A NdFeB magnet with high remanence and high coercivity and a method for preparing the same

Abstract

The present invention relates to a high remanence and high coercivity neodymium iron boron magnet, wherein the neodymium iron boron magnet comprises R2T 14 B main phase grains and grain boundary phase A; the NdFeB magnet includes R, M, B and Fe, R includes RL and RH, wherein RL includes at least one of Pr, Nd, La, Ce and Y, RH includes at least one of Dy, Tb, Gd and Ho, M includes Co and Cu and optional M', M' includes one or more of Cr, Ni, Ga, Al, Zr, Nb and Ti; the content of R in the grain boundary phase A is 29-55at%, the content of Co is 3-7at%, and the content of Cu is 7-20at%. The NdFeB magnet provided by the present invention has low impurity element content, effectively improves the diffusion depth of heavy rare earth elements, and has high coercivity and high remanence.

Description

Technical Field

[0001] The present invention belongs to the field of NdFeB magnets, and in particular relates to a NdFeB magnet with high remanence and high coercivity and a preparation method thereof. Background Art

[0002] Sintered NdFeB magnets are widely used in many fields such as automotive industry, medical equipment, electronic information, aerospace, etc. due to their excellent magnetic properties. In recent years, with the continuous improvement of the performance of sintered NdFeB magnets, its application fields are also expanding, and the requirements for magnet properties (such as magnetic properties and high temperature stability) are becoming higher and higher. One of the common methods for preparing high coercive force NdFeB magnets is to add heavy rare earth elements such as Dy, Tb, Ho, etc. to the magnet by grain boundary diffusion, that is, to arrange heavy rare earth elements on the surface of the magnet, and use the concentration difference of heavy rare earth on the surface and inside of the magnet as the diffusion power. The NdFeB magnets prepared by grain boundary diffusion have excellent comprehensive magnetic properties and consume a small amount of heavy rare earth. However, the diffusion depth of heavy rare earth elements in magnets produced by grain boundary diffusion process is limited, and as the thickness of the magnet increases, it is difficult for heavy rare earth elements to diffuse into the interior of the magnet, and the diffusion efficiency is low, resulting in limited improvement in the coercive force of the magnet and poor magnetic properties.

[0003] In addition, in order to improve the high temperature stability of the magnet, the prior art usually introduces the element Co into the NdFeB magnet. CN115346746A discloses that the prior art uses a diffusion source containing Co and other components such as light rare earth and / or heavy rare earth for composite grain boundary diffusion treatment. Since the enrichment of light rare earth and / or heavy rare earth in the grain boundary phase will hinder the Co element from continuing to penetrate into the grain boundary phase, so that the Co element rarely or almost does not enter the grain boundary phase, it is difficult to effectively improve the magnetic properties and temperature stability. Therefore, the patent uses M1-Co metal powder arranged on the surface of the magnet for diffusion to increase the content of the Co element in the grain boundary phase, improve the magnetic properties and temperature stability of the magnet. However, due to the absence of heavy rare earth elements in the diffusion source, the coercive force of the magnet is limited, which is difficult to meet the needs of high-performance magnets. Summary of the invention

[0004] The purpose of the present invention is to provide a NdFeB magnet with high remanence and high coercivity and a preparation method thereof. The NdFeB magnet prepared by the method provided by the present invention has low impurity element content, effectively improved diffusion depth of heavy rare earth elements, less remanence decrease, high coercivity and high squareness.

[0005] In order to achieve the above object, the present invention provides a NdFeB magnet in a first aspect, wherein the NdFeB magnet comprises R2T 14 B main phase grains and grain boundary phase A;

[0006] The NdFeB magnet includes R, M, B and Fe, R includes RL and RH, wherein RL includes at least one of Pr, Nd, La, Ce and Y, RH includes at least one of Dy, Tb, Gd and Ho, Fe is iron, B is boron, M includes Co, Cu and optionally M', wherein M' includes one or more of Cr, Ni, Ga, Al, Zr, Nb and Ti;

[0007] The content of R in the grain boundary phase A is 29-55 at%, the content of Co is 3-7 at%, and the content of Cu is 7-20 at%.

[0008] Optionally, M includes Ga, and the content of Ga in the grain boundary phase A is 2-11 at %.

[0009] Optionally, the NdFeB magnet satisfies one or more of the following conditions:

[0010] A. The impurities include one or more of C, N and O; the content of impurity elements in the NdFeB magnet is less than 1500ppm;

[0011] B. The N content in the NdFeB magnet is less than 200 ppm.

[0012] Optionally, the NdFeB magnet has an R content of 28.5-31wt%, an M content of 0.8-3wt%, a B content of 0.94-1.02wt%, and the remainder is iron and unavoidable impurities; and / or,

[0013] The NdFeB magnet has a Co content of 1-1.5 wt %, a Cu content of 0.15-0.3 wt %, a Ga content of 0.2-0.4 wt %, and a Zr and / or Ti content of 0.05-0.35 wt %.

[0014] Optionally, the D50 grain size of the main phase grains is 2.5-4 μm.

