Neodymium iron boron magnet and preparation method thereof

Abstract

The present application discloses a NdFeB magnet and a preparation method thereof. The NdFeB magnet comprises the following components: R: 28wt%~31.5wt%, B: 0.86wt%~1.05wt%, Ni: 0.03wt%~0.15wt%, Cu: 0.1wt%~0.5 wt%, Co: 0.5wt%~2 wt%, M: 0.3wt%~3wt%, Fe: 64.4wt%~67wt%; wherein the NdFeB magnet comprises main phase grains and grain boundary phase, wherein the grain boundary phase comprises R a T b X c M d‑c Phase, 35at%≤a≤65at%, 30at%≤b≤60at%, 5at%≤d≤10at%, c / d≥0.6. The NdFeB magnet of the embodiment of the present application has good performance.

Description

Technical Field

[0001] The present invention relates generally to the field of magnet recovery technology and more specifically to a neodymium iron boron magnet and a method for preparing the same. Background Art

[0002] Sintered NdFeB magnets, due to their excellent magnetic properties, are widely used in a wide range of applications, including aerospace, electronics and communications, clean energy, transportation, medical devices, and household appliances. However, the production process of sintered NdFeB magnets generates significant amounts of waste due to equipment failure, collisions, and contamination. Furthermore, magnets from end-of-life end-use products (such as motors) are often unusable due to oil contamination, damage, or corrosion. The global production of waste NdFeB magnets is enormous annually. However, rare earth resources (such as neodymium, praseodymium, and dysprosium), their core components, are non-renewable and scarce. Therefore, effectively recycling and reusing waste NdFeB magnets remains a pressing challenge within the industry. Recycling and reusing waste NdFeB magnets not only reduces the depletion of primary rare earth resources and lowers raw material costs, but also mitigates environmental pollution caused by improper disposal of waste magnets containing heavy metals and rare earth elements.

[0003] The surface of NdFeB magnets often needs to be electroplated due to corrosion protection requirements, such as electroplated nickel or copper-nickel layers. When waste NdFeB magnets are recycled, the electroplated coating can cause serious degradation in the performance of the recovered magnets. In order to avoid the degradation of the recovered magnet performance, the prior art often uses a stripping process to remove the surface coating of waste NdFeB magnets. However, the stripping process not only increases the recycling cost, but also damages the rare earth content inside the magnet, resulting in a waste of resources. In addition, the surface of the magnet after stripping is prone to residual organic matter, which can still cause serious degradation in the performance of the recovered magnet, which is not conducive to ensuring the magnetic properties of the recovered magnet.

[0004] In view of this, there is an urgent need to provide a new solution for recycling and reusing waste NdFeB magnets to achieve high-value utilization of recycled magnets. 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 NdFeB magnet, comprising the following components: R: 28wt%~31.5wt%, B: 0.86wt%~1.05wt%, Ni: 0.03wt%~0.15wt%, Cu: 0.1wt%~0.5 wt%, Co: 0.5wt%~2 wt%, M: 0.3wt%~3wt%, Fe: 64.4wt%~67wt%; wherein, the NdFeB magnet comprises a main phase grain and a grain boundary phase, wherein the grain boundary phase comprises R aT b X c M d-c phase, 35at%≤a≤65at%, 30at%≤b≤60at%, 5at%≤d≤10at%, 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, and Nb; X includes Ni and Cu.

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

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

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

[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 a neodymium iron boron magnet, the preparation method comprising: 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; subjecting a waste neodymium iron boron magnet comprising a nickel coating or a nickel-copper coating to a second hydrogen crushing, screening treatment and a second air flow milling in sequence 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%; subjecting a mixed powder consisting of the first alloy powder and the second alloy powder to a molding treatment, a sintering treatment and an aging treatment to obtain a neodymium iron boron magnet.

[0012] In some embodiments, the preparation method further includes: preparing a NdFeB alloy quick-setting sheet from a predetermined first alloy raw material; performing a first hydrogen crushing on the NdFeB alloy quick-setting sheet to obtain a first alloy coarse powder, and controlling the oxygen content [O] of the first alloy coarse powder to be 500ppm~1100ppm; performing a first air flow mill crushing on the first alloy coarse powder to obtain the first alloy powder.

[0013] In other embodiments, the first alloy raw material includes the following components: R: 28wt%~31.5wt%, B: 0.86wt%~1.05wt%, M: 0.3wt%~3wt%, Cu: 0.1wt%~0.55wt%, T: 64.5wt%~70wt%; 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, and Nb.

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

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

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

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

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

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

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

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

[0022] In other embodiments, the heat treatment includes a diffusion process and a tempering process in sequence; the diffusion temperature of the diffusion process is 800~950℃, and the diffusion time is 5~20h; the tempering temperature of the tempering process is 450~550℃, and the tempering time is 3~8h.

[0023] As can be seen from the NdFeB magnet and its preparation method provided above, the embodiment of the present application prepares NdFeB magnets 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 and the median particle size D50 of the second alloy powder, and controlling the Ni content in the second alloy powder, a grain boundary phase including R a T b X c M d-c Phase NdFeB magnets, which realize the recycling and reuse of waste NdFeB magnets including nickel plating or nickel-copper plating. Since the preparation method of the embodiment of the present application does not require the stripping process of the waste magnets, and the Ni element in the generated NdFeB magnets (or recycled magnets) mainly enters the grain boundary phase through process control, it can effectively avoid serious degradation of the performance of the recycled magnets and avoid the waste of rare earth resources, which is conducive to ensuring the magnetic properties of the recycled magnets and realizing the high-value utilization of the recycled magnets. The recycled magnets described in this article refer to magnets obtained after processing waste NdFeB magnets. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] 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:

[0025] Figure 1 An exemplary flow chart showing a method for preparing a neodymium iron boron magnet according to an embodiment of the present application is shown;

[0026] Figure 2 Shows a scanning electron microscope photograph of Example 1 of the present application;

[0027] Figure 3 A scanning electron microscope photograph of Example 4 of the present application is shown. DETAILED DESCRIPTION

[0028] 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 the embodiments. 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.

[0029] 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.

[0030] 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.

[0031] The specific implementation of the present application will be described in detail below with reference to the accompanying drawings.

