Neodymium iron boron magnets and their preparation methods

Abstract

This application provides a neodymium iron boron magnet and its preparation method, comprising the following steps: pressing neodymium iron boron magnet powder to prepare a square compact; the surface corresponding to the S pole and the surface corresponding to the N pole of the square compact are orientation surfaces M, and any two face-to-face surfaces of the remaining surfaces are H surfaces; forming a first diffusion layer on the orientation surface M using a first diffusion source and forming a second diffusion layer on the H surface using a second diffusion source to prepare a preform; subjecting the preform to solidification diffusion treatment, degassing treatment, sintering treatment and tempering treatment in sequence to prepare a neodymium iron boron magnet; wherein, the first diffusion source and the second diffusion source are independently selected from: X a Y b and R c Z d At least one of the following. This preparation method can effectively control and improve the grain boundary diffusion efficiency and stability, thereby improving the magnetic coercivity of NdFeB magnets and increasing production efficiency.

Description

Technical Field

[0001] This invention relates to the field of alloy technology, and in particular to a neodymium iron boron magnet and its preparation method. Background Technology

[0002] Neodymium iron boron magnets, also known as neodymium iron boron magnets, are composed of neodymium, iron, and boron (Nd2Fe). 14 B) forms a tetragonal crystal with a magnetic energy product (BHmax) greater than that of samarium cobalt magnets, making it one of the materials with the largest magnetic energy product in the world. It is currently the second most powerful permanent magnet after holmium magnets at absolute zero, and is also the most commonly used rare-earth magnet. Neodymium iron boron magnets are widely used in electronic products such as hard drives, mobile phones, headphones, and battery-powered tools.

[0003] With the rapid development of new energy vehicles, energy-saving variable frequency air conditioners, industrial robots, and servo motors, the demand for sintered NdFeB magnets is gradually increasing. Furthermore, with intensifying market competition and customers' focus on cost control, grain boundary diffusion technology for sintered NdFeB magnets is becoming mainstream in this field due to its high cost-effectiveness. Traditional grain boundary diffusion techniques often involve preparing a blank, processing it, cleaning the surface, and then performing diffusion coating followed by diffusion heat treatment to improve the coercivity of the substrate. However, this technology has high equipment costs, a long process flow, limited product specifications (generally 2–10 mm thick magnetic sheets), and complex composite coating processes.

[0004] Therefore, how to provide a short-range, high-efficiency diffusion technology that can cover thick magnets to fill the gap in short-range, high-efficiency diffusion technology is a technical problem that still needs to be solved in this field. Summary of the Invention

[0005] Based on this, this application provides a neodymium iron boron magnet and its preparation method, which can effectively control and improve the grain boundary diffusion efficiency, obtain a neodymium iron boron magnet with good performance, and provide a short-range preparation method for the diffusion production of high-thickness products, which can fill the gap in short-range high-efficiency diffusion technology.

[0006] The technical solution of this application is as follows:

[0007] The first aspect of this application provides a method for preparing a neodymium iron boron magnet, comprising the following steps:

[0008] The powder of neodymium iron boron magnets is pressed to prepare a square compact; the surface corresponding to the S magnetic pole and the surface corresponding to the N magnetic pole of the square compact are the orientation surface M, and any two face-to-face surfaces among the remaining surfaces are the H surface;

[0009] A first diffusion layer is formed on the orientation surface M using a first diffusion source, and a second diffusion layer is formed on the H surface using a second diffusion source to prepare a preform.

[0010] The preform is subjected to solidification diffusion treatment, degassing treatment, sintering treatment and tempering treatment in sequence to prepare neodymium iron boron magnets;

[0011] Wherein, the first diffusion source and the second diffusion source are independently selected from: X a Y b and R c Z d At least one of them;

[0012] X is a rare earth element and includes at least one heavy rare earth element; Y and Z are each independently selected from at least one non-metallic element and a non-rare earth metallic element; R is a non-heavy rare earth metallic element and is different from Z.

[0013] 20w%≤a≤99.9wt%, 0.1wt%≤b≤80wt%, a+b=100%;

[0014] 0≤c≤99.9wt%, 0.1wt%≤d≤100wt%, c+d=100%.

