Sintered neodymium-iron-boron magnet having high magnetic performance and high resistivity, and preparation method therefor and use thereof

Abstract

The present invention provides a sintered neodymium-iron-boron magnet having high magnetic performance and high resistivity, and a preparation method therefor and a use thereof. The sintered neodymium-iron-boron magnet of the present invention comprises main phase grains and grain boundaries. Components of each main phase grain comprise R2T14B. The grain boundaries are located between the main phase grains and comprise two-grain boundaries and triple-junction boundaries. Each two-grain boundary is located between any two main phase grains, and each triple-junction boundary is located among any three or more main phase grains. The triple-junction boundaries comprise regions of a first Cu-rich phase and regions of a second Cu-rich phase. The sintered neodymium-iron-boron magnet provided by the present invention comprises two non-ferromagnetic Cu-rich phases, which can impede the propagation of a demagnetizing field among grains, thereby enhancing coercivity. In addition, the Cu-rich phases have a low Fe content, so that the propagation of electrons among the main phase grains can be impeded within the grain boundaries, and an isolation effect is achieved, thereby improving the resistivity of the magnet, and reducing the eddy current loss in motors.

Description

A sintered NdFeB magnet with high magnetic properties and high resistivity, its preparation method and application

[0001] This application claims priority to the earlier application filed on May 29, 2024, with the China National Intellectual Property Administration, patent application number 202410677153.3, entitled "A Sintered NdFeB Magnet with High Magnetic Properties and High Resistivity, its Preparation Method and Application". The entire contents of the earlier application are incorporated herein by reference. Technical Field

[0002] This invention belongs to the field of neodymium iron boron magnets, specifically relating to a sintered neodymium iron boron magnet with high magnetic properties and high resistivity, its preparation method, and its application. Background Technology

[0003] Sintered neodymium iron boron (NdFeB) magnets possess excellent comprehensive magnetic properties and are widely used in numerous fields such as consumer electronics, communications, medical devices, and automobiles. Automotive motors are a core application area for NdFeB magnets. Automotive motors require NdFeB magnets with high remanence and high coercivity, while also demanding high resistivity to ensure minimal eddy currents in the motor after installation, thereby improving motor efficiency. Increasing the coercivity of the magnets is challenging. A common method is to add a certain amount of heavy rare earth elements Dy and / or Tb to the NdFeB magnets; however, the reserves of these two elements are limited and their prices are high. Therefore, finding ways to improve the coercivity of magnets without using or with minimal use of heavy rare earth elements, while simultaneously reducing material costs, is of great significance.

[0004] To improve the overall performance of the product, patent document CN111724960A discloses an RTB-based permanent magnet, whose composition M includes at least Ga, Cu, and Zr, and contains Zr-B compounds at the grain boundaries between the two main phase particles. The coercivity of the product is improved through the formation of ZrB compounds. However, because the amount of ZrB compounds formed is not very large, the performance improvement is limited. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a neodymium iron boron material and its manufacturing method, which can improve the coercivity of magnets and reduce costs without using or with less use of heavy rare earth elements, while ensuring that the magnets have high remanence and are easy to magnetize.

[0006] To overcome the shortcomings of the existing technology, the present invention provides the following technical solution:

[0007] A sintered NdFeB magnet, comprising main phase grains and grain boundaries; the main phase grains are composed of R2T. 14B; The grain boundaries are located between the main phase grains, and the grain boundaries include two grain boundaries and triangular grain boundaries; wherein, the two grain boundaries are located between any two main phase grains, and the triangular grain boundaries are located between any three or more main phase grains;

[0008] The triangular grain boundary includes a first Cu-rich phase region and a second Cu-rich phase region; wherein...

[0009] The first Cu-rich phase includes R, T, Cu and Ga, wherein the mass ratio of R, T, Cu and Ga is (72-90):(1-8):(8-20):(1-3);

[0010] The second Cu-rich phase includes R, T, Cu and Ga, wherein the mass ratio of R, T, Cu and Ga is (50-74):(5-10):(20-40):(2-5).

