Method for preparing organic suspension for increasing coercivity of sintered neodymium-iron-boron magnets and use thereof

Abstract

The application discloses a preparation method and application of an organic suspension liquid for improving the coercivity of a sintered neodymium-iron-boron magnet, and relates to the technical field of rare earth permanent magnets, and comprises the following specific steps: S1, raw material pretreatment and preparation; S2, heavy rare earth powder preparation; and S3, organic suspension liquid preparation. The organic suspension liquid for improving the coercivity of the sintered neodymium-iron-boron magnet has the advantages that the heavy rare earth powder used is smaller in particle size, is easier to enter the magnet in the grain boundary diffusion process, effectively improves the coercivity of the magnet, is more economical in the use of medium rare earth, and is more remarkable in cost benefit; the high molecular resin used in the organic suspension liquid is low in melting point and low in C content, can be converted into volatile matter for effective removal during sintering, and reduces the influence of impurity elements on the performance of the magnet.

Description

Technical Field

[0001] This invention relates to the field of rare earth permanent magnet technology, specifically to a method for preparing and applying an organic suspension for improving the coercivity of sintered NdFeB magnets. Background Technology

[0002] Sintered NdFeB, as a third-generation permanent magnet material, is widely used in new energy vehicles, industrial motors, consumer electronics, and medical devices due to its excellent magnetic properties. Especially in recent years, the rise of new energy vehicles has propelled the application market for sintered NdFeB magnets towards higher-end applications, meaning that the performance of sintered NdFeB magnets needs to reach a new level. However, the actual coercivity of sintered NdFeB is far lower than its theoretical value, and NdFeB without special treatment cannot meet the requirements of some application scenarios.

[0003] In the art, heavy rare earth elements are typically introduced during the fabrication of magnets to significantly improve their coercivity through grain boundary diffusion. Common methods for heavy rare earth diffusion include magnetron sputtering, coating, and electrophoretic deposition. However, these methods suffer from drawbacks such as low heavy rare earth utilization and high production costs. Existing technologies also include coating suspensions specifically designed for grain boundary diffusion in sintered NdFeB magnets, but these often suffer from poor dispersion and coating consistency due to improper solvent selection, powder particle size, and processing techniques. Therefore, this invention relates to a novel coating-type diffusion source suspension. Compared to the methods described above, this method offers higher heavy rare earth utilization, lower cost, and superior magnet performance. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for preparing an organic suspension for improving the coercivity of sintered NdFeB magnets and its application, thus solving the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides a method for preparing and applying an organic suspension for improving the coercivity of sintered NdFeB magnets, comprising the following specific steps:

[0006] S1. Raw material pretreatment and preparation;

[0007] S2. Preparation of heavy rare earth powders, as detailed below:

[0008] S201. Melting and alloying: Pretreated dysprosium or terbium, praseodymium or neodymium, and metallic raw materials are added to a vacuum induction melting furnace, and the furnace is evacuated to 1×10⁻⁶. -3 Pa, argon gas is introduced for protection, the temperature is raised to 1350-1500℃, and the temperature is held for 2-3 hours to completely melt the raw material. After stirring evenly, copper mold is used for rapid cooling and casting to obtain a fast-solidifying casting sheet with a thickness of 0.05-0.2mm.

[0009] S202, hydrogen crushing treatment;

[0010] S203, ultrafine grinding;

[0011] S204, mixed modification: In an argon-protected powder mixer, first add heavy rare earth fine powder, then add 0.1-0.5% lubricant and 0.01-0.1% antioxidant in proportion to improve powder dispersibility and antioxidant properties;

[0012] S3. Preparation of organic suspension, as detailed below:

[0013] S301. Mix in an inert environment. In a glove box protected by nitrogen or argon, weigh the raw materials according to the mass percentage and add them to the mixing container in sequence.

[0014] S302, graded stirring and dispersion;

[0015] S303, Viscosity and Stability Control: After stirring, check the viscosity of the suspension. If it deviates from 150,000-200,000... Adjust by adding dispersant or resin; let the suspension stand for 18-30 hours, and check that the amount of clear liquid in the upper layer is ≤5% to ensure dispersion stability.

