Neodymium-iron-boron magnet and method for producing same

Abstract

The application relates to the technical field of neodymium-iron-boron magnets, in particular to a neodymium-iron-boron magnet and a preparation method thereof, which comprises the following preparation steps: S1. alloy matrix and modified auxiliary alloy are respectively placed in a vacuum induction melting furnace for melting, and are poured into thin sheets to obtain main-phase alloy cast sheets and modified auxiliary-phase alloy cast sheets; S2. the main-phase alloy cast sheets and the modified auxiliary-phase alloy cast sheets are mixed and then crushed into coarse powder, and the coarse powder is placed in an airflow mill and is crushed into fine powder; S3. a powder modifier is uniformly sprayed on the flowing magnetic powder through an atomizing nozzle at a discharge port, and after mixing, the mixture is magnetized and oriented in a directional magnetic field, and after being pressed, a green body is obtained through cold isostatic pressing; and S4. the green body is sintered, and after heat preservation, two-stage tempering treatment is carried out, and finally, the neodymium-iron-boron magnet is obtained. The synchronous improvement of remanence, coercive force and magnetic energy product is realized through the synergistic effect of the modified auxiliary alloy and the powder modifier, and the trade-off relationship between the coercive force and the remanence in the traditional technology is broken.

Description

Technical Field

[0001] This invention relates to the field of neodymium iron boron magnet technology, specifically to a neodymium iron boron magnet and its preparation method. Background Technology

[0002] Neodymium iron boron (NdFeB) permanent magnets are widely used in new energy vehicle drive motors, wind power generation, industrial robots, aerospace, and high-end consumer electronics due to their excellent magnetic properties. With the global industrial transformation towards intelligence and green technology, especially against the backdrop of the rapid development of the humanoid robot industry, the market demand for high-performance NdFeB magnets is experiencing explosive growth. It is predicted that if 1 billion humanoid robots are deployed, the demand for NdFeB magnets will exceed 100 times the current global production. However, high-end applications such as drive motors and servo systems require magnets to maintain stable magnetic properties even at high temperatures (120-200℃), which places stringent requirements on the magnets' coercivity and temperature stability.

[0003] There are two main traditional technical approaches to improving the high-temperature coercivity of NdFeB magnets: one is to add heavy rare earth elements (such as Dy and Tb) to form (Nd,HRE)2Fe with a higher anisotropic field. 14 The first approach is to refine the grain size, thereby increasing coercivity by reducing the effective demagnetization factor. However, both of these techniques have significant drawbacks.

[0004] First, traditional methods of adding heavy rare earth elements suffer from both a "magnetic dilution effect" and cost pressures. Heavy rare earth elements Dy and Tb are scarce and expensive, accounting for 30%-50% of the final NdFeB price. When adding heavy rare earth elements through traditional smelting methods, these atoms not only distribute at grain boundaries but also extensively penetrate the main phase grains, forming antiferromagnetic coupling with Fe atoms. This leads to a significant decrease in remanence and energy product of the magnet. This contradiction of "sacrificing overall performance for improved coercivity" has long been a technical bottleneck that the industry has been unable to overcome.

[0005] Secondly, although grain boundary diffusion technology can partially alleviate the above contradictions, it still faces problems such as insufficient diffusion depth and low utilization rate of heavy rare earth elements. The grain boundary diffusion technology proposed in the early 21st century can improve coercivity while reducing the amount of heavy rare earth elements used by infiltrating heavy rare earth elements into the magnet along the grain boundary and forming a highly anisotropic field shell on the grain surface. However, the following defects have been exposed in the industrial application of this technology: (1) The diffusion depth is limited and it is usually only applicable to thin magnets with a thickness of less than 4 mm. It is difficult to achieve uniform strengthening for thick magnets (>6 mm) required for high-power motors; (2) The utilization efficiency of heavy rare earth elements is low. In fact, less than 30% of the heavy rare earth elements actually enter the effective strengthening position of the grain boundary, and a large amount of expensive resources are wasted in the surface area; (3) The diffusion heat treatment time is long (20-30 hours), the energy consumption is high, and it is easy to cause abnormal growth of surface grains, which will damage the microstructure of the magnet; (4) The heavy rare earth shell is not uniform, which leads to the existence of a coercivity gradient inside the magnet, and the overall performance is constrained by the weakest area.