[0011] In this invention, the region rich in the first Cu phase refers to the triangular grain boundary containing the first Cu-rich phase; the region rich in the second Cu phase refers to the triangular grain boundary containing the second Cu-rich phase, as shown in Figure 5.

[0012] According to an embodiment of the present invention, R is a rare earth element; R includes Nd, and at least one selected from the following rare earth elements: Y, La, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc; wherein T is at least one of Fe and Co.

[0013] According to an embodiment of the present invention, in the first Cu-rich phase, the mass ratio of R, T, Cu and Ga is, for example, 80:5:10:2, 76.96:2.5:18.05:2.49, 80.3:4.27:12.92:2.51, or 80.1:3.17:14.95:1.81.

[0014] According to an embodiment of the present invention, in the second Cu-rich phase, the mass ratio of R, T, Cu and Ga is, for example, 60:5:30:3, 68.09:7.32:22.44:2.15, 66.51:7.9:23.04:2.55, or 66.67:5.96:25.17:2.2.

[0015] According to an embodiment of the present invention, the area ratio of the first Cu-rich phase to the region of the first Cu-rich phase is denoted as P. 11 5% ≤ P 11 ≤30%, for example, 12%, 15%, 25%.

[0016] According to an embodiment of the present invention, the area ratio of the first Cu-rich phase region to all triangular grain boundaries is denoted as P. 12 P12 ≥8%, for example, 8.52% or 12.5%.

[0017] According to an embodiment of the present invention, the area ratio of the second Cu-rich phase to the region of the second Cu-rich phase is denoted as P. 21 P 21 ≥40%, for example, 50% or 60%.

[0018] According to an embodiment of the present invention, the area ratio of the second Cu-rich phase region to all triangular grain boundaries is denoted as P. 22 P 22 ≥30%, for example, 32% or 38%.

[0019] According to an embodiment of the present invention, the ratio of the area of ​​the triangular grain boundary to the total area of ​​the grain boundary is denoted as P, where P ≥ 70%, for example, 70% or 80%.

[0020] According to an embodiment of the present invention, the first Cu-rich phase is preferably located at the edge of the region containing the first Cu-rich phase, adjacent to the main phase grain; or the second Cu-rich phase is preferably located at the edge of the region containing the second Cu-rich phase, adjacent to the main phase grain. Further, the junction of the main phase grain and the triangular grain boundary of the region containing the first Cu-rich phase or the region containing the second Cu-rich phase is referred to as the edge of the main phase grain; wherein, the Cu atom concentration of the portion of the edge of the main phase grain near the main phase grain is set as [Cu1] (in this invention, [Cu1] is approximately equivalent to the atomic concentration of the main phase grain); the Cu atom concentration of the portion of the edge of the main phase grain near the triangular grain boundary is set as [Cu2] (in this invention, [Cu2] is approximately equivalent to the Cu atom concentration in the triangular grain boundary);

[0021] [Cu1] and [Cu2] satisfy the following relationship: [Cu2] / [Cu1]≥20, for example, 25, 30, 35, 40, 45, 50.

[0022] According to an embodiment of the present invention, the edge of the main phase grain that satisfies the above relationship [Cu2] / [Cu1]≥20 has a certain width L, 20nm≤L≤100nm, for example 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, or 90nm.

[0023] According to an embodiment of the present invention, in the sintered NdFeB magnet, the grain boundaries preferably comprise a thin layer of rare earth-rich phase.

[0024] According to an embodiment of the present invention, the sintered NdFeB magnet, based on a mass ratio of 100%, comprises the following components:

[0025] R, 30wt% to 35wt% (e.g., 31wt%, 32wt%, 33wt%, 34wt%), R is a rare earth element, R includes Nd, and at least one selected from the following rare earth elements: Y, La, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc;

[0026] B, 0.9wt% to 1.3wt% (e.g., 1wt%, 1.1wt%, 1.2wt%);

[0027] M1 is Cu, 0.25wt% to 2wt% (e.g., 0.25wt%, 0.5wt%, 0.75wt%, 1.0wt%, 1.5wt%);

[0028] M2 is at least one of Zr and Ti, in an amount of 0.1 wt% to 0.6 wt% (e.g., 0.15 wt%, 0.25 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%).

