Method for increasing the coercivity of neodymium-iron-boron magnets and magnets produced by this method

Abstract

The application relates to the field of neodymium-iron-boron preparation technology, in particular to a method for improving the coercive force of a neodymium-iron-boron magnet and a magnet prepared by the method, and the specific method is as follows: (S1) preparing heavy rare earth slurry by mixing and stirring heavy rare earth diffusion source powder, an organic binder, spherical high-temperature-resistant ceramic powder and an organic solvent; (S2) coating the heavy rare earth slurry onto the surface of a neodymium-iron-boron magnet and drying to form a heavy rare earth coating; and (S3) high-temperature diffusion and aging treatment. The method for improving the coercive force of the neodymium-iron-boron magnet and the magnet prepared by the method have high hardness and strength of the heavy rare earth coating, the magnet is not easy to scratch and wear during the production process, shrinkage is not generated during the diffusion process, the supply of the heavy rare earth is stable, the performance of the neodymium-iron-boron magnet after diffusion is higher and more uniform, and the consumption of the heavy rare earth is low.

Description

Technical Field

[0001] This invention relates to the field of neodymium iron boron magnet production, and more particularly to a method for improving the coercivity of neodymium iron boron magnets and magnets prepared by the method. Background Technology

[0002] Neodymium iron boron (NdFeB) sintered permanent magnets are widely used in air conditioning, automobiles, medical and industrial fields. With the development of technology, NdFeB sintered permanent magnets are required to be smaller and thinner, while also needing to have higher remanence and coercivity.

[0003] In the alloy of NdFeB sintered permanent magnets, the coercivity of NdFeB sintered permanent magnets can be improved by adding terbium and dysprosium. However, using the traditional composition ratio method will cause dysprosium or terbium to enter the main phase grains, which will significantly reduce its remanence and consume a large amount of heavy rare earth elements.

[0004] Chinese patent CN107578912A discloses a method for preparing neodymium iron boron (NdFeB) magnets with high coercivity. The method involves mixing heavy rare earth powder with an antioxidant, binder, and organic solvent to prepare a suspension, which is then coated onto the surface of the NdFeB magnet. After drying, high-temperature diffusion and aging treatment are performed to increase the magnet's coercivity. This method is widely used due to its high production efficiency and material utilization. However, the heavy rare earth coating prepared by this method has low hardness and strength, making it easily scratched or worn, resulting in localized heavy rare earth element deficiencies and affecting the diffusion effect. Furthermore, this type of coating layer is prone to irregular shrinkage during the diffusion heating process, causing localized heavy rare earth element deficiencies and excessive accumulation of heavy rare earth elements in some areas on the NdFeB magnet surface, resulting in poor uniformity of the NdFeB magnet's performance after diffusion.

[0005] When the coating on the surface of a NdFeB magnet diffuses at high temperatures, heavy rare earth elements are supplied in excess in a short period of time. This causes excessive reaction between the NdFeB magnet surface and the heavy rare earth elements, resulting in excessive consumption of heavy rare earth elements. Meanwhile, the interior of the NdFeB magnet suffers from poor diffusion due to insufficient supply of heavy rare earth elements. Ultimately, this leads to a significant difference in performance between the surface and the center of the magnet after diffusion, and an excessive total consumption of rare earth elements. Summary of the Invention

[0006] Purpose of the invention: In order to solve the problems of low hardness and strength of heavy rare earth coatings in the prior art, easy scratches and wear during production, easy shrinkage during diffusion, poor diffusion uniformity and large consumption of heavy rare earth due to excessive supply of heavy rare earth elements in a short period of time, the present invention provides a method for improving the coercivity of neodymium iron boron magnets and magnets prepared by the method.

[0007] Technical solution: To achieve the above objectives, the present invention provides a method for improving the coercivity of neodymium iron boron magnets.

[0008] Includes the following steps:

[0009] (S1) Prepare a heavy rare earth slurry by mixing and stirring heavy rare earth diffusion source powder, organic binder, spherical high-temperature resistant ceramic powder, and organic solvent. The particle size of the spherical high-temperature resistant ceramic powder is required to be 5-10 times that of the diffusion source powder, and the weight of the spherical high-temperature resistant ceramic powder is 10%-30% of the weight of the heavy rare earth diffusion source powder.

[0010] (S2) The above-mentioned heavy rare earth slurry is coated onto the surface of the neodymium iron boron magnet and dried to form a heavy rare earth coating. The heavy rare earth coating is composed of a basic skeleton structure of spherical high-temperature resistant ceramic powder. The heavy rare earth diffusion source powder is distributed in the gaps of the skeleton structure formed by the spherical high-temperature resistant ceramic powder and is distributed in a three-dimensional network.

[0011] (S3) The neodymium iron boron magnets coated with heavy rare earth elements are subjected to high-temperature diffusion and aging treatment under vacuum or argon protection conditions.

[0012] Preferably, in step (S1), the heavy rare earth diffusion source powder is at least one of pure terbium, pure dysprosium, dysprosium hydride, and terbium hydride powder, and the average particle size range of the heavy rare earth diffusion source powder is 2-10 μm.

[0013] Preferably, in step (S1), the organic adhesive is a resin-based adhesive or a rubber-based adhesive.