[0015] In the above method, specific diffusion layers are formed on different surfaces of the square compact: at least part of the diffusion layers formed on the orientation planes M and H corresponding to the two magnetic poles contain specific heavy rare earth diffusion sources or specific non-heavy rare earth metal diffusion sources. In this way, during the subsequent diffusion sintering process, the non-heavy rare earth diffusion sources can cause the compact to open the diffusion channels, allowing the heavy rare earth diffusion sources to penetrate and wrap around the main phase grains on the orientation plane M, reconstructing the main phase grain boundaries to form a core-shell structure, thereby effectively controlling and improving the grain boundary diffusion efficiency and stability, and thus improving the magnetic coercivity of the NdFeB magnet.

[0016] Meanwhile, the above preparation process effectively improves the grain boundary diffusion efficiency and stability. Even for high-thickness square compacts, it can effectively improve the grain boundary diffusion efficiency and shorten the subsequent diffusion sintering time, greatly reducing time costs. It is a short-range, high-efficiency diffusion technology that can cover high-thickness magnets and can fill the gap in short-range, high-efficiency diffusion technology.

[0017] In some embodiments, the Y is selected from at least one of H, O, F, N, Al, Cu, Co, Ga, Sn, Zr, Ti, Si, and Fe; and / or

[0018] X is at least one of Pr, Nd, Dy, Tb, Ho, and Gd, and includes at least one of Tb, Ho, and Gd; and / or

[0019] The X a Y b The particle size is <100μm.

[0020] In some embodiments, R and Z are each independently selected from at least one of Pr, Nd, Al, Cu, Co, Ga, Sn, Zr, Ti, Si, and Fe, and R and Z are different; and / or

[0021] Under normal pressure, the R c Z d Melting point ≤ 900℃; and / or

[0022] The R c Z d The particle size is <100μm.

[0023] In some embodiments, the mass percentage of the first diffusion layer is 0.1% to 1.5% based on the total mass of the first diffusion layer and the second diffusion layer; optionally, it is 0.2% to 0.8%.

[0024] Controlling the mass percentage of the first diffusion layer can further improve diffusion efficiency and stability.

[0025] In some embodiments, both the first diffusion source and the second diffusion source comprise: X a Y b and R c Z d ;or

[0026] The components of the first diffusion source include X a Y b The components of the second diffusion source include R c Z d ;or

[0027] The components of the second diffusion source include X a Y b The components of the first diffusion source include R c Z d .

[0028] In some embodiments, the steps of forming the first diffusion layer and the second diffusion layer are performed by vibration powder application, spraying, or printing.

[0029] In some embodiments, the conditions for the curing diffusion treatment include: a vacuum degree <5×10⁻⁶. -2 Pa, heat treatment at 120±30℃ for 0.5h~1h; and / or

[0030] The exhaust treatment steps include: sequentially performing heat preservation treatments at temperature ranges of 400±50℃, 600±50℃, and 800±60℃; and / or

[0031] The sintering conditions include: a vacuum degree <5×10⁻⁻¹ 2 Pa, heat treatment at 880℃~1080℃ for 2h~20h; and / or

[0032] The conditions for the tempering process include: a vacuum degree < 5 × 10⁻⁴ 2 Heat treatment at 440℃~700℃ for 2h~10h.

[0033] In some embodiments, the oxygen content is controlled to be ≤500ppm during the formation of the first diffusion layer and the formation of the second diffusion layer.

[0034] In some embodiments, the density of the square compact is >4 g / cm³. 3 ; and / or

[0035] The size of the orientation surface M is ≤35mm, the size of the H surface is ≤50mm, and the size of the remaining surfaces in the square blank is ≤60mm.

[0036] A second aspect of this application provides a neodymium iron boron magnet, which is prepared using the method for preparing neodymium iron boron magnets of the first aspect. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the square pressed blank obtained in Example 1.

[0038] In the diagram: S represents the South Pole; N represents the North Pole. Detailed Implementation

[0039] To facilitate understanding of this application, a more complete description is provided below, along with preferred embodiments. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0041] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0042] The "range" disclosed in this application can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. Ranges defined in this way can include or exclude endpoints. Any endpoint can be included or excluded independently, and they can be combined arbitrarily; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is expected that ranges of 60–110 and 80–120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are also listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0" and "5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥ 2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0043] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0044] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0045] One embodiment of this application provides a method for preparing a neodymium iron boron magnet, comprising the following steps S10 to S30.

