A magnet diffusion source film and a preparation method and application thereof

Abstract

The application belongs to the technical field of rare earth permanent magnet materials, and relates to a magnet diffusion source film and a preparation method and application thereof. The diffusion source film comprises, in sequence, an upper base film, a diffusion source and a lower base film. The preparation method comprises the following steps: preparing a diffusion source sol; attaching the diffusion source sol to the lower base film; covering the upper base film to form an initial diffusion source film with a sandwich structure; and performing heating and drying and cooling treatment on the initial diffusion source film to obtain the diffusion source film. Diffusion performed by using the diffusion source film has a good diffusion coercivity amplification effect, has a small damage to remanence of a magnet, can fully play the advantages of grain boundary diffusion, and has good uniformity and consistency of performance of the prepared diffusion magnet, and the effect is more stable, so that the diffusion source film can be applied to fields with higher requirements for magnet performance precision.

Description

Technical Field

[0001] This invention belongs to the field of rare earth permanent magnet materials technology, and relates to a magnet diffusion source thin film, its preparation method and application. Background Technology

[0002] Neodymium iron boron (NdFeB) permanent magnets, as key magnetic functional materials, support the rapid development of the new energy vehicle industry. Currently, the consumption of high-performance, high-coercivity NdFeB magnets in a single new energy vehicle is 3-5 kg. It is predicted that by 2025, global consumption of NdFeB magnets for new energy vehicles will increase from less than 3,000 tons in 2020 to approximately 35,100 tons, showing explosive growth in demand. NdFeB magnets for new energy vehicles need to possess high coercivity (H). cj To meet the requirements for demagnetization resistance and stability under extreme service conditions, it is also necessary to have uniform and consistent remanence (B). r To meet the requirements of precision magnetic circuit design and noise reduction during motor operation.

[0003] The development and application of grain boundary diffusion technology has boosted the rapid development of neodymium iron boron magnets for new energy vehicles. The principle is to attach a small amount of diffusion source containing modified elements to the surface of the magnet in a certain way, and then use a specific heat treatment process to make the diffusion source enter the interior of the magnet along the grain boundary, optimize the composition and microstructure of the magnet, and ultimately achieve the purpose of improving the coercivity of the magnet without excessively damaging the remanence of the magnet.

[0004] Currently, the composition system of diffusion sources has evolved from single rare earth elements to multi-element alloys or compounds (mixtures) containing multiple elements. Correspondingly, the attachment methods of diffusion sources have also become increasingly diversified, commonly including vapor deposition, magnetron sputtering, immersion, screen printing, and spraying. Among these, vapor deposition and magnetron sputtering use high temperature or high voltage to preferentially volatilize the diffusion source, which is then deposited on the magnet surface in the form of free ions. Therefore, this method has low attachment efficiency, and due to the fluctuations in the volatilization and deposition rates of different elements, it is difficult to generate a specific (designated) and uniform multi-element target component diffusion source on the magnet surface, making it unsuitable for the precise attachment of the latest multi-element diffusion sources developed in the industry. In contrast, immersion, screen printing, and spraying first prepare the diffusion source as a powder, then mix it with an organic solvent to prepare a diffusion source slurry, and finally attach the diffusion source slurry to the magnet surface by liquid immersion, dip application, or atomized spraying. Because it is applicable to all diffusion source composition systems and has high attachment efficiency, grain boundary diffusion technology based on immersion, screen printing, and spraying methods has received widespread attention and research in the industry.

[0005] However, numerous studies have found that the viscosity or adhesion effect of flowable liquid slurry is greatly affected by environmental conditions. Furthermore, due to the roughness differences that easily occur on the surface of pre-processed magnets, the quality of the diffusion source adhered after the magnet is immersed or attached to the liquid slurry fluctuates. This makes it difficult to ensure the consistency of diffusion source weight gain in large-scale (batch) attachment processes, resulting in differences in the performance of industrially produced diffusion magnets. This fails to meet the stringent requirements for high uniformity and consistency of magnets used in high-end new energy vehicles (differences in magnet remanence will affect the uniformity of magnetic moment of magnet blocks in the motor, and slight fluctuations in magnetic moment will cause the permanent magnet rotor to vibrate during rotation).

[0006] Meanwhile, screen printing and spraying equipment are expensive to build and maintain, and the processes are complex. This means that the inherently flowable liquid properties of the diffusion source slurry introduce certain instabilities and limitations, greatly restricting the application of NdFeB grain boundary diffusion technology and its products in high-end fields. Therefore, developing a stable solid-state diffusion source system and diffusion method suitable for the batch attachment and subsequent diffusion of multi-component diffusion sources is of great significance for the application of diffusion technology and the development of high-performance NdFeB permanent magnet materials. Summary of the Invention

[0007] To address the aforementioned problems in the prior art, the present invention aims to provide a magnetic diffusion source thin film, its preparation method, and its application, thereby overcoming the shortcomings of the prior art.

[0008] One objective of this invention is achieved through the following technical solution:

[0009] A magnetic diffusion source thin film, comprising, in sequence, an upper substrate thin film, a diffusion source, and a lower substrate thin film;

[0010] Diffusion sources include those with the general formula RE a W b The alloy and binder, wherein RE is at least one of Dy, Tb, Pr, Nd, La, Ce, Y, Gd, Ho; W is at least one of Cu, Al, Ga, In, Sn, Fe, Co, Ni, Ti, Zr, Mg; a and b are mass percentages, 50≤a≤100, and satisfy a+b=100.