[0029] M3 is at least one of V, Cr, Mn, Ga, Si, Al, Nb, W and Mo, in an amount of 0.1 wt% to 1.0 wt% (e.g., 0.15 wt%, 0.25 wt%, 0.3 wt%, 0.4 wt%, 0.8 wt%).

[0030] The remainder consists of T and unavoidable impurities, where T is at least one of Fe and Co.

[0031] This invention also provides a method for preparing the above-mentioned sintered NdFeB magnet, the method comprising:

[0032] (1) Powder preparation process: preparing alloy micro powder; the alloy micro powder includes R, T, B and M, and R, T, B and M have the meanings described above;

[0033] (2) Pressing process: The alloy micro powder is ground to obtain magnetic powder and pressed to obtain a pressed blank;

[0034] (3) Sintering process: The pressed blank in step (2) is sintered to obtain a sintered blank;

[0035] (4) Aging process: The sintered blank in step (3) is subjected to multi-stage aging treatment to obtain sintered NdFeB magnets.

[0036] According to an embodiment of the present invention, the alloy micro powder can be obtained by methods known in the art, for example, preparing raw materials according to the composition of sintered NdFeB magnets and preparing R-Fe-BM alloy sheets by rapid solidification thin strip method, and then subjecting the R-Fe-BM alloy sheets to hydrogen explosion treatment to obtain the R-Fe-BM alloy micro powder.

[0037] According to an embodiment of the present invention, in step (2), the average particle size of the magnetic powder is 2 to 5 μm, for example, 3 μm or 4 μm.

[0038] According to an embodiment of the present invention, in step (2), the alloy micro powder can be ground to obtain magnetic powder using a method known in the art, for example, the alloy micro powder can be ground by air jet milling to obtain the magnetic powder.

[0039] According to an embodiment of the present invention, in step (2), before pressing, a lubricant may be added to the magnetic powder, for example, 0.1-0.5 wt% lubricant is added and then mixed for 0.5-6 hours.

[0040] According to an embodiment of the present invention, in step (3), the conditions for the sintering treatment include: a sintering temperature of 900-1100℃ (e.g., 1000℃) and a sintering time of 2-8h (e.g., 3h, 4h, 5h, 6h, 7h).

[0041] According to an embodiment of the present invention, in step (4), the multi-level timeliness processing includes first-level timeliness processing, second-level timeliness processing and third-level timeliness processing. Preferably, the multi-stage aging treatment specifically includes: performing a first-stage aging treatment on the sintered magnet at a temperature T1 of 500℃~700℃ (e.g., 600℃) for 1~6 hours, followed by natural cooling in the furnace for 10 minutes at a cooling rate δT11≤5℃ / min, then cooling with a fan at a cooling rate δT12: 7~15℃ / min until the temperature drops below 200℃; then heating to a temperature T2 of 800℃~950℃ (e.g., 900℃) for a second-stage aging treatment for 1~3 hours, followed by cooling with a fan at a cooling rate δT2: 7~15℃ / min until the temperature drops below 200℃; and then heating to a temperature T3 of 400~600℃ (e.g., 500℃) for a third-stage aging treatment for 2~8 hours, followed by cooling with a fan at a cooling rate δT3: 7~15℃ / min until the temperature drops below 200℃.

[0042] According to an embodiment of the present invention, the sintered NdFeB magnet in step (4) may optionally undergo diffusion treatment.

[0043] According to an embodiment of the present invention, the diffusion treatment is a grain boundary diffusion treatment. Preferably, prior to the diffusion treatment, a pretreatment known in the art may be performed, such as processing the sintered NdFeB magnet to the required size, and then optionally performing degreasing, pickling, etc.

