R-t-b rare earth permanent magnet with corner reinforcement and method for manufacturing the same

Abstract

The application discloses an R-T-B rare earth permanent magnet with reinforced corners and a preparation method thereof. A coating surface of a magnet diffusion source is divided into a corner area and a non-corner area. The corner area of the magnet is coated with a diffusion source containing Zr, Ti or Nb elements, and the non-corner area of the magnet is coated with a heavy rare earth element diffusion source not containing the elements. In the process of grain boundary diffusion, the Zr, Ti or Nb elements diffuse into the R-rich phase of the grain boundary of the magnet, and the R-rich phase of the grain boundary of the magnet is strengthened by solid solution or generation of second phase precipitates, so that the strength of the corners of the magnet is improved. The application improves the mechanical properties of the corner area of the magnet by the method of partition grain boundary diffusion without affecting the non-corner area of the magnet, can significantly reduce the rate of missing edges and corners of the magnet in the process of transportation and assembly without reducing the magnetic properties of the magnet, and has important significance for reducing the cost of neodymium iron boron products.

Description

Technical Field

[0001] This invention relates to an edge-reinforced RTB rare-earth permanent magnet and its preparation method, belonging to the field of rare-earth magnets. Background Technology

[0002] Grain boundary diffusion is a new technology developed in recent years. It can significantly improve the coercivity of RTB rare earth permanent magnets while ensuring that the magnet has high remanence. It is a commonly used method for preparing high-performance RTB rare earth permanent magnets.

[0003] Grain boundary diffusion treatment first involves coating the magnet surface with a diffusion source layer containing heavy rare earth elements, followed by heating to a specified temperature and holding for a period of time. During the high-temperature stage, the heavy rare earth elements in the diffusion source on the magnet surface diffuse along the R-rich phase at the grain boundaries into the magnet interior, forming a shell layer with a highly anisotropic field on the surface of the main phase grains. Furthermore, the grain boundary diffusion process introduces additional rare earth elements into the magnet, increasing the total rare earth content and making the R-rich phase at the grain boundaries between the main phase grains more continuous, thereby achieving de-exchange coupling between the main phase grains. Therefore, grain boundary diffusion improves the coercivity of the magnet by enhancing the anisotropic field on the main phase grain surface and optimizing the distribution of the R-rich phase at the grain boundaries.

[0004] While RTB rare-earth permanent magnets possess high magnetic properties, their inherent material characteristics result in significant brittleness. During machining, processing stress can cause numerous microcracks at the magnet's edges and corners. In subsequent product transportation and assembly, even minor impacts can lead to these cracks, resulting in chipped or missing edges on the product.

[0005] Adding certain amounts of high-melting-point metal elements such as Zr, Ti, and Nb to magnets can strengthen the R-rich phase at the grain boundaries through solid solution or the formation of a second precipitate, thereby improving the mechanical properties of the magnets. However, as the content of non-magnetic elements increases, the remanence of the magnet decreases. Secondly, during transportation and assembly, the edges and corners of NdFeB magnets are prone to defects due to impacts, while other parts of the magnet rarely experience collision defects. This means that by using certain methods to ensure the presence of Zr, Ti, and Nb elements in the corner areas of the magnet without affecting other areas, the yield rate of NdFeB magnets can be improved without compromising their magnetic properties. Summary of the Invention

[0006] To address the issue that neodymium iron boron magnets are prone to edge chipping and corner breakage during transportation and assembly, this invention provides an edge-reinforced RTB rare earth permanent magnet and its preparation method.

[0007] The technical solution adopted in this invention is as follows:

[0008] An edge-reinforced RTB rare-earth permanent magnet, the magnet comprising the following components by mass fraction:

[0009] R: 28.5–34.0 wt.%, R is composed of RL and RH, the RH content is 0.1 wt.%–10.0 wt.% of the magnet mass, and RH is at least one of Dy, Tb, and Ho; the balance of R is RL, where RL represents one or more elements selected from Nd, Pr, La, Ce, Er, Gd, Sm, Tm, Lu, and Y that contain at least one light rare earth element; the light rare earth element is one or more of La, Ce, Pr, and Nd;

[0010] B: 0.85–1.1 wt.%

[0011] M: 0.01~8.0wt.%, M represents multiple elements selected from Al, Cu, Ga, Ni, Zn, Sn, Mn, Cr, Zr, Ti, Nb containing at least M and X, where X is one or more of Zr, Ti, and Nb; and M is one or more of Al, Ga, and Cu.

[0012] The balance is T and other unavoidable impurities, where T is Fe or Fe and Co;

[0013] The magnet has at least one surface A, wherein the content of light rare earth elements in the corner region of surface A is not less than the average light rare earth content of surface A; the light rare earth elements are one or more of La, Ce, Pr, and Nd; and the corner region of surface A contains X, wherein X is one or more of Zr, Ti, and Nb.

[0014] Furthermore, surface A is the coating surface of the magnet coating diffusion source.

[0015] Furthermore, preferably, 0.05 to 2.5 wt.% of the RH, which accounts for 0.05 to 2.5 wt.% of the magnet mass, is obtained through grain boundary diffusion.

[0016] M or X in a magnet can be obtained entirely through grain boundary diffusion, or partially through grain boundary diffusion.

[0017] Preferably, in the magnet, RL is more than 70% Nd;

[0018] Preferably, in the magnet, X is Zr;

[0019] Preferably, in the magnet, M is Ga or Cu.

[0020] Furthermore, within a depth range of 0.6 mm perpendicularly from the magnet to surface A, the X content in the corner region is 0.05–1.2 wt.%.

[0021] The magnet has an average X content of 0.05–0.8 wt.%.

[0022] The corner area refers to the surface area within a width range of 0 to K mm from the edge line, where K is the width of the corner area and ranges from 0.2 to 0.6. The non-corner area refers to the surface area outside the width range of K mm from the edge line.

[0023] The corner body region is the volume region enclosed by the corner area and a depth of 0.6 mm perpendicularly from surface A. The non-corner body region is the magnetic region outside the corner body region.

[0024] The non-corner regions of the magnet do not contain X, or the X content in the non-corner regions is lower than the X content in the corner regions of the magnet.

[0025] The corner-reinforced RTB rare-earth permanent magnet is preferably prepared according to the following method:

[0026] (1) An H1 diffusion source coating area and an H2 diffusion source coating area are set on the diffusion surface of the RTB magnet substrate, and the diffusion source is coated in sections. The H1 diffusion source coating area is coated with diffusion source H1, and the H2 diffusion source coating area is coated with diffusion source H2. The H1 diffusion source coating area is the corner area of ​​the diffusion surface, and the H2 diffusion source coating area is the non-corner area of ​​the diffusion surface.

[0027] The corner area refers to the surface area within a width range of 0 to K mm from the edge line, where K is 0.2 to 0.6. The non-corner area refers to the surface area outside the width range of K mm from the edge line.

[0028] Schematic diagrams of the corner and non-corner regions of some common shaped magnets are shown below. Figure 1 As shown.

[0029] The diffusion source H1 comprises the following components by mass fraction:

[0030] R1: 50.0–80.0 wt.%, R1 comprises RL1 and RH1, where RH1 is one or more of Dy, Tb, and Ho, and accounts for 30.0–70.0 wt.% of the mass of H1. The balance of R1 is RL1, where RL1 represents one or more elements selected from Nd, Pr, La, Ce, Er, Gd, Sm, Tm, Lu, and Y that contain at least one light rare earth element; the light rare earth element is one or more of La, Ce, Pr, and Nd; preferably RL1 is Nd and Pr.

