Doping preparation method of high-temperature stable rare earth magnet assembly

Abstract

The invention discloses a doping preparation method of a high-temperature stable rare earth magnet assembly, and relates to a magnetic material and a preparation technology thereof. Heavy rare earth elements such as terbium and dysprosium are compositely doped into a neodymium iron boron matrix, and technological parameters such as ball milling, compression molding, sintering and magnetic field oriented annealing are optimized, so that the coercive force and magnetic energy product stability of the magnet under a high-temperature working condition are remarkably improved. The method gives consideration to magnetic performance and cost control, is suitable for high-temperature application scenes such as a welding tool magnetic attraction device, effectively solves the problem that the magnetic performance attenuation of a conventional NdFeB magnet at high temperature is fast, improves the high-temperature reliability of the magnet, and prolongs the service life of the magnet.

Description

Technical Field

[0001] This invention relates to magnetic materials and their preparation techniques, particularly a doping preparation method for a high-temperature stable rare-earth magnet component. Background Technology

[0002] Rare earth permanent magnets are among the most widely used magnetic materials in current industrial and high-tech fields, and their importance stems from their advantages such as high energy product, high coercivity, and excellent magnetic stability. Based on their main composition and performance characteristics, rare earth permanent magnets typically include neodymium iron boron (NdFeB) and samarium cobalt (SCo). Among them, NdFeB permanent magnets, with their highest energy product, are known as the "King of Permanent Magnets" and have become important magnetic materials for electric vehicle drive motors, wind turbines, precision sensors, and various industrial automation equipment.

[0003] The typical matrix phase of neodymium iron boron magnets is Nd2Fe. 14 Neodymium iron boron (NdFeB) magnets have a Curie temperature of approximately 320 °C or higher and exhibit high remanence, high coercivity, and a large energy product. However, NdFeB magnets generally suffer from problems such as a relatively low upper limit of operating temperature and a large absolute value of the coercivity temperature coefficient, which leads to easy decay of magnetic properties in high-temperature environments and insufficient stability in some high-temperature processing scenarios.

[0004] To improve the high-temperature performance of NdFeB magnets, technological research and development mainly focuses on two directions: first, enhancing the temperature stability of the magnet by optimizing the material composition and microstructure; and second, improving the internal magnetic domain structure and grain boundary phases of the magnet through process design and heat treatment, thereby increasing coercivity and high-temperature demagnetization resistance. Existing technologies include various methods to improve high-temperature performance by adding heavy rare earth elements or using grain boundary diffusion processes to adjust the microphase composition of the magnet. For example, patent CN104036945A discloses a method for regenerating NdFeB magnets using rare earth terbium hydride nanoparticle doping, resulting in magnets with higher high-temperature stability.

[0005] Furthermore, regarding improvements in high-temperature stability, patent CN103559971A describes the synthesis of nano-rare-earth permanent magnet materials with high intrinsic coercivity and higher operating temperatures. These materials exhibit lower irreversible flux loss and higher heat resistance under high-temperature conditions.

[0006] On the other hand, existing technologies also involve controlling the temperature coefficients of remanence and coercivity by changing the alloy composition and optimizing the microstructure through alloy heat treatment processes, thereby achieving temperature stability of the magnet. For example, published patent CN118888239B significantly reduces the absolute value of the remanence temperature coefficient of the magnet by optimizing the formula design and heat treatment process, thus improving temperature stability.

[0007] However, the above-mentioned technical solutions still have limitations: some solutions consume a large amount of heavy rare earth elements, resulting in increased costs; while improving high-temperature coercivity, some solutions may sacrifice magnetic energy product or affect the uniformity of the magnet's microstructure. Especially in high-temperature processing equipment such as welding tools, the magnet needs to have good high-temperature stability, while also taking into account cost, material utilization, and processing adaptability.

[0008] Therefore, developing a rare earth permanent magnet preparation process that can effectively improve the stability of high-temperature magnetic properties and adapt to industrial production still has important technological value and industrial significance. Summary of the Invention

[0009] Based on the problems raised in the background technology mentioned above, this invention proposes a doping preparation method for high-temperature stable rare earth magnet components.

[0010] The technical solution is as follows: A method for preparing a high-temperature stable rare-earth magnet assembly by doping includes the following steps: (1) Using neodymium iron boron matrix powder as the main raw material, a mixed powder raw material is prepared according to the mass fraction, wherein the neodymium iron boron matrix powder is 100 parts; (2) Add heavy rare earth doped powder according to the mass fraction, wherein terbium powder is 3 to 7 parts, dysprosium powder is 2 to 6 parts, cobalt powder is 1 to 5 parts, and terbium ball milling dispersant is 0.01 to 0.05 parts; (3) Add grain boundary modifying element powder according to the following mass parts: 0.1-1.0 parts for copper and 0.1-1.0 parts for aluminum; (4) The above components are ball-milled under inert gas protection. 80-120 parts of solvent are added during ball milling. The ball milling time is 6-12 hours. After ball milling, the solvent is removed by drying. (5) Under inert gas protection conditions, the ball milled mixed powder is isostatically pressed into a magnet blank, with a forming pressure of 400-800 MPa; (6) Place the blank into a vacuum or inert gas sintering furnace and perform pre-sintering and main sintering according to the procedure; (7) The sintered body is subjected to magnetic field directional annealing at a temperature of 600-850℃ for 1-4 hours. (8) Control the cooling rate to 5-20℃ / minute to cool to room temperature; (9) The annealed magnet is machined to the required size and magnetized under a magnetizing magnetic field strength of 2.0 to 3.0 T to obtain a high-temperature stable rare earth magnet assembly.

[0011] Preferably, the particle size of the NdFeB matrix powder is controlled to be 2–6 µm.

[0012] Preferably, the inert gas is N2 or Ar.

