Method for preparing magnet by recovering grain boundary diffusion magnetic sheets and magnet

Abstract

The invention belongs to the technical field of neodymium iron boron heavy rare earth decrement utilization, and particularly discloses a method for preparing a magnet by recycling grain boundary diffusion magnetic sheets and the magnet. The method comprises the following steps: sequentially carrying out demagnetization treatment, surface treatment and crushing treatment on a recovered grain boundary diffusion magnetic sheet to obtain core-shell structure neodymium iron boron powder; the core-shell structure powder serves as grain boundary powder to be added to be mixed with neodymium iron boron raw material powder, compression molding is conducted, and a neodymium iron boron blank is obtained; performing sintering treatment and tempering treatment on the neodymium-iron-boron green body in sequence to obtain a magnet; the neodymium iron boron raw material powder does not comprise heavy rare earth elements. According to the method, the recovered grain boundary diffusion magnetic sheet is used as grain boundary powder to be added into the magnet sintering process, and coercive force improvement under extreme utilization of heavy rare earth is achieved. The core-shell structure powder serves as an additive in the sintering process, and heavy rare earth elements are distributed to form a more uniform core-shell structure. Compared with an existing grain boundary diffusion process, the effect of improving the coercive force of the large magnet is particularly remarkable.

Description

Technical Field

[0001] The present invention relates to the field of reduced utilization of neodymium iron boron heavy rare earth, and in particular to a method for preparing a magnet by recycling grain boundary diffusion magnetic sheets and the magnet. Background Art

[0002] As a core foundational material for high-tech industries, the technological development of rare earth permanent magnets directly determines the growth of strategic industries such as new energy and electronic information. These materials, with their superior magnetic properties, offer unique advantages in improving energy conversion efficiency and precisely controlling signal transmission, playing an irreplaceable and crucial role in driving technological innovation and industrial upgrading in modern industry. The rapid development of emerging industries worldwide has created a significant supply gap for rare earth resources, leading to an increasingly pronounced imbalance between supply and demand.

[0003] CN109935462A discloses a method for preparing a grain boundary diffused heavy rare earth NdFeB magnet and the NdFeB magnet. In the preparation method, NdFeB powder is pressed into a NdFeB rough billet, which is then immersed in a heavy rare earth source melt. The heavy rare earth source melt is actively immersed in the NdFeB rough billet, so that solid solution and penetration occur between the heavy rare earth source melt and the NdFeB rough billet, filling gaps and defects in the NdFeB rough billet. At the same time, the heavy rare earth elements diffuse at the grain boundaries in the NdFeB rough billet, improving the grain boundary diffusion efficiency of the heavy rare earth elements. This makes it feasible to enhance the coercive force of thicker NdFeB magnets using the grain boundary diffusion heavy rare earth element process. A NdFeB magnet with a thickness greater than 5 mm and a coercive force enhancement effect greater than that of the existing grain boundary diffusion heavy rare earth element process is obtained.

[0004] CN119040821A discloses a method for improving the grain boundary diffusion efficiency of NdFeB magnets based on vapor deposition. From the perspective of improving the density of the diffusion source, a high-density plasma film-forming environment is constructed by adopting an ionized physical vapor deposition technology based on bipolar high-power pulsed magnetron sputtering technology and an ion source. The energy and flux of the film-forming ions are regulated by positive pulse parameters to improve the controllability and preparation efficiency of the high-density heavy rare earth grain boundary diffusion source.

[0005] CN110890210A discloses a method for improving the coercive force of an arc-shaped NdFeB magnet, comprising mixing heavy rare earth powder with an organic binder and an organic solvent to form a heavy rare earth slurry, applying a layer of the heavy rare earth slurry to a flexible film by screen printing and curing to form a heavy rare earth coating, then transferring the heavy rare earth coating to the surface of the arc-shaped magnet to be diffused and applying pressure to ensure that the heavy rare earth coating and the surface to be diffused are closely adhered, and then subjecting the arc-shaped NdFeB magnet with the heavy rare earth coating to a high-temperature diffusion aging treatment to improve the coercive force of the NdFeB magnet. This method can form a uniform and controllable heavy rare earth coating on the surface of the arc-shaped NdFeB magnet to ensure uniform diffusion of the magnet's arc-shaped surface, and greatly improves the utilization rate of the heavy rare earth material through screen printing and transfer coating.

