Neodymium-iron-boron magnet and preparation method thereof

Abstract

The invention discloses a neodymium iron boron magnet and a preparation method thereof. The neodymium-iron-boron magnet comprises the following components: 28 wt% to 31.5 wt% of R, 0.86 wt% to 1.05 wt% of B, 0.03 wt% to 0.15 wt% of Ni, 0.1 wt% to 0.5 wt% of Cu, 0.5 wt% to 2 wt% of Co, 0.3 wt% to 3 wt% of M and 64.4 wt% to 67 wt% of Fe. The neodymium-iron-boron magnet comprises main phase grains and grain boundary phases, the grain boundary phases comprise RaTbXcMd-c phases, a is larger than or equal to 35 at% and smaller than or equal to 65 at%, b is larger than or equal to 30 at% and smaller than or equal to 60 at%, d is larger than or equal to 5 at% and smaller than or equal to 10 at%, and c / d is larger than or equal to 0.6. The neodymium-iron-boron magnet provided by the embodiment of the invention has relatively good performance.

Description

Technical Field

[0001] This application generally relates to the technical field of magnet recycling. More specifically, this application relates to a neodymium iron boron magnet and a method for preparing the same. Background Art

[0002] Sintered neodymium iron boron is widely used in many fields such as aerospace, electronic communication, clean energy, transportation, medical devices, and household appliances due to its excellent magnetic properties. However, during the production process of sintered neodymium iron boron, a large amount of waste will be generated due to equipment failures, collisions, or contamination. In addition, the magnets generated after the end products (such as motors, etc.) are scrapped are often unable to be directly reused due to oil stains, damage, or rust. The number of waste neodymium iron boron magnets generated globally each year is huge, but rare earth resources (such as neodymium, praseodymium, dysprosium, etc.) as their core components are non-renewable and scarce. Therefore, how to effectively recycle waste neodymium iron boron has always been an urgent problem in the industry. Recycling and reusing waste neodymium iron boron magnets can not only alleviate the consumption of primary rare earth resources and reduce raw material costs, but also reduce environmental pollution caused by improper disposal of waste magnets containing heavy metals and rare earth elements.

[0003] The surface of neodymium iron boron magnets often needs to be surface electroplated for anti-corrosion requirements, such as electroplating a nickel layer or a copper-nickel layer. When recycling and reusing waste neodymium iron boron magnets, the electroplated coating will cause serious deterioration of the performance of the recycled magnets. In order to avoid the deterioration of the performance of the recycled magnets, the prior art often uses a stripping process to remove the surface coating of the waste neodymium iron boron magnets. However, the stripping process not only increases the recycling cost, but also damages the rare earth content inside the magnet, resulting in waste of resources. In addition, the surface of the stripped magnet is prone to residual organic matter, which will still cause serious deterioration of the performance of the recycled magnet, and is not conducive to ensuring the magnetic performance of the recycled magnet.

[0004] In view of this, there is an urgent need to provide a new solution for recycling and reusing waste neodymium iron boron magnets to achieve high-value utilization of the recycled magnets. Summary of the Invention

[0005] In order to solve at least one or more of the above-mentioned technical problems, this application proposes solutions for a neodymium iron boron magnet and a method for preparing the same in multiple aspects.

[0006] In a first aspect, this application provides a neodymium iron boron magnet, the neodymium iron boron magnet comprising the following components: R: 28 wt% - 31.5 wt%, B: 0.86 wt% - 1.05 wt%, Ni: 0.03 wt% - 0.15 wt%, Cu: 0.1 wt% - 0.5 wt%, Co: 0.5 wt% - 2 wt%, M: 0.3 wt% - 3 wt%, Fe: 64.4 wt% - 67 wt%; wherein, the neodymium iron boron magnet comprises main phase grains and a grain boundary phase, and the grain boundary phase comprises R aT b X c M d-c Phase, 35 at% ≤ a ≤ 65 at%, 30 at% ≤ b ≤ 60 at%, 5 at% ≤ d ≤ 10 at%, c / d ≥ 0.6; R is a rare earth element, R includes Pr and Nd; T includes Fe and / or Co; M includes at least one of Al, Ga, Ti, Sn, Zr, Nb; X includes Ni and Cu.

[0007] In some embodiments, the Ni content in the main phase grains is 0 to 0.4 at%.

[0008] In other embodiments, the NdFeB magnet further includes oxygen element, carbon element, nitrogen element, where the oxygen content is [O], the carbon content is [C], the nitrogen content is [N], and 500 ppm ≤ [O] ≤ 1600 ppm, [C] ≤ 1400 ppm, [N] ≤ 400 ppm are satisfied.

[0009] In still other embodiments, R further includes heavy rare earth elements, and within a depth range of 0.1 to 100 μm below at least one surface perpendicular to the orientation direction of the NdFeB magnet, in the microstructure observation plane at any depth, the main phase grains have a heavy rare earth shell layer, and the heavy rare earth element content in the heavy rare earth shell layer of the main phase grains is 2.5 at% to 4.5 at%.

[0010] In some embodiments, R further includes at least one of Dy and Tb.

[0011] In a second aspect, the present application provides a method for preparing an NdFeB magnet, the preparation method including: obtaining a first alloy powder, where the median particle size D50 of the first alloy powder is 3.8 μm to 4.3 μm, the first alloy powder includes R, B, Cu, M, and T elements, R is a rare earth element, R includes Pr and Nd, T includes Fe and / or Co; M includes at least one of Al, Ga, Ti, Sn, Zr, Nb; subjecting the waste NdFeB magnet including a nickel coating or a nickel - copper coating to second hydrogen pulverization, screening treatment, and second jet - milling pulverization in sequence to obtain a second alloy powder, where the median particle size D50 of the second alloy powder is controlled to be 4.0 μm to 4.5 μm, and the Ni content in the second alloy powder is controlled to be 0.05 wt% to 0.2 wt%; subjecting the mixed powder composed of the first alloy powder and the second alloy powder to shaping treatment, sintering treatment, and aging treatment to obtain the NdFeB magnet.

[0012] In some embodiments, the preparation method further includes: preparing a NdFeB alloy rapidly solidified sheet from a first alloy raw material with a predetermined configuration; performing first hydrogen pulverization on the NdFeB alloy rapidly solidified sheet to obtain a first alloy coarse powder, and controlling the oxygen content [O] of the first alloy coarse powder to be 500 ppm to 1100 ppm; performing first jet milling on the first alloy coarse powder to obtain the first alloy powder.

[0013] In some other embodiments, the first alloy raw material includes the following components: R: 28 wt% to 31.5 wt%, B: 0.86 wt% to 1.05 wt%, M: 0.3 wt% to 3 wt%, Cu: 0.1 wt% to 0.55 wt%, T: 64.5 wt% to 70 wt%; wherein, R is a rare earth element, R includes Pr and Nd, T includes Fe and / or Co; M includes at least one of Al, Ga, Ti, Sn, Zr, Nb.

[0014] In still some other embodiments, in the screening process, a second alloy coarse powder obtained after second hydrogen pulverization is screened using a sieve mesh with a mesh number of 7 to 30, and the second alloy coarse powder passing through the sieve mesh is subjected to second jet milling.

[0015] In some embodiments, the preparation method further includes: via the screening process, further controlling the Cu content in the second alloy powder to be 0.1 wt% to 0.35 wt%.

[0016] In some other embodiments, the preparation method further includes: mixing the first alloy powder and the second alloy powder according to a mass ratio of 1: (1 to 3) to obtain the mixed powder.

[0017] In still some other embodiments, during the sintering process, the vacuum degree in the sintering device is controlled to be 10 -2 Pa to 10 2 Pa.

[0018] In some embodiments, the sintering temperature of the sintering process is 1000 °C to 1100 °C, and the sintering time is 4 h to 10 h.

[0019] In some other embodiments, the aging temperature of the aging process is 400 °C to 500 °C, and the aging time is 4 h to 10 h.

[0020] In still some other embodiments, the aging process includes a primary aging process and a secondary aging process, wherein the primary aging process temperature is 850 °C to 950 °C, the primary aging process time is 2 h to 6 h, the secondary aging process temperature is 450 °C to 650 °C, and the secondary aging process time is 3 h to 10 h.

[0021] In some embodiments, the preparation method further includes: coating a heavy rare earth slurry onto at least one surface of the NdFeB magnet perpendicular to its orientation direction, and then performing a heat treatment to obtain a diffused NdFeB magnet.

