METHOD FOR PRODUCING AN RTB PERMANENT MAGNET AND RTB PERMANENT MAGNET

Abstract

Method for manufacturing an RTB permanent magnet, comprising the following steps: Providing a press body that has an R 1 -TB material, where R 1 comprises one or more rare earth elements selected from the group consisting of Nd, Pr, La, Ce, Sm, Dy, Tb, Ho, Er, Gd, Sc, Y and Eu, preferably comprising Nd or Pr; comprising T Fe and / or Co, and optionally one or more elements selected from the group consisting of Al, Cu, Zn, In, Si, P, S, Ti, V, Cr, Mn, Ni, Ga, Ge, Zr, Nb, Mo, Pd, Ag, Cd, Sn, Sb, Hf, Ta and W; and B is boron; Pre-sintering of the press body at a temperature between 900 °C and 990 °C to produce a pre-sintered block with an actual density of 6.0 - 7.4 g / cm³ 3 preferably 6.5 - 7.3 g / cm³ 3 to obtain; Coating the pre-sintered block with a heavy rare-earth composite powder; and Performing a secondary sintering and a heat diffusion process for the coated block to obtain the RTB permanent magnet with a density, which is at least 99.5% of the theoretical density, wherein R has at least one heavy rare earth element and at least one rare earth element that is not a heavy rare earth element.

Description

Technical area

[0001] The invention relates to a method for producing an RTB permanent magnet and to the permanent magnet produced by this method, in particular to a method for producing an RTB permanent magnet with high saturation magnetization Br and high coercive field strength Hcj. background

[0002] Due to the excellent magnetic properties of R-Fe-B permanent magnets, Nd-Fe-B permanent magnets used in various types of motors are also expected to improve motor performance, reduce motor weight and size, and efficiently achieve energy-saving effects. Therefore, more attention has been paid to the application of Nd-Fe-B permanent magnets in automotive motors and household appliances. In particular, the growing demand for energy conservation and environmental protection has made the use of Nd-Fe-B permanent magnet materials economically viable in the motors of hybrid electric vehicles, electric vehicles, and air conditioning compressors. Typical requirements for the use of sintered R-Fe-B permanent magnet materials in these high-performance motors include high saturation magnetization Br and high coercive field strength Hcj.

[0003] In an R-Fe-B-based sintered permanent magnet, using heavy rare earth elements (such as Dy or Tb) to replace part of the rare earth element R in an R2Fe14B phase can improve the coercive force Hcj. Furthermore, to achieve high coercive force Hcj at high temperatures, it is necessary to add a large amount of the heavy rare earth element RH. However, when using heavy rare earth elements RH to replace light rare earth elements (Pr or Nd) in R-Fe-B-based sintered permanent magnets, although the coercive force Hcj is improved, the residual magnetic flux density Br is inevitably reduced. Because Dy2Fe14B or Tb2Fe14B have a larger magnetocrystalline anisotropy field than Nd2Fe14B, the partial substitution of Nd by heavy rare earth Dy or Tb dramatically promotes HA and greatly increases Hcj.However, this replacement reduces the saturation magnetization, Ms, resulting in a significant reduction in the remanence, Br, and the maximum energy product, (BH)max. This is mainly due to the antiferromagnetic bonding of the atomic magnetic moments of Fe and Dy / Tb in the bulk phase. It also leads to a reduction in the total magnetic moment of the magnet. Furthermore, the element quantity and supply of Dy and Tb are limited, resulting in higher costs for the final products.

[0004] CN 1 898 757 A provides a coating technique for a magnet surface. The sintered block is machined into small and thin magnets, and then the magnets are immersed in a dispersion of micrometer-sized heavy rare earth powder (containing one or more of Dy, Tb, oxide, oxyfluoride, and fluoride) in an organic solvent to coat. Heat treatment is then carried out under vacuum or in an inert gas state at a temperature equal to or lower than the sintering temperature. The resulting effect is a significant improvement in the coercive force Hcj and a slight decrease in the remanence Br. This is because the heavy rare earth elements exist only in the grain boundary phase and not in the bulk phase. This process not only conserves the resources of the heavy rare earth elements but also prevents a decrease in the remanence Br.However, this invention relates to powder improvement, and in the actual manufacturing process, the discrepancy between different product batches is huge, making it difficult to meet the requirements of performance stability and consistency. Furthermore, the heavy rare earth infiltration technique involves a coating and diffusion process, and the technical scheme of the application mainly refers to the coating process. However, regarding the subsequent heat diffusion process, the influence of the channel is more significant than the influence of temperature, time, or other parameters of the heat treatment process. This is not mentioned in this application, resulting in irregularities in the heat diffusion process.

[0005] CN 102 610 355 A provides a heat diffusion process on the surface of a sintered magnet by applying heavy rare earth fluoride, nitrate, and phosphate powder, thereby solving the problem of uneven distribution of molten powder on the magnet surface after heat diffusion. Consequently, this process improves the cohesive force between the substrate and the coating and improves corrosion resistance. The reason for the uneven distribution is that the powder's solubility in water or organic solvents is very poor, and therefore, during the coating process, the powder cannot be evenly distributed on the magnet surface. Although the invention solves the problem of uneven distribution of the powder applied to the substrate, it does not clearly specify the requirements of the heat diffusion process. The problem of uneven distribution during the heat diffusion process remains.

[0006] Chinese patent application CN 103 098 151 A discloses a sintered rare earth magnet, a method for its production, and a motor and automobile using the same. The sintered rare earth magnet comprises a group of main phase grains, each composed of an RTB-based rare earth magnet comprising a core and a shell covering the core, the thickness of the shell being 500 nm or less. R includes a light rare earth element and a heavy rare earth element. Furthermore, a Zr compound is present in a grain boundary phase of the group of main phase grains and / or the shell.

[0007] Chinese patent application CN 103 646 772 A teaches a method for manufacturing a sintered R-Fe-B magnet. The manufacturing method comprises, first, using a conventional method for manufacturing the R-Fe-B sintered magnet and cleaning the sintered magnet through steps such as oil removal, acid washing, and water deionization; second, spreading metal Dy (dysprosium) on the bottom of a material container in any desired shape and then filling the interior of the material container with zirconia, silicon dioxide, or alumina powder; third, inserting the sintered magnet into the powder in a direction perpendicular to a magnetization direction or sequentially arranging the Dy metal plate, the refractory powder particles, the sintered magnet, and the refractory powder particles inside the material container in a layered manner.wherein the lower end of the magnet is not in contact with the Dy particles at the bottom of the material container and adjacent magnets are not in contact with each other, and finally placing the material container in the sintering furnace and performing a heat treatment in vacuum or in an argon (Ar) protective atmosphere at a temperature of 750-1000°C and allowing the Dy to enter the interior of the sintered magnet along a grain boundary by diffusion.

[0008] WO 00 / 48 209 A1 discloses a permanent magnet with substantially stable magnetic properties, comprising as the active magnetic component a sintered product of densified particulate intermetallic iron-boron-rare earth material, the sintered product having pores that are substantially unconnected to one another, a density of at least 87 percent of theoretical density, and a composition consisting essentially of about 13 to about 19 percent rare earth elements by atomic percent, about 4 to about 20 percent boron, and about 61 to about 83 percent iron, with or without impurities, the rare earth content consisting of more than 50% praseodymium with an effective amount of a light rare earth selected from the group consisting of cerium, lanthanum, yttrium, and mixtures thereof, and the remainder being neodymium.

[0009] A sintered magnet with good residual flux density and coercive field strength is known from CN 102 473 498 A. The sintered magnet is provided with a group of crystal grains for an RTB rare-earth magnet with a core and a shell covering the core. The percentage of the mass of the heavy rare-earth elements in the shell is higher than the percentage of the mass of the heavy rare-earth elements in the core, and the thickest section of the shell in the crystal grains faces a grain boundary triple point. A lattice defect forms between the core and the shell.