[0006] Furthermore, the issue of magnetic powder flowability has long been overlooked, hindering the improvement of orientation degree. In the preparation of sintered NdFeB, fine powder (3-4μm) has a large specific surface area and is prone to agglomeration, which increases the rotational resistance of particles during magnetic field orientation, making it difficult to achieve the ideal orientation degree and ultimately affecting the performance of remanence and magnetic energy product. Existing processes mostly use dry mixing or simple addition of lubricants, which makes it difficult to achieve uniform coating and easily introduces impurities. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the purpose of this invention is to provide a neodymium iron boron magnet and its preparation method.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a neodymium iron boron magnet includes the following preparation steps: S1. By mass, 90-100 parts of the alloy matrix and 3-6 parts of the modified auxiliary alloy are placed in a vacuum induction melting furnace and melted under argon protection. The melt is then cast into thin sheets (0.2-0.5 mm thick) using a rapid solidification casting process to obtain the main phase alloy casting sheet and the modified auxiliary phase alloy casting sheet. S2. After mixing the main phase alloy casting and the modified auxiliary phase alloy casting obtained in step S1, put them into a hydrogen explosion furnace. Utilizing the hydrogen absorption and expansion characteristics of rare earth phases, the casting is broken into coarse powder along the grain boundaries. The coarse powder after hydrogen explosion is placed in an air jet mill and pulverized into fine powder under a high-pressure nitrogen atmosphere (controlling the powder particle size to 3-4 μm). S3. In step S2, 0.05-0.1 parts of powder modifier are uniformly sprayed onto the flowing magnetic powder through the outlet of the air mill via an atomizing nozzle. After mixing in the mixer for 1-2 hours, the powder is placed into the mold of the molding press, magnetized and oriented in a directional magnetic field, and then pressed. After cold isostatic pressing, a green blank is obtained. S4. Place the green blank obtained in step S3 into a vacuum sintering furnace and preheat it to 190-200℃, then heat it to 1060-1100℃ for sintering. After holding it at this temperature for 4-5 hours, perform a two-stage tempering treatment to finally obtain the neodymium iron boron magnet.

[0009] The modified auxiliary alloys include auxiliary phase alloy A and auxiliary phase alloy B, with a mass ratio of 2-5:1; The preparation of auxiliary phase alloy A includes the following steps: S11. By mass, 40-50 parts of terbium oxide, 20-30 parts of dysprosium oxide and 20-30 parts of ammonium bifluoride are mixed and fluorinated in a tube furnace at 300-400℃ under argon protection for 3-5 hours to obtain a composite fluoride; S12. The composite fluoride obtained in step S11 and 3-8 parts of aluminum powder are mixed in a three-dimensional mixer at a speed of 30-50 rpm for 2-4 hours, and then the mixture is taken out. S13. Place the mixture in a vacuum induction melting furnace, evacuate it, and then fill it with argon gas to bring the pressure to 0.05-0.06 MPa. Heat it to 1350-1400℃, hold it for 20-30 minutes, and then cool it to room temperature to obtain auxiliary phase alloy A.

[0010] Preferably, the preparation of auxiliary phase alloy B includes the following steps: S21. By mass, 40-50 parts Cu, 20-30 parts Al, 5-10 parts Ga, and 5-10 parts Ni are placed in a V-type mixer and mixed for 2-3 hours to obtain a mixed metal. S22. Place the mixed metal obtained in step S21 into a vacuum induction melting furnace, evacuate and fill with argon gas to make the pressure 0.05-0.06 MPa, heat to 1150-1250℃ and hold for 15-25 min, and cool to room temperature to obtain auxiliary phase alloy B.

