A method for grain boundary diffusion of sintered neodymium-iron-boron magnets

Abstract

The application discloses a sintered Nd-Fe-B magnet grain boundary diffusion method, and a preparation method thereof comprises the following steps: coating a diffusion raw material containing at least one of Dy, Tb and Ho on a surface of a magnet to form a surface coating with coated areas and non-coated areas being distributed at intervals, and then performing a heat treatment process to form a sintered Nd-Fe-B diffusion magnet with a high-low fluctuation distribution structure of heavy rare earth concentration. Compared with a conventional grain boundary diffusion magnet preparation method, the coated areas and the non-coated areas are distributed at intervals on the surface of the magnet, the use amount of the diffusion source is saved, and the production cost of an enterprise is greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of magnetic materials technology, and in particular to a method for grain boundary diffusion in sintered NdFeB magnets. Background Technology

[0002] In response to the ongoing energy transformation both domestically and globally, my country is demanding the acceleration of the planning and construction of a new energy system and the unwavering promotion of green and low-carbon energy development. Energy conservation in motor systems, as one of the nation's ten major energy-saving projects, is a crucial measure for developing a low-carbon economy. Compared to asynchronous motors, rare-earth permanent magnet synchronous motors eliminate the need for excitation windings in their rotors, relying instead on magnets to provide a constant magnetic field. This reduces iron and copper losses, and offers advantages such as small size, light weight, high energy conversion efficiency, and precise motor speed control. They are essential components for developing green and energy-saving industries such as new energy vehicles, wind power generation, and energy-efficient home appliances.

[0003] However, under certain conditions during operation (such as high eddy current losses and poor heat dissipation), the temperature of the magnets in a permanent magnet motor can rise, potentially affecting the stable output of the magnetic field source and, in severe cases, causing motor failure. To meet the requirements of permanent magnet motors operating at high temperatures, heavy rare earth elements Tb / Dy are typically added to the permanent magnet material to replace Nd, forming a Tb₂Fe magnet with a high magnetocrystalline anisotropy field. 14 B, Dy2Fe 14 B, increasing the coercivity of the magnet H cJ This improves temperature resistance. In early industrial production, Tb and Dy were added to the magnet through traditional alloy smelting, resulting in a relatively uniform distribution of Tb / Dy elements within the main phase grains. However, the grain boundary diffusion technology, which has emerged in recent years, differs from traditional Tb / Dy introduction methods. It involves coating the magnet surface with a layer of heavy rare earth-containing material, followed by heat treatment to allow the heavy rare earth elements to enter the magnet along the liquid phase grain boundaries. During cooling to room temperature, a heavy rare earth-rich shell forms on the surface of the main phase grains. According to the coercivity mechanism of NdFeB, antimagnetic domains first form on the surface of the main phase grains. The heavy rare earth-rich shell formed through grain boundary diffusion technology possesses a high magnetocrystalline anisotropy field, suppressing the nucleation of antimagnetic domains. Compared to traditional Tb / Dy introduction methods, grain boundary diffusion technology reduces the consumption of heavy rare earth Tb / Dy; simultaneously, Tb / Dy does not excessively enter the main phase grains and interact with Fe atoms through antiferromagnetic coupling, thus reducing the remanence of the magnet. r It also reduces the amount of magnetization by a small amount, and can produce high remanence and high coercivity magnets that cannot be obtained by traditional smelting methods.

[0004] Heavy rare earth elements (Tb / Dy) are not only expensive but also serve as a strategic reserve resource, making their importance self-evident. To more efficiently utilize Tb / Dy and improve its utilization rate, researchers have recently made some improvements based on conventional grain boundary diffusion technology. The paper "Reutilization of Dy strips in rotating diffusion to enhance coercivity of sintered Nd-Fe-B magnets" mentions a new grain boundary diffusion method. This method involves mixing a magnet with zirconium oxide spheres and metallic Dy in a 1:1:3 weight ratio, then placing the mixture in a rotating furnace at 3 m / s. High-temperature treatment causes the metallic Dy to evaporate and coat the magnet surface, and the Dy elements on the surface then diffuse along the grain boundaries into the magnet's interior. While this method allows for the reuse of metallic Dy, each surface of the magnet will be coated with heavy rare earth elements. In current industrial production, diffusion sources are usually coated on the surface perpendicular to the orientation direction of the magnet. This is because the diffusion effect of heavy rare earth elements along the orientation direction is better than that in the non-orientation direction. Secondly, if every surface of the magnet is coated with a diffusion source, it will result in a waste of heavy rare earth elements.

