Sintered neodymium-iron-boron magnet and method for producing the same

Abstract

The present disclosure relates to a sintered neodymium-iron-boron magnet and a method for preparing the same, the magnet comprising a main phase and a grain boundary phase, a ratio of an average grain size of a surface layer of the magnet to an average grain size of a central region of the magnet being 1.05-1.35; wherein the surface layer of the magnet refers to a region at a distance of 35 μm or less from a surface of the magnet; and the central region of the magnet refers to a region at a distance of 500 μm or more from the surface of the magnet. The sintered neodymium-iron-boron magnet has a sum of a maximum magnetic energy product (BH)max and an intrinsic coercivity HcJ of greater than 80; and a remanence Br of greater than 13 KGs; the maximum magnetic energy product (BH)max has a unit of MGOe, and the intrinsic coercivity HcJ has a unit of KOe.

Description

Technical Field

[0001] This disclosure relates to the field of rare earth magnets, and more specifically, to a sintered NdFeB magnet and its preparation method. Background Technology

[0002] Sintered NdFeB magnets are widely used in fields such as electronics, medical care, transportation, wind power generation, and aerospace due to their excellent comprehensive magnetic properties. In recent years, with the implementation of my country's plans and policies to vigorously develop clean and green new energy, the market demand for sintered NdFeB magnets, as a key link in the new energy industry chain, has been increasing, especially with the development of high-speed motors and their application in the field of electric vehicles.

[0003] Currently, there are two main methods to improve the overall performance of sintered NdFeB magnets:

[0004] One approach involves adding heavy rare earth element Dy(Tb) to the raw materials during smelting. The light rare earth elements (mainly Nd and Pr) in the main phase are replaced by the heavy rare earth element Dy(Tb), thereby enhancing coercivity by increasing the anisotropy field of the grains. CN103887028A discloses a method to obtain ultra-high performance sintered NdFeB magnets with (BH)max(MGOe)+HcJ(KOe)≥70 by controlling the composition formula, adding 2.0-13.5wt% of Dy and Tb elements during raw material smelting, and simultaneously controlling process conditions to optimize the boundary rare earth-rich phase and microstructure.

[0005] Another approach is grain boundary diffusion, which not only preserves the remanence of the magnet but also allows for the production of magnets with the same coercivity as those produced by traditional direct alloying methods using lower concentrations of heavy rare earth elements (HREEs). Furthermore, it significantly improves the overall magnetic properties of the magnet. However, current grain boundary diffusion processes primarily rely on concentration gradients to drive the diffusion of HREEs. Because the concentration of HREEs on the magnet's surface is high while the concentration inside is low, the effective diffusion depth is limited, and the distribution of HREEs is prone to unevenness, thus affecting the overall magnetic properties of the magnet. Additionally, due to insufficient diffusion driving force, strict size control is required for the processed samples, generally limiting it to thin-film magnets with a thickness of less than 5 mm.

[0006] Therefore, there is a need to find a grain boundary diffusion method that can increase the diffusion depth, improve the utilization rate of heavy rare earth elements, overcome the limitations of the current grain boundary diffusion process, and significantly improve the overall magnetic properties of the magnet. Summary of the Invention

[0007] The purpose of this disclosure is to provide a sintered NdFeB magnet and a method for preparing the same. This method can promote the diffusion of heavy rare earth elements into the central region of the sintered magnet during the grain boundary diffusion process, thereby further improving the overall magnetic properties of the sintered NdFeB magnet.

[0008] To achieve the above objectives, the first aspect of this disclosure provides a sintered NdFeB magnet, which includes a main phase and a grain boundary phase, wherein the ratio of the average grain size of the magnet surface layer to the average grain size of the magnet central region is 1.05 to 1.35.

[0009] The magnet surface layer refers to the area less than 35 μm from the magnet surface; the magnet center region refers to the area more than 500 μm from the magnet surface.

[0010] The sintered NdFeB magnet contains 29.2-32.5 wt% R, 0.87-0.93 wt% B, 0.3-0.55 wt% Ga, 0.10-0.65 wt% M, and the balance T;

[0011] Wherein, R is a rare earth element, which is Nd, or a combination of Nd and at least one element from the group consisting of Y, La, Ce, Pr, Sm, Eu, Gd, Ho, Er, Tm, Yb, Dy, Tb and Lu. Based on the total weight of the sintered NdFeB magnet, the content of RE is 0.5 to 6.5 wt%, and RE is Dy and / or Tb.

[0012] M is selected from at least one of Cu, Al, Zr, Nb, Mn, Mg, Si, Cr, and Ti;

[0013] T is Fe, or a mixture of Fe and Co, wherein the Fe content in T is more than 80 wt%.

[0014] Optionally, the grain boundary phase includes a triangular grain boundary phase; among the triangular grain boundary phases, the number of small-area triangular grain boundary phases accounts for more than 80% of the total number of all triangular grain boundary phases; the small-area triangular grain boundary phases have an area of ​​less than 2.5 μm. 2 The triangular grain boundary phase.

[0015] Optionally, the sum of the maximum energy product (BH)max and the intrinsic coercivity HcJ of the sintered NdFeB magnet is greater than 80; and the remanence Br is greater than 13 KGs; the unit of the maximum energy product (BH)max is MGOe, and the unit of the intrinsic coercivity HcJ is KOe.

[0016] Optionally, the ratio of the average grain size of the magnet surface layer to the average grain size of the magnet central region is 1.13 to 1.35; the O content in the sintered NdFeB magnet is less than 600 ppm.

[0017] The second aspect of this disclosure provides a method for preparing sintered NdFeB magnets, the method comprising the following steps:

[0018] S1. Preparation of sintered NdFeB magnet substrate;

[0019] S2. A diffusion source containing RE is attached to the surface of the sintered NdFeB magnet substrate, followed by grain boundary diffusion treatment and tempering treatment; RE is Dy and / or Tb;

[0020] The grain boundary diffusion treatment includes an initial diffusion heat treatment and an N-stage diffusion process segment, where N≥1. Each stage of the diffusion process segment includes, in sequence, a high-temperature diffusion heat treatment and a low-temperature diffusion heat treatment.

[0021] The initial diffusion heat treatment conditions include: a temperature of 800–980°C and a time of 6–12 hours;

[0022] The conditions for the low-temperature diffusion heat treatment include: a temperature of 850–950°C and a time of 6–12 hours.

[0023] The temperature of the high-temperature diffusion heat treatment is lower than that of the sintering treatment, and 50 to 200°C higher than that of the low-temperature diffusion heat treatment, and the time is 2 to 8 hours.

