Preparation method of neodymium-iron-boron magnet with high mechanical service characteristics

Abstract

The application belongs to the technical field of neodymium-iron-boron magnet production, and relates to a preparation method of a neodymium-iron-boron magnet with high mechanical service characteristics. The application discloses a preparation method of a neodymium-iron-boron magnet with high mechanical service characteristics, which comprises the following steps: sequentially performing sintering heat treatment and tempering heat treatment on a neodymium-iron-boron green body; the sintering heat treatment comprises six stages: a vacuum extraction stage, an exhaust stage, a slow heating stage, a sintering stage, a slow cooling stage and a rapid cooling stage; the slow heating stage is "wave-shaped" slow heating, the sintering stage is "wave-shaped" sintering heat preservation, and the slow cooling stage is "wave-shaped" slow cooling. The preparation method of the neodymium-iron-boron magnet with high mechanical service characteristics can improve the mechanical performance of the neodymium-iron-boron magnet while ensuring the magnetic performance of the neodymium-iron-boron magnet.

Description

Technical Field

[0001] This invention belongs to the field of neodymium iron boron magnet production technology, and relates to a method for preparing neodymium iron boron magnets with high mechanical service characteristics. Background Technology

[0002] Sintered NdFeB, as a third-generation rare-earth permanent magnet material, possesses both high coercivity and high remanence, and its development and application reflect the significant development needs of emerging industries. However, with the improvement of magnetic properties and the continuous expansion of application fields of rare-earth permanent magnet materials, the poor plasticity and toughness, difficult machining, and poor impact and vibration resistance of sintered NdFeB permanent magnets have become serious weaknesses, restricting the further expansion of their application range. In particular, as magnetic functional devices are developing towards miniaturization, thinning, high functionality, and high precision, the machining precision of magnets in high-precision instruments is becoming increasingly demanding. The brittleness of NdFeB magnets is gradually being exposed; their poor machinability makes them prone to cracking, peeling, and chipping during processing, assembly, and use, significantly reducing the yield and machining accuracy of the magnets, thus limiting the application of rare-earth permanent magnet materials in high-precision instruments. Improving the strength and toughness of NdFeB magnets in mechanical service has become an important research direction in the industry.

[0003] The powder metallurgy preparation process of sintered NdFeB permanent magnet materials involves fabricating magnets through rapid solidification casting, hydrogen crushing, air jet milling, orientation forming, cold isostatic pressing, sintering, and tempering. The final magnet products exhibit significant brittleness, with fracture primarily manifesting as intergranular crack propagation. Numerous studies have shown that cracks always propagate along weak areas of the magnet. Therefore, strengthening or repairing weak areas or defects in the magnet's microstructure is crucial for improving the mechanical properties of NdFeB magnets. Currently, the common method to enhance magnet mechanical properties is to introduce a toughening second phase (intergranular phase) as an additive. While this method can significantly optimize the magnet's mechanical properties, the introduction of the second phase inevitably causes substantial damage to the magnet's magnetic properties (especially remanence and energy product), weakening the magnet's external magnetic moment and hindering its application in high-precision fields. The key to further developing neodymium iron boron permanent magnet materials lies in how to improve the mechanical properties of magnets through intrinsic structure optimization without introducing a second phase. This is of great significance for the application and development of rare earth permanent magnet materials. Summary of the Invention

[0004] The purpose of this invention is to address the aforementioned problems in the existing technology by proposing a preparation method that can significantly improve the mechanical service characteristics of NdFeB magnets without introducing a second phase. Under the condition that the magnet composition design is basically not affected, the magnet is guaranteed to have both high mechanical and permanent magnetic properties, which is applicable to improving the mechanical properties of NdFeB magnets with different composition systems.

[0005] One objective of this invention is achieved through the following technical solution:

[0006] A method for preparing a neodymium iron boron magnet with high mechanical service characteristics includes: subjecting a neodymium iron boron green blank to sintering heat treatment and tempering heat treatment in sequence; the sintering heat treatment includes six stages: vacuum stage, exhaust stage, slow heating stage, sintering stage, slow cooling stage, and rapid cooling stage;

[0007] The slow heating phase is a "wave-like" slow heating, starting from the initial temperature T11, increasing by 20~50℃ and holding for a period of time, then decreasing by 5~15℃ and holding for a period of time, and so on until the target temperature T12 is reached.

[0008] The sintering stage is a "wave-like" sintering and heat preservation process. Within the range of 800~1600℃, a temperature range with an upper and lower temperature difference of 5~50℃ is selected as the sintering temperature. When the temperature reaches the upper limit temperature point T21 of the temperature range, it is kept at that temperature. Then, the temperature drops by 5~50℃ to the lower limit temperature point T22 of the temperature range and is kept at that temperature. Then, the temperature rises back to the upper limit temperature point T21 of the temperature range and is kept at that temperature. This cycle is repeated for 1~30 hours.

[0009] The slow cooling stage is a "wave-like" slow cooling process. Starting from the sintering temperature, the temperature drops by 40~200℃ and is held at that temperature, then rises by 5~35℃ and is held at that temperature, until the temperature drops to temperature point T3, which is 600~900℃.

[0010] Preferably, the vacuuming stage is performed at room temperature, and the vacuum level is controlled to be no higher than 10 after the stage. - 2 Pa, and this vacuum level is maintained after the completion of the five subsequent stages of sintering heat treatment.