[0005] Patent CN202010337174.2 discloses a method for grain boundary diffusion of heavy rare earth elements in sintered NdFeB magnets. First, the magnet undergoes low-temperature grain boundary diffusion treatment with low-melting-point alloy powder containing no heavy rare earth elements to increase grain boundary diffusion channels and improve grain boundary continuity. Then, the magnet undergoes high-temperature grain boundary diffusion treatment with compound powder rich in heavy rare earth elements. While this two-stage diffusion method facilitates the diffusion of heavy rare earth elements, it adds multiple production steps, increases material manufacturing costs, and is not conducive to industrial mass production.

[0006] While the technologies and methods mentioned in the above literature and patents have improved the utilization rate of heavy rare earth elements to some extent, they are still some distance from practical application. Summary of the Invention

[0007] The purpose of this invention is to provide a method for grain boundary diffusion in sintered NdFeB magnets, which has the advantages of high utilization of diffusion sources and superior overall magnetic properties of the magnets.

[0008] The technical solution of the present invention is a method for grain boundary diffusion of sintered NdFeB magnets, comprising the following steps: coating the surface of the magnet with a diffusion material containing at least one of Dy, Tb, and Ho to form a surface coating with alternating coated and uncoated regions, and then performing a heat treatment process to form a sintered NdFeB diffused magnet with a high-low distribution of heavy rare earth concentration.

[0009] In the aforementioned method for grain boundary diffusion in sintered NdFeB magnets, the diffusion material composition contained in the coating on the surface of the sintered NdFeB thin sheet magnet is R. 1-a-b T a X b Where R is one or more of the heavy rare earth elements Dy, Tb, and Ho; T is one or more of La, Ce, Pr, Nd, Gd, Al, Co, Cu, Ga, Zr, Ti, Nb, and Fe; X is one or more of H, O, N, C, F, Cl, and B; and a and b are weight percentages, where 0 wt.% ≤ a < 20 wt.% and 0 wt.% ≤ b < 5 wt.%.

[0010] In the aforementioned method for grain boundary diffusion in sintered NdFeB magnets, the spacing between adjacent coated regions of the surface coating is D, which ranges from 0.01 mm to D to 4 mm.

[0011] In the aforementioned method for grain boundary diffusion of sintered NdFeB magnets, the spacing between adjacent coated regions of the surface coating is D, preferably ranging from 0.1 mm to D to 1 mm.

[0012] In the aforementioned method for grain boundary diffusion of sintered NdFeB magnets, the spacing between adjacent coated regions of the surface coating is D, preferably ranging from 0.2 mm to D to 0.5 mm.

[0013] In the aforementioned method for grain boundary diffusion of sintered NdFeB magnets, the surface coatings, which are distributed alternately in the covered and uncovered regions, are formed by a masking method, including but not limited to screen printing, magnetron sputtering, and spraying processes.

[0014] In the aforementioned method for grain boundary diffusion in a sintered NdFeB magnet, the thickness of the sintered NdFeB sheet magnet is 0.1 mm to 20 mm.

[0015] In the aforementioned method for grain boundary diffusion in a sintered NdFeB magnet, the concentration of heavy rare earth elements in the sintered NdFeB diffused magnet exhibits a periodic high-low fluctuation distribution, with the heavy rare earth element concentration in the coated region being higher than that in the uncoated region.

[0016] In the aforementioned method for grain boundary diffusion in sintered NdFeB magnets, the highest concentration of heavy rare earth elements (C) in the coating region located 100 μm from the magnet surface is C. 100 The lowest concentration of heavy rare earth elements in the uncoated region is C' 100 , △C1=C 100 -C' 100 ,0wt.%<△C1≤20wt.%.

[0017] In the aforementioned method for grain boundary diffusion in sintered NdFeB magnets, the highest concentration of heavy rare earth elements (C) in the coating region located 200 μm from the magnet surface is C. 200The lowest concentration of heavy rare earth elements in the uncoated region is C' 200 △C2=C 200 -C' 200 ,0wt.%<△C2≤10wt.%.

[0018] In the aforementioned method for grain boundary diffusion in sintered NdFeB magnets, the highest concentration of heavy rare earth elements (C) in the coating region located 500 μm from the magnet surface is C. 500 The lowest concentration of heavy rare earth elements in the uncoated region is C' 500 , △C5=C 500 -C' 500 ,0wt.%<△C5≤2wt.%.

