A method for preparing corrosion-resistant NdFeB magnets

Abstract

The present invention discloses a method for preparing corrosion-resistant NdFeB magnets. In the preparation process of the present invention, the NdFeB magnets are first pretreated, and then an anti-corrosion coating is sprayed on the surface of the NdFeB magnets to form a corrosion-resistant coating; the coating not only provides the NdFeB magnets with good corrosion resistance, hydrophobicity, and wear resistance, but also, after the corrosion-resistant coating is applied, the remanence and coercive force of the NdFeB magnets are almost unaffected, and the changes are negligible. The preparation method provided by the present invention can efficiently produce NdFeB magnets with excellent corrosion resistance by optimizing the coating formula and preparation process, and the preparation process is simple, easy to operate, low in cost, and suitable for large-scale industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of NdFeB magnets, and in particular to a method for preparing a corrosion-resistant NdFeB magnet. Background Art

[0002] Since its introduction, the rare earth permanent magnet material neodymium iron boron (NdFeB) has been highly sought after for its numerous advantages, including its small size, light weight, excellent magnetic properties, low cost, and abundant resources. Dubbed the "King of Magnets," it is widely used in automotive, computer, machinery, energy, and pharmaceutical industries. However, due to its multiphase structure, the large potential difference between phases, and its highly active electrochemical properties, NdFeB magnets are susceptible to corrosion in high-temperature, high-humidity environments and corrosive electrolytes, ultimately destroying the magnet's internal structure and thus its magnetic properties. The poor corrosion resistance of sintered NdFeB magnets limits their use in many applications, making improving their corrosion resistance a pressing issue. Currently, there are two main methods for improving the corrosion resistance of NdFeB magnets: adding alloying elements to the magnet, known as alloying, primarily improves the magnet's inherent corrosion resistance; and applying a protective coating to the magnet surface, known as surface coating, aims to isolate the magnet from corrosive media such as oxygen and water.

[0003] The alloying method involves adding elements such as Al, Cr, W, Co, and Zr to the NdFeB raw material. This addition partially replaces the Fe element, inhibiting corrosion of the main phase. Furthermore, the added elements can form Nd-rich grain boundary phases, such as Nd3Co, with improved corrosion resistance, which also inhibits the corrosion rate of the magnet. However, the alloying method also has some drawbacks. First, the addition of other elements to replace Fe in the magnet will form a large amount of non-ferromagnetic phases, which significantly reduce the overall magnetic properties of the magnet. Furthermore, the alloying method requires the addition of large amounts of rare W and Co elements, which significantly increases production costs and resource consumption. Compared with the traditional modification method of alloying, the surface coating method does not require treatment of the entire substrate, but only requires surface modification, making it more economical and practical.

[0004] CN108018497A discloses a neodymium iron boron magnet and a method for preparing an aluminum alloy coating on the surface of the neodymium iron boron magnet. This invention addresses the microscopic morphology of the magnet surface and utilizes a vacuum aluminum alloy coating method and a vacuum composite aluminum alloy coating method. First, a thin layer of aluminum and soft metal alloy is formed on the surface of the neodymium iron boron magnet to densify the loose and porous surface of the neodymium iron boron. Then, an aluminum and hard metal alloy is formed on the aluminum alloy surface to harden the coating surface and improve corrosion resistance. This invention utilizes a physical vapor deposition process to form a composite aluminum alloy coating on the surface of the neodymium iron boron magnet, which not only improves the coating hardness but also improves the coating's corrosion resistance. However, vacuum plating, vacuum composite plating, and physical vapor deposition processes typically require specialized vacuum equipment, which is expensive to purchase and requires high operating and maintenance costs. This results in complex processes and high costs.

[0005] CN117542599A discloses a corrosion-resistant NdFeB magnet and its preparation method. While the invention introduces rare earth elements such as Ce and Ga to reduce Nd enrichment and oxidation, the scarcity and strategic nature of rare earth resources make their large-scale use potentially problematic due to unstable supply. Furthermore, increasing difficulty in rare earth mining and changes in market demand can lead to rising raw material costs. Furthermore, in practical applications, long-term exposure to complex environmental conditions can affect the coating's performance, potentially impacted by various factors such as high temperature, high humidity, and strong acids and alkalis. This can lead to uncertainty regarding the coating's corrosion resistance and protective effect on the magnet. Summary of the Invention

[0006] In view of the above-mentioned shortcomings of the prior art, the present invention provides a method for preparing corrosion-resistant NdFeB magnets. By optimizing the coating formulation and preparation process, the present invention's preparation method can efficiently produce NdFeB magnets with excellent corrosion resistance. Furthermore, the preparation process is simple, easy to operate, and low in cost, making it suitable for large-scale industrial production.

[0007] To achieve the above object, the present invention provides a method for preparing a corrosion-resistant NdFeB magnet, comprising the following steps:

[0008] The NdFeB substrate is pretreated to obtain a pretreated NdFeB magnet substrate; an anti-corrosion coating is sprayed on the surface of the pretreated NdFeB magnet substrate, and then cured to obtain a NdFeB magnet with a surface coated with a corrosion-resistant coating, thereby obtaining a corrosion-resistant NdFeB magnet.

[0009] Preferably, the pretreatment of the NdFeB substrate is specifically as follows:

[0010] The NdFeB substrate is immersed in a 4-6wt% alkaline degreasing agent aqueous solution for 8-12 minutes to remove oil, and then rinsed with water; the sample is then immersed in a 4-6wt% nitric acid aqueous solution for pickling for 8-12 minutes, and then rinsed with water; then immersed in water, ultrasonically oscillated for 8-15 minutes at an ultrasonic frequency of 20-50KHz and an ultrasonic power of 800-1000W, and then washed with water. After taking out, rinse with water and dry.

[0011] Preferably, the spray gun discharge rate of the anti-corrosion coating during spraying is 32-34 g / min, and the spraying pressure is controlled to be 0.3-0.5 MPa. During the spraying process, it should be ensured that the surface coating is uniform without sagging and defects.

[0012] Preferably, the preparation method of the anti-corrosion coating comprises the following steps, calculated by weight:

[0013] 6-10 parts of composite nanoparticles, 3-6 parts of modified phytic acid and 1-3 parts of a surfactant are added to 40-60 parts of a mixed solution of water and acetone in a mass ratio of 1-3:1, and the mixture is stirred at 300-500 rpm for 15-25 minutes. Then, 20-40 parts of a water-based epoxy resin are added, and the mixture is stirred at 800-1000 pm for 30-50 minutes to obtain an anti-corrosion coating.

[0014] Preferably, the surfactant is selected from one or more of sodium lauryl sulfate, sodium dodecylbenzene sulfonate, and polyethylene glycol.

