Neodymium-iron-boron magnet and preparation method thereof

Abstract

The invention discloses a neodymium-iron-boron magnet and a preparation method thereof. Raw materials of the neodymium-iron-boron magnet comprise a neodymium-iron-boron magnet base body and slurry containing a heavy rare earth element RE '. The component composition of the neodymium iron boron magnet base body is REx (Fe < 100-a > Ma) < 100-x-y > By, wherein RE is at least two of La, Ce, Pr and Nd and certainly contains Pr, and the mass of Pr in RE accounts for 25%-35% of the total mass of RE; m is selected from at least one of Co, Cu, Al, Nb, Ti, Zr and Ga; a, x and y represent numerical values obtained by multiplying the weight percentage of each element by 100, 28.5 < = x < = 31, 0.85 < = y < = 1.02, and 1.9 < = a < = 4.4; rE'is at least one of Pr, Gd, Tb, Dy, Ho and Er. After raw materials are made into neodymium iron boron alloy powder, a neodymium iron boron magnet base body is obtained through magnetic field forming, sintering and aging treatment, then the surface of the magnet base body is coated with slurry, elements in the slurry permeate into the interior from the surface of a flaky magnet through grain boundary diffusion, and the neodymium iron boron magnet is obtained. The use of heavy rare earth elements can be reduced, and meanwhile, the magnetic performance of the magnet is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of rare earth permanent magnet materials, and particularly relates to a neodymium iron boron magnet and a preparation method thereof. Background Art

[0002] Sintered neodymium iron boron magnets are widely used in the fields of wind power generation, new energy vehicles, and air-conditioning compressors. Due to the changing working environment, the sintered neodymium iron boron magnets used are required to have excellent coercivity performance.

[0003] For sintered neodymium iron boron magnets produced by the single alloy process, especially when producing magnets of grades above SH, UH, and EH, the coercivity of the magnets is generally increased by adding medium and heavy rare earth elements. However, medium and heavy rare earth resources are precious, and the raw material market price of medium and heavy rare earths has been rising in recent years. At the same time, in recent years, the demand for neodymium iron boron magnets in the fields of wind power generation, new energy vehicles, and air-conditioning compressors has increased rapidly. Therefore, increasing the coercivity of the magnets by adding medium and heavy rare earth elements faces heavy cost pressure. The grain boundary diffusion technology can concentrate the heavy rare earth elements at the grain boundaries of the magnet, improve the coercivity of the magnet, and help reduce production costs and avoid the reduction of magnetic energy product.

[0004] However, the grain boundary diffusion is affected by the diffusion depth and diffusion efficiency, resulting in poor grain boundary diffusion effect. The present invention develops a rare earth diffusion source, realizes the precise control of the microzone metallurgical reaction through the grain boundary diffusion technology, and optimizes the diffusion process and improves the magnet performance by using the low heavy rare earth multi-component composite diffusion technology and the heavy rare earth segregation structure design. Summary of the Invention

[0005] The first object of the present invention is to provide a neodymium iron boron magnet in view of the above problems.

[0006] The second object of the present invention is to provide a preparation method of a neodymium iron boron magnet. The magnet prepared by this method has high coercivity and low production cost.

[0007] To achieve the above object, the present invention is realized by the following technical solutions: The first aspect of the present invention provides a neodymium iron boron magnet, the raw materials of which include a neodymium iron boron magnet matrix and a slurry containing a heavy rare earth element RE'; the composition of the neodymium iron boron magnet matrix is: RE x (Fe 100-a M a ) 100-x-y B y; wherein, RE is at least two of La, Ce, Pr, and Nd and must contain Pr, and the mass of Pr in RE is 25% - 35% of the total mass of RE; M is selected from at least one of Co, Cu, Al, Nb, Ti, Zr, and Ga; a, x, and y represent the values obtained by multiplying the weight percentages of each element by 100, and 28.5 ≤ x ≤ 31, 0.85 ≤ y ≤ 1.02, 1.9 ≤ a ≤ 4.4; the RE' is at least one of Pr, Gd, Tb, Dy, Ho, Er, La, and Ce; The microstructure of the NdFeB magnet includes a main phase and a grain boundary phase. The main phase is RE'' 2 Fe 14 B, and RE'' is at least two of La, Ce, Pr, and Nd and must contain Pr; the grain boundary phase is a rare earth-rich phase, including Pr 2 Fe, Nd 2 Fe, (PrNd) 2 Fe, Pr 3 Fe, Nd 3 Fe, (PrNd) 3 Fe, etc.

[0008] Preferably, by weight percentage, the content of each element in M in the magnet matrix is: Co 0.6 - 1.2%, Ga 0.2 - 0.5%, Ti 0.1 - 0.25%, Al 0.05 - 0.2%, Cu 0.2 - 0.4%, Zr 0.15 - 0.3%.

[0009] In the present invention, the mass of Pr is 25 - 35% of the total mass of RE. The addition of Pr can improve the coercivity of the product, but too much addition will cause the temperature coefficient of the product to deteriorate, and too little addition will cause cost increase and still not meet the coercivity performance of the product.

[0010] The Nd element can provide the magnetic properties of the magnet. Too little will cause the product performance to deteriorate or even oxidize; but too much use will cause a significant increase in cost. The use of the Co element can increase the Curie temperature of the magnet and improve the corrosion resistance. Too much use will cause the magnet to form soft magnetism, resulting in a reduction in product performance and an increase in cost; too little will cause the temperature coefficient of the product not to meet the use conditions and be more vulnerable to corrosion under harsh conditions, thus shortening the magnet life. The role of Ga is to enhance the coercivity of the magnet and improve the mechanical properties. Too much use will cause a reduction in magnet performance and a decrease in the Curie temperature, increasing the cost; too little will cause insufficient performance optimization and poor temperature stability. The role of Ti is to refine the grains and enhance the thermal stability of the magnet. Too much use will cause poor workability of the product and a decrease in the Curie temperature of the product; too little will cause insufficient performance optimization and affect the diffusibility of the product grain boundary.

[0011] Preferably, the microstructure of the neodymium iron boron magnet further includes a third phase, and the third phase includes Nd 6 Fe 13 Ga phase.

[0012] Preferably, by weight percentage, the composition of the neodymium iron boron magnet matrix is: Pr 7%-12%, Nd 16.5%-24.5%, Co 0.6-1.2%, Ga 0.2-0.5%, Ti 0.1-0.25%, Al 0.05-0.2%, Cu 0.2-0.4%, Zr 0.15-0.3%, B 0.85-1.02%, and the balance is Fe.

[0013] More preferably, by weight percentage, the raw material composition of the neodymium iron boron magnet matrix is: Pr 8%-11%, Nd 17.5%-23.5%, Co 0.8-1.0%, Ga 0.25-0.4%, Ti 0.1-0.2%, Al 0.05-0.15%, Cu 0.2-0.3%, Zr 0.2-0.3%, B 0.88-1.0%, and the balance is Fe.