[0013] Preferably, the method for preparing the terbium-containing ball milling dispersant is as follows: According to the mass fractions, 10-15 parts of terbium isooctanoate, 8-12 parts of epichlorohydrin, and 200-270 parts of anhydrous ethanol were added to a three-necked reactor. Nitrogen gas was introduced to remove oxygen for 20-30 minutes. Then, 0.3-0.8 parts of anhydrous triethylamine were added, and the temperature was raised to 55-65℃ and reacted at a constant temperature for 4-6 hours. Next, 50-70 parts of mercaptoacetic acid ethanolamine and 2-4 parts of anhydrous triethylamine were added, and the temperature was maintained at 55-65℃ for 0.5-2 hours. After the reaction was completed, excess epichlorohydrin and ethanol were removed by vacuum distillation under vacuum conditions of -0.08 to -0.09 MPa and 50-60℃. The mixture was then vacuum dried at 70℃ for 3 hours to obtain a terbium-containing ball milling dispersant.

[0014] Preferably, the weight ratio of the ball milling media to the powder is 3:1 to 6:1.

[0015] Preferably, the inert gas pressure during the sintering process is 0.01 to 0.10 MPa.

[0016] Preferably, the temperature of the pre-sintering stage is 400-500℃ and maintained for 30-60 minutes; the temperature of the main sintering stage is 1030-1100℃ and maintained for 2-6 hours.

[0017] Preferably, the magnetic field strength applied in the magnetic field directional annealing step is 1.2 to 2.5 T.

[0018] The core of this preparation method is a two-step tandem reaction of "etherification grafting-epoxy ring-opening addition," ultimately generating a core-shell complex centered on Tb³⁺. In the first step, the carboxyl group of terbium isooctanoate undergoes an etherification reaction with epichlorohydrin under the action of anhydrous triethylamine, achieving the grafting of epoxypropoxy groups and introducing active sites for subsequent reactions. In the second step, the thiol group of thioglycolic acid ethanolamine initiates a nucleophilic ring-opening addition to the epoxy group, forming a stable covalent bond. Simultaneously, the amino and hydroxyl groups in the molecule form multiple auxiliary coordinations with Tb³⁺, constructing a complex structure that combines coordination stability and steric hindrance. This reaction not only preserves the compatibility of Tb³⁺ with the magnet matrix but also enhances the interaction with magnetic powder through modification of organic segments, laying a structural foundation for optimizing the magnet's microstructure and improving its high-temperature magnetic properties.

[0019] Terbium-containing ball milling dispersants have the following effects: 1) Enhances the stability of the magnet's high-temperature magnetic properties, significantly improves the attenuation trend of magnetic properties with temperature changes, and enhances the magnet's long-term reliable operation capability under high-temperature conditions.

[0020] 2) Optimize the uniformity of the internal microstructure of the magnet, reduce defects such as porosity and agglomeration, strengthen the interfacial bonding between the matrix phase and the doped phase, and achieve synergistic improvement of the core magnetic properties.

[0021] 3) Improve the utilization efficiency of rare earth elements, avoid resource waste, and enhance process adaptability while ensuring the high performance of magnets, without having to make major adjustments to the original production process.

[0022] Compared with the prior art, the present invention has the following advantages: The magnet prepared by this invention exhibits significantly improved high-temperature magnetic stability due to the use of terbium and dysprosium composite doping and optimized sintering process, resulting in a higher Curie temperature, higher coercivity, and a smaller temperature coefficient. Simultaneously, the reasonable control of heavy rare earth element addition effectively reduces material costs and resource consumption, and enhances the reliability and magnetic durability of the magnetic attraction device for welding tools during high-temperature processing. Detailed Implementation

[0023] The features of the present invention are further illustrated below through embodiments, but the scope of protection of this patent is not limited to the embodiments. Example 1

[0024] A method for preparing a high-temperature stable rare-earth magnet assembly by doping includes the following steps: (1) Preparation of main raw materials: Neodymium iron boron matrix powder is selected as the main raw material, with a dosage of 100 kg; the NdFeB matrix powder is tested by a laser particle size analyzer, the powder particle size is controlled within 2 μm, and the powder purity is ≥99.5%, and it is ready for use.

[0025] (2) Addition of heavy rare earth doped powder: Weigh the heavy rare earth doped powder according to the mass ratio, including 3 kg of terbium powder, 2 kg of dysprosium powder and 1 kg of cobalt powder, and add 0.01 kg of terbium-containing ball milling dispersant. Put the above powder into a V-type mixer (model V-50, speed 20 r / min) and premix for 15 minutes to ensure that the initial dispersion is uniform.

[0026] The preparation method of the terbium-containing ball milling dispersant is as follows: 10 kg of terbium isooctanoate, 8 kg of epichlorohydrin, and 200 kg of anhydrous ethanol are weighed and added to a 500 L three-necked reactor. Nitrogen gas is introduced into the reactor at a flow rate of 0.5 m³ / h for 20 minutes to remove oxygen. Then, 0.3 kg of anhydrous triethylamine is added, and the stirrer is turned on (80 r / min). The temperature is raised to 55 °C and reacted for 4 hours. After the reaction, 50 kg of mercaptoacetic acid ethanolamine and 2 kg of anhydrous triethylamine are added to the reactor, and the reaction is maintained at 55 °C for 0.5 hours. After the reaction, the material is transferred to a vacuum distillation column and distilled under vacuum conditions of -0.08 MPa and 50 °C for 2 hours to remove excess epichlorohydrin and ethanol. The distilled material is then placed in a vacuum drying oven and dried under vacuum at 70 °C for 3 hours to obtain the terbium-containing ball milling dispersant, which is collected for later use.

[0027] (3) Addition of grain boundary modifying element powder: Weigh the grain boundary modifying element powder according to the mass ratio, including 0.1 kg of copper powder and 0.1 kg of aluminum powder; add the above powder to the premix in step (2), and continue to mix in the V-type mixer for 20 minutes to obtain mixed powder raw material.

[0028] (4) Ball milling treatment: The mixed powder raw material obtained in step (3) is fed into a planetary ball mill (model QM-3SP4, ball mill jar volume 5L), and hard alloy balls are selected as the ball milling medium. The weight ratio of ball milling medium to powder is 3:1. 80kg of anhydrous ethanol is added into the ball mill jar as a solvent. After sealing the ball mill jar, nitrogen gas is introduced for protection (pressure 0.02MPa). The ball mill speed is set to 300r / min and the ball milling time is 6 hours. After the ball milling is completed, the slurry is sent to a vacuum drying oven and dried at 60℃ and -0.08MPa for 4 hours to completely remove the solvent and obtain a dry mixed powder.

