A recycled sintered neodymium-iron-boron magnet and a method for producing the same
The composite magnetic powder preparation method solves the problem of recycling waste sintered NdFeB magnets, achieving efficient recycling and performance improvement, and is suitable for industrial applications.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- BEIKUANG MAGNETS FUYANG CO LTD
- Filing Date
- 2026-05-09
- Publication Date
- 2026-06-23
Smart Images
Figure CN122266910A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of sintered NdFeB magnet preparation technology, and more specifically, to a regenerated sintered NdFeB magnet and its preparation method. Background Technology
[0002] Sintered NdFeB magnets, as permanent magnet materials with the best overall performance, are widely used in strategic industries such as new energy vehicles, wind power generation, and industrial servo systems. Global demand for high-performance sintered NdFeB magnets continues to grow, but traditional sintered NdFeB magnets suffer from two major problems: first, they rely heavily on heavy rare earth elements (Dy / Tb, 2.5%-3%) to improve coercivity, resulting in high production costs; second, their coercivity decays severely at high temperatures, grain boundaries are prone to oxidation, and corrosion resistance is insufficient, failing to meet the long-term stable operation requirements of high-end equipment.
[0003] Meanwhile, with the widespread application of sintered NdFeB magnets, a large number of waste magnets are constantly being generated. These waste magnets contain abundant rare earth resources, and direct disposal not only causes a serious waste of rare earth resources but also leads to environmental pollution problems.
[0004] Currently, the main recycling methods for waste NdFeB magnets include pyrometallurgical recycling and wet recycling. However, these methods have drawbacks such as complex processes, high energy consumption, and limited rare earth recovery rates. Furthermore, they are difficult to directly preserve the original crystal structure and magnetic properties of the magnets. The performance of regenerated magnets is often far lower than that of original magnets, which limits their application in high-end fields. In existing technologies, single-element doping or traditional regeneration processes are difficult to balance the magnetic properties, high-temperature stability, corrosion resistance and cost control of magnets, and there is a lack of technical solutions for preparing high-performance magnets by regenerating waste magnetic blocks and mixing them with conventional dual alloy powders.
[0005] Therefore, we propose a method for regenerating sintered NdFeB magnets and its preparation to solve the above problems. Summary of the Invention
[0006] In order to overcome the above-mentioned defects of the prior art, the embodiments of the present invention provide a regenerated sintered NdFeB magnet and a method for preparing the same, so as to solve the problems mentioned in the background art.
[0007] To achieve the above objectives, the present invention provides the following technical solution: a regenerated sintered NdFeB magnet, wherein the regenerated sintered NdFeB magnet is prepared by magnetic field forming, sintering and aging of composite magnetic powder, wherein the composite magnetic powder is obtained by mixing regenerated magnetic powder and conventional NdFeB bimetallic powder at a mass ratio of 20%-40%:60%-80%; The regenerated magnetic powder is derived from waste sintered NdFeB magnetic blocks and is produced by gas atomization powdering process. The particle size D50 is 3.0μm-4.5μm and the oxygen content is ≤300ppm. The conventional NdFeB bimetallic powder comprises, by mass percentage: Nd 22%-30%, Pr 5%-6%, Dy 0.6%-0.8%, Ho 0.8%-1.0%, Yb 0.15%-0.25%, Nb 0.20%-0.30%, Si 0.04%-0.06%, Cu 0.21%-0.23%, Al 0.31%-0.33%, B 1.00%-1.02%, with the balance being Fe; The main phase of the regenerated sintered NdFeB magnet is The main phase has a grain size of 3-4 μm, and a Nd-Cu-Al-Yb-Si pentagonal composite grain boundary phase is formed at the grain boundaries, with a grain boundary phase continuity of ≥96%.
[0008] In a preferred embodiment, the mass ratio of the regenerated magnetic powder to the conventional NdFeB bimetallic powder is 30%:70%.
[0009] In a preferred embodiment, in the conventional NdFeB bimetallic powder, Ho replaces more than 50% of Dy, and the total amount of heavy rare earth Dy+Ho is 1.4%-1.8%.
[0010] In a preferred embodiment, the conventional NdFeB bimetallic powder has a particle size D50 of 2.7 μm-4.0 μm and an oxygen content of ≤200 ppm.
[0011] In a preferred embodiment, the regenerated sintered NdFeB magnet meets the following performance indicators: room temperature coercivity Hcj ≥ 2000 kA / m, and maximum energy product (BH)max ≥ 400 kJ / m. 3 At 200℃, the coercivity is ≥900kA / m, and the corrosion rate after 1000h of neutral salt spray testing is ≤0.002g / (m²). 2 •h), magnet density ≥7.60g / cm³ 3 Oxygen content ≤500ppm.