[0014] Preferably, by weight percentage, the raw material composition of the slurry containing heavy rare earth element RE' is: Pr 15-20%, Dy + Tb 55-60%, Cu 5-10%, Al 5-10%.

[0015] Preferably, the heavy rare earth content of the neodymium iron boron magnet ≤ 0.8 wt%; the intrinsic coercivity > 23 kOe; the remanence > 14.1 kGs; the magnetic energy product > 47 MGOe.

[0016] The second aspect of the present invention provides a method for preparing a neodymium iron boron magnet, and the specific steps of the preparation method are as follows: Step S1: The raw materials of the neodymium iron boron magnet matrix are melted and cast to obtain alloy cast sheets, the alloy cast sheets are hydrogenated and crushed to obtain alloy coarse powder, and then ground by a jet mill to obtain neodymium iron boron alloy powder with an average particle size of 2.7 μm - 3.2 μm; Step S2: The neodymium iron boron alloy powder is formed into a green body by magnetic field molding, and then sintered and aged to obtain the neodymium iron boron magnet matrix; Step S3: The neodymium iron boron magnet matrix is sliced to obtain sheet magnets, a slurry containing heavy rare earth element RE' is sprayed on the sheet magnets, and then the elements in the slurry are infiltrated from the surface of the sheet magnets to the inside through grain boundary diffusion, and the neodymium iron boron magnet is obtained after tempering treatment.

[0017] Preferably, in the step S1, the melting temperature is 1350 - 1450 °C, the casting temperature is 1400 - 1480 °C, and the rotational speed of the rapid solidification copper roll is 28 - 36 r / min; and / or, the average thickness of the alloy cast sheet is 0.15 - 0.35 mm. More preferably, in the step S1, the casting temperature is 1430 - 1470 °C, and the rotational speed of the rapid solidification copper roll is 29 - 32 r / min; and / or, the average thickness of the alloy cast sheet is 0.25 - 0.35 mm.

[0018] Preferably, the hydrogen pulverization method includes hydrogen absorption and dehydrogenation. The hydrogen absorption pressure is 50 kPa - 100 kPa, and the dehydrogenation temperature is 520 °C - 580 °C. More preferably, the hydrogen absorption pressure is 60 kPa - 90 kPa, and the dehydrogenation temperature is 540 °C - 570 °C.

[0019] Preferably, during the grinding process of the jet mill, an antioxidant and a lubricant are also added, and the total addition amount of the antioxidant and the lubricant is 0.8‰ - 1.2‰ of the total mass of the alloy coarse powder. More preferably, the total addition amount of the antioxidant and the lubricant is 0.9‰ - 1‰ of the total mass of the alloy coarse powder.

[0020] Preferably, the addition amount of the antioxidant is 0.0‰ - 0.5‰ of the total mass of the alloy coarse powder; and / or, the addition amount of the lubricant is 0.4‰ - 1.0‰ of the total mass of the alloy coarse powder.

[0021] The inventor found that excessive addition of the antioxidant or the lubricant will increase the C content of the magnet, thereby affecting the magnet performance; too little addition will affect the orientation degree of the product, and the product performance cannot be fully exerted. If too much lubricant is added, excessive bonding will occur between the neodymium iron boron powder particles, resulting in aggravated particle agglomeration. During the magnetic field orientation process, these agglomerated particles are difficult to be evenly dispersed and arranged, thus affecting the orientation degree of the magnet, and further causing serious damage to the equipment during the product powder making process; but if the addition amount is too little, the orientation degree of the product will be reduced, resulting in low magnet performance. Excessive addition of the antioxidant will cause changes in the physical and chemical properties of the powder, and too little addition will cause the reduction of the product protection effect and product oxidation.

[0022] Preferably, the temperature of the grinding gas of the jet mill is 8 - 16 °C. More preferably, the temperature of the grinding gas of the jet mill is 10 - 15 °C; and / or, the average particle size of the fine powder obtained after the jet mill is 2.75 um - 3.0 um.

[0023] Preferably, in the step S2, the conditions for magnetic field forming include: the magnetic field strength of the orientation magnetic field is 1.7 T - 2.2 T; the forming pressure is 3 - 7 MPa; and / or, the density of the green body is 3.9 - 4.2 g / cm3 Preferably, the magnetic field strength of the orientation magnetic field is 1.9 T to 2.0 T; the molding pressure is 4 - 6 MPa; and / or, the density of the green body is 4.05 g / cm 3 .

[0024] Preferably, in step S2, the sintering temperature is 1040°C to 1080°C, and the sintering time is 6 - 10 h. More preferably, the sintering temperature is 1050°C to 1060°C, and the sintering time is 6 - 8 h. Sintering under these conditions can make the sintered NdFeB magnet more densified, reduce the pores in the magnet, improve the microstructure of the magnet, and is beneficial to the improvement of the magnet density and magnetic performance indexes such as remanence and coercivity. The inventor found in the experiment that when the sintering temperature is too high, grain growth will occur, and the magnet performance will deteriorate rapidly and irreversibly. When the temperature is too low, the density of the magnet will be insufficient or the product will be oxidized, which also affects the magnet performance.

[0025] Preferably, the aging treatment in step S2 includes at least three stages of aging; more preferably, the aging treatment is carried out in sequence of aging 1, aging 2, and aging 3; the temperature of aging 1 is 880°C to 920°C, holding for 2 - 6 h, and cooling to room temperature with the furnace; the temperature of aging 2 is 780°C to 840°C, holding for 2 - 6 h, and cooling to room temperature with the furnace; the temperature of aging 3 is 430°C to 480°C, holding for 4 - 8 h, and cooling to room temperature with the furnace.

[0026] By first carrying out the treatments of aging 1 and aging 2, a rare-earth-rich liquid phase can be formed. Then, by carrying out the aging treatment at 430°C to 480°C (eutectic temperature point), it can ensure that the rare-earth-rich phase is continuously distributed and uniformly wraps the main-phase grains, avoiding the exchange coupling between the main-phase grains.

[0027] More preferably, the temperature of aging 1 is 880°C to 910°C, holding for 2 - 4 h, and cooling to room temperature with the furnace; the temperature of aging 2 is 800°C to 830°C, holding for 2 - 4 h, and cooling to room temperature with the furnace; the temperature of aging 3 is 440°C to 470°C, holding for 6 - 8 h, and cooling to room temperature with the furnace.

[0028] In the present invention, through multi-stage aging treatment and controlling the treatment temperature and treatment time of the three stages of aging, a thin-layer continuous distribution of Nd-rich phase can be formed on the grain boundaries of the magnet, effectively increasing the demagnetizing coupling effect between the magnet grains. At the same time, by reducing the boron content in the formula and regulating the phase formation process of the third phase Nd 6 Fe 13 Ga, the optimization of the spatial distribution of the grain boundary phase is initially realized, while reducing the ferromagnetism of the grain boundary phase, enhancing the coercivity of the magnet, and greatly improving the coercivity index of the magnet, thereby obtaining a sintered NdFeB permanent magnet without heavy rare earths.