[0015] Preferably, the preparation method of the modified phytic acid comprises the following steps, in parts by weight:

[0016] 0.1-0.3 parts of phytic acid and 2-3 parts of ethylene glycol monomethyl ether are mixed and stirred at 500-800 rpm for 20-30 minutes; then 4.5-5 parts of cardanol glycidyl ether are added, mixed and stirred at 300-500 rpm for 15-25 minutes, and 0.02-0.1 parts of tetrabutylammonium chloride are added as a catalyst during the mixing and stirring process to obtain a mixture; then the mixture is mixed and stirred at 80-90° C. and 300-500 rpm for 1-3 hours to obtain modified phytic acid.

[0017] In the preparation method of the above-mentioned modified phytic acid, phytic acid is a natural organic acid containing 6 phosphate groups in the molecule, each of which carries multiple hydroxyl groups and phosphorus-oxygen double bonds; one end of cardanol glycidyl ether has an epoxy group and the other end has an unsaturated long carbon chain hydrocarbon. When the two are mixed, the epoxy group of cardanol glycidyl ether can react with the hydroxyl group of phytic acid to form an esterification bond, thereby being grafted onto phytic acid, and tetrabutylammonium chloride, as a catalyst, accelerates this reaction process to obtain modified phytic acid. The inventors have found that the modified phytic acid can form a chemical bond with the magnet surface, thereby contributing to the formation of a dense protective film of the anti-corrosion coating on the magnet surface, and the long carbon chain structure of cardanol glycidyl ether gives the modified phytic acid a certain hydrophobicity, which can reduce the contact of water molecules with the magnet surface, effectively block the erosion of corrosive media, and reduce the corrosion rate. Therefore, the introduction of modified phytic acid is conducive to improving the corrosion resistance and hydrophobicity of NdFeB.

[0018] Preferably, the particle size of the composite nanoparticles is 10-100 nm; the preparation method of the composite nanoparticles comprises the following steps, calculated by weight:

[0019] 0.5-2 parts of magnetic nanoparticles are added to 180-220 parts of a mixed solution of ethanol and water in a volume ratio of 5:1, and ultrasonically treated for 2-5 minutes at an ultrasonic frequency of 20-50KHz and an ultrasonic power of 30-60W to obtain a magnetic nanoparticle dispersion; then 2-6 parts of 25-30wt% ammonia water are added to the magnetic nanoparticle dispersion, and then 0.5-1.2 parts of ethyl orthosilicate are added under ultrasonic conditions of an ultrasonic frequency of 20-50KHz and an ultrasonic power of 50-120W, and the ultrasonic treatment is continued for 2-3 hours, washed with water 2-3 times, and vacuum dried at 50-60°C to obtain core-shell nanospheres; 1-3 parts of the core-shell nanospheres prepared above are added to the The modified core-shell nanoparticles are added to 80-100 parts of anhydrous ethanol solvent, mixed and stirred evenly, and then 0.02-0.1 parts of maleic anhydride are added, mixed and stirred at 75-85° C. and 200-500 rpm for 1-3 hours, filtered, and solids are collected. The solids are washed 1-2 times with anhydrous ethanol solvent and dried at 95-105° C. for 8-12 hours to obtain modified core-shell nanoparticles; the modified core-shell nanoparticles obtained above are placed in a polylysine aqueous solution with a concentration of 1-4 mg / mL, wherein the mass ratio of the modified core-shell nanoparticles to the polylysine aqueous solution is 1:8-10, mixed and stirred to form a uniformly dispersed suspension, reacted at room temperature for 1-3 hours, filtered and dried to obtain composite nanoparticles.

[0020] Further preferably, the magnetic nanoparticles are selected from one or more of CoFe2O4, NiFe2O4, γ-Fe2O3, and Fe3O4.

[0021] In the preparation method of above-mentioned composite nanoparticles, by sol-gel method, utilize tetraethyl orthosilicate to hydrolyze and condense under the catalysis of ammonia, form uniform silicon dioxide coating on the surface of magnetic nanoparticles, namely obtain the nano microsphere of core-shell structure.The formation of silicon dioxide coating not only can protect magnetic nanoparticle kernel, prevents it from being oxidized or corroded in corrosive environment, but also gives a large amount of hydroxyl groups on the surface of core-shell nano microsphere structure.In subsequent preparation process, maleic anhydride can generate carboxyl with the hydroxyl reaction on the surface of core-shell nano microsphere under mild conditions, thereby realizes the surface modification to core-shell nano microsphere, makes its surface carry carboxylate ion (-COO-), obtains the modified core-shell nano microsphere with negative charge on surface.Modified core-shell nano microsphere can generate electrostatic attraction with the positively charged polylysine introduced afterwards, thereby forms covering layer, is firmly coated on the surface of modified core-shell nano microsphere, obtains composite nanoparticles. The polylysine coating within the composite nanoparticles provides them with excellent biocompatibility and surface modification capabilities, preventing the nanoparticles from agglomerating and allowing them to be evenly dispersed within the epoxy resin matrix. This allows the composite nanoparticles to be used in the anti-corrosion coating of the present invention, thereby facilitating the formation of a smooth, dense anti-corrosion coating on the magnet surface, thereby improving the corrosion resistance and hydrophobicity of the NdFeB magnet. Furthermore, polylysine exhibits certain antibacterial activity, imparting excellent antibacterial properties to the composite nanoparticles, thereby improving the antibacterial properties of the NdFeB magnet.

[0022] Preferably, the curing treatment temperature is 140-180° C., and the treatment time is 1-3 hours.

[0023] Preferably, the thickness of the corrosion-resistant coating is 5-20 μm.

[0024] Beneficial effects of the present invention:

[0025] 1. Compared with the prior art, the present invention sprays a corrosion-resistant coating on the surface of the NdFeB magnet in the preparation method of the corrosion-resistant NdFeB magnet. The coating can form a dense protective layer on the surface of the magnet, effectively blocking the erosion of the corrosive medium. This coating not only provides the NdFeB magnet with good corrosion resistance, hydrophobicity, antibacterial and wear resistance, but also after the corrosion-resistant coating is applied, the remanence and coercive force of the NdFeB magnet are almost unaffected, and the changes are negligible. This shows that the coating significantly improves the corrosion resistance of the magnet without affecting the magnetic properties. The present invention can efficiently produce NdFeB magnets with excellent corrosion resistance by optimizing the coating formula and preparation process, and the preparation method provided is simple in process, easy to operate, and suitable for large-scale industrial production.