[0010] The RTB sintered magnet known from CN 104 137 197 A is an RTB sintered magnet with R2T14B crystal grains and is characterized in that it contains, at grain boundaries formed by at least two adjacent R2T14B crystal grains, ROC concentration sections in which the R, O and C concentration is greater than in the R2T14B crystal grains, wherein the ratio (O / R) of O atoms to R atoms in the ROC concentration sections is between 0.4 and 0.7. Summary of the invention

[0011] As mentioned above, existing technologies for manufacturing RTB permanent magnets mainly focus on the effects of the coating powder and the heat treatment process, rather than on the internal structure of the magnet. It has now been discovered that, in addition to the effects of the powder composition used to coat the magnets and the heat treatment process on the coercive force Hcj of the magnet, the diffusion channel in such magnets could significantly influence the subsequent diffusion of heavy rare earth elements. Experimental studies have shown that after the pre-sintering process, the pores in the pre-sintered block are an important diffusion channel, greatly enhancing the diffusion effect of heavy rare earth elements.Thus, the present invention is based on the finding that an RTB-based permanent magnet has improved coercive field strength Hcj and / or improved distribution uniformity of heavy rare earth elements. The object of the present invention is to provide a method for producing sintered RTB permanent magnets with high remanence Br and high coercive field strength Hcj. The remanence Br and coercive field strength Hcj of the magnets produced by this method can be significantly higher than those of magnets produced by existing methods. Furthermore, the perpendicularity SQ and the stability and uniformity between different batches can be significantly improved with the presently described manufacturing method.

[0012] In one aspect, the present invention provides a manufacturing method of an RTB permanent magnet, comprising the steps of: providing a compact consisting of an R 1 -TB structure, where R 1 one or more rare earth elements selected from the group consisting of Sc, La, Ce, Pr, Nd, Sm, Gd, Y, Tb, Dy, Ho, Er and Eu (preferably containing at least Nd or Pr); T comprises Fe and / or Co, and optionally contains one or more elements selected from the group consisting of Al, Cu, Zn, In, Si, P, S, Ti, V, Cr, Mn, Ni, Ga, Ge, Zr, Nb, Mo, Pd, Ag, Cd, Sn, Sb, Hf, Ta and W; and B is boron.

[0013] The manufacturing process includes sintering the compact at a temperature of 900 - 990 °C to produce a pre-sintered block with an actual density of 6.0 - 7.4 g / cm 3The pre-sintered block is then coated with a heavy rare earth composite powder and sintered again (during which thermal diffusion of heavy rare earth elements into the magnet occurs) to obtain the RTB permanent magnet, where R comprises at least one heavy rare earth element and at least one non-heavy rare earth element.

[0014] In some embodiments, the actual density of the pre-sintered block is 80 - 98% (e.g. 85 - 97%) of the theoretical density.

[0015] In some embodiments, the heavy rare earth composite powder contains one or more of heavy rare earth oxides, fluorides, oxyfluorides, hydrides, rare earth intermetallics comprising heavy rare earth elements, heavy rare earth compounds of the type R2Fe14B, or heavy rare earth nitrate hydrate salts.

[0016] In some embodiments, the heavy rare earth composite powder contains one or more of Dy, Tb, or Ho.

[0017] In some embodiments, the compact is manufactured by the following steps: (1) Producing a strip piece from starting materials (which may include mixing the starting materials, melting the produced mixture, and pouring the molten mixture to produce a strip piece); (2) pulverizing the strip piece by hydrogen attrition to obtain a coarse powder; (3) Pulverizing the coarse powder by jet milling to obtain a fine powder with a particle size D50 of 3 ~ 6 µm; and (4) Pressing the fine powder to produce the compact.

[0018] In some embodiments, the coarse powder may have a hydrogen concentration in the range of 800 - 3000 ppm (e.g., 1000 - 2000 ppm).

[0019] In some embodiments, the compact may be sintered in vacuum or inert gas to obtain the pre-sintered block.

[0020] In some embodiments, coating the pre-sintered block comprises dispersing the heavy rare earth composite powder in an organic solvent to produce a slag and immersing the pre-sintered block in the slag.

[0021] In some embodiments, sintering the coated block comprises heating the coated block to a first temperature (e.g., 820-950°C) under vacuum (e.g., in a covered metal container in a vacuum furnace), cooling, and heating the coated block to a second temperature (e.g., 450-620°C) under vacuum to obtain the RTB permanent magnet. During the aforementioned heating process, heavy rare earth elements (e.g., Dy, Tb, or Ho) on the surface of the coated block can be diffused into the magnet.

[0022] In some embodiments, the heavy rare earth composite powder is dispersed into the organic solvent at a concentration of 0.01 - 1.0 g / ml.

[0023] In some embodiments, the container may contain a mixed powder as a sintering aid at the bottom, and the mixed powder may contain 10-20% alumina and 80-90% magnesium oxide. Objects of the invention

[0024] The object of the present invention is to provide a method for improving the diffusion of heavy rare earth elements in an RTB permanent magnet, for improving the coercive field strength Hcj and for improving the perpendicularity SQ by modifying the structure of sintered magnets.

[0025] Compared to magnets manufactured using conventional methods, the diffusion of heavy rare earth elements along the orientation direction in the matrix is ​​more consistent in magnets manufactured using the methods disclosed herein, and the perpendicularity (SQ) is significantly improved. Furthermore, the manufacturing methods described herein can significantly improve batch-to-batch consistency in a continuous manufacturing process. BRIEF DESCRIPTION OF THE DRAWINGS Fig.Figure 1 shows the microstructures of magnets after thermal diffusion as described in Example 4 and Comparative Example 4-2. DISCLOSURE OF THE INVENTION

[0026] In some embodiments, the invention provides a method for manufacturing an RTB permanent magnet with improved properties, which may include the following steps: (1) Providing a compact having an R 1 -TB material, where R 1 one or more rare earth elements selected from the group consisting of Nd, Pr, La, Ce, Sm, Dy, Tb, Ho, Er, Gd, Sc, Y and Eu (preferably containing at least Nd or Pr); and T comprises Fe and / or Co, and optionally one or more elements selected from Al, Cu, Zn, In, Si, P, S, Ti, V, Cr, Mn, Ni, Ga, Ge, Zr, Nb, Mo, Pd, Ag, Cd, Sn, Sb, Hf, Ta and W; and B is boron. (2) Pre-sintering of the compact (ie first sintering process) at a suitable temperature (e.g. 900 - 990°C) to obtain a pre-sintered block; (3) coating the pre-sintered block with a heavy rare earth composite powder to produce a coated block; and (4) sintering the coated block (ie, second sintering process) to obtain the RTB permanent magnet, wherein R comprises at least one heavy rare earth element and at least one rare earth element other than a heavy rare earth element.

[0027] In some embodiments, the compact may be manufactured by the following steps: (1) Producing a strip piece from starting materials (e.g., mixing the starting materials, melting the prepared mixture, and pouring the molten mixture to produce the strip piece); (2) Coarse grinding: pulverizing the strip pieces by hydrogen attrition to obtain a coarse powder; (3) Preparation of fine powder: pulverizing the coarse powder by jet milling to obtain a fine powder with a particle size D5 of 3 ~ 6 µm; and (4) Pressing the fine powder to produce the compact.

[0028] To produce the strip, the raw materials can first be mixed and combined in a specific ratio. The resulting mixture can then be melted in a furnace and cast at a copper conduction velocity of at least 1 m / s, resulting in a strip with a thickness of 0.2–0.5 mm. Without wishing to be bound by theory, it is assumed that when the strip thickness is greater than 0.2 mm, the microstructure of the strip on the roll surface does not occupy a large proportion of a fine-grained region. And when the strip thickness is less than 0.5 mm, it is relatively difficult to form a large proportion of a coarse-grained region in the microstructure of the strip on the surface opposite the roll surface. Both of these would adversely affect the subsequent particle size distribution of the heavy rare earth composite powder on the surface of the strip.

[0029] During the coarse grinding process, the strip piece can undergo hydrogen attrition to obtain a coarse powder. The hydrogen content in the coarse powder can range from 800 to 3000 ppm (preferably 1000-2000 ppm), as measured using an ONH2000 analyzer manufactured by ELTRA (TM) (Stevensville, Michigan). While not wishing to be bound by theory, it is assumed that if the hydrogen content is greater than or equal to 800 ppm, sufficient diffusion channels are present in the subsequent pre-sintered block. If the hydrogen content is less than or equal to 3000 ppm, the pores in the pre-sintered block can ensure that the pre-sintered block achieves a true density of more than 99.5% of its theoretical density.In some embodiments, when the hydrogen content in the coarse powder ranges from 1000 to 2000 ppm, the then-fabricated RTB permanent magnet may have an actual density of more than 99.5% of the theoretical density, and the pre-sintered block may have a sufficient amount of diffusion channels at the same time.

