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

Abstract

Disclosed in the present invention are a neodymium-iron-boron magnet, and a preparation method therefor and the use thereof. The neodymium-iron-boron magnet comprises a first demagnetization-prone region, a region where demagnetization is not prone to happen and a second demagnetization-prone region, which are sequentially arranged in the direction perpendicular to a magnetizing direction, wherein the ratio of the coercive force of the region where demagnetization is not prone to happen to that of the first demagnetization-prone region is (0.7-1):1 and is not 1:1, and the first demagnetization-prone region and the second demagnetization-prone region have the same coercive force. The distribution of heavy rare-earth elements satisfies the following conditions: the concentration ratio △1 of heavy rare-earth elements at a vertical distance of 0.5 mm from a surface layer to heavy rare-earth elements at a vertical distance of 1 mm from the surface layer is 1-1.2; the concentration ratio △2 of heavy rare-earth elements at a vertical distance of 1 mm from the surface layer to heavy rare-earth elements at a vertical distance of 1.5 mm from the surface layer is 1-1.25; and the concentration ratio △3 of heavy rare-earth elements at a vertical distance of 1.5 mm from the surface layer to heavy rare-earth elements at a vertical distance of 2 mm from the surface layer is 1-1.3. The neodymium-iron-boron magnet can ensure a high coercive force, high thermal stability, high squareness and a high magnetic torque while reducing the amount of heavy rare earth in the neodymium-iron-boron magnet.

Description

Neodymium iron boron magnet and its preparation method and application Technical Field

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

[0002] Since its introduction, NdFeB permanent magnets have been widely used in the automotive, wind power, home appliances, industrial robots and other fields. Due to the different working conditions in various fields, the performance requirements for magnetic steel in their respective fields are also different. In recent years, with the vigorous development of new energy vehicles, the demand for magnetic steel in the main drive motor has increased dramatically. Since the normal operating temperature of the main drive motor is mainly concentrated in the range of 120-180°C, NdFeB requires higher coercivity and thermal stability. In order to improve the temperature resistance of rare earth permanent magnets, a large amount of heavy rare earths Dy and Tb are usually added to increase the main phase magnetocrystalline anisotropy field, such as adding heavy rare earth elements through grain boundary diffusion technology. Conventional grain boundary diffusion technology uses a physical vapor deposition method to deposit the diffusion source on the surface of the magnet and then use high temperature and a certain pressure to make the diffusion source penetrate into the interior of the magnet along the grain boundary.

[0003] Although grain boundary diffusion technology can significantly increase the coercive force while ensuring the unchanged remanence by adding additional heavy rare earth elements, thus meeting its application in various fields, heavy rare earth resources are scarce and expensive, and the effective utilization rate of heavy rare earth in traditional grain boundary diffusion technology is relatively low. Therefore, traditional grain boundary diffusion technology will cause unnecessary waste of heavy rare earth, increase production costs, and seriously restrict the application of NdFeB magnets in various industries.

[0004] Summary of the Invention

[0005] To address the technical problem of unnecessary waste caused by the addition of heavy rare earth elements to achieve high coercivity and thermal stability in NdFeB magnets, the present invention provides a NdFeB magnet, a preparation method, and applications thereof. The NdFeB magnet of the present invention can achieve high coercivity, high thermal stability, high squareness, and high magnetic moment while reducing the amount of heavy rare earth elements used in the NdFeB magnet.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] The present invention provides a neodymium iron boron magnet, comprising a first easily demagnetized region, a non-easily demagnetized region, and a second easily demagnetized region arranged in sequence perpendicular to a magnetization direction; a coercive force ratio of the non-easily demagnetized region to the first easily demagnetized region is (0.7-1):1, and is not 1:1; and the first easily demagnetized region and the second easily demagnetized region have the same coercive force;