[0032] In a first aspect, the present application provides a NdFeB magnet comprising the following components: R: 28 wt% to 31.5 wt%, B: 0.86 wt% to 1.05 wt%, Ni: 0.03 wt% to 0.15 wt%, Cu: 0.1 wt% to 0.5 wt%, Co: 0.5 wt% to 2 wt%, M: 0.3 wt% to 3 wt%, Fe: 64.4 wt% to 67 wt%; wherein the NdFeB magnet comprises a main phase grain and a grain boundary phase, and the grain boundary phase comprises R a T b X c M d-c phase, 35at%≤a≤65at%, 30at%≤b≤60at%, 5at%≤d≤10at%, 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, and Nb; X includes Ni and Cu.

[0033] For example, the mass content of the R element in the NdFeB magnet can be, for example, 28wt%, 28.5wt%, 29wt%, 29.5wt%, 30wt%, 30.5wt%, 31wt%, 31.5wt%, etc., or other values ​​within the range of 28wt% to 31.5wt%.

[0034] Illustratively, the mass content of the boron (B) element in the NdFeB 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%.

[0035] Illustratively, the mass content of Ni element in the NdFeB magnet can be, for example, 0.03wt%, 0.04wt%, 0.05wt%, 0.06wt%, 0.07wt%, 0.08wt%, 0.09wt%, 0.1wt%, 0.11wt%, 0.12wt%, 0.13wt%, 0.14wt%, 0.15wt%, etc., or other values ​​within the range of 0.03wt% to 0.15wt%.

[0036] For example, the mass content of the Cu element in the NdFeB 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%.

[0037] Exemplarily, the mass content of the Co element in the NdFeB magnet can be, for example, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, 2wt%, etc., or other values ​​within the range of 0.5wt% to 2wt%.

[0038] Exemplarily, the mass content of the M element in the NdFeB magnet can be, for example, 0.3wt%, 0.5wt%, 0.6wt%, 0.8wt%, 1wt%, 1.2wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.8wt%, 2wt%, 2.2wt%, 2.4wt%, 2.5wt%, 2.6wt%, 2.8wt%, 3wt%, or other values ​​within the range of 0.3wt% to 3wt%.

[0039] Exemplarily, the mass content of the Fe element in the NdFeB magnet can be, for example, 64.4wt%, 64.5wt%, 64.6wt%, 64.8wt%, 65wt%, 65.2wt%, 65.4wt%, 65.5wt%, 65.6wt%, 65.8wt%, 66wt%, 66.2wt%, 66.4wt%, 66.5wt%, 66.6wt%, 66.8wt%, 67wt%, etc., or other values ​​within the range of 64.4wt% to 67wt%.

[0040] The R mentioned above a T b X c M d-c Phase refers to the grain boundary phase formed by the combination of R element, T element, X element and M element, among which X c The total atomic content of Ni and Cu is c. The NdFeB magnet of the embodiment of the present application can be prepared by using waste NdFeB magnets. a T b X c M d-c The Ni in the phase usually comes from the coating of the scrap NdFeB magnet, and the Cu can come from at least one of the coating of the scrap NdFeB magnet, the substrate of the scrap NdFeB magnet, and the first alloy powder described below.

[0041] For example, R a T b X c M d-c The atomic content a of the R element of the phase can be 35at%, 38at%, 40at%, 42at%, 45at%, 48at%, 50at%, 52at%, 55at%, 58at%, 60at%, 62at%, 65at%, etc., or other values ​​within the range of 35at% to 65at%.

[0042] For example, R a T b X c M d-cThe atomic content b of the T element of the phase can be 30at%, 32at%, 35at%, 38at%, 40at%, 42at%, 45at%, 48at%, 50at%, 52at%, 55at%, 58at%, 60at%, etc., or other values ​​within the range of 30at% to 60at%.

[0043] For example, 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%, or other values ​​within the range of 5 at% to 10 at%. For example, c / d can be, for example, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, or other values ​​within the range of 0.6 to 1.

[0044] In the embodiment of the present application, c / d≥0.6, indicating that in R a T b X c M d-c Among the elements in the phase other than R and T, the sum of the atomic contents of Ni and Cu accounts for a relatively high proportion. Since Ni and Cu have relatively low melting points, this lowers the melting point of the grain boundary phase. The formation of this low-melting-point grain boundary phase allows Ni to concentrate in the grain boundary phase, inhibiting Ni from entering the main phase and improving magnet performance. Furthermore, this grain boundary phase has excellent wettability and boundary repair capabilities, creating a favorable diffusion channel that facilitates the subsequent diffusion of heavy rare earth elements.

[0045] In some embodiments, the Ni content in the main phase grains of the NdFeB magnet is 0-0.4 at%. For example, the Ni content in the main phase grains of the NdFeB 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 0-0.4 at%.

[0046] The Ni content in the main phase grains of the NdFeB magnet is 0~0.4at%, indicating that the main phase grains of the NdFeB magnet of the embodiment of the present application do not contain Ni element or contain only a small amount of Ni element, which further illustrates that the Ni element is mainly concentrated in the grain boundary phase, thereby preventing the Ni element from entering the main phase grains and interfering with the arrangement of the magnetic moments inside the grains, reducing the influence on the magnetization intensity of the main phase grains, and avoiding the abnormal growth of the main phase grains, so that the NdFeB magnet can maintain a relatively high coercive force and remanence level.

[0047] In other embodiments, the NdFeB magnet further includes oxygen, carbon, and nitrogen, wherein the oxygen content is [O], the carbon content is [C], and the nitrogen content is [N], and satisfies 500ppm≤[O]≤1600ppm, [C]≤1400ppm, and [N]≤400ppm.

[0048] For example, the [O] content of the NdFeB magnet can be 500ppm, 600ppm, 700ppm, 800ppm, 900ppm, 1000ppm, 1100ppm, 1200ppm, 1300ppm, 1400ppm, 1500ppm, 1600ppm, or any value within a range thereof. Controlling the oxygen content of the NdFeB magnet within the range of 500ppm to 1600ppm helps prevent primary phase grain growth, control primary phase size, and thus ensure the magnetic properties of the NdFeB magnet.

