Neodymium iron boron magnets, their preparation methods and applications

Abstract

This invention discloses neodymium iron boron (NdFeB) magnets, their preparation methods, and applications. In the NdFeB magnets, the heavy rare earth elements (Tb) content is the same in the first, second, third, and fourth easily demagnetized regions; the heavy rare earth elements (Tb) content is the same in the first, second, third, and fourth transition regions; the Tb content ratio between the non-easily demagnetized region and the first easily demagnetized region is (0-0.9):1; the Dy content ratio between the first easily demagnetized region and the non-easily demagnetized region is (0-0.9):1; and the Tb content ratio between the first transition region and the first easily demagnetized region is (0.5-0.96):1. The NdFeB magnets of this invention possess excellent anti-demagnetization properties while maintaining the remanence of the NdFeB magnets.

Description

Technical Field

[0001] This invention specifically relates to neodymium iron boron magnets, their preparation methods, and applications. Background Technology

[0002] Since its invention, neodymium iron boron (NdFeB) permanent magnet materials have been widely used in automobiles, wind power, home appliances, industrial robots, and other fields. Due to the different operating conditions in each field, the performance requirements for the magnets in these products also vary. In recent years, the booming development of new energy vehicles has led to a sharp increase in the demand for magnets in main drive motors. Since the normal operating temperature of main drive motors is mainly concentrated in the range of 120–180℃, NdFeB materials require higher coercivity and thermal stability. To improve the temperature resistance of NdFeB permanent magnet materials, large amounts of heavy rare earth elements (Dy and Tb) are typically added to increase the anisotropic field of the main phase magnetocrystalline structure. However, the scarcity and high price of heavy rare earth resources severely restrict the application of NdFeB magnets in various industries.

[0003] With the increasing demand for high-performance magnets, grain boundary diffusion technology is gradually becoming more widely known and accepted. Conventional grain boundary diffusion technology uses a physical vapor deposition method to deposit the diffusion source onto the magnet surface, then uses high temperature and pressure to allow the diffusion source to penetrate along the grain boundaries into the magnet's interior. The biggest advantage of this technology is that it significantly improves coercivity while maintaining almost no change in remanence using only a small amount of heavy rare earth elements. In terms of the effective utilization rate of heavy rare earth elements, traditional grain boundary diffusion products offer a substantial improvement over non-grain boundary diffusion products.

[0004] However, in the actual use of NdFeB magnets, the performance requirements for each part of the magnet are not the same. For example, in motors, the reverse magnetic field generated when the coil is energized is not uniform. Depending on the application requirements, the shape of the magnet also needs to be different. Therefore, how to design a NdFeB magnet that meets the needs of different applications, accurately utilizes heavy rare earth elements, saves costs, and ensures good coercivity and remanence while also possessing good anti-demagnetization ability is a problem that urgently needs to be solved. Summary of the Invention

[0005] The present invention aims to overcome the shortcomings of existing NdFeB magnets, such as high cost and poor demagnetization resistance, and provides NdFeB magnets, their preparation methods and applications. The NdFeB magnets of the present invention can have good demagnetization resistance while ensuring the remanence of the NdFeB magnets.

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

[0007] The present invention provides a neodymium iron boron magnet, wherein 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 Z-axis, and the X-axis is parallel to one side of the upper surface;

[0008] The neodymium iron boron magnet includes a non-demagnetizing region, a transition region, and a demagnetizing region; the demagnetizing region includes a first demagnetizing region, a second demagnetizing region, a third demagnetizing region, and a fourth demagnetizing region respectively disposed at the four corners of the cuboid along the Z-axis direction and not in contact with each other;

[0009] The transition region is located at the boundary between the easily demagnetized region and the non-easily demagnetized region, and includes a first transition region, a second transition region, a third transition region, and a fourth transition region corresponding to the first easily demagnetized region, the second easily demagnetized region, the third easily demagnetized region, and the fourth easily demagnetized region, respectively.

[0010] The first, second, third, and fourth easily demagnetized regions have the same heavy rare earth content;

[0011] The first transition zone, the second transition zone, the third transition zone, and the fourth transition zone have the same heavy rare earth content;

[0012] The Tb content ratio of the non-demagnetizing region to the first demagnetizing region is (0-0.9):1;

[0013] The ratio of Dy content in the first easily demagnetized region to that in the non-easily demagnetized region is (0-0.9):1;

[0014] The Tb content ratio of the first transition region and the first easily demagnetized region is (0.5-0.96):1.

[0015] In this invention, the heavy rare earth elements may be derived from the substrate and / or diffusion process.

[0016] In this invention, the content of heavy rare earth elements refers to the percentage of the mass of heavy rare earth elements in a certain region relative to the total mass of the magnet in that region. For example, the content of Tb in the first easily demagnetized region means the percentage of the mass of Tb in the first easily demagnetized region relative to the total mass of the magnet in the first easily demagnetized region.

[0017] In this invention, the diffusion weight gain of heavy rare earth elements refers to the percentage of the mass of heavy rare earth elements introduced into a certain region by diffusion relative to the total mass of the magnet in that region. For example, the diffusion weight gain of Tb in the first easily demagnetized region refers to the percentage of the mass of Tb introduced into the first easily demagnetized region by diffusion relative to the total mass of the magnet in the first easily demagnetized region.

[0018] In this invention, "the diffusion weight gain of heavy rare earth elements is the same" means that the types of heavy rare earth elements introduced by diffusion in each region are the same, and the diffusion weight gain of each type of heavy rare earth element is the same.

