R-Fe-B Sintered Magnet, Its Manufacturing Method, and Applications

Abstract

The present invention provides an R-Fe-B sintered magnet and its manufacturing method and application. The R-Fe-B sintered magnet of the present invention has an oxide adhesive coating layer on the surface, and the R-Fe-B sintered magnet is obtained by a temperature-retention heat treatment including alternating low-temperature heat treatment and high-temperature heat treatment from an R-Fe-B magnet having a composite diffusion layer on the surface, in which the temperature range of the low-temperature heat treatment is 750°C to 830°C, and the temperature range of the high-temperature heat treatment is 830°C to 970°C, to obtain a neodymium iron boron element having an oxide adhesive coating layer on the surface. The manufacturing method of the R-Fe-B sintered magnet of the present invention optimizes the grain boundary diffusion of the R-Fe-B magnet and improves the coercive force distribution of the magnet. The present invention further provides applications of the R-Fe-B sintered magnet in the fields of automobiles, wind power generation, household motors, medical equipment, mobile communication equipment, etc.

Description

Technical Field

[0001] This application claims the priority of a prior application filed with the China National Intellectual Property Administration on June 28, 2021, with a patent application number of 202110723269.2 and an invention title of "R-Fe-B Sintered Magnet and Its Manufacturing Method and Application". The above prior application is incorporated herein by reference in its entirety.

[0002] The present invention relates to an R-Fe-B sintered magnet, its manufacturing method and application, and belongs to the field of rare earth permanent magnet materials.

Background Art

[0003] Due to its excellent properties, the R-Fe-B magnet is widely applied in fields such as wind power generation, household motors, medical devices, and mobile communications. In particular, due to the recent global low-carbonization of automotive technology, the ownership of new energy vehicles in China has already ranked first in the world. In the next 10 to 15 years, the high-end neodymium iron boron permanent magnet material will witness rapid growth, and it is predicted that the market application of sintered neodymium iron boron will further expand.

[0004] The coercivity of R-Fe-B magnets is a decisive factor in determining the magnetic strength and retention time of permanent magnet materials. In the conventional process, to improve the coercivity, mainly heavy rare earth elements Dy and Tb are directly added to the melting furnace. However, the usage amount of heavy rare earth elements is relatively large, and adopting such a method to improve the coercivity sacrifices the residual magnetism. As the coercivity increases, the residual magnetism of the magnet clearly decreases. Furthermore, due to the scarcity of heavy rare earth elements determining their high price, the cost of the magnet increases dramatically. In the R-Fe-B field, the grain boundary diffusion method has been industrialized. By diffusing heavy rare earth elements such as Dy and Tb from the magnet surface along the grain boundaries into the magnet interior to improve the grain boundary microstructure, the coercivity of Nd-Fe-B sintered magnets is improved, and the grain boundary scattering field is effectively reduced, weakening the magnetic exchange coupling effect, magnetizing the grain boundaries, and significantly improving the coercivity without much reduction in the magnet residual magnetism. Currently, the main methods to achieve grain boundary diffusion include vapor deposition technology, arc ion plating technology, magnetron sputtering technology, roller coating technology, etc. (see Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4, Patent Document 5). In the above methods, different methods and equipment are adopted to achieve the placement of heavy rare earths on the magnet surface. Among them, the applicant, in Patent Document 5, realizes the effect of placing heavy rare earth elements on the magnet surface by placing an organic layer containing heavy rare earth elements on the magnet surface. In such a method, the control over the thickness and uniformity of the heavy rare earth layer is high, it is not easy to fall off, mass production is easy, and the heavy rare earth powder is wrapped in an organic substance and is not easily oxidized even when left in the air. During the heat treatment process, the organic substance desorbs from the magnet, and the heavy rare earth elements diffuse into the magnet interior along the grain boundaries.

[0005] The grain boundary diffusion technology realizes the improvement of Hcj by diffusing the heavy rare earths arranged on the magnet surface along the grain boundaries into the magnet interior. It uses the concentration difference of heavy rare earths between the magnet surface and interior at high temperature as the diffusion driving force. In the case of magnets with a relatively small thickness, heavy rare earths are likely to diffuse to the central part of the magnet, and the uniformity of the Hcj distribution between the magnet surface and interior is relatively good. However, as the magnet thickness increases, simply adopting the method of arranging more heavy rare earths on the magnet surface will clearly increase the Hcj difference between the magnet surface and interior, and the heavy rare earth layer arranged on the surface will destroy the magnet surface state, requiring post-processing. On the other hand, since a relatively large amount of heavy rare earths on the surface are likely to diffuse into the interior of the crystal grains, the residual magnetism of the magnet surface part clearly decreases, the effect of grain boundary diffusion decreases. Compared with various developments of the equipment and methods for arranging heavy rare earths at the magnet surface part, for magnets with a relatively large product thickness, improving the diffusion depth and the consistency between the Hcj of the magnet surface and interior after diffusion are the urgent problems to be solved currently.

[0006] The patent documents related to the above prior art are as follows.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Means for Solving the Problems

[0008] To solve the above technical problems, the present invention provides an R-Fe-B magnet body, which includes an R-Fe-B magnet and a composite diffusion layer, and the composite diffusion layer exists on the surface of the R-Fe-B magnet.

[0009] According to an embodiment of the present invention, the thickness of the R-Fe-B magnet in the magnet orientation direction is Z, and Z≧3.95 mm. Preferably, 15.05 mm≧Z≧3.95 mm. Preferably, the dimensional tolerance of Z is ±0.05 mm, for example, ±0.03 mm.

[0010] According to an embodiment of the present invention, in the R-Fe-B magnet, R is any one or more selected from rare earth elements Nd, Pr, Tb, Dy, Gd, Ho.

[0011] According to an embodiment of the present invention, in the R-Fe-B magnet, preferably, the content of R is 27 wt% - 34 wt%, for example, 27 wt% - 30 wt%.

