Preparation method of neodymium-iron-boron magnet with low demagnetization rate

Abstract

The invention belongs to the technical field of permanent magnet materials, and relates to a preparation method of a neodymium-iron-boron magnet with low demagnetization rate, which comprises the following steps: cutting the neodymium-iron-boron magnet along the orientation direction to obtain A0; the A0 magnet is subjected to permeation source coating, permeation and aging treatment, A1 and A2 are obtained, the coercive force of A1 is larger than the coercive force of A2, and the difference value of A1 and A2 is smaller than or equal to 3 kOe; the m magnets A1 and the n magnets A2 are stacked to form a combined magnet A3, wherein m / (m + n) is larger than or equal to 0.4 and smaller than or equal to 0.6; wherein the magnets A1 are located at the two ends of the A3, the number of the magnets A1 at each end is larger than or equal to 2, and the magnets A2 are located in the middle of the A3; and the combined magnet A3 is cut in the direction perpendicular to the orientation direction, and a magnet A4 is obtained. According to the method, the magnets A1 and A2 with different coercive forces are combined, and the quantity proportion and the arrangement position of the magnets A1 and A2 are controlled, so that the internal performance of the magnets is accurately regulated and controlled, and the demagnetization rate of the magnets in service is effectively reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of permanent magnetic materials and relates to a method for preparing a neodymium iron boron magnet with a low demagnetization rate. Background Art

[0002] In recent years, with the continued development of new energy vehicles, humanoid robots, and other fields, market demand for high-performance NdFeB permanent magnets has continued to grow, and industry competition has become increasingly fierce. Reducing production costs and improving product performance have become key development trends within the industry. While technologies such as grain refinement and grain boundary diffusion can effectively reduce heavy rare earth usage and lower material costs, they still cannot meet the cost requirements of downstream applications. Therefore, developing new technologies and processes to further reduce the production cost of magnets has become a pressing issue for those skilled in the art.

[0003] Existing micromagnetic simulation results indicate that permanent magnet motors have varying anti-demagnetization requirements and coercivity requirements at different locations in different applications. Therefore, leveraging this characteristic to develop new technologies and processes to achieve performance control across different magnet regions and reduce material costs has become a key research topic for many companies and research institutions.

[0004] In its patent CN113035556B, Jinli Permanent Magnets mentioned a selective diffusion technology. By regulating the coating agent composition and ratio of the easily demagnetized and non-demagnetized areas of the magnetic steel, a gradient performance magnet with higher coercivity in the easily demagnetized area and lower coercivity in the non-demagnetized area is prepared. Although this method can effectively achieve the regulation of the performance of different areas, the control of the diffusion agent coating area and weight is complex. The design of this type of diffusion agent coating platform is difficult, and the feasibility of actual industrial production is low. In its patent CN113053607B, Jinli Permanent Magnets mentioned a method for preparing three-dimensional grain boundary diffusion magnets. The method mainly achieves the preparation of magnets with gradient performance differences by coating and diffusing the diffusant on all six sides of the magnet and regulating the diffusion depth by the length of the diffusion time. This method will increase the complexity of the infiltration process and has no obvious advantages in reducing the use of heavy rare earths and reducing material costs. In its CN111653404B patent, Zhenghai Magnetic Materials mentioned a method for preparing gradient performance magnets by infiltrating in a direction perpendicular to the orientation. By coating and infiltrating a diffusion source on a surface parallel to the orientation direction and infiltrating along the width direction perpendicular to the orientation, a gradient performance magnet with high coercivity on both sides of the width direction and low coercivity in the middle is achieved. This method has high requirements for the magnet specifications and a very narrow range of specifications in the width direction of the final magnetic steel product. As a whole, the application range of this method is very narrow. Summary of the Invention

[0005] In order to solve the above problems existing in the prior art, the purpose of the present invention is to provide a method for preparing a NdFeB magnet with low demagnetization rate, so as to overcome the shortcomings of the prior art.

