Sintered neodymium iron boron pressure-assisted grain boundary diffusion enhancing method and magnet thereof

Abstract

The invention relates to the technical field of sintered neodymium-iron-boron magnet preparation technologies, in particular to a sintered neodymium-iron-boron pressure-assisted grain boundary diffusion enhancing method and a sintered neodymium-iron-boron magnet, and the sintered neodymium-iron-boron pressure-assisted grain boundary diffusion enhancing method comprises the following steps: S1, after a neodymium-iron-boron magnet is sintered, low-temperature pre-aging cooling is performed to normal temperature; s2, performing slicing, diffusion pretreatment, rare earth diffusion source coating, non-rare earth diffusion source pressure compounding and diffusion heat treatment on the pre-aged magnet; the composition of a sintered neodymium-iron-boron magnet matrix is RE < x > M < y > B < z > Fe < 100-x-y-z >, wherein RE comprises at least two elements of Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu; the strength and toughness of the magnetic steel are improved, the unfilled corner rate is reduced, meanwhile, the grain boundary phase width is increased through pre-aging, a channel is provided for diffusion, the diffusion effect is improved, and the temperature coefficient of a product is improved, so that a diffusion source, especially a spraying or printing diffusion source, is better combined with a substrate.

Description

Technical Field

[0001] The invention relates to the technical field of sintered NdFeB magnet preparation technology, and in particular to a method for sintered NdFeB pressure-assisted enhanced grain boundary diffusion and a magnet thereof. Background Art

[0002] In the field of industrial motors and new energy, sintered NdFeB permanent magnets are key functional materials that provide a stable magnetic field for motors. How to ensure that the magnets do not demagnetize in a high temperature and reverse magnetic field environment is the focus of sintered NdFeB magnet research and development. On the one hand, enhancing the magnet's anti-demagnetization ability can increase the magnet's Pc value during the design stage, but the size of the magnet will increase at this time, which is not very economical; on the other hand, it can enhance the magnet's coercive force and improve the magnet's own anti-demagnetization ability.

[0003] In new energy motors, magnets are usually distributed in an embedded V-shape. During operation, eddy currents occur, causing the temperature to rise rapidly, with the highest temperature reaching 150-180°C. At the same time, there is a demagnetization field generated by the back electromotive force, so the coercive force of the magnet is required to be relatively high at high temperatures.

[0004] At present, the main method for producing high-operating temperature and high-coercivity sintered NdFeB magnets for motors is grain boundary diffusion technology. Grain boundary diffusion technology is to cover the surface of sintered magnets with fluorides, oxides or alloy compounds of heavy rare earths such as Dy and Tb, and then diffuse the heavy rare earths along the low-melting-point rare earth-rich liquid phase of the grain boundary through heat treatment below the sintering temperature. In this way, the heavy rare earths Dy and Tb diffused in the liquid phase replace the Nd in the surface layer of the main phase grains to form a shell layer of Re2Fe14B with high magnetocrystalline anisotropy (Re is Nd and Dy or Tb). The center of the main phase grains is not affected too much. Therefore, while enhancing the magnetocrystalline anisotropy field of the surface layer of the grains, it does not have much effect on the intrinsic properties of the entire magnet. Compared with traditional alloy methods or element addition methods, for magnets with the same coercivity level, the grain boundary diffusion method can save the amount of Dy and Tb heavy rare earths, and is a technology for efficient utilization of heavy rare earths.

[0005] At present, the main process of grain boundary diffusion is: diffusion substrate sintering - slicing - diffusion source coating - diffusion heat treatment - aging heat treatment, in which the low melting point Nd-rich phase is the main channel for grain boundary diffusion. After diffusion treatment, heavy rare earth elements diffuse along the sintered NdFeB grain boundaries. However, since the heavy rare earth pure Dy and Tb elements diffuse from the surface to the inside of the magnet, after diffusion, a concentration gradient of Dy and Tb elements is formed from the surface to the inside of the magnet. The diffusion depth and efficiency are limited, the surface heavy rare earth Dy and Tb content is too high, the internal heavy rare earth content is low, and the coercive force of the magnet is limited, resulting in the waste of heavy rare earth Dy and Tb in the diffusion source. Improving the utilization rate and diffusion efficiency of heavy rare earth is the main technical direction for preparing high-performance low-heavy rare earth magnets. In addition, after sintering the diffusion substrate, due to insufficient precipitation of the grain boundary phase, the mechanical properties of the magnet are poor, and there is a problem of missing corners when sintering directly.

