Composite diffusing agents for grain boundary diffusion in NdFeB magnets, grain boundary diffusion methods for NdFeB magnets, and NdFeB magnets.

Abstract

This application provides a composite diffusing agent for grain boundary diffusion in NdFeB magnets, a method for grain boundary diffusion in NdFeB magnets, and NdFeB magnets. The composite diffusing agent comprises 20wt%~50wt% of a diffusion precursor, 50wt%~80wt% of a diffusion alloy, and 0.5wt%~5wt% of additives; the diffusion precursor comprises one or more of magnesium oxide and zinc oxide; the diffusion alloy comprises an RAlCu alloy, where R represents one or more of La, Ce, Pr, Nd, Dy, and Tb; the additive comprises Al 70 Cu 30 Alloy and first thermoplastic binder, Al, by total mass of additives 70 Cu 30 The alloy has a mass fraction greater than or equal to 40%. The composite diffusing agent of this application can reduce the amount of heavy rare earth elements used in the grain boundary diffusion of NdFeB magnets, improve diffusion efficiency, simplify the diffusion process, and improve magnet performance.

Description

Technical Field

[0001] This application relates to the field of magnetic materials technology, and in particular to a composite diffusing agent for grain boundary diffusion of NdFeB magnets, a grain boundary diffusion method for NdFeB magnets, and NdFeB magnets. Background Technology

[0002] Sintered NdFeB magnets possess advantages such as high energy product, high remanence, and high coercivity, leading to their widespread application in new energy vehicle drive motors, wind power generation, elevator traction machines, electroacoustic devices, maglev trains, military equipment, and human magnetic resonance imaging (MRI) scanners. However, the relatively low Curie temperature of NdFeB magnets (approximately 350℃~400℃) limits their application under high-temperature conditions.

[0003] To improve the high-temperature resistance of sintered NdFeB magnets, heavy rare earth elements such as dysprosium (Dy) and terbium (Tb) need to be added to the magnets to form (Dy / Tb)2Fe. 14 The B phase is used to improve the coercivity and high-temperature magnetic properties of magnets. However, heavy rare earth elements such as dysprosium and terbium are extremely scarce and expensive, which would significantly increase material costs. Furthermore, due to the (Dy / Tb)₂Fe 14 The B phase has low remanence, so adding heavy rare earth elements will increase the coercivity of the magnet but also reduce its remanence.

[0004] Grain boundary diffusion treatment technology involves attaching heavy rare earth elements such as dysprosium and terbium, and their compounds, to the surface of NdFeB magnets, and then subjecting them to high-temperature treatment to allow them to diffuse into the interior of the magnet's grain boundaries. Compared to the traditional direct addition of heavy rare earth elements, this technology can significantly improve the magnet's coercivity with a smaller amount of heavy rare earth elements, while minimizing the adverse effects of heavy rare earth elements on the magnet's remanence. Therefore, grain boundary diffusion treatment technology has developed rapidly in recent years. However, although the improvement effect of grain boundary diffusion treatment technology on magnet performance is very significant, current grain boundary diffusion technologies still have problems such as low utilization rate of heavy rare earth elements, low diffusion efficiency, complex processes, and high costs. Summary of the Invention

[0005] Based on this, this application provides a composite diffusing agent for grain boundary diffusion of NdFeB magnets, a grain boundary diffusion method for NdFeB magnets, and NdFeB magnets. The composite diffusing agent can reduce the amount of heavy rare earth elements used in grain boundary diffusion of NdFeB magnets, improve diffusion efficiency, simplify the diffusion process, and improve magnet performance.

[0006] The technical solution proposed in this application is as follows:

[0007] According to a first aspect of this application, a composite diffusing agent for grain boundary diffusion in NdFeB magnets is provided, comprising 20wt%~50wt% of a diffusion precursor, 50wt%~80wt% of a diffusion alloy, and 0.5wt%~5wt% of additives;

[0008] The diffusion precursor includes one or more of magnesium oxide and zinc oxide;

[0009] The diffusion alloy includes a RAlCu alloy, wherein R represents one or more of La, Ce, Pr, Nd, Dy, and Tb;

[0010] The additives include Al 70 Cu 30 The alloy and the first thermoplastic binder, based on the total mass of the additives, of the Al 70 Cu 30 The mass fraction of the alloy is greater than or equal to 40%.

