WO2019169875A1

WO2019169875A1 - High-coercivity neodymium iron boron magnet and preparation method therefor

Info

Publication number: WO2019169875A1
Application number: PCT/CN2018/111930
Authority: WO
Inventors: 刘仲武; 曾慧欣; 周庆; 余红雅; 钟喜春
Original assignee: 华南理工大学
Priority date: 2018-03-05
Filing date: 2018-10-25
Publication date: 2019-09-12
Also published as: ZA202005694B; CN108565105A

Abstract

The present invention belongs to the field of permanent magnet materials, and discloses a high-coercivity neodymium iron boron magnet and a method for preparing same. First, a low-melting-point non-rare-earth alloy having a melting point of 450°C to 950°C is prepared; a surface diffusion medium is then placed onto the surface of the neodymium iron boron magnet to form a diffusion couple, or a metal oxide film is magnetron-sputtered onto a neodymium iron boron substrate as a surface diffusion medium; finally, the described neodymium iron boron magnet is subjected to diffusion heat treatment in a vacuum to obtain a high-coercivity neodymium iron boron magnet. The surface diffusion process of the present invention is simple and effective and does not use rare-earth alloys or compounds as diffusion media; on the basis of significantly reducing the content of rare-earth elements in neodymium iron boron magnets, it is possible to effectively improve the distribution of the grain boundary phase of a magnetic body, significantly increasing the coercivity of the magnet.

Description

High coercivity neodymium iron boron magnet and preparation method thereof

Technical field

The invention belongs to the field of permanent magnet materials, and particularly relates to a high coercivity NdFeB magnet and a preparation method thereof.

Background technique

The third-generation rare earth permanent magnet neodymium iron boron (NdFeB) magnet has a high maximum magnetic energy product ((BH) _max ) and its superior comprehensive magnetic properties, and is widely used in aerospace, hybrid electric vehicles, wind power generation, medical equipment and other fields. . In the past two decades, the comprehensive performance of China's industrial production of NdFeB permanent magnets has made great progress, and the maximum magnetic energy product (MGOe) + intrinsic coercivity (kOe) has reached more than 75. With the continuous development and development of new application fields represented by power motors, higher requirements are imposed on the comprehensive properties such as coercivity and thermal stability of NdFeB. At the same time, reducing rare earth content and reducing material costs have become an important research and development direction in the field of NdFeB.

Coercivity is one of the most important technical magnetic parameters of permanent magnets. The coercive force of NdFeB magnets decreases sharply with increasing temperature, which limits its application in high temperature applications. In traditional industrial production, in order to improve the coercive force and thermal stability of the magnet, the heavy rare earths Dy and Tb are usually added to the magnet during smelting, and the Nd ₂ Fe ₁₄ B main phase is replaced by Dy and Tb. Nd in the middle to increase the anisotropy field of the main phase. However, the reserves of rare earth resources on the earth are very limited, and the price of heavy rare earths is expensive, and the cost of NdFeB is greatly increased while the performance is improved. In addition, the antiferromagnetic coupling of heavy rare earth atoms such as Dy and Tb with Fe atoms will also reduce the remanence of the magnet, thus affecting the overall performance of the magnet. Therefore, reducing and eliminating the use of heavy rare earth elements is of great significance for improving the cost performance of NdFeB permanent magnets.