[0024] The sintered NdFeB magnet substrate obtained in step S1 contains 28.9-32.5 wt% R, 0.87-0.93 wt% B, 0.3-0.55 wt% Ga, 0.10-0.65 wt% M, and the balance T;

[0025] Wherein, R is a rare earth element, the rare earth element is Nd, or a combination of Nd and at least one element from the group below: Y, La, Ce, Pr, Sm, Eu, Gd, Ho, Er, Tm, Yb, Dy, Tb and Lu, and the content of RE is 0.5 to 6.5 wt% based on the total weight of the sintered NdFeB magnet substrate, and RE is Dy and / or Tb;

[0026] M is selected from at least one of Cu, Al, Zr, Nb, Mn, Mg, Si, Cr, and Ti;

[0027] T is Fe, or a mixture of Fe and Co, wherein the Fe content in T is more than 80 wt%.

[0028] Optionally, in step S1, the sintered NdFeB magnet substrate is prepared using the following steps:

[0029] S01. The alloy raw materials are placed in a vacuum induction furnace for melting and casting to obtain alloy fast-solidification sheets;

[0030] S02. After hydrogen crushing treatment of the alloy quick-setting sheet, alloy hydrogenated powder is obtained.

[0031] S03. After micronizing the alloy hydrogenation powder, alloy micro powder is obtained;

[0032] S04. After the alloy micro powder is placed in a magnetic field for orientation forming, the resulting pressed blank is sintered and machined in a vacuum environment to obtain the sintered NdFeB magnet substrate.

[0033] Optionally, in step S01, R1-T1-B-Ga-M1 main alloy rapid solidification sheet and R2-T2-M2 auxiliary alloy rapid solidification sheet are prepared by a dual alloying method.

[0034] The R1-T1-B-Ga-M1 main alloy rapid solidification sheet contains 28.9-32.5 wt% R1, 0.87-0.93 wt% B, 0.3-0.55 wt% Ga, 0.10-0.65 wt% M1 and the balance T1;

[0035] Wherein, R1 is a rare earth element, which is Nd, or a combination of Nd and at least one element from the group consisting of Y, La, Ce, Pr, Sm, Eu, Gd, Ho, Er, Tm, Yb, Dy, Tb and Lu; M1 is selected from at least one of Cu, Al, Zr, Nb, Mn, Mg, Si, Cr and Ti; T1 is Fe or a mixture of Fe and Co;

[0036] The RE1 content in the R1-T1-B-Ga-M1 main alloy rapid solidification sheet is 0.5-5.2 wt%, and RE1 is Dy and / or Tb;

[0037] The R2-T2-M2 auxiliary alloy quick-setting sheet contains 60-85 wt% R2, 3.0-6.0 wt% M2 and the balance T2;

[0038] Wherein, R2 is selected from one or more of Nd, Pr, Dy and Tb, M2 is selected from at least one of Ga, Cu and Al, and T2 is Fe or a mixture of Fe and Co;

[0039] The RE2 content in the R2-T2-M2 auxiliary alloy quick-setting sheet is 0-80 wt%, and RE2 is Dy and / or Tb;

[0040] The thickness of the R1-T1-B-Ga-M1 main alloy quick-setting sheet and the R2-T2-M2 auxiliary alloy quick-setting sheet are each independently 0.13-0.46 mm.

[0041] Optionally, in step S02, the method for preparing the alloy hydrogenation powder includes:

[0042] The main alloy hydrogenated powder is obtained by hydrogenating the R1-T1-B-Ga-M1 main alloy quick-solidifying sheet and the auxiliary alloy hydrogenated powder is obtained by hydrogenating the R2-T2-M2 auxiliary alloy quick-solidifying sheet. The main alloy hydrogenated powder and the auxiliary alloy hydrogenated powder are then mixed to obtain the alloy hydrogenated powder.

[0043] In the alloy hydrogenation powder, the mass content of the main alloy hydrogenation powder is more than 95%, and the mass content of the auxiliary alloy hydrogenation powder is less than 5%.

[0044] Optionally, the temperature of the high-temperature diffusion heat treatment is 96%-99% of the sintering temperature; the diffusion source containing RE includes one or more of RE oxides, RE fluorides, elemental RE, or RE alloys.

[0045] The RE-containing diffusion source contains 60-100 wt% RE.

[0046] The third aspect of this disclosure provides a sintered NdFeB magnet prepared by the method described in the second aspect, wherein the sum of the maximum energy product (BH)max and the intrinsic coercivity HcJ of the sintered NdFeB magnet is greater than 80; and the remanence Br is greater than 13 kgs; wherein the unit of the maximum energy product (BH)max is MGOe, and the unit of the intrinsic coercivity HcJ is KOe.

[0047] Through the above technical solution, the sintered NdFeB magnet of this disclosure has a high content of small-area triangular grain boundary phases, which improves the coercivity and remanence of the magnet. Furthermore, the larger grain size on the magnet surface helps to weaken the effect of demagnetization coupling on the surface region, allowing more heavy rare earth elements to diffuse towards the center without reducing the surface coercivity, forming a thicker high-coercivity region and improving the overall coercivity distribution. The sintered NdFeB magnet of this disclosure has relatively balanced remanence and intrinsic coercivity, representing a high-performance magnet with a further increased sum of maximum energy product and intrinsic coercivity.

[0048] The preparation method disclosed herein employs a diffusion heat treatment process including an N-stage diffusion stage. The low-temperature diffusion heat treatment enables heavy rare earth elements from the diffusion source to diffuse along the grain boundaries of the substrate and effectively concentrate them within a narrow area near the grain boundaries, thereby increasing the coercivity (HcJ) of the magnet and reducing the loss of remanence (Br). The high-temperature diffusion heat treatment process, without reducing the surface coercivity, allows more heavy rare earth elements to diffuse towards the center, increasing the diffusion depth and forming a thicker high-coercivity region, thus improving the overall coercivity distribution. This method can reduce the amount of rare earth elements used and is simple to operate and easy to control, making it suitable for large-scale production.

[0049] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0050] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings:

[0051] Figure 1 This is a flow chart of the grain boundary diffusion process of one specific embodiment of the method for preparing sintered NdFeB magnets disclosed herein.

[0052] Figure 2 This is a SEM image of a sintered NdFeB magnet substrate before diffusion in one specific embodiment of the method for preparing sintered NdFeB magnets disclosed herein.

[0053] Figure 3 This is a SEM image of the surface layer of a sintered NdFeB magnet prepared after diffusion in one specific embodiment of the method for preparing sintered NdFeB magnets disclosed herein.