[0022] In some other embodiments, the heat treatment sequentially includes a diffusion process and a tempering process; the diffusion temperature of the diffusion process is 800 - 950 °C, and the diffusion time is 5 - 20 h; the tempering temperature of the tempering process is 450 - 550 °C, and the tempering time is 3 - 8 h.

[0023] As can be seen from the NdFeB magnet and its preparation method provided above, in the embodiments of the present application, the NdFeB magnet is prepared by mixing a first alloy powder with a second alloy powder prepared from waste NdFeB magnets, and by controlling the median particle size D50 of the first alloy powder, the median particle size D50 of the second alloy powder, and the Ni content in the second alloy powder, a NdFeB magnet with a grain boundary phase including R a T b X c M d-c phase is generated, realizing the recycling and reuse of waste NdFeB magnets including nickel coatings or nickel - copper coatings. Since the preparation method of the embodiments of the present application does not require a stripping process for waste magnets, and through process control, the Ni element in the generated NdFeB magnet (or recycled magnet) mainly enters the grain boundary phase, thus effectively avoiding serious deterioration of the performance of the recycled magnet, avoiding waste of rare earth resources, being beneficial to ensuring the magnetic properties of the recycled magnet, and realizing the high - value utilization of the recycled magnet. The recycled magnet mentioned herein refers to the magnet obtained after treating waste NdFeB magnets. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] By reading the following detailed description with reference to the accompanying drawings, the above - mentioned and other objects, features, and advantages of the exemplary embodiments of the present application will become easily understandable. In the drawings, several embodiments of the present application are shown in an exemplary and non - restrictive manner, and the same or corresponding reference numerals represent the same or corresponding parts, where: Figure 1 shows an exemplary flowchart of the preparation method of the NdFeB magnet according to the embodiments of the present application; Figure 2 shows a scanning electron microscope photograph of Example 1 of the present application; Figure 3 shows a scanning electron microscope photograph of Example 4 of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative efforts fall within the protection scope of the present application.

[0026] It should be understood that the terms "including" and "comprising" used in the specification and claims of the present application indicate the presence of the 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 their combinations.

[0027] It should also be understood that the terms used in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. As used in the specification and claims of the present application, unless the context clearly indicates otherwise, the singular forms "a", "an", and "the" are intended to include the plural forms. It should be further understood that the term "and / or" used in the specification and claims of the present application refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0028] The following will describe in detail the specific implementation manners of the present application in conjunction with the accompanying drawings.

[0029] In a first aspect, the present application provides a neodymium-iron-boron magnet, and the neodymium-iron-boron magnet includes the following components: R: 28 wt% - 31.5 wt%, B: 0.86 wt% - 1.05 wt%, Ni: 0.03 wt% - 0.15 wt%, Cu: 0.1 wt% - 0.5 wt%, Co: 0.5 wt% - 2 wt%, M: 0.3 wt% - 3 wt%, Fe: 64.4 wt% - 67 wt%; wherein, the neodymium-iron-boron magnet includes main phase grains and grain boundary phases, and the grain boundary phases include R a T b X c M d-c phase, 35 at% ≤ a ≤ 65 at%, 30 at% ≤ b ≤ 60 at%, 5 at% ≤ d ≤ 10 at%, c / d ≥ 0.6; R is a rare earth element, and R includes Pr and Nd; T includes Fe and / or Co; M includes at least one of Al, Ga, Ti, Sn, Zr, and Nb; X includes Ni and Cu.

[0030] Exemplarily, the mass content of the R element in the neodymium iron boron magnet can be, for example, 28 wt%, 28.5 wt%, 29 wt%, 29.5 wt%, 30 wt%, 30.5 wt%, 31 wt%, 31.5 wt%, etc., or other values within the range of 28 wt% to 31.5 wt%.

[0031] Exemplarily, the mass content of the boron (B) element in the neodymium iron boron magnet can be, for example, 0.86 wt%, 0.87 wt%, 0.88 wt%, 0.89 wt%, 0.9 wt%, 0.91 wt%, 0.92 wt%, 0.93 wt%, 0.94 wt%, 0.95 wt%, 0.96 wt%, 0.97 wt%, 0.98 wt%, 0.99 wt%, 1.0 wt%, 1.01 wt%, 1.02 wt%, 1.03 wt%, 1.04 wt%, 1.05 wt%, etc., or other values within the range of 0.86 wt% to 1.05 wt%.

[0032] Exemplarily, the mass content of the Ni element in the neodymium iron boron magnet can be, for example, 0.03 wt%, 0.04 wt%, 0.05 wt%, 0.06 wt%, 0.07 wt%, 0.08 wt%, 0.09 wt%, 0.1 wt%, 0.11 wt%, 0.12 wt%, 0.13 wt%, 0.14 wt%, 0.15 wt%, etc., or other values within the range of 0.03 wt% to 0.15 wt%.

[0033] Exemplarily, the mass content of the Cu element in the neodymium iron boron magnet can be, for example, 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%, etc., or other values within the range of 0.1 wt% to 0.5 wt%.

[0034] Exemplarily, the mass content of the Co element in the neodymium iron boron 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%, etc., or other values within the range of 0.5 wt% to 2 wt%.

[0035] Exemplarily, the mass content of element M in the neodymium iron boron magnet can be, for example, 0.3 wt%, 0.5 wt%, 0.6 wt%, 0.8 wt%, 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 the range of 0.3 wt% to 3 wt%.

[0036] Exemplarily, the mass content of element Fe in the neodymium iron boron magnet can be, for example, 64.4 wt%, 64.5 wt%, 64.6 wt%, 64.8 wt%, 65 wt%, 65.2 wt%, 65.4 wt%, 65.5 wt%, 65.6 wt%, 65.8 wt%, 66 wt%, 66.2 wt%, 66.4 wt%, 66.5 wt%, 66.6 wt%, 66.8 wt%, 67 wt%, etc., or other values within the range of 64.4 wt% to 67 wt%.

[0037] R described above a T b X c M d-c The R-T-X-M phase refers to the grain boundary phase formed by the combination of elements R, T, X, and M, where X c represents that the total atomic content of Ni and Cu elements is c. The neodymium iron boron magnet of the embodiment of the present application can be prepared by using waste neodymium iron boron magnets. R a T b X c M d-c Ni in the R-T-X-M phase usually comes from the coating of the waste neodymium iron boron magnet, and Cu can come from at least one of the coating of the waste neodymium iron boron magnet, the substrate of the waste neodymium iron boron magnet, and the first alloy powder described below.

[0038] Exemplarily, R a T b X c M d-c The atomic content a of element R in the R-T-X-M phase can be 35 at%, 38 at%, 40 at%, 42 at%, 45 at%, 48 at%, 50 at%, 52 at%, 55 at%, 58 at%, 60 at%, 62 at%, 65 at%, etc., or other values within the range of 35 at% to 65 at%.

[0039] Exemplarily, R a T b X c M d-cThe atomic content b of the T element in the phase can be 30 at%, 32 at%, 35 at%, 38 at%, 40 at%, 42 at%, 45 at%, 48 at%, 50 at%, 52 at%, 55 at%, 58 at%, 60 at%, etc., or other values within the range of 30 at% to 60 at%.

[0040] Exemplarily, the atomic content d can be 5 at%, 5.5 at%, 6 at%, 6.5 at%, 7 at%, 7.5 at%, 8 at%, 8.5 at%, 9 at%, 9.5 at%, 10 at%, etc., or other values within the range of 5 at% to 10 at%. Exemplarily, c / d can be, for example, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, etc., or other values within the range of 0.6 to 1.

[0041] In the embodiments of the present application, c / d ≥ 0.6, indicating that in the R a T b X c M d-c Among the other elements in the phase except for the R element and the T element, the sum of the atomic contents of the Ni element and the Cu element has a relatively high proportion. Since the melting points of Ni and Cu are relatively low, the melting point of the grain boundary phase is thus reduced. The formation of this low-melting-point grain boundary phase can concentrate the Ni element in the grain boundary phase, inhibit the Ni element from entering the main phase, and improve the magnetic properties of the magnet. In addition, this grain boundary phase also has good wettability and the ability to repair the boundary, and can construct a good diffusion channel, which is beneficial to the diffusion of subsequent heavy rare earth elements.

[0042] In some embodiments, the Ni content in the main phase grains of the neodymium-iron-boron magnet is 0 to 0.4 at%. Exemplarily, the Ni content in the main phase grains of the neodymium-iron-boron magnet can be 0, 0.05 at%, 0.1 at%, 0.15 at%, 0.2 at%, 0.25 at%, 0.3 at%, 0.35 at%, 0.4 at%, etc., or other values within the range of 0 to 0.4 at%.

