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

Abstract

The invention relates to the technical field of neodymium-iron-boron magnet production, in particular to a preparation method of a neodymium-iron-boron magnet with a high mechanical service characteristic. The invention discloses a preparation method of a neodymium-iron-boron magnet with a high mechanical service characteristic. The preparation method comprises the following steps: sequentially carrying out sintering heat treatment and tempering heat treatment on a neodymium-iron-boron green body; the sintering heat treatment comprises six stages: a vacuumizing stage, an exhausting stage, a slow heating stage, a sintering stage, a slow cooling stage and a rapid cooling stage; the slow heating stage is wave type slow heating, the sintering stage is wave type sintering heat preservation, and the slow cooling stage is wave type slow cooling. According to the preparation method of the neodymium-iron-boron magnet with the mechanical service characteristic, on the basis that the magnetic performance of the neodymium-iron-boron magnet is guaranteed, the mechanical performance is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of neodymium iron boron magnet production, and relates to a preparation method of neodymium iron boron magnet with high mechanical service characteristics. Background Art

[0002] As the third-generation rare earth permanent magnet material, sintered neodymium iron boron has both high coercivity and high remanence characteristics. Its development and application reflect the major development demand direction in emerging industrial fields. With the improvement of the magnetic properties of rare earth permanent magnet materials and the continuous expansion of their application fields, the poor plastic toughness, difficult machining, and poor shock and vibration resistance of sintered neodymium iron boron permanent magnet materials have become its serious weaknesses, restricting the further expansion of the application range of permanent magnet materials. Especially as magnetic functional devices are developing towards miniaturization, thinning, high functionality, and high precision, in high-precision instruments and meters, the processing accuracy requirements for magnets are getting higher and higher. The brittleness problem of neodymium iron boron magnets has gradually emerged. It has poor machinability and is prone to cracking, peeling, and chipping during processing, assembly, and use, greatly reducing the yield and processing accuracy of the magnets and restricting the application of rare earth permanent magnet materials in high-precision instruments and meters. Improving the mechanical service characteristics of neodymium iron boron, such as strength and toughness, has become an important research direction in the industry.

[0003] Due to the powder metallurgy preparation process of sintered neodymium iron boron permanent magnet materials, that is, magnets are prepared through processes such as rapid solidification casting, hydrogen crushing, air jet milling, orientation forming, cold isostatic pressing, sintering and tempering, etc. The final magnet products show greater brittleness, and the crack propagation mode during the fracture process mainly presents an intergranular fracture. A large number of studies have shown that cracks always extend along the weak areas of the magnet. Therefore, strengthening or repairing the weak areas or defects in the microstructure of the magnet has become an important way to improve the mechanical properties of neodymium iron boron magnets. Currently, usually, a means of introducing a toughening second phase (intergranular phase) as an additive into the magnet is adopted to enhance the mechanical properties of the magnet. Although the mechanical properties of the magnet can be significantly optimized through this method, the introduction of the second phase inevitably causes a large reduction in the magnetic properties of the magnet (especially remanence and magnetic energy product), resulting in a weakening of the external magnetic moment of the magnet and bringing difficulties to the application of the magnet in high-tech fields. How to improve the mechanical properties of the magnet through intrinsic structure optimization without introducing an additional second phase has become the key to promoting the further development of neodymium iron boron permanent magnet materials and is of great significance for the application and development of rare earth permanent magnet materials. Summary of the Invention

[0004] The object of the present invention is to address the above problems existing in the prior art, and propose a preparation method that can significantly improve the mechanical service characteristics of neodymium iron boron magnets without introducing a second phase. Under the condition of basically not affecting the magnet composition design, it ensures that the magnet has both high mechanical and permanent magnetic properties, and is applicable to improving the mechanical properties of neodymium iron boron magnets with different composition systems.

[0005] One object of the present invention is achieved by the following technical solutions:

[0006] A preparation method of a neodymium-iron-boron magnet with high mechanical service characteristics, comprising: sequentially performing sintering heat treatment and tempering heat treatment on a neodymium-iron-boron green compact; the sintering heat treatment includes six stages: a vacuum pumping stage, an exhaust stage, a slow heating stage, a sintering stage, a slow cooling stage, and a rapid cooling stage;

[0007] The slow heating stage is "wave-like" slow heating, starting from the initial temperature T11, heating by 20-50°C each time and holding the temperature, then decreasing by 5-15°C and holding the temperature, and so on in cycles until the target temperature T12;

[0008] The sintering stage is "wave-like" sintering and heat preservation. In the range of 800-1600°C, a temperature range interval with an upper and lower temperature difference of 5-50°C is taken as the sintering temperature. When the temperature reaches the upper limit temperature point T21 of the temperature range interval, heat preservation is carried out, then it is decreased by 5-50°C to the lower limit temperature T22 of the temperature range interval and heat preservation is carried out, and then it is increased back to the upper limit temperature point T21 of the temperature range interval and heat preservation is carried out, and so on in cycles for 1-30 h;

[0009] The slow cooling stage is "wave-like" slow cooling. Starting from the sintering temperature, each time it is decreased by 40-200°C and heat preservation is carried out, then it is increased by 5-35°C and heat preservation is carried out until the temperature drops to the temperature point T3, and T3 is 600-900°C.