[0019] In this invention, the specific location of the upper surface is not specifically limited. Those skilled in the art will generally understand that the upper surface refers to the surface opposite to a plane when the magnet is placed on a plane.

[0020] In this invention, the Tb content ratio of the non-demagnetizing region to the first demagnetizing region can be (0-0.2):1, for example, 0.08:1, 0.17:1 or 0.02:1.

[0021] In this invention, the Tb diffusion weight gain ratio of the non-demagnetizing region to the first demagnetizing region can be (0-0.05):(0.3-1), preferably (0-0.05):(0.3-0.6), for example 0.05:0.6, 0.05:0.3 or 0.01:0.6.

[0022] In this invention, the content ratio of Dy in the first easily demagnetized region to that in the non-easily demagnetized region can be (0-0.8):1, for example, 0.1:1.

[0023] In this invention, the diffusion weight gain ratio of Dy in the first easily demagnetized region to that in the non-easily demagnetized region can be (0-0.05):(0.3-1), preferably (0-0.05):(0.3-0.5), for example 0.05:0.5.

[0024] In this invention, the diffusion weight gain ratio of Tb in the first transition region and the first easily demagnetized region can be (0.5-0.8):1, for example 0.8:1.

[0025] In this invention, the Tb content ratio of the first transition region and the first easily demagnetized region can be (0.5-0.9):1, for example, 0.8:1.

[0026] In this invention, the diffusion weight gain of Dy in the first easily demagnetized region is 0.05 wt% or less, for example, 0.05 wt%.

[0027] In this invention, the Dy content of the first easily demagnetized region is 0-3.1 wt%, for example, it can be 0.05 wt%.

[0028] In this invention, the diffusion weight gain of Dy in the first transition region can be 0.05wt%-0.9wt%, preferably 0.1wt%-0.4wt%, for example 0.25wt%.

[0029] In this invention, the content of Dy in the first transition region can be 0.05-3.9 wt%, for example 0.25 wt%.

[0030] In this invention, the diffusion weight gain of Dy in the non-demagnetizing region can be 0.1wt%-1wt%, preferably. The content of the base is 0.4wt%-0.7wt%, for example, 0.5wt%.

[0031] In this invention, the content of Dy in the non-demagnetizing region can be 0.1-4 wt%, for example, 0.5 wt%.

[0032] In this invention, the Tb diffusion weight gain of the first easily demagnetized region can be 0.1wt%-1wt%, for example, 0.6wt%.

[0033] In this invention, the Tb content in the first easily demagnetized region can be 0.1wt%-2.5wt%, for example, 0.6wt%.

[0034] In this invention, the Tb diffusion weight gain in the non-demagnetizing region can be 0.05 wt% or less, for example, 0.

[0035] In this invention, the Tb content in the non-demagnetizing region can be 0 wt%-1.6 wt%, for example, 0.01 wt%, 0.02 wt%, or 0.05 wt%. In this invention, the diffusion weight gain of Tb in the first transition region can be 0.05 wt%-0.9 wt%, for example, 0.35 wt%, 0.53 wt%, or 0.48 wt%.

[0036] In this invention, the Tb content in the first transition region can be 0.1wt%-2.4wt%, for example 0.35wt% or 0.48wt%.

[0037] In this invention, on any plane perpendicular to the orientation direction, the Tb diffusion weight gain ratio between the first easily demagnetized region and the non-easily demagnetized region is 1:(1 / L-1), where L is the spacing between the sampling regions and the value of L is >1.

[0038] In this invention, the neodymium iron boron magnet can be represented by the chemical formula R1-R2-TBM, wherein R1 includes one or more of Pr, Nd, Ce, Er, Tm, Y, Lu, Gd and Ho; R2 is Dy and / or Tb; T includes one or more of Zn, Si, V, Cr, Mn, Ni, Ge, Ti, Nb, Mo, Pd, Ag, Cd, Sb, Hf, Ta, W, O, C, N, S, F and P; and M includes one or more of Cu, Al, Co, Ga, Zr and Ti.

[0039] In some implementations, the M element is entirely derived from a NdFeB substrate.

[0040] In other embodiments, the M element comprises a diffusion-introduced M element, wherein the diffusion-introduced M element preferably accounts for 0%-0.4% of the mass percentage of the NdFeB magnet.

[0041] In some preferred embodiments, the coercivity of the first, second, third, and fourth demagnetizing regions is the same.

[0042] In some preferred embodiments, the coercivity of the first transition region, the second transition region, the third transition region, and the fourth transition region is the same.

[0043] In this invention, the ratio of the coercivity of the non-demagnetizing region to the first demagnetizing region can be (0.7-0.96):1, more preferably (0.8-0.9):1, for example 0.86:1, 0.88:1 or 0.90:1.

[0044] In this invention, the coercivity difference between the first easily demagnetized region and the non-easily demagnetized region can be 0-10 kOe, more preferably 2-5 kOe, for example 2.6 kOe, 3.1 kOe or 3.6 kOe.

[0045] In this invention, the ratio of the coercivity of the first transition region to the first demagnetizing region can be (0.8-0.98):1, for example, 0.96:1.

[0046] In this invention, the coercivity of the first easily demagnetized region is not lower than that of the first transition region, and the coercivity of the first transition region is not lower than that of the non-easily demagnetized region.

[0047] In this invention, the residual magnetism of the first, second, third, and fourth easily demagnetized regions is the same; the residual magnetism of the first, second, third, and fourth transition regions is the same.

