A neodymium iron boron magnet, its preparation method and application

Abstract

This invention discloses a neodymium iron boron (NdFeB) magnet, its preparation method, and its applications. The NdFeB magnet of this invention comprises a first easily demagnetized region, a first transition region, a non-easily demagnetized region, a second transition region, and a second easily demagnetized region, sequentially distributed along a direction perpendicular to the orientation. All three regions—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 rectangular. By controlling the combination of Tb and Dy contents introduced by diffusion in the transition region, the easily demagnetized region, and the non-easily demagnetized region, this invention can reduce interdiffusion of Tb or Dy across regions caused by the Tb concentration gradient difference in the transition region. Furthermore, by setting the easily demagnetized region, the non-easily demagnetized region, and the transition region to be rectangular, this invention can improve the demagnetization resistance of the four corners and the long side of the NdFeB magnet.

Description

Technical Field

[0001] This invention relates to a neodymium iron boron magnet, its preparation method, and its application. Background Technology

[0002] Since its invention, neodymium iron boron (NdFeB) permanent magnet materials have been widely used in automobiles, wind power, home appliances, industrial robots, and other fields. Due to the different operating conditions in each field, the performance requirements for the magnets in these products also vary. In recent years, the booming development of new energy vehicles has led to a sharp increase in the demand for magnets in main drive motors. Since the normal operating temperature of main drive motors is mainly concentrated in the range of 120–180℃, NdFeB magnets require higher coercivity and thermal stability. To improve the temperature resistance of rare earth permanent magnets, 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 has gradually become known and accepted. Conventional grain boundary diffusion technology uses a physical vapor deposition method to deposit a diffusion source onto the magnet surface, and 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.

[0004] In terms of the effective utilization rate of heavy rare earth elements, traditional grain boundary diffusion products have significantly improved compared to non-grain boundary diffusion products. However, in order to further improve the utilization rate of heavy rare earth elements and reduce unnecessary waste, and to make the diffusion area more accurate and quantifiable, another objective of this invention is to use neodymium iron boron magnets to identify easily demagnetized and non-easily demagnetized regions under the operating conditions of a main drive motor. We found that easily demagnetized regions are all located near the corners of the rotor air gap, while demagnetization is not obvious in the area near the rotor and the middle of the magnets. Therefore, for easily demagnetized regions, high-performance magnets with the same remanence and low-performance magnets with the same remanence are bonded together to prepare the required combined magnets, thereby saving the use of heavy rare earth elements in the non-easily demagnetized regions.

[0005] In practical applications of NdFeB magnets, the performance requirements for each part of the magnet are not the same. For example, in a motor, because the reverse magnetic field generated when the coil is energized is not uniform, NdFeB magnets exhibit easily demagnetized regions, difficult-to-demagnetize regions, and transitional regions between these two regions. Due to the characteristics of these regions, the coercivity of each region needs to be matched to ensure that the easily demagnetized and transitional regions have sufficient coercivity while preventing attenuation of surface magnetism and magnetic flux in the difficult-to-demagnetize regions. Simultaneously, the transitional and difficult-to-demagnetize regions should have the highest remanence. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a neodymium iron boron material, its preparation method, and its applications. This material, through the coordination of HRE content in the easily demagnetized region, transition region, and difficult-to-demagnetize region, can improve the demagnetization resistance of neodymium iron boron magnets.

[0007] The present invention mainly solves the above technical problems through the following technical solutions.

[0008] The present invention provides a neodymium iron boron magnet, the 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 the 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;

[0009] The Tb diffusion weight gain is the same in the first easily demagnetized region and the second easily demagnetized region; the Dy diffusion weight gain is the same in the first easily demagnetized region and the second easily demagnetized region.

[0010] The Tb diffusion weight gain is the same in the first transition region and the second transition region; the Dy diffusion weight gain is the same in the first transition region and the second transition region.

[0011] The Tb diffusion weight gain ratio between the first transition region and the first easily demagnetized region is (0.8-1):1;

[0012] The Tb diffusion weight gain ratio between the center of the non-demagnetizing region and the first demagnetizing region is (0-0.05):(0.3-1);

[0013] The Dy diffusion weight gain ratio between the first easily demagnetized region and the non-easily demagnetized region is (0-0.05):(0.3-1).

[0014] In this invention, the diffusion weight gain means the percentage of the mass of Tb or Dy introduced into a certain region by diffusion to the total mass of the magnet in that region. For example, the diffusion weight gain of Tb in the first easily demagnetized region means the percentage of the mass of Tb introduced into the first easily demagnetized region by diffusion to the total mass of the magnet in the first easily demagnetized region.

