Multi-stage sintering process for neodymium-iron-boron permanent magnet material

Abstract

The invention discloses a neodymium iron boron permanent magnet material multi-stage sintering process, and relates to the technical field of permanent magnet material preparation. The process sequentially comprises the six core steps of charging, first-stage heating and degassing, second-stage heating and pre-sintering, high vacuum establishment and high-temperature sintering, controllable cooling and tempering treatment, and material densification and microstructure optimization are achieved through standardization charging arrangement, progressive temperature zone regulation and control, key node high-vacuum strengthening and precise cooling and tempering cooperation. The process is definite in parameter quantification, adapts to preparation of neodymium-iron-boron magnets with different performance requirements, improves the product performance consistency and stability, is high in industrial operability, and is suitable for large-scale production in the fields of new energy automobiles, motors and the like.

Description

Technical Field

[0001] This invention relates to the field of permanent magnet material preparation technology, specifically to a multi-stage sintering process for neodymium iron boron permanent magnet materials. Background Technology

[0002] Neodymium iron boron (NdFeB) permanent magnets, with their excellent energy product, high coercivity, and high remanence, have become indispensable core functional materials in modern industry. The sintering process, a crucial step in the preparation of NdFeB permanent magnets, directly determines the magnet's density, microstructure, and final magnetic properties. Its core principle is to induce particle bonding, atomic diffusion, and grain growth in the powder green body through high-temperature treatment, achieving densification and forming a stable Nd₂Fe₂. 14 B main phase and optimized grain boundary phase structure.

[0003] However, existing NdFeB sintering processes still face numerous technical challenges. In the furnace loading stage, traditional processes lack standardized material box arrangement specifications; the number of boxes in each layer is arbitrary, and the total number of layers is not fixed. This leads to uneven distribution of the temperature and airflow fields within the furnace, resulting in significant differences in heating and gas exposure for green blanks in different locations. This directly causes high performance dispersion in mass production, making it difficult to meet the stringent consistency requirements of high-end applications. Some processes excessively increase the furnace loading in pursuit of production capacity, further exacerbating the non-uniformity of the furnace environment and causing localized under-sintering or over-sintering of the magnets.

[0004] In the heating and degassing stages, existing technologies mostly employ a single vacuum pumping and fixed heating rate mode, failing to tailor the design to the volatilization characteristics of impurities in different temperature ranges. If physically adsorbed water, organic binders, and other impurities in the low- and medium-temperature stages are not sufficiently removed, they will decompose and generate gases during high-temperature sintering, forming porosity defects, or react with rare earth elements to produce harmful substances that contaminate grain boundaries. Conversely, if carbonized residues in the medium- and high-temperature stages are not effectively removed, it will affect the smooth progress of the subsequent densification process. Furthermore, using the same degassing parameters for materials with different performance requirements makes it difficult to balance the production efficiency of ordinary materials with the low-oxygen purity requirements of high-performance materials.

[0005] The core problem in high-vacuum sintering is the lack of coordination between vacuum control and temperature changes. Most processes maintain a constant vacuum throughout, failing to implement intensive control within the critical 800-900℃ range. This temperature range is crucial for Nd₂Fe₂. 14 The stage where the B phase begins to form and the grain boundary liquid phase is about to appear is also the period when low-melting-point metal impurities volatilize in large quantities. At this time, insufficient vacuum will prevent impurities from being discharged quickly, and they are prone to depositing or dissolving back into the grain boundaries, causing grain boundary contamination, which significantly affects the coercivity and temperature stability of the magnet. In addition, some processes lack vacuum sealing test steps, and air infiltration will cause rare earth element oxidation, further degrading the magnetic properties.

[0006] There is also room for optimization in the cooling and tempering processes. Improper control of the cooling rate can lead to large thermal stress inside the magnet, causing cracks and defects. Inadequate vacuum environment control and unreasonable selection of cooling methods during tempering can fail to fully utilize the optimization effect of tempering on grain boundary phases, and cannot effectively eliminate residual stress generated during sintering, thus affecting the stability of magnet performance.

[0007] As an important auxiliary component in the sintering process, the material box lacks systematic and standardized management in the current process. Problems such as inadequate pre-use inspection, improper handling during transportation, and haphazard storage after use can lead to cracks, oxidation, or moisture absorption in the material box. When reused, this can introduce impurities, disrupt the vacuum environment inside the furnace, and indirectly affect the sintering quality.

[0008] Furthermore, the existing process suffers from low parameter standardization, with some key parameters relying on operator experience for adjustment. This leads to significant performance fluctuations during mass production and insufficient stability in industrial production. In summary, existing NdFeB sintering processes suffer from problems such as non-standard furnace loading, insufficient degassing, lack of vacuum control at critical stages, inadequate coordination between cooling and tempering, inadequate material box management, and narrow application scenarios. These issues hinder further improvements in the performance of NdFeB permanent magnet materials and the stability of industrial production. Developing a multi-stage sintering process with standardized procedures, coordinated parameters, and broad application scenarios has become a pressing technical challenge in this field.

[0009] The above background information is provided only to aid in understanding the inventive concept and technical solution of this invention. It does not necessarily belong to the prior art of this patent application. In the absence of clear evidence that the above information was disclosed on the filing date of this patent application, the above background information should not be used to evaluate the novelty and inventiveness of this application. Summary of the Invention

[0010] The main objective of this invention is to propose a multi-stage sintering process for neodymium iron boron permanent magnet materials, in order to solve the technical problems existing in the prior art, such as insufficient removal of impurities, lack of vacuum control in key stages, and insufficient coordination of process parameters, which in turn affect the microstructure and core magnetic properties of the magnet.

[0011] To achieve the above technical objectives, the present invention adopts the following technical solution:

[0012] A multi-stage sintering process for neodymium iron boron permanent magnet materials includes the following steps: S1, loading the furnace; S2, first-stage heating and degassing; S3, second-stage heating and pre-sintering; S4, establishing high vacuum and high-temperature sintering; S5, controlled cooling; S6, tempering treatment.

[0013] Preferably, the specific steps for loading the furnace are as follows: the formed NdFeB green billets are loaded into the material boxes of the sintering furnace, the material boxes are arranged in layers in the furnace, and 8-12 material boxes are evenly placed in each layer, with a total of six layers in the furnace.

[0014] Preferably, the specific steps of the first stage of heating and degassing are as follows: after loading the furnace, vacuum pumping is performed for 30 minutes, and then the furnace temperature is raised from room temperature to 200-400℃ at a heating rate of 5-10℃ / min, and held at this temperature range.

[0015] Preferably, the specific steps of the second stage of heating and pre-sintering are as follows: the first stage of heating and degassing continues to heat up to 600-800℃ at a heating rate of 5-8℃ / min, and is held at this temperature range; then the temperature is increased to 800-900℃ at a heating rate of 5-8℃ / min.

[0016] Preferably, the specific steps for establishing high vacuum and high-temperature sintering are as follows: after heating to 800-900℃, stabilize within this temperature range for 5-30 minutes, and then increase the vacuum level inside the furnace to 1.0×10⁻⁶. -3 During the process, alcohol is used to check for leaks in the equipment, and then the temperature is increased to 1000-1100℃ at a rate of 3-12℃ / min, and held within this temperature range.

[0017] Preferably, the specific steps of controllable cooling are as follows: after the sintering process is completed, the sintered body is cooled to below 70°C at a cooling rate of 5-15°C / min.

[0018] Preferably, the specific steps of the tempering treatment are as follows: placing the cooled sintered body in a heat treatment furnace and evacuating it to a vacuum level better than 1.0 × 10⁻⁶. -1 After maintaining a vacuum level of Pa for 30 minutes, the temperature is raised to the tempering temperature and held for a period of time, followed by forced cooling using air cooling.