[0006] The current grain boundary diffusion attachment process can be divided into two categories: one is to use the oxide or fluoride of heavy rare earth Dy or Tb mixed with solvent to form a slurry, and then attach it to the magnet surface by spraying, brushing or dipping; the other is to use heavy rare earth Dy or Tb alloys (such as Dy-Fe, Tb-Fe, Dy-Co, Tb-Co alloys) or heavy rare earth Dy or Tb single substances to attach to the magnet surface by electroplating, electrophoresis or vapor deposition. The diffusion attachment heavy rare earth compound spraying, brushing or dipping process has the following problems: first, the attachment layer will locally peel off, resulting in large fluctuations in the performance of the final product and affecting the product quality; second, the presence of fluorine or oxygen and other elements harmful to the magnet in the diffusion source is not conducive to further improvement of product performance. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a method and magnet for sintered NdFeB pressure-assisted enhanced grain boundary diffusion, which increases the strength and toughness of magnetic steel and reduces the nick rate, and at the same time increases the width of the grain boundary phase by pre-aging, provides a channel for diffusion, enhances the diffusion effect, improves the temperature coefficient of the product, and makes the diffusion source, especially the sprayed or printed diffusion source, better combined with the substrate.

[0008] The present invention discloses a method for sintering NdFeB with pressure-assisted enhancement of grain boundary diffusion and a magnet thereof, and a method for sintering NdFeB with pressure-assisted enhancement of grain boundary diffusion, comprising the following steps:

[0009] S1. After sintering, the NdFeB magnet is cooled to room temperature by low temperature pre-aging;

[0010] S2, slicing, diffusion pre-treatment, rare earth diffusion source coating, non-rare earth diffusion source pressure compounding and diffusion heat treatment of the pre-aged magnet;

[0011] A sintered NdFeB magnet matrix is ​​composed of RE x M y Bz Fe 100-x-y-z , wherein RE includes at least two elements of Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, M includes at least three elements of C, O, Mg, Al, Si, Ca, Ti, Sc, V, Co, Ni, Cu, Zn, Ga, Zr, Nb, Mo, In, Sn, Sb, Ta, W, and Bi, x, y, and z are the weight percentages of their respective elements, and 28.5% wt≤x≤34% wt, 0.1% wt≤y≤5% wt, and 0.8% wt≤z≤1.4% wt.

[0012] Preferably, the processing method of the sintered NdFeB magnet matrix comprises the following steps:

[0013] S1, will be composed of RE x M y B z Fe 100-x-y-z The main alloy is melted to make strip casting sheets;

[0014] S2, subjecting the obtained belt casting sheet to hydrogen crushing treatment, the hydrogen crushing temperature is 400℃-600℃, and the hydrogen crushing time is not less than 3h, to obtain sintered NdFeB coarse material;

[0015] S3, the obtained sintered NdFeB coarse material is subjected to air flow milling, the air flow milling speed is 2800-3800r / min, and the sintered NdFeB fine powder with SMD particle size of 2.6-3.2μm is obtained;

[0016] S4, subjecting the obtained sintered NdFeB fine powder to oriented pressing and isostatic pressing to obtain a sintered NdFeB green body;

[0017] S5. Sintering the sintered NdFeB green body in a vacuum or inert gas atmosphere at a sintering temperature of 900°C-1100°C for 6-8 hours to obtain a sintered NdFeB cooked body.

