A yttrium-containing rare earth permanent magnet material, a preparation method thereof and application thereof
By introducing rare earth oxides and heavy rare earth compounds as diffusion sources into yttrium-containing rare earth permanent magnet materials, and utilizing thermodynamic driving mechanisms to form a yttrium-rich oxide layer and a heavy rare earth-rich shell, the problem of improving the coercivity and thermal stability of yttrium-containing permanent magnet materials is solved, achieving efficient and low-cost performance improvement.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NINGBO INST OF MATERIALS TECH & ENG CHINESE ACAD OF SCI
- Filing Date
- 2026-05-13
- Publication Date
- 2026-06-12
Smart Images
Figure CN122202041A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of rare earth permanent magnet material production technology, specifically relating to a yttrium-containing rare earth permanent magnet material, its preparation method, and its application. Background Technology
[0002] Since its inception, neodymium iron boron (Nd-Fe-B) permanent magnet materials have been recognized for their excellent room-temperature magnetic properties, especially their extremely high energy product (BH). max Neodymium iron boron (NdFeB) magnets have become an indispensable key functional material in modern industry and are hailed as the "King of Magnets." However, traditional sintered NdFeB magnets face two major technical bottlenecks: one is the main phase of NdFeB magnets, Nd2Fe... 14 B has a relatively low Curie temperature (approximately 312°C), resulting in poor temperature stability of its magnetic properties; secondly, its coercivity (H) decreases at high temperatures. cj The degradation of the heat capacity will be significant, which greatly limits its application in high-temperature conditions, such as in new energy vehicle drive motors, elevator traction machines, wind turbines and other applications that require long-term stable operation above 100°C.
[0003] To address the aforementioned issues, grain boundary diffusion technology is widely recognized as the most efficient and cost-effective method for improving the coercivity and thermal stability of NdFeB magnets. Its core principle involves using heavy rare earth elements, such as dysprosium (Dy) or terbium (Tb), to rapidly diffuse along the boundaries of the main phase grains of the magnet at temperatures above the melting point of the grain boundary phase. These heavy rare earth elements displace the main phase grains (Nd2Fe) 14 B) Some of the surface neodymium (Nd) atoms form a Dy / Tb-rich (Nd,Dy / Tb)2Fe. 14 B-type high-magnetic-crystalline anisotropic field "shell" structure. This hard magnetic shell can effectively pin the movement of magnetic domain walls, thereby significantly improving the coercivity of the material. The advantage of GBD technology is that it enriches heavy rare earth elements only in key regions on the grain surface, rather than adding them uniformly throughout the entire magnet. Therefore, it can significantly improve coercivity while minimizing the impact on remanence (B). r The dilution effect of the magnetic energy product greatly saves expensive and scarce heavy rare earth resources. Existing studies have shown that through grain boundary diffusion of Dy / Tb, the coercivity of magnets can be increased from 16.7 kOe to 28.4 kOe, while the coercivity temperature coefficient (β) is also significantly improved.
[0004] However, the persistently high prices and tight supply of Dy and Tb have increased the cost pressure on traditional GBD technology. Therefore, developing high-performance NdFeB magnet fabrication technologies with reduced or even no Dy / Tb has become a research hotspot in this field. In exploring alternative elements, existing research involves adding or partially replacing Nd with other elements (such as Y, La, Ce, etc.) in NdFeB magnets, aiming to optimize magnetic properties while reducing costs. Among these, the rare earth element yttrium (Y) is particularly valuable due to its relatively abundant resources, low price, and the presence of Y₂Fe₃. 14 The boron phase possesses high saturation magnetization and is considered a potential alternative element. However, Y₂Fe 14 The magnetocrystalline anisotropy field of the B phase is much lower than that of Nd2Fe. 14 The B phase is present in the magnet. Therefore, simply adding Y to the magnet often fails to effectively improve coercivity and may even lead to a decrease in coercivity due to the dilution of the anisotropy of the main phase. For NdFeB magnets that already contain Y, how to effectively improve their coercivity has become a specific and urgent technical problem. If the traditional Dy / Tb grain boundary diffusion method is used to treat yttrium-containing permanent magnet materials, the Y elements present on the surface of the matrix grains and at the grain boundaries may hinder or slow down the effective diffusion and enrichment of Dy / Tb, affecting the formation quality of the shell structure and resulting in unsatisfactory coercivity improvement.