[0054] Figure 4 This is a distribution diagram of Tb elements at different depths from the magnet surface in the grains and grain edges + grain boundary phases in a specific embodiment of the sintered NdFeB magnet disclosed herein.

[0055] Figure 5 This is a test diagram of the average grain size of a portion of the sintered NdFeB magnet prepared after diffusion in one specific embodiment of the sintered NdFeB magnet disclosed herein. Detailed Implementation

[0056] The specific embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this disclosure.

[0057] The first aspect of this disclosure provides a sintered NdFeB magnet, which includes a main phase and a grain boundary phase, wherein the ratio of the average grain size of the surface layer of the magnet to the average grain size of the central region of the magnet is 1.05 to 1.35.

[0058] In this disclosure, "magnet surface" refers to the region at a distance of 35 μm or less from the magnet surface. This can be understood as the set of locations within the magnet at a distance of 35 μm or less from any surface. "Magnet center region" refers to the region at a distance of 500 μm or more from the magnet surface, again referring to the set of locations within the magnet at a distance of 500 μm or more from any surface.

[0059] In one specific embodiment of this disclosure, the sintered NdFeB magnet contains 29.2-32.5 wt% R, 0.87-0.93 wt% B, 0.3-0.55 wt% Ga, 0.10-0.65 wt% M, and the balance T; preferably, the sintered NdFeB magnet contains 29.2-31.5 wt% R, 0.88-0.92 wt% B, 0.35-0.5 wt% Ga, 0.1-0.4 wt% M, and the balance T. Wherein, R is a rare earth element, wherein the rare earth element is Nd, or a combination of Nd and at least one element from the group consisting of Y, La, Ce, Pr, Sm, Eu, Gd, Ho, Er, Tm, Yb, Dy, Tb and Lu, and the content of RE is 0.5 to 6.5 wt% based on the total weight of the sintered NdFeB magnet, wherein RE is Dy and / or Tb; M is selected from at least one of Cu, Al, Zr, Nb, Mn, Mg, Si, Cr and Ti; T is Fe, or a mixture of Fe and Co, wherein the content of Fe in T is 80 wt% or more. In a preferred embodiment of this disclosure, the content of B can be 0.87wt%, 0.90wt%, 0.91wt%, 0.915wt%, 0.92wt%, 0.93wt%, or any value between two of them; the content of Ga can be 0.30wt%, 0.35wt%, 0.40wt%, 0.45wt%, 0.50wt%, 0.55wt%, or any value between two of them; the content of R can be 29.5wt%, 30.0wt%, 30.5wt%, 31.0wt%, 31.5wt%, or any value between two of them; and the content of M can be 0.10wt%, 0.15wt%, 0.20wt%, 0.25wt%, 0.30wt%, 0.35wt%, 0.40wt%, or any value between two of them.

[0060] In the above embodiments, the appropriate content of R in the sintered NdFeB magnet can prevent the precipitation of the α-Fe phase during the cooling process of the alloy liquid during smelting, thereby reducing the remanence Br and coercivity HcJ of the sintered NdFeB magnet; and it also avoids the waste of resources caused by excessive use of rare earth elements. The inclusion of an appropriate amount of B in the sintered NdFeB magnet is beneficial for the formation of the R2Fe14B main phase, avoiding the formation of the R2T17 phase which would reduce the proportion of the main phase, and can further improve the coercivity HcJ and remanence Br of the magnet; it also avoids the formation of a B-rich phase at the grain boundaries of the magnet, further improving the magnetic properties of the magnet. The inclusion of an appropriate amount of Ga in the sintered NdFeB magnet can further improve the temperature coefficient, which is beneficial for increasing the formation of the RT-Ga phase at high temperatures and reducing the R2T17 phase, thereby further improving the coercivity HcJ and remanence Br.

[0061] The grain boundary phases of the sintered NdFeB magnets prepared in this disclosure include triangular grain boundary phases, and the number of small-area triangular grain boundary phases accounts for more than 80% of the total number of triangular grain boundary phases. Increasing the proportion of small-area triangular grain boundary phases can improve the intrinsic coercivity HcJ and remanence Br of the sintered NdFeB magnets. By adjusting the ratio of the average grain size of the magnet surface layer to the average grain size of the magnet central region, the distribution of intrinsic coercivity HcJ can be improved. In this disclosure, the "small-area triangular grain boundary phase" refers to a phase with an area less than 2.5 μm. 2 The triangular grain boundary phase.

[0062] The sum of the maximum magnetic energy product (BH)max and the intrinsic coercivity HcJ of the sintered NdFeB magnet prepared by this disclosure is greater than 80; and the remanence Br is greater than 13 KGs; the unit of the maximum magnetic energy product (BH)max of the magnet is MGOe, and the unit of the intrinsic coercivity HcJ is KOe.

[0063] In a preferred embodiment of this disclosure, the ratio of the average grain size of the magnet surface layer to the average grain size of the magnet central region is 1.13 to 1.35, for example, it can be 1.13, 1.15, 1.20, 1.25, 1.30, 1.35, or any value between two of them.

[0064] In one specific embodiment of this disclosure, the O content in the sintered NdFeB magnet is less than 600 ppm, which helps to maintain the main phase content, avoid the appearance of the α-Fe phase, and further improve the coercivity HcJ of the magnet.

[0065] The second aspect of this disclosure provides a method for preparing sintered NdFeB magnets, the method comprising the following steps: S1, preparing a sintered NdFeB magnet substrate; S2, attaching a diffusion source containing RE to the surface of the sintered NdFeB magnet substrate, and then performing grain boundary diffusion treatment and tempering treatment; wherein RE is Dy and / or Tb.

[0066] In this disclosure, in step S1, the thickness of the prepared sintered NdFeB magnet substrate can vary within a wide range. Specifically, the thickness of the sintered NdFeB magnet substrate in the magnetization direction is 1-15 mm, for example, 3 mm, 5 mm, 10 mm, or 15 mm. Here, "magnetization direction" refers to the direction in which the diffusion source containing heavy rare earth elements diffuses from the surface of the sintered NdFeB magnet substrate towards the grain boundaries within the sintered NdFeB magnet substrate. The concentration of heavy rare earth elements has a gradient along the thickness direction. The "method of attaching a diffusion source containing RE" can employ conventional techniques in the art, such as vacuum evaporation, impregnation, magnetron sputtering, ion plating, etc., with magnetron sputtering being preferred.