[0011] Preferably, the upper substrate film is a flexible film, and its material is one or more of polyvinyl alcohol, polyurethane, polycarbonate, and polyethylene terephthalate.

[0012] Preferably, the lower substrate film is a flexible film, and its material is one or more of polyvinyl alcohol, polyurethane, polycarbonate, and polyethylene terephthalate.

[0013] The materials of the upper and lower substrate films can be the same or different, depending on the needs.

[0014] Preferably, the thicknesses of the upper substrate film and the lower substrate film are 0.001–2 mm, more preferably 0.01–1 mm. The thicknesses of the upper substrate film and the lower substrate film can be the same or different, depending on the requirements.

[0015] The length of the lower substrate film is greater than or equal to the length of the diffusion source, and the width of the lower substrate film is greater than or equal to the width of the diffusion source. The length and width of the upper substrate film are not particularly limited, but preferably, the length and width of the upper substrate film are greater than or equal to the length and width of the diffusion source, respectively.

[0016] Preferably, the RE in the diffusion source a W b , where 50≤a≤99, and a+b=100.

[0017] Preferably, the adhesive in the diffusion source is one or more of polyurethane adhesive, polyacrylate adhesive, polyvinyl alcohol adhesive, polyvinyl formal adhesive, epoxy resin, and phenolic resin.

[0018] Preferably, the general formula is RE a W b The mass ratio of the alloy to the binder is 2-10:1-2; more preferably, the mass ratio is 3-4:1-2.

[0019] The second objective of this invention is achieved through the following technical solution:

[0020] A method for preparing a magnetic diffusion source thin film includes the following steps:

[0021] 1) Preparation of diffusion source sol;

[0022] 2) Adhere the diffusion source sol to the underlying substrate film;

[0023] 3) An initial diffusion source film with a "sandwich" structure is formed by adding an upper substrate film;

[0024] 4) The initial diffusion source film is heated, dried, and cooled to obtain the diffusion source film.

[0025] Preferably, the method for preparing the diffusion source sol includes the following steps:

[0026] Let the general formula be RE a W b The alloy is made into alloy powder; the alloy powder is mixed with dispersant and binder to obtain initial colloid; the initial colloid is stirred to release gas, thus obtaining diffusion source sol.

[0027] The general formula is RE a Wb The alloy is produced into alloy powder through one or more processes, such as coarse crushing (using a crusher, the crushed coarse powder has a particle size between 1 and 50 mm), hydrogen crushing, and air jet milling. Preferably, the average particle size of the alloy powder is 2 to 50 micrometers.

[0028] In the preparation method of the diffusion source sol, preferably, the dispersant is a liquid solvent, including one or more of the following: alcohol solvents (such as ethanol, propanol, butanol, etc.), ketone solvents (such as acetone, butanone, cyclohexanone, etc.), ether solvents (such as diethyl ether, isopropyl ether, butyl ether, tetrahydrofuran, etc.), and ester solvents (such as ethyl acetate, ethyl propionate, etc.).

[0029] In the preparation method of diffusion source sol, preferably, the mass ratio of alloy powder, dispersant and binder is 2-10:1-10:1-2; more preferably, the mass ratio is 3-4:2-4:1-2.

[0030] In the preparation method of the diffusion source sol, preferably, the mixing of alloy powder with dispersant and binder is carried out in an oxygen-controlled environment, wherein the oxygen content in the oxygen-controlled environment is ≤100ppm.

[0031] In the preparation method of the diffusion source sol, preferably, the initial colloid is stirred for ≥30 min, more preferably 30–300 min. The stirring speed can be 100–2000 rpm.

[0032] Preferably, the viscosity of the diffusion source sol is 100–3000 mPa·s.

[0033] In step 2) of the method for preparing the diffusion source film, there are many ways to attach the diffusion source sol to the underlying substrate film, such as spraying, screen printing, brushing, and casting. Preferably, the diffusion source sol is attached to the underlying substrate film by spraying. During the spraying process, the diffusion source sol is deposited on the surface of the underlying substrate film through a spray gun. The height of the spray gun is 10–50 cm, and the liquid flow rate of the spray gun is 50–500 ml / min.

[0034] In step 2) of the method for preparing the diffusion source film, preferably, the thickness of the diffusion source sol attached to the lower substrate film is 0.001 to 2 mm, and more preferably 0.01 to 1 mm.

[0035] In step 3) of the method for preparing the diffusion source film, preferably, the upper substrate film and the lower substrate film with the diffusion source sol attached are pressed together by two rollers to form the initial diffusion source film. Preferably, the radial pressure of the two rollers is 0.5 to 5 N. The two rollers rotate in opposite directions under the action of the tail-end traction force, and the rollers themselves do not generate a spin-driving force.

[0036] In step 4) of the method for preparing the diffusion source film, preferably, the heating and drying can be performed using at least one of, for example, heat source drying, hot air drying, infrared drying, and microwave drying, with a heating and drying time ≥ 10 min. More preferably, the heating and drying time is 20–100 min.