[0046] S10: The powder of neodymium iron boron magnet is pressed to prepare a square compact; the surface corresponding to the S magnetic pole and the surface corresponding to the N magnetic pole of the square compact are the orientation surface M, and any two face-to-face surfaces among the other surfaces are the H surface.

[0047] S20: A first diffusion layer is formed on the orientation surface M using a first diffusion source, and a second diffusion layer is formed on the H surface using a second diffusion source to prepare a preform.

[0048] S30: The preform is subjected to solidification and diffusion treatment, degassing treatment, sintering treatment and tempering treatment in sequence to prepare neodymium iron boron magnets.

[0049] The first diffusion source and the second diffusion source are independently selected from: X a Y b and R c Z d At least one of them.

[0050] X is a rare earth element and includes at least one heavy rare earth element; Y and Z are each independently selected from at least one non-metallic element and a non-rare earth metallic element; R is a non-heavy rare earth metallic element and is different from Z.

[0051] 20w%≤a≤99.9wt%, 0.1wt%≤b≤80wt%, a+b=100%.

[0052] 0≤c≤99.9wt%, 0.1wt%≤d≤100wt%, c+d=100%.

[0053] In the above method, specific diffusion layers are formed on different surfaces of the square compact: the diffusion layers formed on the orientation planes M and H corresponding to the two magnetic poles contain at least a portion of diffusion sources containing specific heavy rare earth elements or diffusion sources containing specific non-heavy rare earth metals. In this way, during the subsequent diffusion sintering process, the non-heavy rare earth diffusion sources can cause the compact to open diffusion channels, allowing the heavy rare earth diffusion sources to penetrate and wrap around the main phase grains on the orientation plane M, reconstructing the main phase grain boundaries to form a core-shell structure, thereby effectively controlling and improving the grain boundary diffusion efficiency and stability, and thus improving the magnetic coercivity of the NdFeB magnet.

[0054] Meanwhile, the above preparation process effectively improves the grain boundary diffusion efficiency and stability. Even for high-thickness square compacts, it can effectively improve the grain boundary diffusion efficiency and shorten the subsequent diffusion sintering time, greatly reducing time costs. It is a short-range, high-efficiency diffusion technology that can cover high-thickness magnets and can fill the gap in short-range, high-efficiency diffusion technology.

[0055] It is understandable that the square blank is a magnetic material, that is, it has two magnetic poles: the south (S) pole and the north (N) pole, and has six surfaces. The surfaces corresponding to the S magnetic pole and the N magnetic pole are the orientation surfaces M. Among the other four surfaces, there are two sets of face-to-face surfaces. Any two face-to-face surfaces are the H surfaces. The other two surfaces do not need to be treated.

[0056] Please refer to the details. Figure 1 , Figure 1 The diagram on the left is a three-dimensional schematic of a square blank in one embodiment. It has two magnetic poles: a south (S) magnetic pole and a north (N) magnetic pole. The surfaces corresponding to the S magnetic pole and the N magnetic pole are orientation surfaces M, which correspond to the M coordinate direction in the right coordinate system. Among the other four surfaces, there are two sets of face-to-face surfaces H and L, which correspond to the H and L coordinate directions in the right coordinate system.

[0057] In some embodiments, the square blank is a rectangular blank.

[0058] In some embodiments, of the four remaining surfaces of the square blank excluding the M-oriented surface, the two smaller, face-to-face surfaces are the H-surfaces.

[0059] It should be noted that the term "size" in this application can be understood as the dimensions of the green body after molding or after molding and isostatic pressing. Figure 1 The actual lengths in the three directions of the right-hand coordinate axis. The H-plane can be either the mold frame direction or the pressing direction. If it is the mold frame direction, it can be controlled through mold design; if it is the pressing direction, it can be adjusted by controlling the powder feeding amount and the density of the pressed blank.

[0060] In some embodiments, at least one of the first diffusion source and the second diffusion source includes X. a Y b And at least one includes R c Z d .

