A grain boundary diffusion method for sintered neodymium-iron-boron magnets

Abstract

The application belongs to the technical field of permanent magnet materials, and relates to a grain boundary diffusion method of sintered neodymium-iron-boron magnets, which comprises the following steps: applying a heavy rare earth alloy penetration source to a sintered neodymium-iron-boron blank, and then applying a light rare earth alloy penetration source; performing grain boundary diffusion treatment and tempering treatment; the light rare earth alloy penetration source comprises light rare earth alloy powder, and the composition is Nd A Al 100‑A , wherein 80wt% <= A <= 90wt%; the heavy rare earth alloy penetration source comprises heavy rare earth alloy powder, and the composition is (Pr C Nd 100‑C ) B Tb 100‑B , wherein 50wt% <= B <= 60wt%, and 20wt% <= C <= 30wt%; the average particle size of the light rare earth alloy powder is smaller than that of the heavy rare earth alloy powder. By adopting the grain boundary diffusion method, the use amount of heavy rare earth is greatly reduced, the coercivity is greatly improved, the consistency of the coercivity of the magnet is effectively improved, and the difference in the coercivity between different diffusion magnets is reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of permanent magnet materials, and relates to a grain boundary diffusion method of sintered neodymium-iron-boron magnets. BACKGROUND

[0002] In recent years, with the rapid development of new energy vehicles, wind power generation, electro-acoustic equipment and other fields, the demand for high-performance sintered neodymium-iron-boron magnets has shown a significant growth trend. These fields not only require magnets to have excellent magnetic properties, but also put forward higher requirements for cost control. In the face of increasingly fierce market competition, how to develop low-cost and high-performance neodymium-iron-boron magnets has become one of the important topics in the industry. Under this background, the grain boundary diffusion technology has attracted the attention of many enterprises and research institutions due to its characteristics of significantly reducing the use of heavy rare earth while greatly improving the coercivity of the magnet.

[0003] At present, although the grain boundary diffusion technology has achieved effective utilization of heavy rare earth resources to some extent, there are still some problems to be solved. One of the most prominent problems is the poor uniformity of the distribution of heavy rare earth in the magnet, which is specifically manifested as follows: high heavy rare earth aggregation content in the surface layer of the magnet penetration direction: in the surface layer of the magnet, heavy rare earth elements are prone to excessive aggregation, resulting in a heavy rare earth content in this part of the region that is much higher than that in the internal region; low internal heavy rare earth content: in comparison, the heavy rare earth content in the internal region of the magnet is significantly lower, which directly affects the performance consistency of the overall magnet; heavy rare earth enrichment in the grain boundary triangle region: in the grain boundary triangle region, heavy rare earth elements are also prone to excessive enrichment, which may cause abnormal local magnetic properties.

[0004] These problems not only cause waste of heavy rare earth resources, but also fail to fully utilize the role of heavy rare earth elements in improving the coercivity of the magnet. Therefore, it is urgent to develop a new grain boundary diffusion technology to achieve more efficient and uniform distribution of heavy rare earth elements, thereby reducing the use of heavy rare earth, improving the penetration efficiency, and ultimately improving the overall performance of the sintered neodymium-iron-boron magnet. SUMMARY

[0005] To solve the above problems in the prior art, the purpose of the present application is to provide a grain boundary diffusion method of sintered neodymium-iron-boron magnets to overcome the shortcomings of the prior art.

[0006] The purpose of the present application is achieved by the following technical solutions:

[0007] A grain boundary diffusion method of sintered neodymium-iron-boron magnets, comprising the following steps:

[0008] applying a first layer of heavy rare earth alloy penetration source to the sintered neodymium-iron-boron blank, and then applying a second layer of light rare earth alloy penetration source;

[0009] The coated sintered neodymium-iron-boron blank is subjected to grain boundary diffusion treatment and tempering treatment;

[0010] The light rare earth alloy permeation source comprises a light rare earth alloy powder, and a composition of the light rare earth alloy powder is Nd A Al 100-A , wherein 80wt%≤A≤90wt%;

[0011] The heavy rare earth alloy permeation source comprises a heavy rare earth alloy powder, and a composition of the heavy rare earth alloy powder is (Pr C Nd 100-C ) B Tb 100-B , wherein 50wt%≤B≤60wt%, 20wt%≤C≤30wt%;

[0012] The average particle size of the light rare earth alloy powder is smaller than the average particle size of the heavy rare earth alloy powder.

[0013] The sintered neodymium-iron-boron blank needs to be pretreated before the permeation source is applied. The pretreatment steps include one or both of degreasing and pickling, and then drying. Degreasing, i.e. cleaning with a solvent or chemical cleaner, removes organic matter and grease from the surface of the blank. Pickling, using an acid solution, removes oxides and rust from the surface. Through these pretreatment steps, the cleanliness and reactivity of the surface of the sintered neodymium-iron-boron blank can be effectively improved, thereby ensuring the successful implementation of subsequent plating or other surface treatment processes.

