High-performance neodymium-iron-boron magnet and preparation method thereof

Abstract

The invention relates to the technical field of neodymium-iron-boron magnets, in particular to a high-performance neodymium-iron-boron magnet and a preparation method thereof. The preparation method comprises the following steps: S1, preparing a mixed material; s2, compression molding; s3, sintering and molding; s4, carrying out pretreatment on the neodymium-iron-boron magnet; and S5, the pretreated neodymium-iron-boron magnet is put into a multifunctional protection solution to be soaked, the soaking time is 10-30 s, and a multifunctional protection film is formed, the multifunctional protection liquid comprises the following substances in parts by weight: 35-42 parts of acrylic resin, 8-10 parts of zinc powder, 5-7 parts of aluminum powder, 5-6 parts of nano zirconium oxide, 12-14 parts of boron nitride, 14-16 parts of a composite coupling agent, 15-18 parts of ethyl acetate and 60-70 parts of deionized water. According to the preparation method of the high-performance neodymium-iron-boron magnet, the comprehensive performance of the magnet can be improved, the corrosion resistance and the mechanical performance of the magnet can be remarkably improved, and the preparation method has important practical application value.

Description

Technical Field

[0001] The present application relates to the technical field of neodymium iron boron magnets, and in particular to a high-performance neodymium iron boron magnet and a preparation method thereof. Background Art

[0002] Since its advent in the 1980s, sintered NdFeB magnets have been widely used in many fields such as wind power generation, automotive industry, and medical equipment due to their superior magnetic properties and high cost-effectiveness, playing an important role in the development of the national economy. However, NdFeB magnets have a multi-phase structure with a large potential difference between the phases. In particular, the chemical activity of the rare earth-rich phase at the grain boundary is high. It is easily corroded in high temperature, high humidity, or when in contact with corrosive media, resulting in a decrease in magnetic properties. This seriously restricts the application of magnets in high temperature, high humidity, electrochemical environments, and other fields that require magnets to have corrosion resistance. Therefore, research on the corrosion behavior and corrosion resistance of NdFeB magnets has become a focus of attention.

[0003] At present, the industry generally adopts alloying method and surface protection technology to improve the corrosion resistance of sintered NdFeB permanent magnet materials. For example, in the existing technology, Dy element is introduced into sintered NdFeB powder by vacuum sputtering deposition, and the surface of the powder particles is ground by air flow. However, this method only introduces Dy element at the grain boundary and fails to simultaneously control the content of other alloying elements in the magnet, which easily changes the electrochemical corrosion potential of the grain boundary phase, thereby affecting the corrosion resistance. There is also a technology that takes advantage of the glossiness and good ductility of aluminum, which can form an oxide film on the surface in the air and has excellent corrosion resistance, and coats the surface of NdFeB magnets with aluminum. Conventional aluminum plating methods are generally ion aluminum plating and organic solution aluminum plating. However, ion aluminum plating equipment is expensive and the cost is very high. The electrolyte for organic solution aluminum plating is difficult to prepare and the process is complicated.

[0004] Therefore, it is urgent to seek a multifunctional coating technology that is simple to operate and easy to control. Summary of the Invention

[0005] In response to the deficiencies in the prior art, the present application provides a high-performance NdFeB magnet and a method for preparing the same. The high-performance NdFeB magnet prepared in the present application has excellent corrosion resistance, comprehensive magnetic properties, mechanical properties and high-temperature resistance.

