Neodymium-iron-boron magnet and preparation method thereof

Abstract

The invention provides a neodymium-iron-boron magnet and a preparation method thereof, and the preparation method comprises the following steps: carrying out pressing treatment on powder of the neodymium-iron-boron magnet to prepare a square pressed blank; the surface corresponding to the S magnetic pole and the surface corresponding to the N magnetic pole of the square compact are orientation surfaces M, and any two face-to-face surfaces in the rest surfaces are H surfaces; forming a first diffusion layer on the orientation surface M by adopting a first diffusion source, forming a second diffusion layer on the surface H by adopting a second diffusion source, and preparing a preformed blank; the preformed blank is subjected to curing diffusion treatment, exhaust treatment, sintering treatment and tempering treatment in sequence, and the neodymium-iron-boron magnet is prepared; wherein the first diffusion source and the second diffusion source are respectively and independently selected from at least one of XaYb and RcZd. According to the preparation method, the grain boundary diffusion efficiency and stability can be effectively improved, then the magnet coercive force of the neodymium-iron-boron magnet is improved, and the production efficiency can be improved.

Description

Technical Field

[0001] The invention relates to the technical field of alloys, and in particular to a neodymium iron boron magnet and a preparation method thereof. Background Art

[0002] NdFeB magnets are also called NdFeB magnets. They are made of neodymium, iron, and boron (Nd2Fe 14 B) forms a tetragonal crystal, whose magnetic energy product (BHmax) is greater than that of samarium cobalt magnets. It is one of the materials with the largest magnetic energy product in the world. It is the permanent magnet with magnetic properties second only to absolute zero holmium magnets and is also the most commonly used rare earth magnet. NdFeB magnets are widely used in electronic products such as hard disks, mobile phones, headphones and battery-powered tools.

[0003] At present, with the rapid development of new energy vehicles, energy-saving variable frequency air conditioners, industrial robots and servo motors, the demand for sintered NdFeB is gradually increasing; and with the intensification of market competition and customers' control of costs, the grain boundary diffusion technology of sintered NdFeB has gradually become the mainstream in this related field with its high cost performance. The grain boundary diffusion technology in the traditional preparation method is often to perform diffusion coating + diffusion heat treatment after the blank is prepared, processed and cleaned on the surface, in order to improve the coercive force of the substrate; but this type of technical equipment has high investment costs, long process flow, limited product specifications (generally 2 to 10 mm thick magnetic sheets), and complex composite coating process flow.

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

[0005] Based on this, the present application provides a NdFeB magnet and a preparation method thereof, which can effectively control and improve the grain boundary diffusion efficiency, obtain NdFeB magnets 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 efficient diffusion technology.

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

[0007] In a first aspect of the present application, a method for preparing a neodymium iron boron magnet is provided, comprising the following steps:

[0008] The powder of the NdFeB 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 orientation planes M, and any two facing surfaces of the remaining surfaces are H planes;

[0009] A first diffusion source is used to form a first diffusion layer on the orientation plane M, and a second diffusion source is used to form a second diffusion layer on the H plane to prepare a preform;

[0010] The preform is sequentially subjected to a solidification diffusion treatment, an exhaust treatment, a sintering treatment and a tempering treatment to prepare a NdFeB magnet;

[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;

[0012] X is a rare earth element and includes at least one heavy rare earth element, Y and Z are independently selected from at least one of non-metallic elements and non-rare earth metal elements, R is a non-heavy rare earth metal 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 green sheet: 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, in the subsequent diffusion sintering process, the non-heavy rare earth diffusion source can prompt the green sheet to open the diffusion channel, so that the heavy rare earth diffusion source penetrates and wraps around the main phase grains on the orientation plane M, reconstructs the main phase grain boundaries to form a core-shell structure, thereby effectively controlling and improving the grain boundary diffusion efficiency and stability, and further improving the magnetic coercive force of the NdFeB magnet.

[0016] At the same time, the above preparation process effectively improves the efficiency and stability of grain boundary diffusion. Even for high-thickness square compacts, the grain boundary diffusion efficiency can be effectively improved, and the subsequent diffusion sintering time can be shortened, greatly reducing the time cost. It is a short-range and efficient diffusion technology that can cover high-thickness magnets and can fill the gap in short-range and efficient diffusion technology.

[0017] 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; and / or

[0018] The 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 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 The melting point is ≤ 900°C; and / or

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

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

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

[0025] In some embodiments, the components of the first diffusion source and the second diffusion source both include: 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 steps of forming the second diffusion layer are performed by vibrating powder, spraying or printing.