[0011] Preferably, the preparation of the powder modifier includes the following steps: S31. By mass, 60-70 parts of n-hexane and 20-30 parts of methyl caprylate are stirred at 20-25°C and 200-300 r / min for 15-20 min to obtain a preliminary mixture; S32. Add 2-5 parts of erucamide to the preliminary mixture obtained in step S31, and stir at 300-400 r / min at 35-40℃ until completely dissolved to obtain the secondary mixture; S33. At 25-30℃, add 1-3 parts of tributyl borate and 1-2 parts of oleic acid to the mixture from the second step, continue stirring for 20-30 minutes, and then filter through a 0.5μm filter membrane to finally obtain the powder modifier.

[0012] Preferably, the alloy matrix is ​​composed of praseodymium-neodymium alloy, iron, and boron, with a mass ratio of 28-32:60-70:1.

[0013] Preferably, the melting temperature of the rapid solidification casting process is 1450-1500℃ and the copper roller speed is 1-2m / s.

[0014] Preferably, the hydrogen absorption pressure in the hydrogen explosion furnace is 0.1-0.2 MPa, the hydrogen absorption time is 2-4 h, and the dehydrogenation temperature is 500-600℃.

[0015] Preferably, the grinding pressure of the air jet mill is 0.6-0.8 MPa, and the speed of the classifying wheel is 3500-4500 rpm.

[0016] Preferably, the orientation magnetic field for magnetization orientation is ≥1.8T, the pressing pressure is 8-15MPa, the cold isostatic pressing pressure is 180-220MPa, and the holding time is 3-5min.

[0017] Preferably, in the two-stage tempering process, the first-stage tempering temperature is 900-950℃, held for 2-3 hours, the second-stage tempering temperature is 480-520℃, held for 3-5 hours, and then cooled to room temperature with the furnace.

[0018] A neodymium iron boron magnet is prepared by the above-described preparation method.

[0019] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention constructs a dual-alloy modification system of "high-efficiency heavy rare earth source + low-melting-point grain boundary optimizer" by modifying auxiliary alloys, which significantly improves the diffusion efficiency of heavy rare earths and the integrity of grain boundary structure. The synergistic effect of auxiliary phase alloy A and auxiliary phase alloy B has high chemical stability, which can avoid the oxidation loss of heavy rare earths. At the same time, fluorine enrichment in the grain boundary phase helps to form a continuous non-magnetic grain boundary layer, enhances the demagnetizing coupling effect between grains, and improves the utilization rate of heavy rare earths.

[0020] 2. This invention avoids the uneven modification caused by particle agglomeration in traditional mixing processes through the synergistic effect of modified auxiliary alloys and powder modifiers. It also blunts sharp edges of the powder, significantly improving powder flowability. This reduces the rotational resistance of particles during magnetic field orientation, increases the degree of orientation, and thus enhances the remanence of the magnet. The synergistic effect of these two modifiers achieves a simultaneous increase in remanence, coercivity, and energy product, breaking the traditional trade-off between coercivity and remanence. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating the fabrication process of the neodymium iron boron magnet of this invention. Figure 2 This is a process flow diagram for preparing auxiliary phase alloy A of the present invention; Figure 3This is a process flow diagram for preparing auxiliary phase alloy B of the present invention; Figure 4 This is a flow chart of the preparation process of the powder modifier of the present invention; Figure 5 This is a graph showing the magnetic performance data of the neodymium iron boron magnet obtained in Example 1 of the present invention. Detailed Implementation

[0022] The present invention will now be clearly and completely described in conjunction with embodiments thereof. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0023] Please see Figure 1-5 The present invention provides a technical solution: Example 1 A method for preparing neodymium iron boron magnets: Before preparing neodymium iron boron magnets, auxiliary phase alloy A, auxiliary phase alloy B, and powder modifier are prepared: The preparation of auxiliary phase alloy A includes the following steps: S11. Mix 40g of terbium oxide, 20g of dysprosium oxide and 20g of ammonium bifluoride, and fluorinate them in a tube furnace at 300℃ under argon protection for 3h to obtain a composite fluoride; S12. The composite fluoride obtained in step S11 and 3g of aluminum powder are mixed in a three-dimensional mixer at a speed of 30rpm for 2 hours, and then the mixture is taken out. S13. Place the mixture in a vacuum induction melting furnace, evacuate it, and then fill it with argon gas to bring the pressure to 0.05 MPa. Heat it to 1350℃, hold it for 20 minutes, and then cool it to room temperature to obtain auxiliary phase alloy A.