[0014] Preferably, in (S1), the organic solvent is a ketone, benzene, or ester solvent.

[0015] Preferably, in step (S1), the spherical high-temperature resistant ceramic powder is at least one of spherical alumina ceramic powder, spherical zirconia ceramic powder, and spherical boron nitride ceramic powder; the particle size range of the spherical high-temperature resistant ceramic powder is 10-100 μm.

[0016] Preferably, in step (S1), the total weight of the heavy rare earth diffusion source powder and the spherical high-temperature resistant ceramic powder accounts for 40%-80% of the heavy rare earth slurry, the weight of the organic binder accounts for 5%-10% of the heavy rare earth slurry, and the remainder is organic solvent.

[0017] Preferably, in step (S2), the heavy rare earth slurry is coated by screen printing or spraying.

[0018] Preferably, in step (S2), the weight of the heavy rare earth diffusion source powder in the heavy rare earth coating applied to the surface of the NdFeB magnet is 0.3%-1.5% of the weight of the NdFeB magnet.

[0019] Preferably, in step (S3), the diffusion temperature for high-temperature diffusion is 850-950℃ and the diffusion time is 3-48h; the aging temperature for aging treatment is 450-650℃ and the aging time is 3-10h.

[0020] The above method can be used to obtain a magnet with high coercivity, which includes a neodymium iron boron magnet and a heavy rare earth coating on the surface of the neodymium iron boron magnet; wherein the heavy rare earth coating includes a basic skeleton structure composed of spherical high-temperature resistant ceramic powder and heavy rare earth diffusion source powder filling the skeleton structure.

[0021] The present invention provides a method for improving the coercivity of a neodymium iron boron magnet and the magnet thereof, which has at least the following technical effects:

[0022] (1) By adding a certain proportion and size of spherical high-temperature resistant ceramic powder to the heavy rare earth slurry, the heavy rare earth coating formed after coating and drying has a special structure. This special structure includes a basic skeleton structure composed of spherical high-temperature resistant ceramic powder, and heavy rare earth diffusion sources distributed in a continuous three-dimensional network within the gaps of the skeleton structure. The spherical high-temperature resistant ceramic powder forming the basic skeleton structure in the heavy rare earth coating improves the overall hardness and strength of the film, enhances its wear resistance and scratch resistance, and prevents the shrinkage of the heavy rare earth film during the diffusion heating process. Therefore, the distribution of heavy rare earth is more uniform during the diffusion process.

[0023] (2) In the heavy rare earth coating, the heavy rare earth diffusion source exists in the gaps of the skeleton formed by the spherical high-temperature resistant ceramic powder and is in a continuous three-dimensional network. During the high-temperature diffusion process, the heavy rare earth diffusion source in the heavy rare earth coating layer continuously and stably diffuses to the NdFeB magnet along the gaps between the ceramic powders, eliminating the short-term oversupply of heavy rare earth diffusion source, improving diffusion performance and diffusion uniformity, and reducing the waste of heavy rare earth. In addition, the presence of spherical ceramic powder divides the heavy rare earth components in the heavy rare earth film layer into a uniform, continuous and network distribution, slowing down the diffusion of oxygen from the surface of the coating to the interior of the coating, and improving the oxidation resistance of the heavy rare earth coating.

[0024] (3) During the coating process, the addition of spherical ceramic powder increases the fluidity and suspension of the slurry, improves the coating accuracy and coating stability. In addition, the increase of ceramic powder improves the degassing channels in heavy rare earth, which is conducive to the volatilization of organic solvents in heavy rare earth slurry and improves production stability. Attached Figure Description

[0025] Figure 1 A schematic diagram showing the surface of a neodymium iron boron magnet after being coated with a heavy rare earth coating;

[0026] Figure 2 A schematic diagram of cutting a neodymium iron boron magnet along the diffusion direction;

[0027] exist Figure 1 In the diagram, 1 represents the neodymium iron boron magnet matrix; 2 represents the spherical high-temperature resistant ceramic powder; and 3 represents the heavy rare earth diffusion source.

[0028] exist Figure 2 In the diagram, #1 and #5 are the outermost samples along the diffusion direction, and #3 is the center sample along the diffusion direction. Detailed Implementation

[0029] The following combination Figures 1 to 2 The principles and features of the present invention are described, and the examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0030] Example 1

[0031] (S1) Using pure Tb powder with a particle size of 2μm as a heavy rare earth diffusion source, rubber-based adhesive, ketone-based organic solvent, and spherical alumina ceramic powder with a particle size of 10μm as raw materials for heavy rare earth slurry, pure Tb powder and spherical alumina powder are first mixed, wherein the weight of spherical alumina ceramic powder is 10% of the weight of pure Tb powder. The mixed powder is used as a diffusion source intermediate. Then, the diffusion source intermediate is mixed with rubber-based adhesive and ketone-based organic solvent at proportions of 40%, 5%, and 55%, respectively, and stirred evenly to prepare heavy rare earth slurry.