[0029] In some embodiments, the curing and diffusion treatment conditions include: -2 Pa, keep warm at 120±30℃ for 0.5h~1h; and / or

[0030] The exhaust treatment step includes: performing heat preservation treatment in the temperature ranges of 400±50°C, 600±50°C, and 800±60°C in sequence; and / or

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

[0032] The tempering treatment conditions include: vacuum degree <5×10- 2 Pa, heat preservation treatment at 440℃~700℃ for 2h~10h.

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

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

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

[0036] A second aspect of the present application provides a neodymium iron boron magnet, which is prepared by the preparation method of the neodymium iron boron magnet of the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of the square compact prepared in Example 1.

[0038] In the figure: S, South Pole; N, North Pole. DETAILED DESCRIPTION

[0039] For ease of understanding of the present application, the present application will be described more fully below, and preferred embodiments of the present application are provided. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present application belongs. The terms used herein in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0041] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0042] The "range" disclosed in the present application can be defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The range defined in this way can be inclusive or exclusive of the end values, and any end value can be included or excluded independently, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a specific parameter, it is understood that the range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are also listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to listing the parameter as, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when a parameter is expressed 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", "optional", and "optional" mean optional, that is, any one of the two parallel schemes of "yes" or "no". If there are multiple "options" in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "option" is independent.

[0044] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0045] An embodiment of the present application provides a method for preparing a NdFeB magnet, comprising the following steps S10 to S30.

[0046] S10: pressing the powder of the NdFeB magnet 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 orientation planes M, and any two facing surfaces of the remaining surfaces are H planes.

[0047] S20: using a first diffusion source to form a first diffusion layer on the orientation plane M, and using a second diffusion source to form a second diffusion layer on the H plane, to prepare a preform.

[0048] S30: performing a solidification diffusion treatment, an exhaust treatment, a sintering treatment and a tempering treatment on the preform in sequence to prepare a NdFeB magnet.

[0049] 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 .

[0050] X is a rare earth element and includes at least one heavy rare earth element, Y and Z are independently selected from at least one of non-metallic elements and non-rare earth metal elements, R is a non-heavy rare earth metal 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 green 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, in the subsequent diffusion sintering process, the non-heavy rare earth diffusion source can prompt the green compact to open the diffusion channel, so that the heavy rare earth diffusion source penetrates and wraps around the main phase grains on the orientation plane M, reconstructs the main phase grain boundary to form a core-shell structure, thereby effectively controlling and improving the grain boundary diffusion efficiency and stability, and further improving the magnetic coercive force of the NdFeB magnet.

[0054] At the same time, the above preparation process effectively improves the efficiency and stability of grain boundary diffusion. Even for high-thickness square compacts, the grain boundary diffusion efficiency can be effectively improved, and the subsequent diffusion sintering time can be shortened, greatly reducing the time cost. It is a short-range and efficient diffusion technology that can cover high-thickness magnets and can fill the gap in short-range and efficient diffusion technology.

[0055] It can be understood that the square compact is a magnetic material, that is, it has two magnetic poles: a south (S) pole and a north (N) pole, and six surfaces. The surface corresponding to the S pole and the surface corresponding to the N pole are orientation planes M. Among the remaining four surfaces, there are two groups of face-to-face corresponding surfaces. Any two face-to-face surfaces are H surfaces, and the remaining two surfaces do not need any treatment.

[0056] Please refer to Figure 1 , Figure 1 It is a schematic diagram of a square compact in one embodiment. The left figure is a three-dimensional schematic diagram of a square compact having two magnetic poles: a south (S) pole and a north (N) pole. The surface corresponding to the S pole and the surface corresponding to the N pole are orientation planes M, i.e., surfaces corresponding to the M coordinate direction in the right coordinates. Among the remaining four surfaces, there are two groups of face-to-face corresponding surfaces H and L, i.e., surfaces corresponding to the H and L coordinate directions in the right coordinates.

[0057] In some of these embodiments, the square compact is a rectangular compact.

[0058] In some of the embodiments, among the remaining four surfaces of the square green compact except the M-oriented surface, two surfaces facing each other and having smaller sizes are H surfaces.

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

[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, the components of the first diffusion source and the second diffusion source include: a Y b and R c Z d。

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

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

[0064] In some of the 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%, 20w%, 25w%, 30w%, 35w%, 40w%, 45w%, 50w%, 55w%, 60w%, 65w%, 70w%, 75w%, 80w%.

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

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

[0071] It will be appreciated that the above particle sizes are average particle sizes.

[0072] In some of the embodiments, R and Z are 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 embodiments, R is selected from at least one of Pr and Nd.

[0074] In some of the embodiments, at normal pressure, R c Z d The melting point is ≤900℃.

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

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

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

[0078] In some of the 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 by any technical means commonly used in the art for forming a diffusion layer, as long as the first diffusion source can be loaded into a layer on the orientation plane M, and is not limited to the above method.