[0019] Preferably, the holding time at 200-400℃ in the furnace loading step is 30-90 minutes.

[0020] Preferably, the holding time at 600-800℃ during the second stage of heating and pre-sintering is 60-150 minutes.

[0021] Preferably, the holding time at 1000-1100℃ during the high vacuum establishment and high temperature sintering steps is 120-480 minutes.

[0022] The beneficial effects of this invention compared to the prior art include:

[0023] 1. Improve the consistency and stability of product performance.

[0024] This invention employs standardized design during the furnace loading stage, clearly defining the arrangement, number of layers, and spacing of the material boxes to ensure uniform temperature and airflow distribution within the furnace, reducing sintering differences in materials at different locations from the outset. A progressive degassing scheme is designed with parameters tailored to the characteristics of impurities in different temperature ranges, achieving thorough removal of impurities such as moisture and organic matter, avoiding performance fluctuations caused by residual impurities. High-vacuum enhanced purification and leak detection steps at critical stages effectively remove low-melting-point metal impurities, ensuring the purity and uniformity of the grain boundary phase. The synergistic design of controllable cooling and tempering reduces thermal stress and oxidation risks, further optimizing microstructure stability. Lifecycle management of the material boxes prevents the introduction of impurities from auxiliary components, ensuring a consistent sintering environment. The synergistic effect of these processes reduces the dispersion of magnet performance in mass production, improves product performance consistency and stability, and meets the stringent requirements for material performance stability in high-end applications.

[0025] 2. Optimize the microstructure and core magnetic properties of the magnet.

[0026] Existing processes suffer from problems such as grain boundary contamination, uneven grain growth, and insufficient densification, which limit the improvement of magnet performance. This invention effectively removes various impurities through a combination of progressive degassing and high-vacuum purification at key nodes, providing a clean environment for grain boundary phase formation and avoiding grain boundary contamination. Standardized furnace loading and temperature control ensure uniform grain growth, while high-temperature sintering parameter matching achieves sufficient densification. The synergistic effect of auxiliary elements and main phase elements in the raw materials further refines the grains and optimizes the grain boundary structure. These design features work together to enhance the Nd2Fe magnet's performance. 14 The B-phase main phase exhibits uniform grain distribution, pure and continuous grain boundary phases, and significantly improved density. This microstructure optimization directly translates into enhanced core magnetic properties, resulting in comprehensive improvements in key indicators such as remanence, coercivity, and energy product, thus supporting the material's application in demanding scenarios.

[0027] 3. Enhance the adaptability and flexibility of the process to different scenarios.

[0028] This invention addresses the different needs of conventional and high-performance materials by adjusting parameters such as vacuum pretreatment time, holding time, and heating rate, thus balancing production efficiency and performance requirements. Core process parameters, such as heating rate, holding time, and cooling rate, are set within reasonable ranges and can be flexibly adjusted according to raw material characteristics, product specifications, and performance requirements, adapting to the preparation of NdFeB magnets of different performance grades. This multi-scenario adaptability design enhances process flexibility, enabling it to meet diverse market demands, reduce switching costs between different product production processes, and improve production efficiency and resource utilization.

[0029] 4. Reduce production energy consumption and costs, and improve the economic efficiency of industrialization.

[0030] The standardized design during the furnace loading stage improves the utilization rate of furnace space, increases the single loading capacity, enhances batch production efficiency, and reduces energy consumption and production costs per unit product. The synergistic effect of progressive degassing and high-vacuum purification reduces product scrap rates due to impurities and increases the yield rate. Lifecycle management of the material bins extends their service life and reduces replacement costs for auxiliary components. Simultaneously, the high degree of process standardization reduces reliance on operator experience, minimizes production losses due to human error, and overall improves the economics of industrialized production.

[0031] 5. Improve the standardization and industrial operability of processes.

[0032] This invention quantifies and standardizes the parameters of each stage, including furnace loading, degassing, sintering, cooling, and tempering, clarifying the operational requirements and parameter ranges for each step and forming clear process operation specifications. Key parameters such as temperature, vacuum level, heating rate, and holding time can be precisely controlled through an automated control system, reducing human intervention and improving process repeatability and stability. The equipment involved in the process consists of conventional industrial sintering furnaces and heat treatment furnaces, requiring no special customization or modification, thus lowering the barrier to industrial application. The material box management process is simple and easy to implement, facilitating execution and supervision during production. The overall process flow is logically clear, with smooth connections between each stage, and convenient operation, making it suitable for large-scale industrial production and possessing excellent prospects for widespread application.

[0033] 6. Reduce environmental impact and achieve green production.

[0034] The process design of this invention emphasizes green production principles. By combining a high-vacuum environment with inert gas protection, oxidation reactions during sintering are reduced, thus lowering the emission of harmful gases. Progressive degassing and high-vacuum purification improve raw material utilization and reduce waste generation. Optimized process parameters reduce energy consumption and minimize the environmental impact of energy consumption. Reusable and standardized management of material boxes reduces waste of auxiliary materials. These designs enable the process to improve product performance and production efficiency while minimizing negative environmental impacts, aligning with the trend of green manufacturing. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to specific embodiments. It should be emphasized that the following description is merely exemplary and is not intended to limit the scope and application of the present invention.

[0036] A multi-stage sintering process for neodymium iron boron permanent magnet materials includes the following steps:

[0037] 1. Loading the furnace

[0038] Select graphite material boxes. After checking that the boxes are free from obvious deformation and cracks, evenly load the formed NdFeB green blanks into the boxes, maintaining a 5-8mm gap between the green blanks to prevent them from sticking together during sintering. Open the sintering furnace door and place the boxes containing the green blanks into the furnace chamber according to the "layered arrangement" principle. Place 8-12 boxes evenly in each layer, and strictly control the total number of furnace layers to six. Adjust the position of the boxes to ensure that there is a 10-15mm gap between the boxes and between the boxes and the furnace wall to ensure airflow and uniform temperature field in the furnace. Close the furnace door and lock it tightly.

[0039] 2. First stage of heating and degassing

[0040] The vacuum pumping system of the sintering furnace was started for 30 minutes for pre-evacuation to remove air and residual gases from the furnace. After pre-evacuation, the vacuum level inside the furnace was confirmed to reach 1.0 × 10⁻⁶. -1 Below Pa, set the heating program to raise the furnace temperature from room temperature to 200-400℃ at a heating rate of 5-10℃ / min. After reaching the target temperature range, start the heat preservation program and set the heat preservation time to 30-90min to complete the removal of physically adsorbed water and low-boiling-point organic matter.

[0041] 3. Second stage of heating and pre-sintering

[0042] After the first stage of heat preservation is completed, there is no need to interrupt the operation of the equipment. Directly set the next stage heating parameters and continue heating at a rate of 5-8℃ / min to 600-800℃. After reaching the target temperature range, start the heat preservation program and set the heat preservation time to 60-150min to complete the decomposition of organic binder and the removal of carbonized residues. At the same time, promote the solid diffusion on the surface of powder particles to form a preliminary sintering neck. After the heat preservation is completed, continue heating at a rate of 5-8℃ / min to 800-900℃. During the heating process, monitor the temperature change in the furnace in real time to ensure that the temperature rises uniformly without fluctuations.