[0018] Preferably, the sintered NdFeB blank is subjected to a pre-aging treatment at a temperature of 400-650°C for a holding time of 4-10h to obtain a semi-finished blank. Pre-aging precipitates grain boundary phases to increase the width of the diffusion channel, which is beneficial to the grain boundary diffusion. After the pre-aging insulation is completed, it is rapidly cooled to room temperature at a rate of 50°C / min. Rapid cooling of the grain boundaries and grains produces certain internal stresses that increase the mechanical properties and anti-chipping ability of the product.

[0019] Preferably, the pre-aged semi-finished blank is sliced ​​into black sheets with a thickness of 3-10 mm in the magnetization direction, and the processed magnet black sheets are subjected to diffusion pretreatments of surface degreasing, sandblasting and rust removal, and ultrasonic pickling.

[0020] Preferably, the rare earth diffusion source coating comprises the following steps:

[0021] S1. Mixing the powder prepared from the rare earth diffusion source with an organic dispersant to prepare a slurry rare earth diffusion source;

[0022] S2. Spray or print the mixed slurry rare earth diffusion source on the surface of the pre-treated black magnet sheet, the coating amount is 0.2%-2% of the weight of the black magnet sheet, and dry the magnet coated with the rare earth diffusion source.

[0023] Preferably, the non-rare earth diffusion source pressure compounding comprises the following steps:

[0024] S1. First, evenly spread a layer of low melting point non-rare earth diffusion source on the lower surface of the mold that fits the magnet, according to 0-1% of the weight of the magnet, and evenly stack the magnets that have been coated with rare earth diffusion source and dried in the mold, and make the magnets contact with the non-rare earth diffusion source on the mold surface;

[0025] S2. Evenly spread a layer of low melting point non-rare earth diffusion source on the upper surface of the magnet, and ensure that the weight of the non-rare earth diffusion source in contact with the upper and lower surfaces of the magnet is equal, and the total weight of the two accounts for 0-1% of the weight of the magnet;

[0026] S3. Use a special pressure molding machine to form the magnet at a pressure of 5-30 MPa, maintain the pressure for 20-60 seconds, and combine the non-rare earth diffusion source with the magnet.

[0027] Preferably, the diffusion heat treatment includes post-processing the non-rare earth diffusion source and the magnet at a treatment temperature of 800-950°C for a holding time of 5-30 hours, and then performing an aging treatment at a treatment temperature of 450-650°C for 4-8 hours to obtain a finished sintered NdFeB magnet.

[0028] Preferably, the preparation method of the rare earth diffusion source comprises designing a composition (RE1) a -(RE2) b -(M1) c -(M2) d , RE1 is one of the light rare earths Pr / Nd, RE2 is one of the heavy rare earths Tb / Dy / Ho, M1 is one of Al / Cu / Ga, wherein Cu is not more than 10%, M2 is one of In / Sn / Bi, 0≤a≤30%, 50%≤b≤100%, 0≤c≤10%, 0≤d≤10%, a+b+c+d=100%, by weight percentage, the alloy is pulverized by smelting, hydrogen crushing and air flow grinding to obtain a diffusion source powder with a particle size of 2-8μm.

[0029] Preferably, the preparation method of the non-rare earth diffusion source includes designing and smelting an alloy composed of at least three elements of Mg, Al, Zn, Ga, Cu, and Ti, wherein the content of Mg and Ti is not more than 20%, and the alloy is ball milled or air flow milled to obtain a powder with a particle size of 2-10 μm.

[0030] Compared with the prior art, the present invention has the following beneficial effects: 1. Pre-aging and rapid cooling are performed after sintering to increase the strength and toughness of the magnetic steel and reduce the corner defect rate. At the same time, pre-aging increases the width of the grain boundary phase to provide a channel for diffusion;

[0031] 2. The diffusion source adopts the design mode of light rare earth, heavy rare earth and low melting point elements to improve the diffusion effect and reduce the use of heavy rare earth by 2%-5% under the same coercivity;

[0032] 3. Add non-rare earth low melting point diffusion sources to increase the diffusion depth and coercivity without introducing heavy rare earths, and improve the temperature coefficient of the product;

[0033] 4. Increasing the pressure during the compounding process can make the diffusion source, especially the sprayed or printed diffusion source, better bonded to the substrate, preventing peeling caused by insufficient bonding force from causing poor product performance consistency. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the process of the present invention;

[0035] Figure 2 It is a schematic diagram of the process of sintering and low-temperature pre-aging cooling of NdFeB magnets. DETAILED DESCRIPTION

[0036] In order to facilitate understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive.

