Method for sintered neodymium-iron-boron pressure-assisted grain boundary diffusion and magnet thereof

Abstract

The present application relates to the technical field of sintered Nd-Fe-B magnet preparation technology, and particularly relates to a sintered Nd-Fe-B pressure-assisted enhanced grain boundary diffusion method and a magnet thereof, which comprises the following steps: S1, after sintering, the Nd-Fe-B magnet is pre-aged at low temperature and cooled to room temperature; S2, the pre-aged magnet is sliced, diffusion pre-processed, coated with a rare earth diffusion source, pressure-combined with a non-rare earth diffusion source, and diffusion heat treated; the composition of a sintered Nd-Fe-B magnet substrate is RE x M y B z Fe 100‑x‑y‑z , wherein RE comprises at least two elements in Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; the method increases the strength and toughness of the magnetic steel and reduces the rate of missing corners, meanwhile, pre-aging increases the grain boundary phase width, provides a channel for diffusion, improves 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.

Description

Technical Field

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

[0002] In the fields of industrial motors and new energy, sintered NdFeB permanent magnets are key functional materials for providing stable magnetic fields for motors. Ensuring that the magnets do not demagnetize in high-temperature and reverse magnetic field environments is a key focus of sintered NdFeB magnet research and development. On the one hand, enhancing the magnets' resistance to demagnetization can be achieved by increasing the Pc value of the magnets during the design phase, but this would increase the size of the magnets, which is not economical. On the other hand, the coercivity of the magnets can be improved to enhance their resistance to demagnetization.

[0003] In new energy motors, magnets are usually embedded in a V-shape. During operation, eddy currents cause the temperature to rise rapidly, reaching as high as 150-180℃. At the same time, there is also a demagnetizing field generated by back electromotive force. Therefore, the magnets are required to have relatively high coercivity at high temperatures.

[0004] Currently, the main method for producing high-temperature, high-coercivity sintered NdFeB magnets for motors is grain boundary diffusion technology. This technology involves coating the surface of the sintered magnet with fluorides, oxides, or alloy compounds of heavy rare earth elements such as Dy and Tb. Then, a heat treatment below the sintering temperature is performed, causing the heavy rare earth elements to diffuse along the low-melting-point rare earth-rich liquid phase at the grain boundaries. In this way, the Dy and Tb diffused in the liquid phase replace Nd in the surface layer of the main phase grains, forming a Re2Fe14B shell with high magnetocrystalline anisotropy (Re is Nd and Dy or Tb). The center of the main phase grains is not significantly affected. Therefore, while enhancing the magnetocrystalline anisotropy field of the grain surface, it does not significantly affect the intrinsic properties of the entire magnet. Compared to traditional alloying or element addition methods, grain boundary diffusion saves on the amount of Dy and Tb heavy rare earth elements needed to achieve the same level of coercivity, making it a highly efficient technology for utilizing heavy rare earth elements.

[0005] The current main process of grain boundary diffusion is: sintering of the diffusion substrate—slicing—coating of the diffusion source—diffusion heat treatment—aging heat treatment. 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 grain boundaries of the sintered NdFeB magnet. However, since pure Dy and Tb elements diffuse from the magnet surface to the interior, a concentration gradient of Dy and Tb elements is formed from the surface to the interior of the magnet. This limits the diffusion depth and efficiency, resulting in excessively high Dy and Tb content on the surface and low content inside, thus limiting the improvement in magnet coercivity and leading to waste of Dy and Tb in the diffusion source. Improving the utilization rate and diffusion efficiency of heavy rare earth elements is the main technical direction for preparing high-performance low-heavy rare earth magnets. Furthermore, insufficient precipitation of the grain boundary phase after sintering of the diffusion substrate results in poor mechanical properties of the magnet, and direct slicing after sintering leads to corner defects.