[0014] The composition of the sintered neodymium-iron-boron blank is not particularly limited, and as an enumeration, the composition of the sintered neodymium-iron-boron blank includes, by mass percentage: Pr 3-10%, Nd 23-30%, HREE 0.5-5%, TM 0-3%, B 0.5-2%, and the balance being Fe; wherein HREE is one or more of Gd, Tb, Dy, Ho, Er, Yb, and TM is one or more of Cu, Ga, Zr, Al, Ti, Co, Cr, Mn.

[0015] Preferably, the heavy rare earth alloy permeation source is applied to the two end faces of the sintered neodymium-iron-boron blank perpendicular to the c-axis, and the light rare earth alloy permeation source is applied to the heavy rare earth alloy permeation source. In the sintered neodymium-iron-boron blank, the c-axis direction is the easy magnetization direction of the magnet.

[0016] Preferably, the heavy rare earth alloy permeation source comprises a heavy rare earth alloy powder, a binder, and an organic solvent.

[0017] Preferably, the heavy rare earth alloy powder accounts for 50-70wt% of the heavy rare earth alloy permeation source, and the binder accounts for 1-8wt% of the heavy rare earth alloy permeation source.

[0018] Preferably, the light rare earth alloy penetration source comprises light rare earth alloy powder, a binder and an organic solvent.

[0019] Preferably, the light rare earth alloy powder accounts for 50-70wt% of the light rare earth alloy penetration source, and the binder accounts for 1-8wt% of the light rare earth alloy penetration source.

[0020] Preferably, the binder is a thermoplastic resin, which is one or more of polyvinyl butyral, polyvinyl acetal and polyvinyl alcohol, and the organic solvent is an ester, a ketone or an alcohol, etc.

[0021] Preferably, the average particle size of the light rare earth alloy powder is 2-4um, and the average particle size of the heavy rare earth alloy powder is 4-6um.

[0022] Preferably, the light rare earth alloy powder and the heavy rare earth alloy powder are obtained by sequentially performing melting, rapid solidification, hydrogen fragmentation and air flow grinding.

[0023] Preferably, the coating amount of the heavy rare earth alloy penetration source is 0.4-0.6wt% of the sintered neodymium-iron-boron blank.

[0024] Preferably, the coating amount of the light rare earth alloy penetration source is 0.4-0.8wt% of the sintered neodymium-iron-boron blank.

[0025] Preferably, the holding temperature of the grain boundary diffusion treatment is 850-950℃, and the holding time is 8-14h.

[0026] Preferably, during the grain boundary diffusion treatment, the vacuum degree in the sintering furnace is ≤1*10 -2 Pa, and after the holding is completed, an inert atmosphere is filled to cool to room temperature.

[0027] Preferably, the holding temperature of the tempering treatment is 450-550℃, and the holding time is 2-5h.

[0028] Preferably, during the tempering treatment, the vacuum degree in the sintering furnace is ≤1*10 -2 Pa, and after the holding is completed, an inert atmosphere is filled to cool to room temperature.

[0029] The inert atmosphere is one or both of nitrogen and argon.

[0030] Compared with the prior art, the present application has the following beneficial effects:

[0031] (1) The present application utilizes the advantages of low melting point and strong diffusion ability of the light rare earth alloy permeation source as the outer coating layer. In the case where the first layer of heavy rare earth alloy permeation source has occupied most of the grain boundary diffusion channels, the light rare earth alloy permeation source partially replaces the outer layer of heavy rare earth alloy permeation source. The light rare earth elements can more easily and effectively diffuse around the grains to form a shell layer, although the composition does not contain heavy rare earth elements, but the coercivity improvement effect close to that of the outer coating heavy rare earth alloy permeation source can be achieved.

[0032] (2) The present application controls the composition, particle size and coating weight ratio of the two permeation source powders of the composite permeation, and comprehensively considers the permeation efficiency, oxidation prevention and post-permeation magnetic properties, etc. to obtain the best matching process. This optimization enables the composite permeation process to more effectively utilize heavy rare earth elements, while reducing the amount of heavy rare earth elements while maintaining the coercivity improvement effect.

[0033] (3) The composite permeation process of the present application is beneficial to the uniform diffusion of elements, which can effectively improve the consistency of the coercivity of the magnet, and reduce the difference in coercivity between different diffusion magnets.

[0034] (4) The present application adopts the method of organic slurry coating, which can be well applied to >5mm substrate magnetic material, making the whole grain boundary diffusion process operation more simple and convenient, and is conducive to large-scale production.

[0035] In summary, by using the grain boundary diffusion method of the present application, the amount of heavy rare earth elements is greatly reduced while the coercivity is greatly improved, the cost of magnet production is effectively reduced, the consistency of the coercivity of the magnet is effectively improved, the difference in coercivity between different diffusion magnets is reduced, and the application of neodymium iron boron magnets in the market is widened. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 (a) and (b) are the coating sequence effect diagrams of the light rare earth alloy permeation source and the heavy rare earth alloy permeation source of the present application and the light rare earth alloy permeation source and the heavy rare earth alloy permeation source of Comparative Examples 19-23.