[0010] Preferably, the vacuum pumping stage is carried out at room temperature, and after the end of this stage, the vacuum degree is controlled not to be higher than 10 - 2 Pa, and this vacuum degree is maintained after the end of the subsequent five stages of the sintering heat treatment.

[0011] Preferably, the exhaust stage is stepwise heating, heating to 2-6 step temperatures in the range of 300-900°C and respectively holding the temperature, and the heating rate is 1-20°C / min.

[0012] More preferably, the last step temperature of the exhaust stage ≤ the initial temperature T11 of the slow heating stage.

[0013] Preferably, the slow heating stage includes: in the range of 700-1100°C, starting from the initial temperature T11, heating by 20-30°C each time and holding the temperature, then decreasing by 5-10°C and holding the temperature, and so on in cycles until the target temperature T12.

[0014] More preferably, the target temperature T12 > the initial temperature T11, and the target temperature T12 - the initial temperature T11 = 100-400°C.

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

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

[0017] Preferably, the heat preservation time in the slow heating stage is 1 - 10 h, the heating rate is 1 - 10 °C / min, and the cooling rate is 1 - 10 °C / min.

[0018] More preferably, the heating rate in the slow heating stage ≤ the cooling rate.

[0019] Preferably, the lower temperature point T22 of the temperature range interval ≤ the target temperature T12 < the upper temperature point T21 of the temperature range interval, or the lower temperature point T22 of the temperature range interval < the target temperature T12 ≤ the upper temperature point T21 of the temperature range interval, or the lower temperature point T22 of the temperature range interval < the target temperature T12 < the upper temperature point T21 of the temperature range interval.

[0020] Preferably, the lower temperature point T22 of the temperature range interval > T3.

[0021] More preferably, the lower temperature point T22 of the temperature range interval - T3 = 100 - 500 °C.

[0022] Preferably, the upper temperature point T21 of the temperature range interval - the lower temperature point T22 of the temperature range interval = 5 - 20 °C.

[0023] Preferably, the sintering stage includes: taking a temperature range interval with a temperature difference of 10 °C up and down in the range of 1000 - 1100 °C as the sintering temperature, insulating when the temperature reaches the upper temperature point T21 of the temperature range interval, then dropping 10 °C to the lower temperature point T22 of the temperature range interval and insulating, then rising back to the upper temperature point T21 of the temperature range interval and insulating, and repeating this cycle for 1 - 10 h; 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, insulating every time the temperature drops 50 - 100 °C and then rising 10 - 20 °C and insulating until the temperature drops to a temperature point T3 within 700 - 850 °C; the heating rate is 5 - 30 °C / min, and the cooling rate is 5 - 30 °C / min.

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

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

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

[0028] The high-temperature temper heat treatment includes holding at a high-temperature tempering temperature T51 of 700-1100 °C for 1-12 h and then rapidly cooling to room temperature;

[0029] The low-temperature temper heat treatment includes holding at a low-temperature tempering temperature T52 of 300-600 °C for 1-12 h and then rapidly cooling to room temperature.

[0030] Preferably, the density of the NdFeB green compact is 3.8-4.4 g / cm 3 .

[0031] More preferably, the density of the NdFeB green compact is 4.1-4.4 g / cm 3 .

[0032] Preferably, the NdFeB green compact is obtained by rapid solidification casting of NdFeB alloy, powder making, and pressing.

[0033] More preferably, the NdFeB 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 28.5 ≤ a ≤ 31.5, 0.88 ≤ b < 0.99, 0.5 ≤ c ≤ 3 are satisfied.

[0034] More preferably, the powder making includes hydrogenation and jet milling.

[0035] Even more preferably, the particle size distribution parameter SMD of the magnetic powder obtained by jet milling is 1-10 μm.

[0036] Even more preferably, the particle size distribution parameter SMD of the magnetic powder obtained by jet milling is 2-2.5 μm.

[0037] Even more preferably, the D 90 / D 10 of the magnetic powder obtained by jet milling is 2-5.

[0038] Even more preferably, the D 90 / D 10It is 3.2 to 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 is 1 to 5 T, and the pressure is 10 to 18 MPa.

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

[0042] The second object of the present invention is achieved by the following technical solutions:

[0043] A neodymium iron boron magnet with high mechanical service characteristics, having a density of 4.2 to 4.6 g / cm 3 .

[0044] Beneficial effects

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

[0046] 1. In the preparation method of the neodymium iron boron magnet with high mechanical service characteristics of the present invention, through six sintering heat treatment stages including the vacuum pumping stage, the exhaust stage, the slow heating stage, the sintering stage, the slow cooling stage, and the rapid cooling stage, while ensuring the magnetic properties of the neodymium iron boron magnet, the improvement of mechanical properties is realized.

[0047] 2. In the preparation method of the neodymium iron boron magnet with high mechanical service characteristics of the present invention, through the effective regulation of the microstructure of the magnet, the optimization of the intrinsic structure of the magnet is achieved, avoiding the tissue composition fluctuations caused by the fluctuations in the second-phase introduction process in the existing mechanical modification methods, and ensuring the uniformity and consistency of the microstructure of the magnet to the greatest extent, so that the magnets prepared in batches have good mechanical and magnetic property consistency and are suitable for industrial large-scale production.