[0037] Example 1

[0038] like Figure 1 to Figure 2 As shown, a method for sintering NdFeB with pressure-assisted enhancement of grain boundary diffusion and a magnet thereof of the present invention;

[0039] S1, will be composed of RE x M y B z Fe 100-x-y-z The main alloy is melted to make strip casting sheets;

[0040] S2, subjecting the obtained belt casting sheet to hydrogen crushing treatment, the hydrogen crushing temperature is 400℃-600℃, and the hydrogen crushing time is not less than 3h, to obtain sintered NdFeB coarse material;

[0041] S3, the obtained sintered NdFeB coarse material is subjected to air flow milling, the air flow milling speed is 3100r / min, and the sintered NdFeB fine powder with SMD particle size of 2.7μm is obtained;

[0042] S4, subjecting the obtained sintered NdFeB fine powder to oriented pressing and isostatic pressing to obtain a sintered NdFeB green body;

[0043] S5, sintering the sintered NdFeB green billet in a vacuum or inert gas atmosphere at a sintering temperature of 1075° C. for 6 hours to obtain a sintered NdFeB cooked billet;

[0044] S6, pre-aging treatment is performed on the sintered NdFeB blank, the pre-aging treatment temperature is 450°C, and the holding time is 6 hours to obtain a semi-finished blank;

[0045] S7, slicing the pre-aged semi-finished blank into black sheets with a thickness of 4.4 mm in the magnetization direction, and performing diffusion pretreatment of surface degreasing, sandblasting and rust removal, and ultrasonic pickling on the processed magnet black sheets;

[0046] S8. Preparation method of rare earth diffusion source, designed composition is (PrNd) 10 Dy 80 (AlGa) 10 The alloy is smelted, hydrogen crushed and air flow milled to obtain a diffusion source powder with a particle size of 2-8 μm;

[0047] S9, rare earth diffusion source coating comprises the following steps:

[0048] Mixing the powder prepared from the rare earth diffusion source with an organic dispersant to prepare a slurry rare earth diffusion source;

[0049] Spray or print the mixed slurry rare earth diffusion source on the surface of the pre-treated magnet black sheet, the coating amount is 0.2%-2% of the weight of the magnet black sheet, and the magnet coated with the rare earth diffusion source is dried;

[0050] S10, non-rare earth diffusion source pressure compounding includes the following steps:

[0051] First, evenly spread a layer of low melting point non-rare earth diffusion source on the lower surface of the mold that fits the magnet, according to 0-1% of the weight of the magnet, and evenly stack the magnets that have been coated with rare earth diffusion source and dried in the mold, and make the magnets contact with the non-rare earth diffusion source on the mold surface;

[0052] Evenly spread a layer of low melting point non-rare earth diffusion source on the upper surface of the magnet, and ensure that the weight of the non-rare earth diffusion source in contact with the upper and lower surfaces of the magnet is equal, and the total weight of the two accounts for 0-1% of the weight of the magnet;

[0053] The magnet is formed by a special pressure molding machine at a pressure of 10 MPa, and the pressure is maintained for 20 seconds to combine the non-rare earth diffusion source with the magnet;

[0054] S11, diffusion heat treatment includes post-processing the combination of the non-rare earth diffusion source and the magnet, the magnet treatment temperature is 950°C, the heat preservation time is 20h, and then aging treatment is performed at a temperature of 480°C for 5h to obtain a finished sintered NdFeB magnet;

