A rare earth amorphous alloy for grain boundary diffusion of iron-based rare earth permanent magnets and its diffusion process

Abstract

The present invention belongs to the field of magnetic materials, and specifically relates to a rare earth amorphous alloy for grain boundary diffusion in iron-based rare earth permanent magnets and a diffusion process thereof. The rare earth amorphous alloy used for grain boundary diffusion in the present invention is composed of rare earth and non-rare earth elements. As a grain boundary diffusion source, it has advantages such as low heavy rare earth content, low melting point, good wettability, and fast atomic migration rate. It can achieve the control of the magnet's microstructure, phase distribution, and chemical composition. While significantly improving magnet performance, it significantly reduces the amount of heavy rare earth used, reduces the diffusion heat treatment temperature, and increases the diffusion depth, achieving efficient utilization of grain boundary diffused heavy rare earth elements and significantly improving the overall magnet performance.

Description

Technical Field

[0001] The present invention belongs to the field of magnetic materials and relates to a rare earth amorphous alloy for grain boundary diffusion of iron-based rare earth permanent magnets and a diffusion process thereof. Specifically, the present invention relates to a method for preparing a high coercive force magnetic material by using a grain boundary diffusion technology and a multi-component low-melting-point rare earth amorphous alloy material composed of rare earth elements and non-rare earth elements, and using the alloy material to cover an iron-based rare earth permanent magnet. Background Art

[0002] Neodymium iron boron (Nd-Fe-B) magnets, as a typical representative of rare earth iron-based permanent magnets, mainly include sintered magnets, bonded magnets and hot-pressed magnets. Currently, commercial products are mainly sintered magnets. Their excellent magnetic properties are conducive to the lightweight and miniaturization of devices. They play an irreplaceable role in new energy vehicles, rail transportation, information science and other fields, and have become a key functional material for the development of high-tech industries.

[0003] Nd-Fe-B magnets have excellent magnetic properties, and the theoretical maximum magnetic energy product can reach 64MGOe. However, the coercive force of the currently industrially mass-produced Nd-Fe-B magnets is only 15-25% of the theoretical value. The low coercive force leads to poor high-temperature anti-demagnetization performance of the device. For high-temperature applications such as drive motors and wind power generation, the performance of ordinary low-coercive force magnets cannot meet the service requirements. Improving the coercive force of Nd-Fe-B magnets to solve the high-temperature demagnetization behavior has become an urgent problem to be solved for this material. Studies have shown that adding heavy rare earth elements dysprosium and terbium to magnets is an effective way to improve the coercive force of magnets. By adding heavy rare earth elements dysprosium and terbium to Re2Fe 14 The coercive force of the magnet can be significantly improved by forming a heavy rare earth shell with a higher anisotropy field around the B main phase grains, and optimizing and regulating the phase composition and microstructure of the grain boundaries so that they can better play a magnetic isolation role.

[0004] The composition of the grain boundary diffusion material source has a significant impact on the diffusion effect. A suitable grain boundary diffusion source is conducive to achieving deeper diffusion and more uniform element distribution in the magnet, thereby improving the utilization rate of heavy rare earth while obtaining better magnetic properties.

[0005] At present, the main sources of grain boundary diffusion are heavy rare earth compounds and heavy rare earth metals, such as oxides, fluorides, hydrides and metal dysprosium and terbium. They generally have the problem of poor reaction kinetics (low reaction activity and high melting point). During thermal diffusion, heavy rare earth elements mainly accumulate on the surface of the magnet and are difficult to enter the interior of the magnet, resulting in low utilization rate. In addition, the O in heavy rare earth compounds is 2- 、F - Impurity element ions such as ions will also enter the magnet during the diffusion process, causing adverse effects on the magnet performance.

[0006] In addition, the current methods for preparing heavy rare earth compound diffusion sources on the surface of magnets mainly include electrophoretic deposition, screen printing, plasma spraying, immersion and physical vapor deposition, which can easily lead to oxidation of the magnet surface to form a high-melting point passivation layer, hindering the diffusion of heavy rare earth elements into the deep part of the magnet.

[0007] Therefore, the research and development of easily diffusible rare earth alloys is the key to promoting the development of Nd-Fe-B magnet grain boundary diffusion technology and is also a technical problem that needs to be urgently solved by those skilled in the art. Summary of the Invention

[0008] In view of this, the purpose of the present invention is to solve the problems existing in the existing grain boundary diffusion technology, such as large usage of heavy rare earth, high diffusion temperature, long diffusion time and low comprehensive magnetic properties of the diffused magnet, and to provide an easily diffused rare earth amorphous alloy composed of rare earth and non-rare earth elements, and to obtain a high coercive force iron-based rare earth permanent magnet material by grain boundary diffusion of the rare earth amorphous alloy.