[0012] According to an embodiment of the present invention, in the R-Fe-B magnet, preferably, the content of B is 0.8 wt% - 1.3 wt%.

[0013] According to an embodiment of the present invention, the R-Fe-B magnet further includes Fe and M, where M is at least one selected from Ti, V, Cr, Mn, Co, Ga, Cu, Si, Al, Zr, Nb, W, Mo.

[0014] According to an embodiment of the present invention, in the R-Fe-B magnet, the content of M may be 0 wt% - 5 wt%, preferably, 0 wt% - 3 wt%, for example, 2 wt%.

[0015] According to an embodiment of the present invention, the total thickness of the composite diffusion layer is less than 200 μm, for example, 10 μm - 180 μm, for example, 50 μm, 80 μm, 100 μm or 150 μm.

[0016] According to an embodiment of the present invention, the composite diffusion layer contains heavy rare earth elements, preferably including heavy rare earth elements, metal oxides, organic solids, and optionally a solvent.

[0017] According to an embodiment of the present invention, the heavy rare earth element is at least one selected from dysprosium metal, terbium metal, dysprosium hydride, terbium hydride, dysprosium fluoride, terbium fluoride, dysprosium oxide, and terbium oxide.

[0018] According to an embodiment of the present invention, the metal oxide is at least one selected from zirconium oxide, calcium oxide, aluminum oxide, and holmium oxide.

[0019] According to an embodiment of the present invention, the metal oxide may be in powder form. For example, the particle size of the metal oxide is selected from 0.5 μm to 10 μm. Preferably, in the metal oxide, the mass percentage of the metal oxide powder with a particle size between 0.5 μm and 3 μm is 70% or more.

[0020] According to an embodiment of the present invention, the organic solid may be in powder form. For example, the organic solid is at least one selected from rosin-modified alkyd resin, thermoplastic phenolic resin, urea resin, and polyvinyl butyral.

[0021] According to an embodiment of the present invention, the solvent is at least one selected from alcohol solvents (such as methanol and ethanol), ether solvents (such as ethyl ether), and aromatic hydrocarbon solvents (such as benzene), preferably an ether solvent, such as ethanol.

[0022] According to an embodiment of the present invention, the composite diffusion layer includes an RH layer and an RL layer, among which, The RH layer contains heavy rare earths, organic solids, and optionally a solvent, The RL layer contains metal oxides, organic solids, and optionally a solvent.

[0023] According to an embodiment of the present invention, the RH layer and the RL layer are at least one layer independent of each other, and are selected from, for example, 1 layer, 2 layers, 3 layers, 4 layers, 5 layers or more.

[0024] According to an embodiment of the present invention, the RH layer and the RL layer are alternately arranged in sequence. Preferably, when the RH layer and the RL layer are alternately arranged, the outer layer away from the surface of the R-Fe-B magnet is preferably the RL layer.

[0025] According to an embodiment of the present invention, the thickness of a single layer of the RH layer is selected from 0.5 μm to 40 μm. Exemplarily, the thickness of the RH layer is 20 μm ± 5 μm, 25 μm ± 5 μm.

[0026] According to an embodiment of the present invention, the thickness of a single layer of the RL layer is selected from 0.5 μm to 15 μm. Exemplarily, the thickness of the RL layer is 3 μm ± 2 μm.

[0027] According to an embodiment of the present invention, the weight of the composite diffusion layer is 0.1 wt% to 3 wt% of the weight of the R-Fe-B magnetic material, for example, 0.9 wt% or 1.2 wt%.

[0028] The present invention further provides an R-Fe-B sintered magnet. The R-Fe-B sintered magnet is obtained by subjecting the R-Fe-B magnet blank to a heat preservation heat treatment. After the composite diffusion layer is subjected to the heat preservation heat treatment, the metal oxide therein forms an oxide adhesion coating layer.

[0029] According to an embodiment of the R-Fe-B sintered magnet of the present invention, among them, the R-Fe-B sintered magnet has an oxide adhesion coating layer on its surface, and let Hcj at the magnet surface in the magnet orientation direction of the R-Fe-B sintered magnet be H1, and Hcj at a position 2.00 mm ± 0.02 mm from the magnet surface along the magnet orientation direction into the magnet be H2. The H1 and H2 have the relationship shown in formula (I). H 1 -H2 ≤50 kA / m (I).

[0030] According to an embodiment of the present invention, the thickness of the oxide adhesion coating layer is less than 20 μm, preferably 10 μm or less, for example, 5 μm.

[0031] Preferably, the oxide adhesion coating layer contains at least one of zirconium oxide, calcium oxide, aluminum oxide, and holmium oxide.

[0032] According to an embodiment of the present invention, the R-Fe-B sintered magnet contains at least one of R, B, Fe, or M having the above-described definitions and contents.

[0033] According to an embodiment of the present invention, the heat preservation heat treatment includes alternately performing a low-temperature heat treatment and a high-temperature heat treatment.

[0034] Preferably, the temperature range of the low-temperature heat treatment is 750°C to 830°C.

[0035] Preferably, the temperature range of the high-temperature heat treatment is 830°C to 970°C.

[0036] According to an embodiment of the present invention, the oxide adhesion coating layer can be completely removed by non-mechanical grinding, for example, methods such as brushing and ultrasonic waves.

[0037] The present invention further provides a method for manufacturing an R-Fe-B sintered magnet, preferably the method for manufacturing an R-Fe-B sintered magnet described above, (1) A step of applying and disposing a composite diffusion layer on the surface of the R-Fe-B magnet to form the R-Fe-B magnet blank; (2) A step of performing heat preservation heat treatment on the R-Fe-B magnet blank in a vacuum or an inert atmosphere to obtain a sintered magnet having an oxide adhesion coating layer on the surface. Preferably, the heat preservation heat treatment includes alternately performing a low-temperature heat treatment and a high-temperature heat treatment, wherein the temperature range of the low-temperature heat treatment is 750°C to 830°C, and the temperature range of the high-temperature heat treatment is 830°C to 970°C.

