A method for grain boundary diffusion of NdFeB waste

Abstract

The present invention provides a method for grain boundary diffusion of NdFeB scrap, comprising the following steps: A) mechanically crushing the NdFeB scrap to obtain coarse magnetic powder; B) subjecting the coarse magnetic powder to HDDR treatment to obtain HDDR magnetic powder; C) subjecting the HDDR magnetic powder to vacuum heat treatment, followed by hydrogenation reduction crushing; and D) embedding the powder obtained in step C) on the surface of a substrate and then subjecting it to grain boundary diffusion treatment. The NdFeB scrap provided by the present invention is modified to prepare the NdFeB scrap into a diffusion source by regulating the distribution of rare earth elements in the scrap, thereby achieving the recovery and efficient utilization of rare earth resources. The method is simple to operate, low-cost, and easily adaptable to mass production applications.

Description

Technical Field

[0001] The invention relates to the technical field of rare earth permanent magnet material production, in particular to a method for grain boundary diffusion of NdFeB waste. Background Art

[0002] NdFeB rare earth permanent magnets, due to their exceptionally high magnetic properties, are widely used in industries such as wind power generation, electric motors, and electronics. They are recognized as essential strategic materials for the development of high-tech and the transformation of traditional industries. In recent years, the continuous expansion of the NdFeB permanent magnet industry and the rapid increase in production capacity have led to a rapid increase in rare earth resource consumption. Intensive utilization of rare earth resources, the development of resource-saving, high-performance NdFeB magnets, and the development of magnet recycling technologies have become key areas of development in this field. Among these, the recycling and reuse of spent NdFeB magnets or NdFeB processing waste, particularly the effective extraction and efficient reuse of the precious rare earth elements in NdFeB magnets, has become a key focus.

[0003] NdFeB is composed of a 2:14:1 tetragonal phase. Normally, the rare earth component in its magnet material accounts for 29% to 34% of the total mass of the magnet, of which about 26.8% is used to form Nd2Fe 14 The B main phase and the remaining approximately 2.2% to 7.2% of rare earths are used for liquid phase sintering and densification in the magnet powder metallurgy preparation process, and eventually form a rare earth-rich intergranular phase. It is of great significance to achieve simple and efficient utilization of this part of rare earth elements in waste magnets during the industrialization process.

[0004] Recently, NdFeB grain boundary diffusion technology has developed rapidly. The principle is to attach a diffusion source containing rare earth components to the surface of the NdFeB magnet. Through a certain heat treatment process, and according to Fick's law of diffusion, the rare earth elements enter the magnet from the surface along the grain boundaries under the action of the concentration gradient driving force, thereby repairing the surface defects of the grains and optimizing the microstructure, ultimately achieving an effective increase in the coercive force of the magnet. If the rare earth components in waste magnets can be used as a diffusion source to modify the magnet products through grain boundary diffusion, it will be possible to fully utilize the valuable rare earth resources in waste magnets and achieve the goal of improving the performance of magnet products.

[0005] However, if waste magnets are extracted to purify rare earth elements, the cycle is long and it is difficult for conventional NdFeB manufacturers to complete the process due to the lack of relevant extraction equipment, or the cost is high; if waste magnets are directly crushed and prepared into diffusion sources attached to the magnet surface, the diffusion process and its control are difficult to achieve due to the lack of a concentration gradient of rare earth elements between the diffusion source and the base magnet.

[0006] In view of this, the present application pre-designs a treatment method utilizing grain boundary diffusion of NdFeB waste. By modifying the NdFeB waste to a certain extent, the rare earth components in the waste are extracted and prepared into a diffusion source that is easy to control and carry out the diffusion reaction, and can be recycled and reused multiple times. This has far-reaching significance for promoting the efficient utilization of rare earth resources and the rapid development of the rare earth permanent magnet field. Summary of the Invention

[0007] The technical problem solved by the present invention is to provide a method for grain boundary diffusion of NdFeB scrap. The method provided in this application can extract rare earth components in NdFeB scrap and prepare them into diffusion sources that are easy to control diffusion reactions and conduct, which can promote the efficient utilization of rare earth resources and improve the magnetic properties of the matrix.