[0048] In this invention, the remanence ratio of the first easily demagnetized region to the non-easily demagnetized region can be (0.99-1):1, for example, 1:1.

[0049] In this invention, the remanence ratio of the first transition region to the non-demagnetizing region can be (0.99-1):1, for example, 1:1.

[0050] In this invention, on any plane perpendicular to the orientation direction, the shapes of the first, second, third, and fourth easily demagnetized regions are each independently selected as rectangular, sector-shaped, or triangular. The shapes of the transition region and the non-easily demagnetized region correspond to the shapes of the easily demagnetized regions.

[0051] When the first, second, third, and fourth easily demagnetized regions are all rectangular, the first, second, third, and fourth transition regions are all L-shaped, and the non-easily demagnetized region is cross-shaped.

[0052] In some preferred embodiments, the first, second, third, and fourth demagnetizing regions are all rectangular and have the same width. The width of the demagnetizing region refers to the distance extending from the edge of the NdFeB magnet along the X-axis or Y-axis.

[0053] In this invention, the first transition region, the second transition region, the third transition region, and the fourth transition region have the same width; the width of the first transition region refers to the distance between the interface between the first transition region and the first easily demagnetized region and the interface between the first transition region and the non-easily demagnetized region along the X-axis or Y-axis direction.

[0054] In some implementations, the ratio of the width of the first demagnetizing region to the total width of the NdFeB magnet may be (0.05-0.6):1.

[0055] In some implementations, the ratio of the width of the non-demagnetizing region to the total width of the NdFeB magnet can be (0.2-1):1. The width of the non-demagnetizing region refers to the distance along the X-axis or Y-axis of the interface between the transition region and the non-demagnetizing region or the edge of the NdFeB magnet.

[0056] In some implementations, the ratio of the width of the first transition region to the total width of the NdFeB magnet can be (0-0.1):1 and not 0, for example, 0.08:1.

[0057] In some implementations, the width of the first transition region is preferably 0-1 mm and not 0.

[0058] In this invention, the ratio of the length to the thickness of the neodymium iron boron magnet can be <3, and preferably the thickness of the neodymium iron boron magnet is 0.5-5mm; the length refers to the distance of one side of the upper surface extending along the positive X-axis; the thickness refers to the distance of the cuboid extending from the upper surface along the positive Z-axis.

[0059] In some specific implementations, the length-to-thickness ratio of the neodymium iron boron magnet is 2.5.

[0060] In this invention, the thickness of the neodymium iron boron magnet can be >5mm, where the thickness refers to the distance the cuboid extends from its upper surface along the positive Z-axis.

[0061] In this invention, the grain boundary structure of the NdFeB magnet includes Re2Fe. 14 B-phase grains and Re-rich phase grain boundaries; the Re2Fe14 The B principal phase grains comprise a core layer and a shell layer; the Re is Dy and / or Tb.

[0062] The term "main phase grain shell" is conventional in the art, namely (Nd, Dy / Tb)2Fe. 14 B. Hard magnetic layer. The meaning of the Re-rich phase grain boundary region is conventional in the art, that is, a two-particle grain boundary region with Re > 95%.

[0063] In some implementations, the thickness of the principal phase grain shell in the first, second, third, and fourth demagnetizing regions is the same.

[0064] In some implementations, the thickness of the main phase grain shell in the first transition region, the second transition region, the third transition region, and the fourth transition region is the same.

[0065] In some implementations, the Re-rich phase grain boundaries of the first, second, third, and fourth demagnetizing regions have the same thickness.

[0066] In some implementations, the Re-rich phase grain boundaries of the first transition region, the second transition region, the third transition region, and the fourth transition region have the same thickness.

[0067] In some implementations, the thickness of the main phase grain shell in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region is preferably 0-4 μm, and more preferably 0-2 μm.

[0068] In some implementations, the thickness of the Re-rich phase grain boundaries in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region is preferably 0-1 μm, but not 0.

[0069] In some implementations, the ratio of the thickness of the shell layer of the main phase grain to the thickness of the Re-rich phase grain boundary in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region is preferably (0-2.0):(0-1), but not 0.

[0070] In some implementations, the main phase grains in the first, second, third, and fourth demagnetizing regions have the same grain size.

[0071] In some implementations, the main phase grains in the first transition region, second transition region, third transition region, and fourth transition region have the same grain size.

[0072] In some implementations, the grain size ratio of the main phase grains in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region is 1:1:1.

[0073] In some implementations, the surface main phase grains of the first easily demagnetized region, the first transition region, and the non-easily demagnetized region have the same grain size, preferably 1-12 μm.

[0074] In some implementations, the grain size of the surface main phase grains in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region is 1-1.5 times the grain size of the central main phase grains.

[0075] In some embodiments, the core layer and shell layer of the main phase grain in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region satisfy the following conditions: the R1 content in the core layer is greater than or equal to the R1 content in the shell layer; the R2 content in the core layer is less than the R2 content in the shell layer; wherein R1 includes one or more of Pr, Nd, Ce, Er, Tm, Y, Lu, Gd, and Ho; and R2 is Dy and / or Tb.

[0076] In some implementations, the R2 content in the main phase grain shell of the first easily demagnetized region, the first transition region, and the non-easily demagnetized region satisfies the following condition:

[0077] When R2 is Tb, the first easily demagnetized region ≥ the first transition region > the non-easily demagnetized region;

[0078] When R2 is Dy, the non-demagnetizing region ≥ the first transition region > the first demagnetizing region.