[0008] In the first easily demagnetized zone, the non-easily demagnetized zone and the second easily demagnetized zone, the distribution of heavy rare earth elements meets the following conditions: the concentration ratio △1 of the heavy rare earth elements at a position 0.5 mm vertically away from the surface and at a position 1 mm vertically away from the surface is 1 to 1.2; the concentration ratio △2 of the heavy rare earth elements at a position 1 mm vertically away from the surface and at a position 1.5 mm vertically away from the surface is 1 to 1.25; the concentration ratio △3 of the heavy rare earth elements at a position 1.5 mm vertically away from the surface and at a position 2 mm vertically away from the surface is 1 to 1.3; wherein the surface refers to the upper surface of the first easily demagnetized zone, the non-easily demagnetized zone and the second easily demagnetized zone perpendicular to the magnetization direction.

[0009] In the present invention, the concentration ratio refers to the ratio of the concentrations of heavy rare earth elements at different locations. For example, the ratio of the concentrations of heavy rare earth elements at a vertical distance of 0.5 mm from the surface to that at a vertical distance of 1 mm from the surface refers to the ratio of the concentration of heavy rare earth elements at a vertical distance of 0.5 mm from the surface to the concentration of heavy rare earth elements at a vertical distance of 1 mm from the surface. The concentration of heavy rare earth elements at a certain location refers to the percentage of the mass of heavy rare earth elements introduced by the diffusion source in the cross section at that location to the sum of the masses of all elements in the NdFeB magnet.

[0010] In the present invention, the coercivity ratio of the non-easily demagnetized region to the first easily demagnetized region is preferably (0.8-0.95):1, for example, 0.947:1, 0.935:1, 0.923:1, 0.863:1 or 0.826:1.

[0011] In the present invention, in the first easily demagnetized region, Δ1 is preferably 1.04-1.1, for example, 1.083, 1.046 or 1.078.

[0012] In the present invention, in the first easily demagnetized region, Δ2 is preferably 1.1-1.2, for example, 1.116, 1.102 or 1.109.

[0013] In the present invention, in the first easily demagnetized region, Δ3 is preferably 1.1-1.2, for example, 1.132, 1.113 or 1.122.

[0014] In the present invention, in the second easily demagnetized region, Δ1 is preferably 1.04-1.1, for example, 1.083, 1.046 or 1.078.

[0015] In the present invention, in the second easily demagnetized region, Δ2 is preferably 1.1-1.2, for example, 1.116, 1.102 or 1.109.

[0016] In the present invention, in the second easily demagnetized region, Δ3 is preferably 1.1-1.2, for example, 1.132, 1.113 or 1.122.

[0017] In the present invention, in the non-demagnetizable region, Δ1 is preferably 1.01-1.11, for example, 1.108, 1.031, 1.015 or 1.056.

[0018] In the present invention, in the non-demagnetizable region, Δ2 is preferably 1.05-1.13, for example, 1.121, 1.103, 1.083 or 1.104.

[0019] In the present invention, in the non-demagnetizable region, Δ3 is preferably 1.05-1.15, for example, 1.126, 1.115, 1.091 or 1.142.

[0020] In the present invention, the sum of the volumes of the first easily demagnetized region and the second easily demagnetized region preferably accounts for 5%-75% of the volume of the NdFeB magnet; the sum of the volumes of the first easily demagnetized region and the second easily demagnetized region more preferably accounts for 15%-50% of the volume of the NdFeB magnet; for example, 20%, 25% or 30%; this volume ratio facilitates stable performance and precise utilization of heavy rare earth Dy\Tb, while also reducing eddy current losses to a certain extent.