[0026] 2. Compared to existing technologies, this invention adds a specific ratio of modified phytic acid and composite nanoparticles to the anti-corrosion coating. The introduction of the modified phytic acid significantly improves the corrosion resistance and hydrophobicity of the coating. The introduction of the composite nanoparticles not only enhances the corrosion resistance of the coating, but also strengthens its wear resistance, adhesion, and antibacterial properties. Furthermore, the synergistic effect of the modified phytic acid and composite nanoparticles gives the coating greater stability and wear resistance during friction. DETAILED DESCRIPTION

[0027] Parameters for specific chemical substances used, sources.

[0028] The NdFeB substrate is N50 commercial sintered NdFeB with a specification of 1.0×1.0×0.5 cm 3 , from Zhejiang Yingluohua Magnetics Co., Ltd.;

[0029] CoFe2O4 magnetic nanoparticles, particle size: 40 nm, product number: PA22961, from Guangdong Wengjiang Chemical Reagent Co., Ltd.

[0030] NiFe2O4 magnetic nanoparticles, particle size: 40nm, from Qinghe County Ruijiang Metal Materials Co., Ltd.

[0031] γ-Fe2O3 magnetic nanoparticles, average particle size: 50 nm, product number: AM-Fe2O3-032-2, from Zhejiang Yamei Nanotechnology Co., Ltd.

[0032] Fe3O4 magnetic nanoparticles, average particle size: 20 nm, product number: AM-Fe3O4-033-1, from Zhejiang Yamei Nanotechnology Co., Ltd.

[0033] Nano-silicon dioxide, particle size: 50 nm, product number: AM-SiO2-021-2, from Zhejiang Yamei Nano Technology Co., Ltd.

[0034] Polylysine, molecular weight: 4000;

[0035] The waterborne epoxy resin is a waterborne acrylic acid modified epoxy ester, model: GS-5000B, sourced from Changzhou Guangshu Chemical Technology Co., Ltd.

[0036] The alkaline degreasing agent aqueous solution contains 12 g / L of sodium hydroxide, 25 g / L of sodium carbonate, 50 g / L of trisodium phosphate and 3 g / L of sodium silicate per liter of solution, and the rest is deionized water.

[0037] Example 1

[0038] A method for preparing a corrosion-resistant NdFeB magnet comprises the following steps:

[0039] The NdFeB substrate is immersed in a 5wt% alkaline degreasing agent aqueous solution for degreasing for 10 minutes, and then rinsed with deionized water; the sample is then immersed in a 5wt% nitric acid aqueous solution for pickling, taken out after 10 minutes, and rinsed with deionized water; then immersed in deionized water, ultrasonically oscillated for 10 minutes under the conditions of ultrasonic frequency 40KHz and ultrasonic power 1000W, taken out, rinsed with deionized water, and dried to obtain the pretreated NdFeB magnet substrate; then the anti-corrosion coating is sprayed on the surface of the pretreated NdFeB magnet substrate, the spray gun discharge rate during spraying is 33g / min, and the spraying pressure is controlled to 0.3MPa. During the spraying process, the surface coating should be ensured to be uniform without sagging and defects. Then the sprayed NdFeB magnet is placed at 150°C for curing for 2h to obtain a NdFeB magnet with a surface coating of a corrosion-resistant coating with a thickness of 10μm, thereby obtaining a corrosion-resistant NdFeB magnet.

[0040] During the pretreatment process of the NdFeB substrate, about 100-200g of NdFeB substrate is treated with 1L of alkaline degreasing agent aqueous solution, and the specific amount can be adjusted according to the degree of oil contamination; about 200-300g of NdFeB substrate is treated with 1L of nitric acid aqueous solution; during the ultrasonic cleaning process, about 500mL of deionized water is used for every 100g of substrate to ensure that the deionized water completely immerses the substrate.

[0041] The preparation method of the anticorrosive coating comprises the following steps:

[0042] 8 parts by weight of composite nanoparticles, 5 parts by weight of modified phytic acid and 2 parts by weight of sodium dodecylbenzenesulfonate were added to 55 parts by weight of a mixed solution of deionized water and acetone in a mass ratio of 1.5:1, and the mixture was stirred at 450 rpm for 18 minutes. Then, 35 parts by weight of water-based epoxy resin was added, and the mixture was stirred at 950 rpm for 40 minutes to obtain an anti-corrosion coating.

[0043] The preparation method of the modified phytic acid comprises the following steps:

[0044] 0.2 parts by weight of phytic acid and 2.5 parts by weight of ethylene glycol monomethyl ether were mixed and stirred at 700 rpm for 25 minutes; then, 4.8 parts by weight of cardanol glycidyl ether were added, mixed and stirred at 350 rpm for 18 minutes, and 0.06 parts by weight of tetrabutylammonium chloride was added as a catalyst during the mixing and stirring process to obtain a mixture; then, the mixture was mixed and stirred at 85° C. and 450 rpm for 2 hours to obtain modified phytic acid.

[0045] The preparation method of the composite nanoparticles comprises the following steps:

[0046] 1 part by weight of CoFe2O4 magnetic nanoparticles was added to 200 parts by weight of a mixed solution of ethanol and deionized water in a volume ratio of 5:1, and ultrasonically treated for 3 minutes at an ultrasonic frequency of 40 kHz and an ultrasonic power of 50 W to obtain a CoFe2O4 magnetic nanoparticle dispersion; then 5 parts by weight of 25 wt% ammonia water was added to the CoFe2O4 magnetic nanoparticle dispersion, and then 1 part by weight of ethyl orthosilicate was added under an ultrasonic state of an ultrasonic frequency of 40 kHz and an ultrasonic power of 100 W, and the ultrasonic treatment was continued for 2.5 hours, washed with deionized water 3 times, and vacuum dried at 55°C to obtain core-shell nanospheres; the 1 part by weight of the prepared The modified core-shell nanospheres were added to 100 parts by weight of anhydrous ethanol solvent, mixed and stirred evenly, and then 0.05 parts by weight of maleic anhydride was added, mixed and stirred at 80°C and 400 rpm for 2 hours, filtered, and the solid was collected. The solid was washed twice with anhydrous ethanol solvent and dried at 100°C for 10 hours to obtain modified core-shell nanospheres; the modified core-shell nanospheres obtained above were placed in a polylysine aqueous solution with a concentration of 1 mg / mL, wherein the mass ratio of the modified core-shell nanospheres to the polylysine aqueous solution was 1:10, mixed and stirred to form a uniformly dispersed suspension, reacted at room temperature for 1.5 hours, filtered and dried to obtain composite nanoparticles.

[0047] Example 2

[0048] A method for preparing a corrosion-resistant NdFeB magnet, which differs from Example 1 in that the method for preparing the anti-corrosion coating comprises the following steps:

[0049] 8 parts by weight of composite nanoparticles, 5 parts by weight of modified phytic acid and 2 parts by weight of sodium dodecylbenzenesulfonate were added to 55 parts by weight of a mixed solution of deionized water and acetone in a mass ratio of 1.5:1, and the mixture was stirred at 450 rpm for 18 minutes. Then, 35 parts by weight of water-based epoxy resin was added, and the mixture was stirred at 950 rpm for 40 minutes to obtain an anti-corrosion coating.