[0006] Current grain boundary diffusion deposition processes can be mainly divided into two categories: one is to mix oxides or fluorides of heavy rare earth elements Dy or Tb with a solvent to form a slurry, which is then applied to the magnet surface by spraying, brushing, or dipping; the other is to use alloys of heavy rare earth elements Dy or Tb (such as Dy-Fe, Tb-Fe, Dy-Co, Tb-Co alloys) or elemental heavy rare earth elements Dy or Tb, which are then applied to the magnet surface by electroplating, electrophoresis, or vapor deposition. The diffusion deposition process of heavy rare earth compounds by spraying, brushing, or dipping has the following problems: first, localized peeling of the deposited layer can occur, leading to significant fluctuations in the final product performance and affecting product quality; second, the presence of elements such as fluorine or oxygen in the diffusion source is harmful to the magnet, hindering further improvement of product performance. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a method and magnet for enhancing grain boundary diffusion using sintered NdFeB pressure-assisted methods, which increases the strength and toughness of the magnet, reduces the corner breakage rate, and simultaneously increases the grain boundary phase width through pre-aging, providing a channel for diffusion, improving the diffusion effect, and improving the temperature coefficient of the product, thereby enabling better bonding between the diffusion source, especially the sprayed or printed diffusion source, and the substrate.

[0008] The present invention discloses a method for pressure-assisted enhancement of grain boundary diffusion in sintered NdFeB magnets and a magnet thereof. The method for pressure-assisted enhancement of grain boundary diffusion in sintered NdFeB magnets includes the following steps:

[0009] S1. After sintering, the NdFeB magnets are pre-aged at low temperature and cooled to room temperature.

[0010] S2. The pre-aged magnet is sliced, pre-diffusion treatment is performed, rare earth diffusion source is coated, non-rare earth diffusion source is pressure composited and diffusion heat treatment is performed.

[0011] A sintered NdFeB magnet matrix has the following composition: RE x M y Bz Fe 100-x-y-z RE includes at least two elements selected from Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; M includes at least three elements selected from 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 for sintered NdFeB magnet substrate includes 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 and produced into strip castings;

[0014] S2. The obtained strip castings are subjected to hydrogen crushing treatment at a temperature of 400℃-600℃ and a time of not less than 3 hours to obtain sintered NdFeB rough material.

[0015] S3. The obtained sintered NdFeB coarse material is subjected to an air jet mill at a speed of 2800-3800 r / min to obtain sintered NdFeB fine powder with an SMD particle size of 2.6-3.2 μm.

[0016] S4. The obtained sintered NdFeB fine powder is subjected to orientation pressing and isostatic pressing to obtain sintered NdFeB green blanks.

[0017] S5. The sintered NdFeB green blank is sintered in a vacuum or inert gas atmosphere at a sintering temperature of 900℃-1100℃ for 6-8 hours to obtain the sintered NdFeB finished blank.

[0018] Preferably, the sintered NdFeB blank is pre-aged at a temperature of 400-650℃ for 4-10 hours to obtain a semi-finished blank. Pre-aging precipitates grain boundary phases, increasing the width of the diffusion channels and facilitating grain boundary diffusion. After pre-aging, the blank is rapidly cooled to room temperature at a rate of 50℃ / min. Rapid cooling generates certain internal stresses between the grain boundaries and grains, increasing the mechanical properties and resistance to corner defects of the product.

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

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

[0021] S1. The powder obtained from the rare earth diffusion source is mixed with an organic dispersant to form a slurry rare earth diffusion source;

[0022] S2. Spray or print a mixture to form a rare earth diffusion source on the surface of the pretreated black magnet sheet. The coating amount is 0.2%-2% of the weight of the black magnet sheet. Then, dry the magnet coated with the rare earth diffusion source.

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

[0024] S1. With the magnet weight greater than 0 and not exceeding 1%, first evenly spread a layer of low melting point non-rare earth diffusion source on the lower surface of the mold that is in contact with the magnet. Then evenly place the magnet that has been coated with rare earth diffusion source and dried in the mold, and make the magnet contact the non-rare earth diffusion source spread on the surface of the mold.