[0009] It should be noted that the present invention can significantly reduce the grain boundary diffusion temperature, realize the synergistic effect of grain boundary diffusion and lattice diffusion during the heat treatment process, and achieve the multiple effects of optimizing the chemical composition of the grain boundary phase, regulating the microstructure of the magnet, and forming a hard magnetic phase layer around the main phase grains, thereby improving the diffusion depth and uniformity, lowering the diffusion temperature, and significantly reducing the amount of heavy rare earth used. It is a low-cost preparation technology for high-performance iron-based rare earth permanent magnets.

[0010] In order to achieve the above object, the present invention adopts the following technical solutions:

[0011] The first technical purpose of the present invention is to provide a rare earth amorphous alloy film for grain boundary diffusion of iron-based rare earth permanent magnets, wherein the rare earth amorphous alloy film has a continuous and uniform amorphous structure, a film resistivity between 150 and 285 mΩcm, a glass transition temperature less than 650°C, and does not contain any organic matter; and the rare earth amorphous alloy contains rare earth elements, and the rare earth elements are a single light rare earth, a single heavy rare earth, or both light and heavy rare earth elements.

[0012] Furthermore, the content of light rare earth and heavy rare earth in the rare earth amorphous alloy is between 10 and 55 at%, and the ratio of light and heavy rare earth elements is determined by the original diffusion magnet substrate and the performance to be achieved after diffusion. The light rare earth elements include at least one of praseodymium, neodymium, lanthanum, and cerium, and the heavy rare earth elements include at least one of dysprosium, terbium, and holmium.

[0013] Furthermore, the rare earth amorphous alloy also includes non-rare earth elements, and the atomic ratio of the total rare earth content to the total non-rare earth content in the film is between 0.3 and 2.15; the non-rare earth elements are elements that have a eutectic reaction with the rare earth, and include at least one of Cu, Zn, Al, Mg, Sn, Ag, Co, Fe, Sb, Ga, In, and Si.

[0014] A second technical objective of the present invention is to provide a method for preparing a high-coercivity iron-based rare earth permanent magnet using the above-mentioned amorphous alloy through grain boundary diffusion, comprising: using an amorphous alloy film containing rare earth elements as a material source for magnet grain boundary diffusion, allowing the rare earth elements and non-rare earth metal elements to enter the interior of the magnet through heat treatment, optimizing the grain boundary structure and enhancing the main phase anisotropy field, and ultimately obtaining a permanent magnet with high coercivity, and specifically comprising the following steps:

[0015] Step 1) Magnet pretreatment: remove contaminants such as oil and oxide layer on the magnet surface;

[0016] Step 2) Preparation of rare earth amorphous alloy film: A low melting point amorphous alloy film composed of rare earth and non-rare earth is prepared on the surface of the magnet using a film forming technology with rapid cooling characteristics under atmosphere protection. The film has an amorphous structure.

[0017] Step 3) Magnet grain boundary diffusion heat treatment process: Place the magnet coated with the rare earth amorphous alloy film in a vacuum furnace, and start heating after the vacuum degree is less than 3Pa. The first heat treatment temperature is 600-950°C, and multiple heat treatments can be performed, each heat treatment lasting 1-12 hours. After the highest temperature is maintained, it is quickly cooled to room temperature. At this time, the rare earth amorphous alloy diffuses into the deep part of the magnet to obtain a diffused state magnet; the second heat treatment temperature is 400-680°C, and after maintaining for 1-5 hours, it is quickly cooled to obtain a high coercive force magnet with a continuous grain boundary phase.

[0018] Furthermore, the iron-based rare earth permanent magnets include but are not limited to single-phase sintered NdFeB magnets, multi-phase sintered NdFeB magnets containing high-abundance rare earth elements such as lanthanum and cerium, and hot-pressed NdFeB magnets.

[0019] It should be noted that when the total molar content of all rare earth elements in the rare earth amorphous alloy film is greater than that of non-rare earth elements, it is called a rare earth-based amorphous alloy; otherwise, it is a rare earth amorphous alloy. In the present invention, the content of non-rare earth elements is greater than that of rare earth elements, so it is called a rare earth amorphous alloy.