[0029] Preferably, in step S3, slicing is performed by machining, and the machining method is one of slicing, multi-wire cutting, wire cutting, and profile grinding. In the present invention, no specific limitation is imposed on the slicing method, and those skilled in the art can select according to actual needs.

[0030] Preferably, in step S3, the thickness of the sheet-shaped magnet is 4 - 6 mm.

[0031] Preferably, the weight of the slurry containing the heavy rare earth element RE' in step 3 is 0.3% - 0.7% of the weight of the sheet-shaped magnet. For example, the weight ratio of the slurry to the sheet-shaped magnet can be 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, or a value within any two of the aforementioned numerical ranges. More preferably, the weight of the slurry containing the heavy rare earth element RE' in step 3 is 0.4% - 0.6% of the weight of the sheet-shaped magnet. The present invention has excellent effects under the condition of lower usage amount, greatly reducing the cost. If the slurry is too much, the volume fraction of the main phase will decrease, resulting in a decrease in the remanence of the magnet; if it is too little, the composition and distribution of the grain boundary phase will be uneven, resulting in insufficient magnetic coercivity.

[0032] Preferably, the specific conditions for grain boundary diffusion in step S3 are: performing grain boundary diffusion for 10 - 15 h at 600 - 1000 °C and a vacuum degree < 8.0×10 -3 Pa; and / or, the temperature of the tempering treatment is 400 - 700 °C, and the time is 6 - 8 h. More preferably, the temperature of the grain boundary diffusion is 800 - 950 °C; the temperature of the tempering treatment is 450 - 470 °C, and the time is 6 - 8 h. Among them, the diffusion temperature is determined by the diffusion source. If the temperature is too high, the remanence of the magnet will decrease; if the temperature is too low, the product cannot be completely diffused into the magnet.

[0033] Compared with the prior art, the present invention has the following beneficial effects: (1) In the present invention, the alloy cast sheet is successively subjected to hydrogen pulverization, jet milling, magnetic field orientation forming, sintering, and aging treatment to obtain a neodymium iron boron magnet matrix; then the neodymium iron boron magnet matrix is prepared into a sheet-shaped neodymium iron boron magnet by slicing. The present invention adopts a low-B system process. By reducing the contents of rare earth, iron, and boron in the formula, the Nd 6 Fe 13 Ga phase formation process is regulated, the spatial distribution of the grain boundary phase is preliminarily optimized, and at the same time, the ferromagnetism of the grain boundary phase is reduced, enhancing the magnetic coercivity of the magnet; the microstructure of the magnet is regulated by the aging temperature, the grain boundary phase of the magnet is repaired, and the stability of the magnet is improved. The obtained magnet has the characteristics of high coercivity and low cost.

[0034] (2) In the present invention, by utilizing the multi-component composite diffusion technology of low heavy rare earths and the design of heavy rare earth segregation structure, the bottleneck of the growth of the comprehensive magnetic properties of sintered NdFeB is broken through. Through the grain boundary diffusion technology, the precise control of the micro-area metallurgical reaction is realized. For magnets with a thickness of more than 5 mm, the coercivity increase exceeds 5 kOe, leading the development of high-performance magnets without heavy rare earths.

[0035] (3) The matrix formula of the present invention does not contain heavy rare earth elements, which promotes the balanced utilization of light and heavy rare earth resources, saves production costs, enables batch production, and improves the product stability and market competitiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0037] Figure 1 It is the SEM image of the NdFeB magnet of Embodiment 3 of the present invention.

[0038] Figure 2 It is the schematic diagram of the SEM micro-area morphology and composition of the NdFeB magnet of Embodiment 3 of the present invention.

[0039] Figure 3 It is the SEM image of the NdFeB magnet of Comparative Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] The terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. Unless otherwise clearly indicated by the context, the singular forms used herein are also intended to include the plural forms. It should also be understood that the term "comprising" does not specifically refer to a certain characteristic, field, integer, step, action, element, and / or component, but excludes the existence or addition of other characteristics, fields, integers, steps, actions, elements, components, and / or groups.

[0041] If a part is described as being on another part, it can be directly on the other part or there may be other parts in between. When a part is described as being directly on another part, there will be no other parts in between.

[0042] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. For terms defined in a dictionary, they should be interpreted as having a meaning consistent with the relevant technical literature and the content disclosed herein, and should not be interpreted in an idealized or overly formal sense.

[0043] The content of the present invention will be described in detail below.

[0044] As an embodiment of the present invention, a neodymium iron boron magnet, the raw materials include a neodymium iron boron magnet matrix and a slurry containing a heavy rare earth element RE'; the composition of the neodymium iron boron magnet matrix is: RE x (Fe 100-a M a ) 100-x-y B y ; wherein, RE is at least two of La, Ce, Pr, Nd and must contain Pr, and the mass of Pr in RE is 25%-35% of the total mass of RE; M is selected from at least one of Co, Cu, Al, Nb, Ti, Zr, Ga; a, x and y represent the values obtained by multiplying the weight percentages of each element by 100, and 28.5≤x≤31, 0.85≤y≤1.02, 1.9≤a≤4.4; by weight percentage, the RE' is at least one of Pr, Gd, Tb, Dy, Ho, Er, La, Ce.

[0045] The microstructure of the neodymium iron boron magnet includes: a main phase and a grain boundary phase, the main phase is RE'' 2 Fe 14 B, RE'' is at least two of La, Ce, Pr, Nd and must contain Pr; the grain boundary phase is a grain boundary rare earth-rich phase, including Pr 2 Fe, Nd 2 Fe, (PrNd) 2 Fe, Pr 3 Fe, Nd 3 Fe, (PrNd) 3 Fe and other compounds.

[0046] As a preferred embodiment of the present invention, a neodymium iron boron magnet, the raw materials include a neodymium iron boron magnet matrix and a slurry containing a heavy rare earth element RE'; the composition of the neodymium iron boron magnet matrix is: RE x (Fe 100-a M a ) 100-x-y B y; wherein, RE is at least two of Pr and La, Ce, Nd and must contain Pr, and the mass of Pr in the RE is 25%-35% of the total mass of the RE; a, x and y represent the values obtained by multiplying the weight percentages of the respective elements by 100, and 28.5 ≤ x ≤ 31, 0.85 ≤ y ≤ 1.02, 1.3 ≤ a ≤ 3; by weight percentage, the contents of the respective elements in the M in the magnet matrix are: Co 0.6-1.2%, Ga 0.2-0.5%, Ti 0.1-0.25%, Al 0.05-0.2%, Cu 0.2-0.4%, Zr 0.15-0.3%; the RE' is at least one of Pr, Gd, Tb, Dy, Ho, Er, La, Ce.