[0011] Preferably, the exhaust stage is a stepped heating process, where the temperature is raised to 2 to 6 steps between 300 and 900°C and held at each step, with a heating rate of 1 to 20°C / min.

[0012] Further preferably, the temperature of the last step of the exhaust stage is less than or equal to the initial temperature T11 of the slow heating stage.

[0013] Preferably, the slow heating phase includes: starting from the initial temperature T11, increasing the temperature by 20-30°C and holding it at that temperature, then decreasing it by 5-10°C and holding it at that temperature, and repeating this cycle until the target temperature T12 is reached.

[0014] More preferably, the target temperature T12 is greater than the initial temperature T11, and the target temperature T12 - the initial temperature T11 = 100~400℃.

[0015] Preferably, the single holding time at the upper temperature point T21 of the sintering stage is the same as the single holding time at the lower temperature point T22 of the temperature range.

[0016] Preferably, the difference between the number of holding times at the upper temperature point T21 of the temperature range and the number of holding times at the lower temperature point T22 of the temperature range during the sintering stage is 0 or 1.

[0017] Preferably, the holding time during the slow heating stage is 1~10h, the heating rate is 1~10℃ / min, and the cooling rate is 1~10℃ / min.

[0018] Further preferably, the heating rate during the slow heating phase is less than or equal to the cooling rate.

[0019] Preferably, the lower limit temperature point T22 of the temperature range is less than the target temperature T12 and less than the upper limit temperature point T21 of the temperature range, or the lower limit temperature point T22 of the temperature range is less than the target temperature T12 and less than the upper limit temperature point T21 of the temperature range, or the lower limit temperature point T22 of the temperature range is less than the target temperature T12 and less than the upper limit temperature point T21 of the temperature range.

[0020] Preferably, the lower limit temperature point T22 of the temperature range is greater than T3.

[0021] Further preferably, the lower limit temperature point T22 of the temperature range - the T3 = 100~500℃.

[0022] Preferably, the upper limit temperature point T21 of the temperature range and the lower limit temperature point T22 of the temperature range are 5~20℃.

[0023] Preferably, the sintering stage includes: taking a temperature range with an upper and lower temperature difference of 10°C within the range of 1000~1100°C as the sintering temperature; holding the temperature at the upper limit temperature point T21 of the temperature range; then lowering the temperature by 10°C to the lower limit temperature point T22 of the temperature range and holding the temperature thereafter; then raising the temperature back to the upper limit temperature point T21 of the temperature range and holding the temperature thereafter; repeating this cycle for 1~10 hours; the heating rate is 0.1~5°C / min, and the cooling rate is 0.1~5°C / min.

[0024] Preferably, the slow cooling stage includes: starting from the sintering temperature, decreasing the temperature by 50~100℃ and holding it at that temperature, then increasing the temperature by 10~20℃ and holding it at that temperature, until the temperature drops to a temperature point T3 within the range of 700~850℃; the heating rate is 5~30℃ / min, and the cooling rate is 5~30℃ / min.

[0025] Preferably, the heat preservation time during the slow cooling stage is 0.5~20h.

[0026] Preferably, the rapid cooling stage includes: stopping heating and filling with circulating inert gas, and cooling down to room temperature by air cooling.

[0027] Preferably, the tempering heat treatment includes two stages: high-temperature tempering heat treatment and low-temperature tempering heat treatment.

[0028] High-temperature tempering heat treatment includes holding at a high-temperature tempering temperature T51 of 700~1100℃ for 1~12 hours and then rapidly cooling to room temperature;

[0029] Low-temperature tempering heat treatment includes holding at a low-temperature tempering temperature of 300~600℃ for 1~12 hours and then rapidly cooling to room temperature.

[0030] Preferably, the density of the NdFeB green blank is 3.8~4.4 g / cm³. 3 .

[0031] Further preferably, the density of the NdFeB green compact is 4.1~4.4 g / cm³. 3 .

[0032] Preferably, the NdFeB green billet is obtained by rapidly solidifying NdFeB alloy into a sheet, then grinding and pressing it.

[0033] Further preferably, the neodymium iron boron alloy, by mass percentage, has the chemical formula R. a B b M c Fe 100-a-b-c Where R is one or more of Pr, Nd, Dy, Tb, La, Ce, Y, Ho and Gd, B is boron, M is one or more of Cu, Al, Ga, Co, Zr and Ti, and Fe is iron; and satisfy 28.5≤a≤31.5, 0.88≤b<0.99, 0.5≤c≤3.

[0034] Further preferably, the powdering process includes hydrogen crushing and air jet milling.

[0035] More preferably, the particle size distribution parameter (SMD) of the magnetic powder obtained by air jet milling is 1~10μm.

[0036] More preferably, the particle size distribution parameter (SMD) of the magnetic powder obtained by air jet milling is 2~2.5μm.

[0037] More preferably, the magnetic powder obtained by air jet milling has a D 90 / D 10 It ranges from 2 to 5.

[0038] More preferably, the magnetic powder obtained by air jet milling has a D 90 / D 10The value is 3.2~4.2.

[0039] Further preferably, the pressing includes orientation pressing and cold isostatic pressing.

[0040] More preferably, the magnetic field strength of the orientation pressing type is 1~5T and the pressure is 10~18MPa.

[0041] More preferably, the cold isostatic pressing pressure is 180~300 MPa and the time is 60~600s.

[0042] The second objective of this invention is achieved through the following technical solution:

[0043] A neodymium iron boron magnet with high mechanical service characteristics and a density of 4.2~4.6 g / cm³ 3 .