[0067] In one specific embodiment of this disclosure, the grain boundary diffusion treatment includes an initial diffusion heat treatment and an N-stage diffusion process segment, where N≥1. Each stage of the diffusion process segment sequentially includes a high-temperature diffusion heat treatment and a low-temperature diffusion heat treatment. The conditions for the initial diffusion heat treatment include a temperature of 800–980°C and a time of 6–12 hours. The conditions for the low-temperature diffusion heat treatment include a temperature of 850–950°C, for example, 850°C, 900°C, 950°C, or any value between these two, and a time of 6–12 hours, for example, 8 hours. The temperature of the high-temperature diffusion heat treatment is lower than the sintering temperature and 50–200°C higher than the temperature of the low-temperature diffusion heat treatment, and the time is 2–8 hours. In a preferred specific embodiment of this disclosure, the temperature of the high-temperature diffusion treatment can be 50°C, 60°C, 80°C, 100°C, 120°C, 140°C, 160°C, 180°C, 200°C higher than the temperature of the low-temperature diffusion heat treatment, or any value between these two.

[0068] In one specific embodiment of this disclosure, the sintered NdFeB magnet substrate obtained in step S1 comprises 28.9-32.5 wt% R, 0.87-0.93 wt% B, 0.3-0.55 wt% Ga, 0.10-0.65 wt% M, and the balance T; wherein R is a rare earth element, the rare earth element being Nd, or a combination of Nd and at least one element from the group consisting of Y, La, Ce, Pr, Sm, Eu, Gd, Ho, Er, Tm, Yb, Dy, Tb, and Lu, and the content of RE is 0.5-6.5 wt% based on the total weight of the sintered NdFeB magnet substrate, and RE is Dy and / or Tb; M is selected from at least one of Cu, Al, Zr, Nb, Mn, Mg, Si, Cr, and Ti; T is Fe, or a mixture of Fe and Co, wherein the content of Fe in T is 80 wt% or more.

[0069] This disclosure employs a diffusion heat treatment method including an N-stage diffusion process. Based on the compositional characteristics and performance requirements of the sintered NdFeB magnet, preferably, an N-stage diffusion process can be performed, for example, N≥2. In one specific embodiment of this disclosure, the N-stage diffusion occurs more than twice, with each stage sequentially including a high-temperature diffusion heat treatment and a low-temperature diffusion heat treatment. Preferably, before the low-temperature diffusion heat treatment in each stage, an attachment diffusion source is applied. The low-temperature diffusion causes the heavy rare earth elements in the diffusion source to diffuse along the grain boundaries of the substrate and effectively concentrate within a narrow area near the grain boundaries. After the N-stage diffusion heat treatment based on the initial diffusion heat treatment, the surface grains of the substrate magnet grow to a certain extent. The larger grain size reduces the number of grain boundary phases required to increase inter-grain demagnetization coupling in the surface region of the magnet. Therefore, the heavy rare earth elements enriched in the surface grain boundaries diffuse towards the central region of the magnet, increasing the diffusion depth and forming a thicker, high-coercivity region. This improves the overall coercivity distribution without reducing the surface coercivity. At the same time, the high-temperature diffusion process promotes the generation of more liquid phases and creates more liquid phase channels, which allows the heavy rare earth elements enriched in the grain boundaries to diffuse further into the central region of the magnet, increasing the diffusion depth.

[0070] In one specific embodiment of this disclosure, step S2 includes the following tempering conditions: a tempering temperature of 450-690°C, for example, 500-535°C; and a tempering time of 0.5-5 hours, for example, 2 hours. The method further includes rapid cooling after tempering to cool the sintered body to below 400°C; the rapid cooling rate can be 6-30°C / min, preferably 8-20°C / min. In the above preferred embodiment, rapid cooling can effectively suppress the segregation of the ferromagnetic phase in the grain boundary phase, thereby improving the coercivity of the magnet.

[0071] In one specific embodiment of this disclosure, the sintered NdFeB magnet substrate is prepared in step S1 using the following steps: S01, alloy raw materials are melted and cast in a vacuum induction furnace to obtain alloy quick-setting sheets; S02, the alloy quick-setting sheets are subjected to hydrogen crushing treatment to obtain alloy hydrogenated powder; S03, the alloy hydrogenated powder is subjected to micro-pulverization treatment to obtain alloy micro powder; S04, the alloy micro powder is placed in a magnetic field for orientation forming treatment, and the resulting formed blank is sintered and machined in a vacuum environment to obtain the sintered NdFeB magnet substrate.

[0072] In one specific embodiment of this disclosure, in step S01, a main alloy rapid-solidification sheet (R1-T1-B-Ga-M1) and an auxiliary alloy rapid-solidification sheet (R2-T2-M2) are prepared by a dual alloying method. The main alloy rapid-solidification sheet (R1-T1-B-Ga-M1) comprises 28.9-32.5 wt% R1, 0.87-0.93 wt% B, 0.3-0.55 wt% Ga, 0.10-0.65 wt% M1, and the balance T1. R1 is a rare earth element, specifically Nd, or a combination of Nd with at least one element from the group consisting of Y, La, Ce, Pr, Sm, Eu, Gd, Ho, Er, Tm, Yb, Dy, Tb, and Lu. M1 is selected from at least one of Cu, Al, Zr, Nb, Mn, Mg, Si, Cr, and Ti. T1 is Fe or a mixture of Fe and Co.

[0073] In a preferred embodiment of this disclosure, the content of R1 can be 29.0 wt%, 29.5 wt%, 30.0 wt%, 30.5 wt%, 31.0 wt%, 31.5 wt%, 32.0 wt%, 32.5 wt%, or any value between two of them; the content of B can be 0.87 wt%, 0.90 wt%, 0.91 wt%, 0.915 wt%, 0.92 wt%, 0.93 wt%, or any value between two of them; the content of Ga can be 0.30 wt%, 0.35 wt%, 0.40 wt%, 0.45 wt%, 0.50 wt%, 0.55 wt%, or any value between two of them. The content of M1 can be 0.10wt%, 0.15wt%, 0.20wt%, 0.25wt%, 0.30wt%, 0.35wt%, 0.40wt%, 0.45wt%, 0.50wt%, 0.55wt%, 0.60wt%, 0.65wt%, or any value between these two.

[0074] In one specific embodiment of this disclosure, the RE1 content in the R1-T1-B-Ga-M1 main alloy rapid solidification sheet is 0.5-5.2 wt%, and RE1 is Dy and / or Tb; for example, the RE1 content can be 0.5 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, 3.0 wt%, 3.5 wt%, 4.0 wt%, 4.5 wt%, 5.0 wt%, or any value between two of them.