[0005] In summary, existing technologies lack a method specifically tailored to the characteristics of yttrium-containing permanent magnet materials to efficiently and cost-effectively improve their coercivity and thermal stability. An innovative process is urgently needed that can cleverly utilize the existing Y element in the matrix to promote the effective utilization of key heavy rare earth elements, thereby breaking through the performance bottleneck of yttrium-containing permanent magnet materials. Summary of the Invention
[0006] This invention provides a yttrium rare-earth permanent magnet material, its preparation method, and its application, overcoming the problem of low efficiency in improving the coercivity of yttrium rare-earth permanent magnet materials in existing technologies. The technical solution adopted by this invention includes:
[0007] The first aspect of this invention provides a method for preparing a yttrium rare-earth permanent magnet material, comprising:
[0008] A base magnet is provided, wherein the base magnet is a yttrium-containing sintered NdFeB magnet produced by powder metallurgy.
[0009] A diffusion source is obtained by uniformly mixing heavy rare earth elements and / or heavy rare earth compounds, rare earth oxides and organic colloids, wherein the standard molar Gibbs free energy of formation of the rare earth oxides is higher than that of yttrium oxide.
[0010] The diffusion source is composited onto the surface of the matrix magnet to obtain a pretreated magnet;
[0011] The pretreated magnet is subjected to diffusion heat treatment, which causes the yttrium element on the surface of the base magnet to combine with the oxygen element in the rare earth oxide to form yttrium oxide. This promotes the migration of yttrium element to the outside of the base magnet, forming a yttrium-rich oxide layer. At the same time, heavy rare earth elements diffuse into the surface region of the grains of the base magnet and fill the yttrium vacancies on the grain surface, forming a heavy rare earth-rich shell and a yttrium-rich crystal nucleus, thus obtaining a yttrium-containing rare earth permanent magnet material.
[0012] A second aspect of the present invention provides a yttrium rare earth permanent magnet material, which is prepared by the above-described preparation method.
[0013] A third aspect of the present invention provides the application of the yttrium-containing rare-earth permanent magnet material in a rare-earth permanent magnet motor.
[0014] Compared with the prior art, the present invention has at least the following beneficial effects:
[0015] (1) Compared with the prior art, the present invention introduces non-yttrium oxides and cleverly utilizes the thermodynamic driving mechanism to achieve a significant synergistic improvement in coercivity and thermal stability. During the diffusion process, yttrium on the surface of the matrix is replaced and precipitated through the "oxygen-stripping" reaction and migrates outward. This not only reduces the concentration of Y on the surface of the main phase grains, but also greatly promotes the inward diffusion and enrichment of functional rare earth elements such as Dy, Tb, and Ho into the grain surface, thereby forming a more complete and uniform high anisotropic field hard magnetic shell, which significantly enhances the demagnetization resistance of the grain surface.
[0016] (2) The method provided by this invention has a controllable process structure, is simple and efficient, and has excellent prospects for industrial application. Moreover, the method provided by this invention successfully controls the distribution of different rare earth elements in the magnet in a directional manner, thereby maximizing the utilization of the material components. At the same time, this technology effectively improves the utilization efficiency of expensive heavy rare earth elements (such as Dy and Tb), and can reduce their usage while achieving the same performance target, which can effectively reduce costs and save resources. Attached Figure Description
[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0018] Figure 1 This is a schematic diagram of the microstructure of the yttrium rare earth permanent magnet material before and after grain boundary diffusion in a typical embodiment of the present invention; Figure 2 This is a microstructure diagram of the magnet at a depth of 50µm from the surface in Embodiment 1 of the present invention; Figure 3 This is a microstructure diagram of the magnet at a depth of 50µm from the surface of the magnet in Comparative Example 4 of this invention.
