Neodymium iron boron magnet and preparation method thereof

Abstract

The present application discloses a neodymium iron boron magnet and a preparation method thereof. The neodymium iron boron magnet comprises the following components: 28 wt% to 30.5 wt% of RL, 0.5 wt% to 2 wt% of RH, 1.0 wt% to 2.5 wt% of M, 0.8 wt% to 1.0 wt% of B, and 65 wt% to 69 wt% of Fe; the distance between at least one set of two opposite surfaces parallel to the orientation direction of the neodymium iron boron magnet is d, the RH concentration difference between any one of the two surfaces and a depth d1 from the surface is ΔC1, the RH concentration difference between a depth d1 and a depth d / 2 is ΔC2, d1 is less than d / 2, the distance between d1 and d / 2 is d2, ΔC1 / ΔC2 is ≥6, the ratio k2 of ΔC2 to d2 satisfies k2>0, and the ratio k1 of ΔC1 to d1 satisfies k1>k2.

Description

Technical Field

[0001] The present application generally relates to the field of magnetic material technology. More specifically, the present application relates to a neodymium iron boron magnet and a method for preparing the same. Background Art

[0002] Sintered NdFeB magnets, as high-performance permanent magnet materials, are widely used in new energy vehicles, wind power generation, industrial automation, and other fields. As motors and other equipment move toward higher power density and miniaturization, higher requirements are placed on the magnets' anti-demagnetization properties (i.e., coercivity). Grain boundary diffusion (GBD) technology, which effectively enhances coercivity by coating the magnet surface with heavy rare earth elements (such as dysprosium and terbium) and then diffusing them at high temperatures, has become a mainstream technology.

[0003] However, conventional grain boundary diffusion methods have significant drawbacks: First, due to the anisotropic nature of grain boundary diffusion, diffusion in the orientation direction is generally more effective than diffusion in the non-orientation direction. Therefore, heavy rare earth elements are typically coated on the surface of the magnet perpendicular to the magnetization direction (i.e., the orientation direction), causing the heavy rare earth elements to diffuse along the orientation direction. This results in heavy rare earth elements being enriched not only in areas susceptible to demagnetization, but also in areas not susceptible to demagnetization, resulting in a waste of heavy rare earth element resources. Second, existing processes for diffusion along the non-orientation direction result in a low grain boundary diffusion depth and poor controllability of the diffusion depth.

[0004] In view of this, there is an urgent need to provide a NdFeB magnet and a preparation method thereof to achieve a gradient-controllable heavy rare earth distribution in the magnet to meet the needs of application scenarios with different performance requirements for different parts of the magnet. Summary of the Invention

[0005] In order to at least solve one or more of the technical problems mentioned above, the present application proposes solutions of neodymium iron boron magnets and preparation methods thereof in multiple aspects.

[0006] In a first aspect, the present application provides a neodymium iron boron magnet, comprising the following components: 28 wt% to 30.5 wt% of RL, 0.5 wt% to 2 wt% of RH, 1.0 wt% to 2.5 wt% of M, 0.8 wt% to 1.0 wt% of B, and 65 wt% to 69 wt% of Fe, wherein RL comprises Nd, RH is a heavy rare earth element, and M comprises Co, Al, Cu, Ga, Zr, Nb, Ti, Mo, Sn, Hf, and W. At least one of the following: the distance between at least one set of two opposite surfaces parallel to the orientation direction of the NdFeB magnet is d, the difference in RH concentration between any one of the two surfaces and the depth d1 from the surface is ΔC1, the difference in RH concentration between the depth d1 and the depth d / 2 is ΔC2, d1<d / 2, the distance between d1 and d / 2 is d2, and ΔC1 / ΔC2≥6, the ratio k2 of ΔC2 to d2 satisfies k2>0, and the ratio k1 of ΔC1 to d1 satisfies k1>k2.

[0007] In some embodiments, d satisfies: 10 mm ≤ d ≤ 50 mm; d1 satisfies: 2 mm ≤ d1 ≤ 5 mm.

[0008] In other embodiments, 10 mm ≤ d ≤ 30 mm.

[0009] In some further embodiments, ΔC1 further satisfies: 1 wt%<ΔC1≤10 wt%; ΔC2 further satisfies: 0.1 wt%≤ΔC2≤1 wt%.

[0010] In some embodiments, RH includes at least one of dysprosium, terbium, holmium, and gadolinium; and / or RL further includes at least one of praseodymium, lanthanum, cerium, scandium, and yttrium.

[0011] In other embodiments, the coercive force difference between any one of the two surfaces and the depth d1 from the surface is ΔHcj1, and the ratio k3 of ΔHcj1 to d1 satisfies: 0.5kOe / mm≤k3≤1kOe / mm; the coercive force difference between the depth d1 and the depth d / 2 is ΔHcj2, and the ratio k4 of ΔHcj2 to d2 satisfies: 0.1kOe / mm≤k4≤0.4kOe / mm.

[0012] In some embodiments, the area from any one of the two surfaces to a depth of d1 from the surface is the surface region of the magnet, and the coercive force of the surface region of the magnet is ≥26 kOe.

[0013] In other embodiments, the region from the depth d1 to the depth d / 2 is the core region of the magnet, and the coercive force of the core region of the magnet is ≥22 kOe.

[0014] In some other embodiments, at any depth d3 between the surface and the depth d1, the distance between d3 and d1 is d4, the RH concentration difference between the surface and the depth d3 is ΔC3, the RH concentration difference between the depth d3 and the depth d1 is ΔC4, the ratio of ΔC3 to d3 is k5, and the ratio of ΔC4 to d4 is k6, satisfying k5>k6.

[0015] In some embodiments, d3 satisfies: 0 mm < d3 ≤ 1 mm.

[0016] In other embodiments, ΔC3 satisfies: 5 wt % ≤ ΔC3 ≤ 10 wt %.

[0017] In yet other embodiments, ΔC4 satisfies: 1 wt % ≤ ΔC4 ≤ 3 wt %.

[0018] In a second aspect, the present application provides a method for preparing a neodymium iron boron magnet, the preparation method comprising: using a first diffusion source containing a heavy rare earth element RH, performing a first coating treatment on at least one set of two opposite surfaces parallel to the orientation direction of the magnet matrix to obtain a first magnet green body; performing a first diffusion treatment on the first magnet green body to obtain a first magnet; using a second diffusion source containing a heavy rare earth element RH, performing a second coating treatment on two surfaces of the first magnet coated with the first diffusion source to obtain a second magnet green body, wherein the RH content in the second diffusion source is greater than the RH content in the first diffusion source; performing a second diffusion treatment on the second magnet green body to obtain a neodymium iron boron magnet, wherein the second diffusion temperature of the second diffusion treatment is lower than the first diffusion temperature of the first diffusion treatment.

[0019] In some embodiments, the preparation method further comprises: cutting the NdFeB magnet along a direction perpendicular to the orientation direction of the NdFeB magnet to obtain a plurality of NdFeB magnets of small size.

[0020] In other embodiments, the first diffusion temperature of the first diffusion treatment is 850°C to 1000°C, and the first diffusion time is 20h to 40h; the second diffusion temperature of the second diffusion treatment is 700°C to 830°C, and the second diffusion time is 10h to 18h.

[0021] In some embodiments, the first diffusion source includes 10 wt % to 30 wt % of an RH element and 70 wt % to 90 wt % of an M1 element, the RH element is a heavy rare earth element, and the M1 element includes at least one of Cu, Al, and Ga.