[0024] The preparation of auxiliary phase alloy B includes the following steps: S21. Place 40g Cu, 20g Al, 5g Ga, and 5g Ni in a V-type mixer and mix for 2 hours to obtain a mixed metal. S22. Place the mixed metal obtained in step S21 into a vacuum induction melting furnace, evacuate and fill with argon gas to bring the pressure down to 0.05 MPa, heat to 1150°C and hold for 15 min, then cool to room temperature to obtain auxiliary phase alloy B.

[0025] The preparation of powder modifiers includes the following steps: S31. Stir 60g of n-hexane and 20g of methyl caprylate at 20°C and 200r / min for 15min to obtain a preliminary mixture; S32. Add 2g of erucamide to the preliminary mixture obtained in step S31, and stir at 300r / min at 35℃ until completely dissolved to obtain the secondary mixture; S33. At 25℃, add 1g of tributyl borate and 1g of oleic acid to the mixture from the second step, continue stirring for 20 minutes, and then filter through a 0.5μm filter membrane to finally obtain the powder modifier.

[0026] S1. Place 90g of alloy matrix (composed of praseodymium-neodymium alloy, iron, and boron in a mass ratio of 28:60:1) and 3g of modified auxiliary alloy (including auxiliary phase alloy A and auxiliary phase alloy B in a mass ratio of 2:1) in a vacuum induction melting furnace and melt them under argon protection. Then, cast them into thin sheets using a rapid solidification casting process (melting temperature of 1450℃ and copper roller speed of 1m / s) to obtain the main phase alloy casting sheet and the modified auxiliary phase alloy casting sheet. S2. After mixing the main phase alloy casting and the modified auxiliary phase alloy casting obtained in step S1, the mixture is placed in a hydrogen explosion furnace and crushed into coarse powder. The hydrogen absorption pressure in the hydrogen explosion furnace is 0.1 MPa, the hydrogen absorption time is 2 h, and the dehydrogenation temperature is 500 °C. The coarse powder after hydrogen explosion is placed in an air jet mill with a crushing pressure of 0.6 MPa and a classifier speed of 3500 rpm. The mixture is crushed into fine powder under a high-pressure nitrogen atmosphere. S3. In step S2, 0.05g of powder modifier is uniformly sprayed onto the flowing magnetic powder through an atomizing nozzle at the outlet of the air jet mill. After mixing in a mixer for 1 hour, the powder is placed into the mold of a molding press. After being magnetized and oriented in a directional magnetic field and pressed, a green body is obtained by cold isostatic pressing. The orientation magnetic field is 1.8T, the pressing pressure is 8MPa, the cold isostatic pressing pressure is 180MPa, and the holding time is 3min. S4. The green blank obtained in step S3 is placed in a vacuum sintering furnace and preheated to 190°C, then heated to 1060°C for sintering. After holding at this temperature for 4 hours, a two-stage tempering process is performed. The first-stage tempering temperature is 900°C and held for 2 hours, and the second-stage tempering temperature is 480°C and held for 3 hours. The blank is then cooled to room temperature with the furnace to finally obtain a neodymium iron boron magnet.

[0027] Example 2 A method for preparing neodymium iron boron magnets: Before preparing neodymium iron boron magnets, auxiliary phase alloy A, auxiliary phase alloy B, and powder modifier are prepared: The preparation of auxiliary phase alloy A includes the following steps: S11. Mix 50g of terbium oxide, 30g of dysprosium oxide and 30g of ammonium bifluoride, and fluorinate them in a tube furnace at 400℃ under argon protection for 5h to obtain a composite fluoride; S12. The composite fluoride obtained in step S11 and 8g of aluminum powder are mixed in a three-dimensional mixer at a speed of 50rpm for 4 hours, and then the mixture is taken out. S13. Place the mixture in a vacuum induction melting furnace, evacuate it, and then fill it with argon gas to bring the pressure to 0.06 MPa. Heat it to 1400℃, hold it for 30 minutes, and then cool it to room temperature to obtain auxiliary phase alloy A.

