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

Abstract

The present disclosure relates to a sintered Nd-Fe-B magnet and a method for preparing the sintered Nd-Fe-B magnet, the method comprising the following steps: S1, preparing a sintered Nd-Fe-B magnet substrate; S2, attaching a diffusion source containing RE to the surface of the sintered Nd-Fe-B magnet substrate, and then performing grain boundary diffusion treatment and tempering treatment; RE is Dy and / or Tb; wherein the grain boundary diffusion treatment comprises an initial diffusion heat treatment and N stages of diffusion process segments, N≥1, each stage of the diffusion process segment comprises, in sequence, a high-temperature diffusion heat treatment and a low-temperature diffusion heat treatment; the low-temperature diffusion heat treatment has a temperature of 850-950 ℃ and a time of 6-12 h; the high-temperature diffusion heat treatment has a temperature lower than the sintering temperature and 50-200 ℃ higher than the temperature of the low-temperature diffusion heat treatment, and a time of 2-8 h. The method can promote the diffusion of heavy rare earth elements to the central region of the sintered magnet in the grain boundary diffusion process, and further improve the comprehensive magnetic properties of the sintered Nd-Fe-B magnet.

Description

Technical Field

[0001] This disclosure relates to the field of rare earth magnets, 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 elements (Dy / Tb) to the raw materials during smelting. The light rare earth elements (mainly Nd and Pr) in the main phase are replaced by Dy / Tb, thereby enhancing coercivity by increasing the anisotropy field of the grains. CN103887028A discloses a method for obtaining high-performance sintered NdFeB magnets by controlling the composition formula, adding 2.0-13.5 wt% 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 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;

[0009] 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.

[0010] The initial diffusion heat treatment conditions include: a temperature of 800–980°C and a time of 6–12 hours;

[0011] The conditions for the low-temperature diffusion heat treatment include: a temperature of 850–950°C and a time of 6–12 hours;

[0012] The high-temperature diffusion heat treatment is performed at a temperature lower than that of the sintering treatment, but 50–200°C higher than that of the low-temperature diffusion heat treatment, and for a duration of 2–8 hours.

[0013] Optionally, the sintered NdFeB magnet substrate obtained in step S1 comprises 28.5-33.5 wt% R, 0.2-2.0 wt% M, 0.87-1.0 wt% B, and the balance T; wherein R is selected from one or more of Nd, Y, La, Ce, Pr, Sm, Eu, Gd, Ho, Er, Tm, Yb, Dy, Tb, and Lu; M is selected from one or more of Cu, Al, Ga, Zr, Nb, Mn, Mg, Co, Zn, Si, Cr, Sn, Ni, and Ti; and T is Fe, or a mixture of Fe and Co, wherein the Fe content in T is more than 90 wt%.

[0014] Optionally, in step S1, the sintered NdFeB magnet substrate is prepared using the following steps:

[0015] S01. The alloy raw materials are placed in a vacuum induction furnace for melting and casting to obtain alloy fast-solidification sheets;

[0016] S02. After hydrogen crushing treatment of the alloy quick-setting sheet, alloy hydrogenated powder is obtained.

[0017] S03. After micronizing the alloy hydrogenation powder, alloy micro powder is obtained;

[0018] 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.

[0019] Optionally, the temperature of the high-temperature diffusion heat treatment is 96%-99% of the sintering temperature.

[0020] Optionally, the RE-containing diffusion source includes one or more of the following: RE oxides, RE fluorides, elemental RE, or RE alloys.

[0021] Optionally, the RE content in the RE-containing diffusion source is 60-100 wt%.

[0022] The second aspect of this disclosure provides a sintered NdFeB magnet prepared by the method described in the first aspect.

[0023] Optionally, the sintered NdFeB magnet comprises 28.9-33.5 wt% R, 0.2-1.5 wt% M, 0.87-1.0 wt% B, and the balance T; wherein R is selected from one or more of Nd, Y, La, Ce, Pr, Sm, Eu, Gd, Ho, Er, Tm, Yb, Dy, Tb, and Lu; M is selected from one or more of Cu, Al, Ga, Zr, Nb, Mn, Mg, Co, Zn, Si, Cr, Sn, Ni, and Ti; and T is Fe, or a mixture of Fe and Co, wherein the Fe content in T is 90 wt% or more.