[0006] Traditional methods increase coercivity by adding heavy rare earth elements, but excessive addition reduces remanence and magnetic energy product, and is costly. While grain boundary diffusion can improve performance locally, it still suffers from low diffusion source utilization, surface heavy rare earth enrichment, and complex processes. Physical vapor deposition (PVD) and screen printing processes can improve diffusion efficiency, but they are expensive and prone to introducing impurities.

[0007] Therefore, it is of great significance to provide a method for preparing bulk magnets with low rare earth content and high coercivity. Summary of the Invention

[0008] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for preparing magnets by recycling grain boundary diffusion magnetic sheets and a magnet. In order to solve the problems of low utilization rate of heavy rare earths, insufficient diffusion depth and significant residual magnetic loss in the traditional grain boundary diffusion process, the present invention performs a series of treatments on the recycled grain boundary diffusion magnetic sheets, and uses the obtained core-shell structured NdFeB powder as grain boundary powder to add to the sintered magnet process to achieve an increase in coercive force under the extreme application of heavy rare earths. The method provided by the present invention has the advantages of simple process, green environmental protection, and saving rare earth resources. It not only realizes the recycling of rare earth elements in the recycled grain boundary diffusion magnetic sheets, but also solves the problems of low utilization rate of heavy rare earths, insufficient diffusion depth and significant residual magnetic loss in the traditional grain boundary diffusion process.

[0009] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a method for recovering grain boundary diffusion magnetic sheets to prepare magnets, the method comprising:

[0011] The recovered grain boundary diffusion magnetic sheets are sequentially subjected to demagnetization treatment, surface treatment and crushing treatment to obtain core-shell structured NdFeB powder; the core-shell structured NdFeB powder is used as grain boundary powder and mixed with NdFeB raw material powder, and the mixture is pressed into shape to obtain a NdFeB blank; the NdFeB blank is sequentially subjected to sintering treatment and tempering treatment to obtain a magnet; the material of the NdFeB raw material powder does not include heavy rare earth elements.

[0012] The present invention performs a series of treatments, including demagnetization, surface treatment, and crushing, on recycled grain boundary diffusion magnetic sheets. The obtained core-shell structured NdFeB powder is then added to the sintering magnet process as grain boundary powder without the need for additional heavy rare earth elements, such as gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and yttrium. This allows for the preparation of bulk magnets with low rare earth content and high coercivity, achieving an increase in coercivity under the ultimate application of heavy rare earth elements. The NdFeB powder with a core-shell structure of uneven thickness obtained from recycled grain boundary diffusion magnetic sheets is used as an additive during the sintering process, and the heavy rare earth elements are distributed to form a more uniform core-shell structure. Compared to existing grain boundary diffusion processes, this method significantly improves the coercivity of bulk magnets, not only achieving the recycling of rare earth elements in recycled grain boundary diffusion magnetic sheets, but also solving the problems of low heavy rare earth utilization, insufficient diffusion depth, and significant residual magnetic loss in traditional grain boundary diffusion processes.

[0013] Preferably, the thickness of the recycled grain boundary diffusion magnetic sheet is less than 5 mm.

[0014] Preferably, the average particle size of the core-shell structured NdFeB powder is 3 μm to 5 μm.

[0015] Preferably, the average particle size of the NdFeB raw material powder is 2 μm to 5 μm.

[0016] Preferably, the mass of the core-shell structure NdFeB powder accounts for 5wt% to 50wt% of the total mass of the core-shell structure NdFeB powder and the NdFeB raw material powder, and preferably 10wt% to 25wt%.

[0017] Preferably, the method for preparing the NdFeB raw material powder comprises: configuring alloy powder according to a stoichiometric ratio, smelting, and crushing to obtain the NdFeB raw material powder.

[0018] Preferably, the smelting method includes using a vacuum melting and rapid solidification furnace for smelting.

[0019] Preferably, the crushing method includes sequentially performing hydrogen crushing and air flow milling.

