Diffusion process using high-abundance rare earth grain boundary diffusion composite diffusor and application

Abstract

The invention belongs to the field of rare earth permanent magnetic material diffusion processes, and particularly relates to a diffusion process and application of a grain boundary diffusion composite diffuser using abundance rare earth. Aiming at the problem of unbalanced utilization of rare earth caused by the existing grain boundary diffusion technology, the invention provides the diffusion process of the grain boundary diffusion composite diffusor using the high-abundance rare earth, the grain boundary diffusion composite diffusor using the high-abundance rare earth is used, and the surface of a neodymium-iron-boron magnet is coated with the diffusor and then is subjected to heat treatment. According to the method, the synergistic effect mechanism of the light rare earth and the heavy rare earth in the diffusor is analyzed and concluded through the system, the light rare earth promotes the utilization of the heavy rare earth, and the diffusion depth and the coercive force improvement effect of the high-abundance light rare earth diffusor are remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of diffusion process of rare earth permanent magnet materials, and particularly relates to a diffusion process of grain boundary diffusion composite diffusion source using high-abundance rare earth. BACKGROUND

[0002] Nd-Fe-B permanent magnet refers to a metal compound Nd2Fe 14 B, which has high saturation magnetization, high anisotropy field, high magnetic energy product and other advantages, and is currently mainly used in new energy vehicles, wind power generation, precision instruments and other fields. With the rapid development of the above-mentioned fields, the demand for high-performance Nd-Fe-B magnets is also increasing. High-performance Nd-Fe-B permanent magnets are currently commonly prepared by grain boundary diffusion process in industry. The grain boundary diffusion process refers to coating Dy, Tb or other heavy rare earth elements on the surface of the magnet, and then performing heat treatment to melt the heavy rare earth diffusion source on the surface of the magnet and the grain boundary phase inside the magnet, so that the heavy rare earth atoms diffuse along the liquid phase of the grain boundary. Compared with the traditional alloying element addition process, i.e. adding elements, mixing and melting all raw materials, and then uniformly mixing, powdering, magnet forming and sintering, this method can obtain high-coercivity magnets with less heavy rare earth elements such as Dy and Tb, thereby effectively reducing the cost. However, the grain boundary diffusion process still requires heavy rare earth elements. At the same time, in the naturally distributed light rare earth resources, Pr and Nd elements account for about 25% of the total amount, and the co-occurring La and Ce elements account for about 73%. The consumption of rare earth elements in the Nd-Fe-B industry accounts for about 40% of the total consumption of rare earth elements, among which the heavy rare earth elements such as Dy and Tb and the light rare earth elements such as Pr and Nd are used more. Since the reserves of La (25500 yuan / ton) and Ce (29000 yuan / ton) are less used and have lower prices, they are far lower than the prices of Pr (755000 yuan / ton) and Nd (697500 yuan / ton). As can be seen, La and Ce elements have abundant reserves and low prices, but are less used due to lower anisotropy field and other reasons, and are in surplus. This leads to a significant structural imbalance in the utilization of rare earth resources.

[0003] In order to improve the above-mentioned situation of using more heavy rare earth elements in grain boundary diffusion and the significant structural imbalance in the utilization of rare earth resources, researchers have tried to use alloy diffusion sources and add light rare earth elements to the alloy diffusion sources. However, there are still some deficiencies. The performance of the magnet after diffusion of the alloy diffusion source with added light rare earth elements is still much lower than that of the magnet without added light rare earth elements. Therefore, developing an alloy diffusion source containing high-abundance light rare earth elements with similar performance improvement as ordinary alloy diffusion sources after diffusion can further reduce the use of heavy rare earth elements in the diffusion source, reduce the cost of the diffusion source, and save heavy rare earth resources. It can also alleviate the imbalance in the utilization of rare earth resources and make full use of the currently accumulated high-abundance light rare earth elements, which is crucial for the rare earth industry and the Nd-Fe-B industry. SUMMARY

[0004] In view of the uneven utilization of rare earth caused by the existing grain boundary diffusion technology, the application provides a diffusion process using a high-abundance rare earth grain boundary diffusion composite diffuser. The application induces the synergistic mechanism of light rare earth and heavy rare earth in the diffuser through systematic analysis, promotes the utilization of heavy rare earth by light rare earth, and significantly improves the diffusion depth and coercivity improvement effect of the high-abundance light rare earth diffuser.

