Preparation method for grain boundary diffusion sintered neodymium-iron-boron permanent magnet material

Abstract

The present invention belongs to the technical field of neodymium-iron-boron permanent magnet materials, and relates to a preparation method for a grain boundary diffusion sintered neodymium-iron-boron permanent magnet material. The preparation method comprises: (1) formulating a master alloy, melting same, and then pulverizing same to obtain a fine master alloy powder; (2) formulating an auxiliary alloy, melting same, and then pulverizing same to obtain a fine auxiliary alloy powder; (3) mixing the fine master alloy powder, the fine auxiliary alloy powder and a nanopowder, adding an auxiliary agent, and then pre-pressing same to obtain a pre-pressed compact, wherein the nanopowder is one or more of a transition metal carbide nanopowder and a transition metal oxide nanopowder; and (4) subjecting the pre-pressed compact to isostatic pressing, sintering, a black-sheet treatment, diffusion-source diffusion, a diffusion heat treatment and an aging treatment, so as to obtain a grain boundary diffusion sintered neodymium-iron-boron permanent magnet material. The preparation method for a grain boundary diffusion sintered neodymium-iron-boron permanent magnet material of the present invention is applicable to products having a large dimension along a magnetization direction.

Description

A method for preparing grain boundary diffusion sintered NdFeB permanent magnet materials Technical Field

[0001] This invention belongs to the field of neodymium iron boron permanent magnet material technology, and relates to a method for preparing grain boundary diffusion sintered neodymium iron boron permanent magnet material. Background Technology

[0002] With the continuous development of my country's industrial level, it has gained a dominant position in the international market in many fields such as wind power generation, new energy power, and intelligent manufacturing. Among them, sintered NdFeB permanent magnet materials, as key components for magnetoelectric conversion, are widely used due to their excellent comprehensive magnetic properties. The continuous advancement of sintered NdFeB permanent magnet material preparation technology, especially with the gradual popularization of grain boundary diffusion technology, has laid the foundation for controlling material costs and improving performance. However, the grain boundary diffusion process still has some problems, such as its inability to match the preparation of large-size products with high magnetization direction (8mm and above) and the long curing time after grain boundary diffusion. Technical issues

[0003] The purpose of this invention is to address the aforementioned problems in the existing technology by proposing a method for preparing grain boundary diffusion sintered NdFeB permanent magnet materials. This method involves designing the composition of the magnet matrix of the grain boundary diffusion sintered NdFeB permanent magnet material, and through the combination of main and auxiliary alloys, forming a PrGa-rich grain boundary phase to reduce the content of ferromagnetic elements in the grain boundaries. Furthermore, the addition of nanoparticles to the magnet matrix further increases the grain boundary width, thereby providing diffusion channels for subsequent preparation processes and facilitating the development of large-size sintered NdFeB permanent magnet materials. Technical solutions

[0004] One objective of this invention can be achieved through the following technical solution:

[0005] A method for preparing a grain boundary diffusion sintered NdFeB permanent magnet material includes:

[0006] (1) The main alloy is proportioned, smelted, and powdered to obtain fine powder of the main alloy; the chemical formula of the main alloy is [(Pr 0.25 Nd 0.75 ) x1 (LR) y1 (HR) 1-x1-y1 ] a1 (TM) b1 (HM) c1 B d1Fe100-a1-b1-c1-d, where 0.7≤x1≤1, 0≤y1≤0.3, 29.5≤a1≤30.5, 0<b1≤5, 0<c1≤0.3, 0.92≤d1≤0.98, LR is one or more of La, Ce, and Y light rare earth elements, HR is one or more of Dy, Tb, Gd, and Ho heavy rare earth elements, TM is one or more of Al, Cu, Co, Mn, and Ga, and HM is one or more of Nb, Zr, Hf, Ti, and V;

[0007] (2) The auxiliary alloy is proportioned, smelted, and powdered to obtain fine auxiliary alloy powder; the chemical formula of the auxiliary alloy is Pr x2 (Ga) a2 Al b2 Ti 1-a2-b2 ) 1-x2 Where 0.3≤x²≤0.9, 0.1≤a²≤0.7, and 0≤b²≤0.5;

[0008] (3) After mixing the main alloy fine powder, auxiliary alloy fine powder and nano powder, add the additives and pre-press to obtain a pre-pressed blank;

[0009] The nanopowder is one or more of transition metal carbide nanopowder and transition metal oxide nanopowder;

[0010] (4) The pre-pressed blank is subjected to isostatic pressing, sintering, black sheet treatment, diffusion source diffusion, diffusion heat treatment, and aging to obtain grain boundary diffusion sintered NdFeB permanent magnet material.

[0011] As a preferred option, in (1) TM, Al≤0.5 and Ga≤0.3, and in HM, Nb+Zr≤0.1.

[0012] As a preferred option, (1) includes: adding the proportioned main alloy into a melting furnace for melting, then casting the main alloy into a casting, and spinning the casting to obtain a main alloy spun sheet; placing the main alloy spun sheet in a hydrogen crushing furnace to hydrogen crush it into coarse main alloy powder, and then using an air jet mill under inert gas protection to obtain fine main alloy powder.

[0013] Further preferred, the main alloy casting is obtained by heating after the vacuum degree of the melting furnace is ≤3Pa; the oxygen content of the main alloy casting is ≤150ppm and the carbon content of the main alloy casting is ≤300ppm.

[0014] The dehydrogenation temperature in the hydrogen crushing furnace is 500~580℃, the hydrogen content of the main alloy coarse powder is ≤800ppm, and the oxygen content of the main alloy coarse powder is ≤1000ppm.

