High-coercivity hot-pressed neodymium-iron-boron magnet, method for preparing same, and use thereof

Abstract

The application belongs to the technical field of hot-pressed Nd-Fe-B magnets, and relates to a high-coercivity hot-pressed Nd-Fe-B magnet and a preparation method and application thereof. The application discloses a preparation method of a high-coercivity hot-pressed Nd-Fe-B magnet, which comprises the following steps: (1) preparing a grain boundary diffusion source slurry from a grain boundary diffusion source mixed powder, wherein the grain boundary diffusion source mixed powder comprises first alloy powder and second alloy powder; (2) coating the grain boundary diffusion source slurry on a diffusion surface of a hot-pressed Nd-Fe-B magnet substrate, wherein the diffusion surface is parallel to an orientation direction; and then performing heat treatment, wherein the heat treatment comprises first-stage heat treatment and second-stage heat treatment; and the prepared high-coercivity hot-pressed Nd-Fe-B magnet comprises a magnet substrate structure and a diffusion alloy between the substrate structures. The application provides key technical support for the large-scale application of high-performance hot-pressed Nd-Fe-B.

Description

Technical Field

[0001] This invention belongs to the field of hot-pressed NdFeB magnet technology, and relates to a high coercivity hot-pressed NdFeB magnet, its preparation method and application. Background Technology

[0002] With the rapid development of emerging fields such as new energy vehicles and intelligent manufacturing, more stringent requirements have been placed on the magnetic properties, temperature resistance, and corrosion resistance of rare earth permanent magnet materials. Compared with traditional sintered NdFeB magnets, hot-pressed NdFeB magnets employ a hot-pressing / hot-fluidization forming process, which has a lower preparation temperature (approximately 800℃). They possess a nanocrystalline structure with a grain size only about one-tenth that of sintered magnets, resulting in superior temperature resistance and corrosion resistance. Therefore, they are expected to be widely used in fields requiring high-temperature stability, such as drive motors for new energy vehicles, high-performance servo motors, and joint motors for humanoid robots.

[0003] Currently, the remanence (a key indicator of magnet strength) of hot-pressed NdFeB magnets can reach 1.5T, approaching the theoretical value of its saturation magnetization (1.6T). However, its coercivity (an important parameter for measuring the magnet's temperature resistance) is approximately 12–18 kOe, only about 20% of the theoretical value. This is mainly due to the presence of a large amount of iron in the grain boundary phase of hot-pressed NdFeB magnets, which has strong magnetism, leading to magnetic coupling between the main phase grains. When a magnetization reversal occurs in one main phase, it easily affects adjacent main phases, thus causing a decrease in coercivity.

[0004] In traditional sintered magnets, the magnetism of the grain boundary phase can be reduced through grain boundary diffusion, achieving magnetic isolation between the main phase grains. However, the nanocrystalline structure of hot-pressed NdFeB magnets is extremely sensitive to temperature; prolonged high-temperature treatment will cause abnormal grain growth, resulting in a significant deterioration of magnetic properties. Although heavy rare earth alloys (such as fluorides and oxides of Dy and Tb) are commonly used as grain boundary diffusion sources, their high melting points result in low diffusion efficiency and limited effectiveness under low-temperature heat treatment conditions. On the other hand, while low-melting-point alloys (such as Nd-Cu and Pr-Cu) can achieve diffusion at lower temperatures of 600–700 °C, the increase in coercivity is limited (approximately 3 kOe) due to insufficient diffusion driving force. Extending the heat treatment time to enhance the diffusion effect will reduce the orientation consistency of the nanocrystals, leading to a significant decrease in remanence and unstable overall performance, making it difficult to meet practical application requirements.

[0005] Chinese patent application text (publication number: CN112941457A) discloses an alloy composite grain boundary diffuser for neodymium iron boron magnets, which is obtained by combining heavy rare earth powder with low melting point alloy powder without heavy rare earth and then mixing with an organic binder; however, the high content of heavy rare earth added leads to the need for higher temperature and longer time for heat treatment, which in turn causes abnormal growth of nanocrystals.

[0006] Chinese patent application text (publication number: CN109979743A) discloses a method for grain boundary diffusion in neodymium iron boron magnets, which involves diffusion of RE containing an amorphous phase. 1-y-z Al y M z Alloy powder is used as a coating powder for heat treatment and grain boundary diffusion, but if the grain boundary diffusion temperature is too high, it can easily lead to abnormal growth of nanocrystals.

[0007] Therefore, developing a low-melting-point permeation source that matches the thermal stability of hot-pressed NdFeB magnet nanocrystals and establishing an efficient and uniform diffusion process remain key technical challenges that urgently need to be overcome. Summary of the Invention

[0008] The purpose of this invention is to address the aforementioned problems in the existing technology by proposing a method for preparing a high-coercivity hot-pressed NdFeB magnet. This method involves mixing a micron-sized low-melting-point first alloy powder with a submicron-sized high-melting-point second alloy powder to form a grain boundary diffusion source slurry, which is then coated onto the surface of the magnet substrate parallel to the orientation direction. After a stepped heat treatment with increasing temperature, the grain boundary phase in the magnet substrate liquefies to form channels. The grain boundary diffusion source then penetrates into the interior of the hot-pressed NdFeB magnet substrate along these channels, thereby suppressing abnormal grain growth and improving coercivity.

[0009] One objective of this invention is achieved through the following technical solution:

[0010] A method for preparing a high-coercivity hot-pressed NdFeB magnet includes:

[0011] (1) Prepare a grain boundary diffusion source slurry by mixing grain boundary diffusion source powders;

[0012] The grain boundary diffusion source mixed powder comprises a first alloy powder and a second alloy powder in a mass ratio of (60-90):(40-10);

[0013] The chemical formula of the first alloy powder, by mass percentage, is Pr. x Al y Ga 100-x-y Where 70≤x≤90, 2≤y≤15;

[0014] The chemical formula of the second alloy powder, by mass percentage, is HR. 100-z Al z , where HR is one or both of Dy and Tb, and 5≤z≤15;

[0015] (2) A grain boundary diffusion source slurry is coated onto the surface to be diffused of a hot-pressed NdFeB magnet substrate, wherein the surface to be diffused is parallel to the orientation direction, and the coating amount of the grain boundary diffusion source slurry is 0.6 to 2.4 wt.%.

[0016] Then, heat treatment is performed, which includes a first-stage heat treatment and a second-stage heat treatment.

[0017] The first stage of heat treatment is carried out at a temperature of 500–600℃ for a duration of 1.5–6 hours.

[0018] The second-stage heat treatment is carried out at a temperature of 700–760°C for a time of 0.5–4 hours.

[0019] Preferably, the orientation direction is the easy magnetization axis (C-axis) of the grains inside the magnet.

[0020] Preferably, the orientation direction is perpendicular to the upper and lower pressing surfaces of the hot-pressed NdFeB magnet substrate.

[0021] Further preferably, the surface to be diffused is perpendicular to the upper and lower pressing surfaces of the hot-pressed NdFeB magnet substrate. Preferably, the melting point of the grain boundary diffusion source mixed powder is 500–550°C.

[0022] Preferably, the melting point of the first alloy powder is 500-550°C, and the melting point of the second alloy powder is 650-700°C.

[0023] Preferably, the chemical formula of the first alloy powder, by mass percentage, is Pr. x Al y Ga 100-x-y Where 75≤x≤88, 5≤y≤10;

[0024] The chemical formula of the second alloy powder, by mass percentage, is HR. 100-z Al z , where HR is one or both of Dy and Tb, and 8≤z≤12.

[0025] Preferably, the mass ratio of the first alloy powder to the second alloy powder is (60-80):(40-20).

[0026] More preferably, the mass ratio of the first alloy powder to the second alloy powder is (70-80):(30-20).

[0027] More preferably, the mass ratio of the first alloy powder to the second alloy powder is 70:30.