[0050] The preparation method of the composite nanoparticles comprises the following steps:

[0051] 1 part by weight of NiFe2O4 magnetic nanoparticles was added to 200 parts by weight of a mixed solution of ethanol and deionized water in a volume ratio of 5:1, and ultrasonically treated for 3 minutes at an ultrasonic frequency of 40 kHz and an ultrasonic power of 50 W to obtain a NiFe2O4 magnetic nanoparticle dispersion; then 5 parts by weight of 25 wt% ammonia water was added to the NiFe2O4 magnetic nanoparticle dispersion, and then 1 part by weight of ethyl orthosilicate was added under an ultrasonic state of an ultrasonic frequency of 40 kHz and an ultrasonic power of 100 W, and the ultrasonic treatment was continued for 2.5 hours, washed 3 times with deionized water, and vacuum dried at 55°C to obtain core-shell nanospheres; 1 part by weight of the core-shell nanospheres prepared above was added The reaction mixture was added to 100 parts by weight of anhydrous ethanol solvent, mixed and stirred evenly, and then 0.05 parts by weight of maleic anhydride was added, mixed and stirred at 80°C and 400 rpm for 2 hours, filtered, and solids were collected. The solids were washed twice with anhydrous ethanol solvent and dried at 100°C for 10 hours to obtain core-shell nanoparticles with maleic anhydride surface modification. The core-shell nanoparticles with maleic anhydride surface modification obtained above were placed in a polylysine aqueous solution with a concentration of 1 mg / mL, wherein the mass ratio of the modified core-shell nanoparticles to the polylysine aqueous solution was 1:10, mixed and stirred to form a uniformly dispersed suspension, reacted at room temperature for 1.5 hours, filtered and dried to obtain composite nanoparticles.

[0052] The preparation method of the modified phytic acid is consistent with that in Example 1.

[0053] Example 3

[0054] A method for preparing a corrosion-resistant NdFeB magnet, which differs from Example 1 in that the method for preparing the anti-corrosion coating comprises the following steps:

[0055] 8 parts by weight of composite nanoparticles, 5 parts by weight of modified phytic acid and 2 parts by weight of sodium dodecylbenzenesulfonate were added to 55 parts by weight of a mixed solution of deionized water and acetone in a mass ratio of 1.5:1, and the mixture was stirred at 450 rpm for 18 minutes. Then, 35 parts by weight of water-based epoxy resin was added, and the mixture was stirred at 950 rpm for 40 minutes to obtain an anti-corrosion coating.

[0056] The preparation method of the composite nanoparticles comprises the following steps:

[0057] 1 part by weight of Fe3O4 magnetic nanoparticles was added to 200 parts by weight of a mixed solution of ethanol and deionized water in a volume ratio of 5:1, and ultrasonically treated for 3 minutes at an ultrasonic frequency of 40 kHz and an ultrasonic power of 50 W to obtain a Fe3O4 magnetic nanoparticle dispersion; then 5 parts by weight of 25 wt% ammonia water was added to the Fe3O4 magnetic nanoparticle dispersion, and then 1 part by weight of ethyl orthosilicate was added under an ultrasonic frequency of 40 kHz and an ultrasonic power of 100 W, and the ultrasonic treatment was continued for 2.5 hours, washed with deionized water 3 times, and vacuum dried at 55°C to obtain core-shell nanospheres; 1 part by weight of the core-shell nanospheres prepared above was added to 1 00 parts by weight of anhydrous ethanol solvent, mixed and stirred evenly, then added 0.05 parts by weight of maleic anhydride, mixed and stirred at 80°C and 400rpm for 2h, filtered, collected the solid, washed the solid twice with anhydrous ethanol solvent, and dried at 100°C for 10h to obtain core-shell nanoparticles after surface modification with maleic anhydride; the core-shell nanoparticles after surface modification with maleic anhydride obtained above were placed in a 1 mg / mL polylysine aqueous solution, wherein the mass ratio of the modified core-shell nanoparticles to the polylysine aqueous solution was 1:10, mixed and stirred to form a uniformly dispersed suspension, reacted at room temperature for 1.5h, filtered and dried to obtain composite nanoparticles.

[0058] The preparation method of the modified phytic acid is consistent with that in Example 1.

[0059] Example 4

[0060] A method for preparing a corrosion-resistant NdFeB magnet, which differs from Example 1 in that the method for preparing the anti-corrosion coating comprises the following steps:

[0061] 8 parts by weight of composite nanoparticles, 5 parts by weight of modified phytic acid and 2 parts by weight of sodium dodecylbenzenesulfonate were added to 55 parts by weight of a mixed solution of deionized water and acetone in a mass ratio of 1.5:1, and the mixture was stirred at 450 rpm for 18 minutes. Then, 35 parts by weight of water-based epoxy resin was added, and the mixture was stirred at 950 rpm for 40 minutes to obtain an anti-corrosion coating.

[0062] The preparation method of the composite nanoparticles comprises the following steps:

[0063] 1 part by weight of γ-Fe2O3 magnetic nanoparticles was added to 200 parts by weight of a mixed solution of ethanol and deionized water in a volume ratio of 5:1, and ultrasonically treated for 3 minutes at an ultrasonic frequency of 40KHz and an ultrasonic power of 50W to obtain a γ-Fe2O3 magnetic nanoparticle dispersion; then 5 parts by weight of 25wt% ammonia water was added to the γ-Fe2O3 magnetic nanoparticle dispersion, and then 1 part by weight of ethyl orthosilicate was added under an ultrasonic state of an ultrasonic frequency of 40KHz and an ultrasonic power of 100W, and the ultrasonic treatment was continued for 2.5h, washed with deionized water 3 times, and vacuum dried at 55°C to obtain core-shell nanospheres; 1 part by weight of the core-shell nanospheres prepared above was added The reaction mixture was added to 100 parts by weight of anhydrous ethanol solvent, mixed and stirred evenly, and then 0.05 parts by weight of maleic anhydride was added, mixed and stirred at 80°C and 400 rpm for 2 hours, filtered, and solids were collected. The solids were washed twice with anhydrous ethanol solvent and dried at 100°C for 10 hours to obtain core-shell nanoparticles with maleic anhydride surface modification. The core-shell nanoparticles with maleic anhydride surface modification obtained above were placed in a polylysine aqueous solution with a concentration of 1 mg / mL, wherein the mass ratio of the modified core-shell nanoparticles to the polylysine aqueous solution was 1:10, mixed and stirred to form a uniformly dispersed suspension, reacted at room temperature for 1.5 hours, filtered and dried to obtain composite nanoparticles.