[0037] Heating and drying can be carried out in a tunnel heating and drying device, in which the initial diffusion source film passes through the tunnel heating and drying device under the traction force of the tail roller. The heating and drying method used in the tunnel heating and drying device can be at least one of heat source drying, hot air drying, infrared drying, and microwave drying.

[0038] The diffusion source sol is heated and dried, and the dispersant evaporates, forming a mixture containing the general formula RE. a W b The diffusion source of alloys and adhesives.

[0039] In step 4) of the method for preparing the diffusion source thin film, preferably, the cooling treatment can be at least one of, for example, cold source cooling, cold gas cooling, and cold liquid cooling, and the cooling treatment time is ≥10 min. More preferably, the cooling treatment time is 20 to 100 min.

[0040] Cooling treatment can be carried out in a tunnel cooling device, where the initial diffusion source film passes through the tunnel cooling device under the traction force of the tail roller. The cooling method of the tunnel cooling device can be at least one of cold source cooling, cold air cooling, and cold liquid cooling.

[0041] Preferably, the diffusion source film is obtained after heating, drying, and cooling, and then collected and stored in a roll. The diffusion source film is collected through a roll with a traction roller at the tail end.

[0042] The third objective of this invention is achieved through the following technical solution:

[0043] The application of the above-mentioned magnet diffusion source film includes the following steps: covering the upper and lower surfaces of the magnet to be diffused with the diffusion source film, and performing diffusion heat treatment to obtain the diffusion magnet product.

[0044] The diffusion source film is cut before use so that it completely covers the diffusion surface of the magnet to be diffused.

[0045] Preferably, the magnet to be diffused is a sintered NdFeB magnet with a thickness of 1–10 mm. The thickness is defined as the straight-line distance between the upper and lower surfaces of the magnet to be diffused, which are covered by the diffusion source film.

[0046] Preferably, the diffusion heat treatment is carried out in a vacuum heat treatment furnace with a vacuum degree ≤1×10⁻⁶. -2 Pa.

[0047] Preferably, the diffusion heat treatment includes: heating from room temperature to 450–600°C and holding for 1–3 hours, then heating to 800–950°C and holding for 1–8 hours, then cooling to room temperature, and finally heating to 400–550°C and holding for 1–8 hours, then cooling to room temperature. Air cooling is preferred.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] 1. The diffusion source film prepared by this invention is a solid diffusion source with good uniformity and stability. The diffusion source film prepared by this invention has a certain degree of flexibility and can be collected into rolls by a roll collection device, which is convenient for long-term large-scale storage and long-distance transportation.

[0050] 2. The diffusion source film prepared by this invention is suitable for diffusion source attachment to magnets of various sizes, and the diffusion source attachment process is simple to operate and suitable for NdFeB enterprises of various sizes. The operation process only requires spreading the diffusion source film on the upper and lower surfaces of the magnet, which makes it easy to control the weight gain of the diffusion source.

[0051] 3. The diffusion source film prepared by this invention has good matching with the magnet to be diffused. In the absence of a diffusion source blank area, after grain boundary diffusion, the performance of the final diffused magnet is uniform and consistent, and the effect is more stable. It can be applied to fields with higher requirements for magnet performance precision.

[0052] 4. Diffusion using the diffusion source film of the present invention has a better diffusion coercivity amplification effect, causes less damage to the remanence of the magnet, and can give full play to the advantages of grain boundary diffusion.

[0053] 5. This invention carefully designs the materials of the upper and lower film layers, preferentially using films made of polyvinyl alcohol, polyurethane, polycarbonate, and polyethylene terephthalate. During the diffusion heat treatment, the films are first subjected to a heat treatment at 450-600°C. At this temperature, the polyvinyl alcohol, polyurethane, polycarbonate, and polyethylene terephthalate films undergo a chemical reaction and decompose into small molecules, releasing small molecule gases including CO, H2O, or CO2. As the diffusion pump extracts these gases, the remaining small molecules, such as cyclic compounds, are present in very small quantities and have virtually no harmful effect on the grain boundary diffusion effect.

[0054] 6. The present invention uses a double-layer film to cover and protect the diffusion source in the middle. Compared with the diffusion source film with the diffusion source attached to a single layer film, it has a better coercivity improvement effect and a more stable improvement effect.

[0055] 7. The diffusion source film prepared using the technical solution of this invention is suitable for various diffusion source composition systems. The preparation process is simple and the production efficiency is high. It can be used for mass production of neodymium iron boron magnets for new energy vehicles with high consistency requirements. Attached Figure Description

[0056] Figure 1 This is a schematic diagram of the structure of a magnetic diffusion source thin film according to the present invention;

[0057] Figure 2 This is a simplified flowchart of the process steps used in the preparation method of a magnet diffusion source thin film according to the present invention.

[0058] Figure 3 This is a scanning electron microscope image of the cross-section of the magnet diffusion source thin film prepared in Example 1 of the present invention.

[0059] Figure 1 In the diagram, 1. Diffusion source; 2. Lower substrate film; 3. Upper substrate film.

