Coating slurry for NdFeB magnets and dipping coating method

Abstract

The present application provides a coating slurry and an immersion coating method for NdFeB magnets. The method comprises immersing a NdFeB substrate in a coating slurry, and then drying it to form a coating on the surface of the NdFeB substrate; heating the NdFeB substrate coated with the coating to remove residual organic matter in the coating; and diffusing and tempering the NdFeB substrate after the heating treatment to obtain a NdFeB magnet; wherein the surface roughness of the NdFeB substrate is 0.55~0.8μm, the coating slurry comprises a diffusion source powder, a resin, a dispersant and a solvent, the diffusion source powder contains heavy rare earth elements, the solvent comprises an alcohol or a mixture of an alcohol and an ester, the particle size of the diffusion source powder is 0.2~8μm, and the viscosity of the coating slurry is 3~800mPa.s. The immersion coating method provided in the present application is suitable for magnets of various shapes, and can obtain a coating with controllable thickness, uniformity, and rapid drying, and the magnet performance consistency is excellent.

Description

Technical Field

[0001] The invention belongs to the technical field of magnetic materials, and in particular relates to a coating slurry for a neodymium iron boron magnet and an immersion coating method for the neodymium iron boron magnet. Background Art

[0002] Sintered NdFeB magnets are widely used in motors, information technology, medical devices, 3C and other fields due to their excellent magnetic properties. In the field of new energy vehicles, the high-energy motors used have high requirements for magnet performance, but the existing sintered NdFeB magnets have reduced coercive force HCJ at high temperatures, which is prone to irreversible thermal demagnetization. In order to improve the coercive force and enhance heat resistance, in recent years, the grain boundary diffusion process is often used to diffuse heavy rare earth elements from the surface of the magnet to the inside of the magnet, so that the heavy rare earth elements are concentrated in the outer shell area of ​​the main phase grains, thereby increasing the coercive force of the magnet and suppressing the reduction of remanence Br.

[0003] The prior art discloses a rotary dip coating method, which ensures the uniformity of the dipping and the dipping effect of the thicker film layer through multiple cycles of dipping-drying-dipping-drying. This method is only applicable to the problem of the diffusion of small batches of products, and the process is complicated in batch production. With the increasing application of rare earth permanent magnets and the diversification of motor design, the requirements for the shape of magnets will become more complicated. When applied to complex-shaped magnets or large-sized products such as robot servo motors, the above-mentioned rotary dry spraying or dip coating method is likely to make the thickness of the inner and outer wall coating layers of complex-shaped products uneven, and the corners of the magnets are prone to knocking when the rolling cage rotates, which is also not applicable. Summary of the invention

[0004] The first object of the present application is to provide a rapid coating process suitable for a variety of products.

[0005] The second purpose of the present application is to solve the problem of increasing the coating thickness while enabling the coating to dry quickly.

[0006] In order to achieve at least one of the above purposes, the first aspect of the present application provides a dip coating method for a NdFeB magnet, comprising:

[0007] Dipping the NdFeB substrate into the coating slurry, and then drying it to form a coating on the surface of the NdFeB substrate;

[0008] heating the NdFeB substrate coated with the coating to remove residual organic matter in the coating; and

[0009] Performing diffusion treatment and tempering treatment on the NdFeB matrix after the heating treatment to obtain the NdFeB magnet;

[0010] Among them, the surface roughness of the NdFeB matrix is ​​0.55~0.8μm, the coating slurry includes diffusion source powder, resin, dispersant and solvent, the diffusion source powder contains heavy rare earth elements, the solvent includes alcohol or a mixture of alcohol and ester, the particle size of the diffusion source powder is 0.2~8μm, and the viscosity of the coating slurry is 3~800mPa.s.

[0011] In some embodiments of the present application, in the coating slurry, the content of the diffusion source powder is 50-90 wt %, the content of the resin is 0.2-2 wt %, the content of the dispersant is 0.2-1 wt %, and the content of the solvent is 7-40 wt %;

[0012] The diffusion source powder includes a heavy rare earth compound or a heavy rare earth alloy, and the heavy rare earth element is selected from one or more of Dy, Tb and Ho.

[0013] In some embodiments of the present application, in the mixture of alcohol and ester, the ester is selected from one or both of ethyl acetate and n-butyl acetate; the content of the alcohol is above 80 wt%, and the alcohol is selected from one or both of ethanol and isopropanol.

[0014] In some embodiments of the present application, the coating slurry also includes a thickener, the content of the thickener is 0.3~2wt%, and the thickener is selected from one or more of terpene resins, aldehyde ketone resins, alkanolamide resins, and amine oxide resins.

[0015] In some embodiments of the present application, the content of the thickener is 0.5-2 wt %, and the thickener is selected from one or more of alkanolamide resins and amine oxide resins.