[0019] Figure labels: 1-Diffusion source; 2-Rare earth oxide particles; 3-Yttrium-rich oxide particles; 4-Yttrium-rich crystal nuclei; 5-Heavy rare earth-rich shell. Detailed Implementation
[0020] In view of the shortcomings of the existing technology, the technical solution of this invention has been proposed through long-term research and extensive practice. For yttrium rare earth permanent magnet materials with grain boundary diffusion, optimizing the design of the matrix composition and the composition of the diffusion source not only significantly enhances the diffusion efficiency and enrichment effect of heavy rare earth elements at the grain boundaries, but also actively controls the distribution of Y elements in the matrix. This greatly improves the coercivity while enhancing the temperature stability of the material, and provides an economical and reliable technical solution for large-scale industrial production.
[0021] The following will provide a further explanation of the technical solution, its implementation process, and its principles.
[0022] The first aspect of this invention provides a method for preparing a yttrium rare-earth permanent magnet material, comprising:
[0023] A base magnet is provided, wherein the base magnet is a yttrium-containing sintered NdFeB magnet produced by powder metallurgy.
[0024] A diffusion source is obtained by uniformly mixing heavy rare earth elements and / or heavy rare earth compounds, rare earth oxides and organic colloids, wherein the standard molar Gibbs free energy of formation of the rare earth oxides is higher than that of yttrium oxide.
[0025] The diffusion source is composited onto the surface of the matrix magnet to obtain a pretreated magnet;
[0026] The pretreated magnet is subjected to diffusion heat treatment, which causes the yttrium element on the surface of the base magnet to combine with the oxygen element in the rare earth oxide to form yttrium oxide. This promotes the migration of yttrium element to the outside of the base magnet, forming a yttrium-rich oxide layer. At the same time, heavy rare earth elements diffuse into the surface region of the grains of the base magnet and fill the yttrium vacancies on the grain surface, forming a heavy rare earth-rich shell and a yttrium-rich crystal nucleus, thus obtaining a yttrium-containing rare earth permanent magnet material.
[0027] In some embodiments, the mass ratio of the base magnet is: R x Y y Fe 100-y-z-v M v B zWherein, 1≤y≤15, 25.5≤x+y≤33, 0.9≤z≤1.1, 0≤v≤2; Y is yttrium, R includes one or more of Pr, Nd, Dy, and Tb, M includes one or more of Co, Al, Cu, Ga, Ti, and Zr, and B is boron.
[0028] When the Y content is below 1 wt%, its optimization of the magnet's coercivity temperature stability is not significant. At a Y content of 15 wt%, the matrix magnet exhibits low room-temperature coercivity and lacks practical value. Excessively low rare earth content is detrimental to the formation of an effective rare earth-rich phase structure. High boron content hinders the formation of fine, uniform columnar crystal structures in rapidly solidified alloys and results in the presence of a boron-rich phase in the final magnet. Conversely, low boron content easily leads to a decrease in the percentage of the main phase, causing a deterioration in the magnet's energy product. Appropriate amounts of methyl monoxide (M) can effectively promote the enrichment of iron-rich grain boundary phases at triangular grain boundaries, optimizing the compositional structure of thin-walled grain boundaries.
[0029] In some implementations, the heavy rare earth elements include, but are not limited to, one or more combinations of Dy, Tb, and Ho.
[0030] In some embodiments, the heavy rare earth compounds include, but are not limited to, combinations of one or more of Dy, Tb, Ho and Pr, Nd, Al, Cu, Ga, Fe, and Co.
[0031] In some embodiments, the rare earth oxides include, but are not limited to, one or more combinations of praseodymium oxide, neodymium oxide, lanthanum oxide, and cerium oxide.
[0032] In some embodiments, the organic adhesive includes, but is not limited to, at least one of terpineol, polyvinyl alcohol, acrylic resin, isopropanol, etc.
[0033] In some embodiments, the diffusion source powder comprises 5-50 wt% rare earth oxides, 50-95 wt% heavy rare earths and / or heavy rare earth compounds, and 20-40 wt% organic binders.