[0029] (5) Isostatic pressing: The dry mixed powder is loaded into a rubber mold and placed into a cold isostatic press (model YLB-630). Isostatic pressing is performed under nitrogen protection (nitrogen pressure 0.01MPa). The molding pressure is set to 400MPa and the holding time is 5 minutes. After molding, a magnet blank is obtained with a blank size of Φ50mm×100mm.

[0030] (6) Sintering treatment: Place the magnet blank into an inert gas protected sintering furnace (model SL-1200), introduce nitrogen into the furnace, and control the inert gas pressure in the furnace to 0.01MPa; carry out pre-sintering and main sintering according to the program: During the pre-sintering stage, the heating rate is 5℃ / min, and the temperature is raised to 400℃ and held for 30 minutes; After the pre-sintering is completed, the temperature is raised to the main sintering temperature of 1030℃ at 8℃ / min and held for 2 hours; During the sintering process, the temperature and pressure in the furnace are monitored in real time to ensure stability.

[0031] (7) Magnetic field directional annealing: The sintered magnet is transferred into a magnetic field annealing furnace (model HTF-1500), and nitrogen gas is introduced into the furnace for protection; a directional magnetic field with a magnetic field strength of 1.2T is applied, and the direction of the magnetic field is consistent with the direction in which the magnet is easily magnetized; the annealing temperature is set to 600℃, the heating rate is 3℃ / min, and the temperature is held for 1 hour after the temperature is reached to complete the magnetic field directional annealing process.

[0032] (8) Cooling treatment: After annealing, control the cooling rate to 5°C / minute so that the magnet is cooled to room temperature with the furnace; maintain a nitrogen atmosphere in the furnace during the cooling process to avoid oxidation of the magnet.

[0033] (9) Machining and magnetization: After cooling, the magnet is taken out and machined using a CNC lathe (model CK6140), and then ground by a surface grinder (model M7130) to obtain a semi-finished magnet of the required size (Φ45mm×95mm); the semi-finished product is placed in a magnetizer (model CM-3T) and magnetized for 30 seconds under a magnetizing magnetic field strength of 2.0T. After magnetization, a high-temperature stable rare earth magnet assembly is obtained. Example 2

[0034] A method for preparing a high-temperature stable rare-earth magnet assembly by doping includes the following steps: (1) Preparation of main raw materials: Neodymium iron boron matrix powder is selected as the main raw material, with a dosage of 100 kg; the NdFeB matrix powder is tested by a laser particle size analyzer, the powder particle size is controlled at 3.5 μm, and the powder purity is ≥99.5%, and it is ready for use.

[0035] (2) Addition of heavy rare earth doped powder: Weigh the heavy rare earth doped powder according to the mass ratio, including 4.5 kg of terbium powder, 3.5 kg of dysprosium powder and 2.5 kg of cobalt powder, and add 0.025 kg of terbium-containing ball milling dispersant. Put the above powder into a V-type mixer (model V-50, speed 25 r / min) and premix for 18 minutes to ensure that the initial dispersion is uniform.

[0036] The preparation method of the terbium-containing ball milling dispersant is as follows: 12 kg of terbium isooctanoate, 10 kg of epichlorohydrin, and 230 kg of anhydrous ethanol are weighed and added to a 500 L three-necked reactor. Nitrogen gas is introduced into the reactor at a flow rate of 0.6 m³ / h for 25 minutes to remove oxygen. Then, 0.5 kg of anhydrous triethylamine is added, and the stirrer is turned on (90 r / min). The temperature is raised to 60 °C and the reaction is maintained for 5 hours. After the reaction, 58 kg of mercaptoacetic acid ethanolamine and 3 kg of anhydrous triethylamine are added to the reactor, and the reaction is maintained at 60 °C for 1 hour. After the reaction, the material is transferred to a vacuum distillation column and distilled under vacuum conditions of -0.085 MPa and 55 °C for 2.5 hours to remove excess epichlorohydrin and ethanol. The distilled material is placed in a vacuum drying oven and dried under vacuum at 70 °C for 3 hours to obtain the terbium-containing ball milling dispersant, which is collected for later use.

[0037] (3) Addition of grain boundary modifying element powder: Weigh the grain boundary modifying element powder according to the mass ratio, including 0.4 kg of copper powder and 0.4 kg of aluminum powder; add the above powder to the premix in step (2), and continue to mix in the V-type mixer for 25 minutes to obtain mixed powder raw material.

[0038] (4) Ball milling: The mixed powder raw material obtained in step (3) is fed into a planetary ball mill (model QM-3SP4, ball mill jar volume 5L), and hard alloy balls are selected as the ball milling medium. The weight ratio of ball milling medium to powder is 4:1. 95kg of anhydrous ethanol is added to the ball mill jar as a solvent. After sealing the ball mill jar, argon gas is introduced for protection (pressure 0.03MPa). The ball mill speed is set to 350r / min and the ball milling time is 8 hours. After the ball milling is completed, the slurry is sent to a vacuum drying oven and dried at 65℃ and -0.085MPa for 4.5 hours to completely remove the solvent and obtain a dry mixed powder.

[0039] (5) Isostatic pressing: The dry mixed powder is loaded into a rubber mold and placed in a cold isostatic press (model YLB-630). Isostatic pressing is performed under argon protection (argon pressure 0.02MPa). The molding pressure is set to 550MPa and the holding time is 6 minutes. After molding, a magnet blank is obtained with a blank size of Φ50mm×100mm.

[0040] (6) Sintering treatment: Place the magnet blank into an inert gas protected sintering furnace (model SL-1200), introduce argon into the furnace, and control the inert gas pressure in the furnace to 0.04MPa; carry out pre-sintering and main sintering according to the program: During the pre-sintering stage, the heating rate is 6℃ / min, and the temperature is raised to 440℃ and held for 40 minutes; After the pre-sintering is completed, the temperature is raised to the main sintering temperature of 1060℃ at 9℃ / min and held for 3.5 hours; The temperature and pressure in the furnace are monitored in real time during the sintering process to ensure stability.

