High-temperature-resistant neodymium-iron-boron magnet and preparation method thereof

Abstract

The invention relates to the technical field of magnet materials, and discloses a high-temperature-resistant neodymium-iron-boron magnet and a preparation method of the high-temperature-resistant neodymium-iron-boron magnet. The high-temperature-resistant neodymium-iron-boron magnet comprises the following components in parts by weight: 25-30 parts of neodymium, 60-65 parts of iron, 1.0-2.0 parts of boron, 3.0-5.0 parts of lanthanum, 0.5-2.0 parts of zirconium, 0.5-1.0 part of molybdenum and 0.1-0.5 part of nano ceramic particles, and the invention further provides a preparation method of the high-temperature-resistant neodymium-iron-boron magnet. S1, preparing and mixing alloy raw materials; s2, nano ceramic coating treatment is carried out; s3, magnetic field assisted pressing forming; and S4, rapid induction sintering. Through the magnetic field assisted directional pressing process, effective control over grain orientation in the pressing forming stage is achieved, magnetic domain arrangement is more ordered, and the residual magnetism and the energy product are improved. Different from a forming mode with disordered grain directions and poor magnetic anisotropy in an existing common cold pressing process, the technical defect that the utilization rate of magnetic performance is low due to poor orientation is overcome.

Description

Technical Field

[0001] The present invention relates to the technical field of magnet materials, and particularly to a high-temperature resistant neodymium iron boron magnet and a preparation method thereof. Background Art

[0002] Due to its excellent magnetic properties, neodymium iron boron permanent magnet materials are widely used in the fields of new energy vehicles, wind power generation, aerospace, etc. However, such magnets are prone to magnetic property degradation in high-temperature environments, seriously restricting their engineering promotion in high-temperature scenarios. Therefore, improving the heat resistance and structural stability of neodymium iron boron magnets has always been an important research direction in the field of magnetic materials.

[0003] Existing technical solutions for improving the thermal stability of magnets mainly include: improving the magnetocrystalline anisotropy field by adding heavy rare earth elements (such as Dy, Tb); optimizing the grain structure and sintering process to inhibit high-temperature demagnetization; and coating the surface of the magnet, etc. Although these measures have improved the high-temperature performance to a certain extent, there are still many deficiencies.

[0004] Firstly, although the method of adding heavy rare earth elements can increase the coercivity, it also leads to a significant decrease in the magnetic energy product. Moreover, the rare earth resources are limited and the cost is high, restricting the feasibility of large-scale applications. Secondly, in the conventional powder sintering process, grain growth is serious and the structure is significantly coarsened, resulting in unstable magnetic domains of the magnet at high temperatures and poor performance consistency. In addition, the existing cold pressing forming processes mostly do not introduce orientation control, resulting in poor anisotropy and low remanence of the formed body, and low magnetic property development efficiency.

[0005] In addition, the currently widely used electric furnace long-time sintering process has low thermal efficiency, long sintering time, easy grain coarsening, uneven tissue distribution, which has an adverse effect on the consistency and batch stability of magnetic properties. At the same time, the lack of an effective annealing step after sintering will also cause the accumulation of residual stress inside the magnet, leading to the formation of microcracks, thereby affecting the service life and structural integrity of the magnet. Summary of the Invention

[0006] Aiming at the deficiencies of the existing technology, the present invention provides a high-temperature resistant neodymium iron boron magnet and a preparation method thereof, which solve the problems of fast magnetic property attenuation, poor structural stability of existing neodymium iron boron magnets under high-temperature conditions, and insufficient tissue control in the preparation process.

[0007] To achieve the above objectives, the present invention is realized through the following technical solutions: A high-temperature resistant neodymium iron boron magnet, by weight, comprises the following components; 25-30 parts of neodymium, 60-65 parts of iron, 1.0-2.0 parts of boron, 3.0-5.0 parts of lanthanum, 0.5-2.0 parts of zirconium, 0.5-1.0 parts of molybdenum, and 0.1-0.5 parts of nano ceramic particles.

[0008] Preferably, the nano ceramic particles are yttrium oxide.