[0019] In the aforementioned method for grain boundary diffusion in sintered NdFeB magnets, the spacing D between adjacent coated regions of the surface coating is in the range of 0.01mm≤D≤0.1mm, and 0wt.%<△C2≤1wt.%.

[0020] In the aforementioned method for grain boundary diffusion in sintered NdFeB magnets, the spacing D between adjacent coated regions of the surface coating is in the range of 0.1 mm ≤ D ≤ 0.2 mm, and 0 wt.% < ΔC2 ≤ 2 wt.%.

[0021] In the aforementioned method for grain boundary diffusion in sintered NdFeB magnets, the spacing D between adjacent coated regions of the surface coating is in the range of 0.2 mm ≤ D ≤ 0.5 mm, and 0 wt.% < ΔC2 ≤ 6 wt.%.

[0022] In the aforementioned method for grain boundary diffusion in sintered NdFeB magnets, the spacing D between adjacent coated regions of the surface coating is in the range of 0.5 mm ≤ D ≤ 1 mm, and 0 wt.% < ΔC2 ≤ 8 wt.%.

[0023] In the aforementioned method for grain boundary diffusion in sintered NdFeB magnets, the spacing D between adjacent coated regions of the surface coating is in the range of 1mm≤D≤4mm, and 0wt.%<△C2≤10wt.%.

[0024] In the aforementioned method for grain boundary diffusion in sintered NdFeB magnets, the heat treatment process involves first holding the magnet at a temperature of 700℃-1000℃ for 1h-40h, and then holding it at a temperature of 400℃-600℃ for 1h-10h.

[0025] In the aforementioned method for grain boundary diffusion in sintered NdFeB magnets, the coating region is located on the surface of the sintered NdFeB magnet perpendicular to the orientation direction.

[0026] In the aforementioned method for grain boundary diffusion in sintered NdFeB magnets, the coated regions exhibit a periodic distribution, with adjacent coated and uncoated regions forming one period, and the number of periods is not less than 2.

[0027] In the aforementioned method for grain boundary diffusion in sintered NdFeB magnets, the shape of the coating region includes, but is not limited to, circles and rectangles.

[0028] In the aforementioned method for grain boundary diffusion in sintered NdFeB magnets, the area of ​​the coated region is A, the area of ​​the uncoated region is B, and the range of A / B is 0.05-100.

[0029] In the aforementioned method for grain boundary diffusion in sintered NdFeB magnets, different positions on the surface of the same magnet have different A / B ratios.

[0030] In the aforementioned method for grain boundary diffusion in sintered NdFeB magnets, the heat treatment process includes a dehydrogenation process, wherein the temperature of the dehydrogenation process is 600℃-800℃.

[0031] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0032] 1. The diffusion source containing heavy rare earth elements does not need to cover all areas of the magnet surface; it only periodically coats the surface perpendicular to the magnet's orientation direction, leaving uncoated areas. Compared to conventional grain boundary diffusion technology, this invention further reduces the amount of heavy rare earth elements used, thus lowering production costs.

[0033] 2. After reducing the amount of heavy rare earth elements used, the remanence B of the magnet prepared by this invention patent is increased. r and coercivity H cJ It outperforms conventional grain boundary diffusion techniques and maintains good squareness H k / H cJ This is because with the reduction in the amount of heavy rare earth elements used, the concentration gradient of the diffusion source in the coated region decreases, and the diffusion rate of heavy rare earth elements into the main phase grains also decreases. Less heavy rare earth element diffusion into the main phase grains reduces the remanence (B) of the magnet. r The performance remains essentially unchanged and is superior to conventional grain boundary diffusion technology. In contrast, more heavy rare earth elements diffuse along the grain boundaries in the coated region, forming a shell structure with a high magnetocrystalline anisotropy on the surface of more main phase grains, thus improving the coercivity H of the magnet. cJ Furthermore, heavy rare earth elements that diffuse along grain boundaries in the liquid phase are classified into two categories based on their diffusion direction: one is along the orientation direction, i.e., diffusing deeper than the magnet surface; the other is perpendicular to the orientation direction, i.e., diffusing into the uncoated region. A shell structure rich in heavy rare earth elements also forms on the surface of the main phase grains in the uncoated region, so the magnet retains good squareness H after diffusion. k / H cJ The overall magnetic properties of the magnet are superior.

