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

Abstract

This invention discloses a grain boundary diffusion method for sintered NdFeB magnets. First, a heavy rare earth diffusion source is coated onto the surface of the sintered NdFeB magnet using screen printing technology, followed by heat treatment to obtain a sintered NdFeB magnet diffuser. The lower surface of the scraper is sequentially arranged with multiple scraper units consisting of a left groove, a planar region, and a right groove. Each scraper unit corresponds to a sintered NdFeB magnet, and the depths of the left and right grooves are set according to the degree of coercivity enhancement of the corresponding sintered NdFeB magnet region. The advantages are that it achieves a tiered enhancement of coercivity in easily demagnetized and difficult-to-demagnetize regions of the sintered NdFeB magnet, balancing the actual coercivity requirements of both regions and avoiding excessively high or low coercivity in the difficult-to-demagnetize region. While meeting the operating requirements of permanent magnet motors, the method is cost-effective, and the simultaneous printing of easily demagnetized and difficult-to-demagnetize regions ensures high production efficiency.

Description

Technical Field

[0001] This invention relates to a grain boundary diffusion method, and more particularly to a grain boundary diffusion method for sintered NdFeB magnets. Background Technology

[0002] Sintered NdFeB magnets, with their high energy product (BH)max and excellent machinability, have become a core functional material in modern industry. Their applications cover key areas such as consumer electronics (e.g., hard disk drives, speakers), inverter air conditioners, and new energy equipment (e.g., electric vehicle drive motors, wind turbines).

[0003] With the rapid development of variable frequency air conditioners, electric vehicles and other fields, permanent magnet motors using sintered NdFeB magnets face two major problems during operation: eddy current loss and insufficient thermal stability. This leads to an increase in the temperature of the sintered NdFeB magnets, which in turn causes certain areas of the sintered NdFeB magnets (also called demagnetizing areas) to be demagnetized preferentially, ultimately causing fluctuations in the magnetic field output of the sintered NdFeB magnets or even demagnetization.

[0004] To address the issue of temperature rise in sintered NdFeB magnets, heavy rare earth elements (Tb / Dy) are typically added to the magnets to partially replace the internal Nd sites, thereby creating a highly anisotropic field (H). A (Nd,Tb / Dy)2Fe 14 The B main phase enhances the coercivity Hcj of sintered NdFeB magnets.

[0005] Currently, there are two common methods for adding heavy rare earth elements (Tb / Dy): direct addition of Tb or Dy and addition using grain boundary diffusion technology. Direct addition of Tb or Dy is implemented during the NdFeB smelting or powdering process. Grain boundary diffusion technology, unlike direct addition, involves coating the surface of the sintered NdFeB magnet with a layer of heavy rare earth diffusion source containing Tb or Dy. Vacuum heat treatment allows the Tb or Dy to penetrate along the liquid phase grain boundaries into the interior of the sintered NdFeB magnet. After cooling, a gradient distribution of Tb / Dy-rich shell structure is formed along the penetration direction, effectively improving the coercivity (Hcj) of the sintered NdFeB magnet. Compared to direct addition, grain boundary diffusion technology reduces the consumption of Tb / Dy and also results in a smaller decrease in the remanence (Br) of the sintered NdFeB magnet.

[0006] On the one hand, during operation, the temperature of the sintered NdFeB magnets rises, causing the easily demagnetized areas to be demagnetized preferentially. Therefore, it is necessary to further increase the coercivity Hcj in these easily demagnetized areas to improve their resistance to demagnetization. Similarly, the coercivity Hcj required for the less easily demagnetized areas of the sintered NdFeB magnets can be appropriately lower. On the other hand, due to their scarcity and strategic value, the prices of heavy rare earth elements Tb and Dy have remained high for a long time.