[0047] The microstructure of the neodymium-iron-boron magnet includes: a main phase, a grain boundary phase, and a third phase, and the main phase is RE'' 2 Fe 14 B, and RE'' is at least two of La, Ce, Pr, Nd and must contain Pr; the grain boundary phase is a grain boundary rare-earth-rich phase, including Pr 2 Fe, Nd 2 Fe, (PrNd) 2 Fe, Pr 3 Fe, Nd 3 Fe, (PrNd) 3 Fe and other compounds; the third phase includes Nd 6 Fe 13 Ga phase.

[0048] As a preferred embodiment of the present invention, a neodymium-iron-boron magnet, the raw materials include a neodymium-iron-boron magnet matrix and a slurry containing a heavy rare-earth element RE'; by weight percentage, the raw material composition of the neodymium-iron-boron magnet matrix is: Pr 7%-12%, Nd 16.5%-24.5%, Co 0.6-1.2%, Ga 0.2-0.5%, Ti 0.1-0.25%, Al 0.05-0.2%, Cu 0.2-0.4%, Zr 0.15-0.3%, B 0.85~1.02%, and the balance is Fe; by weight percentage, the raw material composition of the slurry containing the heavy rare-earth element RE' is: Pr 15~20%, Dy + Tb 55~60%, Cu 5~10%, Al 5~10%.

[0049] The microstructure of the neodymium-iron-boron magnet includes: a main phase, a grain boundary phase, and a third phase, and the main phase is RE'' 2 Fe 14 B, RE'' is at least two of La, Ce, Pr, Nd and must contain Pr, and the grain boundary phase is a grain boundary rare-earth-rich phase, including Pr 2Fe, Nd 2 Fe, (PrNd) 2 Fe, Pr 3 Fe, Nd 3 Fe, (PrNd) 3 Compounds such as Fe; the third phase includes Nd 6 Fe 13 Ga phase

[0050] As a preferred embodiment of the present invention, a neodymium iron boron magnet, the raw materials include a neodymium iron boron magnet matrix and a slurry containing heavy rare earth element RE'; by weight percentage, the raw material composition of the neodymium iron boron magnet matrix is: Pr 8% - 11%, Nd 17.5% - 23.5%, Co 0.8 - 1.0%, Ga 0.25 - 0.4%, Ti 0.1 - 0.2%, Al 0.05 - 0.15%, Cu 0.2 - 0.3%, Zr 0.2 - 0.3%, B 0.88 - 1.0%, and the balance is Fe; by weight percentage, the raw material composition of the slurry containing heavy rare earth element RE' is Pr 15 - 20%, Dy + Tb 55 - 60%, Cu 5 - 10%, Al 5 - 10%.

[0051] The microstructure of the neodymium iron boron magnet includes: a main phase, a grain boundary phase, and a third phase. The main phase is RE'' 2 Fe 14 B, where RE'' is at least two of La, Ce, Pr, Nd and must contain Pr; the grain boundary phase is a grain boundary rare earth rich phase, including Pr 2 Fe, Nd 2 Fe, (PrNd) 2 Fe, Pr 3 Fe, Nd 3 Fe, (PrNd) 3 Compounds such as Fe; the third phase includes Nd 6 Fe 13 Ga phase

[0052] As an embodiment of the present invention, a preparation method of a neodymium iron boron magnet, the specific steps of the preparation method are as follows: Step S1: Melting the raw materials of the neodymium iron boron magnet matrix at 1350 - 1450 °C according to the ratio, and then rapidly casting and cooling. The casting temperature is 1400 - 1480 °C, and the rotational speed of the rapid solidification copper roll is 28 - 36 r / min; an alloy cast sheet with an average thickness of 0.15 - 0.35 mm is obtained; The alloy cast sheet is subjected to hydrogen crushing under the conditions of a hydrogen absorption pressure of 50 kPa to 100 kPa and a dehydrogenation temperature of 520 °C to 580 °C to obtain alloy coarse powder with an average particle size of 5 to 50 μm; after adding an antioxidant and a lubricant (the addition amounts of the antioxidant and the lubricant are 0‰ to 0.5‰ and 0.4‰ to 1‰ respectively, and the total amount is 0.8‰ to 1.2‰), it is ground by a jet mill (the temperature of the grinding gas is 8 to 16 °C) to obtain neodymium iron boron alloy powder with an average particle size of 2.7 μm to 3.2 μm; Step S2: The neodymium iron boron alloy powder is formed by a magnetic field to obtain a green body with a density of 3.9 to 4.2 g / cm 3 The magnetic field strength of the orientation magnetic field is 1.7 T to 2.2 T, and the forming pressure is 3 - 4 MPa; then it is sintered at 1040 °C to 1080 °C for 6 - 10 h, and after furnace cooling, aging 1, aging 2, and aging 3 treatments are carried out in sequence. The temperature of the aging 1 is 880 °C to 920 °C, the holding time is 2 - 6 h, and it is furnace cooled to room temperature; the temperature of the aging 2 is 780 °C to 840 °C, the holding time is 2 - 6 h, and it is furnace cooled to room temperature; the temperature of the aging 3 is 430 °C to 480 °C, the holding time is 4 - 8 h, and it is furnace cooled to room temperature to obtain a neodymium iron boron magnet matrix with high density; Step S3: The neodymium iron boron magnet matrix is sliced by machining to obtain a sheet magnet, and a slurry containing a heavy rare earth element RE' is sprayed on the sheet magnet. The weight of the slurry containing the heavy rare earth element RE' is 0.3% - 0.7% of the weight of the sheet magnet. At 600 - 1000 °C and a vacuum degree < 8.0×10 -3 Pa, grain boundary diffusion is carried out for 10 - 15 h to penetrate the heavy rare earth element from the surface of the sheet magnet into the interior of the sheet magnet, and after tempering treatment at 400 - 700 °C for 6 - 8 h, the neodymium iron boron magnet is obtained.