[0049] For example, the [C] of the NdFeB magnet can be 1400ppm, 1300ppm, 1200ppm, 1100ppm, 1000ppm, 950ppm, 900ppm, 850ppm, 800ppm, 750ppm, 700ppm, 650, 600ppm, 550ppm, 500ppm, 450ppm, 400ppm, 350ppm, 300ppm, 250ppm, 200ppm, 150ppm, 100ppm, 50ppm, 0ppm, or other values ​​below 1400ppm. Controlling the carbon content of the NdFeB magnet below 1400ppm is beneficial to avoiding the formation of excessive carbides, thereby helping to ensure the magnetic properties of the NdFeB magnet.

[0050] For example, the [N] of the NdFeB magnet can be 400 ppm, 350 ppm, 300 ppm, 250 ppm, 200 ppm, 150 ppm, 100 ppm, 50 ppm, 0 ppm, or other values ​​below 400 ppm. Controlling the nitrogen content of the NdFeB magnet below 400 ppm helps avoid the formation of excessive nitrides, thereby helping to ensure the magnetic properties of the NdFeB magnet.

[0051] In yet other embodiments, R may further include a heavy rare earth element, and within a microstructural observation plane at any depth within a range of 0.1 to 100 μm below at least one surface perpendicular to the orientation direction of the NdFeB magnet, the main phase grains have a heavy rare earth shell, and the heavy rare earth element content in the heavy rare earth shell 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.

[0052] Illustratively, on the microstructure observation surface at any of the above-mentioned depths, the content of heavy rare earth elements in the heavy rare earth shell can be 2.5at%, 2.6at%, 2.7at%, 2.8at%, 2.9at%, 3.0at%, 3.1at%, 3.2at%, 3.3at%, 3.4at%, 3.5at%, 3.6at%, 3.7at%, 3.8at%, 3.9at%, 4.0at%, 4.1at%, 4.2at%, 4.3at%, 4.4at%, 4.5at%, etc., or other values ​​within the range of 2.5at% to 4.5at%.

[0053] The at least one surface perpendicular to the orientation direction of the NdFeB magnet may include one or more surfaces. The 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.

[0054] From the above description, it can be understood that, in some embodiments of the NdFeB magnet of the present application, within the depth range of 0.1~100μm below at least one surface perpendicular to its orientation direction, in the microstructure observation plane at any depth, the main phase grains include a heavy rare earth shell, and the heavy rare earth shell has a high content of heavy rare earth elements, indicating that the heavy rare earth elements penetrate relatively smoothly from the orientation plane of the magnet into the interior of the magnet, which is beneficial to improving the coercive force of the NdFeB magnet.

[0055] In order to facilitate the understanding of the NdFeB magnets of the present application, Figure 1 The preparation method of the above-mentioned NdFeB magnet is described in detail.

[0056] Figure 1 An exemplary flow chart of a method for preparing a NdFeB magnet according to an embodiment of the present application is shown. Figure 1 As shown in, the preparation method 100 may include: in step S102, obtaining a first alloy powder, wherein the median particle size D50 of the first alloy powder is 3.8μm~4.3μm, and 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, and Nb; in step S104, subjecting a waste NdFeB magnet including a nickel coating or a nickel-copper coating to a second hydrogen crushing, screening treatment and a second air flow milling in sequence to obtain a second alloy powder, wherein the median particle size D50 of the second alloy powder is controlled to be 4.0μm~4.5μm, and the Ni content in the second alloy powder is controlled to be 0.05wt%~0.2wt%; in step S106, the mixed powder consisting of the first alloy powder and the second alloy powder is subjected to a molding treatment, a sintering treatment and an aging treatment to obtain a NdFeB magnet.

[0057] For example, 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, 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 the pulverization operation.

[0058] For example, 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, 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 pulverizing with the second jet mill.

[0059] For example, 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.

[0060] By controlling the median particle size D50 of the first alloy powder and the median particle size D50 of the second alloy powder to be both in the micron level, 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 suppress the abnormal growth of grains during the sintering process, thereby controlling the grain size of the main phase, and increasing the amount of grain boundary phase in the NdFeB magnet prepared from the mixed powder, thereby facilitating the Ni element in the first alloy powder to enter the grain boundary phase rather than the main phase grains, thereby making it easier to generate R a T b X c M d-c At the same time, by using a first alloy powder that does not contain Ni and controlling the Ni content of the second alloy powder within a reasonable range, it is helpful to control the Ni content in the mixed powder. In addition, under the synergistic effect of controlling the median particle size D50 of the first alloy powder and the median particle size D50 of the second alloy powder, the entry of Ni into the main phase grains is further reduced, and Ni is promoted to combine with elements such as R and T to form grain boundary phases.

[0061] In some embodiments, the preparation method 100 may also include: preparing a NdFeB alloy quick-setting sheet from a predetermined first alloy raw material; performing a first hydrogen crushing on the NdFeB alloy quick-setting sheet to obtain a first alloy coarse powder, and controlling the oxygen content [O] of the first alloy coarse powder to be 500ppm~1100ppm; performing a first air flow mill crushing on the first alloy coarse powder to obtain a first alloy powder.

[0062] In other embodiments, the first alloy raw material may include the following components: R: 28wt%~31.5wt%, B: 0.86wt%~1.05wt%, M: 0.3wt%~3wt%, Cu: 0.1wt%~0.55wt%, T: 64.5wt%~70wt%; 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, and Nb.

[0063] For example, the mass content of the R element in the first alloy raw material can be, for example, 28 wt%, 28.5 wt%, 29 wt%, 29.5 wt%, 30 wt%, 30.5 wt%, 31 wt%, 31.5 wt%, or other values ​​within the range of 28 wt% to 31.5 wt%.

[0064] Illustratively, the mass content of the B element in the first alloy raw material 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%.

[0065] Illustratively, the mass content of the M element in the first alloy raw material can 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%, or other values ​​within the range of 0.3 wt% to 3 wt%.

[0066] Illustratively, the mass content of the Cu element in the first alloy raw material 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%, 0.55 wt%, or other values ​​within the range of 0.1 wt% to 0.55 wt%.

[0067] Illustratively, the mass content of the T element 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%, or other values ​​within the range of 64.5 wt% to 70 wt%.