[0048] 3. The present invention regulates the particle size distribution parameters SMD, D 90 / D 10 ; For the neodymium iron boron magnet powder with a small SMD, the specific surface area of the magnet powder particles is large, the number of contact points between the magnet powder particles increases, and they can better fill each other, improving the green density and helping to improve the magnetic and mechanical properties of the magnet; D90 / D10 is used to characterize the width of the particle size distribution. The particle size distribution of the neodymium iron boron magnet powder of the present invention is relatively narrow, and the particle sizes are relatively uniform, which is beneficial to the forming uniformity of the neodymium iron boron magnet and ensures the performance.

[0049] 4. Sintering heat treatment and tempering heat treatment of the neodymium iron boron green body with a relatively large density in the present invention are beneficial to the subsequent liquid phase sintering and uniform densification shrinkage process.

[0050] 5. The preparation method of the NdFeB magnet with high mechanical service characteristics of the present invention does not need to introduce a second-phase component, which can reduce the raw material cost and the production cost in the process. Detailed implementation mode

[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 used to help understand the present invention and are not used to specifically limit the present invention.

[0052] If there is no special description, the raw materials used in the embodiments of the present invention are all common raw materials in the art, and the methods used in the embodiments are all conventional methods in the art.

[0053] In this article, the preparation method of the NdFeB magnet with high mechanical service characteristics can be applied to NdFeB magnets with different composition systems.

[0054] In this article, the steps of making the rapid solidification cast sheet, making powder, and pressing can be carried out by using the existing technology.

[0055] In this article, the preparation method of the NdFeB magnet with high mechanical service characteristics includes:

[0056] (1) Mix and melt the NdFeB alloy. By mass percentage, its chemical formula is 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 28.5 ≤ a ≤ 31.5, 0.88 ≤ b < 0.99, 0.5 ≤ c ≤ 3 are satisfied.

[0057] (2) Make the rapid solidification cast sheet of the NdFeB alloy, perform hydrogen breaking, airflow milling to make powder, and obtain the NdFeB green body by orientation pressing and cold isostatic pressing.

[0058] (3) Carry out sintering heat treatment and tempering heat treatment on the NdFeB green body to obtain the NdFeB magnet with high mechanical service characteristics.

[0059] The sintering heat treatment includes six stages: vacuum pumping stage, exhaust stage, slow heating stage, sintering stage, slow cooling stage, and fast cooling stage.

[0060] The vacuum pumping stage is carried out at room temperature. After the end of this stage, the vacuum degree is controlled not to be higher than 10 -2 Pa, and this vacuum degree is maintained after the end of the subsequent five stages of the sintering heat treatment.

[0061] The exhaust stage is a stepped heating, heating to 2 - 6 stepped temperatures in the range of 300 - 900 °C and keeping warm respectively.

[0062] The slow heating stage is "wavy" slow heating. Starting from the initial temperature T11, it rises by 20-50 °C each time and is kept warm, then drops by 5-15 °C and is kept warm, and this cycle continues until the target temperature T12;

[0063] The target temperature T12 > the initial temperature T11, and the target temperature T12 - the initial temperature T11 = 100-400 °C;

[0064] The last step temperature of the exhaust stage ≤ the initial temperature T11 of the slow heating stage;

[0065] The sintering stage is "wavy" sintering and heat preservation. In the range of 800-1600 °C, a temperature range interval with an upper and lower temperature difference of 5-50 °C is taken as the sintering temperature. When the temperature reaches the upper limit temperature point T21 of the temperature range interval, it is kept warm, then drops by 5-50 °C to the lower limit temperature T22 of the temperature range interval and is kept warm, and then rises back to the upper limit temperature point T21 of the temperature range interval and is kept warm. This cycle repeats for 1-30 h;

[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 "wavy" slow cooling. Starting from the sintering temperature, it drops by 40-200 °C each time and is kept warm, then rises by 5-35 °C and is kept warm until the temperature drops to the temperature point T3, and T3 is 600-900 °C;

[0068] The rapid cooling stage includes: stopping heating and filling with circulating inert gas, and cooling 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] The high-temperature tempering heat treatment includes keeping warm at the high-temperature tempering temperature T51 of 700-1100 °C for 1-12 h and then rapidly cooling to room temperature;

[0071] The low-temperature tempering heat treatment includes keeping warm at the low-temperature tempering temperature T52 of 300-600 °C for 1-12 h and then rapidly cooling to room temperature.

[0072] In this article, the mechanical property test method of the high mechanical service property NdFeB magnet includes:

[0073] The prepared NdFeB magnet is in accordance with the standard size of 15 mm × 6 mm × 5 mm (orientation direction) (GB / T232-2010 Metallic materials - Bend test method) and The specimens were machined in the direction of orientation and subjected to 10 tests for 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).

[0074] Example 1

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

[0076] (2) The NdFeB alloy was cast by rapid solidification process to obtain NdFeB rapid solidification sheet, and then hydrogen crushing and air flow grinding were performed to obtain particle size distribution parameters SMD of 2.3 μm and D 90 / D 10 The NdFeB magnetic powder is 3.8; the NdFeB magnetic powder is oriented and pressed in a magnetic field greater than 1.8T, and then cold isostatically pressed to obtain a density of 4.2g / cm 3 NdFeB green compact;

[0077] (3) Placing the NdFeB green body into a vacuum heat treatment furnace for sintering heat treatment.