[0009] A preparation method of a high-temperature resistant neodymium iron boron magnet, comprising the following steps; S1. Preparation and mixing of alloy raw materials: Weigh powders of neodymium, iron, boron, lanthanum, zirconium and molybdenum according to the mass ratio, and carry out ball milling and mixing in an inert atmosphere to obtain a pre-alloyed mixed powder; S2. Nano-ceramic coating treatment: Add the mixed powder into an alcohol dispersion liquid containing yttrium oxide for ultrasonic treatment and adsorption; S3. Magnetic field-assisted pressing and forming: After drying and heat treatment of the mixed powder after coating treatment, a coated magnetic powder is obtained, and the coated magnetic powder is subjected to magnetic field-assisted pressing and forming; S4. Rapid induction sintering: Carry out rapid induction sintering on the formed green body; S5. Low-temperature annealing treatment: Carry out annealing treatment at 500 - 600 °C; S6. Surface protection treatment: Apply a fluorocarbon resin surface coating to the surface of the magnet, and the coating thickness is 2 - 10 μm.

[0010] Preferably, the ball milling treatment in step S1 is carried out in an argon protection atmosphere, and the ball milling time is 12 - 24 hours.

[0011] Furthermore, ball milling not only realizes the uniform mixing of components, but also promotes preliminary mechanical alloying, providing good precursor conditions for subsequent structure control. The inert atmosphere can effectively avoid the oxidation of the powder during ball milling, and improve the activity and purity of the components.

[0012] Preferably, the alcohol dispersion liquid in step S2 is ethanol or isopropanol, and the particle size of the nano yttrium oxide particles is 10 - 50 nm.

[0013] Furthermore, the yttrium oxide particles form a good dispersion state in the alcohol medium, and are adsorbed on the powder surface with the assistance of ultrasonic waves, forming a dense and uniform ceramic coating layer during subsequent heat treatment. This layer can effectively block the diffusion and reaction of oxygen at the grain boundaries during sintering and high-temperature applications, significantly improving the oxidation resistance and high-temperature stability of the magnet.

[0014] Preferably, the heat treatment temperature in step S3 is 150 - 250 °C, and the time is 0.5 - 1 hour.

[0015] Preferably, the pressure applied during pressing and forming in step S3 is 100 - 200 MPa, and the directional forming is carried out in a magnetic field of 0.5 - 2.0 T.

[0016] Furthermore, magnetic field pressing causes the magnetic powder to be oriented and arranged along a specific direction under the guidance of an external magnetic field, so that the final sintered body has good grain consistency and anisotropy, improving the remanence value and magnetic energy product. At the same time, the high density formed during the pressing process provides a structural basis for subsequent sintering.

[0017] Preferably, in the rapid induction sintering in step S4, the temperature is 850 - 950 °C, the heat preservation time is 5 - 10 minutes, and the sintering pressure is 30 - 60 MPa.

[0018] Furthermore, compared with traditional electric furnace sintering, rapid induction sintering can complete the densification process in an extremely short time, inhibit abnormal grain growth, maintain refined microstructure, and improve the uniformity and repeatability of the magnet. At the same time, pressure-assisted sintering improves the density and reduces the porosity, which helps to enhance the overall magnetic response.

[0019] Preferably, in the low-temperature annealing treatment step in step S5, the annealing temperature is 500 - 600 °C, the annealing time is 1 - 2 hours, and the annealing atmosphere is argon.

[0020] Furthermore, the annealing process can effectively release the internal residual stress of the material, readjust the grain boundary microstructure and magnetic domain distribution, reduce the probability of microcrack generation, and significantly enhance the mechanical stability and service reliability of the magnet, especially suitable for long-term high-temperature operation scenarios.

[0021] Preferably, in the surface protection treatment step in step S6, a fluorocarbon resin spraying or electroless nickel plating process is used, the coating thickness is 2 - 10 μm, and the curing temperature is 80 - 120 °C.