[0007] The current mainstream method for grain boundary diffusion in sintered NdFeB magnets employs conventional grain boundary diffusion technology, without distinguishing between easily demagnetized and difficult-to-demagnetize regions. A layer of heavy rare earth diffusion sources of uniform thickness is coated onto the surface of the sintered NdFeB magnet, followed by vacuum heat treatment to obtain the sintered NdFeB magnet diffuser. The sintered NdFeB magnet diffuser obtained by this method exhibits high coercivity in both easily and difficult-to-demagnetize regions, meeting the operating requirements of permanent magnet motors. However, the coercivity in the difficult-to-demagnetize regions is significantly higher than the actual requirements, resulting in a large amount of heavy rare earth (Tb / Dy) used and higher costs.

[0008] To utilize heavy rare earth Tb / Dy more efficiently and reduce costs, researchers have proposed some new improvements based on conventional grain boundary diffusion technology. For example, Chinese patent CN222571844U discloses a screen printing selective diffusion method for sintered NdFeB magnets. The screen is designed with areas where the printing material cannot pass through and areas that can pass through. The heavy rare earth diffusion source is then used as the printing material. The screen ensures that easily demagnetized areas of the sintered NdFeB magnet are coated with heavy rare earth Tb / Dy, while areas that are not easily demagnetized are not coated. After heat treatment, a sintered NdFeB magnet diffuser is obtained. For example, Chinese patent application CN120413271A discloses a high-throughput selective diffusion agent and its application. It employs additive manufacturing to print a high-throughput selective diffusion agent (i.e., a heavy rare earth diffusion source) onto the edge region of the magnetic pole surface of a sintered NdFeB magnet, resulting in a printed magnet. The printed area is coated with heavy rare earth Tb / Dy, while the unprinted area is not coated. Vacuum heat treatment is then performed to obtain a sintered NdFeB magnet diffuser. Although the amount of heavy rare earth Tb / Dy used in these two patented technologies is relatively small, the coercivity of the non-demagnetizing region of the sintered NdFeB magnet diffuser is not improved and remains very low, making it difficult to meet the operating requirements of most permanent magnet motors. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a grain boundary diffusion method for sintered NdFeB magnets that can improve the coercivity of easily demagnetized and difficult-to-demagnetize regions in a layered manner, taking into account the actual needs of coercivity in both regions, avoiding excessively high or low coercivity in the difficult-to-demagnetize regions, and meeting the operating conditions of permanent magnet motors while having a low cost.

[0010] The technical solution adopted by this invention to solve the above-mentioned technical problems is as follows: a grain boundary diffusion method for sintered NdFeB magnets, firstly, using screen printing technology to cover the surface of sintered NdFeB magnets with heavy rare earth diffusion sources, and then performing heat treatment to obtain a sintered NdFeB magnet diffuser; the sintered NdFeB magnet is cuboid in shape, with its orientation direction along its thickness direction; the width direction of the sintered NdFeB magnet is taken as the left-right direction, the length direction as the front-back direction, and the thickness direction as the up-down direction; the sintered NdFeB magnet is divided into three cuboid regions along its width direction, wherein the middle region is a region that is not easily demagnetized, and the left and right side regions are regions that are easily demagnetized; in the screen printing technology, the squeegee is cuboid in shape; the squeegee has multiple squeegee unit bodies arranged sequentially along its length direction on its lower surface, each squeegee unit body consisting of a left groove, a planar region, and a right groove arranged sequentially from left to right, the planar region being the left groove and the right groove. On the lower surface of the squeegee, the left and right grooves are recessed upwards from the lower surface of the squeegee to a predetermined depth and extend through the entire structure. The lower end faces of the left and right grooves, as well as the planar area, are rectangular. The width of the lower end face of the left groove in the left-right direction is equal to the width of the left side region of the sintered NdFeB magnet, the width of the lower end face of the right groove in the left-right direction is equal to the width of the right side region of the sintered NdFeB magnet, and the width of the planar area in the left-right direction is equal to the width of the middle region of the sintered NdFeB magnet. During screen printing, each squeegee unit corresponds to the projection position of one sintered NdFeB magnet in the width direction. The depth of each of the left and right grooves is set according to the coercivity enhancement degree of the corresponding sintered NdFeB magnet region. The higher the required coercivity enhancement degree, the greater the corresponding groove depth; the lower the required coercivity enhancement degree, the smaller the corresponding groove depth.