[0080] In a specific example, the first diffusion source can be applied to the pressed green orientation surface M by rubber sponge printing, until the pressed green orientation surface M 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 vibrating powder spreading, spraying or printing.

[0082] It should be noted that the step of forming the second diffusion layer can be performed by any technical means commonly used in the art for forming a diffusion layer, as long as the second diffusion source can be loaded into a layer on the H-plane, and is not limited to the above method.

[0083] Specifically, the second diffusion source is evenly distributed on the bottom of the graphite box through a vibrating powder distribution device, and then packed in a graphite box according to the principle of placing the H surface of the square compact up and down, and then the second diffusion source powder is applied through a vibrating powder distribution device until the H surface of the compact is covered with a preset weight of the second diffusion layer.

[0084] It should be noted that there is no specific order for the steps of forming the first diffusion layer and the steps of forming the second diffusion layer. The second diffusion layer can be formed first or the first diffusion layer can be formed first.

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

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

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

[0088] In some of these embodiments, the sizes of the two surfaces in the orientation plane M may be the same or different.

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

[0090] In some of these embodiments, the sizes of the two surfaces in the H-plane may be the same or different.

[0091] In some of the embodiments, the size of the remaining surface of the square compact is ≤60 mm; optionally, the size is ≤50 mm; further optionally, the size is ≤40 mm.

[0092] It can be understood that the meaning of the dimensions here is the same as above and will not be repeated here.

[0093] In some of these embodiments, the pressing process may be performed by isostatic pressing, which may increase the density.

[0094] In some embodiments, the curing and diffusion treatment conditions include: -2 Pa, keep warm at 120±30℃ for 0.5h~1h.

[0095] In some of the embodiments, the exhaust treatment step includes: performing heat preservation treatment in each temperature range of 400±50°C, 600±50°C, and 800±60°C in sequence.

[0096] In some of the embodiments, the heat preservation treatment is carried out at 400±50°C, 600±50°C, and 800±60°C for 1h~2h, 2h~3h, and 3h~5h respectively.

[0097] In some embodiments, the sintering process conditions include: vacuum degree <5×10-2 Pa, heat preservation treatment at 880℃~1080℃ for 2h~20h.

[0098] In some embodiments, the tempering treatment conditions include: in a vacuum degree of <5×10- 2 Pa, heat preservation 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 of these embodiments, the inert gas includes at least one of nitrogen or argon.

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

[0102] The NdFeB magnet has excellent magnet coercive force.

[0103] The present application will be described below in conjunction with specific embodiments, but the present application is not limited to the following embodiments. It should be understood that the attached claims summarize the scope of the present application. Under the guidance of the concept of the present application, technical personnel in the field 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 embodiments.

[0105] Example 1

[0106] (1) Select 54H powder of NdFeB magnet with preset specifications and performance, performance: residual magnetization intensity (Br) 14.51 kGs, coercive force (Hcj) = 17.22 kOe, squareness Hk / Hcj = 98.5%, powder SMD = 2.9 μm, the designed billet size after isostatic pressing is M = 28 mm, H = 40 mm, L = 50 mm, and a square compact is obtained after isostatic pressing, with a density of 4.5 g / cm 3 The schematic diagram of the square compact is shown in Figure 1 shown.

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

[0108] The oxygen content is controlled to be ≤100ppm, and the printing paste of the first diffusion source is printed on the orientation surface M by double-sided printing to form a first diffusion layer of a predetermined thickness; the alloy powder of the second diffusion source is evenly distributed on the bottom of the graphite box by a vibration powder distribution device, and then the printed blank is placed in the graphite box according to the principle of placing the H surface up and down, and the second diffusion source is evenly distributed on the H surface by a vibration powder distribution device to form a second diffusion layer to obtain a preform. Among them, based on the total mass of the first diffusion layer and the second diffusion layer, the mass proportion of the first diffusion layer (referred to as weight gain ratio) is 0.4wt%.

[0109] (3) Place the preform in a vacuum of <5×10 -2 The sample was heated in a Pa environment and kept at 120°C for 30 minutes to solidify and diffuse the printed first diffusion layer; then, insulation and exhaust steps were set at 380°C, 600°C, and 850°C, and the insulation times were 60 minutes, 120 minutes, and 300 minutes, respectively, and then sintered at 950°C for 720 minutes, and then tempered at 500°C for 240 minutes. After taking out of the furnace, the product was prepared into a D10×10 standard sample column to obtain a standard sample of NdFeB magnet.

[0110] (4) The NdFeB magnets were tested using NIM-6500C. The measurement results are shown in Table 1.

[0111] Embodiments 2 to 4

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

[0113] The other steps are the same as those 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), the second diffusion source is applied to the orientation plane M, and the first diffusion source is applied to the H plane.

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

[0118] Please see Table 1 for the test results.

