone and the first easily demagnetized zone in Comparative Example 1 is too low, specifically 0.14:1. The coercive force ratio of the first transition zone and the first easily demagnetized zone of the NdFeB magnet in Comparative Example 1 is approximately 0.9:1, and the coercive force difference between the first easily demagnetized zone and the non-easily demagnetized zone is 2.5 kOe. The NdFeB magnet obtained in Comparative Example 1 has poor anti-demagnetization ability, and its demagnetization rate at 130°C is 10%, which is higher than that of Examples 1-3.

[0131] The Tb diffusion weight gain ratio of the first transition zone and the first easily demagnetized zone in Comparative Example 2 is too low, specifically 0.6:1, and the Dy diffusion weight gain in the transition zone and the non-easy demagnetization zone is 0. The coercive force ratio of the first transition zone and the first easily demagnetized zone of the NdFeB magnet prepared therefrom is 0.92:1, and the coercive force difference between the first easily demagnetized zone and the non-easy demagnetization zone is 11.5 kOe. The NdFeB magnet prepared in Comparative Example 2 has poor anti-demagnetization ability, and its demagnetization rate at 130°C is as high as 38.5%, which is much higher than that of Examples 1-3.

[0132] The embodiments described above are merely preferred embodiments of the present invention, intended to facilitate understanding and application of the present invention by those skilled in the art. Obviously, anyone skilled in the art can modify or alter these embodiments without inventive effort and apply them to other embodiments. Therefore, the present invention is not limited to the embodiments described above; any equivalent variations, simple modifications, and modifications made within the scope of the present invention remain within the scope of the present invention.

Claims

1. A neodymium iron boron magnet, characterized in that: The NdFeB magnet comprises a first easily demagnetized region, a first transition region, a non-easy demagnetized region, a second transition region, and a second easily demagnetized region, which are sequentially distributed along a direction perpendicular to the orientation direction; the first easily demagnetized region, the second easily demagnetized region, the non-easy demagnetized region, the first transition region, and the second transition region are all rectangular; The Tb diffusion weight gain of the first easy demagnetization region and the second easy demagnetization region is the same; the Dy diffusion weight gain of the first easy demagnetization region and the second easy demagnetization region is the same; The Tb diffusion weight gain of the first transition zone and the second transition zone is the same; the Dy diffusion weight gain of the first transition zone and the second transition zone is the same; The Tb diffusion weight gain ratio between the first transition region and the first easily demagnetized region is (0.8-1):1; The Tb diffusion weight gain ratio between the center of the non-demagnetization-prone region and the first demagnetization-prone region is (0-0.05): (0.3-1); The Dy diffusion weight gain ratio of the first easily demagnetized region to the non-easily demagnetized region is (0-0.05): (0.3-1).

2. The NdFeB magnet according to claim 1, wherein: The Dy diffusion weight gain ratio of the first transition zone to the non-demagnetization-prone zone is (0.05-0.9):1, preferably (0.14-0.90):1, for example 0.25:1; And / or, the Dy diffusion weight gain ratio of the first transition zone to the first easily demagnetized zone is (0-0.05): (0.05-0.9), preferably, the Dy diffusion weight gain of the first transition zone is 0; and / or, the Dy diffusion weight gain in the first easily demagnetized region is 0.05wt% or less, for example, 0; and / or, the Dy diffusion weight gain in the first transition zone is 0.05wt%-0.9wt%, preferably 0.1wt%-0.45wt%; And / or, the Dy diffusion weight gain of the non-demagnetizable region is 0.1wt%-1wt%, preferably 0.4wt%-0.7wt%, for example 0.5wt%; and / or, the Tb diffusion weight gain in the first easily demagnetized region is higher than the Tb diffusion weight gain in the first transition region; and / or, the Tb diffusion weight gain in the first transition region is higher than the Tb diffusion weight gain in the center of the non-demagnetization-prone region; And / or, the Tb diffusion weight gain ratio between the first transition region and the first easily demagnetized region is preferably (0.9-1):1, for example, 0.68:0.7; And / or, the Tb diffusion weight gain ratio between the center of the non-demagnetization-prone region and the first demagnetization-prone region is 0:0.7; And / or, the Tb diffusion weight gain of the first easily demagnetized region is 0.1wt%-1wt%, preferably 0.3wt%-0.7wt%, for example 0.7wt%; And / or, the Tb diffusion weight gain in the center of the non-demagnetization-prone region is 0.05wt% or less, for example, 0; And / or, the Tb diffusion weight gain in the first transition zone is 0.1wt%-1wt%, preferably 0.24wt%-0.7wt%, for example 0.68wt% or 0.7wt%.

