Neodymium-iron-boron magnet and method for producing same

Abstract

The application provides a neodymium-iron-boron magnet and a preparation method thereof. The method comprises the following steps: cutting a rare earth-free magnet into a base material with a predetermined size, the rare earth-free magnet comprising LRE (Pr and Nd), M1 (one or more elements selected from Cu, Ga, Ti, Zr, Al, Co and Nb), and the size of the base material in the diffusion direction being less than or equal to 3 mm; performing pre-diffusion treatment on the base material by using a pre-diffusion source to obtain a pre-diffusion base material, the pre-diffusion source comprising; preparing a diffusion slurry by using a diffusion source alloy, the diffusion source alloy comprising HRE (one or both of Dy and Tb) and M2 (one or more elements selected from Al, Cu and Ga); and performing diffusion treatment on the pre-diffusion base material by using the diffusion slurry to obtain the neodymium-iron-boron magnet. By pre-diffusion and control of the composition and content of the diffusion source alloy, the heavy rare earth element is only diffused on the surface of the magnet during the diffusion treatment, and the improvement of high remanence and high coercivity can be considered.

Description

Technical Field

[0001] This invention relates to the field of magnetic materials technology, and in particular to a neodymium iron boron magnet and its preparation method. Background Technology

[0002] Sintered NdFeB permanent magnets, due to their excellent magnetic properties, have been widely used in power equipment, medical devices, the automotive industry, wind power generation, and consumer electronics. Among these applications, the research and industrialization of heavy rare earth-free sintered NdFeB magnets is of great significance for reducing dependence on heavy rare earth resources such as Dy and Tb, achieving balanced and efficient utilization of rare earth resources, and reducing production costs. Grain boundary diffusion technology is a key process for improving the coercivity of NdFeB magnets. This technology involves attaching heavy rare earth elements to the magnet surface, followed by heat treatment to diffuse these elements along grain boundaries into the magnet's interior. This forms a highly magnetocrystalline anisotropic shell structure on the surface of the main phase grains, significantly improving the magnet's coercivity and achieving efficient utilization of heavy rare earth elements.

[0003] However, in the practical application and processing of high-remanence, heavy rare-earth-free magnets, especially when the magnets are processed into miniaturized and thinner devices and then subjected to grain boundary diffusion treatment, the small size of the diffusion direction makes it easy for heavy rare-earth elements to over-diffuse and penetrate too deeply. Over-diffusion will damage the magnetic properties of the magnet matrix, causing a decrease in remanence in the matrix with high remanence after diffusion treatment, making it difficult to achieve a synergistic improvement in both high remanence and high coercivity.

[0004] Therefore, how to accurately suppress the excessive diffusion of heavy rare earth elements during the diffusion process of heavy rare earth-free magnets has become a key issue that urgently needs to be addressed in the industrialization of high-performance, heavy rare earth-free, small-sized NdFeB magnets. Summary of the Invention

[0005] In view of this, in order to solve the aforementioned technical problems, this application provides a neodymium iron boron magnet and a method for preparing the same.

[0006] The preparation method provided in this application includes: A heavy-earth-free magnet is cut into a substrate with a predetermined size, wherein the composition of the heavy-earth-free magnet is... LRE represents Pr and Nd, M1 represents one or more elements selected from Cu, Ga, Ti, Zr, Al, Co, and Nb, and based on the total mass fraction of the weightless rare earth magnet, 28.8 wt.% ≤ a ≤ 30.5 wt.%, 0.4 wt.% ≤ b ≤ 3 wt.%, 0.86 wt.% ≤ c ≤ 0.94 wt.%, wherein the size of the substrate in the diffusion direction is less than or equal to 3 mm; The substrate is pre-diffused using a pre-diffusion source to obtain a pre-diffusion substrate, wherein the composition of the pre-diffusion source is: Wherein, based on the total mass fraction of the pre-diffusion source, 55wt.%≤d≤65wt.%, 30wt.%≤e≤40wt.%, and 1wt.%≤f≤8wt.%; A diffusion slurry is prepared using a diffusion source alloy, wherein the composition of the diffusion source alloy is as follows: HRE is one or both of Dy and Tb, M2 is one or more of Al, Cu, and Ga, and based on the total mass fraction of the diffusion source alloy, 15wt.%≤g≤20wt.%, 50wt.%≤h≤70wt.%, 10wt.%≤i≤20wt.%; and The pre-diffusion substrate is diffused using the diffusion slurry to obtain the neodymium iron boron magnet; Wherein, the diffusion depth of the elements in the diffusion source alloy from the outside to the inside along the diffusion direction after diffusion treatment is less than 200 μm.

