High-coercivity sintered neodymium-iron-boron permanent magnet material and method for producing the same

Abstract

The application belongs to the technical field of permanent magnetic materials, and relates to a high-coercivity sintered neodymium-iron-boron permanent magnetic material and a preparation method thereof. The preparation method comprises the following steps: under the condition of a protective atmosphere, ReM rare earth alloy sheets and neodymium-iron-boron green compacts are placed in isolation through an isolation net; then, first diffusion treatment, second diffusion treatment and sintering treatment are sequentially performed under vacuum extraction; subsequently, the high-coercivity sintered neodymium-iron-boron permanent magnetic material is obtained after the isolation net is separated from the neodymium-iron-boron green compacts after tempering treatment. The preparation method provided by the application is simple to operate, does not need to repeatedly perform slicing after traditional sintering, and can also meet the demand of large-oriented thickness neodymium-iron-boron green compacts, effectively improves the coercivity of the neodymium-iron-boron magnet, reduces the process cost of grain boundary diffusion, and has the prospect of wide application.

Description

Technical Field

[0001] This invention belongs to the field of permanent magnet material technology, and relates to a neodymium iron boron permanent magnet material, and more particularly to a high coercivity sintered neodymium iron boron permanent magnet material and its preparation method. Background Technology

[0002] Sintered NdFeB materials, due to their high remanence (Br) and maximum energy product (BHmax), have become important fundamental functional materials, widely used in new energy vehicles, wind power generation, high-speed rail, consumer electronics, home appliances, and aerospace. With the rapid depletion of fossil fuels and the increasingly serious environmental problems they cause, green energy, especially renewable energy, has become a core global concern. This shift has significantly accelerated the development of high-tech industries such as new energy vehicles, wind power generation, and industrial permanent magnet motors, leading to a rapid increase in demand for NdFeB permanent magnet materials.

[0003] To meet the high coercivity requirements of NdFeB magnets, a grain boundary diffusion process is typically employed to allow heavy rare earth elements or alloys to penetrate along grain boundaries into the magnet's interior. This strengthens the surface region of the hard magnetic grains, significantly improving coercivity while reducing the amount of heavy rare earth elements and mitigating their adverse effects on remanence and energy product. Furthermore, the grain boundary diffusion process enables precise distribution of rare earth elements at the magnet's grain boundaries, enhancing both coercivity and thermal stability. However, as the requirements for NdFeB magnets continue to increase, higher air gap magnetic fields are needed. High-performance, thick magnets can provide greater magnetic field strength, enabling the application of strong air gap magnetic fields suitable for high-performance motors. However, due to the dense microstructure of the magnet, the diffusion driving force is insufficient, and the grain boundary diffusion depth is limited, restricting the increase in coercivity for magnets thicker than 10 mm. Existing technologies using grain boundary diffusion can only process magnets thinner than 8 mm, requiring post-sintering slicing for grain boundary diffusion and subsequent grinding, resulting in complex processes and increased costs.

[0004] Therefore, there is a need to provide a high-coercivity sintered NdFeB permanent magnet material and its preparation method to further improve coercivity, making it suitable for magnet thicknesses of 10 mm or more and simplifying the process. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a high-coercivity sintered NdFeB permanent magnet material and its preparation method. The preparation method eliminates the need for repeated traditional sintering followed by slicing and grain boundary diffusion, while meeting the requirements for thick magnets. It effectively improves the coercivity of NdFeB magnets and significantly reduces the process cost of grain boundary diffusion.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a high-coercivity sintered NdFeB permanent magnet material, the method comprising the following steps:

[0008] Under a protective atmosphere, ReM rare earth alloy sheets and NdFeB green blanks are isolated and placed through an isolation mesh; then, under vacuum conditions, a first diffusion treatment, a second diffusion treatment, and a sintering treatment are performed sequentially; after tempering, they are separated from the isolation mesh to obtain the high coercivity sintered NdFeB permanent magnet material.

[0009] The Re element in the ReM rare earth alloy sheet includes heavy rare earth elements, and the M element includes any one or a combination of at least two of Al, Zn, Ga or Cu.

[0010] The temperature of the first diffusion treatment is 750℃-850℃;

[0011] The temperature for the second diffusion treatment is 850℃-920℃;

[0012] The sintering temperature is 1020℃-1075℃.

[0013] The ReM rare earth alloy sheet of the present invention is placed on the lower side of the orientation direction of the NdFeB green blank, that is, the thickness direction of the ReM rare earth alloy sheet is parallel to the orientation direction of the NdFeB green blank.

[0014] The preparation method provided by this invention involves subjecting NdFeB green blanks and ReM rare earth alloy sheets to a first diffusion treatment, a second diffusion treatment, and a sintering treatment in a single process. This eliminates the need for traditional sintering and slicing methods for magnets, effectively opening diffusion channels at grain boundaries. This allows rare earth elements to diffuse deeper in a non-dense state and optimizes the grain boundary phase structure of the NdFeB magnet, solving the problems of insufficient diffusion depth and low coercivity in thick magnets. Furthermore, the first diffusion treatment, second diffusion treatment, and sintering process allow for deeper diffusion of rare earth elements while reducing their entry into the main phase, thus minimizing the decrease in remanence after diffusion. This optimizes the microstructure of the NdFeB magnet, effectively improving the anisotropic field of the epitaxial layer and suppressing the nucleation of antimagnetic domains, thereby enhancing the coercivity of the NdFeB permanent magnet material. The preparation method provided by this invention also significantly reduces the process cost of grain boundary diffusion while improving the coercivity of NdFeB magnets.