3. The NdFeB magnet according to claim 1, wherein: A first interface is formed between the first transition region and the first easily demagnetized region, and a second interface is formed between the second transition region and the second easily demagnetized region; Wherein, the Tb diffusion weight gain in the first interface and the second interface is the same, and the Tb diffusion weight gain ratio between the first interface and the first easily demagnetized region is preferably (0.9-1):1; Wherein, the Dy diffusion weight gain in the first interface and the second interface is the same, and the Dy diffusion weight gain ratio between the first interface and the first easily demagnetized region is preferably 1:(0-0.05), more preferably 1:0; And / or, a third interface is formed between the first transition region and the non-demagnetization region, and a fourth interface is formed between the second transition region and the non-demagnetization region; The Dy diffusion weight gain in the third interface is the same as that in the fourth interface, and the Dy diffusion weight gain ratio between the third interface and the non-demagnetization-prone region is preferably (0.3-1):1; The Tb diffusion weight gain in the third interface is the same as that in the fourth interface, and the Tb diffusion weight gain ratio between the third interface and the center of the non-demagnetizable region is preferably 1:(0-0.05), and more preferably 1:

0.

4. The NdFeB magnet according to claim 1, characterized in that: The first easily demagnetized region and the second easily demagnetized region have the same coercive force, and the first transition region and the second transition region have the same coercive force; Wherein, the coercivity of the first easily demagnetized region ≥ the coercivity of the first transition region ≥ the coercivity of the non-easily demagnetized region; The coercivity ratio of the first transition region to the first easily demagnetized region is preferably (0.95-1):1, more preferably (0.98-1):1, for example 0.99:1; The difference in coercivity between the first easily demagnetized region and the non-easy demagnetized region is preferably 0-10 kOe, more preferably 2-5 kOe, for example 2.5 kOe or 4 kOe; The coercive force ratio of the non-demagnetized region to the first demagnetized region is preferably (0.7-0.96):1, more preferably (0.8-0.9):1, for example, 0.85:

1. And / or, the remanence of the first easily demagnetized region is the same as the remanence of the second easily demagnetized region, and the remanence of the first transition region is the same as the remanence of the second transition region; Wherein, the remanence ratio of the first easily demagnetized region to the non-easy demagnetized region is preferably (0.99-1):1; Wherein, the remanence ratio of the first transition zone to the non-demagnetization zone is preferably (0.99-1):1; And / or, the width of the first easily demagnetized region is the same as the width of the second easily demagnetized region, and the width of the first transition region is the same as the width of the second transition region; Wherein, the width ratio between the first transition zone and the NdFeB magnet is preferably (0-0.1):1, for example, 0.093:1; Wherein, the width ratio between the non-demagnetization zone and the NdFeB magnet is preferably (0.2-0.7):1; Wherein, the width ratio between the first easily demagnetized region and the NdFeB magnet is preferably (0.05-0.4):1; Wherein, the width of the first transition zone and the second transition zone is preferably 0-1 mm, and is not 0.

5. The NdFeB magnet according to claim 1, characterized in that: The grain boundary structure of the magnet includes Re2Fe 14 B main phase grains and Re-rich phase grain boundaries; the Re2Fe 14 The B main phase grains include a main phase grain shell; the Re is Dy and / or Tb; The thickness of the main phase grain shell of the first easy demagnetization zone is the same as the thickness of the main phase grain shell of the second easy demagnetization zone; the thickness of the main phase grain shell of the first transition zone is the same as the thickness of the main phase grain shell of the second transition zone; the thickness of the Re-rich grain boundary of the first easy demagnetization zone is the same as the thickness of the Re-rich grain boundary of the second easy demagnetization zone, and the thickness of the Re-rich grain boundary of the first transition zone is the same as the thickness of the Re-rich grain boundary of the second transition zone; Wherein, in the first easily demagnetized region, the thickness of the main phase grain shell is preferably 0-4 μm, more preferably 0-2 μm; the thickness of the Re grain boundary is preferably 0-1 μm, but not 0; the ratio of the thickness of the main phase grain shell to the thickness of the Re-rich grain boundary is preferably (0-2.0): (0-1), but not 0; Wherein, in the first transition zone, the thickness of the main phase grain shell is preferably 0-4 μm, more preferably 0-2 μm; the thickness of the Re-rich grain boundary is preferably 0-1 μm, but not 0; the ratio of the thickness of the main phase grain shell to the thickness of the Re-rich grain boundary is preferably (0-2.0): (0-1), but not 0; Among them, in the non-demagnetized zone, the thickness of the main phase grain shell is preferably 0-4μm, more preferably 0-2μm; the thickness of the Re-rich grain boundary is preferably 0-1μm, but not 0; the ratio of the thickness of the main phase grain shell to the thickness of the Re-rich grain boundary is preferably (0-2.0): (0-1), but not 0.