[0007] In some embodiments of this application, the content of heavy rare earth elements in the neodymium iron boron magnet at a depth of 150 μm from the diffusion surface along the diffusion direction is ≥3.2 wt.%.

[0008] In some embodiments of this application, the average particle size of the diffusion source alloy <60μm.

[0009] In some embodiments of this application, the pre-diffusion treatment includes: The pre-diffusion source is attached to the surface of the substrate by vacuum evaporation or magnetron sputtering; The substrate with the pre-diffusion source attached is subjected to a pre-high temperature treatment at a temperature of 800~900℃ for 0.5~4h to obtain the pre-diffusion substrate.

[0010] In some embodiments of this application, the diffusion treatment of the pre-diffusion substrate using the diffusion slurry includes: The diffusion slurry is attached to the surface of the pre-diffusion substrate, wherein the weight gain of heavy rare earth elements after attachment is 0.05~0.1 wt.%; and The pre-diffusion substrate with the diffusion slurry attached is subjected to high-temperature treatment and aging treatment in sequence, wherein the high-temperature treatment is performed at a temperature of 950~1050℃ for a time of 0.5~4h, and the aging treatment is performed at a temperature of 400~700℃ for a time of 2~8h.

[0011] In some embodiments of this application, the diffusion treatment of the pre-diffusion substrate using the diffusion slurry further includes: The pre-diffusion substrate with the diffusion slurry attached is subjected to a degreasing treatment, wherein the degreasing treatment is performed at a temperature of 350~450℃ for 4~5 hours.

[0012] In some embodiments of this application, the preparation method further includes: The raw materials prepared according to the preset ratio are melted and cast in sequence to obtain quick-setting sheets; The rapidly solidifying sheets were subjected to hydrogen crushing and air jet milling to obtain alloy powder; The alloy powder is pressed into a compact to obtain a pressed blank; and The pressed blank is subjected to sintering and aging treatment to obtain the heavy rare earth-free magnet.

[0013] In some embodiments of this application, the smelting temperature is 1300~1500℃, the hydrogen absorption pressure of the hydrogen crushing is 0.1~0.5MPa, the dehydrogenation temperature is 500~600℃, the grinding chamber pressure of the air jet mill is 0.3~0.8MPa, the classifier wheel speed is 2000~3500r / min, and the average particle size of the alloy powder is... The thickness is 2.5~3.8μm, and the sintering treatment temperature is 950~1050℃ and the time is 10~24h.

[0014] The neodymium iron boron magnets provided in this application are prepared by any of the preparation methods described above.

[0015] The neodymium iron boron magnet prepared in this application has a diffusion depth of less than 200 μm, as the heavy rare earth elements diffuse only on the surface of the magnet during the diffusion process. Therefore, it can effectively suppress the main phase from participating in the intergranular reaction during the subsequent aging process and avoid damage to the heavy rare earth shell constructed in the high-temperature diffusion stage, thereby achieving a synergistic improvement in both high remanence and high coercivity.

[0016] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments will be briefly described below. Obviously, the drawings described below only relate to some embodiments of the present invention and are not intended to limit the present invention.

[0018] Figure 1 A process flow diagram for preparing neodymium iron boron magnets is provided for one embodiment of this application.

[0019] Figure 2 A process flow diagram for preparing neodymium iron boron magnets is provided for another embodiment of this application. Detailed Implementation

[0020] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0021] The specific embodiments of the present invention will be described in more detail below with reference to the accompanying drawings and examples, so as to better understand the solution of the present invention and its advantages in various aspects. However, the specific embodiments and examples described below are for illustrative purposes only and are not intended to limit the present invention.

[0022] For small-sized NdFeB magnets without heavy rare earth elements, the small size of the diffusion direction makes them prone to excessive diffusion and penetration of heavy rare earth elements. Therefore, to precisely control the diffusion depth of heavy rare earth elements in small-sized NdFeB magnets without heavy rare earth elements, it is necessary to precisely control the composition of the grain boundary phase so that heavy rare earth elements diffuse only on the surface of the magnet. The small-sized NdFeB magnets mentioned in this application refer to NdFeB magnets with a mass of less than 10g.

[0023] The preparation of heavy rare earth NdFeB magnet substrates involves precipitation during an aging process using a low-B content formulation. Phase (R represents rare earth element, M represents alloying element) and optimize the rare earth content of grain boundary phase to construct a good microstructure, achieve effective demagnetization coupling, and improve the coercivity of the substrate.