[0068] Neodymium iron boron alloy quick-setting sheet is a thin sheet of alloy material, which is made from a first alloy raw material through a quick-setting process. In some embodiments, the first alloy raw material with a predetermined configuration can be placed in a vacuum induction furnace, and the NdFeB alloy quick-setting sheet can be prepared through smelting and quick-setting treatment; wherein the vacuum degree of the vacuum induction furnace can be controlled to 10 -2 ~10 2 Pa, the melting temperature can be controlled to 1300°C to 1500°C, and the casting temperature can be controlled to 1400°C to 1500°C for rapid solidification. In other embodiments, the thickness of the prepared NdFeB alloy rapid solidification sheet is 0.2 to 0.5 mm.

[0069] 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 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 of any of the above values. Exemplarily, the thickness of the NdFeB alloy quick-setting sheet is 0.20mm, 0.25mm, 0.30mm, 0.35mm, 0.40mm, 0.45mm, 0.50mm, or any value within the range of any of the above values.

[0070] In other embodiments, the NdFeB alloy quick-setting sheet is subjected to a first hydrogen pulverization to obtain a first alloy coarse powder, and the oxygen content [O] of the first alloy coarse powder is controlled to be 500ppm~1100ppm. The hydrogen pulverization process generally includes hydrogenation (or hydrogen absorption), pulverization, and dehydrogenation. In the first hydrogen pulverization process of the embodiment of the present application, the hydrogen absorption pressure can be 0.1Mpa~0.5Mpa, the dehydrogenation temperature can be 400℃~600℃, and after dehydrogenation, an inert gas is introduced to bring the pressure in the system to 50kPa~70kPa, and the charging time is 1min~10min, so that the oxygen content [O] of the first alloy coarse powder can be controlled to be within the range of 500ppm~1100ppm. Other process conditions in the first hydrogen pulverization can be conventional settings, such as the hydrogen absorption temperature can be, for example, 300℃~600℃, and the dehydrogenation pressure can be, for example, 0.1Mpa~0.5Mpa.

[0071] Illustratively, the oxygen content [O] of the first alloy coarse powder may 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.

[0072] Illustratively, the hydrogen absorption pressure may 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.

[0073] Illustratively, 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.

[0074] Exemplarily, the inflation time may 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.

[0075] By controlling the oxygen content [O] of the first alloy coarse powder within the range of 500ppm to 1100ppm, the oxygen content of the NdFeB magnet produced from the mixed powder can be controlled, thereby reducing the problem of excessive oxides forming within the NdFeB magnet due to excessive oxygen content, which in turn affects the magnet's performance. Specifically, these oxides can destroy the main phase grain structure of the NdFeB magnet, reducing the magnetic moment of the main phase grains, thereby reducing the magnet's remanence. They can also disrupt the continuity and uniformity of the grain boundary phase, reducing the wettability and diffusion ability of the grain boundary phase, thereby reducing the coercive force.

[0076] In some embodiments, the first alloy coarse powder is subjected to a first jet mill to obtain a first alloy powder. In other embodiments, during the first jet mill, 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 can be controlled to be 0 to 200 ppm, and the speed of the jet mill classifying wheel can be controlled to be 2800 rpm to 3200 rpm, so as to control the median particle size D50 of the first alloy powder to be within the range of 3.8 μm to 4.3 μm.

[0077] Illustratively, during the first air flow mill pulverization, the grinding chamber pressure of the air flow mill can be controlled to 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.

[0078] Illustratively, the grinding chamber oxygen content 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.

[0079] For example, the rotational speed of the classifying wheel of the air jet mill in the first air 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.

[0080] In some other embodiments, in the screening process of step S104, a screen with a mesh size 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 after passing through the screen is subjected to a second air flow mill to control the Ni content in the second alloy powder to be within the range of 0.05 wt% to 0.2 wt%. The mesh size refers to the number of holes per square centimeter. For example, the mesh size of the screen can be 7 mesh, 8 mesh, 9 mesh, 10 mesh, 11 mesh, 12 mesh, 13 mesh, 14 mesh, 15 mesh, 16 mesh, 17 mesh, 18 mesh, 19 mesh, 20 mesh, 21 mesh, 22 mesh, 23 mesh, 24 mesh, 25 mesh, 26 mesh, 27 mesh, 28 mesh, 29 mesh, or 30 mesh.

[0081] The second hydrogen pulverization process allows the substrate and coating of the waste NdFeB magnets to be at least partially separated. In other words, at least a portion of the coating can be peeled off from the substrate surface in the form of flakes. A sieve with an appropriately selected mesh size is then used for screening, so that the peeled coating flakes remain on the sieve, while a smaller particle size of powder, primarily composed of the substrate components, passes through the sieve and becomes the undersize, or second alloy coarse powder, after passing through the sieve. This effectively reduces the content of the coating components in the second alloy coarse powder after passing through the sieve.

[0082] In some embodiments, the Cu content in the second alloy powder can be controlled to be 0.1wt%~0.35wt% through screening. Since the screening process can effectively reduce the content of the coating component in the second alloy coarse powder after passing through the screen, when the waste NdFeB magnet contains a nickel-copper coating, the screening process can also help control the Cu content in the second alloy coarse powder after passing through the screen, thereby achieving control of the Cu content in the second alloy powder. For example, the Cu content in the second alloy powder can be controlled to be 0.1wt%, 0.12wt%, 0.15wt%, 0.18wt%, 0.2wt%, 0.22wt%, 0.25wt%, 0.28wt%, 0.3wt%, 0.32wt%, 0.35wt%, etc., or other values ​​within the range of 0.1wt%~0.35wt%.

[0083] 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, thereby obtaining a second alloy coarse powder. Other process conditions of the second hydrogen pulverization can be conventional settings, 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.

[0084] Illustratively, the dehydrogenation temperature of 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.

[0085] Illustratively, the hydrogen absorption temperature of 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.

[0086] In other embodiments, the grinding chamber pressure of the jet mill in the second jet mill is 0.5 MPa~0.6 MPa, and the speed of the jet mill classifying wheel is 2700 r / min~3100 r / min, so as to control the median particle size D50 of the second alloy powder in the range of 4.0 μm~4.5 μm.