[0028] The preparation of auxiliary phase alloy B includes the following steps: S21. Place 50g Cu, 30g Al, 10g Ga, and 10g Ni in a V-type mixer and mix for 3 hours to obtain a mixed metal. S22. Place the mixed metal obtained in step S21 into a vacuum induction melting furnace, evacuate and fill with argon gas to make the pressure 0.06 MPa, heat to 1250℃ and hold for 25 min, and cool to room temperature to obtain auxiliary phase alloy B.

[0029] The preparation of powder modifiers includes the following steps: S31. Stir 70g of n-hexane and 30g of methyl caprylate at 25°C and 300r / min for 20min to obtain a preliminary mixture; S32. Add 5g of erucamide to the preliminary mixture obtained in step S31, and stir at 400r / min at 40℃ until completely dissolved to obtain the secondary mixture; S33. Add 3g of tributyl borate and 2g of oleic acid to the mixture in the second step at 30℃, continue stirring for 30min, and then filter with a 0.5μm filter membrane to finally obtain the powder modifier.

[0030] S1. Place 100g of alloy matrix (composed of praseodymium-neodymium alloy, iron, and boron in a mass ratio of 32:70:1) and 6g of modified auxiliary alloy (including auxiliary phase alloy A and auxiliary phase alloy B in a mass ratio of 5:1) in a vacuum induction melting furnace and melt them under argon protection. Then, cast them into thin sheets using a rapid solidification casting process (melting temperature of 1500℃ and copper roller speed of 2m / s) to obtain the main phase alloy casting sheet and the modified auxiliary phase alloy casting sheet. S2. After mixing the main phase alloy casting and the modified auxiliary phase alloy casting obtained in step S1, the mixture is placed in a hydrogen explosion furnace and crushed into coarse powder. The hydrogen absorption pressure in the hydrogen explosion furnace is 0.2 MPa, the hydrogen absorption time is 4 h, and the dehydrogenation temperature is 600 °C. The coarse powder after hydrogen explosion is placed in an air jet mill with a crushing pressure of 0.8 MPa and a classifier speed of 4500 rpm. The mixture is crushed into fine powder under a high-pressure nitrogen atmosphere. S3. In step S2, 0.1g of powder modifier is uniformly sprayed onto the flowing magnetic powder through an atomizing nozzle at the outlet of the air mill. After mixing in a mixer for 2 hours, the powder is placed into the mold of a molding press. After being magnetized and oriented in a directional magnetic field and pressed, a green body is obtained by cold isostatic pressing. The orientation magnetic field is 1.9T, the pressing pressure is 15MPa, the cold isostatic pressing pressure is 220MPa, and the holding time is 5min. S4. The green blank obtained in step S3 is placed in a vacuum sintering furnace and preheated to 200°C, then heated to 1100°C for sintering. After holding at this temperature for 5 hours, a two-stage tempering process is performed. The first-stage tempering temperature is 950°C and held for 3 hours, and the second-stage tempering temperature is 520°C and held for 5 hours. The blank is then cooled to room temperature with the furnace to finally obtain a neodymium iron boron magnet.

[0031] Example 3 A method for preparing neodymium iron boron magnets: Before preparing neodymium iron boron magnets, auxiliary phase alloy A, auxiliary phase alloy B, and powder modifier are prepared: The preparation of auxiliary phase alloy A includes the following steps: S11. Mix 45g of terbium oxide, 25g of dysprosium oxide and 25g of ammonium bifluoride, and fluorinate them in a tube furnace at 350℃ under argon protection for 4h to obtain a composite fluoride; S12. The composite fluoride obtained in step S11 and 5g of aluminum powder are mixed in a three-dimensional mixer at a speed of 40rpm for 3h and then the mixture is taken out. S13. Place the mixture in a vacuum induction melting furnace, evacuate it, and then fill it with argon gas to bring the pressure to 0.055 MPa. Heat it to 1355℃, hold it for 25 minutes, and then cool it to room temperature to obtain auxiliary phase alloy A.