[0008] In view of this, the present application provides a method for grain boundary diffusion of NdFeB scrap, comprising the following steps:

[0009] A) Mechanically crushing NdFeB waste to obtain coarse magnetic powder;

[0010] B) subjecting the coarsely crushed magnetic powder to HDDR treatment to obtain HDDR magnetic powder;

[0011] C) subjecting the HDDR magnetic powder to vacuum heat treatment, and then subjecting it to hydrogenation reduction and crushing;

[0012] D) The powder obtained in step C) is buried on the surface of the substrate and then subjected to grain boundary diffusion treatment.

[0013] Preferably, the HDDR processing is specifically as follows:

[0014] The steps of the hydrogenation and disproportionation stage are as follows: placing the coarse crushed magnetic powder in a hydrogen heat treatment furnace, introducing 10-50 kPa of hydrogen at room temperature, heating to 100-300° C., then replenishing the hydrogen to 80-100 kPa, maintaining the temperature and pressure for 0.5-4 hours, continuing to heat to 800-1000° C., then maintaining the hydrogen pressure at 10-50 kPa, maintaining the temperature and pressure for 30-240 minutes, and completing the hydrogenation and disproportionation stage;

[0015] Steps of the recombinant stage: Evacuate the furnace to a vacuum degree of not less than 1×10 -2 Pa, keep warm for 60 to 120 minutes to complete the recombination stage.

[0016] Preferably, the temperature of the vacuum heat treatment is 1000-1500°C, and the vacuum degree is not less than 1×10 -3 Pa, time is 1 to 10 hours.

[0017] Preferably, the process of hydrogenation reduction crushing is specifically as follows:

[0018] The vacuum heat-treated powder is placed in a heat treatment furnace, and 5kPa to 100kPa hydrogen-argon mixed gas is introduced for 1 to 6 hours; then vacuum is evacuated and heated to 100 to 500°C for 1 to 10 hours.

[0019] Preferably, the embedding method is specifically as follows:

[0020] The powder obtained in step C) is spread on the bottom of the crucible, and then the substrate is placed therein. The powder is then poured into the crucible until it covers the upper surface of the substrate.

[0021] Preferably, the height of the base is 3 to 10 mm, and the diameter is 6 to 10 mm.

[0022] Preferably, the particle size of the coarse magnetic powder is 50 μm to 500 μm.

[0023] Preferably, the substrate is a sintered NdFeB magnet.

[0024] Preferably, the grain boundary diffusion treatment is specifically as follows:

[0025] The powder obtained in step C) is buried on the surface of the substrate and then placed in a vacuum heat treatment furnace, heated to 800-1000°C in a vacuum environment, with a vacuum degree of not less than 1×10 -2 Pa, keep warm for 1 to 10 hours, then keep warm at 450 to 550 ° C for 1 to 10 hours, and pass argon to cool to room temperature.

[0026] Preferably, the NdFeB waste is selected from one or more of NdFeB material machining scraps, waste magnets, waste rapid solidification alloys and waste rapid quenching strips.

[0027] The present application provides a method for grain boundary diffusion of NdFeB scrap, which first mechanically crushes the NdFeB scrap, then subjects the obtained coarsely crushed magnetic powder to HDDR treatment, then vacuum heat treatment the obtained magnetic powder, followed by hydrogenation reduction crushing, and finally burying the crushed powder on the surface of a substrate and subjecting it to crystallization diffusion treatment. The present application performs HDDR treatment on coarse magnetic powder, which can induce microcracks or breakage in the waste particles during a low-temperature process, causing the nano-scale grains in the particles to swallow up and grow. Only the swallowing and growth of the nano-scale grains formed after the HDDR treatment can squeeze the rare earth-rich phase to the periphery of the particles, and reduce rare earth oxidation through subsequent hydrogenation, reduction and crushing, so that the rare earth on the outer layer of the particles has good diffusivity and wettability, thereby forming a concentration gradient between the rare earth on the outer layer of the particles and the matrix, generating a good diffusion driving force, and facilitating the diffusion reaction; and the subsequent heat treatment and hydrogenation, reduction and crushing of the HDDR magnetic powder in the present application cooperate with each other to maximize the regulation of the rare earth component distribution of the magnetic powder and ensure the diffusion effect of the rare earth; therefore, the method provided by the present application can extract the rare earth components in NdFeB waste and prepare them into diffusion sources that are easy to control diffusion reactions and carry out, promote the efficient utilization of rare earth resources, and improve the magnetic properties of the matrix. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The figure is a schematic flow chart of the method for grain boundary diffusion of NdFeB scrap according to the present invention. DETAILED DESCRIPTION