[0087] Illustratively, during the second air flow mill pulverization, the grinding chamber pressure of the air flow 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.

[0088] For example, the rotational speed of the classifying wheel of the air jet mill in the second air jet mill 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.

[0089] In some embodiments, the substrate of the waste NdFeB magnet may include the following components: R: 28wt%~31.5wt%; B: 0.86wt%~1.05wt%, M1: 0.3wt%~3wt%, T: 64.5wt%~70wt%; wherein R is a rare earth element, R includes Pr and Nd; M1 includes at least one of Al, Cu, Ga, Ti, Sn, Zr, and Nb; T includes Fe and / or Co.

[0090] It is understood that the base material of scrap NdFeB magnets is not limited to the composition described in this embodiment, and scrap NdFeB magnets of other compositions can also be recycled based on actual needs. In some preferred embodiments, a first alloy raw material with a composition similar to that of the base material of the scrap NdFeB magnets can be used to prepare a first alloy powder, which can be mixed with a second alloy powder with a similar composition, so that the composition of the NdFeB magnets prepared from the mixed powder is within a controllable range.

[0091] Furthermore, in some other embodiments, the preparation method 100 may further include: in step S106, the first alloy powder and the second alloy powder may be mixed in a mass ratio of 1:(1-3) to obtain the mixed powder. For example, the mass ratio of the first alloy powder to the second alloy powder may be 1:1, 1:1.5, 1:2, 1:2.5, 1:3, etc., or other values ​​within the range of 1:(1-3).

[0092] By mixing the first alloy powder and the second alloy powder in a mass ratio of 1:(1-3), one mass of the first alloy powder can be used to recycle multiple masses of waste NdFeB magnets, thereby achieving effective utilization of waste NdFeB magnets.

[0093] In some other embodiments, the vacuum degree in the sintering device can be controlled to be 10 -2 Pa ~10 2 In some embodiments, the sintering temperature of the sintering process may be 1000° C. to 1100° C., and the sintering time may be 4 h to 10 h. For example, the sintering temperature may 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., or other values ​​within the range of 1000° C. to 1100° C. For example, the sintering time may be 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, or other values ​​within the range of 4 h to 10 h.

[0094] In other embodiments, the aging temperature of the aging treatment can be 400°C to 500°C, and the aging time can be 4h to 10h. Aging treatment refers to a process in which a material is kept warm at a specific temperature for a long time to improve its structure and performance. For example, in the embodiment 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. For example, 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.

[0095] In some other embodiments, the aging treatment may include a primary aging treatment and a secondary aging treatment, wherein the primary aging treatment temperature is 850°C to 950°C, the primary aging treatment time is 2 hours to 6 hours, and the secondary aging treatment temperature is 450°C to 650°C, and the secondary aging treatment time is 3 hours to 10 hours. For example, the primary aging treatment temperature may 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, or other values ​​within the range of 850°C to 950°C. For example, the primary aging treatment time may be, for example, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, or other values ​​within the range of 2 hours to 6 hours. Illustratively, 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. Illustratively, the secondary aging treatment time is 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, etc., or other values ​​within the range of 3 h to 10 h.

[0096] In some other embodiments, the mixed powder composed of the first alloy powder and the second alloy powder can first undergo a forming process and / or an isostatic pressing process, and then undergo a sintering process and an aging process. The forming process refers to the process of pressing the mixed powder into a blank of the desired shape and size through a specific mold and a pressure device. The isostatic pressing process refers to a forming process in which a uniform pressure is applied to the blank using a liquid or gas as a pressure transmission medium. Compared with conventional pressing, the isostatic pressing process can ensure that the blank is subjected to uniform pressure in all directions, thereby improving the density uniformity and dimensional accuracy of the blank.

[0097] In some embodiments, the preparation method 100 may further include: applying a heavy rare earth slurry to 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 axis (i.e., the crystallographic C axis) 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 opposing surfaces). The surface perpendicular to the orientation direction of the NdFeB magnet may be referred to as an orientation plane. That is, in this embodiment, the heavy rare earth slurry may be applied to one or more orientation planes of the NdFeB magnet so that the heavy rare earth slurry diffuses along the orientation direction of the NdFeB magnet.

[0098] In other embodiments, the heat treatment includes a diffusion process and a tempering process in sequence; the diffusion process has a diffusion temperature of 800°C to 950°C and a diffusion time of 5 hours to 20 hours; the tempering process has a tempering temperature of 450°C to 550°C and a tempering time of 3 hours to 8 hours. For example, the diffusion temperature can be, for example, 800°C, 820°C, 850°C, 880°C, 900°C, 920°C, 950°C, or other values ​​within the range of 800°C to 950°C. For example, the diffusion time is 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, or any value within the range of 5 hours to 20 hours.

[0099] For example, the tempering temperature may be 450° C., 460° C., 470° C., 480° C., 490° C., 500° C., 510° C., 520° C., 530° C., 540° C., 550° C., or other values ​​within the range of 450° C. to 550° C. For example, the tempering time may be 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, or other values ​​within the range of 3 h to 8 h.

[0100] In some embodiments, the heavy rare earth slurry may include 75wt% to 84wt% of a compound containing a heavy rare earth element, 15wt% to 24wt% of an organic solvent, and 0.1wt% to 5wt% of a binder. In other embodiments, the organic solvent is selected from ethanol and / or acetone. In yet 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 a heavy rare earth element alloy. In other embodiments, the heavy rare earth element includes one or more of Dy and Tb.

[0101] Combination of the above Figure 1An exemplary description of the preparation method of the NdFeB magnet according to the embodiment of the present application is given. It can be understood that the embodiment of the present application achieves the control of the Ni content in the recycled magnet within a controllable range by mixing a first alloy powder and a second alloy powder obtained by utilizing 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, and promotes the Ni element to enter the grain boundary phase of the recycled magnet, while avoiding or reducing the Ni element from entering the main phase grains of the recycled magnet as much as possible.