[0034] 3. The preparation method of the present invention is suitable for industrial mass production, with high utilization of diffusion source and no need for secondary diffusion. Attached Figure Description

[0035] Figure 1 The following is a schematic diagram of the process of the present invention: (a) is a three-dimensional schematic diagram of the sintered NdFeB thin sheet magnet after the diffusion source is coated on the surface; (b) is a partial longitudinal cross-sectional schematic diagram of the sintered NdFeB thin sheet magnet after the diffusion source is coated on the surface; (c) is a partial longitudinal cross-sectional schematic diagram of the sintered NdFeB diffusion magnet.

[0036] Figure 2 This is a three-dimensional schematic diagram of the diffusion source coated on the surface of the sintered NdFeB thin sheet magnet in Embodiment 1 of the present invention;

[0037] Figure 3 This is a three-dimensional schematic diagram of the diffusion source coated on the surface of the sintered NdFeB thin sheet magnet in Embodiment 2 of the present invention. Detailed Implementation

[0038] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the present invention.

[0039] Example 1: A method for grain boundary diffusion in sintered NdFeB magnets, comprising the following steps:

[0040] (1) Take magnetic properties B r =14.13kGs, H cJ =12.36kOe, H k / H cJ =97.9% commercial N50 magnets were used as the base, and then cut into three thin slices of 15mm×11mm×2mm by wire cutting, with the orientation direction parallel to the thickness direction (2mm);

[0041] (2) Place 3 thin films in a 3% dilute nitric acid solution and ultrasonically clean for 1 minute to remove oil and other impurities attached to the surface; then place the thin films in anhydrous ethanol and ultrasonically clean for 1 minute, and then dry them to prepare for coating the diffusion source.

[0042] (3) Cover the uncoated areas of the three thin sheets with 0.3 mm iron sheets, and then use a magnetron sputtering coating machine to coat the surface of the thin sheet magnets with metal Dy; the argon gas pressure during magnetron sputtering is 0.2 Pa, the DC current is 15 A, and the sputtering time is 20 min; the sintered NdFeB thin sheet magnets after coating are as follows: Figure 2As shown; on the orientation surfaces of these three thin slices, the spacing D between adjacent coated regions is 1 mm; the widths of individual coated regions are 3 mm, 2 mm, and 1 mm, respectively; with adjacent coated and uncoated regions as one period, the number of periods are 2, 3, and 5, respectively; the total area A of the coated regions is 4.5, 2.67, and 1.2 times larger than the total area B of the uncoated regions, respectively; the weight gain of the thin slices after coating Dy is 0.75 wt.%, 0.67 wt.%, and 0.5 wt.%, respectively.

[0043] (4) The sintered NdFeB sheet coated with Dy is placed in a molybdenum box and then placed in a tube furnace for vacuum heat treatment. The heat treatment process is as follows: the diffusion treatment temperature is 900℃ and the time is 12h; the aging treatment temperature is 500℃ and the time is 4h.

[0044] (5) The magnetic properties of the sample were tested using a permanent magnet material measuring instrument; the Dy content of the coated and uncoated areas at distances of 100 μm, 200 μm and 500 μm from the sample surface was analyzed using an electron probe.

[0045] Comparative Example 1: Sintered NdFeB diffused magnets prepared by conventional grain boundary diffusion process, specifically including the following steps:

[0046] (1) Take magnetic properties B r =14.13kGs, H cJ =12.36kOe, H k / H cJ =97.9% commercial N50 magnets were used as the base material, and then wire cut into thin slices of 15mm×11mm×2mm size, with the orientation direction parallel to the thickness direction (2mm);

[0047] (2) Place the sheet in a 3% dilute nitric acid solution and ultrasonically clean it for 1 minute to remove oil and other impurities adhering to the surface; then place the sheet in anhydrous ethanol and ultrasonically clean it for 1 minute, and then dry it to prepare for coating the diffusion source.

[0048] (3) Metal Dy was deposited on the orientation surface of the thin-film magnet using a magnetron sputtering coating machine. The argon gas pressure during magnetron sputtering was 0.2 Pa, the DC current was 15 A, and the sputtering time was 20 min. There was only one coated area on the orientation surface, and no uncoated area. The area of ​​the coated area was 15 mm × 11 mm. The weight gain of the thin film after coating with Dy was 0.85 wt.%.