[0015] Preferably, the heavy rare earth element includes Tb.

[0016] Preferably, the Re element further includes light rare earth elements; the light rare earth elements include Pr.

[0017] Preferably, based on a mass percentage of 100 wt% for the ReM rare earth alloy sheet, the mass percentage of Tb is 35 wt%-85 wt%, the mass percentage of Pr is 7 wt%-20 wt%, the mass percentage of Al is 2 wt%-10 wt%, the mass percentage of Zn is 2 wt%-10 wt%, the mass percentage of Ga is 0 wt%-10 wt%, and the mass percentage of Cu is 0 wt%-15 wt%.

[0018] Preferably, based on a mass percentage of 100 wt% for the ReM rare earth alloy sheet, the mass percentage of Tb is 70 wt%-75 wt%, the mass percentage of Pr is 7 wt%-12 wt%, the mass percentage of Al is 3 wt%-7 wt%, the mass percentage of Zn is 4 wt%-8 wt%, and the mass percentage of Cu is 5 wt%-10 wt%.

[0019] Preferably, the thickness of the ReM rare earth alloy sheet is 2mm-5mm.

[0020] Preferably, the composition of the NdFeB green blank, in 100wt% by weight, is: 29.4%≤Pr+Nd≤31%, 0.9%≤B≤0.98%, Cu+Ga+Al≤0.5%, 0.1%≤Zr+Ti≤0.25%, Co≤2%, with the balance being iron.

[0021] Preferably, the neodymium iron boron green blank is prepared by a one-time molding method; the pressing magnetic field of the one-time molding is 2T-2.5T, and the pressing pressure is 22t-35t.

[0022] Preferably, the green density of the NdFeB green compact is 4.2 g / cm³. 3 -4.5g / cm 3 .

[0023] Preferably, the thickness of the NdFeB green blank in the orientation direction is 8mm-15mm, and more preferably 10mm-15mm.

[0024] Preferably, the mesh size of the isolation net is 40-80 mesh.

[0025] Preferably, the first diffusion treatment takes 2-5 hours.

[0026] Preferably, the vacuum degree of the first diffusion process is 1×10⁻⁶. -3 Pa-1×10 -2 Pa.

[0027] Preferably, the second diffusion treatment takes 4-8 hours.

[0028] Preferably, the vacuum degree of the second diffusion treatment is 1×10⁻⁶.-3 Pa-1×10 -2 Pa.

[0029] Preferably, the sintering treatment time is 3h-6h.

[0030] Preferably, the vacuum degree of the sintering process is 1×10⁻⁶. -3 Pa-1×10 -2 Pa.

[0031] Preferably, the tempering process includes a vacuum degree of 1×10⁻⁶. -3 Pa-1×10 -2 The first and second tempering processes were carried out sequentially under the condition of Pa.

[0032] Preferably, the temperature of the first tempering treatment is 860℃-910℃.

[0033] Preferably, the first tempering process takes 3-5 hours.

[0034] Preferably, the temperature of the second tempering treatment is 410℃-520℃.

[0035] Preferably, the second tempering treatment takes 3-5 hours.

[0036] In a second aspect, the present invention provides a high coercivity sintered NdFeB permanent magnet material, wherein the high coercivity sintered NdFeB permanent magnet material is prepared by the preparation method described in the first aspect.

[0037] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) The preparation method provided by the present invention involves subjecting neodymium iron boron green blanks and ReM rare earth alloy sheets to a first diffusion treatment, a second diffusion treatment, and a sintering treatment. This allows rare earth elements to diffuse deeper in a non-dense state and optimizes the grain boundary phase structure of the neodymium iron boron magnet. This solves the problems of insufficient diffusion depth and low coercivity in large-orientation-thickness neodymium iron boron green blanks. The second diffusion treatment, while allowing rare earth elements to diffuse deeper, reduces the entry of rare earth elements into the main phase, reduces the decrease in remanence after diffusion, optimizes the microstructure of the neodymium iron boron magnet, and can effectively improve the anisotropic field of the grain epitaxial layer, suppress the nucleation of antimagnetic domains, and improve the coercivity of the magnet.

[0040] (2) The preparation method provided by the present invention performs diffusion treatment and sintering treatment on the NdFeB green blank, eliminating the need for diffusion in the traditional sintered magnet slicing diffusion method, simplifying the grain boundary diffusion process, effectively improving the coercivity of NdFeB magnets while significantly reducing the process cost of grain boundary diffusion. Attached Figure Description

[0041] Figure 1 This is a schematic diagram showing the placement of the ReM rare earth alloy sheet and the neodymium iron boron green blank in this invention. Detailed Implementation

[0042] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0043] An embodiment of the present invention provides a method for preparing a high coercivity sintered NdFeB permanent magnet material, the method comprising the following steps:

[0044] Under a protective atmosphere, ReM rare earth alloy sheets and NdFeB green blanks are isolated and placed through an isolation mesh; then, under vacuum conditions, a first diffusion treatment, a second diffusion treatment, and a sintering treatment are performed sequentially; after tempering, they are separated from the isolation mesh to obtain the high coercivity sintered NdFeB permanent magnet material.