[0016] In some embodiments of the present application, the surface roughness of the NdFeB substrate is 0.65-0.8 μm;

[0017] The NdFeB substrate is immersed in the coating slurry for 1 to 40 seconds at a temperature of 10 to 40°C.

[0018] In some embodiments of the present application, the heating treatment is performed in a vacuum or argon atmosphere, and the pressure of the argon atmosphere is 10-3000 Pa;

[0019] The heating treatment is performed at a temperature of 200-450°C and a time of 10-150 minutes;

[0020] The diffusion treatment is performed at a temperature of 620-950°C and a time of 2-40 hours;

[0021] The temperature of the tempering treatment is 450-700° C., and the time is 1-10 hours.

[0022] In some embodiments of the present application, immersing the NdFeB substrate in the coating slurry includes: fixing the NdFeB substrate and then immersing the substrate in the coating slurry.

[0023] In some embodiments of the present application, during dipping, the coating slurry satisfies: c(L) / c(M)=0.95~1.05, c(H) / c(M)=0.95~1.05;

[0024] Among them, c(L) is the concentration of heavy rare earth elements in the bottom layer of the coating slurry, c(M) is the concentration of heavy rare earth elements in the middle layer of the coating slurry, and c(H) is the concentration of heavy rare earth elements in the upper layer of the coating slurry. The heights of the bottom, middle and upper layers of the coating slurry respectively account for 1 / 3 of the total height of the coating slurry, and the total height of the coating slurry is 50~400mm.

[0025] A second aspect of the present application provides a coating slurry for a NdFeB magnet, comprising a diffusion source powder, a resin, a dispersant and a solvent;

[0026] The diffusion source powder contains heavy rare earth elements, the solvent includes alcohol or a mixture of alcohol and ester, the particle size of the diffusion source powder is 0.2-8 μm, and the viscosity of the coating slurry is 3-800 mPa.s.

[0027] In some embodiments of the present application, in the coating slurry, the content of the diffusion source powder is 50~90wt%, the content of the resin is 0.2~2wt%, the content of the dispersant is 0.2~1wt%, and the content of the solvent is 7~40wt%.

[0028] In some embodiments of the present application, in the mixture of alcohol and ester, the ester is selected from one or both of ethyl acetate and n-butyl acetate, the content of the alcohol is above 80 wt%, and the alcohol is selected from one or both of ethanol and isopropanol.

[0029] In some embodiments of the present application, the viscosity of the coating slurry is 3 to 500 mPa.s;

[0030] The coating slurry also includes a thickener, the content of which is 0.3-2 wt %; the thickener is selected from one or more of terpene resins, aldehyde-ketone resins, alkanolamide resins, and amine oxide resins.

[0031] The dip coating method provided in the present application is suitable for magnets of various shapes, and can obtain a coating with controllable thickness, uniformity, and rapid drying, and can achieve a three-dimensional heavy rare earth diffusion effect, with excellent magnet performance consistency.

[0032] The coating slurry provided in the present application can form a thick and uniform coating on the surface of the magnet after coating, and can be dried quickly.

[0033] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings constituting a part of the present disclosure are used to provide a further understanding of the present disclosure. The illustrative embodiments of the present disclosure and their descriptions are used to explain the present disclosure and do not constitute improper limitations on the present disclosure.

[0035] Figure 1 A process flow chart of the immersion coating of NdFeB magnets provided in one embodiment of the present application is shown. DETAILED DESCRIPTION

[0036] In the following, only some exemplary embodiments are briefly described. As those skilled in the art will appreciate, the described embodiments may be modified in various ways without departing from the spirit or scope of the present invention. Therefore, the drawings and descriptions are considered to be exemplary and non-restrictive in nature.

[0037] The disclosure below provides many different embodiments or examples for realizing different structures of the present invention. In order to simplify the disclosure of the present invention, the components and installations of specific examples are described below. Of course, they are only examples and are not intended to limit the present invention. In addition, the present invention may repeat reference numbers and / or reference letters in different examples, and such repetition is for the purpose of simplicity and clarity, and does not itself indicate the relationship between the various embodiments and / or installations discussed. In addition, the present invention provides examples of various specific processes and materials, but those of ordinary skill in the art may recognize the application of other processes and / or the use of other materials.

[0038] In the present invention, the terms "first", "second" and other ordinal numbers are used only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0039] In addition, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. It will also be understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology and the present invention, and will not be interpreted in an idealized or overly formal sense unless explicitly defined in this article.

[0040] As used herein, "about" or "approximately" is inclusive of the stated value and means within an acceptable range of deviation from the particular value as determined by one skilled in the art, taking into account the measurement in question and the errors associated with the measurement of the particular quantity (i.e., the limitations of the measurement system). For example, "about" can mean within one or more standard deviations, or within ±30%, ±20%, ±10%, or ±5% of the stated value.