[0049] (4) The sintered NdFeB sheet coated with Dy is placed in a molybdenum box and then placed in a tube furnace for vacuum heat treatment. The heat treatment process is as follows: the diffusion treatment temperature is 900℃ and the time is 12h; the aging treatment temperature is 500℃ and the time is 4h.

[0050] (5) The magnetic properties of the sample were tested using a permanent magnet material measuring instrument; the Dy content of the coated area at a distance of 100 μm, 200 μm and 500 μm from the sample surface was analyzed using an electron probe.

[0051] The distance D between adjacent coated regions, the number of coated regions, the area ratio (A / B) of coated and uncoated regions, the weight gain of the diffusion source, and the magnetic properties after diffusion are listed in Table 1 for the samples of Example 1 and Comparative Example 1; the results of Dy content at different depths from the sample surface are listed in Table 2.

[0052] Table 1. Area of ​​diffusion source, ratio of covered to uncovered area (A / B), weight gain of diffusion source, and magnetic properties after diffusion.

[0053]

[0054] As shown in Table 1, compared with conventional grain boundary diffusion technology, the diffusion magnet prepared by this invention not only significantly reduces the amount of diffusion source used, but also increases the remanence B of the magnet. r and coercivity H cJ It also significantly improves the squareness H. k / H cJ It has also been maintained relatively well.

[0055] Table 2. Dy content at different depths from the sample surface

[0056]

[0057] The Dy content data at different depths from the sample surface in Table 2 prove that a small portion of the Dy element in the diffusion magnet prepared by this invention enters the interior of the main phase grains, while most of the Dy element diffuses along the grain boundaries to the uncoated region and to a deeper location from the surface.

[0058] Example 2: A method for grain boundary diffusion in sintered NdFeB magnets, specifically including the following steps:

[0059] (1) Take magnetic properties B r =13.35kGs, H cJ =18.1kOe, H k / H cJ =98.1% of commercial 45H magnets were used as the base, and then four thin slices of 20mm×20mm×1.8mm were cut out by wire cutting, with the orientation direction parallel to the thickness direction (1.8mm).

[0060] (2) Place 4 thin films in a 3% dilute nitric acid solution and ultrasonically clean for 1 minute to remove oil and other impurities attached to the surface; then place the thin films in anhydrous ethanol and ultrasonically clean for 1 minute, and then dry them to prepare for coating the diffusion source.

[0061] (3) The prepared diffusion raw materials (dysprosium hydride: anhydrous ethanol = 1:1) are coated onto the orientation surface by printing. The coated sintered NdFeB thin film magnet is as follows: Figure 3 As shown, the weight gain of magnets with adjacent covered area spacing D of 0.16 mm, 0.4 mm, 1 mm, and 1.3 mm were 0.60 wt.%, 0.57 wt.%, 0.50 wt.%, and 0.47 wt.%, respectively; the area ratio (A / B) of the covered area to the uncovered area was 30.50, 11.76, 4.26, and 3.11, respectively.

[0062] (4) Place the four coated sintered NdFeB sheets into a molybdenum box, and then place them in a tube furnace for vacuum heat treatment. The heat treatment process is as follows: dehydrogenation temperature is 650℃, dehydrogenation time is 1h; diffusion treatment temperature is 900℃, time is 10h; aging treatment temperature is 500℃, time is 4h.

[0063] (5) The magnetic properties of the sample were tested using a permanent magnet material measuring instrument; the Dy content was analyzed in any coated area and any uncoated area at a distance of 100μm, 200μm and 500μm from the sample surface using an electron probe.

[0064] Comparative Example 2: Sintered NdFeB diffused magnets prepared by conventional grain boundary diffusion process, specifically including the following steps:

[0065] (1) Take magnetic properties B r =13.35kGs, H cJ =18.1kOe, H k / H cJ =98.1% of commercial 45H magnets were used as the base, and then a thin sheet of 20mm×20mm×1.8mm was cut out by wire cutting, with the orientation direction parallel to the thickness direction (1.8mm);

[0066] (2) Place the sheet in a 3% dilute nitric acid solution and ultrasonically clean it for 1 minute to remove oil and other impurities adhering to the surface; then place the sheet in anhydrous ethanol and ultrasonically clean it for 1 minute, and then dry it to prepare for coating the diffusion source.