[0020] Furthermore, the rare earth amorphous alloy and the magnet are in direct and close contact, and the bonding force is greater than 10 MPa.

[0021] Furthermore, the rare earth amorphous alloy film formation method includes but is not limited to technologies with ultra-fast cooling rates such as evaporation, magnetron sputtering, ion plating, thermal spraying and laser cladding, and the total mass of impurities such as O, N and C in the film is less than 0.2%.

[0022] Furthermore, when the magnet covered with the rare earth amorphous alloy film is subjected to the thermal diffusion treatment, it is not necessary to keep the temperature between 300 and 500° C., and no impurity carbon element is formed inside the film during the thermal treatment process.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The rare earth alloy film layer covering the surface of the magnet in the present invention has an amorphous structure. The alloy diffusion source is in close contact with the magnet surface and can exhibit excellent kinetic behavior during the diffusion process. Good liquid-liquid diffusion can reduce heavy rare earth consumption, lower the heat treatment temperature and shorten the heat treatment time.

[0025] 2. The new amorphous alloy diffusion source composed of rare earth elements and non-rare earth elements is conducive to achieving good coordination between grain boundary diffusion and lattice diffusion, promoting the formation of hard magnetic shell on the surface of main phase grains and the continuous and uniform distribution of weak magnetic non-magnetic grain boundary phase.

[0026] 3. The melting point of the rare earth amorphous alloy diffusion source can be regulated according to the phase composition of the magnet, so that it is close to the melting point of the magnet grain boundary phase. The heavy rare earth elements in the diffusion source can be infiltrated into the interior of the magnet at a lower temperature, thereby significantly improving the utilization rate of the heavy rare earth. At the same time, it can also prevent the main phase grains from growing due to high temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0028] Figure 1 This is the XRD spectrum of the rare earth Tb amorphous alloy film prepared by magnetron co-sputtering in Example 1.

[0029] Figure 2 This is a cross-sectional SEM photograph of the magnet of Example 2 after diffusion of rare earth PrTb amorphous alloy.

[0030] Figure 3 This is a SEM photograph of the cross section of the magnetron co-sputtered DyTb amorphous alloy film on the silicon substrate surface in Example 3.

[0031] Figure 4This is the XRD spectrum of the rare earth Dy amorphous alloy film prepared by plasma spraying in Example 4.

[0032] Figure 5 This is the SEM photo of the rare earth Dy amorphous alloy powder of Example 4.

[0033] Figure 6 This is a cross-sectional SEM photograph of the magnet of Example 5 after diffusion of the rare earth Tb amorphous alloy film.

[0034] Figure 7 This is a SEM photograph of the alloy powder used in Example 6 to prepare rare earth Dy amorphous alloy thin film by laser cladding. DETAILED DESCRIPTION

[0035] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0036] The term "embodiment" is used herein specifically to describe any embodiment as "exemplary," and should not be construed as superior or preferable to other embodiments. Performance indicators in the embodiments of this application were tested using conventional testing methods in the art, unless otherwise specified. It should be understood that the terms used in this application are intended solely to describe specific implementations and are not intended to limit the disclosure herein.

[0037] Unless otherwise specified, the technical and scientific terms used herein have the same meanings as commonly understood by ordinary technicians in the technical field to which this application belongs; other experimental methods and technical means not specifically specified in this application refer to experimental methods and technical means commonly used by ordinary technicians in this field.

[0038] In the description of the present invention, it should be understood that the terms "middle", "upper", "lower", "ascend", "descend", "vertical", "surface", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0039] In order to better illustrate the content of this application, numerous specific details are provided in the specific examples below. It should be understood by those skilled in the art that this application can be implemented without certain specific details. In the examples, some methods, means, instruments, equipment, etc. well known to those skilled in the art are not described in detail in order to highlight the main purpose of this application.

[0040] Under the premise of no conflict, the technical features disclosed in the embodiments of this application can be combined arbitrarily, and the resulting technical solutions belong to the contents disclosed in the embodiments of this application.

[0041] The invention discloses a rare earth amorphous alloy used for grain boundary diffusion of an iron-based rare earth permanent magnet and a diffusion process thereof.

[0042] For a better understanding of the present invention, the present invention is further specifically described below through the following examples, but it should not be understood as limiting the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above invention content are also considered to fall within the scope of protection of the present invention.