[0011] In any embodiment, the D50 particle size of the diffusion precursor is 2 μm to 100 μm.

[0012] In any embodiment, the mass fraction of R element in the RAlCu alloy is 40%~70%, the mass fraction of Al element is 10%~40%, and the mass fraction of Cu element is 5%~30%.

[0013] In any embodiment, the D50 particle size of the RAlCu alloy is 2μm to 100μm.

[0014] In any embodiment, the first thermoplastic binder comprises one or more of polyethylene and polyurethane.

[0015] In any implementation, the Al 70 Cu 30 The D50 particle size of the alloy is 1μm~50μm.

[0016] According to a second aspect of this application, a method for grain boundary diffusion in a neodymium iron boron magnet is provided, comprising the following steps:

[0017] A slurry is formed by mixing a dispersant, an organic solvent, a second thermoplastic binder, and the composite dispersant according to any one of claims 1 to 6;

[0018] The slurry is coated onto the surface of the sintered NdFeB magnet;

[0019] The neodymium iron boron magnets coated with the slurry are subjected to diffusion heat treatment.

[0020] In any embodiment, the dispersant comprises one or more of polyethylene glycol, polyethylene wax, and zinc stearate.

[0021] In any embodiment, the organic solvent includes one or more of anhydrous ethanol, acetone, isopropanol, and ethyl acetate.

[0022] In any embodiment, the second thermoplastic binder comprises one or more of polyamide and vinyl acetate.

[0023] In any embodiment, the mass ratio of the dispersant, the organic solvent, the second thermoplastic binder, and the composite dispersant is 0.5~2:0.5~2:1~3:95~98.

[0024] In any embodiment, the coating thickness of the slurry on the surface of the neodymium iron boron magnet is 10 μm to 500 μm.

[0025] In any embodiment, the neodymium iron boron magnet is a sheet magnet, and the thickness of the neodymium iron boron magnet is less than or equal to 14 mm.

[0026] In any embodiment, the diffusion heat treatment is carried out under an inert gas protective atmosphere, the temperature of the diffusion heat treatment is 450℃~1100℃, and the time of the diffusion heat treatment is 2h~6h.

[0027] According to a third aspect of this application, a neodymium iron boron magnet is provided, which is prepared by the grain boundary diffusion method of the neodymium iron boron magnet of the second aspect of this application.

[0028] Compared with traditional technologies, this application has at least the following beneficial effects:

[0029] In this composite diffusing agent, magnesium oxide and zinc oxide serve as diffusion precursors. These precursors melt at relatively low temperatures during grain boundary diffusion, allowing them to penetrate the grain boundaries of the magnet first, forming diffusion channels for subsequent diffusion alloy penetration. This reduces the diffusion temperature, increases the diffusion depth, and improves diffusion efficiency. Simultaneously, the diffusion precursors themselves also isolate the main phase grains, enhance the anisotropic field of the magnet, and improve the magnet's coercivity. The RAlCu alloy can coat Nd2Fe NdFe magnets. 14 B-phase grains form a reinforcing shell with high coercivity at grain boundaries and on the outer layer of grains, which can improve the coercivity of the magnet; Al 70 Cu 30The alloy and thermoplastic binder enable the components to form a stable liquid-solid composite phase during grain boundary diffusion, ensuring uniform diffusion on the upper and lower surfaces of the magnet and inhibiting excessive enrichment of rare earth elements in the diffusion alloy on the magnet surface. Simultaneously, it improves the overall adhesion of the composite diffusing agent and avoids uneven diffusion on the upper and lower surfaces of the magnet due to gravity. When this composite diffusing agent is used for grain boundary diffusion in NdFeB magnets, the synergistic effect of the diffusion precursor, diffusion alloy, and additive components in specific proportions effectively reduces the amount of heavy rare earth elements used in NdFeB magnet grain boundary diffusion, improves diffusion efficiency, simplifies the diffusion process, and enables the NdFeB magnet to simultaneously possess high coercivity and remanence. Attached Figure Description