[0044] Beneficial effects

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] 1. The method for preparing NdFeB magnets with high mechanical service characteristics of the present invention improves the mechanical properties by using six sintering heat treatment stages: vacuuming stage, exhaust stage, slow heating stage, sintering stage, slow cooling stage, and rapid cooling stage.

[0047] 2. The method for preparing NdFeB magnets with high mechanical service characteristics in this invention achieves optimization of the intrinsic structure of the magnet by effectively controlling the microstructure of the magnet. This avoids the fluctuations in the microstructure caused by the introduction of the second phase in the existing mechanical modification method, and maximizes the uniformity and consistency of the microstructure of the magnet. This results in magnets prepared in batches having good mechanical and magnetic performance consistency, which is suitable for large-scale industrial production.

[0048] 3. The present invention regulates the particle size distribution parameters SMD and D of NdFeB magnetic powder. 90 / D 10 The NdFeB magnet powder with small SMD has a large specific surface area and more contact points between the magnet powder particles, which can better fill each other, increase the green density, and help improve the magnetic and mechanical properties of the magnet. D90 / D10 is used to characterize the width of the particle size distribution. The NdFeB magnet powder of the present invention has a relatively narrow particle size distribution and relatively uniform particle size, which is beneficial to the uniformity of NdFeB magnet molding and ensures performance.

[0049] 4. The present invention provides sintering heat treatment and tempering heat treatment for NdFeB green blanks with high density, which is beneficial to the subsequent liquid phase sintering and uniform densification shrinkage process.

[0050] 5. The method for preparing NdFeB magnets with high mechanical service characteristics according to the present invention does not require the introduction of a second phase component, which can reduce the cost of raw materials and the production cost of the process. Detailed Implementation

[0051] The technical solution of the present invention will be further described and illustrated below through specific embodiments. It should be understood that the specific embodiments described herein are only for the purpose of helping to understand the present invention and are not intended to limit the present invention.

[0052] Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used in the art, and the methods used in the embodiments are all conventional methods in the art.

[0053] In this paper, the preparation method of NdFeB magnets with high mechanical service characteristics is applicable to NdFeB magnets with different composition systems.

[0054] In this paper, the steps of preparing rapid-solidification casting sheets, powder preparation, and pressing can be carried out using existing technologies.

[0055] This paper describes a method for preparing neodymium iron boron magnets with high mechanical service characteristics, including:

[0056] (1) The proportion of NdFeB alloy smelted by mass percentage is R a B b M c Fe 100-a-b-c R is one or more of Pr, Nd, Dy, Tb, La, Ce, Y, Ho and Gd, B is boron, M is one or more of Cu, Al, Ga, Co, Zr and Ti, and Fe is iron; and satisfies 28.5≤a≤31.5, 0.88≤b<0.99, 0.5≤c≤3;

[0057] (2) The neodymium iron boron alloy is made into a rapid solidification casting sheet, which is then crushed by hydrogen and ground into powder by air jet milling, oriented molding, and cold isostatic pressing to obtain neodymium iron boron green billet;

[0058] (3) The neodymium iron boron green blank is subjected to sintering heat treatment and tempering heat treatment to obtain neodymium iron boron magnets with high mechanical service characteristics;

[0059] Sintering heat treatment includes six stages: vacuuming stage, degassing stage, slow heating stage, sintering stage, slow cooling stage, and rapid cooling stage.

[0060] The vacuuming phase is conducted at room temperature. After this phase, the vacuum level is controlled to be no higher than 10. -2 Pa, and this vacuum level is maintained after the completion of the five subsequent stages of sintering heat treatment;

[0061] The exhaust stage is a stepped heating process, with the temperature raised to 2 to 6 steps between 300 and 900°C and held at each step.

[0062] The slow heating phase is a "wave-like" slow heating, starting from the initial temperature T11, increasing by 20~50℃ and holding for a period of time, then decreasing by 5~15℃ and holding for a period of time, and so on until the target temperature T12 is reached.

[0063] The target temperature T12 is greater than the initial temperature T11, and the target temperature T12 - the initial temperature T11 = 100~400℃;

[0064] The temperature of the last step in the exhaust stage is less than or equal to the initial temperature T11 of the slow heating stage.

[0065] The sintering stage is a "wave-like" sintering and heat preservation process. Within the range of 800~1600℃, a temperature range with an upper and lower temperature difference of 5~50℃ is selected as the sintering temperature. When the temperature reaches the upper limit temperature point T21 of the temperature range, it is kept at that temperature. Then, the temperature drops by 5~50℃ to the lower limit temperature point T22 of the temperature range and is kept at that temperature. Then, the temperature rises back to the upper limit temperature point T21 of the temperature range and is kept at that temperature. This cycle is repeated for 1~30 hours.

[0066] The T22 ≤ the T12 < the T21, or the T22 < the T12 ≤ the T21, or the T22 < the T12 < the T21;

[0067] The slow cooling stage is a "wave-like" slow cooling process. Starting from the sintering temperature, the temperature drops by 40~200℃ and is held at that temperature, then rises by 5~35℃ and is held at that temperature, until the temperature drops to temperature point T3, which is 600~900℃.

[0068] The rapid cooling stage includes: stopping heating and introducing circulating inert gas, and cooling down to room temperature by air cooling;

[0069] The tempering heat treatment includes two stages: high-temperature tempering heat treatment and low-temperature tempering heat treatment.