[0012] In a preferred embodiment, a method for preparing a regenerated sintered NdFeB magnet includes the following steps: S1. Pre-treatment of waste magnetic blocks: Select waste sintered NdFeB magnetic blocks, the main components of which are... Phase, heavy rare earth content ≤3%, magnetic properties satisfying room temperature coercivity Hcj≥1800kA / m, maximum energy product (BH)max≥400kJ / m 3 After removing surface oil, rust and impurities through mechanical grinding and ultrasonic cleaning, the magnetic blocks are then crushed into 5mm-10mm particles. S2. Waste magnetic block powder making: The pretreated magnetic block particles are melted and then atomized into powder. The powder is then classified and purified to obtain regenerated magnetic powder with a particle size D50 of 3.0-4.5μm and an oxygen content of ≤300ppm. S3. Preparation of conventional NdFeB bimetallic powder: Weigh the following raw materials by mass percentage: Nd 22%-30%, Pr 5%-6%, Dy 0.6%-0.8%, Ho 0.8%-1.0%, Yb 0.15%-0.25%, Nb 0.20%-0.30%, Si 0.04%-0.06%, Cu 0.21%-0.23%, Al 0.31%-0.33%, B 1.00%-1.02%, with the balance being Fe. Then, through vacuum induction melting, dual-zone water-cooled copper mold casting, hydrogen crushing, segmented dehydrogenation, and air jet milling, conventional NdFeB bimetallic powder with a particle size D50 of 2.7μm-4.0μm and an oxygen content ≤200ppm is obtained. S4. Mixing and powder preparation: The regenerated magnetic powder and the conventional NdFeB bimetallic powder are mixed at a mass ratio of 20%-40%:60%-80% to obtain composite magnetic powder; S5. Magnetic field forming: The composite magnetic powder is pressed and formed in an orientation magnetic field to obtain a green blank; S6. Sintering and aging: The green blank is subjected to vacuum sintering and two-stage aging treatment to obtain the regenerated sintered NdFeB magnet.
[0013] In a preferred embodiment, step S2 specifically includes: feeding the pretreated waste sintered NdFeB magnetic block particles into a vacuum induction melting furnace, and melting the particles at a vacuum degree ≤ 2× Under Pa conditions, the temperature is raised to 1520℃-1540℃ and held for 20min-30min to completely melt the magnetic block particles and form a uniform recycled alloy melt. Argon atomization is used to introduce the recycled alloy molten liquid into the atomization chamber through a guide tube with an outlet diameter of 2mm-3mm. The vacuum degree of the atomization chamber is first evacuated to ≤5× Pa, then high-purity argon gas with a purity of 99.9995% is introduced to maintain the pressure in the atomization chamber at 0.3MPa-0.5MPa, and the molten liquid is broken up by impact with a high-speed argon gas jet with a gas velocity of 300m / s-400m / s. During the atomization process, the temperature of the molten liquid is controlled at 1420℃-1480℃, and the argon gas flow rate is 80L / min-100L / min; The atomized powder is classified by a cyclone classifier, collecting powder with a particle size D50 of 3.0-4.5μm, and then subjected to a vacuum degree ≤3× Under Pa conditions, the temperature is first raised to 420℃ and held for 2 hours, then raised to 560℃ and held for 3 hours for vacuum dehydrogenation purification treatment, finally obtaining regenerated magnetic powder with a flowability ≥25s / 50g.
[0014] In a preferred embodiment, steps S3 and S4 specifically include: In step S3, the raw material purity requirements are Fe ≥ 99.99%, Nd / Pr / Dy / Ho ≥ 99.95%, and the remaining metals ≥ 99.6%, and a vacuum degree ≤ 2× A vacuum induction melting process was employed, with a pressure of 1540℃-1560℃ and a holding time of 30 minutes. The copper was then cast using a dual-zone water-cooled mold, where the water temperature in the first zone was 25℃ and the water temperature in the second zone was 15℃. The cooling rate was [missing information]. -10 5 The process involves preparing thin sheets with a thickness of 0.2 mm to 0.5 mm by applying hydrogen pressure at 0.05 MPa to 0.2 MPa for 2.5 h to 5 h, followed by staged dehydrogenation by holding at 400 °C for 1.5 h and then at 540 °C for 2.5 h, and finally air jet milling with 0.15% composite additives to obtain the conventional NdFeB bimetallic powder. In step S4, under argon protection, the regenerated magnetic powder is mixed with the conventional NdFeB bimetallic powder at an argon flow rate of 0.5L / min-1.0L / min, a stirring rate of 300r / min-500r / min, and a stirring time of 30min-60min to obtain a composite magnetic powder with an oxygen content ≤350ppm and a flowability ≥24s / 50g.