[0079] The present invention also provides a method for preparing the above-mentioned neodymium iron boron magnet, which includes the following steps: applying a diffusion source Dy to the non-corner regions of the upper and lower surfaces of a neodymium iron boron substrate, and applying a diffusion source Tb to the four sides perpendicular to the upper surface, corresponding to the corner regions of the upper surface, so that the diffusion source Tb diffuses through grain boundaries perpendicular to the orientation direction, thereby obtaining the neodymium iron boron magnet; wherein, the corner regions form easily demagnetized regions through grain boundary diffusion; and the non-corner regions form non-easily demagnetized regions and transition regions.

[0080] As is known to those skilled in the art in this invention, during grain boundary diffusion, the Dy or Tb in the diffusion source does not completely diffuse into the magnet, and its utilization rate is generally 85%-95%. Therefore, in the actual preparation process, a larger amount of Dy or Tb is usually applied.

[0081] In some preferred embodiments, the method for preparing the NdFeB magnet preferably includes the following steps: applying a Tb diffusion source to the easily demagnetized region on the side surface of the NdFeB substrate, and applying a Dy diffusion source to the non-easily demagnetized region on the upper surface or side surface of the NdFeB substrate to perform grain boundary diffusion, thereby obtaining the NdFeB magnet.

[0082] In the preferred embodiment described above, during the diffusion process, a Tb diffusion source is applied only to the side surface of the easily demagnetized region, while no Tb diffusion source is applied to the non-easily demagnetized region. However, after diffusion, a small amount of Tb applied to the easily demagnetized region may diffuse toward the center of the magnet. The diffused Tb will be distributed at the boundary between the easily demagnetized region and the non-easily demagnetized region, where the Tb content is low.

[0083] In this invention, those skilled in the art know 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 amount of Dy or Tb diffusion is achieved.

[0084] In some implementations, the diffusion source is pure Dy.

[0085] 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. The mass percentage of M in the Dy-M alloy is 0-40%, and not zero.

[0086] In other embodiments, the diffusion source is a Dy hydride or a Dy fluoride.

[0087] In some implementations, the diffusion source is pure Tb.

[0088] 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. The mass percentage of M in the Tb-M alloy is 0-40%, and not zero.

[0089] In other embodiments, the diffusion source is a Tb hydride or a Tb fluoride.

[0090] In some implementations, the diffusion source is pure Tb.

[0091] 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. The mass percentage of M in the Tb-M alloy is 0-40%, and not zero.

[0092] In other embodiments, the diffusion source is a Tb hydride or a Tb fluoride.

[0093] In this invention, the diffusion source can be applied using methods conventional in the art, such as coating.

[0094] The coating method is preferably spraying or printing. The dewaxing temperature for spraying is preferably 200–400°C, and the dewaxing temperature for printing is preferably 100–500°C.

[0095] When the diffusion source is applied by the coating method, the diffusion source, solvent and binder are generally mixed in a certain proportion to form a slurry.

[0096] The solvent may be, for example, water, alcohol, ketone or ester.

[0097] In some preferred embodiments, the diffusion source is applied by coating. In the diffusion source used in the non-demagnetizing region, the mass concentration of Dy is preferably 0.3%-1%; in the diffusion source used in the easily demagnetizing region, the mass concentration of Tb is preferably 0.3%-1.2%; in the diffusion source used in the first transition region, the mass concentration of Tb is preferably 0.3%-1.2%; and the mass concentration of Dy is preferably 0.3%-1%. The percentages represent the mass percentage of Dy or Tb in the diffusion source.

[0098] In this invention, the temperature of the heat treatment during grain boundary diffusion is preferably 750–950°C, for example, 900°C.

[0099] In this invention, the heat treatment time during grain boundary diffusion is preferably 5 to 30 hours, for example, 10 hours.

[0100] In this invention, the heat treatment in the grain boundary diffusion generally includes an aging treatment.

[0101] The aging treatment temperature is preferably 300–600°C, for example, 500°C.

[0102] The aging process is preferably carried out over a period of 1 to 10 hours, for example, 3 hours.

[0103] The present invention also provides an application of the above-mentioned neodymium iron boron magnet in magnetic steel.

[0104] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0105] The reagents and raw materials used in this invention are all commercially available.

[0106] The positive and progressive effects of this invention are as follows:

[0107] This invention, by setting up an easily demagnetized zone, a transition zone, and a non-easily demagnetized zone, and controlling the diffusion weight gain ratio of Tb and Dy introduced by diffusion, can reduce the attenuation of the surface magnetism and magnetic flux of NdFeB magnets while ensuring the remanence of the NdFeB magnets, thereby improving the demagnetization resistance of NdFeB magnets. This also matches the characteristic of magnets being easily demagnetized at the four corners and not easily demagnetized at the center in practical applications. Attached Figure Description

[0108] Figure 1 This is a schematic diagram of the structure of each region of a neodymium iron boron magnet.

[0109] Figure 2 This is a schematic diagram of the structure of the main phase grain nuclei and shells in each region of a neodymium iron boron magnet.

[0110] Figure 3 The neodymium iron boron magnet of Example 1 Figure 1 The diagram shows the diffusion weight gain distribution of Tb for test lines 1 and 2.

[0111] Figure 4 The neodymium iron boron magnet of Example 1 Figure 1 The diagram shows the diffusion weight gain distribution of Dy for test lines 1 and 2.