[0045] The Re element in the ReM rare earth alloy sheet includes heavy rare earth elements, and the M element includes any one or a combination of at least two of Al, Zn, Ga or Cu.

[0046] The temperature of the first diffusion treatment is 750℃-850℃;

[0047] The temperature for the second diffusion treatment is 850℃-920℃;

[0048] The sintering temperature is 1020℃-1075℃.

[0049] The ReM rare earth alloy sheet of the present invention is placed on the lower side of the orientation direction of the NdFeB green blank, that is, the thickness direction of the ReM rare earth alloy sheet is parallel to the orientation direction of the NdFeB green blank.

[0050] The preparation method provided by this invention involves subjecting NdFeB green blanks and ReM rare earth alloy sheets to a first diffusion treatment, a second diffusion treatment, and a sintering treatment in a single process. This eliminates the need for the traditional diffusion method of sintering magnet slices, effectively opening diffusion channels at grain boundaries. This allows rare earth elements to diffuse deeper in a non-dense state and optimizes the grain boundary phase structure of the NdFeB magnet, solving the problems of insufficient diffusion depth and low coercivity in thick magnets. Furthermore, the process of first diffusion treatment, second diffusion treatment, and sintering treatment allows for deeper diffusion of rare earth elements while reducing the entry of rare earth elements into the main phase, minimizing the decrease in remanence after diffusion. This optimizes the microstructure of the NdFeB magnet, effectively improving the anisotropic field of the grain epitaxial layer and suppressing the nucleation of antimagnetic domains, thereby increasing the coercivity of the NdFeB permanent magnet material. The preparation method provided by this invention can also significantly reduce the process cost of grain boundary diffusion while improving the coercivity of NdFeB magnets.

[0051] The preparation method provided by this invention, through temperature control of the first diffusion treatment, the second diffusion treatment, and the sintering treatment, enables rare earth elements to diffuse deeper while reducing the entry of rare earth elements into the main phase, reducing the crystallization of residual magnetism after diffusion, optimizing the microstructure of NdFeB magnets, effectively enhancing the anisotropic field of the grain epitaxial layer, suppressing the nucleation of antimagnetic domains, and improving the coercivity of NdFeB permanent magnet materials.

[0052] In this invention, if the temperature of the first diffusion treatment is too low, rare earth elements will not be able to enter the interior of the neodymium iron boron magnet smoothly; if the temperature of the second diffusion treatment is too high, rare earth elements will enter the main phase, and the amount of rare earth diffusion along the grain boundary will decrease, resulting in a decrease in magnetic properties.

[0053] Therefore, the temperature of the first diffusion treatment is 750℃-850℃, for example, it can be 750℃, 780℃, 800℃, 820℃, 840℃ or 850℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0054] The temperature of the second diffusion treatment is 850℃-920℃, for example, it can be 850℃, 860℃, 880℃, 900℃ or 920℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0055] The sintering temperature is 1020℃-1075℃, for example, it can be 1020℃, 1040℃, 1050℃, 1060℃ or 1075℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0056] In some embodiments, the isolation mesh includes any one of molybdenum mesh, nickel-chromium alloy mesh, or 310s stainless steel mesh.

[0057] In some embodiments, the isolation is performed in a sintering tank.

[0058] In some embodiments, the heavy rare earth element includes Tb.

[0059] In some embodiments, the Re element further includes light rare earth elements; the light rare earth elements include Pr.

[0060] In some embodiments, based on a mass percentage of 100 wt% for the ReM rare earth alloy sheet, the mass percentage of Tb is 35 wt%-85 wt%, the mass percentage of Pr is 7 wt%-20 wt%, the mass percentage of Al is 2 wt%-10 wt%, the mass percentage of Zn is 2 wt%-10 wt%, the mass percentage of Ga is 0 wt%-10 wt%, and the mass percentage of Cu is 0 wt%-15 wt%.

[0061] In some embodiments, based on a mass percentage of 100 wt% for the ReM rare earth alloy sheet, the mass percentage of Tb is 70 wt%-75 wt%, for example, 70 wt%, 71 wt%, 72 wt%, 73 wt%, 74 wt%, or 75 wt%; the mass percentage of Pr is 7 wt%-12 wt%, for example, 7 wt%, 8 wt%, 10 wt%, 11 wt%, or 12 wt%; the mass percentage of Al is 3 wt%-7 wt%, for example, 3 wt%, 4 wt%, 5 wt%, 6 wt%, or 7 wt%; the mass percentage of Zn is 4 wt%-8 wt%, for example, 4 wt%, 5 wt%, 6 wt%, 7 wt%, or 8 wt%; and the mass percentage of Cu is 5 wt%-10 wt%, for example, 5 wt%, 6 wt%, 8 wt%, 9 wt%, or 10 wt%.

[0062] In some embodiments, the thickness of the ReM rare earth alloy sheet is 2mm-5mm, for example, it can be 2mm, 3mm, 4mm or 5mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0063] Optionally, the ReM rare earth alloy sheet is first prepared by induction melting and then sliced.

[0064] In some embodiments, the composition of the NdFeB green blank, based on a mass percentage of 100wt%, is: 29.4%≤Pr+Nd≤31%, 0.9%≤B≤0.98%, Cu+Ga+Al≤0.5%, 0.1%≤Zr+Ti≤0.25%, Co≤2%, with the balance being iron.