[0031] X1: 10-30 wt.%, X1 is one or more of Zr, Ti, and Nb; preferably Zr;

[0032] M1: 5.0–40.0 wt.%, M1 is one or more of Al, Ga, and Cu; preferably Ga;

[0033] The diffusion source H2 is one or more mixtures of pure metals, alloys, or compounds containing heavy rare earth elements, wherein the heavy rare earth element is at least one of Dy, Tb, and Ho. Preferably, the content of heavy rare earth elements in H2 is greater than 70%.

[0034] Furthermore, the content of heavy rare earth elements in the diffusion source H1 is lower than that in H2.

[0035] H1 preferably consists of the following components: R1: 65-75%, X1: 15-25%, M1: 10-15%, more preferably R1: 70%, X1: 20%, M1: 10%.

[0036] The coating thickness of diffusion source H1 can be the same as or different from that of diffusion source H2, but preferably the coating thickness of diffusion source H1 is the same as that of diffusion source H2.

[0037] The coating amount of diffusion source H1 is generally 0.5 to 2.0% of the magnet mass; the coating amount of diffusion source H2 is generally 0.5 to 2.0% of the magnet mass.

[0038] (2) The magnet with the diffusion source coated in the partition is subjected to diffusion treatment at a diffusion temperature of 800℃~1000℃ and a holding time of 6~30h. After cooling, it is tempered to obtain the RTB rare earth permanent magnet.

[0039] This invention also provides a method for preparing an edge-reinforced RTB rare-earth permanent magnet, the method comprising the following steps:

[0040] (1) An H1 diffusion source coating area and an H2 diffusion source coating area are set on the diffusion surface of the RTB magnet substrate, and the diffusion source is coated in sections. The H1 diffusion source coating area is coated with diffusion source H1, and the H2 diffusion source coating area is coated with diffusion source H2. The H1 diffusion source coating area is the corner area of ​​the diffusion surface, and the H2 diffusion source coating area is the non-corner area of ​​the diffusion surface.

[0041] The corner area refers to the surface area within a width range of 0 to K mm from the edge line, where K is the width of the corner area and the range of K is 0.2 to 0.6. The non-corner area refers to the surface area outside the width range of K mm from the edge line.

[0042] The diffusion source H1 comprises the following components by mass fraction:

[0043] R1: 50.0–80.0 wt.%, R1 comprises RL1 and RH1, where RH1 is one or more of Dy, Tb, and Ho, and accounts for 30.0–70.0 wt.% of the mass of H1. The balance of R1 is RL1, where RL1 represents one or more elements selected from Nd, Pr, La, Ce, Er, Gd, Sm, Tm, Lu, and Y that contain at least one light rare earth element; the light rare earth element is one or more of La, Ce, Pr, and Nd.

[0044] X1: 10-30 wt.%, X1 is one or more of Zr, Ti, and Nb;

[0045] M1: 5.0–40.0 wt.%, M1 is one or more of Al, Ga, and Cu;

[0046] The diffusion source H2 is one or more of a pure metal, alloy or compound containing heavy rare earth elements, wherein the heavy rare earth elements are at least one of Dy, Tb and Ho.

[0047] Furthermore, the content of heavy rare earth elements in the diffusion source H1 is lower than that in H2;

[0048] (2) The magnet with the diffusion source coated in the partition is subjected to diffusion treatment at a diffusion temperature of 800℃~1000℃ and a holding time of 6~30h. After cooling, it is tempered to obtain the RTB rare earth permanent magnet.

[0049] In step (1), the diffusion surface refers to the magnet surface coated with the diffusion source, which can generally be a magnet surface that is perpendicular to the magnet orientation direction, parallel to the magnet orientation direction, or at any angle to the magnet orientation direction.

[0050] Surface A is the diffusion surface.

[0051] The preferred diffusion surfaces are two surfaces perpendicular to the orientation direction of the magnet.

[0052] In step (1), the partitioned coating of the diffusion source can be achieved in the following ways:

[0053] The magnet's corner areas are covered using masking plate 1, exposing the non-corner areas as the H2 diffusion source coating area, where diffusion source H2 is applied. Then, masking plate 2 is used to cover the non-corner areas of the magnet, exposing the corner areas as the H1 diffusion source coating area, where diffusion source H1 is applied. Alternatively, masking plate 2 can be used first to cover the non-corner areas of the magnet, exposing the corner areas as the H1 diffusion source coating area, where diffusion source H1 is applied. Then, masking plate 1 is used to cover the corner areas of the magnet, exposing the non-corner areas as the H2 diffusion source coating area, where diffusion source H2 is applied. Changing the coating order of diffusion sources H1 and H2 will not affect the final result.

[0054] The shielding plate 1 consists of a shielding area 1 and a hollow area 1. The shielding area 1 corresponds to the corner area of ​​the magnet, and the hollow area 1 corresponds to the non-corner area of ​​the magnet.

[0055] The shielding plate 2 consists of a shielding area 2 and a hollow area 2. The shielding area 2 corresponds to the non-corner area of ​​the magnet, and the hollow area corresponds to the corner area of ​​the magnet.

[0056] The shielding plate 1 or shielding plate 2 can be made of polymer plastic or metal such as stainless steel.

[0057] The diffusion source can be coated by PVD, spraying, or printing.

[0058] When the diffusion source is coated by PVD, the diffusion source H1 is obtained by melting and casting a large ingot; when the diffusion source is coated by spraying or printing, the diffusion source H1 is obtained as a powdered diffusion source by melting and spun SC sheets, hydrogen crushing and air jet milling.

[0059] When applying a diffusion source by printing, the printing coating needs to be dried between two applications.

[0060] The printing and coating of diffusion sources has the advantage of simple operation and is very suitable for mass production of products. Therefore, in this invention, screen printing is preferred for coating the diffusion source.

[0061] Furthermore, the diffusion source is preferably coated in sections using screen printing, which specifically includes the following steps:

[0062] (a) A perforated area and a non-perforated area are set on the screen. The positions of the perforated area and the obscuring area of ​​the printing screen are changed according to the product size and the size of the corner area. At least printing screen 1 and printing screen 2 are included. The perforated area of ​​printing screen 1 corresponds to the non-corner area of ​​the magnet, and the obscuring area corresponds to the corner area of ​​the magnet. The perforated area of ​​printing screen 2 corresponds to the corner area of ​​the magnet, and the obscuring area corresponds to the non-corner area of ​​the magnet. Printing screen 1 and printing screen 2 may include multiple perforated areas or obscuring areas, and multiple magnetic sheets are printed at the same time.

[0063] (b) Align the shaded area of ​​printing screen 1 with the corner area of ​​the magnet, and align the cutout area with the non-corner area, to form the H2 diffusion source coating area. Print diffusion source H2, dry, and then align the shaded area of ​​printing screen 2 with the non-corner area of ​​the magnet, and align the cutout area with the corner area of ​​the magnet, to form the H1 diffusion source coating area. Print diffusion source H1, and dry; or perform zone coating in the reverse order of the above.

[0064] The RTB magnet substrate of the present invention is obtained by processing a sintered bulk neodymium iron boron magnet to the required shape and size, and then cleaning and drying the magnet after surface treatment.

[0065] The surface treatment of the magnet is to remove oil and rust from the magnet surface by grinding, acid washing, or sandblasting.

[0066] In step (2), the diffusion process is generally carried out in a vacuum diffusion furnace.

[0067] In the tempering process, the tempering temperature is 400℃~600℃ (preferably 480℃~420℃), and the tempering time is 2h~10h (preferably 3h~5h).

