Neodymium-iron-boron magnet with improved magnetic properties based on grain boundary diffusion and method for producing same

Abstract

The application discloses a neodymium-iron-boron magnet based on grain boundary diffusion for improving magnetic properties and a preparation method thereof. The preparation method comprises the following steps: mixing neodymium-iron-boron magnetic powder, a lubricant and nanotubes or micropipes to obtain mixed magnetic powder; performing orientation compression molding, isostatic pressing and vacuum sintering on the mixed magnetic powder to obtain a diffusion base material; cutting the diffusion base material according to size requirements, grinding off a surface oxide layer, and cleaning to obtain a cleaned base material; uniformly spraying an alloy diffusion source on the surface of the cleaned base material to perform grain boundary diffusion to obtain a magnet; and performing secondary tempering treatment on the magnet to obtain a grain boundary diffusion magnet. In the method, nanotubes or micropipes are added into the neodymium-iron-boron magnetic powder, diffusion channels penetrating through the grain boundaries are formed in the sintering process, and then the magnet is subjected to grain boundary diffusion by using a rare earth alloy diffusion source, so that the grain boundary diffusion depth of heavy rare earth elements is significantly improved, and the magnetic properties of the magnet are improved. The neodymium-iron-boron magnet prepared by the method has excellent performance.

Description

Technical Field

[0001] This invention belongs to the field of rare earth permanent magnet materials technology, and particularly relates to a neodymium iron boron magnet with improved magnetic properties based on grain boundary diffusion and its preparation method. Background Technology

[0002] Since its introduction in the 1980s, neodymium iron boron (NdFeB) permanent magnets have rapidly become one of the core functional materials in modern industry due to their superior energy product and coercivity. Their widespread application in new energy vehicle drive motors, wind turbine generators, industrial servo motors, and consumer electronics has driven the process of energy efficiency and low-carbon transformation. However, with the increasing power density of new energy vehicle motors and the growing demand for high-temperature operation in industrial equipment, the performance stability of NdFeB magnets under high-temperature environments faces severe challenges. Currently, the industry mainly enhances high-temperature coercivity by doping NdFeB magnets with heavy rare earth elements such as terbium (Tb) or dysprosium (Dy) into the NdFeB magnet lattice, but this method has limitations: firstly, heavy rare earth doping leads to a simultaneous decrease in remanence and energy product; secondly, the global reserves of elements such as Tb and Dy are scarce and their prices are high, severely restricting the large-scale application of high-performance magnets. How to maintain or even improve the high-temperature performance of magnets while reducing the amount of heavy rare earth elements has become a key bottleneck for technological upgrading in the industry.

[0003] In recent years, grain boundary diffusion technology has provided a new approach to solving the aforementioned problems. This technology utilizes grain boundaries as rapid diffusion channels to diffuse Tb / Dy atoms to the surface of the main phase grains, forming a shell with a high anisotropic field, thereby significantly improving coercivity with minimal impact on remanence. However, the dense microstructure of sintered NdFeB magnets severely limits the penetration depth of heavy rare earth elements, making it difficult to meet the requirements of thick magnets in applications such as new energy vehicle drive motors and megawatt-level wind turbines. The fundamental reason is that the grain boundary structure of conventional sintered magnets lacks a continuous diffusion path, resulting in hindered migration of heavy rare earth atoms in the thickness direction. Therefore, how to construct efficient diffusion channels through microstructure design to overcome the physical limitations of grain boundary diffusion depth has become a core technological challenge driving the upgrading of the high-performance NdFeB magnet industry. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a neodymium iron boron magnet with improved magnetic properties based on grain boundary diffusion and its preparation method, which addresses the shortcomings of the prior art.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing neodymium iron boron magnets based on grain boundary diffusion to enhance magnetic properties includes the following steps:

[0007] (1) Mix neodymium iron boron magnetic powder, lubricant and nanotubes or microtubes to obtain mixed magnetic powder;

[0008] (2) The mixed magnetic powder is oriented, pressed, isostatically pressed, and vacuum sintered to obtain a diffusion substrate;

[0009] (3) Cut the diffusion substrate according to the size requirements, grind off the surface oxide layer, clean it, and obtain a clean substrate;

[0010] (4) The alloy diffusion source is uniformly sprayed onto the cleaned substrate surface to perform grain boundary diffusion and obtain a magnet;

[0011] (5) The magnet is subjected to a two-stage tempering process to obtain a grain boundary diffusion magnet.