[0060] Figure 3 In the diagram, A represents the upper substrate film; B represents the lower substrate film; and C represents the diffusion source. Detailed Implementation

[0061] The technical solution of the present invention will be further described and illustrated below with reference to specific embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are only for the purpose of helping to understand the present invention and are not intended to limit the specific scope of the present invention. Furthermore, the accompanying drawings used herein are merely for better illustrating the content disclosed in the present invention and do not limit the scope of protection. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used in the art, and the methods used in the embodiments are all conventional methods in the art.

[0062] Figure 1 The schematic diagram of a magnetic diffusion source thin film provided by the present invention shows that the magnetic diffusion source thin film includes, from top to bottom, an upper substrate thin film 2, a diffusion source 1, and a lower substrate thin film 3. Figure 2 A simplified process flow diagram for preparing a magnet diffusion source film is shown in one embodiment. The preparation process simply includes: spraying diffusion source sol onto a lower substrate film; pressing the upper substrate film and the lower substrate film with diffusion source sol attached together by two rollers to form an initial diffusion source film; passing the initial diffusion source film through a tunnel heating and drying device under the traction force of the tail roller; and then passing it through a tunnel cooling device under the traction force of the tail roller to obtain the diffusion source film; and collecting it into a roll for storage by a roll collection device.

[0063] Example 1

[0064] Let the general formula be Pr 20 Tb 50 Cu 30The alloy (by mass percentage) was prepared into alloy powder with an average particle size of 15 μm through coarse crushing, hydrogen crushing, and air jet milling. In an environment with an oxygen content of 80 ppm, the alloy powder, dispersant (a mixture of ethanol and diethyl ether, volume ratio 4:1), and binder (polyacrylate adhesive) were stirred at a mass ratio of 3:2:2 (500 rpm) for 50 min to obtain a diffusion source sol with a viscosity of 500 mPa·s. The diffusion source sol was then applied to a lower substrate film (polycarbonate film, average thickness 70 μm) by spraying (spray thickness 350 μm) at a spray gun height of 15 cm and a liquid flow rate of 3... 50 ml / min; the upper substrate film (polycarbonate film, average thickness 70 μm) and the lower substrate film with the diffusion source sol attached are pressed together by two rollers to form the initial diffusion source film. The radial pressure of the two rollers is 4 N, and the rollers rotate with the traction force; the initial diffusion source film is passed through the tunnel heating and drying device under the traction force of the tail roller, and is dried with hot air for 40 minutes; after drying, it is further fed into the tunnel cooling device by a conveyor belt, and the diffusion source film is cooled with cooling nitrogen for 20 minutes to obtain the diffusion source film; finally, the diffusion source film is collected by a drum with a traction roller at the tail end.

[0065] Figure 3 The image shows a scanning electron microscope (SEM) image of the cross-section of the magnet diffusion source thin film prepared in Example 1 of this invention. It can be seen that the diffusion source is located between the upper and lower substrate thin films and has a uniform thickness.

[0066] First, five commercial N55 magnets of the same composition from the same batch were selected as the substrate and subjected to wire electrical discharge machining to obtain five magnets. A cylindrical magnet with a thickness of 4mm was polished and labeled as 1-1, 1-2, 1-3, 1-4, and 1-5. Then, eight diffusion source discs that could completely cover the diffusion surface of the magnet to be diffused were cut from the diffusion source film roll.

[0067] The diffusion source discs are attached to the upper and lower surfaces of magnets 1-1, 1-2, 1-3, and 1-4 respectively, and then placed together with magnets 1-5 (which are not covered with diffusion sources) into the mold on the sintering furnace tray.

[0068] A heat treatment tray containing the diffusion source film and the magnet to be diffused was placed in a vacuum heat treatment furnace. After closing the furnace door and evacuating the furnace, a program was set to perform grain boundary diffusion treatment on the sintered NdFeB magnet. The specific program was as follows: First, the furnace temperature was raised to 480℃ and held for 2 hours. Then, the temperature was raised to 900℃ and held for 6 hours, followed by rapid air cooling to room temperature. Finally, the temperature was raised to 500℃ and held for 4 hours, followed by rapid air cooling to room temperature, with the vacuum level remaining less than 7.5 × 10⁻⁶ throughout the process. -3 Pa.

[0069] The magnetic properties of the diffused magnet were tested, and the results are shown in Table 1 below.

[0070] Table 1

[0071]

[0072] In this example, no oxidation or rust occurred on the magnet surface, nor were there any blank areas in the diffusion source, indicating that the diffusion source and diffusion substrate of the present invention have good matching. Furthermore, data comparison shows that the remanence and energy product of magnets 1-1, 1-2, 1-3, and 1-4 are reduced, while the coercivity is significantly increased compared to magnet 1-5. Therefore, the diffusion source film prepared by the technical solution of the present invention can effectively improve the coercivity of NdFeB magnets.