[0022] Furthermore, fluorocarbon resin has excellent corrosion resistance and thermal stability, which can effectively isolate oxygen and moisture in the air; while the nickel plating layer can form a highly dense metal protective film, improving the surface chemical corrosion resistance and preventing the performance degradation of the magnet during service.

[0023] The present invention provides a high-temperature resistant neodymium iron boron magnet and its preparation method. It has the following beneficial effects: 1. By adopting the nano-yttrium oxide ceramic particle coating technology, the present invention constructs an interfacial barrier layer on the surface of the magnetic powder, effectively restricting oxygen diffusion and grain boundary reaction at high temperatures, thereby improving the thermal stability and magnetic retention rate of the magnet. Compared with the neodymium iron boron system in the prior art without interfacial coating and prone to oxidation and debonding, it solves the problems of fast high-temperature demagnetization and serious performance attenuation.

[0024] 2. Through the magnetic field-assisted directional pressing process, the present invention realizes the effective control of grain orientation during the pressing and forming stage, makes the magnetic domain arrangement more orderly, and improves the remanence and energy product. Different from the forming method with disordered grain directions and poor magnetic anisotropy in the existing ordinary cold pressing process, it solves the technical shortcoming of low utilization rate of magnetic properties caused by poor orientation.

[0025] 3. By adopting a rapid induction sintering path, the present invention shortens the sintering time, suppresses the tendency of grain growth, constructs a refined and uniform microstructure system, and improves the consistency and repeatability of magnetic properties. Compared with the technical means of coarse grains and discrete tissue distribution under the traditional long-time heat preservation electric furnace sintering process, it effectively overcomes the problems of large performance fluctuations between batches and uncontrollable structure.

[0026] 4. Through the low-temperature annealing treatment link, the present invention releases residual stress after sintering, reorganizes the magnetic domain structure, and enhances the mechanical stability and service life of the magnet. Compared with the technical solutions in the existing process that omit the annealing treatment and it is difficult to relieve the internal stress residue, it solves the problems of easy generation of microcracks and high risk of degradation during long-term use. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a flowchart of the method of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0029] Please refer to the attached Figure 1 ; Example 1: Medium-temperature optimized magnet preparation process Raw material ratio (parts by mass): 27 parts of neodymium, 62 parts of iron, 1.5 parts of boron, 4.0 parts of lanthanum, 1.0 part of zirconium, 0.8 part of molybdenum, 0.3 part of yttrium oxide nanoparticles.

[0030] Ball milling and mixing (S1): Carry out ball milling treatment under an argon atmosphere. The ball milling time is 16 hours, and the ball-to-material ratio is 12:1.

[0031] Nanoceramic coating (S2): Put the mixed powder into an ethanol dispersion liquid (solid-liquid ratio of 1:5), and perform ultrasonic treatment for 30 minutes. The particle size of the used yttrium oxide is 20 nm.

[0032] Heat treatment and pressing (S3): Drying conditions: 80 °C, hot air drying for 2 hours; Heat treatment conditions: 200 °C, 1 hour; Pressing pressure: 150 MPa; Magnetic field strength: 1.2 T, maintained for 3 minutes.

[0033] Rapid induction sintering (S4): Temperature: 900 °C, holding for 8 minutes, applied pressure is 45 MPa.

[0034] Low-temperature annealing treatment (S5): Annealing temperature: 550 °C, time: 1 hour, atmosphere: argon.

[0035] Surface protection treatment (S6): Spray fluorocarbon resin coating, thickness: 5 μm, curing temperature: 100 °C, curing time: 30 minutes.

[0036] Example 2: Process for high-neodymium and low-lanthanum strengthened magnet Raw material ratio: Neodymium 30 parts, iron 60 parts, boron 2.0 parts, lanthanum 3.0 parts, zirconium 2.0 parts, molybdenum 1.0 part, yttrium oxide 0.2 part.

[0037] Ball milling and mixing: Ball milling for 20 hours under argon protection, ball-to-material ratio 15:1.

[0038] Nanocoating treatment: Using isopropanol as the dispersion medium, yttrium oxide particle size is 15 nm, ultrasonic time 45 minutes.

