High-efficiency preparation method of NdFeB magnets based on grain boundary diffusion

Abstract

The present invention relates to the field of magnetic material preparation, and in particular to a high-efficiency method for preparing NdFeB magnets based on grain boundary diffusion. The method comprises: etching the surface of NdFeB magnet raw material; detecting the surface roughness of the deoxidized NdFeB magnet; determining the coating thickness and coating method of a coating paste based on the surface roughness; mixing grain boundary diffusion powder with an acetone solution to produce the coating paste; applying the coating paste to the surface of the deoxidized NdFeB magnet; placing the thick-coated NdFeB magnet in a low-frequency alternating magnetic field; determining a coercive force curve of the thick-coated NdFeB magnet; adjusting the detection distance of the alternating magnetic field; and sequentially introducing argon gas into the low-frequency alternating magnetic field region and performing diffusion heat treatment to produce a finished NdFeB magnet that meets the requirements. The present invention improves the magnetic properties of NdFeB magnets by grain boundary diffusion of heavy rare earth elements.

Description

Technical Field

[0001] The present invention relates to the field of magnetic material preparation, and in particular to a high-efficiency preparation method of NdFeB magnets based on grain boundary diffusion. Background Art

[0002] Neodymium iron boron (NdFeB) magnets are permanent magnets with high magnetic energy product, high coercivity, and high remanence. They are widely used in numerous fields, including electronics, electrical engineering, machinery, medicine, and aerospace. With the continuous advancement of technology, the demand for high-performance NdFeB magnets continues to grow, especially in emerging sectors such as new energy vehicles, wind power generation, and energy-saving home appliances, which place higher demands on both performance and production. Traditional NdFeB magnet production methods primarily enhance magnetic properties by optimizing alloy composition and improving smelting and sintering processes. These methods typically require large amounts of rare earth elements (rare earth elements) such as neodymium, dysprosium, and terbium, which are limited and expensive. Furthermore, traditional production processes are complex and energy-intensive. To address these limitations, grain boundary diffusion (GBD) technology has emerged. GBD introduces additives such as heavy rare earth elements into the grain boundaries of NdFeB magnets to increase their coercivity. Compared with traditional methods, grain boundary diffusion can significantly improve the coercivity of NdFeB magnets at a relatively low addition amount of heavy rare earth elements while maintaining high remanence and magnetic energy product.

[0003] Chinese patent publication number CN111430142B discloses a method for preparing NdFeB magnets by grain boundary diffusion, the method comprising: providing a NdFeB prefabricated magnet; forming a heavy rare earth film on the surface of the NdFeB prefabricated magnet; subjecting the NdFeB prefabricated magnet with the heavy rare earth film to heat treatment and tempering to obtain a prefabricated body, wherein the prefabricated body comprises a normal shell layer and a transition layer and an abnormal shell layer sequentially covering the normal shell layer, wherein the heavy rare earth content in the main phase grains in the normal shell layer gradually decreases from the edge of the main phase grains to the center of the main phase grains, and the heavy rare earth content in the main phase grains in the abnormal shell layer gradually increases from the edge of the main phase grains to the center of the main phase grains; and removing the abnormal shell layer to obtain the NdFeB magnet. The method of the present invention enables thicker NdFeB magnets to increase their coercivity using grain boundary diffusion, improving the adaptability of grain boundary diffusion to NdFeB magnet thickness and resolving the problem of grain boundary diffusion being limited by magnet thickness. However, this invention suffers from the inability to detect the surface roughness of NdFeB magnets without oxide film, making it impossible to control the coating thickness of the coating paste and optimize the coating method of the coating paste. Summary of the Invention

[0004] To this end, the present invention provides a high-efficiency preparation method for NdFeB magnets based on grain boundary diffusion, which is used to overcome the problem in the prior art that the surface roughness of the NdFeB magnets without oxide film cannot be detected, and thus the coating thickness of the coating paste liquid cannot be controlled and the coating method of the coating paste liquid cannot be optimized.