[0006] One object of the present invention is achieved by the following technical solutions:

[0007] A method for preparing a neodymium iron boron magnet with low demagnetization rate comprises the following steps:

[0008] S1. Cutting the NdFeB magnet along the orientation direction to obtain a NdFeB magnet A0 with a thickness of 0.5 to 3.5 mm, wherein the angle between the cutting direction and the orientation direction is ≤5°;

[0009] S2. Performing infiltration source coating, infiltration, and aging treatment on the surface-cleaned A0 magnet to obtain NdFeB magnets A1 and A2 with different coercive forces, wherein the coercive force of NdFeB magnet A1 is greater than that of NdFeB magnet A2, and the difference between the two is ≤3 kOe;

[0010] S3. Stacking the A1 magnet and the A2 magnet to form a combined magnet A3, wherein the combined magnet A3 consists of m A1 magnets and n A2 magnets, and satisfies 0.4≤m / (m+n)≤0.6; wherein the A1 magnets are located at both ends of the combined magnet A3, and the number of A1 magnets at each end is ≥2, and the A2 magnet is located in the middle of the combined magnet A3;

[0011] S4. Cut the combined magnet A3 along a cutting direction perpendicular to the orientation direction to obtain a final NdFeB magnet A4.

[0012] In step S1:

[0013] NdFeB magnet is a rare earth permanent magnet material with neodymium, iron and boron as main components, which is prepared through smelting, casting, crushing, pressing, orientation and sintering.

[0014] Preferably, in step S1, the angle between the cutting direction and the orientation direction is 0, that is, the cutting direction is parallel to the orientation direction.

[0015] When performing step S2, the surface of the NdFeB magnet A0 needs to be cleaned, which includes the following steps: degreasing, pickling, and drying.

[0016] In step S2:

[0017] Preferably, the penetration source K1 used to obtain the NdFeB magnet A1 is: Pr x Co y Ga 100-x-y and HR 100-a Al a Mixed alloy powder, Prx Co y Ga 100-x-y The mass fraction of is 30-50wt%;

[0018] The penetration source K2 used to obtain the NdFeB magnet A2 is: HR 100-b-c Ni b Al c ;

[0019] Wherein, x is 70 to 90, y is 2 to 7, a is 8 to 15, b is 2 to 7, c is 8 to 15, and HR is Dy and / or Tb.

[0020] The permeation source coating step includes dispersing the permeation source in a solvent to form a slurry, and then coating the slurry on the surface of the A0 magnet. The slurry is applied to both end faces of the A0 magnet perpendicular to the c-axis. In NdFeB magnet A1, the amount of slurry applied is such that the mass of the permeation source K1 is 1.15-1.7 wt% of the mass of the A0 magnet. In NdFeB magnet A2, the amount of slurry applied is such that the mass of the permeation source K2 is 0.3-1.1 wt% of the mass of the A0 magnet.

[0021] The infiltration step comprises: subjecting the coated A0 magnet to infiltration treatment, wherein the insulation temperature of the infiltration treatment is 850-950° C. and the insulation time is 9-20 hours.

[0022] The aging treatment step includes: performing aging treatment on the A0 magnet after infiltration and diffusion, wherein the holding temperature of the aging treatment is 450-550° C. and the holding time is 3-6 hours.

[0023] After aging treatment, the double end faces of the magnet subjected to infiltration treatment were finely ground to obtain A1 and A2.

[0024] Preferably, the difference between the coercive force of the NdFeB magnet A1 and the coercive force of the NdFeB magnet A2 is 0.5-3 kOe.

[0025] In step S3:

[0026] The stacking method is: the A1 magnets, the A2 magnets, and the A1 and A2 magnets are connected through end faces perpendicular to the c-axis, and then stacked in sequence to form a combined magnet A3.

[0027] The end surface perpendicular to the c-axis is coated with an adhesive for fixed connection of the A1 and A2 magnets.

[0028] The adhesive is epoxy resin, and the usage is 3~8*10 -4 g / mm 3 .

[0029] In step S4 , the thickness of the final NdFeB magnet A4 is 1 to 5 mm.

[0030] Another object of the present invention is achieved through the following technical solutions:

[0031] A neodymium iron boron magnet with low demagnetization rate is prepared by the above preparation method.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The present invention achieves precise control of the internal performance of the magnet by combining NdFeB magnets A1 and A2 with different coercive forces and controlling their quantity ratio and arrangement position, effectively solving the problem of abnormal service performance of the magnet caused by the mismatch between the easily demagnetized area and the high coercive force area.