[0032] (S2) The above-mentioned heavy rare earth slurry is coated onto two 10*10mm surfaces of the above-mentioned 10*10*5mm NdFeB substrate using screen printing, and after drying, a heavy rare earth coating layer with a special structure is formed, and the weight ratio of heavy rare earth in the coating layer to the weight of the NdFeB substrate is controlled to be 0.8%; wherein, the NdFeB substrate is obtained by melting, powdering, molding, sintering and aging processes to obtain N48H grade blanks, and then processed to obtain a substrate with a size of 10*10*5mm.

[0033] (S3) The neodymium iron boron coated with heavy rare earth coating is subjected to diffusion aging under magnetic vacuum. The diffusion aging process is 850℃*48h+500℃*5h. After the diffusion is completed, the overall magnetic properties of the product are tested.

[0034] After diffusion, the product was cut into 5 pieces along the diffusion direction, and the magnetic properties of the magnets at different positions along the diffusion direction were tested.

[0035] To fully demonstrate the technical advantages of this patented solution compared to traditional coating and diffusion solutions, the following comparative example 1 is provided.

[0036] Comparative Example 1

[0037] (S1) Using pure Tb powder with a particle size of 2μm as a heavy rare earth diffusion source, rubber-based adhesive, and ketone-based organic solvent powder as raw materials for heavy rare earth slurry, the pure Tb powder diffusion source, rubber-based adhesive, and ketone-based organic solvent are mixed and stirred evenly at proportions of 40%, 5%, and 55% respectively to prepare heavy rare earth slurry.

[0038] (S2) The above-mentioned heavy rare earth slurry is coated onto two 10*10mm surfaces of the above-mentioned 10*10*5mm NdFeB substrate by screen printing, and then dried to form a heavy rare earth coating layer. The weight ratio of heavy rare earth in the coating layer to the weight of the NdFeB substrate is controlled to be 0.8%. The NdFeB substrate is an N48H grade blank obtained by melting, powdering, molding, sintering and aging processes, and then processed to obtain a substrate with a size of 10*10*5mm.

[0039] (S3) The neodymium iron boron magnet with the heavy rare earth coating is subjected to diffusion aging under vacuum. The diffusion process is 850℃*48h+500℃*5h. After the diffusion is completed, the overall magnetic properties of the product are tested.

[0040] After diffusion, the product was cut into 5 pieces along the diffusion direction, and the magnetic properties of the magnets at different positions along the diffusion direction were tested.

[0041] To compare the scratch resistance of the heavy rare earth coatings in the examples and comparative examples, the coated surfaces of the sample coated with the heavy rare earth coating in Example 1 and the sample coated with the heavy rare earth coating with a special structure in Comparative Example 1 were brought into contact and subjected to mutual friction test. The proportion of the area of ​​the heavy rare earth film layer on the surface of the samples in Example 1 and Comparative Example 1 that was scratched and exposed to the substrate was counted to the total coated area. The statistical data were recorded in Table 1 and named as scratch ratio.

[0042] To compare the shrinkage resistance of the heavy rare earth coatings in the high-temperature diffusion process in the examples and comparative examples, 100 pieces of each of the diffusion products in Example 1 and Comparative Example 1 were taken. The ratio of the number of samples with heavy rare earth film shrinkage after diffusion to the total number of samples was counted. The statistical data was recorded in Table 1 and named as shrinkage ratio.

[0043] The performance of the NdFeB magnet before diffusion, the overall performance of the NdFeB magnet after diffusion in Example 1, and the overall performance of the NdFeB magnet after diffusion in Example 1 are compared. The comparison table is as follows.

[0044] Table 1 compares the magnet performance obtained from Example 1 and Comparative Example 1.

[0045] Sample Name scratch ratio Shrinkage ratio Br(KGS) Hcj(KOe) Hk / Hcj N48H matrix / / 13.8 17.10 0.982 Example 1 0％ 0％ 13.62 27.50 0.975 Comparative Example 1 20％ 7％ 13.60 26.90 0.968

[0046] As shown in Table 1, the sample coated with the special structured heavy rare earth coating in Example 1 did not show any scratches during the mutual friction test with the sample coated with the heavy rare earth coating in Comparative Example 1, while the sample in Comparative Example 1 showed scratches in 20% of cases, indicating that the heavy rare earth coating in Example 1 has stronger scratch resistance. Furthermore, the heavy rare earth coating on the surface of the sample in Comparative Example 1 showed shrinkage in 7% of cases during high-temperature diffusion, while the heavy rare earth coating on the surface of the sample in Example 1 did not show any shrinkage during high-temperature diffusion, indicating that the heavy rare earth coating with the special structure prepared in Example 1 has stronger shrinkage resistance compared to the heavy rare earth coating prepared in Comparative Example 1.

[0047] As shown in Table 1, under the same heavy rare earth weight gain conditions, the Br content decreased by 0.18 kgs, Hcj increased by 10.4 kOe, and squareness decreased by 0.007 after magnet diffusion in Example 1. In Comparative Example 1, the Br content decreased by 0.2 kgs, Hcj increased by 9.8 kOe, and squareness decreased by 0.014 after magnet diffusion. These results indicate that both the diffusion schemes in Example 1 and Comparative Example 1 can improve the performance of NdFeB magnets. However, under the same heavy rare earth weight gain conditions, the scheme in Example 1 showed a smaller decrease in remanence, a greater increase in coercivity, and a smaller decrease in squareness.