[0024] However, the inventors discovered that when the substrate of the heavy rare-earth NdFeB magnet underwent subsequent diffusion treatment, the increase in coercivity after diffusion treatment was often less than expected. The inventors believe this may be due to the presence of impurities in the grain boundary phase. The relative scarcity of Fe in the phase leads to the main phase heavy rare earth shell participating in intergranular reactions during the aging process after diffusion treatment, which damages the already formed heavy rare earth shell structure and weakens the effect of the heavy rare earth shell on improving coercivity.

[0025] This application addresses small-sized NdFeB magnets without heavy rare earth elements, which require controlling the diffusion depth to suppress the decay of remanence, while also facing the problem of poor coercivity improvement after substrate diffusion.

[0026] Figure 1 This application illustrates a method for preparing a neodymium iron boron magnet, comprising steps S1 to S4.

[0027] S1: Cut the weightless rare earth magnet into a substrate with a predetermined size.

[0028] The heavy rare earth-free magnet described in this application refers to a magnet in which the sum of the contents of Dy and Tb is less than 0.1 wt.% of the total mass fraction of the heavy rare earth-free magnet.

[0029] The composition of the heavy rare earth-free magnet used in this application is as follows: Where LRE represents Pr and Nd, and M1 represents one or more elements selected from Cu, Ga, Ti, Zr, Al, Co, and Nb, the total mass fraction of the heavy rare-earth magnet is 28.8 wt.% ≤ a ≤ 30.5 wt.%, 0.4 wt.% ≤ b ≤ 3 wt.%, and 0.86 wt.% ≤ c ≤ 0.94 wt.%. In some embodiments of this application, a can be, for example, 29 wt.%, 29.5 wt.%, 30 wt.%, or 30.5 wt.%, b can be, for example, 0.4 wt.%, 0.6 wt.%, 0.8 wt.%, 1 wt.%, 1.5 wt.%, or 3 wt.%, and c can be, for example, 0.86 wt.%, 0.88 wt.%, 0.9 wt.%, 0.92 wt.%, or 0.94 wt.%. When the LRE content satisfies the above-mentioned 28.8wt.%≤a≤30.5wt.% and the B content satisfies the above-mentioned 0.86wt.%≤c≤0.94wt.%, a heavy rare earth magnet with high remanence can be prepared.

[0030] The size of the substrate can be selected according to the actual application. In particular, the size of the substrate used in this application in the diffusion direction can be less than or equal to 3 mm.

[0031] S2: The substrate is pre-diffused using a pre-diffusion source to obtain a pre-diffusion substrate.

[0032] The composition of the pre-diffusion source is Of which, based on the total mass fraction of the pre-diffusion source, 55wt.%≤d≤65wt.%, 30wt.%≤e≤40wt.%, and 1wt.%≤f≤8wt.%.

[0033] In some embodiments of this application, d can be, for example, 55 wt.%, 60 wt.%, or 65 wt.%, e can be, for example, 30 wt.%, 35 wt.%, or 40 wt.%, and f can be, for example, 1 wt.%, 3 wt.%, 5 wt.%, or 8 wt.%. Pr and Ga are introduced into the matrix grain boundaries through a pre-diffusion source, which can promote the formation of rare-earth silicides that hinder grain boundary channels in the magnet. If the Si content is less than 1 wt.%, it will not have an effect; if the Si content is greater than 8 wt.%, it will cause a significant deterioration in magnetic properties. Since Si is insoluble in the main phase, introducing Si into the grain boundaries through pre-diffusion limits the formation of difficult-to-diff microregions on the surface during the subsequent HRE diffusion process, allowing HRE to accumulate near the magnet surface and effectively controlling the significant decrease in Br caused by excessive HRE entry.

[0034] Optionally, the pre-diffusion treatment includes: The pre-diffusion source is attached to the substrate surface by vacuum evaporation or magnetron sputtering; The substrate with the pre-diffusion source attached is subjected to a pre-high temperature treatment at a temperature of 800~900℃ for 0.5~4h to obtain a pre-diffusion substrate.

[0035] Optionally, the total weight gain from pre-diffusion is 0.1 to 1.5% of the substrate mass.

[0036] S3: Diffusion slurry is prepared using a diffusion source alloy.

[0037] The composition of the diffusion source alloy used in this application is as follows: HRE is one or both of Dy and Tb, and M2 is one or more of Al, Cu, and Ga. Specifically, based on the total mass fraction of the diffusion source alloy, 15wt.%≤g≤20wt.%, 50wt.%≤h≤70wt.%, and 10wt.%≤i≤20wt.%.