[0028] Preferably, the average particle size of the first alloy powder is 1 to 5 μm, and the average particle size of the second alloy powder is 0.1 to 5 μm.

[0029] More preferably, the average particle size of the first alloy powder is 2 to 5 μm, and the average particle size of the second alloy powder is 0.1 to 2 μm.

[0030] More preferably, the average particle size of the first alloy powder is 2.1 to 3 μm, and the average particle size of the second alloy powder is 1 to 2 μm.

[0031] Preferably, the grain boundary diffusion source slurry comprises 50-80 wt.% grain boundary diffusion source mixed powder, 1-10 wt.% binder and 20-40 wt.% solvent;

[0032] The adhesive includes one or more of hydroxyethyl cellulose, titanium dioxide, acrylic resin, polyacrylic acid, and polymethyl methacrylate;

[0033] The solvent includes one or more of ethanol, butyl acetate, acetone, methanol, terpineol, menthol, geraniol, and nerol.

[0034] More preferably, the grain boundary diffusion source slurry comprises 30-50 wt.% of a first alloy powder, 10-30 wt.% of a second alloy powder, 3-8 wt.% of a binder, and 15-38 wt.% of a solvent.

[0035] More preferably, the grain boundary diffusion source slurry comprises 35-45 wt.% of a first alloy powder, 15-26 wt.% of a second alloy powder, 4-6 wt.% of a binder, and 28-35 wt.% of a solvent.

[0036] Preferably, the grain boundary diffusion source slurry further includes additives, which include one or more of antioxidants, lubricants, and fillers.

[0037] Preferably, the temperature of the first stage heat treatment is 530–580°C and the time is 2–4 hours; the temperature of the second stage heat treatment is 720–740°C and the time is 1–2 hours.

[0038] Further preferred, the time for the first stage heat treatment is greater than the time for the second stage heat treatment.

[0039] Further preferably, the temperature of the second stage heat treatment is greater than the temperature of the first stage heat treatment, and the difference between the two is 150 to 200°C.

[0040] Further preferred, the temperature of the first stage heat treatment is 550℃ and the time is 3h; the temperature of the second stage heat treatment is 730℃ and the time is 1.5h.

[0041] More preferably, the temperature of the first-stage heat treatment is greater than the melting point of the grain boundary diffusion source mixed powder.

[0042] Preferably, the hot-pressed NdFeB magnet matrix comprises R, T, M, and B elements, wherein the content of each element is as follows by mass percentage:

[0043] 27wt.% ≤ R ≤ 33wt.%;

[0044] 0.8 wt.% ≤ B ≤ 1.2 wt.%;

[0045] 0wt.% ≤ M ≤ 6wt.%;

[0046] 60wt.%≤T≤75wt.%;

[0047] Wherein, R is a rare earth element, and includes at least one light rare earth element; M includes one or more of Al, Cu, Ga, Nb, Ti, V, Zr, Mo, and Sn; T includes Fe and / or Co.

[0048] Further preferably, the hot-pressed NdFeB magnet matrix comprises R, T, M, and B elements, wherein the content of each element is as follows (by mass percentage):

[0049] 28.5 wt.% ≤ R ≤ 32 wt.%;

[0050] 0.8 wt.% ≤ B ≤ 1.1 wt.%;

[0051] 2wt.% ≤ M ≤ 5wt.%;

[0052] 62wt.%≤T≤70wt.%;

[0053] Wherein, R is one or more of the light rare earth elements Pr, Nd, Ce, Gd, and La; M includes one or more of Al, Cu, Ga, Nb, Ti, V, Zr, Mo, and Sn; and T includes Fe and / or Co.

[0054] More preferably, the hot-pressed NdFeB magnet matrix comprises R, T, M, and B elements, wherein the content of each element is as follows by mass percentage:

[0055] 28.5 wt.% ≤ R ≤ 32 wt.%;

[0056] 0.8 wt.% ≤ B ≤ 1.1 wt.%;

[0057] 2wt.% ≤ M ≤ 5wt.%;

[0058] 62wt.%≤T≤70wt.%;

[0059] Wherein, R is one or more of the light rare earth elements Pr, Nd, Ce, Gd, and La; M includes one or more of Al, Cu, Ga, Nb, Ti, V, Zr, Mo, and Sn; and T includes Fe and Co.

[0060] Preferably, the hot-pressed NdFeB magnet matrix comprises main phase grains and grain boundary phases.

[0061] In a further preferred embodiment, during the heat treatment process, the grain boundary phase in the hot-pressed NdFeB magnet matrix liquefies to form channels, and the grain boundary diffusion source penetrates into the interior of the hot-pressed NdFeB magnet matrix along the channels and is distributed in the channels formed by the liquefaction of the grain boundary phase.

[0062] Preferably, the hot-pressed NdFeB magnet matrix is ​​prepared by orienting, hot-pressing, and hot-deforming NdFeB magnetic powder.

[0063] Preferably, the thickness of the hot-pressed NdFeB magnet substrate is 1–20 mm.

[0064] The second objective of this invention is achieved through the following technical solution:

[0065] A high-coercivity hot-pressed NdFeB magnet comprises a main phase grain and a grain boundary phase, wherein the grain boundary phase comprises (Nd,Dy)₂Fe 14 B phase and / or (Nd,Tb)2Fe 14 Phase B.

[0066] Preferably, the high coercivity hot-pressed NdFeB magnet comprises a magnet matrix and a diffusion alloy between the matrix and the matrix.

[0067] Further preferably, the diffusion alloy is an alloy formed by penetrating a grain boundary diffusion source into a channel formed by grain boundary phase liquefaction. Even more preferably, the diffusion alloy is an alloy formed by penetrating a grain boundary diffusion source into a grain boundary region between matrix structures through a channel formed by magnet grain boundary phase liquefaction, reacting or fusing with elements at the grain boundaries to form an alloy used for directional enhancement of magnet coercivity.

[0068] Preferably, the coercivity of the high coercivity hot-pressed NdFeB magnet is >20kOe.

[0069] Further preferred, the coercivity of the high coercivity hot-pressed NdFeB magnet is >21kOe.

[0070] Preferably, the coercivity of the high coercivity hot-pressed NdFeB magnet is greater than that of the hot-pressed NdFeB magnet matrix, and the difference is greater than 5 kOe.

[0071] Preferably, the performance consistency of the high coercivity hot-pressed NdFeB magnet is ≤3%. The third objective of this invention is achieved through the following technical solution:

[0072] Application of a high coercivity hot-pressed NdFeB magnet in the fields of new energy vehicles, industrial robots and aerospace.

[0073] Compared with the prior art, the present invention has the following beneficial effects:

[0074] 1. This invention uses the grain boundary diffusion method to achieve local and precise addition of heavy rare earth elements. The diffusion source melts into a liquid phase during the heat treatment process, driving the heavy rare earth elements to diffuse along the grain boundary into the interior of the magnet, forming a shell with a high magnetocrystalline anisotropy field on the surface of the main phase grains; and by adjusting the heat treatment process, the excessive accumulation of heavy rare earth elements on the surface of the magnet is avoided while suppressing grain growth.

[0075] 2. This invention achieves a synergistic effect between a low-melting-point first alloy powder Pr-Al-Ga and a high-melting-point second alloy powder HR-Al, successfully reducing the melting point of the diffusion source to a critical temperature of 500-550°C. This critical temperature is significantly lower than the critical temperature (~600°C) at which nanocrystals begin to grow abnormally in hot-pressed NdFeB magnets, fundamentally inhibiting the growth of the main phase grains. Combined with a stepped-heating grain boundary diffusion heat treatment process, heavy rare earth elements can be driven to penetrate into the magnet interior at the first-stage heat treatment temperature.

[0076] 3. The diffusion source alloy of the present invention is a combination of micron-sized low-melting-point first alloy powder and submicron-sized high-melting-point second alloy powder. The submicron-sized high-melting-point alloy liquefies at a lower temperature, opening up grain boundary channels for subsequent diffusion. Subsequently, the micron-sized low-melting-point alloy continuously supplies heavy rare earth elements during heating, ensuring their deep penetration and uniform distribution inside the magnet. Thus, while ensuring the microstructure of the magnet, the coercivity is improved, expanding the application environment of the magnet.