[0078] Vacuuming stage: vacuum to 9.0×10 -3 Pa and maintain this vacuum degree;

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

[0080] "Wave-like" slow heating stage: with 850℃ as the initial temperature, the heating rate is 3℃ / min and the cooling rate is 5℃ / min. After each 30℃ rise in temperature, the temperature is kept for 15min, then the temperature is dropped by 5℃ and kept for 2min. This cycle is repeated until the temperature reaches the target temperature of 1080℃.

[0081] "Wave-type" sintering and heat preservation stage: in the temperature range of 1075-1085℃, the temperature is raised and lowered at a rate of 1℃ / min. The cycle lasts for 4 hours.

[0082] "Wave-like" slow cooling stage: with a heating and cooling rate of 10℃ / min, keep the temperature for 20 minutes after each 100℃ drop, then rise 20℃ and keep the temperature for 20 minutes, and repeat this cycle until the temperature drops below 850℃;

[0083] Fast cooling stage: Stop heating and fill the vacuum heat treatment furnace with circulating inert gas, and cool down to room temperature by air cooling.

[0084] Then perform temper heat treatment. Heat up to 900 °C and hold for 2 h, stop heating and fill the vacuum heat treatment furnace with circulating inert gas, and cool down to room temperature by air cooling; heat up again, heat up to 480 °C and hold for 2 h, stop heating and fill the vacuum heat treatment furnace with circulating inert gas, and cool down to room temperature by air cooling to obtain the NdFeB magnet 1 with high mechanical service characteristics.

[0085] Perform performance testing on the NdFeB magnet 1 with high mechanical service characteristics. The magnetic properties of the NdFeB magnet 1 with high mechanical service characteristics are remanence Br = 14.59 kGs, coercivity Hcj = 14.82 kOe, maximum energy product (BH)m = 50.95 MGsOe, and squareness Hk / Hcj = 0.931; the mechanical property test results of the NdFeB magnet 1 with high mechanical service characteristics are shown in Table 1.

[0086] Table 1. Mechanical property test results of the NdFeB magnet with high mechanical service characteristics in Example 1

[0087]

[0088] Example 2

[0089] (1) Prepare a NdFeB alloy with the chemical formula (PrNd) 21.3 (LaCe) 9.2 B 0.89 Ti 0.2 Al 0.3 Co 0.8 Fe bal (by mass percentage);

[0090] (2) Obtain NdFeB rapid solidification flakes through the rapid solidification casting process of the NdFeB alloy, and then through hydrogen crushing and air jet milling, obtain NdFeB magnetic powder with a particle size distribution parameter SMD of 2.5 μm and D 90 / D 10 of 4.2; Orient and compact the NdFeB magnetic powder under a magnetic field greater than 1.8 T, and then perform cold isostatic pressing to obtain a NdFeB green compact with a density of 4.3 g / cm 3 ;

[0091] (3) Place the NdFeB green compact into a vacuum heat treatment furnace for sintering heat treatment;

[0092] Vacuum pumping stage: Vacuum to 7.5×10 -3 Pa and maintain this vacuum degree;

[0093] Exhaust stage: Heat up to 300 °C at a rate of 10 °C / min and hold for 1 h, then heat up to 550 °C at a rate of 10 °C / min and hold for 1 h, and then heat up to 790 °C at a rate of 10 °C / min and hold for 2.5 h;

[0094] "Wave-like" slow heating stage: Starting from 790 °C as the initial temperature, perform heating and cooling operations at a heating rate of 5 °C / min and a cooling rate of 5 °C / min. After the temperature rises 20 °C each time, hold for 10 min, then drop 5 °C and hold for 5 min. Repeat this cycle until the temperature rises to the target temperature of 1030 °C;

[0095] "Wave-like" sintering and holding stage: In the temperature range of 1025 - 1035 °C, perform cyclic heating and cooling operations at a heating and cooling rate of 1 °C / min. This cyclic heating and cooling operation lasts for 4 h;

[0096] "Wave-like" slow cooling stage: At a heating and cooling rate of 10 °C / min, after the temperature drops 80 °C each time, hold for 20 min, then rise 10 °C and hold for 20 min. Repeat this cycle until the temperature drops below 750 °C;

[0097] Fast cooling stage: Stop heating and fill the vacuum heat treatment furnace with circulating inert gas, and cool down to room temperature by air cooling.

[0098] Then perform temper heat treatment. Heat up to 750 °C and hold for 2 h, stop heating and fill the vacuum heat treatment furnace with circulating inert gas, and cool down to room temperature by air cooling; Heat again, heat up to 450 °C and hold for 2 h, stop heating and fill the vacuum heat treatment furnace with circulating inert gas, and cool down to room temperature by air cooling to obtain the neodymium iron boron magnet 2 with high mechanical service characteristics.