[0005] To achieve the above objectives, the present invention provides a high-efficiency preparation method for NdFeB magnets based on grain boundary diffusion, comprising:

[0006] Etching the surface of the NdFeB magnet raw material to output a NdFeB magnet without an oxide film;

[0007] Detecting the surface roughness of the deoxidized NdFeB magnet;

[0008] Determining the coating thickness and coating method of the coating paste liquid on the surface of the deoxidized NdFeB magnet according to the surface roughness, wherein the coating thickness is negatively correlated with the surface roughness;

[0009] mixing the grain boundary diffusion powder with the acetone solution to output the coating paste liquid;

[0010] Applying the coating paste liquid on the surface of the deoxidized NdFeB magnet according to the coating thickness and the coating method to output a thick-coated NdFeB magnet;

[0011] placing the thick-coated NdFeB magnet in a low-frequency alternating magnetic field;

[0012] A curve diagram for determining the coercive force of the thick-coated NdFeB magnet according to the difference between the magnetic field intensity of the low-frequency alternating magnetic field and the magnetic field intensity of the thick-coated NdFeB magnet;

[0013] Adjusting the detection distance of the alternating magnetic field according to the mutation point in the curve graph of the coercive force of the thick-coated NdFeB magnet;

[0014] Introducing argon gas into the low-frequency alternating magnetic field region and performing diffusion heat treatment in sequence to output finished NdFeB magnets that meet the requirements;

[0015] Wherein, the coating method includes a multi-port injection method and a single-port injection method.

[0016] Furthermore, the etching process includes:

[0017] removing impurities and contaminants from the surface of the NdFeB magnet;

[0018] Setting etching parameters of the argon ion beam according to the model and size of the NdFeB magnet;

[0019] The argon ion beam etching equipment bombards the surface of the NdFeB magnet to output the etched NdFeB magnet;

[0020] The etched NdFeB magnet is cleaned with deionized water, and the etched NdFeB magnet is dried to output an NdFeB magnet without an oxide film.

[0021] Furthermore, if the roughness of the deoxidized NdFeB magnet is less than or equal to a preset first roughness, a single-port injection method is adopted;

[0022] If the roughness of the NdFeB magnet without the oxide film is greater than a preset first roughness, the number of injection ports for injecting the coating paste liquid is increased.

[0023] Furthermore, if the roughness of the NdFeB magnet without the oxide film is greater than a preset first roughness and less than or equal to a preset second roughness, the coating thickness of the coating paste liquid is increased.

[0024] Furthermore, the preparation process of the grain boundary diffusion powder includes:

[0025] Selecting ground NdFeB powder, calcium hydride reduction powder, and NdNiCu ternary alloy powder of the same model as the NdFeB magnet, and mixing them in a preset first ratio to output a mixed powder;

[0026] The mixed powder is ground to output grain boundary diffusion powder.

[0027] Furthermore, the preparation process of the coating paste liquid includes:

[0028] Mixing the grain boundary diffusion powder with analytical grade acetone in a preset second ratio to achieve a preset viscosity;

[0029] A glass rod is used to stir the mixed liquid of the grain boundary diffusion powder and the analytically pure acetone for a preset time to output a paste liquid for coating.

[0030] Furthermore, the curve graph for determining the coercive force of the thick-coated NdFeB magnet includes:

[0031] Placing the thick-coated NdFeB magnet and the low-frequency alternating magnetic field generator in the low-frequency alternating magnetic field area;

[0032] Measuring the magnetic field strength of the low-frequency alternating magnetic field generator and the thick-coated NdFeB magnet respectively, and calculating the difference between the magnetic field strengths of the two;

[0033] Establish a plane coordinate system, increase the magnetic field intensity of the low-frequency alternating magnetic field, and plot the corresponding coordinate points in the coordinate system;

[0034] Connecting the coordinate points with a smooth curve can obtain a curve graph of the coercive force of the thick-coated NdFeB magnet.

[0035] Furthermore, the diffusion heat treatment includes:

[0036] Place the thick-coated NdFeB magnet in a heating furnace;

[0037] Connect the pipe of the argon gas bottle to the heating furnace;

[0038] Adjust the heating furnace to the preset temperature;

[0039] After the diffusion heat treatment is completed, the thick-coated NdFeB magnet is cooled.

[0040] Furthermore, the etching parameters include argon ion energy, argon ion beam diameter, etching time and etching angle;

[0041] The etching angle is the angle between the etching direction and the normal direction of the surface of the NdFeB magnet raw material.

[0042] Furthermore, if the coercive force value corresponding to the mutation point in the coercive force curve of the thick-coated NdFeB magnet is greater than the coercive force value of the preset finished NdFeB magnet, the detection distance of the alternating magnetic field is increased;

[0043] The detection distance of the alternating magnetic field is the distance between the magnetic field intensity detection device and the low-frequency alternating magnetic field generator.