[0025] S2. A layer of low-melting-point non-rare earth diffusion source is uniformly spread on the upper surface of the magnet, and 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 sources accounts for more than 0 and less than 1% of the weight of the magnet.

[0026] S3. Use a special pressure forming machine to press the magnet at a pressure of 5-30MPa for 20-60s to combine the non-rare earth diffusion source with the magnet.

[0027] Preferably, the diffusion heat treatment includes post-treatment of combining a non-rare earth diffusion source with the magnet at a temperature of 800-950℃ and a holding time of 5-30h, followed by aging treatment at a temperature of 450-650℃ and a time of 4-8h, to obtain the finished sintered NdFeB magnet.

[0028] Preferably, the method for preparing the rare earth diffusion source includes designing the composition as (RE1). a -(RE2) b -(M1) c -(M2) d RE1 is one of the light rare earth elements Pr / Nd, RE2 is one of the heavy rare earth elements Tb / Dy / Ho, M1 is one of the Al / Cu / Ga elements, where Cu is not greater than 10%, and M2 is one of the In / Sn / Bi elements. The weight percentages are: 0≤a≤30%, 50%≤b≤100%, 0≤c≤10%, 0≤d≤10%, and a+b+c+d=100%. The alloy is smelted, hydrogenated, and air-jet milled to obtain diffusion source powder with a particle size of 2-8μm.

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

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Pre-aging and rapid cooling after sintering increase the strength and toughness of the magnet and reduce the corner defect rate. At the same time, pre-aging increases the width of the grain boundary phase, providing a channel for diffusion.

[0031] 2. 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 amount of heavy rare earth used by 2%-5% under the same coercivity.

[0032] 3. Adding non-rare earth low-melting-point diffusion sources increases diffusion depth and coercivity without introducing heavy rare earth elements, and can also improve the temperature coefficient of the product.

[0033] 4. Increasing the pressure of the composite process can better bond the diffusion source, especially the sprayed or printed diffusion source, with the substrate, preventing peeling caused by insufficient bonding, which can lead to poor product performance consistency. Attached Figure Description

[0034] Figure 1 This is a flowchart illustrating the present invention;

[0035] Figure 2 This is a schematic diagram of the process steps for sintering and low-temperature pre-aging of neodymium iron boron magnets. Detailed Implementation

[0036] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

[0037] Example 1

[0038] like Figures 1 to 2 As shown, this invention discloses a method for pressure-assisted enhancement of grain boundary diffusion in sintered NdFeB magnets and the magnet thereof;

[0039] S1, will be composed of RE x M y B z Fe 100-x-y-z The main alloy is melted and produced into strip castings;

[0040] S2. The obtained strip castings are subjected to hydrogen crushing treatment at a temperature of 400℃-600℃ and a time of not less than 3 hours to obtain sintered NdFeB rough material.

[0041] S3. The obtained sintered NdFeB coarse material is subjected to an air jet mill at a speed of 3100 r / min to obtain sintered NdFeB fine powder with an SMD particle size of 2.7 μm.

[0042] S4. The obtained sintered NdFeB fine powder is subjected to orientation pressing and isostatic pressing to obtain sintered NdFeB green blanks.

[0043] S5. The sintered NdFeB green blank is sintered in a vacuum or inert gas atmosphere at a sintering temperature of 1075℃ for 6 hours to obtain the sintered NdFeB finished blank.

[0044] S6. Pre-aging treatment is performed on the sintered NdFeB blank. The pre-aging treatment temperature is 450℃ and the holding time is 6h to obtain a semi-finished blank.

[0045] S7. After pre-aging, the semi-finished blank is sliced ​​into black sheets with a thickness of 4.4mm in the magnetization direction. The processed magnet black sheets are then subjected to surface degreasing, sandblasting and rust removal, and ultrasonic pickling as a diffusion pretreatment.