The coercivity mechanism of sintered NdFeB is dominated by the nucleation of reverse domains, so the microstructure of the grain boundary phase plays a crucial role in the coercivity of NdFeB magnets. Optimizing the grain boundary phase by a certain means can reduce the nucleation of the magnetization domain and improve the coercive force. Based on this mechanism, the grain boundary diffusion process of NdFeB magnets was proposed around 2003. It does not add heavy rare earth elements during the initial smelting preparation of the magnet, but the heavy rare earth or its compound is fixed after the magnet is formed. The method is applied to the surface of the magnet and then subjected to a diffusion heat treatment to diffuse the heavy rare earth-containing diffusion medium from the surface of the magnet along the grain boundary into the magnet. Since the diffuser is only distributed at the grain boundary, the heavy rare earth element does not enter the main phase, greatly reducing the use of heavy rare earth elements. At the same time, the grain boundary heavy rare earth can improve the performance of the boundary phase, so that the coercive force is greatly improved, and the residual magnetism is not lowered. Further reducing the use of heavy rare earths, since 2010, researchers have developed grain boundary diffusion with low melting point rare earth alloys (such as Pr-Cu alloys) containing no or less heavy rare earth Dy, Tb, which can rapidly diffuse into such compounds. The new phase formed by the reaction of the magnet with the grain boundary phase effectively controls the fluidity and wettability of the grain boundary, optimizes the distribution of the grain boundary phase, and reduces the magnetic exchange coupling between the main phase grains. Can increase the coercivity.

However, up to now, in the process of increasing the coercive force by grain boundary diffusion, in the selection of the diffusion medium, rare earth element, rare earth alloy or rare earth compound has been used without exception, although the coercive force is increased, but it is also increased. The consumption of rare earth elements. If the amount of rare earth elements can be further reduced, it is of great significance for reducing the cost of NdFeB magnets.

Summary of the invention

In view of the shortcomings and deficiencies of the above prior art, the primary object of the present invention is to provide a method for preparing a high coercivity NdFeB magnet. The method adopts a non-rare earth alloy or a metal oxide, and the solid diffusion process used is based on the principle of “grain boundary diffusion”, and the grain boundary is used as a channel to adjust the grain boundary phase distribution and optimize the grain boundary phase composition and structure during the diffusion process. The effect is to improve the coercive force of the NdFeB magnet, thereby achieving the improvement of the coercive force of the NdFeB magnet at the lowest cost.

Another object of the present invention is to provide a neodymium iron boron magnet prepared by the above method.

The object of the invention is achieved by the following technical solutions:

A preparation method of a high coercivity neodymium iron boron magnet, comprising the following preparation steps:

(1) preparing a low melting non-rare earth alloy having a melting point of 450 to 950 ° C, preparing an oxide as a surface diffusion medium;

(2) placing the surface diffusion medium of step (1) on the surface of the neodymium iron boron magnet in a certain manner to form a diffusion couple;

(3) The NdFeB magnet which forms the diffusion couple in the step (2) is subjected to diffusion heat treatment under vacuum to obtain a high coercivity NdFeB magnet.

Further, the low melting non-rare earth alloy in the step (1) is a low melting point alloy such as Al-Cu, Al-Zn or Cu-Zn having different nominal compositions, and the oxide is MgO, ZnO, etc., and induction melting can be employed. An alloy ingot is prepared by argon arc smelting or powder metallurgy.

Further, the neodymium iron boron magnet of the step (2) may be a neodymium iron boron magnet prepared by different processes, including sintered neodymium iron boron, bonded neodymium iron boron or hot pressed heat deformation neodymium iron boron.

Further, the surface of the neodymium iron boron magnet in the step (2) refers to the upper and lower surfaces perpendicular to the direction of easy magnetization of the neodymium iron boron magnet.

Further, the method of placing the surface diffusion medium on the surface of the neodymium iron boron magnet in the step (2) comprises breaking the alloy ingot into powder to cover the surface of the magnet or cutting the alloy ingot into a sheet on the surface of the magnet, or using the physical gas phase The method of deposition is to deposit a thin film on the surface of the magnet, and it should be ensured that the diffusion medium is in direct contact with the magnet to form a diffusion couple.

Further, the pressure of the vacuum in the step (3) is ≤1×10 ⁻² Pa, the temperature of the diffusion heat treatment is 500 to 800° C., and the time of the diffusion heat treatment is 1 to 5 h.

A high coercivity neodymium iron boron magnet is prepared by the above method.

The preparation method of the invention and the obtained product have the following advantages and beneficial effects:

(1) The method of the present invention is simple and effective, and the content of rare earth in the neodymium iron boron magnet is lowered, and the coercive force is improved as compared with the original magnet.