[0006] In a first aspect, the present application provides a method for preparing a high-performance NdFeB magnet, using the following technical solution: A method for preparing a high-performance NdFeB magnet comprises the following steps: S1. Preparing a mixture: uniformly mixing NdFeB powder and semi-metallic ferrimagnetic powder according to parts by mass to obtain a mixture; S2. Compression molding: The mixed material is compressed under vacuum conditions to obtain a compact; S3. Sintering: Under argon protection, the compact is sintered and tempered twice to obtain NdFeB magnets; S4, pre-treating the NdFeB magnet to obtain a pre-treated NdFeB magnet; S5. Dipping in a multifunctional protective liquid: placing the pretreated NdFeB magnet into the multifunctional protective liquid for immersion for 10-30 seconds to form a multifunctional protective film on the surface of the NdFeB magnet, then taking it out, pre-curing it at 110-120°C for 5-8 minutes for leveling, and then curing it at 180-200°C for 30-40 minutes to obtain a high-performance NdFeB magnet, wherein the multifunctional protective liquid comprises the following substances in parts by weight: 35-42 parts of acrylic resin, 8-10 parts of zinc powder, 5-7 parts of aluminum powder, 5-6 parts of nano-zirconium oxide, 12-14 parts of boron nitride, 14-16 parts of a composite coupling agent, 15-18 parts of ethyl acetate, and 60-70 parts of deionized water.

[0007] By adopting the above technical solution, the mixing step: By uniformly mixing NdFeB powder with semi-metallic ferrimagnetic powder, the two materials are physically mixed and chemically bonded. This mixing not only improves the mechanical strength of the NdFeB magnet but also enhances its magnetic properties. The cubic crystal structure of the semi-metallic ferrimagnetic powder facilitates energy absorption, while its high magnetocrystalline anisotropy further enhances the magnet's performance. The pressing step: Pressing under vacuum conditions helps minimize the effects of impurities, ensuring the purity and performance of the magnet. The vacuum environment also helps reduce the occurrence of adverse reactions such as oxidation. The sintering step: Sintering under argon protection and secondary tempering ensure the uniformity and stability of the magnet. Argon protection prevents oxidation and other harmful reactions, while the secondary tempering further enhances the magnet's mechanical strength and magnetic properties. The dipping step: The synergistic effect of the various components of the multi-functional protective solution significantly improves the magnet's corrosion resistance and high-temperature resistance. The curing step: Through the pre-curing and curing processes, the multi-functional protective solution forms a stable protective film on the magnet surface. The pre-curing process helps level the coating, while the curing process ensures strong adhesion and long-term stability. In summary, this application achieves the preparation of high-performance NdFeB magnets through carefully designed steps and material combinations. In this application, the functions and synergistic effects of the various components of the multifunctional protective liquid are as follows: Acrylic resin, as one of the main components of the multifunctional protective liquid, provides the coating's basic structure and adhesion. It can combine with the filler coated with the composite coupling agent to enhance the bond strength between the coating and the NdFeB magnet. Furthermore, acrylic resin has excellent chemical and weather resistance, which helps improve the coating's corrosion resistance and high-temperature resistance. Zinc powder and aluminum powder act as sacrificial anodes in the multifunctional protective liquid. During the corrosion process, they form a protective film that seals pores and cracks on the NdFeB magnet's surface, effectively isolating the magnet from corrosive media such as oxygen and moisture in the air. Furthermore, the corrosion products formed during the corrosion process further fill the pores and cracks, improving the magnet's corrosion resistance. Nano-zirconia has excellent mechanical properties and chemical stability. It provides excellent adhesion within the multifunctional protective liquid, promoting a tight bond between the coating and the NdFeB magnet. Furthermore, the surface affinity of nano-zirconia helps improve the uniformity and adhesion of the coating. Boron nitride exhibits excellent thermal conductivity, enhancing the high-temperature resistance of the NdFeB magnet. Furthermore, boron nitride acts as a reinforcement within the coating, improving its mechanical strength and wear resistance. The composite coupling agent acts as a connector and reinforcement within the multifunctional protective liquid. It improves the adhesion between zinc powder, aluminum powder, nano-zirconia, and boron nitride and the NdFeB magnet, while enhancing the coating's adhesion and protective effectiveness. Ethyl acetate and deionized water, used as solvents and diluents, help adjust the viscosity and fluidity of the multifunctional protective liquid, making it easier to form a uniform protective film on the surface of the NdFeB magnet.They also help improve the coating's permeability and adhesion. In summary, the components of the multifunctional protective fluid work synergistically to enhance the corrosion resistance, high-temperature resistance, and overall magnetic properties of NdFeB magnets. Acrylic resin provides basic adhesion and chemical resistance; zinc and aluminum powders enhance corrosion resistance through sacrificial anodic protection; nano-zirconia and boron nitride provide bonding and thermal conductivity, respectively; the composite coupling agent enhances the bond between the coating and the magnet; and ethyl acetate and deionized water adjust the coating's viscosity and fluidity. These components work together to ensure the NdFeB magnet's dimensional stability and excellent overall performance in high-temperature environments.