[0015] In a preferred embodiment, steps S5 and S6 specifically include: In step S5, the composite magnetic powder is subjected to gradient pressurization in an orientation magnetic field of 1.8T-2.3T, with a pre-pressurization pressure of 90MPa and a holding time of 5s, and a final pressurization pressure of 200MPa and a holding time of 15s, to obtain a density ≥4.0g / cm³. 3 Green blanks with an orientation degree ≥ 97%; In step S6, the green blank is in a vacuum degree ≤3× The regenerated sintered NdFeB magnet was subjected to a stepped heating process in a vacuum sintering furnace at the following rates: 5°C / min from room temperature to 400°C, 3°C / min from 400°C to 840°C, and 2°C / min from 840°C to the sintering temperature. After pre-firing at 840°C for 2 hours, the magnet was sintered at 1040°C-1080°C for 4-7 hours. Subsequently, the temperature was lowered to 880°C-920°C for primary aging and held for 3-7 hours. Then, the temperature was lowered to 440°C-520°C for secondary aging and held for 3-7 hours. Finally, the magnet was cooled to room temperature with the furnace at a cooling rate of 60°C / h to obtain the regenerated sintered NdFeB magnet.
[0016] The technical effects and advantages of this invention are as follows: This invention aims to achieve the resource-based recycling of waste magnetic blocks while ensuring that the magnets possess low dependence on heavy rare earth elements, high magnetic properties, and high stability. The magnets are prepared by mixing regenerated magnetic powder and conventional NdFeB dual-alloy powder in a specific ratio. The regenerated magnetic powder is obtained through gas atomization powdering of waste magnetic blocks, and the conventional NdFeB dual-alloy powder employs a multi-component optimized design. The gas atomization powdering process is shorter, resulting in higher powder sphericity (≥90%) and improved flowability by 15%-20%, which is beneficial for subsequent mixing uniformity and magnetic field orientation. Simultaneously, the rapid solidification process corresponding to gas atomization powdering can suppress elemental segregation, making the multi-component distribution in the dual-alloy powder more uniform and strengthening the synergistic effect of "Nd-Pr-Ho-Yb-Nb-Si". This invention reduces magnet production costs and rare earth resource consumption while achieving efficient recycling of waste magnets. The preparation process is stable and controllable, suitable for industrial mass production. Attached Figure Description
[0017] Figure 1 This is a comparison chart of performance data between the embodiments and comparative examples of the present invention. Detailed Implementation
[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0019] Reference Figure 1 A regenerated sintered NdFeB magnet is prepared by magnetic field forming, sintering and aging of composite magnetic powder. The composite magnetic powder is obtained by mixing regenerated magnetic powder and conventional NdFeB bimetallic powder at a mass ratio of 20%-40%:60%-80%. Among them, the regenerated magnetic powder is derived from waste sintered NdFeB magnetic blocks and is produced by gas atomization powder making process. The particle size D50 is 3.0μm-4.5μm and the oxygen content is ≤300ppm. Conventional NdFeB bimetallic powder, by mass percentage, comprises: Nd 22%-30%, Pr 5%-6%, Dy 0.6%-0.8%, Ho 0.8%-1.0%, Yb 0.15%-0.25%, Nb 0.20%-0.30%, Si 0.04%-0.06%, Cu 0.21%-0.23%, Al 0.31%-0.33%, B 1.00%-1.02%, with the balance being Fe; The main phase of regenerated sintered NdFeB magnets is The main phase has a grain size of 3-4 μm, and a Nd-Cu-Al-Yb-Si pentagonal composite grain boundary phase is formed at the grain boundaries, with a grain boundary phase continuity of ≥96%.
[0020] The mass ratio of recycled magnetic powder to conventional NdFeB bimetallic powder is 30%:70%; In conventional NdFeB bimetallic powder, Ho replaces more than 50% of Dy, and the total amount of heavy rare earth Dy+Ho is 1.4%-1.8%.
[0021] The particle size D50 of conventional NdFeB bimetallic powder is 2.7μm-4.0μm, and the oxygen content is ≤200ppm.
[0022] Regenerated sintered NdFeB magnets meet the following performance specifications: room temperature coercivity Hcj ≥ 2000 kA / m, maximum energy product (BH)max ≥ 400 kJ / m 3 At 200℃, the coercivity is ≥900kA / m, and the corrosion rate after 1000h of neutral salt spray testing is ≤0.002g / (m²). 2 •h), magnet density ≥7.60g / cm³ 3 Oxygen content ≤500ppm.