[0024] Through the above technical solution, the preparation method disclosed herein employs a diffusion heat treatment including an N-stage diffusion process. The low-temperature diffusion heat treatment enables heavy rare earth elements in the diffusion source to diffuse along the grain boundaries of the substrate and effectively concentrate them within a narrow range 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, forming a thicker high-coercivity region, and improving the overall coercivity distribution. The method disclosed herein can reduce the amount of rare earth used, and is simple to operate, easy to control, and suitable for large-scale production.

[0025] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0026] 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:

[0027] Figure 1 This is a flow chart of the grain boundary diffusion process of a specific embodiment of the method for preparing sintered NdFeB magnets disclosed herein.

[0028] Figure 2This 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. Detailed Implementation

[0029] 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.

[0030] The first aspect of this disclosure provides a method for preparing sintered NdFeB magnets, the method comprising the following steps:

[0031] S1. Preparation of sintered NdFeB magnet substrate;

[0032] 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.

[0033] 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 in the thickness direction. The "method of attaching a diffusion source containing RE" can employ conventional techniques in the art, such as vacuum evaporation, impregnation, spraying, magnetron sputtering, ion plating, etc., with magnetron sputtering being preferred.

[0034] 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 embodiment of this disclosure, the temperature of the high-temperature diffusion heat 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.

[0035] In one specific embodiment of this disclosure, the sintered NdFeB magnet substrate obtained in step S1 comprises 28.5-33.5 wt% R, 0.2-2.0 wt% M, 0.87-1.0 wt% B, and the balance T; wherein R is selected from one or more of Nd, Y, La, Ce, Pr, Sm, Eu, Gd, Ho, Er, Tm, Yb, Dy, Tb, and Lu; M is selected from one or more of Cu, Al, Ga, Zr, Nb, Mn, Mg, Co, Zn, Si, Cr, Sn, Ni, and Ti; and T is Fe, or a mixture of Fe and Co, wherein the Fe content in T is 90 wt% or more. The sintered NdFeB magnet substrate also includes unavoidable impurity elements, such as O, N, and C.

[0036] In a preferred embodiment of this disclosure, the content of R can be 28.5 wt%, 29.5 wt%, 30.0 wt%, 30.5 wt%, 31.0 wt%, 31.5 wt%, 32.5 wt%, 33.5 wt%, or any value between these two; the content of M can be 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%. The content of B can be 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.8 wt%, 2.0 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%, 0.95 wt%, 0.98 wt%, 1.0 wt%, or any value between two of them.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] In one embodiment of this disclosure, in step S01, R1-T1-B1-M1 main alloy quick-setting sheet and R2-T2-B2-M2 auxiliary alloy quick-setting sheet are prepared by a dual alloying method, or RTBM single alloy quick-setting sheet is prepared by a single alloying method.

[0041] In a preferred embodiment of this disclosure, in step S01, R1-T1-B1-M1 main alloy quick-setting sheet and R2-T2-B2-M2 auxiliary alloy quick-setting sheet are prepared by a dual alloying method; the R1-T1-B1-M1 main alloy quick-setting sheet contains 28.5-33.5 wt% R1, 0.87-1.0 wt% B, 0.2-2.0 wt% M1 and the balance T1; wherein R1 is selected from one or more of Nd, Y, La, Ce, Pr, Sm, Eu, Gd, Ho, Er, Tm, Yb, Dy, Tb and Lu; M1 is selected from one or more of Cu, Al, Ga, Zr, Nb, Mn, Mg, Co, Zn, Si, Cr, Sn, Ni and Ti; T1 is Fe, or a mixture of Fe and Co, wherein the Fe content in T1 is more than 90 wt%.

[0042] In one specific embodiment of this disclosure, the R2-T2-B2-M2 auxiliary alloying rapid solidification sheet comprises 50-86 wt% R2, 2.5-6.5 wt% M2, 0-1.2 wt% B2, and the balance T2; wherein R2 is selected from one or more of Nd, Y, La, Ce, Pr, Sm, Eu, Gd, Ho, Er, Tm, Yb, Dy, Tb, and Lu; M2 is selected from one or more of Cu, Al, Ga, Zr, Nb, Mn, Mg, Co, Zn, Si, Cr, Sn, Ni, and Ti; T2 is Fe, or a mixture of Fe and Co, wherein the Fe content in T2 is 90 wt% or more.

[0043] In one specific embodiment of this disclosure, the thickness of the R1-T1-B1-M1 main alloy quick-setting sheet and the R2-T2-B2-M2 auxiliary alloy quick-setting sheet are each independently 0.13-0.46 mm.