[0119] Comparative Example 1

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

[0121] (2) The square pressed blank is vacuum sintered: after the vacuum degree is less than 5Pa, it is heated, and insulation and exhaust steps are set at 380°C, 600°C, and 850°C, respectively, with insulation times of 60min, 120min, and 300min, respectively. Then, it is sintered at 1070°C for 300min. After sintering, it is aged: the first temperature is 900°C, the insulation time is 150min, the second aging temperature is 500°C, and the insulation time is 300min. After being taken out of the furnace, it is processed into a D10*10 standard sample column blank. The performance is tested using NIM-6500C, and the measurement results are Br=14.51kGs and Hcj=17.22kOe.

[0122] (3) The components of the first diffusion source and the second diffusion source, and the weight gain ratio of the first diffusion layer are controlled the same as those in Example 1. The steps are basically the same as step (2) of Example 1. The only difference is that after the surface of the blank in the above step (2) is cleaned to be oil-free and rust-free, the first diffusion layer and the second diffusion layer are obtained in an environment of normal temperature and pressure without oxygen control. The first diffusion layer is obtained by conventional screen printing; the second diffusion layer is obtained by vibrating powder spreading. The implementation steps are the same as step (2) in Example 1.

[0123] (4) Place the preform in a vacuum of <5×10 -2 The product was heated in a Pa environment, and the insulation steps were set at 450℃ and 800℃, with insulation time of 30min and 150min respectively, and then at 910℃, insulation time of 600min and 500℃, insulation time of 240min. After being taken out of the furnace, the product was prepared into a D10×10 standard sample column to obtain a standard sample of NdFeB magnet.

[0124] (5) The NdFeB magnets were tested using NIM-6500C. 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 residual magnetization, Hcj is the intrinsic coercivity, and Hk / Hcj is the squareness.

[0128] Comparative analysis of the test results of Examples 1 to 5 and Comparative Example 1 shows that the method for preparing NdFeB magnets of the present invention can effectively improve the grain boundary diffusion efficiency to increase the intrinsic coercive force of the magnet, thereby obtaining NdFeB magnets with good performance.

[0129] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described 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 only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of this patent shall be subject to the attached claims.

Claims

1. A method for preparing a neodymium iron boron magnet, characterized in that: The steps include: The powder of the NdFeB 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 orientation planes M, and any two facing surfaces of the remaining surfaces are H planes; A first diffusion source is used to form a first diffusion layer on the orientation plane M, and a second diffusion source is used to form a second diffusion layer on the H plane to prepare a preform; The preform is sequentially subjected to a solidification diffusion treatment, an exhaust treatment, a sintering treatment and a tempering treatment to prepare a NdFeB 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; X is a rare earth element and includes at least one heavy rare earth element, Y and Z are independently selected from at least one of non-metallic elements and non-rare earth metal elements, R is a non-heavy rare earth metal 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 NdFeB magnet according to claim 1, wherein: 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 The 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 NdFeB magnet according to claim 2, wherein: The R and the Z are independently selected from at least one of Pr, Nd, Al, Cu, Co, Ga, Sn, Zr, Ti, Si, and Fe, and the R and the Z are different; and / or Under normal pressure, the R c Z d The melting point is ≤ 900°C; and / or The R c Z d The particle size is <100μm.

4. The method for preparing a NdFeB 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 proportion of the first diffusion layer is 0.1% to 1.5%.

5. The method for preparing a NdFeB magnet according to any one of claims 1 to 3, characterized in that: The components of the first diffusion source and the second diffusion source both include: 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 NdFeB magnet according to any one of claims 1 to 3, characterized in that: The steps of forming the first diffusion layer and the steps of forming the second diffusion layer are performed by vibrating powder, spraying or printing.

7. The method for preparing a NdFeB magnet according to any one of claims 1 to 3, characterized in that: The curing and diffusion treatment conditions include: in a vacuum degree of <5×10 -2 Pa, keep warm at 120±30℃ for 0.5h~1h; and / or The exhaust treatment step includes: performing heat preservation treatment in the temperature ranges of 400±50°C, 600±50°C, and 800±60°C in sequence; and / or The sintering conditions include: vacuum degree <5×10- 2 Pa, heat preservation treatment at 880℃~1080℃ for 2h~20h; and / or The tempering treatment conditions include: vacuum degree <5×10- 2 Pa, heat preservation treatment at 440℃~700℃ for 2h~10h.

8. The method for preparing a NdFeB magnet according to any one of claims 1 to 3, characterized in that: In the process of forming the first diffusion layer and the process of forming the second diffusion layer, the oxygen content is controlled to be ≤500 ppm.

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

10. A neodymium iron boron magnet, characterized in that: The NdFeB magnet is prepared by the method for preparing the NdFeB magnet as claimed in any one of claims 1 to 9.

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