[0043] The Ni content in the main phase grains of the neodymium-iron-boron magnet is 0 to 0.4 at%, indicating that the main phase grains of the neodymium-iron-boron magnet in the embodiments of the present application do not contain the Ni element or only contain a small amount of the Ni element. This further indicates that the Ni element is mainly concentrated and distributed in the grain boundary phase, thereby facilitating the avoidance of problems such as the interference of the Ni element entering the main phase grains with the magnetic moment arrangement inside the grains, the reduction of the influence on the magnetization intensity of the main phase grains, and the abnormal growth of the main phase grains, so that the neodymium-iron-boron magnet can maintain a relatively high coercivity and remanence level.

[0044] In some other embodiments, the neodymium iron boron magnet further includes oxygen element, carbon element, and nitrogen element, where the oxygen content is [O], the carbon content is [C], and the nitrogen content is [N], and 500 ppm ≤ [O] ≤ 1600 ppm, [C] ≤ 1400 ppm, [N] ≤ 400 ppm are satisfied.

[0045] Exemplarily, [O] of the neodymium iron boron magnet can be 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, 1100 ppm, 1200 ppm, 1300 ppm, 1400 ppm, 1500 ppm, 1600 ppm, etc., or any value within the range composed of any of the above values. Controlling the oxygen content of the neodymium iron boron magnet within the range of 500 ppm to 1600 ppm is beneficial to avoiding the growth of main phase grains, controlling the size of the main phase, and thus beneficial to ensuring the magnetic properties of the neodymium iron boron magnet.

[0046] Exemplarily, [C] of the neodymium iron boron magnet can be 1400 ppm, 1300 ppm, 1200 ppm, 1100 ppm, 1000 ppm, 950 ppm, 900 ppm, 850 ppm, 800 ppm, 750 ppm, 700 ppm, 650, 600 ppm, 550 ppm, 500 ppm, 450 ppm, 400 ppm, 350 ppm, 300 ppm, 250 ppm, 200 ppm, 150 ppm, 100 ppm, 50 ppm, 0 ppm, etc., or other values below 1400 ppm. Controlling the carbon content of the neodymium iron boron magnet below 1400 ppm is beneficial to avoiding the formation of excessive carbides, and thus beneficial to ensuring the magnetic properties of the neodymium iron boron magnet.

[0047] Exemplarily, [N] of the neodymium iron boron magnet can be 400 ppm, 350 ppm, 300 ppm, 250 ppm, 200 ppm, 150 ppm, 100 ppm, 50 ppm, 0 ppm, etc., or other values below 400 ppm. Controlling the nitrogen content of the neodymium iron boron magnet below 400 ppm is beneficial to avoiding the formation of excessive nitrides, and thus beneficial to ensuring the magnetic properties of the neodymium iron boron magnet.

[0048] In still some other embodiments, R can further include heavy rare earth elements, and within the depth range of 0.1 to 100 μm below at least one surface perpendicular to the orientation direction of the neodymium iron boron magnet, in the microscopic structure observation plane at any depth, the main phase grains have a heavy rare earth shell layer, and the content of heavy rare earth elements in the heavy rare earth shell layer of the main phase grains is 2.5 at% to 4.5 at%. In some embodiments, R further includes at least one of Dy and Tb.

[0049] Exemplarily, on the microstructure observation surface at any of the above depths, the content of heavy rare earth elements in the heavy rare earth shell layer can be 2.5 at%, 2.6 at%, 2.7 at%, 2.8 at%, 2.9 at%, 3.0 at%, 3.1 at%, 3.2 at%, 3.3 at%, 3.4 at%, 3.5 at%, 3.6 at%, 3.7 at%, 3.8 at%, 3.9 at%, 4.0 at%, 4.1 at%, 4.2 at%, 4.3 at%, 4.4 at%, 4.5 at%, etc., or other values within the range of 2.5 at% to 4.5 at%.

[0050] At least one surface perpendicular to the orientation direction of the NdFeB magnet described above may include one or more surfaces. The aforementioned microstructure observation surface may refer to a cross-section perpendicular to the orientation direction of the NdFeB magnet within the depth range of 0.1 to 100 μm.

[0051] Through the above description, it can be understood that for the NdFeB magnets in some embodiments of the present application, within the depth range of 0.1 to 100 μm below at least one surface perpendicular to its orientation direction, in the microstructure observation surface at any depth, the main phase grains include a heavy rare earth shell layer, and the content of heavy rare earth elements in the heavy rare earth shell layer is relatively high, indicating that the heavy rare earth elements penetrate into the magnet interior relatively smoothly from the orientation surface of the magnet, thus being beneficial to improving the coercivity of the NdFeB magnet.

[0052] To facilitate the understanding of the NdFeB magnets in the embodiments of the present application, the following will be combined with Figure 1 A detailed description will be given of the preparation method for preparing the aforementioned NdFeB magnet.

[0053] Figure 1 An exemplary flowchart of the preparation method of the NdFeB magnet in the embodiments of the present application is shown. As Figure 1 shown, the preparation method 100 may include: In step S102, a first alloy powder is obtained, where the median particle size D50 of the first alloy powder is 3.8 μm to 4.3 μm, the first alloy powder includes elements R, B, Cu, M, and T, R is a rare earth element, R includes Pr and Nd, T includes Fe and / or Co; M includes at least one of Al, Ga, Ti, Sn, Zr, and Nb; In step S104, the waste NdFeB magnet including a nickel plating layer or a nickel-copper plating layer is sequentially subjected to second hydrogen pulverization, screening treatment, and second jet milling pulverization to obtain a second alloy powder, where the median particle size D50 of the second alloy powder is controlled to be 4.0 μm to 4.5 μm, and the Ni content in the second alloy powder is controlled to be 0.05 wt% to 0.2 wt%; In step S106, the mixed powder composed of the first alloy powder and the second alloy powder is subjected to shaping treatment, sintering treatment, and aging treatment to obtain the NdFeB magnet.

[0054] Exemplarily, the median particle size D50 of the first alloy powder can be, for example, 3.8 μm, 3.9 μm, 4.0 μm, 4.1 μm, 4.2 μm, 4.3 μm, etc., or other values within the range of 3.8 μm to 4.3 μm. The median particle size D50 of the first alloy powder can be controlled by a comminution operation.

[0055] Exemplarily, the median particle size D50 of the second alloy powder can be controlled to be 4.0 μm, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, etc., or other values within the range of 4.0 μm to 4.5 μm. The median particle size D50 of the second alloy powder can be controlled by comminution with a second jet mill.

[0056] Exemplarily, in step S104, the Ni content in the second alloy powder can be controlled to be 0.05 wt%, 0.06 wt%, 0.07 wt%, 0.08 wt%, 0.09 wt%, 0.1 wt%, 0.11 wt%, 0.12 wt%, 0.13 wt%, 0.14 wt%, 0.15 wt%, 0.16 wt%, 0.17 wt%, 0.18 wt%, 0.19 wt%, 0.2 wt%, etc., or other values within the range of 0.05 wt% to 0.2 wt%. The Ni content in the second alloy powder can be controlled by the screening process in step S104.

[0057] By controlling both the median particle size D50 of the first alloy powder and the median particle size D50 of the second alloy powder to be in the micron range, and controlling the median particle size D50 of the first alloy powder to be smaller than the median particle size D50 of the second alloy powder, it is beneficial to inhibit the abnormal growth of grains during the sintering process, thereby controlling the main phase grain size, and it is beneficial to increase the number of grain boundary phases in the Nd-Fe-B magnet prepared from the mixed powder, so that the Ni element in the first alloy powder is more likely to enter the grain boundary phase rather than the main phase grains, and then it is easier to generate the a T b X c M d-c phase. At the same time, by using the first alloy powder without Ni element and controlling the Ni content of the second alloy powder within a reasonable range, it helps to control the Ni content in the mixed powder, and then, in synergistic action with controlling the median particle size D50 of the first alloy powder and the median particle size D50 of the second alloy powder, further reduces the entry of Ni element into the main phase grains, and promotes the combination of Ni element with elements such as R and T to form the grain boundary phase.

[0058] In some embodiments, the preparation method 100 may further include: preparing a Nd-Fe-B alloy rapid solidification sheet from a first alloy raw material with a predetermined configuration; performing first hydrogen pulverization on the Nd-Fe-B alloy rapid solidification sheet to obtain a first alloy coarse powder, and controlling the oxygen content [O] of the first alloy coarse powder to be 500 ppm to 1100 ppm; performing first jet milling on the first alloy coarse powder to obtain a first alloy powder.