[0030] To better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments or examples, or the best mode of conduct of these applications as currently understood. In the drawings:

[0031] Figure 1 The overall EPMA distribution of Tb element in the magnet prepared in Example 1 of this application, from the surface to a depth of 800 μm;

[0032] Figure 2 This is an EPMA distribution map of Tb element at a depth of 50 μm from the surface of the magnet prepared in Example 1 of this application;

[0033] Figure 3 This is an EPMA distribution map of Tb element at a depth of 150 μm from the surface of the magnet prepared in Example 1 of this application;

[0034] Figure 4 The EPMA distribution map of Tb element at a depth of 800 μm from the surface of the magnet prepared in Example 1 of this application. Detailed Implementation

[0035] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, a detailed description of specific embodiments of this application is provided. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. Unless otherwise specifically stated, all raw materials, reagents, instruments, and equipment used in this application are commercially available or can be prepared by existing methods.

[0037] Currently, the grain boundary diffusion technology for NdFeB magnets still faces challenges such as low utilization of heavy rare earth elements, low diffusion efficiency, complex processes, and high costs. To address these issues, this application provides a composite diffusing agent for NdFeB magnet grain boundary diffusion, a grain boundary diffusion method for NdFeB magnets, and a corresponding NdFeB magnet. This effectively reduces the amount of heavy rare earth elements used in NdFeB magnet grain boundary diffusion, improves diffusion efficiency, simplifies the diffusion process, and enhances magnet performance.

[0038] One embodiment of this application provides a composite diffusing agent for grain boundary diffusion in NdFeB magnets. The composite diffusing agent comprises, by mass ratio: 20wt%~50wt% of a diffusion precursor, 50wt%~80wt% of a diffusion alloy, and 0.5wt%~5wt% of additives. The diffusion precursor includes one or more of magnesium oxide and zinc oxide; the diffusion alloy includes an RAlCu alloy, where R represents one or more of La, Ce, Pr, Nd, Dy, and Tb; and the additives include Al. 70 Cu 30 Alloy and first thermoplastic binder, and by total mass of the additive, Al 70 Cu 30 The mass fraction of the alloy is greater than or equal to 40%.

[0039] Currently, in the grain boundary diffusion technology of NdFeB magnets, in order to obtain a more ideal grain boundary diffusion effect, an excessive amount of heavy rare earth diffusion sources is usually applied. This results in some diffusion sources failing to penetrate into the NdFeB magnet, or a large amount of heavy rare earth elements accumulating on the surface or even entering the interior of the main phase grains, failing to achieve the diffusion enhancement effect and thus causing low utilization of heavy rare earths. On the other hand, the diffusion efficiency of the diffusion source during grain boundary diffusion is low, leading to long diffusion cycles, insufficient diffusion depth, and poor concentration gradients. Furthermore, most existing grain boundary diffusion technologies require harsh conditions such as high temperature and high vacuum, resulting in complex processes, high equipment requirements, and high overall process costs.

[0040] The composite diffusing agent for grain boundary diffusion of NdFeB magnets described in this application includes a specific content and type of diffusion precursor, diffusion alloy, and additives. Magnesium oxide and zinc oxide, as diffusion precursors, melt at relatively low temperatures during grain boundary diffusion and penetrate into the grain boundaries of the NdFeB magnet first, forming diffusion channels for the subsequent penetration of the diffusion alloy. This diffusion precursor lowers the diffusion temperature, increases the diffusion depth, and improves the diffusion efficiency. Simultaneously, the diffusion precursor itself also isolates the main phase grains, enhances the anisotropic field of the magnet, and improves the coercivity of the magnet. The diffusion alloy RAlCu can coat the NdFeB magnet (Nd2Fe). 14 The formation of a highly coercive reinforcing shell on the grain boundaries and outer layers of the boron (B) main phase grains is the main factor contributing to the improved coercivity of NdFeB magnets. The Al content in the additives... 70 Cu 30 The alloy and the first thermoplastic binder enable the components to form a stable liquid-solid composite phase during the grain boundary diffusion process, ensuring uniform diffusion on the upper and lower surfaces of the magnet and inhibiting the excessive enrichment of rare earth elements in the diffusion alloy on the magnet surface. At the same time, it can also improve the overall adhesion of the composite diffuser and avoid the problem of uneven diffusion on the upper and lower surfaces of the magnet due to gravity.