[0015] In this invention, the center of the non-demagnetizing region is defined as the central cross section of the non-demagnetizing region along the distribution direction of each region.

[0016] In this invention, the Dy diffusion weight gain ratio of the first transition region to the non-demagnetizing region can be (0.05-0.9):1, preferably (0.14-0.90):1, for example 0.25:1.

[0017] In this invention, the Dy diffusion weight gain ratio of the first transition region to the first easily demagnetized region can be (0-0.05):(0.05-0.9), and preferably, the Dy diffusion weight gain of the first transition region is 0.

[0018] In this invention, the Dy diffusion weight gain of the first easily demagnetized region can be 0.05wt% or less, for example, 0.

[0019] In this invention, the Dy diffusion weight gain in the first transition region can be 0.05wt%-0.9wt%, more preferably 0.1wt%-0.45wt%.

[0020] In this invention, the Dy diffusion weight gain in the non-demagnetizing region can be 0.1wt%-1wt%, preferably 0.4wt%-0.7wt%, for example 0.5wt%.

[0021] In this invention, the Tb diffusion weight gain in the first easily demagnetized region is preferably higher than that in the first transition region.

[0022] In this 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-demagnetizing region.

[0023] In this 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.

[0024] In this invention, the Tb diffusion weight gain ratio between the center of the non-demagnetizing region and the first demagnetizing region is preferably 0:0.7.

[0025] In this invention, the Tb diffusion weight gain of the first easily demagnetized region can be 0.1wt%-1wt%, preferably 0.3wt%-0.7wt%, for example 0.7wt%.

[0026] In this invention, the Tb diffusion weight gain at the center of the non-demagnetizing region can be 0.05 wt% or less, for example, 0.

[0027] In this invention, the Tb diffusion weight gain in the first transition region can be 0.1wt%-1wt%, preferably 0.24wt%-0.7wt%, for example 0.68wt% or 0.7wt%.

[0028] In this 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.

[0029] Wherein, the Tb diffusion weight gain in the first interface and the second interface is the same, and the Tb diffusion weight gain of the first interface and the first easily demagnetized region is preferably (0.9-1):1.

[0030] Wherein, the mass concentration of Dy 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.

[0031] In this invention, a third interface is formed between the first transition region and the non-demagnetizing region, and a fourth interface is formed between the second transition region and the non-demagnetizing region.

[0032] Wherein, the Dy diffusion weight gain in the third interface is the same as that in the fourth interface, and the Dy diffusion weight gain in the third interface and the non-demagnetizing region is preferably (0.3-1):1.

[0033] Wherein, 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-demagnetizing region is preferably 1:(0-0.05), more preferably 1:0.

[0034] 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 introduced by diffusion; 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.

[0035] In some implementations, the M element is entirely derived from a NdFeB substrate.

[0036] In other embodiments, the M element comprises diffusion-introduced M element, wherein the diffusion-introduced M element accounts for a preferred mass percentage of 0%-0.4% of the NdFeB magnet.

[0037] In some preferred embodiments, the coercivity of the first demagnetizing region and the second demagnetizing region is the same, and the coercivity of the first transition region and the second transition region is the same.

[0038] Wherein, the coercivity of the first easily demagnetized region is greater than or equal to the coercivity of the first transition region and greater than or equal to the coercivity of the non-easily demagnetized region.

[0039] The coercivity ratio of the first transition zone to the first demagnetizing zone is preferably (0.95-1):1, more preferably (0.98-1):1, and for example, 0.99:1.

[0040] The coercivity 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.

[0041] The coercivity ratio of the non-demagnetizing region to the first demagnetizing region is preferably (0.7-0.96):1, more preferably (0.8-0.9):1, for example 0.85:1.

[0042] In some preferred embodiments, the residual magnetism of the first easily demagnetized region is the same as that of the second easily demagnetized region, and the residual magnetism of the first transition region is the same as that of the second transition region.

[0043] Preferably, the remanence ratio of the first easily demagnetized region to the non-easily demagnetized region is (0.99-1):1.

[0044] Preferably, the remanence ratio of the first transition region to the non-demagnetizing region is (0.99-1):1.

[0045] In some preferred embodiments, the width of the first demagnetizing region is the same as the width of the second demagnetizing 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.

[0046] Preferably, the width ratio of the first transition region to the width of the neodymium iron boron magnet is (0-0.1):1, for example, 0.093:1.