(2) Compared with the conventional grain boundary diffusion process, the present invention uses a non-rare earth alloy and a metal oxide as a grain boundary diffusion medium, and does not use a rare earth at all, which increases the coercive force and reduces the cost of the magnet.

(3) The present invention uses a non-rare earth alloy and a metal oxide as a diffusion medium, and is different from the conventional rare earth alloy or rare earth compound in the mechanism of coercivity improvement, and the coercivity improvement mechanism of the non-rare earth alloy and the metal oxide is also different. .

(4) The treatment process of the non-rare earth alloy of the present invention is simple and feasible, and the alloy preparation method has a simple process and low cost, and is suitable for mass production.

DRAWINGS

1 is a demagnetization curve of a high-coercivity NdFeB magnet obtained by diffusion heat treatment of a raw sintered NdFeB magnet and a non-rare earth alloy Al ₇₅ Cu ₂₅ powder in Example 1 of the present invention.

2 is a view of the original sintered NdFeB magnet in Example 1 of the present invention, which is subjected to heat treatment at 800 ° C / 2 h and then 500 ° C / 3 h, and is contacted with Al ₆₅ Cu ₃₅ , Al ₇₅ Cu ₂₅ and Al ₈₅ Cu ₁₅ powder. Demagnetization curve of high coercivity NdFeB magnet after diffusion heat treatment.

3 is a scanning electron microscope backscattered electron image of an untreated original sintered NdFeB magnet in Example 1.

4 is a scanning electron microscope backscattered electron image of a high coercivity NdFeB magnet obtained by diffusion heat treatment of an Al ₇₅ Cu ₂₅ alloy in the diffusion direction surface in Example 1 of the present invention.

5 is a scanning electron microscope backscattered electron image of a core portion of a high coercivity NdFeB magnet obtained by diffusion heat treatment of an Al ₇₅ Cu ₂₅ alloy in Example 1 of the present invention.

6 is a high-coercivity NdFeB magnet obtained by the original sintered NdFeB magnet and the non-rare earth alloys Al ₆₅ Cu ₃₅ , Al ₇₅ Cu ₂₅ and Al ₈₅ Cu ₁₅ after contact diffusion heat treatment in Example 2 of the present invention; Demagnetization curve.

Fig. 7 is a graph showing the initial demagnetization curve of the metal oxide diffusion-treated NdFeB magnet in Example 7 and the demagnetization curve of the NdFeB magnet treated by the metal oxide diffusion process of the present invention.

Fig. 8 is a schematic view showing scanning electron microscope backscattering of a neodymium iron boron magnet in which the metal oxide diffusion treatment is not performed in the seventh embodiment.

9 is a schematic view showing back-scattering of a magnetic core scanning electron microscope of a neodymium iron boron magnet treated by the metal oxide diffusion process of the present invention in Embodiment 7.

Fig. 10 is a schematic view showing the backscattering of a magnetic core scanning electron microscope of a neodymium iron boron magnet treated by the metal oxide diffusion process of the present invention.

Detailed ways

The present invention will be further described in detail below with reference to the embodiments and drawings, but the embodiments of the present invention are not limited thereto.

The low melting non-rare earth alloy used in the following examples was prepared by the following method:

(1) Preparation of non-rare earth Al-Cu alloy by argon arc melting, the preparation steps are as follows:

Step 1: Mixing the purity of 99.99% metal Al and metal Cu according to the molecular formulas Al ₆₅ Cu ₃₅ , Al ₇₅ Cu ₂₅ and Al ₈₅ Cu ₁₅ respectively;

Step 2: The well-matched metals Al and Cu are placed in the crucible of the argon arc melting furnace, vacuumed to 5×10 ^-3 Pa, smelted under the protection of argon gas, and repeatedly smelted several times to obtain a uniform composition of Al. ₆₅ Cu ₃₅ , Al ₇₅ Cu ₂₅ , and Al ₈₅ Cu ₁₅ alloy.