[0029] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0030] In view of the problems in the prior art of purifying rare earth elements from waste magnets and the difficulty in controlling the diffusion process, the present application provides a method for grain boundary diffusion of NdFeB waste, which first performs HDDR treatment on the NdFeB waste and combines it with subsequent vacuum heat treatment, hydrogenation reduction crushing and buried grain boundary diffusion treatment to effectively extract and utilize the rare earth elements in the waste magnets, facilitate the diffusion reaction, and ultimately improve the performance of the magnet matrix. The flow diagram of the method for grain boundary diffusion of NdFeB waste in the present application is shown in the figure. Figure 1 More specifically, an embodiment of the present invention discloses a method for grain boundary diffusion of NdFeB scrap, comprising the following steps:

[0031] A) Mechanically crushing NdFeB waste to obtain coarse magnetic powder;

[0032] B) subjecting the coarsely crushed magnetic powder to HDDR treatment to obtain HDDR magnetic powder;

[0033] C) subjecting the HDDR magnetic powder to vacuum heat treatment, and then subjecting the HDDR magnetic powder to hydrogenation reduction and crushing;

[0034] D) The powder obtained in step C) is buried on the surface of the substrate and then subjected to grain boundary diffusion treatment.

[0035] In the method for treating NdFeB scrap grain boundary diffusion, the present application first mechanically crushes the NdFeB scrap to obtain coarse magnetic powder. According to the present invention, the NdFeB scrap is first dried before mechanical crushing. The drying method is well known to those skilled in the art and is not particularly limited in this application. The mechanical crushing is well known to those skilled in the art and is not particularly limited in this application. The coarse magnetic powder obtained after the mechanical crushing has a particle size of 50 to 500 μm, and specifically, the particle size of the coarse magnetic powder is 100 to 300 μm.

[0036] The present application then subjects the coarsely crushed magnetic powder to an HDDR process to obtain HDDR magnetic powder. The present application adjusts the traditional HDDR process to facilitate ensuring the diffusion effect of rare earths. Specifically, the HDDR process described in the present application is as follows:

[0037] The steps of the hydrogenation and disproportionation stage are as follows: placing the coarse crushed magnetic powder in a hydrogen heat treatment furnace, introducing 10-50 kPa of hydrogen at room temperature, heating to 100-300° C., then replenishing the hydrogen to 80-100 kPa, maintaining the temperature and pressure for 0.5-4 hours, continuing to heat to 800-1000° C., then maintaining the hydrogen pressure at 10-50 kPa, maintaining the temperature and pressure for 30-240 minutes, and completing the hydrogenation and disproportionation stage;

[0038] Steps of the recombinant stage: Evacuate the furnace to a vacuum degree of not less than 1×10 -2 Pa, keep warm for 60 to 120 minutes to complete the recombination stage.

[0039] More specifically, the steps of the hydrogenation and disproportionation stage are as follows: placing the coarse crushed magnetic powder in a hydrogen heat treatment furnace, introducing 20-40 kPa of hydrogen at room temperature, heating to 150-250° C., then replenishing the hydrogen to 85-95 kPa, maintaining the temperature and pressure for 1-3 hours, continuing to heat to 850-950° C., then maintaining the hydrogen pressure at 20-40 kPa, maintaining the temperature and pressure for 50-200 minutes, and completing the hydrogenation and disproportionation stage;

[0040] Steps of the recombinant stage: Evacuate the furnace to a vacuum degree of not less than 1×10 -2 Pa, keep warm for 80 to 100 minutes to complete the recombination stage.