[0041] The following is a more detailed description of the specific embodiments of the present invention in conjunction with the accompanying drawings and examples, so that the scheme of the present invention and its advantages in various aspects can be better understood. However, the specific embodiments and examples described below are only for the purpose of illustration, rather than for limiting the present invention.

[0042] Figure 1 A dip coating method for NdFeB magnets provided in an embodiment of the present application is shown, comprising the following steps S1 to S3.

[0043] S1: The NdFeB substrate is immersed in the coating slurry, and then dried to form a coating on the surface of the NdFeB substrate.

[0044] Dip coating is suitable for all types and sizes of magnets.

[0045] The coating slurry used in the present application includes diffusion source powder, resin, dispersant and solvent. The diffusion source powder contains heavy rare earth elements. Optionally, the heavy rare earth elements are selected from one or more of Dy, Tb and Ho. Optionally, the diffusion source powder includes a heavy rare earth compound or a heavy rare earth alloy, the heavy rare earth compound is, for example, a fluoride or hydride of a heavy rare earth, and the heavy rare earth alloy is, for example, an alloy of a heavy rare earth and a transition metal (such as Ti, Co, Ni) or a low melting point metal (such as Al, Cu, Ga).

[0046] The particle size of the diffusion source powder used in this application is 0.2~8μm. If the particle size is too fine, the specific surface area is large, such as heavy rare earth hydride and heavy rare earth alloy powders, which are more easily contaminated by impurities, such as oxidation. If the particle size is too coarse, it is easy to settle in the slurry, resulting in uneven distribution of heavy rare earth in the coating. In some specific embodiments of the present application, the particle size of the diffusion source powder can be 0.2μm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm or 8μm.

[0047] Optionally, in the coating slurry, the content of the diffusion source powder is 50-90wt%. Within this range, combined with the dipping coating method, the content of the diffusion source powder in the coating formed on the surface of the NdFeB substrate can be within a preferred range, thereby improving the performance of the magnet. In some specific embodiments of the present application, the content of the diffusion source powder can be 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt% or 50wt%.

[0048] The dispersant used in the present application may optionally include amide organic matter, lipids, methyl laurate, etc., including but not limited to oleamide, stearamide, erucamide, oleoyl glycol amine, etc. The particle size of the diffusion source powder used in the present application is micron-level, and the dispersant is conducive to the uniform distribution of the diffusion source powder in the solvent and prevents the sedimentation of the diffusion source powder during the impregnation process. Optionally, the content of the dispersant is 0.2~1wt%. In some specific embodiments of the present application, the content of the dispersant may be 0.2wt%, 0.4wt%, 0.6wt%, 0.8wt% or 1wt%.

[0049] The solvent used in the present application includes a mixture of alcohol or alcohol and ester. Optionally, the content of the solvent is 7-40 wt%. In some specific embodiments of the present application, the content of the solvent may be 7wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt% or 40wt%. Alcohol or a mixture of alcohol and ester is conducive to the uniform distribution of the diffusion source powder, and can be quickly volatilized during subsequent drying. Optionally, in the mixture of alcohol and ester, the content of alcohol is more than 80wt%. Alcohol is selected from ethanol and / or isopropanol. The existing dip coating method generally uses a suspension slurry with ethanol as a solvent. The compound powder of heavy rare earth in the suspension slurry is very easy to settle, resulting in instability of the slurry over time, and then the thickness / weight of the coating is difficult to control. In addition, the adhesion of ethanol is limited, so the thickness of the coating is difficult to control thicker, which will affect the increase in coercivity, and the coating is easy to fall off during the entire process before the diffusion heat treatment after the subsequent coating, further causing the coating to be unevenly distributed on the coating surface. The present application prefers a mixture of alcohol and ester. The presence of ester is conducive to the uniform distribution of diffusion source powder in the solvent, inhibits the sedimentation rate of diffusion source powder, and can overcome the problem of limited adhesion of the coating. However, if the content is too much, it is not conducive to the volatilization of the solvent. The ester can be ethyl acetate, n-butyl acetate, etc.

[0050] The resin used in this application may optionally include polyvinyl butyral (PVB), acrylic resin, etc. Optionally, the molecular weight of PVB may be 20,000 to 50,000. Optionally, the acrylic resin may be BR-73, BR-85, BR-106, etc. Optionally, in the coating slurry, the content of the resin is 0.2 to 2 wt%. In some specific embodiments of the present application, the content of the resin may be 0.2 wt%, 0.4 wt%, 0.6 wt%, 0.8 wt%, 1 wt%, 1.2 wt%, 1.4 wt%, 1.6 wt%, 1.8 wt% or 2 wt%. The resin of the present application may improve the rheology of the slurry and enhance the coating stability on the one hand, and may improve the adhesion and coating strength on the other hand, and prevent the coating from falling off.