[0073] Example 2: Comparison of the effects of different diffusion heat treatment methods

[0074] Let the general formula be Nd 15 Dy 70 Al 15 The alloy (by mass percentage) was prepared into alloy powder with an average particle size of 25 μm through coarse crushing, hydrogen crushing, and air jet milling. In an environment with an oxygen content of 80 ppm, the alloy powder was stirred at a mass ratio of 3:2:2 with a dispersant (ethanol) and a binder (a mixture of polyurethane adhesive and polyacrylate adhesive in a volume ratio of 3:2) at 500 rpm for 50 min to obtain a diffusion source sol with a viscosity of 500 mPa·s. The diffusion source sol was then applied to a lower substrate film (polyurethane film, average thickness 100 μm) by spraying (500 μm thickness) from a spray gun at a height of 15 cm. The flow rate is 400 ml / min. The upper substrate film (polyurethane film with an average thickness of 100 μm) and the lower substrate film with the diffusion source sol attached are pressed together by two rollers to form the initial diffusion source film. The radial pressure of the two rollers is 4 N, and the rollers can rotate freely. The initial diffusion source film is passed through a tunnel heating and drying device under the traction force of the tail roller and dried with hot air for 40 minutes. After drying, it is further fed into a tunnel cooling device by a conveyor belt and cooled with cold air for 20 minutes to obtain the diffusion source film. Finally, the diffusion source film is collected by a drum with a traction roller at the tail end.

[0075] First, six commercial N55 magnets of the same composition from the same batch were selected as the substrate and subjected to wire electrical discharge machining to obtain six magnets. The cylindrical magnets were polished and labeled as 2-1, 2-2, 2-3, 2-4, 2-5, and 2-6 respectively; then 12 diffusion source discs that could completely cover the diffusion surface of the magnet to be diffused were cut from the diffusion source film roll.

[0076] The diffusion source discs are attached to the upper and lower surfaces of magnets 2-1, 2-2, 2-3, 2-4, 2-5, and 2-6 respectively, and then placed into the mold on the sintering furnace tray.

[0077] Heat treatment trays containing diffusion source films and magnets to be diffused are placed in different vacuum heat treatment furnaces. After the furnace doors are closed and a vacuum is drawn, different programs are set for diffusion treatment.

[0078] The specific procedure is as follows: For magnets 1 and 2, the furnace temperature is first raised to 300℃ and held for 2 hours. Then, the temperature is raised to 900℃ and held for 6 hours, followed by rapid air cooling to room temperature. The furnace is then reheated to 500℃, held for 4 hours, and then rapidly air-cooled to room temperature. For magnets 3 and 4, the furnace temperature is first raised to 450℃ and held for 2 hours. Then, the temperature is raised to 900℃ and held for 6 hours, followed by rapid air cooling to room temperature. The furnace is then reheated to 500℃, held for 4 hours, and then rapidly air-cooled to room temperature. For magnets 5 and 6, the furnace temperature is directly raised to 900℃, held for 6 hours, rapidly air-cooled to room temperature, and then reheated to 500℃, held for 4 hours, and then rapidly air-cooled to room temperature. During this process, the vacuum level is less than 7.5 × 10⁻⁶. - 3 Pa.

[0079] The magnetic properties of the diffused magnet were tested, and the results are shown in Table 2.

[0080] Table 2

[0081]

[0082] In this example, no oxidation or rust occurred on the magnet surface, nor were there any blank areas in the diffusion source, indicating that the diffusion source and diffusion substrate of this invention have good matching. Furthermore, data comparison shows that the remanence and energy product of all magnets decreased, but the decrease in magnets 2-3 and 2-4 was less than that of magnets 2-1, 2-2, 2-5, and 2-6; in terms of coercivity, the increase in magnets 2-1, 2-2, 2-5, and 2-6 was smaller than that of magnets 2-3 and 2-4. Magnets 2-3 and 2-4, using the diffusion heat treatment process used in this invention for grain boundary diffusion, exhibit the best overall performance. Therefore, the NdFeB magnet diffusion source prepared by this invention, through grain boundary diffusion, requires first holding at a specific temperature range to completely crack and decompose the upper and lower substrate films, allowing them to be discharged externally, before high-temperature diffusion for better results.

[0083] Example 3: Comparison of the effects of different hot air drying times

[0084] Let the general formula be Tb 75 Fe 10 Al 10 Ga5 (mass percentage) alloy was prepared into alloy powder with an average particle size of 25 μm through coarse crushing, hydrogen crushing, and air jet milling. In an environment with an oxygen content of 80 ppm, the alloy powder was stirred at a mass ratio of 3:2:2 (600 rpm) with a dispersant (a mixture of ethanol and acetone, volume ratio 4:1) and a binder (a mixture of polyvinyl alcohol formal adhesive and phenolic resin, volume ratio 6:1) for 50 min to obtain a diffusion source sol with a viscosity of 500 mPa·s. The diffusion source sol was then applied to a lower substrate film (polyethylene terephthalate) by spraying (spray thickness 500 μm). On a polyethylene terephthalate (PET) film with an average thickness of 100 μm, the spray gun height is 15 cm and the liquid flow rate of the spray gun is 400 ml / min. The upper substrate film (PET film with an average thickness of 100 μm) and the lower substrate film with the diffusion source sol attached are pressed together by two rollers to form the initial diffusion source film. The radial pressure of the two rollers is 4 N, and the rollers can rotate freely. The initial diffusion source film is passed through a tunnel heating and drying device under the traction force of the tail roller. Hot air drying is used to dry the diffusion source films with a spacing of 1 meter for 10, 20, 30, and 40 minutes respectively, corresponding to the labels A, B, C, and D.

