Neodymium-iron-boron sintered permanent magnets and their manufacturing methods and applications

Abstract

To significantly improve the coercivity of a permanent magnet and also improve the utilization rate of an RH in a diffusion source.SOLUTION: The present invention provides a sintered neodymium-iron-boron permanent magnet, and a preparation method and use thereof. The permanent magnet described in the present invention includes a crystal grain and a grain boundary phase. The grain boundary phase is located on an epitaxy of the crystal grain, and the grain boundary phase includes at least an RH. The crystal grain includes at least Nd2Fe14B. In the grain boundary phase within a depth of 100 μm from the surface to the center, the area of the grain boundary phase with an RH content of more than 6 wt.% accounts for 50% or more of the total area of the grain boundary phase. The present invention adopts an RH and an RL as the diffusion source for composite diffusion, significantly improving the coercivity of the permanent magnet and the utilization rate of the RH in the diffusion source.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to the technical field of manufacturing rare earth permanent magnet materials, and in particular to a neodymium-iron-boron based sintered permanent magnet manufactured by grain boundary diffusion, and a manufacturing method and application thereof. [Background technology]

[0002] This application claims priority to a prior application, bearing patent application number 202211138844.3 and entitled "Neodymium iron boron based sintered permanent magnet and its manufacturing method and application," filed with the State Intellectual Property Office of the People's Republic of China on September 19, 2022. The above-mentioned prior application is incorporated herein by reference in its entirety.

[0003] Due to their excellent magnetic properties, sintered NdFeB magnets are widely used in the new energy industry and are important basic functional materials for achieving the ambitious goal of carbon neutrality. Among them, there is a growing demand for sintered NdFeB in industries such as wind power generation and electric vehicles, which require not only high magnetic properties but also relatively strong temperature resistance. In order to prevent the performance of magnets from decreasing even under high temperature conditions, it is necessary to increase the coercive force of magnets. Among the methods for increasing the coercive force of magnets, the two-alloy method and heavy rare earth grain boundary diffusion technology are currently the most effective and easily realized methods. The two-alloy method improves the grain boundary microstructure of magnets by mixing two alloys with different components, which can effectively increase the coercive force of magnets.

[0004] Heavy rare earth grain boundary diffusion technology promotes the rational penetration of heavy rare earth into the magnet by adjusting the distribution of heavy rare earth, and realizes the maximum improvement of the coercivity per unit mass of heavy rare earth. Therefore, the combination of two alloys and grain boundary diffusion technology has been researched to manufacture high coercivity magnets, but the performance of the obtained magnets does not meet expectations, mainly because the grain boundary phase components and grain boundary structure of the diffusion base magnet in heavy rare earth grain boundary diffusion technology play a decisive role in the penetration of heavy rare earth and the flow dispersion inside the magnet. Summary of the Invention [Problem to be solved by the invention]

[0005] In NdFeB magnets produced by the two-alloy method, due to differences in the components of the main phase and auxiliary phase, there is an obvious difference in the concentration of the constituent elements, which has a serious impact on the penetration of heavy rare earth elements into the magnet. Ultimately, the improvement of the coercive force of the magnet is not obvious, and the utilization rate of heavy rare earth elements is not high. [Means for solving the problem]

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] The present invention provides a NdFeB based sintered permanent magnet, the permanent magnet having crystal grains and a grain boundary phase, the grain boundary phase being located in the epitaxy of the crystal grains, the grain boundary phase containing at least RH; The crystal grains are at least Nd2Fe 14 Contains B; In the grain boundary phase within a depth of 100 μm from the surface to the center, the area of ​​the grain boundary phase having an RH content of more than 6 wt% accounts for 50% or more, preferably 70% or more, for example 70%, 80%, or 90%, of the total area of ​​the grain boundary phase.

[0008] According to an embodiment of the present invention, in the grain boundary phase within a depth of 100 μm from the surface to the center, the area of ​​the grain boundary phase having an RH content of more than 13 wt% accounts for 1% or more, preferably 10% or more, for example 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, or 20%, of the total area of ​​the grain boundary phase.

[0009] According to an embodiment of the present invention, the grain boundary phase of the permanent magnet is more lubricated and the structure in the grain boundary phase is more uniform.