[0068] Neodymium iron boron (NdFeB) magnets are relatively brittle, making them prone to chipping and breakage during transportation and assembly due to impacts. Furthermore, machining processes during NdFeB magnet manufacturing can create microcracks at the magnet's edges, further increasing the likelihood of edge breakage from impacts. Improving the mechanical properties of NdFeB magnets can reduce this chipping rate. Traditional methods involve adding Zr, Ti, and Nb to the magnet's raw materials. These elements strengthen the R-rich phase at the grain boundaries through solid solution or the formation of second-phase precipitates, thereby improving the magnet's mechanical properties. However, as the content of non-magnetic elements increases, the remanence of the magnet gradually decreases. Since defects in NdFeB magnets are primarily concentrated in the edge and corner regions, improving the mechanical properties of these areas alone can significantly reduce the chipping rate during transportation and assembly.

[0069] Based on the above reasons, this invention provides a corner-reinforced RTB rare-earth permanent magnet and its preparation method. By analyzing the regions of the magnet prone to mechanical property defects, the magnet diffusion source coating surface is divided into corner and non-corner regions. The corner regions of the magnet are coated with a diffusion source containing Zr, Ti, and Nb elements, while the non-corner regions are coated with a heavy rare-earth element diffusion source that does not contain the above elements. During grain boundary diffusion, Zr, Ti, and Nb elements diffuse into the R-rich phase of the magnet's grain boundaries, and Zr, Ti, and Nb are enriched only in the corner regions of the magnet. The R-rich phase of the grain boundaries in the corner regions of the magnet is strengthened through solid solution or the formation of second-phase precipitates, thereby improving the strength and other mechanical properties of the magnet's corners. In addition, the diffusion source in the corner regions of the magnet contains a certain amount of light rare-earth elements, which can repair microcracks caused by machining during grain boundary diffusion, eliminate the deteriorating effect of machining on the mechanical properties of the magnet's corners, and further improve the magnet's corner resistance to impact. This is of great significance for reducing the rate of edge chipping and corner breakage in products.

[0070] This invention improves the mechanical properties of the corner regions of a magnet through partitioned grain boundary diffusion without affecting the non-corner regions. This method significantly reduces the rate of edge chipping and breakage during transportation and assembly of the magnet without compromising its magnetic properties, which is of great significance for reducing the cost of NdFeB products.

[0071] The diffusion source H1 of this invention contains 10-30 wt.% of one or more of Zr, Ti, and Nb elements. During grain boundary diffusion, these elements diffuse along the R-rich phase at the grain boundaries of the magnet into the interior of the magnet. The R-rich phase at the grain boundaries of the magnet is strengthened by solid solution or by forming a second-phase precipitate with other elements, thereby increasing the strength of the magnet's edges and corners and enhancing its impact resistance. In this invention, the X content in the corner region is 0.05-1.2 wt.% within a depth range of 0.6 mm perpendicular to surface A.

[0072] Furthermore, the presence of a certain concentration of RL in diffusion source H1 can repair micro-cracks caused by machining during grain boundary diffusion, further improving the mechanical properties of the magnet's edges and corners. During machining, the impact and stress can cause micro-cracks at the magnet's edges and corners. In subsequent product transportation and assembly, even slight bumps between products can lead to crack propagation and chipped edges / corners. The RL added in H1 diffuses into the magnet's interior through the grain boundaries during grain boundary diffusion. The molten RL repairs cracks located in the R-rich phase at the magnet's grain boundaries, thus eliminating the deteriorating effect of machining defects on the mechanical properties of the magnet's edges and corners. In this invention, diffusion source H1 contains RL while diffusion source H2 does not. Therefore, the RL content in the light rare earth element region of the magnet surface A after the grain boundary diffusion source is not lower than the average light rare earth content of surface A.

[0073] The diffusion source H1 also contains 30.0–70.0 wt.% RH. After RH diffuses through the grain boundaries, it forms a shell rich in heavy rare earth element RH on the surface of the main phase grains of the magnet. Due to the high anisotropic field of this shell, it can significantly improve the coercivity of the NdFeB magnet. Meanwhile, the 5–40 wt.% M1 in the diffusion source H1 can lower the melting point of the diffusion source. At the same time, during grain boundary diffusion, it can lower the melting point of the R-rich phase at the magnet grain boundaries, thereby increasing the RH diffusion depth and enhancing the repair ability of RL for microcracks.

[0074] This invention coats the surface of the non-corner regions of the magnet with a diffusion source H2 that does not contain Zr, Ti, or Nb. The diffusion source H2 is a pure metal, alloy, or compound containing at least one of the heavy rare earth elements Dy, Tb, and Ho. Since the diffusion source of heavy rare earth elements can also generate certain diffusion internal stress, which can reduce the mechanical properties of the magnet's corners, in this invention, the heavy rare earth element content of H1 is lower than that of H2.

[0075] In this invention, the diffuse coating method can be PVD, spraying, or printing.

[0076] In this invention, the diffusion source H1 is prepared by batching and melting according to the actual composition. When using PVD coating, the diffusion source can be directly prepared into a large ingot through melting. When using coating or printing methods to coat the diffusion source, it is necessary to prepare a powdered diffusion source by melting SC sheets, hydrogen crushing, and air jet milling.

[0077] The diffusion source H2 can be directly made from commercially available ingots or powders containing at least one of the heavy rare earth elements Dy, Tb, and Ho, in pure metals, alloys, or compounds.

[0078] The beneficial effects of this invention are as follows: By analyzing the regions of the magnet prone to mechanical performance defects, the magnet diffusion source coating surface is divided into corner and non-corner regions. The corner regions of the magnet are coated with diffusion sources containing Zr, Ti, and Nb elements, while the non-corner regions are coated with diffusion sources lacking these elements. During grain boundary diffusion, Zr, Ti, and Nb elements diffuse into the R-rich phase at the grain boundaries of the magnet, strengthening the R-rich phase through solid solution or the formation of second-phase precipitates, thereby improving the strength of the magnet's corners. This invention improves the mechanical properties of the magnet's corner regions through partitioned grain boundary diffusion without affecting the non-corner regions. This method can significantly reduce the rate of edge chipping and corner breakage during transportation and assembly of the magnet without reducing its magnetic properties, which is of great significance for reducing the cost of NdFeB products. Attached Figure Description

[0079] Figure 1 Schematic diagram of the corner and non-corner areas of common shaped magnets.

[0080] Figure 2 Schematic diagrams of magnet selection area printing in Experiments No. 2 and No. 4.

[0081] Figure 3 Experiment No. 2: Cross-sectional view of the corner area of ​​the magnet. Detailed Implementation

[0082] Sintered RTB magnets are prepared using a process of melting and spun SC sheets, hydrogen breaking, air jet milling, orientation forming, isostatic pressing, vacuum sintering, and aging. Large NdFeB magnets are then machined to the required shape and size, and after surface treatment, the magnets are cleaned and dried to obtain the RTB magnet substrate.

[0083] An H1 diffusion source coating area and an H2 diffusion source coating area are set on the diffusion surface of the RTB magnet substrate. The diffusion source is coated in sections, with the H1 diffusion source coating area coated with diffusion source H1 and the H2 diffusion source coating area coated with diffusion source H2. The H1 diffusion source coating area is the corner area of ​​the diffusion surface, and the H2 diffusion source coating area is the non-corner area of ​​the diffusion surface.

[0084] The corner area refers to the surface area within a width range of 0 to K mm from the edge line, where K is 0.2 to 0.6. The non-corner area refers to the surface area outside the width range of K mm from the edge line.

[0085] Schematic diagrams of the corner and non-corner regions of some common shaped magnets are shown below. Figure 1 As shown.

[0086] The magnet with a diffusion source coated in a partition is subjected to diffusion treatment at a temperature of 800℃~1000℃ for 6~30h. After the diffusion is completed, it is cooled to room temperature and then heated to 400~600℃ for 2~10h to obtain the magnet.