[0038] According to an embodiment of the present invention, the manufacturing method improves the coercivity distribution of the magnet by optimizing grain boundary diffusion.

[0039] According to an embodiment of the present invention, the low-temperature heat treatment may be a low-temperature diffusion heat preservation heat treatment, and the high-temperature heat treatment may be a high-temperature diffusion heat preservation heat treatment. Exemplarily, the heat preservation heat treatment includes a first low-temperature diffusion heat preservation heat treatment, a first high-temperature diffusion heat preservation heat treatment, a second low-temperature diffusion heat preservation heat treatment, and a second high-temperature diffusion heat preservation heat treatment.

[0040] According to an embodiment of the present invention, the total time of the heat preservation heat treatment is ≥8 h, and the times of the low-temperature heat treatment and the high-temperature heat treatment are the same or different. For example, the low-temperature heat treatment time is ≤5 h, and the high-temperature heat treatment time is ≤5 h.

[0041] Preferably, it is necessary to increase the temperature from the low-temperature heat treatment to the high-temperature heat treatment, and the heating rate is 4°C / min to 10°C / min.

[0042] Preferably, it is further necessary to cool from the high-temperature heat treatment to the low-temperature heat treatment. The cooling adopts a vacuum cooling method without heating output.

[0043] According to an embodiment of the present invention, the method further includes performing an aging heat preservation treatment after the heat preservation heat treatment. In the present invention, the aging heat preservation treatment refers to a heat treatment process in which an alloy workpiece is left at a relatively high temperature or its performance, shape, and dimensions are maintained at room temperature after solution treatment, cold plastic deformation, casting, or forging, and changes with time.

[0044] According to an embodiment of the present invention, the aging heat preservation treatment includes, after the heat preservation heat treatment, rapidly cooling to room temperature, further heating to 430°C to 650°C for aging treatment, holding for 1 h to 72 h, and then further rapidly cooling to room temperature. Exemplarily, the aging heat preservation treatment includes, after the heat preservation heat treatment, rapidly cooling to room temperature, further heating to 500°C for aging treatment, holding for 4 h, and then further rapidly cooling to room temperature.

[0045] According to an embodiment of the present invention, applying and disposing the composite diffusion layer includes applying a slurry on the surface of the R-Fe-B magnet and then drying to form the composite diffusion layer.

[0046] According to an embodiment of the present invention, the above drying can be realized by drying equipment known in the art such as a vacuum dryer or a hot air dryer. The temperature and time of the above drying are not particularly limited as long as the solvent in the slurry can be dried. As an example, the drying temperature is 35°C to 100°C, and the drying time is 5 s to 600 s.

[0047] According to an embodiment of the present invention, the coating method may adopt at least one coating method selected from brush coating, roller coating, dip coating, spray coating, etc. For example, for a magnet with a regular rectangular shape, preferably, a coating method such as brush coating or roller coating is used to form a composite diffusion layer on the magnet surface, and for a magnet with an irregular shape, preferably, a coating method such as dip coating or spray coating is used to form a composite diffusion layer on the magnet surface.

[0048] Exemplarily, when the dip coating method is selected, the entire R-Fe-B magnet is immersed in the slurry for 1 second to 10 seconds, for example, 3 seconds to 5 seconds.

[0049] According to an embodiment of the present invention, after drying, the weight of the above R-Fe-B magnet blank increases by 0.1 wt% to 3 wt% compared to the weight of the R-Fe-B magnet, for example, increases by 0.9 wt% or 1.2 wt%.

[0050] According to an embodiment of the present invention, the solid content of the above slurry is 30 wt% to 90 wt%, preferably 40 wt% to 60 wt%.

[0051] According to an embodiment of the present invention, the above slurry is selected from the RH layer slurry and / or the RL layer slurry.

[0052] According to an embodiment of the present invention, the above RH slurry contains heavy rare earth elements, organic solids, and a solvent. Preferably, the mass ratio of the heavy rare earth elements, organic solids, and solvent is (40 - 70):(3 - 10):(20 - 50), for example, 60:5:35 or 55:5:40.

[0053] According to an embodiment of the present invention, the above RL layer slurry contains metal oxides, organic solids, and a solvent. Preferably, the mass ratio of the metal oxides, organic solids, and solvent is (30 - 70):(3 - 10):(20 - 50), for example, 55:5:40 or 50:6:44.

[0054] Preferably, the above metal oxides, heavy rare earth elements, organic solids, and solvent are as described above.

[0055] Preferably, the method for manufacturing the above slurry includes adding the above metal oxides, heavy rare earth elements, or organic solids to a solvent and stirring to form a uniform slurry. Preferably, in the present invention, the usage amounts of the above metal oxides, heavy rare earth elements, organic solids, and solvent are not particularly limited, and may be determined according to the characteristics of the R-Fe-B sintered magnet. Preferably, in the present invention, the stirring conditions are not particularly limited, and any stirring method that can form a uniform slurry can be applied to the present invention. For example, the normal stirring method in the technical field is adopted for stirring, and the stirring time may be 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, or in the range between any two of the above numerical values.

[0056] Exemplarily, the above slurry is selected from the RH layer slurry and the RL layer slurry.

[0057] In a specific embodiment, the RL layer slurry contains 55 wt% zirconia, 5 wt% rosin-modified alkyd resin, and 40 wt% ethanol, and the RH layer slurry contains 60 wt% terbium fluoride, 5 wt% rosin-modified alkyd resin, and 35 wt% ethanol.

[0058] In another specific embodiment, the RL layer slurry contains 50 wt% aluminum oxide, 6 wt% rosin-modified alkyd resin, and 44 wt% ethanol, and the RH layer slurry contains 55 wt% terbium fluoride, 5 wt% rosin-modified alkyd resin, and 40 wt% ethanol.