[0010] According to an embodiment of the present invention, the grain boundary phase comprises RH and / or RL.

[0011] Preferably, the RL represents at least one light rare earth element selected from Pr, Nd, La and Ce.

[0012] Preferably, the RH represents at least one heavy rare earth element selected from Dy, Tb and Ho.

[0013] According to an embodiment of the present invention, the permanent magnet is obtained by powdering, pressing and sintering the raw material of the permanent magnet to obtain a blank, disposing a diffusion source on the surface of the blank, and then performing a diffusion process.

[0014] According to an embodiment of the present invention, the raw material of the permanent magnet includes a main alloy and / or an auxiliary alloy, preferably includes a main alloy and an auxiliary alloy.

[0015] According to an embodiment of the present invention, the main alloy includes at least R1, Fe, B and M1, among which: R1 is selected from at least one of Pr, Nd, Ce, La, Dy, and Tb, and the content of R1 is 29 wt% or more and 32.2 wt% or less, for example, 29 wt%, 30 wt%, 31 wt%, or 32 wt%; the content of B is more than 0.8 wt% and 0.94 wt% or less, for example, 0.81 wt%, 0.85 wt%, 0.88 wt%, 0.9 wt%, or 0.93 wt%; M1 is selected from Ga and Cu, and optionally includes at least one of Al, Zr, Ti, and Co, the content of M is greater than 0 and not greater than 2.5 wt% (e.g., 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%), and Ga accounts for 0-0.5 wt% (e.g., 0 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%) of the total amount of M, and Cu accounts for 0-0.4 wt% (e.g., 0 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%) of the total amount of M.

[0016] According to an embodiment of the present invention, the auxiliary alloy includes at least R2, Fe, B and M2, among which: R2 is selected from at least one of Pr, Nd, Dy, and Tb, and the content of R2 is 30 wt% or more and 33.3 wt% or less, for example, 30 wt%, 31 wt%, 32 wt%, 33 wt%; The content of B is greater than 0.94 wt% and less than or equal to 1.1 wt%, for example, 0.95 wt%, 0.96 wt%, 0.97 wt%, 0.98 wt%, 0.99 wt%, 1 wt%, 1.1 wt%; M2 is selected from Ga and Cu, and optionally includes at least one of Al, Zr, Ti, and Co, the content of M is greater than 0 and less than or equal to 3 wt% (e.g., 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%), and Ga accounts for 0-0.5 wt% (e.g., 0 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%) of the total amount of M, and Cu accounts for 0-0.4 wt% (e.g., 0 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%) of the total amount of M.

[0017] According to an embodiment of the present invention, the B content in the main alloy is less than the B content in the auxiliary alloy.

[0018] According to an embodiment of the present invention, the sintering includes multi-stage variable-speed temperature-ramp sintering in a vacuum atmosphere.

[0019] Preferably, the multi-stage variable-speed heating sintering can reliably remove impurities such as hydrogen gas, nitrogen gas, and additives such as antioxidants from the blank, making the diffusion process more likely to proceed.

[0020] Preferably, the multi-stage variable-speed heating includes heating to 300-400° C. at a heating rate of 1-3° C. / min, heating to 700-800° C. at a heating rate of 4-6° C. / min, and after maintaining the temperature at 700-800° C. for a certain period of time, heating to 1000-1100° C. at a heating rate of 7-10° C. / min. Furthermore, the temperature maintaining time is 30-90 min.

[0021] According to an embodiment of the present invention, the diffusion source comprises RH and RL, where RH and RL have the above-mentioned meanings.

[0022] Preferably, in the diffusion source, the mass ratio of RL to RH is greater than 0 and less than or equal to 0.5, for example, 0.1, 0.2, 0.3, 0.4, 0.5.

[0023] The present invention further provides a method for producing the above-mentioned neodymium-iron-boron based permanent magnet, the method comprising the steps of: (1) Powdering process: mixing and crushing the raw materials for permanent magnets to obtain magnetic powder; (2) Press molding step: Press molding the magnetic powder under the action of a magnetic field to obtain a green compact; (3) Sintering process: the green compact is sintered to obtain a blank; (4) Diffusion treatment: disposing a diffusion material on the surface of the blank obtained in step (3), and then performing a permeation treatment to obtain the neodymium-iron-boron-based permanent magnet. Includes.

