Preparation method of neodymium-iron-boron magnet grain boundary diffusion source

Abstract

The invention relates to a preparation method of a neodymium-iron-boron magnet grain boundary diffusion source, belongs to the technical field of rare earth permanent magnet materials, and is used for solving the problems that an existing coating process is poor in diffusion uniformity, poor in magnet performance, prone to causing diffusion element waste and the like. The specific preparation method comprises the steps of raw material preparation, layered smelting, rolling, patch diffusion and heat treatment. Rare earth metal, low-melting-point metal and high-melting-point metal are smelted into multi-element alloy, then the multi-element alloy is prepared into an alloy sheet with the thickness of 0.02-1 mm through a rolling technology, and then the alloy sheet is attached to the surface of a magnet for grain boundary diffusion. Compared with a traditional powder coating method, the method has the advantages that diffusion is uniform, coercive force is remarkably improved, and the method is environmentally friendly, efficient, suitable for special-shaped magnets and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of rare earth permanent magnet materials, and particularly relates to a preparation method of a diffusion source for grain boundary diffusion of a neodymium-iron-boron magnet. BACKGROUND

[0002] Since the advent of neodymium-iron-boron (NdFeB) permanent magnet materials in the 1980s, they have rapidly become an indispensable key material in modern industry due to their extremely high maximum magnetic energy product, remanence, and coercive force, and are widely used in new energy vehicles, wind power generation, consumer electronics, medical devices, aerospace, and other fields. However, as the application scenarios continue to expand, the performance requirements for neodymium-iron-boron magnets are also becoming increasingly high, especially in terms of coercive force and thermal stability in high-temperature environments, and traditional neodymium-iron-boron magnets still have certain limitations.

[0003] Currently, the enterprise mass production grain boundary diffusion preparation method is the traditional powder coating method, in which heavy rare earth powder or compounds are mixed with organic solvents and then coated on the surface of the magnet. For example, patent CN120497029A discloses a grain boundary diffusion magnet and a production process thereof, and patent CN120497027A discloses a diffusion source for a neodymium-iron-boron magnet and a preparation method and application thereof, both of which use organic solvents to assist in preparing the slurry, and volatilization will occur during the sintering process, causing environmental pollution. In addition, although the coating method is simple, it requires high uniformity of the slurry coating, which is difficult to control. Large deviations will result in poor diffusion uniformity and waste of diffusion elements. At the same time, regardless of the use of coating, screen printing, and other processes in the early stage, there are problems such as poor magnet performance due to uneven coating or even no coating, and difficulty in direct detection and special shape adaptation. SUMMARY

[0004] In view of the above analysis, the embodiments of the present application aim to provide a preparation method of a diffusion source for grain boundary diffusion of a neodymium-iron-boron magnet, to solve at least one of the problems of poor magnet performance, heavy pollution, and difficulty in special shape adaptation existing in the traditional powder coating method of the existing grain boundary diffusion preparation method.

[0005] The embodiments of the present application provide a preparation method of a diffusion source for grain boundary diffusion of a neodymium-iron-boron magnet, comprising the following steps:

[0006] (1) smelting the pretreated raw materials to obtain an ingot;

[0007] (2) rolling the ingot to obtain an alloy sheet;

[0008] (3) bonding the alloy sheet and the neodymium-iron-boron magnet after heat treatment.

[0009] Further, in step (1), the pretreatment is to remove the oxides on the surface of the raw materials.

[0010] Further, in step (1), the smelting comprises in sequence a rapid smelting stage, a sufficient smelting stage and a slow smelting stage.

[0011] Further, the current of the rapid smelting stage is 2.8-3A, the time is 30-40s, the current of the sufficient smelting stage is 2-2.2A, the time is 40-60s, and the current of the slow smelting stage is 0.8-1A, the time is 30-40s.

[0012] Further, the sufficient smelting stage further comprises electromagnetic stirring, the stirring frequency of the electromagnetic stirring is 10-50Hz, and the stirring power is 3-8kW.

[0013] Further, in step (2), the temperature of rolling is 60-90% of the melting point temperature of the raw material when smelting.

[0014] Further, in step (2), the atmosphere during rolling is an argon protection environment, and the vacuum degree is preferably extracted to high vacuum 1.0×10 -3 Pa below, and then filled with argon to 0.5Mpa.

[0015] Further, in step (2), the rolling comprises rough rolling and finish rolling, the single pass reduction rate of the rough rolling is 30-40%, and the single pass reduction rate of the finish rolling is 5-10%.

[0016] Further, in step (2), the thickness of the alloy sheet is 0.02-1mm.

[0017] Further, in step (2), the roughness of the alloy sheet is Ra≤5μm.

[0018] Further, in step (3), the neodymium-iron-boron magnet is further subjected to polishing and cleaning treatment.

[0019] Further, in step (3), the heat treatment is first heat preservation at 800-1000℃ for 3-15h, and then heat preservation at 460-600℃ for 2-5h.

[0020] Compared with the prior art, the present application can at least achieve one of the following beneficial effects:

[0021] 1. The diffusion method of the present application first melts the raw material and then rolls it, and then performs heat treatment bonding with the Nd-Fe-B magnet to realize grain boundary diffusion of the Nd-Fe-B magnet. The alloy after melting is uniform in composition, the microstructure is controlled by rolling process, the internal defects of the alloy are reduced, the density of the diffusion source is improved, the coercive force is improved, and the magnetic properties after diffusion are improved. The alloy prepared by the rolling process has good ductility and flexibility, and can be used for tile-shaped products such as tiles, and can be used for tile-shaped design by rolling process, and can also be used for bonding and coating, realizing grain boundary diffusion of special-shaped products, and realizing precise multi-dimensional diffusion of the edge position of the magnet which is easy to demagnetize.