[0038] The HRE content is 15-20 wt.%. In some embodiments of this application, g can be, for example, 15 wt.%, 16 wt.%, 17 wt.%, 18 wt.%, 19 wt.%, or 20 wt.%. When g is higher than 20 wt.%, the concentration of heavy rare earth elements is too high, the diffusion chemical potential is high, the diffusion efficiency is improved, the diffusion depth is easily increased, and the diffusion depth of heavy rare earth elements cannot be controlled. When g < 15 wt.%, the concentration of heavy rare earth elements in the diffusion source is too low, making it difficult to form an effective core-shell structure on the magnet surface to improve the magnet's coercivity. Conventional diffusion sources have a high HRE content. During the diffusion process, due to the diffusion source entering the magnet, there is a significant increase in HRE content and a decrease in Fe content on the substrate surface. The magnetic density on the substrate surface is diluted. At the same time, HRE lowers the diffusion melting point, making it easy for excessive HRE to enter the magnet interior. For small-sized magnets, this can lead to a significant decrease in the magnet's remanence. By controlling the concentration of heavy rare earth elements in the diffusion alloy within the above range, the proportion of the main phase on the surface can be maintained, ensuring that HRE can effectively enter the interior of the magnet without going too deep, thus achieving the best balance between improving coercivity and suppressing the decline in remanence.

[0039] The Fe content is 50-70 wt.%. In some embodiments of this application, h can be, for example, 50 wt.%, 55 wt.%, 60 wt.%, 65 wt.%, or 70 wt.%. The high Fe content in the diffusion source alloy can, on the one hand, suppress excessive diffusion of heavy rare earth elements and prevent a significant decrease in remanence; on the other hand, it can regulate the melting point of the grain boundary phase in the substrate during diffusion, increasing the melting point of the near-surface grain boundary phase and controlling the degree of melting of the main phase in the near-surface region, thereby suppressing the enrichment and waste of heavy rare earth elements on the surface that is detrimental to their entry into the magnet body. Furthermore, due to the high Fe content in the grain boundary phase during subsequent aging, it can be directly used for aging. The construction of the phase, rather than the supply of Fe elements by the main phase depletion heavy rare earth shell, can effectively maintain the diffusion effect and maximize the coercivity.

[0040] If the Fe content is higher than 70 wt.%, then the Fe element is excessive, which can easily lead to an excessively high proportion of Fe in the liquid phase, affecting the demagnetizing coupling effect of grain boundaries and hindering the coercivity of the magnet.

[0041] The content of M2 is 10~20 wt.%. In some embodiments of this application, i can be, for example, 12 wt.%, 14 wt.%, 16 wt.%, 18 wt.%, or 20 wt.%. When i is less than 10 wt.%, the M2 element in the liquid phase will be deficient, and it cannot be effectively generated in the subsequent intergranular reaction. Phase adjustment of microstructure. When i is greater than 20 wt.%, excessive M2 elements will cause excessive intergranular reactions during subsequent aging treatment, causing the main phase heavy rare earth shell to participate in the reaction, affecting the diffusion effect and hindering the improvement of coercivity.

[0042] This application introduces Si into the pre-diffusion source to generate trace amounts of rare earth silicides that hinder grain boundary channels, thus laying the foundation for suppressing the HRE diffusion depth in the subsequent diffusion process. In the diffusion process, by limiting the alloy composition of the diffusion source to the aforementioned range, and especially by strictly controlling the content of Fe and heavy rare earth elements, the synergistic effect of Fe, heavy rare earth elements, and alloying elements (M2) effectively suppresses the participation of the main phase in intergranular reactions during subsequent aging, preventing damage to the heavy rare earth shell built during the high-temperature diffusion stage. This ensures the improvement of diffusion coercivity while simultaneously suppressing the diffusion depth of heavy rare earth elements.

[0043] Optionally, in this application, the diffusion depth of the elements in the diffusion source alloy from the outside to the inside along the diffusion direction is less than 200 μm after diffusion treatment, and the diffusion only occurs on the surface of the magnet.

[0044] Optionally, the average grain size of the diffusion source alloy <60μm. Particle size is too large, resulting in poor diffusion.

[0045] S4: The pre-diffusion substrate is diffused using a diffusion slurry to obtain a neodymium iron boron magnet.