[0077] 4. This invention employs a temperature-increasing stepped heat treatment process for grain boundary diffusion, which differs from the conventional temperature-reducing stepped heat treatment process. This invention first performs diffusion treatment in a low-temperature range of 500-600℃ to drive heavy rare earth elements to begin penetrating into the interior of the magnet, and then activates them with a short-term high temperature of 700-760℃ to promote the migration and uniform distribution of heavy rare earth elements along the grain boundary depth. Under the premise of strictly suppressing grain growth, this invention achieves a significant improvement in coercivity.

[0078] 5. The preparation method of the high coercivity hot-pressed NdFeB magnet of the present invention can effectively improve the coercivity of the heavy rare earth magnet matrix, and while achieving high performance, it significantly reduces the dependence on expensive heavy rare earth raw materials and costs; in addition, the present invention can effectively reduce energy consumption in the production process by controlling the parameters of the heat treatment process compared with the traditional process, and achieve synergistic optimization of performance improvement and cost reduction and energy saving.

[0079] 6. The method for preparing high coercivity hot-pressed NdFeB magnets of the present invention can effectively process large-size magnets, ensure that their overall magnetic properties are uniform and consistent, meet the needs of high-end applications for large-size high-performance magnets, and broaden the application scenarios.

[0080] 7. The preparation method of the high coercivity hot-pressed NdFeB magnet of the present invention has a stable and controllable process, which greatly ensures the high efficiency and high pass rate of mass production of small-sized magnets, and provides key technical support for the large-scale and low-cost manufacturing of high-performance hot-pressed NdFeB magnets. Attached Figure Description

[0081] Figure 1 This is a microstructure diagram and a corresponding schematic diagram of the hot-pressed NdFeB magnet matrix of the present invention.

[0082] Figure 2 This is a flowchart illustrating the preparation process of the high coercivity hot-pressed NdFeB magnet of the present invention.

[0083] Figure 3 This is an EDS image of the diffusion alloy in the high coercivity hot-pressed NdFeB magnet of Embodiment 1 of the present invention, which penetrates into the channels formed by the liquefaction of the grain boundary phase.

[0084] Figure 4 This is an EDS image of the high coercivity hot-pressed NdFeB magnet matrix structure in Embodiment 1 of the present invention.

[0085] Figure 5 This is a comparison diagram of the magnetic properties of the hot-pressed NdFeB magnet substrate (a) and the high coercivity hot-pressed NdFeB magnet (b) in Embodiment 1 of the present invention. Detailed Implementation

[0086] The technical solution of the present invention will be further described and illustrated below through specific embodiments. It should be understood that the specific embodiments described herein are only for the purpose of helping to understand the present invention and are not intended to limit the present invention.

[0087] Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used in the art, and the methods used in the embodiments are all conventional methods in the art.

[0088] In this paper, the fabrication process of the high coercivity hot-pressed NdFeB magnet of the present invention is shown in the following flowchart. Figure 1 As shown.

[0089] In one embodiment of the present invention, the hot-pressed NdFeB magnet substrate is a commercially available product.

[0090] In one embodiment of the present invention, the method for preparing a hot-pressed NdFeB magnet substrate includes:

[0091] S1. Cold pressing pre-pressing step: Neodymium iron boron magnetic powder is cold-pressed to obtain a cold blank;

[0092] S2. Hot pressing step: The cold blank is placed in the forming equipment for hot pressing treatment to obtain the hot-pressed blank;

[0093] S3. Hot deformation step: The hot-pressed blank is placed in the forming equipment for hot deformation treatment to obtain the hot-pressed NdFeB magnet matrix.

[0094] In one embodiment of the present invention, the method for preparing a hot-pressed NdFeB magnet substrate includes:

[0095] S1. Cold pressing pre-pressing step: Neodymium iron boron rapid quenching powder (average particle size 50-100nm) is loaded into the mold and cold-pressed to obtain a cold blank by applying pressure in both directions through upper and lower double pressure heads;

[0096] The density of the cold-cured billet is 5.3–5.7 g / cm³. 3 .

[0097] S2. Hot pressing step: The cold blank is placed in the forming equipment for hot pressing treatment to obtain the hot-pressed blank;

[0098] In the hot pressing process, the heating temperature is 400–800℃, the pressure is 100–800MPa, and the hot pressing time is 30–50s.

[0099] The hot pressing process employs one or more of microwave heating and hot pressing sintering.

[0100] The density of the hot-pressed blank is ≥7.5 g / cm³. 3 .

[0101] S3. Hot deformation step: The hot-pressed blank is placed in the forming equipment for hot deformation treatment, which simultaneously achieves orientation.

[0102] The orientation direction is the direction of thermal deformation and pressure application;

[0103] In the aforementioned heat deformation treatment, the heating temperature is 500–900℃, the pressure is 300–500MPa, and the heat deformation time is 50–70s;

[0104] The heat deformation process employs one or more of microwave heating and hot pressing sintering.

[0105] Hot-pressed NdFeB magnet matrix.

[0106] In one embodiment of the present invention, at least one side of the hot-pressed NdFeB magnet substrate has a coating, the coating comprising a first coating and a second coating;

[0107] The first coating contains 70-95 parts boron nitride and 5-30 parts glass powder;

[0108] The second coating contains graphite powder;

[0109] The first coating is located between the magnet substrate and the second coating;

[0110] The thickness of the first coating is 0.05–0.15 mm, and the thickness of the second coating is 0.1–0.3 mm.

[0111] In one embodiment of the present invention, the method for preparing a hot-pressed NdFeB magnet substrate includes:

[0112] Neodymium iron boron magnetic powder is cold-pressed into a cold blank.

[0113] A solution of composite lubricant A is uniformly coated on the surface of the cold blank. Composite lubricant A is a composite material formed by boron nitride powder and graphite powder in a mass ratio of (0.9~1.2):1. After drying, it is placed in a molding equipment for hot pressing to obtain a hot-pressed blank.

[0114] A solution of composite lubricant B is uniformly coated on the surface of the hot-pressed blank. Composite lubricant B is a composite material formed by boron nitride powder and graphite powder in a mass ratio of (0.4~0.7):1. After drying, it is placed in a molding equipment for heat deformation treatment to obtain a hot-pressed NdFeB magnet matrix.

[0115] In one embodiment of the present invention, the hot-pressed NdFeB magnet matrix comprises R, T, M, and B elements, wherein the content of each element is as follows by mass percentage:

[0116] 27wt.% ≤ R ≤ 33wt.%;

[0117] 0.8 wt.% ≤ B ≤ 1.2 wt.%;

[0118] 0wt.% ≤ M ≤ 6wt.%;

[0119] 60wt.%≤T≤75wt.%;

[0120] Wherein, R is a rare earth element, and includes at least one light rare earth element; M includes one or more of Al, Cu, Ga, Nb, Ti, V, Zr, Mo, and Sn; T includes Fe and / or Co.

[0121] In one embodiment of the present invention, the chemical formula of the hot-pressed NdFeB magnet matrix, by mass percentage, is Nd. 23 Pr7Fe bal (CoAlCuGa)4B1, where bal refers to the balance.

[0122] In one embodiment of the present invention, the neodymium iron boron magnetic powder is a commercially available product.

[0123] In one embodiment of the present invention, the preparation process of the first alloy powder and the second alloy powder includes:

[0124] Alloy raw materials are prepared in proportion and directly ground into powder to obtain first alloy powder and second alloy powder respectively.

[0125] In one embodiment of the present invention, the preparation process of the first alloy powder and the second alloy powder includes:

[0126] The alloy raw materials for preparing the first alloy powder were smelted at 1380℃, hydrogen crushed, and air jet milled to obtain the first alloy powder with an average particle size of 2.3μm.