[0037] Figure 2 (a) is the SEM diagram and EPMA point scanning schematic diagram of the magnet of Example 1, and (b) is the SEM diagram and EPMA point scanning schematic diagram of the magnet of Comparative Example 2.

[0038] Figure 3 (a) is the SEM diagram and EPMA point scanning schematic diagram of the magnet with the highest coercivity, and (b) is the SEM diagram and EPMA point scanning schematic diagram of the magnet with the lowest coercivity. DETAILED DESCRIPTION

[0039] The technical solutions of the present application are further described and illustrated below by means of specific examples and drawings. It should be understood that the specific examples described herein are only used to help understand the present application and are not used to limit the present application. The drawings used herein are only used to better illustrate the disclosed content of the present application and do not limit the scope of protection. If not otherwise specified, the raw materials used in the examples of the present application are all commonly used raw materials in the art, and the methods used in the examples are all conventional methods in the art.

[0040] Example 1

[0041] The grain boundary diffusion method of the sintered neodymium-iron-boron magnet of the present example comprises the following steps:

[0042] 1) A 45SH blank with a composition of (Pr 20％ Nd 80％ ) 31％ Dy 2％ Cu 0.12％ Ga 0.2％ Zr 0.15％ Al 0.25％ Co 1.2％ B 0.93％ Fe 64.15％ is cut into an outer size of 20mm*20mm*6mm and marked as A0, and the surface thereof is subjected to oil removal, pickling, and drying treatment.

[0043] 2) A heavy rare earth alloy penetration source is coated as a first layer on the two end faces of the blank perpendicular to the c-axis, and the coating amount is 0.5wt% of the blank, and a light rare earth alloy penetration source is coated as a second layer on the heavy rare earth alloy penetration source, and the coating amount is 0.5wt% of the blank, and the specific implementation effect can be seen from Figure 1 (a).

[0044] 3) The coated sintered neodymium-iron-boron blank is placed in a vacuum sintering furnace, and when the vacuum degree of the vacuum sintering furnace reaches 1*10 -3 Pa order of magnitude, heating is started, and diffusion treatment is carried out at 900℃ for 12h, and after the heat preservation is completed, argon is filled to cool to room temperature. Then when the vacuum degree of the vacuum sintering furnace reaches 1*10 -3 Pa order of magnitude, heating is started, and tempering treatment is carried out at 515℃ for 4h, and after the heat preservation is completed, argon is filled to cool to room temperature. The magnet is taken out of the vacuum sintering furnace and marked as A1.

[0045] The preparation method of the light rare earth alloy penetration source comprises the following steps: according to the composition of Nd 85 Al 15The heavy rare earth alloy permeation source is prepared by sequentially performing melting, rapid solidification, hydrogen crushing and jet milling to obtain a heavy rare earth alloy powder with an average particle size of 5.4 um, and then adding a binder polyvinyl butyral and an organic solvent butanol to obtain the heavy rare earth alloy permeation source, wherein the heavy rare earth alloy powder accounts for 50 wt% of the heavy rare earth alloy permeation source, and the binder accounts for 3 wt% of the heavy rare earth alloy permeation source.

[0046] The preparation method of the heavy rare earth alloy permeation source comprises the following steps: cutting a 45SH blank with a composition of (Pr 25 Nd 75 ) 60 Tb 40 The heavy rare earth alloy permeation source is prepared by sequentially performing melting, rapid solidification, hydrogen crushing and jet milling to obtain a heavy rare earth alloy powder with an average particle size of 5.4 um, and then adding a binder polyvinyl butyral and an organic solvent butanol to obtain the heavy rare earth alloy permeation source, wherein the heavy rare earth alloy powder accounts for 50 wt% of the heavy rare earth alloy permeation source, and the binder accounts for 3 wt% of the heavy rare earth alloy permeation source.

[0047] Example 2

[0048] The grain boundary diffusion method of the sintered neodymium-iron-boron magnet in this embodiment comprises the following steps:

[0049] 1) A 45SH blank with a composition of (Pr 20％ Nd 80％ ) 31％ Dy 2％ Cu 0.12％ Ga 0.2％ Zr 0.15％ Al 0.25％ Co 1.2％ B 0.93％ Fe 64.15％ is cut into an outer size of 20mm*20mm*6mm, and the surface is subjected to oil removal, pickling and drying treatment.

[0050] 2) The heavy rare earth alloy permeation source is coated as a first layer on the two end surfaces of the blank perpendicular to the c-axis, and the coating amount is 0.45 wt% of the blank, and the light rare earth alloy permeation source is coated as a second layer on the heavy rare earth alloy permeation source, and the coating amount is 0.6 wt% of the blank, and the specific implementation effect can be seen in Figure 1 (a).

[0051] 3) The coated sintered neodymium-iron-boron blank is placed in a vacuum sintering furnace, and when the vacuum degree of the vacuum sintering furnace reaches 1*10 -3 Pa order of magnitude, heating is started, and diffusion treatment is performed at 900℃ for 12h, and after the heat preservation is completed, argon is filled to cool to room temperature. Then when the vacuum degree of the vacuum sintering furnace reaches 1*10 -3Pa order of magnitude, start heating, tempering treatment at 515 DEG C for 4h, after holding end, fill argon cooling to room temperature. The magnet from vacuum sintering furnace, marked as A2.