[0011] Compared with the prior art, the advantages of this invention lie in that multiple scraper units, each consisting of a left groove, a planar region, and a right groove, are sequentially arranged on the lower surface of the scraper. Each scraper unit corresponds to a sintered NdFeB magnet and is used for screen printing on the sintered NdFeB magnet. Since the depths of the left and right grooves in the scraper unit are set according to the coercivity enhancement level of the corresponding sintered NdFeB magnet region, the depths of the left and right grooves can be adaptively set according to the coercivity enhancement level in the easily demagnetized areas of the sintered NdFeB magnet, thus coating the easily demagnetized areas of the sintered NdFeB magnet with a phase coating. A thicker heavy rare earth diffusion source is used, while a relatively thinner heavy rare earth diffusion source is printed on a planar area in the non-demagnetizing region of the sintered NdFeB magnet. This ensures that the coercivity of the sintered NdFeB magnet diffuser obtained after heat treatment is adapted to its actual needs, achieving a tiered increase in coercivity between the easily demagnetized and non-demagnetized regions of the sintered NdFeB magnet. This approach balances the actual coercivity requirements of both regions, avoiding excessively high or low coercivity in the non-demagnetizing region. It meets the operating requirements of the permanent magnet motor while maintaining low cost. Furthermore, the simultaneous printing of the easily demagnetized and non-demagnetized regions ensures high production efficiency.

[0012] Furthermore, the distance between two adjacent scraper units is greater than or equal to 0 and less than or equal to 10 mm.

[0013] Furthermore, the scraper material is stainless steel, brass, polyurethane, neoprene rubber, or silicone rubber.

[0014] Furthermore, in the aforementioned screen printing technology, the mesh count is 40-300 mesh.

[0015] Furthermore, the angle between the scraper and the wire mesh is θ, where 10°≤θ≤80°.

[0016] Furthermore, the heavy rare earth diffusion source composition is R. 1-a-b T a A b R contains one or more of the heavy rare earth elements Dy, Tb, and Ho; T contains one or more of the elements La, Ce, Pr, Nd, Gd, Al, Co, Cu, Ga, Zr, Ti, Nb, and Fe; A contains one or more of the elements H, O, N, C, F, Cl, and B; and a and b are weight percentages, with 0 wt% ≤ a < 20 wt% and 0 wt% ≤ b < 5 wt%.

[0017] Furthermore, the heat treatment process is as follows: first, the temperature is kept at 700℃-1000℃ for 1h-40h, and then at 400℃-600℃ for 1h-10h. Attached Figure Description

[0018] Figure 1 The following is a flowchart illustrating the grain boundary diffusion method for sintered NdFeB magnets according to Embodiment 1 of the present invention: (a) is a schematic diagram of the scraper structure; (b) is a schematic diagram of the coating on different regions of the surface of a sintered NdFeB magnet corresponding to a scraper unit after the heavy rare earth diffusion source is printed using a scraper; (c) is a cross-sectional schematic diagram of the sintered NdFeB magnet with coating after the heavy rare earth diffusion source is printed using a scraper; (d) is a cross-sectional schematic diagram of different regions of the sintered NdFeB magnet diffuser after heat treatment. Figure 2 The following is a flowchart illustrating the grain boundary diffusion method for sintered NdFeB magnets according to Embodiment 2 of the present invention: (a) is a schematic diagram of the scraper structure; (b) is a schematic diagram of the coating on different regions of the surface of a sintered NdFeB magnet corresponding to a scraper unit after the heavy rare earth diffusion source is printed using a scraper; (c) is a cross-sectional schematic diagram of the sintered NdFeB magnet with coating after the heavy rare earth diffusion source is printed using a scraper; (d) is a cross-sectional schematic diagram of different regions of the sintered NdFeB magnet diffuser after heat treatment. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0020] Example 1: As Figure 1 As shown, a method for grain boundary diffusion in sintered NdFeB magnets includes the following steps: Step 1: Take a sintered NdFeB magnet with Br=14.53kGs, Hcj=13.05kOe, Hk / Hcj=98.3% and grade N55, and cut it into 48 rectangular thin slices with dimensions (length×width×thickness) of 15mm×15mm×4mm using wire cutting technology. The orientation of the 48 rectangular thin slices is the same as its thickness direction.