[0059] In some other embodiments, the first alloy raw material may include the following components: R: 28 wt% to 31.5 wt%, B: 0.86 wt% to 1.05 wt%, M: 0.3 wt% to 3 wt%, Cu: 0.1 wt% to 0.55 wt%, T: 64.5 wt% to 70 wt%; wherein, R is a rare earth element, R includes Pr and Nd, T includes Fe and / or Co; M includes at least one of Al, Ga, Ti, Sn, Zr, Nb.

[0060] Exemplarily, the mass content of the R element in the first alloy raw material may be, for example, 28 wt%, 28.5 wt%, 29 wt%, 29.5 wt%, 30 wt%, 30.5 wt%, 31 wt%, 31.5 wt%, etc., or other values within the range of 28 wt% to 31.5 wt%.

[0061] Exemplarily, the mass content of the B element in the first alloy raw material may be, for example, 0.86 wt%, 0.87 wt%, 0.88 wt%, 0.89 wt%, 0.9 wt%, 0.91 wt%, 0.92 wt%, 0.93 wt%, 0.94 wt%, 0.95 wt%, 0.96 wt%, 0.97 wt%, 0.98 wt%, 0.99 wt%, 1.0 wt%, 1.01 wt%, 1.02 wt%, 1.03 wt%, 1.04 wt%, 1.05 wt%, etc., or other values within the range of 0.86 wt% to 1.05 wt%.

[0062] Exemplarily, the mass content of the M element in the first alloy raw material may be, for example, 0.3 wt%, 0.5 wt%, 0.8 wt%, 1.0 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt%, 2.0 wt%, 1.2 wt%, 1.5 wt%, 2.8 wt%, 3.0 wt%, etc., or other values within the range of 0.3 wt% to 3 wt%.

[0063] Exemplarily, the mass content of the Cu element in the first alloy raw material may be, for example, 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%, etc., or other values within the range of 0.1 wt% to 0.55 wt%.

[0064] Exemplarily, the mass content of element T in the first alloy raw material can be, for example, 64.5 wt%, 65 wt%, 65.5 wt%, 66 wt%, 66.5 wt%, 67 wt%, 67.5 wt%, 68 wt%, 68.5 wt%, 69 wt%, 69.5 wt%, 70 wt%, etc., or other values within the range of 64.5 wt% to 70 wt%.

[0065] The Nd-Fe-B alloy rapid solidification sheet is a flaky alloy material made from the first alloy raw material through a rapid solidification process. In some embodiments, the first alloy raw material with a predetermined configuration can be placed in a vacuum induction furnace, and the Nd-Fe-B alloy rapid solidification sheet can be prepared through melting treatment and rapid solidification treatment; wherein, the vacuum degree of the vacuum induction furnace can be controlled at 10 -2 ~10 2 Pa, the melting temperature can be controlled at 1300 °C to 1500 °C, and the casting temperature can be controlled at 1400 °C to 1500 °C for rapid solidification treatment. In other embodiments, the thickness of the prepared Nd-Fe-B alloy rapid solidification sheet is 0.2 to 0.5 mm.

[0066] Exemplarily, the melting temperature of the vacuum induction furnace is 1300 °C, 1320 °C, 1350 °C, 1380 °C, 1400 °C, 1420 °C, 1450 °C, 1480 °C, 1500 °C or any value within the range composed of any of the above values. Exemplarily, the casting temperature of the vacuum induction furnace is 1400 °C, 1410 °C, 1420 °C, 1430 °C, 1440 °C, 1450 °C, 1460 °C, 1470 °C, 1480 °C, 1490 °C, 1500 °C or any value within the range composed of any of the above values. Exemplarily, the thickness of the Nd-Fe-B alloy rapid solidification sheet is 0.20 mm, 0.25 mm, 0.30 mm, 0.35 mm, 0.40 mm, 0.45 mm, 0.50 mm or any value within the range composed of any of the above values.

[0067] In some other embodiments, the Nd-Fe-B alloy rapidly solidified sheet is subjected to first hydrogen pulverization to obtain first alloy coarse powder, and the oxygen content [O] of the first alloy coarse powder is controlled to be 500 ppm to 1100 ppm. The hydrogen pulverization process generally includes hydrogenation (or hydrogen absorption), pulverization, and dehydrogenation. In the first hydrogen pulverization process of the embodiments of the present application, the hydrogen absorption pressure can be 0.1 Mpa to 0.5 Mpa, the dehydrogenation temperature can be 400 °C to 600 °C, and an inert gas is filled after dehydrogenation to make the pressure in the system reach 50 kPa to 70 kPa, and the gas filling time is 1 min to 10 min, so that the oxygen content [O] of the first alloy coarse powder can be controlled within the range of 500 ppm to 1100 ppm. Other process conditions in the first hydrogen pulverization can be set conventionally. For example, the hydrogen absorption temperature can be 300 °C to 600 °C, and the dehydrogenation pressure can be 0.1 Mpa to 0.5 Mpa.

[0068] Exemplarily, the oxygen content [O] of the first alloy coarse powder can be 500 ppm, 550 ppm, 600 ppm, 650 ppm, 700 ppm, 750 ppm, 800 ppm, 850 ppm, 900 ppm, 950 ppm, 1000 ppm, 1050 ppm, 1100 ppm, etc., or other values within the range of 500 ppm to 1100 ppm.

[0069] Exemplarily, the hydrogen absorption pressure can be 0.1 Mpa, 0.2 Mpa, 0.3 Mpa, 0.4 Mpa, 0.5 Mpa, etc., or other values within the range of 0.1 Mpa to 0.5 Mpa.

[0070] Exemplarily, the dehydrogenation temperature can be 400 °C, 410 °C, 420 °C, 430 °C, 440 °C, 450 °C, 460 °C, 470 °C, 480 °C, 490 °C, 500 °C, 510 °C, 520 °C, 530 °C, 540 °C, 550 °C, 560 °C, 570 °C, 580 °C, 590 °C, 600 °C, etc., or other values within the range of 400 °C to 600 °C.

[0071] Exemplarily, the gas filling time can be 1 min, 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, etc., or other values within the range of 1 min to 10 min.

[0072] By controlling the oxygen content [O] of the first alloy coarse powder within the range of 500 ppm to 1100 ppm, it is beneficial to control the oxygen content of the NdFeB magnet prepared from the mixed powder, thereby reducing the problem that excessive oxide formation inside the NdFeB magnet due to too high oxygen content affects the magnet performance. Specifically, these oxides will damage the main phase grain structure of the NdFeB magnet, reduce the magnetic moment of the main phase grains, thus reducing the remanence of the magnet, and will also damage the continuity and uniformity of the grain boundary phase, reducing the wettability and diffusion ability of the grain boundary phase, thereby reducing the coercivity.

[0073] In some embodiments, the first alloy coarse powder is pulverized by a first jet mill to obtain the first alloy powder. In other embodiments, during the first jet mill pulverization, the pressure in the grinding chamber of the jet mill can be controlled to be 0.6 MPa to 0.7 MPa, the oxygen content in the grinding chamber is 0 to 200 ppm, and the rotational speed of the classification wheel of the jet mill is 2800 r / min to 3200 r / min, so as to control the median particle size D50 of the first alloy powder within the range of 3.8 μm to 4.3 μm.

[0074] Exemplarily, during the first jet mill pulverization, the pressure in the grinding chamber of the jet mill can be controlled to be 0.6 MPa, 0.61 MPa, 0.62 MPa, 0.63 MPa, 0.64 MPa, 0.65 MPa, 0.66 MPa, 0.67 MPa, 0.68 MPa, 0.69 MPa, 0.7 MPa, etc., or other values within the range of 0.6 MPa to 0.7 MPa.

[0075] Exemplarily, the oxygen content in the grinding chamber can be 0 ppm, 10 ppm, 20 ppm, 30 ppm, 40 ppm, 50 ppm, 60 ppm, 70 ppm, 80 ppm, 90 ppm, 100 ppm, 110 ppm, 120 ppm, 130 ppm, 140 ppm, 150 ppm, 160 ppm, 170 ppm, 180 ppm, 190 ppm, 200 ppm, etc., or other values within the range of 0 to 200 ppm.