[0041] (7) Magnetic field directional annealing: The sintered magnet is transferred into a magnetic field annealing furnace (model HTF-1500), and argon gas is introduced into the furnace for protection; a directional magnetic field with a magnetic field strength of 1.7T is applied, and the direction of the magnetic field is consistent with the direction in which the magnet is easily magnetized; the annealing temperature is set to 700℃, the heating rate is 4℃ / min, and the temperature is held for 2 hours after the temperature is reached to complete the magnetic field directional annealing treatment.

[0042] (8) Cooling treatment: After annealing, control the cooling rate to 10℃ / minute so that the magnet is cooled to room temperature with the furnace; maintain the argon atmosphere in the furnace during the cooling process to avoid oxidation of the magnet.

[0043] (9) Machining and magnetization: After cooling, the magnet is taken out and machined using a CNC lathe (model CK6140), and then ground by a surface grinder (model M7130) to obtain a semi-finished magnet of the required size (Φ45mm×95mm); the semi-finished product is placed in a magnetizer (model CM-3T) and magnetized for 35 seconds under a magnetizing magnetic field strength of 2.4T. After magnetization, a high-temperature stable rare earth magnet assembly is obtained. Example 3

[0044] A method for preparing a high-temperature stable rare-earth magnet assembly by doping includes the following steps: (1) Preparation of main raw materials: Neodymium iron boron matrix powder is selected as the main raw material, with a dosage of 100 kg; the NdFeB matrix powder is tested by a laser particle size analyzer, and the powder particle size is controlled within 5 μm, and the powder purity is ≥99.5%, and it is ready for use.

[0045] (2) Addition of heavy rare earth doped powder: Weigh the heavy rare earth doped powder according to the mass ratio, including 6 kg of terbium powder, 5 kg of dysprosium powder and 4 kg of cobalt powder, and add 0.04 kg of terbium-containing ball milling dispersant. Put the above powder into a V-type mixer (model V-50, speed 30 r / min) and premix for 22 minutes to ensure that the initial dispersion is uniform.

[0046] The preparation method of the terbium-containing ball milling dispersant is as follows: 14 kg of terbium isooctanoate, 11 kg of epichlorohydrin, and 250 kg of anhydrous ethanol are weighed and added to a 500 L three-necked reactor. Nitrogen gas is introduced into the reactor at a flow rate of 0.7 m³ / h for 28 minutes to remove oxygen. Then, 0.7 kg of anhydrous triethylamine is added, and the stirrer is turned on (95 r / min). The temperature is raised to 63 °C and the reaction is maintained at a constant temperature for 5.5 hours. After the reaction, 65 kg of mercaptoacetic acid ethanolamine and 3.5 kg of anhydrous triethylamine are added to the reactor, and the reaction is maintained at 63 °C for 1.5 hours. After the reaction, the material is transferred to a vacuum distillation column and distilled under vacuum conditions of -0.088 MPa and 58 °C for 3 hours to remove excess epichlorohydrin and ethanol. The distilled material is then placed in a vacuum drying oven and dried under vacuum at 70 °C for 3 hours to obtain the terbium-containing ball milling dispersant, which is collected for later use.

[0047] (3) Addition of grain boundary modifying element powder: Weigh the grain boundary modifying element powder according to the mass ratio, including 0.8 kg of copper powder and 0.8 kg of aluminum powder; add the above powder to the premix in step (2), and continue to mix in the V-type mixer for 30 minutes to obtain mixed powder raw material.

[0048] (4) Ball milling treatment: The mixed powder raw material obtained in step (3) is fed into a planetary ball mill (model QM-3SP4, ball mill jar volume 5L), and hard alloy balls are selected as the ball milling medium. The weight ratio of ball milling medium to powder is 5:1. 110kg of anhydrous ethanol is added to the ball mill jar as a solvent. After sealing the ball mill jar, nitrogen gas is introduced for protection (pressure 0.04MPa). The ball mill speed is set to 400r / min and the ball milling time is 10 hours. After the ball milling is completed, the slurry is sent to a vacuum drying oven and dried at 70℃ and -0.09MPa for 5 hours to completely remove the solvent and obtain a dry mixed powder.

[0049] (5) Isostatic pressing: The dry mixed powder is loaded into a rubber mold and placed into a cold isostatic press (model YLB-630). Isostatic pressing is carried out under nitrogen protection (nitrogen pressure 0.03MPa). The molding pressure is set to 700MPa and the holding time is 7 minutes. After molding, a magnet blank is obtained with a blank size of Φ50mm×100mm.

[0050] (6) Sintering treatment: Place the magnet blank into an inert gas protected sintering furnace (model SL-1200), introduce nitrogen into the furnace, and control the inert gas pressure in the furnace to 0.07MPa; carry out pre-sintering and main sintering according to the program: During the pre-sintering stage, the heating rate is 7℃ / min, and the temperature is raised to 480℃ and held for 50 minutes; After the pre-sintering is completed, the temperature is raised to the main sintering temperature of 1080℃ at 10℃ / min and held for 5 hours; During the sintering process, the temperature and pressure in the furnace are monitored in real time to ensure stability.

[0051] (7) Magnetic field directional annealing: The sintered magnet is transferred into a magnetic field annealing furnace (model HTF-1500), and nitrogen gas is introduced into the furnace for protection; a directional magnetic field with a magnetic field strength of 2.2T is applied, and the direction of the magnetic field is consistent with the direction in which the magnet is easily magnetized; the annealing temperature is set to 800℃, the heating rate is 5℃ / min, and the temperature is held for 3 hours after reaching the set temperature to complete the magnetic field directional annealing treatment.

[0052] (8) Cooling treatment: After annealing, control the cooling rate to 15℃ / minute so that the magnet is cooled to room temperature with the furnace; maintain a nitrogen atmosphere in the furnace during the cooling process to avoid oxidation of the magnet.

[0053] (9) Machining and magnetization: After cooling, the magnet is taken out and machined using a CNC lathe (model CK6140), and then ground by a surface grinder (model M7130) to obtain a semi-finished magnet of the required size (Φ45mm×95mm); the semi-finished product is placed in a magnetizer (model CM-3T) and magnetized for 40 seconds under a magnetizing magnetic field strength of 2.8T. After magnetization, a high-temperature stable rare earth magnet assembly is obtained. Example 4

[0054] A method for preparing a high-temperature stable rare-earth magnet assembly by doping includes the following steps: (1) Preparation of main raw materials: Neodymium iron boron matrix powder is selected as the main raw material, with a dosage of 100 kg; the NdFeB matrix powder is tested by a laser particle size analyzer, and the powder particle size is controlled within 6 μm, and the powder purity is ≥99.5%, and it is ready for use.