[0041] In the aforementioned HDDR process, the present invention utilizes a continuous hydrogenation and disproportionation phase with increasing temperature and introducing hydrogen. This process can induce further microcracks in the waste particles during the low-temperature process, allowing for more complete hydrogen disproportionation reactions during the subsequent high-temperature phase. The HDDR process efficiently refines the NdFeB scrap magnetic powder to achieve nanocrystalization, and utilizes the principle of abnormal grain engulfment to control the microscopic distribution of the rare earth-rich phase. To achieve this effect, the vacuum heat treatment temperature is further controlled to 1000-1500°C.

[0042] The present application then performs vacuum heat treatment on the magnetic powder obtained by HDDR treatment, and then performs hydrogenation reduction crushing to cooperate with HDDR treatment, maximize the control of the rare earth component distribution of the magnetic powder, and ensure the diffusion effect of rare earth. The temperature of the vacuum heat treatment is 1000-1500℃, and the vacuum degree is not less than 1×10 -3 Pa, for 1 to 10 hours; specifically, the temperature of the vacuum heat treatment is 1000 to 1100°C, and the time is 3 to 7 hours. The hydrogenation reduction crushing is specifically as follows: placing the vacuum heat-treated powder in a heat treatment furnace, passing 5kPa to 100kPa of hydrogen-argon mixed gas, and holding the pressure for 1 to 6 hours; then evacuating and heating to 100 to 500°C, and holding the temperature for 1 to 10 hours; specifically, the pressure of the hydrogen-argon mixed gas is 10 to 80kPa, and the pressure is held for 2 to 5 hours, and the heating temperature is 200 to 400°C, and the time is 3 to 8 hours.

[0043] Finally, the present application buries the powder obtained by the hydrogenation reduction crushing on the surface of the substrate and then performs a grain boundary diffusion treatment; the burying is to bury the substrate in the powder, specifically by spreading the powder on the bottom of the crucible, then placing the substrate, and then pouring the powder into the crucible until it covers the upper surface of the substrate. The substrate is a magnet substrate well known to those skilled in the art. For example, the substrate is a sintered NdFeB magnet, such as an N55 sintered NdFeB magnet. The grain boundary diffusion treatment is specifically as follows:

[0044] The powder obtained by hydrogen reduction and crushing is buried on the surface of the substrate and then placed in a vacuum heat treatment furnace, heated to 800-1000 °C in a vacuum environment, and the vacuum degree is not less than 1×10 -2 Pa, keep warm for 1 to 10 hours, then keep warm at 450 to 550 ° C for 1 to 10 hours, and pass argon to cool to room temperature.

[0045] More specifically, the heating temperature is 850-950° C., the holding time is 3-8 hours, and the subsequent heating temperature is 480-520° C., and the holding time is 3-7 hours.

[0046] In the present application, the NdFeB scrap is the NdFeB scrap well known to those skilled in the art. For example, the NdFeB scrap can be selected from one or more of NdFeB material machining scraps, waste magnets, waste rapid-setting alloys and waste rapid-quenching strips. When NdFeB scrap powder is diffused, its rare earth components lose their wettability and diffusibility due to oxidation problems, which is a technical difficulty. The present invention specially combines a specific hydrogenation reduction crushing treatment to solve this problem. In addition, the Fe content in NdFeB scrap is relatively high, and the melting point of Fe element is relatively high (higher than the grain boundary diffusion treatment temperature), which is not conducive to diffusion. The present invention cleverly uses continuous HDDR treatment, heat treatment, and hydrogenation reduction crushing treatment to form a "core-layer" structure in which low-melting-point, easily diffusible rare earth-rich components are distributed around the outer layer of the high-melting-point Fe-rich component core. This allows the outer rare earth components to diffuse more easily into the interior of the target magnet to enhance the coercive force, and also allows the iron-rich core of the scrap powder after diffusion heat treatment to be more easily separated from the target magnet (the residue on the magnet surface after diffusion has a high melting point and can be cleaned only by ultrasonic cleaning, which is convenient and quick).

[0047] The method for grain boundary diffusion of scrap NdFeB provided in this application has the following advantages by adopting a continuous processing method:

[0048] 1) The present invention utilizes vacuum heat treatment on HDDR magnetic powder to cause the nano-scale grains in the particles to merge and grow. Extensive research by the inventors has shown that only through the engulfment and growth of the nano-scale grains formed after HDDR treatment can the rare earth-rich phase be squeezed out to the periphery of the particles. Furthermore, hydrogenation reduction and fragmentation reduce rare earth oxidation, resulting in better diffusivity and wettability of the rare earth in the outer layer of the particles. This creates a rare earth concentration gradient between the outer layer of the particles and the matrix, generating a good diffusion driving force and facilitating the diffusion reaction.

