A method for preparing high coercivity sintered NdFeB rare earth permanent magnet materials

Abstract

This invention discloses a method for preparing high-coercivity sintered NdFeB rare-earth permanent magnet materials. The method includes the following steps: preparing an Nd-Fe-B compact, pre-sintering it to a semi-dense state, and then processing it into a thin substrate of the required thickness; forming a diffusion coating layer on the surface of the thin substrate using a spray diffusion method, followed by a first-stage diffusion process; polishing the surface of the resulting first-stage diffused magnet; performing a second-stage diffusion process; polishing the surface of the resulting second-stage diffused magnet; performing a third-stage diffusion process; polishing the surface of the resulting third-stage diffused magnet; and then performing first-stage and second-stage tempering respectively to obtain the high-coercivity sintered NdFeB rare-earth permanent magnet material. This method effectively expands the grain boundary phase channels of the magnet substrate, significantly improves the diffusion efficiency of the diffusion source, promotes the formation of a hard magnetic phase shell structure with stronger magnetocrystalline anisotropy, improves the wettability of the grain boundary phase, and enhances the intrinsic coercivity of the Nd-Fe-B magnet.

Description

Technical Field

[0001] This invention relates to the field of rare earth magnetic material preparation, and in particular to a method for preparing a high coercivity sintered NdFeB rare earth permanent magnet material. Background Technology

[0002] Currently, sintered NdFeB magnets are widely used in high-tech fields such as machinery manufacturing, electronic products, new energy motors, high-end instruments, and wind power generation due to their excellent magnetic properties. The main methods for producing high-coercivity sintered NdFeB rare-earth permanent magnet materials include alloying technology, grain refinement, and grain boundary diffusion technology. Grain boundary diffusion technology includes magnetron sputtering, vapor deposition, chemical deposition, electrophoresis, and physical coating. Their common feature is that a certain amount of heavy rare-earth powder is deposited on the magnet surface, followed by heat treatment at a certain temperature, allowing the heavy rare-earth elements covering the magnet surface to diffuse into the magnet's interior, forming a uniform hard magnetic shell at the main phase grain boundary layer to improve its coercivity. However, the above methods have small diffusion depths and low diffusion efficiency.

[0003] Methods for preparing high-coercivity sintered NdFeB magnets via grain boundary diffusion mainly include magnetron sputtering, spraying, coating, evaporation, screen printing, and electrophoretic deposition. However, traditional grain boundary diffusion methods have low diffusion efficiency, resulting in only a small increase in the coercivity of the magnets and making it impossible to prepare higher-performance products, thus having significant limitations.

[0004] How to further improve the diffusion efficiency of heavy rare earth diffusion sources and prepare high coercivity sintered NdFeB rare earth permanent magnet materials is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] This invention discloses a method for preparing high coercivity sintered NdFeB rare earth permanent magnet materials to solve any of the above-mentioned and other potential problems in the prior art.

[0006] To achieve the above objectives, the technical solution of this invention is: a method for preparing high coercivity sintered NdFeB rare earth permanent magnet materials, wherein the method prepares high coercivity sintered NdFeB magnets through pre-sintering and a three-stage grain boundary diffusion method; specifically including the following steps:

[0007] S1) Prepare Nd-Fe-B compacts, then pre-sinter them to a semi-dense state before processing to prepare sheet substrates of the required thickness;

[0008] S2) The diffusing agent is sprayed onto the surface of the thin substrate obtained in S1) to form a diffusion coating layer, and then a primary diffusion process is performed to obtain a primary diffusion magnet.

[0009] S3) After grinding away the residual diffusion layer and defect layer on the surface of the primary diffusion magnet obtained in S2), the diffusion agent is sprayed onto the surface of the primary diffusion magnet to form a diffusion coating layer, and then a secondary diffusion process is performed to obtain a secondary diffusion magnet.

[0010] S4) Polish the surface of the secondary diffuser magnet obtained in S3), then spray the diffuser onto the surface of the secondary diffuser magnet to form a diffusion layer, and then perform a tertiary diffusion process to obtain a tertiary diffuser magnet.

[0011] S5) Polish the surface of the three-stage diffused magnet obtained in S4), and perform first-stage and second-stage tempering respectively to obtain high coercivity sintered NdFeB rare earth permanent magnet material.

[0012] Furthermore, the pre-sintering process parameters in S1) are: vacuum degree of 1.0 × 10⁻⁶. -4 -9.0×10 -3 Pa, temperature 1000-1030℃, time 3-5 hours; density of the thin film substrate 6.8-7.3 g / cm³ 3 .