[0070] High-temperature tempering heat treatment includes holding at a high-temperature tempering temperature T51 of 700~1100℃ for 1~12 hours and then rapidly cooling to room temperature;

[0071] Low-temperature tempering heat treatment includes holding at a low-temperature tempering temperature of 300~600℃ for 1~12 hours and then rapidly cooling to room temperature.

[0072] In this paper, the mechanical performance testing methods for NdFeB magnets with high mechanical service characteristics include:

[0073] The prepared neodymium iron boron magnets were machined to standard dimensions of 15mm×6mm×5mm (orientation direction) (GB / T232-2010 Metallic Materials Bending Test Method) and Ø3mm×6mm (orientation direction), and then subjected to bending strength (three-point bending test, with the force direction parallel to the orientation direction) and compressive strength (with the force direction parallel to the orientation direction) tests, with a test sample size of 10.

[0074] Example 1

[0075] (1) The chemical formula of the batching and smelting is (PrNd). 29.5 B 0.98 Zr 0.1 Cu 0.2 Al 0.1 Co 1.0 Fe bal Neodymium iron boron alloy (by mass percentage);

[0076] (2) Neodymium iron boron alloy was processed into rapidly solidified neodymium iron boron flakes through a rapid solidification casting process, and then subjected to hydrogen crushing and air jet milling to obtain particle size distribution parameters SMD of 2.3 μm and D. 90 / D 10 Neodymium iron boron (NdFeB) magnetic powder with a density of 3.8 was obtained by oriented pressing of the NdFeB magnetic powder under a magnetic field greater than 1.8T, followed by cold isostatic pressing. 3 Neodymium iron boron green blanks;

[0077] (3) Place the neodymium iron boron green blank into a vacuum heat treatment furnace for sintering heat treatment.

[0078] Vacuuming stage: Vacuum to 9.0 × 10⁻⁶ -3 Pa and maintain this vacuum level;

[0079] Exhaust stage: Heat to 320℃ at a rate of 8℃ / min and hold for 0.5h, then heat to 600℃ at a rate of 8℃ / min and hold for 1h, and then heat to 850℃ at a rate of 10℃ / min and hold for 2h.

[0080] The “wave-like” slow heating phase: with an initial temperature of 850℃, the heating and cooling operations are carried out at a heating rate of 3℃ / min and a cooling rate of 5℃ / min. After each 30℃ increase in temperature, the temperature is held for 15 minutes, then decreased by 5℃ and held for 2 minutes. This cycle is repeated until the temperature rises to the target temperature of 1080℃.

[0081] "Wave-like" sintering and heat preservation stage: The temperature is increased and decreased in cycles at a rate of 1℃ / min within the temperature range of 1075~1085℃, and this cycle of increasing and decreasing continues for 4 hours.

[0082] The “wave-like” slow cooling stage: the temperature rises and falls at a rate of 10℃ / min, and after each drop of 100℃, it is held for 20 minutes, then rises by 20℃ and is held for 20 minutes. This cycle is repeated until the temperature drops to below 850℃.

[0083] Rapid cooling stage: Heating is stopped and circulating inert gas is introduced into the vacuum heat treatment furnace, and the temperature is reduced to room temperature by air cooling.

[0084] Then, a tempering heat treatment was performed, with the temperature raised to 900℃ and held for 2 hours. Heating was stopped and a circulating inert gas was introduced into the vacuum heat treatment furnace. The furnace was then cooled to room temperature by air cooling. The furnace was then heated again, with the temperature raised to 480℃ and held for 2 hours. Heating was stopped and a circulating inert gas was introduced into the vacuum heat treatment furnace. The furnace was then cooled to room temperature by air cooling to obtain a neodymium iron boron magnet with high mechanical service characteristics.

[0085] The performance of a high-mechanical-service-characteristic NdFeB magnet 1 was tested. The magnetic property of the high-mechanical-service-characteristic NdFeB magnet 1 is remanence. B r=14.59kGs, coercivity H cj = 14.82 kOe, magnetic energy product ( BH m = 50.95MGsOe, squareness H k / H cj=0.931; The mechanical performance test results of the high mechanical service characteristics NdFeB magnet 1 are shown in Table 1.

[0086]

[0087] Example 2

[0088] (1) The chemical formula of the batching and smelting is (PrNd). 21.3 (LaCe) 9.2 B 0.89 Ti 0.2 Al 0.3 Co 0.8 Fe bal Neodymium iron boron alloy (by mass percentage);

[0089] (2) Neodymium iron boron alloy was processed into rapidly solidified neodymium iron boron flakes through a rapid solidification casting process, and then subjected to hydrogen crushing and air jet milling to obtain particle size distribution parameters SMD of 2.5 μm and D. 90 / D 10 Neodymium iron boron (NdFeB) magnetic powder with a density of 4.2 g / cm³ was obtained by oriented pressing of the NdFeB magnetic powder under a magnetic field greater than 1.8 T, followed by cold isostatic pressing. 3 Neodymium iron boron green blanks;

[0090] (3) Place the neodymium iron boron green billet into a vacuum heat treatment furnace for sintering heat treatment;

[0091] Vacuuming stage: Vacuum to 7.5 × 10⁻⁶ -3 Pa and maintain this vacuum level;

[0092] Exhaust stage: Heat to 300℃ at a rate of 10℃ / min and hold for 1 hour, then heat to 550℃ at a rate of 10℃ / min and hold for 1 hour, and then heat to 790℃ at a rate of 10℃ / min and hold for 2.5 hours.