[0048] The neodymium iron boron magnets before diffusion, the neodymium iron boron magnets after diffusion in Example 1, and the neodymium iron boron magnets after diffusion in Comparative Example 1 were all uniformly cut into 5 parts along the diffusion direction and their magnetic properties were tested. The uniformity of the magnet performance after diffusion was compared, and the comparison table is as follows.

[0049] Table 2 compares the uniformity of magnet performance obtained from Example 1 and Comparative Example 1.

[0050]

[0051]

[0052] As shown in Table 2, under the same heavy rare earth weighting and diffusion process conditions, the coercivity deviation between the outermost and center samples along the diffusion direction after magnet diffusion in Example 1 is 1.85 KOe, and the Hcj of the sample at the center is increased by 8.7 KOe compared to the matrix. In Comparative Example 1, the coercivity deviation between the outermost and center samples along the diffusion direction after magnet diffusion is 2.3 KOe, and the Hcj of the sample at the center is increased by 8 KOe compared to the matrix. Furthermore, the performance at the center of the magnet after diffusion in Example 1 is 0.7 KOe higher than that at the center of the magnet after diffusion in Comparative Example 1. Through the above comparison, it can be seen that the magnet diffusion depth in Example 1 is deeper and the diffusion is more uniform.

[0053] Example 2

[0054] (S1) Four raw materials were used as the raw materials for the heavy rare earth slurry: dysprosium hydride powder with a particle size of 5 μm and pure dysprosium powder were mixed in a 1:1 ratio. The raw materials were resin binder, ester organic solvent and spherical zirconia ceramic powder with a particle size of 35 μm. First, the heavy rare earth diffusion source powder and spherical zirconia powder were mixed, wherein the weight of zirconia ceramic powder was 15% of the weight of heavy rare earth diffusion source powder. The mixed powder was used as the diffusion source intermediate. Then, the diffusion source intermediate was mixed with resin binder and ester organic solvent in proportions of 60%, 10% and 30% respectively and stirred evenly.

[0055] (S2) The above-mentioned heavy rare earth slurry is screen-printed onto two 10*10mm surfaces of the 10*10*3mm NdFeB substrate, and dried to form a heavy rare earth coating layer with a special structure. The weight ratio of heavy rare earth in the coating layer to the weight of the NdFeB substrate is controlled to be 0.3%. The NdFeB substrate is an N55H grade blank obtained through melting, powdering, molding, sintering and aging processes.

[0056] The substrate is then processed to obtain a size of 10*10*3mm.

[0057] (S3) The neodymium iron boron magnet with the heavy rare earth coating is subjected to diffusion aging in an argon protective atmosphere. The diffusion process is 900℃*3h+450℃*3h. After the diffusion is completed, the overall magnetic properties of the product are tested.

[0058] The product after diffusion was uniformly cut into three pieces along the diffusion direction, and the magnetic properties of the magnets at different positions along the diffusion direction were tested. To fully demonstrate the technical advantages of this patented solution compared to traditional coating diffusion solutions, a comparative example 2 was provided.

[0059] (S1) Dysprosium hydride powder with a particle size of 5μm and pure dysprosium powder are mixed in a 1:1 ratio as heavy rare earth diffusion source powder. Resin binder and ester organic solvent are used as raw materials for heavy rare earth slurry. The heavy rare earth diffusion source powder, resin binder and ester organic solvent are mixed in proportions of 60%, 10% and 30% respectively and stirred evenly to prepare heavy rare earth slurry.

[0060] (S2) The above-mentioned heavy rare earth slurry is coated onto two 10*10mm surfaces of the above-mentioned 10*10*3mm NdFeB substrate using screen printing, and after drying, a heavy rare earth coating layer with a special structure is formed, and the weight ratio of heavy rare earth in the coating layer to the weight of the NdFeB substrate is controlled to be 0.3%; wherein, the NdFeB substrate is an N55H grade blank obtained through melting, powdering, molding, sintering and aging processes, and then processed to obtain a substrate with a size of 10*10*3mm.

[0061] (S3) The neodymium iron boron magnet with the heavy rare earth coating is subjected to diffusion aging in an argon protective atmosphere. The diffusion process is 900℃*3h+450℃*3h. After the diffusion is completed, the overall magnetic properties of the product are tested.

[0062] After diffusion, the product was cut into three pieces along the diffusion direction, and the magnetic properties of the magnets at different positions along the diffusion direction were tested.

[0063] To compare the scratch resistance of the heavy rare earth coatings in the examples and comparative examples, the coated surfaces of the sample coated with the heavy rare earth coating in Example 2 and the sample coated with the heavy rare earth coating with a special structure in Comparative Example 2 were brought into contact and subjected to mutual friction test. The proportion of the area of ​​the heavy rare earth film layer on the surface of the samples in Example 2 and Comparative Example 2 that was scratched and exposed to the substrate was counted to the total coated area. The statistical data were recorded in Table 3 and named as scratch ratio.

[0064] To compare the shrinkage resistance of the heavy rare earth coatings during high-temperature diffusion in the examples and comparative examples, 100 pieces of the diffused product from Example 2 and 100 pieces of the diffused product from Comparative Example 2 were taken respectively. The ratio of the number of samples with heavy rare earth film shrinkage after diffusion to the total number of samples was counted. The statistical data was recorded in Table 3 and named as shrinkage ratio.