[0015] A second aspect of the present invention provides a method for preparing a neodymium iron boron magnet, wherein the method comprises:

[0016] S1, attaching the diffusion source to the surface of the NdFeB substrate to form a film layer;

[0017] S2, performing a first diffusion treatment and a second diffusion treatment on the NdFeB substrate with a film layer attached to the surface to obtain a magnet after diffusion treatment;

[0018] S3, tempering the magnet after the diffusion treatment to obtain a neodymium iron boron magnet;

[0019] Wherein, the NdFeB substrate includes R1, M1, B and Fe; R1 includes at least one of the rare earth elements Dy, Tb, Pr, Nd, Ce, La, Y, Ho and Gd, M1 includes Co and Cu and optionally M1', the M1' includes one or more of Cr, Ni, Ga, Al, Zr, Nb and Ti, the content of R1 in the NdFeB substrate is 28.5-31wt%, the content of M1 is 0.6-2.5wt%, the content of B is 0.94-1.02wt%, the content of Co is 0.5-2.5wt%, and the balance is Fe and impurity elements, the impurity elements include one or more of C, O and N; the content of impurity elements in the NdFeB substrate is less than 1500ppm, and the content of N is less than 200ppm;

[0020] The diffusion source includes RH1, M2 and R2, RH1 includes at least one of Dy, Tb and Ho, R2 includes at least one of rare earth elements Pr and Nd, M2 includes Co and optionally M2', and M2' includes one or more of Ga, Al and Cu; the content of RH1 in the diffusion source is 30-70wt%, the content of M2 is 5-30wt%, the content of R2 is 20-50wt%, and the content of Co is 1-15wt%;

[0021] The temperature of the second diffusion treatment is 840-880°C, and the holding time is 4-20h; the ratio of the temperature of the first diffusion treatment to the temperature of the second diffusion treatment is 1.01-1.08, and the ratio of the holding time of the first diffusion treatment to the holding time of the second diffusion treatment is 0.1-0.3.

[0022] Optionally, the method satisfies one or more of the following conditions:

[0023] The content of R1 in the NdFeB substrate is 29.5-30.5wt%, the content of M1 is 0.6-1.5wt%, the content of B is 0.96-1.0wt%, and the balance is Fe and impurity elements;

[0024] The content of Dy in the NdFeB substrate is 2-4wt%;

[0025] The NdFeB substrate has a Co content of 1-1.5 wt %, a Cu content of 0.1-0.3 wt %, a Ga content of 0.1-0.5 wt %, and a Zr and / or Ti content of 0.05-0.35 wt %.

[0026] Optionally, the method satisfies one or more of the following conditions: before step S3, step S2 is repeated to obtain the magnet after the diffusion treatment;

[0027] The total number of times step S2 is performed is 2 to 8 times.

[0028] Optionally, the method further comprises: sequentially performing a molding process and a sintering process on the NdFeB raw alloy powder to obtain the NdFeB substrate;

[0029] The D50 particle size of the NdFeB raw alloy powder is 2-5 μm;

[0030] The molding process is an oriented pressing molding process, and the oriented pressing molding process is performed under the condition that the oriented magnetic induction intensity is 1.8~2.3T;

[0031] The sintering process includes a first-stage sintering process and a second-stage sintering process. The temperature of the first-stage sintering process is 750-980°C and the sintering time is 8-10 hours. The temperature of the second-stage sintering process is 1000-1080°C and the sintering time is 8-12 hours. The vacuum degree of the sintering process is 10 -5 ~10 -2 Pa; the density of the NdFeB substrate obtained by sintering is 7.5~7.8g / cm 3 .

[0032] Optionally, in S1, the weight gain of the NdFeB substrate with the film layer attached to the surface is 0.5-1.5%;

[0033] The content of RH1 in the diffusion source is 45-65wt%, the content of M2 is 10-20wt%, and the content of R2 is 30-40wt%; the content of Co in the diffusion source is 5-10wt%.

[0034] Optionally, the method satisfies one or more of the following conditions: in step S3, the tempering treatment temperature is 450-690° C., and the holding time is 0.5-4 h.

[0035] The third aspect of the present invention provides a neodymium iron boron magnet prepared by the method described in the second aspect of the present invention.