[0032] The preparation of auxiliary phase alloy B includes the following steps: S21. Place 44g Cu, 26g Al, 7g Ga, and 8g Ni in a V-type mixer and mix for 2.5 hours to obtain a mixed metal. S22. The mixed metal obtained in step S21 is placed in a vacuum induction melting furnace, vacuumed and filled with argon gas to a pressure of 0.055 MPa, heated to 1200℃ and held for 20 min, and then cooled to room temperature to obtain auxiliary phase alloy B.

[0033] The preparation of powder modifiers includes the following steps: S31. Stir 64g of n-hexane and 24g of methyl caprylate at 22°C and 220r / min for 18min to obtain a preliminary mixture; S32. Add 3g of erucamide to the preliminary mixture obtained in step S31, and stir at 350r / min at 38℃ until completely dissolved to obtain the secondary mixture; S33. Add 2g of tributyl borate and 1.5g of oleic acid to the mixture in the second step at 28℃, continue stirring for 28min, and then filter with a 0.5μm filter membrane to finally obtain the powder modifier.

[0034] S1. Place 95g of alloy matrix (composed of praseodymium-neodymium alloy, iron, and boron in a mass ratio of 30:64:1) and 5g of modified auxiliary alloy (including auxiliary phase alloy A and auxiliary phase alloy B in a mass ratio of 3:1) in a vacuum induction melting furnace and melt them under argon protection. Then, cast them into thin sheets using a rapid solidification casting process (melting temperature of 1455℃ and copper roller speed of 1.5m / s) to obtain the main phase alloy casting sheet and the modified auxiliary phase alloy casting sheet. S2. After mixing the main phase alloy casting and the modified auxiliary phase alloy casting obtained in step S1, the mixture is placed in a hydrogen explosion furnace and crushed into coarse powder. The hydrogen absorption pressure in the hydrogen explosion furnace is 0.15 MPa, the hydrogen absorption time is 3 h, and the dehydrogenation temperature is 550 °C. The coarse powder after hydrogen explosion is placed in an air jet mill with a crushing pressure of 0.7 MPa and a classifier speed of 4000 rpm. The mixture is crushed into fine powder under a high-pressure nitrogen atmosphere. S3. In step S2, 0.08g of powder modifier is uniformly sprayed onto the flowing magnetic powder through an atomizing nozzle at the outlet of the air mill. After mixing in a mixer for 1.5h, the powder is placed into the mold of the molding press. After being magnetized and oriented in a directional magnetic field and pressed, a green body is obtained by cold isostatic pressing. The orientation magnetic field is 2T, the pressing pressure is 12MPa, the cold isostatic pressing pressure is 210MPa, and the holding time is 4min. S4. The green blank obtained in step S3 is placed in a vacuum sintering furnace and preheated to 195°C, then heated to 1080°C for sintering. After holding at this temperature for 4.5 hours, a two-stage tempering process is performed. The first-stage tempering temperature is 930°C and held for 2.5 hours, and the second-stage tempering temperature is 500°C and held for 4 hours. The blank is then cooled to room temperature with the furnace to finally obtain a neodymium iron boron magnet.

[0035] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that no modified auxiliary alloy was added in this comparative example; the other steps are exactly the same in Comparative Example 1 and Example 1.

[0036] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that no powder modifier was added in this comparative example; the other steps are exactly the same in Comparative Example 2 and Example 1.

[0037] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is that no auxiliary phase alloy A was added in this comparative example; the other steps are exactly the same in Comparative Example 3 and Example 1.

[0038] Comparative Example 4 The only difference between Comparative Example 4 and Example 1 is that no auxiliary phase alloy B was added in this comparative example; the other steps are exactly the same in Comparative Example 4 and Example 1.