[0020] Preferably, the components of the NdFeB raw material powder include NdFeB alloy containing RE, Fe, B and M elements, RE contains one or more of Nd, Pr, La, Ce, and M contains one or more of Co, Ca, Cu, Al, Zr, Ti, wherein the mass fraction of RE is 30% to 36%, the mass fraction of Fe is less than or equal to 68%, the mass fraction of B is less than or equal to 1%, and the mass fraction of M is less than or equal to 2%.

[0021] Preferably, the press-forming method includes sequentially performing orientation pressing and cold isostatic pressing.

[0022] Preferably, the vacuum degree of the sintering and tempering treatment is 1×10 -3 Below Pa.

[0023] Preferably, the sintering temperature is 1000° C. to 1100° C., and the sintering holding time is 3 h to 6 h.

[0024] Preferably, the tempering treatment includes a first tempering, a second tempering and a third tempering performed in sequence.

[0025] Preferably, the temperature of the first tempering is 820° C. to 920° C., and the time is 3 h to 5 h.

[0026] Preferably, the second tempering temperature is 620° C. to 720° C., and the time is 3 h to 5 h.

[0027] Preferably, the third tempering temperature is 400° C. to 520° C., and the time is 3 h to 5 h.

[0028] Preferably, the demagnetization treatment includes vacuum thermal demagnetization treatment.

[0029] Preferably, the surface treatment method includes any one of etching, mechanical grinding, high-temperature burning, sand blasting, shot blasting or pickling, or a combination of at least two of them.

[0030] Preferably, the crushing method comprises sequentially performing coarse crushing, hydrogen crushing and air flow milling on the surface-treated recycled grain boundary diffusion magnetic sheets.

[0031] Preferably, the coarse crushing is carried out under an inert atmosphere.

[0032] Preferably, the coarse crushing method includes crushing using a jaw crusher.

[0033] Preferably, the hydrogen crushing process includes hydrogen absorption and vacuum dehydrogenation treatment in sequence.

[0034] Preferably, the hydrogen absorption temperature of the hydrogen fragment is 200°C to 300°C.

[0035] Preferably, the method further comprises air cooling the magnet in an inert atmosphere after the tempering treatment is completed.

[0036] In a second aspect, the present invention provides a magnet, which is prepared by the method described in the first aspect, and has a thickness greater than 2 cm, a length greater than 3 cm, and a width greater than 3 cm.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The present invention subjects recycled grain boundary diffusion magnetic sheets to a series of treatments, including demagnetization, surface treatment, and crushing. The resulting core-shell NdFeB powder is then added to the sintered magnet process as grain boundary powder, achieving an increase in coercivity for the ultimate application of heavy rare earth elements. The method provided by the present invention offers advantages such as simplicity, environmental friendliness, and conservation of rare earth resources. It not only enables the recycling of rare earth elements from recycled grain boundary diffusion magnetic sheets, but also addresses the low utilization rate of heavy rare earth elements, insufficient diffusion depth, and significant residual magnetic loss associated with conventional grain boundary diffusion processes. DETAILED DESCRIPTION

[0039] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely for the purpose of helping to understand the present invention and should not be regarded as specific limitations of the present invention.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention pertains; the terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the present invention; the terms "including" and "having" and any variations thereof in the present invention are intended to cover non-exclusive inclusions.

[0041] In the description of the present invention, technical terms such as "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the technical features indicated. In the description of the embodiments of the present invention, the meaning of "plurality" is more than two, unless otherwise specifically defined.

[0042] In one embodiment, the present invention provides a method for recovering grain boundary diffusion magnetic sheets to prepare magnets, the method comprising:

[0043] The recovered grain boundary diffusion magnetic sheets are sequentially subjected to demagnetization treatment, surface treatment and crushing treatment to obtain core-shell structured NdFeB powder; the core-shell structured NdFeB powder is used as grain boundary powder and mixed with NdFeB raw material powder, and the mixture is pressed into shape to obtain a NdFeB blank; the NdFeB blank is sequentially subjected to sintering treatment and tempering treatment to obtain a magnet; the material of the NdFeB raw material powder does not include heavy rare earth elements.