[0075] In one specific embodiment of this disclosure, the R2-T2-M2 auxiliary alloying rapid-setting sheet comprises 60-85 wt% R2, 3.0-6.0 wt% M2, and the balance T2; wherein R2 is selected from one or more of Nd, Pr, Dy, and Tb, M2 is selected from at least one of Ga, Cu, and Al; T2 is Fe, or a mixture of Fe and Co; in a preferred specific embodiment of this disclosure, the content of R2 can be 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, 85 wt%, or any value between two of them; the content of M2 can be 3.0 wt%, 3.5 wt%, 4.0 wt%, 4.5 wt%, 5.0 wt%, 5.5 wt%, 6.0 wt%, or any value between two of them.

[0076] In a preferred embodiment of this disclosure, the RE2 content in the R2-T2-M2 auxiliary alloy quick-setting sheet is 0-80 wt%, and RE2 is Dy and / or Tb; for example, the RE2 content can be 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt%, or any value between two of them.

[0077] In one specific embodiment of this disclosure, the thickness of the R1-T1-B-Ga-M1 main alloy quick-setting sheet and the R2-T2-M2 auxiliary alloy quick-setting sheet are each independently 0.13-0.46 mm.

[0078] In one specific embodiment of this disclosure, in step S02, the preparation method of the alloy hydrogenation powder includes: subjecting the R1-T1-B-Ga-M1 main alloy rapid solidification sheet to hydrogen crushing treatment to obtain main alloy hydrogenation powder; subjecting the R2-T2-M2 auxiliary alloy rapid solidification sheet to hydrogen crushing treatment to obtain auxiliary alloy hydrogenation powder; and then mixing the main alloy hydrogenation powder and the auxiliary alloy hydrogenation powder to obtain the alloy hydrogenation powder. In one specific embodiment of this disclosure, the mass content of the main alloy hydrogenation powder is above 95%, and the mass content of the auxiliary alloy hydrogenation powder is below 5%. In this disclosure, the mass content of the main alloy hydrogenation powder cannot be 100%, and the mass content of the auxiliary alloy hydrogenation powder cannot be 0%.

[0079] In one specific embodiment of this disclosure, in the micronization process of step S03, an additive is further added. The additive includes one or more of zinc stearate, calcium stearate, and polyethylene glycol octane. The resulting alloy micronized powder has a D50 particle size of 2-4.8 μm.

[0080] In one specific embodiment of this disclosure, in step S04, the density of the resulting molded compact can be 3.9-4.6 g / cm³.3 .

[0081] In one specific embodiment of this disclosure, in step S04, the sintering conditions include: a temperature of 950-1080℃, for example, 1046-1076℃; and a time of 5-15 hours, for example, 8 hours. In a further embodiment, the vacuum degree inside the vacuum sintering furnace is 10... -2 -10 -5 Pa, for example, can be 10. -2 Pa; In another further embodiment, a protective gas is introduced into the vacuum sintering furnace, the pressure of which can be 5-20 kPa, and the protective gas can be Ar.

[0082] In one specific embodiment of this disclosure, the temperature of the high-temperature diffusion heat treatment is 96%-99% of the sintering temperature, preferably 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, 99%, or any value between these two. Before the high-temperature diffusion heat treatment, each diffusion process stage further includes cooling to below 300°C, for example, 150-300°C. The heating rate of the high-temperature diffusion heat treatment is 8°C / min or higher, for example, 8-30°C / min. Within the above-mentioned preferred high-temperature diffusion heat treatment temperature range, it is further beneficial for the main phase to transform into a liquid phase, generating a uniform core-shell, avoiding abnormal grain growth, and further improving the magnet performance.

[0083] In one specific embodiment of this disclosure, the RE-containing diffusion source includes one or more of RE oxides, RE fluorides, elemental RE, or RE alloys; the RE content in the RE-containing diffusion source is 60-100 wt%.

[0084] In one specific embodiment of this disclosure, in the initial diffusion heat treatment and each stage of the diffusion process, based on the total mass of the sintered NdFeB magnet substrate before diffusion, the amount of RE attached is 0.1-1 wt%, for example, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, or any value between these two; more preferably, the amount of RE attached decreases sequentially in the Nth stage of the diffusion process.

[0085] In this disclosure, "attachment amount" refers to the percentage increase in weight of the sintered NdFeB magnet after attaching the diffusion source, based on the mass of the magnet substrate before diffusion, during the initial diffusion heat treatment and each stage of the diffusion process.

[0086] The third aspect of this disclosure provides a sintered NdFeB magnet prepared by the method described in the second aspect, wherein the sum of the maximum energy product (BH)max and the intrinsic coercivity HcJ of the sintered NdFeB magnet is greater than 80; and the remanence Br is greater than 13 kgs; wherein the unit of the maximum energy product (BH)max is MGOe, and the unit of the intrinsic coercivity HcJ is KOe.

[0087] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited thereto.

[0088] In the following embodiments and comparative examples of this disclosure:

[0089] The average grain size was determined by analyzing the SEM test images of the magnet using image analysis software (ImageProPlus was used in this study). A suitable magnification was selected so that the number of main phase grains in the field of view was greater than 200. A suitable scale was selected, and three fields of view (one field of view in this study) at the same distance from the surface and with the same magnification were statistically analyzed. The maximum distance in the same direction within the cross-section of the main phase grains in the field of view was measured, resulting in a total of more than 600 data points. The average value of all the acquired data points was calculated to characterize the average grain size at that location.

[0090] Test method for determining the percentage of small-area triangular grain boundary phases in the total number of triangular grain boundary phases: Test method: Image analysis software (ImageProPlus was used for calculation in this case) was used to analyze the SEM test image of the magnet. An appropriate magnification was selected to adjust the field of view. An appropriate scale was selected and the grain boundary phases in the field of view were selected based on the contrast. The polygon area of ​​each grain boundary phase was calculated, and the percentage of small-area triangular grain boundary phases in the total number of triangular grain boundary phases was calculated.

[0091] Example 1

[0092] An alloy raw material containing 1.8 wt% Tb, 0.9 wt% B, 0.11 wt% Al, 0.12 wt% Cu, 0.4 wt% Ga, 27.4 wt% PrNd, and the balance Fe was used to prepare rapidly solidified flakes with a thickness of 0.23 mm using a rapid solidification process. These flakes were then hydrogen-crushed and micronized using an air jet mill to produce NdFeB micropowder with a D50 of 3.0 μm. Finally, under Ar protection, the powder was oriented and pressed to obtain a density of 3.9 cm³. 3 The pressed blank is subjected to a vacuum degree of 10. -2 Sintered NdFeB blanks were obtained by sintering at 1070℃ for 8 hours under conditions of Pa. The blanks were then machined to obtain a thickness (in the magnetization direction).