[0102] The NdFeB magnet prepared according to the embodiment of the present application can not only make the Ni element absent or present within a controllable range in the main phase grains (i.e., the Ni content in the main phase grains is 0-0.4at%), thereby avoiding or reducing the influence of the Ni element on the magnet properties (such as coercive force 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 helps lower the melting point of the grain boundary phase, giving it good wettability and boundary repair capabilities, helping to improve diffusion channel obstructions caused by impurity elements that may be present in the recycled magnet, thereby constructing a good diffusion channel and facilitating subsequent diffusion using heavy rare earth slurry. Compared to magnets recycled through the stripping process, the NdFeB magnets prepared in the embodiments of this application have significantly improved diffusion increments after heavy rare earth element diffusion, with the coercive force increase after diffusion reaching approximately 5000Oe to 7000Oe.

[0103] Furthermore, the preparation method of the embodiment of the present application can also control the oxygen content of the recovered magnet by controlling the oxygen content of the first alloy coarse powder, thereby further ensuring the structure and size of the main phase grains in the prepared NdFeB magnet, as well as the proportion, continuity and uniformity of the grain boundary phase 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, which is more conducive to the magnetic properties of the NdFeB magnet.

[0104] It can also be understood that, by controlling the process conditions in the preparation method of the embodiment of the present application, the first alloy raw material close to the base material composition of the waste NdFeB magnet can be used to prepare the first alloy powder in the embodiment of the present application, without the need to use rare earth phase-rich alloy powder (i.e., alloy powder with a higher 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.

[0105] Examples and Comparative Examples:

[0106] The raw material compositions of all 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 remainder and is not listed in Table 1. Since the raw materials of Examples 4 and 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 Examples 4, 5, Comparative Example 2, and Comparative Example 4 are not shown in Table 1.

[0107] The key process parameters of all embodiments and comparative examples are shown in Table 2. The performance test results of the magnet samples of each embodiment 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 embodiment and comparative example are shown in Table 4. Figure 2 A scanning electron microscope photograph of Example 1 of the present application is shown. Figure 3 A scanning electron microscope photograph of Example 4 of the present application is shown.

[0108] Example 1:

[0109] The prepared first alloy raw material is cast through a rapid solidification process to obtain NdFeB alloy rapid solidification sheets. The NdFeB alloy rapid solidification sheets are subjected to a first hydrogen pulverization process to obtain a first alloy coarse powder. The first alloy coarse powder is subjected to a first air flow mill to obtain a first alloy powder. The hydrogen absorption pressure of the first hydrogen pulverization process is 0.3 MPa, the dehydrogenation temperature is 560°C, and after dehydrogenation, an inert gas is filled to 60 kPa for 5 minutes. During the first air flow milling process, the grinding chamber pressure of the air flow mill is 0.68 MPa, the oxygen content in the grinding chamber is controlled at 80 ppm, the air flow mill classifying wheel speed is 3100 r / min, and the average particle size D50 of the first alloy powder is 4.0 μm. Waste NdFeB magnets including nickel-copper plating are subjected to a second hydrogen pulverization process, screening with a 20-mesh screen, and a second air flow milling process to obtain a second alloy powder. The second hydrogen pulverization process involved a hydrogen absorption pressure of 0.35 MPa and a dehydrogenation temperature of 550°C. After dehydrogenation, the inert gas was filled to 70 kPa for 5 minutes. During the second jet mill pulverization process, the grinding chamber pressure was 0.6 MPa, the oxygen content in the grinding chamber was controlled at 120 ppm, and the classifying wheel speed was 2900 rpm. The average particle size (D50) of the second alloy powder was 4.2 μm.

[0110] A mixed powder is prepared by mixing a first alloy powder and a second alloy powder in a mass ratio of 1:1. The mixed powder is then formed, sintered, and aged to obtain a NdFeB magnet. The sintering temperature is 1060°C for 6 hours, and the aging treatment is divided into two stages: a primary aging treatment at 900°C for 6 hours, and a secondary aging treatment at 500°C for 6 hours.

[0111] Example 2:

[0112] The prepared first alloy raw material is cast through a rapid solidification process to obtain NdFeB alloy rapid solidification sheets, which are then subjected to a first hydrogen crushing process to obtain a first alloy coarse powder, which is then subjected to a first air flow milling process to obtain a first alloy powder. The hydrogen absorption pressure of the first hydrogen crushing process is 0.3 MPa, the dehydrogenation temperature is 560°C, and after dehydrogenation, an inert gas is introduced to a pressure of 60 kPa for 5 minutes. During the first air flow milling process, the grinding chamber pressure of the air flow mill is 0.68 MPa, the oxygen content in the grinding chamber is controlled at 80 ppm, the classifying wheel speed of the air flow mill is 3200 r / min, and the average particle size D50 of the first alloy powder is 3.8 μm.

[0113] Scrap NdFeB magnets, including nickel plating, were subjected to a second hydrogen pulverization, followed by screening with a 30-mesh screen, and a second jet milling process to produce a second alloy powder. The hydrogen absorption pressure during the second hydrogen pulverization process was 0.35 MPa, the dehydrogenation temperature was 550°C, and after dehydrogenation, the air was filled with inert gas to 70 kPa for 5 minutes. During the second jet milling process, the grinding chamber pressure was 0.6 MPa, the oxygen content in the grinding chamber was controlled at 120 ppm, and the classifier wheel speed was 3000 r / min. The average particle size D50 of the second alloy powder was 4.0 μm.

[0114] A mixed powder is prepared by mixing the first alloy powder and the second alloy powder in a mass ratio of 1:2. The mixed powder is then formed, sintered, and aged to obtain a NdFeB magnet. The sintering temperature is 1060°C for 6 hours, and the aging treatment is divided into two stages: a primary aging treatment at 900°C for 6 hours, and a secondary aging treatment at 500°C for 6 hours.

[0115] Example 3:

[0116] The prepared first alloy raw material is cast through a rapid solidification process to obtain NdFeB alloy rapid solidification sheets, which are then subjected to a first hydrogen crushing process to obtain a first alloy coarse powder. The first alloy coarse powder is then subjected to a first air flow mill to obtain a first alloy powder. The hydrogen absorption pressure of the first hydrogen crushing process is 0.3 MPa, the dehydrogenation temperature is 560°C, and after dehydrogenation, an inert gas is introduced to a pressure of 60 kPa for 5 minutes. During the first air flow milling process, the grinding chamber pressure of the air flow mill is 0.68 MPa, the oxygen content in the grinding chamber is controlled at 80 ppm, the classifying wheel speed of the air flow mill is 2800 r / min, and the average particle size D50 of the first alloy powder is 4.3 μm.