[0043] Example 1:

[0044] 1) using a mixed acid of 4.8% nitric acid and 1.5 mol / L citric acid containing 0.02 wt% benzotriazole (BTA) as a corrosion inhibitor to remove oil stains, oxide layers, and other contaminant films from the magnet surface, controlling the solution solubility to be less than 45° C. and the single immersion time to be less than 20 seconds, performing acid immersion treatment multiple times according to the contamination of the magnet surface until the magnet surface completely turns silvery white, and then completing the cleaning, and obtaining a magnet substrate A to be coated after drying;

[0045] 2) A magnet substrate A that has passed the pretreatment is fixed on a fixture plate, and a Tb amorphous alloy thin film is deposited on the magnet surface by magnetron sputtering. The non-rare earth elements are Cu and Ga, and the total content of the two non-rare earth elements in the film is 52.6 at %. During the coating process, a titanium sheet is placed on the surface of the target material for microalloying. After the coating, the magnet gains a weight of 0.53±0.07 wt %. An aluminum-titanium alloy thin film with a thickness of approximately 145 nm is continuously deposited on the surface of the rare earth Tb amorphous alloy film as a thermal diffusion protection layer. After the above two coating processes, a coated magnet B is obtained;

[0046] 3) Placing the coated magnet B in a vacuum tube furnace, evacuating the temperature to below 3 Pa, and then heating to 850°C. After holding for 6 hours, the magnet is cooled in the furnace to obtain a diffused magnet C. After cooling in the furnace, the magnet C is tempered at 480°C for 2 hours to obtain a tempered magnet D, which is a high-performance diffused magnet.

[0047] The magnetic properties of the magnet before and after diffusion were measured using a permanent magnet magnetic measuring instrument (BH instrument) as shown in Table 1.

[0048] Table 1 Magnet performance data before and after Tb amorphous alloy film diffusion in Example 1

[0049] Br Hc <![CDATA[(BH) max ]]> Hk Hk / Hcj original 14.18kGs 12.64kOe 47.99MGOe 12.34kOe 97.6 Example 1 14.08kGs 24.04kOe 50.22MGOe 22.98kOe 96.1

[0050] Example 2:

[0051] 1) sandblasting to remove oil and oxide layers on the surface of the magnet. The sandblasting pressure was 0.2 MPa, the angle between the spray gun and the normal line of the magnet surface was greater than 45°, the sandblasting trajectory was linear, and the same position was not repeatedly sandblasted. Then, ultrasonic cleaning was performed in anhydrous ethanol to remove sand and other contaminants, thereby obtaining a silvery white magnet substrate A to be coated.

[0052] 2) Magnetic substrate A was fixed to a fixture plate, and a PrTb amorphous alloy thin film was deposited on the magnet surface by magnetron sputtering. The non-rare earth elements were Al and Ga, with a total content of 54.5 at %. The magnet gained 0.43 wt % after coating. An aluminum alloy thin film approximately 120 nm thick was then deposited on the PrTb amorphous alloy film to obtain a coated magnet B.

[0053] 3) Plating the coated magnet B in a vacuum tube furnace, evacuating the vacuum to below 3 Pa, and then heating to 880°C. After holding at this temperature for 8 hours, the magnet is cooled in the furnace to obtain a diffused magnet C. Magnet C is then tempered at 510°C for 4 hours to obtain a tempered magnet D, which is a high-performance grain boundary diffusion magnet.

[0054] The magnetic properties of the magnet before and after diffusion were measured using a permanent magnet magnetic measuring instrument (BH instrument) as shown in Table 2.

[0055] Table 2 Magnet performance data before and after diffusion of PrTb amorphous alloy film in Example 2

[0056] Br Hc <![CDATA[(BH) max ]]> Hk Hk / Hcj original 14.18kGs 12.64kOe 47.99MGOe 12.34kOe 97.6 Example 2 14.15kGs 22.80kOe 50.25MGOe 22.38kOe 98.2

[0057] Example 3:

[0058] 1) Mechanically polishing to remove oil and oxide layers on the surface of the magnet, and then ultrasonically cleaning in anhydrous ethanol to remove adsorbed contaminants such as gravel to obtain a magnet substrate A to be coated;

[0059] 2) Magnetic substrate A was fixed to a fixture plate and a TbDy amorphous alloy thin film was deposited on the magnet surface by magnetron sputtering. The non-rare earth elements Cu and Fe were present in the film, with a total content of 50.8 at %. The average weight gain of the magnet after coating was 0.85 wt %. A 180 nm thick titanium-chromium-aluminum alloy thin film was deposited on the surface of the TbDy amorphous alloy film to obtain a coated magnet B.