[0065] The performance of the NdFeB magnet before diffusion, the overall performance of the NdFeB magnet after diffusion in Example 2, and the overall performance of the NdFeB magnet after diffusion in Example 2 are compared. The comparison table is as follows.

[0066] Table 3 compares the magnet performance obtained from Example 1 and Comparative Example 1.

[0067] Sample Name scratch ratio Shrinkage ratio Br(KGS) Hcj(KOe) Hk / Hcj N55H matrix / / 14.61 15.52 0.989 Example 2 0％ 0％ 14.52 19.33 0.981 Comparative Example 2 10％ 11％ 14.51 18.82 0.980

[0068] As shown in Table 3, the sample coated with the special structured heavy rare earth coating in Example 2 did not show any scratches during the mutual friction test with the sample coated with the heavy rare earth coating in Comparative Example 2, while the sample in Comparative Example 2 showed scratches, with a scratch rate of 10%. This indicates that the heavy rare earth coating in Example 2 has stronger scratch resistance. Furthermore, the heavy rare earth coating on the surface of the sample in Comparative Example 2 showed shrinkage in 11% during the high-temperature diffusion process, while the heavy rare earth coating on the surface of the sample in Example 2 did not show any shrinkage during the high-temperature diffusion process. This indicates that the heavy rare earth coating with the special structure prepared in Example 2 has stronger shrinkage resistance compared to the heavy rare earth coating prepared in Comparative Example 2.

[0069] As shown in Table 3, under the same heavy rare earth weight gain conditions, after magnet diffusion in Example 2, Br decreased by 0.09 kgs, Hcj increased by 3.81 kOe, and squareness decreased by 0.008. In Comparative Example 2, after magnet diffusion, Br decreased by 0.1 kgs, Hcj increased by 3.3 kOe, and squareness decreased by 0.009. These results indicate that both the diffusion schemes in Example 2 and Comparative Example 2 can improve the performance of NdFeB magnets; however, the scheme in Example 2, under the same heavy rare earth weight gain conditions, shows a greater increase in coercivity.

[0070] The neodymium iron boron magnets before diffusion, the neodymium iron boron magnets after diffusion in Example 2, and the neodymium iron boron magnets after diffusion in Comparative Example 2 were all uniformly cut into 3 parts along the diffusion direction and their magnetic properties were tested. The uniformity of the magnet performance after diffusion was compared, and the comparison table is as follows.

[0071] Table 4 compares the uniformity of magnet performance between Example 2 and Comparative Example 2.

[0072]

[0073]

[0074] As shown in Table 4, under the same heavy rare earth weighting and diffusion process conditions, the coercivity deviation between the outermost and innermost samples along the diffusion direction after magnet diffusion in Example 2 is 0.8 KOe, and the Hcj of the sample at the innermost position is 3 KOe higher than that of the matrix. In Comparative Example 2, the coercivity deviation between the outermost and innermost samples along the diffusion direction after magnet diffusion is 1.3 KOe, and the Hcj of the sample at the innermost position is 2.06 KOe higher than that of the matrix. In addition, the performance at the center of the magnet after diffusion in Example 2 is 0.94 KOe higher than that at the center of the magnet after diffusion in Comparative Example 2. Through the above comparison, it can be seen that the magnet diffusion depth in Example 2 is deeper and the diffusion is more uniform.

[0075] Example 3

[0076] (S1) Four raw materials were used as the raw materials for the heavy rare earth slurry: terbium hydride powder with a particle size of 10 μm as the heavy rare earth diffusion source, rubber-based adhesive, benzene-based organic solvent, and spherical boron nitride ceramic powder with a particle size of 100 μm. First, terbium hydride powder and spherical boron nitride powder were mixed, wherein the weight of boron nitride ceramic powder was 10% of the weight of terbium hydride powder. The mixed powder was used as the diffusion source intermediate. Then, the diffusion source intermediate was mixed with rubber-based adhesive and benzene-based organic solvent at proportions of 80%, 6%, and 14%, respectively, and stirred evenly to prepare the heavy rare earth slurry.

[0077] (S2) The above-mentioned heavy rare earth slurry is applied to two 10*10mm surfaces of the above-mentioned 10*10*6mm NdFeB substrate by spraying, and then dried to form a heavy rare earth coating layer with a special structure. The weight ratio of heavy rare earth in the coating layer to the weight of the NdFeB substrate is controlled to be 1.0%. The NdFeB substrate is an N55H grade blank obtained by melting, powdering, molding, sintering and aging processes, and then processed to obtain a substrate with a size of 10*10*6mm.

[0078] (S3) The neodymium iron boron magnet with the heavy rare earth coating is subjected to diffusion aging in an argon protective atmosphere. The diffusion process is 950℃*30h+600℃*10h. After diffusion, the overall magnetic properties of the product are tested.

[0079] The product after diffusion was uniformly cut into 5 pieces along the diffusion direction, and the magnetic properties of the magnets at different positions along the diffusion direction were tested. To fully demonstrate the technical advantages of this patented solution compared with the traditional coating diffusion solution, we also set up a comparative example 3.