[0052] The preparation method of the light rare earth alloy permeation source comprises the following steps: according to the composition of Nd 88 Al 12 , the light rare earth alloy powder with an average particle size of 2.7 um is prepared by sequentially performing melting, rapid solidification, hydrogen crushing and jet milling, the binder polyvinyl butyral and the organic solvent butanol are added and stirred uniformly to prepare the light rare earth alloy permeation source, wherein the light rare earth alloy powder accounts for 50 wt% of the light rare earth alloy permeation source, and the binder accounts for 3 wt% of the light rare earth alloy permeation source.

[0053] The preparation method of the heavy rare earth alloy permeation source comprises the following steps: according to the composition of (Pr 25 Nd 75 ) 50 Tb 50 , the heavy rare earth alloy powder with an average particle size of 4.6 um is prepared by sequentially performing melting, rapid solidification, hydrogen crushing and jet milling, the binder polyvinyl butyral and the organic solvent butanol are added and stirred uniformly to prepare the heavy rare earth alloy permeation source, wherein the heavy rare earth alloy powder accounts for 50 wt% of the heavy rare earth alloy permeation source, and the binder accounts for 3 wt% of the heavy rare earth alloy permeation source.

[0054] Comparative Example 1

[0055] The difference between Comparative Example 1 and Example 1 is that the heavy rare earth alloy permeation source is directly coated on the two end surfaces of the blank perpendicular to the c-axis in Comparative Example 1, the coating amount of the heavy rare earth alloy permeation source is 0.5 wt% of the blank, and no light rare earth alloy permeation source is coated. The grain boundary diffusion method of Comparative Example 1 specifically comprises the following steps:

[0056] 1) the same as step 1) of Example 1.

[0057] 2) the heavy rare earth alloy permeation source is coated as the first layer on the two end surfaces of the blank perpendicular to the c-axis, and the coating amount is 0.5 wt% of the blank.

[0058] 3) the same as step 3) of Example 1. The magnet is taken out from the vacuum sintering furnace and marked as A3.

[0059] Comparative Example 2

[0060] The difference between Comparative Example 2 and Comparative Example 1 is only that the coating amount of the heavy rare earth alloy permeation source in Comparative Example 2 is 1 wt% of the blank, and the others are the same as those in Comparative Example 1. The finally prepared diffusion magnet is marked as A4.

[0061] Comparative Examples 3-6

[0062] The difference between Comparative Example 3, Comparative Example 4 and Example 1 is only that the average particle size of the light rare earth alloy powder of Comparative Example 3, Comparative Example 4 is different from that of Example 1, and the others are the same as Example 1, and the specific average particle size of Comparative Example 3, Comparative Example 4 is shown in Table 1, and the prepared diffusion magnets are respectively marked as A5, A6; The difference between Comparative Example 5, Comparative Example 6 and Example 1 is only that the average particle size of the heavy rare earth alloy powder of Comparative Example 5, Comparative Example 6 is different from that of Example 1, and the others are the same as Example 1, and the specific average particle size of Comparative Example 5, Comparative Example 6 is shown in Table 1, and the prepared diffusion magnets are respectively marked as A7, A8.

[0063] Table 1 Infiltration process parameters of Example 1, Comparative Examples 3-6

[0064]

[0065] Comparative Examples 7-10

[0066] The difference between Comparative Example 7, Comparative Example 8 and Example 2 is only that the composition content of the light rare earth alloy powder of Comparative Example 7, Comparative Example 8 is different from that of Example 2, and the others are the same as Example 2, and the specific composition content of the light rare earth alloy powder of Comparative Example 7, Comparative Example 8 is shown in Table 2, and the prepared diffusion magnets are respectively marked as A9, A10; The difference between Comparative Example 9, Comparative Example 10 and Example 2 is only that the composition content of the heavy rare earth alloy powder of Comparative Example 9, Comparative Example 10 is different from that of Example 2, and the others are the same as Example 2, and the specific composition content of the heavy rare earth alloy powder of Comparative Example 9, Comparative Example 10 is shown in Table 2, and the prepared diffusion magnets are respectively marked as A11, A12.

[0067] Table 2 Infiltration process parameters of Example 2, Comparative Examples 7-10

[0068]

[0069] Comparative Examples 11-14

[0070] The difference between Comparative Example 11, Comparative Example 12 and Example 1 is only that the coating amount of the light rare earth alloy infiltration source of Comparative Example 11, Comparative Example 12 is different from that of Example 1, and the others are the same as Example 1, and the specific coating amount of the light rare earth alloy infiltration source of Comparative Example 11, Comparative Example 12 is shown in Table 3, and the prepared diffusion magnets are respectively marked as A13, A14; The difference between Comparative Example 13, Comparative Example 14 and Example 1 is only that the coating amount of the heavy rare earth alloy infiltration source of Comparative Example 13, Comparative Example 14 is different from that of Example 1, and the others are the same as Example 1, and the specific coating amount of the heavy rare earth alloy infiltration source of Comparative Example 13, Comparative Example 14 is shown in Table 3, and the prepared diffusion magnets are respectively marked as A15, A16.