[0085] After drying, the film is further fed into a tunnel cooling device via a conveyor belt, where it is cooled with cold air for 20 minutes to obtain the diffusion source film. Finally, the diffusion source film is collected by a drum with a traction roller at the tail end.

[0086] First, five commercial N55 magnets of the same composition from the same batch were selected as the substrate and subjected to wire electrical discharge machining to obtain five magnets. Cylindrical magnets, 4mm thick, are polished and labeled 3-1, 3-2, 3-3, 3-4, and 3-5 respectively.

[0087] Then, two diffusion source discs that can completely cover the diffusion surface of the magnet to be diffused are cut from the diffusion source film rolls A, B, C, and D respectively. The diffusion source discs A, B, C, and D are attached to the upper and lower surfaces of magnets 3-1, 3-2, 3-3, and 3-4 respectively. Then, magnet 5, which is not covered with a diffusion source, is placed into the mold on the sintering furnace tray.

[0088] A heat treatment tray containing the diffusion source film and the magnet to be diffused is placed in a vacuum heat treatment furnace. After closing the furnace door and evacuating the vacuum, the diffusion process is initiated. The specific procedure is as follows: First, the furnace temperature is raised to 500℃, held for 2 hours, then raised to 900℃, held for 6 hours, and rapidly cooled to room temperature by air cooling. Finally, the temperature is raised to 520℃, held for 8 hours, and rapidly cooled to room temperature by air cooling, with the vacuum level remaining less than 7.5 × 10⁻⁶ throughout the process. -3 Pa;

[0089] The magnetic properties of the diffused magnet were tested, and the results are shown in Table 3.

[0090] Table 3

[0091]

[0092] In this embodiment, no oxidation or rust occurred on the magnet surface, nor were there any blank areas in the diffusion source, indicating that the diffusion source and the diffusion substrate of this invention have good matching. Furthermore, data comparison shows that the remanence of magnets 3-1, 3-2, 3-3, and 3-4 decreased. Regarding coercivity, the increase in coercivity for magnets 3-1 and 3-2 was lower than that for magnets 3-3 and 3-4, but both were higher than that for magnet 3-5. This indicates that sufficient drying time is required during the diffusion source film preparation process to ensure the stability of its diffusion performance and improve coercivity.

[0093] Example 4

[0094] Let the general formula be Tb 70 Cu 30The alloy (by mass percentage) was prepared into alloy powder with an average particle size of 15 μm through coarse crushing, hydrogen crushing, and air jet milling. The alloy powder was then stirred with a dispersant (ethanol) and a binder (polyvinyl alcohol adhesive) at a mass ratio of 3:2:2 (500 rpm) for 50 min in an environment with an oxygen content of 80 ppm, yielding a diffusion source sol with a viscosity of 500 mPa·s. This diffusion source sol was then applied to a lower substrate film (polycarbonate film, average thickness 70 μm) by spraying (350 μm thickness) at a spray gun height of 15 cm and a liquid flow rate of 350 ml / min. The upper substrate film (polycarbonate film, average thickness 70μm) and the lower substrate film with the diffusion source sol attached are pressed together by two rollers to form the initial diffusion source film. The radial pressure of the two rollers is 4N, and the rollers can rotate freely. The initial diffusion source film is then passed through a tunnel heating and drying device under the traction force of the tail roller and dried with hot air for 40 minutes. After drying, it is further fed into a tunnel cooling device by a conveyor belt and cooled with cold air for 20 minutes to obtain the diffusion source film. Finally, the diffusion source film is collected by a drum with a traction roller at the tail end.

[0095] Thirty commercial N55 magnets of the same composition from the same batch were selected as the substrate and subjected to wire electrical discharge machining to obtain 30 magnets. Cylindrical magnets with a thickness of 4mm are polished and labeled with numbers 4-1, 4-2, 4-3, 4-4, ... 4-28, 4-29, 4-30.

[0096] Twenty diffusion source discs, capable of completely covering the diffusion surface of the magnet to be diffused, were cut from the diffusion source film roll of Example 4; the diffusion source discs were then attached to the upper and lower surfaces of magnets 4-1 to 4-10 respectively, and then placed in the mold on the sintering furnace tray.

[0097] A heat treatment tray containing the diffusion source film and the magnet to be diffused was placed in a vacuum heat treatment furnace. After closing the furnace door and evacuating the furnace, the diffusion process was initiated. The specific procedure was as follows: First, the furnace temperature was raised to 480℃ and held for 2 hours. Then, the temperature was raised to 900℃ and held for 6 hours, followed by rapid air cooling to room temperature. Finally, the temperature was raised to 500℃ and held for 4 hours, followed by rapid air cooling to room temperature, with the vacuum level remaining less than 7.5 × 10⁻⁶ throughout the process. -3 Pa.

[0098] The magnetic properties of magnets 4-1 to 4-10 after diffusion were tested, and the test results are shown in Table 4.

[0099] Table 4

[0100]

[0101] Comparative Example 1

[0102] Using a traditional direct spraying method, the diffusion source sol (spray thickness 350 μm) prepared in Example 4 was sprayed onto the upper and lower surfaces of magnets 4-11 to 4-20. Then, the heat treatment trays holding the magnets to be diffused were placed in a vacuum heat treatment furnace. After the furnace door was closed and a vacuum was drawn, the diffusion treatment program was set. The specific program was as follows: First, the furnace temperature was raised to 480°C and held for 2 hours. Then, the temperature was raised to 900°C and held for 6 hours, followed by rapid air cooling to room temperature. Finally, the temperature was raised to 500°C and held for 4 hours, followed by rapid air cooling to room temperature, with the vacuum degree remaining less than 7.5 × 10⁻⁶ throughout the process. -3 Pa.