[0060] 3) Placing the coated magnet B in a vacuum tube furnace, evacuating the vacuum to below 3 Pa, and then heating to 800°C. After holding the temperature for 12 hours, the magnet is cooled to room temperature in the furnace to obtain a diffused magnet C. The diffused magnet C is then tempered at 500°C for 3 hours to obtain a tempered magnet D, which is a high-performance grain boundary diffusion magnet.

[0061] The magnetic properties of the magnet before and after diffusion were measured using a permanent magnet magnetic measuring instrument (BH instrument) as shown in Table 3.

[0062] Table 3 Magnet performance data before and after diffusion of DyTb amorphous alloy film in Example 3

[0063] Br Hc <![CDATA[(BH) max ]]> Hk Hk / Hcj original 14.18kGs 12.64kOe 47.99MGOe 12.34kOe 97.6Hcj Example 3 14.28kGs 23.59kOe 49.63MGOe 21.24kOe 90.5Hcj

[0064] Example 4:

[0065] 1) Using a laser rust remover to remove oil and oxide layers on the surface of the magnet to make it appear silvery white, and then ultrasonically cleaning in alcohol to remove pollutants adsorbed on the surface to obtain a magnet substrate A to be coated;

[0066] 2) Magnetic substrate A was fixed to a fixture plate. A rare earth Dy amorphous alloy film was deposited on the surface of substrate A using argon plasma spraying using DyCu alloy powder and AlZn alloy powder. The magnet gained 0.78 wt% after coating. A 200 nm thick aluminum-zirconium alloy film was then deposited on the surface of the Dy amorphous alloy film to produce coated magnet B.

[0067] 3) Plating the coated magnet B in a vacuum tube furnace, evacuating the furnace to below 2 Pa, and then heating to 900°C. After holding for 6 hours, the furnace is rapidly cooled to obtain a diffused magnet C. The diffused magnet C is then tempered at 480°C for 3 hours to obtain a tempered magnet D, which is a high-performance grain boundary diffusion magnet.

[0068] The magnetic properties of the magnet before and after diffusion were measured using a permanent magnet magnetic measuring instrument (BH instrument) as shown in Table 4.

[0069] Table 4 Magnet performance data before and after diffusion of rare earth Dy amorphous alloy film in Example 4

[0070] Br Hc <![CDATA[(BH) max ]]> Hk Hk / Hcj original 14.01kGs 12kOe 48.48MGOe 11.76kOe 98 Example 4 13.49kGs 19.19kOe 44.17MGOe 18.61kOe 97

[0071] Example 5:

[0072] 1) sandblasting to remove oil and oxide layers on the surface of the magnet. The sandblasting pressure was 0.18 MPa, the angle between the spray gun and the normal line of the magnet surface was 60°, the sandblasting trajectory was linear, and the sandblasting was not repeated in the same area. The magnet substrate A to be coated was then ultrasonically cleaned in deionized water and alcohol respectively.

[0073] 2) Magnetic substrate A was fixed to a fixture plate, and a rare earth Tb amorphous alloy thin film was deposited on the magnet surface by magnetron sputtering. Non-rare earth elements also included Mg and Fe, with a total content of 53.8 at %. The magnet gained 1.04 wt % after coating. The outermost layer of the rare earth Tb amorphous alloy thin film was a 278 nm thick CuAl alloy thin film. After the above coating process, coated magnet B was obtained.

[0074] 3) Placing the coated magnet B in a vacuum tube furnace, evacuating the vacuum to below 3 Pa, and then heating to 750°C. After holding for 3 hours, the temperature is further raised to 860°C. After holding for 5 hours, the furnace is cooled to obtain a diffused magnet C. The diffused magnet C is then tempered at 500°C for 2 hours to obtain a tempered magnet D, which is a high-performance grain boundary diffusion magnet.

[0075] The magnetic properties of the magnet before and after diffusion were measured using a permanent magnet magnetic measuring instrument (BH instrument) as shown in Table 5.

