High-temperature-resistant sintered neodymium-iron-boron magnet, preparation method therefor, and use thereof

Abstract

Disclosed in the present invention are a high-temperature-resistant sintered neodymium-iron-boron magnet, a preparation method therefor, and the use thereof. The magnet is represented by R-Fe-B-M, and comprises on the basis of mass percentages, 100% in total: 29wt%-35wt% of R, R being a rare earth element, 0.9wt%-1.3wt% of B, and less than 5 wt% of M, M being one or more selected from Ti, V, Cr, Mn, Co, Ga, Cu, Si, Al, Zr, Nb, W and Mo, with the balance being iron and unavoidable impurities. Crystal grains of the sintered neodymium-iron-boron magnet of the present invention have a smaller dimensional change rate in different directions at high temperatures, such that the probability of forming demagnetizing fields is reduced and the coercivity of the neodymium-iron-boron magnet at high temperatures is improved, thereby improving the characteristic of resisting demagnetization at high temperatures of the sintered neodymium-iron-boron magnet.

Description

A high temperature sintered NdFeB magnet and its preparation method and application

[0001] This application claims priority to a prior application, patent application number 202311275411.7, filed with the State Intellectual Property Office of China on September 28, 2023, entitled “A High-Temperature-Resistant Sintered NdFeB Magnet, Its Preparation Method, and Application.” The entire text of the prior application is incorporated herein by reference. Technical Field

[0002] The present invention relates to the technical field of NdFeB series sintered magnets, and in particular to a high-temperature sintered NdFeB magnet and a preparation method and application thereof. Background Art

[0003] Since their introduction, sintered permanent magnets (or sintered NdFeB magnets) have rapidly gained widespread application in numerous fields, including electronics, energy, communications, and equipment, due to their excellent magnetic properties and high cost-performance ratio. In recent years, the automotive industry has seen increasing adoption of permanent magnets. However, the high temperatures generated by automotive motors during operation can cause permanent magnets to lose their magnetism, resulting in reduced performance.

[0004] In order to solve the problem of high-temperature demagnetization of permanent magnet materials, in addition to optimizing and upgrading the motor cooling system, improving the coercive force of permanent magnet materials is a more effective way to solve the problem of high-temperature demagnetization of permanent magnet materials.

[0005] Currently, there are three main methods for increasing the coercivity of permanent magnets. The first is to increase the anisotropy field of the magnet by adding heavy rare earth elements, such as dysprosium (Dy), terbium (Tb), or holmium (Ho), thereby increasing the coercivity. The second is grain refinement. As the grain size decreases, the internal defects of the grains decrease, the internal demagnetization field decreases, and the coercivity of the magnet increases. The third is grain boundary diffusion. This technique diffuses the heavy rare earth elements along the grain boundaries, significantly increasing the anisotropy constant at the grain boundaries, achieving a significant increase in the coercivity of the magnet while using a small amount of heavy rare earth elements.

[0006] To meet the high-temperature demagnetization requirements of existing automotive motors, all three methods mentioned above utilize heavy rare earth elements to varying degrees. With the recent surge in heavy rare earth prices, using less heavy rare earth to produce more heat-resistant permanent magnet materials is a key research focus for various companies.

[0007] Summary of the Invention

[0008] After conducting in-depth research on the above issues, the inventors found that sintered NdFeB magnets have anisotropic characteristics. In addition to the anisotropic characteristics of the magnets in the magnetic field orientation, the anisotropic characteristics of the magnets are also manifested as anisotropy in the expansion coefficient. Sintered NdFeB magnets have different thermal expansion coefficients in different directions. For example, in the direction of the easy magnetization axis (the orientation direction of the magnet), as the temperature increases, it appears to expand; in the direction of the difficult magnetization axis (perpendicular to the orientation direction of the magnet), as the temperature increases, it appears to contract. Due to the existence of such differences in expansion ratios in different directions, the grains of the sintered NdFeB magnets will change at high temperatures. This change may cause a demagnetization field, thereby resulting in a decrease in the coercive force of the NdFeB magnets at high temperatures.