[0044] Compared with the prior art, the beneficial effects of the present invention are that, by setting an etching process, the present invention controls the coating thickness and coating method of the coating paste liquid, the diffusion heat treatment and the curve diagram of the coercive force of the thick-coated NdFeB magnet, and by etching the NdFeB magnet, the problem of being unable to determine the optimal etching effect, thereby affecting the diffusion effect, is overcome; by detecting the surface roughness of the thick-coated NdFeB magnet, the problem of being unable to monitor the permeability of the thick-coated NdFeB magnet surface, thereby being unable to determine the penetration effect of the coating paste liquid, is overcome; by conducting preliminary experiments on the injection method and thickness of the coating paste liquid respectively, the problem of the diffusion effect being affected by improper operation of the coating paste liquid during the coating process is overcome.

[0045] Furthermore, the present invention overcomes the problem that heavy rare earth elements in grain boundary diffusion powder cannot penetrate into the interior of the magnet due to the oxide film on the surface of the NdFeB magnet by providing an etching process. The oxide film on the surface of the NdFeB magnet is removed by etching, thereby improving the diffusion efficiency of the heavy rare earth elements. Etching also overcomes the problem that the grain boundary diffusion process is unstable due to the uneven surface roughness of the NdFeB magnet, thereby leading to unqualified preparation quality, thereby improving the stability of the preparation quality.

[0046] Furthermore, the present invention overcomes the problem of excessive fluidity of the coating paste liquid due to too low viscosity, unqualified coating thickness, and local excessive thickness or thinness, which leads to uneven coating on the surface of the NdFeB magnet after the oxide film is removed, and then leads to uneven distribution of heavy rare earth elements on the surface of the NdFeB magnet after the oxide film is removed, by setting a preset viscosity, thereby improving the quality of the magnet.

[0047] Furthermore, the present invention overcomes the problem of the increased ability to change the flow path of the coating paste liquid due to the surface roughness of the deoxidized NdFeB magnet exceeding the preset roughness by setting a preset roughness. Therefore, a multi-entry injection method is set for this area. By calculating the roughness of the deoxidized NdFeB magnet, the problem of uneven concentration can be discovered in time, thereby improving the consistency of the magnet performance.

[0048] Furthermore, the present invention overcomes the problem of difficulty in directly measuring the coercive force of thick-coated NdFeB magnets by setting up a coercive force curve graph. The coercive force curve graph is determined by measuring the difference change between the low-frequency alternating magnetic field and the magnetic field strength of the thick-coated NdFeB magnet, providing an indirect but effective method for measuring the coercive force, thereby making the results more intuitive and accurate.

[0049] Furthermore, the present invention overcomes the problem that the alternating magnetic field has a strong effect on the thick-coated NdFeB magnet due to the close detection distance, thereby causing significant changes in the internal magnetic domain structure or magnetic state of the thick-coated NdFeB magnet by setting a preset coercive force value of the finished NdFeB magnet, thereby improving the accuracy of detecting the change in the magnetic state of the thick-coated NdFeB magnet. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 This is an overall flow chart of a high-efficiency method for preparing NdFeB magnets based on grain boundary diffusion according to an embodiment of the present invention;

[0051] Figure 2 This is a specific flow chart of a process for preparing a coating paste liquid in a high-efficiency method for preparing NdFeB magnets based on grain boundary diffusion according to an embodiment of the present invention;

[0052] Figure 3 This is a specific flow chart of the diffusion heat treatment in the high-efficiency preparation method of NdFeB magnets based on grain boundary diffusion according to an embodiment of the present invention;

[0053] Figure 4 The figure is a logic flow chart of a high-efficiency preparation method of NdFeB magnets based on grain boundary diffusion according to an embodiment of the present invention. DETAILED DESCRIPTION

[0054] In order to make the objects and advantages of the present invention more clearly understood, the present invention is further described below in conjunction with embodiments; it should be understood that the specific embodiments described herein are merely used to explain the present invention and are not intended to limit the present invention.