[0051] The viscosity of the coating slurry used in the present application is 3~800mPa.s, and further optionally 3~500mPa.s. Compared with the viscosity of traditional slurries, the viscosity of the slurry system of the present invention is increased to 3~800mPa.s. The present invention finds that if the slurry viscosity is too low, the coating formed on the surface of the magnet is not easy to be thick, the coating weight gain is not high, and the coercive force level is not very high; if the slurry viscosity is too high, the coating is easy to be too thick and cause local unevenness. When the slurry viscosity is 3~800 mPa.s, the ideal coating thickness can be achieved. In some specific embodiments of the present application, the viscosity of the coating slurry may be 3mPa.s, 10mPa.s, 50mPa.s, 100mPa.s, 150mPa.s, 200mPa.s, 250mPa.s, 300mPa.s, 350mPa.s, 400mPa.s, 450mPa.s, 500mPa.s, 550mPa.s, 600mPa.s, 650mPa.s, 700mPa.s, 750mPa.s or 800mPa.s.

[0052] The NdFeB matrix used in this application can be homemade or commercially available. The NdFeB matrix can be pre-treated before impregnation. The surface roughness of the NdFeB matrix after pre-treatment is 0.55~0.8μm, and preferably, the surface roughness of the NdFeB matrix is ​​0.65~0.8μm. The pre-treatment method can be degreasing water washing, sandblasting, coarsening, etc. By pre-treating the NdFeB matrix before impregnation, on the one hand, impurities on the surface of the matrix can be removed, and further, by increasing the surface roughness of the NdFeB matrix, when the slurry viscosity is increased, while achieving an increase in coating thickness, the displacement and agglomeration of heavy rare earth particles during the impregnation process can be suppressed, thereby making the heavy rare earth particles more evenly distributed in the coating. In some specific embodiments of the present application, the surface roughness of the NdFeB substrate may be 0.55 μm, 0.60 μm, 0.65 μm, 0.70 μm, 0.75 μm or 0.80 μm.

[0053] In addition, the coating thickness and the drying rate are in conflict. When the coating thickness increases, the drying rate of the substrate coating after dipping will drop significantly. When the coating is difficult to dry quickly, the heavy rare earth powder in the coating may move or agglomerate, which will continue to affect the uniform distribution of the heavy rare earth in the coating. Due to the effect of gravity, it is difficult for the coating to maintain a consistent thickness at various positions of the substrate. Therefore, when the coating thickness increases, the problem of drying rate still needs to be solved. Optionally, the drying time of the coating is 1 to 40 seconds. Optionally, the coating slurry also includes a thickener, which is selected from one or more of terpene resins and aldehyde-ketone resins. The above-mentioned thickener can not affect the drying rate of the coating after the substrate coating is thickened without affecting the solvent system. When the above-mentioned thickener is selected, the content of the thickener in the coating slurry may be 0.3 to 2wt%. In some specific embodiments of the present application, the content of the thickener may be 0.3wt%, 0.5wt%, 1wt%, 1.5wt% or 2wt%.

[0054] Optionally, the thickener is a low molecular thickener. The low molecular thickener can be preferably adapted to the above solvent system, and can make the slurry more stable while adjusting the viscosity of the slurry, and does not affect the drying rate under the solvent system, and can prevent the diffusion source powder from agglomerating. When the slurry is more stable, the coating of a single magnet can be completely dried within 1 to 40 seconds, making the thickness uniform and controllable. The low molecular thickener can be an alkanolamide resin and / or an amine oxide resin, such as coconut oil-based dimethyl tertiary amine, tetradecylamine oxide. Optionally, in the slurry coating slurry, the content of the low molecular thickener is 0.5 to 2wt%. In some specific embodiments of the present application, the content of the low molecular thickener can be 0.5wt%, 1.5wt% or 2wt%.

[0055] Optionally, during the dipping, the NdFeB substrate can be fixed before being dipped into the coating slurry. For example, for a larger NdFeB substrate, it can be fixed at a suitable interval before subsequent dipping, which is convenient for the substrate to complete the entire dipping process, and on the other hand ensures that all surfaces of the substrate are in full contact with the slurry and can be evenly coated, such as by fixing it in a hanging manner. Compared with the dipping coating method of rotating in a rolling cage, the problem of easy knocking of the corners of the magnet can be prevented.

[0056] Optionally, during dipping, the coating slurry satisfies the conditions of c(L) / c(M)=0.95~1.05, c(H) / c(M)=0.95~1.05. In some specific embodiments of the present application, the values ​​of c(L) / c(M) and c(H) / c(M) may be 0.95, 0.96, 0.97, 0.98, 0.99, 1, 1.01, 1.02, 1.03, 1.04 or 1.05, respectively.