[0015] Further optimization yields a main alloy fine powder with an average particle size of 3.8~4.3μm.

[0016] As a preferred option, in (2), 0.6≤x2≤0.8, 0.3≤a2≤0.5, and 0≤b2≤0.3.

[0017] As a preferred option, (2) includes: adding the proportioned auxiliary alloy into a melting furnace for melting, then casting to obtain auxiliary alloy castings, and spinning to obtain auxiliary alloy spun sheets; placing the auxiliary alloy spun sheets in a hydrogen crushing furnace to hydrogen crush into auxiliary alloy coarse powder, and then using air jet milling under inert gas protection to obtain auxiliary alloy fine powder.

[0018] Further optimization, (2) after the vacuum degree of the melting furnace is ≤3Pa, the auxiliary alloy casting is started to be heated and cast; the oxygen content of the auxiliary alloy casting is ≤150ppm and the carbon content of the auxiliary alloy casting is ≤300ppm;

[0019] The dehydrogenation temperature in the hydrogen crushing furnace is 500~580℃, the hydrogen content of the auxiliary alloy coarse powder is ≤800ppm, and the oxygen content of the auxiliary alloy coarse powder is ≤1000ppm.

[0020] Further optimization yields an auxiliary alloy fine powder with an average particle size of 3.2~3.6μm.

[0021] As a preferred option, the mass ratio of the main alloy fine powder, the auxiliary alloy fine powder, and the nano powder in (3) is (90~99):(0.5~9.5):(0.1~0.5).

[0022] Further optimization yields a mass ratio of (90~99):(0.5~9.5):(0.1~0.5) for the main alloy fine powder, auxiliary alloy fine powder, and nano powder.

[0023] Preferably, the transition metal carbide nanopowder contains one or more of niobium carbide (NbC), tantalum carbide (TaC), vanadium carbide (VC), zirconium carbide (ZrC), and tungsten carbide (WC).

[0024] The transition metal oxide nanopowder includes one or more of the following: iron(II,III) oxide, titanium dioxide (titanium dioxide), aluminum oxide, and zinc oxide.

[0025] Preferably, the average particle size of the nanoparticles is 10~80nm.

[0026] Further optimization yields nanoparticles with an average particle size of 20-60 nm.

[0027] Preferably, the additives in (3) include one or more of lubricants, aviation gasoline, and antioxidants.

[0028] Further optimization is made, in (3), the mass ratio of the mixed powder of main alloy fine powder, auxiliary alloy fine powder and nano powder to lubricant is (0.2~1.2):1; the mass ratio of the mixed powder of main alloy fine powder, auxiliary alloy fine powder and nano powder to aviation gasoline is (0.2~5):1.

[0029] As a preferred option, (4) the medium static pressure is 180~220Mpa and the pressure holding time is 5~60s.

[0030] Preferably, in (4), the sintering temperature is 1000~1070℃, the sintering time is 6~12h, and the vacuum degree is <5×10 -2 Pa; The average grain size of the magnet after sintering is ≤6μm.

[0031] The present invention employs a low-temperature, long-time sintering process to refine the grains, thereby improving the coercivity of the magnet; however, excessively high temperatures can lead to abnormal grain growth.

[0032] As a preferred embodiment, the black sheet treatment in (4) includes machining the sintered magnet into a black sheet and performing surface treatment, wherein the surface treatment includes one or more of acid washing, alkali washing, sandblasting, and laser polishing.

[0033] As a preferred embodiment, the diffusion source in (4) includes diffusion source alloy powder, organic solvent, and photocuring agent in a mass ratio of (5~30):(1~8):1.

[0034] Further preferred, the diffusion source includes diffusion source alloy powder, organic solvent, and photocuring agent in a mass ratio of (11~18):(2~5):1.

[0035] Further optimization reveals that the diffusion source alloy powder is Dy a2 M 1-a2 Alloy, Tb b2 M 1-b2 One or more of the elements, M being one or more of Fe, Ga, Cu, Al, and Co, 0.6≤a²≤1, 0.6≤b²≤1;

[0036] Organic solvents include one or more of ethanol, polyvinyl alcohol, benzyl alcohol, and ethylene glycol;

[0037] The photocuring agent is a cationic photoinitiator, including one or more of the following: diazonium salt, diaryliodomonium salt, triarylthionium salt, alkylthionium salt, iron aromatic salt, sulfonyloxy ketone, and triarylsiloxane.

[0038] As a preferred embodiment, the diffusion of the diffusion source in (4) includes coating the diffusion source onto a black sheet, curing it by irradiation with light of wavelength 250~800nm, and drying it.

[0039] Further preferably, the wavelength is 250~450nm.

[0040] Further preferably, the irradiation curing time is 1~30 min.

[0041] Further preferred, after the diffusion source is applied, the weight gain of the black sheet is 0.6~0.8wt%.

[0042] Preferably, in (4), the diffusion heat treatment has a diffusion temperature of 850~950℃, a diffusion time of 10~20h, and a vacuum degree of <10. -3 Pa.

[0043] As a preferred option, the aging temperature in (4) is 360~650℃ and the aging time is 2~12h.