[0034] In some embodiments, the diffusion source is in the form of a powder, wherein the average particle size of the heavy rare earth elements in the diffusion source is 1-10 µm, the average particle size of the heavy rare earth compounds is 1-10 µm, and the average particle size of the rare earth oxides is 0.5-5 µm.
[0035] In some implementations, the substrate magnet gains 0.5 to 2 wt% weight after the diffusion source is attached to it.
[0036] In some implementations, the diffusion source is combined with the substrate magnet by means of screen printing or spraying.
[0037] In some embodiments, the diffusion heat treatment is performed at a temperature of 800-1000°C for a time of 2-60 hours.
[0038] Preferably, the diffusion heat treatment is performed at a temperature of 850~950℃ for a time of 5~40 h.
[0039] Specifically, during the diffusion heat treatment process, Y element migrates outward and reacts to form the stable Y₂O₃ phase, "capturing" and fixing Y element from the grain boundaries; the inward diffusion of elements such as Dy / Tb / Ho is enhanced. As Y is replaced and migrates outward at the grain surface and grain boundaries, "vacancies" of Y are left in the grain surface region, allowing Dy / Tb / Ho to penetrate more quickly and deeply along the grain boundaries and replace Nd (or other rare earth elements) on the surface of the main phase grains, forming a uniform, dense Dy / Tb / Ho-rich shell structure with a high anisotropic field. According to the method of the present invention, the average thickness of the formed heavy rare earth-rich shell can be precisely controlled within the range of 1.5 µm.
[0040] In some embodiments, the preparation method further includes annealing the yttrium-containing rare earth permanent magnet material after completing the diffusion heat treatment.
[0041] Furthermore, the annealing process specifically includes: holding the yttrium-containing rare earth permanent magnet material at 400~600℃ for 2~10h, and then cooling it to room temperature.
[0042] In some more specific embodiments, the preparation method of the yttrium-containing rare-earth permanent magnet material specifically includes the following steps:
[0043] (1) According to R x Y y Fe 100-y-z-v M v B z The raw materials are prepared according to the specified ratio and melted under inert gas protection to obtain a rapidly solidified alloy sheet. The rapidly solidified alloy sheet is then subjected to hydrogen crushing and air jet milling to obtain magnetic powder. The obtained magnetic powder is oriented and shaped under a magnetic field to obtain a shaped blank, which is then made into a green blank. The green blank is then sintered to obtain a yttrium-containing rare earth permanent magnet matrix magnet.
[0044] (2) The raw materials were batched according to the composition design of heavy rare earth compounds, and then melted in a crucible of a rapid solidification furnace to obtain diffusion source alloy sheets. The rapidly solidified sheets were subjected to hydrogen crushing treatment, and high-purity hydrogen gas (pressure 0.2~0.25MPa) was introduced at room temperature for hydrogen absorption. Subsequently, the mixture was heated at 300~500 ℃ and a vacuum degree ≤10 -2Under Pa conditions, hydrogen is thoroughly dehydrogenated over a long period of time, breaking the rapidly solidified flakes into alloy coarse powder of about 100~150 μm. The hydrogen-crushed coarse powder is then fed into an air jet mill, using high-pressure nitrogen (pressure 0.6~0.8 MPa) as the grinding gas source to prepare alloy diffusion source powder.
[0045] (3) A diffusion source is obtained by mixing alloy powder, rare earth oxide and organic adhesive; the diffusion source is attached to the surface of the base magnet by screen printing or spraying to obtain a pretreated magnet; the pretreated magnet is subjected to high temperature diffusion heat treatment at 800~1000℃ for 2~60h, then annealed, held at 400~600℃ for 2~10h, and cooled to room temperature to obtain a yttrium rare earth permanent magnet material with high coercivity and temperature resistance.