[0009] To improve the deficiencies of the prior art, the present invention provides a high-temperature sintered NdFeB magnet, wherein the magnet is represented by R-Fe-BM and comprises:

[0010] R 29wt%~35wt%, R is a rare earth element,

[0011] B 0.9wt%~1.3wt%;

[0012] M is less than 5 wt%, and M is selected from one or more of Ti, V, Cr, Mn, Co, Ga, Cu, Si, Al, Zr, Nb, W and Mo;

[0013] The rest is iron and inevitable impurities.

[0014] According to an embodiment of the present invention, R is selected from at least one of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), scandium (Sc), and yttrium (Y). Preferred are praseodymium (Pr) and neodymium (Nd).

[0015] According to an embodiment of the present invention, the magnet comprises, based on a mass ratio of 100%, 30 wt% to 33 wt% of R, where R is a rare earth element.

[0016] B 0.9wt%~1.1wt%;

[0017] M 0.5wt% to 4.5wt%, M is selected from one or more of Ti, V, Cr, Mn, Co, Ga, Cu, Si, Al, Zr, Nb, W and Mo;

[0018] The rest is iron and inevitable impurities.

[0019] In the present invention, the reference temperature is set to T0 (e.g., room temperature or 20°C), and the measurement temperature is set to T(°C). The magnet size L0 is measured at T0, and the magnet size L(T) is measured after the magnet temperature is raised to T; T-T0 = ΔT, and L(T)-L0 = ΔL. The linear expansion coefficient of a sintered NdFeB magnet is C = [ΔL / L0] / ΔT. This linear expansion coefficient includes the linear expansion coefficient C1 parallel to the magnetization direction, the linear expansion coefficient C2 perpendicular to the magnetization direction and parallel to the pressing direction, the linear expansion coefficient C3 in another direction perpendicular to the magnetization direction, and the average linear expansion coefficient C4 of the two directions perpendicular to the magnetization direction.

[0020] According to the embodiment of the present invention, the linear expansion coefficient C1 parallel to the magnetization direction of the magnet is (5 to 8)*10 -6 / ℃,

[0021] The linear expansion coefficient C2 perpendicular to the magnetization direction and parallel to the pressing direction is (-3 to -0.6)*10 -6 / ℃,

[0022] The linear expansion coefficient C3 in another direction perpendicular to the magnetization direction is (-4 to -1)*10 -6 / ℃,

[0023] The average linear expansion coefficient C4 in two directions perpendicular to the magnetization direction is (-3.5 to -0.8)*10 -6 / ℃, where C4 = (C2 + C3) / 2;

[0024] Moreover, 1.5≤|C1 / C4|≤8.

[0025] In the present invention, as the temperature of the sintered NdFeB magnet increases, it expands in the direction parallel to the magnetization direction and contracts in the other two directions perpendicular to the magnetization direction. Therefore, C1 is greater than 0, C2 is less than 0, and C3 is less than 0.

[0026] The present invention also provides a method for preparing the sintered NdFeB magnet, the method comprising:

[0027] (1) preparing R-Fe-BM alloy sheets by using a rapid solidification thin strip method;

[0028] (2) hydrogenating the alloy sheet for hydrogenation treatment, heating the alloy sheet to 250-350°C for dehydrogenation treatment, and then filling the alloy sheet with argon gas to a pressure of 30 kPa or above for heating and heat preservation. After the heat preservation, the alloy sheet is cooled to obtain alloy powder;

[0029] (3) The alloy powder in step (2) is jet-milled to obtain magnetic powder, which is then subjected to pressing, sintering, and tempering to prepare the magnet.

[0030] According to an embodiment of the present invention, in step (1), the rapid-setting thin strip method is a technology well known in the art.