[0044] Preferably, the conditions for the grain boundary diffusion treatment include: a diffusion temperature of 850–950°C and a diffusion time of at least 3 hours.

[0045] Preferably, during the diffusion process, the diffusion source is selected from at least one of the following elements: Dy, Tb, Ho, Nd, Pr.

[0046] Preferably, the diffusion treatment can be at least one of the treatment methods known in the art, such as thermal spraying, coating, sputtering, or immersion.

[0047] The present invention also provides applications of the above-described sintered NdFeB magnets, such as in motors.

[0048] The beneficial effects of this invention are:

[0049] When preparing sintered NdFeB magnets, adding rare earth elements will cause Nd2Fe to form at the grain boundaries. 17 The first phase, a soft magnetic phase, reduces the coercivity of the magnet. However, adding Cu along with rare earth elements forms the NdFeCuM phase at the grain boundaries. This non-ferromagnetic phase hinders the propagation of the demagnetizing field between grains, thus improving coercivity. The inventors discovered that, in addition to adding heavy rare earth elements, enhancing the non-ferromagnetism of the grain boundaries can also significantly improve the coercivity of sintered NdFeB magnets. Moreover, this non-ferromagnetism at the grain boundaries can hinder the propagation of electrons between the main phase particles, acting as an isolation mechanism, thereby increasing the resistivity of the sintered NdFeB magnet and reducing eddy current losses in motors.

[0050] The sintered NdFeB magnet provided by this invention has two non-ferromagnetic Cu-rich phases, which can hinder the propagation of the demagnetizing field between grains, thereby improving coercivity. At the same time, the Cu-rich phase has a low Fe content, which can hinder the propagation of electrons between the main phase grains in the grain boundaries, playing an isolation role, thereby increasing the magnet resistivity and reducing the eddy current loss of the magnet in the motor. Attached Figure Description

[0051] Figure 1 is a TEM microstructure of the first Cu-rich phase in Example 1 (under any field of view).

[0052] Figure 2 is a TEM microstructure of the second Cu-rich phase in Example 1 (under another field of view).

[0053] Figure 3 is a compositional analysis diagram of the Cu-rich phase and the main phase grains in Example 1.

[0054] Figure 4 is a schematic diagram showing the distribution of the first and second Cu-rich phases in Example 1 (under other views); where, label 1 refers to the second Cu-rich phase (composition RE). 68.09 (FeCo) 7.32 Cu 22.44 Ga 2.15 ), both marked 2 and 3 are the first Cu-rich phase (composition RE). 76.96 (FeCo) 2.5 Cu18.05 Ga 2.49 ).

[0055] In this invention, the subscripts in the composition of the Cu-rich phase all refer to the mass percentage of each element.

[0056] Figure 5 is a schematic diagram of grain boundaries in sintered NdFeB magnets. Detailed Implementation

[0057] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0058] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0059] Magnetic performance testing: NIM-62000 magnetic analyzer from the National Institute of Metrology, China;

[0060] Resistivity testing: AT516 DC resistance tester;

[0061] Structural composition analysis: Field emission transmission electron microscopy (JEOL-2010F TEM);

[0062] Area ratio calculation: Image-Pro Plus software was used for analysis.

[0063] Examples 1-2 and Comparative Examples 1-2

[0064] Examples 1-2 and Comparative Examples 1-2 prepared raw materials according to the composition table of NdFeB materials in Table 1 (all units are wt%), and sintered NdFeB magnets were prepared using the following methods:

[0065] Alloy sheets were prepared by rapid solidification thin strip method, and then the alloy sheets were subjected to hydrogen explosion treatment to obtain alloy micro powder.

[0066] The alloy micro powder was ground by an air jet mill to obtain powder with a particle size D50 = 3.5 μm.

[0067] After adding 0.3 wt% lubricant to the air jet mill powder, the mixture was mixed for 2 hours and then pressed under an orientation field with a magnetic field strength of 2 T to obtain a green body.

[0068] The green body was sintered in a vacuum sintering furnace at 1040℃ for 4 hours. After holding at that temperature, it was cooled to below 200℃ to obtain the sintered green body.