[0044] The present invention performs a series of treatments on the recycled grain boundary diffusion magnetic sheets, including demagnetization, surface treatment, and crushing. The obtained core-shell structured NdFeB powder is used as grain boundary powder and added to the sintering magnet process without the need for additional heavy rare earths. This allows the preparation of large-scale magnets with low rare earth content and high coercivity, thus achieving an increase in coercivity under the extreme application of heavy rare earths. The NdFeB powder with a core-shell structure of uneven thickness obtained from the recycled grain boundary diffusion magnetic sheets is used as an additive in the sintering process, and the heavy rare earth elements are distributed to form a more uniform core-shell structure. Compared with the existing grain boundary diffusion process, the effect of improving the coercivity of large-scale magnets is significant, not only realizing the recycling of rare earth elements in the recycled grain boundary diffusion magnetic sheets, but also solving the problems of low heavy rare earth utilization, insufficient diffusion depth, and significant residual magnetic loss in the traditional grain boundary diffusion process.

[0045] In some embodiments, the thickness of the recycled grain boundary diffusion magnetic sheet is less than 5 mm, for example, it can be 4.5 mm, 4.3 mm, 4.1 mm, 3.5 mm, 3 mm, or 2 mm, including but not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0046] In some embodiments, the average particle size of the core-shell structured NdFeB powder is 3 μm to 5 μm, for example, 3 μm, 3.5 μm, 4 μm, 4.5 μm or 5 μm, including but not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0047] In some embodiments, the average particle size of the NdFeB raw material powder is 2 μm to 5 μm, for example, it can be 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm or 5 μm, including but not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0048] In some embodiments, the mass of the core-shell structured NdFeB powder accounts for 5wt% to 50wt% of the total mass of the core-shell structured NdFeB powder and the NdFeB raw material powder, for example, it can be 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt% or 50wt%, including but not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable, preferably 10wt% to 25wt%.

[0049] In some embodiments, the method for preparing the NdFeB raw material powder includes: configuring alloy powder according to a stoichiometric ratio, smelting, and crushing to obtain the NdFeB raw material powder.

[0050] In some embodiments, the smelting method includes using a vacuum melting and rapid solidification furnace for smelting.

[0051] In some embodiments, the crushing method includes sequentially performing hydrogen crushing and / or air flow milling.

[0052] In some embodiments, the components of the NdFeB raw material powder include NdFeB alloy containing RE, Fe, B and M elements, RE contains one or more of Nd, Pr, La, Ce, and M contains one or more of Co, Ca, Cu, Al, Zr, and Ti, wherein the mass fraction of RE is 30% to 36%, the mass fraction of Fe is less than or equal to 68%, the mass fraction of B is less than or equal to 1%, and the mass fraction of M is less than or equal to 2%.

[0053] In some embodiments, the press-forming method includes sequentially performing orientation pressing and cold isostatic pressing.

[0054] In some embodiments, the vacuum degree of the sintering and tempering treatments is 1×10 -3 Pa or less, for example, 0.1×10 -3 Pa, 0.2×10 -3 Pa, 0.4×10 -3 Pa, 0.6×10 -3 Pa, 0.8×10 -3 Pa or 1×10 -3 Pa, including but not limited to the listed values, other unlisted values ​​within the numerical range are also applicable.

[0055] In some embodiments, the sintering treatment temperature is 1000°C to 1100°C, for example, it can be 1000°C, 1010°C, 1020°C, 1030°C, 1040°C, 1050°C, 1060°C, 1070°C, 1080°C, 1090°C or 1100°C, including but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable; the sintering holding time is 3h to 6h, for example, it can be 3h, 3.5h, 4h, 4.5h, 5h, 5.5h or 6h, including but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0056] In some embodiments, the tempering treatment includes a first tempering, a second tempering, and a third tempering performed sequentially.

[0057] In some embodiments, the temperature of the first tempering is 820°C to 920°C, for example, it can be 820°C, 840°C, 860°C, 880°C, 900°C or 920°C, including but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable; the time is 3h to 5h, for example, it can be 3h, 3.5h, 4h, 4.5h or 5h, including but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0058] In some embodiments, the temperature of the second tempering is 620°C to 720°C, for example, it can be 620°C, 640°C, 660°C, 680°C, 700°C or 720°C, including but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable; the time is 3h to 5h, for example, it can be 3h, 3.5h, 4h, 4.5h or 5h, including but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0059] In some embodiments, the temperature of the third tempering is 400°C to 520°C, for example, it can be 400°C, 420°C, 440°C, 460°C, 480°C, 500°C or 520°C, including but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable; the time is 3h to 5h, for example, it can be 3h, 3.5h, 4h, 4.5h or 5h, including but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0060] In some embodiments, the demagnetization treatment comprises vacuum thermal demagnetization treatment.