[0047] The width of the non-demagnetizing region is preferably (0.2-0.7):1 with respect to the width of the neodymium iron boron magnet.

[0048] The width of the first easily demagnetized region is preferably (0.05-0.4):1 with that of the neodymium iron boron magnet.

[0049] Preferably, the widths of the first transition zone and the second transition zone are 0-1 mm and are not 0.

[0050] In some preferred embodiments, the grain size of the main phase grains in the first easily demagnetized region is the same as that in the second easily demagnetized region; the grain size of the main phase grains in the first transition region is the same as that in the second transition region; wherein, the ratio of the grain size of the main phase grains in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region is preferably 1:1:1.

[0051] In some preferred embodiments, 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; the central main phase grains of the first easily demagnetized region, the first transition region, and the non-easily demagnetized region have the same grain size; wherein, in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region, the grain size of the surface main phase grains is preferably 1-1.5 times the grain size of the central main phase grains.

[0052] The term "surface" refers to a surface perpendicular to the orientation direction, and "center" refers to the mid-plane along the orientation direction.

[0053] Preferably, the grain size of the main phase grains on the surface of the first easily demagnetized region is 1-12 μm.

[0054] Preferably, the grain size of the main phase grains on the surface of the first transition region is 1-12 μm.

[0055] Preferably, the grain size of the main phase grains on the surface of the non-demagnetizing region is 1-12 μm.

[0056] In some preferred embodiments, in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region, the main phase grain nucleus and the main phase grain shell satisfy the following conditions: the R1 content in the main phase grain nucleus is greater than or equal to the R1 content in the main phase grain shell; the R2 content in the main phase grain nucleus is less than the R2 content in the main phase grain shell.

[0057] Preferably, 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 conditions:

[0058] When R2 is Tb, the first easily demagnetized region ≥ the first transition region > the non-easily demagnetized region.

[0059] When R2 is Dy, the non-demagnetizing region ≥ the first transition region > the first demagnetizing region.

[0060] In this invention, the grain boundary structure of the magnet includes Re2Fe. 14 B-phase grains and Re-rich phase grain boundaries; the Re2Fe 14 The B main phase grains contain a main phase grain shell; Re is Dy and / or Tb.

[0061] 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%.

[0062] In some preferred embodiments, the thickness of the main phase grain shell layer in the first easily demagnetized region is the same as the thickness of the main phase grain shell layer in the second easily demagnetized region; the thickness of the main phase grain shell layer in the first transition region is the same as the thickness of the main phase grain shell layer in the second transition region; the thickness of the Re-rich grain boundary in the first easily demagnetized region is the same as the thickness of the Re-rich grain boundary in the second easily demagnetized region; and the thickness of the Re-rich grain boundary in the first transition region is the same as the thickness of the Re-rich grain boundary in the second transition region.

[0063] 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. 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 can be 0.2 μm.

[0064] In the first transition 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; 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 region is 1 μm, the thickness of the Re-rich grain boundary can be 0.2 μm.

[0065] In the non-demagnetizing 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; 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-demagnetizing region is 1 μm, the thickness of the Re-rich grain boundary can be 0.2 μm.

[0066] The present invention also provides a method for preparing the NdFeB magnet, comprising the following steps: applying a diffusion source to the upper surface of a first easily demagnetized region, a first transition region, a non-easily demagnetized region, a second transition region, and a second easily demagnetized region distributed perpendicular to the orientation direction on a NdFeB substrate, and performing grain boundary diffusion parallel to the orientation direction to obtain the NdFeB magnet; wherein the diffusion source contains Dy and / or Tb.

[0067] 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.

[0068] In some preferred embodiments, the method for preparing the NdFeB magnet preferably includes the following steps: applying a Tb diffusion source to the upper surface of the first easily demagnetized region and the second easily demagnetized region, applying a Dy diffusion source to the upper surface of the non-easily demagnetized region, and performing grain boundary diffusion parallel to the orientation direction to obtain the NdFeB magnet.

[0069] In the preferred embodiment described above, during the diffusion process, a Tb diffusion source is applied only to the upper surfaces of the first and second easily demagnetized regions, while no Tb diffusion source is applied to the non-easily demagnetized regions. However, after diffusion, a small amount of Tb applied to the first and second easily demagnetized regions may diffuse towards the center of the non-easily demagnetized regions. The diffused Tb is mainly distributed at the boundary between the easily demagnetized and non-easily demagnetized regions, and the Tb content in the center of the non-easily demagnetized regions is relatively low.