[0087] After secondary aging, the magnet surface was sandblasted to expose a fresh surface. ICP was used to measure the magnet composition, and SEM and EPMA were used to analyze the magnet microstructure and micro-area composition. NIM was used to measure the magnetic properties of the magnets; 11 samples were tested in each group of experiments, and the average magnetic property values ​​were calculated. A drop test was conducted on 200 products at a height of 1 meter, repeated once. Magnets with dimensions larger than 0.3 mm in area at their corners were tested. 2 Products in defective areas are considered unqualified products, and the pass rate of products is calculated.

[0088] Example 1:

[0089] Sintered RTB magnets were prepared using a process of sintering and spinning SC sheets, hydrogen breaking, air jet milling, orientation forming, isostatic pressing, vacuum sintering, and aging.

[0090] The sintered and aged magnets were machined into magnetic sheets with dimensions of 10mm x 10mm x 5mm (length x width x height), with the height direction aligned with the magnet's orientation. The magnet surface was then cleaned of oil and rust using acid pickling, followed by rinsing with water and drying.

[0091] The powder of diffusion source H1 was prepared by sintering SC sheets, hydrogen breaking, and air jet milling. The powder particle size SMD was 1.5 μm. The heavy rare earth element powder composition of diffusion source H1 is as follows:

[0092] R: 70 wt.%, R includes RL and RH, where RH is Tb and accounts for 60% of the mass ratio of H1, and the balance of R is RL, which consists of Pr and Nd in a mass ratio of 25:75.

[0093] Zr: 20wt.%

[0094] Ga: 10wt.%

[0095] The diffusion source H2 contains heavy rare earth element powder, which is commercial terbium hydride powder (Tb content 98.2 wt.%), with a powder particle size SMD 1.5 μm.

[0096] The screen printing coating is prepared according to the following ratio: the mass ratio of heavy rare earth diffusion source powder, terpineol, polyvinyl butyral and alumina is 70:26:2:2. After being mixed evenly, the screen printing coating is obtained.

[0097] Diffusion sources were printed on two surfaces of the magnet perpendicular to the orientation direction, with a diffusion source layer thickness of 15 μm. In Experiment No. 1, diffusion source H2 was printed on all two surfaces of the magnet. In Experiment No. 2, diffusion sources were coated in sections: diffusion source H1 was coated on the corner areas of the magnet, and diffusion source H2 was coated on the non-corner areas. The width of the corner areas was 0.4 mm. Experiment No. 2 achieved the section coating of diffusion sources by designing two different sizes of printing screens. The schematic diagram of the printing screens for the magnet in Experiment No. 2 is shown below. Figure 2 As shown. Figure 2 The printing screen in the middle can print three magnetic sheets of the same size at the same time.

[0098] use Figure 2 The masking area of ​​the printed screen on the left is aligned with the corner area of ​​the magnet, and the cut-out area is aligned with the non-corner area, serving as the H2 diffusion source coating area. The H2 diffusion source is printed, dried, and then... Figure 2 The masked area of ​​the printed screen on the right is aligned with the non-corner area of ​​the magnet, and the cut-out area is aligned with the corner area of ​​the magnet, serving as the H1 diffusion source coating area. Diffusion source H1 is then printed. Drying is then performed.

[0099] After one side of the magnet is printed, it is dried in a 50°C oven, and then the second side is printed and dried again.

[0100] The magnet was placed in a vacuum diffusion furnace and heated to 950°C for 15 hours. After the heating was completed, it was cooled to room temperature and then heated to 520°C for 4 hours to obtain the magnet.

[0101] After secondary aging, the magnet surface was sandblasted to expose a fresh surface. ICP was used to measure the magnet composition, and SEM and EPMA were used to analyze the magnet microstructure and micro-area composition. NIM was used to measure the magnetic properties of the magnets; 11 samples were tested in each group of experiments, and the average magnetic property values ​​were calculated. A drop test was conducted on 200 products at a height of 1 meter, repeated once. Magnets with dimensions larger than 0.3 mm in area at their corners were tested. 2 Products in defective areas are considered unqualified products, and the pass rate of products is calculated.

[0102] The magnet matrix compositions of Experiment No. 1 and Experiment No. 2 are the same. The compositions of the magnet matrix and the magnets after grain boundary diffusion are shown in Table 1.

[0103] Table 1

[0104] No. Nd Pr Co Cu Ga Tb Fe Zr matrix 27.6 0.60 0.97 0.1 0.1 / Bal / 1 27.7 0.61 0.97 0.1 0.1 0.21 Bal / 2 27.7 0.60 0.97 0.1 0.11 0.20 Bal 0.1

[0105] The magnetic properties and pass rate of the magnets are shown in Table 2:

[0106] Table 2

[0107] Experiment No. Br(kGs) Hcj(kOe) Pass rate (%) 1 14.5 21.1 80％ 2 14.5 21.0 96％

[0108] As shown in Tables 1 and 2, the Tb content of magnets No. 1 and No. 2 is basically the same after grain boundary diffusion. However, because magnet No. 2 adopted the partitioned grain boundary diffusion method, i.e., the diffusion source in the coating area at the corner of the magnet contains a certain amount of Zr, the magnet contains 0.1 wt.% Zr after grain boundary diffusion. Meanwhile, the magnetic properties of the magnets in Table 2 show that the magnetic properties of magnets No. 1 and No. 2 are basically the same after grain boundary diffusion, but the pass rate of magnet No. 2 is significantly higher than that of magnet No. 1. This indicates that the partitioned grain boundary diffusion method provided by this invention can effectively improve the mechanical properties at the corners of NdFeB magnets, thereby reducing the rate of edge chipping and corner breakage in the products.

[0109] like Figure 3 As shown, the corner regions of the magnet were precisely wire-cut, and their composition was tested. The results showed that the average Zr content at the magnet corners was 0.4 wt.%, significantly higher than the average Zr content of the magnet. This indicates that after coating the surface of the magnet corner region with a Zr-containing diffusion source and performing grain boundary diffusion, Zr will accumulate at the magnet corners. PEMA point scanning analysis revealed that Zr is mainly distributed in the R-rich phase at the grain boundaries of the magnet. Zr can strengthen the R-rich phase at the grain boundaries of the magnet through solid solution or the formation of second-phase precipitates, thereby improving the mechanical properties at the magnet corners. Furthermore, since the Zr enrichment area is concentrated only at the magnet corners, it does not affect the magnetic properties of the magnet.

[0110] EPMA surface scanning analysis was used to analyze the average light rare earth element (LREE) content in the corner region of magnet surface A and the overall average LREE content of surface A. The results showed that the LREE content in the corner region of magnet surface A was not lower than the average LREE content of surface A. In this invention, the corner diffusion source H1 partially replaced RH with LREE element RL. After diffusion at the grain boundaries, RL mainly concentrates in the grain boundary phase of the magnet, repairing microcracks caused by machining at the magnet corners, thereby enhancing the mechanical properties of the magnet corners. Furthermore, due to the high diffusion rate of RL, it does not only accumulate in the corner region of the magnet; therefore, the LREE content in the corner region of magnet surface A is not lower than the average LREE content of surface A. Moreover, as shown in Table 2, the magnetic properties of the magnet in Experiment No. 2 were not reduced compared to Experiment No. 1. Therefore, replacing RH with LREE element RL in the diffusion source H1 of this invention does not lead to a decrease in magnetic properties.