[0053] As a preferred embodiment of the present invention, a method for preparing a neodymium iron boron magnet, the specific steps of the preparation method are as follows: Step S1: According to the ratio, the raw materials of the neodymium iron boron magnet matrix are melted at 1350 - 1450 °C, and then rapidly cast and cooled. The casting temperature is 1430 - 1470 °C, and the rotational speed of the rapid solidification copper roll is 29 - 32 r / min; an alloy cast sheet with an average thickness of 0.25 - 0.35 mm is obtained; The alloy cast sheet is subjected to hydrogen crushing under the conditions of a hydrogen absorption pressure of 60 kPa to 90 kPa and a dehydrogenation temperature of 540 °C to 570 °C to obtain alloy coarse powder with an average particle size of 4 - 50 μm; after adding an antioxidant and a lubricant (the addition amounts of the antioxidant and the lubricant are 0.0‰ to 0.5‰ and 0.4‰ to 1.0‰ respectively, and the total amount is 0.9‰ to 1‰), it is ground by a jet mill (the temperature of the grinding gas is 10 - 15 °C) to obtain neodymium-iron-boron alloy powder with an average particle size of 2.75 μm to 3.0 μm; Step S2: The neodymium-iron-boron alloy powder is formed by a magnetic field to obtain a green body with a density of 4.05 g / cm 3 The magnetic field strength of the orientation magnetic field is 1.9 T to 2.0 T, and the forming pressure is 4 - 6 MPa; then it is sintered at 1050 °C to 1060 °C for 6 - 8 h, and after furnace cooling, aging 1, aging 2, and aging 3 treatments are carried out in sequence. The temperature of the aging 1 is 880 °C to 910 °C, and it is kept warm for 2 - 4 h and then furnace cooled to room temperature; the temperature of the aging 2 is 800 °C to 830 °C, and it is kept warm for 2 - 4 h and then furnace cooled to room temperature; the temperature of the aging 3 is 440 °C to 470 °C, and it is kept warm for 6 - 8 h and then furnace cooled to room temperature to obtain a neodymium-iron-boron magnet matrix with high density; Step S3: The neodymium-iron-boron magnet matrix is sliced by any one of multi-wire cutting, wire cutting, and profile grinding to obtain a sheet magnet, and a slurry containing a heavy rare earth element RE' is sprayed on the sheet magnet. The weight of the slurry containing the heavy rare earth element RE' is 0.4% - 0.6% of the weight of the sheet magnet. At 800 - 950 °C and a vacuum degree < 8.0×10 -3 Pa, grain boundary diffusion is carried out to penetrate the heavy rare earth element from the surface of the sheet magnet into the interior of the sheet magnet, and after tempering treatment at 450 - 470 °C for 6 - 8 h, the neodymium-iron-boron magnet is obtained.

[0054] The neodymium-iron-boron magnet and its preparation method of the present invention will be described below with reference to the accompanying drawings and embodiments. However, the present invention can be implemented in various different ways and is not limited to the embodiments described herein.

[0055] The raw material ratios of the neodymium-iron-boron magnet matrixes in Examples 1 - 5 and Comparative Examples 1 - 5 are shown in Table 1 below, and the raw material ratios of the slurries are shown in Table 2 below.

[0056] Table 1

[0057] Table 2

[0058] Example 1 This example discloses a neodymium-iron-boron magnet, and the raw materials include the neodymium-iron-boron magnet matrix RE x(Fe 100-a M a ) 100-x-y B y and a slurry containing heavy rare earth element RE', and the specific raw material ratio is shown in Table 1; the microstructure of the NdFeB magnet includes: a main phase, a grain boundary phase, and a third phase, and the main phase includes PrNd 2 Fe 14 B; the grain boundary phase is a grain boundary rare earth-rich phase, including Pr 2 Fe, Nd 2 Fe, (PrNd) 2 Fe, Pr 3 Fe, Nd 3 Fe, (PrNd) 3 Fe and other compounds; the third phase includes Nd 6 Fe 13 Ga phase.

[0059] This embodiment discloses a preparation method of a NdFeB magnet, and the specific steps are as follows: Step S1: According to the raw material ratio of the NdFeB magnet matrix, weigh 228 kg of PrNd, 16 kg of Pr, 36.8 kg of B-Fe (the proportion of B in B-Fe is 20 wt%), 6.4 kg of Co, 2 kg of Cu, 0.4 kg of Al, 1.76 kg of Zr, 0.8 kg of Ti, 2.8 kg of Ga, and 445.04 kg of Fe, melt at 1450 °C, and then rapidly cast and cool. The casting temperature is 1450 °C, and the rotational speed of the rapid solidification copper roll is 29 r / min; an alloy cast sheet with an average thickness of 0.275 mm is obtained; Under the conditions of a hydrogen absorption pressure of 80 kPa and a dehydrogenation temperature of 560 °C, the alloy cast sheet is hydrogenated and crushed to obtain alloy coarse powder with an average particle size of 25 μm; after adding 0.45‰ of antioxidant and 0.45‰ of lubricant, it is ground by a jet mill (the temperature of the grinding gas is 10 °C) to obtain NdFeB alloy powder with an average particle size of 2.9 μm; the antioxidant is purchased from Tianjin Yuesheng, with the brand number 3#; the lubricant is purchased from Tianjin Yuesheng, with the brand number 6#.

[0060] Step S2: The NdFeB alloy powder is formed by magnetic field to obtain a density of 4.05 g / cm 3The embryo body, the magnetic field strength of the orientation magnetic field is 1.9 T, and the forming pressure is 4.5 MPa; then sinter at 1065 °C for 7 h, and after furnace cooling, perform aging 1, aging 2, and aging 3 treatments in sequence. The temperature of the aging 1 is 900 °C, hold for 3 h, and furnace cool to room temperature; the temperature of the aging 2 is 800 °C, hold for 3 h, and furnace cool to room temperature; the temperature of the aging 3 is 465 °C, hold for 6 h, and furnace cool to room temperature to obtain a neodymium iron boron magnet matrix with high density; at the same time, measure the magnetic properties of the neodymium iron boron magnet matrix.

[0061] Step S3: After slicing the neodymium iron boron magnet matrix to obtain a sheet magnet, then spray a slurry containing heavy rare earth element RE' around the surface of the sheet magnet. The weight of the slurry containing heavy rare earth element RE' is 0.6% of the weight of the sheet magnet. Perform grain boundary diffusion at 900 °C and a vacuum degree of 5.0×10 -3 Pa, penetrate the heavy rare earth element from the surface of the sheet magnet into the interior of the sheet magnet, and then perform tempering treatment at 465 °C for 6 h to obtain the neodymium iron boron magnet.

[0062] Example 2 This example discloses a neodymium iron boron magnet, and the raw materials include a neodymium iron boron magnet matrix RE x (Fe 100-a M a ) 100-x-y B y and a slurry containing heavy rare earth element RE'. The specific raw material ratio is shown in Table 1; the microstructure of the neodymium iron boron magnet includes: a main phase and a grain boundary phase. The main phase includes PrNd 2 Fe 14 B; the grain boundary phase is a grain boundary rare earth-rich phase, including Pr 2 Fe, Nd 2 Fe, (PrNd) 2 Fe, Pr 3 Fe, Nd 3 Fe, (PrNd) 3 Fe and other compounds; the third phase includes Nd 6 Fe 13 Ga phase.

[0063] This example discloses a preparation method of a neodymium iron boron magnet, and the specific steps are as follows: Step S1: According to the raw material ratio of the neodymium iron boron magnet substrate, weigh PrNd: 236.8 kg, Pr: 7.2 kg, B-Fe: 36.8 kg (the proportion of B in B-Fe is 20 wt%), Co: 6.4 kg, Cu: 2.24 kg, Al: 0.48 kg, Zr: 1.6 kg, Ti: 0.88 kg, Ga: 3.2 kg, Fe: 504.4 kg, melt at 1450 °C, and then rapidly cast and cool. The casting temperature is 1445 °C, and the rotational speed of the rapid solidification copper roll is 30 r / min; an alloy cast sheet with an average thickness of 0.29 mm is obtained; The alloy cast sheet is subjected to hydrogen crushing under the conditions of a hydrogen absorption pressure of 75 kPa and a dehydrogenation temperature of 560 °C to obtain alloy coarse powder with an average particle size of 25 μm; after adding 0.45‰ antioxidant and 0.45‰ lubricant, it is ground by a jet mill (the temperature of the grinding gas is 11 °C) to obtain neodymium iron boron alloy powder with an average particle size of 2.85 μm; the antioxidant is purchased from Tianjin Yuesheng, with the brand number 3#; the lubricant is purchased from Tianjin Yuesheng, with the brand number 6#.