[0044] In one specific embodiment of this disclosure, in step S02, the preparation method of the alloy hydrogenation powder includes: subjecting the R1-T1-B1-M1 main alloy rapid solidification sheet to hydrogen crushing treatment to obtain main alloy hydrogenation powder; subjecting the R2-T2-B2-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%.

[0045] 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.

[0046] 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 .

[0047] In one specific embodiment of this disclosure, in step S04, the sintering conditions include: a temperature of 950-1080℃, for example, 1045-1076℃; 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.

[0048] 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.

[0049] 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. In one specific embodiment of this disclosure, the RE content in the RE-containing diffusion source is 60-100 wt%.

[0050] 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.

[0051] 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.

[0052] The second aspect of this disclosure provides a sintered NdFeB magnet prepared by the method described in the first aspect.

[0053] In one specific embodiment of this disclosure, the sintered NdFeB magnet comprises 28.9-33.5 wt% R, 0.2-2.0 wt% M, 0.87-1.0 wt% B, and the balance T.

[0054] In one specific embodiment of this disclosure, R is selected from one or more of Nd, Y, La, Ce, Pr, Sm, Eu, Gd, Ho, Er, Tm, Yb, Dy, Tb and Lu; M is selected from one or more of Cu, Al, Ga, Zr, Nb, Mn, Mg, Co, Zn, Si, Cr, Sn, Ni and Ti; T is Fe, or a mixture of Fe and Co, wherein the Fe content in T is 90 wt% or more.

[0055] In a preferred embodiment of this disclosure, the content of R can be 28.9 wt%, 29.5 wt%, 30.0 wt%, 30.5 wt%, 31.0 wt%, 31.5 wt%, 32.5 wt%, 33.5 wt%, or any value between these two; the content of M can be 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%. The content of B can be 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.8 wt%, 2.0 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%, 0.95 wt%, 0.98 wt%, 1.0 wt%, or any value between two of them.

[0056] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited thereto.

[0057] Example 1

[0058] The alloy raw materials were divided into main alloys and auxiliary alloys. The main alloy, containing 0.97 wt% B, 0.2 wt% Al, 0.1 wt% Cu, 0.51 wt% Ga, 1.0 wt% Co, 31 wt% PrNd, and the balance Fe, and the auxiliary alloy, containing 0.89 wt% B, 0.15 wt% Al, 0.1 wt% Cu, 0.51 wt% Ga, 1.0 wt% Co, 32.5 wt% PrNd, and the balance Fe, were both rapidly solidified into 0.23 mm thick sheets using a rapid solidification process and then hydrogenated. These sheets were then mixed at a ratio of 98% main alloy hydrogenated powder to 2% 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 3.6 μm. Finally, it was oriented and pressed under Ar protection to obtain a density of 4.2 cm⁻¹. 3 The pressed blank is subjected to a vacuum degree of 10. -2 Sintered NdFeB blanks were obtained by sintering at 1000℃ for 6 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 490℃ for 4 hours to obtain sintered NdFeB magnets.

[0059] The magnetic properties of the sintered NdFeB substrate were tested and found to be 13.72 KGs remanence, 46.72 MGOe maximum energy product (BH)max, and 27.56 KOe intrinsic coercivity HcJ.

[0060] Example 2

[0061] An alloy raw material containing 1.1 wt% Tb, 0.9 wt% B, 0.08 wt% Al, 0.12 wt% Cu, 0.33 wt% Ga, 28.7 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. -2Sintered NdFeB blanks were obtained by sintering at 1058℃ for 8 hours under the conditions of Pa. Through machining, sintered NdFeB substrates with a thickness (magnetization direction) of 4mm × 12mm × 12mm were obtained. A magnetron sputtering diffusion source Tb was applied to the substrate surface with an adhesion amount of 0.35wt%. Then, an initial diffusion heat treatment was performed: holding at 850℃ for 8.5 hours and then cooling to 250℃. Next, a first-stage grain boundary diffusion heat treatment was performed: a high-temperature heat treatment at 1030℃ for 4 hours and then cooling to room temperature. A magnetron sputtering diffusion source Tb was applied again with an adhesion amount of 0.1wt%. Finally, a first-stage grain boundary diffusion low-temperature heat treatment was performed: holding at 900℃ for 8 hours and then tempering at 510℃ for 2 hours to obtain sintered NdFeB magnets.