[0008] Preferably, in step S1, the mass ratio of the NdFeB powder to the semi-metallic ferrimagnetic powder is 100:5-7, and the NdFeB powder is Nd with an average particle size of 3-6 μm. 14 Fe80B6 powder, the semi-metallic ferrimagnetic powder is a perovskite semi-metallic ferrimagnetic powder Sr2FeReO6 with an average particle size of 1-5 μm.

[0009] By adopting the above technical solution, NdFeB powder is used as the main component of the magnet, and NdFeB powder provides the main magnetic properties of the magnet. 14 Fe80B6 powder has excellent magnetic and mechanical properties. However, this powder can encounter some challenges during magnet preparation, such as powder aggregation and difficulty in uniform distribution. Semi-metallic ferrimagnetic powder, as a reinforcing phase, exhibits cubic crystal characteristics, providing excellent energy absorption and high magnetocrystalline anisotropy. Perovskite semi-metallic ferrimagnetic powder Sr2FeReO6, with an average particle size of 1-5μm, exhibits excellent mechanical strength and magnetic properties. Furthermore, the addition of semi-metallic ferrimagnetic powder helps improve the distribution of NdFeB powder. The semi-metallic ferrimagnetic powder is dispersed within the NdFeB powder, resulting in a tighter and more regular arrangement of the phases, significantly enhancing the mechanical strength and overall magnetic properties of the NdFeB magnet. Furthermore, the addition of semi-metallic ferrimagnetic powder improves the magnet's high-temperature and corrosion resistance. In summary, the selection of a mass ratio of 100:5-7 for NdFeB powder to semi-metallic ferrimagnetic powder is based on considerations for improving the magnet's overall performance.

[0010] Preferably, in step S2, the pressing pressure is 180-200 MPa.

[0011] Preferably, in step S3, the sintering process is: sintering at 1050-1100° C. for 2-3 hours, and then cooling to room temperature at a rate of 5-6° C. / min.

[0012] Preferably, in step S3, the process of the secondary tempering treatment is: heating to 900-930°C at a heating rate of 13-15°C / min for primary tempering treatment, keeping warm for 1.5 hours, then cooling to 450-480°C for secondary tempering treatment, keeping warm for 2 hours.

[0013] Preferably, in step S4, the process conditions for pre-treating the NdFeB magnet are as follows: chamfering the NdFeB magnet with a chamfering machine for 2-3 hours, alkali washing and degreasing in a 2.5% mass concentration sodium hydroxide solution for 10-20 minutes, ultrasonic cleaning in deionized water for 3-4 minutes, then activating in a 3.5% mass concentration nitric acid solution for 0.3-0.5 minutes, and then ultrasonic cleaning in deionized water for 2-3 minutes. After drying with cold air, a pretreated NdFeB magnet is obtained.

[0014] Preferably, in step S5, the average particle size of the zinc powder is 0.5-1 μm, the average particle size of the aluminum powder is 0.5-2 μm, the average particle size of the nano zirconium oxide is 50-80 nm, and the average particle size of the boron nitride is 0.1-0.3 μm.

[0015] Preferably, in step S5, the composite coupling agent is composed of γ-glycidyloxypropyltriethoxysilane and isopropyl tris(dioctylpyrophosphate) titanate in a mass ratio of 3:5.