[0055] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0056] It will be understood by those skilled in the art that, unless otherwise stated, the singular forms "a", "an", and "the" used herein may also include the plural forms. It should be further understood that the term "comprising" used in this specification refers to the presence of features, integers, steps, operations, elements / components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements / components. It should be understood that when we say that a module is "connected" or "coupled" to another module, it can be directly connected or coupled to the other module, or there can be an intermediate unit. In addition, "connected" or "coupled" as used herein may include wireless connection or wireless coupling.

[0057] See also Figure 1 、 Figure 2 、 Figure 3 as well as Figure 4 As shown in the figure, they are respectively an overall flow chart of the high-efficiency preparation method of NdFeB magnets based on grain boundary diffusion according to an embodiment of the present invention, a specific flow chart of the preparation process of the coating paste liquid, a specific flow chart of the diffusion heat treatment, and a logic flow chart. The high-efficiency preparation method of NdFeB magnets based on grain boundary diffusion according to the present invention comprises:

[0058] Step S1, preparing a solid cylindrical NdFeB magnet of model N45M, with a diameter of 10 mm and a thickness of 15 mm, and etching the surface of the NdFeB magnet raw material to output a NdFeB magnet without an oxide film;

[0059] Step S2, detecting the surface roughness of the NdFeB magnet without the oxide film;

[0060] Step S3, determining the coating thickness and coating method of the coating paste liquid on the surface of the deoxidized NdFeB magnet according to the surface roughness, wherein the coating thickness is negatively correlated with the surface roughness;

[0061] Step S4, mixing the grain boundary diffusion powder with the acetone solution to output the coating paste liquid;

[0062] Step S5, applying the coating paste liquid on the surface of the deoxidized NdFeB magnet according to the coating thickness and the coating method to output a thick-coated NdFeB magnet;

[0063] Step S6, placing the thick-coated NdFeB magnet in a low-frequency alternating magnetic field;

[0064] Step S7, determining a curve graph of the coercive force of the thick-coated NdFeB magnet according to the difference between the magnetic field intensity of the low-frequency alternating magnetic field and the magnetic field intensity of the thick-coated NdFeB magnet;

[0065] Step S8, adjusting the detection distance of the alternating magnetic field according to the mutation point in the curve of the coercive force of the thick-coated NdFeB magnet;

[0066] Step S9, introducing argon gas into the low-frequency alternating magnetic field region and performing diffusion heat treatment to output a finished NdFeB magnet that meets the requirements;

[0067] Wherein, the coating method includes a multi-port injection method and a single-port injection method.

[0068] In practice, the present invention controls the coating thickness and coating method of the coating paste liquid, the diffusion heat treatment and the coercive force curve of the thick-coated NdFeB magnet by setting an etching process, and overcomes the problem of being unable to determine the optimal etching effect, thereby affecting the diffusion effect, by etching the NdFeB magnet; by detecting the surface roughness of the thick-coated NdFeB magnet, the problem of being unable to monitor the permeability of the thick-coated NdFeB magnet surface, thereby being unable to determine the penetration effect of the coating paste liquid, is overcome; by conducting preliminary experiments on the injection method and thickness of the coating paste liquid respectively, the problem of affecting the diffusion effect due to improper operation of the coating paste liquid during the coating process is overcome.

[0069] Specifically, the etching process includes:

[0070] removing impurities and contaminants from the surface of the NdFeB magnet;

[0071] The etching parameters of the argon ion beam were set as follows: argon ion energy of 700 eV, argon ion beam diameter of 20 mm, etching time of 20 min, and etching angle of 50°;

[0072] The argon ion beam etching equipment bombards the surface of the NdFeB magnet to output the etched NdFeB magnet;

[0073] Washing the etched NdFeB magnet with deionized water, and placing the etched NdFeB magnet in a vacuum drying oven for drying to produce a NdFeB magnet without an oxide film;

[0074] The bombardment is achieved by focusing an argon ion beam, which is a prior art well known to those skilled in the art, and the bombardment method will not be described in detail here.

[0075] In practice, the present invention overcomes the problem that heavy rare earth elements in grain boundary diffusion powder cannot penetrate into the interior of the magnet due to the oxide film on the surface of the NdFeB magnet by providing an etching process. The oxide film on the surface of the NdFeB magnet is removed by etching, thereby improving the diffusion efficiency of the heavy rare earth elements. Etching also overcomes the problem that the grain boundary diffusion process is unstable due to the uneven surface roughness of the NdFeB magnet, thereby leading to unqualified preparation quality, thereby improving the stability of the preparation quality.