[0044] Preferably, the method for preparing the grain boundary diffusion sintered NdFeB permanent magnet material includes:

[0045] (1) The main alloy is proportioned according to the following chemical formula [(Pr 0.25 Nd 0.75 ) x1 (LR) y1 (HR) 1-x1-y1 ] a1 (TM) b1 (HM) c1 B d1 Fe100-a1-b1-c1-d, where 0.7≤x1≤1, 0≤y1≤0.3, 29.5≤a1≤30.5, 0<b1≤5, 0<c1≤0.3, 0.92≤d1≤0.98, LR is one or more of La, Ce, and Y light rare earth elements, HR is one or more of Dy, Tb, Gd, and Ho heavy rare earth elements, TM is one or more of Al, Cu, Co, Mn, and Ga, and HM is one or more of Nb, Zr, Hf, Ti, and V;

[0046] The proportioned main alloy is added to a melting furnace for melting, then cast into a main alloy casting, and then spun into a main alloy spun sheet. The melting temperature is 1485~1505℃, the casting temperature is 1415~1465℃, and the thickness of the main alloy spun sheet is 0.15~0.45mm.

[0047] The main alloy slabs were placed in a hydrogen crushing furnace and hydrogen-crushed into coarse powder. Under inert gas protection, fine powder was obtained by air jet milling. The average particle size of the fine powder was 3.8~4.3μm.

[0048] (2) The auxiliary alloy is prepared according to the following chemical formula: Pr x2 (Ga) a2 Al b2 Ti 1-a2-b2 ) 1-x2 The proportions are as follows: 0.3 ≤ x² ≤ 0.9, 0.1 ≤ a² ≤ 0.7, 0 ≤ b² ≤ 0.5;

[0049] The proportioned auxiliary alloy is added to a melting furnace for melting, and then cast into auxiliary alloy castings and spun into auxiliary alloy spun sheets. The melting temperature is 1485~1505℃, the casting temperature is 1415~1465℃, and the thickness of the auxiliary alloy spun sheets is 0.15~0.45mm.

[0050] The auxiliary alloy slabs were placed in a hydrogen crushing furnace and hydrogenated to form coarse auxiliary alloy powder. Under inert gas protection, fine auxiliary alloy powder was obtained by air jet milling. The average particle size of the fine auxiliary alloy powder was 3.2~3.6μm.

[0051] (3) The main alloy fine powder, auxiliary alloy fine powder and nano powder are mixed in a mass ratio of (90~99):(0.5~9.5):(0.1~0.5), and then the additives are added and mixed evenly. The mixture is pre-pressed under a magnetic field strength H>2000Gs; the nano powder is one or more of transition metal carbide nano powder and transition metal oxide nano powder.

[0052] (4) The pre-pressed blank is subjected to isostatic pressing. The isostatic pressing pressure is 180~220 MPa, and the holding time is 5~60 s.

[0053] (5) Then sintering is carried out at a temperature of 1000~1070℃ for 6~12h, with a vacuum degree of <5×10 -2 Pa; The average grain size of the magnet after sintering is ≤6μm;

[0054] (6) The sintered magnet is machined into a black sheet and then surface treated to obtain a surface-treated black sheet. The surface treatment includes one or more of pickling, alkali washing, sandblasting, and laser polishing.

[0055] (7) Mix the diffusion source alloy powder, organic solvent and photocuring agent in a mass ratio of (5~30):(1~8):1 to form a slurry, apply it to the surface-treated black sheet, and then irradiate it with light of wavelength 250~800nm ​​to cure and dry it to obtain the diffused magnet.

[0056] The diffused magnet is then transferred to a diffusion furnace at a diffusion temperature of 850–950°C for 10–20 hours, with a vacuum level <10. -3 Pa;

[0057] (8) Then aging is carried out at a temperature of 360~650℃ for 2~4h. After aging, inert gas is immediately introduced into the furnace and the furnace is cooled to 60~80℃. Grain boundary diffusion sintered NdFeB permanent magnet material is obtained.

[0058] Further preferred, in (1), Al≤0.5 and Ga≤0.3 in TM, and Nb+Zr≤0.1 in HM.

[0059] Further preferred, in step (1), the main alloy casting is obtained by heating after the vacuum degree of the melting furnace is ≤3Pa; the oxygen content of the main alloy casting is ≤150ppm and the carbon content of the main alloy casting is ≤300ppm.

[0060] The dehydrogenation temperature in the hydrogen crushing furnace is 500~580℃, and the hydrogen content of the main alloy coarse powder is ≤800ppm and the oxygen content is ≤1000ppm.

[0061] The main alloy fine powder includes main alloy coarse powder and antioxidant in a mass ratio of 1:(0.5~1.2).

[0062] More preferably, the antioxidant is one or more of glycerol, zinc stearate, silicate, silicone oil, and n-octane.

[0063] Further preferred, in (2), 0.6≤x2≤0.8, 0.3≤a2≤0.5, and 0≤b2≤0.3.

[0064] Further preferred, in step (2), the auxiliary alloy casting is started after the vacuum degree of the melting furnace is ≤3Pa; the oxygen content of the auxiliary alloy casting is ≤150ppm and the carbon content of the auxiliary alloy casting is ≤300ppm.

[0065] The dehydrogenation temperature in the hydrogen crushing furnace is 500~580℃, and the hydrogen content of the auxiliary alloy coarse powder is ≤800ppm and the oxygen content is ≤1000ppm.

[0066] The auxiliary alloy fine powder includes auxiliary alloy coarse powder and antioxidant in a mass ratio of 1:(0.5~1.2).

[0067] More preferably, the antioxidant is one or more of glycerol, zinc stearate, silicate, silicone oil, and n-octane.

[0068] Further preferably, the transition metal carbide nanopowder in (3) includes one or more of niobium carbide (NbC), tantalum carbide (TaC), vanadium carbide (VC), zirconium carbide (ZrC), and tungsten carbide (WC); the transition metal oxide nanopowder includes one or more of iron tetroxide, titanium dioxide (titanium dioxide), aluminum oxide, and zinc oxide.