[0057] Among them, c(L) is the concentration of heavy rare earth elements in the bottom layer of the coating slurry, c(M) is the concentration of heavy rare earth elements in the middle layer of the coating slurry, and c(H) is the concentration of heavy rare earth elements in the upper layer of the coating slurry. The heights of the bottom, middle and upper layers of the coating slurry account for 1 / 3 of the total height of the coating slurry. That is, the slurry is divided into three regions, namely the bottom layer L, the middle layer M and the upper layer H, in a certain volume space according to the height. If the slurry liquid level is Y, then the heights of the bottom layer L, the middle layer M and the upper layer H are all 1 / 3Y, and the slurry page height Y is 50~400mm.

[0058] After research, the inventors found that when the slurry viscosity is between 3 and 800 mPa.s for dipping coating, when the heavy rare earth concentration meets the above conditions, the concentration fluctuation can be controlled within an ideal range, the heavy rare earth coating formed at various positions of the NdFeB matrix after dipping is evenly distributed, and the heavy rare earth content of the NdFeB matrix coating fluctuates little between single batches, and the magnet performance consistency after diffusion is excellent.

[0059] The slurry concentration can be regulated by rotating the container carrying the slurry at a certain rate so that the concentration fluctuation of the slurry in each area can be controlled, or by using a stirring device so that the slurry is in a non-static state when the magnet substrate is impregnated.

[0060] Optionally, the immersion time of the NdFeB matrix in the coating slurry is 1 to 40 seconds. Within the above time range, the immersion coating can be completed without wasting extra time. Optionally, the immersion temperature is 10 to 40°C. The above temperature range is conducive to improving the efficiency of immersion coating. In some specific embodiments of the present application, the immersion time may be 1s, 5s, 10s, 15s, 20s, 25s, 30s, 35s or 40s. In some specific embodiments of the present application, the immersion temperature may be 10°C, 15°C, 20°C, 25°C, 30°C, 35°C or 40°C.

[0061] Optionally, the method for preparing the NdFeB matrix can be: using a quick-setting process to prepare an alloy quick-setting sheet, the quick-setting sheet is hydrogen-crushed and an additive is added to perform air flow milling to obtain an alloy powder, and the average particle size of the alloy powder is D 50 The alloy powder is pressed into shape under magnetic field orientation, and the magnetic field strength is 1.8~2.5T to obtain a compact; the compact is placed in a sintering furnace, and sintered and aged in a vacuum or inert atmosphere to obtain a blank; the blank is machined into a NdFeB matrix of a specific size.

[0062] S2: The NdFeB substrate coated with the coating is subjected to a heating treatment to remove residual organic matter in the coating.

[0063] After drying in step S1, most of the organic matter in the coating slurry is heated and volatilized. The purpose of this step is to remove the residual organic matter after drying. This step can also be called a degreasing step.

[0064] Optionally, the heat treatment is performed in a vacuum or argon atmosphere to prevent the diffusion source in the coating from being oxidized. Optionally, the pressure of the argon atmosphere is 10 to 3000 Pa. In some specific embodiments of the present application, the pressure of the argon atmosphere may be 10 Pa, 100 Pa, 300 Pa, 600 Pa, 900 Pa, 1200 Pa, 1500 Pa, 1800 Pa, 2100 Pa, 2300 Pa, 2500 Pa, 2700 Pa or 3000 Pa.

[0065] Optionally, the temperature of the heat treatment is 200-450°C, and the time is 10-150 min. In some specific embodiments of the present application, the temperature of the heat treatment may be 200°C, 250°C, 300°C, 350°C, 400°C or 450°C. In some specific embodiments of the present application, the time of the heat treatment may be 10 min, 30 min, 60 min, 90 min, 120 min or 150 min.

[0066] S3: performing diffusion treatment and tempering treatment on the NdFeB matrix after the heating treatment to obtain a NdFeB magnet.

[0067] After degreasing, diffusion treatment and tempering treatment can be carried out. Optionally, the temperature of the diffusion treatment is 620~950℃, and the time is 2~40h. In some specific embodiments of the present application, the temperature of the diffusion treatment may be 620℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃ or 950℃. In some specific embodiments of the present application, the time of the diffusion treatment may be 2h, 5h, 10h, 15h, 20h, 25h, 30h, 35h or 40h.

[0068] Optionally, the tempering temperature is 450-700°C and the time is 1-10 hours. In some specific embodiments of the present application, the tempering temperature may be 450°C, 500°C, 550°C, 600°C, 650°C or 700°C. In some specific embodiments of the present application, the tempering time may be 1 hour, 2 hours, 4 hours, 6 hours, 8 hours or 10 hours.

[0069] Optionally, the composition of the NdFeB matrix is ​​RTBM, wherein the content of R is 28-30.5wt%, the content of M is 0-3wt% and does not include 0, the content of B is 0.85-1.05wt%, the content of T is the remainder of R, B and M, and T includes Fe, or T includes Fe and Co. Generally speaking, the content of T can be 65.45-70wt%, preferably, the content of Fe in the T accounts for more than 97wt% of the total amount of T, preferably, the R includes Nd and other rare earth elements. Preferably, the other rare earth elements include any one of Pr, La, Ce, Dy, Tb or Ho or a combination of at least two.