6. The NdFeB magnet according to claim 1, characterized in that: The grain size of the main phase grains in the first easily demagnetized zone is the same as that of the main phase grains in the second easily demagnetized zone; the grain size of the main phase grains in the first transition zone is the same as that of the main phase grains in the second transition zone; wherein the ratio of the grain sizes of the main phase grains in the first easily demagnetized zone, the first transition zone and the non-easy demagnetized zone is preferably 1:1:1; And / or, the grain sizes of the surface main phase grains in the first easily demagnetized zone, the first transition zone and the non-easy demagnetized zone are the same; the grain sizes of the central main phase grains in the first easily demagnetized zone, the first transition zone and the non-easy demagnetized zone are the same; wherein, in the first easily demagnetized zone, the first transition zone and the non-easy demagnetized zone, the grain size of the surface main phase grains is preferably 1-1.5 times the grain size of the central main phase grains; Wherein, the grain size of the main phase grains on the surface of the first easily demagnetized region is preferably 1-12 μm; Wherein, the grain size of the main phase grains in the surface layer of the first transition zone is preferably 1-12 μm; Wherein, the grain size of the main phase grains on the surface of the non-demagnetization-prone region is preferably 1-12 μm; And / or, in the first easily demagnetized region, the first transition region and the non-easy demagnetized region, the main phase grain core and the main phase grain shell satisfy the following conditions: the R1 content in the main phase grain core is greater than or equal to the R1 content in the main phase grain shell; the R2 content in the main phase grain core is less than the R2 content in the main phase grain shell; The R2 content in the main phase grain shell layer of the first easily demagnetized region, the first transition region and the non-easy demagnetized region preferably meets the following conditions: When R2 is Tb, the first easily demagnetized region ≥ the first transition region > the non-easy demagnetized region; When R2 is Dy, the non-demagnetization zone ≥ the first transition zone > the first demagnetization zone.

7. The method for preparing a NdFeB magnet according to any one of claims 1 to 6, characterized in that: It includes the following steps: A diffusion source is applied to the upper surface of the first easily demagnetized region, the first transition region, the non-easy demagnetized region, the second transition region and the second easily demagnetized region distributed perpendicular to the orientation direction of the NdFeB substrate, and grain boundary diffusion is carried out parallel to the orientation direction to obtain the NdFeB magnet; the diffusion source contains Dy and / or Tb.

8. The method for preparing a NdFeB magnet according to claim 7, wherein: The diffusion source is applied by coating; Wherein, the coating method 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; And / or, the temperature of the heat treatment in the grain boundary diffusion is 750-950° C., for example, 900° C.; And / or, the heat treatment time in the grain boundary diffusion is 5 to 30 hours, for example, 10 hours; And / or, the heat treatment in the grain boundary diffusion generally includes an aging treatment; Wherein, the temperature of the aging treatment is preferably 300-600°C, for example, 500°C; The aging treatment time is preferably 1 to 10 hours, for example 3 hours; And / or, the method for preparing the NdFeB magnet comprises the following steps: applying a Tb diffusion source on the upper surface of the first easily demagnetized region and the second easily demagnetized region, and applying a Tb diffusion source on the upper surface of the non-easy demagnetized region. A Dy diffusion source is applied to carry out grain boundary diffusion parallel to the orientation direction, thereby obtaining the NdFeB magnet.

9. A NdFeB magnet obtained by the method for preparing a NdFeB magnet according to claim 7 or 8.

10. Use of the NdFeB magnet according to any one of claims 1 to 6 or 9 in magnetic steel.

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