(2) Preparation of non-rare earth Al-Zn alloy by induction melting, the preparation steps are as follows:

Step 1: the purity of 99.99% metal Al, metal Zn and metal Cu according to the formula (total mass 10g);

Step 2: The ratio of good metal Al, metal Zn and metal Cu is placed in the crucible of the induction melting furnace, vacuumed to 5×10 ^-3 Pa, smelted under the protection of argon, and repeatedly smelted several times to obtain the composition. A uniform Al-Zn alloy.

(3) Preparation of non-rare earth Cu-Zn alloy by induction melting, the preparation steps are as follows:

Step 1: Mixing the purity of 99.99% metal Cu and metal Zn according to the molecular formula (total mass 10g);

Step 2: The metal Cu and metal Zn are loaded into the crucible of the induction melting furnace, vacuumed to 5×10 ^-3 Pa, smelted under the protection of argon gas, and repeatedly smelted several times to obtain a uniform composition of Cu. -Zn alloy.

Example 1

(1) The smelted Al ₆₅ Cu ₃₅ , Al ₇₅ Cu ₂₅ , and Al ₈₅ Cu ₁₅ alloys were crushed using a crusher under the protection of nitrogen, and the crushed powder was sieved to obtain a uniform particle size of 0.3 mm. powder;

(2) Cutting a commercial sintered NdFeB magnet into a 4×4×2 mm sheet, and laying the prepared non-rare earth Al ₆₅ Cu ₃₅ , Al ₇₅ Cu ₂₅ , and Al ₈₅ Cu ₁₅ alloy powder on the upper and lower surfaces of the magnet ( Vertically easy to magnetize direction) to form a diffusion couple;

(3) The above magnet is placed in a tube furnace and evacuated to 1 × 10 ^-2 Pa, diffusion heat treated at 800 ° C for 2 hours, and then tempered at 500 ° C for 3 hours to obtain a high coercivity NdFeB magnet. .

1 is a demagnetization curve of a high-coercivity NdFeB magnet obtained by diffusion heat treatment of a raw sintered NdFeB magnet and a non-rare earth alloy Al ₇₅ Cu ₂₅ powder in the present embodiment. It can be seen from the curve of Fig. 1 that the coercive force of the sintered NdFeB magnet has been significantly improved after diffusion through the non-rare earth alloy Al-Cu, from 1000kA/m to 1125kA/m, with an increase of 12%. The magnetic power is hardly reduced.

2 is a prior art sintered NdFeB magnet, a NdFeB magnet heat treated at 800 ° C / 2 h and then 500 ° C / 3 h, and a contact diffusion heat treatment of Al ₆₅ Cu ₃₅ , Al ₇₅ Cu ₂₅ and Al ₈₅ Cu ₁₅ powder The demagnetization curve of the high coercivity NdFeB magnet. As can be seen from the graph of Fig. 2, the magnet after simple heat treatment has a significant improvement in coercivity compared to the original magnet. It is indicated that the coercive force of the magnet can be further improved by a simple heat treatment, and the flow is simple and effective. Compared with the simple heat-treated magnet, the magnet after thermal diffusion of Al ₆₅ Cu ₃₅ , Al ₇₅ Cu ₂₅ and Al ₈₅ Cu _{15 has} a larger amplitude, indicating that the non-rare earth alloy Al ₆₅ Cu ₃₅ , Al ₇₅ Cu The diffusion of ₂₅ and Al ₈₅ Cu ₁₅ can successfully enter the inside of the magnet, improve the magnet structure, and increase the coercive force.

Figure 3 is a scanning electron microscopy backscattered electron image of an untreated original sintered NdFeB magnet. The dark black part is the main phase of sintered NdFeB, Nd ₂ Fe ₁₄ B, and the bright white part is the grain boundary rich phase. Different color contrasts in the 钕 phase are caused by different oxygen content. It can be seen from Fig. 3 that in the existing field of view, the main phases of the original sintered NdFeB magnets are adhered to each other, thereby increasing the magnetic exchange coupling between the main phases, thereby limiting the correction. Strong improvement.