[0022] In some other embodiments, the second diffusion source includes 40 wt % to 70 wt % of the RH element and 30 wt % to 60 wt % of the M2 element, and the M2 element includes Co.

[0023] In some further embodiments, the M2 element includes Co and also includes at least one of Cu, Al, Ti, and Zr.

[0024] In some embodiments, the coating amount of the first diffusion source is 0.8 wt % to 1.5 wt % of the mass of the magnet substrate; the coating amount of the second diffusion source is 1.8 wt % to 2.5 wt % of the mass of the magnet substrate.

[0025] In other embodiments, the first coating process includes at least one of vacuum evaporation, magnetron sputtering or coating; the second coating process includes at least one of vacuum evaporation, magnetron sputtering or coating.

[0026] Through the NdFeB magnet and its preparation method provided above, the NdFeB magnet of the embodiment of the present application satisfies ΔC1 / ΔC2≥6, k1>k2, and d1<d / 2, indicating that along the non-orientation direction of the NdFeB magnet, the concentration gradient of heavy rare earth elements RH in the surface area (0~d1) of the magnet is greater than that in the core area (d1~d / 2) of the magnet, so that the NdFeB magnet can meet the higher requirements of motors and other applications for the anti-demagnetization performance of the magnet near the edge, and k2>0, indicating that a small amount of heavy rare earth elements RH is still retained in the area near the core area of ​​the magnet, which can avoid excessive attenuation of coercive force to balance the overall performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The above and other objects, features and advantages of the exemplary embodiments of the present application will become readily understood by reading the detailed description below with reference to the accompanying drawings. In the accompanying drawings, several embodiments of the present application are shown in an exemplary and non-limiting manner, and the same or corresponding reference numerals represent the same or corresponding parts, wherein:

[0028] Figure 1 A schematic diagram of a neodymium iron boron magnet according to an embodiment of the present application is shown;

[0029] Figure 2 A schematic diagram showing a trend of RH concentration variation of a NdFeB magnet according to an embodiment of the present application;

[0030] Figure 3 A schematic flow chart of the preparation method of some embodiments of the present application is shown;

[0031] Figure 4 A schematic diagram showing a large-sized NdFeB magnet cut into small-sized NdFeB magnets according to an embodiment of the present application is shown;

[0032] Figure 5 The figure shows the test results of the electron probe EPMA of the NdFeB magnet of Example 1 at a distance of 500 μm from the coating surface;

[0033] Figure 6 The figure shows the test results of the electron probe EPMA of the NdFeB magnet of Example 1 at a distance of 3 mm from the coating surface;

[0034] Figure 7 The graph showing the relationship between the coercive force and the diffusion depth of the NdFeB magnet of Example 1 is shown. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without making creative efforts are within the scope of protection of this application.

[0036] It should be understood that the terms "include" and "comprising" used in the description and claims of this application indicate the presence of described features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or collections thereof.

[0037] It should also be understood that the terms used in this specification are for the purpose of describing specific embodiments only and are not intended to limit this application. As used in this specification and claims, the singular forms "a," "an," and "the" are intended to include the plural forms unless the context clearly indicates otherwise. It should also be further understood that the term "and / or" as used in this specification and claims refers to any and all possible combinations of one or more of the associated listed items, including and including these combinations.

[0038] The specific implementation of the present application will be described in detail below with reference to the accompanying drawings.

[0039] Figure 1 A schematic diagram of a neodymium iron boron magnet according to an embodiment of the present application is shown. Figure 2 A schematic diagram showing the RH concentration variation trend of the NdFeB magnet according to the embodiment of the present application is shown. Figure 1 and Figure 2 Provide explanation.

[0040] like Figure 1 and Figure 2 As shown in FIG, at least one set of two opposite surfaces (eg, Figure 1The distance between two surfaces S1 and S2 is d, the RH concentration difference between any surface S1 and S2 (for example, S1) and the depth d1 from the surface is ΔC1, the RH concentration difference between the depth d1 and the depth d / 2 is ΔC2, d1<d / 2, the distance between d1 and d / 2 is d2, and ΔC1 / ΔC2≥6, the ratio k2 of ΔC2 to d2 satisfies k2>0, and the ratio k1 of ΔC1 to d1 satisfies k1>k2.

[0041] The NdFeB magnet of the embodiment of the present application satisfies ΔC1 / ΔC2≥6, k1>k2, and d1<d / 2, indicating that along the non-orientation direction of the NdFeB magnet, the difference in the heavy rare earth element RH concentration in the surface region (0~d1) of the magnet is significantly greater than that in the core region (d1~d / 2), and the heavy rare earth element RH concentration gradient in the surface region (0~d1) of the magnet is greater than that in the core region (d1~d / 2). In other words, there is a significant gradient change in the heavy rare earth element concentration distribution between the surface region (0~d1) and the core region (d1~d / 2), enabling the NdFeB magnet to meet the high requirements of motors and other devices for anti-demagnetization performance near the edge of the magnet. In addition, k2>0 indicates that a small amount of heavy rare earth element RH exists near the core region of the magnet, which can avoid excessive attenuation of coercive force to balance the overall performance, and at the same time indicates that the diffusion depth of the heavy rare earth element is further increased.

[0042] The orientation direction is the macroscopic arrangement direction of the easy magnetization axis (i.e., the crystallographic C axis) of the grains inside the magnet. The at least one set of two opposite surfaces parallel to the orientation direction 101 of the NdFeB magnet 100 can be one set of opposite surfaces or two sets of opposite surfaces (e.g., Figure 1 , and another set of two opposing surfaces S3 and S4. In other words, the NdFeB magnet of the present embodiment has at least one set of two opposing surfaces that meet the aforementioned characteristics. The at least one set of two opposing surfaces is typically a diffusion surface (or coating surface) of the heavy rare earth element RH. The distance d between the at least one set of diffusion surfaces (or coating surfaces) is such that the NdFeB magnet meets the aforementioned characteristics (e.g., ΔC1 / ΔC2 ≥ 6, k2 > 0, and k1 > k2).

[0043] In other embodiments, 6≤ΔC1 / ΔC2≤25. For example, ΔC1 / ΔC2 can be 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 20.5, 21, 21.5, 22, 22.5, 23, 23.5, 24, 24.5, 25, etc., or other values ​​greater than or equal to 6.

[0044] In some embodiments, the NdFeB magnet includes the following components: 28 wt% to 30.5 wt% of RL, 0.5 wt% to 2 wt% of RH, 1.0 wt% to 2.5 wt% of M, 0.8 wt% to 1.0 wt% of B, and 65 wt% to 69 wt% of Fe, wherein RL includes Nd element, RH is a heavy rare earth element, and M includes at least one of Co, Al, Cu, Ga, Zr, Nb, Ti, Mo, Sn, Hf, and W.

[0045] For example, the weight content of the RL element in the NdFeB magnet can be, for example, 28wt%, 28.5wt%, 29wt%, 29.5wt%, 30wt%, 30.5wt%, or other values ​​within the range of 28wt% to 30.5wt%. In other embodiments, in addition to neodymium (Nd), RL also includes at least one of praseodymium (Pr), lanthanum (La), cerium (Ce), scandium (Sc), and yttrium (Y).

[0046] For example, the mass content of the RH element in the NdFeB magnet can be, for example, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2 wt%, or other values ​​within the range of 0.5 wt% to 2 wt%. In other embodiments, RH can include at least one of dysprosium (Dy), terbium (Tb), holmium (Ho), and gadolinium (Gd).