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

[0047] S9. Rare earth diffusion source coating includes the following steps:

[0048] The powder obtained from the rare earth diffusion source is mixed with an organic dispersant to form a slurry rare earth diffusion source;

[0049] Spray or print a mixture to form a rare earth diffusion source on the surface of the pretreated black magnet sheet. The coating amount is 0.2%-2% of the weight of the black magnet sheet. Then, the magnet coated with the rare earth diffusion source is dried.

[0050] S10, Non-Rare Earth Diffusion Source Pressure Composite includes the following steps:

[0051] With the magnet weight greater than 0 and not exceeding 1%, first evenly spread a layer of low melting point non-rare earth diffusion source on the lower surface of the mold that is in contact with the magnet. Then evenly place the magnet that has been coated with rare earth diffusion source and dried in the mold, and make the magnet contact the non-rare earth diffusion source spread on the surface of the mold.

[0052] A layer of low-melting-point non-rare earth diffusion source is uniformly spread on the upper surface of the magnet, and 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 sources accounts for more than 0 and less than 1% of the weight of the magnet.

[0053] The magnet is subjected to a pressure of 10MPa for 20s using a special pressure forming machine to combine the non-rare earth diffusion source with the magnet.

[0054] S11. Diffusion heat treatment includes combining the non-rare earth diffusion source with the magnet and then treating it. The magnet is treated at 950℃ for 20 hours and then aged at 480℃ for 5 hours to obtain the 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 magnets and reduce the corner breakage rate. At the same time, pre-aging increases the width of the grain boundary phase, providing 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 amount of heavy rare earth by 2%-5% under the same coercivity. The addition of non-rare earth low melting point diffusion sources increases the diffusion depth and coercivity without introducing heavy rare earths, and can also improve the temperature coefficient of the product. The addition of a pressure composite process can make the diffusion source, especially the sprayed or printed diffusion source, better bond with the substrate, preventing peeling caused by insufficient bonding force, which would lead to a deterioration in product performance consistency.

[0056] Example 2

[0057] Based on Example 1, S1-S9 are the same as in Example 1. The difference from Example 1 is that in S10, the magnet is combined with the non-rare earth diffusion source by using a special pressure forming machine at a pressure of 20MPa for 20s. S11 is the same as in Example 1.

[0058] Example 3

[0059] Based on Example 1, S1-S9 are the same as in Example 1. The difference from Example 1 is that in S10, the magnet is combined with the non-rare earth diffusion source by using a special pressure forming machine at a pressure of 30MPa for 20s. S11 is the same as in Example 1.

[0060] Comparative Example 1

[0061] S1-S9 are the same as in Example 1, except that S10 is omitted. 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. 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 S6 and S10 are not performed. The remaining steps are the same as in Example 1.

[0066] Magnets prepared in Examples 1-3 and Comparative Examples 1-3 were processed into 7mm×7mm samples and their magnetic properties at 20℃ and 150℃ were measured. The remanence (Br) and coercivity (Hcj) of the magnetic properties were tested using the NIM-62000 rare earth permanent magnet measurement system of the National Institute of Metrology of China.

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

[0068] Table 1. Processing techniques and magnetic properties of each of Examples 1-2 and Comparative Examples 1-3;

[0069]

[0070] In Table 1, " / " indicates that the item was not performed;

[0071] In Example 3, the magnet experienced localized cracking 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, it is necessary to ensure that the upper and lower surfaces of the magnet are flat to prevent macroscopic cracks from forming during the pressurization process.

[0072] Seven magnets from each of Example 1 and Comparative Example 3 were subjected to an irreversible thermal demagnetization test under open circuit conditions. The magnets were baked at 170°C for 2 hours according to GB / T 40794-2021, the method for detecting irreversible loss of rare earth permanent magnet materials at high temperature. The change rate of magnetic moment before and after the test was measured as the irreversible loss rate. The results are shown in Table 2.