[0064] Step S2: The neodymium iron boron alloy powder is formed by a magnetic field to obtain a green body with a density of 4.08 g / cm 3 The magnetic field strength of the orientation magnetic field is 1.9 T, and the forming pressure is 5 MPa; then it is sintered at 1060 °C for 8 h, and after furnace cooling, aging 1, aging 2, and aging 3 treatments are carried out in sequence. The temperature of aging 1 is 900 °C, holding for 3 h, and furnace cooling to room temperature; the temperature of aging 2 is 800 °C, holding for 3 h, and furnace cooling to room temperature; the temperature of aging 3 is 465 °C, holding for 6 h, and furnace cooling to room temperature to obtain a neodymium iron boron magnet substrate with high density; at the same time, the magnetic properties of the neodymium iron boron magnet substrate are measured.

[0065] Step S3: The neodymium iron boron magnet substrate is sliced to obtain a sheet-shaped magnet, and then a slurry containing heavy rare earth element RE' is sprayed on the periphery of the surface of the sheet-shaped magnet. The weight of the slurry containing heavy rare earth element RE' is 0.5% of the weight of the sheet-shaped magnet. Grain boundary diffusion is carried out at 900 °C and a vacuum degree of 5.0×10 -3 Pa conditions to penetrate the heavy rare earth element from the surface of the sheet-shaped magnet into the inside of the sheet-shaped magnet, and then temper at 465 °C for 6 h to obtain the neodymium iron boron magnet.

[0066] Example 3 This example discloses a neodymium iron boron magnet, and the raw materials include a neodymium iron boron magnet substrate RE x (Fe 100-a M a ) 100-x-y B yand a slurry containing heavy rare earth elements RE', and the specific raw material ratios are shown in Table 1; the microstructure of the NdFeB magnet includes: a main phase and a grain boundary phase, and the main phase includes PrNd 2 Fe 14 B; the grain boundary phase is a grain boundary rare earth-rich phase, including Pr 2 Fe, Nd 2 Fe, (PrNd) 2 Fe, Pr 3 Fe, Nd 3 Fe, (PrNd) 3 Fe and other compounds; the third phase includes Nd 6 Fe 13 Ga phase.

[0067] This embodiment discloses a preparation method of a NdFeB magnet, and the specific steps are as follows: Step S1: According to the raw material ratio of the NdFeB magnet substrate, weigh 219.2 kg of PrNd, 24 kg of Pr, 36 kg of B-Fe (the proportion of B in B-Fe is 20 wt%), 8 kg of Co, 2.4 kg of Cu, 0.0 kg of Al, 2.4 kg of Zr, 0.0 kg of Ti, 2.4 kg of Ga, and 505.6 kg of Fe, melt at 1450 °C, and then rapidly cast and cool. The casting temperature is 1450 °C, and the rotational speed of the rapid solidification copper roll is 29 r / min; an alloy cast sheet with an average thickness of 0.275 mm is obtained; Under the conditions of a hydrogen absorption pressure of 80 kPa and a dehydrogenation temperature of 560 °C, hydrogen crush the alloy cast sheet to obtain alloy coarse powder with an average particle size of 28 μm; after adding 0.45‰ of antioxidant and 0.45‰ of lubricant, grind it through a jet mill (the temperature of the grinding gas is 10 °C) to obtain NdFeB alloy powder with an average particle size of 2.9 μm; the antioxidant is purchased from Tianjin Yuesheng, with the brand number 3#; the lubricant is purchased from Tianjin Yuesheng, with the brand number 6#.

[0068] Step S2: Form the NdFeB alloy powder by magnetic field molding to obtain a green body with a density of 4.05 g / cm 3 ³, the magnetic field strength of the orientation magnetic field is 1.9 T, and the molding pressure is 4 MPa; then sinter at 1065 °C for 7 h, cool with the furnace, and then perform aging 1, aging 2, and aging 3 treatments in sequence. The temperature of aging 1 is 900 °C, keep warm for 3 h, and cool with the furnace to room temperature; the temperature of aging 2 is 800 °C, keep warm for 3 h, and cool with the furnace to room temperature; the temperature of aging 3 is 450 °C, keep warm for 5 h, and cool with the furnace to room temperature to obtain a NdFeB magnet substrate with high density; at the same time, measure the magnetic properties of the NdFeB magnet substrate.

[0069] Step S3: The NdFeB magnet substrate is sliced to obtain sheet magnets, and then a slurry containing heavy rare earth element RE' is sprayed on the periphery of the surface of the sheet magnets. The weight of the slurry containing heavy rare earth element RE' is 0.6% of the weight of the sheet magnets. Grain boundary diffusion is carried out at 900 °C and a vacuum degree of 5.0×10 -3 Pa, and the heavy rare earth element penetrates from the surface of the sheet magnet into the interior of the sheet magnet. After tempering treatment at 450 °C for 6 h, the NdFeB magnet is obtained.

[0070] Example 4-5 Example 4-5 provides an NdFeB magnet. The specific implementation manner is the same as that of Example 3. The difference from Example 3 lies in the different slurry compositions. The specific slurry compositions are shown in Table 2.

[0071] Comparative Example 1 This comparative example discloses an NdFeB magnet. The specific implementation manner is the same as that of Example 3. The difference from Example 3 lies in the different element ratios from those of Example 3. According to the raw material ratio of the NdFeB magnet substrate, PrNd: 219.2 kg, Pr: 24 kg, B-Fe: 40.8 kg (the proportion of B in B-Fe is 20 wt%), Co: 12 kg, Cu: 3.2 kg, Al: 4.8 kg, Zr: 1.6 kg, Ti: 0.8 kg, Ga: 2.4 kg, Fe: 491.2 kg, melting is carried out at 1450 °C, and then rapid casting and cooling are carried out. The casting temperature is 1450 °C, and the rotational speed of the rapid solidification copper roll is 29 r / min; an alloy cast sheet with an average thickness of 0.275 mm is obtained; The alloy cast sheet is subjected to hydrogen crushing under the conditions of a hydrogen absorption pressure of 80 kPa and a dehydrogenation temperature of 560 °C to obtain alloy coarse powder with an average particle size of 28 μm; after adding 0.45‰ of antioxidant and 0.45‰ of lubricant, it is ground by a jet mill (the temperature of the grinding gas is 10 °C) to obtain NdFeB alloy powder with an average particle size of 2.9 μm; the antioxidant is purchased from Tianjin Yuesheng, with the brand number 3#; the lubricant is purchased from Tianjin Yuesheng, with the brand number 6#.