[0070] The dip coating method provided in the present application is suitable for magnets of various shapes, and can obtain a coating with controllable thickness, uniformity, and rapid drying, and the magnet performance consistency is excellent.

[0071] The present application also provides a coating slurry for NdFeB magnets, which is specifically described above and will not be repeated here.

[0072] The coating slurry provided in the present application can form a coating with controllable thickness and uniformity on the surface of the magnet after coating, and can be dried quickly.

[0073] The present invention will be described below with reference to specific embodiments. The process condition values ​​taken in the following embodiments and comparative examples are exemplary, and their possible numerical ranges are as shown in the aforementioned summary of the invention. For process parameters not particularly noted, conventional techniques can be used. Unless otherwise specified, reagents and instruments used in the technical scheme provided by the present invention can be purchased from conventional channels or the market. It should be noted that, in the absence of conflict, the features in the embodiments in this application and the embodiments can be combined with each other.

[0074] The specific preparation steps of the NdFeB matrix in the following examples and comparative examples are as follows:

[0075] In the smelting process, the prepared raw materials are put into a vacuum induction melting furnace, heated to 1350°C, fully melted into alloy steel liquid, poured onto a rapid cooling roller and rapidly cooled to form an alloy sheet. After secondary cooling, an alloy sheet with a thickness of 0.25 mm is obtained.

[0076] In the powder making process, the obtained alloy sheet is subjected to hydrogen embrittlement treatment and air flow mill grinding to obtain air flow milled powder with an average particle size SMD of 3.0 μm.

[0077] In the molding process, 0.2 wt% of lubricant is added to the air flow mill, and the mixture is mixed by a mixer for 120 minutes until the mixture is evenly dispersed. The mixture is pressed under nitrogen protection and an external 2T magnetic field, and a green body is obtained after cold isostatic pressing.

[0078] In the sintering process, the green body is placed in a vacuum sintering furnace, kept at 1045℃ for 300min, cooled to room temperature; then kept at 1080℃ for 300min, cooled to room temperature. The green body after sintering is further subjected to the first aging treatment at 900℃ for 240min, and the second aging treatment at 530℃ for 240min, and then cooled out of the furnace to obtain the NdFeB magnet blank.

[0079] Machining process: The NdFeB magnet blank is processed into a sheet of 30*20*4mm (ie, the thickness in the orientation direction is 4mm) to obtain a NdFeB matrix.

[0080] Example 1

[0081] This embodiment prepares a neodymium iron boron magnet, and the specific steps are as follows:

[0082] Preparation of NdFeB matrix: the raw material composition is 29.5wt% PrNd, 0.6wt% Co, 0.92wt% B, 0.2wt% Cu, 0.15wt% Ga and 0.2wt% Zr, and the remainder is Fe and unavoidable impurities. The above raw materials are prepared according to the specific preparation steps of the NdFeB matrix mentioned above, wherein a single batch of magnets has a total of 50 magnets.

[0083] Pretreatment: The NdFeB substrate is subjected to degreasing, water washing and sandblasting operations in sequence. After the above treatments, the surface roughness of the NdFeB substrate is about 0.79 μm.

[0084] Preparation of coating slurry: Evenly mix the diffusion source powder, resin, dispersant and solvent. The diffusion source powder is dysprosium hydride powder, and its content in the coating slurry is 80wt%; the resin is PVB, and its content is 0.21wt%; the dispersant is oleic acid amide, and its content is 0.9wt%; the solvent is a mixture of ethanol and ethyl acetate, and the solvent content is 18.89 wt%, and the proportion of ethanol in the solvent is 90%. The viscosity of the obtained coating slurry is about 3mPa.s.

[0085] Dipping: Dip the NdFeB substrate into the coating slurry and then dry it to form a coating on the surface of the NdFeB substrate. The dipping time is about 30 seconds and the dipping temperature is room temperature. During dipping, the speed of the stirring device in the slurry is about 400r / min. During dipping, the viscosity of the coating slurry satisfies c(L) / c(M)=1.06, c(H) / c(M)=0.94, and the total height of the coating slurry is about 300mm. The drying temperature is about 80℃.

[0086] Degreasing: The coated NdFeB substrate is heated under vacuum to remove residual organic matter in the coating. The heating temperature is about 300°C and the heating time is about 60 minutes.

[0087] Diffusion and tempering: The NdFeB matrix after the heating treatment is subjected to diffusion treatment and tempering treatment to obtain the NdFeB magnet. The temperature of the diffusion treatment is about 800°C and the time is about 25h. The temperature of the tempering treatment is about 600°C and the time is about 6h.