[0016] By employing the above-mentioned technical solution, γ-glycidoxypropyltriethoxysilane can form chemical bonds with inorganic materials such as zirconium oxide and boron nitride, as well as covalent bonds with organic materials such as acrylic resins. This chemical bond formation helps improve the bonding strength between the inorganic filler and the organic matrix. Furthermore, during the curing process, γ-glycidoxypropyltriethoxysilane forms a network structure, further enhancing the mechanical properties and corrosion resistance of the coating. Isopropyl tris(dioctylpyrophosphate) titanate: This is an organic titanate coupling agent with excellent bonding and heat resistance. It forms strong chemical bonds with a variety of materials and can also improve their surface properties. In a multifunctional protective fluid, isopropyl tris(dioctylpyrophosphate) titanate helps improve the bonding between aluminum and zinc powders and NdFeB magnets. The synergistic effect of γ-glycidoxypropyltriethoxysilane and isopropyl tris(dioctylpyrophosphate) titanate significantly enhances the effectiveness of the composite coupling agent. γ-Glycidyloxypropyltriethoxysilane is primarily responsible for forming chemical bonds between the inorganic filler and the organic matrix, while isopropyl tri(dioctylpyrophosphate) titanate is primarily responsible for improving the bonding between the aluminum and zinc powders and the NdFeB magnets. This synergistic effect ensures the uniformity and stability of the multifunctional protective film, thereby improving the corrosion resistance, mechanical properties, and high-temperature resistance of the NdFeB magnets.

[0017] Preferably, in step S5, the multifunctional protective liquid is prepared by adding a composite coupling agent, ethyl acetate and deionized water to a reactor in parts by mass, heating to 45° C., stirring for 3-4 hours, then sequentially adding zinc powder, aluminum powder, nano zirconium oxide and boron nitride to the reactor, stirring for 0.5 hours, then adding acrylic resin to the reactor, heating to 55° C., stirring for 0.5-1 hours, and cooling to room temperature to obtain a multifunctional protective liquid.

[0018] In a second aspect, the present application provides a high-performance NdFeB magnet, which adopts the following technical solution: As a general technical concept, the present application also provides the above-mentioned high-performance NdFeB magnet, which is prepared using the above-mentioned method for preparing the high-performance NdFeB magnet.

[0019] In summary, the beneficial technical effects of this application are: 1. Improved magnetic and mechanical properties: By introducing semi-metallic ferrimagnetic powder, not only the mechanical strength of the NdFeB magnet is improved, but also the magnetic properties of the magnet are enhanced. The use of this composite material enables the magnet to have excellent dimensional stability in high temperature environments.

[0020] 2. Enhanced corrosion resistance: The aluminum and zinc powders in the multifunctional protective liquid form a protective coating on the surface of the NdFeB magnet, effectively sealing the pores and cracks on the surface and isolating the magnet from oxygen and moisture in the air. At the same time, the corrosion products formed during the corrosion of aluminum and zinc further fill the pores and cracks, hindering the movement of the corrosive medium.

[0021] 3. Improved Adhesion: The use of a composite coupling agent enhances the adhesion between zinc powder, aluminum powder, nano-zirconia, and boron nitride and the NdFeB magnet, thereby increasing the coating's service life. At the same time, the acrylic resin combined with the composite coupling agent-coated filler further enhances the bonding strength between the coating and the NdFeB magnet.

[0022] 4. Improve high temperature resistance: Boron nitride in the multifunctional protective liquid has excellent thermal conductivity and can improve the high temperature resistance of NdFeB magnets.

[0023] 5. Improved Overall Performance: The high-performance NdFeB magnets produced using the method provided in this application exhibit excellent corrosion resistance, comprehensive magnetic properties, mechanical properties, and high-temperature resistance. These improvements enable the magnets to have a longer service life and a wider range of applications in practical applications. DETAILED DESCRIPTION

[0024] The embodiments of the present application will be described in detail below with reference to the examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present application and should not be considered as limiting the scope of the present application. In the examples, if specific conditions are not specified, the conditions are carried out according to conventional conditions or manufacturer recommendations. The reagents or instruments used are not specified by the manufacturer and are conventional products that can be purchased commercially.

[0025] In the following examples, 100 parts represents 10 g, the average particle size of zinc powder is 0.7 μm, the average particle size of aluminum powder is 1.5 μm, the average particle size of nano zirconium oxide is 60 nm, and the average particle size of boron nitride is 0.2 μm.