[0046] Optionally, this step includes: Adhere the diffusion slurry to the surface of the pre-diffused substrate; and The pre-diffusion substrate with the diffusion slurry attached was subjected to high-temperature treatment and aging treatment in sequence.

[0047] The diffusion paste can be applied to the substrate surface by means of screen printing, magnetron sputtering, vapor deposition, coating or impregnation.

[0048] Optionally, after the diffusion slurry is attached to the surface of the pre-diffusion substrate, the weight gain of heavy rare earth elements is 0.05~0.1 wt.%.

[0049] Optionally, the diffusion slurry includes 75-84 wt% of a diffusion source alloy, 15-24 wt% of an organic solvent and 0.1-5 wt% of a binder, wherein the organic solvent is selected from one or more of ethanol, acetone or terpineol, and the binder is selected from one or more of PVB, dammar resin, shellac and alkyd resin.

[0050] Optionally, the high-temperature treatment temperature is 950~1050℃. In some embodiments of this application, the high-temperature treatment temperature can be, for example, 950℃, 970℃, 990℃, 1010℃, 1030℃, or 1050℃. At temperatures below 950℃, the energy is too low, making it difficult for heavy rare earth elements in the diffusion source alloy to effectively enter the magnet and improve its performance. When the temperature exceeds 1050℃, the temperature is too high, easily leading to significant grain growth on the surface, affecting the magnet's anti-demagnetization ability. Optionally, the heating rate of the high-temperature treatment is 5~10℃ / min.

[0051] Optionally, the high-temperature treatment time is 0.5 to 4 hours. In some embodiments of this application, the high-temperature treatment time can be, for example, 0.5 hours, 1 hour, 2 hours, 3 hours, or 4 hours. If the time is less than 0.5 hours, the diffusion time is too short, and the heavy rare earth elements cannot completely enter the interior of the magnet. If the time is greater than 4 hours, the diffusion time is too long, which will cause an excessive amount of heavy rare earth elements to enter the interior of the small product, increasing the diffusion depth and thus significantly reducing the remanence (Br).

[0052] Optionally, the aging treatment temperature is 400~700℃ and the time is 2~8h. Aging treatment can optimize the internal microstructure of the magnet and improve its coercivity.

[0053] When the diffusion slurry contains substances such as alcohols or esters, the substrate with the diffusion slurry attached needs to be degreased before high-temperature treatment. Optionally, the degreasing treatment temperature is 350~450℃ and the time is 4~5 hours.

[0054] Figure 2 This application illustrates a method for preparing a neodymium iron boron magnet according to another embodiment. Figure 1 Based on the preparation method shown, the method further includes the following step S0.

[0055] S0: Preparation of heavy rare earth-free magnets.

[0056] Optionally, this step may include: The raw materials prepared according to the preset ratio are melted and cast in sequence to obtain quick-setting sheets; The quick-setting flakes were crushed by hydrogen and pulverized by air jet milling to obtain alloy powder; Alloy powder is pressed into a compact to obtain a pressed blank; and The pressed blank is sintered and aged to obtain a heavy rare earth-free magnet.

[0057] Optionally, the melting temperature is 1300~1500℃.

[0058] Optionally, the hydrogen absorption pressure of the hydrogen crusher is 0.1~0.5MPa, the dehydrogenation temperature is 500~600℃, the grinding chamber pressure of the air jet mill is 0.3~0.8MPa, and the classifier speed is 2000~3500r / min.

[0059] Optionally, the average particle size of the resulting alloy powder The thickness is 2.5~3.8μm.

[0060] Optionally, the sintering temperature is 950~1050℃, for example 950℃, 970℃, 990℃, 1010℃, 1030℃, or 1050℃. The sintering time is 10~24h. By sintering at a relatively low temperature for a long time, grain growth is controlled and the microstructure is optimized, thereby effectively improving the coercivity of the magnet.

[0061] Optionally, the aging treatment temperature is 450~600℃, for example, 450℃, 500℃, 550℃ or 600℃, and the aging treatment time is 4~12h.

[0062] The neodymium iron boron magnet prepared in this application can effectively suppress the main phase from participating in intergranular reactions during the subsequent low-temperature aging process because the heavy rare earth elements diffuse only on the magnet surface during the diffusion treatment. This avoids damage to the heavy rare earth shell constructed during the high-temperature diffusion stage, thereby achieving a synergistic improvement in both high remanence and high coercivity.