[0069] Sintered NdFeB magnets are obtained by aging the sintered billet. The aging treatment method specifically includes: first-stage aging at T1 = 600℃ for 3 hours, followed by natural cooling in the furnace for 10 minutes at a cooling rate δT11 ≤ 5℃ / min, then cooling with a blower at a cooling rate δT12 = 7~15℃ / min until the temperature drops below 200℃. Second-stage aging is then performed at T2 = 900℃ for 1.5 hours, followed by cooling with a blower at a cooling rate δT2 = 7~15℃ / min until the temperature drops below 200℃. Third-stage aging is then performed at T3 = 500℃ for 4 hours, followed by cooling with a blower at a cooling rate δT3 = 7~15℃ / min until the temperature drops below 200℃.

[0070] Table 1: Raw material composition of Examples 1-2 and Comparative Examples 1-2 (all units are wt%)

[0071] The sintered NdFeB magnets prepared in Examples 1-2 and Comparative Examples 1-2 were subjected to magnetic property tests to obtain remanence and coercivity; the material resistivity was also tested. The test results are shown in Table 2.

[0072] Table 2: Performance of Sintered NdFeB Magnets in Examples 1-2 and Comparative Examples 1-2

[0073] The sintered NdFeB magnet of Example 1 was analyzed using a field emission transmission electron microscope (JEOL-2010F TEM) for microstructure and composition analysis. Figures 1 and 2 show the TEM microstructure under different fields of view.

[0074] Figure 1 shows the TEM microstructure of the first Cu-rich phase under any field of view, indicated by the dashed line. By analyzing the composition of the first Cu-rich phase under multiple fields of view within the magnet, and calculating the area of ​​the first Cu-rich phase and its associated triangular grain boundary region (i.e., the region containing the first Cu-rich phase), the area percentage of the region containing the first Cu-rich phase is calculated and denoted as P. 11 The area of ​​the region rich in Cu phase relative to all triangular grain boundaries is denoted as P. 12 The results are shown in Table 3.

[0075] The dashed line in Figure 2 shows the TEM microstructure of the second Cu-rich phase under another field of view. The composition of the second Cu-rich phase in the magnet was analyzed under different fields of view, and the area percentage of the second Cu-rich phase in the region was calculated and denoted as P. 21 The area of ​​the second Cu-rich phase relative to all triangular grain boundaries is denoted as P. 22 The results are shown in Table 3.

[0076] In addition, the ratio of the area of ​​all triangular grain boundaries to the total area of ​​all grain boundaries in multiple different fields of view in the magnet is calculated and denoted as P. The results are shown in Table 3.

[0077] The composition of different Cu-rich phases and the main phase grains adjacent to the corresponding Cu-rich phases in Examples 1 and 2 was analyzed in detail using a double aberration-corrected transmission electron microscope (FEI Themis G2 300TEM). The composition of the edges of the main phase grains in the magnets is as follows:

[0078] In the field of view corresponding to Figure 1, the composition of the first Cu-rich phase in the magnet is: RE 80.3 (FeCo) 4.27 Cu 12.92 Ga 2.51 In the field of view corresponding to Figure 2, the composition of the second Cu-rich phase in the magnet is: RE 66.51 (FeCo) 7.9 Cu 23.04 Ga 2.55 .

[0079] Based on the above tests, the composition of the first Cu-rich phase in the triangular grain boundary corresponding to any field of view of the magnet in Example 2 is: RE 80.1 (FeCo) 3.17 Cu 14.95 Ga 1.81 The composition of the second Cu-rich phase is: RE 66.67 (FeCo) 5.96 Cu 25.17 Ga 2.2 .

[0080] When the magnets of Comparative Examples 1 and 2 were analyzed and tested using the above-mentioned analytical method, no triangular grain boundaries containing the first or second Cu-rich phase were detected in the magnet of Comparative Example 1 within the field of view; no triangular grain boundaries containing the first Cu-rich phase were detected in the magnet of Comparative Example 2, only triangular grain boundaries containing the second Cu-rich phase were detected. The composition of the second Cu-rich phase detected in any field of view was: RE 50.2 (FeCo) 9.8 Cu 25.11 Ga 2.3 .