[0059] According to an embodiment of the present invention, the coating further includes applying the slurry to the surface of the R-Fe-B magnet in multiple portions.

[0060] Preferably, the coating is performed at least 2 times, for example, 3 times, 4 times, or 5 times.

[0061] According to an embodiment of the present invention, when the slurry is applied in multiple portions, the slurries may be the same or different, and preferably, they are different slurries.

[0062] Preferably, when the slurry is applied in multiple portions, the RH layer slurry and the RL layer slurry are respectively adopted, and the composite diffusion layers are respectively applied alternately.

[0063] Preferably, at the time of the final coating, the RL layer slurry is selected as the slurry.

[0064] According to an embodiment of the present invention, in the dried composite diffusion layer, the RH layer and the RL layer are alternately arranged.

[0065] Preferably, in the composite diffusion layer after drying, the thickness of the RH layer applied once is 0.5 μm to 40 μm, for example, 0.5 μm, 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 30 μm, or in the range between any two of the above numerical values.

[0066] Preferably, in the composite diffusion layer after drying, the thickness of the RL layer applied once is 0.5 μm to 15 μm, for example, 0.5 μm, 1 μm, 3 μm, 5 μm, 7 μm, 10 μm, 15 μm, or in the range between any two of the above numerical values.

[0067] According to an embodiment of the present invention, before applying the slurry, the above R-Fe-B magnet may be further sequentially washed with an acid solution and deionized water, and then dried. The above acid solution may be selected from acid solutions known in the art, for example, an aqueous hydrogen chloride solution, an aqueous nitric acid solution, etc.

[0068] According to an embodiment of the present invention, the above heat preservation heat treatment or aging heat preservation treatment is performed in a vacuum or an inert atmosphere. For example, the above inert atmosphere is selected from nitrogen gas, argon gas, etc.

[0069] According to an embodiment of the present invention, in the case of heat preservation heat treatment, the above R-Fe-B magnet body can achieve space saving by adopting a contact arrangement.

[0070] The present invention further provides an application of the above R-Fe-B sintered magnet in the fields of automobiles, wind power generation, household motors, medical devices or mobile communication devices, preferably in the field of new energy vehicles.

[0071] The present invention further provides a motor, and the above motor includes the above R-Fe-B sintered magnet.

[0072] Preferably, the above motor includes a power take-off motor, a steering EPS motor, and a micromotor.

[0073] Preferably, the micro motor includes an electric water pump motor, a steering-linked fog lamp motor, a sunroof motor, an air conditioner motor, a wiper motor, etc.

Advantages of the Invention

[0074] The present invention provides an R-Fe-B sintered magnet and a method for manufacturing the same. By alternately arranging a composite diffusion layer containing heavy rare earth RH and metal oxide powder RL on the surface of the R-Fe-B magnet, the structure of the heavy rare earth layer arranged on the surface is improved, the grain boundary diffusion of the R-Fe-B magnet is optimized, the uniformity of the distribution of the magnet coercivity is improved. Compared with CN106158347A, in this application, by alternately increasing the RL layer, the distribution of the heavy rare earth RH on the magnet surface is improved. In the diffusion process, a specific RL layer effectively reduces the concentration difference in the diffusion process of the RH layer and the heavy rare earth inside the magnet, thereby reducing the driving force of the diffusion process of the heavy rare earth along the magnet surface into the magnet inside in the grain boundary diffusion process. Also, in the grain boundary diffusion stage, a method of alternately maintaining high and low temperatures is adopted to realize the adjustment of the diffusion rate and concentration of the heavy rare earth. The uniformity of the Hcj distribution inside the diffusion magnet with a large thickness is poor, and the problem that the heavy rare earth concentrates on the magnet surface and is difficult to diffuse into the center of the magnet is optimized, reducing the difference between Hcj at the surface and the center position of the diffusion magnet. For a magnet with a thickness ≥ 4 mm, the difference between the coercive force H1 on the magnet surface and the coercive force H2 at a position 2 mm from the inside of the magnet is ≤ 50 kA / m, improving the squareness of the whole magnet, thereby improving the heat resistance of the magnet. Also, after heat-treating the selected metal oxide powder, an oxide adhesive coating layer is formed on the magnet surface to solve the problem of direct contact blocking of the magnet during the high-temperature treatment process, increasing the input amount during the heat treatment process, being advantageous for mass production, and since the organic solid powder and metal oxide powder do not enter the magnet inside after diffusion, no obvious increase is seen in the content of C and O elements in the magnet.

[0075] In contrast to CN106158347A, in this application, by alternately increasing the RL layer, the distribution of the heavy rare earth RH on the magnet surface is improved. In the diffusion process, the RL layer can effectively reduce the concentration difference in the diffusion process of the RH layer of the heavy rare earth, preventing the significant aggregation of the heavy rare earth on the magnet surface and its entry into the crystal grain main phase, thereby significantly reducing the remanence of the magnet. In the actual mass production process, the total number of RL and RH layers is ≤ 5 layers. If the number of alternately arranged layers is too large, the production cost will increase. On the other hand, if there are too many RL layers, the diffusion rate will decrease, resulting in a longer diffusion holding time and a lower overall diffusion efficiency. Moreover, in the process of alternately arranging RL and RH, arranging the RL layer on the outermost layer can protect the RH layer from damage. And the RL layer can form an oxide adhesive coating layer on the magnet surface after heat treatment. The oxide adhesive coating layer can isolate the magnets and prevent the blocking of the magnets during the high-temperature holding process.

[0076] After heat treatment, the sintered magnet has an oxide adhesive coating layer on its surface, with a thickness of less than 20 μm, preferably 10 μm. It is easy to clean and can be completely cleaned, for example, by a brush or ultrasonic waves, and can be completely removed without relying on mechanical grinding. The oxide adhesive coating layer can realize the isolation of the magnets when the magnets are overlapped for diffusion treatment and can increase the diffusion input amount. In terms of thickness, preferably, it is 10 μm or less, and more preferably, it is 6 μm or less.