[0036] Through the above technical scheme, the present invention uses a NdFeB substrate with a low content of impurity elements (C, N, O), reduces the combination of R elements and impurity elements, effectively avoids the generation of secondary phases outside the main phase grains, ensures that the substrate has a smooth diffusion channel, and helps to improve the diffusion depth of heavy rare earth elements (such as Dy and Tb) in subsequent diffusion treatment. At the same time, the composition of the diffusion source is reasonably designed, the content of R2, Co and M2 is controlled, and the eutectic temperature of the R-Fe system is reduced, which can effectively promote the diffusion, effectively improve the diffusion depth, and promote the element Co to penetrate deeper into the grain boundary phase; and R2, especially the addition of element Pr, can effectively reduce the eutectic point / melting point, which can not only ensure that the light rare earth elements and low melting point elements contained in the diffusion source further optimize the grain boundary structure of the NdFeB substrate during the diffusion process, but also provide a diffusion concentration gradient of heavy rare earth elements, promote the diffusion of heavy rare earth elements inside the substrate, and improve the diffusion depth of heavy rare earth. The method of the present invention adopts a segmented diffusion process to diffuse the substrate, wherein the first diffusion treatment adopts a high-temperature short-time heat treatment, which can form a uniform heavy rare earth shell on the surface of the main phase grains, effectively avoiding a large number of heavy rare earth elements from being retained on the surface of the main phase, and effectively promoting the diffusion of heavy rare earth elements and element Co into the interior of the magnet; and the second diffusion treatment adopts a low-temperature long-time heat treatment, which can further promote the diffusion of heavy rare earth elements into the interior of the magnet, effectively control the diffusion rate, and further improve the uniformity of the diffusion; in addition, the present invention repeats the above-mentioned segmented diffusion process multiple times, the purpose of which is to further improve the diffusion of heavy rare earth elements to the center of the magnet and the uniformity of the diffusion according to the composition of the substrate and the diffusion source provided by the present invention, and can effectively control the main phase grain size, thereby improving the coercive force of the magnet. The NdFeB magnet prepared by the method provided by the present invention can generate a grain boundary phase A in the grain boundary phase, so that the elements Co and Cu are enriched in the grain boundary phase, the influence of the anti-shell layer on the diffusion depth of the heavy rare earth element during the diffusion process is reduced, and the magnetic properties are improved; in addition, the grain boundary phase A is evenly distributed along the grain boundary, which can inhibit the abnormal growth of grains and prevent the phenomenon that the magnetic properties of the NdFeB magnet decrease due to the abnormal growth of grains, thereby effectively improving the diffusion depth of the heavy rare earth element and having a good diffusion effect, so that the prepared NdFeB magnet has high coercive force, high remanence and high squareness.

[0037] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention but do not constitute a limitation of the present invention. In the accompanying drawings:

[0039] Figure 1 This is a SEM image of the microstructure of the NdFeB magnet of Example 1 of the present invention.

[0040] Figure 2 This is an EPMA detection image of the Dy element of the NdFeB magnet of Example 1 of the present invention at a distance of 500 μm from the diffusion surface. DETAILED DESCRIPTION

[0041] The specific implementation of the present disclosure is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described herein is only used to illustrate and explain the present disclosure, and is not used to limit the present disclosure.

[0042] The present disclosure provides a neodymium iron boron magnet in a first aspect, wherein the neodymium iron boron magnet comprises R2T 14 B main phase grains and R-containing grain boundary phase, the R-containing grain boundary phase includes grain boundary phase A; the NdFeB magnet includes R, M, B and Fe, R includes RL and RH, wherein RL includes at least one of Pr, Nd, La, Ce and Y, RH includes at least one of Dy, Tb, Gd and Ho, Fe is iron, B is boron, the M includes Co, Cu and optionally M', the M' includes one or more of Cr, Ni, Ga, Al, Zr, Nb and Ti; the content of R in the grain boundary phase A is 29-55at%, the content of Co is 3-7at%, and the content of Cu is 7-20at%, wherein the diffusion depth of the RH heavy rare earth elements in the NdFeB magnet is above 500μm.

[0043] The present invention reasonably designs the components of the substrate and the diffusion source, so that the R-containing grain boundary phase in the NdFeB magnet provided by the present invention includes the grain boundary phase A, and the grain boundary phase A is evenly distributed along the grain boundary, which can inhibit the abnormal growth of grains and prevent the phenomenon that the magnetic properties of the NdFeB magnet decrease due to the abnormal growth of grains; in addition, due to the enrichment of Co and Cu in the grain boundary phase, the eutectic temperature of the R-Fe system is reduced, which can effectively promote the diffusion and effectively increase the diffusion depth, so that the diffusion depth of the heavy rare earth elements in the NdFeB magnet can reach more than 500μm. The remanence of the magnet provided by the present invention decreases less, and it has high coercive force and high squareness.

[0044] In the present disclosure, the diffusion depth refers to the distribution of the heavy rare earth element RH in the grain boundary phase region more than 500 μm from the surface of the NdFeB magnet.

[0045] In a specific implementation manner, M includes Ga, and the content of Ga in the grain boundary phase A is 2-11 at %.

[0046] In a specific embodiment, the impurities include one or more of C, N and O; the content of impurity elements in the NdFeB magnet is less than 1500ppm; and the content of N is less than 200ppm. The NdFeB magnet provided by the present disclosure has a low content of impurity elements, and it is difficult for the R element to combine with the impurity elements separately, which effectively avoids the formation of secondary phases outside the main phase grains, and helps to increase the diffusion depth of heavy rare earth elements (such as Dy and Tb).

[0047] In a specific implementation manner, the content of R in the NdFeB magnet is 28.5-31wt%, the content of M is 0.8-3.0wt%, the content of B is 0.94-1.02wt%, and the balance is iron and unavoidable impurities.

[0048] In a specific embodiment, the Co content in the NdFeB magnet is 1-1.5wt%, the Cu content is 0.15-0.3wt%, the Ga content is 0.2-0.4wt%, and the Zr and / or Ti content is 0.05-0.35wt%. In the above embodiment, when the NdFeB magnet contains Zr and Ti, the total content of Zr and Ti in the NdFeB magnet is 0.1-0.35wt%; when the NdFeB magnet does not contain Ti, the Zr content in the NdFeB magnet is 0.05-0.3wt%; when the NdFeB magnet does not contain Zr, the Ti content in the NdFeB magnet is 0.05-0.3wt%.