[0022] 2. The melting method of the present application comprises a rapid melting stage, a sufficient melting stage and a slow melting stage. In the early stage of melting, the volatilization of the raw material can be reduced; in the middle stage of melting, the electric arc is close to the liquid surface, and the bottom metal is fully melted through the breakdown effect of the electric arc; in the later stage of melting, the molten liquid is slowly cooled to release stress and prevent the ingot from cracking.

[0023] 3. The single-pass reduction ratio control method of the present application can maintain good quality of the alloy and prevent cracking, thereby improving the coercive force of the magnet.

[0024] 4. The alloy sheet prepared by the rolling method of the present application can realize precise diffusion: the alloy prepared by the rolling process has a thickness of 0.01-1mm, which is set according to the thickness of the diffusion magnet. The thinner the magnet, the lower the thickness of the alloy required. Too low thickness may not be enough for diffusion, and the performance may not meet the requirements. Too high thickness will cause waste.

[0025] 5. The heat treatment method of the present application can optimize the microstructure of the magnet by low-temperature tempering, improve the demagnetization coupling effect, improve the coercive force, and significantly improve the performance of the magnet.

[0026] 6. The alloy sheet prepared by the rolling method of the present application can realize environmental protection and high efficiency: the rolling process does not produce organic pollutants during the rolling process, which is environmentally friendly and efficient. The process is simple: the rolling process uses the tile method combined with the heat treatment process, without the need for complex equipment, and has the potential for large-scale industrial application.

[0027] 7. The alloy sheet prepared by the rolling method of the present application improves the yield: the traditional powder coating method has the problem that part of the magnet cannot be coated with the diffusion source. The rolling method for preparing the diffusion source alloy sheet can effectively reduce the problem of low yield caused by uneven coating. In the case of the same composition, the coercive force of the magnet using the rolling diffusion source is improved more obviously.

[0028] The technical solutions in the present application can be combined with each other to realize more preferred combination solutions. Other features and advantages of the present application will be described in the subsequent description, and some advantages will become apparent from the description, or will be understood by implementing the present application. The purposes and other advantages of the present application can be realized and obtained from the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 Comparison of coercivity after diffusion by different preparation methods for different diffusion sources;

[0030] Figure 2 Comparison of diffusion depth for Example 1 and Comparative Example 2;

[0031] Figure 3 Tb 85 Cu 15 SEM images of the alloy before and after rolling. DETAILED DESCRIPTION

[0032] The present application will be further described by the following examples, but is limited to the following examples, and other application fields of equivalent technical solutions also belong to the scope of the present application, and the patent protection scope of the present application should be limited by the claims.

[0033] Since the neodymium-iron-boron (NdFeB) permanent magnet material was introduced in the 1980s, it has rapidly become an indispensable key material in modern industry due to its extremely high maximum magnetic energy product, remanence and coercivity, and is widely used in new energy vehicles, wind power generation, consumer electronics, medical devices, aerospace, etc. However, as the application scenarios continue to expand, the performance requirements for neodymium-iron-boron magnets are also becoming higher and higher. At present, the enterprise mass production grain boundary diffusion preparation method is a coating method, in which heavy rare earth powder or compound is mixed with an organic solvent and coated on the surface of the magnet. The organic solvent is used to assist the preparation of the slurry, and volatilization occurs during the sintering process, causing environmental pollution. Secondly, although the coating method is simple, it requires high uniformity of the slurry coating, which is difficult to control. Large deviations will cause poor diffusion uniformity and waste of diffusion elements. At the same time, regardless of the use of coating, screen printing, magnetron sputtering and other processes in the early stage, some magnets have poor performance due to uneven coating or even no coating, and direct detection cannot be realized.

[0034] In order to solve the above problems, the present application provides a preparation method of a diffusion source for grain boundary diffusion of a neodymium-iron-boron magnet, mainly comprising the following steps:

[0035] (1) smelting the pretreated raw materials to obtain an ingot;

[0036] (2) rolling the ingot to obtain an alloy sheet;

[0037] (3) The alloy sheet and the neodymium iron boron magnet are bonded together after heat treatment.

[0038] Specifically, in step (1), the pretreatment involves removing oxides from the surface of the raw material.

[0039] Preferably, surface oxides are removed by methods such as grinding, cutting, and pickling.

[0040] Specifically, the raw materials in this invention include rare earth metals or rare earth alloys, low-melting-point metals, and high-melting-point metals.

[0041] Preferably, the rare earth metal includes one or more of Pr, Nd, Dy, Tb, and Ho;

[0042] The rare earth alloy includes one or more of PrNd, DyFe, and Ho;

[0043] The low-melting-point metal includes one or more of Cu, Al, and Ga;

[0044] The high-melting-point metal includes one or more of Nb, Zr, Hf, and Ti.

[0045] It should be noted that the present invention obtains multi-element alloys, such as binary alloys, ternary alloys, and quaternary alloys, by melting the pretreated raw materials.

[0046] Preferably, in step (1), before smelting, the process further includes placing the processed low-melting-point and volatile metal raw materials at the bottom of the container, the high-melting-point metal raw materials in the middle of the container, and the non-volatile metal raw materials at the top of the container.

[0047] It should be noted that this stacking method ensures uniform composition, resulting in more uniform and thorough melting. Without this method, low-melting-point metals and volatile rare-earth metals would rapidly volatilize and be lost in the early stages of melting, while high-melting-point metals, due to their high density and melting point, would settle and fail to fully alloy, leading to uneven composition. Preventing uneven composition ensures more uniform melting.