[0069] Further preferred, the nanopowder in (3) is a combination of transition metal carbide nanopowder and transition metal oxide nanopowder.

[0070] Further preferred, the mass ratio of diffusion source alloy powder, organic solvent and photocuring agent in (7) is (11~18):(2~5):1.

[0071] Further optimization reveals that the diffusion source alloy powder is Dy a2 M 1-a2Alloy, Tb b2 M 1-b2 One or more of the following, where M is one or more of the elements Fe, Ga, Cu, Al, Co, etc., and 0.6≤a2≤1, 0.6≤b2≤1;

[0072] Organic solvents include one or more of ethanol, polyvinyl alcohol, benzyl alcohol, and ethylene glycol;

[0073] The photocuring agent is a cationic photoinitiator, including one or more of the following: diazonium salt, diaryliodomonium salt, triarylthionium salt, alkylthionium salt, iron aromatic salt, sulfonyloxy ketone, and triarylsiloxane.

[0074] A grain boundary diffusion sintered NdFeB permanent magnet material with a thickness of 1~10mm and an Hcj of 20~33kOe.

[0075] As a preferred option, the thickness of the grain boundary diffusion sintered NdFeB permanent magnet material is 8~10mm, and the Hcj is 20~28kOe. Beneficial effects

[0076] Compared with the prior art, the present invention has the following beneficial effects:

[0077] 1. This invention designs the matrix composition of the magnet for grain boundary diffusion sintered NdFeB permanent magnet materials. By combining the main alloy and auxiliary alloy, a PrGa-rich grain boundary phase is formed, reducing the content of ferromagnetic elements in the grain boundaries. Furthermore, nanopowder is added to the magnet matrix to further increase the grain boundary width, thereby providing diffusion channels for subsequent preparation processes and contributing to the development of large-size sintered NdFeB permanent magnet materials.

[0078] 2. In the grain boundary phase of this invention, Ga tends to be distributed at the grain boundary, replacing the Fe site in the grain boundary, thereby reducing the ferromagnetism at the grain boundary; while Pr tends to be distributed on the surface of the main phase grains, and its corresponding 2:14:1 phase has a higher anisotropic field strength (Ha). The combined effect of the two helps to improve the magnetic properties of the magnet matrix, especially the coercivity.

[0079] 3. This invention adds a photocuring agent to the diffusion source. Through the photocuring process, the drying temperature of the drying tunnel is reduced, saving energy while improving the bonding strength of the diffusion source slurry on the surface of the black sheet magnet, which helps to improve the diffusion effect.

[0080] 4. This invention can produce sintered NdFeB permanent magnet materials with superior comprehensive magnetic properties under the same magnet matrix or the same diffusion steps, and is suitable for mass production.

[0081] 5. The method for preparing the grain boundary diffusion sintered NdFeB permanent magnet material of the present invention is applicable to large-size products with high magnetization direction (8mm and above). Attached Figure Description

[0082] Figure 1 is a cross-sectional metallographic image of the main alloy sheet in Embodiment 1 of the present invention.

[0083] Figure 2 is a cross-sectional metallographic image of the black sheet after surface treatment before diffusion in Embodiment 1 of the present invention.

[0084] Figure 3 is a cross-sectional metallographic image of the grain boundary diffusion sintered NdFeB permanent magnet material in Embodiment 1 of the present invention. Embodiments of the present invention

[0085] The following are specific embodiments of the present invention, which further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0086] Unless otherwise specified, the materials used in this invention are commercially available products, and the methods used are conventional technical means.

[0087] In this article, the black sheet is an intermediate product state in the production process of neodymium iron boron magnets. Example 1

[0088] (1) The main alloy is prepared according to the chemical formula [(Pr 0.25 Nd 0.75 ) 0.9 Ce 0.08 Dy 0.02 ] 30.4 Al 0.5 Cu 0.1 Ga 0.1 Zr 0.05 Ti 0.05 Nb 0.05 B 0.94 Fe 67.81 Prepare the proportions;

[0089] The proportioned main alloy was added to a melting furnace with a vacuum degree ≤3Pa. The furnace was heated to 1495±5℃ for melting and cast at 1440±5℃ to obtain a main alloy casting. The casting was then spun to obtain a main alloy slab. The oxygen content of the main alloy casting was ≤100ppm, the carbon content was ≤150ppm, and the thickness of the spun main alloy slab was 0.30mm. As shown in Figure 1, the microstructure of the spun main alloy slab has a well-distributed columnar crystal structure and no other impurity phases.

[0090] The main alloy slabs were placed in a hydrogen crushing furnace and hydrogenated to form coarse powder. Zinc stearate, an antioxidant, was added (the mass ratio of coarse powder to antioxidant was 1:0.7). Under nitrogen protection, fine powder of the main alloy was obtained by air jet milling. The average particle size of the fine powder of the main alloy was 4.1 μm.

[0091] (2) The auxiliary alloy is prepared according to the chemical formula Pr 0.65 (Ga) 0.65 Al 0.2Ti 0.15 ) 0.35 The auxiliary alloy is proportioned and then added to a melting furnace with a vacuum degree ≤3Pa. The furnace is heated to 1495±5℃ for melting and cast at 1430±5℃ to obtain auxiliary alloy castings. The castings are then spun to obtain auxiliary alloy spun sheets. The oxygen content of the castings is ≤150ppm, the carbon content is ≤300ppm, and the thickness of the auxiliary alloy spun sheets is 0.28mm.