[0111] This invention employs a partitioned diffusion source coating method to achieve partitioned grain boundary diffusion in NdFeB magnets. Diffusion sources containing Zr, Ti, and Nb are coated on the corner regions of the magnet, while diffusion sources without these elements are coated on the non-corner regions. During grain boundary diffusion, Zr, Ti, and Nb diffuse into the R-rich phase at the magnet's grain boundaries, strengthening this phase through solid solution or the formation of second-phase precipitates, thereby improving the strength of the magnet's corners. This invention improves the mechanical properties of the magnet's corner regions through partitioned grain boundary diffusion without affecting the non-corner regions. This method can significantly reduce the rate of edge chipping and breakage during magnet transportation and assembly without compromising the magnet's magnetic properties, which is of great significance for reducing the cost of NdFeB products.

[0112] Example 2:

[0113] Sintered RTB magnets were prepared using a process of sintering and spinning SC sheets, hydrogen breaking, air jet milling, orientation forming, isostatic pressing, vacuum sintering, and aging.

[0114] The sintered and aged magnets were machined into magnetic sheets with dimensions of 10mm x 10mm x 5mm (length x width x height), with the height direction aligned with the magnet's orientation. The magnet surface was then cleaned of oil and rust using acid pickling, followed by rinsing with water and drying.

[0115] The powder of diffusion source H1 was prepared by sintering SC sheets, hydrogen breaking, and air jet milling. The powder particle size SMD was 1.5 μm. The heavy rare earth element powder composition of diffusion source H1 is as follows:

[0116] R: 70 wt.%, R includes RL and RH, where RH is Tb and accounts for 60% of the mass ratio of H1, and the balance of R is RL, which consists of Pr and Nd in a mass ratio of 25:75.

[0117] Zr: 20wt.%

[0118] Ga: 10wt.%

[0119] The diffusion source H2 contains heavy rare earth element powder, which is commercial terbium hydride powder with a particle size SMD of 1.5 μm.

[0120] The screen printing coating is prepared according to the following ratio: the mass ratio of heavy rare earth diffusion source powder, terpineol, polyvinyl butyral and alumina is 70:26:2:2. After being mixed evenly, the screen printing coating is obtained.

[0121] Diffusion sources were printed on two surfaces of the magnet perpendicular to the orientation direction, with a diffusion source layer thickness of 20 μm. In Experiment No. 3, diffusion source H2 was printed on both surfaces of the magnet. In Experiment No. 4, diffusion sources were coated in sections: diffusion source H1 was coated on the corner areas of the magnet, and diffusion source H2 was coated on the non-corner areas. The width of the corner areas was 0.4 mm. The diffusion sources were coated by printing. After one side of the magnet was printed, it was dried in an oven at 50°C before printing on the second side, followed by drying again.

[0122] The magnet was placed in a vacuum diffusion furnace and heated to 950°C for 15 hours. After the heating was completed, it was cooled to room temperature and then heated to 520°C for 4 hours to obtain the magnet.

[0123] After secondary aging, the magnet surface was sandblasted to expose a fresh surface. ICP was used to measure the magnet composition, and SEM and EPMA were used to analyze the magnet microstructure and micro-area composition. NIM was used to measure the magnetic properties of the magnets; 11 samples were tested in each group of experiments, and the average magnetic property values ​​were calculated. A drop test was conducted on 200 products at a height of 1 meter, repeated once. Magnets with dimensions larger than 0.3 mm in area at their corners were tested. 2 Products in defective areas are considered unqualified products, and the pass rate of products is calculated.

[0124] The magnet matrix compositions of Experiments No. 3 and No. 4 are the same. The compositions of the magnet matrix and the magnets after grain boundary diffusion are shown in Table 3.

[0125] Table 3

[0126] No. Nd Pr Co Cu Ga Tb Fe Zr matrix 27.6 0.60 0.97 0.1 0.1 / Bal 0.1 3 27.8 0.61 0.97 0.1 0.1 0.22 Bal 0.1 4 27.8 0.60 0.97 0.1 0.12 0.22 Bal 0.16

[0127] The magnetic properties and pass rate of the magnets are shown in Table 4:

[0128] Table 4

[0129] Experiment No. Br(kGs) Hcj(kOe) Pass rate (%) 3 14.45 22.0 85％ 4 14.45 22.0 98％

[0130] As shown in Tables 3 and 4, the Tb content of magnets No. 3 and No. 4 is basically the same after grain boundary diffusion. Since the magnet matrix in this embodiment contains 0.1 wt.% Zr, the Zr content in magnet No. 3 is the same as that in the matrix after grain boundary diffusion, while the Zr content in magnet No. 4 is significantly higher than that in magnet No. 1. Furthermore, the magnets' magnetic properties show that the addition of a certain amount of Zr to the matrix reduces the remanence of magnets No. 3 and No. 4, but the magnetic properties of magnets No. 3 and No. 4 are basically the same. The pass rate of magnets shows that the addition of 0.1 wt.% Zr to the magnet matrix increases the final pass rate of magnet No. 3, but it is still lower than that of magnet No. 4. This indicates that when the magnet matrix contains a certain amount of Zr, the method provided by this invention can significantly improve the mechanical properties at the magnet's edges and corners, thereby reducing the rate of edge chipping and breakage.

[0131] Using precision wire cutting, such as Figure 3 The Zr content in the corner regions of the cut magnets shown in the figure was measured for Experiments No. 3 and No. 4. The results are shown in Table 5.

[0132] Table 5

[0133] Experiment No. Zr content in corner areas (wt.%) 3 0.1 4 0.52

[0134] The results show that the average Zr content in the corner region of magnet No. 4 is significantly higher than that in the non-corner region, indicating that after coating the corner region with a Zr-containing diffusion source and performing grain boundary diffusion, Zr will accumulate at the corner of the magnet. PEMA spot scan analysis revealed that Zr is mainly distributed in the R-rich phase at the grain boundaries of the magnet. Zr can strengthen the R-rich phase at the grain boundaries of the magnet through solid solution or the formation of second-phase precipitates, thereby improving the mechanical properties at the corners of the magnet. Furthermore, since the Zr enrichment area is concentrated only at the corners of the magnet, it does not affect the magnetic properties of the magnet.

[0135] EPMA surface scanning analysis was used to analyze the average light rare earth element (LREE) content in the corner region of magnet surface A and the overall average LREE content of surface A. The results showed that the LREE content in the corner region of magnet surface A was not lower than the average LREE content of surface A. In this invention, the diffusion source H1 in the corner region uses a partial replacement of RH with the LREE element RL. After diffusion at the grain boundaries, RL mainly concentrates in the grain boundary phase of the magnet, repairing microcracks caused by machining at the magnet corners, thereby enhancing the mechanical properties of the magnet corners. Furthermore, due to the high diffusion rate of RL, it does not only accumulate in the corner region of the magnet; therefore, the LREE content in the corner region of magnet surface A is not lower than the average LREE content of surface A. Moreover, as shown in Table 4, the magnetic properties of magnet No. 4 were not reduced compared to magnet No. 3. Therefore, the replacement of RH with the LREE element RL in the diffusion source H1 of this invention does not lead to a decrease in magnetic properties.

[0136] This invention employs a partitioned diffusion source coating method to achieve partitioned grain boundary diffusion in NdFeB magnets. Diffusion sources containing Zr, Ti, and Nb are coated on the corner regions of the magnet, while diffusion sources without these elements are coated on the non-corner regions. During grain boundary diffusion, Zr, Ti, and Nb diffuse into the R-rich phase at the magnet's grain boundaries, strengthening this phase through solid solution or the formation of second-phase precipitates, thereby improving the strength of the magnet's corners. This invention improves the mechanical properties of the magnet's corner regions through partitioned grain boundary diffusion without affecting the non-corner regions. This method can significantly reduce the rate of edge chipping and breakage during magnet transportation and assembly without compromising the magnet's magnetic properties, which is of great significance for reducing the cost of NdFeB products.