[0030] During the fine powder production process, the coarse powder can be jet-milled to produce a fine powder with a particle size D50 of 3~6 μm (measured by a laser diffraction method; D50 is the value of the particle diameter at 50% in the cumulative distribution). Without wishing to be bound by theory, it is assumed that when D50 is greater than or equal to 3 μm, the nitrogen and oxygen concentration in the sintered block is low, thus not affecting diffusion. Without wishing to be bound by theory, it is assumed that when D50 is less than or equal to 6 μm, the pre-sintered block can achieve more than 99.5% of the theoretical density using a low-temperature sintering process.

[0031] During the pressing process, the powder can be pressed in a vertical sealed compressor in a 1T-3T (e.g. 1.8-3T) magnetic field to produce a compact with the desired shape.

[0032] During the sintering process of the compact, the compact can be transferred to a sintering furnace under vacuum or in an inert gas atmosphere. This pre-sintering process can be carried out below the theoretical sintering temperature to produce a pre-sintered block with a density of 80%-98% (e.g., 85-97%) of the theoretical density, which can create a sufficient number of diffusion channels for the subsequent diffusion of heavy rare earth elements. The sintering temperature can be 900-1040°C (e.g., preferably 910-990°C).

[0033] The actual density of the pre-sintered block can be 6.0 ~ 7.4 g / cm 3 , preferably 6.5 ~ 7.3 g / cm 3 , The actual density can, for example, be at least 6 g / cm 3 (e.g. at least 6.1 g / cm 3 , at least 6.2 g / cm 3 , at least 6.3 g / cm 3 , at least 6.4 g / cm 3 or at least 6.5 g / cm 3) and a maximum of approx. 7.4 g / cm 3 (e.g. maximum 7.3 g / cm 3 , maximum 7.2 g / cm 3 , maximum 7.1 g / cm 3 , maximum 7 g / cm 3 , maximum 6.9 g / cm 3 , maximum 6.8 g / cm 3 , or a maximum of 7 g / cm 3 ). Without wishing to be bound by theory, it is assumed that if the density of the pre-sintered block is greater than 6.0 g / cm 3 the pre-sintered block cannot be easily oxidized during the subsequent diffusion process to cause poor performance; if the density of the pre-sintered block is less than 7.4 g / cm 3, the pre-sintered block could significantly improve the diffusion of heavy rare earth elements during the subsequent diffusion process due to the presence of a sufficient number of diffusion channels. The average grain size of the pre-sintered block is 1.1 ~ 1.5 times (e.g., 1.2 ~ 1.4 times) the particle size D50 of the fine powders. Without wishing to be bound by theory, it is believed that the manufacturing process described here can produce a compact with a small grain size and a rare earth element phase that is more evenly distributed, which can facilitate the subsequent diffusion of heavy rare earth elements.

[0034] The coating and second sintering (which involves heat diffusion) can be carried out using the following steps: During the coating process, the pre-sintered block can first be machined into a desired shape. The heavy rare earth composite powder can be dispersed in an organic solvent to form a slag. The machined pre-sintered block can then be immersed in the slag to form a coated block, in which the pre-sintered block is coated with heavy rare earth composite powder. The coated block can then be transferred to a container (e.g., a covered metal container).

[0035] During the second sintering process, the aforementioned container can be placed in a vacuum furnace, which can then be placed under vacuum and heated to a first temperature (e.g., 820–950°C or 850–940°C) for a sufficient time. The sintering temperature during the second sintering process can, for example, be at least 820°C. During this process, the first diffusion occurs, as the heavy rare earth elements in the heavy rare earth composite powder diffuse into the coated block. The container can then be cooled (e.g., to room temperature).

[0036] This process can optionally be repeated by placing the container under vacuum and heating it to a second temperature (e.g., 450–620°C or 460–550°C) for a sufficient time, during which the second diffusion of heavy rare earth elements takes place. The sintering temperature during this process can be at least 450°C, for example. The container can then be cooled to obtain the RTB permanent magnet.

[0037] During the machining process, the pre-sintered block can be machined into a desired shape with a size (e.g., a size in the magnetic orientation) less than or equal to 10 mm (e.g., less than or equal to 5 mm).

[0038] During the coating process, the heavy rare earth composite powder can be dispersed in the organic solvent to obtain a slag. The pre-sintered block can be immersed in the slag under ultrasonic stirring and then placed in a covered container (e.g., a metal container).

[0039] During the coating process, the heavy rare earth composite powder may contain one or more of the following: heavy rare earth oxides, fluorides, oxyfluorides, or hydrides; intermetallic rare earth compounds; heavy rare earth R2Fe14B compounds; or heavy rare earth nitrate hydrates. The heavy rare earth composite powder may, for example, contain intermetallic rare earth compounds such as DyAl2.

[0040] During the coating process, the heavy rare earth composite powder can be dispersed in the organic solvent at a concentration of 0.01–1.0 g / ml (e.g., 0.1–0.8 g / ml). Without wishing to be bound by theory, it is assumed that within this concentration range, the heavy rare earth composite powder is sufficiently dissolved in the solvent, and that the powder applied to the pre-sintered block can be evenly distributed over its surface.

[0041] The particle size of the powder applied to the pre-sintered block can be in the range of 1 ~ 50 µm, more preferably in the range of 3 ~ 25 µm.

[0042] During the coating process, the organic solvent can be selected from alcohols, alkanes containing 5 to 16 carbon atoms, or esters. Examples of suitable organic solvents include ethyl acetate, ethanol, and cyclohexane.

[0043] In some embodiments, the container may contain a mixed powder at the bottom of the container. The mixed powder may contain 10-20% alumina and 80-90% magnesium oxide. During the second sintering process, the mixed powder may be used as a sintering aid, which may enable the pre-sintered block to quickly reach more than 99.5% of its theoretical density in 24 hours at a low temperature of 820-950°C.

[0044] During the second sintering process, the container can be placed under vacuum in a vacuum furnace and then heated to a first temperature (e.g., 820–950°C) for a sufficient time, during which the first diffusion process of heavy rare earth elements into the coated block takes place. The coated block can then be quenched by Ar gas using an Ar gas blower to a temperature below 80°C. A second diffusion process can be performed by heating the container under vacuum to a second temperature (e.g., 450–620°C). The coated block can then be quenched by Ar gas to a temperature below 80°C to obtain an RTB permanent magnet. After the heat diffusion treatment, the permanent magnet can have a density of 99.5% of the theoretical density. It is assumed that an aging process also takes place during the diffusion process.The described manufacturing process can produce an RTB magnet with a significant increase in coercive field strength Hcj and a substantially uniform distribution of heavy rare earth elements in the grain boundary. During the second sintering process, the holding time for the first diffusion can be 12-24 hours (e.g., 15-20 hours). The holding time for the second diffusion can be 1-8 hours (e.g., 2-7 hours).

[0045] Without wishing to be bound by theory, it is assumed that the grain size of the low-density pre-sintered block is not changed during the second sintering process. It is assumed that if the first diffusion time is more than 12 hours, the pre-sintered block can achieve more than 99.5% of the theoretical density, ensuring consistency in the diffusion depth and diffusion uniformity of the heavy rare earth elements. It is also assumed that if the first diffusion time is less than 24 hours, the pre-sintered block will not exhibit abnormal grain growth, which would lead to deterioration of the magnetic properties.On the contrary, although a conventional method for producing a high-density magnet can achieve uniform diffusion of heavy rare earth elements after the initial heat diffusion is carried out for 12 hours, such a method produces a magnet with abnormal grain growth, resulting in deterioration of magnetic properties. In other words, a conventional manufacturing method can only produce high-density magnets that have one of the two effects, but not both (i.e., uniform diffusion and low abnormal grain growth).

[0046] In the diffusion process, the first and second diffusion steps can be performed under vacuum of less than 0.2 Pa. Typically, the first diffusion is performed at a temperature between 820 and 950°C. If the temperature is higher than 950°C, the diffusion effect is assumed to be unattainable.