[0031] According to an embodiment of the present invention, in step (2), the hydrogen absorption pressure of the hydrogenation treatment is 100 to 200 kPa, preferably 140 to 180 kPa, and the hydrogen absorption time is 30 to 180 min, preferably 90 to 150 min.

[0032] According to an embodiment of the present invention, in step (2), the dehydrogenation time is 180 to 360 minutes.

[0033] According to an embodiment of the present invention, in step (2), the dehydrogenation temperature is 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C or 350°C.

[0034] According to an embodiment of the present invention, in step (2), after dehydrogenation is completed, argon is filled to above 30 kPa, for example, 30-60 kPa, illustratively 30 kPa, 35 kPa, 40 kPa, 45 kPa, 50 kPa, 5 kPa or 60 kPa.

[0035] According to an embodiment of the present invention, in step (2), the holding temperature is 700-800°C, for example, 720°C, 740°C, 760°C, 780°C or 800°C.

[0036] According to an embodiment of the present invention, in step (2), the insulation time is 60 to 180 minutes.

[0037] According to an embodiment of the present invention, in step (2), during the cooling process, at a temperature above 350° C., the argon pressure is ≥ 20 kPa, for example, 20-60 kPa, illustratively 20 kPa, 30 kPa, 40 kPa, 50 kPa or 60 kPa.

[0038] According to an embodiment of the present invention, in step (3), the alloy powder in step (2) is mixed with a lubricant and subjected to a jet mill grinding process to obtain magnetic powder.

[0039] According to an embodiment of the present invention, in step (3), the particle size D50 of the magnetic powder is 2 to 5 μm.

[0040] According to an embodiment of the present invention, in step (3), the content of the lubricant is 0.03 to 0.5 wt %, preferably 0.05 to 0.1 wt %, of the alloy powder in step (2).

[0041] According to an embodiment of the present invention, in step (3), the magnetic powder is pressed and formed under a magnetic field orientation. Preferably, the orientation magnetic field is 1.5 to 2.5 T.

[0042] According to an embodiment of the present invention, in step (3), the sintering temperature is 800-1200° C., preferably 900-1080° C., and the holding time is 3-20 hours, preferably 3-8 hours.

[0043] According to an embodiment of the present invention, in step (3), the tempering treatment is a secondary tempering treatment, for example, the secondary tempering treatment is carried out in a vacuum tempering furnace; the primary tempering temperature is 700-900°C, and the holding time is 3-7h, and the secondary tempering temperature is 450-600°C, and the holding time is 3-7h.

[0044] According to an embodiment of the present invention, the method further comprises step (4): performing grain boundary diffusion treatment on the magnet, wherein the diffusion source is at least one of heavy rare earth elements Dy, Tb, Ho, Nd, and Pr.

[0045] According to an embodiment of the present invention, in step (4), the content of the diffused heavy rare earth is 0.1-1.5 wt%, preferably 0.2-1.2 wt%.

[0046] According to an embodiment of the present invention, in step (4), the diffusion temperature is 800-950° C., and the diffusion time is at least 3 h, preferably 3-30 h.

[0047] According to an embodiment of the present invention, in step (4), the grain boundary diffusion treatment method can be at least one of a thermal spraying method, a coating method, a sputtering method, an immersion method, and the like.

[0048] According to an embodiment of the present invention, in step (4), before the diffusion treatment, the magnet may be subjected to treatments such as degreasing and pickling.

[0049] As an exemplary implementation method of the present invention, the preparation method of the high temperature resistant sintered NdFeB magnet specifically includes:

[0050] 1) R-Fe-BM alloy sheets were obtained by rapid solidification ribbon method;

[0051] 2) hydrogenating the alloy sheet at a hydrogen absorption pressure of 100 to 200 kPa for a hydrogen absorption time of 30 to 180 minutes; after hydrogen absorption, heating the sheet to 250 to 350° C. for dehydrogenation for 180 to 360 minutes; after dehydrogenation, filling the sheet with argon to a pressure of 30 kPa or higher, then heating the sheet to 700 to 800° C. for a holding time of 60 to 180 minutes; and cooling the sheet after the holding time, wherein the argon pressure is ≥ 20 kPa when the temperature is above 350° C. during the cooling process;