[0070] 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.

[0071] In some implementations, the diffusion source is pure Dy.

[0072] 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.

[0073] In other embodiments, the diffusion source is a Dy hydride or a Dy fluoride.

[0074] In some implementations, the diffusion source is pure Tb.

[0075] 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.

[0076] In other embodiments, the diffusion source is a Tb hydride or a Tb fluoride.

[0077] In some implementations, the diffusion source is pure Tb.

[0078] 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.

[0079] In other embodiments, the diffusion source is a Tb hydride or a Tb fluoride.

[0080] In this invention, the diffusion source can be applied using methods conventional in the art, such as coating.

[0081] 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.

[0082] When the diffusion source is applied by the coating method, the diffusion source is generally mixed with solvent and binder in a certain proportion to form a slurry.

[0083] The solvent may be, for example, water, alcohol, ketone or ester.

[0084] In a preferred embodiment of the present invention, 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.

[0085] In this invention, the temperature of the heat treatment during grain boundary diffusion is preferably 750–950°C, for example, 900°C.

[0086] In this invention, the heat treatment time during grain boundary diffusion is preferably 5 to 30 hours, for example, 10 hours.

[0087] In this invention, the heat treatment in the grain boundary diffusion generally includes an aging treatment.

[0088] The aging treatment temperature is preferably 300–600°C, for example, 500°C.

[0089] The aging process is preferably carried out over a period of 1 to 10 hours, for example, 3 hours.

[0090] The present invention also provides a neodymium iron boron magnet prepared by the above-described method for preparing neodymium iron boron magnets.

[0091] The present invention also provides an application of the above-mentioned neodymium iron boron magnet in magnetic steel.

[0092] 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.

[0093] The reagents and raw materials used in this invention are all commercially available.

[0094] The positive and progressive effects of this invention are as follows:

[0095] The neodymium iron boron magnet described in this invention includes a transition region. By controlling the Tb and Dy contents introduced by diffusion in the transition region, the easily demagnetized region, and the non-easily demagnetized region, the interdiffusion of Tb or Dy across regions caused by the Tb concentration gradient difference in the transition region can be reduced. This reduces the gradient decrease in the performance of the boundary region, resulting in a weakened anti-demagnetization effect. While maintaining the remanence of the neodymium iron boron magnet, the attenuation of the surface magnetism and magnetic flux of the neodymium iron boron magnet is reduced, thus improving the anti-demagnetization capability of the neodymium iron boron magnet. Furthermore, this invention sets the easily demagnetized region, the non-easily demagnetized region, and the transition region to be rectangular, which improves the anti-demagnetization capability of the four corners and the long side of the neodymium iron boron magnet. Attached Figure Description

[0096] Figure 1 This is a schematic diagram of the structure of each region of a neodymium iron boron magnet.

[0097] 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.

[0098] Figure 3 This is a scanning electron microscope image of the easily demagnetized region of NdFeB in Example 3.

[0099] Figure 4 for Figure 3 Line scan of the Dy content in the grain shell.

[0100] Figure 5 for Figure 3 Line scan of Tb content in the grain shell.

[0101] Figure 6 for Figure 3 Line scan image of Nd content in the grain shell.

[0102] Figure 7 This is a scanning electron microscope image of the non-demagnetizing region of neodymium iron boron in Example 3.

[0103] Figure 8 for Figure 7 Line scan of the Dy content in the grain shell.

[0104] Figure 9 for Figure 7 Line scan of Tb content in the grain shell.

[0105] Figure 10 for Figure 7 Line scan image of Nd content in the grain shell.

[0106] Figure 11 This is a scanning electron microscope image of the neodymium iron boron transition region in Example 3.

[0107] Figure 12 for Figure 11 Line scan of the Dy content in the grain shell.

[0108] Figure 13 for Figure 11 Line scan of Tb content in the grain shell.

[0109] Figure 14 for Figure 11 Line scan image of Nd content in the grain shell.

[0110] Figure label:

[0111] 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 nucleus. Detailed Implementation

[0112] 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.

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

[0114] A diffusion source is applied to a NdFeB substrate along a first easily demagnetized region, a first transition region, a non-easily demagnetized region, a second transition region, and a second easily demagnetized region distributed perpendicular to the orientation direction, and grain boundary diffusion is performed parallel to the orientation direction to obtain the NdFeB 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 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.

[0116] The parameters of each region of the neodymium iron boron magnets in Examples 1-3 and Comparative Examples 1-2 are listed in Tables 1-2 below, and the elemental content of the neodymium iron boron substrates used in Examples 1-3 and Comparative Examples 1-2 is shown in Table 3.