[0021] In the present invention, the volume ratio of the first easily demagnetized region and the second easily demagnetized region can be (1-2):1, preferably 1:1. In actual use, the volume ratio of the first easily demagnetized region and the second easily demagnetized region has special requirements for the magnetic steel assembly position. The easily demagnetized region with a higher ratio is assembled near the air gap of the motor rotor, and the easily demagnetized region with a lower ratio is assembled in the inner direction of the rotor. The temperature and reverse field at the inner direction of the rotor are slightly lower than those near the air gap of the motor rotor. The volume ratio of the two easily demagnetized regions can be slightly adjusted appropriately, but the actual assembly is more difficult, easy to mix materials, and the installation efficiency is low. Therefore, in actual design, the volume ratio of the first easily demagnetized region and the second easily demagnetized region is preferably 1:1.

[0022] In the present invention, the coercivity difference ΔHcJ at adjacent positions of 1 mm along the magnetization direction of the non-easily demagnetized region is preferably ≤2 kOe, more preferably ≤1 kOe, for example 0.9 kOe.

[0023] In the present invention, the coercive force difference ΔHcJ at adjacent positions of 1 mm along the magnetization direction of the first easily demagnetized region is preferably ≤1 kOe, for example, 0.7 kOe or 0.8 kOe.

[0024] In the present invention, the coercive force difference ΔHcJ at adjacent positions of 1 mm along the magnetization direction of the second easily demagnetized region is preferably ≤1 kOe, for example, 0.7 kOe or 0.8 kOe.

[0025] In the present invention, the regions of the first easily demagnetized region, the non-easily demagnetized region and the second easily demagnetized region can preferably be obtained through a simulation cloud map under working conditions.

[0026] The present invention also provides a method for preparing the above-mentioned NdFeB magnet, which comprises the following steps: applying a first diffusion source, a second diffusion source and a third diffusion source on the upper surfaces of a first NdFeB substrate, a second NdFeB substrate and a third NdFeB substrate respectively, performing a first grain boundary diffusion treatment, a second grain boundary diffusion treatment and a third grain boundary diffusion treatment parallel to the magnetization direction to form a first easily demagnetized region, a second easily demagnetized region and a non-easy demagnetized region, wherein the first easily demagnetized region, the non-easy demagnetized region and the second easily demagnetized region are arranged in sequence perpendicular to the magnetization direction to obtain the NdFeB magnet; wherein the first diffusion source and the second diffusion source are of the same type, and the coating thickness of the first diffusion source and the second diffusion source is the same; and the coating thickness ratio of the first diffusion source to the third diffusion source is (1-35):1.

[0027] In the present invention, the first, second, and third grain boundary diffusion treatments can be performed using conventional methods in the art. For example, the first, second, and third grain boundary diffusion treatments can each independently include: coating a diffusion source on the surface of the NdFeB substrate; and diffusing the elements in the diffusion source into the NdFeB substrate under heat treatment conditions.

[0028] The coating method is preferably vapor deposition or vapor diffusion.

[0029] The heat treatment steps are preferably as follows: first heating to 700-950°C and diffusing for 24-60h in a vacuum or argon atmosphere; cooling to 200°C and then heating to 400-600°C and keeping warm for 1-6h, and finally cooling to room temperature.

[0030] In the present invention, when both the first diffusion source and the third diffusion source are diffusion sources containing Tb, the coating thickness ratio of the first diffusion source to the third diffusion source is preferably (1-2.3):1.

[0031] The coating thickness of the first diffusion source is preferably 25-35 μm, and the coating thickness of the third diffusion source is preferably 15-25 μm.

[0032] In the present invention, when the first diffusion source is a diffusion source containing Tb and the third diffusion source is a diffusion source containing Dy, the ratio of the coating thicknesses of the first diffusion source to the third diffusion source is preferably (3.18-35):1.

[0033] The coating thickness of the first diffusion source is preferably 25-35 μm, and the coating thickness of the third diffusion source is preferably 1-11 μm.

[0034] In the present invention, the duration of the first, second, and third grain boundary diffusion treatments can be determined based on the coating thickness and type of the diffusion source. For example, the duration of the first, second, and third grain boundary diffusion treatments can each independently meet the following conditions: the first grain boundary diffusion treatment preferably lasts 63-67 hours; the second grain boundary diffusion treatment preferably lasts 63-67 hours; and the third grain boundary diffusion treatment preferably lasts 40-60 hours.