[0063] The present invention will now be described with reference to specific embodiments. The process conditions and values ​​used in the following embodiments and comparative examples are exemplary, and their possible ranges are as shown in the foregoing description of the invention. For process parameters not specifically noted, conventional techniques can be used. Unless otherwise specified, the reagents and instruments used in the technical solutions provided by the present invention can all be purchased from conventional channels or the market. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0064] Example 1 This embodiment prepares a neodymium iron boron magnet, and the specific preparation process is as follows: 1) According to The raw materials are prepared according to the composition, and the above raw materials are smelted at 1500℃. The molten alloy obtained by smelting is cast into a cooling roller to obtain a quick-setting sheet.

[0065] 2) The rapidly solidifying flakes were hydrogen-crushed to obtain coarse alloy powder. The hydrogen absorption pressure for hydrogen crushing was 0.3 MPa, and the dehydrogenation temperature was 550℃. The coarse alloy powder was then pulverized using an air jet mill to obtain alloy powder. During air jet milling, the grinding chamber pressure was 0.7 MPa, and the classifier speed was 3300 r / min. The average particle size D of the obtained alloy powder was... 50 It is 2.8μm.

[0066] 3) The alloy powder is pressed into a compact under the condition of orientation magnetic induction intensity of 2T.

[0067] 4) The pressed blank was sintered at 1050℃ for 10 hours and then aged at 550℃ for 8 hours to obtain a heavy rare earth-free magnet. Magnetic performance testing showed that the heavy rare earth-free magnet had a B... r =14.8kGs, H cj =15kOe.

[0068] 5) The weightless rare earth magnet was cut by multi-wire cutting to obtain a substrate with dimensions of 2mm (orientation direction) * 2mm * 1.7mm.

[0069] 6) Use a pre-diffusion source, the composition of which is Pr. 65 Ga 30 Si5 was used to magnetron sputter the substrate with the pre-diffusion direction being the orientation direction. The pre-high temperature treatment was carried out at 800℃ for 2 hours. The total weight gain of the pre-diffusion source was 0.7% of the substrate mass, and a pre-diffused substrate was obtained.

[0070] 7) Prepare the diffusion source alloy according to Table 1, and then crush the diffusion source alloy into particles of average size. The diffusion source alloy powder is 55 μm in diameter. A diffusion slurry was prepared by mixing the diffusion source alloy powder with terpineol and PVB (molecular weight 20,000~50,000) at a weight ratio of 75:23:2. The diffusion slurry was then applied to the surface of the pre-diffused substrate by screen printing, with the diffusion direction being the orientation direction. The weight gain of heavy rare earth elements was 0.1 wt.%.

[0071] 8) The pre-diffusion substrate with the diffusion slurry attached is degreased in a vacuum environment and kept at 400℃ for 4 hours.

[0072] 9) The pre-diffusion substrate after degreasing treatment is heated to 960℃ at 7℃ / min and kept at that temperature for 4 hours for high-temperature treatment. After the heat treatment is completed, it is cooled to room temperature.

[0073] 10) After high-temperature treatment, aging treatment is carried out at a temperature of 500℃ for 8 hours to obtain neodymium iron boron magnets.

[0074] Example 2 Neodymium iron boron magnets were prepared using the same raw materials and preparation methods as in Example 1, except that the diffusion source alloy composition was as shown in Table 1.

[0075] Example 3 Neodymium iron boron magnets were prepared using the same raw materials and preparation methods as in Example 1. The difference was that the diffusion source alloy composition was as shown in Table 1, and the high-temperature treatment in step 9) was carried out at 1050°C for 1 hour.

[0076] Example 4 Neodymium iron boron magnets were prepared using the same method as in Example 1, except that the raw material used in step 1) was... From this raw material, a heavy rare earth-free magnet was prepared; magnetic performance testing showed that the heavy rare earth-free magnet had a B... r =14.1kGs, H cj =19kOe. Another difference is that in step 5), the heavy rare earth magnet is cut by multi-wire cutting to obtain a substrate with dimensions of 3mm (orientation direction) * 2.1mm * 1.5mm.

[0077] Example 5 Neodymium iron boron magnets were prepared using the same raw materials and preparation method as in Example 1, except that the pre-diffusion source composition was Pr. 55 Ga 37 Si8.

[0078] Comparative Examples 1-3 Neodymium iron boron magnets were prepared using the same raw materials and preparation methods as in Example 1, except that the diffusion source alloy used in step 7) is different, as shown in Table 1.

[0079] Comparative Example 4 Neodymium iron boron magnets were prepared using the same method as in Example 1, except that the raw material used in step 1) was... From this raw material, a heavy rare-earth-free magnet was prepared. Magnetic performance testing showed that the heavy rare-earth-free magnet had a B... r =13.5kGs, H cj =21kOe.