[0093] A sintered NdFeB substrate measuring 4mm x 10mm x 10mm was prepared by magnetron sputtering a diffusion source Tb onto its surface at a concentration of 0.3wt%. An initial diffusion heat treatment was then performed, consisting of holding at 850℃ for 8 hours and then cooling to 250℃. A first-stage grain boundary diffusion heat treatment was then performed, consisting of holding at 1030℃ for 4 hours and then cooling to room temperature. A second magnetron sputtering of Tb was then performed, with a concentration of 0.1wt%. Finally, a first-stage grain boundary diffusion low-temperature heat treatment was performed, consisting of holding at 900℃ for 8 hours and then tempering at 510℃ for 2 hours, resulting in a sintered NdFeB magnet.

[0094] Example 2

[0095] An alloy raw material containing 3.2 wt% Tb, 2 wt% Dy, 0.9 wt% B, 0.1 wt% Al, 0.12 wt% Cu, 0.3 wt% Ga, 0.02 wt% Zr, 25 wt% PrNd, and the balance Fe was rapidly solidified into 0.23 mm thick sheets using a rapid solidification process. These sheets were then hydrogen-crushed and micronized using an air jet mill to produce NdFeB micropowder with a D50 of 3.0 μm. The powder was then oriented and pressed under Ar protection to obtain a density of 4.1 cm³. 3 The pressed blank is subjected to a vacuum degree of 10. -2 Sintered NdFeB blanks were obtained by sintering at 1058℃ for 8 hours under the conditions of Pa. After machining, sintered NdFeB substrates with a thickness (magnetization direction) of 5mm × 10mm × 10mm were obtained. A magnetron sputtering diffusion source Tb was then applied to the substrate surface at a deposition rate of 0.3wt%. An initial diffusion heat treatment was then performed: holding at 850℃ for 8 hours followed by cooling to 250℃. A first-stage grain boundary diffusion heat treatment was then performed: holding at 1038℃ for 3 hours followed by cooling to room temperature. A second magnetron sputtering diffusion source Tb was then applied. The amount of Tb is 0.12 wt%, and then the first-stage grain boundary diffusion low-temperature heat treatment is carried out. The first-stage grain boundary diffusion low-temperature heat treatment process is: holding at 850℃ for 8 hours and cooling to 250℃. Then the second-stage grain boundary diffusion heat treatment is carried out. The second-stage grain boundary diffusion high-temperature heat treatment is carried out under the conditions of holding at 1040℃ for 1.5 hours and then cooling to room temperature. The Tb diffusion source is then sputtered again with an adhesion amount of 0.1 wt%. Then the second-stage grain boundary diffusion low-temperature heat treatment is carried out. The second-stage grain boundary diffusion low-temperature heat treatment process is: holding at 850℃ for 8 hours and cooling to 500℃ for tempering for 2 hours to obtain sintered NdFeB magnets.

[0096] Example 3

[0097] An alloy raw material containing 6.1 wt% Tb, 0.92 wt% B, 0.1 wt% Al, 0.1 wt% Cu, 0.4 wt% Ga, 22.8 wt% PrNd, and the balance Fe was rapidly solidified into 0.23 mm thick sheets using a rapid solidification process. These sheets were then hydrogen-crushed and micronized using an air jet mill to produce NdFeB micropowder with a D50 of 3.0 μm. The powder was then oriented and pressed under Ar protection to obtain a density of 4.1 cm³. 3 The pressed blank, under vacuum, is 10 -2 Sintered NdFeB blanks were obtained by sintering at 1076℃ for 8 hours under the conditions of Pa. After machining, sintered NdFeB substrates with a thickness (magnetization direction) of 15mm × 20mm × 20mm were obtained. A magnetron sputtering diffusion source Tb was then applied to the substrate surface at a deposition rate of 0.3wt%. An initial diffusion heat treatment was then performed: holding at 950℃ for 8 hours followed by cooling to 250℃. A first-stage grain boundary diffusion heat treatment was then performed: holding at 1040℃ for 3 hours followed by cooling to room temperature. A second magnetron sputtering diffusion source Tb was then applied. The amount of Tb is 0.12 wt%. Then, the first-stage grain boundary diffusion low-temperature heat treatment is carried out. The first-stage grain boundary diffusion low-temperature heat treatment process is: holding at 950℃ for 8 hours, cooling to 250℃, and then carrying out the second-stage grain boundary diffusion high-temperature heat treatment. The conditions are: holding at 1060℃ for 1.5 hours and then cooling to room temperature. Then, the Tb diffusion source is sputtered again with an adhesion amount of 0.1 wt%. Then, the second-stage grain boundary diffusion low-temperature heat treatment is carried out. The second-stage grain boundary diffusion low-temperature heat treatment process is: holding at 950℃ for 8 hours, cooling to 520℃ and tempering for 2 hours to obtain sintered NdFeB magnets.

[0098] Example 4

[0099] The alloy raw materials were divided into main alloys and auxiliary alloys. The main alloy containing 0.4 wt% Tb, 0.92 wt% B, 0.19 wt% Al, 0.16 wt% Cu, 0.4 wt% Ga, 28.5 wt% PrNd, and the balance Fe, and the auxiliary alloy containing 55 wt% Tb, 2.1 wt% Al, 0.9 wt% Cu, 5 wt% PrNd, and the balance Fe, were both rapidly solidified into 0.23 mm thick sheets using a rapid solidification process and then hydrogen-cured. The hydrogenated powders of the main alloy and auxiliary alloy were mixed at a ratio of 99.6% to 0.4% to obtain alloy hydrogenated powder. This powder was then processed using an air jet mill to prepare alloy micro-powder with a D50 particle size of 3.0 μm. Under Ar protection, the powder was oriented and pressed to obtain a density of 3.9 cm³. 3 The pressed blank is subjected to a vacuum degree of 10. -2Sintered NdFeB blanks were obtained by sintering at 1076℃ for 8 hours under the conditions of Pa. The blanks were then machined to obtain sintered NdFeB substrates with a thickness (magnetization direction) of 3mm × 10mm × 10mm. A magnetron sputtering diffusion source Tb was applied to the substrate surface with an adhesion amount of 0.3wt%. An initial diffusion heat treatment was then performed: holding at 850℃ for 8 hours and then cooling to 250℃. Next, a first-stage grain boundary diffusion heat treatment was performed: a high-temperature heat treatment at 1040℃ for 4 hours followed by cooling to room temperature. Another magnetron sputtering diffusion source Tb was applied with an adhesion amount of 0.1wt%. Finally, a first-stage grain boundary diffusion low-temperature heat treatment was performed: holding at 850℃ for 8 hours and then tempering at 535℃ for 2 hours to obtain sintered NdFeB magnets.