[0023] A method for preparing a regenerated sintered NdFeB magnet includes the following steps: S1. Pre-treatment of waste magnetic blocks: Select waste sintered NdFeB magnetic blocks. The main components of waste sintered NdFeB magnetic blocks are... Phase, heavy rare earth content ≤3%, magnetic properties satisfying room temperature coercivity Hcj≥1800kA / m, maximum energy product (BH)max≥400kJ / m 3 After removing surface oil, rust and impurities through mechanical grinding and ultrasonic cleaning, the magnetic blocks are then crushed into 5mm-10mm particles. S2. Waste magnetic block powder making: The pretreated magnetic block particles are melted and then atomized into powder. The powder is then classified and purified to obtain regenerated magnetic powder with a particle size D50 of 3.0-4.5μm and an oxygen content of ≤300ppm. Step S2 specifically includes: feeding the pretreated waste sintered NdFeB magnetic block particles into a vacuum induction melting furnace, and melting the particles at a vacuum degree ≤ 2× Under Pa conditions, the temperature is raised to 1520℃-1540℃ and held for 20min-30min to completely melt the magnetic block particles and form a uniform recycled alloy melt. Argon atomization is used to introduce the recycled alloy molten liquid into the atomization chamber through a guide tube with an outlet diameter of 2mm-3mm. The vacuum degree of the atomization chamber is first evacuated to ≤5× Pa, then high-purity argon gas with a purity of 99.9995% is introduced to maintain the pressure in the atomization chamber at 0.3MPa-0.5MPa, and the molten liquid is broken up by impact with a high-speed argon gas jet with a gas velocity of 300m / s-400m / s. During the atomization process, the temperature of the molten liquid is controlled at 1420℃-1480℃, and the argon gas flow rate is 80L / min-100L / min; The atomized powder is classified by a cyclone classifier, collecting powder with a particle size D50 of 3.0-4.5μm, and then subjected to a vacuum degree ≤3× Under Pa conditions, the temperature is first raised to 420℃ and held for 2 hours, then raised to 560℃ and held for 3 hours for vacuum dehydrogenation purification treatment, finally obtaining regenerated magnetic powder with a flowability ≥25s / 50g.
[0024] S3. Preparation of conventional NdFeB bimetallic powder: Weigh the following raw materials by mass percentage: Nd 22%-30%, Pr 5%-6%, Dy 0.6%-0.8%, Ho 0.8%-1.0%, Yb 0.15%-0.25%, Nb 0.20%-0.30%, Si 0.04%-0.06%, Cu 0.21%-0.23%, Al 0.31%-0.33%, B 1.00%-1.02%, with the balance being Fe. Then, through vacuum induction melting, dual-zone water-cooled copper mold casting, hydrogen crushing, segmented dehydrogenation, and air jet milling, conventional NdFeB bimetallic powder with a particle size D50 of 2.7μm-4.0μm and an oxygen content ≤200ppm is obtained. In step S3, the raw material purity requirements are Fe ≥ 99.99%, Nd / Pr / Dy / Ho ≥ 99.95%, and other metals ≥ 99.6%, with a vacuum degree ≤ 2× A vacuum induction melting process was employed, with a pressure of 1540℃-1560℃ and a holding time of 30 minutes. The copper was then cast using a dual-zone water-cooled mold, where the water temperature in the first zone was 25℃ and the water temperature in the second zone was 15℃. The cooling rate was [missing information]. -10 5 Thin sheets with a thickness of 0.2 mm to 0.5 mm were prepared by ℃ / s, followed by hydrogen crushing under hydrogen pressure of 0.05 MPa to 0.2 MPa for 2.5 h to 5 h, staged dehydrogenation by holding at 400℃ for 1.5 h and then at 540℃ for 2.5 h, and air jet milling with 0.15% composite additives to obtain conventional NdFeB bimetallic powder.
[0025] S4. Mixing and powder preparation: Mix the recycled magnetic powder with conventional NdFeB bimetallic powder at a mass ratio of 20%-40%:60%-80% to obtain composite magnetic powder; In step S4, under argon protection, the regenerated magnetic powder is mixed with conventional NdFeB bimetallic powder at an argon flow rate of 0.5L / min-1.0L / min, a stirring rate of 300r / min-500r / min, and a stirring time of 30min-60min to obtain composite magnetic powder with an oxygen content ≤350ppm and a flowability ≥24s / 50g.
[0026] S5. Magnetic Field Molding: The composite magnetic powder is pressurized in an orientation magnetic field to form a green body; in step S5, the composite magnetic powder is subjected to gradient pressing in an orientation magnetic field of 1.8T-2.3T, with a pre-pressurization pressure of 90MPa and a holding time of 5s, and a final pressurization pressure of 200MPa and a holding time of 15s, to obtain a green body with a density ≥4.0g / cm³. 3 Green blanks with an orientation degree ≥ 97%.
[0027] S6. Sintering and aging: The green blank is subjected to vacuum sintering and two-stage aging treatment to obtain regenerated sintered NdFeB magnets.
[0028] In step S6, the green blank is kept under a vacuum degree ≤3× The temperature was increased in a vacuum sintering furnace at a stepwise rate: 5℃ / min from room temperature to 400℃, 3℃ / min from 400℃ to 840℃, and 2℃ / min from 840℃ to the sintering temperature. After pre-firing at 840℃ for 2 hours, the magnet was sintered at 1040℃-1080℃ for 4-7 hours. Then, the temperature was lowered to 880℃-920℃ for primary aging and held for 3-7 hours. The temperature was then lowered to 440℃-520℃ for secondary aging and held for 3-7 hours. Finally, the magnet was cooled to room temperature with the furnace at a cooling rate of 60℃ / h to obtain the regenerated sintered NdFeB magnet.