[0005] The application provides a diffusion process using a high-abundance rare earth grain boundary diffusion composite diffuser, and a high-abundance rare earth grain boundary diffusion composite diffuser is used.

[0006] Preferably, the diffusion process specifically comprises the following steps:

[0007] (1) cutting the neodymium-iron-boron magnet along the easy magnetization axis into a sample with a thickness of 3-10 mm, ensuring that the cutting surface is flat, and then washing and drying;

[0008] (2) preparing an alloy diffusion source LRE-HRE-M: wherein LRE is a light rare earth element containing La and Ce, accounting for 10-70 at.%, HRE is one of Dy, Tb and Ho, accounting for 5-20 at.%, and M is one or more of Cu, Al, Ga and Zn, accounting for 5-30 at.%; after preparing the alloy diffusion source LRE-HRE-M, the diffusion source powder with a particle size of less than 200 μm is prepared by crushing;

[0009] (3) mixing the diffusion source powder and organic components into slurry, wherein the organic components include organic binders;

[0010] applying the slurry to the surface of the magnet perpendicular to the c-axis by screen printing or spraying process at a coating amount of 0.1-5% of the total mass of the magnet, and drying to form a diffusion layer;

[0011] (4) performing heat treatment under vacuum conditions, and the heat treatment comprises a high-temperature diffusion stage and a tempering treatment stage.

[0012] Preferably, in step (1), the ensuring that the cutting surface is flat, and then washing and drying, specifically comprises: mechanically polishing and polishing the cutting surface, and then ultrasonic cleaning with anhydrous ethanol or acetone and drying at 80-120℃.

[0013] Preferably, in step (2), the alloy diffusion source LRE-HRE-M is prepared by arc melting method.

[0014] Preferably, in step (3), the diffusion source powder and the organic components are mixed into slurry at a mass ratio of (75-85):(15-25).

[0015] Preferably, in step (4), the heat treatment is performed under a vacuum degree of 6*10-3 Pa.

[0016] Preferably, in step (4), the high-temperature diffusion stage specifically comprises: heat preservation at 750-950 DEG C for 2-60 hours to form a low-melting-point liquid phase channel to promote heavy rare earth diffusion; and the tempering stage comprises: tempering at 400-600 DEG C for 2-8 hours to form a core-shell structure magnet.

[0017] The application also provides an application of the diffusion process to prepare high-performance low-cost neodymium-iron-boron magnets.

[0018] Compared with the prior art, the application has the following beneficial effects:

[0019] 1. The melting point of the diffusion source is reduced due to the use of the alloy diffusion source, which helps to improve the diffusion efficiency.

[0020] 2. The utilization rate of heavy rare earth is improved, and the diffusion depth and the improvement range of the coercive force are increased by utilizing the synergistic effect between light and heavy rare earth.

[0021] 3. The use of heavy rare earth is saved, and the cost of the diffusion material is reduced.

[0022] 4. The high-abundance light rare earth such as La and Ce with high yield is fully used, and the problem of unbalanced utilization of rare earth resources is alleviated. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the specific embodiments or the prior art, the following will briefly introduce the drawings needed to be used in the specific embodiments or the prior art description, and the following will refer to the drawings to specifically describe some specific embodiments of the application in an exemplary but non-limiting manner. The same reference signs in the drawings indicate the same or similar components or parts. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings:

[0024] Figure 1 is a demagnetization curve diagram of the original magnet in case 1 and the magnet after diffusion of different diffusion materials;

[0025] Figure 2 is a cost comparison diagram calculated in case 1;

[0026] Figure 3 is an EPMA diagram of the magnet after diffusion of different diffusion materials in case 1;

[0027] Figure 4 is a heavy rare earth diffusion depth diagram of the magnet after diffusion of different diffusion materials in case 1. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application.