[0117] Schematic diagrams of the neodymium iron boron magnets in Examples 1-3 and Comparative Examples 1-2 are shown below. Figure 1 and Figure 2 As shown, the direction of arrow M represents the magnetization direction of the NdFeB magnet, and the direction of 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.

[0118] Table 1. Diffusion weight gain of Dy and Tb in each region of Examples 1-3 and Comparative Examples 1-2.

[0119]

[0120] 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 1-2.

[0121]

[0122] Table 3. Mass concentration of each element in the substrates of Examples 1-3 and Comparative Examples 1-2

[0123]

[0124] Example 1

[0125] The neodymium iron boron magnets of Examples 1-3 and Comparative Examples 1-3 were subjected to the following tests:

[0126] 1. Coercivity test: Samples of Examples 1-3 and Comparative Examples 1-3 were prepared with a sample size of W2~3±0.1*L19±0.1*T4±0.1mm. Two samples were stacked and tested at room temperature (temperature ≤200℃) using a coil with a size of W3*L19~20*T2.7mm on a permanent magnet precision measurement system NIM-62000.

[0127] 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.

[0128] 3. The test method and instrument for line scan images are as follows: The selected area of ​​the magnet surface is microscopically photographed under the EMMA equipment. The equipment model is JEOL 8530f, and the magnification is X3000. Line scans are performed on the two main phases to characterize the distribution of elements such as Dy / Nd.

[0129] The technical effects of Examples 1-3 and Comparative Examples 1-2 are listed in Table 4 below:

[0130] Table 4 shows the coercivity and demagnetization resistance of different regions in the magnets of Examples 1-3 and Comparative Examples 1-2.

[0131]

[0132] Note: ① In the table, "First Demagnetization Zone / Second Easy Demagnetization Zone" means either the first easy demagnetization zone or the second easy demagnetization zone; ② In the table, "First Transition Zone / Second Transition Zone" means either the first transition zone or the second transition zone.

[0133] As shown in the table above, the coercivity ratio between the first transition region and the first easily demagnetized region of the NdFeB magnets prepared in Examples 1-3 is between (0.97-0.99):1, and the coercivity difference between the first easily demagnetized region and the non-easily demagnetized region is between 2.5-5 kOe, exhibiting excellent demagnetization resistance. The demagnetization rate of the NdFeB magnets in Examples 1-3 at 130℃ is only 4.3%-8.1%.

[0134] And by Figure 3-6 It can be seen that in Example 3, the Tb content in the main phase grain shell and Re-rich grain boundaries of the easily demagnetized region is higher than the Dy content. Figure 7-10 It can be seen that in Example 3, the Dy content is higher than the Tb content in the main phase grain shell and Re-rich grain boundaries of the non-demagnetizing region. Figure 11-14 It can be seen that the main phase grain shell and Re-rich grain boundaries in the transition region of Example 3 contain both Dy and Tb.

[0135] The Tb diffusion weight gain ratio of the first transition region to the first easily demagnetized region in Comparative Example 1 is too low, specifically 0.14:1. The coercivity ratio of the first transition region to the first easily demagnetized region of the NdFeB magnet in Comparative Example 1 is about 0.9:1. The coercivity difference between the first easily demagnetized region and the non-easily demagnetized region is 2.5 kOe. The NdFeB magnet prepared in Comparative Example 1 has poor demagnetization resistance, and its demagnetization rate at 130°C is 10%, which is higher than that of Examples 1-3.

[0136] The Tb diffusion weight gain ratio of the first transition region to the first easily demagnetized region in Comparative Example 2 was too low, specifically 0.6:1, and the Dy diffusion weight gain of both the transition region and the non-easily demagnetized region was 0. The coercivity ratio of the first transition region to the first easily demagnetized region of the neodymium iron boron magnet prepared therefrom was 0.92:1, and the coercivity difference between the first easily demagnetized region and the non-easily demagnetized region was 11.5 kOe. The neodymium iron boron magnet prepared in Comparative Example 2 had poor demagnetization resistance, and its demagnetization rate at 130°C was as high as 38.5%, which was much higher than that of Examples 1-3.