[0029] Example 1 1. Preparation of regenerated magnetic powder: (1) Raw material pretreatment: The pretreated waste magnetic block particles are put into a vacuum induction melting furnace, and the vacuum degree is ≤2× Under Pa conditions, the temperature is raised to 1520-1540℃ and held for 20-30 minutes to completely melt the magnetic block particles and form a uniform recycled alloy melt, ensuring that there are no unmelted solid particles in the melt.
[0030] (2) Gas atomization powder production: Argon atomization process is adopted. The recycled alloy molten liquid is introduced into the atomization chamber through a guide tube with an outlet diameter of 2-3 mm. The vacuum degree of the atomization chamber is first evacuated to ≤5×10 -2Then, 99.9995% high-purity argon gas is introduced to maintain the pressure in the atomization chamber at 0.3-0.5 MPa. The molten liquid falls under gravity and collides and breaks up with the high-speed argon gas jet (gas velocity 300-400 m / s), forming fine droplets that quickly solidify. During atomization, the molten liquid temperature is controlled to be stable at 1500-1520℃, and the argon gas flow rate is 80-100 L / min to ensure uniform powder particle size.
[0031] (3) Powder classification and purification: The atomized powder is classified by a cyclone classifier, and powder with a particle size D50 of 3.0-4.5μm is collected; then it is subjected to vacuum degassing and purification treatment at a vacuum degree ≤3× Under Pa conditions, the temperature was first raised to 420℃ and held for 2 hours, then raised to 560℃ and held for 3 hours to remove moisture and residual impurities from the powder. The resulting regenerated magnetic powder had an oxygen content ≤300ppm and a flowability ≥25s / 50g.
[0032] 2. Preparation of conventional NdFeB bialloy powder: Raw materials (Nd 25%, Pr 5.5%, Dy 0.7%, Ho 0.9%, Yb 0.2%, Nb 0.25%, Si 0.05%, Cu 0.22%, Al 0.32%, B 0.90%, Fe balance) were weighed according to the optimal composition. After vacuum induction melting, the powder was cast into thin sheets by double-zone water cooling. After hydrogen crushing, dehydrogenation, and air jet milling, bialloy powder with D50=3.2μm and oxygen content of 190ppm was obtained.
[0033] 3. Mixing and powder preparation: Regenerated magnetic powder and bi-alloy powder are mixed at a mass ratio of 30%:70% and stirred at 400r / min for 45min under argon protection to obtain composite magnetic powder.
[0034] 4. Magnetic field forming: Gradient pressure is applied in a 2.0T orientation magnetic field (90MPa×5s→190MPa×15s), green body density is 4.1g / cm³. 3 Orientation degree 97.5%.
[0035] 5. Sintering and aging: The vacuum sintering furnace is heated in stages, pre-sintered at 840℃ for 2 hours, sintered at 1060℃ for 5 hours; aged at 900℃ for 4 hours for the first stage, aged at 480℃ for 4 hours for the second stage, and cooled with the furnace to obtain the regenerated magnet.
[0036] Performance test results: Hcj = 2120 kA / m, (BH)max = 425 kJ / m 3 At 200℃, Hcj = 950 kA / m; at 250℃, Hcj = 705 kA / m; the corrosion rate after 1000 hours of salt spray is 0.0017 g / (m²). 2 •h), density 7.63 g / cm³ 3 The oxygen content is 340 ppm.
[0037] Example 2 1. Preparation of regenerated magnetic powder: (1) Raw material pretreatment: The pretreated waste magnetic block particles are put into a vacuum induction melting furnace, and the vacuum degree is ≤2× Under Pa conditions, the temperature is raised to 1520-1540℃ and held for 20-30 minutes to completely melt the magnetic block particles and form a uniform recycled alloy melt, ensuring that there are no unmelted solid particles in the melt.
[0038] (2) Gas atomization powder production: Argon atomization process is adopted. The recycled alloy molten liquid is introduced into the atomization chamber through a guide tube with an outlet diameter of 2-3 mm. The vacuum degree of the atomization chamber is first evacuated to ≤5×10 -2 Then, 99.9995% high-purity argon gas is introduced to maintain the pressure in the atomization chamber at 0.3-0.5 MPa. The molten liquid falls under gravity and collides and breaks up with the high-speed argon gas jet (gas velocity 300-400 m / s), forming fine droplets that quickly solidify. During atomization, the molten liquid temperature is controlled to be stable at 1500-1520℃, and the argon gas flow rate is 80-100 L / min to ensure uniform powder particle size.
[0039] (3) Powder classification and purification: The atomized powder is classified by a cyclone classifier, and powder with a particle size D50 of 3.0-4.5μm is collected; then it is subjected to vacuum degassing and purification treatment at a vacuum degree ≤3× Under Pa conditions, the temperature was first raised to 420℃ and held for 2 hours, then raised to 560℃ and held for 3 hours to remove moisture and residual impurities from the powder. The resulting regenerated magnetic powder had an oxygen content ≤300ppm and a flowability ≥25s / 50g.