[0100] Example 5

[0101] The alloy raw materials were divided into main alloys and auxiliary alloys. The main alloy, containing 1 wt% Tb, 0.91 wt% B, 0.1 wt% Al, 0.1 wt% Cu, 0.4 wt% Ga, 27.9 wt% PrNd, and the balance Fe, and the auxiliary alloy, containing 55 wt% Tb, 1 wt% Al, 2 wt% Cu, 5 wt% PrNd, and the balance Fe, were both rapidly solidified into 0.23 mm thick sheets using a rapid solidification process and then hydrogen-cured. These were then mixed at a ratio of 99% main alloy hydrogenated powder to 1% auxiliary alloy hydrogenated powder to obtain alloy hydrogenated powder. This powder was then processed using an air jet mill to prepare alloy micro-powder with a D50 particle size of 3.0 μm. Finally, it was oriented and pressed under Ar protection to obtain a density of 3.9 cm³. 3 The pressed blank is subjected to a vacuum degree of 10. -2 Sintered NdFeB blanks were obtained by sintering at 1070℃ for 8 hours under the conditions of Pa. After machining, sintered NdFeB substrates with a thickness (magnetization direction) of 4mm × 10mm × 10mm were obtained. A magnetron sputtering diffusion source Tb was applied to the surface of the substrate with an adhesion amount of 0.3wt%. Then, an initial diffusion heat treatment was performed, which was carried out at 850℃ for 8 hours and then cooled to 250℃. Then, a first-stage grain boundary diffusion heat treatment was performed, which was carried out at 1030℃ for 4 hours and then cooled to room temperature. A magnetron sputtering diffusion source Tb was applied again with an adhesion amount of 0.1wt%. Then, a first-stage grain boundary diffusion low-temperature heat treatment was performed, which was carried out at 900℃ for 8 hours and then cooled to 510℃ for tempering for 2 hours to obtain sintered NdFeB magnets.

[0102] Example 6

[0103] The alloy raw materials were divided into main alloys and auxiliary alloys. The main alloy, containing 0.5 wt% Tb, 0.92 wt% B, 0.1 wt% Al, 0.05 wt% Cu, 0.4 wt% Ga, 29.2 wt% PrNd, and the balance Fe, and the auxiliary alloy, containing 60 wt% Tb, 1.2 wt% Al, 1.8 wt% Cu, 10 wt% PrNd, and the balance Fe, were both rapidly solidified into 0.23 mm thick sheets using a rapid solidification process and then hydrogen-cured. These were then mixed at a ratio of 97% main alloy hydrogenated powder to 3% auxiliary alloy hydrogenated powder to obtain alloy hydrogenated powder. This powder was then processed using an air jet mill to prepare alloy micro-powder with a D50 particle size of 3.0 μm. Finally, it was oriented and pressed under Ar protection to obtain a density of 4.0 cm³. 3 The pressed blank is subjected to a vacuum degree of 10. -2 Sintered NdFeB blanks were obtained by sintering at 1046℃ for 8 hours under the conditions of Pa. After machining, sintered NdFeB substrates with a thickness (magnetization direction) of 10mm × 10mm × 10mm were obtained. A magnetron sputtering diffusion source Tb was then applied to the substrate surface at a deposition rate of 0.3wt%. An initial diffusion heat treatment was then performed: holding at 950℃ for 8 hours followed by cooling to 250℃. A first-stage grain boundary diffusion heat treatment was then performed: holding at 1020℃ for 3 hours followed by cooling to room temperature. A second magnetron sputtering diffusion source Tb was then applied. The amount of Tb is 0.12 wt%. Then, the first-stage grain boundary diffusion low-temperature heat treatment is carried out. The first-stage grain boundary diffusion low-temperature heat treatment process is: holding at 950℃ for 8 hours, cooling to 250℃, and then carrying out the second-stage grain boundary diffusion high-temperature heat treatment. The conditions are: holding at 1030℃ for 1.5 hours and then cooling to room temperature. Then, the Tb diffusion source is sputtered again with an adhesion amount of 0.1 wt%. Then, the second-stage grain boundary diffusion low-temperature heat treatment is carried out. The second-stage grain boundary diffusion low-temperature heat treatment process is: holding at 950℃ for 8 hours, cooling to 525℃ and tempering for 2 hours to obtain sintered NdFeB magnets.

[0104] Comparative Example 1

[0105] The raw material ratio and preparation method of sintered NdFeB substrate in Comparative Example 1 are the same as those in Example 4, except that the diffusion process is different. The surface of the prepared sintered NdFeB substrate is coated with a magnetron sputtering diffusion source Tb with an adhesion amount of 0.4wt%. Then, after diffusion heat treatment at 850℃ for 20h, it is cooled to 535℃ and tempered for 2h to obtain a sintered NdFeB magnet.

[0106] Test case

[0107] The magnets prepared in the examples and comparative examples were subjected to compositional tests, magnetic property tests, and SEM tests. The composition of the sintered NdFeB magnets is shown in Table 1; the remanence Br, maximum energy product (BH)max, and intrinsic coercivity HcJ of the sintered NdFeB magnets are shown in Table 2.

[0108] The microstructures of Example 4 before and after grain boundary diffusion were tested, and the results are as follows: Figure 2 , Figure 3 As shown.

[0109] The test image of the partial average grain size of the sintered NdFeB magnet prepared in Example 4 is shown below. Figure 5 As shown.

[0110] The distribution of Tb element at different depths from the magnet surface in Example 3 of the test was observed within the grains and grain edges + grain boundaries. The results are as follows: Figure 4 As shown.

[0111] Table 1 Composition of Sintered NdFeB Magnets

[0112]

[0113] Table 2

[0114]

[0115]

[0116] The magnetic properties of the sintered NdFeB magnets prepared by the method of this disclosure are further improved, with the sum of the maximum energy product (BH)max and the intrinsic coercivity HcJ being greater than 80; and the remanence Br being greater than 13 KGs.

[0117] The preferred embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0118] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0119] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A sintered NdFeB magnet, comprising a main phase and a grain boundary phase, characterized in that, The ratio of the average grain size on the surface of the magnet to the average grain size in the central region of the magnet is 1.05 to 1.