[0064] The preparation method of the modified phytic acid is consistent with that in Example 1.

[0065] Comparative Example 1

[0066] A method for preparing a corrosion-resistant NdFeB magnet, which differs from Example 1 in that the method for preparing the anti-corrosion coating comprises the following steps:

[0067] 8 parts by weight of core-shell nanospheres, 5 parts by weight of modified phytic acid and 2 parts by weight of sodium dodecylbenzenesulfonate were added to 55 parts by weight of a mixed solution of deionized water and acetone in a mass ratio of 1.5:1, and the mixture was stirred at 450 rpm for 18 minutes. Then, 35 parts by weight of water-based epoxy resin was added, and the mixture was stirred at 950 rpm for 40 minutes to obtain an anti-corrosion coating.

[0068] The preparation method of the core-shell nanospheres comprises the following steps:

[0069] 1 part by weight of CoFe2O4 magnetic nanoparticles was added to 200 parts by weight of a mixed solution of ethanol and deionized water in a volume ratio of 5:1, and ultrasonic treatment was performed at an ultrasonic frequency of 40 kHz and an ultrasonic power of 50 W for 3 minutes to obtain a CoFe2O4 magnetic nanoparticle dispersion; then 5 parts by weight of 25wt% ammonia water were added to the CoFe2O4 magnetic nanoparticle dispersion, and then 1 part by weight of ethyl orthosilicate was added under ultrasonic conditions of an ultrasonic frequency of 40 kHz and an ultrasonic power of 100 W, and ultrasonic treatment was continued for 2.5 hours. The mixture was washed three times with deionized water and dried in a vacuum at 55°C to obtain core-shell nanospheres.

[0070] The preparation method of the modified phytic acid is consistent with that in Example 1.

[0071] Comparative Example 2

[0072] A method for preparing a corrosion-resistant NdFeB magnet, which differs from Example 1 in that the method for preparing the anti-corrosion coating comprises the following steps:

[0073] 8 parts by weight of composite nanoparticles, 5 parts by weight of modified phytic acid and 2 parts by weight of sodium dodecylbenzenesulfonate were added to 55 parts by weight of a mixed solution of deionized water and acetone in a mass ratio of 1.5:1, and the mixture was stirred at 450 rpm for 18 minutes. Then, 35 parts by weight of water-based epoxy resin was added, and the mixture was stirred at 950 rpm for 40 minutes to obtain an anti-corrosion coating.

[0074] The preparation method of the modified phytic acid comprises the following steps:

[0075] 0.2 parts by weight of phytic acid and 2.5 parts by weight of ethylene glycol monomethyl ether were mixed and stirred at 700 rpm for 25 minutes; then, 4.8 parts by weight of ethylene glycol diglycidyl ether were added, mixed and stirred at 350 rpm for 18 minutes, and 0.06 parts by weight of tetrabutylammonium chloride was added as a catalyst during the mixing and stirring process to obtain a mixture; then, the mixture was mixed and stirred at 85° C. and 450 rpm for 2 hours to obtain modified phytic acid.

[0076] The preparation method of the composite nanoparticles is consistent with that of Example 1.

[0077] Comparative Example 3

[0078] A method for preparing a corrosion-resistant NdFeB magnet, which differs from Example 1 in that the method for preparing the anti-corrosion coating comprises the following steps:

[0079] 8 parts by weight of composite nanoparticles, 5 parts by weight of phytic acid and 2 parts by weight of sodium dodecylbenzenesulfonate were added to 55 parts by weight of a mixed solution of deionized water and acetone in a mass ratio of 1.5:1, and the mixture was stirred at 450 rpm for 18 minutes. Then, 35 parts by weight of water-based epoxy resin was added, and the mixture was stirred at 950 rpm for 40 minutes to obtain an anti-corrosion coating.

[0080] The preparation method of the composite nanoparticles is consistent with that of Example 1.

[0081] Comparative Example 4

[0082] A method for preparing a corrosion-resistant NdFeB magnet, which differs from Example 1 in that the method for preparing the anti-corrosion coating comprises the following steps:

[0083] 8 parts by weight of nano-silica, 5 parts by weight of modified phytic acid and 2 parts by weight of sodium dodecylbenzenesulfonate were added to 55 parts by weight of a mixed solution of deionized water and acetone in a mass ratio of 1.5:1, and the mixture was stirred at 450 rpm for 18 minutes. Then, 35 parts by weight of water-based epoxy resin was added, and the mixture was stirred at 950 rpm for 40 minutes to obtain an anti-corrosion coating.

[0084] The preparation method of the modified phytic acid is consistent with that in Example 1.

[0085] Test Example 1

[0086] Performance Testing

[0087] The NdFeB magnets prepared in Examples 1-4 and Comparative Examples 1-4 of the present invention were selected as the NdFeB magnet samples of the experimental group. At the same time, a commercial NdFeB magnet matrix (N50 commercial sintered NdFeB, size 1.0×1.0×0.5 cm) was selected. 3 , sourced from Zhejiang Yingluohua Magnetics Co., Ltd.) as the control group of NdFeB magnet samples; the following performance tests were conducted:

[0088] Neutral salt spray test

[0089] The salt spray corrosion test was conducted using a salt spray chamber (XW-YWP) to simulate the accelerated corrosion of magnets in a humid salt solution. Three magnets from each group were selected for the salt spray test. All magnet samples were placed in the chamber for the test. The test solution consisted of a 5wt% NaCl aqueous solution with a pH of 6.5-7.2. The chamber temperature was maintained at 35±2°C and the relative humidity was greater than 95%, maintaining a closed salt spray environment. Changes in the surface morphology of the magnets in each group were recorded every 24 hours, and photographs were taken to record the experimental data. The salt spray test duration was measured until the magnet samples in each group reached the same level of corrosion (visible rust or rust spots on the sample surface). The test results are shown in Table 1 below.

[0090] High temperature and high humidity test

[0091] Three magnets from each group were placed in a high-temperature, high-humidity test chamber (DX-HAST-350A). The chamber was filled with pure water and the machine was turned on. Every 48 hours, the machine was turned on to observe and record the corrosion changes on the surface of each magnet sample. The test duration was measured until the samples reached the same level of corrosion (visible rust or rust spots on the sample surface). The experimental conditions were 120°C and 90% humidity. The test results are shown in Table 1 below.