[0112] Figure label:

[0113] 1-First easily demagnetized region, 2-First transition region, 3-Non-easily demagnetized region, 4-Second transition region, 5-Second easily demagnetized region, 6-Third easily demagnetized region, 7-Third transition region, 8-Fourth transition region, 9-Fourth easily demagnetized region, 10-Main phase grain shell, 11-Main phase grain nucleus. Detailed Implementation

[0114] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0115] Examples 1-3 and Comparative Examples 1-3

[0116] A diffusion source Dy is applied to the non-corner regions of the upper and lower surfaces of a NdFeB substrate, and a diffusion source Tb is applied to the four sides perpendicular to the upper surface, corresponding to the corner regions of the upper surface. The diffusion source Tb diffuses at the grain boundaries perpendicular to the orientation direction to obtain the NdFeB magnet. The utilization rate of Dy or Tb in the diffusion source is 85%-95%.

[0117] The heat treatment during grain boundary diffusion is carried out at a temperature of 900℃ for 10 hours. After the heat treatment, an aging treatment is also included, which is carried out at a temperature of 500℃ for 3 hours.

[0118] The parameters of each region of the NdFeB magnets in Examples 1-3 and Comparative Examples 1-3 are listed in Tables 1-2 below, and the elemental contents of the NdFeB substrates used in Examples 1-3 and Comparative Examples 1-3 are shown in Table 3. Since the content of heavy rare earth metals in the substrate is 0, the diffusion weight gain of heavy rare earths in Examples 1-3 and Comparative Examples 1-3 is equal to their content.

[0119] Schematic diagrams of the neodymium iron boron magnets in Examples 1-3 and Comparative Examples 1-3 are shown below. Figure 1 As shown, the first easily demagnetized region 1, the second easily demagnetized region 5, the third easily demagnetized region 6, and the fourth easily demagnetized region 9 are all rectangular; the first transition region 2, the second transition region 4, the third transition region 7, and the fourth transition region 8 are all L-shaped, and the non-easily demagnetized region 3 is cross-shaped; the thickness of the NdFeB magnet is 3 mm, and the length-to-thickness ratio is 2.5. Arrow M represents the magnetization direction of the NdFeB magnet, and arrow P represents the orientation direction of the NdFeB magnet; surface A represents the surface layer of the NdFeB magnet, and surface B represents the middle layer of the NdFeB magnet. The structure of the main phase grain nucleus and shell is as follows... Figure 2 As shown, 10 is the main phase grain shell and 11 is the main phase grain nucleus. Figure 3 The neodymium iron boron magnet of Example 1 Figure 1 The diagram shows the diffusion weight gain distribution of Tb along test line 1 and test line 2. It can be seen that along test line 1, from the first easily demagnetized region to the non-easily demagnetized region, the distribution of Tb approximates a linear function distribution. Figure 4 The neodymium iron boron magnet of Example 1 Figure 1 The diagram shows the diffusion weight gain distribution of Dy for test lines 1 and 2.

[0120] Table 1. Dy and Tb diffusion weight gain in each region of Examples 1-3 and Comparative Examples 1-3

[0121]

[0122]

[0123] Table 2. Coercivity ratios and width ratios of the transition zone to the NdFeB magnet in each region of Examples 1-3 and Comparative Examples 1-3.

[0124]

[0125] Table 3. Mass concentration of each element in the substrates of Examples 1-3 and Comparative Examples 1-3

[0126]

[0127] Example 1

[0128] The neodymium iron boron magnets of Examples 1-3 and Comparative Examples 1-3 were subjected to the following tests:

[0129] 1. Coercivity test: Samples of Examples 1-3 and Comparative Examples 1-3 were prepared with a sample size of W2~3±0.1*L15±0.1*T5.6±0.1mm. Single sample was tested using a coil with a size of W3*L15~16*T2.7mm and a permanent magnet precision measurement system NIM-62000 at room temperature (temperature ≤200℃).

[0130] 2. Demagnetization Rate Test: Using electromagnetic simulation software, Ansys Workbench, with an input speed of 1300 rpm, and the temperature adjusted to the corresponding operating condition, back EMF data of the motor was collected over the same time period, and changes in the magnet contour plot were observed to determine whether demagnetization had occurred. The formula for calculating the demagnetization rate is: Demagnetization Rate = (High-Temperature Back EMF - Room-Temperature Back EMF) / Room-Temperature Back EMF.

[0131] The technical effects of Examples 1-3 and Comparative Examples 1-3 are listed in Table 4 below:

[0132] Table 4. Coercivity and demagnetization resistance of different regions in the magnets of Examples 1-3 and Comparative Examples 1-3.

[0133]

[0134] ① In Tables 1, 2, and 4, "easy demagnetization zone" means the first easy demagnetization zone, the second easy demagnetization zone, the third easy demagnetization zone, or the fourth easy demagnetization zone; ② In the tables, "transition zone" means the first transition zone, the second transition zone, the third transition zone, or the fourth transition zone.

[0135] As shown in the table above, the neodymium iron boron magnets prepared in Examples 1-3 of the present invention have a remanence of 14.31 kGs or higher and a demagnetization rate of less than 6.1% at 130°C, exhibiting excellent demagnetization resistance.

[0136] In Comparative Example 1, only Dy diffusion was used in the easily demagnetized region, transition region, and non-easily demagnetized region, and the Tb diffusion weight gain was 0. The resulting NdFeB magnets had poor demagnetization resistance, and their demagnetization rate at 130°C was 15.5%, which was higher than that of the Example.