[0099] Perform performance tests on the neodymium iron boron magnet 2 with high mechanical service characteristics. The magnetic properties of the neodymium iron boron magnet 2 with high mechanical service characteristics are: remanence Br = 12.72 kGs, coercivity Hcj = 13.25 kOe, maximum energy product (BH)m = 37.39 MGsOe, squareness Hk / Hcj = 0.925; The test results of the mechanical properties of the neodymium iron boron magnet 2 with high mechanical service characteristics are shown in Table 2.

[0100] Table 2. Test results of the mechanical properties of the neodymium iron boron magnet with high mechanical service characteristics in Example 2

[0101]

[0102] Comparative Example 1

[0103] (1) The chemical formula of the ingredient melting is (PrNd) 29.5 B 0.98 Zr 0.1 Cu0.2 Al 0.1 Co 1.0 Fe bal (by mass percentage) neodymium-iron-boron alloy;

[0104] (2) The neodymium-iron-boron alloy is obtained as a neodymium-iron-boron rapid solidification sheet through the rapid solidification casting process, and then through hydrogen crushing and jet milling, neodymium-iron-boron magnetic powder with a particle size distribution parameter SMD of 2.6 μm and D 90 / D 10 of 4.3 is obtained; the neodymium-iron-boron magnetic powder is subjected to orientation pressing under a magnetic field greater than 1.8 T, and then cold isostatic pressing is carried out to obtain a neodymium-iron-boron green compact with a density of 4.2 g / cm 3 ;

[0105] (3) The neodymium-iron-boron green compact is placed in a vacuum heat treatment furnace for sintering heat treatment;

[0106] Vacuum pumping stage: The vacuum is pumped to 9.0×10 -3 Pa and this vacuum degree is maintained;

[0107] Exhaust stage: The temperature is raised to 320 °C at a rate of 8 °C / min and held for 0.5 h, then immediately the temperature is raised to 600 °C at a rate of 8 °C / min and held for 1 h, and then the temperature is raised to 850 °C at a rate of 10 °C / min and held for 2 h;

[0108] Sintering holding stage: The temperature is raised to 1080 °C at a rate of 10 °C / min and held for 4 h;

[0109] Fast cooling stage: Heating is stopped and circulating inert gas is introduced into the vacuum heat treatment furnace, and the temperature is cooled to room temperature by air cooling.

[0110] Then stress relief heat treatment is carried out. After heating to 900 °C, it is held for 2 h, heating is stopped and circulating inert gas is introduced into the vacuum heat treatment furnace, and the temperature is cooled to room temperature by air cooling; heating again, after heating to 480 °C, it is held for 2 h, heating is stopped and circulating inert gas is introduced into the vacuum heat treatment furnace, and the temperature is cooled to room temperature by air cooling, obtaining neodymium-iron-boron magnet 1.

[0111] Compared with Comparative Example 2, the magnet of Example 1 has a finer and longer crack path during the fracture process, which is beneficial to stress absorption, and the grains are more uniform and finer, having the organizational structure characteristics of an ideal high mechanical property magnet.

[0112] The neodymium-iron-boron magnet 1 is subjected to performance testing. The magnetic properties of the neodymium-iron-boron magnet 1 are remanence Br = 14.56 kGs, coercivity Hcj = 14.62 kOe, magnetic energy product (BH)m = 50.82 MGsOe, squareness Hk / Hcj = 0.927; the mechanical property test results of the neodymium-iron-boron magnet 1 are shown in Table 3.

[0113] Table 3. Test Results of the Mechanical Properties of the NdFeB Magnet in Comparative Example 1

[0114]

[0115] Comparative Example 2

[0116] (1) The formula of the alloy for batching and melting is (PrNd) 29.5 B 0.98 Zr 0.1 Cu 0.2 Al 0.1 Co 1.0 Fe bal (by mass percentage) NdFeB alloy;

[0117] (2) The NdFeB alloy is obtained by a rapid solidification casting process to obtain NdFeB rapid solidification sheets, and then through rotary tooth crushing to obtain NdFeB coarse particles; the formula of the alloy for batching and melting is Pr 70 Cu 10 Al 10 Ga 10 (by mass percentage) ductile alloy, which is obtained by a rapid solidification casting process to obtain ductile alloy rapid solidification sheets, and through rotary tooth crushing to obtain ductile alloy coarse particles; the NdFeB coarse particles and the ductile alloy coarse particles are uniformly mixed in a ratio of 99.5:0.5 (mass ratio) to obtain NdFeB double alloy coarse powder; the NdFeB double alloy coarse powder is subjected to hydrogen crushing and air jet milling to obtain NdFeB magnetic powder with a particle size distribution parameter SMD of 2.7 μm and D 90 / D 10 of 4.8; the NdFeB magnetic powder is oriented and pressed under a magnetic field greater than 1.8 T, and then cold isostatically pressed to obtain a NdFeB green compact with a density of 4.2 g / cm 3 ;

[0118] (3) The NdFeB green compact is placed in a vacuum heat treatment furnace for sintering heat treatment;

[0119] Vacuum pumping stage: Vacuum to 9.0×10 -3 Pa and maintain this vacuum degree;

[0120] Exhaust stage: Heat up at a rate of 8 °C / min to 320 °C and hold for 0.5 h, then heat up at a rate of 8 °C / min to 600 °C and hold for 1 h, and then heat up at a rate of 10 °C / min to 850 °C and hold for 2 h;

[0121] Sintering holding stage: Heat up at a rate of 10 °C / min to 1080 °C and hold for 4 h;

[0122] Fast cooling stage: Stop heating and fill the vacuum heat treatment furnace with circulating inert gas, and cool down to room temperature by air cooling.