[0077] The applicant has found that in the high-temperature heat treatment process, the metal oxide powder does not react with or reduce the activity of the heavy rare earth RH. On the other hand, the metal oxide powder does not react with the neodymium iron boron magnet and does not damage the surface state of the magnet even when it comes into contact with the magnet surface at a high temperature. When the particle size of the selected metal oxide powder is larger than 10 μm, due to the mutual contact between the magnets during the high-temperature diffusion treatment process, oversized particles are likely to damage the surface state of the magnet, and dents are formed on the magnet surface, which need to be shaved off in the post-treatment process to ensure the product appearance. On the one hand, the processing cost increases, and in the design process of the base substrate, an increase in dimensions is required, resulting in a large waste. On the other hand, when the particle size is <0.5 μm, the diffusion rate cannot be effectively controlled because the particle size of the metal oxide powder is too small, and the concentration difference in the content of heavy rare earths between the magnet surface and the central position after diffusion cannot be effectively reduced. Moreover, when the metal oxide powder is too small, the effect of reducing the blocking between the magnets decreases, the magnets are likely to stick and difficult to separate. When the powder with a particle size range of 0.5 μm to 3 μm accounts for more than 70%, the particle size of the metal oxide powder is slightly smaller than the size of the main phase crystal grains of the magnet. In batch verification, effective control of the particle size of the metal oxide powder on the diffusion rate of heavy rare earths can be achieved. On the one hand, because the particle size of the metal oxide powder is slightly smaller than the crystal grain size, during the diffusion process, it does not prevent the diffusion of heavy rare earths along the grain boundaries on the surface of the crystal grains, and does not damage the magnet surface state in the high-temperature diffusion environment.

[0078] When the organic solvent of the present invention selects ethanol, it can further reduce the extra load on the airtightness, exhaust capacity, safety, etc. of the equipment and help increase the equipment cost.

[0079] The total thickness of the composite diffusion layer of the present invention is less than 200 μm, preferably 10 μm to 100 μm. Controlling the thickness of the composite diffusion layer within a certain range is because if the thickness is too small, the distribution of heavy rare earths will be uneven, and as a result, the distribution of heavy rare earth elements diffused throughout the magnet will be uneven, and the effect of the RL layer arranged on the magnet surface to adjust the diffusion concentration will not be obvious, ultimately leading to poor uniformity of the magnet. If the thickness is too large, on the one hand, since the content of heavy rare earths is too high, during the heat treatment process, excessive heavy rare earths cannot be completely diffused into the magnet, and aggregates are formed on the magnet surface, eroding the magnet surface and affecting the surface state of the magnet, and the heavy rare earths deposited on the magnet surface will lead to waste of raw materials. On the other hand, since the content of organic substances is too high, during the heat treatment process, a large amount of organic substances will desorb, affecting the atmosphere of the heat treatment device, causing an increase in carbon and oxygen elements of the magnet, and ultimately affecting the performance of the magnet.

[0080] In the heat preservation and heat treatment stage of the present invention, an alternating heat preservation process of low temperature and high temperature is adopted to ensure that the heavy rare earths arranged on the surface always diffuse into the magnet internally with a high concentration gradient, and to improve the diffusion efficiency. Although the diffusion temperature in the diffusion process is relatively single, in the actual diffusion process, if the diffusion treatment is always carried out at a relatively single temperature, since the grain boundary channel is fixed, a large amount of heavy rare earths enter the main phase during the diffusion process, and the optimal grain boundary diffusion effect cannot be realized. Moreover, when heavy rare earths enter the main phase, the residual magnetism of the magnet decreases significantly. Especially for magnets with a thickness of ≥ 4 mm, because the thickness of the magnet is relatively large, simply arranging more heavy rare earth RH layers on the surface and adopting a higher diffusion temperature will reduce the diffusion effect. A large amount of heavy rare earth RH is distributed in the grain boundaries close to the magnet surface, and a large amount of heavy rare earths penetrate into the main phase, resulting in a large Hcj difference between the magnet surface and the interior, and a significant decrease in the magnet residual magnetism Br compared to the base. The present invention alternately arranges RL and RH layers on the magnet surface and adopts a low-temperature and high-temperature alternating heat treatment process. In the high-temperature heat treatment and heat preservation stage, the grain boundaries are in a sufficient molten state, providing power for the heavy rare earth RH to diffuse into the grain boundaries, adjusting the structure of the RH layer by the RL layer to reduce the concentration difference of the RH layer, causing the RH layer on the magnet surface to deposit on the magnet surface at high temperature, allowing RH to diffuse and enter the interior of the main phase, and preventing the reduction of the grain boundary diffusion effect. In the low-temperature heat treatment and heat preservation stage, the diffusion rate of the RH layer arranged on the surface into the magnet decreases. At this time, the RH that diffuses and enters the grain boundaries is replaced by Nd elements in the grain boundaries, and the Nd elements in the replaced grain boundaries are precipitated outside the magnet. By reducing the magnet RH that diffuses and enters during the low-temperature heat treatment and heat preservation stage, the Tb in the grain boundaries is replaced by Nd elements, and a part of the Nd elements is precipitated from the magnet, completing the improvement of the diffusion efficiency, improving the uniformity of the RH distribution in the magnet, and being beneficial to the diffusion of RH into the magnet interior.