[0040] 2. Preparation of conventional NdFeB bialloy powder: Raw materials (Nd 24%, Pr 5.0%, Dy 0.6%, Ho 0.8%, Yb 0.15%, Nb 0.20%, Si 0.04%, Cu 0.21%, Al 0.31%, B 0.94%, Fe balance) were weighed according to the optimal composition. After vacuum induction melting, the powder was cast into thin sheets by double-zone water cooling. After hydrogen crushing, dehydrogenation, and air jet milling, bialloy powder with D50=3.2μm and oxygen content of 190ppm was obtained.
[0041] 3. Mixing and powder preparation: Regenerated magnetic powder and bi-alloy powder are mixed at a mass ratio of 20%:80% and stirred at 400r / min for 45min under argon protection to obtain composite magnetic powder.
[0042] 4. Magnetic field forming: Gradient pressure is applied in a 2.0T orientation magnetic field (90MPa×5s→190MPa×15s), green body density is 4.1g / cm³. 3 Orientation degree 97.5%.
[0043] 5. Sintering and aging: The vacuum sintering furnace is heated in stages, pre-sintered at 840℃ for 2 hours, sintered at 1060℃ for 5 hours; aged at 900℃ for 4 hours for the first stage, aged at 480℃ for 4 hours for the second stage, and cooled with the furnace to obtain the regenerated magnet.
[0044] Performance test results: Hcj = 2050 kA / m, (BH)max = 418 kJ / m 3 At 200℃, Hcj = 920 kA / m; the corrosion rate after 1000 hours of salt spray is 0.0019 g / (m²). 2 •h), density 7.61 g / cm³ 3 The oxygen content is 380 ppm.
[0045] Example 3 1. Preparation of regenerated magnetic powder: (1) Raw material pretreatment: The pretreated waste magnetic block particles are put into a vacuum induction melting furnace, and the vacuum degree is ≤2× Under Pa conditions, the temperature is raised to 1520-1540℃ and held for 20-30 minutes to completely melt the magnetic block particles and form a uniform recycled alloy melt, ensuring that there are no unmelted solid particles in the melt.
[0046] (2) Gas atomization powder production: Argon atomization process is adopted. The recycled alloy molten liquid is introduced into the atomization chamber through a guide tube with an outlet diameter of 2-3 mm. The vacuum degree of the atomization chamber is first evacuated to ≤5×10 -2 Then, 99.9995% high-purity argon gas is introduced to maintain the pressure in the atomization chamber at 0.3-0.5 MPa. The molten liquid falls under gravity and collides and breaks up with the high-speed argon gas jet (gas velocity 300-400 m / s), forming fine droplets that quickly solidify. During atomization, the molten liquid temperature is controlled to be stable at 1500-1520℃, and the argon gas flow rate is 80-100 L / min to ensure uniform powder particle size.
[0047] (3) Powder classification and purification: The atomized powder is classified by a cyclone classifier, and powder with a particle size D50 of 3.0-4.5μm is collected; then it is subjected to vacuum degassing and purification treatment at a vacuum degree ≤3× Under Pa conditions, the temperature was first raised to 420℃ and held for 2 hours, then raised to 560℃ and held for 3 hours to remove moisture and residual impurities from the powder. The resulting regenerated magnetic powder had an oxygen content ≤300ppm and a flowability ≥25s / 50g.
[0048] 2. Preparation of conventional NdFeB bimetallic powder: Raw materials (Nd 26%, Pr 6%, Dy 0.8%, Ho 1.0%, Yb 0.25%, Nb 0.30%, Si 0.06%, Cu 0.23%, Al 0.33%, B 0.98%, Fe balance) were weighed according to the optimal composition. After vacuum induction melting, the powder was cast into thin sheets by double-zone water cooling. After hydrogen crushing, dehydrogenation, and air jet milling, bimetallic powder with D50=3.2μm and oxygen content of 190ppm was obtained.
[0049] 3. Mixing and powder preparation: Regenerated magnetic powder and bi-alloy powder are mixed at a mass ratio of 40%:60% and stirred at 400r / min for 45min under argon protection to obtain composite magnetic powder.
[0050] 4. Magnetic field forming: Gradient pressure is applied in a 2.0T orientation magnetic field (90MPa×5s→190MPa×15s), green body density is 4.1g / cm³. 3 Orientation degree 97.5%.
[0051] 5. Sintering and Aging: The vacuum sintering furnace was heated in stages: pre-firing at 840℃ for 2 hours, sintering at 1060℃ for 5 hours; primary aging at 900℃ for 4 hours, secondary aging at 480℃ for 4 hours, followed by furnace cooling to obtain the regenerated magnet. Performance test results: Hcj = 2010 kA / m, (BH)max = 410 kJ / m 3 At 200℃, Hcj = 910 kA / m; the corrosion rate after 1000 hours of salt spray is 0.0020 g / (m²). 2 •h), density 7.59 g / cm³ 3 The oxygen content is 420 ppm.