[0035] In the present invention, when the third diffusion source is a diffusion source containing Dy, the time of the third grain boundary diffusion treatment is preferably 40-50 hours.

[0036] In the present invention, when the third diffusion source is a diffusion source containing Tb, the time of the third grain boundary diffusion treatment is preferably 53-57 hours.

[0037] In the present invention, the first NdFeB substrate, the second NdFeB substrate and the third NdFeB substrate may be three parts of the same NdFeB substrate, or three independent NdFeB substrates.

[0038] When the first NdFeB substrate, the second NdFeB substrate and the third NdFeB substrate are three independent NdFeB substrates, they are bonded together after being subjected to the first grain boundary diffusion treatment, the second grain boundary diffusion treatment and the third grain boundary diffusion treatment.

[0039] In the present invention, the types of the first diffusion source, the second diffusion source and the third diffusion source can be conventional in the art. For example, the types of the first diffusion source, the second diffusion source and the third diffusion source are each independently one or more of heavy rare earth metals, heavy rare earth oxides, heavy rare earth hydrofluorides, heavy rare earth fluorides, heavy rare earth hydrogenates, heavy rare earth fluorides and heavy rare earth-M alloys, wherein the M element includes one or more of Al, Co, Cu, Ga, Sn, Pb and In elements.

[0040] Wherein, when the first diffusion source and the second diffusion source are heavy rare earth-M alloy, the content of M element is preferably 2wt%-30wt%, and the content of heavy rare earth is preferably 70wt%-98wt%.

[0041] In the present invention, the element contents in the first NdFeB substrate, the second NdFeB substrate, and the third NdFeB substrate each independently satisfy the following conditions:

[0042] The content of light rare earth elements is preferably 25wt%-29wt%, for example, 25wt%, 25.7wt%, 25.8wt% or 26.8wt%;

[0043] The content of Cu element is preferably 0.1wt%-0.3wt%, for example 0.2wt% or 0.15wt%;

[0044] The content of Al element is preferably 0.1wt%-0.3wt%, for example 0.2wt% or 0.1wt%;

[0045] The Ga content is preferably 0.1wt%-0.3wt%, more preferably 0.2wt%-0.3wt%, for example 0.3wt% or 0.15wt%;

[0046] The content of Fe element is preferably 66wt%-70wt%;

[0047] The content of the T element is preferably 0.1 wt%-0.25 wt%, for example 0.2 wt% or 0.18 wt%, wherein the T element includes Ti and / or Zr.

[0048] In the present invention, the preparation method of the first NdFeB substrate, the second NdFeB substrate and the third NdFeB substrate can be conventional in the art, for example, a green body is obtained through batching, smelting, hydrogen cracking, air flow milling, pressing, sintering, etc., and the green body is then mechanically processed and cleaned to obtain the NdFeB substrate.

[0049] The present invention also provides a NdFeB magnet produced by the above-mentioned NdFeB magnet production method.

[0050] The present invention also provides an application of the above-mentioned NdFeB magnet in magnetic steel.

[0051] On the basis of conforming to the common sense in this field, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0052] The reagents and raw materials used in the present invention are commercially available.

[0053] The positive progress effect of the present invention is:

[0054] By controlling the heavy rare earth element concentration and coercivity ratio at various points within the easily demagnetized and non-easily demagnetized regions, the NdFeB magnet of the present invention achieves high coercivity, high squareness, high magnetic moment, and low demagnetization rate while reducing the heavy rare earth content of the NdFeB magnet. The low demagnetization rate of the NdFeB magnet at high temperatures demonstrates its good high-temperature stability. This invention reduces the heavy rare earth content of the NdFeB magnet, minimizes unnecessary heavy rare earth waste, and lowers production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] FIG1 is a schematic diagram of the first easily demagnetized region, the second easily demagnetized region, and the non-easy demagnetized region of the NdFeB magnets prepared in Examples 1 to 5.