[0061] In some embodiments, both the first diffusion source and the second diffusion source comprise: X a Y b and R c Z d。

[0062] In some embodiments, the components of the first diffusion source include X. a Y b The components of the second diffusion source include R c Z d。

[0063] In some embodiments, the components of the second diffusion source include X. a Y b The components of the first diffusion source include R c Z d .

[0064] In some embodiments, the value of 'a' includes, but is not limited to: 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, 90wt%, 95wt%, and 99wt%.

[0065] In some embodiments, the value of b includes, but is not limited to: 0.1wt%, 0.5wt%, 1wt%, 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, and 80wt%.

[0066] In some embodiments, the value of c includes, but is not limited to: 0, 0.1wt%, 0.5wt%, 1wt%, 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, 90wt%, 95wt%, and 99wt%.

[0067] In some embodiments, the value of d includes, but is not limited to: 0.1wt%, 0.5wt%, 1wt%, 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, 90wt%, 95wt%, 99wt%, and 100%.

[0068] In some embodiments, Y is selected from at least one of H, O, F, N, Al, Cu, Co, Ga, Sn, Zr, Ti, Si, and Fe.

[0069] In some embodiments, X is at least one of Pr, Nd, Dy, Tb, Ho, and Gd, and includes at least one of Tb, Ho, and Gd.

[0070] In some of these embodiments, X a Y b The particle size is <100μm.

[0071] It is understood that the above particle size is the average particle size.

[0072] In some embodiments, R and Z are each independently selected from at least one of Pr, Nd, Al, Cu, Co, Ga, Sn, Zr, Ti, Si, and Fe, and R and Z are different.

[0073] In some of these embodiments, R is selected from at least one of Pr and Nd.

[0074] In some of these embodiments, under normal pressure, R c Z d Its melting point is ≤900℃.

[0075] In some of these embodiments, R c Z d The particle size is <100μm.

[0076] In some embodiments, the mass percentage of the first diffusion layer is 0.1% to 1.5% based on the total mass of the first diffusion layer and the second diffusion layer; optionally, it is 0.2% to 0.8%.

[0077] Controlling the mass percentage of the first diffusion layer can further improve diffusion efficiency and stability.

[0078] In some embodiments, the step of forming the first diffusion layer is performed by spraying or printing.

[0079] It should be noted that the step of forming the first diffusion layer can be carried out using any technique commonly used in the field that can form a diffusion layer, as long as the first diffusion source can be loaded into layers on the orientation plane M, and is not limited to the above-mentioned methods.

[0080] In a specific example, the orientation surface M of the compact can be brought closer together by a rubber sponge printing method to apply a first diffusion source until the orientation surface M of the compact is covered with a first diffusion layer of a preset weight.

[0081] In some embodiments, the step of forming the second diffusion layer is performed by vibratory powder application, spraying, or printing.

[0082] It should be noted that the step of forming the second diffusion layer can be carried out using any technique commonly used in the field that can form a diffusion layer, as long as the second diffusion source can be loaded into a layer on the H surface, and is not limited to the above-mentioned method.

[0083] Specifically, the second diffusion source is first evenly distributed on the bottom of the graphite box using a vibrating powder distribution device. Then, the graphite box is filled according to the principle of placing the H-side of the square compact vertically. The second diffusion source powder is then applied using the vibrating powder distribution device until the H-side of the compact is covered with a second diffusion layer of a preset weight.

[0084] It should be noted that there is no specific order in which the steps of forming the first diffusion layer and forming the second diffusion layer are performed; the second diffusion layer can be formed first or the first diffusion layer can be formed first.

[0085] In some embodiments, the oxygen content is controlled to be ≤500ppm during the formation of the first diffusion layer and the second diffusion layer. Optionally, the oxygen content is controlled to be ≤300ppm; more preferably, the oxygen content is controlled to be ≤100ppm.

[0086] In some embodiments, the density of the square compact is >4 g / cm³. 3 Optionally, the density of the square compact is >4.5 g / cm³. 3 ; Further optionally, the density of the square compact is >5 g / cm³ 3 ;

[0087] In some embodiments, the size of the orientation face M is ≤35mm; optionally, the size of the orientation face M is ≤30mm; further optionally, the size of the orientation face M is ≤25mm.