[0052] Comparative example (traditional native magnet): Composition: Nd 29%, Pr 5.5%, Dy 2.8%, Cu 0.22%, Al 0.32%, B 1.01%, Fe balance. Prepared using traditional water-cooled spinning, single-stage dehydrogenation, and conventional sintering processes.
[0053] Performance test results: Hcj = 1850 kA / m, (BH)max = 405 kJ / m 3 At 200℃, Hcj = 800 kA / m; the corrosion rate after 1000 hours of salt spray is 0.0085 g / (m²). 2 •h), density 7.50 g / cm³ 3 The oxygen content is 678 ppm.
[0054] A performance comparison table can be found in the instruction manual. Figure 1 .
[0055] Included in the instruction manual Figure 1The performance data from the examples and comparative examples show that the recycled sintered NdFeB magnets prepared by this invention are significantly superior to traditional virgin magnets in terms of magnetic properties, high-temperature stability, and corrosion resistance. At the same time, it realizes the efficient recycling of waste magnetic resources, reduces the amount of heavy rare earth elements used and the production cost, and has important industrial application value.
[0056] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A regenerated sintered NdFeB magnet, characterized in that; The regenerated sintered NdFeB magnet is prepared by magnetic field forming, sintering and aging of composite magnetic powder. The composite magnetic powder is obtained by mixing regenerated magnetic powder and conventional NdFeB bi-alloy powder at a mass ratio of 20%-40%:60%-80%. The regenerated magnetic powder is derived from waste sintered NdFeB magnetic blocks and is produced by gas atomization powdering process. The particle size D50 is 3.0μm-4.5μm and the oxygen content is ≤300ppm. The conventional NdFeB bimetallic powder comprises, by mass percentage: Nd 22%-30%, Pr 5%-6%, Dy 0.6%-0.8%, Ho 0.8%-1.0%, Yb 0.15%-0.25%, Nb 0.20%-0.30%, Si 0.04%-0.06%, Cu 0.21%-0.23%, Al 0.31%-0.33%, B 1.00%-1.02%, with the balance being Fe; The main phase of the regenerated sintered NdFeB magnet is The main phase has a grain size of 3-4 μm, and a Nd-Cu-Al-Yb-Si pentagonal composite grain boundary phase is formed at the grain boundaries, with a grain boundary phase continuity of ≥96%.
2. The regenerated sintered NdFeB magnet according to claim 1, characterized in that: The mass ratio of the regenerated magnetic powder to the conventional NdFeB bimetallic powder is 30%:70%.
3. A regenerated sintered NdFeB magnet according to claim 1, characterized in that: In the conventional NdFeB bimetallic powder, Ho replaces more than 50% of Dy, and the total amount of heavy rare earth Dy + Ho is 1.4%-1.8%.
4. The regenerated sintered NdFeB magnet and its preparation method according to claim 1, characterized in that: The conventional NdFeB bimetallic powder has a particle size D50 of 2.7μm-4.0μm and an oxygen content of ≤200ppm.
5. A regenerated sintered NdFeB magnet according to claim 1, characterized in that: The regenerated sintered NdFeB magnets meet the following performance requirements: room temperature coercivity Hcj ≥ 2000 kA / m, maximum energy product (BH)max ≥ 400 kJ / m 3 At 200℃, the coercivity is ≥900kA / m, and the corrosion rate after 1000h of neutral salt spray testing is ≤0.002g / (m²). 2 •h), magnet density ≥7.60g / cm³ 3 Oxygen content ≤500ppm.
6. A method for preparing a regenerated sintered NdFeB magnet, characterized in that, Includes the following steps: S1. Pre-treatment of waste magnetic blocks: Select waste sintered NdFeB magnetic blocks, the main components of which are... Phase, heavy rare earth content ≤3%, magnetic properties satisfying room temperature coercivity Hcj≥1800kA / m, maximum energy product (BH)max≥400kJ / m 3 After removing surface oil, rust and impurities through mechanical grinding and ultrasonic cleaning, the magnetic blocks are then crushed into 5mm-10mm particles. S2. Waste magnetic block powder making: The pretreated magnetic block particles are melted and then atomized into powder. The powder is then classified and purified to obtain regenerated magnetic powder with a particle size D50 of 3.0-4.5μm and an oxygen content of ≤300ppm. S3. Preparation of conventional NdFeB bimetallic powder: Weigh the following raw materials by mass percentage: Nd 22%-30%, Pr 5%-6%, Dy 0.6%-0.8%, Ho 0.8%-1.0%, Yb 0.15%-0.25%, Nb 0.20%-0.30%, Si 0.04%-0.06%, Cu 0.21%-0.23%, Al 0.31%-0.33%, B 1.00%-1.02%, with the balance being Fe. Then, through vacuum induction melting, dual-zone water-cooled copper mold casting, hydrogen crushing, segmented dehydrogenation, and air jet milling, conventional NdFeB bimetallic powder with a particle size D50 of 2.7μm-4.0μm and an oxygen content ≤200ppm is obtained. S4. Mixing and powder preparation: The regenerated magnetic powder and the conventional NdFeB bimetallic powder are mixed at a mass ratio of 20%-40%:60%-80% to obtain composite magnetic powder; S5. Magnetic field forming: The composite magnetic powder is pressed and formed in an orientation magnetic field to obtain a green blank; S6. Sintering and aging: The green blank is subjected to vacuum sintering and two-stage aging treatment to obtain the regenerated sintered NdFeB magnet.