[0073] Table 2 Irreversible losses of magnets in Example 1 and Comparative Example 3 under open-circuit conditions at 170°C;

[0074]

[0075] As can be seen from the table, after pre-aging and pressure-assisted grain boundary diffusion in the spraying process, the magnetic properties and coercivity temperature coefficient are significantly improved, the irreversible loss rate is significantly improved, and the product consistency is significantly enhanced.

[0076] Example 4

[0077] S1. Melt the main alloy with the composition RExMyBzFe100-xyz to produce strip castings;

[0078] S2. The obtained strip castings are subjected to hydrogen crushing treatment at a temperature of 400℃-600℃ and a time of not less than 3 hours to obtain sintered NdFeB rough material.

[0079] S3. The obtained sintered NdFeB coarse material is subjected to an air jet mill at a speed of 3200 r / min to obtain sintered NdFeB fine powder with an SMD particle size of 2.6 μm.

[0080] S4. The obtained sintered NdFeB fine powder is subjected to orientation pressing and isostatic pressing to obtain sintered NdFeB green blanks.

[0081] S5. The sintered NdFeB green blank is sintered in a vacuum or inert gas atmosphere at a sintering temperature of 1075℃ for 6 hours to obtain the sintered NdFeB finished blank.

[0082] S6. Pre-aging treatment is performed on the sintered NdFeB blank. The pre-aging treatment temperature is 500℃ and the holding time is 6h to obtain a semi-finished blank.

[0083] S7. After pre-aging, the semi-finished blank is sliced ​​into black sheets with a thickness of 5mm in the magnetization direction. The processed magnet black sheets are then subjected to surface degreasing, sandblasting and rust removal, and ultrasonic pickling as a pre-diffusion treatment.

[0084] S8. Preparation method of rare earth diffusion source, designed composition is (PrNdTb) 90 (AlCu) 10 The alloy is smelted, hydrogenated and air-jet milled to obtain diffusion source powder with a particle size of 2-8μm;

[0085] S9. Rare earth diffusion source coating includes the following steps:

[0086] The design composition and smelting process involved (MgZnTi). 60 (AlGa) 40 The alloy is composed of powder particles with a particle size of 2-10μm obtained by ball milling.

[0087] S10, Rare Earth Diffusion Source Coating includes the following steps:

[0088] The powder obtained from the rare earth diffusion source is mixed with an organic dispersant to form a slurry rare earth diffusion source;

[0089] A rare earth diffusion source is prepared by spraying or printing a mixture onto the surface of a pre-treated black magnet sheet. The coating amount is 0.45% of the weight of the black magnet sheet. The magnet coated with the rare earth diffusion source is then dried.

[0090] S11, Non-rare earth diffusion source pressure recombination includes the following steps:

[0091] At 0.2% of the magnet's weight, first evenly spread a layer of low-melting-point non-rare earth diffusion source on the lower surface of the mold that is in contact with the magnet. Then, evenly place the magnets that have been coated with rare earth diffusion source and dried in the mold, and make the magnets contact the non-rare earth diffusion source spread on the surface of the mold.

[0092] A layer of low-melting-point non-rare-earth diffusion source is uniformly spread on the upper surface of the magnet, ensuring 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 magnet's weight.

[0093] S12. Use a special pressure forming machine to press the magnet at 10MPa pressure for 30s to combine the non-rare earth diffusion source with the magnet.

[0094] S13. Diffusion heat treatment includes combining the non-rare earth diffusion source with the magnet and then treating it. The magnet is treated at 900℃ for 20 hours, followed by aging treatment at 510℃ for 6 hours to obtain the finished sintered NdFeB magnet.

[0095] Example 5

[0096] The difference from Example 4 is that in S6, the sintered NdFeB blank is pre-aged at a temperature of 600°C for 6 hours to obtain a semi-finished blank. The remaining steps are the same as in Example 4.