[0076] Table 5 Magnet performance data before and after diffusion of rare earth Tb amorphous alloy film in Example 5

[0077]

[0078]

[0079] Example 6:

[0080] 1) using a mixed acid of 5.5% nitric acid and 2.0 mol / L citric acid containing 0.05 wt% benzotriazole (BTA) as a corrosion inhibitor to remove oil stains, oxide layers and other contaminant films on the surface of the magnet, controlling the solution solubility to be less than 45° C. and the single treatment time to be less than 10 seconds, performing acid leaching treatment 1 to 3 times depending on the contamination of the magnet surface, and completing cleaning when the magnet surface completely turns silvery white, and obtaining a magnet substrate A to be coated after drying;

[0081] 2) Magnet substrate A was mounted on a laser cladding sample plate and heated to 150°C. A rare earth Dy amorphous alloy thin film was deposited by laser cladding using DyAl amorphous alloy powder and CuAlZn alloy powder. The magnet gained 1.54% wt% after cladding. A 124 nm thick aluminum film was then deposited on the outermost surface of the Dy amorphous alloy film to produce coated magnet B.

[0082] 3) Placing the coated magnet B in a vacuum tube furnace, evacuating the vacuum to below 3 Pa, and then heating to 750°C. After holding for 6 hours, the temperature is further raised to 900°C. After holding for 4 hours, the furnace is cooled to obtain a diffused magnet C. The diffused magnet C is then tempered at 520°C for 3 hours to obtain a tempered magnet D, which is a high-performance grain boundary diffusion magnet.

[0083] The magnetic properties of the magnet before and after diffusion were measured using a permanent magnet magnetic measuring instrument (BH instrument) as shown in Table 6.

[0084] Table 6 Magnet performance data before and after diffusion of rare earth Dy amorphous alloy in Example 6

[0085] Br Hc <![CDATA[(BH) max ]]> Hk Hk / Hcj original 13.78kGs 16.57kOe 46.65MGOe 13.20kOe 98 Example 6 13.59kGs 24.96kOe 45.31MGOe 23.96kOe 96

[0086] In order to further demonstrate the beneficial effects of the present invention and to better understand the present invention, the following comparative examples are provided to further illustrate the technical features disclosed in the present invention, but they should not be construed as limiting the present invention. Other improvements made by those skilled in the art based on the above invention without inventive work are also considered to fall within the scope of protection of the present invention.

[0087] Comparative Example 1

[0088] 1) using a mixed acid of 4.8% nitric acid and 1.5 mol / L citric acid containing 0.02 wt% benzotriazole (BTA) as a corrosion inhibitor to remove oil stains, oxide layers, and other contaminant films from the magnet surface, controlling the solution solubility to be less than 45° C. and the single immersion time to be less than 20 seconds, performing acid immersion treatment multiple times according to the contamination of the magnet surface until the magnet surface completely turns silvery white, and then completing the cleaning, and obtaining a magnet substrate A to be coated after drying;

[0089] 2) The magnet substrate A was fixed on a fixture plate, and a pure rare earth metal Tb thin film was deposited on the magnet surface by magnetron sputtering. A trace amount of titanium was added during the sputtering process to control the Tb deposited on the magnet surface to be the same as in Example 1. The coating was stopped at the same time. A 145 nm thick aluminum-titanium alloy thin film was deposited on the surface of the metal Tb film to obtain a coated magnet B.

[0090] 3) Placing the coated magnet B in a vacuum tube furnace, evacuating the temperature to below 3 Pa, and then heating to 850°C. After holding for 6 hours, the magnet is cooled in the furnace to obtain a diffused magnet C. After cooling in the furnace, the magnet C is tempered at 480°C for 2 hours to obtain a tempered magnet D, which is a high-performance diffused magnet.

[0091] The magnetic properties of the magnet before and after diffusion were measured using a permanent magnet magnetic measuring instrument (BH instrument) as shown in Table 1.

[0092] Table 7 Magnet performance data before and after rare earth Tb film diffusion in comparative example 1

[0093] Br Hc <![CDATA[(BH) max ]]> Hk Hk / Hcj original 14.18kGs 12.64kOe 47.99MGOe 12.34kOe 97.6 Comparative Example 1 14.10kGs 21.17kOe 50.16MGOe 19.76kOe 93.3

[0094] Comparative Example 1 and Example 1 are identical except for the different diffusion source components. The diffusion source in Example 1 is a rare earth Tb amorphous alloy film with an amorphous microstructure, while the metal Tb film in Comparative Example 1 is a crystalline structure. The performance of the diffusion-treated magnets was tested, and the results are shown in Table 7. As can be seen from Table 7, the coercive force H of Comparative Example 1 is cj Only 21.17kOe, while the coercive force H of the diffusion magnet of Example 1 is cj It is 24.04kOe, which shows that when using the same heavy rare earth Tb, a higher coercive force of the magnet can be obtained by adopting a rare earth amorphous alloy as the source of magnet grain boundary diffusion material while consuming the same heavy rare earth.