[0043] 4. High vacuum establishment and high temperature sintering

[0044] Once the furnace temperature reaches 800-900℃, pause the heating process and maintain this temperature for 5-30 minutes to ensure uniform temperature throughout the furnace. Then, activate the high vacuum system to raise the vacuum level inside the furnace to 1.0×10⁻⁶. -3 During the process, key sealing areas such as the furnace door gasket and pipe joints are wiped with alcohol swabs for leak detection. The vacuum level is observed to ensure it remains stable. If the vacuum level drops, the sealing problem is investigated and the seal is resealed. After the leak detection is successful, the heating program is set to heat to 1000-1100℃ at a heating rate of 3-12℃ / min. Once the target temperature range is reached, the holding program is started, with the holding time set to 120-480min to complete the densification of the material and the Nd2Fe2O3 reaction. 14 B-phase grain growth.

[0045] 5. Controllable cooling

[0046] After the high-temperature sintering and holding period, the heating module is turned off, and the controllable cooling system is started. The cooling rate is set to 5-15℃ / min. During the cooling process, inert gas (argon or nitrogen) is introduced into the furnace, and the gas flow rate is controlled at 0.5-1.0 m³ / min. 3 / h To prevent oxidation of the magnet surface, monitor the furnace temperature in real time, and stop the cooling system and inert gas supply when the temperature drops below 70℃.

[0047] 6. Tempering treatment

[0048] Open the sintering furnace door and quickly transfer the cooled sintered body into the heat treatment furnace. Close and lock the furnace door, and start the vacuum pumping system of the heat treatment furnace to evacuate to a vacuum level better than 1.0 × 10⁻⁶. -1 Set the vacuum level to Pa and maintain this vacuum for 30 minutes to remove air from the furnace. Set the heating program to raise the temperature to the preset tempering temperature of 500-600℃. After reaching the target temperature, hold the temperature for 120-240 minutes. After the holding period, start the air cooling system to force-cool the sintered body until the furnace temperature drops to room temperature. Open the furnace door and take out the finished magnet.

[0049] Technical principle of the invention:

[0050] The technical principle of this invention is based on the sintering characteristics of neodymium iron boron permanent magnet materials and the synergistic effect of various process steps. Through the optimization of raw material ratios and the systematic design of process parameters, a comprehensive improvement in material performance is achieved, as detailed below:

[0051] The standardized design during the furnace loading stage, with six layers of material boxes and 8-12 material boxes per layer, ensures uniform temperature and airflow distribution throughout the furnace, preventing localized overheating or incomplete sintering. The reasonable spacing between the material boxes promotes gas flow within the furnace, reducing the possibility of raw material oxidation and laying a structural foundation for the uniformity of subsequent process stages. The fixed total number of loading layers (six) ensures sufficient loading volume per batch while avoiding excessive temperature differences between the upper and lower parts of the furnace caused by too many layers.

[0052] The parameter design for the first stage of heating and degassing involves a 30-minute pre-evacuation process to quickly remove air from the furnace and reduce the initial oxygen content. The combination of a low-to-medium temperature range of 200-400℃ and a 30-90 minute holding period provides sufficient kinetic conditions for the gentle removal of adsorbed moisture and low-boiling-point organic matter, preventing cracking of the green body due to violent volatilization of impurities. A heating rate of 5-10℃ / min ensures both removal efficiency and prevents material stress caused by sudden temperature increases, achieving a balance between removal effectiveness and structural protection.

[0053] The selection of parameters for the second stage of heating and pre-sintering: The medium-high temperature range of 600-800℃ is the optimal temperature range for the decomposition of organic binders and the removal of carbonized residues. A holding time of 60-150 minutes ensures sufficient decomposition and volatilization of impurities. Simultaneously, the moderate atomic diffusion rate within this temperature range promotes solid-state diffusion on the powder particle surface, forming a preliminary sintering neck, improving the structural strength of the green body, and providing structural support for the subsequent high-temperature densification process. A heating rate of 5-8℃ / min avoids excessive particle growth due to excessively high temperatures, maintaining particle uniformity. The transition design to 800-900℃ provides a temperature connection for subsequent high-vacuum purification and high-temperature sintering, avoiding structural fluctuations caused by sudden temperature changes.

[0054] The synergistic mechanism of high vacuum establishment and high-temperature sintering is the core technical highlight of this invention. The temperature range of 800-900℃ is suitable for Nd2Fe. 14 This is a critical stage where the B phase begins to form and the grain boundary liquid phase is about to appear, and it is also the period when low-melting-point metal impurities volatilize intensively. A 5-30 minute temperature stabilization step ensures uniform temperature throughout the furnace, providing a uniform temperature base for subsequent vacuum-enhanced purification. The vacuum level is then increased to 1.0 × 10⁻⁶. -3 The high vacuum level of Pa generates a strong pumping effect, rapidly removing concentrated, volatile low-melting-point impurities and residual gases, preventing their deposition or re-dissolution at grain boundaries, thus achieving grain boundary-oriented purification. An alcohol leak detection step ensures the vacuum system's airtightness, preventing air infiltration from compromising the purification effect. The high-temperature range of 1000-1100℃ provides sufficient energy for atomic diffusion, promoting the liquid-phase sintering process and achieving full densification of the material. The synergistic effect of a holding time of 120-480 min and a heating rate of 3-12℃ / min ensures uniform grain growth while preventing abnormal grain growth, resulting in an optimized microstructure.

[0055] The controlled cooling rate, maintained at 5-15℃ / min, reduces the internal temperature gradient of the magnet, lowers the probability of thermal stress, and prevents cracking defects. Inert gas protection during cooling further prevents surface oxidation of the magnet, ensuring its performance. The adjustable cooling rate adapts to the cooling requirements of magnets of different sizes, enhancing process flexibility.

[0056] The combined effect of the vacuum environment and air cooling during tempering is superior to 1.0×10⁻⁶. -1 A vacuum level of Pa prevents magnet oxidation during tempering; a tempering temperature of 500-600℃ optimizes the composition and distribution of grain boundary phases, eliminating residual stress generated during sintering; maintaining the minimum operating temperature of the cooling water ensures the stability and uniformity of the air-cooling effect, further improving the performance stability of the magnet. Flexible adjustment of the tempering holding time allows for the fabrication of magnets with different performance requirements.

[0057] The technical mechanism of the material box's full life cycle management lies in: inspecting and removing defective material boxes before use to avoid the introduction of impurities; standardizing transportation to prevent material box damage and ensure structural integrity; and storing in an oven after use to reduce oxidation and moisture adsorption, ensuring that the vacuum environment inside the furnace and the purity of the materials will not be compromised when reused. These measures ensure the stability of the sintering environment at the auxiliary component level, indirectly improving the consistency of product performance.

[0058] The various process steps work in close synergy. Uniform furnace loading provides the foundation for subsequent temperature and vacuum control; progressive degassing provides a clean material environment for high-temperature sintering; high-vacuum enhancement and purification at key nodes optimizes grain boundary formation conditions; high-temperature sintering achieves densification and grain optimization; controllable cooling and tempering ensure stable performance; and material box management ensures process continuity. The overall process system revolves around the core objectives of cleanliness, homogenization, and densification. The coordinated operation of various parameters and steps produces technical results superior to optimization of any single step.

[0059] To make the present invention more fully disclosed, more specific embodiments are described below.

[0060] Example 1:

[0061] 1. Loading the furnace

[0062] Graphite material boxes are selected. After checking that the boxes are free from obvious deformation and cracks, the formed NdFeB green blanks are evenly loaded into the boxes, maintaining a 6mm gap between the green blanks to prevent them from sticking together during sintering. The furnace door of the sintering furnace is opened, and the boxes containing the green blanks are placed into the furnace chamber according to the principle of "layered arrangement". Ten boxes are evenly placed in each layer, and the total number of furnace layers is strictly controlled to be six. The position of the boxes is adjusted to ensure that a 12mm gap is maintained between the boxes and between the boxes and the furnace wall to ensure airflow and uniform temperature field in the furnace. The furnace door is closed and locked tightly.