[0024] According to an embodiment of the present invention, in step (1), the raw materials of the permanent magnet include a main alloy and / or an auxiliary alloy, preferably a main alloy and an auxiliary alloy.

[0025] Preferably, the raw material of the permanent magnet includes a main alloy and an auxiliary alloy, and the mass ratio of the main alloy to the auxiliary alloy is (1-5):1, for example, 2.7:1.

[0026] According to an embodiment of the present invention, said main alloy and auxiliary alloy have the meanings mentioned above.

[0027] According to an embodiment of the present invention, the main alloy and the auxiliary alloy are obtained by a method known in the art, for example, a melt spinning process is used to produce the quenched main alloy flakes and the quenched auxiliary alloy flakes, respectively. For example, the raw materials of the main alloy and the auxiliary alloy are separately prepared, and the raw materials are melted in an inert atmosphere such as vacuum or argon gas, and then poured onto the surface of a rotating quench roll, and then dropped onto a quench disk for further cooling to obtain the quenched main alloy flakes and the quenched auxiliary alloy flakes, respectively.

[0028] According to an embodiment of the present invention, in step (1), the particle size of the magnetic powder is 1 to 10 μm.

[0029] According to an embodiment of the present invention, in step (1), the crushing includes coarse crushing and fine pulverization.

[0030] Preferably, the rough crushing is selected from, for example, hydrogen embrittlement.

[0031] Preferably, the fine pulverization is performed by, for example, a jet mill. Furthermore, the jet mill is performed under an inert gas atmosphere. Furthermore, the inert gas is selected from nitrogen gas, helium gas, etc. In the present invention, the hydrogen embrittlement, intermediate pulverization, or jet mill can be performed by a method known in the art.

[0032] For example, the main alloy flakes and the auxiliary alloy flakes are crushed by hydrogen embrittlement, stirred and mixed for 1 to 4 hours, pulverized by jet mill polishing, and further stirred and mixed for 1 to 4 hours to obtain a mixed magnetic powder.

[0033] According to an embodiment of the present invention, in step (2), the magnetic field may be a magnetic field known in the art, for example, a magnetic field having a magnetic field strength of 2T.

[0034] According to an embodiment of the present invention, in step (2), the press molding can be carried out in an apparatus known in the art, for example, in the cavity of a press mill.

[0035] According to an embodiment of the present invention, in step (2), after press forming, the blank can be further densified by cold isostatic pressing.

[0036] According to an embodiment of the present invention, in step (3), the sintering process includes performing sintering by increasing the temperature at multiple variable speeds from 1000 to 1100° C. in a vacuum atmosphere, and then obtaining the blank.

[0037] Preferably, in the sintering process, the vacuum degree is 10 -1 Pa or less.

[0038] Preferably, in the sintering process, the sintering time is 1 to 10 hours, for example, 5 hours.

[0039] Preferably, the multi-stage variable-speed heating includes heating to 300-400° C. at a heating rate of 1-3° C. / min, heating to 700-800° C. at a heating rate of 4-6° C. / min, and after maintaining the temperature at 700-800° C. for a certain period of time, heating to 1000-1100° C. at a heating rate of 7-10° C. / min. Furthermore, the temperature maintaining time is 30-90 min.

[0040] For example, the multi-stage variable-speed heating includes heating to 300-400°C at a heating rate of 3°C / min, heating to 670°C at a heating rate of 5°C / min, maintaining the temperature at 670°C for 70 min, and heating to 1040°C at a heating rate of 8°C / min.

[0041] According to an embodiment of the present invention, the sintering process may be followed by an ageing process.

[0042] Preferably, the aging treatment includes a first stage aging treatment at a temperature of 800 to 950° C. and keeping the temperature for 2 to 5 hours; and a second stage aging treatment at a temperature of 450 to 600° C. and keeping the temperature for 2 to 4 hours.

[0043] Exemplarily, the aging treatment includes a first stage aging treatment at 900° C. for 4 hours, and a second stage aging treatment at 530° C. for 3 hours.

[0044] According to an embodiment of the present invention, after the sintering step and before the diffusion treatment, the blank can be machined to a target size and then pickled.

[0045] Illustratively, the target size can be selected as needed, for example, less than 10 mm thick.