35. The magnet surface layer refers to the area less than 35 μm from the magnet surface; the magnet center region refers to the area more than 500 μm from the magnet surface. The sintered NdFeB magnet contains 29.2-32.5 wt% R, 0.87-0.93 wt% B, 0.3-0.55 wt% Ga, 0.10-0.65 wt% M, and the balance T; Wherein, R is a rare earth element, and the rare earth element is Nd, or a combination of Nd and at least one element from the following group: Y, La, Ce, Pr, Sm, Eu, Gd, Ho, Er, Tm, Yb, Dy, Tb and Lu. Based on the total weight of the sintered NdFeB magnet, the content of RE is 0.5~6.5wt%, and RE is Dy and / or Tb. M is selected from at least one of Cu, Al, Zr, Nb, Mn, Mg, Si, Cr, and Ti; T is Fe, or a mixture of Fe and Co, wherein the Fe content in T is above 80 wt%.

2. The sintered NdFeB magnet according to claim 1, wherein, The grain boundary phase includes triangular grain boundary phases; among the triangular grain boundary phases, the number of small-area triangular grain boundary phases accounts for more than 80% of the total number of all triangular grain boundary phases; the small-area triangular grain boundary phases have an area of ​​less than 2.5 μm. 2 The triangular grain boundary phase.

3. The sintered NdFeB magnet according to claim 1, wherein, The sum of the maximum energy product (BH)max and the intrinsic coercivity HcJ of the sintered NdFeB magnet is greater than 80; and the remanence Br is greater than 13 kgs; the unit of the maximum energy product (BH)max is MGOe, and the unit of the intrinsic coercivity HcJ is KOe.

4. The sintered NdFeB magnet according to claim 1, wherein, The ratio of the average grain size on the surface of the magnet to the average grain size in the central region of the magnet is 1.13 to 1.

35. The sintered NdFeB magnet contains less than 600 ppm of oxygen.

5. A method for preparing the sintered NdFeB magnet according to any one of claims 1-4, characterized in that, The method includes the following steps: S1. Preparation of sintered NdFeB magnet substrate; S2. A diffusion source containing RE is attached to the surface of the sintered NdFeB magnet substrate, followed by grain boundary diffusion treatment and tempering treatment; RE is Dy and / or Tb; The grain boundary diffusion treatment includes an initial diffusion heat treatment and an N-stage diffusion process segment, where N ≥ 1. Each stage of the diffusion process segment includes, in sequence, a high-temperature diffusion heat treatment and a low-temperature diffusion heat treatment. The initial diffusion heat treatment conditions include: a temperature of 800~980℃ and a time of 6~12h; The conditions for the low-temperature diffusion heat treatment include: a temperature of 850~950℃ and a time of 6~12h; The high-temperature diffusion heat treatment is at a temperature lower than that of the sintering treatment, and 50-200°C higher than that of the low-temperature diffusion heat treatment, for a duration of 2-8 hours. The sintered NdFeB magnet substrate obtained in step S1 contains 28.9-32.5 wt% R, 0.87-0.93 wt% B, 0.3-0.55 wt% Ga, 0.10-0.65 wt% M, and the balance T; Wherein, R is a rare earth element, and the rare earth element is Nd, or a combination of Nd and at least one element from the following group: Y, La, Ce, Pr, Sm, Eu, Gd, Ho, Er, Tm, Yb, Dy, Tb and Lu. Based on the total weight of the sintered NdFeB magnet substrate, the content of RE is 0.5~6.5wt%, and RE is Dy and / or Tb. M is selected from at least one of Cu, Al, Zr, Nb, Mn, Mg, Si, Cr, and Ti; T is Fe, or a mixture of Fe and Co, wherein the Fe content in T is above 80 wt%.

6. The method according to claim 5, wherein, In step S1, the sintered NdFeB magnet substrate is prepared using the following steps: S01. The alloy raw materials are placed in a vacuum induction furnace for melting and casting to obtain alloy fast-solidification sheets; S02. After hydrogen crushing treatment of the alloy quick-setting sheet, alloy hydrogenated powder is obtained. S03. After micronizing the alloy hydrogenation powder, alloy micro powder is obtained; S04. After the alloy micro powder is placed in a magnetic field for orientation forming, the resulting pressed blank is sintered and machined in a vacuum environment to obtain the sintered NdFeB magnet substrate.

7. The method according to claim 6, wherein, In step S01, R1-T1-B-Ga-M1 main alloy rapid solidification sheet and R2-T2-M2 auxiliary alloy rapid solidification sheet were prepared by a dual alloying method. The R1-T1-B-Ga-M1 main alloy rapid solidification sheet contains 28.9-32.5 wt% R1, 0.87-0.93 wt% B, 0.3-0.55 wt% Ga, 0.10-0.65 wt% M1 and the balance T1; Wherein, R1 is a rare earth element, which is Nd, or a combination of Nd and at least one element from the group consisting of Y, La, Ce, Pr, Sm, Eu, Gd, Ho, Er, Tm, Yb, Dy, Tb and Lu; M1 is selected from at least one of Cu, Al, Zr, Nb, Mn, Mg, Si, Cr and Ti; T1 is Fe or a mixture of Fe and Co; The RE1 content in the R1-T1-B-Ga-M1 main alloy rapid solidification sheet is 0.5-5.2 wt%, and RE1 is Dy and / or Tb; The R2-T2-M2 auxiliary alloy quick-setting sheet contains 60-85 wt% R2, 3.0-6.0 wt% M2 and the balance T2; Wherein, R2 is selected from one or more of Nd, Pr, Dy and Tb, M2 is selected from at least one of Ga, Cu and Al, and T2 is Fe or a mixture of Fe and Co; The RE2 content in the R2-T2-M2 auxiliary alloy quick-setting sheet is 0-80 wt%, and RE2 is Dy and / or Tb; The thickness of the R1-T1-B-Ga-M1 main alloy quick-setting sheet and the R2-T2-M2 auxiliary alloy quick-setting sheet are each independently 0.13-0.46 mm.

8. The method according to claim 7, wherein, In step S02, the method for preparing the alloy hydrogenation powder includes: The main alloy hydrogenated powder is obtained by hydrogenating the R1-T1-B-Ga-M1 main alloy quick-solidifying sheet and the auxiliary alloy hydrogenated powder is obtained by hydrogenating the R2-T2-M2 auxiliary alloy quick-solidifying sheet. The main alloy hydrogenated powder and the auxiliary alloy hydrogenated powder are then mixed to obtain the alloy hydrogenated powder. In the alloy hydrogenation powder, the mass content of the main alloy hydrogenation powder is more than 95%, and the mass content of the auxiliary alloy hydrogenation powder is less than 5%.

9. The method according to claim 5, wherein, The temperature of the high-temperature diffusion heat treatment is 96%-99% of the sintering temperature; The diffusion source containing RE includes one or more of the following: oxides of RE, fluorides of RE, elemental RE, or alloys of RE. The RE-containing diffusion source contains 60-100 wt% RE.

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