[0063] 2. First stage of heating and degassing

[0064] The vacuum pumping system of the sintering furnace was started for 30 minutes for pre-evacuation to remove air and residual gases from the furnace. After pre-evacuation, the vacuum level inside the furnace was confirmed to reach 1.0 × 10⁻⁶. -1 Below Pa, the heating program is set to raise the furnace temperature from room temperature to 300℃ at a heating rate of 7℃ / min. After reaching the target temperature range, the heat preservation program is started, and the heat preservation time is set to 60min to complete the removal of physically adsorbed water and low-boiling-point organic matter.

[0065] 3. Second stage of heating and pre-sintering

[0066] After the first stage of heat preservation is completed, there is no need to interrupt the operation of the equipment. Directly set the next stage heating parameters and continue heating at a heating rate of 6℃ / min to 700℃. After reaching the target temperature range, start the heat preservation program and set the heat preservation time to 90min to complete the decomposition of organic binder and the removal of carbonized residues. At the same time, promote the solid diffusion on the surface of powder particles to form a preliminary sintering neck. After the heat preservation is completed, continue heating at a heating rate of 6℃ / min to 850℃. During the heating process, monitor the temperature change in the furnace in real time to ensure that the temperature rises uniformly without fluctuations.

[0067] 4. High vacuum establishment and high temperature sintering

[0068] Once the furnace temperature reaches 850℃, the heating process is paused, and this temperature is maintained for 15 minutes to ensure uniform temperature throughout the furnace. Then, the high-vacuum system is activated to raise the vacuum level inside the furnace to 1.0 × 10⁻⁶. -3 During the process, key sealing areas such as the furnace door gasket and pipe joints are wiped with alcohol swabs for leak detection. The vacuum level is observed to ensure it remains stable. If the vacuum level drops, the sealing problem is investigated and the seal is resealed. After the leak detection is successful, the heating program is set to heat to 1050℃ at a heating rate of 5℃ / min. Once the target temperature range is reached, the holding program is started, with a holding time set to 240min, to complete the densification of the material and the Nd2Fe2O3 reaction. 14 B-phase grain growth.

[0069] 5. Controllable cooling

[0070] After the high-temperature sintering and holding period, the heating module is turned off, and the controllable cooling system is started. The cooling rate is set to 8℃ / min. During the cooling process, inert gas (argon) is introduced into the furnace, and the gas flow rate is controlled at 0.7m³ / min. 3 / h To prevent oxidation of the magnet surface, monitor the furnace temperature in real time, and stop the cooling system and inert gas supply when the temperature drops to 65℃.

[0071] 6. Tempering treatment

[0072] Open the sintering furnace door and quickly transfer the cooled sintered body into the heat treatment furnace. Close and lock the furnace door, and start the vacuum pumping system of the heat treatment furnace to evacuate to a vacuum level better than 1.0 × 10⁻⁶. -1 Set the vacuum level to Pa, maintain this vacuum for 30 minutes to purge the air from the furnace, set the heating program to raise the temperature to the preset tempering temperature of 550℃, hold the temperature for 120 minutes after reaching the target temperature, start the air cooling system to force-cool the sintered body until the furnace temperature drops to room temperature, open the furnace door and take out the finished magnet.

[0073] Example 2:

[0074] 1. Loading the furnace

[0075] Graphite material boxes are selected. After checking that the boxes are free from obvious deformation and cracks, the formed NdFeB green blanks are evenly loaded into the boxes, with a 5mm gap between the green blanks to prevent them from sticking together during sintering. The furnace door of the sintering furnace is opened and the boxes containing the green blanks are placed into the furnace chamber according to the principle of "layered arrangement". Eight boxes are evenly placed in each layer and the total number of furnace layers is strictly controlled to be six. The position of the boxes is adjusted to ensure that a 10mm gap is maintained between the boxes and between the boxes and the furnace wall to ensure airflow and uniform temperature field in the furnace. The furnace door is closed and locked tightly.

[0076] 2. First stage of heating and degassing

[0077] The vacuum pumping system of the sintering furnace was started for 30 minutes for pre-evacuation to remove air and residual gases from the furnace. After pre-evacuation, the vacuum level inside the furnace was confirmed to reach 1.0 × 10⁻⁶. -1 Below Pa, the heating program is set to raise the furnace temperature from room temperature to 250°C at a heating rate of 5°C / min. After reaching the target temperature range, the heat preservation program is started, and the heat preservation time is set to 90min to complete the removal of physically adsorbed water and low-boiling-point organic matter.

[0078] 3. Second stage of heating and pre-sintering

[0079] After the first stage of heat preservation is completed, there is no need to interrupt the operation of the equipment. Directly set the next stage heating parameters and continue heating at a heating rate of 5℃ / min to 650℃. After reaching the target temperature range, start the heat preservation program and set the heat preservation time to 120min to complete the decomposition of organic binder and the removal of carbonized residues. At the same time, promote the solid diffusion on the surface of powder particles to form a preliminary sintering neck. After the heat preservation is completed, continue heating at a heating rate of 5℃ / min to 820℃. During the heating process, monitor the temperature change in the furnace in real time to ensure that the temperature rises uniformly without fluctuations.

[0080] 4. High vacuum establishment and high temperature sintering

[0081] Once the furnace temperature reaches 820℃, the heating process is paused, and this temperature is maintained for 20 minutes to ensure uniform temperature throughout the furnace. Then, the high-vacuum system is activated to raise the vacuum level inside the furnace to 1.0 × 10⁻⁶. -3 During the process, key sealing areas such as the furnace door gasket and pipe joints are wiped with alcohol swabs for leak detection. The vacuum level is observed to ensure it remains stable. If the vacuum level drops, the sealing problem is investigated and the seal is resealed. After the leak detection is successful, the heating program is set to heat to 1030℃ at a heating rate of 4℃ / min. Once the target temperature range is reached, the holding program is started, with a holding time set to 300min, to complete the densification of the material and the Nd2Fe2O3 reaction. 14 B-phase grain growth.

[0082] 5. Controllable cooling

[0083] After the high-temperature sintering and holding period, the heating module is turned off, and the controllable cooling system is started. The cooling rate is set to 6℃ / min. During the cooling process, inert gas (nitrogen) is introduced into the furnace, and the gas flow rate is controlled at 0.6m³ / min. 3 / h To prevent oxidation of the magnet surface, monitor the furnace temperature in real time, and stop the cooling system and inert gas supply when the temperature drops to 60℃.

[0084] 6. Tempering treatment

[0085] Open the sintering furnace door and quickly transfer the cooled sintered body into the heat treatment furnace. Close and lock the furnace door, and start the vacuum pumping system of the heat treatment furnace to evacuate to a vacuum level better than 1.0 × 10⁻⁶. -1 Set the vacuum level to Pa, maintain this vacuum for 30 minutes to purge the air from the furnace, set the heating program to raise the temperature to the preset tempering temperature of 530℃, hold the temperature for 150 minutes after reaching the target temperature, start the air cooling system to force-cool the sintered body until the furnace temperature drops to room temperature, open the furnace door and take out the finished magnet.

[0086] Example 3:

[0087] 1. Loading the furnace

[0088] Graphite material boxes are selected. After checking that the boxes are free from obvious deformation and cracks, the formed NdFeB green blanks are evenly loaded into the boxes, maintaining an 8mm gap between the green blanks to prevent them from sticking together during sintering. The furnace door of the sintering furnace is opened, and the boxes containing the green blanks are placed into the furnace chamber according to the principle of "layered arrangement". 12 boxes are evenly placed in each layer, and the total number of furnace layers is strictly controlled to be six. The position of the boxes is adjusted to ensure that there is a 15mm gap between the boxes and between the boxes and the furnace wall to ensure airflow and uniform temperature field in the furnace. The furnace door is closed and locked tightly.