[0123] Then, a tempering heat treatment is carried out. The temperature is raised to 900 °C and held for 2 h. Then, the heating is stopped and circulating inert gas is filled into the vacuum heat treatment furnace, and the temperature is cooled to room temperature by air cooling. Then, it is heated again. The temperature is raised to 480 °C and held for 2 h. Then, the heating is stopped and circulating inert gas is filled into the vacuum heat treatment furnace, and the temperature is cooled to room temperature by air cooling to obtain the neodymium iron boron magnet 2.

[0124] The neodymium iron boron magnet 2 is subjected to performance testing. The performance of the neodymium iron boron magnet 2 is as follows: remanence Br = 14.24 kGs, coercivity Hcj = 14.91 kOe, maximum energy product (BH)m = 49.18 MGsOe, squareness Hk / Hcj = 0.926. The mechanical property test results of the neodymium iron boron magnet 2 are shown in Table 4.

[0125] Table 4. Mechanical property test results of the neodymium iron boron magnet in Comparative Example 2

[0126]

[0127] Comparative Example 3

[0128] (1) Ingredients are melted to prepare a neodymium iron boron alloy with the chemical formula (PrNd) 29.5 B 0.98 Zr 0.1 Cu 0.2 Al 0.1 Co 1.0 Fe bal (by mass percentage);

[0129] (2) The neodymium iron boron alloy is obtained as a neodymium iron boron rapid solidification sheet through a rapid solidification casting process, and then through hydrogen crushing and jet milling, neodymium iron boron magnetic powder with a size distribution parameter SMD of 2.3 μm and D 90 / D 10 of 3.8 is obtained. The neodymium iron boron magnetic powder is subjected to orientation pressing under a magnetic field greater than 1.8 T, and then cold isostatic pressing is carried out to obtain a neodymium iron boron green compact with a density of 4.2 g / cm 3 ;

[0130] (3) The neodymium iron boron green compact is placed in a vacuum heat treatment furnace for sintering heat treatment;

[0131] Vacuum pumping stage: the same as in Example 1;

[0132] Exhaust stage: the same as in Example 1;

[0133] Heating stage: starting from an initial temperature of 850 °C, the temperature is raised to the target temperature of 1080 °C at a heating rate of 10 °C / min;

[0134] "Wave-like" sintering holding stage: the same as in Example 1;

[0135] "Wave-like" slow cooling stage: the same as in Example 1;

[0136] Quick cooling stage: The same as in Example 1.

[0137] Then, temper heat treatment was carried out in the same manner as in Example 1 to obtain the NdFeB magnet 3.

[0138] The NdFeB magnet 3 was subjected to performance testing. The magnetic properties of the NdFeB magnet 3 were remanence Br = 14.24 kGs, coercivity Hcj = 14.91 kOe, maximum energy product (BH)m = 49.18 MGsOe, and squareness Hk / Hcj = 0.926; the mechanical property test results of the NdFeB magnet 3 are shown in Table 5.

[0139] Table 5. Mechanical property test results of the NdFeB magnet in Comparative Example 3

[0140]

[0141] Comparative Example 4

[0142] (1) Ingredients were melted to prepare a NdFeB alloy with the chemical formula (PrNd) 29.5 B 0.98 Zr 0.1 Cu 0.2 Al 0.1 Co 1.0 Fe bal (by mass percentage);

[0143] (2) The NdFeB alloy was obtained as a NdFeB rapid solidification sheet through a rapid solidification casting process, and then hydrogenated and crushed and air-milled to obtain NdFeB magnetic powder with a size distribution parameter SMD of 2.3 μm and D 90 / D 10 of 3.8; the NdFeB magnetic powder was oriented and compacted under a magnetic field greater than 1.8 T, and then cold isostatically pressed to obtain a NdFeB green compact with a density of 4.2 g / cm 3 ;

[0144] (3) The NdFeB green compact was placed in a vacuum heat treatment furnace for sintering heat treatment;

[0145] Vacuum pumping stage: The same as in Example 1;

[0146] Exhaust stage: The same as in Example 1;

[0147] "Wave-like" slow heating stage: The same as in Example 1;

[0148] Sintering holding stage: Hold at 1080 °C for 4 h;

[0149] "Wave-like" slow cooling stage: The same as in Example 1;

[0150] Quick cooling stage: The same as in Example 1.

[0151] Then, perform tempering heat treatment, which is the same as in Example 1, to obtain the NdFeB magnet 4.

[0152] Perform performance tests on the NdFeB magnet 4. The magnetic properties of the NdFeB magnet 4 are remanence Br = 14.65 kGs, coercivity Hcj = 13.87 kOe, maximum energy product (BH)m = 51.15 MGOe, and squareness Hk / Hcj = 0.911; the mechanical property test results of the NdFeB magnet 4 are shown in Table 6.