[0055] In this embodiment, pre-aging and rapid cooling are performed after sintering to increase the strength and toughness of the magnetic steel and reduce the nick rate. At the same time, pre-aging increases the width of the grain boundary phase to provide a channel for diffusion. The diffusion source adopts a design mode of light rare earth, heavy rare earth, and low melting point elements to improve the diffusion effect, and reduce the use of heavy rare earth by 2%-5% under the same coercive force. Non-rare earth low melting point diffusion sources are added to increase the diffusion depth and coercive force improvement effect without introducing heavy rare earths, and the temperature coefficient of the product can be improved. Increasing the pressure compounding process can make the diffusion source, especially the sprayed or printed diffusion source, better bonded to the substrate to prevent peeling caused by insufficient bonding force, resulting in poor product performance consistency.

[0056] Example 2

[0057] On the basis of Example 1, S1-S9 are the same as Example 1. The difference from Example 1 is that in S10, the magnet is formed by a special pressure molding machine at a pressure of 20 MPa for 20 seconds to combine the non-rare earth diffusion source with the magnet. S11 is the same as Example 1.

[0058] Example 3

[0059] On the basis of Example 1, S1-S9 are the same as Example 1. The difference from Example 1 is that in S10, the magnet is formed by a special pressure molding machine at a pressure of 30 MPa for 20 seconds to combine the non-rare earth diffusion source with the magnet. S11 is the same as Example 1.

[0060] Comparative Example 1

[0061] S1-S9 are the same as in Example 1, except that S10 is not performed, and S11 is the same as in Example 1;

[0062] Comparative Example 2

[0063] S1-S5 are the same as in Example 1, except that S6 is not performed, and the remaining steps are the same as in Example 1;

[0064] Comparative Example 3

[0065] S1-S5 are the same as in Example 1, except that the process of S6 and the process of S10 are not performed, and the remaining steps are the same as in Example 1;

[0066] The magnets obtained in Examples 1-3 and Comparative Examples 1-3 were processed into 7 mm × 7 mm samples and their magnetic properties at 20°C and 150°C were measured. The remanence (Br) and coercive force (Hcj) in the magnetic properties were tested using the NIM-62000 rare earth permanent magnet measurement system of the Institute of Metrology, Chinese Academy of Metrology.

[0067] The processing technology and magnetic properties of Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Table 1 below:

[0068] Table 1 Processing technology and magnetic properties of each embodiment 1 to 2 and comparative examples 1 to 3;

[0069]

[0070]

[0071] In Table 1, “ / ” means that the item was not performed;

[0072] In Example 3, local cracking occurred in the magnet under a pressure of 30 MPa. Therefore, the pressure should not be too high during the pressure-assisted grain boundary diffusion process. At the same time, the upper and lower surfaces of the magnet should be flat to prevent macro cracks from occurring during the pressurization process.

[0073] Seven magnets processed in Example 1 and Comparative Example 3 were taken for irreversible thermal demagnetization test. The condition was open circuit. They were baked at 170°C for 2 hours according to GB / T40794-2021 high temperature irreversible loss detection method for rare earth permanent magnet materials. The magnetic moment change rate before and after was measured as the irreversible loss rate. The results are shown in Table 2.

[0074] Table 2 Irreversible losses of the magnets of Example 1 and Comparative Example 3 under open circuit conditions at 170°C;

[0075]

[0076] It can be seen from the table that after pre-aging and pressure-assisted grain boundary diffusion of the spraying process, the magnetic properties and coercive force temperature coefficient are significantly improved, the irreversible loss rate is significantly improved, and the product consistency is significantly improved;

[0077] Example 4

[0078] S1, smelting a main alloy having a composition of RExMyBzFe100-xyz to prepare a strip casting sheet;

[0079] S2, subjecting the obtained belt casting sheet to hydrogen crushing treatment, the hydrogen crushing temperature is 400℃-600℃, and the hydrogen crushing time is not less than 3h, to obtain sintered NdFeB coarse material;