[0012] In the above-mentioned method for preparing NdFeB magnets based on grain boundary diffusion to enhance magnetic properties, preferably, in step (1), the mass percentage of the nanotubes or microtubes in the mixed magnetic powder is 0.5% to 2.0%.

[0013] In the above-mentioned method for preparing neodymium iron boron magnets based on grain boundary diffusion to enhance magnetic properties, preferably, in step (1), the nanotubes are carbon nanotubes.

[0014] In the above-mentioned method for preparing NdFeB magnets based on grain boundary diffusion to enhance magnetic properties, preferably, in step (1), the composition of the NdFeB magnetic powder, based on a mass percentage of 100%, includes: Re: 26%–33%, where Re is selected from at least one of Pr, Nd, Dy, Tb, Ho, and Gd; Cu: 0–0.5%; Al: 0–0.9%; Ti: 0–0.5%; Zr: 0–0.5%; Co: 0.1–5%; Ga: 0.1–1.0%; B: 0.8–0.95%; and the remainder is Fe.

[0015] In the above-mentioned method for preparing neodymium iron boron magnets based on grain boundary diffusion to enhance magnetic properties, preferably, in step (3), the thickness of the diffusion substrate after cutting is 3mm to 15mm; the cleaning is performed by ultrasonic cleaning, and the cleaning solution is an alcohol solution.

[0016] In the above-described method for preparing NdFeB magnets based on grain boundary diffusion to enhance magnetic properties, preferably, in step (4), the alloy diffusion source has a composition of R. x M 1-x 0≤x≤90, R contains at least one of the four elements Pr, Nd, Tb, and Dy, and M contains at least one of the five elements Al, Cu, Ga, Co, Sn, and Si. Further preferably, 40≤x≤90.

[0017] In the above-mentioned method for preparing NdFeB magnets based on grain boundary diffusion to enhance magnetic properties, preferably, in step (4), the temperature of the grain boundary diffusion is 800℃~1000℃ and the time is 10h~20h; in step (5), the temperature of the secondary tempering treatment is 400℃~600℃ and the time is 2h~6h.

[0018] In the above-mentioned method for preparing neodymium iron boron magnets based on grain boundary diffusion to enhance magnetic properties, preferably, in step (4), the temperature of grain boundary diffusion is 850℃~950℃ and the time is 12h~18h.

[0019] In the above-mentioned method for preparing NdFeB magnets based on grain boundary diffusion to enhance magnetic properties, preferably, in step (5), the temperature of the secondary tempering treatment is 460℃~550℃ and the time is 2h~4h.

[0020] As a general inventive concept, the present invention also provides a neodymium iron boron magnet with enhanced magnetic properties based on grain boundary diffusion prepared by the above-described preparation method.

[0021] Compared with the prior art, the advantages of the present invention are as follows:

[0022] (1) This invention relates to a method for preparing NdFeB magnets based on grain boundary diffusion to enhance magnetic properties. By adding nanotubes or microtubes to the NdFeB magnetic powder before mixing, diffusion channels that penetrate grain boundaries are formed in the magnet's grain boundary phase after sintering. This facilitates the entry of diffusion sources into the magnet's interior during subsequent grain boundary diffusion, improving the depth and efficiency of grain boundary diffusion. The diffusion thickness of the NdFeB substrate can be increased from 5 mm in conventional processes to 15 mm. The improvement in grain boundary diffusion depth by nanotubes or microtubes is based on their high aspect ratio and tubular structure, which facilitates the diffusion source to penetrate deep into the magnet's interior along the tubular structure. Nanotubes or microtubes are key to improving the coercivity of thick magnets. The method of this invention adds carbon nanotubes during the powder mixing stage, which, compared to adding them in other stages such as the melting stage, can minimize the reaction between carbon and other elements in the magnet. This technology overcomes the limitations of traditional grain boundary diffusion processes on magnet thickness, improves the grain boundary diffusion efficiency of NdFeB magnets, and is suitable for the industrial preparation of magnets with high coercivity and large thickness. It also expands the industrial application prospects of grain boundary diffusion technology in the development of high-performance NdFeB magnets with low heavy rare earth content.