[0127] The alloy raw materials for preparing the second alloy powder were smelted at 1420℃, hydrogenated, and jet milled to obtain the second alloy powder with an average particle size of 1.7μm.

[0128] In this paper, the performance testing of high coercivity hot-pressed NdFeB magnets includes:

[0129] The high coercivity hot-pressed neodymium iron boron magnet with a size of 35mm×20mm×4mm obtained by the present invention was processed into 28 samples with a size of 5mm×5mm×4mm. Ten of these samples (including at least four end points and the middle part) were randomly selected for performance testing.

[0130] Coercivity value: The average coercivity value of 10 samples of the high coercivity hot-pressed NdFeB magnet of this invention;

[0131] Performance consistency: The average of the ratios of the performance value of each of the 10 samples to the average performance value of the 10 samples.

[0132] Example 1

[0133] The fabrication of the high coercivity hot-pressed NdFeB magnet in this embodiment includes:

[0134] (1) 70g of first alloy powder Pr with an average particle size of 2.3μm was used. 85 Al9Ga6, 30g of second alloy powder Tb with an average particle size of 1.7μm 90 Al 10 7.5g of binder (titanium dioxide) and 52.5g of solvent (terpineol) were mixed to obtain a grain boundary diffusion source slurry;

[0135] (2) Hot-pressed NdFeB magnet substrate with dimensions of 35mm×20mm×4mm (orientation direction) 23 Pr7Fe bal A grain boundary diffusion source paste was uniformly coated on four surfaces of (CoAlCuGa)4B1 parallel to the orientation direction. The total coating amount of the grain boundary diffusion source paste was 1 wt.%, and the coating amount on each surface was the same. After drying, it was placed in a high-temperature sintering furnace for heat treatment. The temperature was raised to the first-stage heat treatment temperature of 550℃ and held for 3 hours. The temperature was then raised to the second-stage heat treatment temperature of 730℃ and held for 1.5 hours. After cooling to room temperature, a high coercivity hot-pressed NdFeB magnet was obtained.

[0136] The performance test results of the high coercivity hot-pressed NdFeB magnet in this embodiment are shown in Table 1.

[0137] Repeat steps (1) and (2) above three times to test the batch consistency of different batches of high coercivity hot-pressed NdFeB magnets. The batch consistency was 2.6%.

[0138] Figure 1 This is a microstructure diagram of a hot-pressed NdFeB magnet matrix. Figure 3 EDS image of a diffusion alloy in a high-coercivity hot-pressed NdFeB magnet that penetrates into channels formed by the liquefaction of the grain boundary phase; Figure 4 The image shows the EDS diagram of the high coercivity hot-pressed NdFeB magnet matrix structure in this embodiment (the peaks of Pr and Nd are close, indicating an error). Figure 5 This is a comparison diagram of the magnetic properties of the hot-pressed NdFeB magnet substrate (a) and the high-coercivity hot-pressed NdFeB magnet (b) in this embodiment.

[0139] Example 2

[0140] The fabrication of the high coercivity hot-pressed NdFeB magnet in this embodiment includes:

[0141] (1) Same as step (1) in Example 1;

[0142] (2) Grain boundary diffusion source slurry was uniformly coated on four surfaces of a hot-pressed NdFeB magnet substrate with dimensions of 35mm×20mm×4mm (orientation direction) parallel to the orientation direction. The total coating amount of the grain boundary diffusion source slurry was 1wt.%, and the coating amount on each surface was the same. After drying, it was placed in a high-temperature sintering furnace for heat treatment. The temperature was raised to the first-stage heat treatment temperature of 550℃ and held for 3 hours. The temperature was then raised to the second-stage heat treatment temperature of 730℃ and held for 4 hours. After cooling to room temperature, a high coercivity hot-pressed NdFeB magnet was obtained.

[0143] The performance test results of the high coercivity hot-pressed NdFeB magnet in this embodiment are shown in Table 1.

[0144] Example 3

[0145] The fabrication of the high coercivity hot-pressed NdFeB magnet in this embodiment includes:

[0146] (1) Same as step (1) in Example 1;

[0147] (2) A grain boundary diffusion source slurry was uniformly coated on four surfaces of a hot-pressed NdFeB magnet substrate with dimensions of 35mm×20mm×4mm (orientation direction) parallel to the orientation direction. The total coating amount of the grain boundary diffusion source slurry was 1wt.%, and the coating amount on each surface was the same. After drying, it was placed in a high-temperature sintering furnace for heat treatment. The temperature was raised to the first-stage heat treatment temperature of 550℃ and held for 3h. The temperature was then raised to the second-stage heat treatment temperature of 730℃ and held for 0.5h. After cooling to room temperature, a high coercivity hot-pressed NdFeB magnet was obtained.

[0148] The performance test results of the high coercivity hot-pressed NdFeB magnet in this embodiment are shown in Table 1.

[0149] Example 4

[0150] The fabrication of the high coercivity hot-pressed NdFeB magnet in this embodiment includes:

[0151] (1) Same as step (1) in Example 1;

[0152] (2) A grain boundary diffusion source slurry was uniformly coated on four surfaces of a hot-pressed NdFeB magnet substrate with dimensions of 35mm×20mm×4mm (orientation direction) parallel to the orientation direction. The total coating amount of the grain boundary diffusion source slurry was 1wt.%, and the coating amount on each surface was the same. After drying, it was placed in a high-temperature sintering furnace for heat treatment. The temperature was raised to the first-stage heat treatment temperature of 550℃ and held for 1h. The temperature was then raised to the second-stage heat treatment temperature of 730℃ and held for 1.5h. After cooling to room temperature, a high coercivity hot-pressed NdFeB magnet was obtained.

[0153] The performance test results of the high coercivity hot-pressed NdFeB magnet in this embodiment are shown in Table 1.

[0154] Example 5

[0155] The fabrication of the high coercivity hot-pressed NdFeB magnet in this embodiment includes:

[0156] (1) Same as step (1) in Example 1;

[0157] (2) A grain boundary diffusion source slurry was uniformly coated on four surfaces of a hot-pressed NdFeB magnet substrate with dimensions of 35mm×20mm×4mm (orientation direction) parallel to the orientation direction. The total coating amount of the grain boundary diffusion source slurry was 1wt.%, and the coating amount on each surface was the same. After drying, it was placed in a high-temperature sintering furnace for heat treatment. The temperature was raised to the first-stage heat treatment temperature of 550℃ and held for 6 hours. The temperature was then raised to the second-stage heat treatment temperature of 730℃ and held for 1.5 hours. After cooling to room temperature, a high coercivity hot-pressed NdFeB magnet was obtained.

[0158] The performance test results of the high coercivity hot-pressed NdFeB magnet in this embodiment are shown in Table 1.

[0159] Example 6

[0160] The fabrication of the high coercivity hot-pressed NdFeB magnet in this embodiment includes:

[0161] (1) Same as step (1) in Example 1;

[0162] (2) Grain boundary diffusion source slurry was uniformly coated on four surfaces of a hot-pressed NdFeB magnet substrate with dimensions of 35mm×20mm×4mm (orientation direction) parallel to the orientation direction. The total coating amount of the grain boundary diffusion source slurry was 0.8wt.%, and the coating amount on each surface was the same. After drying, it was placed in a high-temperature sintering furnace for heat treatment. The temperature was raised to the first-stage heat treatment temperature of 550℃ and held for 3 hours. The temperature was then raised to the second-stage heat treatment temperature of 730℃ and held for 1.5 hours. After cooling to room temperature, a high coercivity hot-pressed NdFeB magnet was obtained.

[0163] The performance test results of the high coercivity hot-pressed NdFeB magnet in this embodiment are shown in Table 1.