[0013] Furthermore, the diffusing agent in S2), S3) and S4) includes a diffusion source alloy fine powder and a binder; the mass ratio of the diffusion source alloy fine powder and the binder is 1:1 to 1:5.

[0014] Furthermore, the chemical formula of the diffusion source alloy powder in S2) is [(Lre)]. x Tm y Ac 1-x-y Lre is one or more of Pr and Nd, 70.0 ≤ x ≤ 100.0 wt.%; Tm is one or more of Cu, Al, and Ga, 0.0 ≤ y ≤ 30.0 wt.%; the remainder is Ac, which is one or more of Fe or Co;

[0015] The chemical formula of the diffusion source alloy powder in S3 is [(Lre)]. x (Hre) y Tm 1-x-y Lre is one or more of Pr and Nd, and 0.0 ≤ x ≤ 90.0 wt.%; 5.0 ≤ y ≤ 100.0 wt.%; the remainder is Tm, which is one or more of Cu, Al, and Ga.

[0016] The chemical formula of the diffusion source alloy powder in S4 is [(Lre)]. x (Hre) y Tm 1-x-yLre is one or more of Pr and Nd, and 0.0≤x≤90.0wt.%; 5.0≤y≤100.0wt.%; the remainder is Tm, which is one or more of Cu, Al and Ga.

[0017] Furthermore, the primary diffusion process in S2) employs multi-stage vacuum heating treatment, specifically: under a vacuum degree not exceeding 1.0 × 10⁻⁶. -3 Pa,

[0018] A volatilization process is carried out by maintaining a temperature of 100-200℃ for 1-2 hours.

[0019] The second stage of diffusion involves further heating to 850-950℃ and holding at that temperature for 8-20 hours.

[0020] The process involves three stages of densification, with the temperature maintained at 1040-1100℃ for 0.5-2 hours, followed by rapid cooling to obtain a dense magnet.

[0021] Furthermore, the process parameters for the secondary diffusion and the tertiary diffusion are the same, specifically:

[0022] The first step is the evaporation process, which involves maintaining a temperature of 100-200℃ for 1-2 hours.

[0023] The second step is the diffusion process, which involves holding the temperature at 850-950℃ for 8-20 hours with a vacuum level not exceeding 1.0×10⁻⁶. - 3 Pa.

[0024] Furthermore, the mass of the diffusing agent sprayed onto the magnet surface before each stage of diffusion in S2), S3) and S4) increases by 0.5%-5.5% compared to the magnet.

[0025] Furthermore, the first-stage tempering process in S5) is as follows: the tertiary diffused magnet is rapidly cooled to room temperature and then subjected to first-stage tempering at a temperature of 880-930℃ for 1-3 hours.

[0026] The process of secondary tempering is as follows: after the primary tempering magnet is rapidly cooled to room temperature, a secondary tempering is performed at a temperature of 450-550℃ for 1-3 hours.

[0027] Furthermore, the thickness of the defect layer in S3) is 0.001-0.01 mm.

[0028] Furthermore, the high coercivity sintered NdFeB permanent magnet prepared by the above method forms a new grain boundary phase, the chemical formula of which is (Nd,RE). x Tm yWhere RE is at least one of Pr, Dy, and Tb, and Tm is at least one of Fe, Al, Cu, and Ga, with 60.0 ≤ x ≤ 70.0 wt.% and 30.0 ≤ y ≤ 40.0 wt.%.

[0029] The beneficial technical effects of this invention are as follows: By employing the above technical solution, the grain boundary phase of the magnet substrate can be further optimized and modified, the diffusion channels of the substrate can be rapidly increased, the diffusion efficiency of the diffusing agent can be effectively improved, and the coercivity of the magnet substrate can be significantly improved, with a maximum increase of 1700 kOe. Furthermore, this technical solution can generate new grain boundary phases (Nd, RE) at the grain boundaries. x wt.%Tm y wt.%, where RE is at least one of Pr, Dy, and Tb, and Tm is at least one of Fe, Al, Cu, and Ga, with 60.0≤x≤70.0 and 30.0≤y≤40.0, can significantly enhance the coupling effect between grain boundaries and the main phase, thereby improving the overall magnetic properties of the magnet. Attached Figure Description

[0030] Figure 1 This is a flowchart illustrating a method for preparing a high-coercivity sintered NdFeB rare-earth permanent magnet material according to the present invention.