[0048] More preferably, the container is a crucible.

[0049] Specifically, in step (1), the melting adopts the method of electric arc melting or induction melting, which includes a rapid melting stage, a full melting stage and a slow melting stage in sequence.

[0050] Specifically, the current during the rapid melting stage is 2.8–3A, for example, 2.8A, 2.82A, 2.84A, 2.86A, 2.88A, 2.90A, 2.92A, 2.94A, 2.96A, 2.98A, or 3A, and the time is 30–40 seconds. The current during the fully melting stage is 2–2.2A, for example, 2A, 2.02A, 2.04A, 2.06A, 2.08A, 2.10A, 2.12A, 2.14A, 2.16A, 2.18A, 2.20A, or 2.2A, and the time is 40 seconds. The current during the slow melting stage is 0.8 to 1A, for example, 0.8A, 0.82A, 0.84A, 0.86A, 0.88A, 0.90A, 0.92A, 0.94A, 0.96A, 0.98A, 1A, and the time is 30 to 40s, for example, 30s, 31s, 32s, 33s, 34s, 35s, 36s, 37s, 38s, 39s, 40s.

[0051] Specifically, the full melting stage also includes electromagnetic stirring. The stirring frequency of the electromagnetic stirring is 10–50 Hz, for example, 10 Hz, 12 Hz, 14 Hz, 16 Hz, 18 Hz, 20 Hz, 22 Hz, 24 Hz, 26 Hz, 28 Hz, 30 Hz, 32 Hz, 34 Hz, 36 Hz, 38 Hz, 40 Hz, 42 Hz, 44 Hz, 46 Hz, 48 Hz, 50 Hz; the stirring power is 3–8 kW, for example, 3 kW, 3.5 kW, 4 kW, 4.5 kW, 5 kW, 5.5 kW, 6 kW, 6.5 kW, 7 kW, 7.5 kW, 8 kW. Too low a power will result in insufficient stirring, while too high a power may cause the molten metal to splash out, leading to inaccurate composition.

[0052] It should be noted that in the initial stage of electric arc melting, a high current of 2.8–3A is used to rapidly melt the metal and reduce the volatilization of raw materials. In the middle stage of melting, the electric arc is brought close to the liquid surface, and the breakdown effect of the arc ensures that the metal at the bottom is fully melted. In the later stage of melting, the current is reduced to 0.8–1A, and the arc is moved around the edge of the molten liquid to slowly cool the liquid, release stress, and prevent the ingot from cracking. After the ingot has completely cooled, it is flipped over, and the above steps are repeated 5 times to ensure uniform melting of the ingot.

[0053] Induction melting initially uses a high-frequency current to rapidly melt the metal and reduce the volatilization of raw materials. Once the metal is completely melted, the current frequency is reduced, and an electromagnetic stirrer is activated. The electromagnetic stirrer frequency is 10–50 Hz, for example, 10 Hz, 12 Hz, 14 Hz, 16 Hz, 18 Hz, 20 Hz, 22 Hz, 24 Hz, 26 Hz, 28 Hz, 30 Hz, 32 Hz, 34 Hz, 36 Hz, 38 Hz, 40 Hz, 42 Hz, 44 Hz, 46 Hz. At Hz, 48Hz, and 50Hz, with a stirring power of 3 to 8kW (e.g., 3kW, 3.5kW, 4kW, 4.5kW, 5kW, 5.5kW, 6kW, 6.5kW, 7kW, 7.5kW, 8kW), refining is performed for 3 to 5 minutes (e.g., 3 minutes, 3.5 minutes, 4 minutes, 4.5 minutes, 5 minutes) to ensure thorough and uniform metal melting. In the later stages of melting, the current frequency is slowly reduced to allow the molten metal to cool down gradually, releasing stress and preventing ingot cracking.

[0054] Furthermore, in step (2), the rolling temperature is 60% to 90% of the melting point temperature of the raw material during smelting, for example, 60%, 65%, 70%, 75%, 80%, 85%, 90%.

[0055] It should be noted that rolling temperatures that are too low will cause cracking; rolling temperatures that are too high may cause localized melting and liquidization, which is not conducive to rolling and will not achieve the desired rolling effect.

[0056] Specifically, in step (2), the rolling process includes rough rolling and finish rolling. The single-pass reduction rate of the rough rolling is 30% to 40%, for example, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, or 40%. The single-pass reduction rate of the finish rolling is 5% to 10%, for example, 5%, 6%, 7%, 8%, 9%, or 10%.

[0057] It should be noted that the single-pass reduction ratio in rough rolling and finish rolling is based on the strength and toughness of the alloy at the rolling temperature. A lower rough rolling reduction ratio is needed for alloys with poor toughness; otherwise, the alloy will crack. Too few single-pass rolling passes reduce efficiency, while too many passes will affect the rolling effect, causing the alloy to crack and resulting in poor quality.

[0058] Specifically, in step (2), the thickness of the alloy sheet is 0.02-1mm, for example, 0.02mm, 0.1mm, 0.2mm, 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1.0mm.

[0059] It should be noted that the thickness mentioned above is set according to the thickness of the diffusion magnet. The thinner the magnet, the lower the required alloy thickness. Too low a thickness may result in insufficient diffusion and failure to meet performance requirements, while too high a thickness will lead to waste.

[0060] The alloy sheet is rolled into a thickness of 0.02-1 mm using an automatic thickness control system. This thickness is set according to the thickness of the diffusion magnet. The thinner the magnet, the lower the required alloy thickness. Too low a thickness may result in insufficient diffusion and failure to meet performance requirements, while too high a thickness would be wasteful.