[0093] The “wave-like” slow heating phase: with an initial temperature of 790℃, the temperature is raised and lowered at a rate of 5℃ / min. After each 20℃ increase, the temperature is held for 10 minutes, then lowered by 5℃ and held for 5 minutes. This cycle is repeated until the temperature reaches the target temperature of 1030℃.

[0094] “Wave-like” sintering and holding stage: The temperature is increased and decreased in cycles at a rate of 1℃ / min within the temperature range of 1025~1035℃, and this cycle of increasing and decreasing temperature lasts for 4 hours.

[0095] The “wave-like” slow cooling stage: the temperature rises and falls at a rate of 10℃ / min, and after each drop of 80℃, it is held for 20 minutes, then rises by 10℃ and is held for 20 minutes. This cycle is repeated until the temperature drops to below 750℃.

[0096] Rapid cooling stage: Heating is stopped and circulating inert gas is introduced into the vacuum heat treatment furnace, and the temperature is reduced to room temperature by air cooling.

[0097] Then, a tempering heat treatment was performed, with the temperature raised to 750°C and held for 2 hours. Heating was stopped and a circulating inert gas was introduced into the vacuum heat treatment furnace. The furnace was then cooled to room temperature by air cooling. The furnace was then heated again, with the temperature raised to 450°C and held for 2 hours. Heating was stopped and a circulating inert gas was introduced into the vacuum heat treatment furnace. The furnace was then cooled to room temperature by air cooling to obtain a neodymium iron boron magnet 2 with high mechanical service characteristics.

[0098] The performance of neodymium iron boron magnet 2 with high mechanical service characteristics was tested. The magnetic property of neodymium iron boron magnet 2 with high mechanical service characteristics is remanence. B r = 12.72 kGs, coercivity H cj = 13.25 kOe, magnetic energy product ( BH m=37.39MGsOe, squareness H k / H cj=0.925; The mechanical performance test results of the NdFeB magnet with high mechanical service characteristics are shown in Table 2.

[0099]

[0100] Comparative Example 1

[0101] (1) The chemical formula of the batching and smelting is (PrNd). 29.5 B 0.98 Zr 0.1 Cu 0.2 Al 0.1 Co 1.0 Fe bal Neodymium iron boron alloy (by mass percentage);

[0102] (2) Neodymium iron boron alloy was processed into rapidly solidified neodymium iron boron flakes through a rapid solidification casting process, and then subjected to hydrogen crushing and air jet milling to obtain particle size distribution parameters SMD of 2.6 μm and D. 90 / D 10 Neodymium iron boron (NdFeB) magnetic powder with a density of 4.3 g / cm³ was obtained by oriented pressing of the NdFeB magnetic powder under a magnetic field greater than 1.8 T, followed by cold isostatic pressing. 3 Neodymium iron boron green blanks;

[0103] (3) Place the neodymium iron boron green billet into a vacuum heat treatment furnace for sintering heat treatment;

[0104] Vacuuming stage: Vacuum to 9.0 × 10⁻⁶ -3 Pa and maintain this vacuum level;

[0105] Exhaust stage: Heat to 320℃ at a rate of 8℃ / min and hold for 0.5h, then heat to 600℃ at a rate of 8℃ / min and hold for 1h, and then heat to 850℃ at a rate of 10℃ / min and hold for 2h.

[0106] Sintering and holding stage: The temperature is increased to 1080℃ at a rate of 10℃ / min and held for 4 hours;

[0107] Rapid cooling stage: Heating is stopped and circulating inert gas is introduced into the vacuum heat treatment furnace, and the temperature is reduced to room temperature by air cooling.

[0108] Then, a tempering heat treatment was performed, with the temperature raised to 900℃ and held for 2 hours. Heating was stopped and a circulating inert gas was introduced into the vacuum heat treatment furnace. The furnace was then cooled to room temperature by air cooling. The furnace was then heated again, with the temperature raised to 480℃ and held for 2 hours. Heating was stopped and a circulating inert gas was introduced into the vacuum heat treatment furnace. The furnace was then cooled to room temperature by air cooling to obtain neodymium iron boron magnet 1.

[0109] Compared with Comparative Example 2, the magnet of Example 1 has a finer and longer crack path during fracture, which is beneficial for stress absorption, and the grains are more uniform and finer, possessing the ideal microstructure characteristics of a magnet with high mechanical performance.

[0110] The performance of neodymium iron boron magnet 1 was tested. The magnetic property of neodymium iron boron magnet 1 is remanence. B r=14.56kGs, coercivity Hcj = 14.62 kOe, magnetic energy product ( BH m = 50.82MGsOe, squareness H k / H cj=0.927; the mechanical property test results of NdFeB magnet 1 are shown in Table 3.