[0088] The NdFeB substrate after pretreatment and the NdFeB magnet coated with the coating after degreasing were weighed respectively to obtain the first weight of the NdFeB substrate and the second weight of the NdFeB magnet, thereby calculating the weight of the coating (weight of the coating = second weight - first weight). On this basis, the average weight and range of the coating weight of the same batch of magnets were calculated, as shown in Table 1, where W AVE Indicates the average coating weight of the same batch of magnets, W R It indicates the extreme difference of coating weight of magnets in the same batch, that is, the difference between the maximum coating weight and the minimum coating weight in the same batch of magnets.

[0089] The thickness of any two surface coatings of the same batch of NdFeB magnets coated with coatings after deesterification was measured and the thickness difference was calculated, as shown in Table 1, where H represents the average value of the coating thickness difference in the same batch of magnets.

[0090] The coating drying time of the same batch of magnets is shown in Table 1, where T represents the time taken for all magnets in the same batch to be completely dried.

[0091] The consistency of the magnetic property increment of the same batch of magnets is shown in Table 1, where ΔHCJ AVE The average value of the coercivity increase after diffusion of the same batch of magnets, ΔHCJ R Indicates the extreme difference in the increase in coercivity of magnets from the same batch after diffusion.

[0092] Example 2

[0093] The difference between this embodiment and embodiment 1 is that the viscosity of the coating slurry is about 10mPa.s, wherein the diffusion source powder is terbium hydride powder, and its content in the coating slurry is 82wt%; the resin is PVB, and its content is 0.25wt%; the dispersant is erucic acid amide, and its content is 0.9wt%; the solvent is a mixture of ethanol and ethyl acetate, and the solvent content is 16.85wt%, and the proportion of ethanol in the solvent is 85%. The performance parameters are shown in Table 1.

[0094] Example 3

[0095] The difference between this embodiment and embodiment 1 is that the viscosity of the coating slurry is about 150mPa.s. The diffusion source powder is terbium hydride powder, and its content in the coating slurry is 86wt%; the resin is BR-73 acrylic resin, and its content is 0.45wt%; the dispersant is oleic acid amide, and its content is 0.35wt%; and the solvent is ethanol, and its content is 13.2wt%. The performance parameters are shown in Table 1.

[0096] Example 4

[0097] The difference between this embodiment and embodiment 1 is that the viscosity of the coating slurry is about 800mPa.s. The diffusion source powder is dysprosium hydride powder, and its content in the coating slurry is 80wt%; the resin is BR-73 acrylic resin, and its content is 0.5wt%; the dispersant is oleyl glycol amine, and its content is 0.5wt%; the solvent is a mixture of ethanol and ethyl acetate, and the solvent content is 18.7wt%, and the proportion of ethanol in the solvent is 90%; and the coating slurry also includes a thickener terpene resin, and the content of the thickener is 0.3wt%. The performance parameters are shown in Table 1.

[0098] Example 5

[0099] The difference between this embodiment and embodiment 1 is that the viscosity of the coating slurry is about 500mPa.s. Among them, the diffusion source powder is terbium hydride powder, and its content in the coating slurry is 79wt%; the resin is PVB, and its content is 1.5wt%; the dispersant is oleic acid amide, and its content is 0.5wt%; the solvent is a mixture of ethanol and ethyl acetate, and the solvent content is 17wt%, and the proportion of ethanol in the solvent is 90%; and the coating slurry also includes a low molecular weight thickener coconut oil dimethyl tertiary amine, and the content of the thickener is 2%. Performance parameters are shown in Table 1.

[0100] Example 6

[0101] The difference between this embodiment and embodiment 1 is that the surface roughness of the NdFeB substrate is about 0.55 μm. The performance parameters are shown in Table 1.

[0102] Example 7

[0103] The difference between this embodiment and embodiment 1 is that during dipping, the coating slurry satisfies c(L) / c(M)=1.02, c(H) / c(M)=0.98. The performance parameters are shown in Table 1.

[0104] Comparative Example 1

[0105] The difference between this embodiment and embodiment 1 is that the solvent does not contain ethanol, and the solvent is all ethyl acetate. The viscosity of the coating slurry is about 2000 mPa.s. The performance parameters are shown in Table 1.

[0106] Comparative Example 2

[0107] The difference between this embodiment and embodiment 1 is that the viscosity of the coating slurry is about 0.1 mPa.s, the content of the diffusion source powder in the coating slurry is 70wt%, the solvent is ethanol, the content of ethanol is 30wt%, and no resin and dispersant are contained. The performance parameters are shown in Table 1.

[0108] Comparative Example 3

[0109] The difference between this embodiment and embodiment 1 is that the surface roughness of the NdFeB substrate is about 0.50 μm. The performance parameters are shown in Table 1.