[0080] Comparative Example 3

[0081] (S1) Using terbium hydride powder with a particle size of 10μm as a heavy rare earth diffusion source, rubber-based adhesive, and benzene-based organic solvent powder as raw materials for heavy rare earth slurry, the terbium hydride powder, rubber-based adhesive, and benzene-based organic solvent are mixed and stirred evenly at proportions of 80%, 6%, and 14% respectively to prepare heavy rare earth slurry.

[0082] (S2) The above-mentioned heavy rare earth slurry is applied to the two 10*10mm surfaces of the above-mentioned 10*10*6mm NdFeB substrate by spraying, and then dried to form a heavy rare earth coating layer with a special structure. The weight ratio of heavy rare earth in the coating layer to the weight of the NdFeB substrate is controlled to be 1.0%. The NdFeB substrate is an N55H grade blank obtained by smelting, powdering, molding, sintering and aging processes, and then processed to obtain a substrate with a size of 10*10*6mm.

[0083] (S3) The neodymium iron boron magnet with the heavy rare earth coating is subjected to diffusion aging in an argon protective atmosphere. The diffusion process is 950℃*30h+600℃*10h. After diffusion, the overall magnetic properties of the product are tested.

[0084] After diffusion, the product was cut into 5 pieces along the diffusion direction, and the magnetic properties of the magnets at different positions along the diffusion direction were tested.

[0085] To compare the scratch resistance of the heavy rare earth coatings in the examples and comparative examples, the samples coated with heavy rare earth coatings in Example 3 and the samples coated with heavy rare earth coatings with special structures in Comparative Example 3 were brought into contact and subjected to mutual friction tests. The proportion of the area of ​​the heavy rare earth film layer on the surface of the samples in Example 3 and Comparative Example 3 that was scratched and exposed to the substrate was counted to the total coating area. The statistical data was recorded in Table 5 and named as the scratch ratio.

[0086] To compare the shrinkage resistance of the heavy rare earth coatings during the high-temperature diffusion process in the examples and comparative examples, 100 pieces of the diffused product from Example 3 and 100 pieces of the diffused product from Comparative Example 3 were taken respectively. The ratio of the number of samples with heavy rare earth film shrinkage after diffusion to the total number of samples was counted. The statistical data was recorded in Table 5 and named as shrinkage ratio.

[0087] The performance of the NdFeB magnet before diffusion, the overall performance of the NdFeB magnet after diffusion in Example 3, and the overall performance of the NdFeB magnet after diffusion in Example 3 are compared as shown in Table 5 below.

[0088] Table 5 compares the magnet performance obtained from Example 1 and Comparative Example 1.

[0089] Sample Name scratch ratio Shrinkage ratio Br(KGS) Hcj(KOe) Hk / Hcj N55H matrix / / 14.61 15.52 0.989 Example 3 0％ 0％ 14.38 26.8 0.980 Comparative Example 3 9％ 6％ 14.36 26 0.975

[0090] As shown in Table 5, the sample coated with the special structured heavy rare earth coating in Example 3 did not show any scratches during the mutual friction test with the sample coated with the heavy rare earth coating in Comparative Example 3, while the sample in Comparative Example 3 showed scratches, with a scratch rate of 9%. This indicates that the heavy rare earth coating in Example 3 has stronger scratch resistance. Furthermore, the heavy rare earth coating on the surface of the sample in Comparative Example 3 showed shrinkage in 6% of cases during high-temperature diffusion, while the heavy rare earth coating on the surface of the sample in Example 3 did not show any shrinkage during high-temperature diffusion. This indicates that the heavy rare earth coating with the special structure prepared in Example 3 has stronger shrinkage resistance compared to the heavy rare earth coating prepared in Comparative Example 3.

[0091] As shown in Table 5, under the same heavy rare earth weight gain conditions, the Br content decreased by 0.23 kgs, Hcj increased by 11.28 kOe, and squareness decreased by 0.009 after magnet diffusion in Example 3. In Comparative Example 3, the Br content decreased by 0.25 kgs, Hcj increased by 10.48 kOe, and squareness decreased by 0.014 after magnet diffusion. These results indicate that both the diffusion schemes in Example 3 and Comparative Example 3 can improve the performance of NdFeB magnets; however, the scheme in Example 3 shows a greater increase in coercivity under the same heavy rare earth weight gain conditions.

[0092] The neodymium iron boron magnets before diffusion, the neodymium iron boron magnets after diffusion in Example 3, and the neodymium iron boron magnets after diffusion in Comparative Example 3 were all uniformly cut into 5 parts along the diffusion direction and their magnetic properties were tested. The uniformity of the magnet performance after diffusion was compared, and the comparison table is as follows.

[0093] Table 6 compares the uniformity of magnet performance obtained from Example 1 and Comparative Example 1.

[0094]

[0095]

[0096] As shown in Table 6, under the same heavy rare earth weighting and diffusion process conditions, the coercivity deviation between the outermost and center samples along the diffusion direction after magnet diffusion in Example 3 is 1.7 KOe, and the Hcj of the sample at the center is 10 KOe higher than that of the matrix. In Comparative Example 3, the coercivity deviation between the outermost and center samples along the diffusion direction after magnet diffusion is 2.55 KOe, and the Hcj of the sample at the center is 8.8 KOe higher than that of the matrix. In addition, the performance at the center of the magnet after diffusion in Example 3 is 1.2 KOe higher than that at the center of the magnet after diffusion in Comparative Example 3. Through the above comparison, it can be seen that the magnet diffusion depth in Example 3 is deeper and the diffusion is more uniform.