[0061] In some embodiments, the surface treatment method includes any one of etching, mechanical grinding, high-temperature burning, sand blasting, shot blasting or acid pickling, or a combination of at least two thereof.

[0062] In some embodiments, the crushing method includes sequentially performing coarse crushing, hydrogen crushing, and air flow milling on the surface-treated recycled grain boundary diffusion magnetic sheets.

[0063] In some embodiments, the coarse crushing is performed under an inert atmosphere, wherein the inert atmosphere comprises nitrogen and / or an inert gas, and the inert gas comprises argon and / or helium.

[0064] In some embodiments, the coarse crushing method includes crushing using a jaw crusher.

[0065] In some embodiments, the hydrogen crushing process includes hydrogen absorption and vacuum dehydrogenation treatment in sequence.

[0066] In some embodiments, the hydrogen absorption temperature of the hydrogen fragmentation is 200°C to 300°C, for example, 200°C, 220°C, 240°C, 260°C, 280°C or 300°C, including but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0067] In some embodiments, the method further comprises air cooling the magnet in an inert atmosphere after the tempering treatment is completed.

[0068] In another specific embodiment, the present invention provides a magnet, which is prepared by the method described in the above specific embodiment, and the thickness of the magnet is greater than 2 cm, for example, it can be 2.1 cm, 2.3 cm, 2.5 cm, 2.7 cm, 3 cm, 3.5 cm, 4 cm or 5 cm; the length is greater than 3 cm, for example, it can be 3.2 cm, 3.4 cm, 3.6 cm, 3.8 cm, 4 cm, 4.5 cm, 5 cm or 6 cm; the width is greater than 3 cm, for example, it can be 3.2 cm, 3.4 cm, 3.6 cm, 3.8 cm, 4 cm, 4.5 cm, 5 cm or 6 cm, including but not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0069] To clearly illustrate the technical solution of the present invention, the rare earth elements in the recycled grain boundary diffusion magnetic sheet in the specific embodiment include Pr, Nd, and Tb, with a heavy rare earth content of 0.8 wt% and a total rare earth content of 31 wt%. The above description is merely for the purpose of clarifying the technical solution of the present invention and is not to be construed as further limiting the present invention.

[0070] Example 1

[0071] This embodiment provides a method for recycling grain boundary diffusion magnetic sheets to prepare magnets, the method comprising:

[0072] (1) Vacuum thermal demagnetization treatment was performed on the recovered grain boundary diffusion magnetic sheets with a thickness of 3 mm. The magnets were washed with nitric acid with a concentration of 2 wt.% to remove the oxide layer on the surface of the recovered grain boundary diffusion magnetic sheets. The magnets were then washed with deionized water and alcohol and dried. Next, the recovered grain boundary diffusion magnetic sheets were coarsely crushed using a jaw crusher under a nitrogen atmosphere. The coarsely crushed powder was then placed in a hydrogen crushing furnace with a hydrogen absorption temperature of 220°C and a hydrogen pressure of 0.8 MPa. After hydrogen absorption saturation, the magnets were subjected to an absolute pressure of 1×10 -3 The hydrogen powder was crushed by air jet mill, and the average particle size of the core-shell structure NdFeB powder was controlled at 3.5 μm by adjusting the speed of the sorting wheel and the pressure of the grinding chamber.

[0073] (2) According to (Pr 0.25 Nd0.75 ) 30.5 Fe bal B 0.95 Co 0.8 Cu 0.2 Ga 0.25 Al 0.2 Zr 0.2 The raw materials are prepared and melted in a vacuum melting and rapid solidification furnace, and then hydrogen crushing and jet milling are performed in sequence to obtain NdFeB raw material powder with an average particle size of 3 μm;

[0074] (3) Under nitrogen atmosphere, 25 wt% of the core-shell structured NdFeB powder obtained in step (1) was mixed with 75 wt% of the NdFeB raw material powder obtained in step (2), and orientation pressing and cold isostatic pressing were performed in sequence to obtain a NdFeB blank; and the degree of vacuum was 0.8×10 -3 Pa conditions, the NdFeB blank was sintered at 1070°C for 3 h, and then subjected to a first tempering treatment at 880°C for 4 h, a second tempering treatment at 680°C for 3 h, and a third tempering treatment at 480°C for 4 h. The NdFeB blank was then air-cooled in an argon atmosphere to obtain a magnet with a thickness of 2.5 cm, a length of 3.3 cm, and a width of 3.5 cm.