[0055] (2) Addition of heavy rare earth doped powder: Weigh the heavy rare earth doped powder according to the mass ratio, including 7 kg of terbium powder, 6 kg of dysprosium powder and 5 kg of cobalt powder, and add 0.05 kg of terbium-containing ball milling dispersant. Put the above powder into a V-type mixer (model V-50, speed 35 r / min) and premix for 25 minutes to ensure that the initial dispersion is uniform.

[0056] The preparation method of the terbium-containing ball milling dispersant is as follows: 15 kg of terbium isooctanoate, 12 kg of epichlorohydrin, and 270 kg of anhydrous ethanol are weighed and added to a 500 L three-necked reactor. Nitrogen gas is introduced into the reactor at a flow rate of 0.8 m³ / h for 30 minutes to remove oxygen. Then, 0.8 kg of anhydrous triethylamine is added, and the stirrer is turned on (100 r / min). The temperature is raised to 65 °C and the reaction is maintained for 6 hours. After the reaction, 70 kg of mercaptoacetic acid ethanolamine and 4 kg of anhydrous triethylamine are added to the reactor, and the reaction is maintained at 65 °C for 2 hours. After the reaction, the material is transferred to a vacuum distillation column and distilled under vacuum at -0.09 MPa and 60 °C for 3.5 hours to remove excess epichlorohydrin and ethanol. The distilled material is placed in a vacuum drying oven and dried under vacuum at 70 °C for 3 hours to obtain the terbium-containing ball milling dispersant, which is collected for later use.

[0057] (3) Addition of grain boundary modifying element powder: Weigh the grain boundary modifying element powder according to the mass ratio, including 1.0 kg of copper powder and 1.0 kg of aluminum powder; add the above powder to the premix in step (2), and continue to mix in the V-type mixer for 35 minutes to obtain mixed powder raw material.

[0058] (4) Ball milling: The mixed powder raw material obtained in step (3) is fed into a planetary ball mill (model QM-3SP4, ball mill jar volume 5L), and hard alloy balls are selected as the ball milling medium. The weight ratio of ball milling medium to powder is 6:1. 120kg of anhydrous ethanol is added to the ball mill jar as a solvent. After sealing the ball mill jar, argon gas is introduced for protection (pressure 0.05MPa). The ball mill speed is set to 450r / min and the ball milling time is 12 hours. After the ball milling is completed, the slurry is sent to a vacuum drying oven and dried at 75℃ and -0.095MPa for 6 hours to completely remove the solvent and obtain a dry mixed powder.

[0059] (5) Isostatic pressing: The dry mixed powder is loaded into a rubber mold and placed into a cold isostatic press (model YLB-630). Isostatic pressing is performed under argon protection (argon pressure 0.04MPa). The molding pressure is set to 800MPa and the holding time is 8 minutes. After molding, a magnet blank is obtained with a blank size of Φ50mm×100mm.

[0060] (6) Sintering treatment: Place the magnet blank into an inert gas protected sintering furnace (model SL-1200), introduce argon into the furnace, and control the inert gas pressure in the furnace to 0.10MPa; carry out pre-sintering and main sintering according to the program: During the pre-sintering stage, the heating rate is 8℃ / min, the temperature is raised to 500℃, and held for 60 minutes; After the pre-sintering is completed, the temperature is raised to the main sintering temperature of 1100℃ at 11℃ / min and held for 6 hours; During the sintering process, the temperature and pressure in the furnace are monitored in real time to ensure stability.

[0061] (7) Magnetic field directional annealing: The sintered magnet is transferred into a magnetic field annealing furnace (model HTF-1500), and argon gas is introduced into the furnace for protection; a directional magnetic field with a magnetic field strength of 2.5T is applied, and the direction of the magnetic field is consistent with the direction in which the magnet is easily magnetized; the annealing temperature is set to 850℃, the heating rate is 6℃ / min, and the temperature is held for 4 hours after the temperature is reached to complete the magnetic field directional annealing treatment.

[0062] (8) Cooling treatment: After annealing, control the cooling rate to 20℃ / minute so that the magnet is cooled to room temperature with the furnace; maintain the argon atmosphere in the furnace during the cooling process to avoid oxidation of the magnet.

[0063] (9) Machining and magnetization: After cooling, the magnet is taken out and machined using a CNC lathe (model CK6140), and then ground by a surface grinder (model M7130) to obtain a semi-finished magnet of the required size (Φ45mm×95mm); the semi-finished product is placed in a magnetizer (model CM-3T) and magnetized for 45 seconds under a magnetizing magnetic field strength of 3.0T. After magnetization, a high-temperature stable rare earth magnet assembly is obtained.

[0064] Comparative Example 1 A method for preparing a high-temperature stable rare-earth magnet assembly by doping includes the following steps: (1) Preparation of main raw materials: Neodymium iron boron matrix powder is selected as the main raw material, with a dosage of 100 kg; the NdFeB matrix powder is tested by a laser particle size analyzer, the powder particle size is controlled within 2 μm, and the powder purity is ≥99.5%, and it is ready for use.

[0065] (2) Addition of heavy rare earth doped powder: Weigh the heavy rare earth doped powder according to the mass ratio, including 3 kg of terbium powder, 2 kg of dysprosium powder and 1 kg of cobalt powder; put the above powder into a V-type mixer (model V-50, speed 20 r / min) and premix for 15 minutes to ensure that the initial dispersion is uniform.

[0066] (3) Addition of grain boundary modifying element powder: Weigh the grain boundary modifying element powder according to the mass ratio, including 0.1 kg of copper powder and 0.1 kg of aluminum powder; add the above powder to the premix in step (2), and continue to mix in the V-type mixer for 20 minutes to obtain mixed powder raw material.