[0076] Specifically, if the roughness of the deoxidized NdFeB magnet is less than or equal to a preset first roughness, a single-port injection method is adopted;

[0077] If the roughness of the NdFeB magnet without the oxide film is greater than a preset first roughness, the number of injection ports for injecting the coating paste liquid is increased.

[0078] Specifically, the surface roughness of the deoxidized NdFeB magnet is measured by a surface roughness measuring instrument. The process of measuring the surface roughness of the deoxidized NdFeB magnet by the surface roughness measuring instrument is a conventional roughness measurement process well known to those skilled in the art. Therefore, the use method of the surface roughness measuring instrument and the roughness measurement process will not be repeated here.

[0079] Optionally, the preset first roughness value range may be [0.1 μm, 0.4 μm].

[0080] Preferably, the preset first roughness is 0.3 μm.

[0081] In a specific embodiment, the roughness of the deoxidized NdFeB magnet is 0.5 μm, which is greater than the preset first roughness. For every 0.1 μm that the roughness of the deoxidized NdFeB magnet is greater than the preset first roughness, the number of injection ports for the coating paste liquid increases by 1 compared with the current number of injection ports for the coating paste liquid. The current number of injection ports for the coating paste liquid is 3, and the increased number of injection ports for the coating paste liquid is 3+(0.5-0.3) / 0.1=5.

[0082] Specifically, the position of the injection port of the coating paste liquid is determined according to the roughness of different areas on the surface of the NdFeB magnet without the oxide film.

[0083] In practice, n sampling points are taken at equal intervals on the surface of the NdFeB magnet without oxide film, and the roughness of the sampling points is measured respectively. The injection port of the coating paste liquid is located at the sampling point where the roughness is greater than the preset first roughness.

[0084] Specifically, if the roughness of the NdFeB magnet without the oxide film is greater than a preset first roughness and less than or equal to a preset second roughness, the coating thickness of the coating paste liquid is increased.

[0085] Optionally, the preset second roughness value range may be [0.4 μm, 0.6 μm].

[0086] Preferably, the preset second roughness is 0.5 μm.

[0087] In a specific embodiment, the roughness of the deoxidized NdFeB magnet is 0.7 μm, which is greater than the preset second roughness. For every 0.1 μm that the roughness of the deoxidized NdFeB magnet is greater than the preset second roughness, the coating thickness of the coating paste liquid increases by 0.5 cm compared with the current coating thickness of the coating paste liquid. The current coating thickness of the coating paste liquid is 2 cm, and the increased coating thickness of the coating paste liquid is 2+[(0.7-0.5) / 0.1]×0.5=3 cm.

[0088] In practice, the present invention overcomes the problem of the flow path change ability of the coating paste liquid becoming stronger due to the surface roughness of the deoxidized NdFeB magnet exceeding the preset roughness by setting a preset roughness. Therefore, a multi-port injection method is set for this area. By calculating the roughness of the deoxidized NdFeB magnet, the problem of uneven concentration can be discovered in time, thereby improving the consistency of the magnet performance.

[0089] Specifically, the preparation of grain boundary diffusion powder includes:

[0090] Select N45M NdFeB powder, calcium hydride reduction powder, and NdNiCu ternary alloy powder, and mix them in a mass ratio of N45M NdFeB powder: calcium hydride reduction powder: NdNiCu ternary alloy powder = 2:1:1 to output a mixed powder;

[0091] The mixed powder is ground using a planetary ball mill to output grain boundary diffusion powder.

[0092] Specifically, the preparation process of the coating paste liquid includes:

[0093] The grain boundary diffusion powder and analytical pure acetone were mixed in a ratio of grain boundary diffusion powder mass: analytical pure acetone volume = 1:2 to achieve a viscosity requirement of 350 mPa·s;

[0094] The mixed liquid of the grain boundary diffusion powder and the analytically pure acetone was stirred for 20 minutes using a glass rod to produce a paste-like liquid for coating.

[0095] In practice, the present invention overcomes the problem of excessive fluidity of the coating paste liquid due to too low viscosity, unqualified coating thickness, and local over-thickness or over-thinness, which leads to uneven coating on the surface of the NdFeB magnet after the oxide film is removed, and further leads to uneven distribution of heavy rare earth elements on the surface of the NdFeB magnet after the oxide film is removed, thereby improving the quality of the magnet.