[0052] 3) mixing the alloy powder with a lubricant, and grinding the mixture with a jet mill to obtain magnetic powder; and then pressing the magnetic powder into a shape under a magnetic field orientation of 1.5 to 2.5 T;

[0053] 4) sintering the compact in a vacuum sintering furnace at a temperature of 900-1080° C. for 3-8 hours; cooling to ≤200° C. after holding, and then performing a primary tempering treatment at 700-900° C. for 3-7 hours; and then performing a secondary tempering treatment at 450-600° C. for 3-7 hours to obtain the sintered NdFeB magnet;

[0054] 5) Diffusion treatment of the magnet in step 4): The magnet in step 4) is processed into a required size, degreased and pickled, and then subjected to grain boundary diffusion treatment; the diffusion temperature is 800-950° C., the diffusion time is at least 3 hours, and the diffusion source is at least one element selected from Dy, Tb, Ho, Nd, and Pr.

[0055] The present invention also provides applications of the sintered NdFeB magnet in the new energy vehicle industry and the wind power generation field.

[0056] Beneficial effects of the present invention:

[0057] The crystal grains of the sintered NdFeB magnet of the present invention have a smaller dimensional change rate along different directions at high temperature, which reduces the probability of forming a demagnetization field, increases the coercive force of the NdFeB magnet at high temperature, and thus improves the demagnetization resistance of the sintered NdFeB magnet at high temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] FIG1 is a graph of the linear expansion coefficient C1 parallel to the magnetization direction of the magnet tested in Example 1;

[0059] FIG2 is a graph of the linear expansion coefficient C2 perpendicular to the magnetization direction and parallel to the pressing direction tested in Example 1;

[0060] FIG3 is a diagram of the linear expansion coefficient C3 in another direction perpendicular to the magnetization direction tested in Example 1. DETAILED DESCRIPTION

[0061] The technical solutions of the present invention will be described in further detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are encompassed within the scope of protection that the present invention is intended to protect.

[0062] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0063] Measurement of the linear expansion coefficient of the sintered NdFeB magnet of the present invention:

[0064] The coefficient of linear expansion was measured using a TMA402F3 thermomechanical analyzer. The static thermomechanical analysis method, which measures the deformation of a material under a programmed temperature control while subjected to a non-vibratory load. The test temperature ranged from 20°C to high temperature, at a rate of 3-5°C / min. The test was conducted in three directions, with the magnet positioned in the center.

[0065] Example 1, Comparative Examples 1-7

[0066] It is prepared according to the following method, by using NdPr, Co, Al, Fe, Cu, Ga, Ti and ferroboron with a purity of at least 99% by weight to high-frequency melt in an argon atmosphere, and pouring the melt onto a rapid cooling roller to form an alloy sheet, wherein the content of each raw material is 31.5% NdPr, 1.0% Co, 0.5% Al, 0.2% Cu, 0.2% Ga, 0.18% Ti, 0.98% B, and the balance is iron and unavoidable impurities.

[0067] The alloy sheet was hydrogenated at a hydrogen absorption pressure of 180 kPa for 120 minutes. After hydrogen absorption, the alloy sheet was treated according to the hydrogenation treatment process in Table 1 and pulverized into a coarse powder. The coarse powder was then jet milled to obtain a magnetic powder with a particle size of D50 = 4.0 μm. 0.3 wt% lubricant was added to the jet milled powder and mixed for 2 hours. The powder was then formed at room temperature and in an orientation field with a magnetic field strength of 2 T. The blank was then placed in a vacuum sintering furnace and sintered at 1030°C for 6 hours. After the insulation was complete, it was cooled to 100°C. The temperature was then raised to 900°C and a primary tempering treatment was performed at 900°C for 3 hours. A secondary tempering treatment was then performed at 520°C for 5 hours. After cooling and removal from the furnace, a neodymium iron boron magnet was obtained.