[0049] In a specific embodiment, the D50 particle size of the main phase grains is 2.5~4μm. In the above embodiment, the NdFeB magnet prepared by the method provided in the present disclosure contains a grain boundary phase A, which can effectively inhibit the growth of the main phase grain size, and the average size of the grains is small, so that the magnet performance is significantly improved. In the present disclosure, the D50 particle size of the main phase grains refers to the average value of the equivalent circular diameter calculated from the cross-sectional area of ​​the main phase grains.

[0050] A second aspect of the present disclosure provides a method for preparing a neodymium iron boron magnet, wherein the method comprises:

[0051] S1, attaching the diffusion source to the surface of the NdFeB substrate to form a film layer;

[0052] S2, performing a first diffusion treatment and a second diffusion treatment on the NdFeB substrate with a film layer attached to the surface to obtain a magnet after diffusion treatment;

[0053] S3, performing tempering treatment on the magnet after the diffusion treatment to obtain a NdFeB magnet.

[0054] Wherein, the NdFeB substrate includes R1, M1, B and Fe; R1 includes at least one of the rare earth elements Dy, Tb, Pr, Nd, Ce, La, Y, Ho and Gd, M1 includes Co, Cu and optionally M', and M' includes one or more of Cr, Ni, Ga, Al, Zr, Nb and Ti, and the content of R1 in the NdFeB substrate is 28.5-31wt%, the content of M1 is 0.6-2.5wt%, the content of B is 0.94-1.02wt%, the content of Co is 0.5-2.5wt%, and the balance is Fe and impurity elements; illustratively, the content of M1 can be 0.6wt%, 0.8wt%, 1wt%, 1.2wt%, 1.8wt%, 2.0wt% or any value in the range of any two thereof;

[0055] The impurity elements include one or more of C, O and N; the content of the impurity elements is less than 1500 ppm, and the content of N is less than 200 ppm;

[0056] The diffusion source includes RH1, M2 and R2, RH1 includes at least one of Dy, Tb and Ho, R2 includes at least one of rare earth elements Pr and Nd, M2 includes Co and optionally M2', and M2' includes one or more of Ga, Al and Cu; the content of RH1 in the diffusion source is 30-70wt%, the content of M2 is 5-30wt%, the content of R2 is 20-50wt%, and the content of Co is 1-15wt%; for example, the content of M2 can be 5wt%, 10wt%, 12 ...2wt%, 12wt%, 10wt%, 12wt%, 12wt%, 12wt%, 12wt%, 12wt%, 12wt%, 12wt%, 12wt%, 12wt%, 12wt%, 12wt%, 1 t%, 15wt%, 20wt%, 25wt%, 28wt%, 30wt% or any value in the range of any two thereof; for example, the content of Co can be 1wt%, 5wt%, 8wt%, 10wt%, 12wt%, 15wt% or any value in the range of any two thereof; for example, the content of R2 can be 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt% or any value in the range of any two thereof;

[0057] In a specific embodiment, the Pr content in R2 is 20-35wt%.

[0058] The temperature of the second diffusion treatment is 840-880°C, and the holding time is 4-20h; the ratio of the temperature of the first diffusion treatment to the temperature of the second diffusion treatment is 1.01-1.08, and the ratio of the holding time of the first diffusion treatment to the holding time of the second diffusion treatment is 0.1-0.3.

[0059] For example, the temperature of the second diffusion treatment can be 840°C, 845°C, 850°C, 860°C, 865°C, 870°C, 880°C or any value in the range of any two thereof; the holding time can be 4, 5, 6, 7.5, 8, 10, 12, 15, 18, 20 or any value in the range of any two thereof; the ratio of the temperature of the first diffusion treatment to the temperature of the second diffusion treatment can be 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08 or any value in the range of any two thereof; the ratio of the holding time of the first diffusion treatment to the holding time of the second diffusion treatment can be 0.1, 0.15, 0.2, 0.25, 0.3 or any value in the range of any two thereof.

[0060] The present invention uses a NdFeB substrate with a low content of impurity elements, making it difficult for rare earth elements to combine with impurity elements separately, effectively avoiding the generation of secondary phases outside the main phase grains, ensuring that the substrate has a smooth diffusion channel, and helping to improve the diffusion depth of heavy rare earth elements (such as Dy and Tb) in subsequent diffusion treatment. At the same time, the composition of the diffusion source is reasonably designed, and Co is introduced to co-enrich with Cu during the diffusion process, so that the eutectic temperature of the R-Fe system is reduced, which can effectively promote the diffusion and effectively improve the diffusion depth; and R2, especially the addition of element Pr, can effectively reduce the eutectic point / melting point, which can not only ensure that the light rare earth elements (such as Pr, Nd) and low melting point elements contained in the diffusion source further optimize the grain boundary structure of the NdFeB substrate during the diffusion process, but also provide a diffusion concentration gradient of heavy rare earth elements, promote the diffusion of heavy rare earth elements inside the substrate, and improve the diffusion depth of heavy rare earth. The present invention adopts a segmented diffusion process to diffuse the substrate, wherein the first diffusion treatment adopts a high-temperature short-time heat treatment, which can form a uniform heavy rare earth shell on the surface of the main phase grains, effectively avoiding more heavy rare earth elements from being retained on the surface of the main phase, and effectively promoting the diffusion of heavy rare earth elements into the magnet; and the second diffusion treatment adopts a low-temperature long-time heat treatment, which can further promote the diffusion of heavy rare earth elements into the magnet, effectively control the diffusion rate, and further improve the uniformity of diffusion. The method provided by the present invention can effectively improve the diffusion depth of heavy rare earth elements, and has a good diffusion effect, significantly improves the coercive force, has high remanence, and has high squareness.