[0046] Preferably, the acid washing refers to washing with an acid solution, for example, a nitric acid solution having a volume concentration of 2 to 6% is selected, ultrasonic washing is performed for 5 to 20 minutes, and then drying is performed in a drying tunnel at 60 to 90°C.

[0047] According to an embodiment of the present invention, in step (4), the diffusion material comprises a powder of RH and a powder of RL, where RH and RL have the above-mentioned meanings.

[0048] Preferably, the powder of RH is selected from at least one of an elemental metal of RH, an alloy of RH, an oxide, a fluoride, a hydride, and an oxyfluoride of RH.

[0049] Preferably, the powder of RL is selected from at least one of an elemental metal of RL, an alloy of RL, an oxide, a fluoride, a hydride, and an oxyfluoride of RL.

[0050] According to an embodiment of the present invention, the mass ratio of the RL powder to the RH powder is greater than 0 and less than or equal to 0.5, such as 0.1, 0.2, 0.3, 0.4, 0.5, for example 0.375.

[0051] According to an embodiment of the present invention, the diffusion material can be disposed on the surface of the blank by selecting a method known in the art, and the present invention is not specifically limited.

[0052] According to an exemplary embodiment of the present invention, a slurry containing the diffusing material is uniformly coated onto a surface of the blank.

[0053] Preferably, the method for producing the slurry containing the diffusion material includes mixing the diffusion material, an optional antioxidant and a diluent, and stirring for 1-4 h to obtain the slurry. Preferably, the antioxidant is selected from at least one of, for example, toluene, 4-hexylresorcinol and dibutylhydroxytoluene. Preferably, the diluent is selected from at least one of, for example, ethanol, benzyl alcohol and acetone. Preferably, the mass of the slurry coated on the surface of the blank accounts for 0.2-1.5% of the mass of the magnet, and is kept in a dry state at a temperature of 50-70°C for 5-10 min.

[0054] According to an embodiment of the present invention, in step (4), the infiltration treatment includes heating to 830-910° C. under vacuum conditions and infiltrating for 6-12 h.

[0055] According to an embodiment of the present invention, the infiltration treatment is followed by a further vacuum aging treatment.

[0056] Preferably, the vacuum aging treatment includes performing vacuum aging treatment under conditions of 440 to 560° C. to obtain the neodymium iron boron based permanent magnet. Preferably, the degree of vacuum is a degree of vacuum known in the art, for example, 10 -1 Pa or less may be selected.

[0057] According to an embodiment of the present invention, a neodymium-iron-boron based permanent magnet is obtained by the above-mentioned manufacturing method, and the neodymium-iron-boron based permanent magnet has the above-mentioned meaning.

[0058] The present invention further provides applications for the above-mentioned neodymium-iron-boron based permanent magnet, for example, in motors. Effect of the Invention

[0059] The present invention uses RH and RL as diffusion sources for composite diffusion. By adding RL to the diffusion source, the concentration difference of RH between the crystal grains and the grain boundary phase can be balanced during the diffusion process, the components of the grain boundary phase can be effectively homogenized, the wettability of the grain boundary phase can be improved, and the structure of the grain boundary phase can be made smoother. At the same time, the RH in the diffusion source can penetrate smoothly and deeply into the interior of the magnet, so that the RH can be distributed more uniformly inside the magnet, which can greatly improve the coercive force of the permanent magnet and improve the utilization rate of RH in the diffusion source.

[0060] The present invention first employs a special sintering process, and in particular by controlling the multi-stage variable-speed heating, it is possible to reliably remove additives such as hydrogen gas, nitrogen gas, and antioxidants from the blank, making it easier for the composite diffusion process to proceed. [Brief description of the drawings]

[0061] [Figure 1] 1 is an EPMA photograph of the magnet produced in Example 1 of the present invention. [Diagram 2] 1 is an EPMA photograph of a magnet produced in Comparative Example 1-1 of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0062] The technical solution of the present invention will be described in more detail below with reference to specific examples. It should be understood that the following examples are merely illustrative and interpretive of the present invention and should not be interpreted as limiting the scope of the claims of the present invention. Any technology realized based on the above content of the present invention is included in the scope of the claims of the present invention.