[0067] (4) Ball milling treatment: The mixed powder raw material obtained in step (3) is fed into a planetary ball mill (model QM-3SP4, ball mill jar volume 5L), and hard alloy balls are selected as the ball milling medium. The weight ratio of ball milling medium to powder is 3:1. 80kg of anhydrous ethanol is added into the ball mill jar as a solvent. After sealing the ball mill jar, nitrogen gas is introduced for protection (pressure 0.02MPa). The ball mill speed is set to 300r / min and the ball milling time is 6 hours. After the ball milling is completed, the slurry is sent to a vacuum drying oven and dried at 60℃ and -0.08MPa for 4 hours to completely remove the solvent and obtain a dry mixed powder.

[0068] (5) Isostatic pressing: The dry mixed powder is loaded into a rubber mold and placed into a cold isostatic press (model YLB-630). Isostatic pressing is performed under nitrogen protection (nitrogen pressure 0.01MPa). The molding pressure is set to 400MPa and the holding time is 5 minutes. After molding, a magnet blank is obtained with a blank size of Φ50mm×100mm.

[0069] (6) Sintering treatment: Place the magnet blank into an inert gas protected sintering furnace (model SL-1200), introduce nitrogen into the furnace, and control the inert gas pressure in the furnace to 0.01MPa; carry out pre-sintering and main sintering according to the program: During the pre-sintering stage, the heating rate is 5℃ / min, and the temperature is raised to 400℃ and held for 30 minutes; After the pre-sintering is completed, the temperature is raised to the main sintering temperature of 1030℃ at 8℃ / min and held for 2 hours; During the sintering process, the temperature and pressure in the furnace are monitored in real time to ensure stability.

[0070] (7) Magnetic field directional annealing: The sintered magnet is transferred into a magnetic field annealing furnace (model HTF-1500), and nitrogen gas is introduced into the furnace for protection; a directional magnetic field with a magnetic field strength of 1.2T is applied, and the direction of the magnetic field is consistent with the direction in which the magnet is easily magnetized; the annealing temperature is set to 600℃, the heating rate is 3℃ / min, and the temperature is held for 1 hour after the temperature is reached to complete the magnetic field directional annealing process.

[0071] (8) Cooling treatment: After annealing, control the cooling rate to 5°C / minute so that the magnet is cooled to room temperature with the furnace; maintain a nitrogen atmosphere in the furnace during the cooling process to avoid oxidation of the magnet.

[0072] (9) Machining and magnetization: After cooling, the magnet is taken out and machined using a CNC lathe (model CK6140), and then ground by a surface grinder (model M7130) to obtain a semi-finished magnet of the required size (Φ45mm×95mm); the semi-finished product is placed in a magnetizer (model CM-3T) and magnetized for 30 seconds under a magnetizing magnetic field strength of 2.0T. After magnetization, a high-temperature stable rare earth magnet assembly is obtained.

[0073] Comparative Example 2 A method for preparing a high-temperature stable rare-earth magnet assembly by doping includes the following steps: (1) Preparation of main raw materials: Neodymium iron boron matrix powder is selected as the main raw material, with a dosage of 100 kg; the NdFeB matrix powder is tested by a laser particle size analyzer, the powder particle size is controlled within 2 μm, and the powder purity is ≥99.5%, and it is ready for use.

[0074] (2) Addition of heavy rare earth doped powder: Weigh the heavy rare earth doped powder according to the mass ratio, including 3 kg of terbium powder, 2 kg of dysprosium powder and 1 kg of cobalt powder, and add 0.01 kg of terbium-containing ball milling dispersant. Put the above powder into a V-type mixer (model V-50, speed 20 r / min) and premix for 15 minutes to ensure that the initial dispersion is uniform.

[0075] The preparation method of the terbium-containing ball milling dispersant is as follows: 10 kg of terbium isooctanoate, 8 kg of epichlorohydrin, and 200 kg of anhydrous ethanol are weighed and added to a 500 L three-necked reactor; nitrogen gas is introduced into the reactor at a flow rate of 0.5 m³ / h for 20 minutes to remove oxygen; then 0.3 kg of anhydrous triethylamine is added, the stirrer is turned on (80 r / min), and the temperature is raised to 55 °C and reacted for 4 hours; after the reaction, 2 kg of anhydrous triethylamine is added to the reactor, and the temperature is maintained at 55 °C for 0.5 hours; after the reaction, the material is transferred to a vacuum distillation column and distilled under vacuum conditions of -0.08 MPa and 50 °C for 2 hours to remove excess epichlorohydrin and ethanol; the distilled material is placed in a vacuum drying oven and dried under vacuum at 70 °C for 3 hours to obtain the terbium-containing ball milling dispersant, which is collected for later use.

[0076] (3) Addition of grain boundary modifying element powder: Weigh the grain boundary modifying element powder according to the mass ratio, including 0.1 kg of copper powder and 0.1 kg of aluminum powder; add the above powder to the premix in step (2), and continue to mix in the V-type mixer for 20 minutes to obtain mixed powder raw material.

[0077] (4) Ball milling treatment: The mixed powder raw material obtained in step (3) is fed into a planetary ball mill (model QM-3SP4, ball mill jar volume 5L), and hard alloy balls are selected as the ball milling medium. The weight ratio of ball milling medium to powder is 3:1. 80kg of anhydrous ethanol is added into the ball mill jar as a solvent. After sealing the ball mill jar, nitrogen gas is introduced for protection (pressure 0.02MPa). The ball mill speed is set to 300r / min and the ball milling time is 6 hours. After the ball milling is completed, the slurry is sent to a vacuum drying oven and dried at 60℃ and -0.08MPa for 4 hours to completely remove the solvent and obtain a dry mixed powder.

[0078] (5) Isostatic pressing: The dry mixed powder is loaded into a rubber mold and placed into a cold isostatic press (model YLB-630). Isostatic pressing is performed under nitrogen protection (nitrogen pressure 0.01MPa). The molding pressure is set to 400MPa and the holding time is 5 minutes. After molding, a magnet blank is obtained with a blank size of Φ50mm×100mm.