[0076] Exemplarily, the rotational speed of the classification wheel of the jet mill during the first jet mill pulverization can be 2800 r / min, 2850 r / min, 2900 r / min, 2950 r / min, 3000 r / min, 3050 r / min, 3100 r / min, 3150 r / min, 3200 r / min, etc., or other values within the range of 2800 r / min to 3200 r / min.

[0077] In still other embodiments, in the screening process of step S104, a screen mesh with a mesh number of 7 to 30 can be used to screen the second alloy coarse powder obtained after the second hydrogen pulverization, and the second alloy coarse powder passing through the screen mesh is subjected to second jet milling to control the Ni content in the second alloy powder within the range of 0.05 wt% to 0.2 wt%. The mesh number refers to the number of holes per square centimeter area. Exemplarily, the mesh number of the screen mesh can be 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30.

[0078] Through the second hydrogen pulverization, the substrate and the coating of the waste NdFeB magnet can be at least partially separated. In other words, at least part of the coating can be peeled off from the substrate surface in the form of flake powder. Then, by selecting a screen mesh with a suitable mesh number for screening, the peeled coating flake powder is left on the screen mesh, and the powder mainly composed of the substrate component and having a smaller particle size leaks through the screen mesh and becomes the undersize material, that is, the second alloy coarse powder passing through the screen mesh. In the second alloy coarse powder passing through the screen mesh, the content of the coating component is effectively reduced.

[0079] In some embodiments, through the screening process, the Cu content in the second alloy powder can also be controlled to be 0.1 wt% to 0.35 wt%. Since the screening process can effectively reduce the content of the coating component in the second alloy coarse powder passing through the screen mesh, in the case where the waste NdFeB magnet contains a nickel-copper coating, the screening process can also help to control the Cu content in the second alloy coarse powder passing through the screen mesh, thereby realizing the control of the Cu content in the second alloy powder. Exemplarily, the Cu content in the second alloy powder can be controlled to be 0.1 wt%, 0.12 wt%, 0.15 wt%, 0.18 wt%, 0.2 wt%, 0.22 wt%, 0.25 wt%, 0.28 wt%, 0.3 wt%, 0.32 wt%, 0.35 wt%, etc., or other values within the range of 0.1 wt% to 0.35 wt%.

[0080] In some embodiments, the hydrogen absorption pressure of the second hydrogen pulverization is 0.1 MPa to 0.5 MPa, and the dehydrogenation temperature is 400 °C to 550 °C, so as to obtain the second alloy coarse powder. Other process conditions of the second hydrogen pulverization can be set conventionally. For example, the hydrogen absorption temperature is 150 °C to 320 °C, and the dehydrogenation pressure can be 0.1 Mpa to 0.5 Mpa. Exemplarily, the hydrogen absorption pressure of the second hydrogen pulverization can be 0.1 MPa, 0.15 MPa, 0.2 MPa, 0.25 MPa, 0.3 MPa, 0.35 MPa, 0.4 MPa, 0.45 MPa, 0.5 MPa, etc., or other values within the range of 0.1 MPa to 0.5 MPa.

[0081] Exemplarily, the dehydrogenation temperature for the second hydrogen pulverization is 400 °C, 410 °C, 420 °C, 430 °C, 440 °C, 450 °C, 460 °C, 470 °C, 480 °C, 490 °C, 500 °C, 510 °C, 520 °C, 530 °C, 540 °C, 550 °C, etc., or other values within the range of 400 °C to 550 °C.

[0082] Exemplarily, the hydrogen absorption temperature for the second hydrogen pulverization can be 150 °C, 160 °C, 170 °C, 180 °C, 190 °C, 200 °C, 210 °C, 220 °C, 230 °C, 240 °C, 250 °C, 260 °C, 270 °C, 280 °C, 290 °C, 300 °C, 310 °C, 320 °C, etc., or other values within the range of 150 °C to 320 °C.

[0083] In some other embodiments, the pressure in the grinding chamber of the jet mill for the second jet mill pulverization is 0.5 MPa to 0.6 MPa, and the rotational speed of the classification wheel of the jet mill is 2700 r / min to 3100 r / min, so as to control the median particle size D50 of the second alloy powder within the range of 4.0 μm to 4.5 μm.

[0084] Exemplarily, when performing the second jet mill pulverization, the pressure in the grinding chamber of the jet mill can be controlled to 0.5 MPa, 0.51 MPa, 0.52 MPa, 0.53 MPa, 0.54 MPa, 0.55 MPa, 0.56 MPa, 0.57 MPa, 0.58 MPa, 0.59 MPa, 0.6 MPa, etc., or other values within the range of 0.5 MPa to 0.6 MPa.

[0085] Exemplarily, the rotational speed of the classification wheel of the jet mill in the second jet mill pulverization can be 2700 r / min, 2750 r / min, 2800 r / min, 2850 r / min, 2900 r / min, 2950 r / min, 3000 r / min, 3050 r / min, 3100 r / min, etc., or other values within the range of 2700 r / min to 3100 r / min.

[0086] In some embodiments, the base material of the waste NdFeB magnet may include the following components: R: 28 wt% to 31.5 wt%; B: 0.86 wt% to 1.05 wt%, M1: 0.3 wt% to 3 wt%, T: 64.5 wt% to 70 wt%; wherein, R is a rare earth element, R includes Pr and Nd; M1 includes at least one of Al, Cu, Ga, Ti, Sn, Zr, Nb; T includes Fe and / or Co.

[0087] It can be understood that the base material of the waste neodymium-iron-boron magnet may not be limited to the components in this embodiment, and waste neodymium-iron-boron magnets with other components can also be recycled according to actual needs. In some preferred embodiments, a first alloy raw material similar to the base material components of the waste neodymium-iron-boron magnet can be selected to prepare the first alloy powder, so as to be mixed with the second alloy powder with similar components, so that the components of the neodymium-iron-boron magnet prepared from the mixed powder can be within a controllable range.

[0088] Further, in some other embodiments, the preparation method 100 may further include: in step S106, the first alloy powder and the second alloy powder can be mixed according to a mass ratio of 1:(1~3) to obtain the aforementioned mixed powder. Exemplarily, the mass ratio of the first alloy powder to the second alloy powder can be 1:1, 1:1.5, 1:2, 1:2.5, 1:3, etc., or other values within the range of 1:(1~3).

[0089] By mixing the first alloy powder and the second alloy powder according to a mass ratio of 1:(1~3), it is possible to use 1 part by mass of the first alloy powder to recycle multiple parts by mass of the waste neodymium-iron-boron magnet, realizing the effective utilization of the waste neodymium-iron-boron magnet.

[0090] In still some other embodiments, the vacuum degree in the sintering device can be controlled to be 10 -2 Pa ~ 10 2 Pa during the sintering process. In some embodiments, the sintering temperature of the sintering process can be 1000°C~1100°C, and the sintering time is 4h~10h. Exemplarily, the sintering temperature can be, for example, 1000°C, 1010°C, 1020°C, 1030°C, 1040°C, 1050°C, 1060°C, 1070°C, 1080°C, 1090°C, 1100°C, etc., or other values within the range of 1000°C~1100°C. Exemplarily, the sintering time can be 4h, 5h, 6h, 7h, 8h, 9h, 10h, etc., or other values within the range of 4h~10h.

[0091] In some other embodiments, the aging temperature for the aging treatment can be 400°C to 500°C, and the aging time can be 4h to 10h. Aging treatment refers to the process of keeping the material at a specific temperature for a long time to improve its organizational structure and properties. Exemplarily, in the embodiments of the present application, the aging temperature can be, for example, 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, etc., or other values within the range of 400°C to 500°C. Exemplarily, the aging time can be, for example, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h, 10h, or other values within the range of 4h to 10h.

[0092] In still some other embodiments, the aging treatment can include a primary aging treatment and a secondary aging treatment. The primary aging treatment temperature is 850°C to 950°C, the primary aging treatment time is 2h to 6h, the secondary aging treatment temperature is 450°C to 650°C, and the secondary aging treatment time is 3h to 10h. Exemplarily, the primary aging treatment temperature can be, for example, 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, 930°C, 940°C, 950°C, etc., or other values within the range of 850°C to 950°C. Exemplarily, the primary aging treatment time can be, for example, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, etc., or other values within the range of 2h to 6h. Exemplarily, the secondary aging treatment temperature is 450°C, 470°C, 490°C, 500°C, 520°C, 540°C, 550°C, 560°C, 580°C, 600°C, 620°C, 640°C, 650°C, etc., or other values within the range of 450°C to 650°C. Exemplarily, the secondary aging treatment time is 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, etc., or other values within the range of 3h to 10h.