[0047] Exemplarily, the mass content of the M element in the NdFeB magnet can be, for example, 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2 wt%, 2.1 wt%, 2.2 wt%, 2.3 wt%, 2.4 wt%, 2.5 wt%, etc., or other values ​​within the range of 1.0 wt% to 2.5 wt%.

[0048] For example, the mass content of the boron (B) element in the NdFeB magnet may be, for example, 0.8 wt%, 0.85 wt%, 0.9 wt%, 0.95 wt%, 1.0 wt%, or other values ​​within the range of 0.8 wt% to 1.0 wt%.

[0049] For example, the mass content of iron (Fe) in the NdFeB magnet can be, for example, 65wt%, 65.5wt%, 66wt%, 66.5wt%, 67wt%, 67.5wt%, 68wt%, 68.5wt%, 69wt%, or other values ​​within the range of 65wt% to 69wt%.

[0050] In some embodiments, 10 mm ≤ d ≤ 50 mm, and 2 mm ≤ d1 ≤ 5 mm. For example, d can be 10 mm, 12 mm, 14 mm, 16 mm, 18 mm, 20 mm, 22 mm, 24 mm, 26 mm, 28 mm, 30 mm, 32 mm, 34 mm, 36 mm, 38 mm, 40 mm, 42 mm, 44 mm, 46 mm, 48 mm, 50 mm, or other values ​​within the range of 10 mm to 50 mm. In other embodiments, 10 mm ≤ d ≤ 30 mm.

[0051] For example, d1 can be 2 mm, 2.5 mm, 3 mm, 3.5 mm, 4 mm, 4.5 mm, 5 mm, or other values ​​within the range of 2 mm to 5 mm. The depth range of d1 indicates that the diffusion depth of the RH element in the NdFeB magnet according to the embodiment of the present application can reach the millimeter level, which is much higher than the diffusion depth of heavy rare earth elements in traditional magnets. It also indicates that the RH concentration in the NdFeB magnet according to the embodiment of the present application has a relatively obvious gradient change (or slope change) at the depth d1, resulting in the enrichment of the RH element in the easily demagnetized region of the NdFeB magnet (near the edge region in the non-oriented direction).

[0052] The NdFeB magnet 100 may be in the shape of a rectangular parallelepiped. Between two opposing surfaces S1 and S2 parallel to the orientation direction C of the NdFeB magnet 100, the concentration of the heavy rare earth element RH gradually decreases along the two surfaces S1 and S2 toward the core region of the magnet. In some further embodiments, ΔC1 further satisfies: 1wt%<ΔC1≤10wt%; ΔC2 further satisfies: 0.1wt%≤ΔC2≤1wt%. Figure 1 The NdFeB magnets shown in Figure 2 Taking the RH concentration change trend shown in as an example, assuming that the RH concentration on the surface of S1 is C0, and the RH concentration at a depth of d1 from the surface of S1 is C1, then ΔC1=C0-C1; assuming that the RH concentration at a depth of d / 2 from the surface of S1 is C2, then ΔC2=C1-C2.

[0053] Illustratively, ΔC1 can be 1.1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, 7 wt%, 7.5 wt%, 8 wt%, 8.5 wt%, 9 wt%, 9.5 wt%, 10 wt%, etc., or other values ​​within the range of 1 wt% to 10 wt%.

[0054] Illustratively, ΔC2 can be 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt%, 0.3 wt%, 0.35 wt%, 0.4 wt%, 0.45 wt%, 0.5 wt%, 0.55 wt%, 0.6 wt%, 0.65 wt%, 0.7 wt%, 0.75 wt%, 0.8 wt%, 0.85 wt%, 0.9 wt%, 0.95 wt%, 1 wt%, etc., or other values ​​within the range of 0.1 wt% to 1 wt%.

[0055] ΔC1 satisfies the following conditions: 1wt%≤ΔC1≤10wt%, indicating that the RH concentration at the surface of the NdFeB magnet 100 in the non-oriented direction is significantly higher than that at depth d1, and that the concentration distribution of heavy rare earth elements in the surface region of the magnet has a large variation range, thereby ensuring a significant increase in the coercivity of the magnet surface region and a controllable coercivity variation trend in the magnet surface region. ΔC2 satisfies the following conditions: 0.1wt%≤ΔC2≤1wt%, indicating that the RH concentration in the core region of the NdFeB magnet 100 in the non-oriented direction slowly decreases, which helps avoid a sudden drop in coercivity.

[0056] In some embodiments, the coercivity difference between any of the two opposing surfaces and a depth d1 from the surface is ΔHcj1, and the ratio k3 of ΔHcj1 to d1 satisfies: 0.5kOe / mm≤k3≤1kOe / mm. In other embodiments, the coercivity difference between the depth d1 and the depth d / 2 is ΔHcj2, and the ratio k4 of ΔHcj2 to d2 satisfies: 0.1kOe / mm≤k4≤0.4kOe / mm. For example, Figure 1 The coercive force difference between the S1 surface of the NdFeB magnet 100 shown in FIG and the depth d1 from the surface is ΔHcj1, and the coercive force difference between the depth d1 and the depth d / 2 is ΔHcj2.

[0057] In some embodiments, the magnet surface region is defined as the region from any of the two opposing surfaces to a depth d1 from the surface, and the coercivity of the magnet surface region is ≥ 26 KOe. For example, the coercivity of the magnet surface region can be 26 KOe, 26.5 KOe, 27 KOe, 27.5 KOe, 28 KOe, 28.5 KOe, 29 KOe, 29.5 KOe, 30 KOe, 30.5 KOe, 31 KOe, or other values ​​greater than 26 KOe.

[0058] In other embodiments, the core region of the magnet is from the depth d1 to the depth d / 2, and the coercive force of the core region of the magnet is ≥ 22 KOe. For example, the coercive force of the core region of the magnet can be 22 KOe, 22.5 KOe, 23 KOe, 23.5 KOe, 24 KOe, 24.5 KOe, 25 KOe, 25.5 KOe, 26 KOe, 26.5 KOe, 27 KOe, or other values ​​above 22 KOe. The coercive force of the core region of the magnet is less than the coercive force of the surface region of the magnet.

[0059] When k3 is in the range of 0.5kOe / mm~1kOe / mm, and the coercivity of the magnet surface area reaches above 26kOe, it indicates that the coercivity gradient of the magnet surface area is large along the non-oriented direction of the NdFeB magnet, and the coercivity is significantly improved, thereby specifically improving the anti-demagnetization ability of the NdFeB magnet near the edge. When k4 is in the range of 0.1kOe / mm~0.4kOe / mm, and the coercivity of the magnet core area can still reach above 22kOe, it indicates that the coercivity gradient of the magnet core area is relatively gentle along the non-oriented direction of the NdFeB magnet, while maintaining a certain coercivity. While meeting the anti-demagnetization ability of the NdFeB magnet core, it is beneficial to reduce the consumption of heavy rare earth in non-essential areas.

[0060] Based on the above, it can be seen that in the non-oriented direction of the NdFeB magnets in the embodiments of this application, the high gradient (such as k1) of the RH concentration in the surface area of ​​the magnet is beneficial for strengthening the coercivity of the easily demagnetized area of ​​the NdFeB magnet, while the low gradient (such as k2) of the RH concentration in the core area of ​​the magnet is beneficial for reducing the waste of heavy rare earth elements. The coercivity gradient and the RH concentration gradient generally change in the same direction, ensuring that the performance distribution of the NdFeB magnet matches actual needs.