[0021] Step 2: First, place the 48 rectangular thin slices into a 3% dilute nitric acid solution and ultrasonically clean for 1 minute to remove oil and other impurities adhering to the surface. Then, place them in anhydrous ethanol and ultrasonically clean for 1 minute. After drying, they are the 48 sintered NdFeB magnets 1 to be processed. Divide the 48 sintered NdFeB magnets 1 into 4 groups of samples, each group of samples including 12 sintered NdFeB magnets 1. Each sintered NdFeB magnet 1 is divided into three rectangular regions along its width. The middle region 2 is the region that is not easy to demagnetize, while the left and right regions 3 and 4 are the regions that are easy to demagnetize.

[0022] Step 3: Prepare one set of standard scrapers and three sets of improved scrapers; the standard scrapers are rectangular and made of stainless steel; such as... Figure 1As shown in (a), each improved scraper is formed by sequentially arranging multiple scraper units 6 along the length of the lower surface (the surface in contact with the wire mesh) of a rectangular stainless steel scraper 5. Each scraper unit 6 consists of a left groove 7, a planar region 8, and a right groove 9 arranged sequentially from left to right. The planar region 8 is the lower surface of the rectangular scraper 5 between the left groove 7 and the right groove 9. Both the left groove 7 and the right groove 9 are rectangular (i.e., square) and extend through the rectangular scraper 5. Their lower end faces and the planar region 8 (i.e., the non-groove region) are rectangular. Figure 1 As shown in Figure (b), the width of the lower end face of the left groove 7 along the left-right direction is equal to the width of the left region 3 of the sintered NdFeB magnet 1; the width of the lower end face of the right groove 9 along the left-right direction is equal to the width of the right region 4 of the sintered NdFeB magnet 1; and the width of the planar region 8 along the left-right direction is equal to the width of the middle region 2 of the sintered NdFeB magnet 1. The specific parameters of one set of conventional scrapers and three sets of improved scrapers (referred to as Group 1, Group 2 and Group 3, respectively) are shown in Table 1. Table 1: Specific parameters of conventional scrapers and three sets of improved scrapers

[0023] In Table 1, the groove depth is the depth of the left groove 7 and the right groove 9, the groove width is the width of the left groove 7 and the right groove 9 along the left and right directions, the width of the non-groove area is the width of the planar area 8 along the left and right directions, and the total width of the scraper unit is the sum of the widths of the left groove 7, the planar area 8 and the right groove 9 along the left and right directions.

[0024] Step 4: Prepare the ink diffusion source, i.e., the heavy rare earth diffusion source: Grind terbium hydride into powder with a particle size of 2.7-3.0 μm using an air jet mill, then mix the powder with alcohol at a mass ratio of 1:1 and stir evenly to obtain the ink diffusion source.