[0062] Example 3

[0063] An alloy raw material containing 4 wt% Tb, 0.87 wt% B, 0.15 wt% Al, 0.13 wt% Cu, 0.4 wt% Ga, 27 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 4.0 cm³. 3 The pressed blank is subjected to a vacuum degree of 10. - 2 Sintered NdFeB blanks were obtained by sintering at 1060℃ for 8 hours under the conditions of Pa. After machining, sintered NdFeB substrates with a thickness (magnetization direction) of 5mm × 12mm × 12mm 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 0.15 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.

[0064] Example 4

[0065] An alloy raw material containing 1.8 wt% Tb, 0.92 wt% B, 0.1 wt% Al, 0.1 wt% Cu, 0.4 wt% Ga, 27.4 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 × 18mm × 18mm 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.

[0066] Example 5

[0067] 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.

[0068] Example 6

[0069] A raw material containing 4 wt% Tb, 1.4 wt% Dy, 0.95 wt% B, 0.1 wt% Al, 0.13 wt% Cu, 0.2 wt% Ga, 1.4 wt% Co, 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 3.9 cm³. 3 The pressed blank is subjected to a vacuum degree of 10. -2 Sintered NdFeB blanks were obtained by sintering at 1045℃ 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 then applied to the substrate surface with an adhesion amount 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 with an adhesion amount of [missing information]. 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.

[0070] Comparative Example 1

[0071] The raw material ratio and preparation method of sintered NdFeB substrate in Comparative Example 1 are the same as those in Example 1, 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 0.4 wt%. Then, only an initial thermal diffusion treatment is performed at 850°C for 20 h, followed by cooling to 490°C for tempering treatment for 4 h to obtain a sintered NdFeB magnet.

[0072] Comparative Example 2

[0073] The raw material ratio and preparation method of sintered NdFeB substrate in Comparative Example 2 are the same as those in Example 6, except that the diffusion process is different. The magnetron sputtering diffusion source Tb on the surface of the prepared sintered NdFeB substrate has an adhesion amount of 0.52wt%. Then, only an initial thermal diffusion treatment of 950°C is performed, which is held at 20h for 20h and then cooled to 525°C for tempering treatment for 2h to obtain sintered NdFeB magnets.

[0074] Test case

[0075] 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.

[0076] The microstructure of the grain boundary diffusion in Example 2 was tested, and the results are as follows: Figure 2 As shown.

[0077] Table 1 Composition of Sintered NdFeB Magnets

[0078]

[0079] Table 2

[0080]

[0081] 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.

[0082] 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.

[0083] 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 method for preparing sintered NdFeB magnets, 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 temperature of the high-temperature diffusion heat treatment is 50-200°C higher than the temperature of the low-temperature diffusion heat treatment. The temperature of the high-temperature diffusion heat treatment is lower than the temperature of the sintering treatment; the temperature of the sintering treatment is 950~1080℃. The high-temperature diffusion heat treatment lasts for 2 to 8 hours.

2. The method according to claim 1, wherein, The sintered NdFeB magnet substrate obtained in step S1 contains 28.5-33.5 wt% R, 0.2-2.0 wt% M, 0.87-1.0 wt% B, and the balance T; R is selected from one or more of Nd, Y, La, Ce, Pr, Sm, Eu, Gd, Ho, Er, Tm, Yb, Dy, Tb and Lu; M is selected from one or more of Cu, Al, Ga, Zr, Nb, Mn, Mg, Co, Zn, Si, Cr, Sn, Ni, and Ti; T is Fe, or a mixture of Fe and Co, wherein the Fe content in T is more than 90 wt%.

3. The method according to claim 1, 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.

4. The method according to claim 1, wherein, The temperature of the high-temperature diffusion heat treatment is 96%-99% of the sintering temperature.

5. The method according to claim 1, wherein, The diffusion source containing RE includes one or more of the following: oxides of RE, fluorides of RE, elemental RE, or alloys of RE.

6. The method according to claim 5, wherein, The RE-containing diffusion source contains 60-100 wt% RE.

7. The sintered NdFeB magnet prepared by the method according to any one of claims 1-6.

8. The sintered NdFeB magnet according to claim 7, wherein, The sintered NdFeB magnet comprises 28.9-33.5 wt% R, 0.2-2.0 wt% M, 0.87-1.0 wt% B, and the balance T; R is selected from one or more of Nd, Y, La, Ce, Pr, Sm, Eu, Gd, Ho, Er, Tm, Yb, Dy, Tb and Lu; M is selected from one or more of Cu, Al, Ga, Zr, Nb, Mn, Mg, Co, Zn, Si, Cr, Sn, Ni, and Ti; T is Fe, or a mixture of Fe and Co, wherein the Fe content in T is more than 90 wt%.

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