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

Abstract

The invention discloses a neodymium-iron-boron magnet and a preparation method and application thereof. The first easy demagnetization area, the non-easy demagnetization area and the second easy demagnetization area are sequentially arranged in the direction perpendicular to the magnetizing direction; the coercive force ratio of the non-easy demagnetization area to the first easy demagnetization area is (0.7-1): 1 and is not 1: 1, and the coercive force of the first easy demagnetization area is the same as that of the second easy demagnetization area; the distribution of the heavy rare earth elements meets the condition that the concentration ratio 1 of the heavy rare earth elements at the position 0.5 mm away from the surface layer and the position 1 mm away from the surface layer is 1-1.2; the concentration ratio 2 of the heavy rare earth elements at the position which is 1 mm away from the surface layer and the position which is 1.5 mm away from the surface layer is 1-1.25; the concentration ratio 3 of the heavy rare earth elements at the position 1.5 mm away from the surface layer and the position 2 mm away from the surface layer is 1-1.3. The neodymium-iron-boron magnet can ensure high coercive force, high thermal stability, high squareness and high magnetic moment on the premise of reducing the heavy rare earth consumption of the neodymium-iron-boron magnet.

Description

Technical Field

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

[0002] Since the advent of NdFeB permanent magnet materials, they have been widely used in automobiles, wind power, home appliances, industrial robots and other fields. Due to the different working conditions in various fields, the performance requirements of magnetic steel for products in their fields are also different. In recent years, new energy vehicles have flourished, and 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 earth Dy and Tb is 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 it penetrate the diffusion source along the grain boundary into the interior of the magnet.

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

[0004] The present invention provides a neodymium iron boron magnet and a preparation method and application thereof to solve the technical problem that unnecessary waste is generated in the process of adding heavy rare earth elements in the prior art to meet the high coercivity and thermal stability of the neodymium iron boron magnet. The neodymium iron boron magnet of the present invention can ensure high coercivity, high thermal stability, high squareness and high magnetic moment under the premise of reducing the amount of heavy rare earth elements used in the neodymium iron boron magnet.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0006] The present invention provides a neodymium iron boron magnet, comprising a first easily demagnetized region, a non-easy demagnetized region, and a second easily demagnetized region arranged in sequence perpendicular to a magnetization direction; a 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 first easily demagnetized region and the second easily demagnetized region have the same coercive force;

[0007] 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 refers to 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.

[0008] In the present invention, the concentration ratio means the ratio of the concentrations of heavy rare earth elements at different positions. For example, the ratio of the concentrations of 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 means the ratio of the concentration of heavy rare earth elements at a position 0.5 mm vertically away from the surface to the concentration of heavy rare earth elements at a position 1 mm vertically away from the surface. The concentration of heavy rare earth elements at a certain position refers to the percentage of the mass of heavy rare earth elements introduced by the diffusion source on the cross section at the position to the sum of the masses of all elements in the NdFeB magnet.

[0009] In the present invention, the coercivity ratio of the non-demagnetized region to the first 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.

[0010] 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.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] In the present invention, in the non-demagnetization-prone region, Δ1 is preferably 1.01-1.11, for example, 1.108, 1.031, 1.015 or 1.056.

[0017] In the present invention, in the non-demagnetization-prone region, Δ2 is preferably 1.05-1.13, for example, 1.121, 1.103, 1.083 or 1.104.

[0018] In the present invention, in the non-demagnetization-prone region, Δ3 is preferably 1.05-1.15, for example, 1.126, 1.115, 1.091 or 1.142.

[0019] In the present invention, the sum of the volumes of the first easily demagnetized zone and the second easily demagnetized zone preferably accounts for 5%-75% of the volume of the NdFeB magnet; the sum of the volumes of the first easily demagnetized zone and the second easily demagnetized zone 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.

[0020] In the present invention, the volume ratio of the first easily demagnetized area and the second easily demagnetized area can be (1-2): 1, preferably 1: 1. In actual use, the volume ratio of the first easily demagnetized area and the second easily demagnetized area has special requirements for the magnetic steel assembly position. The easily demagnetized area with a higher proportion is assembled near the air gap of the motor rotor, and the easily demagnetized area with a lower proportion is assembled at the inner direction of the rotor. The temperature and reverse field at the inner direction of the assembled rotor are slightly lower than those near the air gap of the motor rotor. The volume ratio of the two easily demagnetized areas can be slightly adjusted appropriately, but the actual assembly is difficult, easy to mix materials, and the installation efficiency is low. Therefore, in actual design, the volume ratio of the first easily demagnetized area and the second easily demagnetized area is preferably 1: 1.