[0137] Example 3:

[0138] Sintered RTB magnets were prepared using a process of sintering and spinning SC sheets, hydrogen breaking, air jet milling, orientation forming, isostatic pressing, vacuum sintering, and aging.

[0139] The sintered and aged magnets were machined into magnetic sheets with dimensions of 10mm x 10mm x 5mm (length x width x height), with the height direction aligned with the magnet's orientation. The magnet surface was then cleaned of oil and rust using acid pickling, followed by rinsing with water and drying.

[0140] The powder of diffusion source H1 was prepared by sintering SC sheets, hydrogen breaking, and air jet milling. The powder particle size SMD was 1.5 μm. The heavy rare earth element powder composition of diffusion source H1 is as follows:

[0141] R: 70 wt.%, R includes RL and RH, where RH is Tb and accounts for 60% of the mass ratio of H1, and the balance of R is RL, which consists of Pr and Nd in a mass ratio of 25:75.

[0142] Zr: 20wt.%

[0143] Ga: 10wt.%

[0144] The diffusion source H2 contains heavy rare earth element powder, which is commercial terbium hydride powder with a particle size SMD of 1.5 μm.

[0145] The screen printing coating is prepared according to the following ratio: the mass ratio of heavy rare earth diffusion source powder, terpineol, polyvinyl butyral and alumina is 70:26:2:2. After being mixed evenly, the screen printing coating is obtained.

[0146] Diffusion sources were printed on two surfaces of the magnet perpendicular to the orientation direction, with a diffusion source layer thickness of 20 μm. Experiments No. 5 through No. 7 used a partitioned coating method for the diffusion sources: diffusion source H1 was coated on the corner areas of the magnet, and diffusion source H2 was coated on the non-corner areas. The width of the corner area was 0.1 mm in Experiment No. 5, 0.4 mm in Experiment No. 6, and 1.0 mm in Experiment No. 7. The diffusion sources were coated by printing. After one side of the magnet was printed, it was dried in a 50°C oven before printing on the second side, followed by another drying.

[0147] The magnet was placed in a vacuum diffusion furnace and heated to 950°C for 15 hours. After the heating was completed, it was cooled to room temperature and then heated to 520°C for 4 hours to obtain the magnet.

[0148] After secondary aging, the magnet surface was sandblasted to expose a fresh surface. ICP was used to measure the magnet composition, and SEM and EPMA were used to analyze the magnet microstructure and micro-area composition. NIM was used to measure the magnetic properties of the magnets; 11 samples were tested in each group of experiments, and the average magnetic property values ​​were calculated. A drop test was conducted on 200 products at a height of 1 meter, repeated once. Magnets with dimensions larger than 0.3 mm in area at their corners were tested. 2 Products in defective areas are considered unqualified products, and the pass rate of products is calculated.

[0149] Experiments No. 5 through No. 7 used magnets with the same matrix composition. The magnet matrix and the magnet composition after grain boundary diffusion are shown in Table 6.

[0150] Table 6

[0151] No. Nd Pr Co Cu Ga Tb Fe Zr matrix 27.6 0.60 0.97 0.1 0.1 / Bal 0.1 5 27.8 0.60 0.97 0.1 0.11 0.22 Bal 0.13 6 27.8 0.60 0.97 0.1 0.11 0.22 Bal 0.16 7 27.8 0.60 0.97 0.1 0.11 0.22 Bal 0.20

[0152] The magnetic properties and pass rate of the magnets are shown in Table 7:

[0153] Table 7

[0154] Experiment No. Br(kGs) Hcj(kOe) Pass rate (%) 5 14.45 22.0 87％ 6 14.45 22.0 98％ 7 14.38 21.9 99％

[0155] As shown in Tables 6 and 7, the Tb content of magnets in Experiments No. 5 to No. 7 was basically the same after grain boundary diffusion, and the Zr content of magnets increased significantly after grain boundary diffusion.

[0156] However, the dimensions of the corner regions of the magnets varied across different experimental groups. In Experiment No. 5, the corner region width was 0.1 mm. Although the mechanical properties of the corners were enhanced after grain boundary diffusion, the narrow corner region resulted in a small volume of the enhanced region, thus limiting the improvement in the mechanical properties of the magnet's corners. When the magnet's corner range was within the scope of this invention (Experiment No. 6), grain boundary diffusion effectively improved the mechanical properties of the corner regions, thereby increasing the product yield. However, when the corner region size was too large (Experiment No. 7), the volume of the enhanced corner region increased. As shown in Table 7, although this also improved the magnet's yield, the remanence of the magnet was significantly reduced due to the large volume fraction of the Zr-enriched region. Therefore, it is necessary to reasonably control the size of the corner regions. In this invention, the corner region size is between 0.2 and 0.6 mm.

[0157] Example 4:

[0158] Sintered RTB magnets were prepared using a process of sintering and spinning SC sheets, hydrogen breaking, air jet milling, orientation forming, isostatic pressing, vacuum sintering, and aging.

[0159] The sintered and aged magnets were machined into magnetic sheets with dimensions of 10mm x 10mm x 5mm (length x width x height), with the height direction aligned with the magnet's orientation. The magnet surface was then cleaned of oil and rust using acid pickling, followed by rinsing with water and drying.

[0160] The powder for diffusion source H1 was prepared by sintering SC sheets, hydrogen breaking, and air jet milling. The powder particle size SMD was 1.5 μm. The heavy rare earth element powder composition of diffusion source H1 in Experiment No. 8 is as follows:

[0161] R: 70 wt.%, R includes RL and RH, where RH is Tb and accounts for 60% of the mass ratio of H1, and the balance of R is RL, which consists of Pr and Nd in a mass ratio of 25:75.

[0162] Zr: 20wt.%

[0163] Ga: 10wt.%

[0164] The heavy rare earth element powder composition of Energy H1 in Experiment No.9 is as follows:

[0165] R: 70 wt.%, R includes RL and RH, where RH is Tb and accounts for 60% of the mass ratio of H1, and the balance of R is RL, which consists of Pr and Nd in a mass ratio of 25:75.

[0166] Zr: 30wt.%

[0167] The diffusion source H2 contains heavy rare earth element powder, which is commercial terbium hydride powder with a particle size SMD of 1.5 μm.

[0168] The screen printing coating is prepared according to the following ratio: the mass ratio of heavy rare earth diffusion source powder, terpineol, polyvinyl butyral and alumina is 70:26:2:2. After being mixed evenly, the screen printing coating is obtained.

[0169] Diffusion sources were printed on two surfaces of the magnet perpendicular to the orientation direction, with a diffusion source layer thickness of 20 μm. Experiments No. 8 and No. 9 both employed a partitioned diffusion source coating method: diffusion source H1 was coated on the corner areas of the magnet, while diffusion source H2 was coated on the non-corner areas, with a coating thickness of 0.4 mm in the corner areas. The diffusion sources were coated by printing. After one side of the magnet was printed, it was dried in a 50°C oven before printing on the second side, followed by another drying.

[0170] The magnet was placed in a vacuum diffusion furnace and heated to 950°C for 15 hours. After the heating was completed, it was cooled to room temperature and then heated to 520°C for 4 hours to obtain the magnet.

[0171] After secondary aging, the magnet surface was sandblasted to expose a fresh surface. ICP was used to measure the magnet composition, and SEM and EPMA were used to analyze the magnet microstructure and micro-area composition. NIM was used to measure the magnetic properties of the magnets; 11 samples were tested in each group of experiments, and the average magnetic property values ​​were calculated. A drop test was conducted on 200 products at a height of 1 meter, repeated once. Magnets with dimensions larger than 0.3 mm in area at their corners were tested. 2 Products in defective areas are considered unqualified products, and the pass rate of products is calculated.