[0016] Optionally, step S1 specifically includes:

[0017] S101, Selected heavy rare earth raw materials, including elemental dysprosium or terbium, praseodymium or neodymium with a purity ≥99.9%, and one or more metals selected from copper, aluminum, gallium, and cobalt, according to chemical formula RE1 x RE2 y M 100-x-y Weigh the raw materials according to the proportions where 10≤x≤70 and 10≤y≤30, and remove the oxide layer from the surface of the raw materials.

[0018] S102, Pretreatment of organic auxiliary materials.

[0019] Optionally, step S102 specifically includes:

[0020] A. Polymer resin: Select polyvinyl acetate or polyvinyl butyral, pulverize to a particle size ≤50μm, and dry in a vacuum drying oven;

[0021] B. Dispersant: Mix ethanol and acetone at a mass ratio of 2-4:1-1.5 and pre-stir for 5-12 minutes until homogeneous;

[0022] C. Defoamer: Mix silicone defoamer with a small amount of dispersant and disperse and activate it using ultrasound.

[0023] Optionally, the raw material mass percentage in step 301 is:

[0024] The ingredients include 40-70% heavy rare earth powder, 2-10% polymer resin, 10-50% dispersant, and 1-3% defoamer.

[0025] Optionally, step S202 specifically includes:

[0026] Place the rapidly solidified casting into the hydrogen breaker furnace and evacuate it to a vacuum level of 5×10. -2 After Pa, high-purity hydrogen gas is introduced, and the hydrogen pressure is controlled at 0.2-0.3 MPa. The mixture is kept at room temperature for 2-4 hours to allow the alloy to absorb hydrogen and become embrittled. Then, a vacuum is applied to 1×10⁻⁶ MPa. -2 Pa, heated to 450-600℃ for dehydrogenation, to obtain coarse powder with a particle size of 80-100μm.

[0027] Optionally, step S203 specifically includes:

[0028] The coarse powder was fed into an air jet mill, where nitrogen was used as the grinding medium to grind it into fine powder with a particle size of 1.0-3.0 μm; the particle size distribution was detected by a laser particle size analyzer.

[0029] Optionally, the graded mixing and dispersion in step S302 includes coarse mixing and fine mixing, specifically including:

[0030] The coarse mixing process specifically involves:

[0031] The mixed raw materials are transferred to a multi-functional vacuum mixing vessel, vacuumed, and stirred to allow the resin and dispersant to initially blend.

[0032] Fine stirring specifically involves:

[0033] The coarsely mixed slurry is transferred to a horizontal sand mill, and the particle size of the agglomerates is monitored by a dynamic light scattering instrument.

[0034] An application of an organic suspension for improving the coercivity of sintered NdFeB magnets, the specific application process is as follows:

[0035] (1) Select sintered NdFeB blanks, use ultrasonic cleaning to remove surface oil stains, and then use plasma treatment to improve surface roughness and enhance coating adhesion;

[0036] (2) A uniform base coating is formed on the surface of the blank by air spraying, and then the coating is scraped and repaired with a precision scraper to control the coating thickness to 50-100μm; for complex shaped magnets, dip coating combined with infrared thermometry is used.

[0037] (3) Place the coated magnet into a hot air circulating oven and keep it at 120-180℃ for 20-40 minutes to allow the polymer resin to initially cure and prevent the coating from peeling off during subsequent heat treatment; after baking, cool to room temperature and use a thickness gauge to check the coating thickness deviation ≤5μm;

[0038] (4) Place the magnet into a vacuum sintering furnace and evacuate it to a vacuum level of 5×10⁻⁶.-4 Pa, heating in stages: room temperature → 500-600℃ → 910-950℃; after holding, cooling with the furnace to below 200℃;

[0039] (5) After diffusion, the magnet is transferred to a tempering furnace, protected by argon gas, heated to 450-550℃, and held for 3-6 hours to eliminate internal stress and stabilize the microstructure of the magnet; secondary tempering is used to further optimize the coercivity stability.

[0040] (6) Post-processing and performance testing.

[0041] Optionally, the post-processing and performance testing are as follows:

[0042] After heat treatment, the magnet was ultrasonically cleaned with anhydrous ethanol to remove residual carbides on the surface. After drying, the surface roughness Ra was measured to be ≤0.2μm.