[0067] (3) The thin sheet was coated with a diffusion material (dysprosium hydride: anhydrous ethanol = 1:1), and the weight gain of the coated sheet was 0.65 wt.%.

[0068] (4) The coated sintered NdFeB sheet is placed in a molybdenum box and then placed in a tube furnace for vacuum heat treatment. The heat treatment process is as follows: the dehydrogenation temperature is 650℃ and the dehydrogenation time is 1h; the diffusion treatment temperature is 900℃ and the time is 10h; the aging treatment temperature is 500℃ and the time is 4h.

[0069] (5) The magnetic properties of the sample were tested using a permanent magnet material measuring instrument; the Dy content of the coated area at a distance of 100 μm, 200 μm and 500 μm from the sample surface was analyzed using an electron probe.

[0070] The distance D between adjacent coated regions, the area ratio (A / B) of coated and uncoated regions, the weight gain of the diffusion source, and the magnetic properties after diffusion are listed in Table 3 for the samples of Example 2 and Comparative Example 2; the Dy content results at different depths from the sample surface are listed in Table 4.

[0071] Table 3. Spacing between adjacent coated regions, area ratio of coated to uncoated regions (A / B), weight gain of diffusion source, and magnetic properties after diffusion.

[0072]

[0073] As shown in Table 3, compared with conventional grain boundary diffusion technology, the diffusion magnet prepared by this invention has a higher utilization rate of the diffusion source and a superior overall magnetic performance.

[0074] Table 4. Dy content at different depths from the sample surface

[0075]

[0076] The Dy content data at different depths from the sample surface in Table 4 prove that the magnet prepared by this invention has the characteristic of a structure with fluctuating distribution of heavy rare earth concentration.

[0077] Example 3: A method for grain boundary diffusion in sintered NdFeB magnets, specifically including the following steps:

[0078] (1) Take magnetic properties B r =12.83kGs, H cJ =12.5kOe, H k / H cJ =98.4% commercial N40 magnets were used as the base, and then six thin slices of 17mm×15mm×2.5mm were cut out by wire cutting, with the orientation direction parallel to the thickness direction (2.5mm).

[0079] (2) Place 6 thin films in a 3% dilute nitric acid solution and ultrasonically clean for 1 minute to remove oil and other impurities attached to the surface; then place the thin films in anhydrous ethanol and ultrasonically clean for 1 minute, and then dry them to prepare for coating the diffusion source.

[0080] (3) Preparation of diffusion raw materials: Using a vacuum melting furnace, a nominal composition of Tb was prepared. 70 Cu 15 Al 15 、Pr3Nd 12 Tb 70Cu5Al 10 、Tb 94 Ti 5.5 B 0.5 Dy 70 Fe 10 Ga 20 Four alloy sheets (wt.%) were then crushed into hydrogen-crushed powder using a hydrogen crushing furnace. The hydrogen-crushed powder was then processed into fine powder with an average particle size of 3.0 μm using an air jet mill. Finally, the fine powder was mixed with anhydrous ethanol at a mass ratio of 1:1 and further ground into diffusion material with an average particle size of 1 μm using a ball mill.

[0081] (4) The diffusion material is coated onto the orientation surface by printing: the orientation surface is divided into 7 coated areas and 6 uncoated areas; the area of ​​a single coated area is 2mm × 15mm, and the area of ​​a single uncoated area is 0.5mm × 15mm. The total area A of the coated areas is 4.67 times the total area B of the uncoated areas. (Tb coating) 70 Cu 15 Al 15 The weight gains of the three thin-film magnets with diffusion raw materials were 0.4 wt.%, 0.8 wt.%, and 1.2 wt.%, respectively; the Pr3Nd coating... 12 Tb 70 Cu5Al 10 The weight gain of the diffused raw material sheet magnet was 1.2 wt.%; Tb coating 94 Ti 5.5 B 0.5 The weight gain of the diffused raw material sheet magnet was 1.2 wt.%; the coating Dy 70 Fe 10 Ga 20 The weight gain of the diffusion-grade sheet magnet was 1.2 wt.%.

[0082] (5) Place the coated sheet into a molybdenum box and then place it in a tube furnace for vacuum heat treatment. The heat treatment process is as follows: the diffusion treatment temperature is 900℃ and the time is 15h; the aging treatment temperature is 500℃ and the time is 4h.