[0071] Table 3 Infiltration process parameters of Example 1, Comparative Examples 11-14

[0072]

[0073]

[0074] Comparative Example 15-18

[0075] Comparative Example 15, Comparative Example 16, Comparative Example 17 and Example 1 are only different in that the light rare earth alloy powder composition of Comparative Example 15, Comparative Example 16, Comparative Example 17 is different from that of Example 1, and the others are the same as Example 1, the light rare earth alloy powder composition of Comparative Example 15, Comparative Example 16, Comparative Example 17 is shown in Table 4, and the prepared diffusion magnets are respectively marked as A17, A18, A19; Comparative Example 18 and Example 1 are only different in that the heavy rare earth alloy powder composition of Comparative Example 18 is different from that of Example 1, and the others are the same as Example 1, the heavy rare earth alloy powder composition of Comparative Example 18 is shown in Table 4, and the prepared diffusion magnets are respectively marked as A20.

[0076] Table 4 Infiltration process parameters of Example 1, Comparative Example 15-18

[0077]

[0078] The magnetic performance measurement samples of A0-A20 diffusion magnets are prepared by wire cutting, centerless grinding and end face grinding methods, and the samples are cylinders, at room temperature 20℃, using pulse magnetic field magnetic measuring instrument test equipment for testing, the magnetic properties of sintered neodymium-iron-boron diffusion magnets prepared by Example 1-2 and Comparative Example 1-18 are obtained, and the test results are shown in Table 5.

[0079] Table 5 Magnetic properties of diffusion magnets of examples and comparative examples

[0080]

[0081]

[0082] By comparing the magnetic properties of the matrix, Comparative Example 1 and Comparative Example 2 samples, the heavy rare earth infiltration efficiency is higher when the coating weight ratio of conventional PrNdTb infiltration is 0.5%, and the coercivity improvement amplitude reaches 6.2kOe; when the coating weight ratio is further increased to 1%, the overall diffusion efficiency decreases, and the coercivity improvement amplitude decreases to 2.3kOe;

[0083] By comparing the magnetic properties of Example 1, Comparative Example 1, Comparative Example 2 samples, the coercivity improvement amplitude is 2.1kOe when the second layer is coated with 0.5% light rare earth alloy infiltration source, which is close to the coercivity improvement amplitude of the second layer coated with 0.5% heavy rare earth alloy infiltration source.

[0084] The samples of Example 1 and Comparative Example 2 were subjected to structure analysis, and the results are shown in Figs. 1-4. Figure 2 (a) and (b) shown in Figs. 1-4, it can be seen that the grain boundary phase of the Nd-Fe-B magnet obtained in Example 1 is more clear and continuous than that of Comparative Example 2, and the thickness of the Tb-containing shell layer is relatively thicker. From the SEM images of (a) and (b) and the schematic diagram of point scanning, the mass ratio of the components is shown in Table 6: Figure 2 (a) and (b) shown in Figs. 1-4, it can be seen that the grain boundary phase of the Nd-Fe-B magnet obtained in Example 1 is more clear and continuous than that of Comparative Example 2, and the thickness of the Tb-containing shell layer is relatively thicker. From the SEM images of (a) and (b) and the schematic diagram of point scanning, the mass ratio of the components is shown in Table 6: Figure 2 (a) and (b) shown in Figs. 1-4, it can be seen that the grain boundary phase of the Nd-Fe-B magnet obtained in Example 1 is more clear and continuous than that of Comparative Example 2, and the thickness of the Tb-containing shell layer is relatively thicker. From the SEM images of (a) and (b) and the schematic diagram of point scanning, the mass ratio of the components is shown in Table 6: Figure 2 (a) and (b) shown in Figs. 1-4, it can be seen that the grain boundary phase of the Nd-Fe-B magnet obtained in Example 1 is more clear and continuous than that of Comparative Example 2, and the thickness of the Tb-containing shell layer is relatively thicker. From the SEM images of (a) and (b) and the schematic diagram of point scanning, the mass ratio of the components is shown in Table 6:

[0085] Table 6

[0086]

[0087] From the data in Table 6, it can be seen that the content of heavy rare earth Tb and light rare earth PrNd in the grain shell layer is higher by using the composite infiltration process than by using the conventional infiltration process, which indicates that the light rare earth alloy infiltration source coated on the outer layer has a relatively high grain boundary diffusion efficiency, which can effectively distribute the light rare earth components in the grain boundary, and also can improve the grain boundary diffusion efficiency of heavy rare earth elements to a certain extent, so that the heavy rare earth can be more uniformly distributed around the grain to form a shell layer.