[0065] In this invention, if the green density of the NdFeB green blank is too low, it will cause the NdFeB green blank to crack during sintering and the magnet will not be densely sintered; if the green density of the NdFeB green blank is too high, it will damage the orientation of the magnet and cause a decrease in remanence.

[0066] Optionally, the NdFeB green billet is prepared using conventional methods in the art, such as rapid solidification casting, hydrogen crushing, air jet milling, and one-time forming. This invention does not specify particular parameter selection, as long as the green density of the NdFeB green billet is 4.2 g / cm³. 3 -4.5g / cm 3 That's all.

[0067] For example, the pressing magnetic field of the one-time molding is 2T-2.5T, such as 2, 2.1, 2.2, 2.4 or 2.5; the pressing pressure of the one-time molding is 22t-35t, such as 22t, 25t, 28t, 30t, 32t or 35t.

[0068] In some embodiments, the green density of the NdFeB green compact is 4.2 g / cm³. 3 -4.5g / cm 3 For example, it could be 4.2 g / cm³ 3 4.3g / cm 3 4.4 g / cm 3 Or 4.5g / cm 3 However, this does not limit the listed values; any other unlisted values ​​within the range are also applicable.

[0069] In some embodiments, the thickness of the NdFeB green blank in the orientation direction is 8mm-15mm, for example, it can be 8mm, 10mm, 12mm, 14mm or 15mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 10mm-15mm.

[0070] In some embodiments, the mesh size of the isolation mesh is 40-80 mesh, for example, it can be 40 mesh, 50 mesh, 60 mesh, 70 mesh or 80 mesh, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0071] In some embodiments, the first diffusion treatment time is 2h-5h, for example, it can be 2h, 3h, 4h or 5h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0072] In some embodiments, the vacuum degree of the first diffusion process is 1×10⁻⁶. -3 Pa-1×10 -2 Pa, for example, could be 1×10 -3Pa, 3×10 -3 Pa, 5×10 -3 Pa, 6×10 -3 Pa, 8×10 -3 Pa or 1×10 -2 Pa, but not limited to the listed values, applies to all other unlisted values ​​within the range.

[0073] In some embodiments, the second diffusion treatment time is 4h-8h, for example, it can be 4h, 5h, 6h, 7h or 8h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0074] In some embodiments, the vacuum degree of the second diffusion process is 1×10⁻⁶. -3 Pa-1×10 -2 Pa, for example, could be 1×10 -3 Pa, 3×10 -3 Pa, 5×10 -3 Pa, 6×10 -3 Pa, 8×10 -3 Pa or 1×10 -2 Pa, but not limited to the listed values, applies to all other unlisted values ​​within the range.

[0075] In some embodiments, the sintering time is 3h-6h, for example, it can be 3h, 4h, 5h or 6h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0076] In some embodiments, the vacuum degree of the sintering process is 1×10⁻⁶. -3 Pa-1×10 -2 Pa, for example, could be 1×10 -3 Pa, 3×10 -3 Pa, 5×10 -3 Pa, 6×10 -3 Pa, 8×10 -3 Pa or 1×10 -2 Pa, but not limited to the listed values, applies to all other unlisted values ​​within the range.

[0077] In some embodiments, the tempering process includes a vacuum degree of 1×10⁻⁶. -3 Pa-1×10 -2 The first and second tempering processes were carried out sequentially under the condition of Pa.

[0078] In some embodiments, the temperature of the first tempering treatment is 860°C-910°C, for example, it can be 860°C, 870°C, 880°C, 890°C, 900°C or 910°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0079] In some embodiments, the first tempering process takes 3-5 hours, for example, 3 hours, 3.5 hours, 4 hours, 4.5 hours or 5 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0080] In some embodiments, the temperature of the second tempering treatment is 410°C-520°C, for example, it can be 410°C, 430°C, 450°C, 480°C, 500°C or 520°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0081] In some embodiments, the second tempering process takes 3-5 hours, for example, 3 hours, 3.5 hours, 4 hours, 4.5 hours or 5 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0082] One embodiment of the present invention provides a high coercivity sintered NdFeB permanent magnet material, which is prepared by the preparation method described in any embodiment.

[0083] Example 1

[0084] This embodiment provides a method for preparing a high coercivity sintered NdFeB permanent magnet material, the method comprising the following steps:

[0085] Under an argon atmosphere, a 3mm thick ReM rare earth alloy and a green billet with a density of 4.3g / cm³ were used. 3 A NdFeB green blank with a thickness of 11 mm along the orientation direction is placed in a sintering glass jar, and the ReM rare earth alloy sheet and the NdFeB green blank are separated by a 40-mesh molybdenum mesh and placed in the sintering glass jar (see [link]). Figure 1 Then, the first diffusion treatment, the second diffusion treatment, and the sintering treatment are performed sequentially. After tempering, the material is separated from the molybdenum mesh to obtain the high coercivity sintered NdFeB permanent magnet material.

[0086] The ReM rare earth alloy sheet, by mass percentage (100wt%), contains 75wt% Tb, 7wt% Pr, 5wt% Al, 5wt% Zn, and 8wt% Cu.

