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

Abstract

Disclosed in the present invention are a neodymium-iron-boron magnet, a preparation method therefor and the use thereof. The magnet comprises a first demagnetization-prone area, a non-demagnetization-prone area, and a second demagnetization-prone area, which are sequentially arranged in a direction perpendicular to a direction of magnetization. Grain boundary diffusion treatment in a direction perpendicular to the direction of magnetization and grain boundary diffusion treatment in a direction parallel to the direction of magnetization are respectively performed on the demagnetization-prone areas and the non-demagnetization-prone area of the neodymium-iron-boron magnet, so as to control the distribution of the concentrations of heavy rare-earth elements in the demagnetization-prone areas of the neodymium-iron-boron magnet in the direction perpendicular to the direction of magnetization and the distribution of the concentrations of heavy rare earth elements in the non-demagnetization-prone area of the neodymium-iron-boron magnet in the direction parallel to the direction of the magnetization. The neodymium-iron-boron magnet can ensure high coercivity, high thermal stability, high squareness and high magnetic moment while reducing the amount of use of heavy rare earths 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] The concentration of the heavy rare earth element in the first easily demagnetized region and the second easily demagnetized region is the same. In the first easily demagnetized region, the concentration ratio Δ4 of the heavy rare earth element at a position 0.5 mm vertically away from the first surface layer and at a position 1 mm vertically away from the first surface layer is 1-1.3;

[0009] In the non-demagnetizable region, a concentration ratio Δ1 of the heavy rare earth element at a position 0.5 mm vertically away from the third surface layer and a position 1 mm vertically away from the third surface layer is 1-1.2; a concentration ratio Δ2 of the heavy rare earth element at a position 1 mm vertically away from the third surface layer and a position 1.5 mm vertically away from the third surface layer is 1-1.25; and a concentration ratio Δ3 of the heavy rare earth element at a position 1.5 mm vertically away from the third surface layer and a position 2 mm vertically away from the third surface layer is 1-1.3;

[0010] Among them, the first surface layer of the NdFeB magnet is the outer surface of the first easily demagnetized zone parallel to the magnetization direction and perpendicular to the arrangement direction, the second surface layer of the NdFeB magnet is the outer surface of the second easily demagnetized zone parallel to the magnetization direction and perpendicular to the arrangement direction; the third surface layer of the NdFeB magnet is the upper surface of the non-easily demagnetized zone perpendicular to the magnetization direction.

[0011] 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 position 0.5 mm vertically away from the first surface layer to a position 1 mm vertically away from the first surface layer refers to the ratio of the concentration of heavy rare earth elements at a position 0.5 mm vertically away from the first surface layer to the concentration of heavy rare earth elements at a position 1 mm vertically away from the first surface layer. 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.

[0012] 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, 0.933:1, 0.932:1, 0.909:1, 0.86:1 or 0.83:1.

[0013] In the present invention, in the first easily demagnetized region, Δ4 is ​​preferably 1.18-1.26, for example, 1.181, 1.205, 1.222 or 1.251.

[0014] In the present invention, in the non-demagnetizable region, Δ1 is preferably 1.02-1.11, for example, 1.106, 1.026, 1.029, 1.058 or 1.06.

[0015] In the present invention, in the non-demagnetizable region, Δ2 is preferably 1.05-1.12, for example, 1.118, 1.1 or 1.079.

[0016] In the present invention, in the non-demagnetizable region, Δ3 is preferably 1.05-1.15, for example, 1.123, 1.11, 1.096 or 1.144.

[0017] 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 neodymium iron boron 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 neodymium iron boron magnet; this volume ratio facilitates the stability of the performance of the neodymium iron boron magnet and the precise utilization of heavy rare earth elements, while also reducing eddy current losses to a certain extent.

[0018] In the present invention, the width of the first easily demagnetized region is preferably smaller than the thickness of the first easily demagnetized region. In the present invention, the width is the length perpendicular to the magnetization direction, and the thickness is the length parallel to the magnetization direction.

[0019] In the present invention, the width of the second easily demagnetized region is preferably smaller than the thickness of the second easily demagnetized region. This length relationship can reduce the amount of heavy rare earth and the diffusion period.

[0020] Wherein, the width of the first easily demagnetized area is preferably ≤5 mm.

[0021] Wherein, the width of the second easily demagnetized region is preferably ≤5 mm.

[0022] In the present invention, the thickness of the first easily demagnetized region is preferably equal to the thickness of the second easily demagnetized region.

[0023] 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.

[0024] In the present invention, at every adjacent 1 mm position along the magnetization direction of the non-easily demagnetized region, preferably, the coercive force difference ΔHcJ is ≤ 2 kOe, more preferably ≤ 1 kOe.