[0088] In some embodiments, the two surfaces in the orientation plane M may have the same or different dimensions.

[0089] In some embodiments, the size of the H-face is ≤50mm, optionally, the size of the H-face is ≤40mm; further optionally, the size of the H-face is ≤30mm.

[0090] In some embodiments, the two surfaces in the H-plane may have the same or different dimensions.

[0091] In some embodiments, the dimensions of the remaining surfaces in the square blank are ≤60mm; optionally, the dimensions are ≤50mm; further optionally, the dimensions are ≤40mm.

[0092] As is understandable, the meaning of the dimensions here is the same as above, and will not be repeated here.

[0093] In some embodiments, the pressing process may be carried out using isostatic pressing, which can increase the density.

[0094] In some embodiments, the conditions for the curing diffusion process include: a vacuum degree <5 × 10⁻⁶. -2 The temperature is 120±30℃ and kept at that temperature for 0.5h~1h.

[0095] In some embodiments, the exhaust treatment step includes: sequentially performing heat preservation treatment at temperature ranges of 400±50℃, 600±50℃, and 800±60℃.

[0096] In some embodiments, heat preservation treatments are performed sequentially at temperature ranges of 400±50℃, 600±50℃, and 800±60℃ for 1h~2h, 2h~3h, and 3h~5h, respectively.

[0097] In some embodiments, the sintering conditions include: a vacuum degree <5×10⁻⁶.2 Heat treatment at 880℃~1080℃ for 2h~20h.

[0098] In some embodiments, the tempering conditions include: a vacuum degree < 5 × 10⁻⁶. 2 Heat treatment at 440℃~700℃ for 2h~10h.

[0099] In some embodiments, after the tempering step, the tempered product is cooled to room temperature in an inert gas.

[0100] In some embodiments, the inert gas includes at least one of nitrogen or argon.

[0101] Another embodiment of this application provides a neodymium iron boron magnet, which is prepared by the above-described method for preparing neodymium iron boron magnets.

[0102] The neodymium iron boron magnet exhibits excellent magnetic coercivity.

[0103] The present application will be described below with reference to specific embodiments, but the present application is not limited to the following embodiments. It should be understood that the appended claims summarize the scope of the present application. Under the guidance of the concept of the present application, those skilled in the art should realize that certain changes made to the various embodiments of the present application will be covered by the spirit and scope of the claims of the present application.

[0104] The following are specific examples.

[0105] Example 1

[0106] (1) 54H powder of neodymium iron boron magnets with preset specifications and performance were selected. The performance was as follows: remanent magnetization (Br) 14.51 kGs, coercivity (Hcj) 17.22 kOe, squareness Hk / Hcj 98.5%, powder SMD 2.9 μm. The designed blank size after isostatic pressing was M = 28 mm, H = 40 mm, L = 50 mm. After isostatic pressing, a square blank was obtained with a density of 4.5 g / cm³. 3 A schematic diagram of a square pressed blank is shown below. Figure 1 As shown.

[0107] (2) Prepare the first diffusion source: Prepare alloy powder with a particle size of 5 μm according to the following composition by mass percentage: Tb: 35%, Pr: 30%, Cu: 15%, Co: 10%, Al: 5%, Ga: 5%, and prepare the printing paste for the first diffusion source; Prepare the second diffusion source: Prepare alloy powder with a particle size of 15 μm according to the following composition by mass percentage: Nd: 60%, Pr: 10%, Cu: 10%, Co: 10%, Ga: 10%.

[0108] The oxygen content is controlled to be ≤100ppm. The printing paste of the first diffusion source is printed onto the orientation surface M by double-sided simultaneous printing to form a first diffusion layer of predetermined thickness. The alloy powder of the second diffusion source is first evenly distributed on the bottom of the graphite box using a vibrating powder distribution device. Then, the printed blank is placed in the graphite box according to the principle of placing the H-face upwards and downwards. The second diffusion source is evenly distributed on the H-face using a vibrating powder distribution device to form a second diffusion layer, thus obtaining a preform. The mass ratio of the first diffusion layer (referred to as the weight gain ratio) is 0.4wt%, based on the total mass of the first and second diffusion layers.