[0049] 2) The matrix is ​​covered with diffusion element powder before grain boundary diffusion treatment, which is simple to operate; after diffusion, the residue on the magnet surface can be cleaned by ultrasonic cleaning, which is convenient and quick;

[0050] 3) The present invention can realize the extraction and utilization of rare earth in NdFeB waste, and the process is simple and easy, does not require chemical purification, is easy to operate and has low cost, and can realize the effective utilization of rare earth resources in waste;

[0051] 4) The residual materials of NdFeB waste after treatment and diffusion can still be recycled and reused, or recycled for other purposes, which can achieve the full recycling of rare earth resources;

[0052] 5) The present invention prepares a diffusion source by processing NdFeB waste, has a stable diffusion effect, has good consistency of the prepared product, is suitable for batch production, and is easy to automate.

[0053] In order to further understand the present invention, the method for grain boundary diffusion of NdFeB scrap provided by the present invention is described in detail below with reference to the examples. The protection scope of the present invention is not limited by the following examples.

[0054] Example 1

[0055] The composition is close to PrNd 32.1 Cu 0.3 Co 1.0 Ti 0.2 Ga 0.4 B 0.98 Fe bal The NdFeB waste with a mass ratio of 100% was placed in a dryer and dried at 100°C for 10 hours; the coarse magnetic powder was mechanically crushed to obtain a particle size distribution of 200 microns to 300 microns; the coarse magnetic powder was placed in a hydrogen heat treatment furnace, 50kPa of hydrogen was introduced at room temperature, and then heated to 200°C, and then the hydrogen was replenished to 80kPa, and the temperature was kept at this temperature for 2 hours, and then heated to 900°C, and then hydrogen was introduced to 50kPa, and the temperature was kept at this temperature for 100 minutes; and then the furnace was evacuated to a vacuum degree of not less than 1×10 -2 Pa, keep warm and pressurized for 90 minutes, gas quench and air cool to room temperature to obtain HDDR magnetic powder; place the HDDR powder in a vacuum heat treatment furnace and heat it to 1000℃ at a heating rate of 10℃ / min and keep it warm for 5 hours, then gas quench and air cool to obtain heat-treated HDDR magnetic powder; then place the treated HDDR magnetic powder in a heat treatment furnace, introduce 50kPa hydrogen-argon mixed gas, and keep the pressure for 5 hours; then evacuate and heat to 300℃, keep it warm for 10 hours, and obtain hydrogenated reduced crushed magnetic powder after cooling; finally, bury the hydrogenated reduced crushed magnetic powder on the surface of a commercial N55 magnet, keep it warm at 900℃ for 8 hours in a vacuum heat treatment furnace, and then keep it warm at 500℃ for 5 hours to obtain diffused magnet 1. The specific process flow is as follows Figure 1 shown.

[0056] In order to verify the advantages of the present invention, the composition is close to PrNd 32.1 Cu 0.3 Co 1.0 Ti 0.2 Ga 0.4 B 0.98 Fe bal (Mass ratio) After mechanical crushing, the NdFeB scrap was not processed by the technical solution designed by the present invention, but was directly buried on the surface of a commercial N55 magnet. The diffusion treatment process was the same to obtain a comparative magnet 1. The magnetic properties of the magnets before and after diffusion were tested, and the test results are shown in Table 1.

[0057] Table 1 Magnetic properties of magnets before and after diffusion

[0058]

[0059]

[0060] Comparison shows that the coercive force of the embodiment is higher than that of the comparative example. The present invention can effectively recycle and utilize NdFeB waste and apply it to grain boundary diffusion.