[0080] Test method: (1) The intrinsic coercivity H of the heavy rare earth magnets was measured respectively. cj1 Residual magnetism B r1 The intrinsic coercivity H of the finally produced neodymium iron boron magnet cj2 Residual magnetism B r2 And calculate △H cj = H cj2 - H cj1 , △B r = B r2 - B r1 .

[0081] (2) Test the initial mass M0 of the pre-diffusion substrate. Coat the surface of the pre-diffusion substrate with a diffusion slurry containing heavy rare earth elements. Place the coated pre-diffusion substrate in a vacuum environment for degreasing treatment to remove organic matter from the slurry. Test the mass M1 of the pre-diffusion substrate after degreasing treatment. According to the formula W=(M1) The weight gain percentage of heavy rare earth elements is calculated as M0) / M0×100%.

[0082] (3) The Fe concentration in three regions at positions 50 μm, 150 μm, and 200 μm from the outside to the inside of the final neodymium iron boron magnet was detected using EDS. Specifically, the sample was ground along a direction perpendicular to the diffusion direction to expose observation surfaces at depths of 50 μm, 150 μm, and 200 μm from the original surface. Within each observation surface, a rectangular region of 20 μm × 20 μm was selected as the EDS measurement region. The concentrations of heavy rare earth elements (HRE) and Fe in the measurement region were tested using EDS. Ten measurement regions were selected in parallel at each depth position for measurement, and the average HRE concentration and average Fe concentration measured in the ten regions were recorded as HRE. 50 and Fe 50 HRE 150 and Fe 150 HRE 200 and Fe 200 Calculate Fe 150 with Fe 200 The difference is denoted as Fe, calculate HRE 150 and HRE200 The difference is denoted as HRE. The smaller the Fe value, the smaller the Fe concentration fluctuation in the surface region of the NdFeB magnet, and the stable Fe content. During the diffusion process, the Fe in the diffusion source makes up for the Fe squeezed out by HRE, and the proportion of the main phase is not affected by the diffusion and does not decrease. The larger the HRE, the greater the degree of HRE aggregation on the surface of the magnet. HRE aggregation on the surface is beneficial to improving the coercivity of the magnet.

[0083] The test results of the neodymium iron boron magnets prepared in the examples and comparative examples are shown in Table 2.

[0084] Table 1

[0085] Table 2

[0086] In Table 2, the concentration of heavy rare earth elements in the embodiments of this application is high at 50 μm, low at 150 μm, and undetectable at 200 μm, indicating that the heavy rare earth elements in the technical solution provided by this application diffuse only on the surface during diffusion treatment. The HRE values ​​were all greater than 3 wt.%, indicating that the heavy rare earth elements were highly concentrated on the surface of the magnet. The low Fe concentration indicates that the Fe concentration in the surface region of the NdFeB magnet fluctuates little, and the Fe content remains stable. During diffusion, the Fe from the diffusion source replenishes the Fe displaced by HRE, and the proportion of the main phase is not affected by diffusion and does not decrease. The HRE content of the NdFeB magnet prepared by the method provided in this application is... cj High increment, and B r The decrease is small, which can achieve a synergistic improvement in high remanence and high coercivity.

[0087] In Comparative Example 1, heavy rare earth elements could still be detected at 200 μm, and Low HRE The higher Fe content indicates that the diffusion depth of heavy rare earth elements is greater than 200 μm, and their aggregation degree on the surface is relatively small. This is because, in Comparative Example 1, the insufficient Fe content promoted the main phase to participate in intergranular reactions, and heavy rare earth elements entered the grain boundary phase from the shell, resulting in a higher content of heavy rare earth elements in the grain boundary phase. This damaged the shell structure, thus the coercivity was not sufficiently improved. At the same time, the heavy rare earth elements further diffused into the interior of the magnet, causing a greater decrease in the Br content of the magnet.

[0088] In Comparative Example 2, the excessive Fe content and insufficient content of heavy rare earth elements and low-melting-point elements resulted in a low concentration of heavy rare earth source in the surface shell. After aging treatment, the insufficient low-melting-point elements prevented the effective formation of [the necessary components]. Phase regulation of microstructure, therefore H cj The increase is low.

[0089] In Comparative Example 3, the introduction of Pr element into the diffusion source alloy suppressed the concentration of heavy rare earth elements in the main phase grain shell layer on the magnet surface, leading to H cj The increase is low.