[0063] Unless otherwise specified, all materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0064] Example 1 The neodymium-iron-boron permanent magnet is manufactured as follows.

[0065] 1. Blank manufacturing: (1) The raw materials are prepared with the following composition, that is, the main alloy is a high Br composition, in which Nd is 31 wt%, B is 0.91 wt%, Ti is 0.3 wt%, Ga is 0.2 wt%, Cu is 0.2 wt%, Al is 0.3 wt%, Co is 1.0 wt%, and the rest is Fe and unavoidable impurities. After preparation, it is heated to 1400°C in a vacuum environment to melt, and kept at that temperature for 15 minutes to ensure the homogenization of each raw material. Then, it is poured onto the surface of a rotating quench roll, and then dropped onto a quench disk for further cooling to obtain main alloy flakes; Using the same method, auxiliary alloy flakes with high Hcj composition were prepared, the composition of which was 32.5% Nd, 0.98 wt% B, 0.4 wt% Ti, 0.3 wt% Ga, 0.3 wt% Cu, 0.3 wt% Al, 1.5 wt% Co, and the rest was Fe and unavoidable impurities; (2) The main alloy quenched flakes and the auxiliary alloy quenched flakes of step (1) were mixed in a mass ratio of 2.7:1, hydrogen pulverized and ball milled, and then jet mill polished to obtain a mixed magnetic powder with a particle size of 1-10 μm and an average particle size of 2.75 μm; (3) 0.07 wt% of fatty acid ester, an antioxidant, was added to the mixed magnetic powder obtained in step (2), and mechanical stirring was continued for 4 h until the powder was uniformly dispersed; (4) The magnetic powder of step (3) was press-molded in a vacuum with a magnetic field strength of 2 T in the magnetic field orientation direction, and then subjected to cold isostatic pressing to obtain a green compact; (5) Sintering: The green compact from step (4) was placed in a vacuum sintering furnace, heated to 300-400°C at a heating rate of 3°C / min, heated to 670°C at a heating rate of 5°C / min, kept at 670°C for 70 min, and then heated to 1040°C at a heating rate of 8°C / min, and sintered for 5 h; (6) Aging treatment: The green compact after the sintering treatment in step (5) was subsequently subjected to a first-stage aging treatment at 900°C for 4 h and a second-stage aging treatment at 530°C for 3 h, to produce a Nd-Fe-B permanent magnet blank by the two-alloy method.

[0066] (7) The blanks were machined into slices measuring 25 mm × 20 mm × 2.5 mm, with 2.5 mm being the thickness in the slice orientation direction.

[0067] (8) The NdFeB flakes obtained in step (7) were pickled with 3% by volume nitric acid, ultrasonically washed with water, and then dried to obtain washed flakes.

[0068] Second, diffusion treatment (1) Preparation of diffusion slurry: Dy metal, Pr metal, 4-hexylresorcinol, and ethanol were mixed in a mass ratio of 8:3:3:1 by mechanical stirring for 2 h to obtain a diffusion slurry containing Dy and Pr.

[0069] (2) The above diffusion slurry was uniformly coated on the surface of the flakes obtained in step (8) in an amount of 0.75% of the mass of the base magnet, and then dried at 60°C for 5 minutes to obtain flakes coated with the metal diffusion sources of Dy and Pr.

[0070] (4) The thin pieces coated in step (3) were first vacuum infiltrated at 870 °C for 10 h.

[0071] (5) The diffused thin piece obtained in step (4) was subjected to vacuum aging treatment at a temperature of 510°C for 4.5 h to obtain a permanent magnet M1 after the mixed diffusion treatment of Dy and Pr.

[0072] Comparative Example 1-1 This comparative example was basically the same as the manufacturing method of Example 1, except that the diffusion source was only Dy metal powder, a heavy metal, and contained no other metal elements; the diffusion source was a mixture of Dy powder, 4-hexylresorcinol, and ethanol in a mass ratio of 11:3:1, the coating amount was 0.55% of the base magnet mass (to match the Dy content in the diffusion source), and the resulting permanent magnet was named M1-1.

[0073] Comparative Example 1-2 This comparative example was basically the same as the manufacturing method of Example 1, except that the diffusion source was light rare earth Pr metal powder and did not contain other metal elements; the diffusion source was a mixture of Pr powder, 4-hexylresorcinol, and ethanol in a mass ratio of 11:3:1, and the coating amount was 0.55% of the base magnet mass; the manufactured permanent magnet was named M1-2.