[0056] The reference numerals are as follows: 1 - first easily demagnetized region, 2 - non-easily demagnetized region, 3 - second easily demagnetized region. DETAILED DESCRIPTION

[0057] The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the examples. Experimental methods in the following examples where specific conditions are not specified were performed according to conventional methods and conditions, or selected according to the product specifications.

[0058] The element contents of the NdFeB substrates used in Examples 1 to 5 and Comparative Examples 1 to 3 are shown in Table 1 below, wherein the element contents of the first NdFeB substrate and the second NdFeB substrate in Examples 1 to 5 are exactly the same:

[0059] Table 1 Note: The “first / second NdFeB substrate” in the table refers to the element content of the first NdFeB substrate and the second NdFeB substrate, wherein the element content of the first NdFeB substrate and the second NdFeB substrate is the same.

[0060] A first diffusion source, a second diffusion source, and a third diffusion source were applied to the upper surfaces of the first, second, and third NdFeB substrates of Examples 1-5, respectively. A first grain boundary diffusion process, a second grain boundary diffusion process, and a third grain boundary diffusion process were performed parallel to the magnetization direction to form a first easily demagnetized region, a second easily demagnetized region, and a non-easily demagnetized region. The first easily demagnetized region, the non-easily demagnetized region, and the second easily demagnetized region were arranged in sequence perpendicular to the magnetization direction. The types and coating thicknesses of the first, second, and third diffusion sources are as shown in Table 2. The first and second diffusion sources are of the same type and have the same coating thickness. The magnetization direction is as indicated by arrow M in Figure 1.

[0061] Comparative Examples 1 to 3 used diffusion sources to perform grain boundary diffusion treatment on a NdFeB substrate. The diffusion sources used in Comparative Examples 1 to 3 and the coating thickness of the diffusion sources are shown in Table 2 below.

[0062] Table 2 Note: ① The “first / second diffusion source type” in the table means the first diffusion source type and the second diffusion source type; ② The “first / second diffusion source coating thickness” in the table means the first diffusion source coating thickness and the second diffusion source coating thickness; ③ The “first / second grain boundary diffusion treatment time” in the table means the time of the first grain boundary diffusion treatment and the time of the second grain boundary diffusion treatment; ④ The “ / ” in the table means that there is no distinction between the easily demagnetized area and the non-easily demagnetized area.

[0063] The first NdFeB substrate and the second NdFeB substrate after the first grain boundary diffusion treatment and the second grain boundary diffusion treatment respectively form the first easily demagnetized region and the second easily demagnetized region of the NdFeB magnets prepared in Examples 1 to 5. The third NdFeB substrate after the third grain boundary diffusion treatment forms the non-easy demagnetized region of the NdFeB magnets prepared in Examples 1 to 5. The easily demagnetized region and the non-easy demagnetized region are connected by bonding. A schematic diagram of the non-easy demagnetized region and the easily demagnetized region of the prepared NdFeB magnet is shown in Figure 1.

[0064] The NdFeB substrates after the grain boundary diffusion treatment formed the NdFeB magnets prepared in Comparative Examples 1 to 3.

[0065] Effect Example 1

[0066] When testing the effect, three groups of samples were prepared from the same sample and tested separately, and the final result was the average value of the three groups.

[0067] 1. Squareness and Coercivity Tests: Samples of the first NdFeB substrate after the first grain boundary diffusion treatment in Examples 1-5, the second NdFeB substrate after the second grain boundary diffusion treatment, and the NdFeB magnets prepared in Comparative Examples 1-3 were prepared with specifications of W2-3±0.1*L19±0.1*T4±0.1mm. Two samples were stacked for measurement, and normal and high temperature tests (temperature ≤ 200°C) were performed using a coil with dimensions of W3*L19-20*T2.7mm on a permanent magnet precision measurement system NIM-62000.