[0021] In the present invention, the difference in coercive force 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.

[0022] In the present invention, the difference in coercive force ΔHcJ at adjacent positions of 1 mm along the magnetization direction of the first easily demagnetized region is preferably ≤1 kOe, such as 0.7 kOe or 0.8 kOe.

[0023] In the present invention, the difference in coercive force ΔHcJ at every adjacent 1 mm position in the second easily demagnetized region along the magnetization direction is preferably ≤1 kOe, such as 0.7 kOe or 0.8 kOe.

[0024] In the present invention, the regions of the first easily demagnetized region, the non-easy demagnetized region and the second easily demagnetized region can preferably be obtained through a simulation cloud map under working conditions.

[0025] 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 in parallel to the magnetization direction to form a first easily demagnetized area, a second easily demagnetized area and a non-easy demagnetized area, wherein the first easily demagnetized area, the non-easy demagnetized area and the second easily demagnetized area are arranged in sequence in a direction 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.

[0026] In the present invention, the first grain boundary diffusion treatment, the second grain boundary diffusion treatment and the third grain boundary diffusion treatment can be performed by conventional methods in the art. For example, the first grain boundary diffusion treatment, the second grain boundary diffusion treatment and the third grain boundary diffusion treatment are each independently: a diffusion source is coated on the surface of the NdFeB substrate, and the elements in the diffusion source are diffused into the NdFeB substrate under heat treatment conditions.

[0027] The coating method is preferably vapor deposition or vapor diffusion.

[0028] The heat treatment steps are preferably as follows: in a vacuum or argon atmosphere, first heating to 700-950°C and diffusing for 24-60h; cooling to 200°C and then heating to 400-600°C and keeping warm for 1-6h, and finally cooling to room temperature.

[0029] In the present invention, when the first diffusion source and the third diffusion source are both diffusion sources containing Tb, the coating thickness ratio of the first diffusion source to the third diffusion source is preferably (1-2.3):1.

[0030] Wherein, the coating thickness of the first diffusion source is preferably 25-35 um, and the coating thickness of the third diffusion source is preferably 15-25 um.

[0031] 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 thickness of the first diffusion source to that of the third diffusion source is preferably (3.18-35):1.

[0032] Wherein, the coating thickness of the first diffusion source is preferably 25-35 um, and the coating thickness of the third diffusion source is preferably 1-11 um.

[0033] In the present invention, the time of the first grain boundary diffusion treatment, the second grain boundary diffusion treatment and the third grain boundary diffusion treatment can be determined according to the coating thickness of the diffusion source and the type of the diffusion source. For example, the time of the first grain boundary diffusion treatment, the second grain boundary diffusion treatment and the third grain boundary diffusion treatment can independently meet the following conditions: the time of the first grain boundary diffusion treatment is preferably 63-67 hours; the time of the second grain boundary diffusion treatment is preferably 63-67 hours; the time of the third grain boundary diffusion treatment is preferably 40-60 hours.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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%.

[0040] In the present invention, the element contents in the first NdFeB substrate, the second NdFeB substrate and the third NdFeB substrate independently satisfy the following conditions:

[0041] The content of light rare earth elements is preferably 25wt%-29wt%, for example, 25wt%, 25.7wt%, 25.8wt% or 26.8wt%;

[0042] The content of Cu element is preferably 0.1wt%-0.3wt%, for example 0.2wt% or 0.15wt%;

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

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

[0045] The content of Fe element is preferably 66wt%-70wt%;

[0046] 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.

[0047] 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 grinding, pressing, sintering, etc., and the green body is then mechanically processed and cleaned to obtain the NdFeB substrate.

[0048] The present invention also provides a NdFeB magnet prepared by the method for preparing the NdFeB magnet.

[0049] The present invention also provides an application of the above-mentioned NdFeB magnet in magnetic steel.

[0050] On the basis of being in accordance with the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0051] The reagents and raw materials used in the present invention are commercially available.

[0052] The positive and progressive effects of the present invention are:

[0053] The NdFeB magnet of the present invention controls the heavy rare earth element concentration and coercivity ratio of each point in the easy demagnetization area and the non-easy demagnetization area, so that under the premise of reducing the heavy rare earth dosage of the NdFeB magnet, it can also ensure high coercivity, high squareness, high magnetic moment and low demagnetization rate. The low demagnetization rate of the NdFeB magnet at high temperature indicates that it has good high temperature stability. The present invention can reduce the heavy rare earth dosage of the NdFeB magnet, reduce unnecessary waste of heavy rare earth, and reduce production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 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.