[0080] S3, the obtained sintered NdFeB coarse material is subjected to air flow milling, the air flow milling speed is 3200r / min, and the sintered NdFeB fine powder with SMD particle size of 2.6μm is obtained;

[0081] S4, subjecting the obtained sintered NdFeB fine powder to oriented pressing and isostatic pressing to obtain a sintered NdFeB green body;

[0082] S5, sintering the sintered NdFeB green billet in a vacuum or inert gas atmosphere at a sintering temperature of 1075° C. for 6 hours to obtain a sintered NdFeB cooked billet;

[0083] S6, pre-aging treatment is performed on the sintered NdFeB blank, the pre-aging treatment temperature is 500°C, and the holding time is 6 hours to obtain a semi-finished blank;

[0084] S7, slicing the pre-aged semi-finished blank into black sheets with a thickness of 5 mm in the magnetization direction, and performing diffusion pretreatment of surface degreasing, sandblasting and rust removal, and ultrasonic pickling on the processed magnet black sheets;

[0085] S8. Preparation method of rare earth diffusion source, designed composition is (PrNdTb) 90 (AlCu) 10 The alloy is smelted, hydrogen crushed and air flow milled to obtain a diffusion source powder with a particle size of 2-8 μm;

[0086] S9, rare earth diffusion source coating comprises the following steps:

[0087] Design composition and smelt (MgZnTi) 60 (AlGa) 40 The alloy is ball-milled to obtain a powder with a particle size of 2-10 μm;

[0088] S10, rare earth diffusion source coating comprises the following steps:

[0089] Mixing the powder prepared from the rare earth diffusion source with an organic dispersant to prepare a slurry rare earth diffusion source;

[0090] Spray or print the mixed slurry rare earth diffusion source on the surface of the pre-treated magnet black sheet, the coating amount is 0.45% of the weight of the magnet black sheet, and dry the magnet coated with the rare earth diffusion source;

[0091] S11, non-rare earth diffusion source pressure compounding includes the following steps:

[0092] First, evenly spread a layer of low melting point non-rare earth diffusion source on the lower surface of the mold that fits the magnet, according to 0.2% of the weight of the magnet, and evenly stack the magnets that have been coated with rare earth diffusion source and dried in the mold, and make the magnets contact with the non-rare earth diffusion source on the mold surface;

[0093] Evenly spread a layer of low melting point non-rare earth diffusion source on the upper surface of the magnet, and ensure that the weight of the non-rare earth diffusion source in contact with the upper and lower surfaces of the magnet is equal, and the total weight of the two accounts for 0.2% of the weight of the magnet;

[0094] S12, using a special pressure molding machine to form the magnet at a pressure of 10 MPa, maintaining the pressure for 30 seconds, to combine the non-rare earth diffusion source with the magnet;

[0095] S13, diffusion heat treatment includes post-processing the combination of non-rare earth diffusion source and magnet, the magnet treatment temperature is 900°C, the heat preservation time is 20h, and then aging treatment is performed, the treatment temperature is 510°C, the time is 6h, and the finished sintered NdFeB magnet is obtained.

[0096] Example 5

[0097] The difference from Example 4 is that in S6, the sintered NdFeB blank is subjected to a pre-aging treatment, the pre-aging treatment temperature is 600° C., the holding time is 6 hours, and a semi-finished blank is obtained. The remaining steps are the same as those in Example 4.

[0098] Comparative Example 4

[0099] The difference from Example 4 is that S9, S11 and S12 are not performed, and the remaining steps are the same as those in Example 4;

[0100] Comparative Example 5

[0101] The difference from Example 4 is that S9 and S11 are not performed, and the remaining steps are the same as those of Example 4;

[0102] Comparative Example 6

[0103] The difference from Example 4 is that S6, S9, S11 and S12 are not performed, and the remaining steps are the same as those in Example 4;

[0104] The processing technology of Examples 4 to 5 and Comparative Examples 4 to 6 is shown in Table 3 below.