[0068] 2. Magnetic moment test: The NdFeB magnets prepared in Examples 1 to 5 and Comparative Examples 1 to 3 were tested with a HT-707 or FM-1 fluxmeter in combination with corresponding coils to obtain magnetic flux values, which were then multiplied by the coil coefficient of the corresponding coil to obtain magnetic moment values.

[0069] 3. Demagnetization Rate Test: Using electromagnetic simulation software (Ansys Workbench), we set the motor speed to 13,000 rpm and then adjusted the temperature to the corresponding operating temperature. We then collected back-EMF data and observed changes in the magnetic steel cloud map over the same period of time to determine if the magnet was demagnetized. The demagnetization rate is calculated using the formula: Demagnetization Rate = (High-Temperature Back-EMF - Room-Temperature Back-EMF) / Room-Temperature Back-EMF.

[0070] 4. Heavy Rare Earth Element Content Testing: The NdFeB magnets prepared in Examples 1-5 and Comparative Examples 1-3 were ground into powder particles, dissolved with reagents, and then analyzed using an inductively coupled plasma optical emission spectrometer. Heavy rare earth element sampling was performed by multi-wire cutting at ±0.03 mm intervals at the desired sampling location. The surface magnetic mud was ultrasonically cleaned, dried, and ground into powder for testing.

[0071] 5. Remanence test: The NdFeB magnets of Examples 1 and 2 were placed in a PFM-14 pulse magnetic property measuring instrument produced by the China National Institute of Metrology to measure the remanence.

[0072] The various effect data of the NdFeB magnets of Examples 1 to 5 and Comparative Examples 1 to 3 are listed in Table 3 below. The remanence and coercive force at various points inside the magnets of Examples 1 and 2 are listed in Table 4:

[0073] Table 3 Note: ① “First / Second Easy Demagnetization Zone” in the table means the first easy demagnetization zone and the second easy demagnetization zone; ② “ / ” in the table means there is no distinction between the easy demagnetization zone and the non-easy demagnetization zone.

[0074] Table 4

[0075] According to the data in Table 4 above, in Examples 1 and 2 of the present invention, the difference in coercivity at every adjacent 1 mm position along the magnetization direction in the easily demagnetized region does not exceed 1 kOe, and the difference in coercivity at every adjacent 1 mm position along the magnetization direction in the non-easily demagnetized region does not exceed 1.2 kOe. In Examples 1 and 2 of the present invention, the remanence of the NdFeB magnet at a distance of 0.5 mm from the surface, 1 mm from the surface, 1.5 mm from the surface, and 2 mm from the surface are all 13.12-13.2 kGs, and the difference in remanence at every adjacent 1 mm position along the magnetization direction does not exceed 0.04 kGs.

[0076] As shown in Tables 1-3 above, the data for Example 1 and Comparative Example 1 show that the substrates for the first easily demagnetized region, the second easily demagnetized region, and the non-easily demagnetized region in Example 1 are the same, while Comparative Example 1 uses the same NdFeB substrate. Both Example 1 and Comparative Example 1 utilize a diffusion source containing Tb. The coating thickness for the easily demagnetized region of Example 1 is 30 μm, while the coating thickness for the non-easily demagnetized region of Example 1 is 20 μm. The coating thickness for the entire substrate of Comparative Example 1 remains unchanged at 30 μm. As can be seen from the above comparison, Example 1 uses a smaller total amount of diffusion source, meaning less heavy rare earth. As shown in Table 3, the NdFeB magnets produced in Example 1 and Comparative Example 1 have comparable squareness, magnetic moment, and demagnetization rate. Therefore, Example 1 can use less heavy rare earth compared to Comparative Example 1, while still achieving comparable NdFeB magnet performance.