[0093] In still some other embodiments, the mixed powder composed of the first alloy powder and the second alloy powder can be first subjected to a forming treatment and / or an isostatic pressing treatment, and then a sintering treatment and an aging treatment. The forming treatment refers to the process of pressing the mixed powder into a blank with the required shape and size through a specific mold and pressure equipment. The isostatic pressing treatment refers to a forming process in which a uniform pressure is applied to the blank by using a liquid or gas as a pressure transmission medium. Compared with ordinary pressing, the isostatic pressing treatment can ensure that the blank is subjected to uniform pressure in all directions, thereby improving the density uniformity and dimensional accuracy of the blank.

[0094] In some embodiments, the preparation method 100 may further include: coating a heavy rare earth slurry onto at least one surface of the NdFeB magnet perpendicular to its orientation direction, and then performing a heat treatment to obtain a diffused NdFeB magnet. The orientation direction is the macroscopic arrangement direction of the easy magnetization axes (i.e., the crystallographic C axes) of the grains inside the magnet. The at least one surface perpendicular to the orientation direction of the NdFeB magnet may include one surface or multiple surfaces (e.g., two opposite surfaces). The surface perpendicular to the orientation direction of the NdFeB magnet may be referred to as the orientation surface. That is to say, in the present embodiment, the heavy rare earth slurry may be coated onto one orientation surface or multiple orientation surfaces of the NdFeB magnet, such that the heavy rare earth slurry diffuses along the orientation direction of the NdFeB magnet.

[0095] In some other embodiments, the heat treatment sequentially includes a diffusion process and a tempering process; the diffusion temperature of the diffusion process is 800°C to 950°C, and the diffusion time is 5 h to 20 h; the tempering temperature of the tempering process is 450°C to 550°C, and the tempering time is 3 h to 8 h. Exemplarily, the diffusion temperature may be, for example, 800°C, 820°C, 850°C, 880°C, 900°C, 920°C, 950°C, etc., or other values within the range of 800°C to 950°C. Exemplarily, the diffusion time is 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, etc., or any value within the range of 5 h to 20 h.

[0096] Exemplarily, the tempering temperature may be, for example, 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, etc., or other values within the range of 450°C to 550°C. Exemplarily, the tempering time is 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h, 8 h, etc., or other values within the range of 3 h to 8 h.

[0097] In some embodiments, the heavy rare earth slurry may include 75 wt% to 84 wt% of a compound containing a heavy rare earth element, 15 wt% to 24 wt% of an organic solvent, and 0.1 wt% to 5 wt% of a binder. In some other embodiments, the organic solvent is selected from ethanol and / or acetone. In still some other embodiments, the binder is selected from one or more of dammar resin, shellac, and alkyd resin. In some embodiments, the compound containing a heavy rare earth element is selected from one or more of a hydride of a heavy rare earth element, an oxide of a heavy rare earth element, a fluoride of a heavy rare earth element, and an alloy of a heavy rare earth element. In some other embodiments, the heavy rare earth element includes one or more of Dy and Tb.

[0098] The above combination Figure 1An exemplary description is given of the preparation method of the NdFeB magnet according to the embodiments of the present application. It can be understood that, in the embodiments of the present application, the first alloy powder and the second alloy powder obtained from waste NdFeB magnets are mixed, and by controlling the median particle size D50 of the first alloy powder, the median particle size D50 of the second alloy powder, and the Ni content in the second alloy powder, the Ni content in the recycled magnet is jointly controlled within a controllable range, and the Ni element is promoted to enter the grain boundary phase of the recycled magnet, while minimizing or reducing the entry of the Ni element into the main phase grains of the recycled magnet.

[0099] For the NdFeB magnet prepared according to the embodiments of the present application, not only can the Ni element be absent or present within a controllable range in the main phase grains (i.e., the Ni content in the main phase grains is 0~0.4 at%), so as to avoid or reduce the influence of the Ni element on the magnetic properties of the magnet (such as coercivity and remanence), but also because the melting point of Ni is relatively low, the Ni element enters the grain boundary phase to form R a T b X c M d-c phase, which is beneficial to reducing the melting point of the grain boundary phase, making the grain boundary phase have good wettability and the ability to repair the boundary, helping to improve the diffusion channel obstruction caused by impurity elements that may exist inside the recycled magnet, thereby enabling the construction of good diffusion channels and facilitating subsequent diffusion using heavy rare earth slurries. Compared with the magnet recycled by the stripping process, after the NdFeB magnet prepared by the embodiments of the present application undergoes heavy rare earth element diffusion, the diffusion increment is significantly improved, and the coercivity increase after diffusion can reach about 5000 Oe~7000 Oe.

[0100] Furthermore, the preparation method of the embodiments of the present application can also control the oxygen content of the recycled magnet by controlling the oxygen content of the first alloy coarse powder. Thus, under the combined action of the oxygen content, the median particle size D50 of the first alloy powder, the median particle size D50 of the second alloy powder, and the Ni content in the second alloy powder, the structure and size of the main phase grains in the prepared NdFeB magnet are further ensured, as well as the proportion, continuity, and uniformity of the grain boundary phase, which is further beneficial to the magnetic properties of the NdFeB magnet.

[0101] It can also be understood that through the control of the process conditions in the preparation method of the embodiments of the present application, the first alloy raw material with a base material composition close to that of the waste NdFeB magnet can be used to prepare the first alloy powder in the embodiments of the present application, without the need to use a rare earth-rich phase alloy powder (i.e., an alloy powder with a high R element content) to improve the performance of the recycled magnet, which is beneficial to saving rare earth resources and reducing the manufacturing cost of the recycled magnet.

[0102] Examples and comparative examples: The raw material components of all the examples and comparative examples are shown in Table 1. It should be noted that the Fe content in the examples and comparative examples is the balance and is not listed in Table 1. Since the raw materials of Example 4 and Example 5 are the same as those of Example 1, the raw materials of Comparative Example 2 are the same as those of Comparative Example 1, and the raw materials of Comparative Example 4 are the same as those of Example 1, the raw materials of Example 4, Example 5, Comparative Example 2, and Comparative Example 4 are not shown in Table 1.

[0103] The key process parameters of all the examples and comparative examples are shown in Table 2. The performance test results of the magnet samples of each example and comparative example are shown in Table 3. The test results of the grain boundary phase composition, the content of some elements in the main phase grains, and the impurity content of the magnet samples of each example and comparative example are shown in Table 4. Figure 2 The scanning electron microscope photograph of Example 1 of the present application is shown. Figure 3 The scanning electron microscope photograph of Example 4 of the present application is shown.

[0104] Example 1: The prepared first alloy raw material is cast by a rapid solidification process to obtain a neodymium-iron-boron alloy rapid solidification sheet. The neodymium-iron-boron alloy rapid solidification sheet is subjected to first hydrogen pulverization to obtain first alloy coarse powder. The first alloy coarse powder is pulverized by a first jet mill to obtain first alloy powder. Among them, the hydrogen absorption pressure of the first hydrogen pulverization is 0.3 MPa, the dehydrogenation temperature is 560 °C, and an inert gas is filled to 60 kPa after dehydrogenation, and the gas filling time is 5 min. When pulverizing by the first jet mill, the pressure in the grinding chamber of the jet mill is 0.68 MPa, the oxygen content in the grinding chamber is controlled at 80 ppm, the rotational speed of the classification wheel of the jet mill is 3100 r / min, and the average particle size D50 of the first alloy powder is 4.0 μm. The waste neodymium-iron-boron magnet including a nickel-copper coating is successively subjected to second hydrogen pulverization, screening treatment with a 20-mesh sieve, and second jet mill pulverization to obtain second alloy powder. Among them, the hydrogen absorption pressure of the second hydrogen pulverization is 0.35 MPa, the dehydrogenation temperature is 550 °C, and an inert gas is filled to 70 kPa after dehydrogenation, and the gas filling time is 5 min. When pulverizing by the second jet mill, the pressure in the grinding chamber of the jet mill is 0.6 MPa, the oxygen content in the grinding chamber is controlled at 120 ppm, the rotational speed of the classification wheel of the jet mill is 2900 r / min, and the average particle size D50 of the second alloy powder is 4.2 μm.

[0105] The mixed powder is composed of the first alloy powder and the second alloy powder mixed in a mass ratio of 1:1. The mixed powder is formed, sintered, and aged to obtain a neodymium-iron-boron magnet. Among them, the sintering temperature is 1060 °C, the sintering time is 6 hours, the aging treatment is divided into two stages. The temperature of the first-stage aging treatment is 900 °C, the time of the first-stage aging treatment is 6 h, the temperature of the second-stage aging treatment is 500 °C, and the time of the second-stage aging treatment is 6 h.