[0061] Furthermore, step (3) also includes polishing and cleaning the neodymium iron boron magnet.

[0062] The neodymium iron boron magnets used in this invention are all existing products. Before bonding the neodymium iron boron magnets to the alloy sheet, the magnets need to be cut, and the rolled alloy sheet needs to be trimmed to ensure that the magnets and alloy sheets are sized to match. Before use, the magnets need to be polished with 400-800 grit sandpaper, followed by acid washing and ultrasonic cleaning with alcohol to remove dirt from the magnet surface.

[0063] Furthermore, in step (3), the heat treatment is first performed at 800-1000℃, for example, 800℃, 850℃, 900℃, 950℃, 1000℃; and then held at 460-600℃, for example, 460℃, 500℃, 550℃, 6 ...

[0064] It should be noted that the rolled diffusion source disc (i.e., alloy sheet) is bonded to the magnet and then placed in a vacuum sintering furnace for heat treatment. If the heat treatment temperature is too low or the holding time is too short, diffusion will be ineffective, resulting in poor magnet performance. If the heat treatment temperature is too high or the holding time is too long, the internal grains of the magnet will grow, also deteriorating the magnet's performance; at even higher temperatures, the magnet may melt. Low-temperature tempering of the magnet can optimize its microstructure, improve demagnetization coupling, and has a significant effect on improving magnet performance.

[0065] Compared with existing technologies, this invention addresses the shortcomings of existing technologies by proposing a novel method for grain boundary diffusion in NdFeB magnets. Compared with traditional powder coating methods, the coercivity of magnets using rolled diffusion sources is significantly improved under the same composition. This preparation method, through rolling the diffusion source, enables uniform and large-scale production of diffusion sources. The combination of patching and precise heat treatment achieves efficient and uniform distribution of diffusion elements, resulting in higher utilization of the diffusion source. Moreover, the rolling method avoids the generation of volatile organic pollutants during the rolling process, making it environmentally friendly and efficient. The alloy sheets obtained through rolling possess good ductility and flexibility, so for irregularly shaped products such as tiles, the shape design of the patches can be achieved through rolling, and they can also be laminated and coated to achieve grain boundary diffusion in irregularly shaped products. Shape design through rolled patches allows for lamination and coating, enabling precise multi-dimensional diffusion at edges where magnets are prone to demagnetization.

[0066] To more clearly describe the present invention, the following embodiments and comparative examples are provided for further illustration.

[0067] Example 1:

[0068] In this embodiment, the component prepared by mass percentage is (Tb) 85 Cu 15 (wt.%) of ingots.

[0069] The method for preparing a neodymium iron boron magnet grain boundary diffusion source according to this embodiment includes the following steps:

[0070] (1) Select terbium (Tb) and copper (Cu) as raw materials, pre-treat the selected raw materials, and remove surface oxides by grinding, cutting and pickling; place the treated volatile rare earth terbium (Tb) at the bottom of the crucible and place copper (Cu) at the top of the crucible.

[0071] The processed raw materials are melted by electric arc melting, which includes a rapid melting stage, a full melting stage, and a slow melting stage. The current in the rapid melting stage is 3A and the time is 30s. The current in the full melting stage is 2.2A and the time is 40s. The current in the slow melting stage is 1A and the time is 30s. After the ingot has completely cooled, the ingot is flipped over and the above steps are repeated 5 times to ensure that the ingot is melted evenly.

[0072] (2) The ingot is rolled at a temperature of 80% of the melting point of the raw material during smelting, i.e., 590°C. The rolling process includes primary rolling and finishing rolling. The single-pass reduction rate of the primary rolling is 30%, and the single-pass reduction rate of the finishing rolling is 5%, to obtain an alloy sheet. The thickness of the alloy sheet is 0.05 mm.

[0073] (3) Commercial N52 magnets were used, and the magnets were cut into D10*5mm thick pieces. The rolled alloy sheets were then cut into D10*0.05mm round pieces. The magnets were first polished with 400-800 grit sandpaper, and then subjected to acid pickling and ultrasonic cleaning with alcohol to remove dirt from the magnet surface. The rolled diffusion source round pieces were then attached to the top of the magnets and placed in a vacuum sintering furnace for heat treatment. The high-temperature heat treatment temperature was 930℃, and the holding time was 4h; the low-temperature heat treatment temperature was 520℃, and the holding time was 4h. Finally, high coercivity NdFeB magnets were obtained.

[0074] Tb in this implementation 85 Cu 15 SEM images of the alloy before and after rolling are as follows: Figure 3 As shown, Figure 3 In the image, 'a' represents the SEM image before rolling. Figure 3 Image b shows the SEM image after rolling. It can be observed that the microstructure of the molten alloy is mainly composed of equiaxed and columnar crystals. The formation of this microstructure is primarily related to the temperature gradient and cooling rate of the melt during solidification. Nucleation occurs first in the melt near the water-cooled copper crucible. Due to the extremely high cooling rate, the crystals do not have sufficient time to grow, resulting in a region of fine equiaxed crystals. In contrast, near the center of the melt, the cooling rate decreases, allowing crystals to preferentially grow along the temperature gradient, forming columnar crystals. During the subsequent hot rolling at 590°C, the equiaxed crystals grow. Under the applied rolling pressure, they deform and elongate, forming large, continuous, elongated grains. This process reduces internal defects in the alloy and develops a new crystal texture; this modified microstructure is beneficial for improving the efficiency of subsequent diffusion processes.