[0034] (2) By reducing the coercive force requirement of the easily demagnetized area (A2), the use of heavy rare earths is significantly reduced, thereby reducing material costs; however, due to the use of a combination method, the service performance of the overall magnet A4 is close to that of traditional magnets with higher coercive force, taking into account both performance and economy.

[0035] (3) Compared with the existing three-dimensional grain boundary diffusion method or selective diffusion technology, the preparation method of the present invention is not limited to the size of the magnet. Therefore, it is suitable for the production of magnets with various specifications and structural designs, and has a wider application space.

[0036] (4) There is no need to adjust the grain boundary diffusion process. The effect can be achieved through cutting and combining. The entire post-processing process is simple and clear, and it is fully feasible for industrial production.

[0037] (5) By controlling the ratio of A1 and A2 in the combined magnet and the parameters such as the magnet thickness, the magnet performance can be flexibly adjusted to avoid problems such as excessive demagnetization resistance of the motor or increased material costs, thus adapting to different application requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 The A0 magnet prepared in step S1 of Example 1;

[0039] Figure 2 The magnets A1 and A2 prepared in step S2 of Example 1;

[0040] Figure 3 The composite magnet A3 obtained by laminating in step S3 of Example 1;

[0041] Figure 4 This is the final magnet prepared in step S4 of Example 1. DETAILED DESCRIPTION

[0042] Below by specific embodiment and accompanying drawing, technical scheme of the present invention is further described explanation, it should be understood that specific embodiment described herein is only for helping to understand the present invention, is not used for specific limitation of the present invention.And accompanying drawing used herein, is only for better illustrating the disclosure of the present invention, does not have limiting effect on protection scope.If no special instructions, the raw materials adopted in the embodiment of the present invention are all raw materials commonly used in this area, and the method adopted in the embodiment is all conventional method in this area.

[0043] In the description of the present invention, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any combination of real numbers between a and b, and includes a and b.

[0044] Example 1

[0045] The preparation method of the NdFeB product of this embodiment is as follows:

[0046] S1: Select a 52M NdFeB magnet blank with a magnetic property of 14.37 kGs, Hcj of 16.24 kOe, and a specification of 19 mm * 54 mm * 35 mm, cut it along the orientation direction to form a magnet with an outer size of 19 mm * 2.05 mm * 35 mm, and mark it as A0. Figure 1 As shown; A0 is degreased, pickled and dried.

[0047] S2: Tb 90 Al 10 With Pr 80 Co5Ga 15 Two alloy infiltration source powders were mixed in a mass percentage of 70%:30% to prepare a new alloy infiltration source K1. K1 was dispersed in ethanol and a binder polyacrylate was added to obtain a slurry. The K1 slurry was coated on the two end faces of the A0 magnet perpendicular to the c-axis (19mm*35mm face) with a coating weight ratio of 1.2% (the weight of the infiltration source K1 was 1.2% of the magnet A0). The coated sintered NdFeB blank was placed in a vacuum furnace for infiltration treatment at a temperature of 900°C for 18 hours; after cooling, it was aged in a vacuum furnace at a temperature of 515°C for 4.5 hours. By double-end fine grinding, a NdFeB magnet A1 with a specification of 19mm*2mm*35mm was obtained. Figure 2 shown.

[0048] The alloy powder composition is Tb 85 Ni5Al 10The alloy infiltration source K2 is dispersed in ethanol, and a binder polyacrylate is added to obtain a slurry. The K2 slurry is coated on the two end faces of the A0 magnet perpendicular to the c-axis (19mm*35mm face), and the coating weight ratio is 0.7% (the weight of the infiltration source K2 is 0.7% of the magnet A0). The coated sintered NdFeB blank is placed in a vacuum furnace for an infiltration treatment at a temperature of 900°C and a time of 18 hours; after cooling, an aging treatment is performed in a vacuum furnace at a temperature of 515°C and a time of 4.5 hours. By double-end fine grinding, a NdFeB magnet A2 with a specification of 19mm*2mm*35mm is obtained.

[0049] S3: Coat the end faces of 4 A1 magnets and 5 A2 magnets perpendicular to the c-axis with epoxy resin (the amount used is 5*10 -4 g / mm 3 ) are connected and then stacked in sequence to form a combined magnet A3, wherein the A1 magnets are located at both ends of the combined magnet A3, and the number of A1 magnets at each end is 2, and 5 pieces of A2 magnets are located in the middle of the combined magnet A3, as shown in FIG. Figure 3 shown.