[0088] Comparing Example 1 with Comparative Examples 3-6, the light rare earth alloy powder is too fine, which is easy to be oxidized and has a low diffusion efficiency, and on the contrary, the grain boundary phase is easy to aggregate. On the other hand, the light rare earth alloy powder is too coarse, which has a high melting point and a poor diffusion ability, so that the light rare earth alloy components cannot be uniformly distributed in the grain boundary, and also cannot improve the diffusion efficiency of heavy rare earth. Therefore, both of them will result in a low performance after infiltration. The first layer of heavy rare earth alloy infiltration source belongs to the stage of optimal diffusion efficiency, heavy rare earth utilization rate and coercivity improvement range, and the size of the powder directly affects the diffusion efficiency of heavy rare earth, so that the powder size that is too coarse or too fine will reduce the infiltration efficiency and the performance after infiltration.

[0089] Comparing Example 2 with Comparative Examples 7-10, the proportion of Al in the light rare earth alloy powder is too low, and the alloy has a low melting point and a low diffusion efficiency, which affects the infiltration efficiency of the light rare earth alloy infiltration source. If the content of Al is too high, the melting point is too low, the proportion of Al entering the main phase grain increases during the grain boundary diffusion process, and the penetration proportion to the deeper layer decreases, which results in that the Hcj of the magnet after infiltration is not improved, and the Br is greatly reduced. If the content of Tb in the heavy rare earth alloy powder is too low, the grain boundary channel cannot be completely wrapped by the Tb shell layer, and the coercivity after infiltration will be obviously reduced. If the content of Tb is too high, the diffusion efficiency and the utilization rate of heavy rare earth will be reduced, the thickness and distribution of the Tb shell layer will not be obviously optimized, the production cost will be greatly increased, and the coercivity improvement range will not be large.

[0090] Comparative Example 1, Comparative Examples 11-14, the coating weight ratio of the light rare earth alloy permeation source is too low, the light rare earth element is distributed in the grain boundary at a low proportion, and the diffusion efficiency of the heavy rare earth is also limited; the coating weight ratio is too large, and on the basis that the grain boundary channel has been occupied, the magnetic body structure cannot be effectively improved, the coercive force is not improved, and on the contrary, too much Al element enters the main phase to reduce the remanence. The coating weight ratio of the heavy rare earth alloy permeation source is too low, the heavy rare earth element cannot be completely distributed around the grain, resulting in a significant decrease in the coercive force after permeation; the coating weight ratio is too high, the subsequent heavy rare earth diffusion efficiency is reduced, and the overall coercive force is not significantly higher than that of the light rare earth alloy permeation source.

[0091] Comparative Example 1 and Comparative Examples 15-18, the light rare earth NdCu alloy permeation source, the Cu melting point is relatively high, the alloy permeation source diffusion efficiency is relatively low; the Pr element in the PrAl alloy is easy to oxidize, and has certain uncertainty to the production process control and actual diffusion efficiency, and the actual diffusion effect is also relatively poor than that of NdAl; the overall diffusion efficiency of the NdGa alloy is close to that of NdAl, but the raw material price of Ga is close to that of Dy, which is much higher than that of Al, and the overall cost performance is not high; therefore, NdAl is the best component combination of the light rare earth alloy permeation source of the present application. Although the addition of Al element in the heavy rare earth alloy permeation source can improve the diffusion efficiency to a certain extent, it affects the subsequent NdAl permeation, and the final permeation effect is also poor.

[0092] Comparative Example 19

[0093] The grain boundary diffusion method of the sintered neodymium-iron-boron magnet of Comparative Example 19 comprises the following steps:

[0094] 1) the same as step 1) of Example 1;

[0095] 2) the light rare earth alloy permeation source is coated as a first layer on the two end faces of the blank perpendicular to the c-axis, and the coating amount is 0.5wt% of the blank, and the heavy rare earth alloy permeation source is coated as a second layer on the heavy rare earth alloy permeation source, and the coating amount is 0.5wt% of the blank, and the specific implementation effect is shown in Figure 1 (b).

[0096] 3) the same as step 3) of Example 1. The magnet is taken out from the vacuum sintering furnace and marked as A21.

[0097] The preparation method of the light rare earth alloy permeation source and the heavy rare earth alloy permeation source is the same as that of Example 1.

[0098] Comparative Example 20

[0099] The difference between Comparative Example 20 and Comparative Example 19 is only that the coating amount of the first layer of light rare earth alloy permeation source of Comparative Example 20 is 0.3% of the blank, and the others are the same as Comparative Example 19. The obtained magnet is marked as A22.

[0100] Comparative Example 21

[0101] Comparative Example 21 differs from Comparative Example 19 only in that the first layer of light rare earth alloy penetrant source was applied at 0.4% of the blank by weight. The magnet obtained was labeled A23.

[0102] Comparative Example 22

[0103] The grain boundary diffusion process of the sintered neodymium-iron-boron magnet of Comparative Example 22 included the following steps:

[0104] 1) Step 1) of Example 2;

[0105] 2) A light rare earth alloy penetrant source was applied as a first layer on the two end faces of the blank perpendicular to the c-axis at 0.6% of the blank by weight, and a heavy rare earth alloy penetrant source was applied as a second layer on the light rare earth alloy penetrant source at 0.45% of the blank by weight. See Figure 1 (b).

[0106] 3) Step 3) of Example 2. The magnet was removed from the vacuum sintering furnace and labeled A24.