[0072] Step S2: The NdFeB alloy powder is formed by a magnetic field to obtain a green body with a density of 4.05 g / cm3. The magnetic field strength of the orientation magnetic field is 1.9 T, and the forming pressure is 4 MPa; then it is sintered at 1065 °C for 7 h and cooled with the furnace. Aging 1, aging 2, and aging 3 treatments are carried out in sequence. The temperature of aging 1 is 900 °C, the heat preservation time is 3 h, and it is cooled with the furnace to room temperature; the temperature of aging 2 is 800 °C, the heat preservation time is 3 h, and it is cooled with the furnace to room temperature; the temperature of aging 3 is 450 °C, the heat preservation time is 5 h, and it is cooled with the furnace to room temperature to obtain a high-density NdFeB magnet substrate; at the same time, the magnetic properties of the NdFeB magnet substrate are measured.

[0073] Step S3: The NdFeB magnet substrate is sliced into sheet magnets, and then a slurry containing a heavy rare earth element RE' is sprayed on the periphery of the surface of the sheet magnet. The weight of the slurry containing the heavy rare earth element RE' is 0.6% of the weight of the sheet magnet. Grain boundary diffusion is carried out at 900 °C and a vacuum degree of 5.0×10-3 Pa, so that the heavy rare earth element penetrates from the surface of the sheet magnet into the interior of the sheet magnet, and then tempering treatment is carried out at 450 °C for 6 h to obtain the NdFeB magnet.

[0074] Comparative Example 2 This comparative example discloses a NdFeB magnet. The specific implementation manner is the same as that of Example 3. The difference from Example 3 is that the temperatures of Aging 1, Aging 2, and Aging 3 are different from those of Example 3. The temperature of Aging 1 is 900 °C, the temperature of Aging 2 is 800 °C, and the temperature of Aging 3 is 490 °C. According to the raw material ratio of the NdFeB magnet substrate, PrNd: 219.2 kg, Pr: 24 kg, B-Fe: 36 kg (the proportion of B in B-Fe is 20 wt%), Co: 8 kg, Cu: 2.4 kg, Al: 0.0 kg, Zr: 2.4 kg, Ti: 0.0 kg, Ga: 2.4 kg, Fe: 505.6 kg are weighed and melted at 1450 °C, and then rapidly cast and cooled. The casting temperature is 1450 °C, and the rotational speed of the rapid solidification copper roll is 29 r / min; an alloy cast sheet with an average thickness of 0.275 mm is obtained; The alloy cast sheet is hydrogenated and crushed under the conditions of a hydrogen absorption pressure of 80 kPa and a dehydrogenation temperature of 560 °C to obtain alloy coarse powder with an average particle size of 28 μm; after adding 0.45‰ of antioxidant and 0.45‰ of lubricant, it is ground by a jet mill (the temperature of the grinding gas is 10 °C) to obtain NdFeB alloy powder with an average particle size of 2.9 μm; the antioxidant is purchased from Tianjin Yuesheng, and the brand is 3#; the lubricant is purchased from Tianjin Yuesheng, and the brand is 6#.

[0075] Step S2: The NdFeB alloy powder is formed by a magnetic field to obtain a green body with a density of 4.05 g / cm 3 The magnetic field strength of the orientation magnetic field is 1.9 T, and the forming pressure is 4 MPa; then it is sintered at 1065 °C for 7 h and cooled in the furnace, and then Aging 1, Aging 2, and Aging 3 treatments are carried out in sequence. The temperature of Aging 1 is 900 °C, the holding time is 3 h, and it is cooled in the furnace to room temperature; the temperature of Aging 2 is 800 °C, the holding time is 3 h, and it is cooled in the furnace to room temperature; the temperature of Aging 3 is 490 °C, the holding time is 5 h, and it is cooled in the furnace to room temperature to obtain a NdFeB magnet substrate with high density; at the same time, the magnetic properties of the NdFeB magnet substrate are measured.

[0076] Step S3: After slicing the NdFeB magnet substrate to obtain sheet magnets, a slurry containing a heavy rare earth element RE' is sprayed on the periphery of the surface of the sheet magnets. The weight of the slurry containing the heavy rare earth element RE' is 0.6% of the weight of the sheet magnets. Grain boundary diffusion is carried out at 900 °C and a vacuum degree of 5.0×10 -3 Pa, and the heavy rare earth element penetrates from the surface of the sheet magnet into the interior of the sheet magnet. After tempering at 490 °C for 6 h, the NdFeB magnet is obtained.

[0077] Comparative Example 3-4 Comparative Example 3-4 provides an NdFeB magnet. The specific implementation manner is the same as that of Comparative Example 2. The difference from Comparative Example 2 lies in the different slurry compositions. The specific slurry compositions are shown in Table 2.

[0078] Comparative Example 5 This comparative example discloses an NdFeB magnet. The specific implementation manner is the same as that of Example 3. The difference from Example 3 lies in the different dosages of additives. 0.45‰ of antioxidant and 1.2‰ of lubricant are added. The antioxidant is purchased from Tianjin Yuesheng, with the brand number 3#; the lubricant is purchased from Tianjin Yuesheng, with the brand number 6#.

[0079] According to the raw material ratio of the NdFeB magnet substrate, PrNd: 219.2 kg, Pr: 24 kg, B-Fe: 36 kg (the proportion of B in B-Fe is 20 wt%), Co: 8 kg, Cu: 2.4 kg, Al: 0.0 kg, Zr: 2.4 kg, Ti: 0.0 kg, Ga: 2.4 kg, Fe: 505.6 kg are weighed and melted at 1450 °C, and then quickly cast and cooled. The casting temperature is 1450 °C, and the rotational speed of the rapid solidification copper roll is 29 r / min; an alloy cast sheet with an average thickness of 0.275 mm is obtained; The alloy cast sheet is hydrogenated and crushed under the conditions of a hydrogen absorption pressure of 80 kPa and a dehydrogenation temperature of 560 °C to obtain alloy coarse powder with an average particle size of 28 μm; after adding 0.45‰ of antioxidant and 1.2‰ of lubricant, it is ground by a jet mill (the temperature of the grinding gas is 10 °C) to obtain NdFeB alloy powder with an average particle size of 2.9 μm; the antioxidant is purchased from Tianjin Yuesheng, with the brand number 3#; the lubricant is purchased from Tianjin Yuesheng, with the brand number 6#.