[0050] S4: Cut the combined magnet A3 along the cutting direction perpendicular to the orientation direction to form a final finished magnet with a specification of 19mm*18mm*4.6mm, such as Figure 4 shown.

[0051] Example 2

[0052] The only difference between Example 2 and Example 1 is that during the preparation of the S2 NdFeB magnet A2, the coating weight ratio of the infiltration source K2 is 0.5%.

[0053] The rest is the same as Example 1.

[0054] Example 3

[0055] The only difference between Example 3 and Example 1 is that the magnet A3 of S3 is composed of 2 A1 magnets and 7 A2 magnets stacked together, wherein the A1 magnet is located at both ends of the combined magnet A3, and the number of A1 magnets at each end is 1, and the 7 A2 magnets are located in the middle of the combined magnet A3.

[0056] The rest is the same as Example 1.

[0057] Example 4

[0058] The only difference between Example 4 and Example 1 is that the magnet A3 of S3 is composed of 7 A1 magnets and 2 A2 magnets stacked together, wherein the A1 magnets are located at both ends of the combined magnet A3, and the number of A1 magnets at one end is 3 and the number of A1 magnets at the other end is 4, and the 2 A2 magnets are located in the middle of the combined magnet A3.

[0059] The rest is the same as Example 1.

[0060] Example 5

[0061] The preparation method of the NdFeB product of this embodiment is as follows:

[0062] S1: Select a 45H NdFeB magnet blank with a magnetic property Br of 13.52 kGs, an Hcj of 18.45 kOe, and a specification of 49 mm * 21 mm * 37 mm. Cut it along the orientation direction to form a magnet with an outer dimension of 49 mm * 3.05 mm * 37 mm, and mark it as A0. Degrease, pickle, and dry A0.

[0063] S2: Dy 90 Al 10 With Pr 80 Co5Ga 15 Two alloy infiltration source powders were mixed in a mass percentage of 60%:40% to prepare a new alloy infiltration source K1. K1 was dispersed in ethanol and a binder polyacrylate was added to obtain a slurry. The K1 slurry was coated on the two end faces of the A0 magnet perpendicular to the c-axis (49mm*37mm faces) with a coating weight ratio of 1.3% (the weight of the infiltration source K1 was 1.3% of the magnet A0). The coated sintered NdFeB blank was placed in a vacuum furnace for infiltration treatment at a temperature of 900°C for 18 hours; after cooling, it was aged in a vacuum furnace at a temperature of 515°C for 4.5 hours. By double-end fine grinding, a NdFeB magnet A1 with a specification of 49mm*3mm*37mm was obtained.

[0064] The alloy powder composition is Dy 85 Ni5Al 10 The alloy infiltration source K2 is dispersed in ethanol, and a binder polyacrylate is added to obtain a slurry. The K2 slurry is coated on the two end faces of the A0 magnet perpendicular to the c-axis (49mm*37mm face), and the coating weight ratio is 0.8% (the weight of the infiltration source K2 is 0.8% of the magnet A0). The coated sintered NdFeB blank is placed in a vacuum furnace for an infiltration treatment at a temperature of 900°C and a time of 18 hours; after cooling, an aging treatment is performed in a vacuum furnace at a temperature of 515°C and a time of 4.5 hours. By double-end fine grinding, a NdFeB magnet A2 with a specification of 49mm*3mm*37mm is obtained.

[0065] S3: Coat the end faces of 4 A1 magnets and 3 A2 magnets perpendicular to the c-axis with epoxy resin (the amount used is 5*10 -4 g / mm 3) are connected and then stacked in sequence to form a combined magnet A3, wherein the A1 magnets are located at both ends of the combined magnet A3, and the number of A1 magnets at each end is 2, and 3 pieces of A2 magnets are located in the middle of the combined magnet A3.

[0066] S4: cutting the combined magnet A3 along a cutting direction perpendicular to the orientation direction to form a final finished magnet with a specification of 49 mm*21 mm*2 mm.

[0067] Example 6

[0068] The only difference between Example 6 and Example 5 is that during the preparation of the S2 NdFeB magnet A2, the coating weight ratio of the infiltration source K2 is 0.4%.