[0137] In Comparative Example 2, only Tb diffusion was used in the easily demagnetized region, transition region, and non-easily demagnetized region, and the Dy diffusion weight gain was 0. The resulting NdFeB magnets had poor demagnetization resistance, and their demagnetization rate at 130°C was as high as 39.2%, which was much higher than that of the Example.

[0138] The diffusion weight gain ratio of Tb between the non-demagnetizing region and the first demagnetizing region, the diffusion weight gain ratio of Dy between the first demagnetizing region and the non-demagnetizing region, and the diffusion weight gain ratio of Tb between the first transition region and the first demagnetizing region in Comparative Example 3 are all outside the scope of this invention. The neodymium iron boron magnets prepared therefrom have poor demagnetization resistance, with a demagnetization rate as high as 15% at 130°C, which is much higher than that of the examples.

[0139] The embodiments described above are merely preferred embodiments of the present invention, enabling those skilled in the art to understand and use the invention. Obviously, anyone skilled in the art can make slight modifications or variations to these embodiments without creative effort and apply them to other embodiments. Therefore, the present invention is not limited to the above embodiments, and any equivalent changes, simple modifications, and alterations made within the scope of the present invention still fall within its coverage.

Claims

1. A neodymium iron boron magnet, characterized in that, The neodymium iron boron magnet is a cuboid. 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 Z-axis and the X-axis is parallel to one side of the upper surface. The neodymium iron boron magnet includes a non-demagnetizing region, a transition region, and a demagnetizing region; the demagnetizing region includes a first demagnetizing region, a second demagnetizing region, a third demagnetizing region, and a fourth demagnetizing region respectively disposed at the four corners of the cuboid along the Z-axis direction and not in contact with each other; The transition region is located at the boundary between the easily demagnetized region and the non-easily demagnetized region, and includes a first transition region, a second transition region, a third transition region, and a fourth transition region corresponding to the first easily demagnetized region, the second easily demagnetized region, the third easily demagnetized region, and the fourth easily demagnetized region, respectively. The first, second, third, and fourth easily demagnetized regions have the same heavy rare earth content; The first transition zone, the second transition zone, the third transition zone, and the fourth transition zone have the same heavy rare earth content; The Tb content ratio of the non-demagnetizing region to the first demagnetizing region is (0-0.9):1; The ratio of Dy content in the first easily demagnetized region to that in the non-easily demagnetized region is (0-0.9):1; The Tb content ratio of the first transition region to the first easily demagnetized region is (0.5-0.8):1; The diffusion weight gain of Tb in the first easily demagnetized region is 0.1wt%-0.6wt%; The diffusion weight gain of Dy in the non-demagnetizing region is 0.1wt%-0.7wt%; The first transition region, the second transition region, the third transition region, and the fourth transition region have the same width; the ratio of the width of the first transition region to the total width of the NdFeB magnet is (0-0.1):1 and is not 0; the width of the first transition region refers to the distance between the interface between the first transition region and the first easily demagnetized region and the interface between the first transition region and the non-easily demagnetized region along the X-axis or Y-axis direction.

2. The neodymium iron boron magnet as described in claim 1, characterized in that, The Tb content ratio of the non-demagnetizing region to the first demagnetizing region is (0-0.2):1; And / or, the Tb diffusion weight gain ratio of the non-demagnetizing region to the first demagnetizing region is (0-0.05):(0.3-1); And / or, the content ratio of Dy in the first easily demagnetized region to that in the non-easily demagnetized region is (0-0.8):1; And / or, the diffusion weight gain ratio of Dy in the first easily demagnetized region to that in the non-easily demagnetized region is (0-0.05):(0.3-1); And / or, the Tb content ratio of the first transition region to the first easily demagnetized region is 0.8:1; And / or, the diffusion weight gain ratio of Tb in the first transition region and the first easily demagnetized region is (0.5-0.9):

1.

3. The neodymium iron boron magnet as described in claim 2, characterized in that, The Tb content ratio of the non-demagnetizing region to the first demagnetizing region is 0.08:1, 0.17:1, or 0.02:1; And / or, the Tb diffusion weight gain ratio of the non-demagnetizing region to the first demagnetizing region is (0-0.05):(0.3-0.6); And / or, the content ratio of Dy in the first easily demagnetized region to that in the non-easily demagnetized region is 0.1:1; And / or, the diffusion weight gain ratio of Dy in the first easily demagnetized region to that in the non-easily demagnetized region is (0-0.05):(0.3-0.5). And / or, the diffusion weight gain ratio of Tb in the first transition region and the first easily demagnetized region is (0.5-0.8):

1.

4. The neodymium iron boron magnet as described in claim 3, characterized in that, The Tb diffusion weight gain ratio between the non-demagnetizing region and the first demagnetizing region is 0.05:0.6, 0.05:0.3, or 0.01:0.6; And / or, the diffusion weight gain ratio of Dy in the first easily demagnetized region to that in the non-easily demagnetized region is 0.05:0.5; And / or, the diffusion weight gain ratio of Tb in the first transition region and the first easily demagnetized region is 0.8:

1.