[0061] Example 2

[0062] The composition is close to PrNd 28.5 Tb 0.8 Dy 1.5 Al 0.2 Cu 0.2 Co 1.0 Zr 0.1 Ga 0.5 B 0.98 Fe bal The NdFeB waste with a mass ratio of 100% is placed in a dryer and dried at 100°C for 10 hours; the coarse magnetic powder is then mechanically crushed to obtain a particle size distribution of 300 μm to 500 μm; the coarse magnetic powder is placed in a hydrogen heat treatment furnace, 50 kPa of hydrogen is introduced at room temperature, and then heated to 300°C, and then the hydrogen is replenished to 100 kPa, and the temperature is kept at this temperature for 4 hours, and then heated to 1000°C, and then hydrogen is introduced to 20 kPa, and the temperature is kept at this temperature for 100 minutes; and then the furnace is evacuated to a vacuum degree of not less than 1×10 -2 Pa, keep the temperature and pressure for 120 minutes, gas quench and air cool to room temperature to obtain HDDR magnetic powder; the HDDR powder is placed in a vacuum heat treatment furnace and heated to 1100℃ at a rate of 10℃ / min and kept at this temperature for 5 hours, and then gas quenched and air cooled to obtain heat-treated HDDR magnetic powder; the treated HDDR magnetic powder is then placed in a heat treatment furnace, and 100kPa hydrogen-argon mixed gas is introduced and the pressure is maintained for 5 hours; then vacuum is evacuated and heated to 400℃, kept at this temperature for 10 hours, and hydrogenated reduced crushed magnetic powder is obtained after cooling; finally, the hydrogenated reduced crushed magnetic powder is buried on the surface of a commercial N55 magnet, kept at 900℃ for 10 hours in a vacuum heat treatment furnace, and then kept at 500℃ for 4 hours to obtain diffused magnet 2.

[0063] In order to verify the advantages of the present invention, a conventional HDDR process different from the HDDR process of the present invention was adopted: the coarsely crushed magnetic powder was placed in a hydrogen heat treatment furnace and heated to 600°C under a vacuum environment; in the hydrogenation and disproportionation stage, 50 kPa of hydrogen was introduced into the hydrogen heat treatment furnace and the temperature and pressure were maintained for 240 minutes; in the slow dehydrogenation stage, the hydrogen pressure in the furnace was adjusted to 10 kPa and the temperature and pressure were maintained for 90 minutes; in the recombination stage, the furnace was evacuated to a vacuum degree of not less than 1×10 -2 Pa, and kept warm for 60 min to obtain HDDR magnetic powder. Other processing techniques were the same as before to obtain comparative magnet 2. The magnetic properties of the magnets before and after diffusion were tested, and the test results are shown in Table 2.

[0064] Table 2 Magnetic properties of magnets before and after diffusion

[0065]

[0066]

[0067] Comparison shows that the coercive force of the embodiment is higher than that of the comparative example. The present invention can effectively recycle and utilize NdFeB waste and apply it to grain boundary diffusion.

[0068] Example 3

[0069] The composition is close to PrNd 21.9 C e8.6 Gd 1.5 Al 0.5 Cu 0.2 Co 0.2 Zr 0.12 Ga 0.12 B 0.94 Fe bal The NdFeB waste with a mass ratio of 100% is placed in a dryer and dried at 100°C for 10 hours; the coarse magnetic powder is then mechanically crushed to obtain a particle size distribution of 100 microns to 200 microns; the coarse magnetic powder is placed in a hydrogen heat treatment furnace, 30kPa of hydrogen is introduced at room temperature, and then heated to 200°C, and then the hydrogen is replenished to 80kPa, and the temperature is kept at this temperature for 2 hours, and then heated to 800°C, and then hydrogen is introduced to 30kPa, and the temperature is kept at this temperature for 90 minutes; and then the furnace is evacuated to a vacuum degree of not less than 1×10 -2 Pa, keep the temperature and pressure for 100 minutes, gas quench and air cool to room temperature to obtain HDDR magnetic powder; the HDDR powder is placed in a vacuum heat treatment furnace and heated to 1050℃ at a rate of 10℃ / min and kept at this temperature for 5 hours, and then gas quenched and air cooled to obtain heat-treated HDDR magnetic powder; the treated HDDR magnetic powder is then placed in a heat treatment furnace, and 10kPa hydrogen-argon mixed gas is introduced and the pressure is maintained for 5 hours; then vacuum is evacuated and heated to 300℃, kept at this temperature for 10 hours, and hydrogenated reduced crushed magnetic powder is obtained after cooling; finally, the hydrogenated reduced crushed magnetic powder is buried on the surface of a commercial N55 magnet, and kept at 920℃ for 10 hours and then kept at 490℃ for 8 hours in a vacuum heat treatment furnace to obtain diffused magnet 3.