[0092] The auxiliary alloy slabs were placed in a hydrogen crushing furnace and hydrogenated into coarse auxiliary alloy powder. Zinc stearate, an antioxidant, was added (the mass ratio of coarse auxiliary alloy powder to antioxidant was 1:0.7). Under nitrogen protection, fine auxiliary alloy powder was obtained by air jet milling. The average particle size of the fine auxiliary alloy powder was 3.4 μm.

[0093] (3) Mix 96 parts of main alloy fine powder, 3.7 parts of auxiliary alloy fine powder and 0.3 parts of niobium carbide nano powder, add 1 part of lubricant and 3 parts of aviation gasoline, mix and stir for 80 minutes, then sieve through a sieve machine to reduce the agglomeration of fine powder, and pre-press it under a magnetic field strength H=2700Gs.

[0094] (4) After vacuum sealing the pre-formed preform, perform isostatic pressing. The isostatic pressing pressure is 200 MPa and the holding time is 20 s.

[0095] (5) Then sintering is carried out at a temperature of 1055℃ for 8 hours, with a vacuum degree of 3×10⁻⁶. -2 Pa; The average grain size of the magnet after sintering is ≤6μm;

[0096] (6) The sintered magnets are machined into black sheets of different specifications: 30*20*3.5(mm), 30*20*5.5(mm), 30*20*8.5(mm), and then pickled and laser polished to obtain black sheets with surface treatment;

[0097] (7) Mix 75 parts of diffusion source alloy powder (TbCuAl alloy powder), 20 parts of organic solvent (anhydrous ethanol), and 5 parts of photocuring agent (cationic photoinitiator sulfonyloxyketone) to form a slurry, then coat it onto a surface-treated black sheet. The black sheet gains 0.7 wt% weight. Then, irradiate and cure it with light of wavelength 250~450 nm for 6 min and dry it in a 70℃ oven to obtain the diffused magnet. Transfer the diffused magnet to a diffusion furnace. The diffusion temperature is 910℃, the diffusion time is 18 h, and the vacuum degree is 2×10 -4 Pa;

[0098] (8) Then aging is carried out at a temperature of 500℃ for 4 hours. After aging, inert gas is immediately introduced into the furnace and the furnace is cooled to 60℃. Grain boundary diffusion sintered NdFeB permanent magnet material is obtained.

[0099] Figure 1 is a cross-sectional metallographic image of the main alloy sheet in this embodiment; Figure 2 is a cross-sectional metallographic image of the black sheet after surface treatment before diffusion in this embodiment, with +1 being the PrGa-rich grain boundary phase; Figure 3 is a cross-sectional metallographic image of the grain boundary diffusion sintered NdFeB permanent magnet material in this embodiment.

[0100] The properties of the grain boundary diffusion sintered NdFeB permanent magnet material prepared in this embodiment are shown in Table 1. Example 2

[0101] (1) The main alloy is prepared according to the chemical formula [(Pr 0.25 Nd 0.75 ) 0.9 Ce 0.08 Dy 0.02 ] 30.4 Al 0.5 Cu 0.1 Ga 0.1 Zr 0.05 Ti 0.05 Nb 0.05 B 0.94 Fe 67.81 Prepare the proportions;

[0102] The proportioned main alloy was added to a melting furnace with a vacuum degree ≤3Pa. The furnace was heated to 1495±5℃ for melting and cast at 1440±5℃ to obtain a main alloy casting. The casting was then spun to obtain a main alloy spun sheet. The oxygen content of the main alloy casting was ≤150ppm, the carbon content was ≤200ppm, and the thickness of the spun sheet was 0.30mm. The microstructure of the spun sheet had a well-distributed columnar crystal structure and no other impurities.

[0103] The main alloy slabs were placed in a hydrogen crushing furnace and hydrogenated to form coarse powder. Zinc stearate, an antioxidant, was added (the mass ratio of coarse powder to antioxidant was 1:0.7). Under nitrogen protection, fine powder of the main alloy was obtained by air jet milling. The average particle size of the fine powder of the main alloy was 4.1 μm.

[0104] (2) The auxiliary alloy is prepared according to the chemical formula Pr 0.65 (Ga) 0.65 Al 0.2 Ti 0.15 ) 0.35 The auxiliary alloy is proportioned and then added to a melting furnace with a vacuum degree ≤3Pa. The furnace is heated to 1495±5℃ for melting and cast at 1430±5℃ to obtain auxiliary alloy castings. The castings are then spun to obtain auxiliary alloy spun sheets. The oxygen content of the auxiliary alloy castings is ≤150ppm, the carbon content is ≤300ppm, and the thickness of the spun auxiliary alloy sheets is 0.28mm.

[0105] The auxiliary alloy slabs were placed in a hydrogen crushing furnace and hydrogenated into coarse auxiliary alloy powder. Zinc stearate, an antioxidant, was added (the mass ratio of coarse auxiliary alloy powder to antioxidant was 1:0.7). Under nitrogen protection, fine auxiliary alloy powder was obtained by air jet milling. The average particle size of the fine auxiliary alloy powder was 3.4 μm.

[0106] (3) Mix 96 parts of main alloy fine powder, 3.7 parts of auxiliary alloy fine powder and 0.3 parts of niobium carbide nano powder, add 1 part of lubricant and 3 parts of aviation gasoline, mix and stir for 80 minutes, then sieve through a sieve machine to reduce the agglomeration of fine powder, and pre-press it under a magnetic field strength H=2600Gs.

[0107] (4) After vacuum sealing the pre-formed preform, perform isostatic pressing. The isostatic pressing pressure is 200 MPa and the holding time is 20 s.