[0025] Step 5: Match the conventional squeegee and the three sets of improved squeegees to the four sets of samples one by one; under the same screen and the same ink diffusion source conditions, screen print the four sets of samples using the conventional squeegee and the three sets of improved squeegees respectively, coating the ink diffusion source onto the two orientation surfaces of each sintered NdFeB magnet 1 in each set of samples, such as... Figure 1 As shown in (b) and (c), 71 represents the coating corresponding to the left groove 7, 81 represents the coating corresponding to the planar area 8, and 91 represents the coating corresponding to the right groove 9. In each improved scraper set and its corresponding sample set, the distribution of the 12 sintered NdFeB magnets 1 in that sample set is consistent with the distribution of the 12 scraper unit bodies 6 in that improved scraper set. Specific screen printing parameters are shown in Table 2 below, and the ink diffusion source thickness (i.e., coating thickness) data covering the surface of the sintered NdFeB magnets 1 is shown in Table 3. Table 2: Screen Printing Parameter Table

[0026] Table 3: Coating Parameter Table

[0027] In Table 3, the coating thickness corresponding to the groove is the average thickness of coating 71 and 91 at the corresponding groove 7 and the right groove 9, formed by coating 12 scraper units 6 of each improved scraper 5 on the corresponding sample. The coating thickness corresponding to the non-groove area is the average thickness of coating 81 at the corresponding planar area 8.

[0028] Analysis of Table 3 shows that, among the three sets of samples screen-printed using three sets of improved squeegees, the average thicknesses of coatings 71 and 91 corresponding to the left groove 7 and right groove 9 are 17.2 μm, 22.1 μm, and 28.3 μm, respectively. The average thicknesses of coating 81 corresponding to the planar area 8 are 10.1 μm, 10.2 μm, and 10.2 μm, respectively. This indicates a significant difference in coating thickness between the non-demagnetizing and easily demagnetized areas among the three sets of samples. In contrast, among the samples screen-printed using a conventional squeegee, the average coating thicknesses in the non-demagnetizing and easily demagnetized areas are 10.1 μm and 10.3 μm, respectively. The coating thicknesses in these two areas are similar and do not show a clear difference.

[0029] Step 6: Place the four groups of printed and coated samples into molybdenum boxes, and then place them in a tube furnace for vacuum heat treatment to obtain four groups of sintered NdFeB magnet diffusers 10. The heat treatment process is as follows: the diffusion treatment temperature is 900℃ and the time is 14h; the aging treatment temperature is 500℃ and the time is 5h.

[0030] Step 7: After heat treatment, different regions of each group of 12 sintered NdFeB magnet diffusers 10 are subjected to [further treatment]. Figure 1 In Figure (d), wire cutting samples were taken at locations 51 and 52, and magnetic properties were tested. The sample dimensions (length × width × thickness) were 7.0 mm × 2.3 mm × 4.0 mm, where 4.0 mm represents the orientation direction. After heat treatment, Figure 1 In Figure (d), the blue dashed box indicates that part A has completely diffused into the interior of the sintered NdFeB magnet. Part A is retained only to illustrate the correspondence between areas 51 and 52 and the coating. The test results are shown in Table 4 below: Table 4: Performance Test Data Table

[0031] In Table 4, Br, Hcj, and Hk / Hcj represent the average values ​​of each group of 12 sintered NdFeB magnet diffusers 10. Analysis of the data in Table 4 shows that, after heat treatment to obtain the corresponding three groups of sintered NdFeB magnet diffusers 10, the average Hcj values ​​in region 51 (corresponding to coating 91) are 22.55 kOe, 23.19 kOe, and 23.60 kOe, respectively, while the average Hcj values ​​in region 52 (corresponding to coating 81) are 20.10 kOe, 20.13 kOe, and 20.04 kOe, respectively. The Hcj differences between regions 51 and 52 for the three groups of sintered NdFeB magnet diffusers 10 are 2.45 kOe, 3.06 kOe, and 3.56 kOe, respectively. Region 51 shows a significant increase in Hcj compared to region 52. Meanwhile, the Br differences in the three sets of sintered NdFeB magnet diffusers 10 in regions 51 and 52 were -0.04 kGs, -0.06 kGs, and -0.09 kGs, respectively, which were relatively small. This indicates that while significantly increasing Hcj, it is possible to avoid a large decrease in Br. In contrast, the set of samples screen-printed using a conventional scraper, after heat treatment to obtain the corresponding set of sintered NdFeB magnet diffusers 10, showed no significant differences in Hcj, Br, and Hk / Hcj in regions 51 and 52, meaning that conventional scrapers cannot achieve zoned processing.