[0081] Table 3: Composition of sintered NdFeB magnets in Examples 1-2 and Comparative Examples 1-2

[0082] As can be seen from the above analysis, the sintered NdFeB magnets manufactured according to the method of the present invention in Examples 1-2 have triangular grain boundaries (regions containing the first Cu-rich phase) and another triangular grain boundary (regions containing the second Cu-rich phase). Furthermore, the proportion of the triangular grain boundaries to the total grain boundaries, the area proportion of the first Cu-rich phase in the triangular grain boundary (region of the first Cu-rich phase), the area proportion of the second Cu-rich phase in the triangular grain boundary (region of the second Cu-rich phase), the [Cu2] / [Cu1] ratio, and the edges of the main phase grains are all within the scope of the present invention. Therefore, the sintered NdFeB magnets have high remanence, high coercivity, and high resistivity. In contrast, Comparative Example 1 has a Cu content of 0.15 wt% in its raw materials, which is lower than the lower limit of 0.25 wt% for Cu content in the raw materials of this application. Due to the excessively low Cu content, the non-ferromagnetic first or second Cu-rich phase cannot appear at the triangular grain boundaries, thus the magnetic properties and resistivity cannot be improved as effectively. In Comparative Example 2, due to the low Ti content in the raw material, the first Cu-rich phase could not be detected at the triangular grain boundaries; only the second Cu-rich phase was detected. Although the magnet performance of Comparative Example 2 was improved to some extent, the improvement was not significant. Furthermore, because the first Cu-rich phase was not formed in the magnet of Comparative Example 2, and only the second Cu-rich phase with a low rare earth content was formed, the resistivity was not effectively improved.

[0083] Comparative Examples 3-8

[0084] Raw materials were prepared according to the composition table of the neodymium iron boron material in Example 1 (all units are wt%).

[0085] Alloy sheets were prepared using a rapid solidification strip method, and then subjected to hydrogen explosion treatment to obtain alloy micropowder. The alloy micropowder was milled using an air jet mill to obtain powder with a particle size D50 = 3.5 μm. The air jet milled powder was mixed with 0.3 wt% lubricant for 2 hours and then pressed under an orientation field with a magnetic field strength of 2 T. The blank was sintered in a vacuum sintering furnace at 1040 °C for 4 hours, and after holding at that temperature, cooled to below 200 °C to obtain a sintered magnet.

[0086] The sintered magnets were subjected to aging treatment, which was carried out in accordance with the methods of Examples 1-2 above, except that the different comparative examples were carried out according to the treatment temperature T1 to T3, cooling rate δT and other conditions listed in Table 4.

[0087] Table 4: Process Comparison of Example 1 and Comparative Examples 3-8

[0088] The sintered NdFeB magnets prepared in Comparative Examples 3-8 were subjected to magnetic property tests to obtain remanence and coercivity; and resistivity was also tested; the test results are shown in Table 5.

[0089] Table 5: Product performance of Example 1 and Comparative Examples 3-8

[0090] As can be seen from Tables 4 and 5, the aging temperatures of Comparative Examples 3-7 were not achieved using the multi-stage aging treatment method of the present invention. Therefore, products containing both the first Cu-rich phase and the second Cu-rich phase of the present invention, forming triangular grain boundaries, could not be obtained. Consequently, the magnetic properties and resistivity of the magnets were affected and not effectively improved. Comparative Example 8 did not undergo a low-speed furnace cooling process after the first-stage aging; instead, it underwent high-speed cooling directly. As a result, triangular grain boundaries containing both the first Cu-rich phase and the second Cu-rich phase of the present invention were not sufficiently formed in the magnet. Therefore, the performance of the product in Comparative Example 8 was also inferior to that in Example 1.