[0153] Table 6. Mechanical property test results of the NdFeB magnet in Comparative Example 4

[0154]

[0155] Comparative Example 5

[0156] (1) Prepare a NdFeB alloy with the chemical formula (PrNd) 29.5 B 0.98 Zr 0.1 Cu 0.2 Al 0.1 Co 1.0 Fe bal (by mass percentage);

[0157] (2) Obtain a NdFeB rapid solidification sheet from the NdFeB alloy through the rapid solidification casting process, and then through hydrogen crushing and jet milling, obtain NdFeB magnetic powder with a particle size distribution parameter SMD of 2.3 μm and D 90 / D 10 of 3.8; subject the NdFeB magnetic powder to orientation pressing under a magnetic field greater than 1.8 T, and then perform cold isostatic pressing to obtain a NdFeB green compact with a density of 4.2 g / cm 3 ;

[0158] (3) Place the NdFeB green compact into a vacuum heat treatment furnace for sintering heat treatment;

[0159] Vacuum pumping stage: the same as in Example 1;

[0160] Exhaust stage: the same as in Example 1;

[0161] "Wave-like" slow heating stage: the same as in Example 1;

[0162] "Wave-like" sintering holding stage: the same as in Example 1;

[0163] Fast cooling stage: the same as in Example 1.

[0164] Then, perform tempering heat treatment, which is the same as in Example 1, to obtain the NdFeB magnet 5.

[0165] The NdFeB magnet 5 is subjected to performance tests. The magnetic properties of the NdFeB magnet 5 are remanence Br = 14.58 kGs, coercivity Hcj = 14.99 kOe, maximum energy product (BH)m = 50.73 MGsOe, and squareness Hk / Hcj = 0.928; the mechanical property test results of the NdFeB magnet 5 are shown in Table 7.

[0166] Table 7. Mechanical property test results of the NdFeB magnet in Comparative Example 5

[0167]

[0168] Comparative Example 6

[0169] (1) The formula for the alloying and melting is (PrNd) 29.5 B 0.98 Zr 0.1 Cu 0.2 Al 0.1 Co 1.0 Fe bal (by mass percentage) NdFeB alloy;

[0170] (2) The NdFeB alloy is obtained as NdFeB rapid solidification flakes through the rapid solidification casting process, and then through hydrogen decrepitation and jet milling, NdFeB magnetic powder with a size distribution parameter SMD of 2.7 μm and D 90 / D 10 of 4.5 is obtained; the NdFeB magnetic powder is subjected to orientation pressing under a magnetic field greater than 1.8 T, and then cold isostatic pressing is carried out to obtain an NdFeB green compact with a density of 4.2 g / cm 3 ;

[0171] (3) The NdFeB green compact is placed in a vacuum heat treatment furnace for sintering heat treatment;

[0172] Vacuum pumping stage: the same as in Example 1;

[0173] Exhaust stage: the same as in Example 1;

[0174] "Wave-like" slow heating stage: the same as in Example 1;

[0175] "Wave-like" sintering holding stage: the same as in Example 1;

[0176] "Wave-like" slow cooling stage: the same as in Example 1;

[0177] Fast cooling stage: the same as in Example 1.

[0178] Then tempering heat treatment is carried out, the same as in Example 1, to obtain the NdFeB magnet 6.

[0179] The neodymium iron boron magnet 6 was subjected to performance tests. The magnetic properties of the neodymium iron boron magnet 6 were remanence Br = 14.60 kGs, coercivity Hcj = 14.41 kOe, maximum energy product (BH)m = 50.99 MGsOe, and squareness Hk / Hcj = 0.917; the mechanical property test results of the neodymium iron boron magnet 6 are shown in Table 8.

[0180] Table 8. Test results of the mechanical properties of the neodymium iron boron magnet in Comparative Example 6

[0181]

[0182] According to the above content, it can be seen that the preparation method of the neodymium iron boron magnet with mechanical service characteristics of the present invention can effectively improve the magnetic properties and mechanical properties of neodymium iron boron magnets with different composition systems such as weightless neodymium iron boron and high-abundance rare earth neodymium iron boron.

[0183] From the comparison of the test results of Example 1 and Comparative Example 1, it can be seen that under the same composition system, the magnet prepared by the traditional sintering heat preservation treatment process in Comparative Example 1 has no obvious difference in magnetic properties from the magnet prepared in Example 1, but the mechanical properties of the neodymium iron boron magnet 1 in Comparative Example 1 are significantly weaker than those of the neodymium iron boron magnet 1 with high mechanical service characteristics in Example 1.

[0184] From the comparison of the test results of Example 1 and Comparative Example 2, it can be seen that although the method of adding a second toughening phase (double alloy method) in Comparative Example 2 to improve the mechanical properties of the magnet can also significantly improve the mechanical properties of the magnet, it will cause significant deterioration of the key magnetic parameters remanence and maximum energy product of the neodymium iron boron magnet, and the consistency of the mechanical properties is poor.

[0185] From the comparison of the test results of Example 1, Comparative Example 3, Comparative Example 4, Comparative Example 5, and Comparative Example 6, it can be seen that Comparative Example 3 lacks the "wavy" slow heating stage, Comparative Example 4 lacks the "wavy" sintering heat preservation stage, Comparative Example 5 lacks the "wavy" slow cooling stage, and Comparative Example 6 controls the airflow mill parameters to increase the particle size distribution parameters SMD and D 90 / D 10 of the neodymium iron boron magnetic powder, resulting in a decrease in mechanical properties.