[0097] Example 4

[0098] (S1) Four raw materials were used as heavy rare earth slurry: terbium hydride powder with a particle size of 5 μm as the heavy rare earth diffusion source, resin binder, ester organic solvent, and spherical zirconia ceramic powder with a particle size of 50 μm. First, terbium hydride powder and spherical zirconia powder were mixed, with the weight of zirconia ceramic powder being 30% of the weight of terbium hydride powder. The mixed powder was used as the diffusion source intermediate. Then, the diffusion source intermediate was mixed with resin binder and ester organic solvent in proportions of 60%, 8%, and 32%, respectively, and stirred evenly to prepare the heavy rare earth slurry.

[0099] (S2) The above-mentioned heavy rare earth slurry is applied to the two 10*10mm surfaces of the above-mentioned 10*10*8mm NdFeB substrate by spraying, and then dried to form a heavy rare earth coating layer with a special structure. The weight ratio of heavy rare earth in the coating layer to the weight of the NdFeB substrate is controlled to be 1.5%. The NdFeB substrate is obtained by smelting, powdering, molding, sintering and aging processes to obtain N42H grade blanks, and then processed to obtain a substrate with a size of 10*10*8mm.

[0100] (S3) The neodymium iron boron magnet coated with heavy rare earth coating is subjected to diffusion aging under vacuum. The diffusion process is 900℃*40h+650℃*8h. After diffusion, the overall magnetic properties of the product are tested.

[0101] The product after diffusion was uniformly cut into 5 pieces along the diffusion direction, and the magnetic properties of the magnets at different positions along the diffusion direction were tested. To fully demonstrate the technical advantages of this patented solution compared to traditional coating diffusion solutions, a comparative example 4 was provided.

[0102] Comparative Example 4

[0103] (S1) Using terbium hydride powder with a particle size of 5μm as a heavy rare earth diffusion source, resin binder and ester organic solvent as raw materials for heavy rare earth slurry, terbium hydride powder, resin binder and ester organic solvent are mixed and stirred evenly in proportions of 60%, 8% and 32% respectively to prepare heavy rare earth slurry.

[0104] (S2) The above-mentioned heavy rare earth slurry is applied to the two 10*10mm surfaces of the above-mentioned 10*10*8mm NdFeB substrate by spraying, and then dried to form a heavy rare earth coating layer with a special structure. The weight ratio of heavy rare earth in the coating layer to the weight of the NdFeB substrate is controlled to be 1.5%. The NdFeB substrate is an N42H grade blank obtained by melting, powdering, molding, sintering and aging processes, and then processed to obtain a substrate with a size of 10*10*8mm.

[0105] (S3) The neodymium iron boron magnet coated with heavy rare earth coating is subjected to diffusion aging under vacuum. The diffusion process is 900℃*40h+650℃*8h. After diffusion, the overall magnetic properties of the product are tested.

[0106] After diffusion, the product was cut into 5 pieces along the diffusion direction, and the magnetic properties of the magnets at different positions along the diffusion direction were tested.

[0107] To compare the scratch resistance of the heavy rare earth coatings in the examples and comparative examples, the coated surfaces of the sample coated with the heavy rare earth coating in Example 4 and the sample coated with the heavy rare earth coating with a special structure in Comparative Example 4 were brought into contact and subjected to mutual friction test. The proportion of the area of ​​the heavy rare earth film layer on the surface of the samples in Example 4 and Comparative Example 4 that was scratched and exposed to the substrate was counted to the total coated area. The statistical data were recorded in Table 7 and named as scratch ratio.

[0108] To compare the shrinkage resistance of the heavy rare earth coatings during the high-temperature diffusion process in the examples and comparative examples, 100 pieces of the diffused product from Example 4 and 100 pieces of the diffused product from Comparative Example 4 were taken respectively. The ratio of the number of samples with heavy rare earth film shrinkage after diffusion to the total number of samples was counted. The statistical data was recorded in Table 7 and named as shrinkage ratio.

[0109] The performance of the NdFeB magnet before diffusion, the overall performance of the NdFeB magnet after diffusion in Example 4, and the overall performance of the NdFeB magnet after diffusion in Example 4 are compared. The comparison table is as follows.

[0110] Table 7 Comparison of magnet performance obtained from Example 1 and Comparative Example 1.

[0111] Sample Name scratch ratio Shrinkage ratio Br(KGS) Hcj(KOe) Hk / Hcj N42H matrix / / 13.20 18.05 0.981 Example 4 0％ 0％ 12.92 30 0.972 Comparative Example 4 21％ 13％ 12.88 29.45 0.968

[0112] As shown in Table 7, the sample coated with the special structured heavy rare earth coating in Comparative Example 4 did not show any scratches during the mutual friction test with the sample coated with the heavy rare earth coating in Example 4, while the sample in Example 4 showed scratches, with a scratch rate of 21%. This indicates that the heavy rare earth coating in Comparative Example 4 has stronger scratch resistance. Furthermore, the heavy rare earth coating on the surface of the sample in Example 4 showed shrinkage in 13% of cases during high-temperature diffusion, while the heavy rare earth coating on the surface of the sample in Comparative Example 4 did not show any shrinkage during high-temperature diffusion. This indicates that the heavy rare earth coating with the special structure prepared in Comparative Example 4 has stronger shrinkage resistance compared to the heavy rare earth coating prepared in Example 4.