[0075] Example 2

[0076] This embodiment provides a method for recycling grain boundary diffusion magnetic sheets to prepare magnets, the method comprising:

[0077] (1) Vacuum thermal demagnetization treatment was performed on the recovered grain boundary diffusion magnetic sheets with a thickness of 4.5 mm. The magnets were washed with nitric acid with a concentration of 2 wt.% to remove the oxide layer on the surface of the recovered grain boundary diffusion magnetic sheets. The magnets were then washed with deionized water and alcohol and dried. Next, the recovered grain boundary diffusion magnetic sheets were coarsely crushed using a jaw crusher under a nitrogen atmosphere. The coarsely crushed powder was then placed in a hydrogen crushing furnace with a hydrogen absorption temperature of 250°C and a hydrogen pressure of 0.8 MPa. After hydrogen absorption saturation, the magnets were subjected to an absolute pressure of 1×10 -3 The hydrogen powder was crushed by air jet mill, and the average particle size of the core-shell structure NdFeB powder was controlled to 2μm by adjusting the speed of the sorting wheel and the pressure of the grinding chamber.

[0078] (2) According to (Pr 0.25 Nd 0.75 ) 30.5 Fe bal B 0.95 Co 0.8 Cu 0.2 Ga 0.25 Al 0.2 Zr0.2 The raw materials are prepared and melted in a vacuum melting and rapid solidification furnace, and then hydrogen crushing and air flow grinding are performed in sequence to obtain NdFeB raw material powder with an average particle size of 2 μm;

[0079] (3) Under nitrogen atmosphere, 5 wt% of the core-shell structured NdFeB powder obtained in step (1) was mixed with 95 wt% of the NdFeB raw material powder obtained in step (2), and orientation pressing and cold isostatic pressing were performed in sequence to obtain a NdFeB blank; and the degree of vacuum was 0.9×10 -3 Pa conditions, the NdFeB blank was sintered at a temperature of 1000°C for 3 hours, and then subjected to a first tempering treatment at a temperature of 820°C for 3 hours, a second tempering treatment at a temperature of 620°C for 3 hours, and a third tempering treatment at a temperature of 400°C for 3 hours. Then, the blank was air-cooled in an argon atmosphere to obtain a magnet with a thickness of 2.2 cm, a length of 4 cm, and a width of 3.5 cm.

[0080] Example 3

[0081] This embodiment provides a method for recycling grain boundary diffusion magnetic sheets to prepare magnets, the method comprising:

[0082] (1) The recovered grain boundary diffusion magnetic sheets with a thickness of 4 mm were subjected to vacuum thermal demagnetization treatment. The magnets were washed with nitric acid with a concentration of 2 wt.% to remove the oxide layer on the surface of the recovered grain boundary diffusion magnetic sheets. The magnets were then washed with deionized water and alcohol and dried. Next, the recovered grain boundary diffusion magnetic sheets were coarsely crushed using a jaw crusher under a nitrogen atmosphere. The coarsely crushed powder was then placed in a hydrogen crushing furnace with a hydrogen absorption temperature of 300°C and a hydrogen pressure of 0.8 MPa. After hydrogen absorption saturation, the magnets were crushed at an absolute pressure of ≤1×10 -3 The hydrogen powder was crushed by air jet mill, and the average particle size of the core-shell structure NdFeB powder was controlled at 4 μm by adjusting the speed of the sorting wheel and the pressure of the grinding chamber.