[0080] Step S2: The NdFeB alloy powder is formed by a magnetic field to obtain a density of 4.05 g / cm 3The embryo body, the magnetic field strength of the orientation magnetic field is 1.9 T, and the forming pressure is 4 MPa; then sinter at 1065 °C for 7 h, and after furnace cooling, perform aging 1, aging 2, and aging 3 treatments in sequence. The temperature of the aging 1 is 900 °C, keep warm for 3 h, and cool to room temperature with the furnace; the temperature of the aging 2 is 800 °C, keep warm for 3 h, and cool to room temperature with the furnace; the temperature of the aging 3 is 450 °C, keep warm for 5 h, and cool to room temperature with the furnace to obtain a neodymium iron boron magnet matrix with high density; at the same time, measure the magnetic properties of the neodymium iron boron magnet matrix.

[0081] Step S3: After slicing the neodymium iron boron magnet matrix to obtain a sheet-shaped magnet, then spray a slurry containing a heavy rare earth element RE' on the periphery of the surface of the sheet-shaped magnet. The weight of the slurry containing the heavy rare earth element RE' is 0.6% of the weight of the sheet-shaped magnet. Perform grain boundary diffusion at 900 °C and a vacuum degree of 5.0×10 -3 Pa conditions, penetrate the heavy rare earth element from the surface of the sheet-shaped magnet into the inside of the sheet-shaped magnet, and then perform tempering treatment at 450 °C for 6 h to obtain the neodymium iron boron magnet.

[0082] The material properties of Examples 1-5 and Comparative Examples 1-5 are shown in Table 3.

[0083] Table 3:

[0084] According to the data in Table 3, it can be seen that in Comparative Example 1, the mass ratio of each element was adjusted, the M content increased, and compared with Example 3, both the remanence and the intrinsic coercivity decreased significantly; in Comparative Examples 2-4, the sintering aging temperature was adjusted, the temperature of aging 3 increased, and compared with Examples 3-5, the remanence was basically the same, and the intrinsic coercivity decreased significantly; in Comparative Example 5, the additive dosage was adjusted, the lubricant usage increased, and compared with Example 3, the remanence was slightly higher, and the intrinsic coercivity decreased significantly.

[0085] The present invention can be implemented in various different ways and is not limited to the above-mentioned embodiments and / or examples. Those of ordinary skill in the art can understand that the present invention can be implemented by other specific ways without changing the technical idea or essential features of the present invention. Therefore, it should be understood that the above-mentioned embodiments and / or examples are exemplary and not used to limit the present invention.

Claims

1. A neodymium iron boron magnet, characterized in that: The raw materials of the NdFeB magnet include a NdFeB magnet matrix and a slurry containing a heavy rare earth element RE'; the composition of the NdFeB magnet matrix is: RE x (Fe 100-a M a ) 100-x-y B y ; Wherein, RE is at least two of La, Ce, Pr, and Nd and must contain Pr, and the mass of Pr in RE is 25%-35% of the total mass of RE; M is selected from at least one of Co, Cu, Al, Nb, Ti, Zr, and Ga; a, x, and y represent the weight percentage of each element multiplied by 100, and 28.5≤x≤31, 0.85≤y≤1.02, and 1.9≤a≤4.4; the RE' is at least one of Pr, Gd, Tb, Dy, Ho, Er, La, and Ce; The structure of the NdFeB magnet includes a main phase and a grain boundary phase. The main phase is RE''2Fe 14 B, RE'' is at least two of La, Ce, Pr, and Nd and must contain Pr; the grain boundary phase is a rare earth-rich phase, including Pr2Fe, Nd2Fe, (PrNd)2Fe, Pr3Fe, Nd3Fe, and (PrNd)3Fe.

2. A neodymium iron boron magnet according to claim 1, characterized in that: Calculated by weight percentage, the content of each element in M ​​in the magnet matrix is: Co 0.6-1.2%, Ga 0.2-0.5%, Ti 0.1-0.25%, Al 0.05-0.2%, Cu 0.2-0.4%, Zr 0.15-0.3%.

3. A NdFeB magnet according to claim 1, characterized in that: Calculated by weight percentage, the composition of the slurry containing the heavy rare earth element RE' includes: Pr 15-20%, Dy +Tb 55-60%, Cu 5-10%, Al 5-10%.

4. A neodymium iron boron magnet according to any one of claims 1 to 3, characterized in that: The NdFeB magnet has a heavy rare earth content of ≤0.8wt%; an intrinsic coercive force of >23kOe; a remanence of >14.1 kGs; and a magnetic product energy of >47 MGOe.

5. A method for preparing a NdFeB magnet according to any one of claims 1 to 4, characterized in that: The specific steps of the preparation method are as follows: Step S1: Smelting and casting the raw materials of the NdFeB magnet matrix to obtain alloy flakes, hydrogen crushing the alloy flakes to obtain alloy coarse powder, and then grinding with a jet mill to obtain NdFeB alloy powder with an average particle size of 2.7 μm to 3.2 μm; Step S2: forming the NdFeB alloy powder into a blank by magnetic field, and then sintering and aging the blank to obtain a NdFeB magnet matrix; Step S3: Slice the NdFeB magnet matrix to obtain a sheet magnet, spray a slurry containing heavy rare earth elements RE' on the sheet magnet, and then penetrate the elements in the slurry from the surface of the sheet magnet to the inside of the sheet magnet through grain boundary diffusion, and obtain the NdFeB magnet after tempering.

6. The method for preparing a NdFeB magnet according to claim 4, characterized in that: During the jet mill grinding process of step S1, an antioxidant and a lubricant are also added, and the total amount of the antioxidant and the lubricant added is 0.8‰ to 1.2‰ of the alloy coarse powder.

7. The method for preparing a NdFeB magnet according to claim 4, characterized in that: In step S2, the conditions for magnetic field molding include: the magnetic field size of the orientation magnetic field is 1.7T~2.2T; the molding pressure is 3-7 MPa; and / or the density of the embryo is 3.9~4.2g / cm 3 ; and / or, in step S2, the sintering temperature is 1040°C~1080°C, and the sintering time is 6-10h.

8. The method for preparing a NdFeB magnet according to claim 4, characterized in that: The aging treatment in step S2 includes at least three stages of aging. Preferably, the aging treatment is aging 1, aging 2, and aging 3 in sequence. The temperature of aging 1 is 880°C to 920°C, kept warm for 2-6 hours, and then cooled to room temperature with the furnace. The temperature of aging 2 is 780°C to 840°C, kept warm for 2-6 hours, and then cooled to room temperature with the furnace. The temperature of aging 3 is 430°C to 480°C, kept warm for 4-8 hours, and then cooled to room temperature with the furnace.

9. The method for preparing a NdFeB magnet according to claim 4, characterized in that: The weight of the slurry containing the heavy rare earth element RE' in step 3 is 0.3%-0.7% of the weight of the sheet magnet.

10. The method for preparing a NdFeB magnet according to claim 4, characterized in that: The specific conditions for the grain boundary diffusion in step S3 are: 600-1000°C and vacuum degree <8.0×10 -3 Grain boundary diffusion is carried out under Pa conditions; and / or, the tempering temperature is 400-700°C and the time is 6-8 h.

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