[0087] The NdFeB green blank is composed of 22.88% Nd, 7.63% Pr, 0.94% B, 0.15% Cu, 0.15% Ga, 0.2% Al, 0.15% Ti, and 0.5% Co, with the balance being iron, based on a 100wt% mass percentage. It is prepared using a one-step molding method, with a pressing magnetic field of 2.3T and a pressing pressure of 26t.

[0088] The first diffusion treatment was performed at a temperature of 760°C for 3 hours with a vacuum degree of 6 × 10⁻⁶. -3 Pa;

[0089] The second diffusion treatment was performed at a temperature of 900°C for 7 hours with a vacuum degree of 4 × 10⁻⁶. -3 Pa;

[0090] The sintering process was carried out at a temperature of 1070℃ for 4 hours and under a vacuum of 6×10⁻⁶. -3 Pa;

[0091] The tempering process includes a vacuum degree of 6×10⁻⁶. -3 The first tempering treatment and the second tempering treatment were carried out sequentially under the condition of Pa. The temperature of the first tempering treatment was 900℃ and the time was 3h. The temperature of the second tempering treatment was 510℃ and the time was 3.5h.

[0092] Example 2

[0093] This embodiment provides a method for preparing a high coercivity sintered NdFeB permanent magnet material, the method comprising the following steps:

[0094] Under an argon atmosphere, a 2mm thick ReM rare earth alloy and a green billet with a density of 4.2 g / cm³ were prepared. 3 A 10mm thick NdFeB green blank in the orientation direction is placed in a sintering glass jar, and the ReM rare earth alloy sheet and the NdFeB green blank are separated by a 40-mesh molybdenum mesh and placed in the sintering glass jar (see [link]). Figure 1 Then, the first diffusion treatment, the second diffusion treatment, and the sintering treatment are performed sequentially. After tempering, the material is separated from the molybdenum mesh to obtain the high coercivity sintered NdFeB permanent magnet material.

[0095] The ReM rare earth alloy sheet, by mass percentage (100wt%), contains 70wt% Tb, 12wt% Pr, 3wt% Al, 5wt% Zn, and 10wt% Cu.

[0096] The NdFeB green blank is composed of 22.88% Nd, 7.63% Pr, 0.94% B, 0.15% Cu, 0.15% Ga, 0.2% Al, 0.15% Ti, and 0.5% Co, with the balance being iron, based on a mass percentage of 100 wt%. It is prepared by a one-time molding method, with a pressing magnetic field of 2.3 T and a pressing pressure of 26 t.

[0097] The first diffusion treatment was performed at a temperature of 750°C for 2 hours with a vacuum degree of 1×10⁻⁶. -3 Pa;

[0098] The second diffusion treatment was performed at a temperature of 850°C for 4 hours with a vacuum degree of 1×10⁻⁶. -3 Pa;

[0099] The sintering process was carried out at a temperature of 1020℃ for 3 hours with a vacuum degree of 1×10⁻⁶. -3 Pa;

[0100] The tempering process includes a vacuum degree of 1×10⁻⁶. -3 The first tempering treatment and the second tempering treatment were carried out sequentially under the condition of Pa. The temperature of the first tempering treatment was 860℃ and the time was 3h. The temperature of the second tempering treatment was 410℃ and the time was 3h.

[0101] Example 3

[0102] This embodiment provides a method for preparing a high coercivity sintered NdFeB permanent magnet material, the method comprising the following steps:

[0103] Under an argon atmosphere, a 5mm thick ReM rare earth alloy and a green billet with a density of 4.5g / cm³ were used. 3 A 15mm thick NdFeB green blank, oriented in the same direction, is placed in a sintering glass jar, with the ReM rare earth alloy sheet and the NdFeB green blank separated by an 80-mesh molybdenum mesh (see [reference]). Figure 1 Then, the first diffusion treatment, the second diffusion treatment, and the sintering treatment are performed sequentially. After tempering, the material is separated from the molybdenum mesh to obtain the high coercivity sintered NdFeB permanent magnet material.

[0104] The ReM rare earth alloy sheet, based on a mass percentage of 100wt%, contains 72wt% Tb, 10wt% Pr, 3wt% Al, 6wt% Zn, and 9wt% Cu.

[0105] The NdFeB green blank is composed of 22.88% Nd, 7.63% Pr, 0.94% B, 0.15% Cu, 0.15% Ga, 0.2% Al, 0.15% Ti, and 0.5% Co, with the balance being iron, based on a mass percentage of 100 wt%. It is prepared by a one-time molding method, with a pressing magnetic field of 2.3 T and a pressing pressure of 26 t.

[0106] The first diffusion treatment was performed at a temperature of 850°C for 5 hours with a vacuum degree of 1×10⁻⁶. -2 Pa;

[0107] The second diffusion treatment was performed at a temperature of 920°C for 8 hours with a vacuum degree of 1×10⁻⁶. -2 Pa;

[0108] The sintering process was carried out at a temperature of 1075°C for 6 hours with a vacuum degree of 1×10⁻⁶. -2 Pa;

[0109] The tempering process includes a vacuum degree of 1×10⁻⁶. -2 The first tempering treatment and the second tempering treatment were carried out sequentially under the condition of Pa. The temperature of the first tempering treatment was 910℃ and the time was 5h. The temperature of the second tempering treatment was 520℃ and the time was 5h.