[0079] (6) Sintering treatment: Place the magnet blank into an inert gas protected sintering furnace (model SL-1200), introduce nitrogen into the furnace, and control the inert gas pressure in the furnace to 0.01MPa; carry out pre-sintering and main sintering according to the program: During the pre-sintering stage, the heating rate is 5℃ / min, and the temperature is raised to 400℃ and held for 30 minutes; After the pre-sintering is completed, the temperature is raised to the main sintering temperature of 1030℃ at 8℃ / min and held for 2 hours; During the sintering process, the temperature and pressure in the furnace are monitored in real time to ensure stability.

[0080] (7) Magnetic field directional annealing: The sintered magnet is transferred into a magnetic field annealing furnace (model HTF-1500), and nitrogen gas is introduced into the furnace for protection; a directional magnetic field with a magnetic field strength of 1.2T is applied, and the direction of the magnetic field is consistent with the direction in which the magnet is easily magnetized; the annealing temperature is set to 600℃, the heating rate is 3℃ / min, and the temperature is held for 1 hour after the temperature is reached to complete the magnetic field directional annealing process.

[0081] (8) Cooling treatment: After annealing, control the cooling rate to 5°C / minute so that the magnet is cooled to room temperature with the furnace; maintain a nitrogen atmosphere in the furnace during the cooling process to avoid oxidation of the magnet.

[0082] (9) Machining and magnetization: After cooling, the magnet is taken out and machined using a CNC lathe (model CK6140), and then ground by a surface grinder (model M7130) to obtain a semi-finished magnet of the required size (Φ45mm×95mm); the semi-finished product is placed in a magnetizer (model CM-3T) and magnetized for 30 seconds under a magnetizing magnetic field strength of 2.0T. After magnetization, a high-temperature stable rare earth magnet assembly is obtained.

[0083] Comparative Example 3 A method for preparing a high-temperature stable rare-earth magnet assembly by doping includes the following steps: (1) Preparation of main raw materials: Neodymium iron boron matrix powder is selected as the main raw material, with a dosage of 100 kg; the NdFeB matrix powder is tested by a laser particle size analyzer, the powder particle size is controlled within 2 μm, and the powder purity is ≥99.5%, and it is ready for use.

[0084] (2) Addition of heavy rare earth doped powder: Weigh the heavy rare earth doped powder according to the mass ratio, including 3 kg of terbium powder, 2 kg of dysprosium powder and 1 kg of cobalt powder, and add 0.01 kg of terbium-containing ball milling dispersant. Put the above powder into a V-type mixer (model V-50, speed 20 r / min) and premix for 15 minutes to ensure that the initial dispersion is uniform.

[0085] The preparation method of the terbium-containing ball milling dispersant is as follows: 10 kg of terbium isooctanoate and 200 kg of anhydrous ethanol are weighed and added to a 500 L three-necked reactor; nitrogen gas is introduced into the reactor at a flow rate of 0.5 m³ / h for 20 minutes to remove oxygen; then 0.3 kg of anhydrous triethylamine is added, the stirrer is turned on (80 r / min), and the temperature is raised to 55 °C and reacted for 4 hours; after the reaction, 50 kg of mercaptoacetic acid ethanolamine and 2 kg of anhydrous triethylamine are added to the reactor, and the reaction is maintained at 55 °C for 0.5 hours; after the reaction, the material is transferred to a vacuum distillation column and distilled under vacuum at -0.08 MPa and 50 °C for 2 hours to remove excess epichlorohydrin and ethanol; the distilled material is placed in a vacuum drying oven and dried under vacuum at 70 °C for 3 hours to obtain the terbium-containing ball milling dispersant, which is collected for later use.

[0086] (3) Addition of grain boundary modifying element powder: Weigh the grain boundary modifying element powder according to the mass ratio, including 0.1 kg of copper powder and 0.1 kg of aluminum powder; add the above powder to the premix in step (2), and continue to mix in the V-type mixer for 20 minutes to obtain mixed powder raw material.

[0087] (4) Ball milling treatment: The mixed powder raw material obtained in step (3) is fed into a planetary ball mill (model QM-3SP4, ball mill jar volume 5L), and hard alloy balls are selected as the ball milling medium. The weight ratio of ball milling medium to powder is 3:1. 80kg of anhydrous ethanol is added into the ball mill jar as a solvent. After sealing the ball mill jar, nitrogen gas is introduced for protection (pressure 0.02MPa). The ball mill speed is set to 300r / min and the ball milling time is 6 hours. After the ball milling is completed, the slurry is sent to a vacuum drying oven and dried at 60℃ and -0.08MPa for 4 hours to completely remove the solvent and obtain a dry mixed powder.

[0088] (5) Isostatic pressing: The dry mixed powder is loaded into a rubber mold and placed into a cold isostatic press (model YLB-630). Isostatic pressing is performed under nitrogen protection (nitrogen pressure 0.01MPa). The molding pressure is set to 400MPa and the holding time is 5 minutes. After molding, a magnet blank is obtained with a blank size of Φ50mm×100mm.

[0089] (6) Sintering treatment: Place the magnet blank into an inert gas protected sintering furnace (model SL-1200), introduce nitrogen into the furnace, and control the inert gas pressure in the furnace to 0.01MPa; carry out pre-sintering and main sintering according to the program: During the pre-sintering stage, the heating rate is 5℃ / min, and the temperature is raised to 400℃ and held for 30 minutes; After the pre-sintering is completed, the temperature is raised to the main sintering temperature of 1030℃ at 8℃ / min and held for 2 hours; During the sintering process, the temperature and pressure in the furnace are monitored in real time to ensure stability.

[0090] (7) Magnetic field directional annealing: The sintered magnet is transferred into a magnetic field annealing furnace (model HTF-1500), and nitrogen gas is introduced into the furnace for protection; a directional magnetic field with a magnetic field strength of 1.2T is applied, and the direction of the magnetic field is consistent with the direction in which the magnet is easily magnetized; the annealing temperature is set to 600℃, the heating rate is 3℃ / min, and the temperature is held for 1 hour after the temperature is reached to complete the magnetic field directional annealing process.

[0091] (8) Cooling treatment: After annealing, control the cooling rate to 5°C / minute so that the magnet is cooled to room temperature with the furnace; maintain a nitrogen atmosphere in the furnace during the cooling process to avoid oxidation of the magnet.