[0164] Example 7

[0165] The fabrication of the high coercivity hot-pressed NdFeB magnet in this embodiment includes:

[0166] (1) Same as step (1) in Example 1;

[0167] (2) A grain boundary diffusion source slurry was uniformly coated on four surfaces of a hot-pressed NdFeB magnet substrate with dimensions of 35mm×20mm×4mm (orientation direction) parallel to the orientation direction. The total coating amount of the grain boundary diffusion source slurry was 0.9wt.%, and the coating amount on each surface was the same. After drying, it was placed in a high-temperature sintering furnace for heat treatment. The temperature was raised to the first-stage heat treatment temperature of 550℃ and held for 3 hours. The temperature was then raised to the second-stage heat treatment temperature of 730℃ and held for 1.5 hours. After cooling to room temperature, a high coercivity hot-pressed NdFeB magnet was obtained.

[0168] The performance test results of the high coercivity hot-pressed NdFeB magnet in this embodiment are shown in Table 1.

[0169] Example 8

[0170] The fabrication of the high coercivity hot-pressed NdFeB magnet in this embodiment includes:

[0171] (1) Same as step (1) in Example 1;

[0172] (2) A grain boundary diffusion source slurry was uniformly coated on four surfaces of a hot-pressed NdFeB magnet substrate with dimensions of 35mm×20mm×4mm (orientation direction) parallel to the orientation direction. The total coating amount of the grain boundary diffusion source slurry was 1.1wt.%, and the coating amount on each surface was the same. After drying, it was placed in a high-temperature sintering furnace for heat treatment. The temperature was raised to the first-stage heat treatment temperature of 550℃ and held for 3 hours. The temperature was then raised to the second-stage heat treatment temperature of 730℃ and held for 1.5 hours. After cooling to room temperature, a high coercivity hot-pressed NdFeB magnet was obtained.

[0173] The performance test results of the high coercivity hot-pressed NdFeB magnet in this embodiment are shown in Table 1.

[0174] Example 9

[0175] The fabrication of the high coercivity hot-pressed NdFeB magnet in this embodiment includes:

[0176] (1) Same as step (1) in Example 1;

[0177] (2) Grain boundary diffusion source slurry was uniformly coated on four surfaces of a hot-pressed NdFeB magnet substrate with dimensions of 35mm×20mm×4mm (orientation direction) parallel to the orientation direction. The total coating amount of the grain boundary diffusion source slurry was 1.2wt.%, and the coating amount on each surface was the same. After drying, it was placed in a high-temperature sintering furnace for heat treatment. The temperature was raised to the first-stage heat treatment temperature of 550℃ and held for 3 hours. The temperature was then raised to the second-stage heat treatment temperature of 730℃ and held for 1.5 hours. After cooling to room temperature, a high coercivity hot-pressed NdFeB magnet was obtained.

[0178] The performance test results of the high coercivity hot-pressed NdFeB magnet in this embodiment are shown in Table 1.

[0179] Example 10

[0180] The fabrication of the high coercivity hot-pressed NdFeB magnet in this embodiment includes:

[0181] (1) Same as step (1) in Example 1;

[0182] (2) Grain boundary diffusion source slurry was uniformly coated on four surfaces of a hot-pressed NdFeB magnet substrate with dimensions of 35mm×20mm×4mm (orientation direction) parallel to the orientation direction. The total coating amount of the grain boundary diffusion source slurry was 1.5wt.%, and the coating amount on each surface was the same. After drying, it was placed in a high-temperature sintering furnace for heat treatment. The temperature was raised to the first-stage heat treatment temperature of 550℃ and held for 3 hours. The temperature was then raised to the second-stage heat treatment temperature of 730℃ and held for 1.5 hours. After cooling to room temperature, a high coercivity hot-pressed NdFeB magnet was obtained.

[0183] The performance test results of the high coercivity hot-pressed NdFeB magnet in this embodiment are shown in Table 1.

[0184] Example 11

[0185] The fabrication of the high coercivity hot-pressed NdFeB magnet in this embodiment includes:

[0186] (1) 90g of first alloy powder Pr with an average particle size of 2.3μm was used. 85 Al9Ga6, 10g of second alloy powder Tb with an average particle size of 1.7μm 90 Al 10 7.5g of binder (titanium dioxide) and 52.5g of solvent (terpineol) were mixed to obtain a grain boundary diffusion source slurry;

[0187] (2) Same as step (2) in Example 1.

[0188] The performance test results of the high coercivity hot-pressed NdFeB magnet in this embodiment are shown in Table 1.

[0189] Example 12

[0190] The fabrication of the high coercivity hot-pressed NdFeB magnet in this embodiment includes:

[0191] (1) 60g of first alloy powder Pr with an average particle size of 2.3μm was used. 85 Al9Ga6, 40g of second alloy powder Tb with an average particle size of 1.7μm 90 Al 10 7.5g of binder (titanium dioxide) and 52.5g of solvent (terpineol) were mixed to obtain a grain boundary diffusion source slurry;

[0192] (2) Same as step (2) in Example 1.

[0193] The performance test results of the high coercivity hot-pressed NdFeB magnet in this embodiment are shown in Table 1.

[0194] Example 13

[0195] The fabrication of the high coercivity hot-pressed NdFeB magnet in this embodiment includes:

[0196] (1) 70g of first alloy powder Pr with an average particle size of 2.3μm was used. 75 Al 10 Ga 15 30g of second alloy powder Tb with an average particle size of 1.7μm 90 Al 10 7.5g of binder (titanium dioxide) and 52.5g of solvent (terpineol) were mixed to obtain a grain boundary diffusion source slurry;

[0197] (2) Same as step (2) in Example 1.

[0198] The performance test results of the high coercivity hot-pressed NdFeB magnet in this embodiment are shown in Table 1.

[0199] Example 14

[0200] The fabrication of the high coercivity hot-pressed NdFeB magnet in this embodiment includes:

[0201] (1) 70g of first alloy powder Pr with an average particle size of 2.3μm was used. 85 Al9Ga6, 30g of second alloy powder Dy with an average particle size of 1.7μm 90 Al 10 7.5g of binder (titanium dioxide) and 52.5g of solvent (terpineol) were mixed to obtain a grain boundary diffusion source slurry;

[0202] (2) Same as step (2) in Example 1.

[0203] The performance test results of the high coercivity hot-pressed NdFeB magnet in this embodiment are shown in Table 1.

[0204] Example 15

[0205] The fabrication of the high coercivity hot-pressed NdFeB magnet in this embodiment includes:

[0206] (1) 70g of first alloy powder Pr with an average particle size of 2.3μm was used. 75 Al 10 Ga 15 30g of second alloy powder Dy with an average particle size of 1.7μm 90 Al 10 7.5g of binder (titanium dioxide) and 52.5g of solvent (terpineol) were mixed to obtain a grain boundary diffusion source slurry;

[0207] (2) Same as step (2) in Example 1.

[0208] The performance test results of the high coercivity hot-pressed NdFeB magnet in this embodiment are shown in Table 1.

[0209] Comparative Example 1

[0210] The preparation of the hot-pressed NdFeB magnet in this comparative example includes:

[0211] A hot-pressed NdFeB magnet substrate with dimensions of 35mm×20mm×4mm (orientation direction) was placed in a high-temperature sintering furnace for heat treatment. The temperature was raised to the first-stage heat treatment temperature of 550℃ and held for 3 hours. The temperature was then raised to the second-stage heat treatment temperature of 730℃ and held for 1.5 hours. The substrate was then cooled to room temperature to obtain the hot-pressed NdFeB magnet.

[0212] The magnetic properties of the hot-pressed NdFeB magnets prepared in this comparative example are shown in Table 1.

[0213] Comparative Example 2

[0214] The preparation of the hot-pressed NdFeB magnet in this comparative example includes:

[0215] (1) Mix 100g of Tb powder with an average particle size of 1.7μm, 7.5g of binder (titanium dioxide) and 52.5g of solvent (terpineol) to obtain a grain boundary diffusion source slurry;

[0216] (2) Same as step (2) in Example 1.

[0217] The magnetic properties of the hot-pressed NdFeB magnets prepared in this comparative example are shown in Table 1.