[0095] Comparative Example 2

[0096] 1) sandblasting to remove oil and oxide layers on the surface of the magnet, with a sandblasting pressure of 0.2 MPa, an angle between the spray gun and the normal line of the magnet surface greater than 45°, a linear sandblasting trajectory, and no repeated sandblasting, followed by ultrasonic cleaning in alcohol to remove sand and other contaminants to obtain a silvery white magnet substrate A to be coated;

[0097] 2) Magnetic substrate A was fixed to a fixture plate, and a PrTb amorphous alloy thin film was deposited on the magnet surface using magnetron sputtering. The magnet gained 0.43 wt% after coating. An aluminum alloy thin film approximately 120 nm thick was then deposited on the PrTb amorphous alloy film to obtain coated magnet B.

[0098] 3) Plating the coated magnet B in a vacuum tube furnace, evacuating to 20 Pa, and then heating to 920°C. After keeping at this temperature for 8 hours, the magnet is cooled in the furnace to obtain a diffused magnet C. Magnet C is then tempered at 500°C for 4 hours to obtain a tempered magnet D, which is a grain boundary diffusion magnet.

[0099] The magnetic properties of the magnet before and after diffusion were measured using a permanent magnet magnetic measuring instrument (BH instrument) as shown in Table 2.

[0100] Table 8 Magnet performance data before and after diffusion of PrTb amorphous alloy film in comparative example 2

[0101] Br Hc <![CDATA[(BH) max ]]> Hk Hk / Hcj original 14.28kGs 12.92kOe 49.99MGOe 12.64kOe 97.8 Example 2 14.23kGs 20.77kOe 49.31MGOe 17.78kOe 85.6

[0102] Comparative Example 2: After changing the heat treatment process system, the pressure was changed from 3Pa to 20Pa, the heat treatment temperature was adjusted from 900℃ to 920℃, and the tempering temperature was reduced from 510℃ to 500℃. The other conditions were kept the same. The results showed that the coercive force H of the magnet after diffusion was cj The squareness Hk / Hcj is 85.6, and the performance is significantly lower than that of Example 2.

[0103] Figure 1 This is the XRD diffraction spectrum of the rare earth Tb amorphous alloy film prepared by magnetron sputtering in Example 1. The broadened diffraction spectrum proves that the film structure is consistent with the diffraction results of amorphous materials, and no sharp diffraction peaks corresponding to any crystalline phase materials appear, indicating that high-quality rare earth amorphous alloy is obtained in this Example 1.

[0104] Figure 2 This is the internal microstructure of the magnet after diffusion in Example 2. The grain size is uniform, the grain boundaries are clear and continuous, and a light gray hard magnetic shell exists around the main phase grains of the heat-treated magnet. The ideal magnet microstructure is obtained by grain boundary diffusion of a new type of rare earth amorphous alloy.

[0105] Figure 3This is a cross-sectional SEM image of a DyTb amorphous alloy film deposited on a silicon substrate placed during the magnet coating process. The upper 5.2-micron-thick film layer is the deposited rare earth amorphous film, the flat region in the middle represents the interface between the film and the silicon substrate, and the lower portion shows a cross-section of the silicon substrate. The fractured rare earth amorphous film is free of defects, lacking typical crystalline film growth structures such as columnar crystals. Aside from a few visible, unusual fracture features closely associated with the substrate, the entire film exhibits typical fracture characteristics of amorphous alloys.

[0106] Figure 4 This is the XRD diffraction pattern of the Dy amorphous alloy thin film prepared by plasma spraying in Example 4. Due to the high plasma spraying temperature, two amorphous diffraction peaks appear at different locations in the prepared film. The rare earth amorphous alloy diffraction peak intensity in the low-angle region is significantly higher, indicating that the film in Example is primarily composed of a rare earth amorphous alloy.

[0107] Figure 5 This is a SEM image of the Dy amorphous alloy powder used in the spray coating process. The powder particle size is 3 to 6 microns. The powder particles have sharp corners and clear edges, showing the morphology characteristic of brittle materials after fracture.