[0074] Example 2 This example was essentially the same as Example 1, with the following exceptions.

[0075] 1. Blank preparation: The main alloy flakes were subjected to hydrogen crushing, medium crushing and coarse crushing separately, and then jet milling to obtain magnetic powder of the main alloy, which was then pressed to obtain a green compact of the main alloy, and sintered to obtain a blank of the main alloy.

[0076] Secondly, the thin piece produced from the blank of the main alloy was subjected to a diffusion treatment, which was the same as that in Example 1. After diffusion, a permanent magnet M2 was obtained.

[0077] Comparative Example 2-1 This comparative example was basically the same as the manufacturing method of Example 2, except that the diffusion source was only Dy metal powder, a heavy metal, and contained no other metal elements; the diffusion source was a mixture of Dy powder, 4-hexylresorcinol, and ethanol in a mass ratio of 11:3:1, and the coating amount was 0.55% of the base magnet mass; the resulting permanent magnet was named M2-1.

[0078] Comparative Example 2-2 This comparative example was basically the same as the manufacturing method of Example 1, except that the diffusion source was light rare earth Pr metal powder and did not contain other metal elements; the diffusion source was a mixture of Pr powder, 4-hexylresorcinol, and ethanol in a mass ratio of 11:3:1, and the coating amount was 0.55% of the base magnet mass; the resulting permanent magnet was named M2-2.

[0079] Example 3 This example was essentially the same as Example 1, with the following exceptions.

[0080] 1. Preparation of blanks: The auxiliary alloy flakes alone were subjected to hydrogen crushing, medium crushing, and coarse crushing, and then jet milling to obtain magnetic powder of the auxiliary alloy, which was then pressed to obtain a green compact of the auxiliary alloy, and sintered to obtain a blank of the auxiliary alloy.

[0081] Secondly, the thin piece produced from the blank of the auxiliary alloy was subjected to a diffusion treatment, which was the same as that in Example 1. After diffusion, a permanent magnet M3 was obtained.

[0082] Comparative Example 3-1 This comparative example was basically the same as the manufacturing method of Example 3, except that the diffusion source was only Dy metal powder, a heavy metal, and contained no other metal elements; the diffusion source was a mixture of Dy powder, 4-hexylresorcinol, and ethanol in a mass ratio of 11:3:1, and the coating amount was 0.55% of the base magnet mass; the resulting permanent magnet was named M3-1.

[0083] Comparative Example 3-2 This comparative example was basically the same as the manufacturing method of Example 3, except that the diffusion source was light rare earth Pr metal powder and did not contain other metal elements; the diffusion source was a mixture of Pr powder, 4-hexylresorcinol, and ethanol in a mass ratio of 11:3:1, and the coating amount was 0.55% of the base magnet mass; the resulting permanent magnet was named M3-2.

[0084] Comparative Example 4 The manufacturing method of this comparative example was basically the same as that of Example 1, except that the sintering conditions were a high-temperature sintering temperature of 1060° C., a high-temperature sintering time of 5 hours, and a temperature rise rate of 8° C. / min.

[0085] Performance tests: The dual-alloy NdFeB magnets M1, M1-1, M1-2, the main alloy NdFeB magnets M2, M2-1, M-2, and the auxiliary alloy NdFeB magnets M3, M3-1, M3-2 were machined into samples measuring 7 mm-7 mm-2.4 mm from the geometric center of the magnets, and magnetic performance tests were conducted. The results are summarized in Table 1.

[0086] [Table 1]

[0087] From Table 1, it can be seen that the coercive force of the dual alloy substrate magnet is obviously higher than that of the main alloy and auxiliary alloy substrate magnets. When Dy metal powder is used as the diffusion source, the coercive force of the dual alloy substrate after diffusion is 1626 KA / m, with an increase of 129 KA / m, which is lower than the increase of 306 KA / m and 330 KA / m of the single alloy substrate after diffusion, respectively, but the increase of the two single alloy substrates is similar; the same phenomenon occurs when Pr metal powder is used as the diffusion source. When the mixed metal powder of Dy and Pr is used as the diffusion source, the coercive force of the dual alloy substrate after diffusion reaches 1871 KA / m, which is obviously higher than the coercive forces of the two single alloy substrates after diffusion, 1442 KA / m and 1762 KA / m. Analyzing the above results, it can be seen that the poor increase in the coercive force of the dual alloy substrate can be obviously improved by mixing Dy and Pr as the diffusion source.