[0069] Example 7

[0070] The only difference between Example 7 and Example 5 is that the magnet A3 of S3 is composed of 2 A1 magnets and 5 A2 magnets stacked together, wherein the A1 magnet is located at both ends of the combined magnet A3, and the number of A1 magnets at each end is 1, and the 5 A2 magnets are located in the middle of the combined magnet A3.

[0071] The rest is the same as Example 5.

[0072] Example 8

[0073] The preparation method of the NdFeB product of this embodiment is as follows:

[0074] S1: Select a 45H NdFeB magnet blank with a magnetic property Br of 13.52 kGs, an Hcj of 18.45 kOe, and a specification of 49 mm * 21 mm * 37 mm. Cut it along the orientation direction to form a magnet with an outer dimension of 7.05 mm * 21 mm * 37 mm, and mark it as A0. Degrease, pickle, and dry A0.

[0075] S2: Dy 90 Al 10 With Pr 80 Co5Ga 15 Two alloy infiltration source powders were mixed in a mass percentage of 60%:40% to prepare a new alloy infiltration source K1. K1 was dispersed in ethanol and a binder polyacrylate was added to obtain a slurry. The K1 slurry was coated on the two end faces of the A0 magnet perpendicular to the c-axis (21mm*37mm faces) with a coating weight ratio of 1.5% (the weight of the infiltration source K1 was 1.5% of the magnet A0). The coated sintered NdFeB blank was placed in a vacuum furnace for infiltration treatment at a temperature of 900°C for 18 hours; after cooling, it was aged in a vacuum furnace at a temperature of 515°C for 4.5 hours, and double-end fine grinding was performed to obtain a NdFeB magnet A1 with a specification of 7mm*21mm*37mm.

[0076] The alloy powder composition is Dy 85 Ni5Al 10 The alloy infiltration source K2 is dispersed in ethanol, and a binder polyacrylate is added to obtain a slurry. The K2 slurry is coated on the two end faces of the A0 magnet perpendicular to the c-axis (21mm*37mm face), and the coating weight ratio is 1% (the weight of the infiltration source K2 is 1% of the magnet A0). The coated sintered NdFeB blank is placed in a vacuum furnace for infiltration treatment at a temperature of 900°C and a time of 18 hours; after cooling, it is aged in a vacuum furnace at a temperature of 515°C and a time of 4.5 hours. By double-end fine grinding, NdFeB magnet A2 with a specification of 7mm*21mm*37mm is obtained.

[0077] S3: Coat the end faces of 4 A1 magnets and 3 A2 magnets perpendicular to the c-axis with epoxy resin (the amount used is 5*10 -4 g / mm 3 ) are connected and then stacked in sequence to form a combined magnet A3, wherein the A1 magnets are located at both ends of the combined magnet A3, and the number of A1 magnets at each end is 2, and 3 pieces of A2 magnets are located in the middle of the combined magnet A3.

[0078] S4: cutting the combined magnet A3 along a cutting direction perpendicular to the orientation direction to form a final finished magnet with a specification of 49 mm*21 mm*2 mm.

[0079] Example 9

[0080] The preparation method of the NdFeB product of this embodiment is as follows:

[0081] S1: Select a 52M NdFeB magnet blank with a magnetic property of 14.37kGs, Hcj of 16.24kOe, and a specification of 19mm*54mm*35mm, cut it along the orientation direction to form a magnet with an outer size of 19mm*2.05mm*35mm, and mark it as A0; then use the same specification of NdFeB magnet blank and cut it along the orientation direction to form a magnet with an outer size of

[0082] A 19mm*4.05mm*35mm magnet, marked as A0', is degreased, pickled, and dried.

[0083] S2: Tb 90 Al 10 With Pr 80 Co5Ga 15Two alloy infiltration source powders were mixed in a mass percentage of 70%:30% to prepare a new alloy infiltration source K1. K1 was dispersed in ethanol and a binder polyacrylate was added to obtain a slurry. The K1 slurry was coated on the two end faces of the A0' magnet perpendicular to the c-axis (19mm*35mm face) with a coating weight ratio of 1.3% (the weight of the infiltration source K1 was 1.3% of the magnet A0). The coated sintered NdFeB blank was placed in a vacuum furnace for infiltration treatment at a temperature of 900°C for 18 hours; after cooling, it was aged in a vacuum furnace at a temperature of 515°C for 4.5 hours. By double-end fine grinding, a NdFeB magnet A1 with a specification of 19mm*4mm*35mm was obtained. Figure 2 shown.