[0108] (5) Then sintering is carried out at a temperature of 1065℃ for 8 hours, with a vacuum degree of 3×10⁻⁶. -2 Pa; The average grain size of the magnet after sintering is ≤6μm;

[0109] (6) The sintered magnets are machined into black sheets of different specifications: 30*20*3.5(mm), 30*20*5.5(mm), 30*20*8.5(mm), and then pickled and laser polished to obtain black sheets with surface treatment;

[0110] (7) Mix 75 parts of diffusion source alloy powder (TbCuAl alloy powder), 20 parts of organic solvent (anhydrous ethanol), and 5 parts of photocuring agent (cationic photoinitiator sulfonyloxyketone) to form a slurry, then coat it onto a surface-treated black sheet. The black sheet gains 0.65 wt% weight. Then, irradiate and cure the slurry with light of wavelength 250~450 nm for 7 min, and dry it in a 70℃ oven to obtain the diffused magnet. Transfer the diffused magnet to a diffusion furnace. The diffusion temperature is 910℃, the diffusion time is 25 h, and the vacuum degree is 2×10⁻⁶. -4 Pa;

[0111] (8) Then aging is carried out at a temperature of 490°C for 6 hours. After aging, inert gas is immediately introduced into the furnace and the furnace is cooled to 60°C. Grain boundary diffusion sintered NdFeB permanent magnet material is obtained.

[0112] The properties of the grain boundary diffusion sintered NdFeB permanent magnet material prepared in this embodiment are shown in Table 1. Example 3

[0113] Compared with Example 1, the difference is that in (3), after mixing 95 parts of main alloy fine powder, 4.3 parts of auxiliary alloy fine powder, 0.4 parts of niobium carbide nanopowder and 0.3 parts of iron oxide nanopowder, 1 part of lubricant and 3 parts of aviation gasoline are added, and the mixture is stirred for 80 minutes. Then, the fine powder is sieved through a sieve to reduce agglomeration, and pre-pressed under a magnetic field strength H=2700Gs.

[0114] The properties of the grain boundary diffusion sintered NdFeB permanent magnet material prepared in this embodiment are shown in Table 1. Example 4

[0115] Compared with Example 1, the difference is that in (3), after mixing 93 parts of main alloy fine powder, 6.2 parts of auxiliary alloy fine powder, 0.3 parts of titanium dioxide nanopowder and 0.5 parts of niobium carbide nanopowder, 1 part of lubricant and 3 parts of aviation gasoline are added, and the mixture is stirred for 80 minutes. Then, the fine powder is sieved through a sieve to reduce agglomeration, and pre-pressed under a magnetic field strength of H=2700Gs.

[0116] The properties of the grain boundary diffusion sintered NdFeB permanent magnet material prepared in this embodiment are shown in Table 1. Example 5

[0117] Compared with Example 1, the difference is that in (1) the main alloy is prepared according to the chemical formula [(Pr 0.25 Nd 0.75 ) 0.9 Ce 0.08 Dy 0.02 ] 30.4 Al 0.6 Cu 0.1 Ga 0.1 Zr 0.3 Ti 0.15 Nb 0.05 B 0.94 Fe 67.36 Prepare the proportions;

[0118] The proportioned main alloy was added to a melting furnace with a vacuum degree ≤3Pa. The furnace was heated to 1495±5℃ for melting and cast at 1440±5℃ to obtain a main alloy casting. The casting was then spun to obtain a main alloy spun sheet. The oxygen content of the main alloy casting was ≤150ppm, the carbon content was ≤200ppm, and the thickness of the spun sheet was 0.30mm. The microstructure of the spun sheet had a well-distributed columnar crystal structure and no other impurities.

[0119] The main alloy slabs were placed in a hydrogen crushing furnace and hydrogenated to form coarse powder of the main alloy. Zinc stearate, an antioxidant, was added (the mass ratio of coarse powder of main alloy to antioxidant was 1:0.7). The main alloy fine powder was obtained by air jet milling under nitrogen protection. The average particle size of the main alloy fine powder was 4.1 μm.

[0120] The properties of the grain boundary diffusion sintered NdFeB permanent magnet material prepared in this embodiment are shown in Table 1. Comparative Example 1

[0121] Compared with Example 1, the difference is that no nanopowder is added in (3).

[0122] The properties of the grain boundary diffusion sintered NdFeB permanent magnet material prepared in this comparative example are shown in Table 1. Comparative Example 2

[0123] Compared with Example 1, the difference lies in (2) where the auxiliary alloy is prepared according to the chemical formula Pr 0.65 Ga 0.35 Prepare the proportions;

[0124] The proportioned auxiliary alloy is added to the melting furnace. The vacuum degree of the melting furnace is ≤3Pa. The temperature is raised to 1495±5℃ for melting. After casting at 1430±5℃, the main alloy casting is obtained. Then, the main alloy casting is obtained by spinning. The oxygen content of the main alloy casting is ≤150ppm, the carbon content is ≤300ppm, and the thickness of the auxiliary alloy casting is 0.28mm.

[0125] The auxiliary alloy slabs were placed in a hydrogen crushing furnace and hydrogenated to form coarse auxiliary alloy powder. Zinc stearate, an antioxidant, was added (the mass ratio of coarse auxiliary alloy powder to antioxidant was 1:0.7). Under nitrogen protection, fine auxiliary alloy powder was obtained by air jet milling. The average particle size of the fine auxiliary alloy powder was 3.4 μm.