[0111]

[0112] Comparative Example 2

[0113] (1) The chemical formula of the batching and smelting is (PrNd). 29.5 B 0.98 Zr 0.1 Cu 0.2 Al 0.1 Co 1.0 Fe bal Neodymium iron boron alloy (by mass percentage);

[0114] (2) Neodymium iron boron alloy is processed into rapidly solidified neodymium iron boron flakes through a rapid solidification casting process, and then crushed by a rotary toother to obtain coarse neodymium iron boron particles; the chemical formula of the batching and smelting is Pr 70 Cu 10 Al 10 Ga 10 (by mass percentage) a tough alloy, which is then processed through a rapid solidification casting process to obtain rapid solidification flakes of the tough alloy, and further processed by rotary tooth crushing to obtain coarse particles of the tough alloy; the coarse particles of NdFeB and the coarse particles of the tough alloy are uniformly mixed at a ratio of 99.5:0.5 (mass ratio) to obtain NdFeB bimetallic coarse powder; the NdFeB bimetallic coarse powder is then subjected to hydrogen crushing and air jet milling to obtain a particle size distribution parameter SMD of 2.7 μm and D... 90 / D 10 Neodymium iron boron (NdFeB) magnetic powder with a density of 4.8 g / cm³ was obtained by oriented pressing of the NdFeB magnetic powder under a magnetic field greater than 1.8 T, followed by cold isostatic pressing. 3 Neodymium iron boron green blanks;

[0115] (3) Place the neodymium iron boron green billet into a vacuum heat treatment furnace for sintering heat treatment;

[0116] Vacuuming stage: Vacuum to 9.0 × 10⁻⁶ -3 Pa and maintain this vacuum level;

[0117] Exhaust stage: Heat to 320℃ at a rate of 8℃ / min and hold for 0.5h, then heat to 600℃ at a rate of 8℃ / min and hold for 1h, and then heat to 850℃ at a rate of 10℃ / min and hold for 2h.

[0118] Sintering and holding stage: The temperature is increased to 1080℃ at a rate of 10℃ / min and held for 4 hours;

[0119] Rapid cooling stage: Heating is stopped and circulating inert gas is introduced into the vacuum heat treatment furnace, and the temperature is reduced to room temperature by air cooling.

[0120] Then, a tempering heat treatment was performed, with the temperature raised to 900℃ and held for 2 hours. Heating was stopped and a circulating inert gas was introduced into the vacuum heat treatment furnace. The furnace was then cooled to room temperature by air cooling. The furnace was then heated again, with the temperature raised to 480℃ and held for 2 hours. Heating was stopped and a circulating inert gas was introduced into the vacuum heat treatment furnace. The furnace was then cooled to room temperature by air cooling to obtain neodymium iron boron magnet 2.

[0121] The performance of neodymium iron boron magnet 2 was tested. The remanence of neodymium iron boron magnet 2 was determined. B r = 14.24 kGs, coercivity H cj = 14.91 kOe, magnetic energy product ( BH m = 49.18MGsOe, squareness H k / H cj=0.926; the mechanical property test results of NdFeB magnet 2 are shown in Table 4.

[0122]

[0123] Comparative Example 3

[0124] (1) The chemical formula of the batching and smelting is (PrNd). 29.5 B 0.98 Zr 0.1 Cu 0.2 Al 0.1 Co 1.0 Fe bal Neodymium iron boron alloy (by mass percentage);

[0125] (2) Neodymium iron boron alloy was processed into rapidly solidified neodymium iron boron flakes through a rapid solidification casting process, and then subjected to hydrogen crushing and air jet milling to obtain particle size distribution parameters SMD of 2.3 μm and D. 90 / D 10 Neodymium iron boron (NdFeB) magnetic powder with a density of 3.8 was obtained by oriented pressing of the NdFeB magnetic powder under a magnetic field greater than 1.8T, followed by cold isostatic pressing. 3 Neodymium iron boron green blanks;

[0126] (3) Place the neodymium iron boron green billet into a vacuum heat treatment furnace for sintering heat treatment;

[0127] Vacuuming stage: Same as in Example 1;

[0128] Exhaust stage: Same as in Example 1;

[0129] Heating phase: Starting at 850℃, the temperature is increased to the target temperature of 1080℃ at a heating rate of 10℃ / min.

[0130] "Wave-like" sintering and heat preservation stage: Same as in Example 1;

[0131] "Wave-like" slow cooling phase: Same as in Example 1;

[0132] Rapid cooling stage: Same as in Example 1.

[0133] Then, a tempering heat treatment was performed, the same as in Example 1, to obtain neodymium iron boron magnet 3.

[0134] The performance of neodymium iron boron magnet 3 was tested. The magnetic property of neodymium iron boron magnet 3 is remanence. B r = 14.24 kGs, coercivity H cj = 14.91 kOe, magnetic energy product ( BH m = 49.18MGsOe, squareness H k / H cj=0.926; the mechanical property test results of NdFeB magnet 3 are shown in Table 5.

[0135]

[0136] Comparative Example 4

[0137] (1) The chemical formula of the batching and smelting is (PrNd). 29.5 B 0.98 Zr 0.1 Cu 0.2 Al 0.1 Co 1.0 Fe bal Neodymium iron boron alloy (by mass percentage);

[0138] (2) Neodymium iron boron alloy was processed into rapidly solidified neodymium iron boron flakes through a rapid solidification casting process, and then subjected to hydrogen crushing and air jet milling to obtain particle size distribution parameters SMD of 2.3 μm and D. 90 / D 10 Neodymium iron boron (NdFeB) magnetic powder with a density of 3.8 was obtained by oriented pressing of the NdFeB magnetic powder under a magnetic field greater than 1.8T, followed by cold isostatic pressing. 3 Neodymium iron boron green blanks;

[0139] (3) Place the neodymium iron boron green billet into a vacuum heat treatment furnace for sintering heat treatment;

[0140] Vacuuming stage: Same as in Example 1;

[0141] Exhaust stage: Same as in Example 1;

[0142] The “wave-like” slow heating phase is the same as in Example 1;

[0143] Sintering and heat preservation stage: heat preservation at 1080℃ for 4 hours;

[0144] "Wave-like" slow cooling phase: Same as in Example 1;

[0145] Rapid cooling stage: Same as in Example 1.