[0105] Table 3 Processing technology of each embodiment 4 to 5 and comparative examples 4 to 7;

[0106]

[0107] In Table 3, “ / ” means that the item was not performed;

[0108] The magnets obtained in Examples 4-5 and Comparative Examples 4-7 were processed into 7 mm × 7 mm samples and their magnetic properties at 20°C and 150°C were measured. The remanence (Br) and coercive force (Hcj) in the magnetic properties were tested using the NIM-62000 rare earth permanent magnet measurement system of the Institute of Metrology, Chinese Academy of Metrology. The results are shown in Table 4.

[0109] Table 4 Processing technology and magnetic properties of Examples 4 to 5 and Comparative Examples 4 to 7;

[0110]

[0111] It can be seen from the table that after pre-aging and pressure-assisted grain boundary diffusion of the spraying process, the coercivity (Hcj) and high-temperature coercivity are significantly improved.

[0112] The main functions achieved by the present invention are: pre-aging and rapid cooling after sintering to increase the strength and toughness of the magnetic steel and reduce the missing corner rate. At the same time, pre-aging increases the width of the grain boundary phase to provide a channel for diffusion;

[0113] The diffusion source adopts the design mode of light rare earth / heavy rare earth / low melting point elements to improve the diffusion effect;

[0114] Adding non-rare earth low melting point diffusion sources can increase the diffusion depth and coercivity enhancement effect without introducing heavy rare earths, and can improve the temperature coefficient of the product;

[0115] Increasing the pressure compounding process can make the diffusion source, especially the sprayed or printed diffusion source, better bonded to the substrate, and prevent peeling caused by insufficient bonding force from causing poor product performance consistency.

[0116] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for sintering NdFeB with pressure-assisted enhanced grain boundary diffusion and a magnet thereof, characterized in that: The method for sintering NdFeB with pressure-assisted enhanced grain boundary diffusion comprises the following steps: S1. After sintering, the NdFeB magnet is cooled to room temperature by low temperature pre-aging; S2, slicing, diffusion pre-treatment, rare earth diffusion source coating, non-rare earth diffusion source pressure compounding and diffusion heat treatment of the pre-aged magnet; A sintered NdFeB magnet matrix is ​​composed of RE x M y B z Fe 100-x-y-z , wherein RE includes at least two elements of Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, M includes at least three elements of C, O, Mg, Al, Si, Ca, Ti, Sc, V, Co, Ni, Cu, Zn, Ga, Zr, Nb, Mo, In, Sn, Sb, Ta, W, and Bi, x, y, and z are the weight percentages of their respective elements, and 28.5% wt≤x≤34% wt, 0.1% wt≤y≤5% wt, and 0.8% wt≤z≤1.4% wt.

2. A method for sintering NdFeB with pressure-assisted enhanced grain boundary diffusion and a magnet thereof as claimed in claim 1, characterized in that: The processing method of sintered NdFeB magnet matrix comprises the following steps: S1, will be composed of RE x M y B z Fe 100-x-y-z The main alloy is melted to make strip casting sheets; S2, subjecting the obtained belt casting sheet to hydrogen crushing treatment, the hydrogen crushing temperature is 400℃-600℃, and the hydrogen crushing time is not less than 3h, to obtain sintered NdFeB coarse material; S3, the obtained sintered NdFeB coarse material is subjected to air flow milling, the air flow milling speed is 2800-3800r / min, and the sintered NdFeB fine powder with SMD particle size of 2.6-3.2μm is obtained; S4, subjecting the obtained sintered NdFeB fine powder to oriented pressing and isostatic pressing to obtain a sintered NdFeB green body; S5. Sintering the sintered NdFeB green body in a vacuum or inert gas atmosphere at a sintering temperature of 900°C-1100°C for 6-8 hours to obtain a sintered NdFeB cooked body.