[0088] For the samples obtained in Example 1 and Comparative Example 1-1, the Pr and Dy metal elements in the micro area inside the magnet (100 μm away from the magnet surface) after diffusion were analyzed using an electron probe microanalyzer (EPMA), and the results are shown in Figures 1 and 2. Figure 2 shows the diffusion of Dy metal into the two-alloy substrate of Comparative Example 1-1, and the different colored areas in Figure 2 show the content distribution of the Dy element, and it can be vaguely observed that a small amount of Dy metal element is enriched in the grain boundary, and it can be seen that a very small amount of Dy metal has entered the magnet (shown in the bright points in Figure 2b). Figure 1 shows the two-alloy substrate of Example 1 after the composite diffusion using the mixed metal powder of Pr and Dy as the diffusion source, and it can be clearly observed that a large amount of Pr and Dy metal is enriched in the grain boundary phase (shown in Figures 1b and c). This shows that when the mixed metal powder of Pr and Dy is used as the diffusion source, Pr and Dy can effectively penetrate into the inside of the magnet and be uniformly distributed.

[0089] Table 2 shows the distribution of Dy in the grain boundary phase in Examples 1 to 4 and Comparative Example 1-1.

[0090] [Table 2]

[0091] As can be seen from Figure 1, adding Pr to the diffusion source promotes the diffusion of Dy into the magnet. The Dy element diffused into the magnet is 14 The grain boundary phase of B contains a large amount of (Nd,Dy)2Fe 14 The B phase is formed, which improves the coercive force of the permanent magnet. At the same time, the Nd element in the main phase replaces Dy and penetrates into the grain boundary phase of the magnet, making the grain boundary phase thicker, more uniform, and more continuous, resulting in an R2Fe 14 The exchange coupling effect of the main phase crystal grains of B is also weakened, improving the coercive force of the magnet.

[0092] As can be seen from Examples 2 and 3, when a blank is produced from a main alloy powder or an auxiliary alloy powder using a mixed metal powder of Pr and Dy as a diffusion source, the increase in the coercivity of the magnet is not as significant as in Example 1, but the coercivity of the magnet is clearly improved compared to the blank before diffusion, and the decrease in Br is also relatively small.

[0093] In Comparative Examples 2-1 and 3-1, when Dy was used as the diffusion source, the increase in Hcj of the magnet was more obvious, but in comparison, the Br value was significantly lower, which shows that this is very disadvantageous for use as a permanent magnet in a motor.

[0094] As can be seen from Example 1 and Comparative Example 4, both of them use two alloys as the substrate and Pr and Dy as the diffusion source, but there is an obvious difference between the product of Example 1 and the product of Comparative Example 4, and the coercive force value of Comparative Example 4 is obviously lower than that of Example 1, because Comparative Example 4 does not use a special sintering system and does not adopt multi-stage variable speed heating in the substrate sintering stage, and hydrogen gas, nitrogen gas, antioxidants, etc. in the blank are not completely removed, which is particularly important in the manufacturing process of the two-alloy substrate, and directly leads to the relatively poor effect of the subsequent diffusion treatment.

[0095] The exemplary embodiments of the present invention have been described above. However, the scope of the claims of the present application is not limited to the above-mentioned embodiments. Any modifications, equivalent replacements, improvements, etc. made within the scope of the spirit and principles of the present invention should be included within the scope of the claims of the present invention.