[0047] Furthermore, after analyzing the cross-section of an RTB permanent magnet manufactured by the presently described method, it is found that the RTB permanent magnet can have the following advantages: 1) After applying the heavy rare earth composite powder to a pre-sintered block and the second sintering process, the heavy rare earth elements are diffused more evenly throughout the magnet. The gradient of the heavy rare earth elements along the depth of the magnet is smaller than in a magnet manufactured by a conventional manufacturing technique with a density above 99.5% of the theoretical density after the same diffusion process. 2) In the region within 1000 µm of the surface, the average concentration of heavy rare earth elements in the grain boundary is at least 0.7 wt.% higher than that in the grain center.In contrast, in the same range, for a magnet with a density above 99.5% of the theoretical density produced by a conventional process, the difference between the average concentration of heavy rare earth elements in the grain boundary and that in the grain center is less than 0.7 wt.%. 3) When coated with the same amount of heavy rare earth composite powder under the same coating conditions, the pre-sintered block described here can achieve deeper diffusion of heavy rare earth elements than a magnet produced by a process that does not involve a primary sintering process.

[0048] In some embodiments, the RTB permanent magnet manufactured by the method described herein may have a coercive field strength of at least about 14 MA / m (e.g., at least about 14.5 MA / m, at least about 15 MA / m, at least about 15.5 MA / m, at least about 16 MA / m, at least about 16.5 MA / m, or at least about 17 MA / m).

[0049] The magnetic properties described here were measured according to the test methods described in GB / T 3217-2013. ExamplesExample 1

[0050] An alloy containing the following metal elements: PrNd (30 wt%), Dy (0.5 wt%), Al (0.4 wt%), Co (1 wt%), Cu (0.1 wt%), Ga (0.1 wt%), B (0.96 wt%), and Fe (balance) was prepared as the starting material. The purity of the metal elements was over 99%. A strip of the alloy with a thickness of 0.25 mm was produced using a strip casting process. The strip was then converted into a coarse powder with a hydrogen content of 1400 ppm using a hydrogen attrition process. The coarse powder was then converted into a fine powder with a particle size D50 of 4.5 µm using a jet milling process. The fine powder was compressed using a vertical sealed compressor in a 2T magnetic field to form a compact. The compact was then transferred to a high vacuum furnace for sintering at a temperature of 1000°C for 2 hours.The density of the obtained pre-sintered block was 7.3 g / cm. 3, which accounted for 96.7% of the theoretical density. The average grain diameter was 6.75 µm. The pre-sintered block was formed into cylinders measuring D10mm×5mm (with the orientation direction having a length of 5 mm). A heavy rare earth composite powder (having a particle size of 1 µm) containing 70 wt% dysprosium nitrate and 30 wt% dysprosium fluoride was dispersed in ethyl acetate at a concentration of 0.05 g / ml to obtain a slag. The pre-sintered block was then immersed in the slag for 15 minutes. Afterward, the coated pre-sintered block was placed in a metal container. A mixed powder containing 15 wt% alumina and 85 wt% magnesium oxide was placed on the bottom of the container to serve as a sintering aid. The container was transferred to a vacuum sintering furnace, in which the coated pre-sintered block was heated for 12 hours under vacuum (10 -2Pa) at a temperature of 890°C. After cooling, the magnet was hardened at 500°C for 5 hours and then cooled to obtain an RTB permanent magnet. After the above-mentioned sintering and diffusion processes, the density of the magnet was 7.52 g / cm 3 , which was 99.6% of the theoretical density. The average main phase grain size of the magnet was 6.80 µm.

[0051] The magnetic properties of the magnet were measured and are shown in Table 1. Comparison example 1-1

[0052] A compact was manufactured under the same conditions and using the same method as in Example 1. The compact was then transferred to a high-vacuum furnace and sintered at 1050°C (higher than the temperature used in Example 1) for 3 hours (longer than the time used in Example 1). Furthermore, the compact was not coated with a heavy rare-earth composite powder. Then, a two-step treatment process was performed. In the first step, heat treatment was carried out at 890°C for 3 hours. In the second step, heat treatment was carried out at 500°C for 5 hours. Afterward, the resulting ingot was cut into cylinders measuring 10 mm x 5 mm. The density of the product was 7.54 g / cm³. 3 , which was 99.9% of the theoretical density. The average main phase grain diameter of the product was 7.90 µm. The magnetic properties of the product were measured and are presented in Table 1. Comparison example 1-2

[0053] A magnet was manufactured in the same manner as in Example 1, except that the compact was sintered at 1050°C to obtain a pre-sintered block.

[0054] Specifically, a compact was prepared under the same conditions and using the same method as in Example 1. The compact was transferred to a high vacuum sintering furnace and sintered at 1050°C for 3 hours to obtain a pre-sintered block having an actual density of 7.54 g / cm 3which is close to the theoretical density. The pre-sintered block was cut into cylinders with a size of D10 mm × 5 mm. A heavy rare earth composite powder (with an average particle size of 1 µm) containing 70 wt% dysprosium nitrate and 30 wt% dysprosium fluoride was dispersed in ethyl acetate at a concentration of 0.05 g / ml to obtain a slag. The pre-sintered block was immersed in the slag for 15 minutes. Afterward, the coated block was placed in a metal container identical to the one used in Example 1. The container was transferred to a vacuum sintering furnace, in which the coated pre-sintered block was sintered for 3 hours under vacuum (10 -2 Pa) at 890°C. After cooling, the magnet was cured for 5 hours at 500°C. The density of the magnet was 7.54 g / cm 3, which was 99.9% of the theoretical density. The magnetic properties of the product were measured and are presented in Table 1. Table 1. Magnetic properties of the magnets obtained from Example 1, Comparative Example 1-1, Comparative Example 1-2 The magnetic properties of examples Br (T) Hcj (MA / m) (BH)max (kJ / m 3 ) HK / Hcj Example 1 1,375 16,02 369,50 0,96 Comparison example 1-1 1,380 12,34 375,31 0,91 Comparison example 1-2 1,375 15,86 370,46 0,90

[0055] Note: (BH)max refers to the maximum energy product and HK refers to the demagnetizing field that reduces the intrinsic magnetization by 10%. Example 2

[0056] A strip piece with a thickness of 0.50 mm was produced from the alloy with the same composition as in Example 1 by strip casting. The strip piece was converted into a coarse powder with a hydrogen content of 800 ppm by hydrogen attrition. A fine powder with a particle size D50 of 6.0 µm was produced from the coarse powder using a jet milling process. The fine powder was pressed using a vertical sealed compressor in a 2T magnetic field to produce a compact. The compact was transferred to a high-vacuum sintering furnace and sintered at a temperature of 900°C for 4 hours. The density of the resulting pre-sintered block was 6.90 g / cm³. 3, which accounted for 91.4% of the theoretical density. The average grain size of the pre-sintered block was 7.30 µm. A heavy rare earth composite powder with a particle size of 50 µm and consisting of 100% dysprosium oxide was dispersed in ethanol at a concentration of 0.01 g / ml to obtain a slag. The pre-sintered block was immersed in the slag for 60 minutes, and the coated block was placed in a metal container. A mixed powder containing 20 wt% alumina and 80 wt% magnesium oxide was placed on the bottom of the container to serve as a sintering aid. The container was transferred to a vacuum sintering furnace, in which the coated pre-sintered block was sintered for 24 hours under vacuum (10 -2 Pa) at 950°C. After cooling, the magnet was hardened at 450°C for 8 hours and then cooled to obtain an RTB permanent magnet. The density of the resulting magnet was 7.52 g / cm 3, which was 99.6% of the theoretical density. The average main phase grain size of the magnet was 7.30 µm. The magnetic properties of the product were measured and are presented in Table 2. Comparison example 2-1

[0057] A compact was manufactured under the same conditions and using the same method as in Example 2. The compact was then transferred to a high-vacuum sintering furnace and sintered at 1070°C (higher than the temperature used in Example 2) for 3 hours. Furthermore, the compact was not coated with a heavy rare-earth composite powder. Then, a two-step treatment process was performed. In the first step, heat treatment was carried out at 950°C for 3 hours. In the second step, heat treatment was carried out at 450°C for 8 hours. The resulting ingot was cut into cylinders measuring 10 mm x 5 mm in diameter, and the magnet density was 7.54 g / cm³. 3The average main phase grain size of the magnet was 10.20 µm. The magnetic properties of the product were measured and are presented in Table 2. Comparison example 2-2

[0058] A magnet was prepared in the same manner as in Example 2, except that the compact was sintered at 1070°C to obtain a pre-sintered block.