[0023] (2) The present invention relates to a NdFeB magnet with enhanced magnetic properties based on grain boundary diffusion. By introducing nanotubes or microtubes as diffusion channels, the grain boundary diffusion depth of the magnet is increased, thereby enhancing the magnetic properties of the magnet. The NdFeB magnet with low heavy rare earth content, high performance, and large thickness prepared based on the above method of the present invention is suitable for the large-scale production of high-performance magnets for new energy vehicle motors, industrial motors, etc. Detailed Implementation

[0024] The present invention will be further described below with reference to the specification and specific preferred embodiments, but this does not limit the scope of protection of the present invention. Unless otherwise specified, the materials and instruments used in the following embodiments are commercially available, and the equipment used is conventional equipment. The carbon nanotubes used in the following embodiments are commercially available carbon nanotubes with a diameter greater than 50 nm; of course, other conventional diameters and lengths of carbon nanotubes can also be used. The lubricant is NdFeB special lubricant 6#, purchased from Tianjin Yuesheng Magnetoelectric Technology Co., Ltd., product number: YSH-06.

[0025] Example 1

[0026] A method for preparing neodymium iron boron magnets based on grain boundary diffusion to enhance magnetic properties includes the following steps:

[0027] (1) The neodymium iron boron magnetic powder (PrNd) obtained by air jet milling 30.7 Cu 0.1 Ga 0.3 Co1Ti 0.1 B 0.92 Fe bal The mixture is combined with lubricant and carbon nanotubes and then mixed evenly in a powder mixer to obtain mixed magnetic powder.

[0028] The lubricant accounts for 0.05% of the mass of the mixed magnetic powder, and the carbon nanotubes account for 0.5% of the mass of the mixed magnetic powder.

[0029] (2) The mixed magnetic powder obtained in step (1) is oriented, pressed, and isostatically pressed, and then vacuum sintered at 1080℃ for 4 hours, with the vacuum degree maintained at 1×10⁻⁶. -3 A diffusion substrate is obtained when the pressure is below Pa.

[0030] (3) Cut the diffusion substrate into cylinders with a diameter of 10 mm and a height of 5 mm, 10 mm and 15 mm, grind off the surface oxide layer, and ultrasonically clean the magnet in an alcohol solution.

[0031] (4) Tb 65 Cu 35 After the diffusion slurry is uniformly sprayed onto the surface of the substrate obtained in step (3), grain boundary diffusion is carried out at 880°C for 12 hours, while the vacuum degree of the furnace is maintained at 1×10⁻⁶. -3 Below Pa.

[0032] (5) The magnet obtained in step (4) is subjected to a two-stage tempering treatment at 480°C for 2 hours, while the vacuum degree of the furnace is maintained at 1×10⁻⁶. -3 A grain boundary diffusion magnet was prepared with a pressure below Pa.

[0033] Comparative Example 1

[0034] (1) The neodymium iron boron magnetic powder (PrNd) obtained by air jet milling 30.7 Cu 0.1 Ga 0.3 Co1Ti 0.1 B 0.92 Fe bal Mix the magnetic powder with the lubricant and mix evenly in a powder mixer to obtain mixed magnetic powder.

[0035] The mass percentage of lubricant in the mixed magnetic powder is 0.05%.

[0036] (2) The mixed magnetic powder obtained in step (1) is oriented, pressed, and isostatically pressed, and then vacuum sintered at 1080℃ for 4 hours, with the vacuum degree maintained at 1×10⁻⁶. -3 A diffusion substrate is obtained when the pressure is below Pa.

[0037] (3) Cut the diffusion substrate into cylinders with a diameter of 10 mm and a thickness of 5 mm, 10 mm and 15 mm, grind off the surface oxide layer, and ultrasonically clean the magnet in an alcohol solution.

[0038] (4) Tb 65 Cu 35 After the diffusion slurry is uniformly sprayed onto the surface of the substrate obtained in step (3), grain boundary diffusion is carried out at 880°C for 12 hours, while the vacuum degree of the furnace is maintained at 1×10⁻⁶. -3 Below Pa.

[0039] (5) The magnet obtained in step (4) is subjected to a two-stage tempering treatment at 480°C for 2 hours, while the vacuum degree of the furnace is maintained at 1×10⁻⁶. -3 A grain boundary diffusion magnet was prepared with a pressure below Pa.

[0040] Analysis of the magnetic performance test data of Example 1 and Comparative Example 1 revealed that the diffusion depth of the magnet with added carbon nanotubes in Example 1 was much greater than that in Comparative Example 1 without added carbon nanotubes, and the magnetic performance of the magnet was significantly improved. The results are shown in Table 1.