[0218] Comparative Example 3

[0219] The preparation of the hot-pressed NdFeB magnet in this comparative example includes:

[0220] (1) 100g of first alloy powder Pr with an average particle size of 2.3μm was used. 85 Al9Ga6, 7.5g binder (titanium dioxide) and 52.5g solvent (terpineol) were mixed to obtain a grain boundary diffusion source slurry;

[0221] (2) Same as step (2) in Example 1.

[0222] The magnetic properties of the hot-pressed NdFeB magnets prepared in this comparative example are shown in Table 1.

[0223] Comparative Example 4

[0224] The preparation of the hot-pressed NdFeB magnet in this comparative example includes:

[0225] (1) 100g of second alloy powder Tb with an average particle size of 1.7μm 90 Al 10 7.5g of binder (titanium dioxide) and 52.5g of solvent (terpineol) were mixed to obtain a grain boundary diffusion source slurry;

[0226] (2) Same as step (2) in Example 1.

[0227] The magnetic properties of the hot-pressed NdFeB magnets prepared in this comparative example are shown in Table 1.

[0228] Comparative Example 5

[0229] The preparation of the hot-pressed NdFeB magnet in this comparative example includes:

[0230] (1) 50g of first alloy powder Pr with an average particle size of 2.3μm was used. 85 Al9Ga6, 50g of second alloy powder Tb with an average particle size of 1.7μm 90 Al 107.5g binder (titanium dioxide) and 52.5g solvent (terpineol) are mixed to obtain a grain boundary diffusion source slurry; (2) is the same as step (2) in Example 1.

[0231] The magnetic properties of the hot-pressed NdFeB magnets prepared in this comparative example are shown in Table 1.

[0232] Comparative Example 6

[0233] The preparation of the hot-pressed NdFeB magnet in this comparative example includes:

[0234] (1) 20g of first alloy powder Pr with an average particle size of 2.3μm was used. 85 Al9Ga6, 80g of second alloy powder Tb with an average particle size of 1.7μm 90 Al 10 7.5g of binder (titanium dioxide) and 52.5g of solvent (terpineol) were mixed to obtain a grain boundary diffusion source slurry;

[0235] (2) Same as step (2) in Example 1.

[0236] The magnetic properties of the hot-pressed NdFeB magnets prepared in this comparative example are shown in Table 1.

[0237] Comparative Example 7

[0238] The preparation of the hot-pressed NdFeB magnet in this comparative example includes:

[0239] (1) 70g of first alloy powder Pr with an average particle size of 2.3μm was used. 60 Al 30 Ga 10 30g of second alloy powder Tb with an average particle size of 1.7μm 90 Al 10 7.5g of binder (titanium dioxide) and 52.5g of solvent (terpineol) were mixed to obtain a grain boundary diffusion source slurry;

[0240] (2) Same as step (2) in Example 1.

[0241] The magnetic properties of the hot-pressed NdFeB magnets prepared in this comparative example are shown in Table 1.

[0242] Comparative Example 8

[0243] The preparation of the hot-pressed NdFeB magnet in this comparative example includes:

[0244] (1) 70g of first alloy powder Pr with an average particle size of 2.3μm was used. 85 Al 156 30g of second alloy powder Tb with an average particle size of 1.7μm 90 Al 107.5g of binder (titanium dioxide) and 52.5g of solvent (terpineol) were mixed to obtain a grain boundary diffusion source slurry;

[0245] (2) Same as step (2) in Example 1.

[0246] The magnetic properties of the hot-pressed NdFeB magnets prepared in this comparative example are shown in Table 1.

[0247] Comparative Example 9

[0248] The preparation of the hot-pressed NdFeB magnet in this comparative example includes:

[0249] (1) 70g of first alloy powder Pr with an average particle size of 2.3μm was used. 85 Ga 15 30g of second alloy powder Tb with an average particle size of 1.7μm 90 Al 10 7.5g of binder (titanium dioxide) and 52.5g of solvent (terpineol) were mixed to obtain a grain boundary diffusion source slurry;

[0250] (2) Same as step (2) in Example 1.

[0251] The magnetic properties of the hot-pressed NdFeB magnets prepared in this comparative example are shown in Table 1.

[0252] Comparative Example 10

[0253] The preparation of the hot-pressed NdFeB magnet in this comparative example includes:

[0254] (1) Same as step (1) in Example 1;

[0255] (2) A grain boundary diffusion source slurry was uniformly coated on four surfaces of a hot-pressed NdFeB magnet substrate with dimensions of 35mm×20mm×4mm (orientation direction) parallel to the orientation direction. The total coating amount of the grain boundary diffusion source slurry was 1wt.%, and the coating amount on each surface was the same. After drying, it was placed in a high-temperature sintering furnace for heat treatment. The temperature was raised to the first-stage heat treatment temperature of 550℃ and held for 3 hours. The temperature was then raised to the second-stage heat treatment temperature of 780℃ and held for 1.5 hours. After cooling to room temperature, a high coercivity hot-pressed NdFeB magnet was obtained.

[0256] The magnetic properties of the hot-pressed NdFeB magnets prepared in this comparative example are shown in Table 1.

[0257] Comparative Example 11

[0258] The preparation of the hot-pressed NdFeB magnet in this comparative example includes:

[0259] (1) Same as step (1) in Example 1;

[0260] (2) A grain boundary diffusion source slurry was uniformly coated on four surfaces of a hot-pressed NdFeB magnet substrate with dimensions of 35mm×20mm×4mm (orientation direction) parallel to the orientation direction. The total coating amount of the grain boundary diffusion source slurry was 1wt.%, and the coating amount on each surface was the same. After drying, it was placed in a high-temperature sintering furnace for heat treatment. The temperature was raised to the first-stage heat treatment temperature of 450℃ and held for 3 hours. The temperature was then raised to the second-stage heat treatment temperature of 730℃ and held for 1.5 hours. After cooling to room temperature, a high coercivity hot-pressed NdFeB magnet was obtained.

[0261] The magnetic properties of the hot-pressed NdFeB magnets prepared in this comparative example are shown in Table 1.

[0262] Comparative Example 12

[0263] The preparation of the hot-pressed NdFeB magnet in this comparative example includes:

[0264] (1) Same as step (1) in Example 1;

[0265] (2) A grain boundary diffusion source slurry was uniformly coated on four surfaces of a hot-pressed NdFeB magnet substrate with dimensions of 35mm×20mm×4mm (orientation direction) parallel to the orientation direction. The total coating amount of the grain boundary diffusion source slurry was 1wt.%, and the coating amount on each surface was the same. After drying, it was placed in a high-temperature sintering furnace for heat treatment. The temperature was raised to the first-stage heat treatment temperature of 450℃ and held for 3 hours. The temperature was then raised to the second-stage heat treatment temperature of 780℃ and held for 1.5 hours. After cooling to room temperature, a high coercivity hot-pressed NdFeB magnet was obtained.

[0266] The magnetic properties of the hot-pressed NdFeB magnets prepared in this comparative example are shown in Table 1.

[0267] Comparative Example 13

[0268] The preparation of the hot-pressed NdFeB magnet in this comparative example includes:

[0269] (1) Same as step (1) in Example 1;

[0270] (2) Grain boundary diffusion source slurry was uniformly coated on four surfaces of a hot-pressed NdFeB magnet substrate with dimensions of 35mm×20mm×4mm (orientation direction) parallel to the orientation direction. The total coating amount of the grain boundary diffusion source slurry was 1wt.%, and the coating amount on each surface was the same. After drying, it was placed in a high-temperature sintering furnace for heat treatment. The temperature was raised to the first-stage heat treatment temperature of 730℃ and held for 1.5h. The temperature was then raised to the second-stage heat treatment temperature of 550℃ and held for 3h. After cooling to room temperature, a high coercivity hot-pressed NdFeB magnet was obtained.