[0032] Example 2: Figure 2 As shown, a method for grain boundary diffusion in sintered NdFeB magnets includes the following steps: Step 1: Take a sintered NdFeB magnet with Br=14.53kGs, Hcj=13.05kOe, Hk / Hcj=98.3% and grade N55, and cut it into 18 rectangular thin slices with dimensions (length×width×thickness) of 18mm×18mm×4mm using wire cutting technology. The orientation of the 18 rectangular thin slices is the same as its thickness direction.

[0033] Step 2: First, place the 18 rectangular thin slices into a 3% dilute nitric acid solution and ultrasonically clean them for 1 minute to remove oil and other impurities adhering to the surface. Then, place them in anhydrous ethanol and ultrasonically clean them for 1 minute. After drying, they are the 18 sintered NdFeB magnets 1 to be processed. Divide the 18 sintered NdFeB magnets 1 into two groups of 9 sintered NdFeB magnets 1 in each group. Each sintered NdFeB magnet 1 is divided into three rectangular regions along its width. The middle region 2 is the region that is not easy to demagnetize, while the left and right regions 3 and 4 are the regions that are easy to demagnetize.

[0034] Step 3: Prepare a set of standard scrapers and a set of improved scrapers. The standard scrapers are rectangular scrapers made of stainless steel; for example... Figure 2As shown in Figure (a), each improved scraper is formed by sequentially arranging multiple scraper units 6 along the length of the lower surface (the surface in contact with the wire mesh) of a rectangular stainless steel scraper 5. Each scraper unit 6 consists of a left groove 7, a planar region 8, and a right groove 9 arranged sequentially from left to right. The planar region 8 is the portion of the lower surface of the rectangular scraper 5 located between the left groove 7 and the right groove 9. The left groove 7 and the right groove 9 extend from front to back, and their cross-sections are both triangular. The lower end faces of the left groove 7 and the right groove 9, and the planar region 8 (non-groove region), are both rectangular. Figure 2 As shown in Figure (b), the width of the lower end face of the left groove 7 along the left-right direction is equal to the width of the left region 3 of the sintered NdFeB magnet 1; the width of the lower end face of the right groove 9 along the left-right direction is equal to the width of the right region 4 of the sintered NdFeB magnet 1; and the width of the planar region 8 along the left-right direction is equal to the width of the middle region 2 of the sintered NdFeB magnet 1. The specific parameters of a set of conventional scrapers and a set of improved scrapers are shown in Table 5. Table 5: Specific parameters of conventional scrapers and a set of improved scrapers

[0035] In Table 5, the groove depth is the depth of the left groove 7 and the right groove 9, the groove width is the width of the left groove 7 and the right groove 9 along the left-right direction, and the width of the non-groove area is the width of the planar area 8 along the left-right direction. The total width of the scraper unit is the sum of the widths of the left groove 7, the planar area 8, and the right groove 9 along the left-right direction. β=45° is the vertex angle of the triangular cross-section of the left groove 7 and the right groove 9.

[0036] Step 4: Prepare the ink diffusion source, i.e., the heavy rare earth diffusion source: Grind terbium hydride into powder with an average particle size of 2.7 to 3.0 μm using an air jet mill. Then mix the powder with alcohol at a mass ratio of 1:1 and stir evenly to obtain the ink diffusion source.