[0041] When the above-mentioned composite diffusing agent is used for grain boundary diffusion in NdFeB magnets, the synergistic effect of the diffusion precursor, diffusion alloy and additive components in a specific ratio can effectively reduce the amount of heavy rare earth elements used in grain boundary diffusion of NdFeB magnets, improve diffusion efficiency, simplify diffusion process and enable NdFeB magnets to have both high coercivity and remanence compared to current grain boundary diffusion methods.

[0042] In some embodiments, the D50 particle size of the diffusion precursor is 2 μm to 100 μm. Controlling the D50 particle size of the diffusion precursor within this range is more conducive to the melting of the diffusion precursor at a lower temperature during grain boundary diffusion, allowing it to penetrate into the grain boundaries of the NdFeB magnet and form diffusion channels for the subsequent diffusion of the diffusion alloy.

[0043] It is understandable that the D50 particle size of the diffusion precursor can be 2μm, 5μm, 8μm, 10μm, 15μm, 18μm, 20μm, 25μm, 28μm, 30μm, 35μm, 38μm, 40μm, 45μm, 48μm, 50μm, 55μm, 58μm, 60μm, 65μm, 68μm, 70μm, 75μm, 78μm, 80μm, 85μm, 88μm, 90μm, 95μm, 98μm, 100μm, or any value within the range formed by any two of the above values.

[0044] It should be noted that the D50 particle size is the median particle size, representing the particle size at 50% of the total particle size distribution, starting from the smallest particle size. In other words, 50% of the particles are smaller than this value, and the other 50% are larger than this value.

[0045] In some embodiments, the R1Cu alloy contains 40%–70% R by mass, 10%–40% Al by mass, and 5%–30% Cu by mass. Using an R1Cu alloy with the above-mentioned elemental composition as a diffusion alloy is beneficial for coating Nd2Fe magnets during grain boundary diffusion. 14 The B-phase grains form a reinforcing shell with high coercivity at grain boundaries and on the outer layer of the grains, which helps to improve the coercivity of NdFeB magnets.

[0046] In some embodiments, the D50 grain size of the RAlCu alloy is 2 μm to 100 μm. Thus, the RAlCu alloy with this grain size is more conducive to the coating of Nd2Fe magnets during grain boundary diffusion. 14 B-phase grains enhance the coercivity of NdFeB magnets.

[0047] It is understandable that the D50 grain size of the RAlCu alloy can be 2μm, 5μm, 8μm, 10μm, 15μm, 18μm, 20μm, 25μm, 28μm, 30μm, 35μm, 38μm, 40μm, 45μm, 48μm, 50μm, 55μm, 58μm, 60μm, 65μm, 68μm, 70μm, 75μm, 78μm, 80μm, 85μm, 88μm, 90μm, 95μm, 98μm, 100μm, or any value within the range formed by any two of the above values.

[0048] In some embodiments, the first thermoplastic binder in the composite diffusing agent includes one or more of polyethylene and polyurethane. Using the aforementioned thermoplastic binder helps improve the adhesion of the diffusing agent during grain boundary diffusion, preventing uneven diffusion on the upper and lower surfaces of the magnet due to gravity.

[0049] In some of these embodiments, Al 70 Cu 30 The D50 grain size of the alloy ranges from 1 μm to 50 μm. Thus, Al... 70 Cu 30 Controlling the D50 particle size of the alloy within the above range is more conducive to the formation of a stable liquid-solid composite phase during grain boundary diffusion, which helps to promote uniform diffusion on the upper and lower surfaces of the magnet and inhibits the excessive enrichment of rare earth elements in the diffusion alloy on the magnet surface.