[0109] (3) Place the preform in a vacuum with a degree <5×10 -2 Heating was performed in a Pa environment, and the temperature was held at 120℃ for 30 minutes to allow the printed first diffusion layer to solidify and diffuse. Subsequently, heat preservation and venting steps were set at 380℃, 600℃, and 850℃, with holding times of 60 minutes, 120 minutes, and 300 minutes, respectively, for venting treatment. Then, the product was sintered at 950℃ for 720 minutes, followed by tempering at 500℃ for 240 minutes. After being removed from the furnace, the product was prepared into a D10×10 standard sample column to obtain a neodymium iron boron magnet standard sample.

[0110] (4) The NIM-6500C was used to test the neodymium iron boron magnets. The measurement results are shown in Table 1.

[0111] Examples 2-4

[0112] Examples 2 to 4 are basically the same as Example 1, except that in step (2), the mass percentage (abbreviated as weight gain ratio) of the first diffusion layer is controlled to be 0.1 wt%, 1 wt%, and 1.5 wt%, respectively.

[0113] The other steps are the same as in Example 1.

[0114] The measurement results are shown in Table 1.

[0115] Example 5

[0116] Example 5 is basically the same as Example 1, except that in step (2), a second diffusion source is applied to the orientation surface M and a first diffusion source is applied to the H surface.

[0117] The other steps are the same as in Example 1.

[0118] The test results are shown in Table 1.

[0119] Comparative Example 1

[0120] (1) Same as step (1) in Example 1.

[0121] (2) Vacuum sintering of the square compact: After vacuum degree <5Pa, heating is carried out, and heat preservation and exhaust steps are set at 380℃, 600℃ and 850℃ respectively, with heat preservation time of 60min, 120min and 300min respectively. Then, it is sintered at 1070℃ for 300min. After sintering, aging treatment is carried out: the first temperature is 900℃ and the heat preservation time is 150min, the second aging temperature is 500℃ and the heat preservation time is 300min. After taking it out of the furnace, it is processed into a standard sample column blank of D10*10. The performance is tested using NIM-6500C. The measurement results are Br=14.51kGs and Hcj=17.22kOe.

[0122] (3) The composition of the first diffusion source and the second diffusion source, and the weight gain ratio of the first diffusion layer are controlled in the same way as in Example 1. The steps are basically the same as in step (2) of Example 1. The only difference is that the blank in step (2) above is cleaned on the surface to achieve a surface free of oil and rust. Then, the first diffusion layer and the second diffusion layer are obtained in an environment with normal temperature and pressure without oxygen control. The first diffusion layer is obtained by conventional screen printing. The second diffusion layer is achieved by vibration powdering. The implementation steps are the same as in step (2) of Example 1.

[0123] (4) Place the preform in a vacuum with a degree <5×10 -2 Heating was performed under Pa conditions, with holding steps set at 450℃ and 800℃ for 30 min and 150 min respectively. Then, the product was heated to 910℃ for 600 min and 500℃ for 240 min. After removal from the furnace, the product was prepared into D10×10 standard sample columns to obtain NdFeB magnet standard samples.

[0124] (5) The NIM-6500C was used to test the neodymium iron boron magnets. The measurement results are shown in Table 1.

[0125] Table 1

[0126] Br(kGs) Hcj(kOe) Hk / Hcj (%) Weight gain ratio ΔHcj(kOe) Substrate 14.51 17.22 98.5 0 / Example 1 14.45 23.58 97.3 0.4wt% 6.36 Example 2 14.47 20.38 97.7 0.1wt% 3.16 Example 3 14.45 23.62 97.1 1.0wt% 6.40 Example 4 14.42 23.65 96.8 1.5wt% 6.43 Example 5 14.39 21.75 97.5 0.4wt% 4.53 Comparative Example 1 14.41 21.53 97.1 0.4wt% 4.31

[0127] Where Br is the remanent magnetization, Hcj is the intrinsic coercivity, and Hk / Hcj is the squareness.

[0128] Comparative analysis of the test results of Examples 1-5 and Comparative Example 1 shows that the method for preparing neodymium iron boron magnets of the present invention can effectively control and improve the grain boundary diffusion efficiency to improve the intrinsic coercivity of the magnet, thereby obtaining a neodymium iron boron magnet with good performance.