[0025] In the present invention, the coercive force of the first easily demagnetized region is preferably 1-7.5 kOe higher than the coercive force of the non-easily demagnetized region, and more preferably 1-3 kOe.

[0026] 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.

[0027] The present invention also provides a method for preparing the above-mentioned NdFeB magnet, which comprises the following steps: applying a first diffusion source and a second diffusion source to the outer surfaces of a first NdFeB substrate and a second NdFeB substrate, respectively, performing a first grain boundary diffusion treatment and a second grain boundary diffusion treatment respectively along a direction perpendicular to the magnetization direction; applying a third diffusion source to the upper surface of a third NdFeB substrate, performing a third grain boundary diffusion treatment along a direction parallel to the magnetization direction, and forming a first easily demagnetized region, a second easily demagnetized region, and a non-easy demagnetized region, respectively; the first easily demagnetized region, the non-easy demagnetized region, and the second easily demagnetized region are arranged in sequence along a direction perpendicular to the magnetization direction, thereby obtaining 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 (1-31):1.

[0028] 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.

[0029] The coating method is preferably vapor deposition or vapor diffusion.

[0030] The heat treatment steps are preferably as follows: in a vacuum or argon atmosphere, first heating to 700-900°C and keeping warm for 1-30 hours, then heating to 900-1000°C and keeping warm for 1-70 hours, then cooling to 400-600°C and keeping warm for 1-6 hours.

[0031] In the present invention, when both the first diffusion source and the third diffusion source are diffusion sources containing Tb, the ratio of the coating thicknesses of the first diffusion source to the third diffusion source is preferably (1-2.06):1.

[0032] The coating thickness of the first diffusion source is preferably 25-31 μm, and the coating thickness of the third diffusion source is preferably 15-25 μm. In the present invention, since the diffusion directions of the easily demagnetized region and the non-easily demagnetized region are different, the diffusion of the easily demagnetized region is perpendicular to the magnetization direction. Compared with the diffusion of the easily demagnetized region parallel to the magnetization direction, the coating thickness can be reduced by 1-2 mm. The heavy rare earth content of the required diffusion source can also be reduced, thus saving the use of heavy rare earth.

[0033] 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 (2.27-31):1.

[0034] The coating thickness of the first diffusion source is preferably 25-31 um, and the coating thickness of the third diffusion source is preferably 1-11 um.

[0035] 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.

[0036] When the third diffusion source is a diffusion source containing Dy, the time for the third grain boundary diffusion treatment is preferably 43-47 hours.

[0037] When the third diffusion source is a diffusion source containing Tb, the time for the third grain boundary diffusion treatment is preferably 53-57 hours.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] Wherein, when the first diffusion source, the second diffusion source or the third diffusion source is a heavy rare earth-M alloy, the content of the M element is preferably 2wt%-30wt%, and the content of the heavy rare earth is preferably 70wt%-98wt%.

[0042] 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:

[0043] The content of light rare earth elements is preferably 25wt%-29wt%, for example, 25wt%, 25.7wt%, 25.8wt% or 26.8wt%;

[0044] The content of Cu element is preferably 0.1wt%-0.3wt%, for example 0.2wt% or 0.15wt%;

[0045] The content of Al element is preferably 0.1wt%-0.3wt%, for example 0.2wt% or 0.1wt%;

[0046] The Ga content is preferably 0.1wt%-0.3wt%, more preferably 0.2wt%-0.3wt%, for example 0.3wt% or 0.15wt%;

[0047] The content of Fe element is preferably 66wt%-70wt%;

[0048] 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.

[0049] In the present invention, the preparation methods 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.

[0050] The present invention also provides a NdFeB magnet produced by the above-mentioned NdFeB magnet production method.

[0051] The present invention also provides an application of the above-mentioned NdFeB magnet in magnetic steel.

[0052] 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.

[0053] The reagents and raw materials used in the present invention are commercially available.

[0054] The positive progress effect of the present invention is:

[0055] The present invention performs grain boundary diffusion treatment perpendicular to and parallel to the magnetization direction on the easily demagnetized region and the non-easily demagnetized region of the NdFeB magnet, respectively. This controls the distribution of the heavy rare earth element concentration and coercivity perpendicular to the magnetization direction in the easily demagnetized region of the NdFeB magnet, and the distribution of the heavy rare earth element concentration and coercivity parallel to the magnetization direction in the non-easily demagnetized region of the NdFeB magnet. This allows the NdFeB magnet to have high coercivity, high squareness, high magnetic moment, and low demagnetization rate while reducing the amount of heavy rare earth elements used in the NdFeB magnet. The low demagnetization rate of the NdFeB magnet at high temperatures indicates its good high-temperature stability. The present invention can reduce the amount of heavy rare earth elements used in the NdFeB magnet, reduce unnecessary waste of heavy rare earth elements, and lower production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] 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.