[0061] In yet other embodiments, at any depth d3 between any of the two opposing surfaces and a depth d1 from the surface, the distance between d3 and d1 is d4, the RH concentration difference between the surface and the depth d3 is ΔC3, the RH concentration difference between the depth d3 and the depth d1 is ΔC4, the ratio of ΔC3 to d3 is k5, and the ratio of ΔC4 to d4 is k6, satisfying k5>k6. In some embodiments, k6>k2.

[0062] In this embodiment, k5>k6 indicates that along the non-oriented direction of the NdFeB magnet, a concentration gradient of the heavy rare earth element RH further exists in the surface region (0-d1) of the magnet. In other words, within the surface region (0-d1), the RH concentration gradient in the shallow surface region (0-d3) is greater than that in the deep surface region (d3-d1), with d3 < d1. This characteristic results in higher demagnetization resistance in the shallow surface region of the NdFeB magnet, followed by the deep surface region, and then the core region (d1-d / 2). This further demonstrates that the present application can more precisely control the distribution of heavy rare earth elements in different regions of the magnet to meet the needs of application scenarios requiring refined magnetic properties.

[0063] In some embodiments, d3 satisfies the following: 0 mm < d3 ≤ 1 mm. For example, d3 may be, for example, 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, or other values ​​within the range of 0 mm < d3 ≤ 1 mm. In other embodiments, ΔC3 satisfies the following: 5 wt % ≤ ΔC3 ≤ 10 wt %. For example, ΔC3 may be 5 wt %, 5.5 wt %, 6 wt %, 6.5 wt %, 7 wt %, 7.5 wt %, 8 wt %, 8.5 wt %, 9 wt %, 9.5 wt %, 10 wt %, or other values ​​within the range of 5 wt % to 10 wt %.

[0064] In yet other embodiments, ΔC4 satisfies the following: 1 wt%≤ΔC4≤3 wt%. For example, ΔC4 may be 1 wt%, 1.2 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.8 wt%, 3 wt%, or other values ​​within a range of 1 wt% to 3 wt%.

[0065] The range of d3 and ΔC3>ΔC4 both indicate that the RH elements in the NdFeB magnet of the embodiment of the present application can be further enriched in the shallow surface area, further realizing a controllable concentration gradient distribution of heavy rare earth elements in the NdFeB magnet, thereby more accurately meeting the application scenario requirements for different coercive force performance in different regions of the magnet.

[0066] Figure 3 Schematic diagram of the preparation method of some embodiments of the present application is shown. Figure 3 As shown, the preparation method 300 may include: in step S301, using a first diffusion source containing a heavy rare earth element RH, performing a first coating treatment on at least one set of two opposite surfaces parallel to the orientation direction of the magnet matrix to obtain a first magnet green body; in step S302, performing a first diffusion treatment on the first magnet green body to obtain a first magnet; in step S303, using a second diffusion source containing a heavy rare earth element RH, performing a second coating treatment on two surfaces of the first magnet coated with the first diffusion source to obtain a second magnet green body, wherein the RH content in the second diffusion source is greater than the RH content in the first diffusion source; in step S304, performing a second diffusion treatment on the second magnet green body to obtain a NdFeB magnet, wherein the second diffusion temperature of the second diffusion treatment is lower than the first diffusion temperature of the first diffusion treatment.

[0067] In some embodiments, the first diffusion source includes 10 wt% to 30 wt% of the RH element and 70 wt% to 90 wt% of the M1 element, wherein the RH element is a heavy rare earth element and the M1 element includes at least one of Cu, Al, and Ga. For example, the mass content of the RH element in the first diffusion source is 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, 26 wt%, 27 wt%, 28 wt%, 29 wt%, 30 wt%, or other values ​​within the range of 10 wt% to 30 wt%. Illustratively, the mass content of the M1 element in the first diffusion source is 70wt%, 71wt%, 72wt%, 73wt%, 74wt%, 75wt%, 76wt%, 77wt%, 78wt%, 79wt%, 80wt%, 81wt%, 82wt%, 83wt%, 84wt%, 85wt%, 86wt%, 87wt%, 88wt%, 89wt%, 90wt%, etc., or other values ​​within the range of 70wt% to 90wt%.

[0068] In other embodiments, the second diffusion source comprises 40-70 wt% of the RH element and 30-60 wt% of the M2 element, where the M2 element includes Co. In yet other embodiments, the M2 element includes Co and at least one of Cu, Al, Ti, and Zr. Because Co has a higher melting point than M1, the melting point of the second diffusion source is higher than that of the first diffusion source. In comparison, the first diffusion source has a low RH content and a low melting point, while the second diffusion source has a high RH content and a high melting point.

[0069] For example, the mass content of the RH element in the second diffusion source is 40 wt%, 42 wt%, 45 wt%, 48 wt%, 50 wt%, 52 wt%, 55 wt%, 58 wt%, 60 wt%, 62 wt%, 65 wt%, 68 wt%, 70 wt%, or other values ​​within the range of 40 wt% to 70 wt%. For example, the mass content of the M2 element in the second diffusion source is 30 wt%, 32 wt%, 35 wt%, 38 wt%, 40 wt%, 42 wt%, 45 wt%, 48 wt%, 50 wt%, 52 wt%, 55 wt%, 58 wt%, 60 wt%, 62 wt%, 65 wt%, 68 wt%, 70 wt%, or other values ​​within the range of 40 wt% to 70 wt%.

[0070] In other embodiments, the first diffusion temperature of the first diffusion treatment is 850°C to 1000°C, and the first diffusion time is 20 hours to 40 hours; the second diffusion temperature of the second diffusion treatment is 700°C to 830°C, and the second diffusion time is 10 hours to 18 hours. For example, the first diffusion temperature of the first diffusion treatment is 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, 930°C, 940°C, 950°C, 960°C, 970°C, 980°C, 990°C, 1000°C, or other values ​​within the range of 850°C to 1000°C. The first diffusion time can be, for example, 20 hours, 22 hours, 24 hours, 25 hours, 26 hours, 28 hours, 30 hours, 32 hours, 34 hours, 35 hours, 36 hours, 38 hours, 40 hours, or other values ​​within the range of 20 hours to 40 hours.

[0071] Illustratively, the second diffusion temperature of the second diffusion treatment is 700° C., 710° C., 720° C., 730° C., 740° C., 750° C., 760° C., 770° C., 780° C., 790° C., 800° C., 810° C., 820° C., 830° C., or other values ​​within the range of 700° C. to 830° C. The second diffusion time can be, for example, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, or other values ​​within the range of 10 hours to 18 hours.

[0072] In some embodiments, the first coating process includes at least one of vacuum evaporation, magnetron sputtering, or coating. In other embodiments, the second coating process includes at least one of vacuum evaporation, magnetron sputtering, or coating. Vacuum evaporation, referred to as evaporation, refers to a process in which a coating material (or film material) is evaporated and vaporized using a certain heating evaporation method under vacuum conditions, and the particles fly to the surface of the substrate and condense into a film. Magnetron sputtering is a type of physical vapor deposition (PVD). Magnetron sputtering uses the interaction between a magnetic field and an electric field to cause electrons to spiral near the target surface. Ions generated by the collision with argon gas collide with the target surface under the action of the electric field, thereby sputtering out the target material.