[0026] Example 1 A method for preparing a high-performance NdFeB magnet comprises the following steps: S1. Prepare a mixture: according to the mass ratio, 100 parts of NdFeB powder and 5 parts of semi-metallic ferrimagnetic powder are mixed evenly to obtain a mixture. The NdFeB powder is Nd with an average particle size of 3 μm. 14 Fe80B6 powder, the semi-metallic ferrimagnetic powder is a perovskite semi-metallic ferrimagnetic powder Sr2FeReO6 with an average particle size of 1 μm; S2, compression molding: the mixture is compressed under a vacuum degree of 200 Pa and a pressure of 180 MPa to obtain a green compact; S3. Sintering: The green compact is sintered under argon protection. The sintering process is as follows: sintering at 1050°C for 3 hours, then cooling to room temperature at a rate of 5°C / min, then heating to 900°C at a heating rate of 13°C / min for a primary tempering treatment, holding the temperature for 1.5 hours, then cooling to 450°C for a secondary tempering treatment, holding the temperature for 2 hours, to obtain a NdFeB magnet. S4. Pre-treating the NdFeB magnets: chamfering the NdFeB magnets with a chamfering machine for 2 hours, alkaline washing and degreasing in a 2.5% sodium hydroxide solution for 10 minutes, ultrasonically cleaning in deionized water for 3 minutes, activating in a 3.5% nitric acid solution for 0.3 minutes, ultrasonically cleaning in deionized water for 2 minutes, and drying with cold air to obtain pre-treated NdFeB magnets; S5, dip coating multifunctional protective liquid: put the pretreated NdFeB magnet into the multifunctional protective liquid for immersion, the immersion time is 10s, and a multifunctional protective film is formed on the surface of the NdFeB magnet. Then take it out, pre-cure it at 110℃ for 5min for leveling, and then cure it at 180℃ for 40min to obtain a high-performance NdFeB magnet, wherein the multifunctional protective liquid includes the following materials in parts by weight: 35 parts of acrylic resin, 8 parts of zinc powder, 5 parts of aluminum powder, 5 parts of nano zirconium oxide, 12 parts of boron nitride, 14 parts of composite coupling agent, 15 parts of ethyl acetate, and 60 parts of deionized water. The composite coupling agent is composed of γ-glycidyloxypropyltriethoxysilane and isopropyl tri(dioctyl pyrophosphate) titanate in a mass ratio of 3:5. The preparation method of the multifunctional protective liquid is as follows: according to the mass parts, the composite coupling agent, ethyl acetate and deionized water are added into a reactor, the temperature is raised to 45°C, and the mixture is stirred for 3 hours. Then, zinc powder, aluminum powder, nano zirconium oxide and boron nitride are added into the reactor in sequence, the mixture is stirred for 0.5 hours, and then acrylic resin is added into the reactor. The mixture is heated to 55°C, stirred for 0.5 hours, and then cooled to room temperature to obtain the multifunctional protective liquid.