[0050] Understandably, Al 70 Cu 30 The D50 grain size of the alloy can be 1μm, 2μm, 5μm, 8μm, 10μm, 15μm, 18μm, 20μm, 25μm, 28μm, 30μm, 35μm, 38μm, 40μm, 45μm, 48μm, 50μm, or any value within the range formed by any two of the above values.

[0051] One embodiment of this application provides a grain boundary diffusion method for neodymium iron boron magnets, the grain boundary diffusion method comprising the following steps:

[0052] First, the dispersant, organic solvent, second thermoplastic binder and the composite dispersant mentioned above in this application are mixed to form a slurry; then the slurry is coated on the surface of the sintered NdFeB magnet; then the NdFeB magnet coated with the slurry is subjected to diffusion heat treatment to obtain a NdFeB magnet with grain boundary diffusion.

[0053] The aforementioned grain boundary diffusion method for NdFeB magnets utilizes the composite diffusing agent described in this application during the grain boundary diffusion process. The diffusion precursor in this composite diffusing agent melts at a relatively low temperature, allowing it to penetrate into the grain boundaries of the NdFeB magnet first, forming diffusion channels for the subsequent penetration of the diffusion alloy. This diffusion precursor also isolates the main phase grains, enhances the magnet's anisotropic field, and improves its coercivity. Finally, the NdFeB magnet is coated with a RAlCu alloy. 14 The B-phase grains form a reinforcing shell with high coercivity at grain boundaries and on the outer layer of the grains, thereby improving the coercivity of NdFeB magnets; through Al 70 Cu 30 The alloy and the first thermoplastic binder enable the components to form a stable liquid-solid composite phase during grain boundary diffusion, inhibiting the excessive enrichment of rare earth elements in the diffusion alloy on the magnet surface. Simultaneously, it improves the overall adhesion of the composite diffuser and enhances the uniformity of magnet diffusion. This grain boundary diffusion method can reduce the amount of heavy rare earth elements used in NdFeB magnet grain boundary diffusion, improve diffusion efficiency, simplify the diffusion process, and enhance magnet performance.

[0054] In some embodiments, the dispersant includes one or more of polyethylene glycol, polyethylene wax, and zinc stearate.

[0055] In some embodiments, the organic solvent includes one or more of anhydrous ethanol, acetone, isopropanol, and ethyl acetate.

[0056] In some embodiments, the second thermoplastic binder comprises one or more of polyamide and vinyl acetate.

[0057] In some embodiments, the mass ratio of dispersant, organic solvent, second thermoplastic binder and composite dispersant is 0.5~2:0.5~2:1~3:95~98.

[0058] In some embodiments, the coating thickness of the slurry on the surface of the NdFeB magnet is 10 μm to 500 μm. By coating the surface of the NdFeB magnet with a slurry of this thickness, it is beneficial to achieve sufficient grain boundary diffusion in the NdFeB magnet, while reducing the amount of heavy rare earth elements used, thereby improving the performance of the NdFeB magnet and reducing production costs.

[0059] It is understandable that the coating thickness of the paste on the surface of the NdFeB magnet can be 10μm, 20μm, 50μm, 80μm, 100μm, 120μm, 150μm, 180μm, 200μm, 220μm, 250μm, 280μm, 300μm, 320μm, 350μm, 380μm, 400μm, 420μm, 450μm, 480μm, 500μm, or any value within the range formed by any two of the above values.

[0060] In some embodiments, the NdFeB magnet is a sheet magnet with a thickness of less than or equal to 14 mm. A sheet magnet of this thickness has a large specific surface area, which is beneficial for the adhesion and diffusion of heavy rare earth elements on its surface, thus more efficiently improving the magnet's coercivity. Furthermore, the main phase grains within the sheet magnet are less affected during diffusion, maintaining a higher remanence level and ensuring the magnet's overall magnetic properties. Moreover, the more regular shape of the sheet magnet makes it easier to achieve a uniform diffusion effect, ensuring consistent magnet performance.

[0061] It is understandable that the thickness of neodymium iron boron magnets can be 0.5mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm, or any value within the range formed by any two of the above values.