[0029] General embodiment:

[0030] The specific steps are as follows

[0031] A. Cut the neodymium-iron-boron magnet along the easy magnetization axis (c-axis) direction into a sample with a thickness of 3-10 mm, and ensure that the cutting surface is flat. Then, mechanically polish and polish the surface of the sample to facilitate uniform coating of the subsequent diffusion paste. After polishing, the surface of the sample is ultrasonically cleaned with anhydrous ethanol or acetone to remove residual grease and swarf, and is dried at 80-120°C for standby.

[0032] B. Prepare an alloy diffusion source LRE-HRE-M, wherein LRE is a plurality of light rare earth elements Pr, Nd, La, Ce, Y, wherein La or Ce must be present, accounting for 50-70 at.%; HRE is one of heavy rare earth elements Dy, Tb, Ho, accounting for 10-30 at.%; M is one or more of transition elements Cu, Al, Ga, Zn with a melting point, accounting for 20-40 at.%. After preparing the alloy, the alloy is crushed, and a hydrogen breaking airflow grinding process is preferably used to obtain more uniform and fine diffusion particles.

[0033] C. Mix the diffusion source powder, organic carrier and organic polymer compound (binder) according to a certain mass ratio (75-85):(15-25), stir uniformly to form a slurry. Control the viscosity of the slurry to ensure uniformity of coating during screen printing. The slurry is uniformly coated on the upper and lower surfaces of the magnet perpendicular to the c-axis by screen printing or spraying process, and the coating amount is controlled at 0.1-5% of the total mass of the magnet. After coating, the sample is placed in an oven for drying, so that the organic carrier is fully volatilized to form a stable diffusion layer.

[0034] D. Place the coated magnet in a high vacuum sintering furnace (vacuum degree ≤6×10-3Pa) for heat treatment, and the specific process is as follows: (1) high temperature diffusion stage: heat at 750-950°C for 2-60 hours to promote the reaction of light rare earth elements and low melting point elements with the grain boundary phase to form a low melting point liquid phase with a melting point less than 900°C, and at the same time, the heavy rare earth elements diffuse into the magnet along the liquid phase channel to form a shell layer; (2) tempering stage: temper at 400-600°C for 2-8 hours to optimize the distribution of the grain boundary phase and eliminate internal stress, and finally obtain a magnet with continuous grain boundary phase and core-shell structure.

[0035] The diffusion method can effectively promote the diffusion of heavy rare earth through the synergistic effect of light and heavy rare earth, form a core-shell structure in the magnet, and improve the coercivity.

[0036] Example 1

[0037] A. A commercial 42M neodymium iron boron magnet was cut along the C-axis direction to a thickness of 5mm, and then the surface of the sample was mechanically polished and polished. After polishing, the sample surface was cleaned by ultrasonic cleaning with anhydrous ethanol to remove residual grease and swarf, and dried at 80°C for standby.

[0038] B. Four elements of La, Ce, Tb, Cu were dosed according to the ratio of La 42 Ce8Tb 20 Cu 30 (at.%) in an arc melting furnace for sufficient melting, and then a 200 mesh screen was used to obtain a diffusion source powder of about 75μm particle size.

[0039] C. The diffusion powder after mechanical crushing was mixed with the binder at a ratio of 75:25 to prepare the diffusion slurry.

[0040] D. The diffusion slurry with a weight ratio of 1.0wt% was uniformly coated on the upper and lower surfaces of the pretreated cerium-rich neodymium iron boron magnet perpendicular to the c-axis by screen printing process, and then sent to a drying oven at 120°C for 20 minutes to complete the diffusion slurry solidification.

[0041] E. The dried coated magnet was placed in a vacuum sintering furnace and diffused at 900°C for 12 hours, and then tempered at 500°C for 3 hours. The demagnetization curve of the diffused magnet is shown in Figure 1 The coercivity Hcj of the diffused magnet is 22.88kOe, and Br is 11.9kGs.

[0042] By Figure 3 , Figure 4 It is found that the heavy rare earth diffusion depth distribution of the magnet using the method is deeper and the diffusion is more sufficient.