[0097] Comparative Example 4

[0098] The difference from Example 4 is that S9, S11 and S12 are not performed, while the remaining steps are the same as in Example 4;

[0099] Comparative Example 5

[0100] The difference from Example 4 is that S9 and S11 are omitted, while the remaining steps are the same as in Example 4;

[0101] Comparative Example 6

[0102] The difference from Example 4 is that steps S6, S9, S11 and S12 are omitted, while the remaining steps are the same as in Example 4;

[0103] The processing techniques of Examples 4-5 and Comparative Examples 4-6 are shown in Table 3 below.

[0104] Table 3. Processing techniques for each of Examples 4-5 and Comparative Examples 4-7;

[0105]

[0106] In Table 3, " / " indicates that the item was not performed;

[0107] Magnets prepared in Examples 4-5 and Comparative Examples 4-7 were processed into 7mm×7mm samples and their magnetic properties at 20℃ and 150℃ were measured. The remanence (Br) and coercivity (Hcj) in the magnetic properties were tested using the NIM-62000 rare earth permanent magnet measurement system of the National Institute of Metrology of China. The results are shown in Table 4.

[0108] Table 4 shows the processing techniques and magnetic properties of Examples 4-5 and Comparative Examples 4-7;

[0109]

[0110] As can be seen from the table, after pre-aging and pressure-assisted grain boundary diffusion in the spraying process, the coercivity (Hcj) and high-temperature coercivity are significantly improved.

[0111] The main functions achieved by this invention are: after sintering, pre-aging and rapid cooling are performed to increase the strength and toughness of the magnet and reduce the corner breakage rate. At the same time, pre-aging increases the width of the grain boundary phase, providing a channel for diffusion.

[0112] The diffusion source adopts a light rare earth / heavy rare earth / low melting point element design mode to improve the diffusion effect;

[0113] Adding non-rare earth low-melting-point diffusion sources can increase diffusion depth and coercivity without introducing heavy rare earth elements, and can also improve the temperature coefficient of the product.

[0114] Increasing the pressure during the composite process can improve the bonding between the diffusion source, especially the sprayed or printed diffusion source, and the substrate, preventing peeling caused by insufficient bonding, which can lead to a decrease in product performance consistency.

[0115] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for pressure-assisted enhancement of grain boundary diffusion in sintered NdFeB magnets, characterized in that, The method for pressure-assisted enhancement of grain boundary diffusion in sintered NdFeB magnets includes the following steps: S1. After sintering, the NdFeB magnets are pre-aged at low temperature and cooled to room temperature. S2. The pre-aged magnet is sliced, pre-diffusion treatment is performed, rare earth diffusion source is coated, non-rare earth diffusion source is pressure composited and diffusion heat treatment is performed. A sintered NdFeB magnet matrix has the following composition: RE x M y B z Fe 100-x-y-z RE includes at least two elements selected from Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; M includes at least three elements selected from 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. Non-rare earth diffusion source pressure recombination includes the following steps: S1. With the magnet weight greater than 0 and not exceeding 1%, first evenly spread a layer of low melting point non-rare earth diffusion source on the lower surface of the mold that is in contact with the magnet. Then evenly place the magnet that has been coated with rare earth diffusion source and dried in the mold, and make the magnet contact the non-rare earth diffusion source spread on the surface of the mold. S2. A layer of low-melting-point non-rare earth diffusion source is uniformly spread on the upper surface of the magnet, and 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 sources accounts for more than 0 and less than 1% of the weight of the magnet. S3. Use a special pressure forming machine to press the magnet at a pressure of 5-30MPa for 20-60s to combine the non-rare earth diffusion source with the magnet.