[0092] Hydrophobicity test

[0093] The contact angle of the sample surface was measured using a contact angle meter. The contact angle is the angle between the tangent line of the liquid-gas interface, measured at the intersection of the solid-liquid-gas three-phase system, and the solid-liquid interface. The contact angle is used to evaluate the hydrophobicity of the sample surface; a larger contact angle indicates better hydrophobicity. The contact angle meter used in this experiment was a KRÜSS DSA25. At room temperature of approximately 25°C and relative humidity of approximately 50%, deionized water droplets were placed on the surfaces of each set of NdFeB magnet samples to measure the contact angle of the stable droplets. Five measurements were taken at different locations on the sample surface, and the average value was taken. The volume of each droplet was 1 μL. The test results are shown in Table 1 below.

[0094] Antibacterial testing

[0095] Three magnet samples from each group were placed in a 250 mL conical flask containing 100 mL PBS buffer (pH = 7.2, concentration 0.01 mol / L) and 10 mL bacterial suspension. The concentration of the bacterial suspension in PBS buffer was 1 × 10 4 -2×10 4 cfu / mL. The test strain used was Escherichia coli (commercially available, catalog number: ATCC 8739). After immersion for 1 hour, 0.5 mL of the sample solution was diluted appropriately and cultured on agar plates for 24 hours. Viable bacteria were then counted. A control group without any coating served as a negative control. The average change in colony count before and after immersion was calculated, and the average was used to evaluate the antibacterial activity. The test results are shown in Table 1 below.

[0096] Scrape test

[0097] Each group of magnet samples was subjected to a scraping test by using 100-grit sandpaper at 50 N / cm 2 The samples were scraped under a pressure of 100°C and the degree of damage to the coating was observed. Damage levels were defined as follows: Level 1: 1-2 scratches; Level 2: 3-4 scratches; Level 3: 5-6 scratches; Level 4: 7-9 scratches; Level 5: 10 or more scratches. The test results are shown in Table 1 below.

[0098] Table 1

[0099]

[0100] As can be seen from Table 1, by comparing Examples 1-4, Comparative Examples 1-4 and the control group, it is found that compared with the control group, the salt spray test time and the high temperature and high humidity test time of Examples 1-4 and Comparative Examples 1-4 are longer than those of the control group, and the contact angle is significantly greater than that of the control group, indicating that the corrosion resistance and hydrophobicity of the NdFeB magnets of the embodiments of the present invention and the comparative example are better than those of the control group, indicating that the introduction of anti-corrosion coatings in the preparation process of NdFeB magnets is beneficial to improving the corrosion resistance and hydrophobicity of NdFeB magnets.

[0101] Comparing Examples 1-4, it was found that the salt spray test duration and the high temperature and high humidity test duration of Example 1 were longer than those of Examples 2-4, and the contact angle was significantly greater than that of Examples 2-4, indicating that the corrosion resistance and hydrophobicity were better than those of Examples 2-4, indicating that the introduction of CoFe2O4 as magnetic nanoparticles in the coating preparation process to prepare composite nanoparticles and the coordinated use of modified phytic acid are more conducive to improving the corrosion resistance and hydrophobicity of NdFeB magnets. The reason for this analysis may be that CoFe2O4 has high thermal stability and structural stability, and can maintain its performance under high temperature and complex environments. This stability enables the composite nanoparticles to play a role in the coating for a long time. In contrast, materials such as NiFe2O4, Fe3O4 and γ-Fe2O3 are more likely to undergo structural changes in high temperature or corrosive environments, so the improvement effect on NdFeB magnets is not as good as CoFe2O4.

[0102] By comparing Example 1 with Comparative Example 1 and Comparative Example 4, it is found that the salt spray test time and the high temperature and high humidity test time of Example 1 are longer than those of Comparative Example 1 and Comparative Example 4, and the contact angle is significantly greater than that of Comparative Example 1 and Comparative Example 4, indicating that the corrosion resistance and hydrophobicity are better than those of Comparative Example 1 and Comparative Example 4. The reason for this may be that compared with the core-shell nanospheres introduced into the coating in Comparative Example 1 and the silica nanoparticles added in Comparative Example 4, the coating in Example 1 introduces composite nanoparticles with a core-shell structure wrapped in an outer layer of polylysine, which not only avoids the agglomeration of the nanoparticles, but also facilitates their uniform dispersion in the epoxy resin system, thereby facilitating the coating to form a dense protective layer on the surface of the magnet, which can effectively block the contact between the corrosive medium and the surface of the magnet; and the amino group on the surface of the polylysine may also interact with the hydroxyl group in the phytic acid modified by the cardanol glycidyl ether to form hydrogen bonds, thereby enhancing the bonding force between the two, which is beneficial to improving the stability of the anti-corrosion coating, thereby further enhancing the corrosion resistance and hydrophobicity of the NdFeB magnet.

[0103] Comparing Example 1 and Comparative Examples 2-3, it was found that the salt spray test time and the high temperature and high humidity test time of Example 1 were longer than those of Comparative Examples 2-3, and the contact angle was significantly greater than that of Comparative Examples 2-3, indicating that the corrosion resistance and hydrophobicity were better than those of Comparative Examples 2-3. The reason for this may be that compared with the phytic acid modified with ethylene glycol diglycidyl ether introduced into the coating in Comparative Example 1 and the phytic acid directly introduced in Comparative Example 2, Example 1 used cardanol glycidyl ether to modify the phytic acid and introduced it into the coating for synergistic use with the composite nanoparticles. Cardanol glycidyl ether has an unsaturated long carbon chain hydrocarbon and a benzene ring in its structure, while ethylene glycol diglycidyl ether lacks such a long aliphatic hydrocarbon chain and aromatic ring, resulting in its insufficient hydrophobicity and flexibility, and its chemical stability is not as good as that of cardanol glycidyl ether. Therefore, cardanol glycidyl ether-modified phytic acid can provide better hydrophobicity and chemical stability than ethylene glycol diglycidyl ether-modified phytic acid, which can reduce the contact between water molecules and the magnet surface and reduce the corrosion rate; at the same time, it may also react with the groups on the surface of the composite nanoparticles to form a cross-linked network, which helps to improve the overall performance of the anti-corrosion coating, thereby enhancing the corrosion resistance and hydrophobicity of the NdFeB magnet.