[0073] As can be seen from the above description, the preparation method of the embodiment of the present application uses a two-step diffusion process to achieve NdFeB magnets with a controllable heavy rare earth element concentration gradient. Specifically, first diffusing a first diffusion source with a low heavy rare earth content and then performing high-temperature, long-term diffusion can help increase the diffusion depth, resulting in a slight improvement in the overall performance of the magnet. In particular, when the melting point of the first diffusion source is relatively low, diffusing the low-melting-point first diffusion source at high temperature first can widen the thin-layer grain boundaries (i.e., the grain boundary phase formed between two adjacent main phase grains) in the magnet, thereby optimizing the diffusion channels in the magnet. Furthermore, by using a second diffusion source for a second diffusion process, the diffusion depth of the heavy rare earth elements can be further increased.

[0074] At the same time, the second diffusion process uses a second diffusion source with a high heavy rare earth content. By controlling the second diffusion temperature to be relatively low, the diffusion gradient of the second diffusion process can be effectively controlled, while promoting the diffusion of some heavy rare earth elements further into the core region of the magnet. In particular, when the melting point of the second diffusion source is relatively high, it is more advantageous to control the diffusion depth of the second diffusion source during the second diffusion process, thereby concentrating the heavy rare earth elements from the second diffusion source primarily in the surface region of the magnet in the non-oriented direction of the magnet. This facilitates controlling the concentration gradient of the heavy rare earth elements and effectively improving the coercivity performance of the magnet edge region using a small amount of heavy rare earth resources, thereby facilitating the conservation and efficient utilization of heavy rare earth resources.

[0075] Furthermore, in some embodiments, the coating amount of the first diffusion source is 0.8 wt% to 1.5 wt% of the mass of the magnet substrate, and the coating amount of the second diffusion source is 1.8 wt% to 2.5 wt% of the mass of the magnet substrate. The coating amount here refers to the total amount coated on at least one set of two opposing surfaces parallel to the orientation direction of the magnet substrate.

[0076] For example, the coating amount of the first diffusion source can be 0.8 wt%, 0.9 wt%, 1 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, or other values ​​within the range of 0.8 wt% to 1.5 wt%. The coating amount of the second diffusion source can be 1.8 wt%, 1.9 wt%, 2 wt%, 2.1 wt%, 2.2 wt%, 2.3 wt%, 2.4 wt%, 2.5 wt%, or other values ​​within the range of 1.8 wt% to 2.5 wt%.

[0077] In other embodiments, the magnet matrix includes the following composition: 28 wt% to 31 wt% R, 1.0 wt% to 2.5 wt% M, 0.8 wt% to 1.0 wt% B, and 65 wt% to 69 wt% Fe, wherein R includes Nd and M includes at least one of Co, Al, Cu, Ga, Zr, Nb, Ti, Mo, Sn, Hf, and W. In other embodiments, R also includes at least one of dysprosium, terbium, holmium, gadolinium, praseodymium, lanthanum, cerium, scandium, and yttrium.

[0078] Illustratively, the mass content of the R element in the magnet matrix can be, for example, 28 wt%, 28.5 wt%, 29 wt%, 29.5 wt%, 30 wt%, 30.5 wt%, 31 wt%, or other values ​​within the range of 28 wt% to 31 wt%.

[0079] Exemplarily, the mass content of the M element in the magnet matrix can be, for example, 1.0wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, 2wt%, 2.1wt%, 2.2wt%, 2.3wt%, 2.4wt%, 2.5wt%, etc., or other values ​​within the range of 1.0wt% to 2.5wt%.

[0080] For example, the mass content of the B element in the magnet matrix can be, for example, 0.8 wt%, 0.85 wt%, 0.9 wt%, 0.95 wt%, 1.0 wt%, or other values ​​within the range of 0.8 wt% to 1.0 wt%.

[0081] Illustratively, the mass content of the Fe element in the magnet matrix can be, for example, 65wt%, 65.5wt%, 66wt%, 66.5wt%, 67wt%, 67.5wt%, 68wt%, 68.5wt%, 69wt%, etc., or other values ​​within the range of 65wt% to 69wt%.

[0082] In some embodiments, the two surfaces may be polished before the first coating process in step S301 and / or before the second coating process in step S303. In other embodiments, after the second diffusion process, the magnet may be aged to obtain a NdFeB magnet.

[0083] It is understood that the magnet matrix in the preparation method 300 can be a large-sized magnet matrix, or can be a small-sized magnet matrix. In some embodiments, when the magnet matrix in the preparation method 300 is a large-sized magnet matrix, the preparation method 300 can further include: cutting the NdFeB magnet along a direction perpendicular to the orientation direction of the NdFeB magnet to obtain a plurality of small-sized NdFeB magnets. For ease of understanding, the following will be combined with Figure 4 An exemplary description is given.

[0084] Figure 4 Schematic diagram showing the cutting of a large-sized NdFeB magnet into small-sized NdFeB magnets according to an embodiment of the present application. Figure 4 As shown in Figure 3 The preparation method 300 shown can prepare a large-sized NdFeB magnet 401. By cutting the NdFeB magnet 401 along a direction perpendicular to the orientation direction C of the NdFeB magnet 401 (for example, the dotted line extension direction in the figure), a plurality of small-sized NdFeB magnets 402 can be obtained.

[0085] Compared with cutting the magnet matrix into small pieces before diffusing them, in the embodiment of the present application, the large-sized magnet matrix is ​​first diffused and then cut into small-sized magnets. There is no need to polish the diffusion surface of the small-sized magnets, which is beneficial to further save heavy rare earth resources. At the same time, it is also beneficial to save time for coating and diffusion treatments to improve diffusion efficiency.

[0086] In addition, the traditional diffusion method is to cut the magnet matrix into small pieces, apply a diffusion source containing heavy rare earth elements on the two opposite sides perpendicular to the orientation direction C, and then diffuse. The heavy rare earth content of the resulting magnet is the highest on the two opposite sides perpendicular to the orientation direction C, and gradually decreases along the orientation direction C toward the core. The coercive force is also the highest on the two opposite sides perpendicular to the orientation direction C, and gradually decreases along the orientation direction C toward the core.

[0087] This traditional diffusion method involves polishing the diffused magnets, which results in a large grinding area and significant waste of heavy rare earth elements. Furthermore, on a surface perpendicular to the orientation direction C, the heavy rare earth content is uniform across all locations. However, motor magnets have both readily demagnetized regions (near the edges) and non-demagnetized regions. The readily demagnetized regions require a higher coercive force. This means that the non-demagnetized regions do not require the same high content of heavy rare earth elements as the readily demagnetized regions, resulting in wasted heavy rare earth elements in these regions.

[0088] The preparation method of the embodiment of the present application is to apply a diffusion source of heavy rare earth elements on two opposite surfaces parallel to the orientation direction C of a large magnet matrix for diffusion, and then cut it into small magnets after the diffusion is completed. The magnet prepared in this way has a high heavy rare earth content and a high coercive force near the edge (easy demagnetization area) on the surface perpendicular to the orientation direction C, while the heavy rare earth content and coercive force are lower in the middle part (non-easy demagnetization area), which meets the requirements for the actual operation of the motor and saves more heavy rare earth.