[0126] The properties of the grain boundary diffusion sintered NdFeB permanent magnet material prepared in this comparative example are shown in Table 1. Comparative Example 3

[0127] Compared with Example 1, the difference is that auxiliary alloy fine powder is not added in (3). In (3), 99.3 parts of main alloy fine powder, 0.4 parts of niobium carbide nanopowder and 0.3 parts of iron oxide nanopowder are mixed and then 1 part of lubricant and 3 parts of aviation gasoline are added. The mixture is stirred for 80 minutes and then sieved through a sieve to reduce the agglomeration of fine powder. It is then pre-pressed under a magnetic field strength of H=2700Gs.

[0128] The properties of the grain boundary diffusion sintered NdFeB permanent magnet material prepared in this comparative example are shown in Table 1. Comparative Example 4

[0129] Compared with Example 1, the difference is that in (3), 95 parts of main alloy fine powder, 3.5 parts of auxiliary alloy fine powder, 1 part of niobium carbide nanopowder, and 0.5 parts of iron oxide nanopowder are mixed, and then 1 part of lubricant and 3 parts of aviation gasoline are added. The mixture is stirred for 80 minutes, and then sieved through a sieve to reduce the agglomeration of fine powder. The mixture is then pre-pressed under a magnetic field strength of H=2700Gs.

[0130] The properties of the grain boundary diffusion sintered NdFeB permanent magnet material prepared in this comparative example are shown in Table 1. Comparative Example 5

[0131] Compared with Example 1, the difference is that in (7), 75 parts of diffusion source alloy powder (TbCuAl alloy powder) and 25 parts of organic solvent (anhydrous ethanol) are mixed and slurried, then coated onto a surface-treated black sheet, the black sheet increases in weight by 0.7wt%, and then cured by irradiation with light of wavelength 250~450nm for 6min, and dried in a drying oven at 70℃ to obtain the diffused magnet; the diffused magnet is transferred to a diffusion furnace, the diffusion temperature is 910℃, the diffusion time is 18h, and the vacuum degree is 2×10 -4 Pa.

[0132] The properties of the grain boundary diffusion sintered NdFeB permanent magnet material prepared in this comparative example are shown in Table 1.

[0133] Table 1. Performance data of grain boundary diffusion sintered NdFeB permanent magnet materials

[0134]

[0135] As shown in the table above, the method for preparing grain boundary diffusion sintered NdFeB permanent magnet materials of the present invention can significantly improve the magnetic properties of sintered NdFeB permanent magnet materials, and can still maintain high comprehensive magnetic properties for large-size sintered NdFeB permanent magnet materials.

[0136] In Comparative Example 1, the absence of nanoparticles limited the diffusion channels of the sintered NdFeB permanent magnet material, resulting in a decrease in the increase of coercivity after diffusion. Specifically, the coercivity of large-size products was 0.8-1 kOe lower than in Example 1. In Comparative Example 4, excessive nanoparticles increased the volume fraction of the non-main phase, leading to a significant decrease in remanence, 0.1-0.2 kGs lower than in Example 1. In Example 5, the change in the main alloy ratio resulted in the magnet matrix ratio not meeting the requirements of Al ≤ 0.5 and Nb + Zr ≤ 0.1, thus affecting the diffusion effect. Due to limitations, the increase in magnet coercivity was 1-1.5 kOe lower than in Example 1. In Comparative Example 2, the ratio of auxiliary alloys was changed, and elements Al and Ti were not added, which led to an increase in the proportion of ferromagnetic phase in the grain boundary phase composition, which was not conducive to the increase in coercivity when diffusing magnets with a large thickness. In Comparative Example 3, no auxiliary alloys were added, which resulted in lower magnetic properties of the magnet matrix and lower coercivity of the magnet material after diffusion. In Comparative Example 5, no photocuring agent was added, which led to a decrease in the bonding strength between the diffusion slurry and the magnet matrix, resulting in poor diffusion effect.

[0137] In summary, this invention designs the composition of grain boundary diffusion sintered NdFeB permanent magnet materials. By combining the main alloy and auxiliary alloy, a PrGa-rich grain boundary phase is formed, reducing the content of ferromagnetic elements in the grain boundaries. Furthermore, the addition of nanoparticles to the matrix further increases the grain boundary width, thereby providing diffusion channels for subsequent processes and contributing to the development of large-size sintered NdFeB permanent magnet materials.

[0138] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A method of producing a grain boundary diffusion sintered neodymium-iron-boron permanent magnet material, characterized in that, The preparation method includes: (1) The main alloy is proportioned, smelted, and powdered to obtain fine powder of the main alloy; the chemical formula of the main alloy is [(Pr 0.25 Nd 0.75 ) x1 (LR) y1 (HR) 1-x1-y1 ] a1 (TM) b1 (HM) c1 B d1 Fe100-a1-b1-c1-d, where 0.7≤x1≤1, 0≤y1≤0.3, 29.5≤a1≤30.5, 0<b1≤5, 0<c1≤0.3, 0.92≤d1≤0.98, LR is one or more of La, Ce, and Y light rare earth elements, HR is one or more of Dy, Tb, Gd, and Ho heavy rare earth elements, TM is one or more of Al, Cu, Co, Mn, and Ga, and HM is one or more of Nb, Zr, Hf, Ti, and V; (2) The auxiliary alloy is prepared by proportioning, smelting and powdering. The chemical formula of the auxiliary alloy is Pr x2 (Ga a2 Al b2 Ti 1-a2-b2 ) 1-x2 wherein 0.3≤x2≤0.9, 0.1≤a2≤0.7, 0≤b2≤0.