[0057] FIG2 is a schematic diagram of the concentration ratio at different positions of the NdFeB magnet.

[0058] The reference numerals are as follows: 1 - first easily demagnetized region, 101 - first surface layer, 2 - non-easily demagnetized region, 201 - second surface layer, 3 - second easily demagnetized region, 301 - third surface layer. DETAILED DESCRIPTION

[0059] 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.

[0060] 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:

[0061] 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.

[0062] A first diffusion source and a second diffusion source were applied to the outer surfaces of the first and second NdFeB substrates of Examples 1-5, respectively. A first grain boundary diffusion process and a second grain boundary diffusion process were performed perpendicular to the magnetization direction, respectively. A third diffusion source was applied to the upper surface of the third NdFeB substrate of Examples 1-5, and a third grain boundary diffusion process was performed parallel to the magnetization direction to form a first easily demagnetized region, a second easily demagnetized region, and a non-easy demagnetization region, respectively. The first easily demagnetized region, the non-easy demagnetization region, and the second easily demagnetized region were arranged sequentially perpendicular to the magnetization direction, thereby obtaining the NdFeB magnets of Examples 1-5. The types and coating thicknesses of the first, second, and third diffusion sources are as shown in Table 2 below. The first and second diffusion sources were of the same type and had the same coating thickness. The magnetization direction was as indicated by arrow M in Figure 1.

[0063] Comparative Examples 1 to 3 used only one diffusion source to perform grain boundary diffusion treatment on a NdFeB substrate. The NdFeB substrates of Comparative Examples 1 to 3 were subjected to grain boundary diffusion treatment parallel to the magnetization direction. The diffusion sources used in Comparative Examples 1 to 3, the coating thickness of the diffusion source, and the grain boundary diffusion treatment time are shown in Table 2 below.

[0064] 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.

[0065] 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.

[0066] The NdFeB substrates after the grain boundary diffusion treatment formed the NdFeB magnets prepared in Comparative Examples 1 to 3.

[0067] Effect Example 1

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] Various effect data of the NdFeB magnets of Examples 1 to 5 and Comparative Examples 1 to 3 are listed in Table 3 below, wherein a schematic diagram of the concentration ratios at different positions of the NdFeB magnets is shown in FIG2 .

[0074] 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.

[0075] Among them, since the first and second easily demagnetized regions of Examples 1-5 in the above table are diffused perpendicular to the magnetization direction, the concentrations of heavy rare earth elements at various positions parallel to the magnetization direction are theoretically the same. However, there will be some differences in the actual preparation process. Therefore, for the first and second easily demagnetized regions, their Δ1, Δ2 and Δ3 are close to 1.

[0076] As shown in Tables 1-3 above, Example 1 and Comparative Example 1 utilize the same NdFeB substrate, and both utilize a Tb-containing diffusion source. The coating thickness in the easily demagnetized region of Example 1 is 28 μm, while the region corresponding to the easily demagnetized region of Comparative Example 1 also utilizes a 28 μm coating thickness. The coating thickness in the non-easily demagnetized region of Example 1 is 23 μm, with a diffusion source weight gain of 7.7‰. The coating thickness in the non-easily demagnetized region of Comparative Example 1 remains unchanged at 28 μm, with a diffusion source weight gain of 8‰. As can be seen from the comparison, Example 1 exhibits a lower diffusion source coating thickness, a 0.3% reduction in weight gain compared to the same type of Tb-diffused diffusion source, and a lower use of heavy rare earth. Table 3 shows that the squareness, magnetic moment, and demagnetization rate of the NdFeB magnets produced by Example 1 and Comparative Example 1 are comparable, indicating that the performance degradation in the non-easily demagnetized region of Example 1 does not affect the final squareness, magnetic moment, and demagnetization rate of the product. Therefore, compared with Comparative Example 1, Example 1 can use less heavy rare earth to obtain a NdFeB magnet with comparable performance.

[0077] The substrate in Comparative Example 2 is identical to that in the easily demagnetized regions of Example 3, and the types and coating thicknesses of the diffusion sources in the corresponding regions are also identical. By controlling the volume of the first and second easily demagnetized regions to 30% of the volume of the NdFeB magnet, Example 3 can reduce the coating thickness of the Dy diffusion source in the non-easily demagnetized region from 8 μm in Comparative Example 2 to 7 μm, and reduce the heavy rare earth weight gain from 8‰ to 7.4‰, while still achieving a demagnetization rate comparable to that of Comparative Example 2. Compared to Comparative Example 2, Example 3 effectively reduces the amount of heavy rare earth used in the diffusion process, achieving the goal of conserving heavy rare earth.