[0046] In the preparation method described above in this invention, the diffusion source includes heavy rare earth elements such as Dy / Tb / Ho and / or alloys, as well as rare earth oxides, wherein the standard molar Gibbs free energy of formation of the rare earth oxides is higher than that of yttrium oxide. After the diffusion source is combined with the base magnet, diffusion heat treatment is performed in a protective atmosphere or vacuum condition. This causes the yttrium element on the surface of the base magnet to combine with the oxygen element in the oxide to form yttrium oxide, which promotes the migration of yttrium element to the outside of the base magnet. At the same time, heavy rare earth elements such as Dy / Tb / Ho diffuse into the surface region of the grains of the base magnet and fill the yttrium vacancies on the grain surface, forming a Y-poor and heavy rare earth rich shell structure.
[0047] In step (1), the average particle size of the magnetic powder is 2~3.5µm, and the vacuum sintering temperature of the green body is 1000~1150℃.
[0048] In step (2), the average particle size of the powder of heavy rare earth or its compound in the diffusion source is 1~10µm.
[0049] In step (3), the substrate magnet gains 0.5 to 2 wt% weight after the diffusion source is attached to it.
[0050] In step (3), the average particle size of the rare earth oxide powder is 0.5~5µm.
[0051] Specifically, taking the coating method as an example: 100 g of composite diffusion source powder was weighed and mixed with 300 g of anhydrous ethanol and 0.5 g of PEG-400 dispersant to form a uniform and stable suspension slurry. The yttrium rare earth permanent magnet material substrate (Nd-Fe-B based, Y content 8 wt%, size 10 mm × 10 mm × 5 mm) was ultrasonically cleaned with acetone for 10 minutes and dried. The suspension was uniformly sprayed onto all surfaces of the substrate using a spray gun (nozzle diameter 0.5 mm) at a pressure of 0.2 MPa, resulting in a weight gain of 1.2 wt%. After spraying, the magnet was dried and cured at 80~120°C for subsequent high-temperature diffusion heat treatment.
[0052] Specifically, taking screen printing as an example: 750 g of composite diffusion source powder is weighed and uniformly mixed with 250 g of terpineol to form a stable diffusion slurry. A yttrium rare earth permanent magnet substrate (Nd-Fe-B based, Y content 8 wt%, size 10 mm × 10 mm × 5 mm) is ultrasonically cleaned with acetone for 10 minutes and dried. The cleaned and dried magnet is fixed on the worktable of the screen printing machine. The prepared slurry is poured into one end of the screen printing plate, and pressure is applied to the slurry using a squeegee, moving it uniformly towards the other end of the plate. Under pressure, the slurry is squeezed through the mesh onto the magnet surface, forming a uniform coating with a weight gain of 1.2 wt%. After spraying, the magnet is dried and cured at 80~120°C for subsequent high-temperature diffusion heat treatment.
[0053] In step (3), the high-temperature grain boundary diffusion process of the yttrium-containing permanent magnet with the attached diffusion source is carried out under an inert atmosphere (argon, nitrogen, or helium) or vacuum conditions (vacuum degree ≤ 10). -3 Under the condition of Pa), the temperature is increased to 850~950°C at a rate of 10°C / min and held for 5~40 h to complete grain boundary diffusion.
[0054] For example, a schematic diagram of the microstructure of the yttrium rare-earth permanent magnet material before and after grain boundary diffusion in a typical embodiment of the present invention is shown below. Figure 1 As shown, the diffusion source 1 is composited on the surface of the matrix magnet. The diffusion source 1 includes rare earth oxide particles 2. During the thermal diffusion process, the yttrium element on the surface of the matrix magnet combines with the oxygen element in the oxide to generate yttrium oxide, which promotes the migration of yttrium element to the outside of the matrix magnet, resulting in yttrium-rich oxide particles 3. At the same time, it causes heavy rare earth elements to diffuse into the surface region of the matrix magnet grains and fill the yttrium vacancies on the surface of the grains, resulting in yttrium-rich nuclei 4 and heavy rare earth-rich shells 5.
[0055] A second aspect of the present invention provides a yttrium rare earth permanent magnet material, which is prepared by the above-described preparation method.
[0056] In some embodiments, the surface of the yttrium-containing rare earth permanent magnet material has a yttrium-rich oxide layer.