[0110] Example 4

[0111] This embodiment provides a method for preparing a high coercivity sintered NdFeB permanent magnet material. Except for replacing 7wt% Pr with Tb in the ReM rare earth alloy sheet composition, the rest is the same as in Example 1.

[0112] Example 5

[0113] This embodiment provides a method for preparing a high coercivity sintered NdFeB permanent magnet material. Except for replacing 5 wt% Zn with Tb in the ReM rare earth alloy sheet composition, the rest is the same as in Example 1.

[0114] Example 6

[0115] This embodiment provides a method for preparing high coercivity sintered NdFeB permanent magnet materials, except that the green density of the NdFeB green blank is 4 g / cm³ by changing the pressing size of the one-time molding. 3 Except for the above, everything else is the same as in Example 1.

[0116] Example 7

[0117] This embodiment provides a method for preparing high coercivity sintered NdFeB permanent magnet materials, except that the green density of the NdFeB green blank is 4.8 g / cm³ by changing the pressing size of the one-time molding process. 3Except for the above, everything else is the same as in Example 1.

[0118] Example 8

[0119] This embodiment provides a method for preparing a high coercivity sintered NdFeB permanent magnet material, the method comprising the following steps:

[0120] Under an argon atmosphere, a 3mm thick ReM rare earth alloy and a green billet with a density of 4.3g / cm³ were used. 3 A NdFeB green blank with a thickness of 11 mm along the orientation direction is placed in a sintering glass jar, and the ReM rare earth alloy sheet and the NdFeB green blank are separated by a 40-mesh molybdenum mesh and placed in the sintering glass jar (see [link]). Figure 1 Then, the first diffusion treatment, the second diffusion treatment, and the sintering treatment are performed sequentially, followed by tempering treatment to obtain the high coercivity sintered NdFeB permanent magnet material.

[0121] The ReM rare earth alloy sheet, by mass percentage (100wt%), contains 75wt% Tb, 7wt% Pr, 5wt% Al, 5wt% Zn, and 8wt% Cu.

[0122] The NdFeB green blank is composed of 22.88% Nd, 7.63% Pr, 0.94% B, 0.15% Cu, 0.15% Ga, 0.2% Al, 0.15% Ti, and 0.5% Co, with the balance being iron, based on a 100wt% mass percentage. It is prepared using a one-step molding method, with a pressing magnetic field of 2.3T and a pressing pressure of 26t.

[0123] The first diffusion treatment was performed at a temperature of 760°C for 3 hours with a vacuum degree of 6 × 10⁻⁶. -3 Pa;

[0124] The second diffusion treatment was performed at a temperature of 900°C for 7 hours with a vacuum degree of 4 × 10⁻⁶. -3 Pa;

[0125] The sintering process was carried out at a temperature of 1070℃ for 4 hours and under a vacuum of 6×10⁻⁶. -3 Pa;

[0126] The tempering process includes a vacuum degree of 6×10⁻⁶. -3 The first tempering treatment was carried out under the condition of Pa, with a temperature of 900℃ and a time of 3h.

[0127] Comparative Example 1

[0128] This comparative example provides a method for preparing sintered NdFeB permanent magnet materials, which is the same as in Example 1 except that the temperature of the first diffusion treatment is 720°C.

[0129] Comparative Example 2

[0130] This comparative example provides a method for preparing sintered NdFeB permanent magnet materials, which is the same as in Example 1 except that the temperature of the second diffusion treatment is 950°C.

[0131] Comparative Example 3

[0132] This comparative example provides a method for preparing sintered NdFeB permanent magnet materials, the method comprising the following steps:

[0133] Under an argon atmosphere, a 3mm thick ReM rare earth alloy and a green billet with a density of 4.3g / cm³ were used. 3 A NdFeB green blank with a thickness of 11 mm along the orientation direction is placed in a sintering glass jar, and the ReM rare earth alloy sheet and the NdFeB green blank are separated by a 40-mesh molybdenum mesh and placed in the sintering glass jar (see [link]). Figure 1 Then, the second diffusion treatment and sintering treatment are performed sequentially. After tempering, the material is separated from the molybdenum mesh to obtain the sintered NdFeB permanent magnet material.

[0134] The ReM rare earth alloy sheet, by mass percentage (100wt%), contains 75wt% Tb, 7wt% Pr, 5wt% Al, 5wt% Zn, and 8wt% Cu.

[0135] The NdFeB green blank is composed of 22.88% Nd, 7.63% Pr, 0.94% B, 0.15% Cu, 0.15% Ga, 0.2% Al, 0.15% Ti, and 0.5% Co, with the balance being iron, based on a 100wt% mass percentage. It is prepared using a one-step molding method, with a pressing magnetic field of 2.3T and a pressing pressure of 26t.

[0136] The second diffusion treatment was performed at a temperature of 900°C for 7 hours with a vacuum degree of 4 × 10⁻⁶. -3 Pa;

[0137] The sintering process was carried out at a temperature of 1070℃ for 4 hours and under a vacuum of 6×10⁻⁶. -3 Pa;

[0138] The tempering process includes a vacuum degree of 6×10⁻⁶. -3The first tempering treatment and the second tempering treatment were carried out sequentially under the condition of Pa. The temperature of the first tempering treatment was 900℃ and the time was 3h. The temperature of the second tempering treatment was 510℃ and the time was 3.5h.