[0061] In the present disclosure, the diffusion source is attached to the surface of the NdFeB substrate by at least one of vacuum physical vapor deposition, patch, coating, electrophoresis and screen printing; preferably, magnetron sputtering is used for attachment. The diffusion source alloy can be in the form of a target, a sheet, a strip or a powder.

[0062] In a specific embodiment, the diffusion source is attached to the surface of the NdFeB substrate by magnetron sputtering; in a further embodiment, the NdFeB substrate can be machined and pre-treated, and then magnetron sputtered. The machining obtains a slice with a thickness of 1 to 10 mm along the magnetization direction. The coated surface of the magnetron sputtering is a surface perpendicular to the magnetization direction, and the weight gain of the NdFeB substrate with the diffusion source film layer attached can be 0.5 to 1.5%. In the above embodiment, the present disclosure can further improve the diffusion depth and diffusion effect of heavy rare earth elements by selecting a diffusion process that is more matched with the diffusion source component design, and the coercive force is significantly improved, the remanence is high, and the squareness is high.

[0063] In a specific embodiment, the content of R1 in the NdFeB substrate is 29.5~30.5wt%, the content of M1 is 0.6~1.5wt%, the content of B is 0.96~1.0wt%, and the balance is Fe and impurity elements; wherein the content of Dy in the NdFeB substrate is 2~4wt%, preferably 2.5~3.5wt%.

[0064] In a specific embodiment, the content of Co in the NdFeB substrate is 1-1.5wt%.

[0065] In a specific embodiment, the content of Cu in the NdFeB substrate is 0.1-0.3wt%, preferably 0.15-0.25wt%.

[0066] In a specific embodiment, M1 further includes Ga, and the content of Ga is 0.1-0.5wt%, preferably 0.25-0.35wt%.

[0067] In a specific embodiment, M1 further includes Zr and / or Ti, and the content of Zr and / or Ti is 0.05-0.35wt%.

[0068] In a specific embodiment, before step S3, step S2 is repeated to obtain the magnet after the diffusion treatment; optionally, the total number of times step S2 is performed is 2 to 8 times. In the above embodiment, the present invention repeats the above segmented diffusion process multiple times, the purpose of which is to further improve the diffusion of heavy rare earth elements to the center of the magnet and the uniformity of the diffusion according to the composition of the substrate and the diffusion source provided by the present invention, and to effectively control the main phase grain size, thereby improving the coercive force of the magnet.

[0069] In a specific embodiment, the method further comprises: sequentially performing a molding process and a sintering process on the NdFeB raw alloy powder to obtain the NdFeB substrate.

[0070] In a specific embodiment, the molding process is an oriented molding and pressing process, and the oriented molding and pressing process is carried out under the condition that the oriented magnetic induction intensity is 1.8~2.3T.

[0071] In a specific embodiment, the sintering treatment includes a first-stage sintering treatment and a second-stage sintering treatment, wherein the temperature of the first-stage sintering treatment is 750-980°C, preferably 800-950°C, and the sintering time is 8-10 hours; the temperature of the second-stage sintering treatment is 1000-1080°C, and the sintering time is 8-12 hours; the vacuum degree of the sintering treatment is 10 -5 ~10 -2 Pa; the magnet density of the NdFeB substrate obtained by sintering is 7.5~7.8g / cm 3 In the above embodiment, the above graded sintering process can effectively avoid the abnormal growth of the main phase grain size, and can effectively control the content of impurity elements in the magnet, provide a better grain boundary structure, and provide a better diffusion channel for subsequent diffusion treatment.

[0072] In a specific embodiment, the method also includes: machining and pre-treating the NdFeB substrate, wherein the machining includes: slicing the NdFeB substrate perpendicular to the magnetization direction to obtain NdFeB magnetic sheets, wherein the thickness along the magnetization direction is 1~10mm; the pre-treatment includes: degreasing, ultrasonic cleaning and drying the NdFeB magnetic sheets in sequence, wherein the drying temperature is 20~80°C.

[0073] In a specific implementation manner, in step S4, the tempering treatment temperature is 450-690° C., preferably 500-540° C., and the holding time is 0.5-4 h.

[0074] In a specific embodiment, the method further comprises: after the tempering treatment, cooling the NdFeB magnet to below 400°C, with a cooling rate of 6-30°C / min, preferably 8-20°C / min. In the above embodiment, rapid cooling after the tempering treatment can effectively suppress the segregation of the ferromagnetic phase in the grain boundary phase, and further improve the coercive force of the magnet.