[0089] Examples and Comparative Examples:

[0090] Example 1:

[0091] Step 1) polishing two opposite surfaces parallel to the orientation direction of the magnet matrix (composition: Al: 0.1wt%, B: 0.94wt%, Co: 1.2wt%, Cu: 0.2wt%, Ga: 0.1wt%, Ti: 0.1wt%, Pr and Nd: 29.7wt%, Fe: balance), and then performing a first coating treatment, coating both opposite surfaces with an equal amount of a first diffusion source, with a total coating amount of the first diffusion source being 1wt% of the weight of the magnet matrix, to obtain a first magnet green compact, wherein the first diffusion source comprises: 20wt% Tb, 30wt% Al, 40wt% Cu, and 10wt% Ga;

[0092] Step 2), performing a first diffusion treatment on the first magnet green body to obtain a first magnet, wherein the first diffusion temperature of the first diffusion treatment is 950° C. and the first diffusion time is 32 hours;

[0093] Step 3) polishing the two opposite surfaces of the first magnet coated with the first diffusion source, and then performing a second coating process, coating the two opposite surfaces with an equal amount of the second diffusion source, with a total coating amount of the second diffusion source being 2.3 wt% of the weight of the magnet substrate, to obtain a second magnet green body, wherein the second diffusion source comprises: 60 wt% Tb, 18 wt% Cu, 15 wt% Co, and 7 wt% Ti;

[0094] Step 4) performing a second diffusion treatment on the second magnet green body to obtain a NdFeB magnet, wherein the second diffusion temperature of the second diffusion treatment is 800° C. and the second diffusion time is 15 hours.

[0095] Example 2:

[0096] Step 1) polishing two opposite surfaces parallel to the orientation direction of the magnet matrix (composition: Al: 0.08wt%, B: 0.85wt%, Co: 0.8wt%, Cu: 0.15wt%, Ga: 0.1wt%, Ti: 0.1wt%, Pr and Nd: 28.5wt%, Fe: balance), and then performing a first coating process, coating both opposite surfaces with an equal amount of a first diffusion source, with a total coating amount of the first diffusion source being 0.85wt% of the weight of the magnet matrix, to obtain a first magnet green compact, wherein the first diffusion source comprises: 12wt% Tb, 32wt% Al, 46wt% Cu, and 10wt% Ga;

[0097] Step 2), performing a first diffusion treatment on the first magnet green body to obtain a first magnet, wherein the first diffusion temperature of the first diffusion treatment is 870° C. and the first diffusion time is 40 hours;

[0098] Step 3) polishing the two opposite surfaces of the first magnet coated with the first diffusion source, and then performing a second coating process, coating the two opposite surfaces with an equal amount of the second diffusion source, with a total coating amount of the second diffusion source being 1.8 wt% of the weight of the magnet substrate, to obtain a second magnet green body, wherein the second diffusion source comprises: 45 wt% Tb, 25 wt% Cu, 8 wt% Al, 15 wt% Co, and 7 wt% Ti;

[0099] Step 4) performing a second diffusion treatment on the second magnet green body to obtain a NdFeB magnet, wherein the second diffusion temperature of the second diffusion treatment is 720° C. and the second diffusion time is 12 hours.

[0100] Example 3:

[0101] Step 1) polishing two opposite surfaces parallel to the orientation direction of the magnet substrate (composition: Al: 0.08wt%, B: 0.85wt%, Co: 0.8wt%, Cu: 0.15wt%, Ga: 0.1wt%, Ti: 0.1wt%, Pr and Nd: 28.5wt%, Fe: balance), and then performing a first coating treatment, coating both opposite surfaces with an equal amount of a first diffusion source, with a total coating amount of the first diffusion source being 1.25wt% of the weight of the magnet substrate, to obtain a first magnet green compact, wherein the first diffusion source comprises: 27wt% Dy, 25wt% Al, 40wt% Cu, and 8wt% Ga;

[0102] Step 2), performing a first diffusion treatment on the first magnet green body to obtain a first magnet, wherein the first diffusion temperature of the first diffusion treatment is 970° C. and the first diffusion time is 28 hours;

[0103] Step 3) polishing the two opposite surfaces of the first magnet coated with the first diffusion source, and then performing a second coating process, coating the two opposite surfaces with an equal amount of the second diffusion source, with a total coating amount of the second diffusion source being 2.4 wt% of the weight of the magnet substrate, to obtain a second magnet green body, wherein the second diffusion source comprises: 67 wt% Tb, 15 wt% Cu, 5 wt% Al, 8 wt% Co, and 5 wt% Ti;

[0104] Step 4) performing a second diffusion treatment on the second magnet green body to obtain a NdFeB magnet, wherein the second diffusion temperature of the second diffusion treatment is 830° C. and the second diffusion time is 11 hours.

[0105] Example 4:

[0106] The preparation steps and conditions are the same as those in Example 1, except that in step 1) two opposite sides of another group parallel to the orientation direction of the magnet matrix are selected (for example, if the two opposite sides selected in Example 1 are parallel to the orientation direction of the magnet matrix, the two opposite sides are selected). Figure 1 The S1 and S2 surfaces shown in the figure, and the S3 and S4 surfaces selected in Example 4) are polished and subsequently coated and diffused.

[0107] Comparative Example 1:

[0108] The two opposite sides parallel to the orientation direction of the magnet matrix (composition: Al: 0.1wt%, B: 0.94wt%, Co: 1.2wt%, Cu: 0.2wt%, Ga: 0.1wt%, Ti: 0.1wt%, Pr and Nd: 29.7wt%, Fe: balance) were polished and then subjected to the first coating treatment. The two opposite sides were coated with equal amounts of diffusion sources. The total coating amount of the diffusion sources was 3.3wt% of the weight of the magnet matrix to obtain a magnet green body, wherein the diffusion sources included: 20wt% Tb, 30wt% Al, 40wt% Cu, and 10wt% Ga. The magnet green body was diffused at a temperature of 950°C and for 32h.

[0109] Comparative Example 2:

[0110] Step 1) polishing two opposite surfaces parallel to the orientation direction of the magnet matrix (composition: Al: 0.1wt%, B: 0.94wt%, Co: 1.2wt%, Cu: 0.2wt%, Ga: 0.1wt%, Ti: 0.1wt%, Pr and Nd: 29.7wt%, Fe: balance), and then performing a first coating treatment, coating both opposite surfaces with an equal amount of a first diffusion source, with a total coating amount of the first diffusion source being 1wt% of the weight of the magnet matrix, to obtain a first magnet green compact, wherein the first diffusion source comprises: 20wt% Tb, 30wt% Al, 40wt% Cu, and 10wt% Ga;

[0111] Step 2), performing a first diffusion treatment on the first magnet green body to obtain a first magnet, wherein the first diffusion temperature of the first diffusion treatment is 750° C. and the first diffusion time is 25 hours;

[0112] Step 3) polishing the two opposite surfaces of the first magnet coated with the first diffusion source, and then performing a second coating process, coating the two opposite surfaces with an equal amount of the second diffusion source, with a total coating amount of the second diffusion source being 2.3 wt% of the weight of the magnet substrate, to obtain a second magnet green body, wherein the second diffusion source comprises: 60 wt% Tb, 18 wt% Cu, 15 wt% Co, and 7 wt% Ti;

[0113] Step 4) performing a second diffusion treatment on the second magnet green body to obtain a NdFeB magnet, wherein the second diffusion temperature of the second diffusion treatment is 900° C. and the second diffusion time is 15 hours.