[0137] 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 includes 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 the orientation; 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; The Tb diffusion weight gain is the same in the first easily demagnetized region and the second easily demagnetized region; the Dy diffusion weight gain is the same in the first easily demagnetized region and the second easily demagnetized region. The Tb diffusion weight gain is the same in the first transition region and the second transition region; the Dy diffusion weight gain is the same in the first transition region and the second transition region. 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-demagnetizing region and the first demagnetizing region is (0-0.05):(0.3-1). The Dy diffusion weight gain ratio between the first easily demagnetized region and the non-easily demagnetized region is (0-0.05):(0.3-1). The Dy diffusion weight gain ratio between the first transition region and the non-demagnetizing region is (0.05-0.9):1; The Dy diffusion weight gain in the non-demagnetizing region is 0.5 wt%-1 wt%; The Tb diffusion weight gain in the first easily demagnetized region is 0.1wt%-1wt%.

2. The neodymium iron boron magnet as described in claim 1, characterized in that, The Dy diffusion weight gain ratio between the first transition region and the non-demagnetizing region is (0.14-0.90):1; And / or, the Dy diffusion weight gain ratio of the first transition region to the first easily demagnetized region is (0-0.05):(0.05-0.9); And / or, the Dy diffusion weight gain of the first easily demagnetized region is 0.05 wt% or less; And / or, the Dy diffusion weight gain in the first transition region is 0.05wt%-0.9wt%; And / or, the Dy diffusion weight gain in the non-demagnetizing region is 0.5 wt%-0.7 wt%; 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 gain in the first transition region is higher than the Tb diffusion gain at the center of the non-demagnetizing region; And / or, the Tb diffusion weight gain ratio of the first transition region to the first easily demagnetized region is (0.9-1):1; And / or, the Tb diffusion weight gain ratio between the center of the non-demagnetizing region and the first demagnetizing region is 0:0.7; And / or, the Tb diffusion weight gain in the first easily demagnetized region is 0.3 wt%-0.7 wt%; And / or, the Tb diffusion weight gain at the center of the non-demagnetizing region is 0.05 wt% or less; And / or, the Tb diffusion weight gain in the first transition region is 0.1wt%-1wt%.

3. The neodymium iron boron magnet as described in claim 2, characterized in that, The Dy diffusion weight gain ratio between the first transition region and the non-demagnetizing region is 0.25:1; And / or, the Dy diffusion weight gain in the first transition region is 0; And / or, the Dy diffusion weight gain of the first easily demagnetized region is 0; And / or, the Dy diffusion weight gain in the first transition region is 0.1wt%-0.45wt%; And / or, the Dy diffusion weight gain in the non-demagnetizing region is 0.5 wt%; And / or, the Tb diffusion weight gain ratio of the first transition region to the first easily demagnetized region is 0.68:0.7; And / or, the Tb diffusion weight gain in the first easily demagnetized region is 0.7 wt%; And / or, the Tb diffusion weight gain at the center of the non-demagnetizing region is 0; And / or, the Tb diffusion weight gain in the first transition region is 0.24 wt%-0.7 wt%.

4. The neodymium iron boron magnet as described in claim 3, characterized in that, The Tb diffusion weight gain in the first transition region is 0.68 wt% or 0.7 wt%.

5. The neodymium iron boron magnet as described in claim 1, characterized in that, 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; And / or, a third interface is formed between the first transition region and the non-demagnetizing region, and a fourth interface is formed between the second transition region and the non-demagnetizing region.

6. The neodymium iron boron magnet as described in claim 5, characterized in that, The Tb diffusion weight gain at the first interface and the second interface is the same; And / or, the Dy diffusion weight gain in the first interface is the same as that in the second interface.

7. The neodymium iron boron magnet as described in claim 6, characterized in that, The Tb diffusion weight gain ratio between the first interface and the first easily demagnetized region is (0.9-1):1; And / or, the Dy diffusion weight gain ratio between the first interface and the first easily demagnetized region is 1:(0-0.05).

8. The neodymium iron boron magnet as described in claim 7, characterized in that, The Dy diffusion weight gain ratio between the first interface and the first easily demagnetized region is 1:

0.

9. The neodymium iron boron magnet as described in claim 5, characterized in that, The third interface and the fourth interface have the same Dy diffusion weight gain; And / or, the Tb diffusion weight gain at the third interface is the same as that at the fourth interface.

10. The neodymium iron boron magnet as described in claim 9, characterized in that, The Dy diffusion weight gain ratio between the third interface and the non-demagnetizing region is (0.3-1):1; And / or, the Tb diffusion weight gain ratio between the third interface and the center of the non-demagnetizing region is 1:(0-0.05).

11. The neodymium iron boron magnet as described in claim 10, characterized in that, The Tb diffusion weight gain ratio between the third interface and the center of the non-demagnetizing region is 1:

0.