[0117] Scrap NdFeB magnets, including nickel-copper plating, were subjected to a second hydrogen pulverization, followed by screening with a 30-mesh screen, and a second jet milling process to produce a second alloy powder. The hydrogen absorption pressure during the second hydrogen pulverization process was 0.35 MPa, the dehydrogenation temperature was 550°C, and after dehydrogenation, inert gas was introduced to 70 kPa for 5 minutes. During the second jet milling process, the grinding chamber pressure was 0.6 MPa, the oxygen content in the grinding chamber was controlled at 120 ppm, and the classifier wheel speed was 2700 rpm. The average particle size (D50) of the first alloy powder was 4.5 μm. The mesh size of the screening process was 20 mesh.

[0118] A mixed powder is prepared by mixing the first alloy powder and the second alloy powder in a mass ratio of 1:3. The mixed powder is then formed, sintered, and aged to obtain a NdFeB magnet. The sintering temperature is 1060°C for 6 hours, and the aging treatment is divided into two stages: a first aging treatment temperature of 900°C for 6 hours, and a second aging treatment temperature of 500°C for 6 hours.

[0119] Example 4:

[0120] The NdFeB magnet prepared in Example 1 was machined to obtain a magnet matrix with a size of 9 mm×6 mm×3.8 mm (in the orientation direction).

[0121] A diffusion source containing the heavy rare earth element Dy is magnetron sputtered on at least one surface of a magnet substrate with an area of ​​9 mm × 6 mm, 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 hours (diffusion process), and then heat treated at 500°C for 6 hours (tempering process). The diffusion heat treatment is carried out in a vacuum atmosphere to obtain a diffused magnet, in which the weight gain of the heavy rare earth element is 0.6wt% of the magnet substrate.

[0122] Example 5:

[0123] The second alloy powder was prepared using the first alloy powder with the same raw material composition as in Example 1 and waste NdFeB magnets with the same composition. The differences were as follows: in the first hydrogen pulverization process, the hydrogen absorption pressure of the hydrogen pulverization was 0.35 MPa, the dehydrogenation temperature was 550°C, and after dehydrogenation, inert gas was filled to 20 kPa for 30 seconds.

[0124] Comparative Example 1:

[0125] A second alloy powder was prepared using a first alloy powder having the same raw material composition as in Example 1 and waste NdFeB magnets having the same composition. The difference was that the second alloy powder was prepared by stripping the coating of the waste NdFeB magnets and then subjected to air flow milling to obtain a second alloy powder with the same particle size as in Example 1.

[0126] Comparative Example 2:

[0127] The same diffusion process as in Example 4 was used, except that the diffused magnet substrate was the NdFeB magnet prepared in Comparative Example 1.

[0128] Comparative Example 3:

[0129] The second alloy powder was prepared using the first alloy powder having the same raw material composition as in Example 1 and waste NdFeB magnets having the same composition. The difference was that no screening process was performed in the preparation process of the second alloy powder.

[0130] Comparative Example 4:

[0131] A second alloy powder was prepared using the same raw material composition as in Example 1 and scrap NdFeB magnets with the same composition. The difference between the two powders was that during the first jet milling process, the grinding chamber pressure was 0.56 MPa, the classifying wheel speed was 2700 r / min, and the average particle size D50 of the first alloy powder was 4.4 μm. During the second jet milling process, the grinding chamber pressure was 0.5 MPa, the classifying wheel speed was 2800 r / min, and the average particle size D50 of the second alloy powder was 4.4 μm.

[0132] Test method:

[0133] The test methods used in this application are as follows:

[0134] (1) Ingredient testing method;

[0135] The composition and content of raw materials, powders and magnets were tested using ICP component analysis equipment.

[0136] (2) Grain boundary phase atomic content test method;

[0137] After magnet sample preparation, scanning electron microscopy (SEM) analysis was performed on any cross-section of the magnet perpendicular to the orientation direction. All primary and grain boundary phases within each microstructural cross-section were counted. The observation area dimensions were, for example, 40 μm × 40 μm and 75 μm × 75 μm, with a magnification of 2000–5000x. EDS (energy dispersive spectrometry) was used to analyze the atomic percentages of each element in the primary and grain boundary phases to determine the grain boundary phase composition.

[0138] (3) Median particle size test method;

[0139] The particle size distribution was measured using a German Sympatec laser particle size analyzer and the D50 was calculated.

[0140] (4) Magnet performance test method

[0141] The permanent magnet material precision measurement system NIM-62000TB is used to test the remanence, coercive force and squareness.

[0142] Table 1: Raw material composition

[0143]

[0144] Table 2: Process conditions

[0145]

[0146] Table 3: Performance test results

[0147]

[0148] Table 4: Test results of grain boundary phase composition, content of some elements in main phase grains and impurity content

[0149]

[0150] Combining Tables 1 to 4 above, we can see that:

[0151] R was generated in the magnet samples of Examples 1 to 5. a T b X c M d-c phase, and the Ni content in the main phase grains is below 0.4at%, resulting in good remanence, coercivity, and squareness, and excellent overall performance. Compared to Example 5, the [O] content of the first alloy coarse powder of Examples 1-4 is controlled within the range of 500ppm to 1100ppm, resulting in a lower [O] content in the prepared NdFeB magnets, and thus the NdFeB magnets of Examples 1-4 have even better magnetic properties.

[0152] Compared with Example 1, the rare earth loss caused by stripping and the organic matter that is inevitably brought in by the stripping result in higher [C] and [N] of the recovered magnet in Comparative Example 1. In addition, it is difficult to completely remove the Ni element of the coating in actual operation, and residual Ni elements still enter the main phase grains, which ultimately causes the magnetic properties of the magnet to deteriorate.

[0153] Comparing Example 4 with Comparative Example 2, the performance of Comparative Example 2 is lower. This is because the magnet substrate of Comparative Example 2 is made by a stripping process, which results in the loss of rare earth elements, and thus there is not enough Nd-rich phase and R a T b X c M d-c phase, which affects the diffusion effect.