[0083] (2) According to (Pr 0.25 Nd 0.75 ) 30.5 Fe bal B 0.95 Co 0.8 Cu 0.2 Ga 0.25 Al 0.2 Zr 0.2 The raw materials are prepared and melted in a vacuum melting and rapid solidification furnace, and then hydrogen crushing and air flow grinding are performed in sequence to obtain NdFeB raw material powder with an average particle size of 5 μm;

[0084] (3) Under nitrogen atmosphere, 50 wt% of the core-shell structured NdFeB powder obtained in step (1) and 50 wt% of the NdFeB raw material powder obtained in step (2) were mixed, and orientation pressing and cold isostatic pressing were performed in sequence to obtain a NdFeB blank; and the vacuum degree was 1×10 -3 Pa conditions, the NdFeB blank was sintered at 1100°C for 6 h, and then subjected to a first tempering treatment at 920°C for 5 h, a second tempering treatment at 720°C for 5 h, and a third tempering treatment at 520°C for 5 h. The blank was then air-cooled in an argon atmosphere to obtain a magnet with a thickness of 2.8 cm, a length of 4.3 cm, and a width of 3.6 cm.

[0085] Example 4

[0086] The present embodiment provides a method for preparing magnets by recycling grain boundary diffusion magnetic sheets. The method is the same as Example 1 except that in step (3), 10 wt% of the core-shell structured NdFeB powder obtained in step (1) is mixed with 90 wt% of the NdFeB raw material powder obtained in step (2), and the NdFeB blank is sintered at a temperature of 1060°C for 3 hours, and then a first tempering treatment at a temperature of 880°C for 3 hours, a second tempering treatment at a temperature of 680°C for 4 hours, and a third tempering treatment at a temperature of 480°C for 4 hours is sequentially performed.

[0087] Example 5

[0088] This embodiment provides a method for preparing magnets by recycling grain boundary diffusion magnetic sheets. The method is the same as Example 1 except that in step (3), 15wt% of the core-shell structure NdFeB powder obtained in step (1) is mixed with 85wt% of the NdFeB raw material powder obtained in step (2), and the NdFeB blank is sintered at a temperature of 1060°C for 3 hours, and then a first tempering treatment at a temperature of 870°C for 3 hours, a second tempering treatment at a temperature of 660°C for 4 hours, and a third tempering treatment at a temperature of 450°C for 4 hours is performed in sequence.

[0089] Example 6

[0090] This embodiment provides a method for preparing magnets by recycling grain boundary diffusion magnetic sheets. The method is the same as Example 1 except that in step (3), 20 wt% of the core-shell structure NdFeB powder obtained in step (1) is mixed with 80 wt% of the NdFeB raw material powder obtained in step (2), and the sintered NdFeB blank is subjected to a first tempering treatment at a temperature of 900°C for a time of 4 hours, a second tempering treatment at a temperature of 700°C for a time of 3 hours, and a third tempering treatment at a temperature of 500°C for a time of 4 hours.

[0091] Example 7

[0092] This embodiment provides a method for recycling grain boundary diffusion magnetic sheets to prepare magnets. The method is the same as that of Example 1, except that in step (3), 3 wt% of the core-shell structure NdFeB powder obtained in step (1) is mixed with 97 wt% of the NdFeB raw material powder obtained in step (2).

[0093] Example 8

[0094] This embodiment provides a method for recycling grain boundary diffusion magnetic sheets to prepare magnets. The method is the same as Example 1 except that in step (3), 55wt% of the core-shell structure NdFeB powder obtained in step (1) is mixed with 45wt% of the NdFeB raw material powder obtained in step (2).

[0095] Example 9

[0096] This embodiment provides a method for recovering grain boundary diffusion magnetic sheets to prepare magnets. The method is the same as that of embodiment 1 except that in step (3), only the first tempering treatment and the third tempering treatment are performed, and the second tempering treatment is not performed.

[0097] Comparative Example 1

[0098] This comparative example provides a method for preparing NdFeB. The method is the same as Example 1 except that step (1) is not performed, and in step (2), core-shell NdFeB powder is not added. The NdFeB raw material powder is only subjected to orientation pressing and cold isostatic pressing in sequence to prepare a NdFeB blank.

[0099] Comparative Example 2

[0100] This comparative example provides a method for preparing NdFeB, which is the same as Example 1 except that step (1) is not performed and 0.3 wt.% Tb micron powder is used to replace the core-shell structure NdFeB powder in step (3).