[0271] The magnetic properties of the hot-pressed NdFeB magnets prepared in this comparative example are shown in Table 1.

[0272] Comparative Example 14

[0273] The preparation of the hot-pressed NdFeB magnet in this comparative example includes:

[0274] (1) Same as step (1) in Example 1;

[0275] (2) A grain boundary diffusion source slurry was uniformly coated on four surfaces of a hot-pressed NdFeB magnet substrate with dimensions of 35mm×20mm×4mm (orientation direction) parallel to the orientation direction. The total coating amount of the grain boundary diffusion source slurry was 1wt.%, and the coating amount on each surface was the same. After drying, it was placed in a high-temperature sintering furnace for heat treatment. The temperature was raised to the first-stage heat treatment temperature of 550℃ and held for 4.5h. After cooling to room temperature, a high coercivity hot-pressed NdFeB magnet was obtained.

[0276] The magnetic properties of the hot-pressed NdFeB magnets prepared in this comparative example are shown in Table 1.

[0277] Comparative Example 15

[0278] The preparation of the hot-pressed NdFeB magnet in this comparative example includes:

[0279] (1) Same as step (1) in Example 1;

[0280] (2) Grain boundary diffusion source slurry was uniformly coated on four surfaces of a hot-pressed NdFeB magnet substrate with dimensions of 35mm×20mm×4mm (orientation direction) parallel to the orientation direction. The total coating amount of the grain boundary diffusion source slurry was 0.7wt.%, and the coating amount on each surface was the same. After drying, it was placed in a high-temperature sintering furnace for heat treatment. The temperature was raised to the first-stage heat treatment temperature of 550℃ and held for 3 hours. The temperature was then raised to the second-stage heat treatment temperature of 730℃ and held for 1.5 hours. After cooling to room temperature, a high coercivity hot-pressed NdFeB magnet was obtained.

[0281] The magnetic properties of the hot-pressed NdFeB magnets prepared in this comparative example are shown in Table 1.

[0282] Comparative Example 16

[0283] The preparation of the hot-pressed NdFeB magnet in this comparative example includes:

[0284] (1) Same as step (1) in Example 1;

[0285] (2) A grain boundary diffusion source slurry was uniformly coated on four surfaces of a hot-pressed NdFeB magnet substrate with dimensions of 35mm×20mm×4mm (orientation direction) parallel to the orientation direction. The total coating amount of the grain boundary diffusion source slurry was 1.8wt.%, and the coating amount on each surface was the same. After drying, it was placed in a high-temperature sintering furnace for heat treatment. The temperature was raised to the first-stage heat treatment temperature of 550℃ and held for 3 hours. The temperature was then raised to the second-stage heat treatment temperature of 730℃ and held for 1.5 hours. After cooling to room temperature, a high coercivity hot-pressed NdFeB magnet was obtained.

[0286] The magnetic properties of the hot-pressed NdFeB magnets prepared in this comparative example are shown in Table 1.

[0287] Comparative Example 17

[0288] The preparation of the hot-pressed NdFeB magnet in this comparative example includes: (1)

[0290] 70g of first alloy powder Pr with an average particle size of 1.7μm was used. 85 Al9Ga6, 30g of second alloy powder Tb with an average particle size of 2.3μm 90 Al 10 7.5g of binder (titanium dioxide) and 52.5g of solvent (terpineol) were mixed to obtain a grain boundary diffusion source slurry;

[0291] (2) Same as step (2) in Example 1.

[0292] The magnetic properties of the hot-pressed NdFeB magnets prepared in this comparative example are shown in Table 1.

[0293] Comparative Example 18

[0294] The preparation of the hot-pressed NdFeB magnet in this comparative example includes: (1)

[0296] 70g of first alloy powder Pr with an average particle size of 1.7μm was used. 85 Al9Ga6, 30g of second alloy powder Tb with an average particle size of 1.7μm 90 Al 10 7.5g of binder (titanium dioxide) and 52.5g of solvent (terpineol) were mixed to obtain a grain boundary diffusion source slurry;

[0297] (2) Same as step (2) in Example 1.

[0298] The magnetic properties of the hot-pressed NdFeB magnets prepared in this comparative example are shown in Table 1.

[0299] Comparative Example 19

[0300] The preparation of the hot-pressed NdFeB magnet in this comparative example includes:

[0301] (1) Same as step (1) in Example 1;

[0302] (2) Grain boundary diffusion source slurry was uniformly coated on four surfaces of a hot-pressed NdFeB magnet substrate with dimensions of 35mm×20mm×4mm (orientation direction) parallel to the orientation direction. The total coating amount of the grain boundary diffusion source slurry was 1wt.%, and the coating amount on each surface was the same. After drying, it was placed in a high-temperature sintering furnace for heat treatment. The temperature was raised to the first-stage heat treatment temperature of 550℃ and held for 3 hours. After cooling to room temperature, the temperature was raised to the second-stage heat treatment temperature of 730℃ and held for 1.5 hours. After cooling to room temperature, a high coercivity hot-pressed NdFeB magnet was obtained.

[0303] The magnetic properties of the hot-pressed NdFeB magnets prepared in this comparative example are shown in Table 1.

[0304] Comparative Example 20

[0305] The preparation of the hot-pressed NdFeB magnet in this comparative example includes:

[0306] (1) Same as step (1) in Example 1;

[0307] (2) Grain boundary diffusion source slurry was uniformly coated on two pressing surfaces of a hot-pressed NdFeB magnet substrate with dimensions of 35mm×20mm×4mm (orientation direction) perpendicular to the orientation direction. The total coating amount of the grain boundary diffusion source slurry was 1wt.%, and the coating amount on each surface was the same. After drying, it was placed in a high-temperature sintering furnace for heat treatment. The temperature was raised to the first-stage heat treatment temperature of 550℃ and held for 3 hours. After cooling to room temperature, the temperature was raised to the second-stage heat treatment temperature of 730℃ and held for 1.5 hours. After cooling to room temperature, a high coercivity hot-pressed NdFeB magnet was obtained.

[0308] The magnetic properties of the hot-pressed NdFeB magnets prepared in this comparative example are shown in Table 1.

[0309] Table 1. Magnetic Performance Data of Hot-Pressed NdFeB Magnets

[0310]

[0311]

[0312] As can be seen from the above, the present invention coats the surface of a hot-pressed NdFeB magnet substrate without heavy rare earth elements with a grain boundary diffusion source slurry comprising a first alloy powder Pr-Al-Ga and a second alloy powder HR-Al in the parallel orientation direction. First, a low-temperature, short-time first-stage heat treatment is performed to liquefy the grain boundary phase, allowing the diffusion source to enter the interior of the magnet. Then, a high-temperature, long-time second-stage heat treatment is performed directly to promote the penetration depth of the diffusion source. This process not only inhibits the growth of the main phase grains but also improves the coercivity of the magnet.

[0313] If the first-stage heat treatment temperature is too low or the time is too short, the grain boundary phase will not liquefy completely, and the diffusion source inside the magnet will accumulate on the surface. If the second-stage heat treatment temperature is too high or the time is too long, the main phase grains will grow. If the order of the two-stage heat treatment is reversed, the main phase grains will grow, and the penetration depth of the diffusion source will be affected.

[0314] Secondly, the mass ratio of the first alloy powder Pr-Al-Ga and the second alloy powder HR-Al in the grain boundary diffusion source slurry is (60-90):(40-10), controlling the melting point of the mixed grain boundary diffusion source powder to be 500-550℃. Using a single first alloy powder or second alloy powder as the grain boundary diffusion source powder causes changes in melting point, affecting the heat treatment effect and thus affecting the magnetic properties of the magnet. Furthermore, the average particle size of the first alloy powder is greater than that of the second alloy powder, forming a multi-scale diffusion channel and constructing a gradient diffusion system.