[0089] 2. First stage of heating and degassing

[0090] The vacuum pumping system of the sintering furnace was started for 30 minutes for pre-evacuation to remove air and residual gases from the furnace. After pre-evacuation, the vacuum level inside the furnace was confirmed to reach 1.0 × 10⁻⁶. -1 Below Pa, the heating program is set to raise the furnace temperature from room temperature to 380℃ at a heating rate of 10℃ / min. After reaching the target temperature range, the heat preservation program is started, and the heat preservation time is set to 30min to complete the removal of physically adsorbed water and low-boiling-point organic matter.

[0091] 3. Second stage of heating and pre-sintering

[0092] After the first stage of heat preservation is completed, there is no need to interrupt the operation of the equipment. Directly set the next stage heating parameters and continue heating at a heating rate of 8℃ / min to 780℃. After reaching the target temperature range, start the heat preservation program and set the heat preservation time to 60min to complete the decomposition of organic binder and the removal of carbonized residues. At the same time, promote the solid diffusion on the surface of powder particles to form a preliminary sintering neck. After the heat preservation is completed, continue heating at a heating rate of 8℃ / min to 880℃. During the heating process, monitor the temperature change in the furnace in real time to ensure that the temperature rises uniformly without fluctuations.

[0093] 4. High vacuum establishment and high temperature sintering

[0094] Once the furnace temperature reaches 880℃, the heating process is paused, and this temperature is maintained for 10 minutes to ensure uniform temperature throughout the furnace. Then, the high-vacuum system is activated to raise the vacuum level inside the furnace to 1.0 × 10⁻⁶. -3 During the process, key sealing areas such as the furnace door gasket and pipe joints are wiped with alcohol swabs for leak detection. The vacuum level is observed to ensure it remains stable. If the vacuum level drops, the sealing problem is investigated and the seal is resealed. After the leak detection is successful, the heating program is set to heat to 1080℃ at a heating rate of 10℃ / min. Once the target temperature range is reached, the holding program is started, with a holding time set to 180min, to complete the densification of the material and the Nd2Fe2O3 reaction. 14 B-phase grain growth.

[0095] 5. Controllable cooling

[0096] After the high-temperature sintering and holding period, the heating module is turned off, and the controllable cooling system is started. The cooling rate is set to 12℃ / min. During the cooling process, inert gas (argon) is introduced into the furnace, and the gas flow rate is controlled at 0.9m³ / min. 3 / h To prevent oxidation of the magnet surface, monitor the furnace temperature in real time, and stop the cooling system and inert gas supply when the temperature drops to 68℃.

[0097] 6. Tempering treatment

[0098] Open the sintering furnace door and quickly transfer the cooled sintered body into the heat treatment furnace. Close and lock the furnace door, and start the vacuum pumping system of the heat treatment furnace to evacuate to a vacuum level better than 1.0 × 10⁻⁶. -1 Set the vacuum level to Pa, maintain this vacuum for 30 minutes to purge the air from the furnace, set the heating program to raise the temperature to the preset tempering temperature of 580℃, hold the temperature for 90 minutes after reaching the target temperature, start the air cooling system to force-cool the sintered body until the furnace temperature drops to room temperature, open the furnace door and take out the finished magnet.

[0099] Example 4:

[0100] 1. Loading the furnace

[0101] Graphite material boxes are selected. After checking that the boxes are free from obvious deformation and cracks, the formed NdFeB green blanks are evenly loaded into the boxes, with a 7mm gap between the green blanks to prevent them from sticking together during sintering. The furnace door of the sintering furnace is opened and the boxes containing the green blanks are placed into the furnace chamber according to the principle of "layered arrangement". Nine boxes are evenly placed in each layer and the total number of furnace layers is strictly controlled to be six. The position of the boxes is adjusted to ensure that a 13mm gap is maintained between the boxes and between the boxes and the furnace wall to ensure airflow and uniform temperature field in the furnace. The furnace door is closed and locked tightly.

[0102] 2. First stage of heating and degassing

[0103] The vacuum pumping system of the sintering furnace was started for 30 minutes for pre-evacuation to remove air and residual gases from the furnace. After pre-evacuation, the vacuum level inside the furnace was confirmed to reach 1.0 × 10⁻⁶. -1 Below Pa, the heating program is set to raise the furnace temperature from room temperature to 280°C at a heating rate of 6°C / min. After reaching the target temperature range, the heat preservation program is started, and the heat preservation time is set to 75min to complete the removal of physically adsorbed water and low-boiling-point organic matter.

[0104] 3. Second stage of heating and pre-sintering

[0105] After the first stage of heat preservation is completed, there is no need to interrupt the operation of the equipment. Directly set the next stage heating parameters and continue heating at a rate of 7℃ / min to 680℃. After reaching the target temperature range, start the heat preservation program and set the heat preservation time to 100min to complete the decomposition of organic binder and the removal of carbonized residues. At the same time, promote the solid diffusion on the surface of powder particles to form a preliminary sintering neck. After the heat preservation is completed, continue heating at a rate of 7℃ / min to 840℃. During the heating process, monitor the temperature change in the furnace in real time to ensure that the temperature rises uniformly without fluctuations.

[0106] 4. High vacuum establishment and high temperature sintering

[0107] Once the furnace temperature reaches 840℃, the heating process is paused, and this temperature is maintained for 25 minutes to ensure uniform temperature throughout the furnace. Then, the high-vacuum system is activated to raise the vacuum level inside the furnace to 1.0 × 10⁻⁶. -3 During the process, key sealing areas such as the furnace door gasket and pipe joints are wiped with alcohol swabs for leak detection. The vacuum level is observed to ensure it remains stable. If the vacuum level drops, the sealing problem is investigated and the seal is resealed. After the leak detection is successful, the heating program is set to heat to 1040℃ at a heating rate of 6℃ / min. Once the target temperature range is reached, the holding program is started, with a holding time set to 270min, to complete the densification of the material and the Nd2Fe2O3 reaction. 14 B-phase grain growth.

[0108] 5. Controllable cooling

[0109] After the high-temperature sintering and holding period, the heating module is turned off, and the controllable cooling system is started. The cooling rate is set to 9℃ / min. During the cooling process, inert gas (nitrogen) is introduced into the furnace, and the gas flow rate is controlled at 0.8m³ / min. 3 / h To prevent oxidation of the magnet surface, monitor the furnace temperature in real time, and stop the cooling system and inert gas supply when the temperature drops to 58℃.

[0110] 6. Tempering treatment

[0111] Open the sintering furnace door and quickly transfer the cooled sintered body into the heat treatment furnace. Close and lock the furnace door, and start the vacuum pumping system of the heat treatment furnace to evacuate to a vacuum level better than 1.0 × 10⁻⁶. -1 Set the vacuum level to Pa, maintain this vacuum for 30 minutes to purge the air from the furnace, set the heating program to raise the temperature to the preset tempering temperature of 540℃, hold the temperature for 180 minutes after reaching the target temperature, start the air cooling system to force-cool the sintered body until the furnace temperature drops to room temperature, open the furnace door and take out the finished magnet.