[0039] Heat treatment and pressing forming: Drying: 70 °C, 2 hours; Heat treatment: 180 °C, 0.5 hour; Pressure: 180 MPa, magnetic field: 1.5 T.

[0040] Rapid sintering: Sintering temperature: 950 °C, time: 6 minutes, pressure: 60 MPa.

[0041] Annealing treatment: Temperature; 600 °C, annealing for 1.5 hours, argon protection.

[0042] Surface treatment: Nickel chemical plating layer, thickness is 8 μm, curing temperature: 90 °C.

[0043] Example 3: Process for economical low-rare-earth consumption magnet Raw material ratio: Neodymium 25 parts, iron 65 parts, boron 1.0 part, lanthanum 5.0 parts, zirconium 0.5 part, molybdenum 0.5 part, yttrium oxide 0.1 part.

[0044] Ball milling and mixing: Under argon protection, ball mill for 12 hours with a ball-to-material ratio of 10:1.

[0045] Coating treatment: Use ethanol, with the particle size of yttrium oxide being 50 nm, and perform ultrasonic treatment for 20 minutes.

[0046] Heat treatment and pressing: Drying temperature: 90 °C, heat treatment temperature: 150 °C, time: 0.5 hour; Pressing: 100 MPa, magnetic field strength: 0.5 T.

[0047] Sintering parameters: Sintering temperature: 850 °C, heat preservation for 10 minutes, sintering pressure: 30 MPa.

[0048] Annealing treatment: Temperature: 500 °C, time: 2 hours, argon atmosphere.

[0049] Surface coating: Spray fluorocarbon resin with a thickness of 2 μm, curing temperature: 80 °C, curing time: 20 minutes.

[0050] Example 4: Process for high-performance temperature-resistant magnets Raw material ratio: 29 parts of neodymium, 61 parts of iron, 1.2 parts of boron, 3.5 parts of lanthanum, 1.8 parts of zirconium, 1.0 part of molybdenum, 0.5 part of yttrium oxide.

[0051] Ball milling and mixing: Ball mill for 24 hours under argon protection with a ball-to-material ratio of 13:1.

[0052] Nanometer coating: The dispersion liquid is isopropanol, the particle size is 10 nm, and the ultrasonic time is 60 minutes.

[0053] Heat treatment and forming: Drying: Hot air at 85 °C for 1.5 hours; Heat treatment: 250 °C for 1 hour; Pressing: 200 MPa, magnetic field strength: 2.0 T.

[0054] Sintering: Rapid induction sintering temperature: 920 °C, heat preservation for 5 minutes, pressure applied: 50 MPa.

[0055] Annealing treatment: Temperature: 580 °C, annealing for 1 hour, under argon protection.

[0056] Surface protection: Fluorocarbon coating thickness: 10 μm, curing temperature: 120 °C, curing time: 45 minutes.

[0057] Comparative Example 1: Compared with Example 1, the difference lies in that the nano-ceramic coating treatment is cancelled, and the rest are the same.

[0058] Comparative Example 2: Compared with Example 2, the difference lies in that it is changed to ordinary cold pressing without magnetic field orientation treatment, and the rest are the same.

[0059] Comparative Example 3: Compared with Example 3, the difference lies in that it is changed to traditional sintering, and the rest are the same.

[0060] Comparative Example 4: Compared with Example 4, the difference lies in that the coating treatment is carried out directly, and the rest are the same.

[0061] Experiment 1: Verify the improvement effect of the high-temperature stability of nano-ceramic coating Comparison groups: Example 1 (coated with yttrium oxide) Comparative Example 1 (coating cancelled) Experiment purpose: Verify whether the nano-yttrium oxide ceramic coating improves the thermal stability and magnetic retention rate of the magnet under high-temperature working conditions.

[0062] Experiment method: Use a vibrating sample magnetometer (VSM) to measure the remanence (Br) and coercivity (Hcj) of the two groups of magnet samples at room temperature and 180 °C; Test environment setting: Temperature measurement accuracy: ±1 °C Heat preservation time: 2 hours The number of samples in each group ≥ 5, take the average value and calculate the standard deviation; At the same time, measure the change in the thickness of the oxide layer (using SEM cross-sectional images) to simulate the influence of long-term high-temperature oxidation.