[0037] Step 5: Under the same screen and ink diffusion source conditions, screen printing is performed on two groups of sintered NdFeB magnets 1 using a conventional squeegee and a set of improved squeegees, respectively. The distribution and arrangement of the nine sintered NdFeB magnets 1 in each group are consistent with the distribution and arrangement of the nine squeegee units 6. The specific printing parameters are shown in Table 6 below: Table 6: Screen Printing Parameter Table

[0038] Step 6: Coat the ink diffusion source onto the two orientation surfaces of the sintered NdFeB magnet 1, and improve the ink diffusion source coating corresponding to the scraper unit 6 of the scraper 5 as follows: Figure 2 As shown in (b) and (c), the coating thickness was tested in areas 71 and 72 corresponding to the coating in the left groove 7, and in coating 81 corresponding to the planar area 8. The specific data are shown in Table 7 below: Table 7: Coating Thickness Data for Regions 71 and 72

[0039] Combination Figure 2 As shown in Table 7 (b) and (c), in the group of samples screen-printed using the improved squeegee, the measured thickness range of coating 81 to coating area 71 is 10.2 μm-22.6 μm. The groove depth corresponding to coating area 71 is greater than that corresponding to coating area 72. Coating 81 corresponds to the non-groove area, which is equivalent to a groove depth of 0. The thickness of coating area 71 is greater than that of coating area 72, and the thickness of coating area 72 is greater than that of coating 81. This indicates that the deeper the groove depth, the thicker the corresponding coating thickness. In contrast, in the group of samples screen-printed using the conventional squeegee, the coating thickness ranges from 10.1 μm to 10.3 μm, with no significant variation in coating thickness at any location.

[0040] Step 7: Place the two sets of sintered NdFeB magnets 1 after printing and coating into a molybdenum box, and then place them in a tube furnace for vacuum heat treatment to obtain two sets of sintered NdFeB magnet diffusers 10. The heat treatment process is as follows: the diffusion treatment temperature is 900℃ and the time is 14h; the aging treatment temperature is 500℃ and the time is 5h.

[0041] Step 8: After heat treatment, for each group of 9 sintered NdFeB magnet diffusers 10, in... Figure 2 In Figure (d), wire cutting samples were obtained from regions 51, 52, and 53, and magnetic properties were tested. The sample dimensions (length × width × thickness) were 7.0 mm × 1.5 mm × 4.0 mm, where 4.0 mm represents the orientation direction. After heat treatment, Figure 2 In Figure (d), the blue dashed box indicates that part B has completely diffused into the interior of the sintered NdFeB magnet. Part B is retained only to illustrate the correspondence between regions 51, 52, and 53 and the coating. The test results are shown in Table 8 below: Table 8: Performance Test Data Table

[0042] In Table 8, region 51 is the diffusion area of ​​coating region 71, region 52 is the diffusion area of ​​coating region 72, and region 53 is the diffusion area of ​​coating region 81. Analysis of the data in Table 8 shows that as the depth of the triangular grooves (left groove 7 and right groove 9) increases, the Hcj value of the corresponding region of the sintered NdFeB magnet diffuser 10 increases. The maximum difference in Hcj between the groove-corresponding region and the non-groove-corresponding region is 3.00 kOe. Simultaneously, the Br value difference between different regions is small, and the Hk / Hcj difference between different regions is also small, which avoids excessive Br decrease while increasing coercivity. This performance distribution of the sintered NdFeB magnet diffuser 10 can meet the working environment requirements of magnets used in specific drive motors.