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

13. The neodymium iron boron magnet as described in claim 12, characterized in that, The coercivity of the first easily demagnetized region is greater than or equal to the coercivity of the first transition region and greater than or equal to the coercivity of the non-easily demagnetized region.

14. The neodymium iron boron magnet as described in claim 13, characterized in that, The coercivity ratio between the first transition zone and the first easily demagnetized zone is (0.95-1):

1.

15. The neodymium iron boron magnet as described in claim 14, characterized in that, The coercivity ratio of the first transition zone to the first demagnetizing zone is (0.98-1):

1.

16. The neodymium iron boron magnet as described in claim 15, characterized in that, The coercivity ratio of the first transition zone to the first demagnetizing zone is 0.99:

1.

17. The neodymium iron boron magnet as described in claim 13, characterized in that, The coercivity ratio between the non-demagnetizing region and the first demagnetizing region is (0.7-0.96):

1.

18. The neodymium iron boron magnet as described in claim 17, characterized in that, The coercivity ratio between the non-demagnetizing region and the first demagnetizing region is (0.8-0.9):

1.

19. The neodymium iron boron magnet as described in claim 18, characterized in that, The coercivity ratio between the non-demagnetizing region and the first demagnetizing region is 0.85:

1.

20. The neodymium iron boron magnet as claimed in claim 13, characterized in that, The coercivity difference between the first easily demagnetized region and the non-easily demagnetized region is 0-10 kOe.

21. The neodymium iron boron magnet as claimed in claim 20, characterized in that, The coercivity difference between the first easily demagnetized region and the non-easily demagnetized region is 2-5 kOe.

22. The neodymium iron boron magnet as claimed in claim 21, characterized in that, The coercivity difference between the first easily demagnetized region and the non-easily demagnetized region is 2.5 kOe or 4 kOe.

23. The neodymium iron boron magnet as described in claim 12, characterized in that, The remanence ratio of the first easily demagnetized region to the non-easily demagnetized region is (0.99-1):

1.

24. The neodymium iron boron magnet as described in claim 12, characterized in that, The remanence ratio of the first transition region to the non-demagnetizing region is (0.99-1):

1.

25. The neodymium iron boron magnet as described in claim 12, characterized in that, The width ratio of the first transition region to the width of the neodymium iron boron magnet is (0-0.1):

1.

26. The neodymium iron boron magnet as described in claim 25, characterized in that, The width ratio of the first transition region to the width of the neodymium iron boron magnet is 0.093:

1.

27. The neodymium iron boron magnet as described in claim 12, characterized in that, The width ratio of the non-demagnetizing region to the width of the neodymium iron boron magnet is (0.2-0.7):

1.

28. The neodymium iron boron magnet as described in claim 12, characterized in that, The width ratio of the first easily demagnetized region to the width of the neodymium iron boron magnet is (0.05-0.4):

1.

29. The neodymium iron boron magnet as described in claim 12, characterized in that, The width of the first transition zone and the second transition zone is 0-1mm, and is not 0.

30. The neodymium iron boron magnet as described in claim 1, characterized in that, The grain boundary structure of the 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; Specifically, the thickness of the main phase grain shell layer in the first easily demagnetized region is the same as the thickness of the main phase grain shell layer in the second easily demagnetized region; the thickness of the main phase grain shell layer in the first transition region is the same as the thickness of the main phase grain shell layer in the second transition region; the thickness of the Re-rich grain boundary in the first easily demagnetized region is the same as the thickness of the Re-rich grain boundary in the second easily demagnetized region; and the thickness of the Re-rich grain boundary in the first transition region is the same as the thickness of the Re-rich grain boundary in the second transition region.

31. The neodymium iron boron magnet as claimed in claim 30, characterized in that, In the first easily demagnetized region, the thickness of the main phase grain shell is 0-4 μm.

32. The neodymium iron boron magnet as claimed in claim 31, characterized in that, In the first easily demagnetized region, the thickness of the main phase grain shell is 0-2 μm.

33. The neodymium iron boron magnet as described in claim 30, characterized in that, In the first easily demagnetized region, the thickness of the Re grain boundary is 0-1 μm, but not 0.

34. The neodymium iron boron magnet as described in claim 30, characterized in that, In the first easily demagnetized region, the ratio of the thickness of the main phase grain shell to the thickness of the Re-rich grain boundary is (0-2.0):(0-1), but not 0.