[0057] In some embodiments, the rare earth elements in the main phase grains of the surface region of the yttrium-containing rare earth permanent magnet material are distributed in a core-shell structure, including a heavy rare earth-rich shell and a crystal nucleus. The atomic percentage of yttrium in the heavy rare earth-rich shell is more than 30% lower than the atomic percentage of yttrium in the crystal nucleus.
[0058] In some embodiments, the thickness of the yttrium-rich oxide layer in the yttrium-containing rare-earth permanent magnet material is 1~100 μm; In some implementations, the heavy rare earth elements in the rich heavy rare earth shell include one or more combinations of Dy, Tb, and Ho.
[0059] In some implementations, the average thickness of the heavy rare earth-rich shell is 0.5 to 1.5 µm.
[0060] Because the yttrium-containing rare-earth permanent magnet material of the present invention has excellent coercivity temperature stability, it can be effectively applied in rare-earth permanent magnet motors.
[0061] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention, without departing from the spirit and scope of the invention, should be covered within the protection scope of this invention.
[0062] For experiments not specifically described in the examples, the procedures or conditions can be performed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available. Other unmentioned raw materials and instruments are all conventionally chosen and do not involve the core technical means of this invention.
[0063] For example, in the embodiments and comparative examples of this application, the following instruments are used for testing, wherein: The temperature demagnetization curve was measured using an ultra-high coercivity permanent magnet measuring instrument (PFM). The microstructure of the magnet was analyzed using a thermal field scanning electron microscope (FEI QUANTA 250 FEG). The diffusion source powder was prepared using a QLMR-100G air jet mill. High-purity Pr, Dy, Al, and Ga metals (purity ≥ 99.9%) were purchased from Zhongnuo New Materials Co., Ltd. Praseodymium oxide, neodymium oxide, lanthanum oxide, etc. were purchased from Fujian Changting Jinlong Rare Earth Co., Ltd.
[0064] Examples 1-10, Comparative Examples 1-5 The preparation method of yttrium-containing rare-earth permanent magnet materials provided in the embodiments and comparative examples of the present invention specifically includes the following steps: (1) A matrix magnet is provided, wherein the matrix magnet is a yttrium-containing sintered NdFeB magnet prepared by powder metallurgy. A rapidly solidified alloy sheet with the corresponding composition is prepared by a rapid solidification method. The specific steps are as follows: Pure Nd, Dy metal and NdPr mixture metal (a mixture of Nd and Pr), metal Y or YFe alloy, electrolytic iron, any one or more metals selected from Co, Al, Cu, Ga, Ti and Zr as element M, and ferroboron (Fe-B alloy) are weighed to meet the composition shown in Table 1. The raw materials are loaded into a crucible of a rapid solidification furnace and melted to obtain a rapidly solidified casting sheet. The prepared casting alloy has a thickness of about 0.1 to 0.5 mm. The NdFeB matrix sheet is hydrogen-treated and then mixed into powder by air jet milling. The grinding gas is argon, and the grinding particle size is about 2~5 μm. The NdFeB powder and lubricant are mixed and placed into a forming press, pressed into blanks under a magnetic field, and packaged into blocks. The bulk raw material is placed into a sintering furnace for sintering at a temperature of approximately 1020~1090℃ for 4 hours. The magnet is then machined into a 10mm×10mm×5mm matrix magnet for grain boundary diffusion.
[0065] (2) Diffusion source preparation: According to the proportion of diffusion source alloy composition in Table 2, the raw materials are put into the crucible of the rapid solidification furnace and melted to obtain diffusion source alloy sheets. The above alloy sheets are hydrogen-crushed into alloy coarse powder of about 100~150 μm. The hydrogen-crushed coarse powder is sent into an air jet mill and high-pressure nitrogen (pressure of 0.6 MPa) is used as the grinding gas source to prepare alloy diffusion source powder, wherein the particle size of heavy rare earth is about 2~3 µm, the particle size of heavy rare earth compound is about 2~3 µm, and the particle size of rare earth oxide is about 2~5 µm.