[0063] Experiment description: Verify the influence of nano-ceramic coating on high-temperature magnetic properties This experiment aims to compare the magnetic property retention ability of Example 1 and Comparative Example 1 under high-temperature conditions, and focus on verifying the effectiveness of yttrium oxide nanoparticle coating in improving the heat resistance degradation of the magnet.

[0064] Sample preparation: According to the processes of Example 1 and Comparative Example 1, prepare two groups of samples, with 5 pieces prepared in each group; The sample size is uniformly 5 mm × 5 mm × 5 mm. After polishing, it is used for magnetic property testing.

[0065] Magnetic property testing at room temperature: Use a vibrating sample magnetometer (VSM) to measure the remanence (Br), coercivity (Hcj) and maximum magnetic energy product (BH)max of the two groups of samples at room temperature; Each group of samples was measured 3 times repeatedly and the average was taken.

[0066] High-temperature heat treatment and performance degradation test; The sample was placed in a muffle furnace at 180 °C for 2 hours of constant temperature, taken out and naturally cooled to room temperature; Test its Br, Hcj and (BH)max again, and calculate the percentage of performance degradation.

[0067] Oxide layer evaluation: Randomly select one sample slice from each of the two groups, and use a scanning electron microscope (SEM) to observe the cross-section; Record the surface oxide layer thickness and the particle bonding interface condition.

[0068] Table 1: Summary; After heat treatment, the attenuation of magnetic properties was significantly differentiated between the two groups. The magnet in Example 1 showed a smaller decline in remanence and more stable coercivity. The yttrium oxide particles may have formed a stable barrier layer at the surface interface, restricting the diffusion of oxygen atoms into the crystal interior.

[0069] The nano-coating layer of the present invention is not only a passive barrier. More importantly, it participates in the microstructure evolution process. In the thermally activated state, it inhibits grain boundary migration and passivates active sites. This control behavior is not easily directly predicted from traditional models, but is truly reflected in the experimental results.

[0070] On the other hand, an irregular oxidation zone was formed on the surface of the comparative sample. Oxidation was obvious near the microcracks. The contact between particles was poor, and the interfacial reaction was more intense. Local debonding occurred at high temperatures, and it was difficult to maintain the consistency of magnetic domains. The performance dropped rapidly, indicating that the structure was not stable.

[0071] Experiment 2: Verify the effect of magnetic field-assisted directional pressing on improving magnetic properties Comparison groups: Example 2 (magnetic field directional pressing) Comparative Example 2 (ordinary pressing) Experiment purpose: Verify whether magnetic field-assisted pressing can improve magnetic anisotropy, remanence and energy product.

[0072] Experiment method: Use a vibrating sample magnetometer (VSM) to measure the Br, Hcj and maximum magnetic energy product (BHmax) of the two groups of samples respectively; Compare the magnet orientation angles (analyze the grain orientation by XRD diffraction intensity) to judge the orientation degree; The sample size was uniformly 5×5×5 mm 3 , and the number of test repetitions was 3.

[0073] Experimental description: Verification of the effect of magnetic field-assisted directional pressing on magnetic anisotropy and magnetic properties. In this experiment, Example 2 and Comparative Example 2 were compared. By varying whether magnetic field-assisted pressing was applied, the effect of magnetic anisotropy on the final magnetic properties was verified.

[0074] Sample preparation: Two groups of samples were prepared strictly according to Example 2 and Comparative Example 2, keeping the raw material ratio, ball milling conditions, sintering temperature, surface treatment, etc. exactly the same; The difference was only whether a magnetic field was applied during the pressing process (Example 2 used a 1.5 T magnetic field, and Comparative Example 2 did not apply a magnetic field).

[0075] Magnetic property measurement: A vibrating sample magnetometer (VSM) was used to measure the remanence (Br), coercivity (Hcj), and maximum magnetic energy product (BH)max of the samples; The test direction was uniformly sampled along the pressing direction.