[0043] In summary, this invention, by sequentially arranging multiple scraper unit bodies 6 on the lower surface of the scraper, each consisting of a left groove 7, a planar region 8, and a right groove 9, corresponds to a sintered NdFeB magnet 1. The depths of the left and right grooves 7 and 9 in the scraper unit body 6 are set according to the degree of coercivity enhancement in the corresponding sintered NdFeB magnet region. This allows for adaptive setting of the depths of the left and right grooves 7 and 9 based on the degree of coercivity enhancement in the easily demagnetized areas of the sintered NdFeB magnet 1, thereby coating the easily demagnetized areas of the sintered NdFeB magnet 1 with a corresponding thickness of heavy rare earth diffusion source. Meanwhile, by printing relatively thin heavy rare earth diffusion sources in the non-demagnetizing areas of the sintered NdFeB magnet in planar region 8, the coercivity of each part of the sintered NdFeB magnet diffuser 10 obtained after heat treatment is adapted to its actual needs. This achieves a tiered increase in coercivity between the easily demagnetized and non-demagnetized areas of the sintered NdFeB magnet, taking into account the actual coercivity requirements of both areas and avoiding excessively high or low coercivity in the non-demagnetized areas. This approach meets the operating requirements of the permanent magnet motor while keeping costs low. In addition, the simultaneous printing of the easily demagnetized and non-demagnetized areas ensures high production efficiency.

Claims

1. A method for grain boundary diffusion in sintered NdFeB magnets, comprising firstly, using screen printing technology to coat the surface of a sintered NdFeB magnet with a heavy rare earth diffusion source, and then performing heat treatment to obtain a sintered NdFeB magnet diffuser; wherein the sintered NdFeB magnet is cuboid in shape, with its orientation along its thickness direction; the width direction of the sintered NdFeB magnet is taken as the left-right direction, the length direction as the front-back direction, and the thickness direction as the up-down direction; the sintered NdFeB magnet is divided into three cuboid regions along its width direction, wherein... The central area is the area that is not easily demagnetized, while the left and right side areas are the areas that are easily demagnetized. The characteristic feature is that, in the screen printing technology, the squeegee is rectangular; the squeegee has multiple squeegee units arranged sequentially along its length on its lower surface. Each squeegee unit consists of a left groove, a planar area, and a right groove arranged sequentially from left to right. The planar area is the lower surface of the squeegee between the left and right grooves. The left and right grooves are recessed upwards from the lower surface of the squeegee to a predetermined depth and extend through the entire squeegee. The lower end faces of the left and right grooves, as well as the planar area, are rectangular. The width of the lower end face of the left groove along the left-right direction is... The width of the left region of the sintered NdFeB magnet is equal to the width of the right region of the sintered NdFeB magnet. The width of the lower end face of the right groove in the left-right direction is equal to the width of the right region of the sintered NdFeB magnet. The width of the planar region in the left-right direction is equal to the width of the middle region of the sintered NdFeB magnet. During screen printing, each squeegee unit corresponds to the projection position of one sintered NdFeB magnet in the width direction. The depth of each part of the left and right grooves is set according to the coercivity enhancement degree of the corresponding sintered NdFeB magnet region. The higher the required coercivity enhancement degree, the greater the corresponding groove depth, and the lower the required coercivity enhancement degree, the smaller the corresponding groove depth.

2. The grain boundary diffusion method for sintered NdFeB magnets according to claim 1, characterized in that, The distance between two adjacent scraper units is greater than or equal to 0 and less than or equal to 10 mm.

3. The grain boundary diffusion method for sintered NdFeB magnets according to claim 1, characterized in that, The scraper material is stainless steel, brass, polyurethane, neoprene rubber, or silicone rubber.

4. The grain boundary diffusion method for sintered NdFeB magnets according to claim 1, characterized in that, In the aforementioned screen printing technology, the mesh count is 40-300 mesh.

5. The grain boundary diffusion method for sintered NdFeB magnets according to claim 4, characterized in that, The angle between the scraper and the wire mesh is θ, where 10°≤θ≤80°.

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

7. The grain boundary diffusion method for sintered NdFeB magnets according to claim 1, characterized in that, The heat treatment process is as follows: first, keep at a temperature of 700℃-1000℃ for 1h-40h, and then keep at a temperature of 400℃-600℃ for 1h-10h.

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