5. (3) After mixing the main alloy fine powder, auxiliary alloy fine powder and nano powder, add the additives and pre-press to obtain a pre-pressed blank; the nano powder is one or more of transition metal carbide nano powder and transition metal oxide nano powder. (4) The pre-pressed blank is subjected to isostatic pressing, sintering, black sheet treatment, diffusion source diffusion, diffusion heat treatment, and aging to obtain grain boundary diffusion sintered NdFeB permanent magnet material.

2. The method of producing a grain boundary diffusion sintered neodymium-iron-boron permanent magnet material according to claim 1, characterized in that In (1), Al≤0.5 and Ga≤0.3 in TM, and Nb+Zr≤0.1 in HM.

3. The method of claim 1, wherein the grain boundary diffusion sintered neodymium-iron-boron permanent magnet material is characterized by, The (1) includes: adding the proportioned main alloy into a melting furnace for melting, then casting the main alloy into a casting, and spinning the casting to obtain a main alloy spun sheet; placing the main alloy spun sheet in a hydrogen crushing furnace to hydrogen crush it into coarse main alloy powder, and then using an air jet mill under inert gas protection to obtain fine main alloy powder.

4. The method of producing a grain boundary diffusion sintered neodymium-iron-boron permanent magnet material according to claim 3, characterized in that The main alloy casting has an oxygen content ≤150ppm and a carbon content ≤300ppm; the main alloy coarse powder has a hydrogen content ≤800ppm and an oxygen content ≤1000ppm; the main alloy fine powder has an average particle size of 3.8~4.3μm.

5. The method of claim 1, wherein the grain boundary diffusion sintered neodymium-iron-boron permanent magnet material is characterized by, The (2) includes: adding the proportioned auxiliary alloy into a melting furnace for melting, then casting to obtain auxiliary alloy castings, and spinning to obtain auxiliary alloy spun sheets; placing the auxiliary alloy spun sheets in a hydrogen crushing furnace to hydrogen crush into auxiliary alloy coarse powder, and then using air jet milling under inert gas protection to obtain auxiliary alloy fine powder.

6. The method of claim 5, wherein the grain boundary diffusion sintered neodymium-iron-boron permanent magnet material is characterized by: The auxiliary alloy casting has an oxygen content ≤150ppm and a carbon content ≤300ppm; the auxiliary alloy coarse powder has a hydrogen content ≤800ppm and an oxygen content ≤1000ppm; the auxiliary alloy fine powder has an average particle size of 3.2~3.6μm.

7. The method of claim 1, wherein the grain boundary diffusion sintered neodymium-iron-boron permanent magnet material is characterized by, The mass ratio of the main alloy fine powder, auxiliary alloy fine powder, and nano powder in (3) is (90~99):(0.5~9.5):(0.1~0.5).

8. The method of claim 1, wherein the grain boundary diffusion sintered neodymium-iron-boron permanent magnet material is characterized by, The transition metal carbide nanopowder in (3) includes one or more of niobium carbide, tantalum carbide, vanadium carbide, zirconium carbide, and tungsten carbide; the transition metal oxide nanopowder includes one or more of iron tetroxide, titanium dioxide, aluminum oxide, and zinc oxide.

9. The method of claim 1, wherein the grain boundary diffusion sintered neodymium-iron-boron permanent magnet material is characterized by, The additives in (3) include one or more of lubricants, aviation gasoline, and antioxidants.

10. The method of claim 1, wherein the grain boundary diffusion sintered neodymium-iron-boron permanent magnet material is characterized by, The (4) medium static pressure is 180-220 Mpa, the pressure maintaining time is 5-60 s; the (4) medium sintering temperature is 1000-1070 ℃, the sintering time is 6-12 h, and the vacuum degree is <5×10 -2 Pa; the average grain size of the magnet after sintering is ≤6 μm.

11. The method of claim 1, wherein the grain boundary diffusion sintered neodymium-iron-boron permanent magnet material is characterized by, The diffusion source in (4) comprises diffusion source alloy powder, organic solvent, and photocuring agent in a mass ratio of (5~30):(1~8):1; the diffusion source alloy powder is Dy a2 M 1-a2 Alloy, Tb b2 M 1-b2 One or more of the following, where M is one or more of Fe, Ga, Cu, Al, and Co elements, 0.6≤a²≤1, 0.6≤b²≤1; the organic solvent includes one or more of ethanol, polyvinyl alcohol, benzyl alcohol, and ethylene glycol; the photocuring agent is a cationic photoinitiator, including one or more of diazonium salts, diaryliodomonium salts, triarylthionium salts, alkylthionium salts, iron aromatic salts, sulfonyloxyketones, and triarylsiloxanes.

12. The method of claim 1, wherein the grain boundary diffusion sintered neodymium-iron-boron permanent magnet material is characterized by, The diffusion of the diffusion source in (4) includes coating the diffusion source onto the black sheet, curing it by irradiation with light of wavelength 250~800nm, and drying it; after the diffusion source is coated, the weight of the black sheet increases by 0.6~0.8wt%.

13. The method of claim 12, wherein the grain boundary diffusion sintered neodymium-iron-boron permanent magnet material is characterized by: The curing time is 1~30 min.

14. The method of claim 1, wherein the grain boundary diffusion sintered neodymium-iron-boron permanent magnet material is characterized by, The diffusion temperature in the diffusion heat treatment in the (4) is 850-950℃, the diffusion time is 10-20h, and the vacuum degree is <10 -3 Pa; the aging temperature in the (4) is 360-650℃, and the aging time is 2-12h.

15. A grain boundary diffusion sintered neodymium-iron-boron permanent magnetic material prepared by the method of claim 1, characterized in that The thickness of the grain boundary diffusion sintered NdFeB permanent magnet material is 1~10mm, and the Hcj is 20~33kOe.

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