[0059] A compact was prepared under the same conditions and using the same procedure as in Example 2. The compact was then transferred to a high vacuum sintering furnace and sintered at 1070°C for 3 hours to obtain a pre-sintered block having an actual density of 7.54 g / cm 3which is close to the theoretical density. The block was cut into cylinders with a size of D10 mm × 5 mm. A heavy rare earth composite powder of 100 wt.% dysprosium oxide was dispersed in ethanol at a concentration of 0.01 g / ml to obtain a slag. The pre-sintered block was immersed in the slag for 60 minutes, and the coated block was placed in a metal container identical to the one used in Example 2. The container was transferred to a vacuum sintering furnace, in which the coated pre-sintered block was sintered for 3 hours under vacuum (10 -2 Pa) at 950°C. After cooling, the magnet was cured for 8 hours at 450°C. The density of the resulting product was 7.54 g / cm 3 The magnetic properties of the product were measured and are shown in Table 2. Table 2. Magnetic properties of the magnets obtained from Example 2, Comparative Example 2-1 and Comparative Example 2-2 The magnetic properties of examples Br (T) Hcj (MA / m) (BH)max (kJ / m 3 ) HK / Hcj Example 2 1,376 14,88 368,95 0,97 Comparison example 2-1 1,380 12,00 374,28 0,91 Comparison example 2-2 1,378 14,77 369,98 0,90 EXAMPLE 3

[0060] A strip piece with a thickness of 0.20 mm was produced by strip casting from an alloy having the same composition as in Example 1. The strip was converted into a coarse powder with a hydrogen content of 3000 ppm by hydrogen attrition. The coarse powder was jet milled into a fine powder with a particle size D50 of 3.0 µm. The fine powder was compressed using a vertical sealed compressor in a 2T magnetic field to produce a compact. The compact was then transferred to a high-vacuum sintering furnace and sintered at 950°C for 1 hour. The density of the resulting pre-sintered block was 6.50 g / cm³. 3, which accounted for 86.1% of the theoretical density. The average grain size of the pre-sintered block was 3.3 µm. The block was then cut into cylinders with a size of D10mm×5mm (with the orientation direction having a length of 5 mm). A heavy rare earth composite powder with a particle size of 25 µm and an intermetallic compound consisting of 20 wt% DyHx and 80 wt% MgCu2 (with 10 wt% Nd, 12 wt% Pr, 35 wt% Dy, 41 wt% Fe, and 2 wt% Co) was dispersed in ethanol at a concentration of 1 g / ml to obtain a slag. The cylindrical block was immersed in the slag for 30 minutes, and the coated block was placed in a metal container. A mixed powder containing 15 wt% alumina and 85 wt% magnesium oxide was placed at the bottom of the container to serve as a sintering aid. The container was transferred to a vacuum sintering furnace, where the coated pre-sintered block was sintered under vacuum (10°C) for 15 hours.-2 Pa) at 920°C. After cooling, the magnet was hardened at 480°C for 5 hours and then cooled to obtain an RTB permanent magnet. The density of the magnet was 7.54 g / cm 3 , which was 99.9% of the theoretical density. The average main phase grain size of the magnet was 3.60 µm. The magnetic properties of the product were measured and are presented in Table 3. Comparison example 3-1

[0061] A compact was manufactured under the same conditions and method as in Example 3 and transferred to a high-vacuum sintering furnace. The compact was sintered at a temperature of 1045°C (higher than the temperature used in Example 3) for 3 hours (longer than the time used in Example 3). Furthermore, the compact was not coated with a heavy rare-earth composite powder. Then, a two-stage treatment process was performed. The first heat treatment process was carried out at 920°C for 3 hours, and the second heat treatment process was carried out at 480°C for 5 hours. The resulting ingot was cut into cylinders measuring 10 mm x 5 mm in diameter. The product density was 7.54 g / cm³. 3 and the average main phase grain size was 5.80 µm. The magnetic properties of the product were measured and are presented in Table 3. Comparison example 3-2

[0062] A magnet was prepared in the same manner as in Example 3, except that the compact was sintered at 1045°C to obtain a pre-sintered block.

[0063] Specifically, a compact was prepared under the same conditions and using the same method as in Example 3 and transferred to a high-vacuum sintering furnace. The compact was sintered at 1045°C for 3 hours to obtain a pre-sintered block having an actual density of 7.54 g / cm 3which is close to the theoretical density. The ingot was cut into cylinders with a size of D10 mm × 5 mm. A heavy rare earth composite powder with a particle size of 25 µm and an intermetallic compound consisting of 20 wt% DyHz and 80 wt% MgCu2 (with 10 wt% Nd, 12 wt% Pr, 35 wt% Dy, 41 wt% Fe, and 2 wt% Co) was dispersed in ethanol at a ratio of 1 g / ml to obtain a slag. The cylindrical pre-sintered ingot was immersed in the slag for 30 minutes, and the coated ingot was placed in a metal container identical to the one used in Example 3. The container was transferred to a vacuum sintering furnace, where the coated pre-sintered ingot was sintered for 15 hours under vacuum (10 -2 Pa) at 920°C. After cooling, the magnet was cured for 5 hours at 480°C. The density of the product was 7.54 g / cm 3The magnetic properties of the product were measured and are shown in Table 3. Table 3. Magnetic properties of the magnets obtained from Example 3, Comparative Example 3-1 and Comparative Example 3-2 The magnetic properties of examples Br (T) Hcj (MA / m) (BH)max (kJ / m 3 ) HK / Hcj Example 3 1,375 17,58 367,67 0,97 Comparison example 3-1 1,378 12,78 373,24 0,93 Comparison example 3-2 1,375 17,46 368,07 0,80 Example 4

[0064] A 0.25 mm thick strip was produced by strip casting from an alloy having the same composition as in Example 1. The strip was converted into a coarse powder with a hydrogen content of 1000 ppm by hydrogen attrition. The coarse powder was jet milled into a fine powder with a particle size D50 of 4.5 µm. The fine powder was compressed using a vertical sealed compressor in a 2T magnetic field to produce a compact. The compact was then transferred to a high-vacuum sintering furnace and sintered at 920°C for 4 hours. The density of the resulting compact was 7.00 g / cm³. 3, which accounted for 92.7% of the theoretical density. The average grain size of the pre-sintered block was 6.30 µm. The block was cut into cylinders measuring 10 mm x 5 mm (with the orientation direction having a length of 5 mm). A heavy rare earth composite powder with a particle size of 3 µm and an intermetallic compound consisting of 20 wt.% terbium fluoride and 20 wt.% Dy2Fe 14 B and 60 wt% MgCu2 (with 10 wt% Nd, 15 wt% Pr, 25 wt% Dy, 7 wt% Tb, 41.9 wt% Fe, 1 wt% Co, and 0.1 wt% Co) was dispersed in ethanol to obtain a slag. The coated pre-sintered block was placed in a metal container. A mixed powder of 10 wt% alumina and 90 wt% magnesium oxide was placed on the bottom of the container to serve as a sintering aid. The container was transferred to a vacuum sintering furnace, where the coated pre-sintered block was sintered for 20 hours under vacuum (10 -2Pa) at 820°C. After cooling, the block was hardened at 620°C for 3 hours and then cooled to obtain an RTB permanent magnet. The density of the resulting magnet was 7.54 g / cm 3 , which was 99.6% of the theoretical density. The average main phase grain size of the magnet was 6.45 µm. The magnetic properties of the product were measured and are presented in Table 4. Comparison example 4-1

[0065] A compact was produced under the same conditions and using the same method as in Example 4 and transferred to a high-vacuum sintering furnace. The compact was sintered at 1060°C for 3 hours. Then, a two-step treatment process was carried out. In the first step, the pre-sintered block was hardened at 820°C for 2 hours. In the second step, it was hardened at 620°C for 3 hours. The resulting block was cut into cylinders measuring 10 mm x 5 mm. The density of the magnet was 7.54 g / cm³. 3 The average main phase grain size of the magnet was 7.25 µm. The magnetic properties of the product were measured and are presented in Table 4. Comparison example 4-2

[0066] A magnet was prepared in the same manner as in Example 4, except that the compact was sintered at 1060°C to obtain a pre-sintered block.