5. The neodymium iron boron magnet as described in claim 1, characterized in that, The diffusion weight gain of Dy in the first easily demagnetized region is 0.05 wt% or less; And / or, the Dy content in the first easily demagnetized region is 0-3.1 wt%; And / or, the diffusion weight gain of Dy in the first transition region is 0.05-0.9 wt%; And / or, the Dy content in the first transition region is 0.05-3.9 wt%; And / or, the diffusion weight gain of Dy in the non-demagnetizing region is 0.4 wt%-0.7 wt%; And / or, the Dy content in the non-demagnetizing region is 0.1-4 wt%; And / or, the Tb content in the first easily demagnetized region is 0.1wt%-2.5wt%; And / or, the Tb diffusion weight gain in the non-demagnetizing region is 0.05 wt% or less; And / or, the Tb content in the non-demagnetizing region is 0wt%-1.6wt%; And / or, the diffusion weight gain of Tb in the first transition region is 0.05-0.9 wt%; And / or, the Tb content in the first transition region is 0.1wt%-2.4wt%; And / or, on any plane perpendicular to the orientation direction, the Tb diffusion weight gain ratio of the first easily demagnetized region to the non-easily demagnetized region is 1:(1 / L-1), where L is the spacing between the sampling regions and the value of L is >1.

6. The neodymium iron boron magnet as described in claim 5, characterized in that, The diffusion weight gain of Dy in the first easily demagnetized region is 0.05 wt%; And / or, the Dy content in the first easily demagnetized region is 0.05 wt%; And / or, the diffusion weight gain of Dy in the first transition region is 0.05-0.4 wt%; And / or, the Dy content in the first transition region is 0.25 wt%; And / or, the diffusion weight gain of Dy in the non-demagnetizing region is 0.5 wt%; And / or, the Dy content of the non-demagnetizing region is 0.5 wt%; And / or, the Tb content in the first easily demagnetized region is 0.6 wt%; And / or, the Tb diffusion weight gain in the non-demagnetizing region is 0.01 wt%, 0.02 wt%, or 0.05 wt%; And / or, the Tb content in the non-demagnetizing region is 0.01 wt%, 0.02 wt%, or 0.05 wt%; And / or, the diffusion weight gain of Tb in the first transition region is 0.2-0.5 wt%; And / or, the Tb content in the first transition region is 0.35 wt% or 0.48 wt%.

7. The neodymium iron boron magnet as described in claim 6, characterized in that, The diffusion weight gain of Dy in the first transition region is 0.25 wt%; And / or, the diffusion weight gain of Tb in the first transition region is 0.35 wt% or 0.48 wt%.

8. The neodymium iron boron magnet as described in claim 1, characterized in that, The coercivity of the first, second, third, and fourth easily demagnetized regions is the same; the coercivity of the first, second, third, and fourth transition regions is the same. And / or, the residual magnetism of the first easily demagnetized region, the second easily demagnetized region, the third easily demagnetized region, and the fourth easily demagnetized region is the same; the residual magnetism of the first transition region, the second transition region, the third transition region, and the fourth transition region is the same.

9. The neodymium iron boron magnet as described in claim 8, characterized in that, The ratio of the coercivity of the non-demagnetizing region to that of the first demagnetizing region is (0.7-0.96):1; And / or, the coercivity difference between the first easily demagnetized region and the non-easily demagnetized region is 0-10 kOe; And / or, the ratio of the coercivity of the first transition region to the first easily demagnetized region is (0.8-0.98):1; And / or, the coercivity of the first easily 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-easily demagnetized region; And / or, the remanence ratio of the first easily demagnetized region to the non-easily demagnetized region is (0.99-1):1; And / or, the remanence ratio of the first transition region to the non-demagnetizing region is (0.99-1):

1.

10. The neodymium iron boron magnet as described in claim 9, characterized in that, The ratio of the coercivity of the non-demagnetizing region to that of the first demagnetizing region is (0.8-0.9):1; And / or, the coercivity difference between the first easily demagnetized region and the non-easily demagnetized region is 2-5 kOe; And / or, the ratio of the coercivity of the first transition region to the first easily demagnetized region is 0.96:1; And / or, the remanence ratio of the first easily demagnetized region to the non-easily demagnetized region is 1:1; And / or, the remanence ratio of the first transition region to the non-demagnetizing region is 1:

1.

11. The neodymium iron boron magnet as described in claim 10, characterized in that, The ratio of the coercivity of the non-demagnetizing region to that of the first demagnetizing region is 0.86:1, 0.88:1, or 0.90:1; And / or, the coercivity difference between the first easily demagnetized region and the non-easily demagnetized region is 2.6 kOe, 3.1 kOe, or 3.6 kOe.

12. The neodymium iron boron magnet as claimed in claim 1, characterized in that, On any plane perpendicular to the orientation direction, the shapes of the first, second, third, and fourth easily demagnetized regions are each independently selected from rectangles, sectors, or triangles. And / or, the ratio of the width of the first easily demagnetized region to the total width of the NdFeB magnet is (0.05-0.4):1; And / or, the ratio of the width of the non-demagnetizing region to the total width of the NdFeB magnet is (0.2-1):1; the width of the non-demagnetizing region refers to the distance along the X-axis or Y-axis of the interface between the transition region and the non-demagnetizing region or the edge of the NdFeB magnet. And / or, the ratio of the width of the first transition region to the total width of the NdFeB magnet is 0.08:1; And / or, the width of the first transition zone is 0-1mm and not 0; And / or, the ratio of the length to the thickness of the neodymium iron boron magnet is <3, where the length refers to the distance of one side of the upper surface extending along the positive X-axis; and the thickness refers to the distance of the cuboid extending from the upper surface along the positive Z-axis. And / or, the thickness of the neodymium iron boron magnet is >5mm, where the thickness refers to the distance the cuboid extends from its upper surface along the positive Z-axis.