[0103] The magnetic properties of magnets 4-11 to 4-20 after diffusion were tested, and the test results are shown in Table 5.

[0104] Table 5

[0105]

[0106]

[0107] Comparative Example 2

[0108] Using an impregnation coating method, the general formula Tb 70 Cu 30 The alloy (by mass percentage) was prepared into alloy powder with an average particle size of 15 μm through coarse crushing, hydrogen crushing, and air jet milling. The diffusion source alloy powder was uniformly dispersed in anhydrous ethanol, and then adhered to the surface of magnets 4-21 to 4-30 using a traditional impregnation process. The heat treatment tray holding the magnets to be diffused was then placed in a vacuum heat treatment furnace. After the furnace door was closed and a vacuum was drawn, the diffusion treatment program was set. The specific program was as follows: first, the furnace temperature was raised to 480℃ and held for 2 hours. Then, the temperature was raised to 900℃, held for 6 hours, and then rapidly cooled to room temperature. Finally, the temperature was raised to 500℃, held for 4 hours, and then rapidly cooled to room temperature, with the vacuum degree being less than 7.5 × 10⁻⁶ throughout the process. -3 Pa.

[0109] The magnetic properties of magnets 4-21 to 4-30 after diffusion were tested, and the test results are shown in Table 6.

[0110] Table 6

[0111]

[0112] In this embodiment and comparative example, no oxidation or rust occurred on the magnet surface, nor were there any blank areas for the diffusion source, indicating that the diffusion source and diffusion substrate of the present invention have good matching. Furthermore, analysis of the performance of magnets 4-1 to 4-30 shows that the remanence of the first batch of magnets (4-1 to 4-10) decreased, but the coercivity was significantly improved. Further analysis and calculation show that the variance of the coercivity of magnets 4-1 to 4-10 is 0.0321, indicating a very stable improvement effect. The second batch of magnets (4-11 to 4-20) also showed a decrease in remanence, and the coercivity was improved to some extent, but further analysis and calculation show that the variance of the coercivity of magnets 4-11 to 4-20 is 0.2912. ， This indicates that the improvement effect fluctuates more significantly, and the performance consistency deteriorates. Finally, in the third batch of magnets (April 21st to April 30th), the remanence also decreased, and the coercivity was improved to some extent. However, further analysis and calculation showed that the variance of the coercivity data for magnets from April 21st to April 30th was 2.6898, indicating that the improvement effect fluctuated greatly and was unstable. In summary, even with the same grain boundary diffusion process, using the magnet diffusion source film of this invention for grain boundary diffusion of sintered NdFeB magnets results in a more stable improvement effect and can be applied to fields with higher precision requirements for magnet performance.

[0113] Comparative Example 3

[0114] Let the general formula be Pr 20 Tb 50 Cu 30 The alloy (by mass percentage) was prepared into alloy powder with an average particle size of 15 μm through coarse crushing, hydrogen crushing, and air jet milling. In an environment with an oxygen content of 80 ppm, the alloy powder was stirred with a dispersant (a mixture of ethanol and diethyl ether, volume ratio 4:1) and a binder (polyacrylate adhesive) at a mass ratio of 3:2:2 (500 rpm) for 50 min to obtain a diffusion source sol with a viscosity of 500 mPa·s. The diffusion source sol was then applied to a substrate film (polycarbonate film, average thickness 70 μm) by spraying (spray thickness 350 μm) at a height of 15 cm and a liquid flow rate of 350 ml / min. The film with the diffusion source slurry was then passed through a tunnel heating and drying device under roller traction and dried with hot air for 40 minutes. After drying, the film was further conveyed into a tunnel cooling device where cooling nitrogen was introduced to cool the diffusion source film for 20 minutes, resulting in a diffusion source film with a single-layer film structure.

[0115] Five commercial N55 magnets of the same composition from the same batch were selected as the substrate and subjected to wire electrical discharge machining to obtain five [magnets / materials]. Cylindrical magnets with a thickness of 4mm are polished and labeled as 5-1, 5-2, 5-3, 5-4, and 5-5. Then, eight diffusion source discs that can completely cover the diffusion surface of the magnets to be diffused are cut from the diffusion source film with a single-layer thin film structure. The diffusion source discs are attached to the upper and lower surfaces of magnets 5-1, 5-2, 5-3, and 5-4 respectively. Then, magnets 5-5 without diffusion source covers are placed in a mold on the tray of the sintering furnace.

[0116] A heat treatment tray containing the diffusion source film and the magnet to be diffused was placed in a vacuum heat treatment furnace. After closing the furnace door and evacuating the furnace, a program was set to perform grain boundary diffusion treatment on the sintered NdFeB magnet. The specific program was as follows: First, the furnace temperature was raised to 480℃ and held for 2 hours. Then, the temperature was raised to 900℃ and held for 6 hours, followed by rapid air cooling to room temperature. Finally, the temperature was raised to 500℃ and held for 4 hours, followed by rapid air cooling to room temperature, with the vacuum level remaining less than 7.5 × 10⁻⁶ throughout the process. -3 Pa; The magnetic properties of the diffused magnet were tested, and the results are shown in Table 7.