[0031] Figure 2 This is a flowchart of Example 1, which uses the preparation method of the present invention.

[0032] Figure 3 The images show SEM comparisons of the pre-sintered and diffused magnets in Example 1, which uses the preparation method of the present invention. Detailed Implementation

[0033] The present invention will be described in detail below through different embodiments. The present invention includes, but is not limited to, the several proportions and schemes described in the table and embodiments. The experimental schemes described in the embodiments are implementation schemes that are not conventional methods, highlighting the difference between the present invention and the conventional diffusion magnet preparation process.

[0034] like Figure 1 As shown, this invention discloses a method for preparing a high coercivity sintered NdFeB rare earth permanent magnet material. This invention uses a heavy rare earth-free NdFeB magnet as the substrate, wherein the components and their percentages are: PrNd: 26.0-32.0 wt.%, Fe: 60-70 wt.%, B: 0.8-1.0 wt.%, Cu: 0.5-3.5 wt.%, Co: 0.5-5 wt.%, Al: 0.08-1.0 wt.%, Ga: 0.2-4 wt.%, Zr: 0.05-1.2 wt.%.

[0035] The preparation process of NdFeB magnet substrate is the same as that of traditional preparation methods, which mainly includes stages such as vacuum melting, hydrogen crushing, air jet milling and orientation molding. In this invention, the thickness of the intermediate product of rapid solidification sheet is 100-350μm, the fine powder obtained after air jet milling has a particle size of 0.5-3.0μm, and the pressed magnet of a set size is obtained after orientation molding.

[0036] The required components and contents of the diffusion source used in the grain boundary diffusion process are as follows: Tb: 65.0-85.0 wt.%, Ga: 5.0-30.0 wt.%, Al: 5.0-30.0 wt.%, Fe: 15.0-30.0 wt.%, Dy: 65.0-85.0 wt.%, Pr: 13.0-100.0 wt.%, Nd: 13.0-100.0 wt.%, Cu: 5.0-30.0 wt.%. The diffusion source used for primary diffusion does not contain heavy rare earth elements. The diffusion sources used for secondary and tertiary diffusion contain one of the heavy rare earth elements, Dy or Tb. In addition to Dy and Tb, the diffusion source also contains two or more of the following elements: Pr, Nd, Al, Cu, Ga, and Fe. All the above element mass fractions are ratios of the mass of each element in the diffusion source to the total mass of the diffusion source.

[0037] 1. Pure Pr powder or pure Nd powder is used as the diffusion source in the primary diffusion process, resulting in better diffusion effect;

[0038] 2. For the two-stage diffusion process and the diffusing agent used in the two-stage diffusion process, the diffusion effect is optimal when the mass fraction of heavy rare earth elements Dy or Tb in the diffusion source is around 76.0 wt.%.

[0039] 3. For the two-stage diffusion process and the diffusion agent in the two-stage diffusion process, the diffusion effect is optimal when the mass fractions of Cu and / or Ga in the diffusion source are 7.0 wt.% and 6.5 wt.%, respectively.

[0040] In this invention, the diffusion source is prepared by vacuum melting rare earth raw materials of different compositions under an argon (Ar) atmosphere to obtain a rapidly solidified sheet with uniform thickness. After being crushed by hydrogen and milled by airflow, the diffusion source fine powder required for grain boundary diffusion is obtained. The particle size of the diffusion source fine powder is 0.5-3 μm, and the average particle size is 2.3 μm.

[0041] The content of heavy rare earth elements in the diffusion source quick-setting tablets is slightly lower than the initial addition amount. The main reason is that some heavy rare earth elements volatilize under high temperature conditions during the smelting process. The decrease in heavy rare earth content in the quick-setting tablets and diffusion source fine powder is <1.0 wt.%.

[0042] The vacuum level required for preparing diffusion-source rapid-condensation sheets is less than 5.0 × 10⁻⁶. -2At Pa, Ar replacement is more effective. The high-temperature refining temperature of the diffusion source is around 1500℃, and the refining time is 5 minutes. When the temperature is reduced to 1200℃, the spun-off process is more effective.

[0043] In this invention, the sintered NdFeB blank magnet sample is set as a cuboid, with a density of 7.0-7.3 g / cm³ after pre-sintering. 3 In actual production, it can be processed into geometric thin sheet shapes for diffusion;

[0044] The prepared binder was mixed with the fine powder of the diffusion source and stirred thoroughly at room temperature. The mass ratio of the two was 1.0:1.2, and the stirring time was 0.5 hours.