[0112] Example 5:

[0113] 1. Loading the furnace

[0114] Graphite material boxes are selected. After checking that the boxes are free from obvious deformation and cracks, the formed NdFeB green blanks are evenly loaded into the boxes, maintaining a 6.5mm gap between the green blanks to prevent them from sticking together during sintering. The furnace door of the sintering furnace is opened, and the boxes containing the green blanks are placed into the furnace chamber according to the principle of "layered arrangement". 11 boxes are evenly placed in each layer, and the total number of furnace layers is strictly controlled to be six. The position of the boxes is adjusted to ensure that a 14mm gap is maintained between the boxes and between the boxes and the furnace wall to ensure airflow and uniform temperature field in the furnace. The furnace door is closed and locked tightly.

[0115] 2. First stage of heating and degassing

[0116] The vacuum pumping system of the sintering furnace was started for 30 minutes for pre-evacuation to remove air and residual gases from the furnace. After pre-evacuation, the vacuum level inside the furnace was confirmed to reach 1.0 × 10⁻⁶. -1 Below Pa, the heating program is set to raise the furnace temperature from room temperature to 350℃ at a heating rate of 9℃ / min. After reaching the target temperature range, the heat preservation program is started, and the heat preservation time is set to 45min to complete the removal of physically adsorbed water and low-boiling-point organic matter.

[0117] 3. Second stage of heating and pre-sintering

[0118] After the first stage of heat preservation is completed, there is no need to interrupt the operation of the equipment. Directly set the next stage heating parameters and continue heating at a heating rate of 6℃ / min to 720℃. After reaching the target temperature range, start the heat preservation program and set the heat preservation time to 80min to complete the decomposition of organic binder and the removal of carbonized residues. At the same time, promote the solid diffusion on the surface of powder particles to form a preliminary sintering neck. After the heat preservation is completed, continue heating at a heating rate of 6℃ / min to 860℃. During the heating process, monitor the temperature change in the furnace in real time to ensure that the temperature rises uniformly without fluctuations.

[0119] 4. High vacuum establishment and high temperature sintering

[0120] Once the furnace temperature reaches 860℃, the heating process is paused, and this temperature is maintained for 18 minutes to ensure uniform temperature throughout the furnace. Then, the high-vacuum system is activated to raise the vacuum level inside the furnace to 1.0 × 10⁻⁶. -3 During the process, key sealing areas such as the furnace door gasket and pipe joints are wiped with alcohol swabs for leak detection. The vacuum level is observed to ensure it remains stable. If the vacuum level drops, the sealing problem is investigated and the seal is resealed. After the leak detection is successful, the heating program is set to heat to 1060℃ at a heating rate of 8℃ / min. Once the target temperature range is reached, the holding program is started, with a holding time set to 210min, to complete the densification of the material and the Nd2Fe2O3 reaction. 14 B-phase grain growth.

[0121] 5. Controllable cooling

[0122] After the high-temperature sintering and holding period, the heating module is turned off, and the controllable cooling system is started. The cooling rate is set to 10℃ / min. During the cooling process, inert gas (argon) is introduced into the furnace, and the gas flow rate is controlled at 0.85m³ / min. 3 / h To prevent oxidation of the magnet surface, monitor the furnace temperature in real time, and stop the cooling system and inert gas supply when the temperature drops to 62℃.

[0123] 6. Tempering treatment

[0124] Open the sintering furnace door and quickly transfer the cooled sintered body into the heat treatment furnace. Close and lock the furnace door, and start the vacuum pumping system of the heat treatment furnace to evacuate to a vacuum level better than 1.0 × 10⁻⁶. -1 Set the vacuum level to Pa, maintain this vacuum for 30 minutes to purge the air from the furnace, set the heating program to raise the temperature to the preset tempering temperature of 560℃, hold the temperature for 130 minutes after reaching the target temperature, start the air cooling system to force-cool the sintered body until the furnace temperature drops to room temperature, open the furnace door and take out the finished magnet.

[0125] Example 6:

[0126] 1. Loading the furnace

[0127] Graphite material boxes are selected. After checking that the boxes are free from obvious deformation and cracks, the formed NdFeB green blanks are evenly loaded into the boxes, maintaining a 6mm gap between the green blanks to prevent them from sticking together during sintering. The furnace door of the sintering furnace is opened, and the boxes containing the green blanks are placed into the furnace chamber according to the principle of "layered arrangement". Ten boxes are evenly placed in each layer, and the total number of furnace layers is strictly controlled to be six. The position of the boxes is adjusted to ensure that a 12mm gap is maintained between the boxes and between the boxes and the furnace wall to ensure airflow and uniform temperature field in the furnace. The furnace door is closed and locked tightly.

[0128] 2. First stage of heating and degassing

[0129] The vacuum pumping system of the sintering furnace was started for 30 minutes for pre-evacuation to remove air and residual gases from the furnace. After pre-evacuation, the vacuum level inside the furnace was confirmed to reach 1.0 × 10⁻⁶. -1 Below Pa, the heating program is set to raise the furnace temperature from room temperature to 320°C at a heating rate of 8°C / min. After reaching the target temperature range, the heat preservation program is started, and the heat preservation time is set to 50min to complete the removal of physically adsorbed water and low-boiling-point organic matter.

[0130] 3. Second stage of heating and pre-sintering

[0131] After the first stage of heat preservation is completed, there is no need to interrupt the operation of the equipment. Directly set the next stage heating parameters and continue heating at a heating rate of 7℃ / min to 750℃. After reaching the target temperature range, start the heat preservation program and set the heat preservation time to 70min to complete the decomposition of organic binder and the removal of carbonized residues. At the same time, promote the solid diffusion on the surface of powder particles to form a preliminary sintering neck. After the heat preservation is completed, continue heating at a heating rate of 7℃ / min to 870℃. During the heating process, monitor the temperature change in the furnace in real time to ensure that the temperature rises uniformly without fluctuations.

[0132] 4. High vacuum establishment and high temperature sintering

[0133] Once the furnace temperature reaches 870℃, the heating process is paused, and this temperature is maintained for 12 minutes to ensure uniform temperature throughout the furnace. Then, the high-vacuum system is activated to raise the vacuum level inside the furnace to 1.0 × 10⁻⁶. -3 During the process, key sealing areas such as the furnace door gasket and pipe joints are wiped with alcohol swabs for leak detection. The vacuum level is observed to ensure it remains stable. If the vacuum level drops, the sealing problem is investigated and the seal is resealed. After the leak detection is successful, the heating program is set to heat to 1070℃ at a heating rate of 7℃ / min. Once the target temperature range is reached, the holding program is started, with a holding time set to 200min, to complete the densification of the material and the Nd2Fe2O3 reaction. 14 B-phase grain growth.

[0134] 5. Controllable cooling

[0135] After the high-temperature sintering and holding period, the heating module is turned off, and the controllable cooling system is started. The cooling rate is set to 9℃ / min. During the cooling process, inert gas (argon) is introduced into the furnace, and the gas flow rate is controlled at 0.75m³ / min. 3 / h To prevent oxidation of the magnet surface, monitor the furnace temperature in real time, and stop the cooling system and inert gas supply when the temperature drops to 63℃.

[0136] 6. Tempering treatment

[0137] Open the sintering furnace door and quickly transfer the cooled sintered body into the heat treatment furnace. Close and lock the furnace door, and start the vacuum pumping system of the heat treatment furnace to evacuate to a vacuum level better than 1.0 × 10⁻⁶. -1 Set the vacuum level to Pa, maintain this vacuum for 30 minutes to purge the air from the furnace, set the heating program to raise the temperature to the preset tempering temperature of 570℃, hold the temperature for 110 minutes after reaching the target temperature, start the air cooling system to force-cool the sintered body until the furnace temperature drops to room temperature, open the furnace door and take out the finished magnet.