[0068] The NdFeB magnets obtained above were processed into products with a size of 10-8-6 mm. The linear expansion coefficient of the products in different directions was tested using a thermomechanical analyzer. The heating rate was 5°C / min and the test temperature range was 20-140°C. The test results are shown in Table 2.

[0069] In addition, the NdFeB magnets obtained above were processed into D10-10 mm products and subjected to magnetic tests at 20°C and 140°C. The test results are shown in Table 3.

[0070] Table 1 Hydrotreatment process corresponding to Example 1 and Comparative Examples 1-7

[0071] The products prepared in Example 1 and Comparative Examples 1-7 were subjected to linear expansion coefficient testing. The linear expansion coefficient testing method is as follows:

[0072] The magnet size is L0 at room temperature T0. After the magnet temperature is raised to the test temperature T (°C), the magnet size L(T) is measured. T-T0 = ΔT, and L(T)-L0 = ΔL. The linear expansion coefficient of a sintered NdFeB magnet is C = [ΔL / L0] / ΔT.

[0073] The test results are shown in Table 2 below.

[0074] Table 2 Linear expansion coefficients of NdFeB products tested in Example 1 and Comparative Examples 1-7

[0075] The products prepared in Example 1 and Comparative Examples 1-7 were tested for Br, Hcj (including 20° C. and 140° C.) and Hcj temperature coefficient. The test results are shown in Table 3 below.

[0076] Table 3 Magnetic properties of NdFeB products of Example 1 and Comparative Examples 1-7

[0077] Comparing the data of Example 1 and Comparative Example 1, it can be seen that the dehydrogenation temperature in Comparative Example 1 is too high, exceeding the requirements of the patented process. Although C1, C2, C3, and C4 are within the range, these values ​​are within the critical range, resulting in |C1 / C4| exceeding the patented range and poor temperature resistance (Hcj temperature coefficient). Furthermore, because the dehydrogenation temperature is too high, the room-temperature Hcj of Comparative Example 1 is low. Combined with the poor temperature resistance, the high-temperature Hcj becomes even lower.

[0078] Comparing the data of Example 1 and Comparative Example 2 shows that due to the excessively low dehydrogenation temperature in Comparative Example 2, C1, C2, C3, C4, and |C1 / C4| all exceed the patent range, resulting in poor temperature resistance (deterioration of the Hcj temperature coefficient). Furthermore, due to the excessively low dehydrogenation temperature, the room-temperature Br of Comparative Example 2 is significantly reduced. Furthermore, this process increases the hydrogen content before sintering, resulting in more cracks in the sintered product and an increased product defect rate.

[0079] From the data of Comparative Example 1, Comparative Example 3 and Comparative Example 4, it can be seen that the argon filling pressure at the end of dehydrogenation in Comparative Example 3 is 0, that is, no argon is filled. The argon filling pressure at the end of dehydrogenation in Comparative Example 4 is 10kPa, which is a relatively low pressure. Both of these comparative examples will cause the alloy flakes to be dehydrogenated at 750°C in the subsequent sequence, resulting in a poor pulverization effect of the alloy flakes, which also causes C1, C2, C3, C4, |C1 / C4| to exceed the scope of the patent, resulting in a poor temperature resistance (Hcj temperature coefficient deterioration). In addition, due to the poor linear expansion coefficient, the product produces too many defects during the sintering cooling process, resulting in a low room temperature Hcj for Comparative Examples 3 and 4. Combined with the poor temperature resistance, the high temperature Hcj becomes even lower.

[0080] Comparing the data of Example 1 and Comparative Example 5 shows that due to the low holding temperature, the transition between the elements of the grains and the grain boundaries is insufficient, resulting in a metastable structure. Although C1, C2, C3, and C4 are all within the range, these values ​​are also within the critical range. Therefore, |C1 / C4| exceeds the patent range, resulting in poor temperature resistance (deterioration of the Hcj temperature coefficient).