[0075] Example 2:

[0076] In this embodiment, the component prepared by mass percentage is Nd. 70 Cu 16 Al 14 (wt.%) of ingots.

[0077] The method for preparing a neodymium iron boron magnet grain boundary diffusion source according to this embodiment includes the following steps:

[0078] (1) Select neodymium (Nd), copper (Cu) and aluminum (Al) raw materials, pre-treat the selected raw materials, and remove surface oxides by grinding, cutting and pickling; put the treated volatile rare earth metal neodymium (Nd) at the bottom of the crucible, aluminum (Al) in the middle of the crucible, and copper (Cu) at the top of the crucible.

[0079] The processed raw materials are melted by electric arc melting, which includes a rapid melting stage, a full melting stage, and a slow melting stage. The current in the rapid melting stage is 2.8A and the time is 40s. The current in the full melting stage is 2A and the time is 60s. The current in the slow melting stage is 0.8A and the time is 40s. After the ingot has completely cooled, the ingot is flipped over and the above steps are repeated 5 times to ensure that the ingot is melted evenly.

[0080] (2) The ingot is rolled at a temperature of 75% of the melting point of the raw material during smelting, i.e., 550°C. The rolling process includes primary rolling and finishing rolling. The single-pass reduction rate of the primary rolling is 35%, and the single-pass reduction rate of the finishing rolling is 10%, to obtain an alloy sheet. The thickness of the alloy sheet is 0.05 mm.

[0081] (3) Commercial N52 magnets were used, and the magnets were cut into D10*5mm thick pieces. The rolled alloy sheets were then cut into D10*0.05mm round pieces. The magnets were first polished with 400-800 grit sandpaper, and then subjected to pickling and ultrasonic cleaning with alcohol to remove dirt from the surface of the magnets. The rolled diffusion source round pieces were then attached to the top of the magnets and placed in a vacuum sintering furnace for heat treatment. The high-temperature heat treatment temperature was 900℃, and the holding time was 8h; the low-temperature heat treatment temperature was 500℃, and the holding time was 5h. Finally, high coercivity NdFeB magnets were obtained.

[0082] Example 3:

[0083] In this embodiment, the component is Tb by mass percentage. 20 Dy 60 Ga 15 Ti5 (wt.%) ingots.

[0084] The method for preparing a neodymium iron boron magnet grain boundary diffusion source according to this embodiment includes the following steps:

[0085] (1) Select terbium (Tb), dysprosium (Dy), gallium (Ga), and titanium (Ti) as raw materials. Pre-treat the selected raw materials by removing surface oxides through grinding, cutting, and acid washing. Place the treated low-melting-point, volatile terbium (Tb) and dysprosium (Dy) at the bottom of the crucible, and place gallium (Ga) in the middle of the crucible. Place the high-melting-point, non-volatile metals at the top of the crucible.

[0086] The processed raw materials are melted by electric arc melting, which includes a rapid melting stage, a full melting stage, and a slow melting stage. The current in the rapid melting stage is 2.88A and the time is 35s. The current in the full melting stage is 2.1A and the time is 50s. The current in the slow melting stage is 0.9A and the time is 35s. After the ingot has completely cooled, the ingot is flipped over and the above steps are repeated 5 times to ensure that the ingot is melted evenly.

[0087] (2) The ingot is rolled at a temperature of 60% of the melting point of the raw material during smelting, i.e., 470°C. The rolling process includes primary rolling and finishing rolling. The single-pass reduction rate of the primary rolling is 35%, and the single-pass reduction rate of the finishing rolling is 5%, to obtain an alloy sheet. The thickness of the alloy sheet is 0.05 mm.

[0088] (3) Using commercial N52 magnets, the magnets were cut into D10*5mm thick pieces, and the rolled alloy sheets were cut into D10*0.05mm round pieces. The magnets were first polished with 400-800 grit sandpaper, then subjected to acid washing and ultrasonic cleaning with alcohol to remove surface contaminants. The rolled diffusion source round pieces were then attached to the top of the magnets and placed in a vacuum sintering furnace for heat treatment. The high-temperature heat treatment temperature was 850℃, and the holding time was 8 hours; the low-temperature heat treatment temperature was 500℃, and the holding time was 3 hours. Finally, high-coercivity NdFeB magnets were obtained.

[0089] Example 4:

[0090] In this embodiment, the component is Dy, prepared by mass percentage. 55 Fe 15 Cu 15 Al 15 (wt.%) Ingots.

[0091] The method for preparing a neodymium iron boron magnet grain boundary diffusion source according to this embodiment includes the following steps:

[0092] (1) Select dysprosium (Dy), iron (Fe), copper (Cu) and aluminum (Al) as raw materials, and pretreat the selected raw materials by grinding, cutting and pickling to remove surface oxides; put the treated low-melting-point volatile dysprosium (Dy) at the bottom of the crucible, put copper (Cu) and aluminum (Al) in the middle of the crucible, and put high-melting-point non-volatile iron (Fe) at the top of the crucible;

[0093] The processed raw materials are melted by electric arc melting, which includes a rapid melting stage, a full melting stage, and a slow melting stage. The current in the rapid melting stage is 3A and the time is 37s. The current in the full melting stage is 2A and the time is 55s. The current in the slow melting stage is 1A and the time is 36s. After the ingot has completely cooled, the ingot is flipped over and the above steps are repeated 5 times to ensure that the ingot is melted evenly.

[0094] (2) The ingot is rolled at a temperature of 90% of the melting point of the raw material during smelting, i.e., 800°C. The rolling process includes primary rolling and finishing rolling. The single-pass reduction rate of the primary rolling is 30%, and the single-pass reduction rate of the finishing rolling is 5%, to obtain an alloy sheet. The thickness of the alloy sheet is 0.05 mm.