[0106] Example 2: The prepared first alloy raw material is subjected to a rapid solidification process for casting to obtain a rapid solidification sheet of neodymium iron boron alloy. The rapid solidification sheet of neodymium iron boron alloy is subjected to first hydrogen pulverization to obtain a first alloy coarse powder, and the first alloy coarse powder is subjected to first jet milling to obtain a first alloy powder. Among them, the hydrogen absorption pressure for the first hydrogen pulverization is 0.3 MPa, the dehydrogenation temperature is 560 °C, after dehydrogenation, an inert gas is filled to 60 kPa, and the gas filling time is 5 min. When performing the first jet milling, the pressure in the grinding chamber of the jet mill is 0.68 MPa, the oxygen content in the grinding chamber is controlled at 80 ppm, the rotational speed of the classification wheel of the jet mill is 3200 r / min, and the average particle size D50 of the first alloy powder is 3.8 μm.

[0107] The waste neodymium iron boron magnet including a nickel plating layer is successively subjected to second hydrogen pulverization, screening treatment with a 30-mesh sieve, and second jet milling to obtain a second alloy powder. Among them, the hydrogen absorption pressure for the second hydrogen pulverization is 0.35 MPa, the dehydrogenation temperature is 550 °C, after dehydrogenation, an inert gas is filled to 70 kPa, and the gas filling time is 5 min. When performing the second jet milling, the pressure in the grinding chamber of the jet mill is 0.6 MPa, the oxygen content in the grinding chamber is controlled at 120 ppm, the rotational speed of the classification wheel of the jet mill is 3000 r / min, and the average particle size D50 of the second alloy powder is 4.0 μm.

[0108] The mixed powder is composed of the first alloy powder and the second alloy powder mixed at a mass ratio of 1:2. The mixed powder is formed, sintered, and aged to obtain a neodymium iron boron magnet. Among them, the sintering temperature is 1060 °C, the sintering time is 6 hours, the aging treatment is divided into two stages. The temperature for the first-stage aging treatment is 900 °C, the time for the first-stage aging treatment is 6 h, the temperature for the second-stage aging treatment is 500 °C, and the time for the second-stage aging treatment is 6 h.

[0109] Example 3: The prepared first alloy raw material is subjected to a rapid solidification process for casting to obtain a rapid solidification sheet of neodymium iron boron alloy. The rapid solidification sheet of neodymium iron boron alloy is successively subjected to first hydrogen pulverization to obtain a first alloy coarse powder, and the first alloy coarse powder is subjected to first jet milling to obtain a first alloy powder. Among them, the hydrogen absorption pressure for the first hydrogen pulverization is 0.3 MPa, the dehydrogenation temperature is 560 °C, after dehydrogenation, an inert gas is filled to 60 kPa, and the gas filling time is 5 min. When performing the first jet milling, the pressure in the grinding chamber of the jet mill is 0.68 MPa, the oxygen content in the grinding chamber is controlled at 80 ppm, the rotational speed of the classification wheel of the jet mill is 2800 r / min, and the average particle size D50 of the first alloy powder is 4.3 μm.

[0110] The waste Nd-Fe-B magnet including a nickel-copper plating layer is sequentially subjected to second hydrogen pulverization, screening treatment with a 30-mesh sieve, and second jet milling pulverization to obtain a second alloy powder. Among them, the hydrogen absorption pressure for the second hydrogen pulverization is 0.35 MPa, the dehydrogenation temperature is 550 °C, an inert gas is filled to 70 kPa after dehydrogenation, and the gas filling time is 5 min. When performing the second jet milling pulverization, the pressure in the grinding chamber of the jet mill is 0.6 MPa, the oxygen content in the grinding chamber is controlled at 120 ppm, the rotational speed of the classification wheel of the jet mill is 2700 r / min, and the average particle size D50 of the first alloy powder is 4.5 μm. The mesh number of the sieve for the screening treatment is 20 mesh.

[0111] The mixed powder is composed of the first alloy powder and the second alloy powder mixed at a mass ratio of 1:3. The mixed powder is molded, sintered, and aged to obtain an Nd-Fe-B magnet. Among them, the sintering temperature is 1060 °C, the sintering time is 6 hours, the aging treatment is divided into two stages. The temperature for the first-stage aging treatment is 900 °C, and the time for the first-stage aging treatment is 6 h. The temperature for the second-stage aging treatment is 500 °C, and the time for the second-stage aging treatment is 6 h.

[0112] Example 4: The Nd-Fe-B magnet prepared in Example 1 is machined to obtain a magnet substrate with dimensions of 9 mm × 6 mm × 3.8 mm (orientation direction).

[0113] A diffusion source containing the heavy rare earth element Dy is magnetron sputtered on at least one surface of 9 mm × 6 mm of the magnet substrate, and diffusion is carried out along the orientation direction. The magnet substrate with the diffusion source attached to the surface is heat treated at 900 °C for 17 h (diffusion process), and then heat treated at 500 °C for 6 h (tempering process). The diffusion heat treatment is carried out in a vacuum atmosphere to obtain the diffused magnet, where the weight increase of the heavy rare earth element is 0.6 wt% of the magnet substrate.

[0114] Example 5: The first alloy powder with the same raw material composition as in Example 1 and the waste Nd-Fe-B magnet with the same composition are used to prepare the second alloy powder. The difference is: in the first hydrogen pulverization process, the hydrogen absorption pressure for hydrogen pulverization is 0.35 MPa, the dehydrogenation temperature is 550 °C, an inert gas is filled to 20 kPa after dehydrogenation, and the gas filling time is 30 s.

[0115] Comparative Example 1: The first alloy powder with the same raw material composition as in Example 1 and the waste Nd-Fe-B magnet with the same composition are used to prepare the second alloy powder. The difference is: the preparation process of the second alloy powder uses a stripping method. After stripping the plating layer of the waste Nd-Fe-B magnet, jet milling pulverization is carried out to obtain the second alloy powder with the same particle size as in Example 1.

[0116] Comparative Example 2: The same diffusion process as in Example 4 is adopted, except that the magnet substrate for diffusion is the NdFeB magnet prepared in Comparative Example 1.

[0117] Comparative Example 3: The first alloy powder with the same raw material composition as in Example 1 and the waste NdFeB magnet with the same composition are used to prepare the second alloy powder. The difference lies in that: in the preparation process of the second alloy powder, screening treatment is not carried out.

[0118] Comparative Example 4: The first alloy powder with the same raw material composition as in Example 1 and the waste NdFeB magnet with the same composition are used to prepare the second alloy powder. The difference lies in that: when the first jet mill is used for grinding, the pressure in the grinding chamber of the jet mill is 0.56 MPa, the rotational speed of the classification wheel of the jet mill is 2700 r / min, and the average particle size D50 of the first alloy powder is 4.4 μm. When the second jet mill is used for grinding, the pressure in the grinding chamber of the jet mill is 0.5 MPa, the rotational speed of the classification wheel of the jet mill is 2800 r / min, and the average particle size D50 of the second alloy powder is 4.4 μm.

[0119] Testing method: The testing method adopted in this application is as follows: (1) Composition testing method; The composition and content of the raw materials, powders, and magnets are tested by an ICP composition analyzer.

[0120] (2) Testing method for the atomic content of the grain boundary phase; After the magnet is prepared into a sample, a scanning electron microscope test is carried out on any cross-section perpendicular to the orientation direction of the magnet. All the main phases and grain boundary phases in each microstructure cross-section are counted. The size of the observation area is, for example, 40 μm × 40 μm and 75 μm × 75 μm; the magnification is 2000 - 5000 times. The atomic percentages of each element in the main phase and grain boundary phase are analyzed by EDS energy spectrum to obtain the composition of the grain boundary phase.

[0121] (3) Median particle size testing method; The particle size distribution is tested by a German Sympatec laser particle size analyzer and D50 is calculated.

[0122] (4) Magnet performance testing method The remanence, coercivity, and squareness are tested by a permanent magnet material precision measurement system NIM - 62000TB.