[0146] Then, a tempering heat treatment was performed, the same as in Example 1, to obtain neodymium iron boron magnet 4.

[0147] The performance of neodymium iron boron magnet 4 was tested. The magnetic property of neodymium iron boron magnet 4 is remanence. B r=14.65kGs, coercivity H cj = 13.87 kOe, magnetic energy product ( BH m=51.15MGsOe, squareness H k / H cj=0.911; the mechanical property test results of NdFeB magnet 4 are shown in Table 6.

[0148]

[0149] Comparative Example 5

[0150] (1) The chemical formula of the batching and smelting is (PrNd). 29.5 B 0.98 Zr 0.1 Cu 0.2 Al 0.1 Co 1.0 Fe bal Neodymium iron boron alloy (by mass percentage);

[0151] (2) Neodymium iron boron alloy was processed into rapidly solidified neodymium iron boron flakes through a rapid solidification casting process, and then subjected to hydrogen crushing and air jet milling to obtain particle size distribution parameters SMD of 2.3 μm and D. 90 / D 10 Neodymium iron boron (NdFeB) magnetic powder with a density of 3.8 was obtained by oriented pressing of the NdFeB magnetic powder under a magnetic field greater than 1.8T, followed by cold isostatic pressing. 3 Neodymium iron boron green blanks;

[0152] (3) Place the neodymium iron boron green billet into a vacuum heat treatment furnace for sintering heat treatment;

[0153] Vacuuming stage: Same as in Example 1;

[0154] Exhaust stage: Same as in Example 1;

[0155] The “wave-like” slow heating phase is the same as in Example 1;

[0156] "Wave-like" sintering and heat preservation stage: Same as in Example 1;

[0157] Rapid cooling stage: Same as in Example 1.

[0158] Then, a tempering heat treatment was performed, the same as in Example 1, to obtain neodymium iron boron magnet 5.

[0159] The performance of neodymium iron boron magnet 5 was tested. The magnetic property of neodymium iron boron magnet 5 is remanence. B r=14.58kGs, coercivity H cj = 14.99 kOe, magnetic energy product ( BH m=50.73MGsOe, squareness H k / H cj=0.928; the mechanical property test results of NdFeB magnet 5 are shown in Table 7.

[0160]

[0161] Comparative Example 6

[0162] (1) The chemical formula of the batching and smelting is (PrNd). 29.5 B 0.98 Zr 0.1 Cu 0.2 Al 0.1 Co 1.0 Fe bal Neodymium iron boron alloy (by mass percentage);

[0163] (2) Neodymium iron boron alloy was processed into rapidly solidified neodymium iron boron flakes through a rapid solidification casting process, and then subjected to hydrogen crushing and air jet milling to obtain particle size distribution parameters SMD of 2.7 μm and D. 90 / D 10 Neodymium iron boron (NdFeB) magnetic powder with a density of 4.5 g / cm³ was obtained by oriented pressing of the NdFeB magnetic powder under a magnetic field greater than 1.8 T, followed by cold isostatic pressing. 3 Neodymium iron boron green blanks;

[0164] (3) Place the neodymium iron boron green billet into a vacuum heat treatment furnace for sintering heat treatment;

[0165] Vacuuming stage: Same as in Example 1;

[0166] Exhaust stage: Same as in Example 1;

[0167] The “wave-like” slow heating phase is the same as in Example 1;

[0168] "Wave-like" sintering and heat preservation stage: Same as in Example 1;

[0169] "Wave-like" slow cooling phase: Same as in Example 1;

[0170] Rapid cooling stage: Same as in Example 1.

[0171] Then, a tempering heat treatment was performed, the same as in Example 1, to obtain neodymium iron boron magnet 6.

[0172] The performance of neodymium iron boron magnet 6 was tested. The magnetic property of neodymium iron boron magnet 6 is remanence. B r=14.60kGs, coercivity H cj = 14.41 kOe, magnetic energy product ( BH m=50.99MGsOe, squareness H k / H cj=0.917; the mechanical property test results of NdFeB magnet 6 are shown in Table 8.

[0173]

[0174] As can be seen from the above, the method for preparing NdFeB magnets with mechanical service characteristics of the present invention can effectively improve the magnetic and mechanical properties of NdFeB magnets with different composition systems, such as weightless NdFeB and high-abundance rare-earth NdFeB.

[0175] A comparison of the test results of Example 1 and Comparative Example 1 shows that, under the same composition system, the magnet prepared by the conventional sintering and heat treatment process in Comparative Example 1 has no significant difference in magnetic properties compared with the magnet prepared in Example 1. However, the mechanical properties of the NdFeB magnet 1 in Comparative Example 1 are significantly weaker than those of the NdFeB magnet 1 with high mechanical service characteristics in Example 1.

[0176] The comparison of the test results of Example 1 and Comparative Example 2 shows that although the mechanical properties of the magnet can be significantly improved by adding a second toughening phase (dual alloy method) in Comparative Example 2, it will cause a significant deterioration in the key magnetic parameters of neodymium iron boron magnets, namely remanence and magnetic energy product, and the consistency of mechanical properties is poor.

[0177] A comparison of the test results of Example 1, Comparative Example 3, Comparative Example 4, Comparative Example 5, and Comparative Example 6 shows that Comparative Example 3 lacks a "wave-like" slow heating stage, Comparative Example 4 lacks a "wave-like" sintering and heat preservation stage, Comparative Example 5 lacks a "wave-like" slow cooling stage, and Comparative Example 6 controls the airflow mill parameters to achieve the desired NdFeB magnetic powder particle size distribution parameters SMD and D. 90 / D 10 The increase led to a decrease in mechanical properties.