[0084] The preparation method of NdFeB magnet A2 with specifications of 19mm*2mm*35mm is the same as that of Example 1.

[0085] S3: 2 A1 magnets and 5 A2 magnets are coated with epoxy resin (5*10 -4 g / mm 3 ) are connected and then stacked in sequence to form a combined magnet A3, wherein the A1 magnet is located at both ends of the combined magnet A3, and the number of A1 magnets at each end is 1, and 5 A2 magnets are located in the middle of the combined magnet A3.

[0086] S4: cutting the combined magnet A3 along a cutting direction perpendicular to the orientation direction to form a final finished magnet with a specification of 19 mm*18 mm*4.6 mm.

[0087] Comparative Example 1

[0088] The preparation method of the NdFeB product of Comparative Example 1 is as follows:

[0089] S1: Select a 52M NdFeB magnet blank with a magnetic property Br of 14.37 kGs, an Hcj of 16.24 kOe, and a specification of 19 mm * 18 mm * 35 mm. Cut it along the vertical orientation direction to form a magnet with an outer dimension of 19 mm * 18 mm * 4.6 mm and mark it as A0. Degrease, pickle, and dry A0.

[0090] S2: Disperse heavy rare earth Tb in ethanol, add binder polyacrylate to obtain slurry, and coat the Tb slurry on both end faces of the A0 magnet perpendicular to the c-axis, with a coating weight ratio of 1.2% (the weight of the infiltration source Tb is 1.2% of the magnet A0). Place the coated sintered NdFeB blank in a vacuum furnace for infiltration treatment at a temperature of 900°C for 18 hours; after cooling, perform aging treatment in a vacuum furnace at a temperature of 515°C for 4.5 hours to obtain a NdFeB product.

[0091] Comparative Example 2

[0092] The preparation method of the NdFeB product of Comparative Example 2 is as follows:

[0093] S1: Select a 52M NdFeB magnet blank with a magnetic property Br of 14.37 kGs, an Hcj of 16.24 kOe, and a specification of 19 mm * 18 mm * 35 mm. Cut it along the vertical orientation direction to form a magnet with an outer dimension of 19 mm * 18 mm * 4.6 mm and mark it as A0. Degrease, pickle, and dry A0.

[0094] S2: Tb 90 Al 10 With Pr 80 Co5Ga 15 Two alloy infiltration source powders were mixed in a mass percentage of 70%:30% to prepare a new alloy infiltration source K1. K1 was dispersed in ethanol and a binder polyacrylate was added to obtain a slurry. The K1 slurry was coated on both end faces of the A0 magnet perpendicular to the c-axis with a coating weight ratio of 1.5%. The coated sintered NdFeB blank was placed in a vacuum furnace for infiltration treatment at a temperature of 900°C for 18 hours. After cooling, it was subjected to aging treatment at a temperature of 515°C for 4.5 hours in a vacuum furnace to obtain a NdFeB product.

[0095] Comparative Example 3

[0096] The preparation method of the NdFeB product of Comparative Example 3 is as follows:

[0097] S1: Select a 52M NdFeB magnet blank with a magnetic property Br of 14.37 kGs, an Hcj of 16.24 kOe, and a specification of 19 mm * 18 mm * 35 mm. Cut it along the vertical orientation direction to form a magnet with an outer dimension of 19 mm * 18 mm * 4.6 mm and mark it as A0. Degrease, pickle, and dry A0.

[0098] S2: The alloy powder composition is Tb 85 Ni5Al 10 The alloy infiltration source K2 is dispersed in ethanol, and a binder polyacrylate is added to obtain a slurry. The K2 slurry is coated on the two end faces of the A0 magnet perpendicular to the c-axis with a coating weight ratio of 1%. The coated sintered NdFeB blank is placed in a vacuum furnace for infiltration treatment at a temperature of 900°C for 18 hours; after cooling, it is aged in a vacuum furnace at a temperature of 515°C for 4.5 hours to obtain a NdFeB product.