[0172] The magnet matrix compositions of Experiments No. 8 and No. 9 are the same. The compositions of the magnet matrix and the magnets after grain boundary diffusion are shown in Table 8.

[0173] Table 8

[0174] No. Nd Pr Co Cu Ga Tb Fe Zr matrix 27.6 0.60 0.97 0.1 0.1 / Bal 0.1 8 27.8 0.60 0.97 0.1 0.11 0.22 Bal 0.16 9 27.8 0.60 0.97 0.1 0.1 0.22 Bal 0.13

[0175] The magnetic properties and pass rate of the magnets are shown in Table 9:

[0176] Table 9

[0177] Experiment No. Br(kGs) Hcj(kOe) Pass rate (%) 8 14.45 22.0 98％ 9 14.45 22.0 91％

[0178] In this embodiment, the composition of diffusion source H1 in Experiment No. 8 is within the recommended range of this invention, but diffusion source H1 in Experiment No. 9 does not contain the M1 element. As shown in Table 8, even though the Zr content in diffusion source H1 in Experiment No. 9 is higher than the Zr content in the magnet in Experiment No. 8, the average Zr content in the magnet in Experiment No. 9 is lower than that in Experiment No. 8 after grain boundary diffusion. As a result, the pass rate of magnet No. 9 is lower than that of magnet No. 8.

[0179] This is because Zr has a high melting point. To accelerate the grain boundary diffusion rate of diffusion source H1, it is necessary to lower the melting point of diffusion source H1. Therefore, in this invention, a certain amount of M1 (Al, Ga, Cu) is added to diffusion source H1 to lower the melting point and accelerate the diffusion efficiency. Thus, although the Zr content in diffusion source H1 in Experiment No. 9 is higher than that in Experiment No. 8, its higher melting point and slower grain boundary diffusion rate result in a weakened strengthening effect on the edges of magnet No. 9, leading to a lower yield. Therefore, in this invention, diffusion source H1 within the composition range recommended by this invention is preferred.

[0180] Example 5:

[0181] Sintered RTB magnets were prepared using a process of sintering and spinning SC sheets, hydrogen breaking, air jet milling, orientation forming, isostatic pressing, vacuum sintering, and aging.

[0182] The sintered and aged magnets were machined into magnetic sheets with dimensions of 10mm x 10mm x 5mm (length x width x height), with the height direction aligned with the magnet's orientation. The magnet surface was then cleaned of oil and rust using acid pickling, followed by rinsing with water and drying.

[0183] The powder for diffusion source H1 was prepared by sintering SC sheets, hydrogen breaking, and air jet milling. The powder particle size SMD was 1.5 μm. The heavy rare earth element powder composition of diffusion source H1 in Experiment No. 10 is as follows:

[0184] R: 75 wt.%, R includes RL and RH, where RH is Tb and accounts for 60% of the mass ratio of H1, and the balance of R is RL, which consists of Pr and Nd in a mass ratio of 25:75.

[0185] Ti: 15wt.%

[0186] Cu: 15wt.%

[0187] The diffusion source H2 contains heavy rare earth element powder, which is commercial terbium hydride powder with a particle size SMD of 1.5 μm.

[0188] The composition of the heavy rare earth element-containing powder of diffusion source H1 in Experiment No. 11 is as follows:

[0189] R: 65 wt.%, R includes RL and RH, RH is Tb and accounts for 55% of the mass ratio of H1, the balance of R is RL, RL is Pr and Nd, and the ratio of Pr to Nd is 25:75 by mass.

[0190] Nb: 25wt.%

[0191] Al: 10 wt.%

[0192] The diffusion source H2 contains heavy rare earth element powder, which is commercial terbium hydride powder with a particle size SMD of 1.5 μm.

[0193] The screen printing coating is prepared according to the following ratio: the mass ratio of heavy rare earth diffusion source powder, terpineol, polyvinyl butyral and alumina is 70:26:2:2. After being mixed evenly, the screen printing coating is obtained.

[0194] Diffusion sources are printed on two surfaces of the magnet perpendicular to the orientation direction, with a diffusion source layer thickness of 20 μm.

[0195] Experiments No. 10 and No. 11 used the same magnet matrix composition. Experiments No. 10 and No. 11 used a partitioned coating of diffusion sources. Diffusion source H1 was coated on the corner area of ​​the magnet, and diffusion source H2 was coated on the non-corner area. The width of the corner area was 0.6 mm.

[0196] The diffusion source is coated by printing. After one side of the magnet is printed, it is dried in a 50°C oven, and then the second side is printed and dried again.

[0197] The magnet was placed in a vacuum diffusion furnace and heated to 950°C for 15 hours. After the heating was completed, it was cooled to room temperature and then heated to 520°C for 4 hours to obtain the magnet.

[0198] After secondary aging, the magnet surface was sandblasted to expose a fresh surface. ICP was used to measure the magnet composition, and SEM and EPMA were used to analyze the magnet microstructure and micro-area composition. NIM was used to measure the magnetic properties of the magnets; 11 samples were tested in each group of experiments, and the average magnetic property values ​​were calculated. A drop test was conducted on 200 products at a height of 1 meter, repeated once. Magnets with dimensions larger than 0.3 mm in area at their corners were tested. 2 Products in defective areas are considered unqualified products, and the pass rate of products is calculated.

[0199] The magnet matrix compositions of Experiments No. 10 and No. 11 are the same. The compositions of the magnet matrix and the magnets after grain boundary diffusion are shown in Table 10.

[0200] Table 10

[0201] No. Nd Pr Co Cu Ga Tb Fe Zr Ti Nb Al matrix 27.6 0.60 0.97 0.1 0.1 / Bal 0.1 / / / 10 27.8 0.60 0.97 0.11 0.1 0.22 Bal 0.1 0.08 / / 11 27.8 0.60 0.97 0.1 0.1 0.22 Bal 0.1 / 0.1 0.02

[0202] The magnetic properties and pass rate of the magnets are shown in Table 11:

[0203] Table 11

[0204] Experiment No. Br(kGs) Hcj(kOe) Pass rate (%) 10 14.45 22.0 97％ 11 14.45 22.0 97％

[0205] As shown in Tables 10 and 11, the Tb content and magnetic properties of magnets in Experiments No. 10 and No. 11 are basically the same after grain boundary diffusion. The pass rate after partitioned diffusion is relatively high. Within the scope of this invention, changing the ratio of diffusion source H1 or replacing elements X1 or M1 does not affect the technical effect of this invention. The H1 diffusion source within the scope of protection of this invention, after partitioned coating, can effectively improve the mechanical properties at the edges and corners of NdFeB magnets, reduce the edge chipping rate of the product, and has no impact on the magnet performance.