[0078] The substrate of Comparative Example 3 is the same as that of the non-easily demagnetized region of Example 5. By applying a 21 μm Tb diffusion source, Comparative Example 3 can only achieve a demagnetization rate of 11.2% for the NdFeB magnet, which cannot meet the actual needs of the motor. Typically, to reduce the demagnetization rate of NdFeB, the coating thickness of the Tb diffusion source is increased based on Comparative Example 3 to meet the actual needs of the motor. However, Example 5 can increase the coating thickness only on the easily demagnetized region. Relatively speaking, the coating thickness of the non-easily demagnetized region is lower. Specifically, the coating thickness of the non-easily demagnetized region is 7 μm lower than that of the easily demagnetized region, achieving the purpose of reducing the use of heavy rare earth. Compared with Comparative Example 3, the demagnetization rate of Example 5 is reduced from 11.2% to 6.6%, which is reduced by about half.

[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; The concentration of the heavy rare earth element in the first easily demagnetized region and the second easily demagnetized region is the same. In the first easily demagnetized region, the concentration ratio △4 of the heavy rare earth element at a position 0.5 mm vertically away from the first surface layer and at a position 1 mm vertically away from the first surface layer is 1-1.3; In the non-demagnetization-prone region, the concentration ratio △1 of the heavy rare earth element at a position 0.5 mm vertically away from the third surface layer and at a position 1 mm vertically away from the third surface layer is 1-1.2; the concentration ratio △2 of the heavy rare earth element at a position 1 mm vertically away from the third surface layer and at a position 1.5 mm vertically away from the third surface layer is 1-1.25; the concentration ratio △3 of the heavy rare earth element at a position 1.5 mm vertically away from the third surface layer and at a position 2 mm vertically away from the third surface layer is 1-1.3; Among them, the first surface layer of the NdFeB magnet is the outer surface of the first easily demagnetized zone parallel to the magnetization direction and perpendicular to the arrangement direction, the second surface layer of the NdFeB magnet is the outer surface of the second easily demagnetized zone parallel to the magnetization direction and perpendicular to the arrangement direction; the third surface layer of the NdFeB magnet is the upper surface of the non-easy demagnetization zone perpendicular to the magnetization direction.

2. The NdFeB magnet according to claim 1, wherein: The coercive force ratio of the non-demagnetizable region to the first demagnetizable region is (0.8-0.95):1, for example, 0.933:1, 0.932:1, 0.909:1, 0.86:1 or 0.83:

1.

3. The NdFeB magnet according to claim 1, wherein: In the first easily demagnetized region, Δ4 is ​​1.18-1.26, for example, 1.181, 1.205, 1.222 or 1.251; And / or, in the non-demagnetizable region, Δ1 is 1.02-1.11, for example, 1.106, 1.026, 1.029, 1.058 or 1.06; And / or, in the non-demagnetization-prone region, Δ2 is 1.05-1.12, for example, 1.118, 1.1 or 1.079; And / or, in the non-demagnetization-prone region, Δ3 is 1.05-1.15, for example, 1.123, 1.11, 1.096 or 1.

144.

4. 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%; And / or, the volume ratio of the first easily demagnetized region to the second easily demagnetized region is (1-2):1, preferably 1:

1.

5. The NdFeB magnet according to claim 1, characterized in that: The width of the first easily demagnetized region is smaller than the thickness of the first easily demagnetized region; wherein the width of the first easily demagnetized region is preferably ≤5 mm; wherein the width is the length along a direction perpendicular to the magnetization direction, and the thickness is the length along a direction parallel to the magnetization direction; And / or, the width of the second easily demagnetized region is smaller than the thickness of the second easily demagnetized region; wherein the width of the second easily demagnetized region is preferably ≤5 mm; And / or, the thickness of the first easily demagnetized region is equal to the thickness of the second easily demagnetized region.

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-demagnetization zone is ≤2kOe, preferably ≤1kOe; And / or, the coercive force of the first easily demagnetized region is 1-7.5 kOe higher than the coercive force of the non-easily demagnetized region, and more preferably 1-3 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 and a second diffusion source are applied to the outer surfaces of the first NdFeB substrate and the second NdFeB substrate respectively, and a first grain boundary diffusion treatment and a second grain boundary diffusion treatment are respectively performed along a direction perpendicular to the magnetization direction; a third diffusion source is applied to the upper surface of the third NdFeB substrate, and a third grain boundary diffusion treatment is performed along a direction parallel to the magnetization direction to form a first easy demagnetization region, a second easy demagnetization region and a non-easy demagnetization region respectively, and the first easy demagnetization region, the non-easy demagnetization region and the second easy demagnetization region are arranged in sequence along 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 (1-31):

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 (1-2.06):1; wherein the coating thickness of the first diffusion source is preferably 25-31um, 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 (2.27-31):1; wherein the coating thickness of the first diffusion source is preferably 25-31um, 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 as claimed in 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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