[0077] The substrate of Comparative Example 2 is the same as the substrate of the non-easily demagnetized area of ​​Example 3. By applying a 6 μm Dy diffusion source, Comparative Example 2 can only achieve a demagnetization rate of 2.5% for the NdFeB magnet, which cannot meet the actual needs of the motor. Typically, to reduce the demagnetization rate of the NdFeB magnet, the coating thickness of the Dy diffusion source is increased based on Comparative Example 2 to meet the actual needs of the motor. However, Example 3 can increase the coating thickness only in the easily demagnetized area. Relatively speaking, the coating thickness in the non-easily demagnetized area is lower to achieve the purpose of reducing the amount of heavy rare earth used. On this basis, the heavy rare earth content in the easily demagnetized area of ​​Example 3 is even lower, further saving the amount of heavy rare earth used. At the same time, the demagnetization rate of Example 3 can be as low as 0.7%, meeting the actual needs of the motor.

[0078] The substrate of Comparative Example 3 is the same as that of the easily demagnetized regions of Example 3, and the types and coating thicknesses of the diffusion sources in the corresponding regions are also the same. By controlling the volume of the first and second easily demagnetized regions to 25% of the volume of the NdFeB magnet, Example 3 can achieve a demagnetization rate comparable to that of Comparative Example 3 even when the coating thickness of the Dy diffusion source in the easily demagnetized regions is reduced from 10 μm in Comparative Example 3 to 6 μm. Compared to Comparative Example 3, Example 3 can effectively reduce the amount of heavy rare earth elements used in the diffusion process, thereby conserving heavy rare earth elements.

[0079] In this invention, because the corners of the magnet in the motor rotor are easily affected by heat and the demagnetization field, they are more susceptible to demagnetization than the non-demagnetized area in the middle of the magnet. Therefore, the design value of the coercivity of the easily demagnetized and non-demagnetized areas directly affects whether the magnet demagnetizes under motor operating conditions. Since the final magnetic performance coercivity is composed of the substrate + diffusion coercivity increment, there are relatively many paths to achieve the final performance, so that the heavy rare earth distribution ratio is relatively weakly correlated with the squareness and magnetic moment. The greatest advantage of this invention is that by strengthening the easily demagnetized area and weakening the coercivity of the non-demagnetized area, the use of heavy rare earth in the non-demagnetized area is reduced, ultimately saving costs.

Claims

1. A neodymium iron boron magnet, characterized in that: The NdFeB magnet comprises a first easily demagnetized region, a non-easy demagnetized region and a second easily demagnetized region arranged in sequence perpendicular to the magnetization direction; the coercive force ratio of the non-easy demagnetized region to the first easily demagnetized region is (0.7-1):1, and is not 1:1, and the coercive forces of the first easily demagnetized region and the second easily demagnetized region are the same; In the first easily demagnetized zone, the non-easy demagnetized zone and the second easily demagnetized zone, the distribution of heavy rare earth elements meets the following conditions: the concentration ratio △1 of the heavy rare earth elements at a position 0.5 mm vertically away from the surface and at a position 1 mm vertically away from the surface is 1-1.2; the concentration ratio △2 of the heavy rare earth elements at a position 1 mm vertically away from the surface and at a position 1.5 mm vertically away from the surface is 1-1.25; the concentration ratio △3 of the heavy rare earth elements at a position 1.5 mm vertically away from the surface and at a position 2 mm vertically away from the surface is 1-1.3; wherein the surface layer is the upper surface of the first easily demagnetized zone, the non-easy demagnetized zone and the second easily demagnetized zone perpendicular to the magnetization direction.

2. The NdFeB magnet according to claim 1, wherein: The coercive force ratio of the non-demagnetized region to the first demagnetized region is (0.8-0.95):1, for example, 0.947:1, 0.935:1, 0.923:1, 0.863:1 or 0.826:

1.