[0045] The mixed dispersant was sprayed onto the surface of the NdFeB sheet substrate that had been polished to a mirror finish until a uniform diffusion layer was formed on the substrate surface. The weight was then measured and recorded.

[0046] The primary diffusion magnet undergoes multi-stage vacuum sintering. The volatilization process is carried out at 200℃ for 2 hours; the diffusion process is followed by heating to 900℃ and holding for 15 hours; the densification process involves holding at 1060℃ for 2 hours followed by rapid cooling to obtain a dense magnet. Secondary and tertiary diffusion processes include both volatilization and diffusion, with the remaining steps identical to the primary diffusion process. The subsequent tempering process involves a primary tempering temperature of 900℃ for 2 hours and a secondary tempering temperature of 500℃ for 2 hours.

[0047] After the magnet sample was tempered for two stages, a surface treatment was performed to completely remove the remaining diffusion source on the surface and then polish the surface.

[0048] The pre-sintered magnet substrate and the multi-stage diffusion sample were subjected to SEM tests and compared. Figure 3 As shown; Example 1

[0049] like Figure 2 As shown, a method for preparing a high-coercivity sintered NdFeB rare-earth permanent magnet material includes the following specific steps:

[0050] (1) Preparation of NdFeB substrate

[0051] The preparation process of NdFeB substrate mainly includes steps such as vacuum melting, hydrogen crushing, air jet milling, and orientation molding. In this embodiment, the NdFeB substrate is prepared according to formulation 5 in Table 3, which does not contain heavy rare earth elements;

[0052] (2) Pre-sintering of NdFeB magnet substrate

[0053] NdFeB magnet substrate pre-sintering: The prepared NdFeB substrate is placed in a vacuum sintering furnace and evacuated to a vacuum level of 7.0 × 10⁻⁶. -3Pa was pre-sintered at 1030℃ for 4 hours. After pre-sintering, the density was measured to be 7.3 g / cm³. 3 ;

[0054] (3) Preparation of dispersant for primary diffusion

[0055] The No. 1 dispersant is a mixture of praseodymium iron (PrFe) alloy fine powder and binder. The mass ratio of Pr metal in the praseodymium iron alloy fine powder is 87%, and the remainder is metallic Fe. The particle size is 0.3-2μm, and the mass ratio of alloy fine powder to binder is 1:1.2.

[0056] (4) The preparation process of the dispersants for secondary and tertiary diffusion is the same as that for the first dispersant, but the components may be the same or different. To reduce the amount of heavy rare earth elements used, the second dispersant is pure Pr powder and Tb. 0.48 Al 0.04 Cu 0.08 Pr 0.4 The mixture of fine powders is shown in Table 2 for specific proportions. Furthermore, dispersant No. 2 and dispersant No. 3 have the same composition.

[0057] (5) First-stage diffusion process: PrFe alloy fine powder mixed slurry is sprayed onto the surface of the pre-sintered magnet to form a uniform diffusion layer on the surface. The weight gain of the diffusion layer is 1.0%-5.0%.

[0058] (6) The multi-stage vacuum sintering process of the primary diffusion magnet involves placing the diffusion magnet into a vacuum sintering furnace for heating and evacuating the vacuum to 7.0 × 10⁻⁶. -3 After Pa, Ar gas was replaced, and this process was repeated three times. A three-stage heat treatment was then performed: first, volatilization was carried out at 200℃ for 2 hours; then, the temperature was increased to 950℃ for primary diffusion, and held for 18 hours; finally, the densification process involved holding at 1070℃ for 2 hours followed by rapid cooling to obtain a dense magnet with a vacuum level not exceeding 1.0 × 10⁻⁶. -3 Pa;

[0059] (7) Secondary diffusion process, which combines pure Pr powder and Tb 0.76 Al 0.16 Cu 0.08 The mixed fine powder dispersant is diffused after spraying. The first stage is the evaporation process, held at 100-200℃ for 2 hours. The second stage diffusion conditions are 950℃ for 15 hours, with a vacuum degree not exceeding 1.0 × 10⁻⁶. -3 Pa. Tertiary diffusion is the same as secondary diffusion;

[0060] (8) Tempering process of diffusion magnet: The three-stage diffusion magnet is placed in a vacuum sintering furnace for tempering. The vacuum conditions and gas replacement process are the same as in step (6). The first tempering temperature is 900℃ and the holding time is 2 hours. The second tempering temperature is 500℃ and the holding time is 2 hours.