[0043] This invention provides a method for preparing an organic suspension for improving the coercivity of sintered NdFeB magnets and its application, which has the following beneficial effects:

[0044] The organic suspension uses heavy rare earth powder with smaller particle size, which makes it easier to enter the magnet during grain boundary diffusion, effectively improving the coercivity of the magnet and saving more medium rare earth content, resulting in more significant cost benefits. The polymer resin used in the organic suspension has a low melting point and low carbon content, which can be converted into volatiles during sintering and effectively removed, reducing the impact of impurity elements on the magnet performance.

[0045] Furthermore, the equipment used in this invention is all used in the process of preparing sintered NdFeB, eliminating the need to purchase other equipment and simplifying the preparation process, thus enabling mass production. Attached Figure Description

[0046] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0047] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0048] Example 1

[0049] (1) Weigh one of dysprosium and terbium or an alloy mixture and add it to the melting furnace. Set the melting temperature to 1450℃. The thickness of the rapidly solidified casting after melting and casting is 0.2 mm. The particle size of the coarse powder after hydrogen crushing is 92 μm. The average particle size of the fine powder after air jet milling is 2.8 μm.

[0050] (2) Weigh 40% heavy rare earth powder and alloy, 10% polyvinyl acetate, 49% acetone, and 1% organosilicon in sequence according to weight percentage; mix and stir 10% polyvinyl acetate, 49% acetone, and 1% organosilicon and transfer them into a vacuum glove box; add 40% heavy rare earth powder and alloy to the mixed organic solvent; and stir in a multi-functional vacuum stirring kettle and a horizontal sand mill to obtain an organic suspension.

[0051] (3) The organic suspension was coated on the surface of the sintered NdFeB blank and heated and baked at 150°C for 30 minutes to obtain a heavy rare earth coating.

[0052] (4) The coated sintered NdFeB blank is placed in a vacuum sintering furnace for heat treatment at a temperature of 950°C for 5 hours. Then it is tempered at a temperature of 550°C for 3 hours to obtain diffused sintered NdFeB.

[0053] Example 2

[0054] (1) Weigh one of dysprosium and terbium or an alloy mixture and add it to the melting furnace. Set the melting temperature to 1450℃. The thickness of the rapidly solidified casting after melting and casting is 0.2 mm. The particle size of the coarse powder after hydrogen crushing is 92 μm. The average particle size of the fine powder after air jet milling is 2.8 μm.

[0055] (2) Weigh 50% of heavy rare earth powder and alloy, 8% of polyvinyl acetate, 41% of acetone, and 1% of organosilicon in sequence according to weight percentage; mix and stir 8% of polyvinyl acetate, 41% of acetone, and 1% of organosilicon and transfer them into a vacuum glove box; add 50% of heavy rare earth powder and alloy to the mixed organic solvent; and stir in a multi-functional vacuum stirring kettle and a horizontal sand mill to obtain an organic suspension.

[0056] (3) The organic suspension was coated on the surface of the sintered NdFeB blank and heated and baked at 120°C for 30 minutes to obtain a heavy rare earth coating.

[0057] (4) The coated sintered NdFeB blank is placed in a vacuum sintering furnace for heat treatment at a temperature of 940°C for 5 hours. Then it is tempered at a temperature of 550°C for 3 hours to obtain diffused sintered NdFeB.

[0058] Example 3

[0059] (1) Weigh one of dysprosium and terbium or an alloy mixture and add it to the melting furnace. Set the melting temperature to 1450℃. The thickness of the quick-solidified casting after melting and casting is 0.2 mm. The particle size of the coarse powder after hydrogen crushing should be 92 μm. The average particle size of the fine powder after air jet milling is 2.8 μm.

[0060] (2) Weigh 60% of heavy rare earth powder and alloy, 6% of polyvinyl acetate, 33% of acetone, and 1% of organosilicon in sequence according to weight percentage; mix and stir 6% of polyvinyl acetate, 33% of acetone, and 1% of organosilicon and transfer them into a vacuum glove box; add 60% of heavy rare earth powder and alloy to the mixed organic solvent; and stir in a multi-functional vacuum stirring kettle and a horizontal sand mill to obtain an organic suspension.

[0061] (3) The organic suspension was coated on the surface of the sintered NdFeB blank and heated and baked at 120°C for 30 minutes to obtain a heavy rare earth coating.

[0062] (4) The coated sintered NdFeB blank is placed in a vacuum sintering furnace for heat treatment. The sintering temperature is 930℃ and the holding time is 5 hours. Then, it is tempered at 550℃ for 3 hours to obtain diffused sintered NdFeB.