[0108] Figure 6 This figure shows the cross-sectional morphology of a magnet using grain boundary diffusion of a TbCu amorphous alloy thin film. The dark gray, light gray, and white phases in the figure correspond to the 2:14:1 main phase, heavy rare earth shell, and grain boundary neodymium-rich phase, respectively. The figure shows that the main phase grains are of moderate size, and that the heavy rare earth elements diffuse into the magnet interior, forming a heavy rare earth shell of appropriate thickness around the main phase grains. The optimized grain boundary phase is continuous and clear, indicating that the coordinated diffusion of components in the rare earth amorphous alloy diffusion source plays a key role in regulating the magnet's microstructure. Furthermore, a suitable thermal diffusion system ensures that the diffusion source penetrates deeper into the magnet while preventing abnormal growth of the main phase grains.

[0109] Figure 7 This is a SEM image of the alloy powder used to prepare rare earth Dy amorphous alloy thin films by laser cladding. The powder is uniform in shape, highly spherical, and has smooth edges without noticeable sharp corners.

[0110] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A rare earth amorphous alloy film for grain boundary diffusion of iron-based rare earth permanent magnets, characterized in that: The rare earth amorphous alloy film has a continuous and uniform amorphous structure, a film resistivity between 150 and 285 mΩcm, a glass transition temperature less than 650°C, and does not contain any organic matter; and the rare earth amorphous alloy contains rare earth elements, which are single light rare earth elements, single heavy rare earth elements, or both light and heavy rare earth elements; The rare earth amorphous alloy film is used as a material source for magnet grain boundary diffusion, and rare earth elements and non-rare earth elements are allowed to penetrate deep into the magnet through heat treatment to obtain a high coercive force diffusion magnet. The specific steps include the following: (1) Magnet pretreatment: remove the contaminant layer on the magnet surface; (2) Preparation of rare earth amorphous alloy film on the surface of magnet: preparing a rare earth amorphous alloy covering layer composed of rare earth elements and non-rare earth elements on the surface of magnet; (3) Magnet grain boundary diffusion heat treatment process: Place the magnet coated with rare earth amorphous alloy film in a vacuum furnace and start heating after the vacuum degree is less than 3Pa. The first heat treatment temperature is 600-950℃, and multiple heat treatments can be performed, each heat treatment lasting 1-12 hours. After heat treatment at the highest temperature, it is quickly cooled to room temperature. At this time, the rare earth amorphous alloy diffuses into the deep part of the magnet to obtain a diffused state magnet; the second heat treatment temperature is 400-680℃, and after heat treatment for 1-5 hours, it is quickly cooled to obtain a high coercive force magnet with continuous grain boundary phase.

2. The rare earth amorphous alloy film for grain boundary diffusion of iron-based rare earth permanent magnets according to claim 1, characterized in that: The total rare earth content in the rare earth amorphous alloy is between 10 and 55 at%, and the ratio of light and heavy rare earth elements is determined by the original magnet substrate and the target performance after diffusion. The light rare earth elements include at least one of praseodymium, neodymium, lanthanum, and cerium, and the heavy rare earth elements include at least one of dysprosium, terbium, and holmium.

3. The rare earth amorphous alloy film for grain boundary diffusion of iron-based rare earth permanent magnets according to claim 1, characterized in that: The rare earth amorphous alloy also includes non-rare earth elements, and the atomic ratio of the total rare earth content to the total non-rare earth content in the film is between 0.3 and 2.15; the non-rare earth elements are elements that have a eutectic reaction with the rare earth, and include at least one of Cu, Zn, Al, Mg, Sn, Ag, Co, Fe, Sb, Ga, In, and Si.

4. The rare earth amorphous alloy film for grain boundary diffusion of iron-based rare earth permanent magnets according to claim 1, characterized in that: The rare earth amorphous alloy is in direct and close contact with the magnet, and the bonding force is greater than 10 MPa.

5. The rare earth amorphous alloy film for grain boundary diffusion of iron-based rare earth permanent magnets according to claim 1, characterized in that: The rare earth amorphous alloy thin film preparation technology is a film-forming technology with the characteristics of rapid cooling, specifically including: evaporation, magnetron sputtering, ion plating, thermal spraying and laser cladding.

6. The rare earth amorphous alloy film for grain boundary diffusion of iron-based rare earth permanent magnets according to claim 1, characterized in that: The non-rare earth elements include at least one of Cu, Zn, Al, Mg, Sn, Ag, Co, Fe, Sb, Ga, In, and Si.

7. The rare earth amorphous alloy film for grain boundary diffusion of iron-based rare earth permanent magnets according to claim 1, characterized in that: The heat treatment process does not require heat preservation between 300 and 500° C. when treating a magnet covered with a rare earth amorphous alloy film, and no impurity carbon element is formed inside the film during the heat treatment process.

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