[0055] The reference numerals are as follows:

[0056] 1-first easily demagnetized region, 2-non-easily demagnetized region, 3-second easily demagnetized region. DETAILED DESCRIPTION

[0057] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out 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

[0060]

[0061]

[0062] Note: The “first / second NdFeB substrate” in the table means 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.

[0063] The first diffusion source, the second diffusion source and the third diffusion source are applied to the upper surfaces of the first NdFeB substrate, the second NdFeB substrate and the third NdFeB substrate of Examples 1 to 5 respectively, and the first grain boundary diffusion treatment, the second grain boundary diffusion treatment and the third grain boundary diffusion treatment are performed parallel to the magnetization direction to form the first easy demagnetization area, the second easy demagnetization area and the non-easy demagnetization area. The first easy demagnetization area, the non-easy demagnetization area and the second easy demagnetization area are arranged in sequence perpendicular to the magnetization direction. The types and coating thicknesses of the first diffusion source, the second diffusion source and the third diffusion source are as shown in Table 2 below; the types of the first diffusion source and the second diffusion source are the same, and the coating thicknesses of the first diffusion source and the second diffusion source are the same; the magnetization direction is as follows: Figure 1 The direction of the arrow M.

[0064] In Comparative Examples 1 to 3, a NdFeB substrate was subjected to grain boundary diffusion treatment using a diffusion source. The diffusion sources used in Comparative Examples 1 to 3 and the coating thickness of the diffusion sources are shown in Table 2 below.

[0065] Table 2

[0066]

[0067]

[0068] Note: ① The meaning of “first / second diffusion source type” in the table is the first diffusion source type and the second diffusion source type; ② The meaning of “first / second diffusion source coating thickness” in the table is the first diffusion source coating thickness and the second diffusion source coating thickness; ③ The meaning of “first / second grain boundary diffusion treatment time” in the table is the first grain boundary diffusion treatment time and the second grain boundary diffusion treatment time; ④ The “ / ” in the table means that there is no distinction between the easily demagnetized area and the non-easy demagnetized area.

[0069] 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 easy demagnetization region and the second easy demagnetization 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 demagnetization region of the NdFeB magnets prepared in Examples 1 to 5, wherein the easy demagnetization region and the non-easy demagnetization region are connected by bonding. The schematic diagram of the non-easy demagnetization region and the easy demagnetization region of the prepared NdFeB magnet is shown in Figure 1 shown.

[0070] The NdFeB substrate after the grain boundary diffusion treatment forms the NdFeB magnets prepared in Comparative Examples 1 to 3.

[0071] Effect Example 1

[0072] 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.

[0073] 1. Squareness and coercive force test: The first NdFeB substrate after the first grain boundary diffusion treatment in the above embodiments 1 to 5, the second NdFeB substrate after the second grain boundary diffusion treatment, and the NdFeB magnets prepared in comparative examples 1 to 3 were sampled with a sample specification of W2~3±0.1*L19±0.1*T4±0.1mm. Two pieces were stacked and tested with a coil of size W3*L19~20*T2.7mm on the permanent magnet precision measurement system NIM-62000 for normal and high temperature tests (temperature ≤200°C).

[0074] 2. Magnetic moment test: The NdFeB magnets prepared in the above Examples 1 to 5 and Comparative Examples 1 to 3 are tested with a HT-707 or FM-1 fluxmeter in combination with corresponding coils to obtain magnetic flux values, which are then multiplied by the coil coefficient of the corresponding coil to obtain magnetic moment values.

[0075] 3. Demagnetization rate test: Use electromagnetic simulation software, model Ansys Workbench, input speed 13000rmp, then adjust its temperature to the corresponding temperature condition, collect the back electromotive force data of the motor under the same time and observe the change of magnetic steel cloud map to identify whether the magnetic steel is demagnetized. The calculation formula of demagnetization rate is: demagnetization rate = (high temperature back electromotive force - normal temperature back electromotive force) / normal temperature back electromotive force.

[0076] 4. Heavy rare earth element content test: The NdFeB magnets prepared in the above Examples 1 to 5 and Comparative Examples 1 to 3 were ground into powder particles and dissolved with reagents, and then tested using an inductively coupled plasma emission spectrometer. The sampling method for heavy rare earth elements is: multi-wire cutting is used to slice and sample at the sampling position ±0.03mm, and the surface magnetic mud is cleaned and dried by ultrasonic wave, and then ground into powder for testing.