[0096] Specifically, the graph for determining the coercive force of thick-coated NdFeB magnets includes:

[0097] Placing the thick-coated NdFeB magnet and the low-frequency alternating magnetic field generator in the low-frequency alternating magnetic field area; initially setting the frequency of the low-frequency alternating magnetic field device to 350 Hz;

[0098] Using a Gauss meter to measure the magnetic field strength of the low-frequency alternating magnetic field generator and the thick-coated NdFeB magnet respectively, and calculate the difference between the two magnetic field strengths;

[0099] A plane coordinate system is established with the low-frequency alternating magnetic field intensity as the horizontal coordinate and the difference in magnetic field intensity as the vertical coordinate. When the frequency of the low-frequency alternating magnetic field device increases by 50 Hz, the corresponding coordinate point is plotted in the coordinate system;

[0100] Connecting the coordinate points with a smooth curve can obtain a curve graph of the coercive force of the thick-coated NdFeB magnet.

[0101] In practice, the present invention overcomes the problem of difficulty in directly measuring the coercive force of thick-coated NdFeB magnets by setting a coercive force curve graph. The coercive force curve graph is determined by measuring the difference change between the low-frequency alternating magnetic field and the magnetic field strength of the thick-coated NdFeB magnet, providing an indirect but effective method for measuring the coercive force, thereby making the results more intuitive and accurate.

[0102] Specifically, the diffusion heat treatment includes:

[0103] Place the thick-coated NdFeB magnet in a heating furnace;

[0104] Connect the pipe of the argon gas bottle to the heating furnace;

[0105] Adjust the heating furnace to 500°C;

[0106] After the diffusion heat treatment is completed, the thick-coated NdFeB magnet is water-cooled.

[0107] Specifically, the etching parameters include argon ion energy, argon ion beam diameter, etching time and etching angle;

[0108] The etching angle is the angle between the etching direction and the normal direction of the surface of the NdFeB magnet raw material.

[0109] Specifically, if the coercive force value corresponding to the mutation point in the coercive force curve of the thick-coated NdFeB magnet is greater than the coercive force value of the preset finished NdFeB magnet, the detection distance of the alternating magnetic field is increased;

[0110] The detection distance of the alternating magnetic field is the distance between the magnetic field intensity detection device and the low-frequency alternating magnetic field generator.

[0111] Optionally, the coercive force value of the preset finished NdFeB magnet may be in the range of [2500KA / m, 3000KA / m];

[0112] Preferably, the coercive force value of the finished NdFeB magnet is preset to be 2700 kA / m.

[0113] In a specific embodiment, the coercive force value corresponding to the mutation point in the curve diagram of the coercive force of the thick-coated NdFeB magnet is 3200KA / m, which is greater than the coercive force value of the preset finished NdFeB magnet. For every 100KA / m by which the coercive force value corresponding to the mutation point is greater than the coercive force value of the preset finished NdFeB magnet, the detection distance of the alternating magnetic field increases by 1 cm compared with the current detection distance of the alternating magnetic field. The current detection distance of the alternating magnetic field is 15 cm, and the increased detection distance of the alternating magnetic field is 15+[(3200-1700) / 100]=20 cm.

[0114] In implementation, the present invention further overcomes the problem that the alternating magnetic field has a stronger effect on the thick-coated NdFeB magnet due to the close detection distance, thereby causing the internal magnetic domain structure or magnetic state of the thick-coated NdFeB magnet to undergo significant changes by setting a preset coercive force value of the finished NdFeB magnet, thereby improving the accuracy of detecting the change in the magnetic state of the thick-coated NdFeB magnet.

[0115] Thus far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art may make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will fall within the scope of protection of the present invention.