[0063] Example 4

[0064] (1) Weigh one of dysprosium and terbium or an alloy mixture and add it to the melting furnace. Set the melting temperature to 1450℃. The thickness of the quick-solidified casting after melting and casting is 0.2 mm. The particle size of the coarse powder after hydrogen crushing should be 92 μm. The average particle size of the fine powder after air jet milling is 2.8 μm.

[0065] (2) Weigh 70% of heavy rare earth powder and alloy, 4% of polyvinyl acetate, 25% of acetone, and 1% of organosilicon in sequence according to weight percentage; mix and stir 4% of polyvinyl acetate, 25% of acetone, and 1% of organosilicon and transfer them into a vacuum glove box; add 70% of heavy rare earth powder and alloy to the mixed organic solvent; and stir in a multi-functional vacuum stirring kettle and a horizontal sand mill to obtain an organic suspension.

[0066] (3) The organic suspension was coated on the surface of the sintered NdFeB blank and heated and baked at 120°C for 30 minutes to obtain a heavy rare earth coating.

[0067] (4) The coated sintered NdFeB blank is placed in a vacuum sintering furnace for heat treatment at a temperature of 920°C for 5 hours. Then it is tempered at a temperature of 550°C for 3 hours to obtain diffused sintered NdFeB.

[0068] Comparative Example 1

[0069] (1) Weigh one of dysprosium and terbium or an alloy mixture and add it to the melting furnace. Set the melting temperature to 1450℃. The thickness of the rapidly solidified casting after melting and casting is 0.18 mm. The particle size of the coarse powder after hydrogen crushing is 84 μm. The average particle size of the fine powder after air jet milling is 2.5 μm.

[0070] (2) Weigh 40% heavy rare earth powder and alloy, 10% polyvinyl alcohol, 49% ethanol, and 1% organosilicon in sequence according to weight percentage; mix and stir 10% polyvinyl alcohol, 49% ethanol, and 1% organosilicon and transfer them into a vacuum glove box; add 40% heavy rare earth powder and alloy to the mixed organic solvent; and stir in a multi-functional vacuum stirring kettle and a horizontal sand mill to obtain an organic suspension.

[0071] (3) The organic suspension was coated on the surface of the sintered NdFeB blank and heated and baked at 150°C for 30 minutes to obtain a heavy rare earth coating.

[0072] (4) The coated sintered NdFeB blank is placed in a vacuum sintering furnace for heat treatment at a temperature of 950°C for 5 hours. Then it is tempered at a temperature of 550°C for 3 hours to obtain diffused sintered NdFeB.

[0073] Comparative Example 2

[0074] (1) Weigh one of dysprosium and terbium or an alloy mixture and add it to the melting furnace. Set the melting temperature to 1450℃. The thickness of the rapidly solidified casting after melting and casting is 0.18 mm. The particle size of the coarse powder after hydrogen crushing is 84 μm. The average particle size of the fine powder after air jet milling is 2.5 μm.

[0075] (2) Weigh 50% of heavy rare earth powder and alloy, 8% of polyvinyl alcohol, 41% of ethanol and 1% of organosilicon in sequence according to weight percentage; mix and stir 8% of polyvinyl alcohol, 41% of ethanol and 1% of organosilicon and transfer them into a vacuum glove box; add 40% of heavy rare earth powder and alloy to the mixed organic solvent; and stir in a multi-functional vacuum stirring kettle and a horizontal sand mill to obtain an organic suspension.

[0076] (3) The organic suspension was coated on the surface of the sintered NdFeB blank and heated and baked at 150°C for 30 minutes to obtain a heavy rare earth coating.

[0077] (4) The coated sintered NdFeB blank is placed in a vacuum sintering furnace for heat treatment. The sintering temperature is 940℃ and the holding time is 6 hours. Then, it is tempered at 550℃ for 4 hours to obtain diffused sintered NdFeB.

[0078] Comparative Example 3

[0079] (1) Weigh one of dysprosium and terbium or an alloy mixture and add it to the melting furnace. Set the melting temperature to 1450℃. The thickness of the rapidly solidified casting after melting and casting is 0.18 mm. The particle size of the coarse powder after hydrogen crushing is 84 μm. The average particle size of the fine powder after air jet milling is 2.5 μm.