[0104] As shown in Table 1, the antibacterial test results of Examples 1-4 and Comparative Examples 1-4 show that the antibacterial properties of Examples 1-4 are significantly higher than those of Comparative Examples 1-4, with Example 1 having the highest antibacterial property. This indicates that the introduction of polylysine-coated composite nanoparticles and the synergistic use of cardanol glycidyl ether-modified phytic acid during the coating preparation process is more conducive to improving the antibacterial properties of NdFeB magnets. Analysis suggests that the reason for this may be that both polylysine and phytic acid introduced during the preparation of the anti-corrosion coating in the embodiments of the present invention have certain antibacterial activity, which can impart certain antibacterial properties to NdFeB magnets. However, compared with polylysine, phytic acid has a weaker antibacterial effect. Therefore, compared with Examples 1-4, Comparative Example 1 and Comparative Example 4, in which polylysine was not introduced during the coating preparation process, had an antibacterial property of less than 60%, and the antibacterial effect was significantly lower than that of Examples 1-4; Comparative Example 2 and Comparative Example 3, in which phytic acid modified with ethylene glycol diglycidyl ether and phytic acid and polylysine-coated composite nanoparticles were added in combination, had an antibacterial property of less than 95%, and the antibacterial effect was lower than that of Examples 1-4. Analysis showed that the reason may be that compared with ethylene glycol diglycidyl ether, cardanol glycidyl ether is more hydrophobic and can more effectively reduce the attachment and growth of bacteria, thereby improving the antibacterial performance.

[0105] As shown in Table 1, the scraping test results of Comparative Examples 1-4, Comparative Examples 1-4 and the control group showed that the control group was damaged to level 3, with more scratches; the damage level of Comparative Example 1-2 was level 1, the damage level of Comparative Example 3-4 was level 1-2, and the damage level was lower than that of the control group, while Example 1-4 was level 0, and no scratches appeared on the NdFeB magnet; This shows that the bonding strength between the coating of the present application and the NdFeB magnet is relatively high, and the coating formed at the same time also has good mechanical properties, which effectively improves the protective performance of the coating on the NdFeB magnet. The reason for the analysis may be that the synergistic use of cardanol glycidyl ether modified phytic acid and composite nanoparticles is conducive to enhancing the bonding strength between the coating and the NdFeB magnet, while improving the mechanical stability of the coating. The phosphate groups in the modified phytic acid can form a strong chemical bond with the surface of the magnet, and the long carbon chain structure in the grafted cardanol glycidyl ether is well compatible with matrix materials such as epoxy resin; the coated polylysine in the composite nanoparticle structure not only has good corrosion resistance, but can also act as a "bionic glue" to enhance the bonding strength between the coating and the substrate; this dual effect of cardanol glycidyl ether-modified phytic acid and composite nanoparticles improves the adhesion and mechanical stability of the coating, making it show a lower degree of damage in the scrape test.

[0106] Test Example 2

[0107] Friction and wear testing

[0108] In order to evaluate the wear resistance and abrasion resistance of the NdFeB magnet prepared by the present invention, a friction and wear test was performed on the magnet. In the friction experiment, the contact angle of the magnet surface may change as the friction cycle increases. If the coating maintains a high contact angle during the friction process, it means that the coating has good hydrophobicity and integrity, and can effectively reduce wear. On the contrary, a significant decrease in the contact angle may mean that the coating is worn or damaged, resulting in a decrease in surface hydrophobicity, thereby increasing the wear rate. By detecting the surface contact angle of the NdFeB magnet after different friction cycles, the wear resistance and durability of the coating can be evaluated. If the coating can still maintain a high contact angle or the contact angle decreases less after multiple frictions, it means that the coating has good wear resistance and abrasion resistance, and can effectively protect the magnet surface.

[0109] The NdFeB magnets prepared in Examples 1-4 and Comparative Examples 1-4 of the present invention were selected as the NdFeB magnets to be tested, and the wear resistance of the corrosion-resistant NdFeB magnets prepared in the present invention was tested using a drag friction test. The NdFeB magnet to be tested was placed with the coated side facing down on 800-grit sandpaper. A 100g weight was placed on the NdFeB magnet, and the magnet was dragged horizontally to generate friction. A horizontal reciprocating motion of 10cm was considered one friction cycle. The surface contact angles of the NdFeB magnets were measured after 0, 100, 200, and 500 friction cycles. The test results are shown in Table 2 below.

[0110] Table 2

[0111]

[0112] As can be seen from Table 2, with the increase of the friction cycle, the contact angles of Examples 1-4 and Comparative Examples 1-4 decrease, and the hydrophobic performance is reduced. By comparing Examples 1-4 and Comparative Examples 1-4, it is found that the contact angle of Examples 1-4 decreases less than that of Comparative Examples 1-4, among which Example 1 has the smallest decrease, indicating that the wear resistance of the NdFeB magnets of Examples 1-4 is better than that of Comparative Examples 1-4.

[0113] Comparative Example 1 and Comparative Example 1 and Comparative Example 4 found that the contact angle of Example 1 decreased less than that of Comparative Example 1 and Comparative Example 4, indicating that the wear resistance is better than that of Comparative Example 1 and Comparative Example 4. The reason for analysis may be that compared to the core-shell nano-microspheres introduced into the coating in Comparative Example 1, and the silica nanoparticles added in Comparative Example 4, the composite nanoparticles with a core-shell structure wrapped in an outer layer with polylysine are introduced into the coating in Example 1. The composite nanoparticles are protected by the dual protection of silica coating and polylysine, which enhances the mechanical properties and stability of the coating. The silica coating provides a stable substrate for the nanoparticles, and the coating of polylysine further enhances the adhesion and wear resistance of the coating. This structure can effectively resist wear and tear during friction, reduce the damage of the coating, and thus is conducive to enhancing the wear resistance of the NdFeB magnet.

[0114] Comparative Example 1 and Comparative Example 2-3 find that, embodiment 1 contact angle decreases amplitude less than comparative example 2-3, illustrate that wear resistance is better than comparative example 2-3, analysis reason may be because compared to the phytic acid of the ethylene glycol diglycidyl ether modified phytic acid introduced in coating in comparative example 1 and the phytic acid directly introduced in comparative example 2, embodiment 1 adopts cardanol glycidyl ether to modify phytic acid, and introduces it in coating and is used in coordination with composite nanoparticles. In embodiment 1, modified phytic acid forms chemical bonding by esterification with the hydroxyl group of phytic acid and the epoxy group of cardanol glycidyl ether, thereby enhancing the adhesion and stability of coating. This modified phytic acid can effectively reduce the peeling and wear of coating during friction, thus contributing to improving the overall performance of anti-corrosion coating, improves the wear resistance of NdFeB magnet. Due to the lack of similar cardanol glycidyl ether structural advantage of ethylene glycol diglycidyl ether modified phytic acid, it is impossible to reach the same lifting effect with it.

[0115] Test Example 3

[0116] Magnetic performance test

[0117] The NdFeB magnets prepared in Examples 1 to 4 of the present invention and the control group magnet (N50 commercial sintered NdFeB, size 1.0×1.0×0.5 cm) were tested using a NIM-2000 DC permanent magnet material magnetic property tester. 3 , from Zhejiang Yingluohua Magnetics Co., Ltd.) to measure the magnet performance and record the experimental magnetic performance data; the specific test results are shown in Table 3 below.