[0061] (9) The pre-sintered magnet and the third-level diffusion magnet were subjected to SEM testing and grain boundary phase analysis respectively. Before the test, the surface of the magnet after the second-level tempering was polished to a mirror state by grinding and polishing. Cylinder sheets with the same volume and diameter of 10 mm were prepared for testing.

[0062] (10) The pre-sintered magnet substrate and the multi-stage diffusion sample were subjected to SEM and energy dispersive spectroscopy multi-point scanning tests to compare the changes in grain boundary phase composition. The results are shown in Table 4. The results show that the first-stage diffusion process can significantly change the Pr and Nd content in the grain boundary phase and form new diffusion channels. After the second-stage and third-stage diffusion, the content of the heavy rare earth element Tb increased significantly, and new grain boundary phases were generated, which is an important reason for the improvement of magnet coercivity.

[0063] Example 2

[0064] In this embodiment, the preparation methods of the magnet substrate and the diffusing agent are the same as in Example 1, wherein the magnet substrate formulation is selected from Example 7 in Table 2. The diffusing agent formulation is selected from Example 2 in Table 1 and Example 2 in Table 2. It should be noted that the diffusing agent formulation examples and magnet substrate examples can be used randomly in combination according to Tables 1, 2 and 3, and the composition of the magnet substrate and the diffusing source can be changed as needed in actual production;

[0065] Table 1. Primary diffusion source composition formulation table

[0066] diffusion source wt.% Pr Nd Al Fe Cu Ga Example 1 70 / / 20 5 5 Example 2 75 / 15 5 5 Example 3 80 / / 5 5 10

[0067] Table 2. Formulation of Secondary and Tertiary Diffusion Sources

[0068] diffusion source wt.% Tb Dy Cu Al Ga Pr Example 1 48 / 8 4 40 Example 2 82 / 14 2 2 / Example 3 48 8 4 / 40 Example 4 / 82 14 2 2 /

[0069] Table 3 Formulation of Pre-sintered Magnet Substrate

[0070] Ingredients wt.% Pr Nd B Fe Al Cu Co Ga Zr Example 1 7.25 23.90 0.75 67.3 0.1 0.15 0.35 0.1 0.10 Example 2 7.38 25.37 0.80 65.5 0.1 0.20 0.40 0.1 0.15 Example 3 7.50 25.85 0.85 64.8 0.1 0.15 0.45 0.1 0.20 Example 4 7.63 23.47 0.75 67.3 0.1 0.20 0.35 0.1 0.10 Example 5 7.75 25.05 0.80 65.5 0.1 0.15 0.40 0.1 0.15 Example 6 7.88 25.42 0.85 64.8 0.1 0.20 0.45 0.1 0.20 Example 7 8.00 22.95 0.80 67.3 0.1 0.15 0.45 0.1 0.15

[0071] Table 4. Grain boundary phase composition of different diffusion magnets

[0072]

[0073]

[0074] The preparation method of a high coercivity sintered NdFeB rare earth permanent magnet material provided in the embodiments of this application has been described in detail above. The description of the above embodiments is only for the purpose of helping to understand the method and core idea of ​​this application; at the same time, for those skilled in the art, there will be changes in the specific implementation and application scope based on the idea of ​​this application. Therefore, the content of this specification should not be construed as a limitation of this application.

[0075] Certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that hardware manufacturers may use different names to refer to the same component. This specification and claims do not distinguish components based on differences in name, but rather on differences in function. The terms "comprising" and "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising / including but not limited to". "Approximately" means that within an acceptable margin of error, those skilled in the art can solve the technical problem and substantially achieve the technical effect within a certain margin of error. The following descriptions in the specification are preferred embodiments for carrying out this application; however, these descriptions are for the purpose of illustrating the general principles of this application and are not intended to limit the scope of this application. The scope of protection of this application shall be determined by the appended claims.

[0076] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or system comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a product or system. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the product or system that includes said element.

[0077] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0078] The foregoing description illustrates and describes several preferred embodiments of this application. However, as previously stated, it should be understood that this application is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the application concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of this application should be within the protection scope of the appended claims.