4 is a scanning electron microscope backscattered electron image of a high coercivity NdFeB magnet obtained by diffusion heat treatment of an Al ₇₅ Cu ₂₅ alloy in the diffusion direction surface of the present embodiment, and the upper part of the image is a diffused Al-Cu alloy. The dark part of the lower layer is a magnet. It can be seen from Fig. 4 that after diffusion, the magnet portion near the surface layer of the diffuser forms a continuous thin layer of rich twin boundary phase, which isolates the main phase grains, weakens the magnetic exchange coupling between the grains, and promotes Increased coercivity. The magnetic properties of sintered NdFeB magnets are closely related to the microstructure. The increase of non-magnetic grain boundary phase isolates the exchange between the main phases and prevents the demagnetization domains at the grain boundaries. Nucleation, therefore, the grain boundary diffusion using a non-rare earth Al-Cu alloy has an optimized effect on the grain boundary of the sintered NdFeB magnet and can be used to improve the coercive force of the magnet.

FIG. 5 is a scanning electron microscope backscattered electron image of a core portion of a high coercivity NdFeB magnet obtained after diffusion heat treatment of an Al ₇₅ Cu ₂₅ alloy in the present embodiment. It can be seen from Fig. 5 that the microstructure of the core is substantially consistent with the microstructure of the untreated sintered NdFeB, indicating that the diffusion will have a diffusion gradient along the diffusion direction, and the diffusion does not penetrate the entire magnet. This is related to the wettability of the diffuser to the magnet and the physical properties of the diffuser itself, as well as the chemical nature of the internal structure of the magnet.

Example 2

(1) cutting the smelted Al ₆₅ Cu ₃₅ , Al ₇₅ Cu ₂₅ and Al ₈₅ Cu ₁₅ alloy wires into 7×7×0.4 mm sheets;

(2) Cutting the commercial sintered NdFeB magnet into 7×7×2mm sheets, and placing the prepared non-rare earth Al ₆₅ Cu ₃₅ , Al ₇₅ Cu ₂₅ and Al ₈₅ Cu ₁₅ alloy sheets on the upper and lower surfaces of the magnet (vertical easy a magnetization direction) forming a diffusion couple;

(3) The above magnet was placed in a tube furnace and evacuated to 1 × 10 ^-2 Pa, treated at 800 ° C for 2 hours, and then tempered at 500 ° C for 3 hours to obtain an improved high coercivity yttrium iron. Boron magnet.

6 is a demagnetization curve of a high coercivity NdFeB magnet obtained by a non-rare earth alloy Al ₆₅ Cu ₃₅ , Al ₇₅ Cu ₂₅ and Al ₈₅ Cu ₁₅ after contact diffusion heat treatment. It can be seen from Fig. 6 that the coercive force is improved after diffusion heat treatment of different composition non-rare earth Al-Cu alloys Al ₆₅ Cu ₃₅ , Al ₇₅ Cu ₂₅ and Al ₈₅ Cu ₁₅ compared with the original NdFeB magnet. The increase was 11%.

Table 1 shows the comparison of the coercive force at the same heat treatment temperature by contact diffusion and sheet contact diffusion of non-rare earth alloys Al ₆₅ Cu ₃₅ , Al ₇₅ Cu ₂₅ and Al ₈₅ Cu ₁₅ powder. It can be seen from the data in Table 1 that the different contact modes of the magnet and the diffuser produce different diffusion effects, and the powder contact diffuses in a better manner than the sheet contact. The way the powder is contacted allows the diffuser to have a tighter contact with the magnet, increasing the wettability between the diffuser and the magnet, making diffusion easier in the magnet, resulting in better coercivity enhancement.