3. The NdFeB magnet according to claim 1, wherein: In the first easily demagnetized region, Δ1 is 1.04-1.1, for example, 1.083, 1.046 or 1.078; And / or, in the first easily demagnetized region, Δ2 is 1.1-1.2, for example, 1.116, 1.102 or 1.109; And / or, in the first easily demagnetized region, Δ3 is 1.1-1.2, for example, 1.132, 1.113 or 1.122; And / or, in the second easily demagnetized region, Δ1 is 1.04-1.1, for example, 1.083, 1.046 or 1.078; And / or, in the second easily demagnetized region, Δ2 is 1.1-1.2, for example, 1.116, 1.102 or 1.109; And / or, in the second easily demagnetized zone, Δ3 is 1.1-1.2, for example, 1.132, 1.113 or 1.

122.

4. The NdFeB magnet according to claim 1, characterized in that: In the non-demagnetization-prone region, Δ1 is 1.01-1.11, for example, 1.108, 1.031, 1.015 or 1.056; And / or, in the non-demagnetization-prone region, Δ2 is 1.05-1.13, for example, 1.121, 1.103, 1.083 or 1.104; And / or, in the non-demagnetizable region, Δ3 is 1.05-1.15, for example, 1.126, 1.115, 1.091 or 1.

142.

5. The NdFeB magnet according to claim 1, characterized in that: The sum of the volumes of the first easily demagnetized region and the second easily demagnetized region accounts for 5%-75% of the volume of the NdFeB magnet, preferably 15%-50%, for example 20%, 25% or 30%; And / or, the volume ratio of the first easily demagnetized region to the second easily demagnetized region is (1-2):1, preferably 1:

1.

6. The NdFeB magnet according to claim 1, characterized in that: The difference in coercivity △HcJ at adjacent positions of 1 mm along the magnetization direction of the non-demagnetized region is ≤2 kOe, preferably ≤1 kOe, for example 0.9 kOe; And / or, the difference in coercivity △HcJ at each adjacent 1mm position of the first easily demagnetized region along the magnetization direction is ≤1kOe, for example, 0.7kOe or 0.8kOe; And / or, at each adjacent 1 mm position of the second easily demagnetized region along the magnetization direction, the difference in coercive force ΔHcJ is ≤1 kOe, for example, 0.7 kOe or 0.8 kOe.

7. A method for preparing a NdFeB magnet as claimed in any one of claims 1 to 6, characterized in that: It includes the following steps: A first diffusion source, a second diffusion source and a third diffusion source are applied to the upper surfaces of the first NdFeB substrate, the second NdFeB substrate and the third NdFeB substrate respectively, and a first grain boundary diffusion treatment, a second grain boundary diffusion treatment and a third grain boundary diffusion treatment are performed in parallel to the magnetization direction to form a first easy demagnetization area, a second easy demagnetization area and a non-easy demagnetization area, wherein the first easy demagnetization area, the non-easy demagnetization area and the second easy demagnetization area are arranged in sequence in a direction perpendicular to the magnetization direction, so as to obtain the NdFeB magnet; wherein the first diffusion source and the second diffusion source are of the same type, and the coating thickness of the first diffusion source and the second diffusion source is the same; The ratio of the coating thickness of the first diffusion source to that of the third diffusion source is (1-35):

1.

8. The method for preparing a NdFeB magnet according to claim 7, wherein: The first diffusion source and the third diffusion source are both diffusion sources containing Tb, and the coating thickness ratio of the first diffusion source to the third diffusion source is (1-2.3):1; wherein the coating thickness of the first diffusion source is preferably 25-35um, and the coating thickness of the third diffusion source is preferably 15-25um; Alternatively, the first diffusion source is a diffusion source containing Tb, the third diffusion source is a diffusion source containing Dy, and the ratio of the coating thickness of the first diffusion source to the third diffusion source is (3.18-35):1; wherein the coating thickness of the first diffusion source is preferably 25-35um, and the coating thickness of the third diffusion source is preferably 1-11um.

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

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

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