[0092] (9) Machining and magnetization: After cooling, the magnet is taken out and machined using a CNC lathe (model CK6140), and then ground by a surface grinder (model M7130) to obtain a semi-finished magnet of the required size (Φ45mm×95mm); the semi-finished product is placed in a magnetizer (model CM-3T) and magnetized for 30 seconds under a magnetizing magnetic field strength of 2.0T. After magnetization, a high-temperature stable rare earth magnet assembly is obtained.

[0093] Test method: 1. Remanence and intrinsic coercivity test Hysteresis loops are tested using a vibrating sample magnetometer or the pulsed magnetic field method.

[0094] 2. Calculation of maximum magnetic energy product It was calculated from the hysteresis loop and measured under different temperature conditions.

[0095] 4. Determination of Curie temperature (Tc) The demagnetization critical point is determined using methods such as differential scanning calorimetry (DSC) and high-temperature magnetic property testing. Test results: Table 1 Remanence (Br) Test Results

[0096] Table 2. Results of Intrinsic Coercivity (Hcj) Test

[0097] Table 3. Test results of maximum magnetic energy product (BH_max)

[0098] Table 4 Curie temperature test results

[0099] The performance of various magnetic properties in the data table fully demonstrates the key role and significant effect of the prepared ball milling aid. The terbium-containing complex structure in the aid plays a dual role of "milling aid and dispersion + rare earth doping enhancement": during the ball milling stage, the steric hindrance effect of the aid effectively inhibits the agglomeration of magnetic powder, promotes the uniform mixing of NdFeB matrix powder with doping elements such as terbium and dysprosium, as well as grain boundary modifying elements, and reduces performance shortcomings caused by uneven mixing; during the sintering process, Tb³⁺ in the aid is uniformly incorporated into Nd₂Fe through targeted diffusion. 14 In the B matrix phase, the stable structure formed by epoxy and mercapto groups optimizes the grain boundary microstructure and enhances the internal bonding force of the magnet. Ultimately, these effects collectively translate into a comprehensive improvement in the remanence, intrinsic coercivity, and maximum energy product of the magnet under different temperature conditions. Simultaneously, it contributes to Curie temperature optimization, effectively alleviating the problem of rapid magnetic performance decay in conventional NdFeB magnets at high temperatures, highlighting the enhancing effect of additives on the high-temperature stability of the magnet.

[0100] Although the present invention has been described in detail above with general descriptions, specific embodiments, and experiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a high-temperature stable rare-earth magnet assembly by doping, characterized in that, Includes the following steps: (1) Using neodymium iron boron matrix powder as the main raw material, a mixed powder raw material is prepared according to the mass fraction, wherein the neodymium iron boron matrix powder is 100 parts; (2) Add heavy rare earth doped powder according to the mass fraction, wherein terbium powder is 3 to 7 parts, dysprosium powder is 2 to 6 parts, cobalt powder is 1 to 5 parts, and terbium ball milling dispersant is 0.01 to 0.05 parts; (3) Add grain boundary modifying element powder according to the following mass parts: 0.1-1.0 parts for copper and 0.1-1.0 parts for aluminum; (4) The above components are ball-milled under inert gas protection. 80-120 parts of solvent are added during ball milling. The ball milling time is 6-12 hours. After ball milling, the solvent is removed by drying. (5) Under inert gas protection conditions, the ball milled mixed powder is isostatically pressed into a magnet blank, with a forming pressure of 400-800 MPa; (6) Place the blank into a vacuum or inert gas sintering furnace and perform pre-sintering and main sintering according to the procedure; (7) The sintered body is subjected to magnetic field directional annealing at a temperature of 600-850℃ for 1-4 hours. (8) Control the cooling rate to 5-20℃ / minute to cool to room temperature; (9) The annealed magnet is machined to the required size and magnetized under a magnetizing magnetic field strength of 2.0 to 3.0 T to obtain a high-temperature stable rare earth magnet assembly; The terbium-containing ball milling dispersion aid is prepared by reacting terbium isooctanoate, epichlorohydrin, anhydrous triethylamine, and mercaptoacetic acid ethanolamine.

2. The doping preparation method of a high-temperature stable rare-earth magnet assembly according to claim 1, characterized in that: The particle size of the neodymium iron boron matrix powder is controlled to be 2–6 µm.

3. The doping preparation method of a high-temperature stable rare-earth magnet assembly according to claim 1, characterized in that: The inert gas is N2 or Ar.

4. The doping preparation method of a high-temperature stable rare-earth magnet assembly according to claim 1, characterized in that: The preparation method of the terbium-containing ball milling dispersant: According to the mass fractions, 10-15 parts of terbium isooctanoate, 8-12 parts of epichlorohydrin, and 200-270 parts of anhydrous ethanol were added to a three-necked reactor. Nitrogen gas was introduced to remove oxygen for 20-30 minutes. Then, 0.3-0.8 parts of anhydrous triethylamine were added, and the temperature was raised to 55-65℃ and reacted at a constant temperature for 4-6 hours. Next, 50-70 parts of mercaptoacetic acid ethanolamine and 2-4 parts of anhydrous triethylamine were added, and the temperature was maintained at 55-65℃ for 0.5-2 hours. After the reaction was completed, excess epichlorohydrin and ethanol were removed by vacuum distillation under vacuum conditions of -0.08 to -0.09 MPa and 50-60℃. The mixture was then vacuum dried at 70℃ for 3 hours to obtain a terbium-containing ball milling dispersant.

5. The doping preparation method of a high-temperature stable rare-earth magnet assembly according to claim 1, characterized in that: The weight ratio of the ball milling media to the powder is 3:1 to 6:

1.

6. The doping preparation method of a high-temperature stable rare-earth magnet component according to claim 1, characterized in that: The inert gas pressure during the sintering process is 0.01 to 0.10 MPa.

7. The doping preparation method of a high-temperature stable rare-earth magnet assembly according to claim 1, characterized in that: The pre-sintering temperature is 400-500℃ and maintained for 30-60 minutes; the main sintering temperature is 1030-1100℃ and maintained for 2-6 hours.

8. The doping preparation method of a high-temperature stable rare-earth magnet assembly according to claim 1, characterized in that: The magnetic field strength applied in the magnetic field directional annealing process is 1.2 to 2.5 T.

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