[0081] In the setting process of the normal diffusion process, a relatively high diffusion temperature of 870°C to 970°C is usually adopted. The higher the temperature, the greater the diffusion driving force provided. Therefore, it is considered that the heavy rare earths arranged on the magnet surface can be diffused deeper along the magnet. However, in the actual measurement process, for magnets with a thickness of 4 mm or more, since the grain boundaries between the crystal grains of the diffusion channel are fixed, when the diffusion temperature is relatively high, while a large amount of heavy rare earths diffuse and enter the main phase, the deposition of heavy rare earths at the grain boundaries is disadvantageous to the diffusion into the magnet along the grain boundaries. The improvement of Hcj on the magnet surface becomes relatively large, and at the central position, the diffusion of heavy rare earths along the grain boundaries is inhibited, so the Hcj difference between the magnet surface and the interior becomes relatively large. The applicant found that in the heat preservation process of low-temperature and high-temperature alternating heat treatment, the temperature range of low-temperature heat treatment is 750°C to 830°C, the temperature range of high-temperature heat treatment is 830°C to 970°C, the low-temperature and high-temperature heat treatment time is ≤5 h, the heat preservation heat treatment time is ≥8 h. In the low-temperature heat treatment diffusion process, when the heat preservation temperature is less than 750°C, the temperature of the heavy rare earths RH arranged on the magnet surface is too low, so it cannot be efficiently diffused. When it is higher than 830°C, the diffusion efficiency is too high, and Tb and Nd at the grain boundaries are not fully replaced, and the depth of RH diffusion decreases. In the high-temperature heat treatment diffusion process, when the heat preservation temperature is higher than 970°C, the temperature is too high, so the heavy rare earths RH arranged on the surface directly enter the main phase, and the effect of grain boundary diffusion cannot be realized.

[0082] Moreover, when the thickness of the magnet in the orientation direction is less than 4 mm, even if an RL layer is arranged on the magnet surface and an alternating heat preservation process is adopted, the improvement of the magnet performance after diffusion is not obvious. When the thickness of the magnet is >15 mm, in the heat treatment process, the heavy rare earth elements diffuse into the magnet through the grain boundaries that are in the liquid phase. Therefore, the diffusion process mainly uses the concentration difference as the driving force. Since the driving force is not large when the concentration difference is low, the diffusion is a slow process. When the thickness of the magnet is greater than 15 mm, since the RH and RL layers arranged on the magnet surface are relatively thick, the magnetic property difference between the magnet surface and the center after diffusion is too large, and the magnetic properties such as the squareness of the magnet deteriorate, and ultimately it affects the temperature resistance of the magnet.

Brief Description of the Drawings

[0083]

Figure 1

Embodiments for Carrying Out the Invention

[0084] Hereinafter, in accordance with specific embodiments, the technical solution of the present invention will be described in more detail. It should be understood that the following embodiments are merely illustrative explanations and interpretations of the present invention and should not be construed as limiting the scope of the claims of the present invention.

[0085] Unless otherwise specified, the raw materials and reagents used in the following examples are all commercially available products or can be manufactured by known methods.

[0086] In the method for analyzing the structure of the grain boundary phase and the main phase in the present invention, the fracture surface of the substrate was scanned by EPMA, the CP image of EPMA was processed with ImagePRO software, and the width, length, etc. of the crystal grain boundaries were analyzed. 〔Example 1〕 First, a neodymium iron boron magnet (R-Fe-B magnet) was prepared, the magnet was processed to form a magnet sheet, the surface of the magnet sheet was washed with an acid solution and deionized water, and then dried to obtain a neodymium iron boron magnet M1. The dimensions of the magnet sheet were 40 mm × 20 mm × 6 mm, the dimensional tolerance was ±0.03 mm, the thickness in the orientation direction of M1 was Z = 6 mm, and the composition of M1 was as shown in the following table.

[0087] Terbium hydride of heavy rare earth elements, organic solid rosin-modified alkyd resin powder, and ethanol were used to produce an RH slurry, and their weight percentages were 60 wt%, 5 wt%, and 35 wt%, respectively. Zirconia as a metal oxide, organic solid rosin-modified alkyd resin powder, and ethanol were used to produce an RL slurry, and their weight percentages were 55 wt%, 5 wt%, and 40 wt%, respectively. The method of dipping and hot air drying was adopted, and the RH layer and the RL layer were sequentially arranged on the surface of the magnet. The RH layer and the RL layer formed a composite diffusion layer to obtain an R-Fe-B magnet body. Among them, the thickness of the RH layer was 20 μm ± 5 μm, the thickness of the RL layer was 3 μm ± 2 μm, and the weight percentage of the above composite diffusion layer in magnet M1 was 1.2% ± 0.2%.

[0088] The treated magnet body including the above composite diffusion layer on the surface was placed in a material box, and diffusion heat preservation heat treatment was carried out in a heat treatment device. The heat treatment process was in a vacuum state. When the vacuum degree ≤ 10 Pa, heating was started, and the diffusion heat treatment process was set as follows.

[0089] (1) Heating: (50~780)°C × 100 min, (2) Low-temperature diffusion heat treatment: 780°C × 240 min, (3) Heating: (780~920)°C × 30 min, (4) High-temperature diffusion heat treatment: 920°C × 240 min, (5) Low-temperature diffusion heat treatment: 780 × 240 min (in the stage of cooling to 780°C, there is no heating output for heat treatment), (6) Heating: (780~920)°C × 30 min, (7) High-temperature diffusion heat treatment: 920°C × 240 min.

[0090] After the diffusion heat treatment, rapid cooling was carried out. After the rapid cooling was completed, the temperature was raised to 500 °C for aging treatment (aging treatment refers to a heat treatment process in which an alloy workpiece, after solution treatment, cold plastic deformation, casting, or forging, is left at a relatively high temperature or its performance, shape, and dimensions are maintained at room temperature and change with time). After holding for 4 h, it was further rapidly cooled to room temperature to obtain the sintered magnet M2. In the heat treatment process, the magnet matrix adopted a contact arrangement, and there was no blocking in the sintered magnet after diffusion. According to the energy spectrum measurement, the surface of M2 was a zirconia powder adhesion coating layer, and the average thickness was 5 μm.

[0091] The above products were measured as follows.