[0075] In a specific embodiment, the method further includes: preparing NdFeB raw alloy sheets by a rapid solidification process, and performing hydrogen crushing and fine grinding on the NdFeB raw alloy sheets to obtain the NdFeB raw alloy powder; the D50 particle size of the NdFeB raw alloy powder is 2~5μm.

[0076] A third aspect of the present disclosure provides a neodymium iron boron magnet prepared by the method described in the second aspect of the present disclosure.

[0077] In a specific implementation manner, the remanence of the NdFeB magnet is greater than 13.6 kGs, the coercive force is greater than 29.5 kOe, and the squareness is greater than 0.96.

[0078] The present invention is further described below by way of examples, but the present invention is not limited thereby. The raw materials used in the examples and comparative examples can be obtained through commercial channels.

[0079] Example 1

[0080] a. Prepare the NdFeB substrate by the following steps:

[0081] The alloy raw material is cast into alloy quick-setting sheets by using a quick-setting process; the alloy quick-setting sheets are hydrogen crushed and finely pulverized to obtain raw alloy powder with a D50 particle size of 2.5 μm; the pressed blank is pressed in an orientation field with a magnetic field strength of 2T at room temperature; the formed compact is placed in a vacuum sintering furnace for sintering to obtain a NdFeB substrate, wherein the vacuum degree of the vacuum sintering furnace is 10 - 3 Pa, the temperature of the first stage sintering treatment is 850℃, the holding time is 8h, the temperature of the second stage sintering treatment is 1058℃, the holding time is 10h;

[0082] Among them, the NdFeB matrix includes R1, M1, B and Fe; R1 includes PrNd and Dy, and M1 includes Co, Cu, Ga, Zr and Ti; the content of PrNd in the NdFeB matrix is ​​26.7wt%, the content of Dy is 3.1wt%, the content of Co is 1.1wt%, the content of Cu is 0.2wt%, the content of Ga is 0.25wt%, the content of Zr is 0.05wt%, the content of Ti is 0.05wt%, the content of B is 0.99wt%, and the balance is Fe and impurity elements, and the impurity elements include C, O and N. The content of C and O in the impurity elements is 1150~1300ppm, and the content of N is 180~190ppm. The magnet density of the NdFeB matrix after sintering is 7.8g / cm 3 .

[0083] b. The NdFeB substrate is processed into a NdFeB magnetic sheet with a thickness (in the orientation direction) of 4mm×10mm in length×10mm in width. The magnetic sheet is degreased, ultrasonically cleaned and dried in sequence at a drying temperature of 70°C. A diffusion source is used to perform magnetron sputtering on the surface of the processed NdFeB magnetic sheet perpendicular to the magnetization direction to obtain a NdFeB substrate with a film layer attached to the surface. The weight gain of the surface attached film layer after magnetron sputtering is 1.0%;

[0084] Among them, the diffusion sources include RH1, M2 and R2, RH1 includes Dy, R2 includes PrNd; M2 includes Co, Cu, Ga and Al; the content of Dy in the diffusion source is 55wt%, the content of Co is 5wt%, the content of Cu is 5wt%, the content of Ga is 5wt%, the content of Al is 5wt%, and the content of PrNd is 25wt%.

[0085] c. Performing a first diffusion treatment and a second diffusion treatment on the NdFeB substrate with a film layer attached to the surface; the temperature of the first diffusion treatment is 905°C, the holding time is 1 hour, the temperature of the second diffusion treatment is 870°C, the holding time is 5 hours; the ratio of the temperature of the first diffusion treatment to the temperature of the second diffusion treatment is 1.04; the ratio of the holding time of the first diffusion treatment to the holding time of the second diffusion treatment is 0.2;

[0086] d. Repeat step c to obtain a magnet after diffusion treatment; the number of repetitions is 3 times.

[0087] e. The magnet after diffusion treatment was tempered at a temperature of 520°C for 3 hours. After tempering at a cooling rate of 15°C / min, NdFeB magnet 1 was obtained, recorded as CT-1. According to elemental analysis, the content of impurity elements (including C, N and O) in NdFeB magnet CT-1 was less than 1500ppm, of which the content of N was less than 200ppm. R in grain boundary phase A included Dy, Pr and Nd.

[0088] Example 2

[0089] The method of Example 1 is adopted, except that in step c, the temperature of the first diffusion treatment is 890°C, the temperature of the second diffusion treatment is 880°C, and the ratio of the first diffusion treatment temperature to the second diffusion treatment temperature is 1.01, to obtain a NdFeB magnet 2, recorded as CT-2.

[0090] Example 3

[0091] The method of Example 1 was adopted, except that in step a, the content of Co in the NdFeB substrate was 0.6 wt %, and NdFeB magnet 3 was obtained, which was recorded as CT-3.

[0092] Example 4

[0093] The method of Example 1 was adopted, except that in step b, the content of Co in the diffusion source was 2 wt %, to obtain a NdFeB magnet 4, which was recorded as CT-4.

[0094] Example 5

[0095] The method of Example 1 was adopted, except that in step b, the content of Co in the diffusion source was 13 wt %, to obtain a NdFeB magnet 5, which was recorded as CT-5.