[0138] Comparative Example 1:

[0139] Compared with Example 6, only the high vacuum establishment and high temperature sintering steps did not involve alcohol leak testing; the remaining steps were completely identical to Example 6.

[0140] High vacuum establishment and high-temperature sintering: After the furnace temperature reaches 870℃, the heating process is paused, and this temperature is maintained for 12 minutes to ensure uniform temperature throughout the furnace. Then, the high vacuum system is activated to raise the vacuum level inside the furnace to 1.0 × 10⁻⁶. -3 Without performing an alcohol leak test, the heating program was directly set to heat to 1070℃ at a rate of 7℃ / min. After reaching the target temperature range, the holding program was initiated, with a holding time set to 200min, to complete the densification of the material and the Nd2Fe... 14 B-phase grain growth.

[0141] Comparative Example 2:

[0142] Compared with Example 6, only the high vacuum establishment and high temperature sintering steps were not stabilized at the same temperature; the rest of the steps were completely the same as in Example 6.

[0143] High vacuum establishment and high-temperature sintering: After the furnace temperature reached 870℃, the heating process was not paused; the high vacuum system was directly activated to raise the vacuum level inside the furnace to 1.0×10⁻⁶. -3During the process, key sealing areas such as the furnace door gasket and pipe joints are wiped with alcohol swabs for leak detection. The vacuum level is observed to ensure it remains stable. If the vacuum level drops, the sealing problem is investigated and the seal is resealed. After the leak detection is successful, the heating program is set to heat to 1070℃ at a heating rate of 7℃ / min. Once the target temperature range is reached, the holding program is started, with a holding time set to 200min, to complete the densification of the material and the Nd2Fe2O3 reaction. 14 B-phase grain growth.

[0144] Comparative Example 3:

[0145] Compared with Example 6, only the total number of furnace loading layers is different in the furnace loading step; the rest of the steps are completely the same as in Example 6.

[0146] Furnace loading: Select graphite material boxes. After checking that the boxes are free from obvious deformation and cracks, evenly load the formed NdFeB green billets into the boxes, maintaining a 6mm gap between the billets to prevent them from sticking together during sintering. Open the sintering furnace door and place the boxes containing the green billets into the furnace chamber according to the "layered arrangement" principle. Place 10 boxes evenly in each layer and control the total number of loading layers to five. Adjust the position of the boxes to ensure that there is a 12mm gap between the boxes and between the boxes and the furnace wall to ensure airflow and uniform temperature field in the furnace. Close the furnace door and lock it tightly.

[0147] Comparative Example 4:

[0148] Compared with Example 6, only the heating rate of the first stage heating and degassing steps is different; the remaining steps are completely the same as in Example 6.

[0149] The first stage of heating and degassing: The vacuum pumping system of the sintering furnace is started for 30 minutes of pre-vacuuming to remove air and residual gases from the furnace. After the pre-vacuuming is completed, the vacuum level inside the furnace is confirmed to reach 1.0 × 10⁻⁶. -1 Below Pa, the heating program is set to raise the furnace temperature from room temperature to 320℃ at a heating rate of 12℃ / min. After reaching the target temperature range, the heat preservation program is started, and the heat preservation time is set to 50min to complete the removal of physically adsorbed water and low-boiling-point organic matter.

[0150] Comparative Example 5:

[0151] Compared with Example 6, only the second stage heating and the 600-800℃ holding time in the pre-sintering step are different; the rest of the steps are completely the same as in Example 6.

[0152] The second stage of heating and pre-sintering: After the first stage of holding is completed, there is no need to interrupt the equipment operation. Directly set the next stage heating parameters and continue heating at a rate of 7℃ / min to 750℃. After reaching the target temperature range, start the holding program. The holding time is set to 30min (less than 60-150min). This completes the decomposition of organic binder and the removal of carbonized residues, while promoting solid diffusion on the surface of powder particles to form a preliminary sintering neck. After the holding is completed, continue heating at a rate of 7℃ / min to 870℃. During the heating process, monitor the temperature changes in the furnace in real time to ensure that the temperature rises uniformly without fluctuations.

[0153] Performance index testing, results, and analysis:

[0154] I. Testing and Experimentation

[0155] (a) The neodymium iron boron permanent magnets prepared in Examples 1-6 and Comparative Examples 1-5 were selected for testing. Ten parallel samples were randomly selected from each sample. After removing surface impurities and burrs, they were cut into uniform sizes (10mm×10mm×5mm) for testing to ensure consistent testing conditions.

[0156] (II) Detection Methods

[0157] 1. Remanence (Br): A vibrating sample magnetometer was used, the test temperature was 25℃, the test accuracy was ±0.001T, and each sample was tested 3 times and the average value was taken.

[0158] 2. Intrinsic coercivity (Hcj): A pulse magnetometer was used, the test temperature was 25℃, the test accuracy was ±1kA / m, and each sample was tested twice and the average value was taken.

[0159] 3. Maximum magnetic energy product ((BH)max): Calculated after measuring the hysteresis loop using a hysteresis loop meter, with a measurement accuracy of ±0.01 kJ / m. 3 ;

[0160] 4. Magnetic coercivity (Hcb): Synchronously detected using a pulse magnetometer, test temperature 25℃, test accuracy ±1kA / m;

[0161] 5. Coercivity ratio (HK / Hcj): Calculated from the detection data of Hk and Hcj, rounded to one decimal place (Hk is detected synchronously by the hysteresis loop instrument).

[0162] 6. Magnetic polarization intensity ((BH)max-PC): Measured by a hysteresis loop meter and rounded to two decimal places.

[0163] (III) Testing Environment The testing environment temperature is controlled at 25±2℃, relative humidity at 50±5%, with no magnetic field interference, and all equipment is qualified by metrology calibration.

[0164] II. Test Results

[0165] The core performance test results of each embodiment and comparative example are shown in Table 1:

[0166]

[0167] Comparative Data Analysis and Theoretical Analysis:

[0168] (I) Comparative Analysis of Core Magnetic Performance Indicators

[0169] Remanence (Br): The Br values ​​of Examples 1-6 ranged from 0.986 to 1.032 T, with Example 6 at 1.032 T and Example 3 at 1.029 T, all higher than all comparative examples. Comparative Example 4 had the lowest Br value of only 0.979 T due to the heating rate in the first stage exceeding the range defined in the claims; Comparative Example 3 had a Br value of 0.998 T, lower than Examples 5-6, because the number of furnace layers deviated from the six-layer design.

[0170] Intrinsic coercivity (Hcj): The Hcj values ​​of the examples ranged from 518 to 620 kA / m, with Example 6 leading at 620 kA / m and Example 3 at 616 kA / m. The Hcj values ​​of the comparative examples were concentrated in the range of 563 to 588 kA / m, all lower than those of Examples 5 and 6. Comparative Example 1 did not undergo alcohol leak testing, and insufficient vacuum sealing led to slight oxidation of rare earth elements, resulting in an Hcj of 588 kA / m, which differed from Example 6 by 32 kA / m.

[0171] Maximum magnetic energy product ((BH)max): In the examples, (BH)max is 169.47-191.27 kJ / m 3 Between, Example 6 had 191.27 kJ / m 3 The highest value was 189.63 kJ / m³ in Example 3. 3 The (BH)max of the comparative example is 165.72-176.83 kJ / m³. 3 The difference between this and Example 6 is 14.44-25.55 kJ / m³. 3 In Comparative Example 5, due to insufficient heat preservation time at 600-800℃, the (BH)max was only 167.35 kJ / m². 3 The difference is most obvious.