[0083] (6) The magnetic properties of the sample were tested using a permanent magnet material measuring instrument; the content of heavy rare earth elements was analyzed in any coated area and any uncoated area at a distance of 100μm, 200μm and 500μm from the sample surface using an electron probe.

[0084] Comparative Example 3: Sintered NdFeB diffused magnets prepared by conventional grain boundary diffusion process, specifically including the following steps:

[0085] (1) Take magnetic properties B r =12.83kGs, H cJ =12.5kOe, Hk / H cJ =98.4% commercial N40 magnets were used as the base, and then thin sheets of 17mm×15mm×2.5mm were cut out by wire cutting, with the orientation direction parallel to the thickness direction (2.5mm).

[0086] (2) Place the sheet in a 3% dilute nitric acid solution and ultrasonically clean it for 1 minute to remove oil and other impurities adhering to the surface; then place the sheet in anhydrous ethanol and ultrasonically clean it for 1 minute, and then dry it to prepare for coating the diffusion source.

[0087] (3) Preparation of diffusion raw materials: Tb alloy sheets were refined using a vacuum melting furnace, and then the alloy sheets were crushed into hydrogen powder using a hydrogen crushing furnace. The hydrogen powder was then processed into fine powder with an average particle size of 3.0 μm using an air jet mill. Finally, the fine powder and anhydrous ethanol were mixed at a weight ratio of 1:1 and further ground into diffusion raw materials with an average particle size of 1 μm using a ball mill.

[0088] (4) The diffusion material is coated onto the orientation surface by printing, and the weight gain of the coated sheet is 0.84 wt.%.

[0089] (5) Place the coated sheet into a molybdenum box and then place it in a tube furnace for vacuum heat treatment. The heat treatment process is as follows: the diffusion treatment temperature is 900℃ and the time is 15h; the aging treatment temperature is 500℃ and the time is 4h.

[0090] (6) The magnetic properties of the sample were tested using a permanent magnet material measuring instrument; the content of heavy rare earth elements in the coated area at a distance of 100 μm, 200 μm and 500 μm from the sample surface was analyzed using an electron probe.

[0091] The distance D between adjacent coated regions, the area ratio (A / B) of coated and uncoated regions, the weight gain of the diffusion source, and the magnetic properties after diffusion are listed in Table 5 for the samples of Example 3 and Comparative Example 3; the results of heavy rare earth content at different depths from the sample surface are listed in Table 6.

[0092] Table 5. Spacing between adjacent coated regions, area ratio of coated to uncoated regions (A / B), weight gain of diffusion source, and magnetic properties after diffusion.

[0093]

[0094] Table 6. Heavy rare earth content at different depths from the sample surface

[0095]

[0096] As shown in Tables 5 and 6, compared with conventional grain boundary diffusion technology, the diffusion magnet prepared by this invention has a higher utilization rate of the diffusion source and a better overall magnetic performance, providing a new method for further efficient utilization of heavy rare earth elements.

[0097] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for grain boundary diffusion in a sintered NdFeB magnet, comprising the following steps: coating the surface of the magnet with a diffusion material containing at least one of Dy, Tb, and Ho to form a surface coating with alternating coated and uncoated regions, and then performing a heat treatment process to form a sintered NdFeB diffusion magnet with a high-low distribution of heavy rare earth concentration; the spacing between adjacent coated regions of the surface coating is D, and its range is 0.01mm≤D≤4mm; the coated regions exhibit a periodic distribution, with adjacent coated and uncoated regions forming one period, and the number of periods is not less than 2.

2. The method for grain boundary diffusion in sintered NdFeB magnets according to claim 1, characterized in that: The diffusion material coating on the surface of the sintered NdFeB thin-film magnet contains R. 1-a-b T a X b R is one or more of the heavy rare earth elements Dy, Tb, and Ho; T is one or more of La, Ce, Pr, Nd, Gd, Al, Co, Cu, Ga, Zr, Ti, Nb, and Fe; X is one or more of H, O, N, C, F, Cl, and B; a and b are weight percentages, where 0 wt.% ≤ a < 20 wt.% and 0 wt.% ≤ b < 5 wt.%.

3. The method for grain boundary diffusion in a sintered NdFeB magnet according to claim 1, characterized in that: The distance between adjacent coated areas of the surface coating is D, and its range is 0.1mm≤D≤1mm.

4. The method for grain boundary diffusion in sintered NdFeB magnets according to claim 1, characterized in that: The distance between adjacent coated areas of the surface coating is D, and its range is 0.2mm≤D≤0.5mm.