[0090] In Comparative Example 4, although the composition of the diffusion source alloy is better, the substrate composition is a high coercivity magnet, that is, the content of rare earth element LRE is higher than 30.5 wt.%. After diffusion using the diffusion source alloy of this application, the increase in coercivity is low, and the technical solution provided by this application does not have a significant effect.

[0091] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are 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 for preparing a neodymium iron boron magnet, characterized in that, include: A heavy-earth-free magnet is cut into a substrate with a predetermined size, wherein the composition of the heavy-earth-free magnet is... LRE represents Pr and Nd, M1 represents one or more elements selected from Cu, Ga, Ti, Zr, Al, Co, and Nb, and based on the total mass fraction of the heavy rare earth magnet, 28.8wt.%≤a≤30.5wt.%, 0.4wt.%≤b≤3wt.%, 0.86wt.%≤c≤0.94wt.%, wherein the size of the substrate in the diffusion direction is less than or equal to 3mm; The substrate is pre-diffused using a pre-diffusion source to obtain a pre-diffusion substrate, wherein the composition of the pre-diffusion source is: Wherein, based on the total mass fraction of the pre-diffusion source, 55wt.%≤d≤65wt.%, 30wt.%≤e≤40wt.%, and 1wt.%≤f≤8wt.%; A diffusion slurry is prepared using a diffusion source alloy, wherein the composition of the diffusion source alloy is as follows: HRE is one or both of Dy and Tb, M2 is one or more of Al, Cu, and Ga, and based on the total mass fraction of the diffusion source alloy, 15wt.%≤g≤20wt.%, 50wt.%≤h≤70wt.%, 10wt.%≤i≤20wt.%; and The pre-diffusion substrate is diffused using the diffusion slurry to obtain the neodymium iron boron magnet; Wherein, the diffusion depth of the elements in the diffusion source alloy from the outside to the inside along the diffusion direction after diffusion treatment is less than 200 μm; The neodymium iron boron magnet has a heavy rare earth element content of ≥3.2 wt.% at a depth of 150 μm from the diffusion surface along the diffusion direction. The diffusion treatment of the pre-diffusion substrate using the diffusion slurry includes: The diffusion slurry is attached to the surface of the pre-diffusion substrate, wherein the weight gain of heavy rare earth elements after attachment is 0.05~0.1 wt.%; and The pre-diffusion substrate with the diffusion slurry attached is subjected to high-temperature treatment and aging treatment in sequence, wherein the high-temperature treatment is performed at a temperature of 950~1050℃ for a time of 0.5~4h, and the aging treatment is performed at a temperature of 400~700℃ for a time of 2~8h.

2. The preparation method according to claim 1, characterized in that, The average particle size of the diffusion source alloy <60μm.

3. The preparation method according to claim 1, characterized in that, The pre-diffusion treatment includes: The pre-diffusion source is attached to the surface of the substrate by vacuum evaporation or magnetron sputtering; The substrate with the pre-diffusion source attached is subjected to a pre-high temperature treatment at a temperature of 800~900℃ for a time of 0.5~4h to obtain the pre-diffusion substrate.

4. The preparation method according to claim 1, characterized in that, The diffusion treatment of the pre-diffusion substrate using the diffusion slurry further includes: The pre-diffusion substrate with the diffusion slurry attached is subjected to a degreasing treatment, wherein the degreasing treatment is performed at a temperature of 350~450℃ for 4~5 hours.

5. The preparation method according to claim 1, characterized in that, Also includes: The raw materials prepared according to the preset ratio are melted and cast in sequence to obtain quick-setting sheets; The rapidly solidifying sheets were subjected to hydrogen crushing and air jet milling to obtain alloy powder; The alloy powder is pressed into a compact to obtain a pressed blank; as well as The pressed blank is subjected to sintering and aging treatment to obtain the heavy rare earth-free magnet.

6. The preparation method according to claim 5, characterized in that, The smelting temperature is 1300~1500℃, the hydrogen absorption pressure of the hydrogen crushing is 0.1~0.5MPa, the dehydrogenation temperature is 500~600℃, the grinding chamber pressure of the air jet mill is 0.3~0.8MPa, the classifier wheel speed is 2000~3500r / min, and the average particle size of the alloy powder is... The thickness is 2.5~3.8μm, and the sintering treatment temperature is 950~1050℃ and the time is 10~24h.

7. A neodymium iron boron magnet, characterized in that, It is prepared by any of the preparation methods described in claims 1 to 6.

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