[0076] Orientation degree analysis: The selected samples were tested by X-ray diffraction (XRD), and the intensity ratio of the diffraction peaks of the (006) plane to the (110) plane (I006 / I110) was calculated to evaluate the orientation degree; The size of all samples was uniformly a φ5×5 mm cylinder.

[0077] Repeatability control: The number of test samples in each group was 5, and the average of three measurements was taken to prevent accidental deviation; All samples were obtained from the same batch of mixed powder to keep the reference consistent.

[0078] Table 2: Summary; By comparing the samples with magnetic field-assisted pressing and those with ordinary pressing, the guiding effect of the magnetic field on the magnetic moment arrangement behavior during the forming process can be clearly verified. When the magnetic powder is not yet dense in the initial stage of pressing, the internal magnetic moments are more likely to complete the adjustment of direction consistency under the drive of the external magnetic field. At this time, there is still relatively high fluidity between the particles, and the orientation of the magnetic moments and the rotation of the particles cooperate with each other, thereby enhancing the overall grain orientation. The establishment of magnetic anisotropy at this stage provides an orientation basis for subsequent sintering shape retention, constituting an integrated texture evolution path from forming to densification.

[0079] During the structure regulation process, the preferential orientation structure formed under the induction of the magnetic field significantly strengthens Nd2Fe 14The c-axis of the B crystal tends to align along the pressing direction. As detected by XRD, the relative intensity of the (006) crystal plane with strong magnetic anisotropy in the diffraction pattern has increased significantly, reflecting a high degree of consistency in the main magnetization direction of the grains. The formation of this microstructure texture effectively reduces the proportion of grains in the non-main magnetization direction and decreases the internal friction and magnetic flux loss caused by the competition between magnetic domains. In contrast, the isotropic structure formed by randomly distributed particles in the ordinary pressed samples limits the improvement space of magnetic parameters, resulting in significantly lower remanence and maximum magnetic energy product levels.

[0080] Experiment 3: Verify the influence of the rapid induction sintering process on grain refinement and structural uniformity Comparison groups: Example 3 (rapid induction sintering) Comparative Example 3 (traditional long-time sintering) Experimental purpose: Prove that rapid sintering can effectively control grain growth, optimize the microstructure, and improve the consistency of magnetic properties.

[0081] Experimental method: Use a scanning electron microscope (SEM) to observe the cross-sectional microstructure and count the grain size distribution; Use XRD to detect whether secondary phase precipitation occurs; Test the sintering density (Archimedes method) and measure the magnetic property uniformity (comparing the standard deviation of samples from 3 different batches).

[0082] Experimental description: Verification of the influence of the rapid induction sintering process on microstructure and magnetic property consistency This experiment aims to compare the differences between Example 3 (using rapid induction sintering) and Comparative Example 3 (traditional electric furnace slow sintering) in terms of structural uniformity, grain control ability, and magnetic property stability.

[0083] Sample preparation: The powder ratios and forming processes of the two groups of samples are exactly the same; Example 3 uses medium-frequency induction sintering (current frequency 100 kHz, sintering peak temperature 980 °C, holding time 8 minutes); Comparative Example 3 uses traditional electric furnace sintering (heating rate 5 °C / min, holding at 980 °C for 90 minutes); Finally, 5×5×3 mm 3 sheet-shaped magnet samples are obtained.

[0084] Grain structure characterization: Select any 3 samples from each group and use a scanning electron microscope (SEM) to observe the cross-sectional structure; Use image analysis software to count the grain sizes and record the particle size distribution range.

[0085] Evaluation of structural uniformity; XRD was used to test whether abnormal phase precipitation (α~Fe, Nd~rich phase) existed; The magnetic properties of three batches of samples prepared at different time points were tested, and the performance standard deviations were compared to evaluate the consistency.

[0086] Magnetic properties test: The Br and Hcj of the samples were measured using a vibrating sample magnetometer (VSM); Five samples were selected from each group, and the mean and standard deviation of the magnetic properties were recorded.