[0091] Specifically:

[0092] Comparative Example 3 did not undergo first-stage aging treatment, therefore no triangular grain boundaries with the first Cu-rich phase appeared in the magnet, resulting in lower magnet performance.

[0093] Although Comparative Examples 4 and 5 underwent a first-stage aging treatment, the treatment temperature was outside the range of the present invention (too low or too high), and the magnets did not exhibit triangular grain boundaries with the first Cu-rich phase. The magnet performance was not as good as that of Example 1.

[0094] Comparative Example 6 did not undergo secondary aging treatment, therefore no triangular grain boundaries with a second Cu-rich phase appeared in the magnet, resulting in reduced magnet performance;

[0095] Comparative Example 7 did not undergo three-stage aging treatment, although it was able to form a small amount of triangular grain boundaries (P) of the first Cu-rich phase. 11 =2.4%) and the triangular grain boundaries of the second Cu-rich phase (P 21 =22.2%), the area ratio P of triangular grain boundaries in the overall grain boundary is 67%. The presence of triangular grain boundaries containing the first Cu-rich phase (the region of the first Cu-rich phase) and triangular grain boundaries containing the second Cu-rich phase (the region of the second Cu-rich phase) improves the product performance to a certain extent. However, without the three-stage aging process, it is impossible to form a thin layer of rare earth-rich phase at the two grain boundaries, so the improvement in product performance is limited.

[0096] Although Comparative Example 8 underwent first-stage, second-stage, and third-stage aging treatments, it did not undergo a slow cooling process after the first-stage aging treatment. Therefore, the formation of the first Cu-rich phase was hindered, ultimately affecting the magnet's performance.

[0097] Through research, the inventors discovered that in step (4), a first-stage aging treatment is first performed, at which the first Cu-rich phase is formed. The temperatures and times for the second and third-stage aging treatments are the same as those commonly used in the sintering of NdFeB magnets, and the mechanisms are the same. Binary eutectic occurs during the second-stage aging, and ternary eutectic occurs during the third-stage aging. Through the action of binary and ternary eutectic, a continuous thin layer of rare earth phase is formed at the grain boundaries of the NdFeB magnet, thereby improving the grain boundary structure and enhancing the magnetic properties of the magnet. The inventors discovered that a region with a second Cu-rich phase appears in the triangular grain boundaries during the second-stage aging process. They speculate that this second Cu-rich phase may be formed independently during the second-stage aging or it may be transformed from the first Cu-rich phase. The formation of both the first and second Cu-rich phases begins at the triangular grain boundaries and influences the composition of the adjacent main phase grains to a certain extent. This results in the Cu atom concentration [Cu1] near the main phase grain edge and the Cu atom concentration [Cu2] near the triangular grain boundary satisfying the relationship: [Cu2] / [Cu1]≥20. Furthermore, the width L of the main phase grain edge satisfying [Cu2] / [Cu1]≥20 satisfies 20nm≤L≤100nm.

[0098] Example 3

[0099] The NdFeB magnets prepared in Example 1 were processed into square sheets with dimensions of 15-15-3 mm. After degreasing and pickling, the sheets underwent Dy grain boundary diffusion treatment. The diffusion amount of Dy was 1.0 wt%, the diffusion temperature was 900℃, and the diffusion time was 10 h. In this example, the grain boundary diffusion was treated using a coating method. Diffused NdFeB magnets were obtained. The performance of the product was tested, and the test results are shown in Table 6.

[0100] Comparative Example 9

[0101] The neodymium iron boron magnet prepared in Comparative Example 2 was processed into square sheets with dimensions of 15-15-3 mm. After degreasing and pickling, the square sheets were subjected to Dy grain boundary diffusion treatment. The diffusion amount of Dy was 1.0 wt%, the diffusion temperature was 900℃, and the diffusion time was 10 h. In this example, the grain boundary diffusion was treated by coating method. The diffused neodymium iron boron magnets were obtained and their performance was tested. The test results are shown in Table 6.