[0154] Compared with Example 1, Comparative Example 3 is difficult to control the Ni content in the second alloy powder because no screening treatment is performed, resulting in a higher total Ni content in the recovered magnet, causing the Ni element to aggregate in the grain boundary phase and more Ni to enter the main phase, thereby deteriorating the magnet's remanence Br and coercive force Hcj and other properties.

[0155] Compared with Example 1, Comparative Example 4 uses a lower speed of the airflow mill classifying wheel, which makes the D50 of the first alloy powder larger and the same as the D50 of the second alloy powder, resulting in a poor synergistic effect after the two are mixed, and R a T b X c M d-c phase, more Ni elements enter the main phase grains, resulting in a decrease in the coercive force of the magnet.

[0156] In addition, from Figure 2 It can be seen that R is formed in the grain boundary phase of the NdFeB magnet prepared in Example 1. a T b X c M d-c Mutually. Figure 3 This is a scanning electron microscope photograph of the NdFeB magnet of Example 4 taken at a depth of 80 μm below the surface, perpendicular to the orientation direction. Figure 3 As can be seen from the figure, the main phase grains of the magnet after diffusion in Example 4 have a heavy rare earth shell. This shows that the NdFeB magnets prepared in the examples of the present application have good diffusion channels, which can achieve good diffusion of the heavy rare earth slurry along the orientation direction of the NdFeB magnet.

[0157] 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 sintered magnet, characterized in that: The NdFeB sintered magnet comprises the following components: R: 28wt%~31.5wt%, B: 0.86wt%~1.05wt%, Ni: 0.03wt%~0.15wt%, Cu: 0.1wt%~0.5wt%, Co: 0.5wt%~2wt%, M: 0.3wt%~3wt%, Fe: 64.4wt%~67wt%; Wherein, the NdFeB sintered magnet includes main phase grains and grain boundary phase, and the grain boundary phase includes R a T b X c M d-c phase, 35at%≤a≤65at%, 30at%≤b≤60at%, 5at%≤d≤10at%, 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, and Nb; X includes Ni and Cu; The Ni content in the main phase grains is 0.05at% to 0.4at%.

2. The NdFeB sintered magnet according to claim 1, wherein The NdFeB sintered magnet further comprises oxygen, carbon and nitrogen, wherein the oxygen content is [O], the carbon content is [C] and the nitrogen content is [N], and the following conditions are satisfied: 500ppm≤[O]≤1600ppm, [C]≤1400ppm and [N]≤400ppm.

3. The NdFeB sintered magnet according to claim 1 or 2, characterized in that: R also includes heavy rare earth elements, and In a microstructure observation plane at any depth within a range of 0.1 to 100 μm below at least one surface perpendicular to the orientation direction of the NdFeB sintered magnet, the main phase grains have a heavy rare earth shell, and the content of heavy rare earth elements in the heavy rare earth shell of the main phase grains is 2.5 at% to 4.5 at%; R further includes at least one of Dy and Tb.

4. A method for preparing a NdFeB sintered magnet according to any one of claims 1 to 3, characterized in that: The preparation method comprises: Obtaining a first alloy powder, wherein the first alloy powder has a median particle size D50 of 3.8 μm to 4.3 μm, and the first alloy powder comprises R, B, Cu, M, and T elements, wherein R is a rare earth element, R comprises Pr and Nd, T comprises Fe and / or Co, and M comprises at least one of Al, Ga, Ti, Sn, Zr, and Nb; performing a second hydrogen pulverization, a screening process, and a second jet mill pulverization on waste NdFeB magnets including a nickel coating or a nickel-copper coating to obtain a second alloy powder, wherein 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 %; The mixed powder consisting of the first alloy powder and the second alloy powder is subjected to a molding process, a sintering process and an aging process to obtain a NdFeB sintered magnet.

5. The preparation method according to claim 4, characterized in that The preparation method further comprises: Prepare a NdFeB alloy quick-setting sheet by using a first alloy raw material of predetermined configuration; performing a first hydrogen crushing on the NdFeB alloy quick-setting sheet to obtain a first alloy coarse powder, wherein the oxygen content [O] of the first alloy coarse powder is controlled to be 500 ppm to 1100 ppm; Grinding the first alloy coarse powder by a first jet mill to obtain the first alloy powder; Wherein, the first alloy raw material includes the following components: R: 28wt%~31.5wt%, B: 0.86wt%~1.05wt%, M: 0.3wt%~3wt%, Cu: 0.1wt%~0.55wt%, T: 64.5wt%~70wt%; Among them, 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.

6. The preparation method according to claim 4, characterized in that In the screening process, a sieve with a mesh size of 7 to 30 is used to screen the second alloy coarse powder obtained after the second hydrogen pulverization, and the second alloy coarse powder that passes through the sieve is subjected to a second air flow mill pulverization.

7. The preparation method according to any one of claims 4 to 6, characterized in that The preparation method further comprises: Through the screening process, the Cu content in the second alloy powder is controlled to be 0.1 wt% to 0.35 wt%.

8. The preparation method according to any one of claims 4 to 6, characterized in that The preparation method further comprises: The first alloy powder and the second alloy powder are mixed in 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 treatment is 1000°C to 1100°C, and the sintering time is 4h to 10h; The aging temperature of the aging treatment is 400°C to 500°C, and the aging time is 4h to 10h; The aging treatment includes primary aging treatment and secondary aging treatment, wherein the primary aging treatment temperature is 850° C. to 950° C., the primary aging treatment time is 2 h to 6 h, the secondary aging treatment temperature is 450° C. to 650° C., and the secondary aging treatment time is 3 h to 10 h.

9. The preparation method according to claim 4, characterized in that The preparation method further comprises: Applying a heavy rare earth slurry to at least one surface of the NdFeB sintered magnet perpendicular to its orientation direction, and then performing a heat treatment to obtain a diffused NdFeB sintered magnet; The heat treatment includes a diffusion process and a tempering process in sequence; the diffusion temperature of the diffusion process is 800-950° C., and the diffusion time is 5-20 hours; the tempering temperature of the tempering process is 450-550° C., and the tempering time is 3-8 hours.

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