[0117] Table 7

[0118]

[0119] Compared with Example 1, it can be seen that the diffusion effect of the diffusion source film with a single-layer thin film structure is poor, the coercivity improvement effect is not as good as that of Example 1, and the consistency of the diffusion magnet with a single-layer thin film structure is lacking, which is not as good as the diffusion source film with a double-layer structure in the technical solution of the present invention.

[0120] All aspects, embodiments, and features of this invention should be considered illustrative in all respects and not limiting of 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 as claimed.

[0121] In the preparation method of this invention, the order of the steps is not limited to the listed order. For those skilled in the art, variations in the order of the steps without creative effort are also within the scope of protection of this invention. Furthermore, two or more steps or actions can be performed simultaneously.

[0122] Finally, it should be noted that the specific embodiments described herein are merely illustrative examples of the invention and are not intended to limit the implementation of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them; it is neither necessary nor possible to exemplify all embodiments here. However, these obvious variations or modifications derived from the essential spirit of the invention still fall within the scope of protection of the invention, and interpreting them as any additional limitation would contradict the spirit of the invention.

Claims

1. An application of a magnetic diffusion source thin film, characterized in that, Includes the following steps: A diffusion source film is applied to the upper and lower surfaces of the magnet to be diffused, and diffusion heat treatment is performed to obtain the diffusion magnet product. The diffusion source film comprises, in sequence, an upper substrate film, a diffusion source, and a lower substrate film; Diffusion sources include those with the general formula RE a W b The alloy and binder, wherein RE is at least one of Dy, Tb, Pr, Nd, La, Ce, Y, Gd, Ho; W is at least one of Cu, Al, Ga, In, Sn, Fe, Co, Ni, Ti, Zr, Mg; a and b are mass percentages, 50≤a≤100, and satisfy a+b=100; The upper and lower substrate films are flexible films, and the materials of the upper and lower substrate films are one or more of polyvinyl alcohol, polyurethane, polycarbonate, and polyethylene terephthalate, respectively. The diffusion heat treatment includes: heating from room temperature to 450~600 ℃ and holding for 1~3 hours, then heating to 800~950 ℃ and holding for 1~8 hours, then cooling to room temperature, and finally heating to 400~550 ℃ and holding for 1~8 hours, then cooling to room temperature.

2. The application according to claim 1, characterized in that, The method for preparing the diffusion source thin film includes the following steps: 1) Preparation of diffusion source sol; 2) Adhere the diffusion source sol to the underlying substrate film; 3) An initial diffusion source film with a "sandwich" structure is formed by adding an upper substrate film; 4) The initial diffusion source film is heated, dried, and cooled to obtain the diffusion source film.

3. The application according to claim 2, characterized in that, The preparation method of the diffusion source sol includes the following steps: Let the general formula be RE a W b The alloy is made into alloy powder; the alloy powder is mixed with dispersant and binder to obtain initial colloid; the initial colloid is stirred to release gas, thus obtaining diffusion source sol.

4. The application according to claim 3, characterized in that, The average particle size of the alloy powder is 2~50 micrometers; And / or, the dispersant is a liquid solvent, including one or more of alcohol solvents, ketone solvents, ether solvents, and ester solvents; And / or, the adhesive is one or more of polyurethane adhesives, polyacrylate adhesives, polyvinyl alcohol adhesives, polyvinyl formal adhesives, epoxy resins, and phenolic resins.

5. The application according to claim 3, characterized in that, The mass ratio of alloy powder, dispersant, and binder is 2~10:1~10:1~2; And / or, the mixing of alloy powder with dispersant and binder is carried out in an oxygen-controlled environment with an oxygen content ≤100ppm; And / or, the viscosity of the diffusion source sol is 100~3000 mPa·s.

6. The application according to claim 3, characterized in that, The diffusion source sol is attached to the underlying substrate film by spraying. The height of the spray gun is 10~50 cm and the liquid flow rate of the spray gun is 50~500 ml / min.

7. The application according to claim 3, characterized in that, The upper substrate film and the lower substrate film with the diffusion source sol attached are pressed together by two rollers to form the initial diffusion source film. The radial pressure of the two rollers is 0.5~5 N.

8. The application according to claim 3, characterized in that, Heating and drying are carried out in a tunnel heating and drying device, which employs at least one of the following heating and drying methods: heat source drying, infrared drying, and microwave drying. And / or, the cooling process is carried out in a tunnel cooling device, and the cooling method of the tunnel cooling device is at least one of cold air cooling and cold liquid cooling.

9. The application according to claim 1, characterized in that, The diffusion source film is cut before use so that it completely covers the diffusion surface of the magnet to be diffused; And / or, diffusion heat treatment is performed in a vacuum heat treatment furnace with a vacuum degree ≤1×10⁻⁶. -2 Pa.

10. The application according to claim 1, characterized in that, The magnet to be diffused is a sintered NdFeB magnet with a thickness of 1~10 mm.

Images