Claims

1. The neodymium iron boron based sintered permanent magnet has crystal grains and a grain boundary phase, the grain boundary phase being located in the epitaxy of the crystal grains, the grain boundary phase containing at least RH, the RH representing at least one heavy rare earth element selected from Dy, Tb and Ho; The crystal grains are composed of at least Nd 2 Fe 14 Contains B; In the grain boundary phase within a depth of 100 μm from the surface to the center, the area of ​​the grain boundary phase with an RH content of more than 6 wt% accounts for 50% or more of the total area of ​​the grain boundary phase. The neodymium-iron-boron sintered permanent magnet is obtained by powdering, pressing, and sintering the raw material of the neodymium-iron-boron sintered permanent magnet to obtain a blank, disposing a diffusion source on the surface of the blank, and then carrying out a diffusion process; The raw materials of the neodymium-iron-boron based sintered permanent magnet include a main alloy and / or an auxiliary alloy. The main alloy comprises at least R 1 , Fe, B and M 1 , wherein R 1 is selected from at least one of Pr, Nd, Ce, La, Dy and Tb, and the content of R 1 is 29wt% or more and 32.2wt% or less; the content of B is more than 0.8wt% and 0.94wt% or less; M 1 is selected from Ga and Cu, and optionally includes or does not include at least one of Al, Zr, Ti and Co, and the content of M is more than 0 and 2.5wt% or less, and Ga accounts for 0-0.5wt% of the total amount of M, and Cu accounts for 0-0.4wt% of the total amount of M; The auxiliary alloy comprises at least R2, Fe, B and M2, wherein R2 is selected from at least one of Pr, Nd, Dy and Tb, and the content of R2 is 30wt% or more and 33.3wt% or less; the content of B is greater than 0.94wt% and less than 1.1wt%; M2 is selected from Ga and Cu, and optionally contains or does not contain at least one of Al, Zr, Ti and Co, and the content of M is greater than 0 and 3wt% or less, and Ga accounts for 0-0.5wt% of the total amount of M, and Cu accounts for 0-0.4wt% of the total amount of M; The mass ratio of the main alloy to the auxiliary alloy is (1-5):1; The diffusion source includes the RH and the RL; in the diffusion source, the mass ratio of the RL to the RH is greater than 0 and is equal to or less than 0.5; The RL represents at least one light rare earth element selected from Pr, Nd, La, and Ce; the RH represents at least one heavy rare earth element selected from Dy, Tb, and Ho; The sintering includes sintering by multi-stage variable rate heating under a vacuum atmosphere; The multi-stage variable speed heating includes heating to 300-400°C at a heating rate of 1-3°C / min, heating to 700-800°C at a heating rate of 4-6°C / min, and after maintaining the temperature at 700-800°C for a certain period of time, heating to 1000-1100°C at a heating rate of 7-10°C / min. A neodymium-iron-boron sintered permanent magnet.

2. In the grain boundary phase within a depth of 100 μm from the surface to the center, the area of ​​the grain boundary phase with an RH content of more than 6 wt% accounts for more than 70% of the total area of ​​the grain boundary phase; 2. The neodymium-iron-boron sintered permanent magnet according to claim 1.

3. In the grain boundary phase, the area of ​​the grain boundary phase having an RH content of more than 13 wt% occupies 1% or more of the total area of ​​the grain boundary phase.

2. The neodymium-iron-boron sintered permanent magnet according to claim 1.

4. The grain boundary phase comprises RH or RL or a combination of RH and RL; the RL represents at least one light rare earth element selected from Pr, Nd, La and Ce; the RH represents at least one heavy rare earth element selected from Dy, Tb and Ho; 2. The neodymium-iron-boron sintered permanent magnet according to claim 1.

5. (1) A powdering step: mixing and crushing the raw materials of a permanent magnet, including a main alloy and / or an auxiliary alloy, to obtain a magnetic powder; (2) Press molding step: Press molding the magnetic powder under the action of a magnetic field to obtain a green compact; (3) Sintering process: the green compact is sintered to obtain a blank; (4) Diffusion treatment: A diffusion material containing the RH powder and the RL powder is arranged on the surface of the blank obtained in step (3), and then the NdFeB sintered permanent magnet is obtained after infiltration treatment. Including, The mass ratio of the RL powder to the RH powder is greater than 0 and less than or equal to 0.5; 5. The method for producing a neodymium-iron-boron based sintered permanent magnet according to claim 1.

6. In step (3), the vacuum degree in the sintering process is 10 -1 Pa or less; and the sintering time in the sintering process is 1 to 10 hours. The method according to claim 5 .

7. In step (4), the infiltration treatment includes heating to 830-910°C under vacuum conditions and infiltrating for 6-12 hours. The method according to claim 5 .

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