[0107] The method of preparing the light rare earth alloy penetrant source and the heavy rare earth alloy penetrant source was the same as Example 2.

[0108] Comparative Example 23

[0109] Comparative Example 23 differs from Comparative Example 22 only in that the first layer of light rare earth alloy penetrant source was applied at 0.4% of the blank by weight. The magnet obtained was labeled A25.

[0110] Comparative Example 24

[0111] The grain boundary diffusion process of the sintered neodymium-iron-boron magnet of Comparative Example 24 included the following steps:

[0112] 1) Step 1) of Example 1;

[0113] 2) A light rare earth alloy penetrant source was applied as a first layer on the two end faces of the blank perpendicular to the c-axis at 0.5% of the blank by weight, and a heavy rare earth alloy penetrant source was applied as a second layer on the light rare earth alloy penetrant source at 0.5% of the blank by weight.

[0114] 3) Step 3) of Example 1. The magnet was removed from the vacuum sintering furnace and labeled A26.

[0115] The method of preparing the light rare earth alloy penetrant source included: applying a light rare earth alloy penetrant source to the two end faces of the blank perpendicular to the c-axis at 0.5% of the blank by weight. 85 Al15 The light rare earth alloy powder with an average particle size of 5.4 um is prepared by sequentially performing melting, rapid solidification, hydrogen fragmentation and jet milling, the light rare earth alloy source is prepared by adding a binder polyvinyl butyral and an organic solvent butanol and stirring uniformly, wherein the light rare earth alloy powder accounts for 50 wt% of the light rare earth alloy source, and the binder accounts for 3 wt% of the light rare earth alloy source.

[0116] The preparation method of the heavy rare earth alloy source comprises the following steps: according to the composition of (Pr 25 Nd 75 ) 60 Tb 40 The heavy rare earth alloy powder with an average particle size of 3.3 um is prepared by sequentially performing melting, rapid solidification, hydrogen fragmentation and jet milling, the heavy rare earth alloy source is prepared by adding a binder polyvinyl butyral and an organic solvent butanol and stirring uniformly, wherein the heavy rare earth alloy powder accounts for 50 wt% of the heavy rare earth alloy source, and the binder accounts for 3 wt% of the heavy rare earth alloy source.

[0117] A1-A2 and A21-A26 each sample selects 8 different diffusion magnetic steels, each magnetic steel adopts the method of wire cutting, centerless grinding and end face grinding to prepare 1 cylinder, under the condition of room temperature 20℃, using the pulse magnetic field magnetic measuring instrument test equipment for testing, the magnetic properties of the sintered neodymium-iron-boron diffusion magnets prepared in examples 1-2 and comparative examples 19-24 are obtained, and the test results are shown in table 7.

[0118] Table 7 Hcj value of examples 1-2 and comparative examples 19-24 and variance of 8 times of measurement

[0119]

[0120] Comparative examples 1 and 21, examples 2 and 23, the first layer is coated with a light rare earth alloy source, and the second layer is coated with a heavy rare earth alloy source, and the maximum coercivity can be relatively higher, but the overall performance consistency is poor, and the coercivity range of different diffusion magnets reaches 1.9 kOe. In the actual production process, the magnetic property quality control is carried out according to the lowest coercivity of the magnet to meet the requirements of the customer, so the process effect is relatively low in the actual production value compared with the present invention.

[0121] The highest and lowest coercivity samples in comparative example 21 are analyzed for the organizational structure, and the results are shown in Figure 3 (a), Figure 3 (b), the sample with high coercivity has a more clear and continuous grain boundary phase distribution, a clear and thick Tb shell layer, and the sample with low coercivity does not have an obvious shell structure, from Figure 3 (a), Figure 3SEM images of (b) and a schematic diagram of point scanning, and the component mass ratio is shown in Table 8:

[0122] Table 8

[0123]

[0124] As can be seen from the data in Table 8, the Tb content in the shell layer of the magnet with low coercivity is significantly lower than that of the magnet with high coercivity, indicating that the effect of the first layer of light rare earth alloy permeation source on opening the diffusion channel is not very obvious, and the diffusion efficiency of the second layer of heavy rare earth alloy permeation source is not effectively improved, and the heavy rare earth element Tb is not effectively distributed around the grain.

[0125] Comparing Comparative Examples 19-21 and Comparative Examples 22-23, the composite permeation process of coating the first layer with a light rare earth alloy permeation source and the second layer with a heavy rare earth alloy permeation source generally has poor coercivity consistency. According to the experimental results, the coating weight ratio of the light rare earth alloy permeation source is best at about 0.4%. If the coating weight ratio is too heavy, too much light rare earth will occupy the diffusion channel, resulting in the subsequent heavy rare earth alloy permeation source being unable to effectively distribute around the grain; if the coating weight ratio is too small, the effect of opening the grain boundary diffusion channel and improving the diffusion efficiency of the subsequent heavy rare earth alloy permeation source cannot be effectively played, and both will cause the magnet coercivity to be low. Comparative Example 24 adopts the composite permeation process of coating the first layer with a large particle size light rare earth alloy permeation source and the second layer with a small particle size heavy rare earth alloy permeation source, and the average coercivity is not as good as that of Example 1, and the coercivity consistency is also poor.