[0067] Specifically, a compact was prepared under the same conditions and using the same method as in Example 4 and transferred to a high-vacuum sintering furnace. The compact was sintered at 1060°C for 3 hours to obtain a pre-sintered block having an actual density of 7.54 g / cm 3 which is close to the theoretical density. The compact was not coated with a heavy rare earth composite powder. The pre-sintered block was cut into cylinders measuring 10 mm x 5 mm. A heavy rare earth composite powder with a particle size of 3 µm and an intermetallic compound consisting of 20 wt.% terbium fluoride, 20 wt.% Dy2Fe 14B and 60 wt.% MgCu2 (with 10 wt.% Nd, 15 wt.% Pr, 25 wt.% Dy, 7 wt.% Tb, 41.9 wt.% Fe, 1 wt.% Co, and 0.1 wt.% Cu) was dispersed in ethanol at a concentration of 0.1 g / ml to obtain a slag. The cylindrical pre-sintered block was immersed in the slag for 15 minutes, and the coated block was placed in a metal container identical to that used in Example 4. The container was transferred to a vacuum sintering furnace, in which the coated pre-sintered block was sintered for 2 hours under vacuum (10 -2 Pa) at 820°C. After cooling, the block was cured at 620°C for 3 hours. The density of the resulting product was 7.54 g / cm 3 The magnetic properties of the product were measured and are shown in Table 4. Table 4. Magnetic properties of the magnets obtained from Example 4, Comparative Example 4-1 and Comparative Example 4-2 The magnetic properties of examples Br (T) Hcj (MA / m) (BH)max (kJ / m 3 ) HK / Hcj Example 4 1,375 16,53 367,67 0,98 Comparison example 4-1 1,378 12,62 373,24 0,93 Comparison example 4-2 1,375 16,50 368,07 0,91

[0068] In a cross-section of the magnets obtained from Example 4, Comparative Example 4-1 and Comparative Example 4-2, the microstructures at different distances from the surface were observed by scanning electron microscopy (SEM, TESCAN VEGA 3 LMH), and the compositions at these locations were analyzed by energy dispersive spectroscopy (EDS).

[0069] Fig. Figure 1 contains the microstructure photos of the magnets obtained after heat diffusion in Example 4 and Comparative Example 4-2. Fig. 1(a)(b)(c)(d) are photographs obtained from the magnet described in Example 4: (a) near the surface, (b) 200 µm from the surface, (c) 500 µm from the surface, and (d) 1000 µm from the surface. Fig.1(e)(f)(g)(h) are photographs obtained from the magnet described in Comparative Example 4-2: (e) near the surface, (f) 200 µm from the surface, (g) 500 µm from the surface, and (h) 1000 µm from the surface. Table 5. Dy+Tb weight percent of the magnets obtained from Example 4 and Comparative Example 4-2 The weight percent of Dy and Tb in the analytical part in the sample Analysis part in the sample Grain boundary in example 4 Grain middle part in example 4 Grain boundary in comparative example 4-2 Grain middle part in comparison example 4-2 Near the surface of the sample 9,7 2,61 13,5 2,41 Depth from the sample surface is 200 µm 2,65 1,34 2,85 2,34 Depth from the sample surface is 500 µm 2,24 1,52 2,75 2,26 Depth from the sample surface is 1000 µm 2,27 1,28 1,82 1,34

[0070] Note: The weight percentages of Dy+Tb in Table 5 are average values ​​of more than 10 grains at the same distance obtained by energy spectrum scanning.

[0071] The photos in Fig.1 and the data in Table 5 show that: 1) The diffusion of heavy rare earth elements was more uniform in the magnet of Example 4 than in the magnet of Comparative Example 4-2. The distribution gradient of heavy rare earth elements from the surface to an inner layer was smaller in the magnet of Example 4 than in the magnet of Comparative Example 4-2. 2) In the magnet of Example 4, within a distance of approximately 1000 µm from the magnet surface, the average content of heavy rare earth elements in the grain boundary was at least 0.7 wt% higher than that in the grain center. However, in the magnet of Comparative Example 4, the difference in the content of heavy rare earth elements between the grain boundary and the grain center within 1000 µm from the magnet surface was less than 0.7 wt%.3) When coated with the same amount of heavy rare earth element under the same conditions, the diffusion depth of the heavy rare earth element was larger in the magnet of Example 4 than in the magnet of Comparative Example 4-2. EXAMPLE 5

[0072] A strip piece with a thickness of 0.30 mm was produced by strip casting from an alloy having the same composition as in Example 1. The strip piece was converted into a coarse powder with a hydrogen content of 2000 ppm by hydrogen attrition. The coarse powder was jet milled into a fine powder with a particle size D50 of 4.0 µm. The fine powder was then compressed using a vertical sealed compressor in a 2T magnetic field to produce a compact. The compact was then transferred to a high-vacuum sintering furnace and sintered at 1000°C for 1 hour. The density of the resulting pre-sintered block was 6.75 g / cm³. 3, which accounted for 89.4% of the theoretical density. The average grain size of the compact was 5.20 µm. The pre-sintered block was cut into cylinders measuring D10mm×5mm (with the orientation direction having a length of 5 mm). A heavy rare earth composite powder with a particle size of 5 µm and an intermetallic compound consisting of 5 wt% terbium oxide, 5 wt% DyGa2, and 90 wt% MgCu2 (with 28 wt% Nd, 25 wt% Dy, 3 wt% Ho, 42.7 wt% Fe, 1 wt% Co, 0.1 wt% Cu, 0.1 wt% Ga, and 0.1 wt% Zr) was dispersed in cyclohexane at a concentration of 0.8 g / ml to obtain a slag. The cylindrical pre-sintered block was immersed in the slag for 45 minutes, and the coated block was placed in a metal container. A mixed powder of 20 wt% alumina and 80 wt% magnesium oxide was placed at the bottom of the container to serve as a sintering aid.The container was then transferred to a vacuum sintering furnace, where the coated pre-sintered block was heated for 18 hours under vacuum (10 °C). -2 Pa) at 920°C. After cooling, the block was hardened for 5 hours at 540°C and then cooled to obtain an RTB permanent magnet. The density of the magnet was 7.54 g / cm 3 The average main phase grain size was 5.30 µm. The magnetic properties of the product were measured and are presented in Table 6. Comparison example 5-1

[0073] A compact was manufactured under the same conditions and method as in Example 5 and transferred to a high-vacuum sintering furnace. The compact was sintered at 1060°C (higher than the temperature used in Example 5) for 3 hours (longer than the time used in Example 5). Furthermore, the compact was not coated with a heavy rare-earth composite powder. Then, a two-step treatment process was performed. In the first step, heat treatment was carried out at 920°C for 2 hours. In the second step, heat treatment was carried out at 540°C for 5 hours. The resulting magnet was cut into cylinders measuring 10 mm x 5 mm. The product density was 7.54 g / cm³. 3 The average main phase grain size was 7.20 µm. The magnetic properties of the product were measured and are presented in Table 6. Comparison example 5-2

[0074] A magnet was prepared in the same manner as in Example 5, except that the compact was sintered at 1060°C to obtain a pre-sintered block.