Table 1 Comparison of Coercive Forces of Different Contact Modes of Diffusion and Magnet

Example 3

(1) The smelted Al-Zn alloy is crushed using a crusher under the protection of nitrogen, and the crushed powder is sieved to obtain a uniform powder having a particle size of 0.3 mm;

(2) cutting a commercial sintered NdFeB magnet into a 4×4×2 mm sheet, and laying the prepared non-rare earth Al-Zn alloy powder on the upper and lower surfaces of the magnet (vertical easy magnetization direction) to form a diffusion couple;

Example 4

(1) cutting the smelted Al-Zn alloy wire into a sheet of 7 × 7 × 0.4 mm;

(2) cutting a commercial sintered NdFeB magnet into a 7×7×2 mm sheet, and placing the prepared non-rare earth Al-Zn alloy sheet on the upper and lower surfaces of the magnet (vertical easy magnetization direction) to form a diffusion couple;

Example 5

(1) The smelted Cu-Zn alloy is crushed using a crusher under the protection of nitrogen, and the crushed powder is sieved to obtain a uniform powder having a particle size of 0.3 mm;

(2) cutting a commercial sintered NdFeB magnet into a 4×4×2 mm sheet, and laying the prepared non-rare earth Cu-Zn alloy powder on the upper and lower surfaces of the magnet (vertical easy magnetization direction) to form a diffusion couple;

Example 6

(1) cutting the smelted Cu-Zn alloy wire into a sheet of 7 × 7 × 0.4 mm;

(2) cutting a commercial sintered NdFeB magnet into a 7×7×2 mm sheet, and placing the prepared non-rare earth Cu-Zn alloy sheet on the upper and lower surfaces of the magnet (vertical easy magnetization direction) to form a diffusion couple;

Example 7

(1) The NdFeB magnet was cut into 10×10×4mm thin pieces by wire cutting, and then placed in a magnetron sputtering apparatus. MgO with a purity of 99.99% was used as a target to deposit a layer of MgO. a film, wherein the sputtering power is 150 W, the working gas pressure is 0.5 Pa, the Ar gas flow rate is 20 sccm, the time is 0.5 h, and the temperature is room temperature;

(2) The above magnet was heat-treated at 900 ° C for 4 hours in an inert gas argon (Ar) to obtain an improved neodymium iron boron magnet.

Fig. 7 is a schematic view showing the change of the demagnetization curve of the original NdFeB magnet and the NdFeB magnet improved by the metal oxide diffusion process. It can be seen from Fig. 7 that the coercive force of the improved NdFeB magnet is improved from 1094 kA/m to 1170 kA/m by the metal oxide diffusion process of MgO without using expensive heavy rare earth, and the residual magnetism Also increased, from 1.19T to 1.20T.

8 is a schematic diagram of SEM backscattering of a neodymium iron boron magnet (a) after being subjected to a metal oxide diffusion process, and FIG. 9 is a neodymium iron boron magnet treated by the metal oxide diffusion process of the present invention (b) Schematic diagram of backscattering of the surface of the magnet by scanning electron microscopy, and FIG. 10 is a schematic diagram of backscattering of the core of the neodymium iron boron magnet (c) after the metal oxide diffusion process of the present invention. Wherein the number A, the number D and the number G represent the main phase particles Nd ₂ Fe ₁₄ B, and the number B, the number C, the number E, the number F and the number H represent the grain boundary rare-earth phase of different morphologies. As can be seen from Fig. 8 and Fig. 10, the microstructure of the grain boundary phase of the neodymium iron boron magnet is obviously optimized by the metal oxide diffusion process of the present invention. The rare earth-rich phase becomes smoother and more straight, suppressing the nucleation of the magnetization domain, which has a significant effect on the improvement of coercivity. Table 2 is the relative atomic percentage and phase composition of the Nd, Pr, Fe, O and Mg elements in the areas marked with numbers A to H in Figures 8 to 10. It is found that the heavy rare earth (Dy or Tb) or its oxidation is currently popular. Compared with the NdFeB magnet treated by the grain boundary diffusion process, the grain boundary diffusion of heavy rare earth (Dy or Tb) or its oxide is mainly through heavy rare earth (Dy or Tb) and the surface of the main phase particles. A displacement reaction occurs to form (Nd, Dy) ₂ Fe ₁₄ B, which increases the local anisotropy field on the surface of the main phase particles, thereby increasing the coercive force of the magnet. However, the Mg in the metal oxide diffusion process of the present invention does not react with the main phase particles, but only exists in the grain boundary phase, and the newly formed Nd-Mg-Fe-O plays a certain role relative to the domain wall. The pinning action increases the coercivity of the magnet.