[0186] In summary, the preparation method of the neodymium iron boron magnet with high mechanical service characteristics of the present invention can ensure that the neodymium iron boron magnet has both high mechanical and permanent magnetic properties under the condition of basically not affecting the magnet composition design, and is applicable to the improvement of the mechanical properties of neodymium iron boron magnets with different composition systems.

[0187] All aspects, embodiments, and features of the present invention should be considered illustrative in all respects and do not limit the present invention. The scope of the present invention is only defined by the claims. Without departing from the spirit and scope of the claimed invention, those skilled in the art will appreciate other embodiments, modifications, and uses.

[0188] In the preparation method of the present invention, the order of each step is not limited to the listed order. For those of ordinary skill in the art, without creative efforts, the sequential changes of each step are also within the protection scope of the present invention. In addition, two or more steps or actions can be carried out simultaneously.

[0189] Finally, it should be noted that the specific embodiments described herein are only examples of the present invention and do not limit the implementation manners of the present invention. Those skilled in the technical field to which the present invention pertains can make various modifications or supplements to the described specific embodiments or use similar ways to replace them. It is not necessary and impossible to list all implementation manners here. And these obvious changes or variations derived from the essential spirit of the present invention still belong to the protection scope of the present invention. Interpreting them as any additional limitation is contrary to the spirit of the present invention.

Claims

1. A method for preparing a NdFeB magnet with high mechanical service properties, characterized in that: The method comprises: subjecting the NdFeB green body to sintering heat treatment and tempering heat treatment in sequence; the sintering heat treatment comprises six stages: vacuuming stage, exhaust stage, slow heating stage, sintering stage, slow cooling stage and fast cooling stage; The slow heating stage is a "wave-like" slow heating, which starts from the initial temperature T11 and rises by 20 to 50°C and keeps warm, then drops by 5 to 15°C and keeps warm, and the cycle continues until the target temperature T12. The sintering stage is a "wave-type" sintering and heat preservation, and a temperature range with an upper and lower temperature difference of 5 to 50°C is taken within the range of 800 to 1600°C as the sintering temperature. When the temperature reaches the upper limit temperature point T21 of the temperature range, it is kept warm, then it drops by 5 to 50°C to the lower limit temperature point T22 of the temperature range and is kept warm, and then it rises back to the upper limit temperature point T21 of the temperature range and is kept warm, and this reciprocating cycle is carried out for 1 to 30 hours; the slow cooling stage is a "wave-type" slow cooling, starting from the sintering temperature, each drop of 40 to 200°C and heat preservation, and then rises by 5 to 35°C and is kept warm until the temperature drops to the temperature point T3, T3 is 600 to 900°C.

2. The method for preparing a NdFeB magnet with high mechanical service properties according to claim 1, characterized in that: The vacuuming stage is carried out at room temperature, and the vacuum degree is controlled to be no higher than 10 -2 Pa, and this vacuum degree is maintained after the subsequent five stages of sintering heat treatment.

3. The method for preparing a NdFeB magnet with high mechanical service properties according to claim 1, characterized in that: The exhaust stage is a step-by-step heating process, where the temperature is raised to 2 to 6 step temperatures between 300 and 900° C. and the temperatures are kept constant respectively.

4. The method for preparing a NdFeB magnet with high mechanical service properties according to claim 3, characterized in that: The last step temperature of the exhaust stage is ≤ the initial temperature T11 of the slow heating stage.

5. The method for preparing a NdFeB magnet with high mechanical service properties according to claim 1, characterized in that: The target temperature T12>the initial temperature T11, and the target temperature T12-the initial temperature T11=100-400°C.

6. The method for preparing a NdFeB magnet with high mechanical service properties according to claim 1, characterized in that: The lower limit temperature point T22 of the temperature range ≤ the target temperature T12 ≤ the upper limit temperature point T21 of the temperature range.

7. The method for preparing a NdFeB magnet with high mechanical service properties 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 keeping the temperature at a high-temperature tempering temperature T51 of 700 to 1100°C for 1 to 12 hours and then rapidly cooling to room temperature; The low temperature tempering heat treatment includes keeping the temperature at a low temperature tempering temperature T52 of 300 to 600°C for 1 to 12 hours and then rapidly cooling to room temperature.

8. The method for preparing a NdFeB magnet with high mechanical service properties according to claim 1, characterized in that: The NdFeB green body is obtained by rapidly solidifying NdFeB alloy sheets, powdering and pressing; the powdering includes hydrogen crushing and air flow milling; and the pressing includes orientation pressing and cold isostatic pressing.

9. The method for preparing a NdFeB magnet with high mechanical service properties according to claim 8, characterized in that: The particle size distribution parameter SMD of the magnetic powder obtained by the air flow milling is 1-10 μm; the D90 / D10 of the magnetic powder obtained by the air flow milling is 2-5.

10. A NdFeB magnet with high mechanical service properties, characterized in that: The magnet is prepared by the method for preparing a NdFeB magnet with high mechanical service properties as described in any one of claims 1 to 9.

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