[0113] As shown in Table 7, under the same heavy rare earth weight gain conditions, after magnet diffusion in Example 4, Br decreased by 0.28 kgs, Hcj increased by 11.95 kOe, and squareness decreased by 0.009. In Comparative Example 4, after magnet diffusion, Br decreased by 0.32 kgs, Hcj increased by 11.4 kOe, and squareness decreased by 0.013. These results indicate that both the diffusion schemes in Example 4 and Comparative Example 4 can improve the performance of NdFeB magnets; however, the scheme in Example 4, under the same heavy rare earth weight gain conditions, shows a greater increase in coercivity.

[0114] The neodymium iron boron magnets before diffusion, the neodymium iron boron magnets after diffusion in Example 4, and the neodymium iron boron magnets after diffusion in Comparative Example 4 were all uniformly cut into 5 parts along the diffusion direction and their magnetic properties were tested. The uniformity of the magnet performance after diffusion was compared, and the comparison table is as follows: Table 8.

[0115] Table 8 compares the uniformity of magnet performance obtained from Example 1 and Comparative Example 1.

[0116]

[0117]

[0118] As shown in Table 8, under the same heavy rare earth weighting and diffusion process conditions, the coercivity deviation between the outermost and center samples along the diffusion direction after magnet diffusion in Example 4 is 2.81 KOe, and the Hcj of the sample at the center is 10.02 KOe higher than that of the matrix. In Comparative Example 4, the coercivity deviation between the outermost and center samples along the diffusion direction after magnet diffusion is 3.75 KOe, and the Hcj of the sample at the center is 9.09 KOe higher than that of the matrix. Furthermore, the performance at the center of the magnet in Example 4 after diffusion is 1.11 KOe higher than that at the center of the magnet in Comparative Example 4. These comparisons indicate that the magnet diffusion depth in Example 4 is deeper and the diffusion is more uniform.

[0119] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method of improving the coercivity of a neodymium-iron-boron magnet, characterized in that, It comprises the following steps: (S1) preparing a heavy rare earth slurry by mixing and stirring heavy rare earth diffusion source powder, organic binder, spherical high-temperature-resistant ceramic powder, organic solvent, wherein the particle size of the spherical high-temperature-resistant ceramic powder is 5-10 times that of the diffusion source powder, and the weight of the spherical high-temperature-resistant ceramic powder is 10%-30% of the weight of the heavy rare earth diffusion source powder; In the step (S1), the heavy rare earth diffusion source powder is at least one of pure terbium, pure dysprosium, dysprosium hydride, and terbium hydride powder, and the average particle size of the heavy rare earth diffusion source powder is 2-10 μm. In the step (S1), the organic binder is a resin-type binder or a rubber-type binder. In the step (S1), the organic solvent is a ketone, benzene, or lipid solvent.

2. The neodymium-iron-boron magnet coercivity boosting method according to claim 1, characterized in that, In the step (S1), the particle size of the spherical high-temperature-resistant ceramic powder is 10-100 μm.

3. The neodymium-iron-boron magnet coercivity boosting method of claim 1, wherein, In the step (S1), the total weight of the heavy rare earth diffusion source powder and the spherical high-temperature-resistant ceramic powder accounts for 40%-80% of the heavy rare earth slurry, the weight of the organic binder accounts for 5%-10% of the heavy rare earth slurry, and the rest is the organic solvent.

4. The neodymium-iron-boron magnet coercivity boosting method of claim 1, wherein, In the step (S2), the heavy rare earth slurry is coated by screen printing or spraying.

5. The neodymium-iron-boron magnet coercivity boosting method of claim 1, wherein, In the step (S2), the weight of the heavy rare earth diffusion source powder in the heavy rare earth coating coated on the surface of the Nd-Fe-B magnet is 0.3%-1.5% of the weight of the Nd-Fe-B magnet.

6. The neodymium-iron-boron magnet coercivity boosting method of claim 1, wherein, In the step (S3), the diffusion temperature of the high-temperature diffusion is 850-950 ℃, and the diffusion time is 3-48 h; the aging temperature of the aging treatment is 450-650 ℃, and the aging time is 3-10 h.

7. The neodymium-iron-boron magnet coercivity boosting method of claim 1, wherein, It comprises a Nd-Fe-B magnet and a heavy rare earth coating arranged on the surface of the Nd-Fe-B magnet, wherein the heavy rare earth coating comprises a basic framework structure composed of spherical high-temperature-resistant ceramic powder and heavy rare earth diffusion source powder filled in the framework structure.

8. The neodymium-iron-boron magnet coercivity enhancing method according to claim 1 or 7, characterized in that, ​ 9. The neodymium-iron-boron magnet coercivity boosting method of claim 1, wherein, ​ 10. A magnet prepared using the method of claim 1-9, wherein, ​

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