[0092] Table 1 Comparison of the overall performance of sintered magnet M2 and magnet M1 Measurement method: Samples of 7 mm×7 mm×6 mm were taken from magnets M1 and M2. Measurement equipment: NIM-62000

[0093]

Table 1

[0094] Table 2 Comparison of Hcj at the magnet surface position and Hcj at a position 2 mm from the magnet surface of sintered magnet M2 Measurement method: As shown in Figure 1, samples of 1 mm×1 mm×1 mm were taken from the surface of the sintered magnet M2 and the location from the surface to 2 mm, and were designated as H1 and H2 respectively. The difference in Hcj between H1 and H2 was 39 kA / m. And by EPMA analysis of the Tb element, in the field of view 1 selected by H1, Tb was mainly distributed at the grain boundaries, and it was found that Tb did not enter the matrix phase much. In the field of view 2 selected by H2, it was obvious that the Tb element existed at the grain boundaries, and it was found that the distribution of the Tb element was relatively uniform at the grain boundaries after diffusion.

[0095] Measurement equipment: PFM06

[0096]

Table 2

[0097] Table 3 Comparison of the Main Compositions of Sintered Magnet M2 and Magnet M1 Measuring Equipment: Spectrometer

[0098] [Table 3]

[0099] Note: The balance is Fe.

[0100] As shown by the above results, by adopting such a method, compared with M1, for M2, the residual magnetism Br decreased by about 0.011 T, Hcj increased by about 820 kA / m, and according to the composition measurement, compared with M1, the Tb of M2 increased by about 0.41 wt%.

[0101] Table 4 Analytical Comparison of the Contents of C and O Elements in Sintered Magnet M2 and Magnet M1 Measuring Equipment: CS Analyzer, ONH Analyzer

[0102] [Table 4]

[0103] As shown in Table 4, in the comparative analysis of the contents of CSON elements before and after magnet diffusion, it was found that neither the content of C nor that of O showed an obvious increase, indicating that the impurity elements generated in the slurry during the diffusion process did not enter the magnet interior. [Example 2] Similar to the neodymium iron boron magnet M1 of Example 1, the dimensions of the magnet sheet are 40 mm × 30 mm × 8 mm, the dimensional tolerance is ±0.03 mm, a composite diffusion layer is arranged on its surface, and heavy rare earth element powder terbium fluoride, organic solid rosin modified alkyd resin powder, and ethanol are adopted to manufacture RH slurry, and their weight percentages are 55 wt%, 5 wt%, and 40 wt% respectively. Aluminum oxide as a metal oxide, organic solid rosin modified alkyd resin powder, and ethanol are adopted to manufacture RL slurry, and their weight percentages are 50 wt%, 6 wt%, and 44 wt% respectively. The method of roller coating and hot air drying is adopted, and the RH layer and RL layer are sequentially arranged on the magnet surface. The RH layer and RL layer form a composite diffusion layer to obtain an R-Fe-B magnet body with an oxide on the surface. Among them, the thickness of the RH layer is 25 μm ± 5 μm, the thickness of the RL layer is 3 μm ± 2 μm, and the weight percentage of the above composite diffusion layer in the magnet M1 is 0.9% ± 0.2%.

[0104] Place the above magnet body in a material box and perform diffusion heat preservation heat treatment in a heat treatment device. Set the heating process as follows, that is, 50°C to 780°C × 100 min + 780°C × 180 min + 780°C to 920°C × 30 min + 920°C × 240 min + 780 min × 360 min (no heating output for heat treatment) + 780°C to 920°C × 30 min + 920°C × 360 min and then quench rapidly. After the rapid quenching ends, heat up to 520°C for aging treatment. After 4 h of heat preservation, quench rapidly to room temperature to obtain magnet M3. By energy spectrum measurement, the surface of M3 was an aluminum oxide powder adhesion coating layer. During the heat treatment process, the magnet body adopted a contact arrangement, and there was no blocking in the sintered magnet after diffusion.

[0105] Table 5 Performance comparison between sintered magnet M3 and magnet M1

[0106]

Table 5

[0107] As shown in Table 5, by adopting such a method, compared with M1, the residual magnetism Br of M3 decreased by about 0.015 T, and the Hcj increased by about 868 kA / m.

[0108] Table 6 Comparison of Hcj at the magnet surface position and Hcj at a position 2 mm from the magnet surface of the sintered magnet M3 Measurement method: Samples of 1 mm×1 mm×1 mm were taken from the surface of the sintered magnet M3 and at a position 2 mm from the surface, respectively. The difference in Hcj between H1 and H2 was 38 kA / m.

[0109] Measuring equipment: PFM06

[0110]

Table 6

[0111] The exemplary embodiments of the present invention have been described above. However, the claims of the present invention are not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc. made by those skilled in the art without departing from the spirit and principles of the present invention should all be included within the scope of the claims of the present invention.

Claims

1. A method for manufacturing an R-Fe-B sintered magnet, wherein the R-Fe-B sintered magnet is obtained by heat treatment of an R-Fe-B magnet body at a holding temperature, the R-Fe-B magnet body includes an R-Fe-B magnet and a composite diffusion layer, the composite diffusion layer includes an RH layer and an RL layer, the RH layer includes a heavy rare earth element, an organic solid, and an optional solvent, the RL layer includes a metal oxide, an organic solid, and an optional solvent, the composite diffusion layer is present on the surface of the R-Fe-B magnet, after the heat treatment at the holding temperature, the metal oxide in the composite diffusion layer forms an oxide adhesion coating layer, the thickness of the R-Fe-B magnet in the magnet orientation direction is Z, and Z ≥ 3.95 mm, the surface of the R-Fe-B sintered magnet has the oxide adhesion coating layer, and let Hcj at the magnet surface in the magnet orientation direction of the R-Fe-B sintered magnet be H1, and let Hcj at a position 2.00 mm ± 0.02 mm from the magnet surface along the magnet orientation direction into the magnet interior be H2, and the difference between the coercive force H1 and the coercive force H2 is ≤ 50 kA / m, H1 and H2 have the relationship shown in formula (I), A method for manufacturing an R-Fe-B sintered magnet, characterized by the above. H1 - H2 ≤ 50 kA / m (I)

2. the thickness of the oxide adhesion coating layer is less than 20 μm, the oxide adhesion coating layer includes at least one of zirconium oxide, calcium oxide, aluminum oxide, and holmium oxide, A method for manufacturing an R-Fe-B sintered magnet according to claim 1, characterized by the above.