[0043] Example 2

[0044] The difference from Example 1 is that in step B: LRE light rare earth element uses Y, La, Ce;

[0045] HRE heavy rare earth element uses Ho;

[0046] Transition element uses Zn;

[0047] Four elements of La, Ce, Tb, Cu were dosed according to the ratio of La 40 Ce8Y2Ho 30Zn 20 The four elements of La, Ce, Tb, Cu are proportioned according to La

[0048] Example 3

[0049] The difference from Example 1 is that in step B: the LRE light rare earth element uses Nd, La, Ce;

[0050] The HRE heavy rare earth element uses Dy;

[0051] The transition group element uses Al;

[0052] The four elements of La, Ce, Tb, Cu are proportioned according to La 50 Ce8Nd2Dy 10 Al 30 The four elements of La, Ce, Tb, Cu are proportioned according to La

[0053] Example 4

[0054] The difference from Example 1 is that in step B: the LRE light rare earth element uses Pr, La, Ce;

[0055] The HRE heavy rare earth element uses Ho;

[0056] The transition group element uses Ga;

[0057] The four elements of La, Ce, Tb, Cu are proportioned according to La 50 Ce8Pr2Ho 15 Ga 25 The four elements of La, Ce, Tb, Cu are proportioned according to La

[0058] The above description is only part of the specific embodiments of the present application, but the protection scope of the present application is not limited to this, any person skilled in the art can easily think of the changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. A grain boundary diffusion composite diffuser diffusion process using high abundance rare earths, characterized by, A grain boundary diffusion composite diffusion source with high abundance of rare earth is used, and the diffusion source is coated on the surface of a neodymium-iron-boron magnet and then heat treated.

2. The diffusion process of claim 1, wherein, Specifically comprising the following steps: (1) cutting the neodymium-iron-boron magnet along the easy magnetization axis into a sample with a thickness of 3-10 mm, ensuring that the cutting surface is flat, and then washing and drying; (2) preparing an alloy diffusion source LRE-HRE-M: wherein LRE is a light rare earth element containing La and Ce, accounting for 40-70 at.%, HRE is one of Dy, Tb and Ho, accounting for 10-30 at.%, and M is one or more of Cu, Al, Ga and Zn, accounting for 20-40 at.%; after the preparation of the alloy diffusion source LRE-HRE-M, the diffusion source powder with a particle size of less than 200 μm is prepared by crushing; (3) mixing the diffusion source powder with organic components into a slurry, wherein the organic components include an organic binder; applying the slurry to the surface of the magnet perpendicular to the c-axis by a screen printing or spraying process with a coating amount of 0.1-5% of the total mass of the magnet, and drying to form a diffusion layer; (4) heat treating under vacuum conditions, and the heat treatment includes a high-temperature diffusion stage and a tempering treatment stage.

3. The diffusion process according to claim 2, wherein in step (1), the ensuring that the cutting surface is flat, and then washing and drying, specifically comprises: mechanically polishing and polishing the cutting surface, and then ultrasonic cleaning with anhydrous ethanol or acetone and drying at 80-120°C.

4. The diffusion process according to claim 2, wherein in step (2), the alloy diffusion source LRE-HRE-M is prepared by an arc melting method.

5. The diffusion process according to claim 2, wherein in step (3), the diffusion source powder and the organic components are mixed into a slurry at a mass ratio of (75-85):(15-25).

6. The diffusion process according to claim 2, wherein in step (4), the heat treatment is performed under a vacuum degree of ≤6×10-3Pa.

7. The diffusion process according to claim 2, wherein in step (4), the high-temperature diffusion stage specifically comprises: 750-950°C for 2-60 hours to form a low-melting-point liquid phase channel to promote the diffusion of heavy rare earth; and the tempering treatment stage comprises: 400-600°C for 2-8 hours to form a core-shell structure magnet.

8. Use of a diffusion process as claimed in any one of claims 1-7, characterized in that, It is applied to the preparation of high-performance low-cost neodymium-iron-boron magnets.

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