[0087] Table 3: Summarize; From the perspective of microstructure control, the experimental results fully verify the feasibility and stability of grain refinement through rapid induction sintering process. Rapid heating and short-time densification process can effectively inhibit the abnormal growth of grains during the heating process and avoid the recrystallization behavior caused by energy accumulation at the grain boundary in the high temperature stage. The concentrated thermal effect and local sintering dynamic balance in this process help to complete sintering densification at a lower time integral, thereby forming a more uniform and refined grain structure in the organization. This microstructural stability lays the foundation for the subsequent magnetic domain arrangement and uniformity of magnetic properties.

[0088] In the path of organizational evolution, since the magnetic powder particles have been inorganically coated in the pretreatment stage, the yttrium oxide ceramic particles exist as thermal barriers between grains during the sintering process, which restricts the diffusion behavior at the interfaces of each particle during induction heating, further suppressing the trend of abnormal diffusion at grain boundaries and impurity generation.

[0089] In terms of magnetic property consistency, the samples in the experimental group showed smaller performance fluctuations and higher repeatability, which is fundamentally due to the convergence of magnetic domain arrangement brought about by the uniformity of the microstructure. The fine grain structure with concentrated particle size distribution helps to reduce the internal stress difference between magnetic domains and improve the coordination of magnetic domain reversal behavior during magnetization. Especially after the rapid sintering is completed and combined with the low-temperature annealing process, the residual stress inside the material is fully released, making the magnetic domain structure more stable, thereby obtaining better magnetic property consistency.

[0090] Experiment 4: Verify the effect of low temperature annealing on magnetic properties and stress release Comparison groups: Example 4 (with annealing treatment) Comparative Example 4 (without annealing treatment) Experimental purpose: To analyze whether low temperature annealing can help eliminate internal residual stress and improve magnetic stability.

[0091] Experimental methods: Use XRD to detect the change in the peak position of the internal stress of the sample; Use VSM to measure the change in Hcj of the sample before and after annealing; At the same time, use a universal testing machine to conduct three-point bending mechanical tests on two groups of samples to observe the consistency of mechanical properties.

[0092] Experimental description: The influence of low-temperature annealing on the stress release and performance stability of magnets.

[0093] In this experiment, by comparing whether low-temperature annealing treatment is carried out, the role of this process in eliminating residual stress, improving structural stability, and improving magnetic property fluctuations is verified.

[0094] Sample preparation: Both groups of samples were pressed and sintered according to the same process (held at 980 °C for 8 minutes); The samples of Example 4 were subjected to low-temperature annealing treatment after sintering (500 °C × 2 h, argon atmosphere, heating / cooling rate 5 °C / min); the samples of Comparative Example 4 had no subsequent heat treatment and were directly cooled for standby.

[0095] Magnetic property testing; Use VSM to test Br and Hcj of the two groups of samples, and particularly record the fluctuation range of Hcj among different batches; Select 5 samples from each group and measure them three times repeatedly.

[0096] Stress analysis: Use XRD for diffraction peak position offset analysis, and estimate the lattice microstrain through the change in the full width at half maximum (FWHM) of the peak position; Observe the micro-structure of the sample cross-section, whether there are micro-cracks or abnormal grain boundaries, and evaluate the residual thermal stress.

[0097] Mechanical property testing: Use a three-point bending test device (loading rate 0.5 mm / min) to measure the fracture load; Combined with observing the fracture surface morphology, infer the structural integrity.

[0098] Table 4: Summary; Low-temperature annealing treatment can effectively release the residual thermal stress inside the magnet without significantly affecting the crystal structure of the main phase. Under the sintering path of rapid heating and short-time heat preservation, non-equilibrium strain accumulation is prone to occur during the densification process of the magnet structure. Especially in the regions of grain boundaries and the distribution of the second phase, micro-stress concentration is likely to be generated due to the difference in thermal conductivity. After low-temperature annealing, atoms slowly relax under the metastable displacement energy barrier, effectively reducing lattice distortion and strain energy accumulation.