5. The method for grain boundary diffusion in a sintered NdFeB magnet according to claim 1, characterized in that: The surface coating, which is distributed between the covered and uncovered areas, is formed by a masking method, including screen printing, magnetron sputtering, or spraying.

6. The method for grain boundary diffusion in a sintered NdFeB magnet according to claim 1, characterized in that: The thickness of the sintered NdFeB thin sheet magnet is 0.1mm-20mm.

7. The method for grain boundary diffusion in a sintered NdFeB magnet according to claim 1, characterized in that: The concentration of heavy rare earth elements in the sintered NdFeB diffused magnet exhibits a periodic high-low distribution, with the concentration of heavy rare earth elements in the coated region being higher than that in the uncoated region.

8. The method for grain boundary diffusion in a sintered NdFeB magnet according to claim 1, characterized in that: The highest concentration of heavy rare earth elements (CR) in the coating region at a distance of 100 μm from the magnet surface is C. 100 The lowest concentration of heavy rare earth elements in the uncoated region is 100 , △C1=C 100 - 100 , 0 wt.%<△C1≤20wt.%.

9. The method for grain boundary diffusion in a sintered NdFeB magnet according to claim 1, characterized in that: The highest concentration of heavy rare earth elements (HREE) in the coating region at a distance of 200 μm from the magnet surface is C. 200 The lowest concentration of heavy rare earth elements in the uncoated region is 200 , △C2=C 200 - 200 , 0 wt.%<△C2≤10wt.%.

10. The method for grain boundary diffusion in a sintered NdFeB magnet according to claim 1, characterized in that: The highest concentration of heavy rare earth elements (CR) in the coating region at a distance of 500 μm from the magnet surface is C. 500 The lowest concentration of heavy rare earth elements in the uncoated region is 500 , △C5=C 500 - 500 , 0 wt.%<△C5≤2wt.%.

11. The method for grain boundary diffusion in a sintered NdFeB magnet according to claim 9, characterized in that: When the spacing D between adjacent coated areas of the surface coating is in the range of 0.01mm≤D≤0.1mm, 0 wt.%<△C2≤1wt.%.

12. The method for grain boundary diffusion in a sintered NdFeB magnet according to claim 9, characterized in that: When the spacing D between adjacent coated areas of the surface coating is in the range of 0.1mm≤D≤0.2mm, 0 wt.%<△C2≤2wt.%.

13. The method for grain boundary diffusion in a sintered NdFeB magnet according to claim 9, characterized in that: When the spacing D between adjacent coated areas of the surface coating is in the range of 0.2mm≤D≤0.5mm, 0 wt.%<△C2≤6wt.%.

14. The method for grain boundary diffusion in a sintered NdFeB magnet according to claim 9, characterized in that: When the spacing D between adjacent coated areas of the surface coating is in the range of 0.5mm≤D≤1mm, 0 wt.%<△C2≤8wt.%.

15. The method for grain boundary diffusion in a sintered NdFeB magnet according to claim 9, characterized in that: When the spacing D between adjacent coated areas of the surface coating is 1mm≤D≤4mm, 0 wt.%<△C2≤10wt.%.

16. The method for grain boundary diffusion in a sintered NdFeB magnet according to claim 1, characterized in that: The heat treatment process involves first holding the temperature at 700℃-1000℃ for 1 hour to 40 hours, and then holding it at 400℃-600℃ for 1 hour to 10 hours.

17. The method for grain boundary diffusion in a sintered NdFeB magnet according to claim 1, characterized in that: The coating area is located on the surface of the sintered NdFeB magnet perpendicular to the orientation direction.

18. The method for grain boundary diffusion in a sintered NdFeB magnet according to claim 1, characterized in that: The shape of the covered area can be circular or rectangular.

19. The method for grain boundary diffusion in a sintered NdFeB magnet according to claim 1, characterized in that: The area of ​​the covered region is A, the area of ​​the uncovered region is B, and the ratio of A to B is 0.05-100.

20. The method for grain boundary diffusion in a sintered NdFeB magnet according to claim 19, characterized in that: Different positions on the same magnet surface have different A / B ratios.

21. The method for grain boundary diffusion in a sintered NdFeB magnet according to claim 16, characterized in that: The heat treatment process includes a dehydrogenation process, and the temperature of the dehydrogenation process is 600℃-800℃.

Images