3. A method for sintering NdFeB with pressure-assisted enhanced grain boundary diffusion and a magnet thereof as claimed in claim 2, characterized in that: The sintered NdFeB blank is pre-aged at a temperature of 400-650°C for 4-10h to obtain a semi-finished blank. Pre-aging precipitates grain boundary phases to increase the width of the diffusion channel, which is beneficial to the grain boundary diffusion. After the pre-aging insulation is completed, it is rapidly cooled to room temperature at a rate of 50°C / min. Rapid cooling of the grain boundaries and grains produces certain internal stresses that increase the mechanical properties and anti-chipping ability of the product.

4. A method for enhancing grain boundary diffusion of sintered NdFeB by pressure-assisted method and magnet thereof as claimed in claim 3, characterized in that: The pre-aged semi-finished blank is sliced ​​into black sheets with a thickness of 3-10 mm in the magnetization direction, and the processed magnet black sheets are subjected to diffusion pretreatments such as surface degreasing, sandblasting and rust removal, and ultrasonic pickling.

5. A method for sintering NdFeB with pressure-assisted enhanced grain boundary diffusion and a magnet thereof as claimed in claim 1, characterized in that: Rare earth diffusion source coating includes the following steps: S1. Mixing the powder prepared from the rare earth diffusion source with an organic dispersant to prepare a slurry rare earth diffusion source; S2. Spray or print the mixed slurry rare earth diffusion source on the surface of the pre-treated black magnet sheet, the coating amount is 0.2%-2% of the weight of the black magnet sheet, and dry the magnet coated with the rare earth diffusion source.

6. A method for enhancing grain boundary diffusion of sintered NdFeB by pressure-assisted method and magnet thereof as claimed in claim 1, characterized in that: The non-rare earth diffusion source pressure compounding includes the following steps: S1. First, evenly spread a layer of low melting point non-rare earth diffusion source on the lower surface of the mold that fits the magnet, according to 0-1% of the weight of the magnet, and evenly stack the magnets that have been coated with rare earth diffusion source and dried in the mold, and make the magnets contact with the non-rare earth diffusion source on the mold surface; S2. Evenly spread a layer of low melting point non-rare earth diffusion source on the upper surface of the magnet, and ensure that the weight of the non-rare earth diffusion source in contact with the upper and lower surfaces of the magnet is equal, and the total weight of the two accounts for 0-1% of the weight of the magnet; S3. Use a special pressure molding machine to form the magnet at a pressure of 5-30 MPa, maintain the pressure for 20-60 seconds, and combine the non-rare earth diffusion source with the magnet.

7. A method for enhancing grain boundary diffusion of sintered NdFeB by pressure-assisted method and magnet thereof as claimed in claim 1, characterized in that: The diffusion heat treatment includes post-processing the combination of the non-rare earth diffusion source and the magnet, the treatment temperature is 800-950°C, the insulation time is 5-30h, and then aging treatment is performed, the treatment temperature is 450-650°C, the time is 4-8h, and the finished sintered NdFeB magnet is obtained.

8. A method for enhancing grain boundary diffusion of sintered NdFeB by pressure-assisted method and magnet thereof as claimed in claim 1, characterized in that: The method for preparing a rare earth diffusion source comprises designing a composition (RE1) a -(RE2) b -(M1) c -(M2) d , RE1 is one of the light rare earths Pr / Nd, RE2 is one of the heavy rare earths Tb / Dy / Ho, M1 is one of Al / Cu / Ga, wherein Cu is not more than 10%, M2 is one of In / Sn / Bi, 0≤a≤30%, 50%≤b≤100%, 0≤c≤10%, 0≤d≤10%, a+b+c+d=100%, by weight percentage, the alloy is pulverized by smelting, hydrogen crushing and air flow grinding to obtain a diffusion source powder with a particle size of 2-8μm.

9. A method for enhancing grain boundary diffusion of sintered NdFeB by pressure-assisted method and magnet thereof as claimed in claim 1, characterized in that: The preparation method of non-rare earth diffusion source includes designing and smelting an alloy composed of at least three elements of Mg, Al, Zn, Ga, Cu and Ti, wherein the content of Mg and Ti is not more than 20%, and the alloy is ball milled or air flow milled to obtain powder with a particle size of 2-10μm.

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