[0102] Table 6: Performance of NdFeB magnets in Example 3 and Comparative Example 9

[0103] As can be seen from the test results of Example 3 and Comparative Example 9, the magnet prepared by Example 1 of the present invention is more conducive to the diffusion of the magnet, and the coercivity and resistivity of the magnet are further improved after diffusion.

[0104] The exemplary embodiments of the present invention have been described above. However, the scope of protection of this application is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A sintered neodymium-iron-boron magnet, characterized in that, The sintered neodymium-iron-boron magnet comprises main phase grains and grain boundaries; a component of the main phase grains comprises R2T 14 B; the grain boundaries are located between the main phase grains, and the grain boundaries comprise two-particle grain boundaries and three-particle grain boundaries; wherein the two-particle grain boundaries are located between any two main phase grains, and the three-particle grain boundaries are located between any three or more main phase grains; The triangular grain boundary comprises a first Cu-rich phase region and a second Cu-rich phase region; wherein, The first Cu-rich phase comprises R, T, Cu and Ga, wherein the mass ratio of R, T, Cu and Ga is (72-90):(1-8):(8-20):(1-3); The second Cu-rich phase comprises R, T, Cu and Ga, wherein the mass ratio of R, T, Cu and Ga is (50-74):(5-10):(20-40):(2-5).

2. The sintered neodymium-iron-boron magnet according to claim 1, characterized in that The area ratio of the first Cu-rich phase in the region of the first Cu-rich phase is denoted as P 11 , 5%≤P 11 ≤30%.

3. The sintered neodymium-iron-boron magnet according to claim 1, characterized in that The area ratio of the first Cu-rich phase to all the triple junctions is denoted as P 12 , P 12 ≥ 8%.

4. The sintered neodymium-iron-boron magnet according to claim 1, characterized in that The area ratio of the second Cu-rich phase in the region of the second Cu-rich phase is denoted as P 21 , P 21 ≥ 40%.

5. The sintered neodymium-iron-boron magnet according to claim 1, characterized in that The area ratio of the second Cu-rich phase to all the triple junctions is denoted as P 22 , P 22 ≥ 30%.

6. The sintered neodymium-iron-boron magnet according to claim 1, characterized in that The ratio of the area of the triangular grain boundary to the total area of the grain boundary is denoted as P, and P≥70%.

7. The sintered neodymium-iron-boron magnet according to claim 1, characterized in that The first Cu-rich phase is located at the edge of the first Cu-rich phase region and is adjacent to the main phase grain, or the second Cu-rich phase is located at the edge of the second Cu-rich phase region and is adjacent to the main phase grain. The intersection of the main phase grain and the triangular grain boundary containing the first Cu-rich phase region or the second Cu-rich phase region is denoted as the main phase grain edge portion; wherein the Cu atom concentration of the portion of the main phase grain edge portion close to the main phase grain is set as [Cu1], and the Cu atom concentration of the portion of the main phase grain edge portion close to the triangular grain boundary is set as [Cu2]; [Cu1] and [Cu2] satisfy the following relationship: [Cu2] / [Cu1]≥20.

8. The sintered neodymium-iron-boron magnet according to claim 7, characterized in that The main phase grain edge portion has a certain width L, and 20nm≤L≤100nm.

9. The sintered neodymium-iron-boron magnet according to claim 1, characterized in that The sintered neodymium-iron-boron magnet comprises the following components by mass ratio of 100%: R, 30wt%-35wt%, R is a rare earth element; R comprises Nd, and at least one selected from the following rare earth elements: Y, La, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc; B, 0.9wt%-1.3wt%; M1 is Cu, 0.25wt%-2wt%; M2, 0.1wt%-0.6wt%; M2 is at least one of Zr and Ti; M3, 0.1wt%-1.0wt%; M3 is at least one of V, Cr, Mn, Ga, Si, Al, Nb, W and Mo; The rest is T and unavoidable impurities, T is at least one of Fe and Co.

10. Use of the sintered neodymium-iron-boron magnet according to any one of claims 1-9 in an electric machine.

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