[0062] In some embodiments, the diffusion heat treatment is performed under an inert gas protective atmosphere at a temperature of 450°C to 1100°C for 2 to 6 hours. Specifically, the NdFeB magnet coated with the slurry can be placed in a diffusion chamber under argon atmosphere protection, and the diffusion heat treatment temperature is controlled at 450°C to 1100°C for 2 to 6 hours to obtain NdFeB magnets with grain boundary diffusion. This diffusion heat treatment process is relatively simple, requires less equipment, and has lower process costs.

[0063] It is understood that the temperature for diffusion heat treatment can be 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, 1100℃, or any value within the range formed by any two of the above values. The time for diffusion heat treatment can be 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, or any value within the range formed by any two of the above values.

[0064] Furthermore, the temperature of the diffusion heat treatment can be selected as 700℃~850℃, and the time of the diffusion heat treatment can be selected as 4h~6h.

[0065] In one embodiment of this application, a neodymium iron boron magnet prepared using the grain boundary diffusion method described above is also provided. This neodymium iron boron magnet has low production cost and good magnetic properties.

[0066] The present application will be further described below with reference to specific embodiments and comparative examples, but should not be construed as limiting the scope of protection of the present application.

[0067] Example 1:

[0068] (1) Initial magnet preparation

[0069] A neodymium iron boron permanent magnet blank prepared by a traditional sintering process without the addition of heavy rare earth element Tb was selected and cut into 6 magnets with dimensions of 20mm × 30mm × 8mm. The 8mm direction is the magnetization direction. Initial magnet performance: remanence B. r Approximately 13.62 kGs, coercivity H cj It is approximately 12.2 kOe.

[0070] (2) Preparation of composite dispersant

[0071] The composite diffusing agent is prepared according to the formulation of this application. The composition of the composite diffusing agent is as follows: diffusion precursor MgO 22wt%, diffusion alloy TbAlCu alloy 75wt% (Tb 30wt%, Al 50wt%, Cu 20wt%), and additive 3wt% (Al 70 Cu 30 The alloy comprises 50 wt% (and a first thermoplastic binder, polyurethane, comprising 50 wt%). The D50 particle size of MgO is 30 μm, and the D50 particle size of the TbAlCu alloy is 30 μm. 70 Cu 30 The D50 particle size of the alloy is 10 μm.

[0072] (3) Grain boundary diffusion heat treatment

[0073] The dispersant polyethylene glycol, the organic solvent anhydrous ethanol, the second thermoplastic binder polyamide, and the composite dispersant from step (2) were mixed in a mass fraction of 0.5wt%:1wt%:1wt%:97.5wt% to form a slurry. The slurry was coated on the upper and lower surfaces of the magnet from step (1), with a coating thickness of 50μm on one side. The magnet was then subjected to diffusion heat treatment at a diffusion temperature of 850℃ for 4.5h under an argon protective atmosphere. After cooling to room temperature, the magnet was removed to obtain a magnet with grain boundary diffusion.

[0074] Example 2:

[0075] This embodiment is basically the same as Embodiment 1, except that: in step (2), the composition of the composite diffusing agent is: diffusion precursor MgO 30wt%, diffusion alloy TbAlCu alloy 68wt% (Tb 25wt%, Al 60wt%, Cu 15wt%), additive 2wt% (Al 70 Cu 30 The alloy comprises 60 wt% and the first thermoplastic binder, polyurethane, comprises 40 wt%.

[0076] Example 3:

[0077] This embodiment is basically the same as Embodiment 1, except that: in step (2), the composition of the composite diffusing agent is: 50wt% of the diffusion precursor ZnO, 49wt% of the diffusion alloy DyAlCu alloy (Dy 30wt%, Al 60wt%, Cu 10wt%), and 1wt% of the additive (Al 70 Cu 30 The alloy is 50 wt%, and the first thermoplastic binder is 50 wt% polyurethane); and in step (3), the diffusion temperature is 600 ℃ and the diffusion time is 4 h.