[0114] Comparative Example 3:

[0115] Step 1) polishing two opposite surfaces parallel to the orientation direction of the magnet matrix (composition: Al: 0.1wt%, B: 0.94wt%, Co: 1.2wt%, Cu: 0.2wt%, Ga: 0.1wt%, Ti: 0.1wt%, Pr and Nd: 29.7wt%, Fe: balance), and then performing a first coating treatment, coating both opposite surfaces with an equal amount of a first diffusion source, with a total coating amount of the first diffusion source being 2.2wt% of the weight of the magnet matrix, to obtain a first magnet green compact, wherein the first diffusion source comprises: 65wt% Tb, 10wt% Al, 20wt% Cu, and 5wt% Ga;

[0116] Step 2), performing a first diffusion treatment on the first magnet green body to obtain a first magnet, wherein the first diffusion temperature of the first diffusion treatment is 950° C. and the first diffusion time is 32 hours;

[0117] Step 3) polishing the two opposite surfaces of the first magnet coated with the first diffusion source, and then performing a second coating process, coating the two opposite surfaces with an equal amount of the second diffusion source, with a total coating amount of the second diffusion source being 2.3 wt% of the weight of the magnet substrate, to obtain a second magnet green body, wherein the second diffusion source comprises: 25 wt% Tb, 40 wt% Cu, 30 wt% Al, and 5 wt% Ti;

[0118] Step 4) performing a second diffusion treatment on the second magnet green body to obtain a NdFeB magnet, wherein the second diffusion temperature of the second diffusion treatment is 800° C. and the second diffusion time is 15 hours.

[0119] Comparative Example 4:

[0120] The two opposite sides parallel to the orientation direction of the magnet matrix (composition: Al: 0.1wt%, B: 0.94wt%, Co: 1.2wt%, Cu: 0.2wt%, Ga: 0.1wt%, Ti: 0.1wt%, Pr and Nd: 29.7wt%, Fe: balance) were polished, and then the first coating treatment was performed, and the two opposite sides were plated with equal amounts of diffusion sources. The total coating amount of the diffusion source was 3.3wt% of the weight of the magnet matrix, and a magnet green body was obtained, wherein the diffusion sources included: 20wt% Tb, 30wt% Al, 40wt% Cu, and 10wt% Ga; the magnet green body was subjected to the first diffusion treatment, the temperature of the first diffusion treatment was 950℃, and the diffusion time was 32h; then after cooling to room temperature, the second diffusion treatment was performed, the temperature of the second diffusion treatment was 800℃, and the diffusion time was 15h.

[0121] The present application also tested the products prepared in the above examples and comparative examples, and the testing method was as follows:

[0122] Test method:

[0123] The test methods used in this application are as follows:

[0124] (1) The composition of the magnet matrix / NdFeB magnet was tested using inductively coupled plasma (ICP) spectroscopic analysis.

[0125] (2) Test method for heavy rare earth element RH concentration:

[0126] Scanning electron microscopy (EDS) was used to measure the heavy rare earth (RH) concentration on the surface of the NdFeB magnet and at different depths from the coated surface. Specifically, at a magnification of 500x, a strip (e.g., 10 microns wide) was measured from the surface of the NdFeB magnet coated with heavy rare earth elements to determine the surface RH mass concentration. Next, a cross-section of the NdFeB magnet perpendicular to the orientation direction was measured, and strips were taken every 200 microns along the diffusion direction to determine the RH mass concentration at that depth. Each depth was tested at least twice, and the average value, ensuring that the heavy rare earth RH concentration fluctuation was ≤0.25wt%, was taken as the RH mass concentration at that depth. In this embodiment, ΔC1 is the difference between the RH mass concentration at the surface and the RH mass concentration at a depth of d1; ΔC2 is the difference between the RH mass concentration at a depth of d1 and the RH mass concentration at a depth of d / 2.

[0127] (3) Test method of coercive force:

[0128] The coercive force of the magnets was measured by a BH curve measuring instrument (NIM-200).

[0129] In order to facilitate the description of the differences between the above embodiments and comparative examples, as well as the test results of each embodiment and each comparative example, the following will be combined with Tables 1 to 3, Figures 5 to 7 Tables 1 to 3 show the test results of the NdFeB magnet samples prepared in the examples and comparative examples. Figure 5 The figure shows the test results of the electron probe EPMA of the NdFeB magnet of Example 1 at a distance of 500 μm from the coating surface; Figure 6 The figure shows the test results of the electron probe EPMA of the NdFeB magnet of Example 1 at a distance of 3 mm from the coating surface; Figure 7 The graph showing the relationship between the coercive force and the diffusion depth of the NdFeB magnet of Example 1 is shown.

[0130] Table 1:

[0131]

[0132] Table 2:

[0133]

[0134] Table 3:

[0135]

[0136] Combined with Table 1~Table 3 and Figures 5 to 7 It can be seen that:

[0137] (1) The NdFeB magnets prepared in Examples 1 to 4 all satisfy ΔC1 / ΔC2≥6, k2>0, and k1>k2, indicating that there is a significant gradient change in the HREE concentration distribution between the surface region (0~d1) and the core region (d1~d / 2) of the magnet, and that HREE RH still exists in the core region of the magnet. As a result, the NdFeB magnet has the characteristics of a deeper HREE diffusion depth, controllable HREE concentration distribution and coercive force increment in different regions, and avoidance of excessive coercive force attenuation, thereby meeting the requirements of application scenarios with different magnetic properties requirements in different regions.

[0138] (2) Through Example 1 and Example 4, diffusion sources are coated on two different opposite surfaces parallel to the orientation direction of the magnet substrate for diffusion treatment. It can be seen that according to the preparation method of the embodiment of the present application, any two opposite surfaces parallel to the orientation direction of the magnet substrate are treated, and NdFeB magnets with a deep diffusion depth of heavy rare earth elements and a gradient distribution of heavy rare earth element concentration can be obtained, thereby meeting high performance requirements such as high coercivity in the surface area of ​​the magnet and avoiding excessive attenuation of coercivity in the core area of ​​the magnet.

[0139] (3) From Tables 1 to 3, it can be seen that compared with Example 1 of the present application, Comparative Example 1 only undergoes one diffusion treatment, and the diffusion depth of the heavy rare earth elements in the prepared NdFeB magnet does not exceed 1 mm, and the coercive force change in the core area of ​​the magnet is 0, indicating that the diffusion depth of the heavy rare earth elements in the NdFeB magnet is limited, the overall magnetic performance improvement effect is limited, and there is a problem of excessive attenuation of the coercive force in the core area of ​​the magnet.

[0140] (4) From Tables 1 to 3, it can be seen that in Comparative Example 4, the diffusion source was only applied once and the diffusion treatment was performed twice. The diffusion depth of the heavy rare earth elements in the NdFeB magnet prepared did not exceed 3 mm in the surface area of ​​the magnet, and the coercive force change in the core area of ​​the magnet was 0. Compared with Comparative Example 1, the diffusion depth of the heavy rare earth elements in the NdFeB magnet of Comparative Example 4 increased, indicating that the second diffusion treatment was beneficial to further improve the diffusion depth of the heavy rare earth elements. However, since the second diffusion source was not applied, the diffusion depth of the heavy rare earth elements was still limited, resulting in limited improvement in the overall magnetic properties of the magnet. In addition, there was also the problem of excessive attenuation of the coercive force in the core area of ​​the magnet.