[0041] Table 1 - Magnetic properties of Example 1 and Comparative Example 1

[0042]

[0043] As shown in Table 1, when the substrate thickness is within 5 mm, the intrinsic coercivity of Example 1 and Comparative Example 1 is comparable, both exceeding 25.9 kOe. As the substrate thickness increases to 10 mm and 15 mm, the intrinsic coercivity of Example 1 shows a slight decreasing trend, but still remains at a high level above 25 kOe, while that of Comparative Example 1 decreases significantly to 23.92 kOe. This demonstrates that in Example 1, the addition of carbon nanotubes to the magnetic powder to create the magnet is beneficial for increasing the diffusion depth of NdFeB grain boundaries, thereby significantly improving the magnetic properties of the magnet.

[0044] Example 2

[0045] A method for preparing neodymium iron boron magnets based on grain boundary diffusion to enhance magnetic properties includes the following steps:

[0046] (1) The neodymium iron boron magnetic powder (PrNd) obtained by air jet milling 30.7 Cu 0.1 Ga 0.3 Co1Ti 0.1 B 0.92 Fe bal The mixture is combined with lubricant and carbon nanotubes and then mixed evenly in a powder mixer to obtain mixed magnetic powder.

[0047] The lubricant accounts for 0.05% of the mass of the mixed magnetic powder, and the carbon nanotubes account for 1.0% of the mass of the mixed magnetic powder.

[0048] (2) The mixed magnetic powder obtained in step (1) is oriented, pressed, and isostatically pressed, and then vacuum sintered at 1080℃ for 4 hours, with the vacuum degree maintained at 1×10⁻⁶. -3 A diffusion substrate is obtained when the pressure is below Pa.

[0049] (3) Cut the diffusion substrate into cylinders with a diameter of 10 mm and a height of 5 mm, 10 mm and 15 mm, grind off the surface oxide layer, and ultrasonically clean the magnet in an alcohol solution.

[0050] (4) Tb 65 Cu 35 After the diffusion slurry is uniformly sprayed onto the surface of the substrate obtained in step (3), grain boundary diffusion is carried out at 880°C for 12 hours, while the vacuum degree of the furnace is maintained at 1×10⁻⁶. -3 Below Pa.

[0051] (5) The magnet obtained in step (4) is subjected to a two-stage tempering treatment at 480°C for 2 hours, while the vacuum degree of the furnace is maintained at 1×10⁻⁶. -3 A grain boundary diffusion magnet was prepared with a pressure below Pa.

[0052] Analysis of the magnetic performance test data of Example 2 and Comparative Example 1 revealed that the diffusion depth of Example 2 was much greater than that of Comparative Example 1, as shown in Table 2.

[0053] Table 2 - Magnetic properties of Example 2 and Comparative Example 1

[0054]

[0055] Comparing Example 2 with Example 1, it was found that adding carbon nanotubes to magnetic powder to make magnets is beneficial to increasing the diffusion depth of NdFeB grain boundaries, thereby significantly improving the magnetic properties of the magnets. Moreover, changing the amount of carbon nanotubes added will affect the final grain boundary diffusion result. Within an appropriate range, the amount of carbon nanotubes added is positively correlated with the increase of intrinsic coercivity of the magnet.

[0056] Example 3

[0057] A method for preparing neodymium iron boron magnets based on grain boundary diffusion to enhance magnetic properties includes the following steps:

[0058] (1) The neodymium iron boron magnetic powder (PrNd) obtained by air jet milling 30.7 Cu 0.1 Ga 0.3 Co1Ti 0.1 B 0.92 Fe bal The mixture is combined with lubricant and carbon nanotubes and then mixed evenly in a powder mixer to obtain mixed magnetic powder.

[0059] The lubricant accounts for 0.05% of the mass of the mixed magnetic powder, and the carbon nanotubes account for 1.5% of the mass of the mixed magnetic powder.

[0060] (2) The mixed magnetic powder obtained in step (1) is oriented, pressed, and isostatically pressed, and then vacuum sintered at 1080℃ for 4 hours, with the vacuum degree maintained at 1×10⁻⁶. -3 A diffusion substrate is obtained when the pressure is below Pa.

[0061] (3) Cut the diffusion substrate into cylinders with a diameter of 10 mm and a height of 5 mm, 10 mm and 15 mm, grind off the surface oxide layer, and ultrasonically clean the magnet in an alcohol solution.