[0078] Example 4:

[0079] This embodiment is basically the same as Embodiment 1, except that: in step (2), the composition of the composite diffusing agent is: 20wt% of diffusion precursor MgO, 79wt% of diffusion alloy LaAlCu alloy (La 50wt%, Al 40wt%, Cu 10wt%), and 1wt% of additive (Al 70 Cu 30 The alloy is 50 wt%, and the first thermoplastic binder is polyurethane 50 wt%); and in step (3), the diffusion temperature is 750 ℃ ​​and the diffusion time is 6 h.

[0080] Example 5:

[0081] This embodiment is basically the same as Embodiment 1, except that: in step (2), the composition of the composite diffusing agent is: 40wt% of the diffusion precursor ZnO, 55wt% of the total mixture of diffusion alloys PrAlCu alloy and DyAlCu alloy (Pr 60wt%, Dy 10%, Al 20wt%, Cu 10wt%), and 5wt% of additives (Al 70 Cu 30 The alloy is 60wt%, and the first thermoplastic binder is polyurethane 40wt%); and in step (3), the diffusion temperature is 700℃ and the diffusion time is 5h.

[0082] Example 6:

[0083] This embodiment is basically the same as Embodiment 1, except that: in step (2), the composition of the composite diffusing agent is: diffusion precursor MgO 30wt%, diffusion alloy TbAlCu alloy 69wt% (Tb 20wt%, Al 60wt%, Cu 20wt%), and additive 1wt% (Al 70 Cu 30 The alloy comprises 50 wt% (aluminum alloy and polyethylene as the first thermoplastic binder), wherein the D50 particle size of MgO is 95 μm, the D50 particle size of TbAlCu alloy is 95 μm, and Al... 70 Cu 30 The D50 particle size of the alloy is 40 μm; and in step (3), the diffusion temperature is 800 °C and the diffusion time is 5 h.

[0084] Comparative Example 1:

[0085] This comparative example is basically the same as Example 1, except that in step (2), the composition of the composite diffusing agent is: diffusion precursor MgO 70wt%, diffusion alloy TbAlCu alloy 25wt% (Tb 25wt%, Al 60wt%, Cu 15wt%), and additive 5wt% (Al 70 Cu 30 The alloy comprises 60 wt% and the first thermoplastic binder, polyurethane, comprises 40 wt%.

[0086] Performance testing methods:

[0087] (1) Remanence B r test

[0088] The remanence of a magnet is measured using a Hall effect probe. Specifically, the magnet is placed in a magnetic field until it reaches saturation magnetization, and then the magnetic field strength is gradually reduced to zero. The magnetic induction intensity produced by the magnet at this point is measured, which is the remanence B. r .

[0089] (2) Coercivity H cj test

[0090] A neodymium iron boron (NdFeB) magnet sample is placed in a strong magnetic field for a period of time to saturate the magnet. Then, the sample is placed at the test position of a coercivity meter, and a reverse magnetic field is applied. The strength of the reverse magnetic field is gradually increased while the magnetometer probe is brought close to the sample to test the stray magnetic field. When the stray magnetic field detected by the probe is zero, the strength of the reverse magnetic field at this point is the coercivity H of the sample. cj .

[0091] The parameters of the above embodiments and comparative examples, as well as the performance data of the NdFeB magnets obtained after grain boundary diffusion, are shown in Table 1.

[0092] Table 1

[0093]

[0094] As shown in Table 1, by using the composite diffusing agent and grain boundary diffusion method of this application, the coercivity of the magnet is greatly improved with very little heavy rare earth content, and the remanence of the magnet hardly decreases or only slightly decreases, achieving a very good performance improvement effect.

[0095] The Tb element EPMA (field emission electron probe microanalysis) distribution in the region 800 μm below the surface of the magnet prepared in Example 1 of this application is shown in the figure. Figures 1 to 4 ,Depend on Figures 1 to 4 It can be seen that the heavy rare earth element Tb effectively diffuses into the interior of the magnet to a depth of at least 800 μm, with good diffusion effect and depth, and a good overall concentration gradient distribution.