[0095] (3) Using commercial N52 magnets, the magnets were cut into D10*5mm thick pieces, and the rolled alloy sheets were cut into D10*0.05mm round pieces. The magnets were first polished with 400-800 grit sandpaper, then subjected to acid washing and ultrasonic cleaning with alcohol to remove surface contaminants. The rolled diffusion source round pieces were then attached to the top of the magnets and placed in a vacuum sintering furnace for heat treatment. The high-temperature heat treatment temperature was 830℃, and the holding time was 8 hours; the low-temperature heat treatment temperature was 460℃, and the holding time was 3 hours. Finally, high-coercivity NdFeB magnets were obtained.

[0096] Example 5:

[0097] In this embodiment, the component is Tb by mass percentage. 85 Cu 15 (wt.%) Ingots.

[0098] The method for preparing a neodymium iron boron magnet grain boundary diffusion source according to this embodiment includes the following steps:

[0099] (1) Select terbium (Tb) and copper (Cu) as raw materials, pre-treat the selected raw materials, and remove surface oxides by grinding, cutting and pickling; place the treated volatile rare earth terbium (Tb) at the bottom of the crucible and place copper (Cu) at the top of the crucible.

[0100] The processed raw materials are melted by electric arc melting, which includes a rapid melting stage, a full melting stage, and a slow melting stage. The current in the rapid melting stage is 3A and the time is 32s. The current in the full melting stage is 2A and the time is 45s. The current in the slow melting stage is 1A and the time is 33s. After the ingot has completely cooled, the ingot is flipped over and the above steps are repeated 5 times to ensure that the ingot is melted evenly.

[0101] (2) The ingot is rolled at a temperature of 80% of the melting point of the raw material during smelting, i.e., 590°C. The rolling process includes primary rolling and finishing rolling. The single-pass reduction rate of the primary rolling is 30%, and the single-pass reduction rate of the finishing rolling is 5%, to obtain an alloy sheet. The thickness of the alloy sheet is 0.05 mm.

[0102] (3) Using commercial N52 magnets, the magnets were cut into tile-shaped magnets with dimensions R39*r36*8*10mm. The rolled alloy sheets were then cut into square pieces with dimensions of 10*9*0.05mm in length, width, and thickness. The magnets were first polished with 400-800 grit sandpaper, and then subjected to acid washing and ultrasonic cleaning with alcohol to remove dirt from the magnet surface. The diffusion source square pieces were then attached to the top of the magnet along the arc surface and placed in a vacuum sintering furnace for heat treatment. The high-temperature heat treatment temperature was 930℃, and the holding time was 13h; the low-temperature heat treatment temperature was 520℃, and the holding time was 4h. Finally, high coercivity NdFeB magnets were obtained.

[0103] Example 6:

[0104] In this embodiment, the component is Tb by mass percentage. 85 Cu 15 (wt.%) Ingots.

[0105] The method for preparing a neodymium iron boron magnet grain boundary diffusion source according to this embodiment includes the following steps:

[0106] (1) Select terbium (Tb) and copper (Cu) as raw materials, pre-treat the selected raw materials, and remove surface oxides by grinding, cutting and pickling; place the treated volatile rare earth terbium (Tb) at the bottom of the crucible and place copper (Cu) at the top of the crucible.

[0107] The processed raw materials are melted by electric arc melting, which includes a rapid melting stage, a full melting stage, and a slow melting stage. The current in the rapid melting stage is 3A and the time is 38s. The current in the full melting stage is 2A and the time is 56s. The current in the slow melting stage is 1A and the time is 38s. After the ingot has completely cooled, the ingot is flipped over and the above steps are repeated 5 times to ensure that the ingot is melted evenly.

[0108] (2) The ingot is rolled at a temperature of 80% of the melting point of the raw material during smelting, i.e., 590°C. The rolling process includes primary rolling and finishing rolling. The single-pass reduction rate of the primary rolling is 30%, and the single-pass reduction rate of the finishing rolling is 5%, to obtain an alloy sheet. The thickness of the alloy sheet is 0.05 mm.

[0109] (3) Using commercial N52 magnets, the magnets were cut into square pieces with dimensions of 40*30*5mm (length, width, and thickness). The rolled alloy sheets were then cut into square pieces with dimensions of 40*30*0.05mm (length, width, and thickness). The magnets were first polished with 400-800 grit sandpaper, then subjected to acid washing and ultrasonic cleaning with alcohol to remove surface contaminants. The diffusion source square pieces were then attached to the top of the magnet along the arc surface and placed in a vacuum sintering furnace for heat treatment. The high-temperature heat treatment temperature was 930℃, and the holding time was 13 hours; the low-temperature heat treatment temperature was 520℃, and the holding time was 4 hours. This resulted in a high-coercivity NdFeB magnet. After diffusion, 10*10mm squares were cut from the corners of the magnet for magnetic performance testing.

[0110] Example 7

[0111] The preparation method of the NdFeB magnet grain boundary diffusion source in this embodiment is similar to that in Embodiment 1, except that in step (1), the arc melting is replaced by induction melting. Specifically, the melting includes a rapid melting stage, a full melting stage and a slow melting stage. The current of the rapid melting stage is 3A and the time is 38s. The current of the full melting stage is 2A and the time is 43s. The current of the slow melting stage is 1A and the time is 31s.