[0099] The release of residual stress directly promotes the stability of the magnetic domain structure, thereby enhancing the consistency and reliability of magnetic properties. The increase in coercivity Hcj and the decrease in the fluctuation amplitude reflect the reduction in the resistance change and the enhanced spatial uniformity during the magnetic domain reversal behavior. When stress exists, the movement of domain walls is restricted, which easily leads to delay or instability of local magnetic domain reversal, affecting the overall magnetic response. After annealing, the structure has better grain boundary continuity and magnetic anisotropy orientation, and the magnetic domain structure tends to be regular, which helps to improve the response stability of the magnet to external disturbances.

[0100] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made therein without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A high-temperature resistant NdFeB magnet, characterized in that, By weight parts, it includes the following components: 25 - 30 parts of neodymium, 60 - 65 parts of iron, 1.0 - 2.0 parts of boron, 3.0 - 5.0 parts of lanthanum, 0.5 - 2.0 parts of zirconium, 0.5 - 1.0 parts of molybdenum, and 0.1 - 0.5 parts of nano ceramic particles.

2. The high-temperature resistant neodymium iron boron magnet according to claim 1, characterized in that The nano ceramic particles are yttrium oxide.

3. A method for preparing a high-temperature resistant NdFeB magnet, which is used to prepare a high-temperature resistant NdFeB magnet as described in any one of claims 1 to 2, and is characterized in that, It includes the following steps: S1. Alloy raw material preparation and mixing: Weigh powders of neodymium, iron, boron, lanthanum, zirconium, and molybdenum according to the mass ratio, and carry out ball milling and mixing under an inert atmosphere to obtain a pre-alloyed mixed powder. S2. Nano ceramic coating treatment: Add the mixed powder into an alcohol dispersion liquid containing yttrium oxide for ultrasonic treatment and adsorption. S3. Magnetic field-assisted pressing and forming: After drying and heat treatment of the mixed powder after coating treatment, a coated magnetic powder is obtained, and the coated magnetic powder is subjected to magnetic field-assisted pressing and forming. S4. Rapid induction sintering: Carry out rapid induction sintering on the formed green body. S5. Low-temperature annealing treatment: Carry out annealing treatment at 500 - 600 °C. S6. Surface protection treatment: Apply a fluorocarbon resin surface coating on the surface of the magnet, and the coating thickness is 2 - 10 μm.

4. The preparation method of a high-temperature resistant neodymium iron boron magnet according to claim 3, wherein, In step S1, the ball milling treatment is carried out under an argon protection atmosphere, and the ball milling time is 12 - 24 hours.

5. The preparation method of a high-temperature resistant neodymium iron boron magnet according to claim 3, characterized in that, In step S2, the alcohol dispersion liquid is ethanol or isopropanol, and the particle size of the nano yttrium oxide particles is 10 - 50 nm.

6. The preparation method of a high-temperature resistant NdFeB magnet according to claim 3, characterized in that, In step S3, the heat treatment temperature is 150 - 250 °C, and the time is 0.5 - 1 hour.

7. The preparation method of a high-temperature resistant NdFeB magnet according to claim 3, characterized in that, In step S3, the pressure applied during pressing and forming is 100 - 200 MPa, and the directional forming is carried out in a magnetic field of 0.5 - 2.0 T.

8. The preparation method of a high-temperature resistant neodymium iron boron magnet according to claim 3, characterized in that, In step S4, the rapid induction sintering temperature is 850 - 950 °C, the holding time is 5 - 10 minutes, and the sintering pressure is 30 - 60 MPa.

9. The preparation method of a high-temperature resistant neodymium iron boron magnet according to claim 3, characterized in that, In step S5, the annealing temperature in the low-temperature annealing treatment step is 500 - 600 °C, the annealing time is 1 - 2 hours, and the annealing atmosphere is argon.

10. The preparation method of a high-temperature resistant NdFeB magnet according to claim 3, characterized in that, In step S6, the surface protection treatment step adopts a fluorocarbon resin spraying or electroless nickel plating process, the coating thickness is 2 - 10 μm, and the curing temperature is 80 - 120 °C.

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