[0081] Comparing the data from Example 1 and Comparative Example 6, we can see that in Comparative Example 6, due to the excessively high holding temperature, the alloy flakes experienced a certain degree of grain growth, resulting in poor alloy flake crushing performance. Although C1, C2, C3, and C4 were all within the specified range, these values ​​were considered to be within the critical range, so |C1 / C4| exceeded the patented range, resulting in poor temperature resistance (deterioration of the Hcj temperature coefficient). Furthermore, due to the alloy flake grain growth, the product's room-temperature Hcj decreased. Combined with the poor temperature resistance, the high-temperature Hcj became even lower.

[0082] Comparing the data from Example 1 and Comparative Example 7, we can see that in Comparative Example 7, due to the low argon pressure introduced during the cooling process above 350°C, the alloy flakes dehydrogenated at higher temperatures. Although C1, C2, C3, and C4 were within the specified range, these values ​​were within the critical range. Therefore, |C1 / C4| exceeded the patented range, resulting in poor temperature resistance (deterioration of the Hcj temperature coefficient). Furthermore, because Comparative Example 7 dehydrogenated at a higher temperature, the product of Comparative Example 7 had a low room-temperature Hcj. Combined with the poor temperature resistance, the high-temperature Hcj was even lower.

[0083] Example 2

[0084] The NdFeB magnets prepared in Example 1 were processed into square pieces with a size of 20-15-3 mm. After degreasing and pickling, the square pieces were subjected to Dy grain boundary diffusion treatment. The Dy diffusion amount was 0.8 wt%, the diffusion temperature was 900 ° C, and the diffusion time was 15 h. In this embodiment, the grain boundary diffusion was treated by a coating method to obtain a sintered NdFeB magnet. The linear expansion coefficient of the product in different directions was tested using a thermomechanical analyzer. The test results are shown in Table 4 below. The heating rate was 5 ° C / min, and the test temperature was 20-140 ° C. In addition, the NdFeB magnets obtained above were subjected to magnetic tests at 20 ° C and 140 ° C. The test results are shown in Table 5 below.

[0085] Table 4 Linear expansion coefficient of NdFeB products in Example 1-2

[0086] Table 5 Magnetic properties of NdFeB products in Example 1-2

[0087] It can be seen from Example 2 that after the blank produced in Example 1 is diffused with heavy rare earth, C1, C2, C3, C4, |C1 / C4| are also within the scope of the patent, and when the blank produced in Example 1 is diffused with heavy rare earth, the product performance is greatly improved and has better temperature resistance.

[0088] Example 3

[0089] The other steps were the same as in Example 1, differing only in the post-hydrogenation treatment process. The dehydrogenation temperature was 350°C, and the argon pressure at the end of dehydrogenation was 30 kPa. The holding temperature was 800°C, and the argon pressure during cooling at temperatures above 350°C was 30 kPa. The expansion coefficients of the tested products are shown in Table 6, and the corresponding product properties are shown in Table 7.

[0090] Table 6 Linear expansion coefficient of NdFeB product in Example 3

[0091] Table 7 Magnetic properties of NdFeB products in Example 3

[0092] Example 4

[0093] The other steps were the same as in Example 1, differing only in the post-hydrogenation treatment process. The dehydrogenation temperature was 250°C, the argon pressure at the end of dehydrogenation was 35 kPa, the holding temperature was 700°C, and the argon pressure during cooling at temperatures above 350°C was 20 kPa. The expansion coefficients of the tested products are shown in Table 8, and the corresponding product properties are shown in Table 9.