[0075] Specifically, a compact was prepared under the same conditions and using the same method as in Example 5 and transferred to a high-vacuum sintering furnace. The compact was sintered at 1060°C for 3 hours to obtain a pre-sintered block having an actual density of 7.54 g / cm 3which is close to the theoretical density. The pre-sintered block was cut into cylinders with a size of D10mm×5mm. A heavy rare earth composite powder with a particle size of 5 µm and an intermetallic compound consisting of 5 wt% terbium oxide, 5 wt% DyGa2, and 90 wt% MgCu2 (with 28 wt% Nd, 25 wt% Dy, 3 wt% Ho, 42.7 wt% Fe, 1 wt% Co, 0.1 wt% Cu, 0.1 wt% Ga, and 0.1 wt% Zr) was dispersed in cyclohexane at a concentration of 0.8 g / ml to obtain a slag. The pre-sintered magnet was immersed in the slag for 45 minutes, and the coated block was placed in a metal container identical to the one used in Example 5. The container was then transferred to a vacuum sintering furnace, where the coated pre-sintered block was heated for 12 hours under vacuum (10 -2 Pa) at 920°C. After cooling, the block was cured for 5 hours at 540°C. The density of the product was 7.54 g / cm3 The magnetic properties of the product were measured and are shown in Table 6. Table 6. Results of the magnetic properties of Example 5, Comparative Example 5-1 and Comparative Example 5-2 The magnetic properties of examples Br (T) Hcj (MA / m) (BH)max (kJ / m 3 ) HK / Hcj Example 5 1,376 16,92 372,21 0,97 Comparison example 5-1 1,381 12,51 378,26 0,93 Comparison example 5-2 1,375 16,74 368,07 0,85 EXAMPLE 6

[0076] A 0.25 mm thick strip was produced by strip casting from an alloy having the same composition as in Example 1. The strip was converted into a coarse powder with a hydrogen content of 1500 ppm by hydrogen attrition. A fine powder with a particle size D50 of 4.0 µm was produced by jet milling. The fine powder was then compressed using a vertical sealed compressor in a 2T magnetic field to produce a compact. The compact was then transferred to a high-vacuum sintering furnace and sintered at 950°C for 3 hours. The density of the pre-sintered block was 7.10 g / cm³. 3, which accounted for 94.0% of the theoretical density. The average grain size was 5.60 µm. The pre-sintered block was cut into cylinders measuring D10mm×5mm (with the orientation direction having a length of 5 mm). A heavy rare earth composite powder composed of an intermetallic compound of 10 wt% holmium nitrate, 50 wt% fluorine dysprosium oxide, and 40 wt% MgCu2 (containing 22 wt% Pr, 30 wt% Dy, 6 wt% Ho, 38.1 wt% Fe, 3 wt% Co, 0.5 wt% Cu, 0.2 wt% Ga, 0.1 wt% Cr, and 0.1 wt% Mn) was dispersed in cyclohexane at a concentration of 0.5 g / ml to obtain a slag. The pre-sintered block was immersed in the slag for 30 minutes, and the coated block was placed in a metal container. A mixed powder of 20 wt% alumina and 80 wt% magnesium oxide was placed at the bottom of the container to serve as a sintering aid.The container containing the coated block was transferred to a vacuum sintering furnace, where the coated pre-sintered block was heated for 16 hours under vacuum (10 °C). -2 Pa) at 940°C. After cooling, the block was hardened at 480°C for 6 hours and then cooled to obtain an RTB permanent magnet. The density of the product was 7.54 g / cm 3 The average main phase grain size was 5.65 µm. The magnetic properties of the product were measured and are presented in Table 7. Comparison example 6-1

[0077] A compact was produced under the same conditions and using the same method as in Example 6 and transferred to a high-vacuum sintering furnace. The compact was sintered for 3 hours at 1060°C (higher than the temperature used in Example 6). Furthermore, the compact was not coated with a heavy rare-earth composite powder. Then, a two-step treatment process was performed. In the first step, the ingot was hardened at 940°C for 2 hours. In the second step, the ingot was hardened at 480°C for 6 hours. The resulting ingot was cut into cylinders with a size of D10*5 mm. The product density was 7.54 g / cm³. 3 The average main phase grain size was 7.20 µm. The magnetic properties of the product were measured and are presented in Table 7. Comparison example 6-2

[0078] A magnet was prepared in the same manner as in Example 6, except that the compact was sintered at 1060°C to obtain a pre-sintered block.

[0079] Specifically, a compact was prepared under the same conditions and using the same method as in Example 6 and transferred to a high-vacuum sintering furnace. The compact was sintered at 1060°C for 3 hours to obtain a pre-sintered block having an actual density of 7.54 g / cm 3which is close to the theoretical density. The ingot was cut into cylinders with a size of D10mm×5mm. A heavy rare earth composite powder with a particle size of 10 µm and an intermetallic compound consisting of 10 wt% holmium nitrate, 50 wt% fluorine dysprosium oxide, and 40 wt% MgCu2 (with 22 wt% Pr, 30 wt% Dy, 6 wt% Ho, 38.1 wt% Fe, 3 wt% Co, 0.5 wt% Cu, 0.2 wt% Ga, 0.1 wt% Cr, and 0.1 wt% Mn) was dispersed in cyclohexane at a concentration of 0.5 g / ml to obtain a slag. The cylindrical pre-sintered block was immersed in the slag for 30 minutes, and the coated block was placed in a metal container identical to that used in Example 6. The container was then transferred to a vacuum sintering furnace, in which the coated pre-sintered block was sintered for 6 hours under vacuum (10 -2Pa) at 940°C. After cooling, the block was cured for 6 hours at 480°C. The density of the product was 7.54 g / cm 3 The magnetic properties of the product were measured and are shown in Table 7. Table 7. Magnetic properties of the magnets obtained from Example 6, Comparative Example 6-1 and Comparative Example 6-2 The magnetic properties of examples Br (T) Hcj (MA / m) (BH)max (kJ / m 3 ) HK / Hcj Example 6 1,376 15,99 372,21 0,98 Comparison example 6-1 1,381 12,51 378,26 0,92 Comparison example 6-2 1,375 16,04 368,07 0,91 EXAMPLE 7

[0080] A strip piece with a thickness of 0.25 mm was produced by strip casting from an alloy having the same composition as in Example 1. The strip piece was then converted into a coarse powder with a hydrogen content of 1500 ppm by hydrogen attrition. The coarse powder was jet-milled to produce a fine powder with a particle size D50 of 5.40 µm. The fine powder was compressed using a vertical sealed compressor in a 2T magnetic field to produce a compact. The compact was transferred to a high-vacuum sintering furnace and sintered at 950°C for 3 hours. The density of the pre-sintered block was 7.10 g / cm³. 3, which was 94.0% of the theoretical density. The average grain size was 5.60 µm. The ingot was cut into cylinders measuring 10 mm x 5 mm (with the orientation direction having a length of 5 mm). A heavy rare earth composite powder with a particle size of 15 µm and an intermetallic compound consisting of 70 wt% holmium nitrate pentahydrate, 20 wt% fluorine dysprosium oxide, and 10 wt% MgCu2 (containing 22 wt% Pr, 30 wt% Dy, 6 wt% Ho, 38.1 wt% Fe, 3 wt% Co, 0.5 wt% Cu, 0.2 wt% Ga, 0.1 wt% Cr, and 0.1 wt% Mn) was dispersed in cyclohexane at a concentration of 0.5 g / ml to obtain a slag. The pre-sintered block was immersed in the slag for 30 minutes, and the coated block was placed in a metal container. The container was then transferred to a vacuum sintering furnace, where the coated pre-sintered block was heated for 24 hours under vacuum (10 -2Pa) at 940°C. After cooling, the block was hardened at 480°C for 6 hours and then cooled to obtain an RTB permanent magnet. The density of the resulting product was 7.50 g / cm 3 The average main phase grain size was 5.70 µm. The magnetic properties of the product were measured and are presented in Table 8. Comparison example 7-1

[0081] A compact was manufactured under the same conditions and using the same method as in Example 7 and transferred to a high-vacuum sintering furnace. The compact was sintered for 3 hours at 1060°C (higher than the temperature used in Example 7). Furthermore, the compact was not coated with a heavy rare-earth composite powder. Then, a two-step treatment process was performed. In the first step, heat treatment was carried out at 940°C for 2 hours. In the second step, heat treatment was carried out at 480°C for 6 hours. The resulting ingot was cut into cylinders measuring 10 mm x 5 mm in diameter. The product density was 7.54 g / cm³. 3 The average main phase grain size was 7.20 µm. The magnetic properties of the product were measured and are presented in Table 8. Comparison example 7-2

[0082] A magnet was prepared in the same manner as in Example 7, except that the compact was sintered at 1060°C to obtain a pre-sintered block.