[0315] Furthermore, unlike the traditional method of coating on the pressed surface of the magnet substrate, which has strict requirements on the thickness of the magnet substrate (the distance between the upper and lower pressed surfaces), the present invention significantly reduces the size requirements of the hot-pressed NdFeB magnet substrate, which is beneficial for the preparation and application of large-size hot-pressed NdFeB magnets.

[0316] In summary, this invention employs grain boundary diffusion technology, constructing a bicomponent diffusion source with a melting gradient by combining low-melting-point Pr-Al-Ga alloy with high-melting-point HR-Al alloy powder, thereby lowering the melting point to a critical range of 500–550°C. This temperature window is lower than the critical temperature (~600°C) for the abnormal growth of nanocrystals in hot-pressed NdFeB magnets, thus suppressing grain coarsening in the early stages of diffusion. Combined with a unique stepped heat treatment process, heavy rare earth elements are first driven to penetrate inward along liquefied grain boundary channels at 500–600°C, followed by a short-term high-temperature treatment at 700–760°C to promote their deep migration and uniform distribution. Ultimately, a highly anisotropic magnetized shell is formed on the surface of the main phase grains, significantly improving coercivity.

[0317] The method of this invention is applicable to heavy rare earth magnet substrates, achieving high performance while reducing dependence on expensive heavy rare earth elements and production costs. Its process is stable and controllable, ensuring uniform performance of large-size magnets and also suitable for efficient mass production of small-size products, providing key technical support for the large-scale application of high-performance hot-pressed NdFeB magnets.

[0318] All aspects, embodiments, and features of this invention should be considered illustrative in all respects and not limiting of the invention; the scope of the invention is defined only by the claims. Other embodiments, modifications, and uses will become apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.

[0319] In the preparation method of this invention, the order of the steps is not limited to the listed order. For those skilled in the art, variations in the order of the steps without creative effort are also within the scope of protection of this invention. Furthermore, two or more steps or actions can be performed simultaneously.

[0320] Finally, it should be noted that the specific embodiments described herein are merely illustrative examples of the invention and are not intended to limit the implementation of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them; it is neither necessary nor possible to exemplify all embodiments here. However, these obvious variations or modifications derived from the essential spirit of the invention still fall within the scope of protection of the invention, and interpreting them as any additional limitation would contradict the spirit of the invention.

Claims

1. A method for preparing a high-coercivity hot-pressed NdFeB magnet, characterized in that, include: (1) Prepare a grain boundary diffusion source slurry by mixing the grain boundary diffusion source powder; The grain boundary diffusion source mixed powder comprises a first alloy powder and a second alloy powder in a mass ratio of (60~90):(40~10); The chemical formula of the first alloy powder, by mass percentage, is Pr. x Al y Ga 100-x-y Where 70≤x≤90, 2≤y≤15; The chemical formula of the second alloy powder, by mass percentage, is HR. 100-z Al z , where HR is one or both of Dy and Tb, and 5≤z≤15; (2) A grain boundary diffusion source slurry is coated onto the surface of the hot-pressed NdFeB magnet substrate to be diffused, wherein the surface to be diffused is parallel to the orientation direction, and the coating amount of the grain boundary diffusion source slurry is 0.6~2.4wt%; Then, heat treatment is performed, which includes a first-stage heat treatment and a second-stage heat treatment. The first stage of heat treatment is carried out at a temperature of 500~600℃ for 1.5~6 hours. The second stage of heat treatment is performed at a temperature of 700~760℃ for a time of 0.5~4h.

2. The method for preparing a high coercivity hot-pressed NdFeB magnet according to claim 1, characterized in that, The melting point of the grain boundary diffusion source mixed powder is 500~550℃.

3. The method for preparing a high coercivity hot-pressed NdFeB magnet according to claim 1, characterized in that, The mass ratio of the first alloy powder to the second alloy powder is (60~80):(40~20).

4. The method for preparing a high coercivity hot-pressed NdFeB magnet according to claim 1, characterized in that, The average particle size of the first alloy powder is 1~5μm, and the average particle size of the second alloy powder is 0.1~5μm.

5. The method for preparing a high coercivity hot-pressed NdFeB magnet according to claim 1, characterized in that, The grain boundary diffusion source slurry comprises 50-80 wt% grain boundary diffusion source mixed powder, 1-10 wt% binder and 20-40 wt% solvent; The adhesive includes one or more of hydroxyethyl cellulose, titanium dioxide, acrylic resin, polyacrylic acid, and polymethyl methacrylate; The solvent includes one or more of ethanol, butyl acetate, acetone, methanol, terpineol, menthol, geraniol, and nerol.

6. The method for preparing a high coercivity hot-pressed NdFeB magnet according to claim 1, characterized in that, The temperature of the first stage heat treatment is 530~580℃ and the time is 2~4h; the temperature of the second stage heat treatment is 720~740℃ and the time is 1~2h.

7. The method for preparing a high coercivity hot-pressed NdFeB magnet according to claim 1, characterized in that, The time for the first stage heat treatment is greater than the time for the second stage heat treatment; the temperature for the second stage heat treatment is greater than the temperature for the first stage heat treatment, and the difference between the two is 150~200℃.

8. The method for preparing a high coercivity hot-pressed NdFeB magnet according to claim 1, characterized in that, The hot-pressed NdFeB magnet matrix comprises R, T, M, and B elements, with the following content by mass percentage: 27wt%≤R≤33wt%; 0.8wt%≤B≤1.2wt%; 0wt%≤M≤6wt%; 60wt%≤T≤75wt%; Wherein, R is a rare earth element, and includes at least one light rare earth element; M includes one or more of Al, Cu, Ga, Nb, Ti, V, Zr, Mo, and Sn; T includes Fe and / or Co.

9. The method for preparing a high coercivity hot-pressed NdFeB magnet according to claim 1, characterized in that, During the heat treatment process, the grain boundary phase in the hot-pressed NdFeB magnet matrix liquefies to form channels, and the grain boundary diffusion source penetrates into the interior of the hot-pressed NdFeB magnet matrix along the channels and is distributed in the channels formed by the liquefaction of the grain boundary phase.

10. A high coercivity hot-pressed NdFeB magnet, characterized in that, It is prepared by the method for preparing high coercivity hot-pressed neodymium iron boron magnets as described in any one of claims 1 to 9.

11. The high coercivity hot-pressed NdFeB magnet according to claim 10, characterized in that, The high coercivity hot-pressed NdFeB magnet comprises a main phase grain and a grain boundary phase, wherein the grain boundary phase includes (Nd, Dy)₂Fe. 14 Phase B and / or (Nd, Tb) 2Fe 14 Phase B.

12. The high coercivity hot-pressed NdFeB magnet according to claim 10, characterized in that, The high coercivity hot-pressed NdFeB magnet comprises a magnet matrix and a diffusion alloy between the matrix and the matrix.

13. The high coercivity hot-pressed NdFeB magnet according to claim 12, characterized in that, The diffusion alloy is formed by the diffusion of a grain boundary source into the channels formed by the liquefaction of the grain boundary phase.

14. The high coercivity hot-pressed NdFeB magnet according to claim 10, characterized in that, The coercivity of the high coercivity hot-pressed NdFeB magnet is >20kOe.

15. The high coercivity hot-pressed NdFeB magnet according to claim 10, characterized in that, The coercivity of the high-coercivity hot-pressed NdFeB magnet is greater than that of the hot-pressed NdFeB magnet matrix, and the difference is greater than 5 kOe.

16. The high coercivity hot-pressed NdFeB magnet according to claim 10, characterized in that, The performance consistency of the high coercivity hot-pressed NdFeB magnet is ≤3%.

17. An application of a high-coercivity hot-pressed NdFeB magnet in the fields of new energy vehicles, industrial robots, and aerospace technology, characterized in that, The high coercivity hot-pressed NdFeB magnet is the high coercivity hot-pressed NdFeB magnet prepared by the preparation method of the high coercivity hot-pressed NdFeB magnet according to any one of claims 1 to 9, or the high coercivity hot-pressed NdFeB magnet according to any one of claims 10 to 16.

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