7. The method for preparing a regenerated sintered NdFeB magnet according to claim 1, characterized in that: Step S2 specifically includes: feeding the pretreated waste sintered NdFeB magnetic block particles into a vacuum induction melting furnace, and melting the particles at a vacuum degree ≤ 2× Under Pa conditions, the temperature is raised to 1520℃-1540℃ and held for 20min-30min to completely melt the magnetic block particles and form a uniform recycled alloy melt. Argon atomization is used to introduce the recycled alloy molten liquid into the atomization chamber through a guide tube with an outlet diameter of 2mm-3mm. The vacuum degree of the atomization chamber is first evacuated to ≤5× Pa, then high-purity argon gas with a purity of 99.9995% is introduced to maintain the pressure in the atomization chamber at 0.3MPa-0.5MPa, and the molten liquid is broken up by impact with a high-speed argon gas jet with a gas velocity of 300m / s-400m / s. During the atomization process, the temperature of the molten liquid is controlled at 1420℃-1480℃, and the argon gas flow rate is 80L / min-100L / min; The atomized powder is classified by a cyclone classifier, collecting powder with a particle size D50 of 3.0-4.5μm, and then subjected to a vacuum degree ≤3× Under Pa conditions, the temperature is first raised to 420℃ and held for 2 hours, then raised to 560℃ and held for 3 hours for vacuum dehydrogenation purification treatment, finally obtaining regenerated magnetic powder with a flowability ≥25s / 50g.
8. The method for preparing a regenerated sintered NdFeB magnet according to claim 6, characterized in that: Steps S3 and S4 specifically include: In step S3, the raw material purity requirements are Fe ≥ 99.99%, Nd / Pr / Dy / Ho ≥ 99.95%, and other metals ≥ 99.6%, with a vacuum degree ≤ 2× A vacuum induction melting process was employed, with a pressure of 1540℃-1560℃ and a holding time of 30 minutes. The copper was then cast using a dual-zone water-cooled mold, where the water temperature in the first zone was 25℃ and the water temperature in the second zone was 15℃. The cooling rate was [missing information]. -10 5 The process involves preparing thin sheets with a thickness of 0.2 mm to 0.5 mm by applying hydrogen pressure at 0.05 MPa to 0.2 MPa for 2.5 h to 5 h, followed by staged dehydrogenation by holding at 400 °C for 1.5 h and then at 540 °C for 2.5 h, and finally air jet milling with 0.15% composite additives to obtain the conventional NdFeB bimetallic powder. In step S4, under argon protection, the regenerated magnetic powder is mixed with the conventional NdFeB bimetallic powder at an argon flow rate of 0.5L / min-1.0L / min, a stirring rate of 300r / min-500r / min, and a stirring time of 30min-60min to obtain a composite magnetic powder with an oxygen content ≤350ppm and a flowability ≥24s / 50g.
9. The method for preparing a regenerated sintered NdFeB magnet according to claim 1, characterized in that: Steps S5 and S6 specifically include: In step S5, the composite magnetic powder is subjected to gradient pressurization in an orientation magnetic field of 1.8T-2.3T, with a pre-pressurization pressure of 90MPa and a holding time of 5s, and a final pressurization pressure of 200MPa and a holding time of 15s, to obtain a density ≥4.0g / cm³. 3 Green blanks with an orientation degree ≥ 97%; In step S6, the green blank is in a vacuum degree ≤3× The regenerated sintered NdFeB magnet was subjected to a stepped heating process in a vacuum sintering furnace at the following rates: 5°C / min from room temperature to 400°C, 3°C / min from 400°C to 840°C, and 2°C / min from 840°C to the sintering temperature. After pre-firing at 840°C for 2 hours, the magnet was sintered at 1040°C-1080°C for 4-7 hours. Subsequently, the temperature was lowered to 880°C-920°C for primary aging and held for 3-7 hours. Then, the temperature was lowered to 440°C-520°C for secondary aging and held for 3-7 hours. Finally, the magnet was cooled to room temperature with the furnace at a cooling rate of 60°C / h to obtain the regenerated sintered NdFeB magnet.