[0066] (3) The alloy diffusion source powder is mixed with oxide powder and organic adhesive to obtain a diffusion source. The diffusion source is then coated onto the surface of the substrate magnet to obtain a pretreated magnet.
[0067] (4) The pretreated magnet is subjected to high-temperature diffusion heat treatment, followed by annealing treatment, and kept at 500°C for 2 hours. Then it is cooled to room temperature to obtain a yttrium rare earth permanent magnet material with high coercivity and temperature resistance.
[0068] The magnetic properties of the magnet were tested and analyzed. The composition characteristics of the core-shell structure of the grains in the magnet were analyzed. The rare earth Y content (Y (shell)) in the grain shell layer and the rare earth Y content (Y (core)) in the grain core layer at a depth of 50µm were statistically analyzed. The average thickness of the Dy / Tb / Ho rich shell layer was calculated. The results are shown in Table 3.
[0069] Table 1. Matrix magnet composition and magnetic properties
[0070] Table 2 Diffusion Source Alloy Composition
[0071] Table 3. Raw materials, process parameters, and performance test results of magnets in Examples 1-10 and Comparative Examples 1-5
[0072] Figure 2 The image shows the microstructure at a depth of 50 µm from the surface of the magnet in Example 1. The average shell thickness of the grains is 1.1 µm. The Y content at A in the grain shell is 7.02 wt.%, and the Y content at B in the grain core is 4.38 wt.%. The atomic percentage of Y in the grain shell is 37.5% lower than that in the grain core. After diffusion, the rare earth Y content in the surface grain shell of the magnet is low, and the shell thickness is thin, resulting in excellent coercivity enhancement of the magnet.
[0073] Comparative Example 1 involved Dy grain boundary diffusion into a 6 wt% Y matrix. The atomic percentage of Y in the grain shell was 25.7% lower than that in the grain nucleus. After diffusion, the Y content in the shell region was higher than in Example 1, and the coercivity increase was 7.91 kOe. In Comparative Example 2, the diffusion source was a mixture of Dy and Ce2O3. Ce elements easily diffused into the magnet grains, reducing intrinsic properties and significantly worsening the magnet coercivity increase, which was only 6.49 kOe. In Comparative Example 3, the matrix Y content was relatively high, reaching 17 wt%, and the matrix coercivity was low, with a coercivity of only 8.56 kOe after diffusion, which did not have good application value. In Comparative Examples 4 and 5, the matrix magnets did not contain rare earth Y. Figure 3 The image shows the microstructure at a depth of 50 µm from the surface of the magnet in Comparative Example 4. After diffusion, the magnet grain shell in the surface region is thicker, and the coercivity of the magnet increases by 6.13 kOe.
[0074] The above embodiments illustrate in detail the complete process from powder preparation to heat treatment, highlighting the structural controllability and process repeatability of the method of the present invention. All aspects, embodiments, features, and examples of the present invention should be considered illustrative in all respects and are not intended to limit the invention; the scope of the invention is defined only by the claims. Other embodiments, modifications, and uses will become apparent to those skilled in the art without departing from the spirit and scope of the invention.
[0075] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.
[0076] Although the invention has been described with reference to illustrative embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the invention, and that elements of the described embodiments can be substituted with substantially equivalents. Furthermore, many modifications can be made without departing from the scope of the invention to adapt particular situations or materials to the teachings of the invention. Therefore, this invention is not intended to be limited to the specific embodiments disclosed for carrying out the invention, but rather is intended to encompass all embodiments falling within the scope of the appended claims.
Claims
1. A method for preparing a yttrium rare-earth permanent magnet material, characterized in that, include: A base magnet is provided, wherein the base magnet is a yttrium-containing sintered NdFeB magnet produced by powder metallurgy. A diffusion source is obtained by uniformly mixing heavy rare earth elements and / or heavy rare earth compounds, rare earth oxides and organic colloids, wherein the standard molar Gibbs free energy of formation of the rare earth oxides is higher than that of yttrium oxide. The diffusion source is composited onto the surface of the matrix magnet to obtain a pretreated magnet; The pretreated magnet is subjected to diffusion heat treatment, which causes the yttrium element on the surface of the base magnet to combine with the oxygen element in the rare earth oxide to form yttrium oxide. This promotes the migration of yttrium element to the outside of the base magnet, forming a yttrium-rich oxide layer. At the same time, heavy rare earth elements diffuse into the surface region of the grains of the base magnet and fill the yttrium vacancies on the grain surface, forming a heavy rare earth-rich shell and a yttrium-rich crystal nucleus, thus obtaining a yttrium-containing rare earth permanent magnet material.