[0080] (2) Weigh 60% of heavy rare earth powder and alloy, 6% of polyvinyl alcohol, 33% of ethanol, and 1% of organosilicon in sequence according to weight percentage; mix and stir 6% of polyvinyl alcohol, 33% of ethanol, and 1% of organosilicon and transfer them into a vacuum glove box; add 40% of heavy rare earth powder and alloy to the mixed organic solvent; and stir in a multi-functional vacuum stirring kettle and a horizontal sand mill to obtain an organic suspension.

[0081] (3) The organic suspension was coated on the surface of the sintered NdFeB blank and heated and baked at 150°C for 30 minutes to obtain a heavy rare earth coating.

[0082] (4) The coated sintered NdFeB blank is placed in a vacuum sintering furnace for heat treatment. The sintering temperature is 930℃ and the holding time is 7 hours. Then, it is tempered at 550℃ for 5 hours to obtain diffused sintered NdFeB.

[0083] Comparative Example 4

[0084] (1) Weigh one of dysprosium and terbium or an alloy mixture and add it to the melting furnace. Set the melting temperature to 1450℃. The thickness of the rapidly solidified casting after melting and casting is 0.18 mm. The particle size of the coarse powder after hydrogen crushing is 84 μm. The average particle size of the fine powder after air jet milling is 2.5 μm.

[0085] (2) Weigh 70% of heavy rare earth powder and alloy, 4% of polyvinyl alcohol, 25% of ethanol and 1% of organosilicon in sequence according to weight percentage; mix 4% of polyvinyl alcohol, 25% of ethanol and 1% of organosilicon and transfer them into a vacuum glove box; add 40% of heavy rare earth powder and alloy to the mixed organic solvent; and stir in a multi-functional vacuum stirring kettle and a horizontal sand mill to obtain an organic suspension.

[0086] (3) The organic suspension was coated on the surface of the sintered NdFeB blank and heated and baked at 150°C for 30 minutes to obtain a heavy rare earth coating.

[0087] (4) The coated sintered NdFeB blank was placed in a vacuum sintering furnace for heat treatment. The sintering temperature was 920℃ and the holding time was 8 hours. Then, it was tempered at 550℃ for 6 hours to obtain diffused sintered NdFeB.

[0088] The magnetic properties of the diffused magnet were measured using a Belgian Metis pulsed field magnetometer. The results are shown in Table 1. The average value was taken from five tests.

[0089] Table 1

[0090]

[0091] As can be seen from Table 1, the magnetic properties of the diffusion-sintered NdFeB magnets prepared using suspension were significantly improved, and the remanence was reduced by a small amount.

[0092] This invention prepares a coated organic suspension for improving the coercivity of sintered NdFeB magnets. By selecting a suitable organic carrier and utilizing the strong mechanical stirring action of a multifunctional vacuum stirring vessel and a horizontal sand mill, the agglomerated powder particles are dispersed through high-speed shearing and grinding, thereby achieving high dispersibility and suspension stability of the organic suspension.