35. The neodymium iron boron magnet as claimed in claim 30, characterized in that, In the first transition region, the thickness of the main phase grain shell is 0-4 μm.

36. The neodymium iron boron magnet as described in claim 35, characterized in that, In the first transition region, the thickness of the main phase grain shell is 0-2 μm.

37. The neodymium iron boron magnet as claimed in claim 30, characterized in that, In the first transition region, the thickness of the Re-rich grain boundaries is 0-1 μm, but not 0.

38. The neodymium iron boron magnet as described in claim 30, characterized in that, In the first transition region, the ratio of the thickness of the main phase grain shell to the thickness of the Re-rich grain boundary is (0-2.0):(0-1), but not 0.

39. The neodymium iron boron magnet as described in claim 30, characterized in that, In the non-demagnetizing region, the thickness of the main phase grain shell is 0-4 μm.

40. The neodymium iron boron magnet as claimed in claim 39, characterized in that, In the non-demagnetizing region, the thickness of the main phase grain shell is 0-2 μm.

41. The neodymium iron boron magnet as claimed in claim 30, characterized in that, In the non-demagnetizing region, the thickness of the Re-rich grain boundary is 0-1 μm, but not 0.

42. The neodymium iron boron magnet as described in claim 30, characterized in that, In the non-demagnetizing region, the ratio of the thickness of the main phase grain shell to the thickness of the Re-rich grain boundary is (0-2.0):(0-1), but not 0.

43. The neodymium iron boron magnet as described in claim 1, characterized in that, The grain size of the main phase grains in the first easily demagnetized region is the same as that in the second easily demagnetized region; the grain size of the main phase grains in the first transition region is the same as that in the second transition region. 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; the central 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, in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region, the main phase grain nucleus and the main phase grain shell satisfy the following conditions: the R1 content in the main phase grain nucleus is greater than or equal to the R1 content in the main phase grain shell; the R2 content in the main phase grain nucleus is less than the R2 content in the main phase grain shell.

44. The neodymium iron boron magnet as described in claim 43, characterized in that, The ratio of the grain size 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, in the first easily demagnetized region, the first transition region, and the non-easily demagnetized region, the grain size of the surface main phase grain is 1-1.5 times the grain size of the central main phase grain.

45. The neodymium iron boron magnet as claimed in claim 44, characterized in that, The grain size of the main phase grains on the surface of the first easily demagnetized region is 1-12 μm; And / or, the grain size of the main phase grains on the surface of the first transition region is 1-12 μm; And / or, the grain size of the main phase grains on the surface of the non-demagnetizing region is 1-12 μm.

46. ​​The neodymium iron boron magnet as described in claim 43, characterized in that, 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.

47. The method for preparing a neodymium iron boron magnet according to any one of claims 1-46, characterized in that, It includes the following steps: A diffusion source is applied to the upper surface of a neodymium iron boron substrate along a first easily demagnetized region, a first transition region, a non-easily demagnetized region, a second transition region, and a second easily demagnetized region distributed perpendicular to the orientation direction, and grain boundary diffusion parallel to the orientation direction is carried out to obtain the neodymium iron boron magnet; the diffusion source contains Dy and / or Tb.

48. The method for preparing a neodymium iron boron magnet as described in claim 47, 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 5~30 h; And / or, the heat treatment in the grain boundary diffusion is followed by an aging treatment; And / or, the method for preparing the NdFeB magnet includes the following steps: applying a Tb diffusion source to the upper surface of the first easily demagnetized region and the second easily demagnetized region, applying a Dy diffusion source to the upper surface of the non-easily demagnetized region, and performing grain boundary diffusion parallel to the orientation direction to obtain the NdFeB magnet.

49. The method for preparing a neodymium iron boron magnet as described in claim 48, characterized in that, The coating method is spraying or printing.

50. The method for preparing a neodymium iron boron magnet as described in claim 49, characterized in that, The dewaxing temperature for the spraying is 200~400℃; Alternatively, the dewaxing temperature for the printing is 100~500℃.

51. The method for preparing a neodymium iron boron magnet as described in claim 48, characterized in that, The heat treatment temperature during the grain boundary diffusion is 900℃; 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.

52. The method for preparing a neodymium iron boron magnet as described in claim 51, characterized in that, The aging treatment temperature is 500℃; And / or, the aging process takes 3 hours.

53. A neodymium iron boron magnet prepared by the method for preparing a neodymium iron boron magnet according to any one of claims 47-52.

54. An application of a neodymium iron boron magnet as described in any one of claims 1-46 and 53 in magnetic steel.

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