[0083] Specifically, a compact was prepared under the same conditions and using the same method as in Example 7 and transferred to a high-vacuum sintering furnace. The compact was sintered at 1060°C for 3 hours to obtain a pre-sintered block having an actual density of 7.54 g / cm 3which is close to the theoretical density. The pre-sintered block was cut into cylinders with a size of D10mm×5mm. A heavy rare earth composite powder composed of an intermetallic compound of 70 wt% holmium nitrate pentahydrate, 20 wt% fluorine dysprosium oxide, and 10 wt% MgCu2 (with 22 wt% Pr, 30 wt% Dy, 6 wt% Ho, 38.1 wt% Fe, 3 wt% Co, 0.5 wt% Cu, 0.2 wt% Ga, 0.1 wt% Cr, and 0.1 wt% Mn) was dispersed in cyclohexane at a concentration of 0.5 g / ml to obtain a slag. The machined pre-sintered block was immersed in the slag for 30 minutes, and the coated block was placed in a metal container identical to that used in Example 7. The container was transferred to a vacuum sintering furnace, in which the coated pre-sintered block was sintered for 6 hours under vacuum (10 -2Pa) at 940°C. After cooling, the block was cured at 480°C for 6 hours and then cooled to room temperature to obtain the final product. The density of the product was 7.54 g / cm 3 The magnetic properties of the product were measured and are shown in Table 8. Table 8. Magnetic properties of the magnets obtained from Example 7, Comparative Example 7-1 and Comparative Example 7-2 The magnetic properties of examples Br (T) Hcj (MA / m) (BH)max (kJ / m 3 ) HK / Hcj Example 7 1,371 15,54 367,19 0,96 Comparison example 7-1 1,381 12,51 378,26 0,92 Comparison example 7-2 1,375 15,68 368,07 0,91 EXAMPLE 8-1

[0084] Cylinders measuring D10mm×5mm were manufactured using the same process as described in Example 4. The cylinders were coated in five batches using the process described in Example 4 and sintered / heat-diffused twice. The process conditions for each batch were kept identical. Fifty cylinders were selected from each batch, and their magnetic properties were measured to compare the consistency of their properties across batches. The results are shown in Table 9 (where the average value is the average obtained from the 50 cylinders, and the range is the difference between the maximum and minimum values ​​obtained from the 50 cylinders). Table 9. The magnetic property results obtained from Example 8-1 Br (T) Hcj(MA / m) (BH) max(kJ / m 3 ) Hk / Hcj Average Area Average Area Average Area Average Area First batch 1,374 0,006 16,70 0,22 372,05 3,34 0,96 0,01 Second batch 1,375 0,007 16,66 0,24 372,53 3,82 0,96 0,01 Third batch 1,374 0,005 16,63 0,15 367,35 3,10 0,96 0,01 Fourth batch 1,374 0,006 16,67 0,25 371,41 3,34 0,97 0,01 Fifth batch 1,374 0,006 16,68 0,20 372,37 3,34 0,96 0,01 EXAMPLE 8-2

[0085] Cylinders measuring D10mm×5mm were manufactured using the same method as described in Comparative Example 4-2. The cylinders were coated in five batches using the method described in Comparative Example 4-2 and sintered / heat-diffused twice. The process conditions of the five batches were kept identical. Fifty cylinders were selected from each batch, and their magnetic properties were measured to compare the consistency of their properties across batches. The results are shown in Table 10 (where the average value is the average obtained from the 50 cylinders, and the range is the difference between the maximum and minimum values ​​obtained from the 50 cylinders). Table 10. The magnetic property results obtained from Example 8-2 Br (T) Hcj(MA / m) (BH) max(kJ / m 3 ) Hk / Hcj Average Area Average Area Average Area Average Area First batch 1,376 0,007 16,58 0,76 373,40 3,58 0,93 0,04 Second batch 1,375 0,006 16,62 0,84 372,93 3,82 0,92 0,06 Third batch 1,375 0,005 16,52 0,72 372,13 3,18 0,93 0,05 Fourth batch 1,374 0,005 16,56 0,73 371,41 4,14 0,94 0,06 Fifth batch 1,375 0,006 16,64 0,69 372,37 3,82 0,92 0,04

[0086] As shown in Tables 9 and 10, the magnets manufactured by the presently disclosed manufacturing method showed better consistency of magnetic properties than those manufactured by a conventional manufacturing method.

Claims

[1] A method for manufacturing an RTB permanent magnet comprising the following steps: Providing a compact having an R 1 -TB material, where R 1 one or more rare earth elements selected from the group consisting of Nd, Pr, La, Ce, Sm, Dy, Tb, Ho, Er, Gd, Sc, Y and Eu, more preferably Nd or Pr; T comprises Fe and / or Co, and optionally one or more elements selected from the group consisting of Al, Cu, Zn, In, Si, P, S, Ti, V, Cr, Mn, Ni, Ga, Ge, Zr, Nb, Mo, Pd, Ag, Cd, Sn, Sb, Hf, Ta and W; and B is boron; Pre-sintering of the compact at a temperature between 900 °C and 990 °C to obtain a pre-sintered block with an actual density of 6.0 - 7.4 g / cm 3 , preferably from 6.5 - 7.3 g / cm 3 to obtain; Coating the pre-sintered block with a heavy rare earth composite powder; and Performing a secondary sintering and a heat diffusion process for the coated block to obtain the RTB permanent magnet with a density, which is at least 99.5% of the theoretical density, wherein R comprises at least one heavy rare earth element and at least one rare earth element that is not a heavy rare earth element. [2] The method of claim 1, wherein the pre-sintered block has a density between 80% and 98% of the theoretical density, more preferably between 85% and 97% of the theoretical density. [3] The method according to claim 1 or 2, wherein the heavy earth composite powder comprises one or more of heavy rare earth oxides, heavy rare earth fluorides, heavy rare earth oxyfluorides or heavy rare earth hydrides, rare earth intermetallic compounds comprising heavy rare earth elements, heavy rare earth compounds of the type R2Fe 14 B, or heavy rare earth nitrate hydrate salts. [4] The method according to any one of claims 1 to 3, wherein the heavy rare earth composite powder comprises one or more elements selected from Dy, Tb or Ho. [5] A method according to any one of claims 1 to 4, wherein the compact is obtained by the following steps: proportionally mixing the starting materials, melting the prepared mixture and pouring the molten mixture to form a strip piece; Pulverizing the strip piece by hydrogen attrition to obtain a coarse powder; Pulverizing the coarse powder by jet milling to obtain a fine powder with a particle size D 50 of 3 ~ 6 µm; and Pressing the fine powder in a vertical sealed compressor to produce the compact. [6] The method according to claim 5, wherein the coarse powder has a hydrogen concentration in the range of 800 - 3000 ppm, more preferably 1000 - 2000 ppm. [7] A method according to any one of claims 1-6, wherein the coating, secondary sintering and heat diffusion operations comprise the following steps: in the coating process, machining the pre-sintered block into a desired shape, dispersing the heavy rare earth composite powder in an organic solvent to form a slag, immersing the machined pre-sintered block in the slag, and then transferring the machined pre-sintered block into a covered container, In the secondary sintering and heat diffusion process, placing the container in a vacuum furnace, placing the furnace under vacuum and then heating the furnace to 820 - 950° C to carry out the secondary sintering and a first diffusion of the heavy rare earth elements, then cooling the furnace, after stopping the cooling of the furnace, placing the furnace under vacuum and then heating the furnace to 450 - 620° C for a second diffusion of the heavy rare earth elements, and then cooling the furnace to obtain the RTB permanent magnet. [8] A method according to claim 7, wherein the holding time of the first diffusion is between 12 and 24 hours, more preferably between 15 and 20 hours. [9] The method according to claim 7 or 8, wherein the heavy rare earth composite powder is dispersed in the organic solvent at a concentration between 0.01 and 1.0 g / ml. [10] A process according to any one of claims 7 to 9, wherein a mixture containing between 10 and 20% alumina and between 80 and 90% magnesia is placed on the bottom of the container. [11] RTB permanent magnet manufactured according to the method of any one of claims 1 to 10, wherein R comprises at least one heavy rare earth element and at least one rare earth element other than a heavy rare earth element, and wherein B is boron; wherein in the region within 1000 µm of a surface of the RTB permanent magnet, the average concentration of heavy rare earth elements at the grain boundary is at least 0.7 wt.% higher than in the grain center. [12] RTB permanent magnet according to claim 11, wherein R comprises Nd, Pr, Dy, Tb or Ho. [13] RTB permanent magnet according to claim 11 or 12, wherein the RTB permanent magnet has a coercive field strength Hcj of at least 14 MA / m.

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