[0062] (4) Tb 65 Cu 35 After the diffusion slurry is uniformly sprayed onto the surface of the substrate obtained in step (3), grain boundary diffusion is carried out at 880°C for 12 hours, while the vacuum degree of the furnace is maintained at 1×10⁻⁶. -3 Below Pa.

[0063] (5) The magnet obtained in step (4) is subjected to a two-stage tempering treatment at 480°C for 2 hours, while the vacuum degree of the furnace is maintained at 1×10⁻⁶. -3A grain boundary diffusion magnet was prepared with a pressure below Pa.

[0064] Analysis of the magnetic performance test data of Example 3, Example 2 and Comparative Example 1 revealed that the diffusion depth of Example 3 was slightly higher than that of Comparative Example 1, but the diffusion effect was significantly lower than that of Example 2. The results are shown in Table 3.

[0065] Table 3 - Magnetic properties of Example 3 and Comparative Example 1

[0066]

[0067] Examples 1-3 used magnets of different thicknesses to perform grain boundary diffusion, verifying the effect of carbon nanotubes on improving the grain boundary diffusion depth of NdFeB. A comparison of the data in Tables 1-3 shows that the addition of carbon nanotubes can increase the grain boundary diffusion depth of NdFeB, but the amount added needs to be controlled within a suitable range; adding too much will lead to a decrease in magnetic properties.

[0068] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the spirit and technical essence of the invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the present invention, shall still fall within the scope of protection of the present invention.

Claims

1. A method for preparing neodymium iron boron magnets based on grain boundary diffusion to enhance magnetic properties, characterized in that, Includes the following steps: (1) Neodymium iron boron magnetic powder, lubricant and nanotubes or microtubes are mixed to obtain mixed magnetic powder, wherein the neodymium iron boron magnetic powder is obtained by air jet milling, and the mass percentage of nanotubes or microtubes in the mixed magnetic powder is 0.5% to 2.0%; (2) The mixed magnetic powder is oriented, pressed, isostatically pressed, and vacuum sintered to obtain a diffusion substrate; (3) Cut the diffusion substrate according to the size requirements, grind off the surface oxide layer, clean it, and obtain a clean substrate. The thickness of the diffusion substrate after cutting is 3mm to 15mm. (4) The alloy diffusion source is uniformly sprayed onto the cleaned substrate surface to perform grain boundary diffusion and obtain a magnet; (5) The magnet is subjected to a two-stage tempering process to obtain a grain boundary diffusion magnet; In step (1), the composition of the neodymium iron boron magnetic powder, based on a mass percentage of 100%, includes: Re: 26%–33%, where Re is selected from at least one of Pr, Nd, Dy, Tb, Ho, and Gd; Cu: 0–0.5%; Al: 0–0.9%; Ti: 0–0.5%; Zr: 0–0.5%; Co: 0.1–5%; Ga: 0.1–1.0%; B: 0.8–0.95%; and the remainder is Fe. In step (4), the composition of the alloy diffusion source is R. x M 1-x , 0≤x≤90, R contains at least one of the four elements Pr, Nd, Tb, and Dy, and M contains at least one of the five elements Al, Cu, Ga, Co, Sn, and Si; In step (4), the temperature for grain boundary diffusion is 800℃~1000℃ and the time is 10h~20h; in step (5), the temperature for the secondary tempering treatment is 400℃~600℃ and the time is 2h~6h.

2. The method for preparing NdFeB magnets based on grain boundary diffusion to enhance magnetic properties according to claim 1, characterized in that: In step (1), the nanotube is a carbon nanotube.

3. The method for preparing NdFeB magnets based on grain boundary diffusion to enhance magnetic properties according to claim 1, characterized in that: In step (3), the cleaning is performed using ultrasonic cleaning and the cleaning solution is an alcohol solution.

4. The method for preparing NdFeB magnets based on grain boundary diffusion to enhance magnetic properties according to claim 1, characterized in that: In step (4), the temperature for grain boundary diffusion is 850℃~950℃ and the time is 12h~18h.

5. The method for preparing NdFeB magnets based on grain boundary diffusion to enhance magnetic properties according to claim 1, characterized in that: In step (5), the temperature of the secondary tempering treatment is 460℃~550℃ and the time is 2h~4h.

6. A neodymium iron boron magnet with enhanced magnetic properties based on grain boundary diffusion, prepared by the preparation method according to any one of claims 1 to 5.

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