[0126] Overall, the diffusion process of coating the first layer with a light rare earth alloy permeation source and the second layer with a heavy rare earth alloy permeation source is seriously affected by the diffusion effect of the first layer of light rare earth alloy permeation source, including strict coating weight ratio requirements, production process control, etc. If the first layer diffusion effect is poor, it will directly lead to a significant reduction in the diffusion efficiency of the second layer of heavy rare earth, and the coercivity will also be greatly reduced, the overall performance consistency is poor, and it is not conducive to actual production. The process of the present application has the light rare earth alloy permeation source in the second layer, the overall improvement in the diffusion efficiency of the first layer of heavy rare earth alloy permeation source is limited, and mainly utilizes the advantages of low melting point and strong diffusion capacity, which is placed in the second layer to replace the heavy rare earth alloy permeation source, to make up for the problem of reduced diffusion efficiency caused by the increase in coating weight ratio.

[0127] Aspects, embodiments, features of the present application should be considered illustrative in all aspects and not limiting the present application, and the scope of the present application is only defined 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 claimed application.

[0128] In the preparation method of the present application, the order of the steps is not limited to the order listed, and for those of ordinary skill in the art, changes in the order of the steps without creative effort are within the scope of the present application. In addition, two or more steps or actions can be performed simultaneously.

[0129] Finally, it should be noted that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the scope of the application. Various modifications or changes in the described embodiments can be made by those skilled in the art, or equivalents can be substituted, without departing from the spirit of the present application. It is intended that the present application embrace all such modifications and changes and, accordingly, the application should be limited only by the scope of the following claims, and the full breadth of equivalents to which such claims are entitled.

Claims

1. A method for grain boundary diffusion in sintered NdFeB magnets, characterized in that, Includes the following steps: A first layer of heavy rare earth alloy permeation source is applied to the sintered NdFeB blank, followed by a second layer of light rare earth alloy permeation source. The coated sintered NdFeB blanks are subjected to grain boundary diffusion treatment and tempering treatment. The light rare earth alloy permeation source comprises light rare earth alloy powder, the composition of which is Nd. A Al 100-A Of which 80wt%≤A≤90wt%; The heavy rare earth alloy permeation source comprises heavy rare earth alloy powder, the composition of which is (Pr C Nd 100-C ) B Tb 100-B Of which 50wt%≤B≤60wt%, and 20wt%≤C≤30wt%; The average particle size of the light rare earth alloy powder is smaller than that of the heavy rare earth alloy powder.

2. The grain boundary diffusion method for sintered NdFeB magnets according to claim 1, characterized in that, The heavy rare earth alloy permeation source is applied to both ends of the sintered NdFeB blank perpendicular to the c-axis, and the light rare earth alloy permeation source is applied to the heavy rare earth alloy permeation source.

3. The grain boundary diffusion method for sintered NdFeB magnets according to claim 1, characterized in that, The light rare earth alloy permeation source includes light rare earth alloy powder, binder, and organic solvent; The heavy rare earth alloy permeation source includes heavy rare earth alloy powder, binder, and organic solvent.

4. The grain boundary diffusion method for a sintered NdFeB magnet according to claim 3, characterized in that, The light rare earth alloy powder accounts for 50-70 wt% of the light rare earth alloy permeation source, and the binder accounts for 1-8 wt% of the light rare earth alloy permeation source. The heavy rare earth alloy powder accounts for 50-70 wt% of the heavy rare earth alloy permeation source, and the binder accounts for 1-8 wt% of the heavy rare earth alloy permeation source.

5. The grain boundary diffusion method for a sintered NdFeB magnet according to claim 1, characterized in that, The average particle size of the light rare earth alloy powder is 2-4 μm; the average particle size of the heavy rare earth alloy powder is 4-6 μm.

6. The grain boundary diffusion method for a sintered NdFeB magnet according to claim 1, characterized in that, The coating amount of the light rare earth alloy permeation source is 0.4 to 0.8 wt% of the sintered NdFeB blank.

7. The grain boundary diffusion method for a sintered NdFeB magnet according to claim 1, characterized in that, The coating amount of the heavy rare earth alloy permeation source is 0.4 to 0.6 wt% of the sintered NdFeB blank.

8. The grain boundary diffusion method for a sintered NdFeB magnet according to claim 1, characterized in that, The holding temperature for the grain boundary diffusion treatment is 850–950℃, and the holding time is 8–14 hours.

9. The grain boundary diffusion method for a sintered NdFeB magnet according to claim 1, characterized in that, The tempering treatment is performed at a temperature of 450–550°C for 2–5 hours.

10. The grain boundary diffusion method for a sintered NdFeB magnet according to claim 1, characterized in that, During the grain boundary diffusion treatment or tempering treatment, the vacuum degree in the sintering furnace is ≤1*10. -2 Pa, after the heat preservation is completed, it is filled with an inert atmosphere and cooled to room temperature.

Images