[0094] Table 8 Linear expansion coefficient of NdFeB product in Example 4

[0095] Table 7 Magnetic properties of NdFeB products in Example 4

[0096] The above is an exemplary description of the embodiments of the present invention. However, the scope of protection of the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc. made by those skilled in the art within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A high temperature sintered NdFeB magnet, characterized in that: The magnet is represented by R-Fe-BM, and based on a mass ratio of 100%, it includes: R 29wt%~35wt%, R is a rare earth element, B 0.9wt%~1.3wt%; M is less than 5wt%, and M is selected from one or more of Ti, V, Cr, Mn, Co, Ga, Cu, Si, Al, Zr, Nb, W and Mo; The remainder is iron and inevitable impurities.

2. The magnet according to claim 1, characterized in that The linear expansion coefficient C1 parallel to the magnetization direction of the magnet is (5~8)*10 -6 / ℃, Preferably, the linear expansion coefficient C2 perpendicular to the magnetization direction and parallel to the pressing direction is (-3 to -0.6)*10 -6 / ℃, Preferably, the linear expansion coefficient C3 in another direction perpendicular to the magnetization direction is (-4 to -1)*10 -6 / ℃, Preferably, the average value C4 of the linear expansion coefficient in two directions perpendicular to the magnetization direction is (-3.5 to -0.8)*10 -6 / ℃, where C4=(C2+C3) / 2; Preferably, 1.5≤|C1 / C4|≤8.

3. The method for preparing a magnet according to claim 1 or 2, characterized in that: The method comprises: (1) preparing R-Fe-BM alloy sheets by using a rapid solidification thin strip method; (2) hydrogenating the alloy flakes for hydrogenation treatment, heating to 250-350° C. for dehydrogenation treatment after the hydrogenation treatment is completed, filling with argon gas to above 30 kPa after the dehydrogenation is completed, heating and heat preservation; cooling after the heat preservation is completed to obtain alloy powder; (3) The alloy powder in step (2) is jet-milled to obtain magnetic powder, and the powder is subjected to pressing, sintering, and tempering to prepare the magnet.

4. The method according to claim 3, characterized in that In step (2), the hydrogen absorption pressure of the hydrogenation treatment is 100 to 200 kPa, and the hydrogen absorption time is 30 to 180 min. Preferably, in step (2), the dehydrogenation time is 180 to 360 minutes.

5. The method according to claim 3 or 4, characterized in that: In step (2), after dehydrogenation is completed, argon is filled to 30-60 kPa. Preferably, in step (2), the insulation temperature is 700-800° C. and the insulation time is 60-180 min. Preferably, in step (2), during the cooling process, when the temperature is above 350° C., the argon pressure is ≥ 20 kPa.

6. The method according to any one of claims 3 to 5, characterized in that: In step (3), the alloy powder in step (2) is mixed with a lubricant and ground with a jet mill to obtain magnetic powder. Preferably, in step (3), the particle size D50 of the magnetic powder is 2 to 5 μm. Preferably, in step (3), the content of the lubricant is 0.03 to 0.5 wt % of the alloy powder in step (2).

7. The method according to any one of claims 3 to 6, characterized in that: In step (3), the magnetic powder is pressed into shape under magnetic field orientation. Preferably, the orientation magnetic field is 1.5-2.5T. Preferably, in step (3), the sintering temperature is 800-1200° C., and the insulation time is 3-20 hours.

8. The method according to any one of claims 3 to 7, characterized in that: In step (3), the tempering treatment is a secondary tempering treatment, for example, the secondary tempering treatment is carried out in a vacuum tempering furnace; the primary tempering temperature is 700-900°C, the holding time is 3-7h, and the secondary tempering temperature is 450-600°C, the holding time is 3-7h.

9. The method according to any one of claims 3 to 8, characterized in that: The method further comprises step (4): performing grain boundary diffusion treatment on the magnet, wherein the diffusion source is at least one of heavy rare earths Dy, Tb, Ho, Nd, and Pr. Preferably, in step (4), the content of the diffused heavy rare earth is 0.1-1.5 wt %. Preferably, in step (4), the diffusion temperature is 800-950° C. and the diffusion time is at least 3 hours.

10. Application of the magnet according to claim 1 or 2 in the new energy automobile industry and wind power generation field.

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