2. The method for pressure-assisted enhanced grain boundary diffusion in sintered NdFeB as described in claim 1, characterized in that, The processing method for sintered NdFeB magnet substrates includes the following steps: S1, will be composed of RE x M y B z Fe 100-x-y-z The main alloy is melted and produced into strip castings; S2. The obtained strip castings are subjected to hydrogen crushing treatment at a temperature of 400℃-600℃ and a time of not less than 3 hours to obtain sintered NdFeB rough material. S3. The obtained sintered NdFeB coarse material is subjected to an air jet mill at a speed of 2800-3800 r / min to obtain sintered NdFeB fine powder with an SMD particle size of 2.6-3.2 μm. S4. The obtained sintered NdFeB fine powder is subjected to orientation pressing and isostatic pressing to obtain sintered NdFeB green blanks. S5. The sintered NdFeB green blank is sintered in a vacuum or inert gas atmosphere at a sintering temperature of 900℃-1100℃ for 6-8 hours to obtain the sintered NdFeB finished blank.

3. The method for pressure-assisted enhanced grain boundary diffusion in sintered NdFeB as described in claim 2, characterized in that, Pre-aging treatment is performed on sintered NdFeB blanks at a temperature of 400-650℃ for 4-10 hours to obtain semi-finished blanks. Pre-aging precipitates grain boundary phases, increasing the width of diffusion channels and facilitating grain boundary diffusion. After pre-aging, the blanks are rapidly cooled to room temperature at a rate of 50℃ / min. Rapid cooling generates internal stress between the grain boundaries and grains, increasing the mechanical properties and resistance to corner defects of the product.

4. The method for pressure-assisted enhanced grain boundary diffusion in sintered NdFeB as described in claim 3, characterized in that, The pre-aged semi-finished blanks are sliced ​​and processed into black sheets with a thickness of 3-10mm in the magnetization direction. The processed magnet black sheets are then subjected to pre-diffusion treatment, including surface degreasing, sandblasting to remove rust, and ultrasonic pickling.

5. The method for pressure-assisted enhanced grain boundary diffusion in sintered NdFeB as described in claim 1, characterized in that, The coating of rare earth diffusion sources includes the following steps: S1. The powder obtained from the rare earth diffusion source is mixed with an organic dispersant to form a slurry rare earth diffusion source; S2. Spray or print a mixture to form a rare earth diffusion source on the surface of the pretreated black magnet sheet. The coating amount is 0.2%-2% of the weight of the black magnet sheet. Then, dry the magnet coated with the rare earth diffusion source.

6. The method for pressure-assisted enhanced grain boundary diffusion in sintered NdFeB as described in claim 1, characterized in that, The diffusion heat treatment includes combining the non-rare earth diffusion source with the magnet and then treating it at a temperature of 800-950℃ for 5-30 hours, followed by aging treatment at a temperature of 450-650℃ for 4-8 hours to obtain the finished sintered NdFeB magnet.

7. The method for pressure-assisted enhanced grain boundary diffusion in sintered NdFeB as described in claim 1, characterized in that, The preparation method of rare earth diffusion sources includes designing components of (RE1). a -(RE2) b -(M1) c -(M2) d RE1 is one of the light rare earth elements Pr / Nd, RE2 is one of the heavy rare earth elements Tb / Dy / Ho, M1 is one of the Al / Cu / Ga elements, where Cu is not greater than 10%, and M2 is one of the In / Sn / Bi elements. The weight percentages are: 0≤a≤30%, 50%≤b≤100%, 0≤c≤10%, 0≤d≤10%, and a+b+c+d=100%. The alloy is smelted, hydrogenated, and air-jet milled to obtain diffusion source powder with a particle size of 2-8μm.

8. The method for pressure-assisted enhanced grain boundary diffusion in sintered NdFeB as described in claim 1, characterized in that, The method for preparing a non-rare earth diffusion source includes designing and smelting an alloy composed of at least three elements: Mg, Al, Zn, Ga, Cu, and Ti, wherein the content of Mg and Ti is no more than 20%, and the alloy is ball-milled or air-jet milled to obtain a powder with a particle size of 2-10 μm.

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