[0178] In summary, the method for preparing NdFeB magnets with high mechanical service characteristics of the present invention ensures that the NdFeB magnets have both high mechanical and permanent magnetic properties without significantly affecting the magnet composition design, and is applicable to improving the mechanical properties of NdFeB magnets with different composition systems.

[0179] All aspects, embodiments, and features of this invention should be considered illustrative in all respects and not limiting of the invention; the scope of the invention is defined only by the claims. Other embodiments, modifications, and uses will become apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.

[0180] In the preparation method of this invention, the order of the steps is not limited to the listed order. For those skilled in the art, variations in the order of the steps without creative effort are also within the scope of protection of this invention. Furthermore, two or more steps or actions can be performed simultaneously.

[0181] Finally, it should be noted that the specific embodiments described herein are merely illustrative examples of the invention and are not intended to limit the implementation of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them; it is neither necessary nor possible to exemplify all embodiments here. However, these obvious variations or modifications derived from the essential spirit of the invention still fall within the scope of protection of the invention, and interpreting them as any additional limitation would contradict the spirit of the invention.

Claims

1. A method for preparing a neodymium iron boron magnet with high mechanical service characteristics, characterized in that, The method includes: subjecting neodymium iron boron green blanks to sintering heat treatment and tempering heat treatment in sequence; the sintering heat treatment includes six stages: vacuum stage, exhaust stage, slow heating stage, sintering stage, slow cooling stage, and rapid cooling stage; The slow heating phase is a "wave-like" slow heating, starting from the initial temperature T11, increasing by 20~50℃ and holding for a period of time, then decreasing by 5~15℃ and holding for a period of time, and so on until the target temperature T12 is reached; the holding time of the slow heating phase is 1~10h, the heating rate is 1~10℃ / min, and the cooling rate is 1~10℃ / min. The sintering stage is a "wave-like" sintering and heat preservation process. Within the range of 800~1600℃, a temperature range with an upper and lower temperature difference of 5~50℃ is selected as the sintering temperature. When the temperature reaches the upper limit temperature point T21 of the temperature range, it is kept at that temperature. Then, the temperature drops by 5~50℃ to the lower limit temperature point T22 of the temperature range and is kept at that temperature. Then, the temperature rises back to the upper limit temperature point T21 of the temperature range and is kept at that temperature. This cycle is repeated for 1~30 hours. The slow cooling stage is a "wave-like" gradual cooling process. Starting from the sintering temperature, the temperature drops by 40-200°C and is held at that temperature, then rises by 5-35°C and is held at that temperature, until the temperature drops to point T3, which is 600-900°C. The holding time of the slow cooling stage is 0.5-20 hours, the heating rate is 5-30°C / min, and the cooling rate is 5-30°C / min. The rapid cooling stage includes: stopping heating and introducing circulating inert gas, and cooling down to room temperature by air cooling; The target temperature T12 - the initial temperature T11 = 100~400℃; The lower limit temperature point T22 of the temperature range interval ≤ the target temperature T12 < the upper limit temperature point T21 of the temperature range interval; The lower limit temperature point T22 of the temperature range - T3 = 100~500℃.

2. The method for preparing a neodymium iron boron magnet with high mechanical service characteristics according to claim 1, characterized in that, The vacuuming phase is conducted at room temperature. After this phase, the vacuum level is controlled to be no higher than 10. -2 Pa, and this vacuum level is maintained after the completion of the five subsequent stages of sintering heat treatment.

3. The method for preparing a neodymium iron boron magnet with high mechanical service characteristics according to claim 1, characterized in that, The exhaust stage involves a stepped heating process, raising the temperature to 2 to 6 steps between 300 and 900°C and holding each step at the same temperature.

4. The method for preparing a neodymium iron boron magnet with high mechanical service characteristics according to claim 3, characterized in that, The temperature of the last step in the exhaust stage is less than or equal to the initial temperature T11 of the slow heating stage.

5. The method for preparing a neodymium iron boron magnet with high mechanical service characteristics according to claim 1, characterized in that, The tempering heat treatment includes two stages: high-temperature tempering heat treatment and low-temperature tempering heat treatment. The high-temperature tempering heat treatment includes holding at a high-temperature tempering temperature T51 of 700~1100℃ for 1~12 hours and then air-cooling down to room temperature; The low-temperature tempering heat treatment includes holding at a low-temperature tempering temperature of 300~600℃ for 1~12 hours and then air-cooling down to room temperature.

6. The method for preparing a neodymium iron boron magnet with high mechanical service characteristics according to claim 1, characterized in that, The NdFeB green billet is obtained by rapidly solidifying NdFeB alloy into a sheet, pulverizing, and pressing; the pulverizing includes hydrogen crushing and air jet milling; the pressing includes orientation molding and cold isostatic pressing.

7. The method for preparing a neodymium iron boron magnet with high mechanical service characteristics according to claim 6, characterized in that, The particle size distribution parameter SMD of the magnetic powder obtained by air jet milling is 1~10μm; the D90 / D10 of the magnetic powder obtained by air jet milling is 2~5.

8. A neodymium iron boron magnet with high mechanical service characteristics, characterized in that, It is prepared by the method for preparing neodymium iron boron magnets with high mechanical service characteristics as described in any one of claims 1 to 7.

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