[0093] 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 equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A process for the preparation of an organic suspension for increasing the coercivity of sintered neodymium-iron-boron magnets, characterized in that The specific steps include the following: S1. Raw material pretreatment and preparation; S101. Selection of heavy rare earth raw materials, selecting dysprosium or terbium, praseodymium or neodymium with a purity ≥99.9%, and one or more metals selected from copper, aluminum, gallium, and cobalt, according to chemical formula RE1. x RE2 y M 100-x-y Weigh the raw materials according to the proportions where 10≤x≤70 and 10≤y≤30, and remove the oxide layer from the surface of the raw materials. S102, Pretreatment of organic auxiliary materials, specifically including: A. Polymer resin: Select polyvinyl acetate or polyvinyl butyral, pulverize to a particle size ≤50μm, and dry in a vacuum drying oven; B. Dispersant: Mix ethanol and acetone at a mass ratio of 2-4:1-1.5 and pre-stir for 5-12 minutes until homogeneous; C. Defoamer: Mix silicone defoamer with a small amount of dispersant and disperse and activate it using ultrasound; S2. Preparation of heavy rare earth powders, as detailed below: S201. Melting and alloying: Pretreated dysprosium or terbium, praseodymium or neodymium, and metallic raw materials are added to a vacuum induction melting furnace, and the furnace is evacuated to 1×10⁻⁶. -3 Pa, argon gas is introduced for protection, the temperature is raised to 1350-1500℃, and the temperature is held for 2-3 hours to completely melt the raw material. After stirring evenly, copper mold is used for rapid cooling and casting to obtain a fast-solidifying casting sheet with a thickness of 0.05-0.2mm. S202, hydrogen decomposition treatment: Place the rapidly solidified casting into the hydrogen decomposition furnace and evacuate to 5×10. -2 After Pa, high-purity hydrogen gas is introduced, and the hydrogen pressure is controlled at 0.2-0.3 MPa. The mixture is kept at room temperature for 2-4 hours to allow the alloy to absorb hydrogen and become embrittled. Then, a vacuum is applied to 1×10⁻⁶ MPa. -2 Pa, heated to 450-600℃ for dehydrogenation, to obtain coarse powder with a particle size of 80-100μm; S203, ultrafine grinding: the coarse powder from hydrogen-crushed powder is fed into an air jet mill, using nitrogen as the grinding medium, to obtain fine powder with a particle size of 1.0-3.0μm; the particle size distribution is detected by a laser particle size analyzer; S204, mixed modification: In an argon-protected powder mixer, first add heavy rare earth fine powder, then add 0.1-0.5% lubricant and 0.01-0.1% antioxidant in proportion to improve powder dispersibility and antioxidant properties; S3. Preparation of organic suspension, as detailed below: S301. Mix in an inert environment. In a glove box protected by nitrogen or argon, weigh the raw materials according to the mass percentage and add them to the mixing container in sequence. S302, graded stirring and dispersion; S303, Viscosity and Stability Control: After stirring, check the viscosity of the suspension. If it deviates from... Adjust by adding dispersant or resin; let the suspension stand for 18-30 hours, and check that the amount of clear liquid in the upper layer is ≤5% to ensure dispersion stability.

2. The production method according to claim 1, characterized by, The percentage of raw material mass in step 301 is: The ingredients include 40-70% heavy rare earth powder, 2-10% polymer resin, 10-50% dispersant, and 1-3% defoamer.

3. The preparation method according to claim 1, characterized in that, Step S302, the staged mixing and dispersion, includes coarse mixing and fine mixing, specifically including: The coarse mixing process specifically involves: The mixed raw materials are transferred to a multi-functional vacuum mixing vessel, vacuumed, and stirred to allow the resin and dispersant to initially blend. Fine stirring specifically involves: The coarsely mixed slurry is transferred to a horizontal sand mill, and the particle size of the agglomerates is monitored by a dynamic light scattering instrument.

4. The application of an organic suspension for improving the coercivity of sintered NdFeB magnets, comprising the method for preparing the organic suspension for improving the coercivity of sintered NdFeB magnets as described in any one of claims 1-3, characterized in that, The specific application process is as follows: (1) Select sintered NdFeB blanks, use ultrasonic cleaning to remove surface oil stains, and then use plasma treatment to improve surface roughness and enhance coating adhesion; (2) A uniform base coating is formed on the surface of the blank by air spraying, and then the coating is scraped and repaired with a precision scraper to control the coating thickness to 50-100μm; for complex shaped magnets, dip coating combined with infrared thermometry is used. (3) Place the coated magnet into a hot air circulating oven and keep it at 120-180℃ for 20-40 minutes to allow the polymer resin to initially cure and prevent the coating from peeling off during subsequent heat treatment; after baking, cool to room temperature and use a thickness gauge to check the coating thickness deviation ≤5μm; (4) Place the magnet into a vacuum sintering furnace and evacuate it to a vacuum level of 5×10⁻⁶. -4 Pa, heating in stages: room temperature → 500-600℃ → 910-950℃; after holding, cooling with the furnace to below 200℃; (5) After diffusion, the magnet is transferred to a tempering furnace, protected by argon gas, heated to 450-550℃, and held for 3-6 hours to eliminate internal stress and stabilize the microstructure of the magnet; secondary tempering is used to further optimize the coercivity stability. (6) Post-processing and performance testing.

5. Use according to claim 4, characterized in that, The post-processing and performance testing are detailed below: After heat treatment, the magnet was ultrasonically cleaned with anhydrous ethanol to remove residual carbides on the surface. After drying, the surface roughness Ra was measured to be ≤0.2μm.

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