[0141] (5) The first diffusion temperature in Comparative Example 2 is lower than the second diffusion temperature, and the first diffusion source RH content in Comparative Example 3 is higher than the second diffusion source RH content. As can be seen from Tables 1 to 3, the ΔC1 / ΔC2 of Comparative Examples 2 and 3 are both less than 6, ΔC2 are both greater than 1wt%, k3 are both less than 0.5kOe / mm, and ΔC3 are both less than 5wt%, indicating that the concentration distribution of heavy rare earth elements in the surface region and the core region of the NdFeB magnets of Comparative Examples 2 and 3 is relatively uniform. In comparison, the concentration distribution of heavy rare earth elements in the surface region and the core region of the NdFeB magnets of the embodiments of the present application is quite different, with a more significant concentration gradient change, so that more heavy rare earth elements are mainly concentrated in the surface region of the magnet, especially the shallow surface region, thereby having a more significant effect on the refinement of the magnetic properties of different regions of the magnet.

[0142] (6) From Figure 5 It can be seen from the figure that at a depth of 500μm from the coating surface of the NdFeB magnet of Example 1, there is an obvious Tb shell (as shown in the gray area) around the main phase grains (black area), indicating that the Tb element has diffused to at least a depth of 500μm from the coating surface of the NdFeB magnet. Figure 6 It can be seen that at a depth of 3 mm from the coating surface of the NdFeB magnet of Example 1, there is still a Tb shell (as shown in the gray area) around the main phase grains (black area), indicating that the Tb element can diffuse to a depth of 3 mm from the coating surface of the NdFeB magnet.

[0143] (7) From Figure 7It can be seen that the surface area of ​​the NdFeB magnet of Example 1 achieves a relatively high coercive force, the core area of ​​the magnet also maintains sufficient coercive force, and the coercive force distribution of the surface area and the core area of ​​the magnet has an obvious gradient change, thereby meeting the demand for refined magnetic properties of different areas of the magnet.

[0144] Although multiple embodiments of the present application have been shown and described herein, it will be apparent to those skilled in the art that such embodiments are provided by way of example only. Those skilled in the art can conceive of many changes, modifications, and alternatives without departing from the thought and spirit of the present application. It should be understood that in the process of practicing the present application, various alternatives to the embodiments of the present application described herein can be adopted. The accompanying claims are intended to define the scope of protection of the present application and therefore cover equivalents or alternatives within the scope of these claims.

Claims

1. A neodymium iron boron magnet, characterized in that: The NdFeB magnet comprises the following components: 28wt%~30.5wt% RL, 0.5wt%~2wt% RH, 1.0wt%~2.5wt% M, 0.8wt%~1.0wt% B, 65wt%~69wt% Fe, Wherein, RL includes Nd element, RH is a heavy rare earth element, and M includes at least one of Co, Al, Cu, Ga, Zr, Nb, Ti, Mo, Sn, Hf, and W; The distance between at least one set of two opposite surfaces parallel to the orientation direction of the NdFeB magnet is d, the RH concentration difference between any one of the two surfaces and the depth d1 from the surface is ΔC1, the RH concentration difference between the depth d1 and the depth d / 2 is ΔC2, d1<d / 2, the distance between d1 and d / 2 is d2, and ΔC1 / ΔC2≥6, the ratio k2 of ΔC2 to d2 satisfies k2>0, and the ratio k1 of ΔC1 to d1 satisfies k1>k2; wherein 10mm≤d≤50mm, 2mm≤d1≤5mm.

2. The NdFeB magnet according to claim 1, wherein 10mm≤d≤30mm.

3. The NdFeB magnet according to claim 1 or 2, characterized in that: ΔC1 also satisfies: 1wt%<ΔC1≤10wt%; ΔC2 also satisfies: 0.1wt%≤ΔC2≤1wt%.

4. The NdFeB magnet according to claim 1, wherein RH includes at least one of dysprosium, terbium, holmium, and gadolinium; and / or The RL also includes at least one of praseodymium, lanthanum, cerium, scandium, and yttrium.

5. The NdFeB magnet according to claim 1 or 2, characterized in that: The NdFeB magnet also meets at least one of the following characteristics: (1) The coercivity difference between any one of the two surfaces and a depth d1 from the surface is ΔHcj1, and the ratio k3 of ΔHcj1 to d1 satisfies: 0.5kOe / mm≤k3≤1kOe / mm; (2) The difference in coercivity between the depth d1 and the depth d / 2 is ΔHcj2, and the ratio k4 of ΔHcj2 to d2 satisfies: 0.1 kOe / mm≤k4≤0.4 kOe / mm; (3) The area from any of the two surfaces to a depth of d1 from the surface is the surface region of the magnet, and the coercive force of the surface region of the magnet is ≥ 26kOe; (4) The area from the depth d1 to the depth d / 2 is the core region of the magnet, and the coercive force of the core region of the magnet is ≥ 22kOe.

6. The NdFeB magnet according to claim 1 or 2, characterized in that: At any depth d3 between the surface and the depth d1, the distance between d3 and d1 is d4, the RH concentration difference between the surface and the depth d3 is ΔC3, the RH concentration difference between the depth d3 and the depth d1 is ΔC4, the ratio of ΔC3 to d3 is k5, and the ratio of ΔC4 to d4 is k6, satisfying k5>k6; Among them, d3 satisfies: 0mm<d3≤1mm; ΔC3 satisfies: 5wt%≤ΔC3≤10wt%; ΔC4 satisfies: 1wt%≤ΔC4≤3wt%.

7. A method for preparing a NdFeB magnet according to any one of claims 1 to 6, characterized in that: The preparation method comprises: Using a first diffusion source containing a heavy rare earth element RH, a first coating treatment is performed on at least one set of two opposite surfaces parallel to the orientation direction of the magnet substrate to obtain a first magnet green body; performing a first diffusion treatment on the first magnet green body to obtain a first magnet; Using a second diffusion source containing a heavy rare earth element RH, performing a second coating process on two surfaces of the first magnet coated with the first diffusion source to obtain a second magnet green body, wherein the RH content in the second diffusion source is greater than the RH content in the first diffusion source; The second magnet green compact is subjected to a second diffusion treatment to obtain a NdFeB magnet, wherein a second diffusion temperature of the second diffusion treatment is lower than the first diffusion temperature of the first diffusion treatment.

8. The preparation method according to claim 7, characterized in that The preparation method further comprises: The NdFeB magnet is cut along a direction perpendicular to the orientation direction of the NdFeB magnet to obtain a plurality of NdFeB magnets of small size.

9. The preparation method according to claim 7 or 8, characterized in that The first diffusion temperature of the first diffusion treatment is 850° C. to 1000° C., and the first diffusion time is 20 h to 40 h; The second diffusion temperature of the second diffusion treatment is 700° C. to 830° C., and the second diffusion time is 10 h to 18 h; The first diffusion source includes 10 wt% to 30 wt% of RH elements and 70 wt% to 90 wt% of M1 elements, wherein the RH elements are heavy rare earth elements, and the M1 elements include at least one of Cu, Al, and Ga; The second diffusion source includes 40 wt % to 70 wt % of RH elements and 30 wt % to 60 wt % of M2 elements, wherein the M2 element includes Co, or the M2 element includes Co and at least one of Cu, Al, Ti, and Zr.

10. The preparation method according to claim 7 or 8, characterized in that: The coating amount of the first diffusion source is 0.8wt% to 1.5wt% of the mass of the magnet substrate; The coating amount of the second diffusion source is 1.8 wt % to 2.5 wt % of the mass of the magnet substrate.

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