[0096] Comparative Example 1

[0097] The method of Example 1 is adopted, except that in step b, the diffusion source does not contain Co, and a neodymium iron boron magnet is obtained, which is recorded as DCT-1.

[0098] Comparative Example 2

[0099] The method of Example 1 is adopted, except that in step c, the multi-stage diffusion process is not adopted, the diffusion treatment temperature is 870° C., and the holding time is 18 h, to obtain a NdFeB magnet, which is recorded as DCT-2.

[0100] Comparative Example 3

[0101] The method of Example 1 is adopted, except that in step a, the content of N in the impurity elements is 450-550 ppm, to obtain a neodymium iron boron magnet, which is recorded as DCT-3.

[0102] Test Case

[0103] The average particle size D50 of the raw alloy powder is measured using a particle size analyzer.

[0104] The NdFeB magnet prepared in Example 1 was scanned and tested by EPMA. The EPMA test results at a depth of 500 μm are as follows: Figure 2 As shown, the heavy rare earth elements can be distinguished based on the electron backscattering image, wherein the gray substrate is the Dy element distribution and the black substrate is the main phase grains.

[0105] The NdFeB magnet prepared in Example 1 was tested for microstructure using SEM to obtain a SEM microstructure image.

[0106] The atomic percentage of each element in the grain boundary phase of the NdFeB magnets of Examples 1 to 5 and Comparative Examples 1 to 3 was tested by EDS energy spectrum analysis. The results are shown in Table 1.

[0107] The magnetic properties of the NdFeB magnets of Examples 1 to 5 and Comparative Examples 1 to 3 were tested using a BH plotter. The results are listed in Table 2.

[0108] Table 1

[0109]

[0110] Table 2

[0111]

[0112] As can be seen from Tables 1 and 2, the method provided by the present disclosure controls the content of impurity elements (C, N, O) to be low by regulating the composition of the NdFeB substrate. At the same time, the composition of the diffusion source is reasonably designed to control the contents of R2, Co and M2 within the specified range of the present application, which can effectively promote the diffusion of heavy rare earth elements, increase the diffusion depth to more than 500 μm, and promote the element Co to penetrate deeper into the grain boundary phase, such as Figure 1As shown, a grain boundary phase A rich in Co and Cu can be generated in the grain boundary phase, so that the elements Co and Cu are enriched in the grain boundary phase, reducing the influence of the anti-shell on the diffusion depth of the heavy rare earth elements during the diffusion process, so that the coercive force of the prepared NdFeB magnet is significantly improved, with high remanence and high squareness.

[0113] By comparing Examples 3, 4 and 5 with Example 1, it can be seen that controlling the Co content in the NdFeB substrate within the range specified in the present application and controlling the Co content in the diffusion source within the range specified in the present application can effectively promote the diffusion of the element Co into the interior of the magnet and promote the enrichment of the elements Co and Cu in the grain boundary phase. The coercive force of the prepared NdFeB magnet is significantly improved and can reach 30.5 kOe.

[0114] By comparing Comparative Example 1 with Example 1, it can be seen that since the diffusion source in Comparative Example 1 does not contain Co, the grain boundary phase A rich in Co and Cu cannot be generated in the grain boundary phase, so that the anti-shell layer hinders the diffusion depth of the heavy rare earth elements during the diffusion process, and the diffusion depth and diffusion effect are significantly reduced, resulting in the coercive force of the NdFeB magnet provided by Comparative Example 1 being lower than that of the examples of the present application.

[0115] By comparing Comparative Example 2 with Example 1, it can be seen that since Comparative Example 2 does not adopt a multi-stage diffusion process, it is impossible to form a uniform heavy rare earth shell on the surface of the main phase grains, so that more heavy rare earth elements are retained on the surface of the main phase, and the heavy rare earth elements and element Co cannot diffuse well into the interior of the magnet. At the same time, the main phase grain size cannot be effectively controlled, thereby reducing the coercive force of the magnet provided by Comparative Example 2.

[0116] By comparing Comparative Example 3 with Example 1, it can be seen that since the content of impurity element N in the NdFeB substrate used in Comparative Example 3 is not within the specified range of the present application, the R element is excessively combined with the impurity element, which promotes the formation of subphases outside the main phase grains, and easily leads to blockage of the diffusion channel of the substrate, thereby reducing the diffusion depth of heavy rare earth elements in subsequent diffusion treatment, and thus the remanence, coercive force and squareness of the magnet provided by Comparative Example 3 are significantly reduced.

[0117] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0118] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0119] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A neodymium iron boron magnet with high remanence and high coercivity, wherein: The NdFeB magnet contains R2T 14 B main phase grains and grain boundary phase A; The NdFeB magnet includes R, M, B and Fe, R includes RL and RH, wherein RL includes at least one of Pr, Nd, La, Ce and Y, RH includes at least one of Dy, Tb, Gd and Ho, Fe is iron, B is boron, M includes Co, Cu and M', and M' includes one or more of Cr, Ni, Ga, Al, Zr, Nb and Ti; The content of R in the grain boundary phase A is 29-55 at%, the content of Co is 3-7 at%, and the content of Cu is 7-20 at%; Wherein, the diffusion depth of the RH heavy rare earth element in the NdFeB magnet is above 500 μm.