Table 2 Figure 8-10 shows the relative atomic percentages and phase composition of the Nd, Pr, Fe, O and Mg elements in the corresponding regions.

Example 8

(1) The NdFeB magnet was cut into 10×10×4mm thin pieces by wire cutting, and then placed in a magnetron sputtering apparatus. A ZnO with a purity of 99.99% was used as a target to deposit a layer of ZnO. a film, wherein the sputtering power is 150 W, the working gas pressure is 0.5 Pa, the Ar gas flow rate is 20 sccm, the time is 0.5 h, and the temperature is room temperature;

Table 2 Figure 8-10 Nd, Pr, Fe, O and Mg components and phase composition of the corresponding areas from No. A to H

The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and modifications may be made without departing from the spirit and scope of the invention. Simplifications should all be equivalent replacements and are included in the scope of the present invention.

Claims

A method for preparing a high coercivity neodymium iron boron magnet, characterized by comprising the following preparation steps:

(1) preparing a low melting non-rare earth alloy and a metal oxide having a melting point of 450 to 950 ° C as a surface diffusion medium;

(2) placing the surface diffusion medium of step (1) on the surface of the neodymium iron boron magnet in a certain manner to form a diffusion couple;

(3) The NdFeB magnet which forms the diffusion couple in the step (2) is subjected to diffusion heat treatment under vacuum to obtain a high coercivity NdFeB magnet.
The method for preparing a high coercivity neodymium iron boron magnet according to claim 1, wherein the low melting non-rare earth alloy in the step (1) is an Al-Cu, Al-Zn or Cu-Zn alloy. And other low melting point binary or ternary alloys containing Al, Cu, Zn, Ga, Ni, Fe, Sn, and the like.
The method for preparing a high coercivity neodymium iron boron magnet according to claim 1, wherein the metal oxide in the step (2) is magnesium oxide and zinc oxide, and other metal oxides.
The method for preparing a high coercivity neodymium iron boron magnet according to claim 1, wherein the neodymium iron boron magnet in the step (2) is a sintered neodymium iron boron magnet and a bonded neodymium iron boron magnet Or hot pressed hot deformation NdFeB magnets.
The method for preparing a high coercivity neodymium iron boron magnet according to claim 1, wherein the surface of the neodymium iron boron magnet in step (2) is perpendicular to the direction of easy magnetization of the neodymium iron boron magnet surface.
The method for preparing a high-coercivity NdFeB magnet according to claim 1, wherein the method of placing the surface diffusion medium on the surface of the NdFeB magnet in the step (2) comprises breaking the alloy ingot The powder is covered on the surface of the magnet, or the alloy ingot is cut into a thin sheet to be placed on the surface of the magnet, or a film of a diffused substance is deposited on the magnet by physical vapor deposition, so that the diffusion medium is in direct contact with the magnet to form a diffusion couple.
A method of preparing a high coercivity neodymium iron boron magnet according to claim 1, wherein the pressure of the vacuum in the step (4) is ≤ 1 × 10 -2 Pa.
The method for preparing a high coercivity neodymium iron boron magnet according to claim 1, wherein the diffusion heat treatment temperature is 500 to 800 ° C, and the diffusion heat treatment time is 1 to 5 hours.
A high coercivity neodymium iron boron magnet produced by the method according to any one of claims 1 to 8.