[0118] Table 3

[0119] Coercivity (Hcj, KA / m) Remanence (Br, T) Example 1 961 1.432 Example 2 960 1.429 Example 3 959 1.431 Example 4 961 1.429 control group 962 1.433

[0120] As shown in Figure 3, compared with the control group without any coating, the changes in the remanence and coercive force of the NdFeB magnets of Examples 1-4 coated with corrosion-resistant coatings of the present application are very small and negligible, indicating that the introduction of anti-corrosion coatings with modified phytic acid and composite nanoparticles in the preparation process of NdFeB magnets to form a corrosion-resistant coating on the surface of the magnet can significantly improve the corrosion protection effect of the corrosion-resistant coating on the NdFeB magnet on the basis of ensuring the magnetic properties of the magnet. The reason for this may be that the addition of magnetic nanoparticles can produce a synergistic effect with the magnetic properties of the NdFeB magnet. In the composite nanoparticles, the magnetic nanoparticles may act as a magnetic enhancement phase, which can improve the overall magnetic properties of the magnet, including remanence and coercive force; in addition, the addition of composite nanoparticles may also optimize the microstructure of the magnet, reduce defects, and thus reduce the influence of the coating on the magnetic properties of the magnet.

Claims

1. A method for preparing a corrosion-resistant NdFeB magnet, characterized in that: The following steps are involved: pre-treating the NdFeB substrate to obtain a pre-treated NdFeB magnet substrate; Then, the anti-corrosion coating is sprayed on the surface of the pre-treated NdFeB magnet substrate, and then cured to obtain a NdFeB magnet with a surface coated with the corrosion-resistant coating, that is, a corrosion-resistant NdFeB magnet; The preparation method of the anti-corrosion coating comprises the following steps, calculated by weight: 6-10 parts of composite nanoparticles, 3-6 parts of modified phytic acid, and 1-3 parts of a surfactant are added to 40-60 parts of a mixed solution of water and acetone in a mass ratio of 1-3:1, and the mixture is stirred at 300-500 rpm for 15-25 minutes. Then, 20-40 parts of a water-based epoxy resin are added, and the mixture is stirred at 800-1000 rpm for 30-50 minutes to obtain an anti-corrosion coating. The preparation method of the modified phytic acid comprises the following steps, calculated by weight: 0.1-0.3 parts of phytic acid and 2-3 parts of ethylene glycol monomethyl ether are mixed and stirred at 500-800 rpm for 20-30 minutes; then 4.5-5 parts of cardanol glycidyl ether are added, and the mixture is mixed and stirred at 300-500 rpm for 15-25 minutes. During the mixing and stirring process, 0.02-0.1 parts of tetrabutylammonium chloride are added as a catalyst to obtain a mixture; and the mixture is mixed and stirred at 80-90° C. and 300-500 rpm for 1-3 hours to obtain modified phytic acid; The composite nanoparticles are prepared by a sol-gel method, using tetraethyl orthosilicate to hydrolyze and condense under the catalysis of ammonia water to form a uniform silica coating layer on the surface of magnetic nanoparticles to prepare nanospheres with a core-shell structure, and then introducing maleic anhydride to modify the surface of the nanospheres with the core-shell structure to prepare modified core-shell nanospheres; the modified core-shell nanospheres obtained above are placed in a polylysine aqueous solution with a concentration of 1-4 mg / mL, wherein the mass ratio of the modified core-shell nanospheres to the polylysine aqueous solution is 1:8-10, mixed and stirred to form a uniformly dispersed suspension, reacted at room temperature for 1-3 hours, filtered and dried to obtain the composite nanoparticles.

2. The method for preparing a corrosion-resistant NdFeB magnet according to claim 1, wherein: The pretreatment of the NdFeB substrate is specifically as follows: the NdFeB substrate is immersed in a 4-6wt% alkaline degreasing agent aqueous solution for degreasing for 8-12 minutes, and then rinsed with water; the sample is then immersed in a 4-6wt% nitric acid aqueous solution for pickling for 8-12 minutes, and then rinsed with water; then immersed in water, ultrasonically oscillated for 8-15 minutes at an ultrasonic frequency of 20-50KHz and an ultrasonic power of 800-1000W, and then rinsed with water and dried.

3. The method for preparing a corrosion-resistant NdFeB magnet according to claim 1, wherein: The surfactant is selected from one or more of sodium lauryl sulfate, sodium dodecylbenzene sulfonate, and polyethylene glycol.

4. The method for preparing a corrosion-resistant NdFeB magnet according to claim 1, wherein: The particle size of the composite nanoparticles is 10-100 nm; the preparation method of the composite nanoparticles comprises the following steps, calculated by weight: 0.5-2 parts of magnetic nanoparticles are added to 180-220 parts of a mixed solution of ethanol and water in a volume ratio of 5:1, and ultrasonically treated for 2-5 minutes at an ultrasonic frequency of 20-50KHz and an ultrasonic power of 30-60W to obtain a magnetic nanoparticle dispersion; then 2-6 parts of 25-30wt% ammonia water are added to the magnetic nanoparticle dispersion, and then 0.5-1.2 parts of ethyl orthosilicate are added under ultrasonic conditions of an ultrasonic frequency of 20-50KHz and an ultrasonic power of 50-120W, and the ultrasonic treatment is continued for 2-3 hours, washed with water 2-3 times, and vacuum dried at 50-60°C to obtain core-shell nanospheres; 1-3 parts of the core-shell nanospheres prepared above are added to the The modified core-shell nanoparticles are added to 80-100 parts of anhydrous ethanol solvent, mixed and stirred evenly, and then 0.02-0.1 parts of maleic anhydride are added, mixed and stirred at 75-85° C. and 200-500 rpm for 1-3 hours, filtered, and solids are collected. The solids are washed 1-2 times with anhydrous ethanol solvent and dried at 95-105° C. for 8-12 hours to obtain modified core-shell nanoparticles; the modified core-shell nanoparticles obtained above are placed in a polylysine aqueous solution with a concentration of 1-4 mg / mL, wherein the mass ratio of the modified core-shell nanoparticles to the polylysine aqueous solution is 1:8-10, mixed and stirred to form a uniformly dispersed suspension, reacted at room temperature for 1-3 hours, filtered and dried to obtain composite nanoparticles.

5. The method for preparing a corrosion-resistant NdFeB magnet according to claim 4, wherein: The magnetic nanoparticles are selected from one or more of CoFe2O4, NiFe2O4, γ-Fe2O3, and Fe3O4.

6. The method for preparing a corrosion-resistant NdFeB magnet according to claim 1, wherein: The curing temperature is 140-180° C., and the curing time is 1-3 hours.

7. The method for preparing a corrosion-resistant NdFeB magnet according to claim 1, wherein: The thickness of the corrosion-resistant coating is 5-20 μm.

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