[0172] Magnetic coercivity (Hcb): The Hcb values ​​of the examples are between 503-605 kA / m, 605 kA / m in example 6, and 600 kA / m in example 3; the Hcb values ​​of the comparative examples are between 548-572 kA / m, all lower than those of examples 5-6, and the trend is consistent with Hcj, reflecting the overall difference in the magnet's resistance to demagnetization.

[0173] Coercivity ratio (HK / Hcj): The HK / Hcj ratios of the examples are between 93.8% and 95.9%, with Example 6 having the highest ratio of 95.9%, indicating that the squareness of the demagnetization curve of the magnets in the examples is better and the performance stability is stronger; the ratios of the comparative examples are between 93.4% and 94.6%, all lower than that of Example 6. Among them, Comparative Example 4 has the worst stability because its ratio is only 93.4% due to its excessively fast heating rate.

[0174] Magnetic polarization intensity ((BH)max-PC): The (BH)max-PC of the examples is between 1.08 and 1.12, that of example 4 is 1.12, and that of example 6 is 1.10; the values ​​of the comparative examples are between 1.03 and 1.07, all of which are lower than those of the examples, indicating that the magnetic polarization capability of the comparative magnets is weaker under the maximum magnetic energy product state.

[0175] (II) Theoretical Analysis

[0176] 1. The necessity of alcohol leak testing: Comparative Example 1 did not undergo alcohol leak testing, and the vacuum system's sealing defects allowed a small amount of air to seep in. The oxide impurities generated by the reaction of rare earth elements with oxygen deposited at the grain boundaries, damaging Nd2Fe. 14 The continuity of the B main phase leads to a decrease in key indicators such as Hcj and (BH)max. The example uses alcohol leak detection to ensure high vacuum sealing, reduce oxidation contamination, guarantee grain boundary purity, and thus improve magnetic properties.

[0177] 2. Technical Value of Temperature Stabilization: In Comparative Example 2, the temperature was not stabilized before the establishment of high vacuum, resulting in uneven furnace temperature within the 800-900℃ range. In some areas, impurities did not volatilize sufficiently, and in others, grains grew prematurely, leading to decreased microstructure uniformity, manifested as lower Br and HK / Hcj ratios compared to Example 6. In this example, the temperature was stabilized within this range for 5-30 minutes, ensuring a uniform temperature field and allowing impurity volatilization and grain pretreatment to proceed simultaneously, laying a uniform microstructure foundation for high-temperature sintering.

[0178] 3. Design Logic of Furnace Loading Layers: Comparative Example 3 changed the number of furnace loading layers to five, breaking the standardized design of six layers. This resulted in poor airflow and uneven temperature distribution within the furnace, leading to differences in the sintering degree of materials at different locations, decreased microstructural consistency, and lower Br and (BH)max compared to Example 6. The standardized six-layer furnace loading in Example 6, through reasonable spacing design, ensures uniform temperature and airflow, improving product performance consistency from the source.

[0179] 4. Importance of parameter coordination: The heating rate of Comparative Example 4 exceeded the limit of the claims. The excessively rapid heating resulted in insufficient removal of low-boiling-point organic matter. During high-temperature sintering, the decomposition produced gas, forming pore defects and causing a comprehensive decline in magnetic properties. In Comparative Example 5, the holding time at 600-800℃ was insufficient. The decomposition of organic binder and the residual carbonized substances contaminated the grain boundaries, hindering atomic diffusion and densification processes.

[0180] Those skilled in the art will recognize that numerous variations are possible with respect to the above description, and the embodiments are merely illustrative of one or more specific implementations.

[0181] Although exemplary embodiments of the invention have been described and illustrated, those skilled in the art will understand that various changes and substitutions can be made thereto without departing from the spirit of the invention. Furthermore, many modifications can be made to adapt specific situations to the doctrine of the invention without departing from the central concepts of the invention described herein. Therefore, the invention is not limited to the specific embodiments disclosed herein, but may include all embodiments and equivalents that fall within the scope of the invention.

[0182] The above description, in conjunction with specific embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various substitutions or modifications can be made to these described embodiments without departing from the inventive concept, and all such substitutions or modifications should be considered within the scope of protection of the present invention.

[0183] Although the invention and its advantages have been described in detail, it should be understood that various changes, substitutions, and modifications can be made without departing from the spirit and scope of the invention. Furthermore, the scope of the invention is not limited to the specific embodiments of the processes, methods, and steps described in the specification. From the disclosure of this invention, those skilled in the art will readily utilize existing or future processes, methods, steps that substantially perform the same function or achieve the same results as the corresponding embodiments described herein. Therefore, the appended claims are intended to cover such processes, methods, steps.

Claims

1. A multi-stage sintering process for neodymium iron boron permanent magnet materials, characterized in that, Includes the following steps: S1. Loading the furnace; S2. First stage heating and degassing; S3. Second stage heating and pre-sintering; S4. High vacuum establishment and high temperature sintering; S5. Controlled cooling; S6. Tempering treatment.

2. The multi-stage sintering process for NdFeB permanent magnet materials according to claim 1, characterized in that, The specific steps for loading the furnace are as follows: the formed NdFeB green billets are loaded into the material boxes of the sintering furnace. The material boxes are arranged in layers in the furnace, with 8-12 material boxes evenly placed in each layer. The total number of loading layers is six.

3. The multi-stage sintering process for NdFeB permanent magnet materials according to claim 1, characterized in that, The specific steps for the first stage of heating and degassing are as follows: after loading the furnace, vacuum gas is first pumped out for 30 minutes, and then the furnace temperature is raised from room temperature to 200-400℃ at a heating rate of 5-10℃ / min, and then kept at this temperature range.

4. The multi-stage sintering process for NdFeB permanent magnet materials according to claim 1, characterized in that, The specific steps for the second stage of heating and pre-sintering are as follows: the first stage of heating and degassing continues to heat up to 600-800℃ at a heating rate of 5-8℃ / min, and is held at this temperature range; then the temperature is increased to 800-900℃ at a heating rate of 5-8℃ / min.

5. The multi-stage sintering process for NdFeB permanent magnet materials according to claim 1, characterized in that, The specific steps for establishing high vacuum and high-temperature sintering are as follows: After heating to 800-900℃, stabilize the temperature within this range for 5-30 minutes, and then increase the vacuum level inside the furnace to 1.0×10⁻⁶. -3 During the process, alcohol is used to check for leaks in the equipment, and then the temperature is increased to 1000-1100℃ at a rate of 3-12℃ / min, and held within this temperature range.

6. The multi-stage sintering process for NdFeB permanent magnet materials according to claim 1, characterized in that, The specific steps for controlled cooling are as follows: After the sintering process is completed, the sintered body is cooled to below 70°C at a cooling rate of 5-15°C / min.

7. The multi-stage sintering process for NdFeB permanent magnet materials according to claim 1, characterized in that, The specific steps of tempering are as follows: place the cooled sintered body in a heat treatment furnace and evacuate to a vacuum level better than 1.0 × 10⁻⁶. -1 After maintaining a vacuum level of Pa for 30 minutes, the temperature is raised to the tempering temperature and held for a period of time, followed by forced cooling using air cooling.

8. The multi-stage sintering process for NdFeB permanent magnet materials according to claim 3, characterized in that, The holding time at 200-400℃ during the furnace loading process is 30-90 minutes.

9. The multi-stage sintering process for NdFeB permanent magnet materials according to claim 4, characterized in that, The holding time at 600-800℃ during the second stage of heating and pre-sintering is 60-150 minutes.

10. The multi-stage sintering process for NdFeB permanent magnet materials according to claim 5, characterized in that, The holding time at 1000-1100℃ during the high vacuum establishment and high temperature sintering steps is 120-480 minutes.

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