[0101] Performance testing:

[0102] The remanence B of the magnets prepared in all the above examples and comparative examples was measured using a NIC-500C multifunctional permanent magnet measuring instrument. r , intrinsic coercivity H cj , Maximum magnetic energy product (BH) max And the squareness H of the demagnetization curve k / H cj The magnet sample size during the test was 7 mm × 7 mm × 4 mm, and the test temperature was 22°C. The test results are shown in Table 1.

[0103] Table 1

[0104] <![CDATA[B r (kG)]]> <![CDATA[H cj (no)]]> <![CDATA[BH(MGOe) max ]]> <![CDATA[H k / H cj (%)]]> Example 1 13.76 13.88 47.93 97.2 Example 2 14.22 10.55 49.22 96.9 Example 3 13.62 16.28 47.23 97.0 Example 4 13.96 11.75 48.82 97.0 Example 5 13.88 12.56 48.55 96.8 Example 6 13.81 13.28 48.19 97.5 Example 7 14.16 10.51 49.25 97.3 Example 8 13.60 16.53 47.16 97.2 Example 9 13.73 13.52 47.68 97.2 Comparative Example 1 14.28 10.26 49.3 96.6 Comparative Example 2 13.73 13.50 47.76 96.8

[0105] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing magnets by recycling grain boundary diffusion magnetic sheets, characterized in that: The method comprises: The recovered grain boundary diffusion magnetic sheets are sequentially subjected to demagnetization treatment, surface treatment, and crushing treatment to obtain core-shell structured NdFeB powder; the core-shell structured NdFeB powder is mixed with NdFeB raw material powder as grain boundary powder, and the mixture is pressed to obtain a NdFeB blank; the NdFeB blank is sequentially subjected to sintering treatment and tempering treatment to obtain a magnet; The material of the NdFeB raw material powder does not include heavy rare earth elements.

2. The method according to claim 1, wherein The thickness of the recycled grain boundary diffusion magnetic sheet is less than 5 mm; And / or, the average particle size of the core-shell structured NdFeB powder is 3 μm to 5 μm; And / or, the average particle size of the NdFeB raw material powder is 2 μm to 5 μm.

3. The method according to claim 1, wherein The mass of the core-shell structure NdFeB powder accounts for 5wt% to 50wt% of the total mass of the core-shell structure NdFeB powder and the NdFeB raw material powder.

4. The method according to claim 1, wherein The preparation method of the NdFeB raw material powder comprises: Alloy powder is prepared according to a stoichiometric ratio, smelted, and crushed to obtain the NdFeB raw material powder.

5. The method according to claim 4, wherein The smelting method includes using a vacuum melting and rapid solidification furnace for smelting; And / or, the crushing method includes hydrogen crushing and / or air flow grinding.

6. The method according to claim 1, wherein The compression molding method includes sequentially performing orientation pressing and cold isostatic pressing; And / or, the vacuum degree of the sintering and tempering treatment is 1×10 -3 Below Pa; And / or, the sintering temperature is 1000° C. to 1100° C., and the sintering holding time is 3 h to 6 h.

7. The method according to claim 1, wherein The tempering treatment includes a first tempering, a second tempering and a third tempering performed in sequence.

8. The method according to claim 7, wherein The first tempering temperature is 820°C to 920°C, and the time is 3h to 5h; And / or, the second tempering temperature is 620°C to 720°C, and the time is 3h to 5h; And / or, the third tempering temperature is 400° C. to 520° C., and the time is 3 h to 5 h.

9. The method according to claim 1, wherein The demagnetization treatment method includes vacuum thermal demagnetization treatment; And / or, the surface treatment method includes any one or a combination of at least two of etching, mechanical grinding, high-temperature burning, sandblasting, shot blasting or pickling; And / or, the crushing method includes sequentially performing coarse crushing, hydrogen crushing and air flow milling on the surface-treated recycled grain boundary diffusion magnetic sheets; And / or, the method further comprises air cooling the magnet in an inert atmosphere after the tempering treatment is completed.

10. A magnet, characterized in that: The magnet is prepared by the preparation method according to any one of claims 1 to 9, and the thickness of the magnet is greater than 2 cm, the length is greater than 3 cm, and the width is greater than 3 cm.