13. The neodymium iron boron magnet as described in claim 12, characterized in that, The first, second, third, and fourth easily demagnetized regions are all rectangular and have the same width; the width of the easily demagnetized region refers to the distance extended from the edge of the NdFeB magnet along the X-axis or Y-axis; And / or, the thickness of the neodymium iron boron magnet is 0.5-5 mm; the thickness refers to the distance the cuboid extends from its upper surface along the positive Z-axis.

14. The neodymium iron boron magnet as described in claim 1, characterized in that, The grain boundary structure of the neodymium iron boron magnet includes Re2Fe 14 B-phase grains and Re-rich phase grain boundaries; the Re2Fe 14 B main phase grains contain a main phase grain shell; Re is Dy and / or Tb; The thickness of the main phase grain shells in the first, second, third, and fourth easily demagnetized regions is the same; the thickness of the main phase grain shells in the first, second, third, and fourth transition regions is the same. The Re-rich phase grain boundaries in the first, second, third, and fourth easily demagnetized regions have the same thickness; the Re-rich phase grain boundaries in the first, second, third, and fourth transition regions have the same thickness.

15. The neodymium iron boron magnet as described in claim 14, characterized in that, In the first easily demagnetized region, the first transition region, and the non-easily demagnetized region, the thickness of the shell layer of the main phase grain is 0-4 μm. And / or, in the first easily demagnetized region, the first transition region and the non-easily demagnetized region, the thickness of the Re-rich phase grain boundary is 0-1 μm, but not 0; And / or, in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region, the ratio of the thickness of the main phase grain shell to the thickness of the Re-rich phase grain boundary is (0-2.0):(0-1), but not 0.

16. The neodymium iron boron magnet as described in claim 15, characterized in that, In the first easily demagnetized region, the first transition region, and the non-easily demagnetized region, the thickness of the shell layer of the main phase grain is 0-2 μm.

17. The neodymium iron boron magnet as described in claim 14, characterized in that, The main phase grains in the first, second, third, and fourth easily demagnetized regions have the same grain size. And / or, the main phase grains in the first transition region, the second transition region, the third transition region, and the fourth transition region have the same grain size; And / or, the grain size ratio of the main phase grains in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region is 1:1:1; And / or, the surface main phase grains of the first easily demagnetized region, the first transition region, and the non-easily demagnetized region have the same grain size; And / or, the central principal phase grains of the first easily demagnetized region, the first transition region, and the non-easily demagnetized region have the same grain size; And / or, the grain size of the surface main phase grains in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region is 1-1.5 times the grain size of the central main phase grain; And / or, the core layer and shell layer of the main phase grain in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region satisfy the following conditions: the R1 content in the core layer is greater than or equal to the R1 content in the shell layer; the R2 content in the core layer is less than the R2 content in the shell layer; wherein, R1 includes one or more of Pr, Nd, Ce, Er, Tm, Y, Lu, Gd, and Ho; and R2 is Dy and / or Tb; And / or, the R2 content in the main phase grain shell of the first easily demagnetized region, the first transition region, and the non-easily demagnetized region satisfies the following condition: When R2 is Tb, the first easily demagnetized region ≥ the first transition region > the non-easily demagnetized region; When R2 is Dy, the non-demagnetizing region ≥ the first transition region > the first demagnetizing region.

18. The neodymium iron boron magnet as claimed in claim 17, characterized in that, The surface main phase grains of the first easily demagnetized region, the first transition region, and the non-easily demagnetized region have a grain size of 1-12 μm; And / or, the grain size of the central principal phase grains in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region is 1-12 μm.

19. A method for preparing a neodymium iron boron magnet as described in any one of claims 1-18, characterized in that, It includes the following steps: A diffusion source Dy is applied to the non-corner regions of the upper and lower surfaces of a NdFeB substrate. A diffusion source Tb is applied to the four sides perpendicular to the upper surface, corresponding to the corner regions of the upper surface. The diffusion source Tb diffuses through grain boundaries perpendicular to the orientation direction, thus obtaining the NdFeB magnet. The corner regions form easily demagnetized regions through grain boundary diffusion, while the non-corner regions form non-easily demagnetized regions and transition regions.

20. The method for preparing a neodymium iron boron magnet as described in claim 19, characterized in that, The diffusion source is applied by coating; And / or, the temperature of the heat treatment in the grain boundary diffusion is 750~950℃; And / or, the heat treatment time in the grain boundary diffusion is 5~30h; And / or, the heat treatment in the grain boundary diffusion is followed by an aging treatment.

21. The method for preparing a neodymium iron boron magnet as described in claim 20, characterized in that, The coating method is spraying or printing; And / or, the dewaxing temperature of the spray coating is 200~400℃; And / or, the dewaxing temperature of the printing is 100~500℃; And / or, the temperature of the heat treatment in the grain boundary diffusion is 900°C; And / or, the heat treatment time in the grain boundary diffusion is 10 h; And / or, the aging treatment temperature is 300~600℃; And / or, the aging process takes 1 to 10 hours.

22. The method for preparing a neodymium iron boron magnet as described in claim 21, characterized in that, The aging treatment temperature is 500℃; And / or, the aging process takes 3 hours.

23. The application of a neodymium iron boron magnet as described in any one of claims 1-18 in magnetic steel.

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