[0129] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0130] The above embodiments merely illustrate several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A method for preparing a neodymium iron boron magnet, characterized in that, Includes the following steps: The powder of neodymium iron boron magnets is pressed to prepare a square compact; the surface corresponding to the S magnetic pole and the surface corresponding to the N magnetic pole of the square compact are the orientation surface M, and any two face-to-face surfaces among the remaining surfaces are the H surface; A first diffusion layer is formed on the orientation surface M using a first diffusion source, and a second diffusion layer is formed on the H surface using a second diffusion source to prepare a preform. The preform is subjected to solidification diffusion treatment, degassing treatment, sintering treatment and tempering treatment in sequence to prepare neodymium iron boron magnets; Wherein, the first diffusion source and the second diffusion source are independently selected from: X a Y b and R c Z d At least one of them; X is a rare earth element and includes at least one heavy rare earth element; Y and Z are each independently selected from at least one non-metallic element and a non-rare earth metallic element; R is a non-heavy rare earth metallic element and is different from Z. 20w%≤a≤99.9wt%, 0.1wt%≤b≤80wt%, a+b=100%; 0≤c≤99.9wt%, 0.1wt%≤d≤100wt%, c+d=100%.

2. The method for preparing a neodymium iron boron magnet as described in claim 1, characterized in that, The Y is selected from at least one of H, O, F, N, Al, Cu, Co, Ga, Sn, Zr, Ti, Si, and Fe; and / or X is at least one of Pr, Nd, Dy, Tb, Ho, and Gd, and includes at least one of Tb, Ho, and Gd; and / or The X a Y b The particle size is <100μm.

3. The method for preparing a neodymium iron boron magnet as described in claim 2, characterized in that, The R and Z are each independently selected from at least one of Pr, Nd, Al, Cu, Co, Ga, Sn, Zr, Ti, Si, and Fe, and the R and Z are different; and / or Under normal pressure, the R c Z d Melting point ≤ 900℃; and / or The R c Z d The particle size is <100μm.

4. The method for preparing a neodymium iron boron magnet according to any one of claims 1 to 3, characterized in that, Based on the total mass of the first diffusion layer and the second diffusion layer, the mass percentage of the first diffusion layer is 0.1% to 1.5%.

5. The method for preparing a neodymium iron boron magnet according to any one of claims 1 to 3, characterized in that, Both the first diffusion source and the second diffusion source contain the following components: X a Y b and R c Z d ;or The components of the first diffusion source include X a Y b The components of the second diffusion source include R c Z d ;or The components of the second diffusion source include X a Y b The components of the first diffusion source include R c Z d .

6. The method for preparing a neodymium iron boron magnet according to any one of claims 1 to 3, characterized in that, The steps of forming the first diffusion layer and the second diffusion layer are performed by vibration powder application, spraying, or printing.

7. The method for preparing a neodymium iron boron magnet according to any one of claims 1 to 3, characterized in that, The conditions for the curing diffusion treatment include: a vacuum degree <5×10⁻⁶. -2 Pa, heat treatment at 120±30℃ for 0.5h~1h; and / or The exhaust treatment steps include: sequentially performing heat preservation treatments at temperature ranges of 400±50℃, 600±50℃, and 800±60℃; and / or The sintering conditions include: a vacuum degree <5×10⁻⁻¹ 2 Pa, heat treatment at 880℃~1080℃ for 2h~20h; and / or The conditions for the tempering process include: a vacuum degree < 5 × 10⁻⁴ 2 Heat treatment at 440℃~700℃ for 2h~10h.

8. The method for preparing a neodymium iron boron magnet according to any one of claims 1 to 3, characterized in that, During the formation of the first diffusion layer and the formation of the second diffusion layer, the oxygen content is controlled to be ≤500ppm.

9. The method for preparing a neodymium iron boron magnet according to any one of claims 1 to 3, characterized in that, The density of the square compact is >4 g / cm³. 3 ; and / or The size of the orientation surface M is ≤35mm, the size of the H surface is ≤50mm, and the size of the remaining surfaces in the square blank is ≤60mm.

10. A neodymium iron boron magnet, characterized in that, It is prepared by the method for preparing neodymium iron boron magnets as described in any one of claims 1 to 9.

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