[0039] Performance testing: The magnetic properties of the neodymium iron boron magnets obtained in Examples 1-3 and Comparative Examples 1-4 were tested according to GB / T 3217-2013, "National Standard for Magnetic Test Methods of Permanent Magnet (Hard Magnetic) Materials". The neodymium iron boron magnets obtained in Examples 1-3 and Comparative Examples 1-4 were processed into cylinders with a bottom diameter of 10 mm and a height of 10 mm. The parallelism of the two end faces was ≤0.02 mm, and the surface roughness Ra was ≤0.8 μm. Using a permanent magnet measurement system, the sample was placed between the two poles of an electromagnet, and a positive magnetic field was applied until saturation magnetization (magnetic field strength ≥2400 kA / m). The magnetic field was then slowly reduced to zero, and then a reverse magnetic field was applied until complete demagnetization. The change in magnetic flux density throughout the process was recorded. The final magnetic property data are shown in Table 1 below. Table 1 Magnetic property data This invention, while testing the magnetic properties of the neodymium iron boron magnet obtained in Example 1, also used an automatic hysteresis loop meter (model AMT-4) to plot the magnetic property data curves. (See attached image.) Figure 5 This is a graph showing the magnetic performance data of the neodymium iron boron magnet obtained in Example 1 of the present invention. The data is derived from Table 1 and the attached... Figure 5 It is evident that the NdFeB magnets obtained in the embodiments of this invention outperform the comparative examples in all magnetic performance data. This demonstrates that the synergistic effect of the modified auxiliary alloy and the powder modifier improves the flowability of the magnetic powder, reduces the resistance to particle rotation during magnetic field orientation, increases the degree of orientation, effectively isolates the main phase grains, enhances the demagnetizing coupling effect between grains, improves the utilization rate of heavy rare earth elements, and achieves a simultaneous increase in remanence and coercivity, breaking the trade-off between the two in traditional technologies. The data comparison of Example 1, Comparative Example 1, and Comparative Examples 3-4 shows that using either auxiliary alloy A or auxiliary alloy B alone cannot achieve the same technical effect as Example 1, i.e., using both auxiliary alloy A and auxiliary alloy B simultaneously. This further demonstrates that the synergistic effect of auxiliary alloy A and auxiliary alloy B avoids the oxidation loss of heavy rare earth elements, helps to form a continuous nonmagnetic grain boundary layer, enhances the demagnetizing coupling effect between grains, and simultaneously improves the utilization rate of heavy rare earth elements. A comparison of the data from Example 1 and Comparative Example 2 shows that the technical effect of Example 1 cannot be achieved without the addition of the powder modifier. This demonstrates the synergistic effect of the modified auxiliary alloy and the powder modifier, which blunts the sharp edges of the powder, significantly improves the powder flowability, reduces the rotational resistance of particles during magnetic field orientation, and increases the degree of orientation, thereby increasing the remanence of the magnet. This achieves a simultaneous increase in remanence, coercivity, and magnetic energy product, breaking the traditional trade-off between coercivity and remanence. The NdFeB magnet prepared by this invention is superior to the comparative example in terms of magnetic properties, and its comprehensive performance meets the stringent requirements of high-end applications such as new energy vehicle drive motors and industrial robot servo systems for high-temperature stability, demagnetization resistance, and long-life reliability of magnets.