[0123] Table 1: Raw material composition

[0124] Table 2: Process conditions

[0125] Table 3: Performance test results

[0126] Table 4: Test results of grain boundary phase composition, content of some elements and impurity content in main phase grains

[0127] It can be seen from Tables 1 to 4 above that: The R a T b X c M d-c phase is generated in the magnet samples of Examples 1 to 5, and the Ni content in the main phase grains is all below 0.4 at%, so that it has good remanence, coercivity and squareness, and has good comprehensive performance. Compared with Example 5, the [O] of the first alloy coarse powder in Examples 1-4 is controlled in the range of 500 ppm to 1100 ppm, so that the [O] of the prepared Nd-Fe-B magnet is lower, and thus the Nd-Fe-B magnets in Examples 1-4 have more excellent magnetic properties.

[0128] Compared with Example 1, in Comparative Example 1, due to the rare earth loss caused by stripping and the inevitable introduction of organic substances, the [C] and [N] of the recycled magnet are both high, and it is difficult to completely remove the Ni element in the coating during actual operation, and there is still residual Ni element entering the main phase grains, ultimately resulting in the deterioration of the magnetic properties of the magnet.

[0129] Comparing Example 4 and Comparative Example 2, the performance of Comparative Example 2 is lower, because the magnet matrix of Comparative Example 2 is prepared by a stripping process, resulting in the loss of rare earth elements, so there is not enough Nd-rich phase and it does not have the R a T b X c M d-c phase, which affects the diffusion effect.

[0130] Compared with Example 1, in Comparative Example 3, due to the lack of screening treatment, it is difficult to control the Ni content in the second alloy powder, resulting in a high total Ni content in the recycled magnet, causing Ni elements to accumulate in the grain boundary phase and more Ni to enter the main phase, thus deteriorating the properties such as the remanence Br and coercivity Hcj of the magnet.

[0131] Compared with Example 1, in Comparative Example 4, due to the use of a lower rotational speed of the airflow mill classification wheel, the D50 of the first alloy powder is larger and the same as that of the second alloy powder, resulting in a poorer synergistic effect after mixing the two, and unable to form the R a T b X c M d-cIn the phase, more Ni elements entered the main phase grains, resulting in a decrease in the coercivity of the magnet.

[0132] In addition, as can be seen from Figure 2 a R a T b X c M d-c phase was formed in the grain boundary phase of the Nd-Fe-B magnet prepared in Example 1. Figure 3 is a scanning electron microscope photograph at a depth of 80 μm below a surface perpendicular to the orientation direction of the Nd-Fe-B magnet in Example 4. As can be seen from Figure 3 the main phase grains of the magnet after diffusion in Example 4 have a heavy rare earth shell layer. It can thus be shown that the Nd-Fe-B magnets prepared in the embodiments of the present application have good diffusion channels, enabling the heavy rare earth slurry to achieve a good diffusion effect along the orientation direction of the Nd-Fe-B magnet.

[0133] 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. Many variations, changes, and alternative approaches can be envisioned by those skilled in the art without departing from the spirit and scope of the present application. It should be understood that various alternative embodiments of the present application described herein can be employed in the practice of the present application. The appended claims are intended to define the scope of protection of the present application and thus cover equivalents or alternative embodiments within the scope of these claims.

Claims

1. A neodymium iron boron magnet, characterized in that, The NdFeB magnet comprises the following components: R: 28 wt% - 31.5 wt%, B: 0.86 wt% - 1.05 wt%, Ni: 0.03 wt% - 0.15 wt%, Cu: 0.1 wt% - 0.5 wt%, Co: 0.5 wt% - 2 wt%, M: 0.3 wt% - 3 wt%, Fe: 64.4 wt% - 67 wt%; Among them, the neodymium iron boron magnet includes a main phase grain and a grain boundary phase, and the grain boundary phase includes R a T b X c M d-c phase, 35 at% ≤ a ≤ 65 at%, 30 at% ≤ b ≤ 60 at%, 5 at% ≤ d ≤ 10 at%, c / d ≥ 0.6; R is a rare earth element, R includes Pr and Nd; T includes Fe and / or Co; M includes at least one of Al, Ga, Ti, Sn, Zr, Nb; X includes Ni and Cu.

2. The NdFeB magnet according to claim 1, characterized in that the Ni content in the main phase grains is 0 - 0.4 at%.

3. The neodymium iron boron magnet according to claim 1, characterized in that, The NdFeB magnet further comprises oxygen element, carbon element, and nitrogen element, wherein the oxygen content is [O], the carbon content is [C], the nitrogen content is [N], and 500 ppm ≤ [O] ≤ 1600 ppm, [C] ≤ 1400 ppm, [N] ≤ 400 ppm are satisfied.

4. The neodymium iron boron magnet according to any one of claims 1-3, characterized in that, R further comprises heavy rare earth elements, and within a depth range of 0.1 - 100 μm from at least one surface perpendicular to the orientation direction of the NdFeB magnet, in the microstructure observation plane at any depth, the main phase grains have a heavy rare earth shell layer, and the heavy rare earth element content in the heavy rare earth shell layer of the main phase grains is 2.5 at% - 4.5 at%; R further comprises at least one of Dy and Tb.

5. A method for preparing a neodymium iron boron magnet, characterized in that, The preparation method comprises: Obtaining a first alloy powder, wherein the median particle size D50 of the first alloy powder is 3.8 μm - 4.3 μm, the first alloy powder comprises R, B, Cu, M, and T elements, R is a rare earth element, R comprises Pr and Nd, T comprises Fe and / or Co; M comprises at least one of Al, Ga, Ti, Sn, Zr, Nb; Successively subjecting the waste NdFeB magnet comprising a nickel plating or a nickel - copper plating to second hydrogen pulverization, screening treatment, and second jet - mill pulverization to obtain a second alloy powder, wherein the median particle size D50 of the second alloy powder is controlled to be 4.0 μm - 4.5 μm, and the Ni content in the second alloy powder is controlled to be 0.05 wt% - 0.2 wt%; Performing a shaping treatment, a sintering treatment, and an aging treatment on the mixed powder composed of the first alloy powder and the second alloy powder to obtain the NdFeB magnet.

6. The preparation method according to claim 5, wherein The preparation method further comprises: Preparing a NdFeB alloy rapid - solidification sheet from a predetermined first alloy raw material; Performing first hydrogen pulverization on the NdFeB alloy rapid - solidification sheet to obtain a first alloy coarse powder, controlling the oxygen content [O] of the first alloy coarse powder to be 500 ppm - 1100 ppm; Performing first jet - mill pulverization on the first alloy coarse powder to obtain the first alloy powder; Wherein, the first alloy raw material comprises the following components: R: 28 wt% - 31.5 wt%, B: 0.86 wt% - 1.05 wt%, M: 0.3 wt% - 3 wt%, Cu: 0.1 wt% - 0.55 wt%, T: 64.5 wt% - 70 wt%; Wherein, R is a rare earth element, R comprises Pr and Nd, T comprises Fe and / or Co; M comprises at least one of Al, Ga, Ti, Sn, Zr, Nb.

7. The preparation method according to claim 5, characterized in that, In the screening process, a screen mesh with a mesh size of 7 mesh to 30 mesh is used to screen the second alloy coarse powder obtained after the second hydrogen pulverization, and the second alloy coarse powder passing through the screen mesh is pulverized by a second jet mill.

8. The preparation method according to any one of claims 5 to 7, characterized in that, The preparation method further includes: Via the screening process, the Cu content in the second alloy powder is further controlled to be 0.1 wt% to 0.35 wt%.

9. The preparation method according to any one of claims 5-7, characterized in that, The preparation method further includes: Mixing the first alloy powder and the second alloy powder according to a mass ratio of 1:(1 - 3) to obtain the mixed powder; During the sintering process, the vacuum degree in the sintering device is controlled to be 10 -2 Pa ~ 10 2 Pa; The sintering temperature of the sintering process is 1000 °C to 1100 °C, and the sintering time is 4 h to 10 h; The aging temperature of the aging process is 400 °C to 500 °C, and the aging time is 4 h to 10 h; The aging process includes a primary aging process and a secondary aging process, wherein the primary aging temperature is 850 °C to 950 °C, the primary aging time is 2 h to 6 h, the secondary aging temperature is 450 °C to 650 °C, and the secondary aging time is 3 h to 10 h.

10. The preparation method according to claim 5, characterized in that, The preparation method further includes: Coating the heavy rare earth slurry on at least one surface of the NdFeB magnet perpendicular to its orientation direction, and then performing heat treatment to obtain the diffused NdFeB magnet; Among them, the heat treatment sequentially includes a diffusion process and a tempering process; the diffusion temperature of the diffusion process is 800 - 950 °C, and the diffusion time is 5 - 20 h; the tempering temperature of the tempering process is 450 - 550 °C, and the tempering time is 3 - 8 h.

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