[0099] Comparative Example 4

[0100] The preparation method of the NdFeB product of Comparative Example 4 is as follows:

[0101] S1: Select a 45H NdFeB magnet blank with a magnetic property Br of 13.52 kGs, an Hcj of 18.45 kOe, and a specification of 49 mm * 21 mm * 37 mm. Cut it along the orientation direction to form a magnet with an outer dimension of 49 mm * 21 mm * 2 mm and mark it as A0. Degrease, pickle, and dry A0.

[0102] S2: Disperse heavy rare earth Dy in ethanol, add binder polyacrylate to obtain slurry, and coat the Dy slurry on both end faces of the A0 magnet perpendicular to the c-axis with a coating weight ratio of 1.2% (the weight of the infiltration source Dy is 1.2% of the magnet A0). Place the coated sintered NdFeB blank in a vacuum furnace for infiltration treatment at a temperature of 900°C for 18 hours; after cooling, perform aging treatment in a vacuum furnace at a temperature of 515°C for 4.5 hours to obtain a NdFeB product.

[0103] Comparative Example 5

[0104] The preparation method of the NdFeB product of Comparative Example 5 is as follows:

[0105] S1: Select a 52M NdFeB magnet blank with a magnetic property Br of 14.37 kGs, an Hcj of 16.24 kOe, and a specification of 19 mm * 54 mm * 35 mm. Cut it along the orientation direction to form a magnet with an outer dimension of 19 mm * 2.05 mm * 35 mm, and mark it as A0. Degrease, pickle, and dry A0.

[0106] Same as Example 1.

[0107] S2: Disperse Tb in ethanol and add a binder such as polyacrylate to obtain a slurry. The Tb slurry is coated on the two end faces of the A0 magnet perpendicular to the c-axis (19mm*35mm faces) with a coating weight ratio of 1.1% (the weight of the infiltration source Tb is 1.1% of the magnet A0). The coated sintered NdFeB blank is placed in a vacuum furnace for infiltration treatment at a temperature of 900°C for 18 hours; after cooling, it is aged in a vacuum furnace at a temperature of 515°C for 4.5 hours, and double-end fine grinding is performed to obtain NdFeB magnet A1 with a specification of 19mm*2mm*35mm.

[0108] Dy was dispersed in ethanol, and a binder polyacrylate was added to obtain a slurry. The Dy slurry was then coated on both end faces of the A0 magnet perpendicular to the c-axis (19mm*35mm faces) with a coating weight ratio of 0.6% (the weight of the infiltration source Dy was 0.6% of the magnet A0). The coated sintered NdFeB blank was placed in a vacuum furnace for an infiltration treatment at a temperature of 900°C for 18 hours. After cooling, an aging treatment was performed in a vacuum furnace at a temperature of 515°C for 4.5 hours. By double-end fine grinding, NdFeB magnet A2 with a specification of 19mm*2mm*35mm was obtained.

[0109] S3-S4: Same as Example 1.

[0110] The NdFeB products of the comparative example and the embodiment were subjected to magnetic flux and motor demagnetization resistance tests, and the results are shown in Table 1.

[0111] Table 1 Magnetic flux and motor demagnetization resistance data of NdFeB products in comparative examples and embodiments

[0112]

[0113]

[0114] By comparing the magnetic flux and motor demagnetization resistance data of the final magnet products of Comparative Example 1 and Example 1, Comparative Example 4 and Example 5, and Comparative Example 5 and Example 1, it can be seen that the magnet product obtained by adopting the preparation process of the present invention can achieve service performance higher than or close to that of the overall magnet while reducing the use of heavy rare earths and lowering production costs.

[0115] Comparative Example 2-3 uses a low-cost diffusion source to directly prepare a monolithic magnet. The results show that the demagnetization rate of the magnet is greatly improved.

[0116] By comparing Example 1 and Example 2, and Example 5 and Example 6, it can be seen that when the coercive force of the non-demagnetization region differs too much from the coercive force of the easy-demagnetization region, the demagnetization resistance of the final motor of the spliced magnet increases significantly, and the service performance deteriorates significantly.

[0117] Comparing Example 1 with Examples 3-4, as well as Examples 5 and 7, it can be seen that if the proportion of magnet A2 in the non-demagnetization region in the combined magnet is too high, the motor's demagnetization resistance will also be too high. While a low proportion has no significant impact on service performance, it will increase the cost of the magnet material. Therefore, the proportion of magnets A1 and A2 in the combined magnet must be controlled within an appropriate range.