[0112] In the initial stage of induction melting, a high-frequency current is used to melt the metal quickly and reduce the volatilization of raw materials. After the metal is completely melted, the current frequency is reduced and an electromagnetic stirrer is turned on. The electromagnetic stirrer frequency is 30Hz and the stirring power is 5kW for refining. The refining time is 4 minutes to ensure that the metal is fully and uniformly melted. In the later stage of melting, the current frequency is slowly reduced to allow the melt to cool down slowly, release stress, and prevent the ingot from cracking.

[0113] Comparative Example 1

[0114] The method for grain boundary diffusion of neodymium iron boron magnets in this comparative example is similar to that in Example 1. The difference is that in step (2), instead of rolling, the ingot is processed into a D10*0.1mm disc by wire cutting and centerless grinding. Then, the surface dirt is removed by grinding and acid washing to prepare a D10*0.05mm diffusion source disc.

[0115] Comparative Example 2

[0116] Tb was prepared through calculation, weighing, and smelting. 85 Cu 15 (wt.%) Diffusion source ingot.

[0117] The ingot was coarsely crushed to a particle size of less than 500 μm in a jaw crusher, and then the ingot was put into a ball mill for ball milling. Ethanol was added as a ball milling aid, and zirconia balls were used as the ball milling media. The particle size ratio was 3:1 for large balls (D=10 mm): small balls (D=5 mm). The ball mill speed was 400 rpm, and the grinding was carried out for 15 hours to prepare diffusion source powder.

[0118] The prepared diffusion source powder was mixed with terpineol and solid PVB in a ratio of 65:30:5 to prepare a slurry. The mixed slurry was then placed in a vacuum disperser to disperse it so that the solid solution distribution of the slurry was uniform.

[0119] Commercial N52 magnets were used, and the magnets were cut into D10*5mm thick magnets. The prepared slurry was applied as a diffusion source by screen printing, and the coating thickness was 0.5mm.

[0120] The sample is placed in a vacuum sintering furnace for heat treatment. The high-temperature heat treatment temperature is 850℃ and the holding time is 8h; the low-temperature heat treatment temperature is 520℃ and the holding time is 4h.

[0121] Comparative Example 3

[0122] The method for grain boundary diffusion of neodymium iron boron magnets in this comparative example is similar to that in Example 1, except that in step (1), all the raw materials are directly mixed in the crucible before melting.

[0123] Comparative Example 4

[0124] The method for grain boundary diffusion of NdFeB magnets in this comparative example is similar to that in Example 1, except that in step (1), the melting process does not distinguish between the rapid melting stage, the full melting stage, and the slow melting stage, and the current of the rapid melting stage is used for all stages, and the total melting time remains unchanged.

[0125] Comparative Example 5

[0126] The grain boundary diffusion method of the NdFeB magnet in this comparative example is similar to that in Example 1, except that in step (2), the single-pass reduction rate of the initial rolling is 50%.

[0127] Comparative Example 6

[0128] The method for grain boundary diffusion of neodymium iron boron magnets in this comparative example is similar to that in Example 1, except that in step (3), only high-temperature heat treatment is used and low-temperature heat treatment is not performed.

[0129] Comparative Example 7

[0130] The method for grain boundary diffusion of neodymium iron boron magnets in this comparative example is similar to that in Example 1, except that the temperature of the high-temperature heat treatment in step (3) is 750°C.

[0131] Comparative Example 8

[0132] The method for grain boundary diffusion of NdFeB magnets in this comparative example is similar to that in Example 1, except that in step (2), instead of rolling, a vacuum spinning furnace is used to obtain alloy sheets.

[0133] Comparative Example 9

[0134] The method for grain boundary diffusion of neodymium iron boron magnets in this comparative example is similar to that in Example 5. The difference is that in step (2), instead of rolling, the ingot is processed into a square sheet with a length, width and thickness of 10*9*0.1mm by wire cutting and centerless grinding. Then, the surface dirt is removed by grinding and acid washing to prepare a diffusion source square sheet with a length, width and thickness of 10*9*0.0.5mm.

[0135] Comparative Example 10

[0136] The method for grain boundary diffusion of neodymium iron boron magnets in this comparative example is similar to that in Example 6. The difference is that in step (2), instead of rolling, the ingot is processed into a 40*30*0.1mm square sheet by wire cutting and centerless grinding. Then, the surface dirt is removed by grinding and acid washing to prepare a 40*30*0.0.5mm diffusion source square sheet.

[0137] The magnets prepared in the examples and comparative examples were subjected to magnetic performance tests. The test methods were in accordance with GB / T 3217-2013 "Magnetic Test Methods for Permanent Magnet (Hard Magnet) Materials". The results are shown in Table 1.

[0138] Table 1. Comparison of Magnetic Properties of Diffused Magnets Prepared by Rolling Process, Melting Process, and Screen Printing Process

[0139]

[0140] As shown in Table 1, through Examples 1, 5, 6, and 7, Tb 85 Cu 15 The coercivity of the magnet using the diffusion source of the present invention ranges from 19.22 to 19.61 kOe, the remanence of the magnet is from 13.762 to 13.872 kGs, and the magnetic energy product of the magnet is from 46.289 to 46.683 MGOe.

[0141] From Table 1 and Figure 1 As can be seen from the examples, compared with Comparative Examples 1-8, the rolling diffusion source of the present invention is more effective in improving coercivity than the smelting diffusion source of the same composition. Compared with Comparative Example 2, the hot-rolled diffusion source of the present invention has a greater improvement in magnet coercivity than the traditional powder coating method, thus improving the magnet performance of the diffusion source.