[0040] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a neodymium iron boron magnet, characterized in that, The preparation steps include the following: S1. By mass, 90-100 parts of the alloy matrix and 3-6 parts of the modified auxiliary alloy are placed in a vacuum induction melting furnace and melted under argon protection. The alloy is then cast into thin sheets using a rapid solidification casting process to obtain the main phase alloy sheet and the modified auxiliary phase alloy sheet. S2. After mixing the main phase alloy casting and the modified auxiliary phase alloy casting obtained in step S1, put them into a hydrogen explosion furnace and crush them into coarse powder. Then, place the coarse powder after hydrogen explosion into an air jet mill and pulverize it into fine powder under a high-pressure nitrogen atmosphere. S3. In step S2, 0.05-0.1 parts of powder modifier are uniformly sprayed onto the flowing magnetic powder through the outlet of the air mill via an atomizing nozzle. After mixing in the mixer for 1-2 hours, the powder is placed into the mold of the molding press, magnetized and oriented in a directional magnetic field, and then pressed. After cold isostatic pressing, a green blank is obtained. S4. Place the green blank obtained in step S3 in a vacuum sintering furnace and heat it to 190-200℃ for preheating, then heat it to 1060-1100℃ for sintering. After holding it at the temperature for 4-5 hours, perform a two-stage tempering treatment to finally obtain a neodymium iron boron magnet. The modified auxiliary alloy includes auxiliary phase alloy A and auxiliary phase alloy B, with a mass ratio of 2-5:1; The preparation of the auxiliary phase alloy A includes the following steps: S11. By mass, 40-50 parts of terbium oxide, 20-30 parts of dysprosium oxide and 20-30 parts of ammonium bifluoride are mixed and fluorinated in a tube furnace at 300-400℃ under argon protection for 3-5 hours to obtain a composite fluoride; S12. The composite fluoride obtained in step S11 and 3-8 parts of aluminum powder are mixed in a three-dimensional mixer at a speed of 30-50 rpm for 2-4 hours, and then the mixture is taken out. S13. Place the mixture in a vacuum induction melting furnace, evacuate the furnace, and then fill it with argon gas to bring the pressure to 0.05-0.06 MPa. Heat the furnace to 1350-1400℃, hold the temperature for 20-30 minutes, and then cool it to room temperature to obtain auxiliary phase alloy A. The preparation of the auxiliary phase alloy B includes the following steps: S21. By mass, 40-50 parts Cu, 20-30 parts Al, 5-10 parts Ga, and 5-10 parts Ni are placed in a V-type mixer and mixed for 2-3 hours to obtain a mixed metal. S22. Place the mixed metal obtained in step S21 into a vacuum induction melting furnace, evacuate and fill with argon gas to make the pressure 0.05-0.06 MPa, heat to 1150-1250℃ and hold for 15-25 min, and cool to room temperature to obtain auxiliary phase alloy B.

2. The method for preparing a neodymium iron boron magnet according to claim 1, characterized in that, The preparation of the powder modifier includes the following steps: S31. By mass, 60-70 parts of n-hexane and 20-30 parts of methyl caprylate are stirred at 20-25°C and 200-300 r / min for 15-20 min to obtain a preliminary mixture; S32. Add 2-5 parts of erucamide to the preliminary mixture obtained in step S31, and stir at 300-400 r / min at 35-40℃ until completely dissolved to obtain the secondary mixture; S33. At 25-30℃, add 1-3 parts of tributyl borate and 1-2 parts of oleic acid to the mixture from the second step, continue stirring for 20-30 minutes, and then filter through a 0.5μm filter membrane to finally obtain the powder modifier.

3. The method for preparing a neodymium iron boron magnet according to claim 1, characterized in that, The alloy matrix is ​​composed of praseodymium-neodymium alloy, iron, and boron in a mass ratio of 28-32:60-70:

1.

4. The method for preparing a neodymium iron boron magnet according to claim 1, characterized in that, The melting temperature of the rapid solidification casting process is 1450-1500℃, and the copper roller speed is 1-2m / s.

5. The method for preparing a neodymium iron boron magnet according to claim 1, characterized in that, The hydrogen absorption pressure in the hydrogen explosion furnace is 0.1-0.2 MPa, the hydrogen absorption time is 2-4 h, and the dehydrogenation temperature is 500-600℃.

6. The method for preparing a neodymium iron boron magnet according to claim 1, characterized in that, The grinding pressure of the air jet mill is 0.6-0.8 MPa, and the speed of the classifying wheel is 3500-4500 rpm.

7. The method for preparing a neodymium iron boron magnet according to claim 1, characterized in that, The magnetization orientation field is ≥1.8T, the pressing pressure is 8-15MPa, the cold isostatic pressing pressure is 180-220MPa, and the holding time is 3-5min.

8. The method for preparing a neodymium iron boron magnet according to claim 1, characterized in that, In the two-stage tempering process, the first-stage tempering temperature is 900-950℃, and the holding time is 2-3 hours. The second-stage tempering temperature is 480-520℃, and the holding time is 3-5 hours. The furnace is then cooled to room temperature.

9. A neodymium iron boron magnet, characterized in that, It is prepared by the preparation method described in any one of claims 1-8.

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