Claims

1. A high-efficiency preparation method for NdFeB magnets based on grain boundary diffusion, characterized in that: include: Etching the surface of the NdFeB magnet raw material to output a NdFeB magnet without an oxide film; detecting the surface roughness of the deoxidized NdFeB magnet; Determining the coating thickness and coating method of the coating paste liquid on the surface of the deoxidized NdFeB magnet according to the surface roughness, wherein the coating thickness is positively correlated with the surface roughness; mixing the grain boundary diffusion powder with the acetone solution to output the coating paste liquid; Applying the coating paste liquid on the surface of the deoxidized NdFeB magnet according to the coating thickness and the coating method to output a thick-coated NdFeB magnet; placing the thick-coated NdFeB magnet in a low-frequency alternating magnetic field; A curve diagram for determining the coercive force of the thick-coated NdFeB magnet according to the difference between the magnetic field intensity of the low-frequency alternating magnetic field and the magnetic field intensity of the thick-coated NdFeB magnet; Adjusting the detection distance of the alternating magnetic field according to the mutation point in the curve graph of the coercive force of the thick-coated NdFeB magnet; Introducing argon gas into the low-frequency alternating magnetic field region and performing diffusion heat treatment in sequence to output finished NdFeB magnets that meet the requirements; Wherein, the coating method includes a multi-port injection method and a single-port injection method; If the roughness of the deoxidized NdFeB magnet is less than or equal to a preset first roughness, a single-port injection method is adopted; If the roughness of the deoxidized NdFeB magnet is greater than a preset first roughness, increasing the number of injection ports for injecting the coating paste liquid; If the roughness of the deoxidized NdFeB magnet is greater than a preset first roughness and less than or equal to a preset second roughness, increasing the coating thickness of the coating paste liquid; If the coercive force value corresponding to the mutation point in the coercive force curve of the thick-coated NdFeB magnet is greater than the coercive force value of the preset finished NdFeB magnet, then the detection distance of the alternating magnetic field is increased; The detection distance of the alternating magnetic field is the distance between the magnetic field intensity detection device and the low-frequency alternating magnetic field generator.

2. The high-efficiency preparation method of NdFeB magnets based on grain boundary diffusion according to claim 1, characterized in that: The etching process includes: removing impurities and contaminants from the surface of the NdFeB magnet; Setting etching parameters of the argon ion beam according to the model and size of the NdFeB magnet; The argon ion beam etching equipment bombards the surface of the NdFeB magnet to output the etched NdFeB magnet; The etched NdFeB magnet is cleaned with deionized water, and the etched NdFeB magnet is dried to output an NdFeB magnet without an oxide film.

3. The high-efficiency preparation method of NdFeB magnets based on grain boundary diffusion according to claim 2, characterized in that: The preparation process of the grain boundary diffusion powder includes: Selecting ground NdFeB powder, calcium hydride reduction powder, and NdNiCu ternary alloy powder of the same model as the NdFeB magnet, and mixing them in a preset first ratio to output a mixed powder; The mixed powder is ground to output grain boundary diffusion powder.

4. The high-efficiency preparation method of NdFeB magnets based on grain boundary diffusion according to claim 3, characterized in that: The preparation process of the coating paste liquid includes: Mixing the grain boundary diffusion powder with analytical grade acetone in a preset second ratio to achieve a preset viscosity; A glass rod is used to stir the mixed liquid of the grain boundary diffusion powder and the analytically pure acetone for a preset time to output a paste liquid for coating.

5. The high-efficiency preparation method of NdFeB magnets based on grain boundary diffusion according to claim 4, characterized in that: The graph for determining the coercive force of thick-coated NdFeB magnets includes: Placing the thick-coated NdFeB magnet and the low-frequency alternating magnetic field generator in the low-frequency alternating magnetic field area; Measuring the magnetic field strength of the low-frequency alternating magnetic field generator and the thick-coated NdFeB magnet respectively, and calculating the difference between the magnetic field strengths of the two; Establish a plane coordinate system, increase the magnetic field intensity of the low-frequency alternating magnetic field, and plot the corresponding coordinate points in the coordinate system; Connecting the coordinate points with a smooth curve can obtain a curve graph of the coercive force of the thick-coated NdFeB magnet.

6. The high-efficiency preparation method of NdFeB magnets based on grain boundary diffusion according to claim 5, characterized in that: The diffusion heat treatment includes: Place the thick-coated NdFeB magnet in a heating furnace; Connect the pipe of the argon gas bottle to the heating furnace; Adjust the heating furnace to the preset temperature; After the diffusion heat treatment is completed, the thick-coated NdFeB magnet is cooled.

7. The high-efficiency preparation method of NdFeB magnets based on grain boundary diffusion according to claim 6, characterized in that: The etching parameters include argon ion energy, argon ion beam diameter, etching time and etching angle; The etching angle is the angle between the etching direction and the normal direction of the surface of the NdFeB magnet raw material.

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