[0077] 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 Institute of Metrology to measure the remanence.

[0078] 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, and the remanence and coercive force of each point inside the magnets of Examples 1 and 2 are listed in Table 4:

[0079] Table 3

[0080]

[0081]

[0082] Note: ① The “first / second easily demagnetized area” in the table means the first easily demagnetized area and the second easily demagnetized area; ② “ / ” in the table means there is no distinction between the easily demagnetized area and the non-easy demagnetized area.

[0083] Table 4

[0084]

[0085]

[0086] According to the data in Table 4 above, in Examples 1 and 2 of the present invention, the difference in coercive force at each adjacent 1mm position in the easy demagnetization area along the magnetization direction does not exceed 1kOe, and the difference in coercive force at each adjacent 1mm position in the non-easy demagnetization area along the magnetization direction does not exceed 1.2kOe. In Examples 1 and 2 of the present invention, the remanence at 0.5mm from the surface, the remanence at 1mm from the surface, the remanence at 1.5mm from the surface, and the remanence at 2mm from the surface of the NdFeB magnet are all 13.12-13.2kGs, and the difference in remanence at each adjacent 1mm position along the magnetization direction does not exceed 0.04kGs.

[0087] From the data of Example 1 and Comparative Example 1 in Tables 1 to 3 above, it can be seen that the substrates of the first easily demagnetized area, the second easily demagnetized area and the non-easy demagnetized area in Example 1 are the same, and Comparative Example 1 uses the same NdFeB substrate. The diffusion sources of Example 1 and Comparative Example 1 both use diffusion sources containing Tb. Among them, the coating thickness of the easily demagnetized area of ​​Example 1 is 30um, the coating thickness of the non-easy demagnetized area of ​​Example 1 is 20um, and the coating thickness of the entire area of ​​the substrate of Comparative Example 1 remains unchanged, both of which are 30um; from the above comparison, it can be seen that the total amount of diffusion source used in Example 1 is smaller, that is, the amount of heavy rare earth used is less. And from Table 3, it can be seen that the squareness, magnetic moment and demagnetization rate of the NdFeB magnets obtained in Example 1 and Comparative Example 1 are comparable. Therefore, compared with Comparative Example 1, Example 1 can use less heavy rare earth to obtain NdFeB magnets with comparable performance.

[0088] The substrate of Comparative Example 2 is the same as the substrate of the non-easy demagnetization area of ​​Example 3. By coating a 6um 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. Usually, in order to reduce the demagnetization rate of the NdFeB magnet, the coating thickness of the Dy diffusion source is increased on the basis of Comparative Example 2 to meet the actual needs of the motor. In Example 3, the coating thickness can be increased only on the easy demagnetization area. Relatively speaking, the coating thickness of the non-easy demagnetization area is lower to achieve the purpose of reducing the use of heavy rare earths. On this basis, the heavy rare earth content in the easy demagnetization area of ​​Example 3 is lower, which further saves the use of heavy rare earths. At the same time, the demagnetization rate of Example 3 can be as low as 0.7%, which meets the actual needs of the motor.

[0089] The substrate of Comparative Example 3 is the same as the substrate of the easy demagnetization zone of Example 3, and the types of diffusion sources and coating thicknesses of the corresponding regions are also the same. By controlling the volumes of the first and second easy demagnetization zones to 25% of the volume of the NdFeB magnet, Example 3 can reduce the coating thickness of the Dy diffusion source in the easy demagnetization zone from 10um in Comparative Example 3 to 6um, while still achieving a demagnetization rate equivalent to that of Comparative Example 3. Compared with Comparative Example 3, Example 3 can effectively reduce the amount of heavy rare earth used in the diffusion process, thereby achieving the purpose of saving heavy rare earth.

[0090] In the present invention, since the corners of the magnetic steel in the motor rotor are easily affected by heat and demagnetization field, it is easier to demagnetize than the non-demagnetization area in the middle of the magnetic steel. Therefore, the design value of the coercive force of the demagnetization area and the non-demagnetization area directly affects whether the magnetic steel is demagnetized under the motor working condition. Since the final magnetic performance coercive force is composed of the substrate + diffusion coercive force increment, there are relatively many paths to achieve the final performance, so that the heavy rare earth distribution ratio and squareness and magnetic moment are relatively weakly correlated. The biggest advantage of the present invention is that it is strengthened by strengthening the demagnetization area and weakening the coercive force of the non-demagnetization area, thereby saving the use of heavy rare earth in the non-demagnetization area and 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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