Claims

1. A corner strengthened R-T-B rare earth permanent magnet, characterized by The magnet comprises the following mass fractions of components: R: 28.5-34.0 wt.%, R is composed of RL and RH, the content of RH is 0.1-10.0 wt.% of the mass of the magnet, RH is at least one of Dy, Tb, Ho; the balance of R is RL, RL represents at least one or more elements containing light rare earth elements selected from Nd, Pr, La, Ce, Er, Gd, Sm, Tm, Lu, Y; the light rare earth elements are one or more of La, Ce, Pr, Nd; B: 0.85-1.1 wt.%, B is composed of BL and BH, the content of BH is 0.1-10.0 wt.% of the mass of the magnet, BH is at least one of Cu, Al, Ga, Ni, Zn, Sn, Mn, Cr, Zr, Ti, Nb; the balance of B is BL, BL represents at least one or more elements containing B and L selected from Cu, Al, Ga, Ni, Zn, Sn, Mn, Cr, Zr, Ti, Nb, L is one or more of Zr, Ti, Nb; MX: 0.01-8.0 wt.%, MX represents at least one or more elements containing M and X selected from Al, Cu, Ga, Ni, Zn, Sn, Mn, Cr, Zr, Ti, Nb, X is one or more of Zr, Ti, Nb; M is one or more of Al, Ga, Cu; the balance is T and other unavoidable impurities, T is Fe or Fe and Co; The magnet has at least one surface A, the content of light rare earth elements in the corner area of the surface A is not less than the average light rare earth content of the surface A; the light rare earth elements are one or more of La, Ce, Pr, Nd; and the corner area of the surface A contains X, X is one or more of Zr, Ti, Nb; The X content of the corner body area of the magnet within a depth range of 0.6 mm perpendicular distance from the surface A is 0.05-1.2 wt.%; the average X content of the magnet is 0.05-0.8 wt.%; The corner area refers to a surface area within a width range of 0-K mm from the edge line of the magnet, K is the width of the corner area, K ranges from 0.2 to 0.6, and the non-corner area refers to a surface area outside the width range of K mm from the edge line; The corner body area is a body area surrounded by the corner area and a depth of 0.6 mm perpendicular distance from the surface A; the non-corner body area of the magnet does not contain X, or the X content in the non-corner body area is lower than the X content in the corner body area of the magnet; the non-corner body area is the area of the magnet outside the corner body area; The surface A is two surfaces perpendicular to the orientation direction of the magnet.

2. The corner strengthened R-T-B based rare earth permanent magnet as claimed in claim 1, wherein The R-T-B rare earth permanent magnet with corner reinforcement is prepared by the following method: (1) setting an H1 diffusion source coating area and an H2 diffusion source coating area on the diffusion surface of the R-T-B magnet substrate, partitioning the diffusion source, coating the diffusion source H1 in the H1 diffusion source coating area, and coating the diffusion source H2 in the H2 diffusion source coating area; the H1 diffusion source coating area is the corner area of the diffusion surface, and the H2 diffusion source coating area is the non-corner area of the diffusion surface; The diffusion source H1 comprises the following mass fractions of components: R1: 50.0-80.0 wt.%, R1 contains RL1 and RH1, RH1 is one or more of Dy, Tb, Ho, and accounts for 30.0-70.0 wt.% of H1, the balance of R1 is RL1, RL1 represents one or more elements containing at least light rare earth elements selected from Nd, Pr, La, Ce, Er, Gd, Sm, Tm, Lu, Y; the light rare earth elements are one or more of La, Ce, Pr, Nd; X1: 10-30 wt.%, X1 is one or more of Zr, Ti, Nb; M1: 5.0-40.0 wt.%, M1 is one or more of Al, Ga, Cu; The diffusion source H2 is one or more mixtures of pure metals, alloys or compounds containing heavy rare earth elements, the heavy rare earth elements being at least one of Dy, Tb, Ho; And the content of heavy rare earth elements in the diffusion source H1 is lower than that in H2; (2) Diffusion treatment is performed on the magnet with the diffusion source coated in sections, the diffusion temperature is 800-1000°C, the holding time is 6-30 h, and then tempering treatment is performed after cooling to obtain the R-T-B rare earth permanent magnet.

3. A method of producing a corner strengthened R-T-B rare earth permanent magnet, characterized by The method comprises the following steps: (1) H1 diffusion source coating area and H2 diffusion source coating area are arranged on the diffusion surface of the R-T-B magnet substrate, the diffusion source is coated in sections, the H1 diffusion source coating area is coated with diffusion source H1, and the H2 diffusion source coating area is coated with diffusion source H2; the H1 diffusion source coating area is the edge corner area of the diffusion surface, and the H2 diffusion source coating area is the non-edge corner area of the diffusion surface; The edge corner area refers to the surface area within the 0-K mm width range from the edge line, K is the width of the edge corner area, and K ranges from 0.2 to 0.6, and the non-edge corner area refers to the surface area outside the K mm width range from the edge line; The diffusion source H1 comprises the following mass fractions of components: R1: 50.0-80.0 wt.%, R1 contains RL1 and RH1, RH1 is one or more of Dy, Tb, Ho, and accounts for 30.0-70.0 wt.% of H1, the balance of R1 is RL1, RL1 represents one or more elements containing at least light rare earth elements selected from Nd, Pr, La, Ce, Er, Gd, Sm, Tm, Lu, Y; the light rare earth elements are one or more of La, Ce, Pr, Nd; X1: 10-30 wt.%, X1 is one or more of Zr, Ti, Nb; M1: 5.0-40.0 wt.%, M1 is one or more of Al, Ga, Cu; The diffusion source H2 is one or more mixtures of pure metals, alloys or compounds containing heavy rare earth elements, the heavy rare earth elements being at least one of Dy, Tb, Ho; And the content of heavy rare earth elements in the diffusion source H1 is lower than that in H2; (2) The magnet coated with the diffusion source in the partition is subjected to diffusion treatment at a diffusion temperature of 800-1000 DEG C for 6-30 h, and then is subjected to tempering treatment after cooling to obtain the R-T-B rare earth permanent magnet.

4. The method of claim 3, wherein The coating amount of the diffusion source H1 is 0.5-2.0% of the mass of the magnet; and the coating amount of the diffusion source H2 is 0.5-2.0% of the mass of the magnet.

5. The method of claim 3, wherein In the step (1), the partitioned coating of the diffusion source is realized by the following manner: The edge and corner regions of the magnet are covered by the shielding sheet 1, and the non-edge and corner regions are exposed as the H2 diffusion source coating region, and then the diffusion source H2 is coated; then the non-edge and corner regions of the magnet are covered by the shielding sheet 2, and the edge and corner regions of the magnet are exposed as the H1 diffusion source coating region, and then the diffusion source H1 is coated; or the non-edge and corner regions of the magnet are covered by the shielding sheet 2, and the edge and corner regions of the magnet are exposed as the H1 diffusion source coating region, and then the diffusion source H1 is coated; then the edge and corner regions of the magnet are covered by the shielding sheet 1, and the non-edge and corner regions are exposed as the H2 diffusion source coating region, and then the diffusion source H2 is coated.

6. The method of claim 3, wherein The coating manner of the diffusion source is PVD, spraying or printing when the diffusion source is coated in the partition.

7. The method of claim 6, wherein The diffusion source is coated in the partition by the silk screen printing, and the method comprises the following steps: (a) The hollow region with holes and the shielding region without holes are arranged on the silk screen, the positions of the hollow region and the shielding region are changed according to the product size and the edge and corner region size, and at least the printing screen 1 and the printing screen 2 are included, wherein the hollow region of the printing screen 1 corresponds to the non-edge and corner region of the magnet, and the shielding region corresponds to the edge and corner region of the magnet; the hollow region of the printing screen 2 corresponds to the edge and corner region of the magnet, and the shielding region corresponds to the non-edge and corner region of the magnet; (b) The shielding region of the printing screen 1 is aligned with the edge and corner region of the magnet, and the hollow region is aligned with the non-edge and corner region, as the H2 diffusion source coating region, the diffusion source H2 is printed, and then is dried; then the shielding region of the printing screen 2 is aligned with the non-edge and corner region of the magnet, and the hollow region is aligned with the edge and corner region of the magnet, as the H1 diffusion source coating region, the diffusion source H1 is printed, and then is dried; or the partitioned coating is carried out in the opposite order.

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