2. The NdFeB magnet according to claim 1, wherein: M includes Ga, and the content of Ga in the grain boundary phase A is 2-11 at %.

3. The NdFeB magnet according to claim 1, wherein: The NdFeB magnet meets one or more of the following conditions: A. Impurities in the NdFeB magnet include one or more of C, N and O; the content of impurity elements in the NdFeB magnet is less than 1500ppm; B. The N content in the NdFeB magnet is less than 200 ppm.

4. The NdFeB magnet according to claim 1, wherein: The NdFeB magnet has an R content of 28.5-31 wt %, an M content of 0.8-3 wt %, a B content of 0.94-1.02 wt %, and the remainder is iron and unavoidable impurities; and / or, The NdFeB magnet has a Co content of 1-1.5 wt %, a Cu content of 0.15-0.3 wt %, a Ga content of 0.2-0.4 wt %, and a Zr and / or Ti content of 0.05-0.35 wt %.

5. The NdFeB magnet according to claim 1, wherein: The D50 particle size of the main phase grains is 2.5-4 μm.

6. A method for preparing a neodymium iron boron magnet with high remanence and high coercivity, wherein: The method includes: S1, attaching the diffusion source to the surface of the NdFeB substrate to form a film layer; S2, performing a first diffusion treatment and a second diffusion treatment on the NdFeB substrate with a film layer attached to the surface to obtain a magnet after diffusion treatment; S3, tempering the magnet after the diffusion treatment to obtain a neodymium iron boron magnet; Wherein, the NdFeB substrate includes R1, M1, B and Fe; R1 includes at least one of the rare earth elements Dy, Tb, Pr, Nd, Ce, La, Y, Ho and Gd, M1 includes Co, Cu and M1', and M1' includes one or more of Cr, Ni, Ga, Al, Zr, Nb and Ti. The content of R1 in the NdFeB substrate is 28.5-31wt%, the content of M1 is 0.6-2.5wt%, the content of B is 0.94-1.02wt%, the content of Co is 0.5-2.5wt%, and the balance is Fe and impurity elements, and the impurity elements include one or more of C, O and N; the content of the impurity elements is less than 1500ppm, and the content of N is less than 200ppm; The diffusion source includes RH1, M2 and R2, RH1 includes at least one of Dy, Tb and Ho, R2 includes at least one of Pr and Nd, M2 includes Co and M2', and M2' includes one or more of Ga, Al and Cu; the content of RH1 in the diffusion source is 30-70wt%, the content of M2 is 5-30wt%, the content of R2 is 20-50wt%, and the content of Co is 1-15wt%; The temperature of the second diffusion treatment is 840-880°C, and the holding time is 4-20h; the ratio of the temperature of the first diffusion treatment to the temperature of the second diffusion treatment is 1.01-1.08, and the ratio of the holding time of the first diffusion treatment to the holding time of the second diffusion treatment is 0.1-0.

3.

7. The method according to claim 6, wherein: The method meets one or more of the following conditions: The content of R1 in the NdFeB substrate is 29.5-30.5wt%, the content of M1 is 0.6-1.5wt%, the content of B is 0.96-1.0wt%, and the balance is Fe and impurity elements; The content of Dy in the NdFeB substrate is 2-4wt%; The NdFeB substrate has a Co content of 1-1.5 wt %, a Cu content of 0.1-0.3 wt %, a Ga content of 0.1-0.5 wt %, and a Zr and / or Ti content of 0.05-0.35 wt %.

8. The method according to claim 6, wherein: The method satisfies one or more of the following conditions: before step S3, step S2 is repeated to obtain the magnet after the diffusion treatment; The total number of times step S2 is performed is 2 to 8 times.

9. The method according to claim 6, wherein: The method further comprises: performing molding and sintering on the NdFeB raw alloy powder in sequence to obtain the NdFeB substrate; The D50 particle size of the NdFeB raw alloy powder is 2-5 μm; The molding process is an oriented pressing molding process, and the oriented pressing molding process is performed under the condition that the oriented magnetic induction intensity is 1.8~2.3T; The sintering process includes a first-stage sintering process and a second-stage sintering process. The temperature of the first-stage sintering process is 750-980°C and the sintering time is 8-10 hours. The temperature of the second-stage sintering process is 1000-1080°C and the sintering time is 8-12 hours. The vacuum degree of the sintering process is 10 -5 ~10 -2 Pa; the density of the NdFeB substrate obtained by sintering is 7.5~7.8g / cm 3 .

10. The method according to claim 6, wherein: In S1, the weight gain of the NdFeB substrate with the film layer attached to the surface is 0.5~1.5%; The content of RH1 in the diffusion source is 45-65wt%, the content of M2 is 10-20wt%, and the content of R2 is 30-40wt%; the content of Co in the diffusion source is 5-10wt%.

11. The method according to claim 6, wherein: The method meets the following conditions: in step S3, the temperature of the tempering treatment is 450-690° C., and the holding time is 0.5-4 h.

12. A neodymium iron boron magnet prepared by the method described in any one of claims 6 to 11.

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