[0142] Comparing Example 5 (the coercivity of the magnet is 19.33 kOe) and Comparative Example 9 (the coercivity of the magnet is 18.23 kOe), it can be seen that for tile-shaped magnets, the alloy prepared by the rolling diffusion source method of the present invention has good ductility and flexibility through the rolling process. Therefore, for irregularly shaped products such as tiles, the improvement of coercivity through patch shape design is more effective, and the magnet performance is significantly improved.

[0143] Compared with Example 6 (the coercivity of the magnet is 19.22 kOe) and Comparative Example 10 (the coercivity of the magnet is 17.53 kOe), the rolling diffusion source preparation method of the present invention is more effective in improving the coercivity for the diffusion effect at the corners of the magnet, and can achieve precise multi-dimensional diffusion at the edges of the magnet that are prone to demagnetization.

[0144] Compared with Example 1, Comparative Example 3 simply mixed all the raw materials directly in the crucible without placing the processed low-melting-point volatile metals at the bottom of the crucible, the high-melting-point metals in the middle of the crucible, and the non-volatile metals at the top of the crucible according to the method of the present invention. As a result, the low-melting-point metals and volatile rare earth metals were rapidly lost in the early stage of smelting, while the high-melting-point metals sank due to their high density and high melting point, and failed to be fully alloyed, resulting in uneven composition, poor coercivity improvement, and poor magnet performance.

[0145] Compared with Example 1, Comparative Example 4 does not distinguish between the rapid melting stage, the full melting stage, and the slow melting stage in the melting process. It uses the current of the rapid melting stage for all stages. The total melting time remains unchanged. High-power, long-term melting will cause rare earth elements to volatilize and the content of effective components to decrease, resulting in poor coercivity improvement effect.

[0146] Compared with Example 1, Comparative Example 5 had an excessively high single-pass rolling reduction ratio, resulting in poor alloy quality, poor magnet performance, and poor coercivity enhancement effect.

[0147] Compared with Example 1, Comparative Example 6 did not undergo low-temperature tempering of the magnet, which could not optimize the magnet's microstructure, and the demagnetizing coupling effect could not be improved, resulting in poor coercivity improvement and no significant effect on improving magnet performance.

[0148] Compared with Example 1, Comparative Example 7 did not have the optimal high-temperature heat treatment temperature, resulting in poor microstructure optimization and poor coercivity improvement.

[0149] Comparative Example 8, compared to Example 1, demonstrates that equiaxed crystal growth is achieved during the rolling process of the present invention. Under applied rolling pressure, they deform and elongate, forming large, continuous, elongated grains. This process reduces internal defects in the alloy and develops a novel crystal texture. This modified microstructure improves the efficiency of subsequent diffusion processes, enhances coercivity, and significantly improves magnet performance.

[0150] Figure 2 In (a), the diffusion depth of the diffusion source in the magnet prepared in Comparative Example 2 is shown. Figure 2 In Figure (b), the diffusion depth of the diffusion source in the magnet prepared in Example 1 is shown. Green represents the diffusion depth. As can be seen from the figure, along the diffusion depth, the diffusion depth of Tb element after rolling is more than twice that of screen printing. This indicates that the use of rolling process increases the diffusion depth, which is the direct reason for the improved diffusion performance. This is because hot rolling process densifies the alloy, reduces internal defects in the alloy, and forms a new microstructure, thus increasing the diffusion depth and improving the magnet performance.

[0151] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a neodymium iron boron magnet grain boundary diffusion source, characterized in that, Includes the following steps: (1) Melt the pretreated raw materials to obtain ingots; (2) The ingot is rolled to obtain an alloy sheet; (3) The alloy sheet and the neodymium iron boron magnet are bonded together after heat treatment.

2. The method for preparing a neodymium iron boron magnet grain boundary diffusion source according to claim 1, characterized in that, In step (1), the pretreatment is to remove oxides from the surface of the raw material.

3. The method for preparing a neodymium iron boron magnet grain boundary diffusion source according to claim 1, characterized in that, In step (1), the smelting process includes a rapid smelting stage, a full smelting stage, and a slow smelting stage.

4. The method for preparing a neodymium iron boron magnet grain boundary diffusion source according to claim 3, characterized in that, The current for the rapid melting stage is 2.8–3A and the time is 30–40s; the current for the fully melting stage is 2–2.2A and the time is 40–60s; and the current for the slow melting stage is 0.8–1A and the time is 30–40s.

5. The method for preparing a neodymium iron boron magnet grain boundary diffusion source according to claim 4, characterized in that, The fully smelting stage also includes electromagnetic stirring, with a stirring frequency of 10–50 Hz and a stirring power of 3–8 kW.

6. The method for preparing a neodymium iron boron magnet grain boundary diffusion source according to any one of claims 1-5, characterized in that, In step (2), the rolling temperature is 60-90% of the melting point temperature of the raw material during smelting.

7. The method for preparing a NdFeB magnet grain boundary diffusion source according to claim 1, characterized in that, In step (2), the rolling process includes primary rolling and finishing rolling. The single-pass reduction rate of the primary rolling is 30-40%, and the single-pass reduction rate of the finishing rolling is 5-10%.

8. The method for preparing a NdFeB magnet grain boundary diffusion source according to claim 1, characterized in that, In step (2), the thickness of the alloy sheet is 0.02 to 1 mm.

9. The method for preparing a neodymium iron boron magnet grain boundary diffusion source according to claim 1, characterized in that, Step (3) also includes polishing and cleaning the neodymium iron boron magnet.

10. The method for preparing a neodymium iron boron magnet grain boundary diffusion source according to claim 1, characterized in that, In step (3), the heat treatment is to first keep the temperature at 800-1000℃ for 3-15 hours, and then keep the temperature at 460-600℃ for 2-5 hours.

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