[0139] Comparative Example 4

[0140] This comparative example provides a method for preparing sintered NdFeB permanent magnet materials, the method comprising the following steps:

[0141] Under an argon atmosphere, a 3mm thick ReM rare earth alloy and a green billet with a density of 4.3g / cm³ were used. 3 A NdFeB green blank with a thickness of 11 mm along the orientation direction is placed in a sintering glass jar, and the ReM rare earth alloy sheet and the NdFeB green blank are separated by a 40-mesh molybdenum mesh and placed in the sintering glass jar (see [link]). Figure 1 Then, the first diffusion treatment and sintering treatment are performed sequentially, followed by tempering treatment and separation from the molybdenum mesh to obtain the sintered NdFeB permanent magnet material.

[0142] The ReM rare earth alloy sheet, by mass percentage (100wt%), contains 75wt% Tb, 7wt% Pr, 5wt% Al, 5wt% Zn, and 8wt% Cu.

[0143] The NdFeB green blank is composed of 22.88% Nd, 7.63% Pr, 0.94% B, 0.15% Cu, 0.15% Ga, 0.2% Al, 0.15% Ti, and 0.5% Co, with the balance being iron, based on a 100wt% mass percentage. It is prepared using a one-step molding method, with a pressing magnetic field of 2.3T and a pressing pressure of 26t.

[0144] The first diffusion treatment was performed at a temperature of 760°C for 3 hours with a vacuum degree of 6 × 10⁻⁶. -3 Pa;

[0145] The sintering process was carried out at a temperature of 1070℃ for 4 hours and under a vacuum of 6×10⁻⁶. -3 Pa;

[0146] The tempering process includes a vacuum degree of 6×10⁻⁶. -3 The first tempering treatment and the second tempering treatment were carried out sequentially under the condition of Pa. The temperature of the first tempering treatment was 900℃ and the time was 3h. The temperature of the second tempering treatment was 510℃ and the time was 3.5h.

[0147] Performance Characterization

[0148] The coercivity and remanence of the permanent magnet materials obtained in the above embodiments and comparative examples were tested using a NIM-62000 hysteresis loop analyzer according to GB / T 3217-2013 "Magnetic Test Methods for Permanent Magnet (Hard Magnetic) Materials". The results are shown in Table 1. The original magnets were the final products prepared using only neodymium iron boron green blanks according to the method of Example 1 without using ReM rare earth alloys.

[0149] Table 1

[0150]

[0151]

[0152] As shown in Table 1, the permanent magnet material obtained by the preparation method provided by the present invention has a coercivity of more than 23.45 kOe and a remanence of more than 13.97 kGs, thus obtaining the high coercivity sintered NdFeB permanent magnet material of the present invention.

[0153] A comparison of Example 4 and Example 1 shows that when the ReM alloy sheet does not contain Pr, the remanence decreases from 14.05 kGs to 14.02 kGs, and the coercivity decreases significantly, directly from 24.01 kOe to 23.01 kOe. This indicates that the synergistic use of heavy rare earth dopant Tb and light rare earth dopant Pr can improve the coercivity of NdFeB permanent magnet materials.

[0154] A comparison of Example 5 and Example 1 shows that when the ReM alloy sheet does not contain Zn, the remanence decreases from 14.05 kGs to 13.95 kGs, and the coercivity decreases significantly, dropping directly from 24.01 kOe to 22.95 kOe. This indicates that the addition of Zn is essential to obtain high coercivity sintered NdFeB permanent magnet materials.

[0155] A comparison of Example 6 and Example 1 shows that when the green density of the NdFeB green blank is low, it will cause the green blank to crack during sintering, resulting in non-dense sintering. Therefore, the remanence is 12.98 kGs and the coercivity is 22.03 kOe.

[0156] A comparison of Example 7 and Example 1 shows that when the green density of the NdFeB green blank is high, it will cause the magnet orientation to be disrupted, resulting in a decrease in remanence. Therefore, the remanence is 13.52 kGs and the coercivity is 23.04 kOe.

[0157] A comparison of Example 8 and Example 1 shows that when only the first tempering treatment is performed, the remanence and coercivity decrease slightly, but the remanence can still reach 14.04 kGs and the coercivity can reach 21.95 kOe.

[0158] As can be seen from the comparison between Comparative Example 1 and Example 1, when the temperature of the first diffusion treatment is too low, the heavy rare earth elements cannot smoothly enter the magnet to form a uniform core-shell structure, and the coercivity is only 22.89 kOe.

[0159] As can be seen from the comparison between Comparative Example 2 and Example 1, when the temperature of the second diffusion treatment is too high, heavy rare earth elements will enter the main phase, the amount of heavy rare earth diffusion along the grain boundary will decrease, resulting in a significant decrease in magnetic properties, with remanence of only 13.75 kGs and coercivity of only 23.02 kOe.

[0160] As can be seen from the comparison between Comparative Example 3 and Example 1, the coercivity is only 22.75 kOe when the first diffusion treatment is not performed.

[0161] As can be seen from the comparison between Comparative Example 4 and Example 1, the coercivity is only 18.92 kOe when the second diffusion treatment is not performed.