2. The preparation method according to claim 1, characterized in that, The mass ratio composition of the base magnet is: R x Y y Fe 100-y-z-v M v B z Wherein, 1≤y≤15, 25.5≤x+y≤33, 0.9≤z≤1.1, 0≤v≤2; Y is yttrium, R includes one or more of Pr, Nd, Dy, and Tb, M includes one or more of Co, Al, Cu, Ga, Ti, and Zr, and B is boron.
3. The preparation method according to claim 1, characterized in that: The heavy rare earth elements include one or more combinations of Dy, Tb, and Ho. And / or, the heavy rare earth compounds include one or more combinations of Dy, Tb, Ho and Pr, Nd, Al, Cu, Ga, Fe, and Co; And / or, the rare earth oxides include one or more combinations of praseodymium oxide, neodymium oxide, lanthanum oxide, and cerium oxide; And / or, the organic adhesive includes at least one of terpineol, polyvinyl alcohol, acrylic resin, and isopropanol.
4. The preparation method according to claim 1, characterized in that: The diffusion source comprises 5-50 wt% rare earth oxides, 50-95 wt% heavy rare earth and / or heavy rare earth compounds, and 20-40 wt% organic colloids. And / or, the diffusion source is in the form of powder, wherein the average particle size of the heavy rare earth elements in the diffusion source is 1~10µm, the average particle size of the heavy rare earth compounds is 1~10µm, and the average particle size of the rare earth oxides is 0.5~5µm. And / or, after the diffusion source is attached to the substrate magnet, the weight of the substrate magnet increases by 0.5~2 wt%; And / or, the diffusion source is combined with the substrate magnet by means of screen printing or spraying.
5. The preparation method according to claim 1, characterized in that: The diffusion heat treatment is performed at a temperature of 800~1000℃ for a time of 2~60h. And / or, the preparation method further includes: annealing the yttrium rare earth permanent magnet material after completing the diffusion heat treatment.
6. The preparation method according to claim 5, characterized in that: The diffusion heat treatment is performed at a temperature of 850~950℃ for a time of 5~40 h. And / or, the annealing process specifically includes: holding the yttrium-containing rare earth permanent magnet material at 400~600℃ for 2~10h, and then cooling it to room temperature.
7. A yttrium rare-earth permanent magnet material, characterized in that: The yttrium-containing rare earth permanent magnet material is prepared by any one of claims 1-6.
8. The yttrium-containing rare-earth permanent magnet material as described in claim 7, characterized in that: The surface of the yttrium-containing rare earth permanent magnet material has a yttrium-rich oxide layer; And / or, the rare earth elements in the main phase grains of the surface region of the yttrium-containing rare earth permanent magnet material are distributed in a core-shell structure, including a heavy rare earth-rich shell and a yttrium-rich nucleus, wherein the atomic percentage of yttrium in the heavy rare earth-rich shell is more than 30% lower than the atomic percentage of yttrium in the yttrium-rich nucleus.
9. The yttrium-containing rare-earth permanent magnet material as described in claim 7, characterized in that: The thickness of the yttrium-rich oxide layer in the yttrium-containing rare earth permanent magnet material is 1~100 μm; And / or, the heavy rare earth elements in the rich heavy rare earth shell include one or more combinations of Dy, Tb, and Ho; And / or, the average thickness of the heavy rare earth-rich shell is 0.5~1.5 µm.
10. The application of the yttrium-containing rare-earth permanent magnet material according to any one of claims 7-9 in a rare-earth permanent magnet motor.