Claims

1. A method for preparing a high-coercivity sintered NdFeB rare-earth permanent magnet material, characterized in that, This method prepares high-coercivity sintered NdFeB magnets through pre-sintering and a three-stage grain boundary diffusion process; specifically, it includes the following steps: S1) Prepare Nd-Fe-B compacts, then pre-sinter them to a semi-dense state before processing them into thin sheet substrates of the required thickness; S2) The diffusing agent is sprayed onto the surface of the thin substrate obtained in S1) to form a diffusion coating layer, and then a primary diffusion process is performed to obtain a primary diffusion magnet. The primary diffusion process employs multi-stage vacuum heating, specifically: under a vacuum degree not exceeding 1.0 × 10⁻⁶. -3 Pa, A volatilization process is carried out by maintaining the temperature at 100-200℃ for 1-2 hours; The second stage of diffusion involves further heating to 850-950℃ and holding at that temperature for 8-20 hours. The process involves three stages of densification, with the temperature maintained at 1040-1100℃ for 0.5-2 hours, followed by rapid cooling to obtain a dense magnet. S3) After grinding away the residual diffusion layer and defect layer on the surface of the primary diffusion magnet obtained in S2), the diffusion agent is sprayed onto the surface of the primary diffusion magnet to form a diffusion coating layer, and then a secondary diffusion process is performed to obtain a secondary diffusion magnet. S4) Polish the surface of the secondary diffuser magnet obtained in S3), then spray the diffuser onto the surface of the secondary diffuser magnet to form a diffusion layer, and then perform a tertiary diffusion process to obtain a tertiary diffuser magnet. S5) Polish the surface of the three-stage diffusion magnet obtained in S4), and perform first-stage and second-stage tempering respectively to obtain high coercivity sintered NdFeB rare earth permanent magnet material; The diffusing agent in S2, S3) and S4) comprises a diffusion source alloy powder and a binder; the mass ratio of the diffusion source alloy powder and the binder is 1:1 to 1:

5. The chemical formula of the diffusion source alloy powder in S2 is [(Lre)]. x Tm y Ac 1-x-y Lre is one or more of Pr and Nd, 70.0 ≤ x ≤ 100.0 wt.%; Tm is one or more of Cu, Al, and Ga, 0.0 ≤ y ≤ 30.0 wt.%; the remainder is Ac, which is one or more of Fe or Co; The chemical formula of the diffusion source alloy powder in S3 is [(Lre)]. x (Hre) y Tm 1-x-y Lre is one or more of Pr and Nd, and 0.0≤x≤90.0 wt.%; 5.0≤y≤100.0 wt.%; the remainder is Tm, which is one or more of Cu, Al, and Ga. The chemical formula of the diffusion source alloy powder in S4 is [(Lre)]. x (Hre) y Tm 1-x-y Lre is one or more of Pr and Nd, and 0.0≤x≤90.0 wt.%; 5.0≤y≤100.0 wt.%; the remainder is Tm, which is one or more of Cu, Al, and Ga. In S3) and S4), Hre is the same element, which is either Dy or Tb; The process parameters for the secondary and tertiary diffusions are the same, specifically: The first step is the evaporation process, which involves maintaining a temperature of 100-200℃ for 1-2 hours; The second step is the diffusion process, which involves holding the temperature at 850-950℃ for 8-20 hours with a vacuum level not exceeding 1.0×10⁻⁶. -3 Pa; The high coercivity sintered NdFeB permanent magnet prepared by the method described above forms a new grain boundary phase, the chemical formula of which is (Nd, RE). x Tm y Where RE is at least one of Pr, Dy, and Tb, and Tm is at least one of Fe, Al, Cu, and Ga, and 60.0 ≤ x ≤ 70.0 wt.%, 30.0 ≤ y ≤ 40.0 wt.%.

2. The preparation method according to claim 1, characterized in that, The pre-sintering process parameters in S1) are: vacuum degree of 1.0 × 10⁻⁶. -4 - 9.0 ×10 -3 Pa, temperature 1000-1030℃, time 3-5 hours; density of the thin film substrate 6.8-7.3 g / cm³ 3 .

3. The preparation method according to claim 1, characterized in that, The mass of the diffusing agent sprayed onto the magnet surface before each diffusion stage in S2), S3) and S4) increases by 0.5% - 5.5% compared to the magnet.

4. The preparation method according to claim 1, characterized in that, The first-stage tempering process in S5) is as follows: the tertiary diffused magnet is rapidly cooled to room temperature and then subjected to first-stage tempering at a temperature of 880-930 ℃ for 1-3 hours. The process of secondary tempering is as follows: after the primary tempering magnet is rapidly cooled to room temperature, a secondary tempering is performed at a temperature of 450-550℃ for 1-3 hours.

5. The preparation method according to claim 1, characterized in that, The thickness of the defect layer in S3) is 0.001 - 0.01 mm.

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