[0162] In summary, the preparation method provided by this invention involves subjecting NdFeB green blanks and ReM rare earth alloy sheets to a first diffusion treatment, a second diffusion treatment, and a sintering treatment. This allows for deeper diffusion of rare earth elements in a non-dense state, solving the problem of insufficient diffusion depth in NdFeB green blanks with large orientation thicknesses. The second diffusion treatment, while deepening the diffusion of rare earth elements, reduces the entry of rare earth elements into the main phase, minimizes the reduction in remanence after diffusion, optimizes the microstructure of the NdFeB magnet, effectively improves the anisotropic field of the grain epitaxial layer, suppresses the nucleation of antimagnetizing domains, and enhances the coercivity of the magnet. The preparation method provided by this invention, by performing diffusion and sintering treatments on the NdFeB green blanks, eliminates the need for traditional sintered magnet slicing diffusion methods, simplifying the grain boundary diffusion process. This significantly reduces the process cost of grain boundary diffusion while effectively improving the coercivity of NdFeB magnets.

[0163] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method of producing a high-coercivity sintered neodymium-iron-boron permanent magnet material, characterized in that, The preparation method comprises the following steps: The ReM rare earth alloy sheet and the neodymium-iron-boron green body are placed apart by a separation net under a protective atmosphere; then first diffusion treatment, second diffusion treatment and sintering treatment are sequentially performed under vacuum; then the separation net is separated after tempering treatment, and the high-coercivity sintered neodymium-iron-boron permanent magnet material is obtained; The Re element in the ReM rare earth alloy sheet comprises heavy rare earth elements, and the M element comprises any one or a combination of at least two of Al, Zn, Ga or Cu; The temperature of the first diffusion treatment is 750-850 DEG C; The temperature of the second diffusion treatment is 850-920 DEG C; The temperature of the sintering treatment is 1020-1075 DEG C; The heavy rare earth elements comprise Tb; The Re element further comprises light rare earth elements; the light rare earth elements comprise Pr; In terms of 100wt% of the mass percentage of the ReM rare earth alloy sheet, the mass percentage of Tb is 35wt%-85wt%, the mass percentage of Pr is 7wt%-20wt%, the mass percentage of Al is 2wt%-10wt%, the mass percentage of Zn is 2wt%-10wt%, the mass percentage of Ga is 0wt%-10wt%, and the mass percentage of Cu is 0wt%-15wt%; The green density of the neodymium-iron-boron green compact is 4.2 g / cm3-4.5 g / cm3 3 .

2. The production method according to claim 1, characterized by, In terms of 100wt% of the mass percentage of the ReM rare earth alloy sheet, the mass percentage of Tb is 70wt%-75wt%, the mass percentage of Pr is 7wt%-12wt%, the mass percentage of Al is 3wt%-7wt%, the mass percentage of Zn is 4wt%-8wt%, and the mass percentage of Cu is 5wt%-10wt%.

3. The preparation method according to claim 1, characterized in that, The thickness of the ReM rare earth alloy sheet is 2-5 mm.

4. The preparation method according to claim 1, characterized in that, The composition of the neodymium-iron-boron green body is 29.4%≤Pr+Nd≤31%, 0.9%≤B≤0.98%, Cu+Ga+Al≤0.5%, 0.1%≤Zr+Ti≤0.25%, Co≤2% in terms of 100wt% of the mass percentage.

5. The preparation method according to claim 1, characterized in that, The neodymium-iron-boron green body is prepared by a one-step forming method; the pressing magnetic field of the one-step forming is 2-2.5 T, and the pressing pressure is 22-35 t.

6. The method of claim 1, wherein, The thickness of the orientation direction of the neodymium-iron-boron green body is 8-15 mm.

7. The production method according to claim 6, characterized by, The thickness of the orientation direction of the neodymium-iron-boron green body is 10-15 mm.

8. The method of claim 1, wherein, The pore size of the separation net is 40-80 mesh.

9. The method of claim 1, wherein, The time of the first diffusion treatment is 2-5 h.

10. The method of claim 1, wherein, The vacuum degree of the first diffusion treatment is 1 x 10 -3 Pa - 1 x 10 -2 Pa.

11. The method of claim 1, wherein, The time of the second diffusion treatment is 4-8 h.

12. The method of claim 1, wherein, The vacuum degree of the second diffusion treatment is 1 x 10 -3 Pa - 1 x 10 -2 Pa.

13. The method of claim 1, wherein, The time of the sintering treatment is 3-6 h.

14. The method of claim 1, wherein, The vacuum degree of the sintering treatment is 1 x 10 -3 Pa - 1 x 10 -2 Pa.

15. The method of claim 1, wherein, The tempering treatment includes first and second tempering treatments successively performed under a vacuum of 1 x 10 -3 Pa-1 x 10 -2 Pa.

16. The method of claim 15, wherein, The temperature of the first tempering treatment is 860-910 DEG C.

17. The preparation method according to claim 15, characterized in that, The time of the first tempering treatment is 3-5 h.

18. The method of claim 15, wherein, The temperature of the second tempering treatment is 410-520 DEG C.

19. The method of claim 15, wherein, The time of the second tempering treatment is 3-5 h.

20. A high-coercivity sintered neodymium-iron-boron permanent magnetic material, characterized in that The high-coercivity sintered neodymium-iron-boron permanent magnet material is prepared by the preparation method in any one of claims 1-19.

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