[0118] By comparing Example 1, Example 9, Example 5, and Example 8, it can be seen that if the thickness of magnet A1 and / or A2 is too large, the demagnetization resistance of the motor of the final magnet will be too high.

[0119] The various aspects, embodiments, and features of the present invention should be considered in all respects as illustrative and not limiting, the scope of which is defined solely by the claims. Other embodiments, modifications, and uses will be apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.

[0120] In the preparation method of the present invention, the order of the steps is not limited to the order listed. Persons skilled in the art will appreciate that variations in the order of the steps are within the scope of the present invention without inventive effort. Furthermore, two or more steps or actions may be performed simultaneously.

[0121] Finally, it should be noted that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit its implementation. Persons skilled in the art may make various modifications, additions, or substitute similar methods for the described specific embodiments. It is not necessary and impossible to provide comprehensive examples of all implementations here. However, obvious variations or modifications arising from the essential spirit of the present invention remain within the scope of protection of the present invention, and interpreting them as any additional limitations would be contrary to the spirit of the present invention.

Claims

1. A method for preparing a low demagnetization rate neodymium iron boron magnet, characterized in that: The following steps are involved: S1. Cutting the NdFeB magnet along the orientation direction to obtain a NdFeB magnet A0 with a thickness of 0.5 to 3.5 mm, wherein the angle between the cutting direction and the orientation direction is ≤5°; S2. Performing infiltration source coating, infiltration, and aging treatment on the surface-cleaned A0 magnet to obtain NdFeB magnets A1 and A2 with different coercive forces, wherein the coercive force of NdFeB magnet A1 is greater than that of NdFeB magnet A2, and the difference between the two is ≤3 kOe; S3. Stacking the A1 magnet and the A2 magnet to form a combined magnet A3, wherein the combined magnet A3 consists of m A1 magnets and n A2 magnets, and satisfies 0.4≤m / (m+n)≤0.6; wherein the A1 magnets are located at both ends of the combined magnet A3, and the number of A1 magnets at each end is ≥2, and the A2 magnet is located in the middle of the combined magnet A3; S4. Cut the combined magnet A3 along a cutting direction perpendicular to the orientation direction to obtain a final NdFeB magnet A4.

2. The preparation method according to claim 1, characterized in that The penetration source K1 used to obtain the NdFeB magnet A1 is: Pr x Co y Ga 100-x-y and HR 100-a Al a Mixed alloy powder, Pr x Co y Ga 100-x-y The mass fraction of is 30-50wt%; wherein, x is 70-90, y is 2-7, a is 8-15, and HR is Dy and / or Tb.

3. The preparation method according to claim 1, characterized in that The penetration source K2 used to obtain the NdFeB magnet A2 is: HR 100-b-c Ni b Al c ; wherein b is 2 to 7, c is 8 to 15, and HR is Dy and / or Tb.

4. The preparation method according to any one of claims 1 to 3, characterized in that The permeation source coating step includes: dispersing the permeation source in a solvent to form a slurry, and then coating the slurry on the surface of the A0 magnet; The slurry is coated on both end surfaces of the A0 magnet perpendicular to the c-axis.

5. The preparation method according to claim 2, characterized in that In the NdFeB magnet A1, the mass of the penetration source K1 is 1.15-1.7 wt% of the mass of the A0 magnet.

6. The preparation method according to claim 3, characterized in that In the NdFeB magnet A2, the mass of the penetration source K2 is 0.3-1.1 wt% of the mass of the magnet A0.

7. The preparation method according to claim 1, characterized in that The insulation temperature of the infiltration treatment is 850-950°C, and the insulation time is 9-20h.

8. The preparation method according to claim 1, characterized in that The holding temperature of the aging treatment is 450-550°C, and the holding time is 3-6 hours.

9. The preparation method according to claim 1, characterized in that The stacking method is: the A1 magnets, the A2 magnets, and the A1 and A2 magnets are connected through end faces perpendicular to the c-axis, and then stacked in sequence to form a combined magnet A3.

10. A neodymium iron boron magnet with low demagnetization rate, characterized in that: It is prepared by the preparation method described in claim 1.

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