[0110] Table 1

[0111]

[0112] As can be seen from Table 1, the weight gain fluctuation range of the magnet coating prepared by the present application is very small, and the thickness of the coating on each surface of the magnet is relatively thick and uniform, indicating that the coating slurry provided by the present application can form a coating with controllable thickness and uniformity on the surface of the magnet after coating. The coating slurry provided by the present application has a very short drying time and can be dried quickly. In addition, as can be seen from Table 1, the NdFeB magnet prepared by the coating method and coating slurry of the present application can achieve three-dimensional heavy rare earth diffusion, with a significant increase in coercive force and good incremental consistency.

[0113] Obviously, the above embodiments are merely examples for clearly explaining the present invention, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A dip coating method for NdFeB magnets, characterized in that: include: Dipping the NdFeB substrate into the coating slurry, and then drying it to form a coating on the surface of the NdFeB substrate; Heating the NdFeB substrate coated with the coating to remove residual organic matter in the coating; as well as Performing diffusion treatment and tempering treatment on the NdFeB matrix after the heating treatment to obtain the NdFeB magnet; The surface roughness of the NdFeB substrate is 0.55-0.8 μm, the coating slurry comprises diffusion source powder, resin, dispersant, solvent and thickener, the diffusion source powder contains heavy rare earth elements, the solvent comprises a mixture of alcohol and ester, the particle size of the diffusion source powder is 0.2-8 μm, and the viscosity of the coating slurry is 150-800 mPa.s; In the coating slurry, the content of the diffusion source powder is 80-90wt%; In the mixture of alcohol and ester, the ester is selected from one or both of ethyl acetate and n-butyl acetate, the content of the alcohol is more than 80wt%, and the alcohol is selected from one or both of ethanol and isopropanol; The content of the thickener is 0.3-2wt%, and the thickener is selected from one or more of terpene resins, aldehyde-ketone resins, alkanolamide resins, and amine oxide resins.

2. The dip coating method according to claim 1, characterized in that In the coating slurry, the content of the resin is 0.2-2 wt %, the content of the dispersant is 0.2-1 wt %, and the content of the solvent is 7-40 wt %; The diffusion source powder includes a heavy rare earth compound or a heavy rare earth alloy, and the heavy rare earth element is selected from one or more of Dy, Tb and Ho.

3. The dip coating method according to claim 1, characterized in that The content of the thickener is 0.5-2wt%, and the thickener is selected from one or more of alkanolamide resins and amine oxide resins.

4. The dip coating method according to claim 1, characterized in that The surface roughness of the NdFeB substrate is 0.65-0.8 μm; The NdFeB substrate is immersed in the coating slurry for 1 to 40 seconds at a temperature of 10 to 40°C.

5. The dip coating method according to claim 1, characterized in that The heating treatment is carried out in a vacuum or argon atmosphere, and the pressure of the argon atmosphere is 10-3000 Pa; The heating treatment is performed at a temperature of 200-450°C and a time of 10-150 minutes; The diffusion treatment is performed at a temperature of 620-950°C and a time of 2-40 hours; The temperature of the tempering treatment is 450-700° C., and the time is 1-10 hours.

6. The dip coating method according to claim 1, characterized in that The method of dipping the NdFeB substrate into the coating slurry comprises: fixing the NdFeB substrate and then dipping the substrate into the coating slurry.

7. The dip coating method according to claim 1, characterized in that During dipping, the coating slurry satisfies: c(L) / c(M)=0.95~1.05, c(H) / c(M)=0.95~1.05; Among them, c(L) is the concentration of heavy rare earth elements in the bottom layer of the coating slurry, c(M) is the concentration of heavy rare earth elements in the middle layer of the coating slurry, and c(H) is the concentration of heavy rare earth elements in the upper layer of the coating slurry. The heights of the bottom, middle and upper layers of the coating slurry respectively account for 1 / 3 of the total height of the coating slurry, and the total height of the coating slurry is 50~400mm.

8. A dip coating slurry for NdFeB magnets, characterized in that: It includes diffusion source powder, resin, dispersant, solvent and thickener; The diffusion source powder contains heavy rare earth elements, the solvent includes a mixture of alcohol and ester, the particle size of the diffusion source powder is 0.2-8 μm, and the viscosity of the dipping coating slurry is 150-800 mPa.s; In the dipping coating slurry, the content of the diffusion source powder is 80-90wt%; In the mixture of alcohol and ester, the ester is selected from one or both of ethyl acetate and n-butyl acetate, the content of the alcohol is more than 80wt%, and the alcohol is selected from one or both of ethanol and isopropanol; The content of the thickener is 0.3-2wt%, and the thickener is selected from one or more of terpene resins, aldehyde-ketone resins, alkanolamide resins, and amine oxide resins.

9. The dip coating slurry according to claim 8, characterized in that In the dipping coating slurry, the content of the resin is 0.2-2 wt %, the content of the dispersant is 0.2-1 wt %, and the content of the solvent is 7-40 wt %.

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