[0070] To verify the advantages of the present invention, HDDR magnetic powder was vacuum heat treated at 800°C using parameters different from those used in the present invention. All other processing conditions remained the same, resulting in Comparative Magnet 3. Magnetic properties of the magnets were tested before and after diffusion, and the test results are shown in Table 3.

[0071] Table 3 Magnetic properties of magnets before and after diffusion

[0072] Magnet type Br(kGs) Hcj(kOe) N55 14.53 13.98 Diffusion Magnet 3 14.34 16.74 Comparison magnet 3 14.33 15.98

[0073] Comparison shows that the coercive force of the embodiment is higher than that of the comparative example. The present invention can effectively recycle and utilize NdFeB waste and apply it to grain boundary diffusion.

[0074] The above embodiments are only intended to help understand the method and core concept of the present invention. It should be noted that, without departing from the principles of the present invention, a number of improvements and modifications may be made to the present invention by those skilled in the art, and such improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0075] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for grain boundary diffusion of NdFeB scrap, comprising the following steps: A) Mechanically crushing NdFeB waste to obtain coarse magnetic powder; B) subjecting the coarsely crushed magnetic powder to HDDR treatment to obtain HDDR magnetic powder; C) subjecting the HDDR magnetic powder to vacuum heat treatment, and then to hydrogenation reduction and crushing; D) burying the powder obtained in step C) on the surface of the substrate and then performing grain boundary diffusion treatment; The HDDR processing is specifically as follows: The steps of the hydrogenation and disproportionation stage are as follows: placing the coarse crushed magnetic powder in a hydrogen heat treatment furnace, introducing 10-50 kPa hydrogen at room temperature, heating to 100-300°C, then replenishing the hydrogen to 80-100 kPa, keeping the temperature and pressure for 0.5-4 hours, continuing to heat to 800-1000°C, then maintaining the hydrogen pressure at 10-50 kPa, keeping the temperature and pressure for 30-240 minutes, and completing the hydrogenation and disproportionation stage; Steps of the recombinant stage: Evacuate the furnace to a vacuum degree of not less than 1×10 -2 Pa, keep warm for 60~120min to complete the recombination stage; The temperature of the vacuum heat treatment is 1000-1500°C, and the vacuum degree is not less than 1×10 -3 Pa, time is 1~10h; The process of hydrogenation reduction crushing is specifically as follows: The vacuum heat-treated powder is placed in a heat treatment furnace, and a 5kPa~100kPa hydrogen-argon mixed gas is introduced, and the pressure is maintained for 1~6 hours; then the vacuum is evacuated and heated to 100~500℃, and the temperature is maintained for 1~10 hours.

2. The method according to claim 1, characterized in that The burying method is specifically as follows: The powder obtained in step C) is spread on the bottom of the crucible, and then the substrate is placed therein. The powder is then poured into the crucible until it covers the upper surface of the substrate.

3. The method according to claim 1 or 2, characterized in that The height of the base is 3-10 mm, and the diameter is 6-10 mm.

4. The method according to claim 1, wherein The particle size of the coarse magnetic powder is 50 μm to 500 μm.

5. The method according to claim 1, wherein The matrix is ​​a sintered NdFeB magnet.

6. The method according to claim 1, characterized in that The grain boundary diffusion treatment is specifically as follows: The powder obtained in step C) is buried on the surface of the substrate and then placed in a vacuum heat treatment furnace, heated to 800-1000°C in a vacuum environment, with a vacuum degree of not less than 1×10 -2 Pa, keep warm for 1~10h, then keep warm at 450~550℃ for 1~10h, and cool to room temperature by passing argon.

7. The method according to claim 1, characterized in that The NdFeB waste is selected from one or more of NdFeB material machining scraps, waste magnets, waste rapid solidification alloys and waste rapid quenching strips.

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