3. The heat treatment at the holding temperature includes alternately performing a low-temperature heat treatment and a high-temperature heat treatment, the temperature range of the low-temperature heat treatment is 750°C to 830°C, the temperature range of the high-temperature heat treatment is 830°C to 970°C, the oxide adhesion coating layer can be removed by a non-mechanical grinding method, A method for manufacturing an R-Fe-B sintered magnet according to claim 1, characterized by the above.

4. 15.05 mm ≥ Z ≥ 3.95 mm, the dimensional tolerance of Z is ±0.05 mm, in the R-Fe-B magnet, R is any one or more selected from the rare earth elements Nd, Pr, Tb, Dy, Gd, and Ho, in the R-Fe-B magnet, the content of R is 27 wt% to 34 wt%, in the R-Fe-B magnet, the content of B is 0.8 wt% to 1.3 wt%, The R-Fe-B magnet further contains Fe and M, where M is at least one selected from Ti, V, Cr, Mn, Co, Ga, Cu, Si, Al, Zr, Nb, W, and Mo. In the R-Fe-B magnet, the content of M is 0 wt% to 5 wt%. The method for manufacturing an R-Fe-B sintered magnet according to claim 1, characterized in that.

5. The total thickness of the composite diffusion layer is less than 200 μm. The heavy rare earth element is at least one selected from metallic dysprosium, metallic terbium, dysprosium hydride, terbium hydride, dysprosium fluoride, terbium fluoride, dysprosium oxide, and terbium oxide. The metal oxide is at least one selected from zirconium oxide, calcium oxide, aluminum oxide, and holmium oxide. The organic solid is at least one selected from rosin-modified alkyd resin, thermoplastic phenolic resin, urea resin, and polyvinyl butyral. The solvent is at least one selected from alcohol-based solvents, ether-based solvents, and aromatic hydrocarbon-based solvents. The RH layer and the RL layer are each independently at least one layer. The RH layer and the RL layer are alternately arranged in sequence. When the RH layer and the RL layer are alternately arranged, the outer layer away from the surface of the R-Fe-B magnet is the RL layer. The thickness of a single layer of the RH layer is selected from 0.5 μm to 40 μm. The thickness of a single layer of the RL layer is selected from 0.5 μm to 15 μm. The weight of the composite diffusion layer is 0.1 wt% to 3 wt% of the weight of the R-Fe-B magnet. The method for manufacturing an R-Fe-B sintered magnet according to claim 1, characterized in that.

6. (1) A step of applying and disposing a composite diffusion layer on the surface of the R-Fe-B magnet to form the R-Fe-B magnet body; (2) A step of performing heat treatment with heat preservation in a vacuum or an inert atmosphere on the R-Fe-B magnet body to obtain a sintered magnet having an oxide adhesion coating layer on the surface. The method for manufacturing an R-Fe-B sintered magnet according to claim 1, characterized in that.

7. The heat treatment with heat preservation includes alternately performing low-temperature heat treatment and high-temperature heat treatment. The temperature range of the low-temperature heat treatment is 750 °C to 830 °C, and the temperature range of the high-temperature heat treatment is 830 °C to 970 °C. The total time of the heat treatment with heat preservation is ≥ 8 h. The manufacturing method further includes performing aging heat treatment after the heat treatment with heat preservation. The aging heat preservation treatment includes rapidly cooling to room temperature after the heat preservation heat treatment, further heating to 430°C to 650°C for aging treatment, holding for 1h to 72h, and then rapidly cooling to room temperature again. The heat preservation heat treatment or the aging heat preservation treatment is carried out in a vacuum or an inert atmosphere. A method for manufacturing an R-Fe-B sintered magnet according to claim 6, characterized in that.

8. Applying and disposing the composite diffusion layer includes applying a slurry to the surface of the R-Fe-B magnet and then drying to form the composite diffusion layer. The application is carried out by at least one of brush coating, roller coating, dip coating, and spray coating. After drying, the weight of the R-Fe-B magnet blank increases by 0.1wt% to 3wt% compared to the weight of the R-Fe-B magnet. The solid content of the slurry is 30wt% to 90wt%. The slurry is selected from the RH layer slurry and the RL layer slurry. A method for manufacturing an R-Fe-B sintered magnet according to claim 6, characterized in that.

9. The RH layer slurry contains heavy rare earth elements, organic solids, and a solvent. The mass ratio of the heavy rare earth elements, organic solids, and the solvent is (40 - 70):(3 - 10):(20 - 50). The RL layer slurry contains metal oxides, organic solids, and a solvent. The mass ratio of the metal oxides, organic solids, and the solvent is (30 - 70):(3 - 10):(20 - 50). The method for manufacturing the slurry includes adding the metal oxides, heavy rare earth elements, and organic solids to the solvent and stirring to form a uniform slurry. Applying further includes applying the slurry to the surface of the R-Fe-B magnet in multiple portions. When the slurry is applied in multiple portions, the slurries may be the same or different. After drying, the composite diffusion layer has the RH layer and the RL layer arranged alternately. A method for manufacturing an R-Fe-B sintered magnet according to claim 8, characterized in that.

10. A method for manufacturing a motor including an R-Fe-B sintered magnet manufactured by the method for manufacturing an R-Fe-B sintered magnet according to claim 1.

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