[0096] Traditional grain boundary diffusion methods, to achieve the magnet performance corresponding to Example 1 of this application, typically require a heavy rare earth element (Tb) content of 1wt% to 1.5wt% in the final product, and the diffusion treatment time usually exceeds 12 hours. In contrast, the final product of Example 1 of this application requires only about 0.5wt% of heavy rare earth element (Tb), and the diffusion treatment time is only 4.5 hours. The composite diffusing agent and grain boundary diffusion method of this application can effectively reduce the amount of heavy rare earth element used in the grain boundary diffusion of NdFeB magnets and improve diffusion efficiency.

[0097] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0098] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A composite diffusing agent for grain boundary diffusion in NdFeB magnets, characterized in that, It includes 20wt%~50wt% diffusion precursor, 50wt%~80wt% diffusion alloy, and 0.5wt%~5wt% additives; The diffusion precursor includes one or more of magnesium oxide and zinc oxide; The diffusion alloy includes a RAlCu alloy, where R represents one or more of La, Ce, Pr, Nd, Dy, and Tb; The additives include Al 70 Cu 30 The alloy and the first thermoplastic binder, based on the total mass of the additives, of the Al 70 Cu 30 The mass fraction of the alloy is greater than or equal to 40%.

2. The composite diffusing agent for grain boundary diffusion in NdFeB magnets according to claim 1, characterized in that, The D50 particle size of the diffusion precursor is 2μm~100μm.

3. The composite diffusing agent for grain boundary diffusion in NdFeB magnets according to claim 1 or 2, characterized in that, The RAlCu alloy contains 40% to 70% R by mass, 10% to 40% Al by mass, and 5% to 30% Cu by mass.

4. The composite diffusing agent for grain boundary diffusion in NdFeB magnets according to claim 1 or 2, characterized in that, The D50 particle size of the RAlCu alloy is 2μm~100μm.

5. The composite diffusing agent for grain boundary diffusion in NdFeB magnets according to claim 1 or 2, characterized in that, The first thermoplastic binder includes one or more of polyethylene and polyurethane.

6. The composite diffusing agent for grain boundary diffusion in NdFeB magnets according to claim 1 or 2, characterized in that, The Al 70 Cu 30 The D50 particle size of the alloy is 1μm~50μm.

7. A method for grain boundary diffusion in a neodymium iron boron magnet, characterized in that, Includes the following steps: A slurry is formed by mixing a dispersant, an organic solvent, a second thermoplastic binder, and the composite dispersant according to any one of claims 1 to 6; The slurry is coated onto the surface of the sintered NdFeB magnet; The neodymium iron boron magnets coated with the slurry are subjected to diffusion heat treatment.

8. The grain boundary diffusion method for NdFeB magnets according to claim 7, characterized in that, The dispersant includes one or more of polyethylene glycol, polyethylene wax, and zinc stearate; And / or, the organic solvent includes one or more of anhydrous ethanol, acetone, isopropanol and ethyl acetate; And / or, the second thermoplastic binder includes one or more of polyamide and vinyl acetate.

9. The method for grain boundary diffusion of a NdFeB magnet according to any one of claims 7 to 8, characterized in that, The mass ratio of the dispersant, the organic solvent, the second thermoplastic binder, and the composite dispersant is 0.5~2:0.5~2:1~3:95~98.

10. The method for grain boundary diffusion of a NdFeB magnet according to any one of claims 7 to 8, characterized in that, The coating thickness of the slurry on the surface of the neodymium iron boron magnet is 10μm~500μm.

11. The method for grain boundary diffusion of a NdFeB magnet according to any one of claims 7 to 8, characterized in that, The neodymium iron boron magnet is a sheet magnet, and the thickness of the neodymium iron boron magnet is less than or equal to 14 mm.

12. The method for grain boundary diffusion of a NdFeB magnet according to any one of claims 7 to 8, characterized in that, The diffusion heat treatment is carried out under an inert gas protective atmosphere, the temperature of the diffusion heat treatment is 450℃~1100℃, and the time of the diffusion heat treatment is 2h~6h.

13. A neodymium iron boron magnet, characterized in that, It is prepared by the grain boundary diffusion method of neodymium iron boron magnets according to any one of claims 7 to 12.

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