[0027] Example 2 A method for preparing a high-performance NdFeB magnet comprises the following steps: S1. Prepare a mixture: according to the mass fraction, 100 parts of NdFeB powder and 7 parts of semi-metallic ferrimagnetic powder are mixed evenly to obtain a mixture. The NdFeB powder is NdFeB with an average particle size of 6 μm. 14 Fe80B6 powder, the semi-metallic ferrimagnetic powder is a perovskite semi-metallic ferrimagnetic powder Sr2FeReO6 with an average particle size of 5 μm; S2, compression molding: the mixture is compressed and molded under a vacuum degree of 200 Pa and a pressure of 200 MPa to obtain a green compact; S3. Sintering: The green compact is sintered under argon protection. The sintering process is as follows: sintering at 1100° C. for 2 hours, then cooling to room temperature at a rate of 6° C. / min, then heating to 930° C. at a heating rate of 15° C. / min for a primary tempering treatment, holding the temperature for 1.5 hours, then cooling to 480° C. for a secondary tempering treatment, holding the temperature for 2 hours, to obtain a NdFeB magnet. S4. Pre-treating the NdFeB magnet: chamfering the NdFeB magnet with a chamfering machine for 3 hours, alkaline washing and degreasing in a 2.5% sodium hydroxide solution for 20 minutes, ultrasonic cleaning in deionized water for 4 minutes, then activating in a 3.5% nitric acid solution for 0.5 minutes, ultrasonic cleaning in deionized water for 3 minutes, and drying with cold air to obtain a pre-treated NdFeB magnet; S5. Dipping multifunctional protective liquid: placing the pretreated NdFeB magnet into the multifunctional protective liquid for immersion for 30 seconds to form a multifunctional protective film on the surface of the NdFeB magnet, then taking it out, pre-curing it at 120°C for 8 minutes for leveling, and then curing it at 200°C for 40 minutes to obtain a high-performance NdFeB magnet, wherein the multifunctional protective liquid comprises the following substances in parts by weight: 42 parts of acrylic resin, 10 parts of zinc powder, 7 parts of aluminum powder, 6 parts of nano-zirconium oxide, 14 parts of boron nitride, 16 parts of composite coupling agent, 18 parts of ethyl acetate, and 70 parts of deionized water. The composite coupling agent is composed of γ-glycidyloxypropyltriethoxysilane and isopropyl tris(dioctylpyrophosphate) titanate in a mass ratio of 3:5. The preparation method of the multifunctional protective liquid is as follows: according to the mass parts, the composite coupling agent, ethyl acetate and deionized water are added to a reactor, the temperature is raised to 45° C., and stirred for 4 hours. Then, zinc powder, aluminum powder, nano zirconium oxide and boron nitride are added to the reactor in sequence. After stirring for 0.5 hours, acrylic resin is added to the reactor, the temperature is raised to 55° C., and stirred for 1 hour. Then, the reactor is cooled to room temperature to obtain the multifunctional protective liquid.

[0028] Example 3 A method for preparing a high-performance NdFeB magnet comprises the following steps: S1. Prepare a mixture: according to the mass fraction, 100 parts of NdFeB powder and 6 parts of semi-metallic ferrimagnetic powder are mixed evenly to obtain a mixture. The NdFeB powder is NdFeB with an average particle size of 4 μm. 14 Fe80B6 powder, the semi-metallic ferrimagnetic powder is a perovskite semi-metallic ferrimagnetic powder Sr2FeReO6 with an average particle size of 2 μm; S2, compression molding: the mixture is compressed under a vacuum degree of 200 Pa and a pressure of 190 MPa to obtain a green compact; S3. Sintering: The green compact is sintered under argon protection. The sintering process is as follows: sintering at 1080°C for 2.3 hours, then cooling to room temperature at a rate of 5.6°C / min, then heating to 920°C at a heating rate of 14°C / min for a primary tempering treatment, holding the temperature for 1.5 hours, then cooling to 460°C for a secondary tempering treatment, holding the temperature for 2 hours, to obtain a NdFeB magnet. S4. Pre-treating the NdFeB magnets: chamfering the NdFeB magnets with a chamfering machine for 2.5 hours, degreasing them with an alkaline wash in a 2.5% sodium hydroxide solution for 13 minutes, ultrasonically cleaning them in deionized water for 3.5 minutes, activating them in a 3.5% nitric acid solution for 0.4 minutes, ultrasonically cleaning them in deionized water for 2.3 minutes, and drying them with cold air to obtain pre-treated NdFeB magnets. S5, dip coating multifunctional protective liquid: put the pretreated NdFeB magnet into the multifunctional protective liquid for immersion, the immersion time is 20s, and a multifunctional protective film is formed on the surface of the NdFeB magnet. Then take it out, pre-cured at 115 ° C for 7 minutes for leveling, and then cured at 190 ° C for 35 minutes to obtain a high-performance NdFeB magnet, wherein the multifunctional protective liquid includes the following materials in parts by weight: 39 parts of acrylic resin, 9 parts of zinc powder, 6 parts of aluminum powder, 5.6 parts of nano zirconium oxide, 13 parts of boron nitride, 15 parts of composite coupling agent, 17 parts of ethyl acetate, and 64 parts of deionized water. The composite coupling agent is composed of γ-glycidyloxypropyltriethoxysilane and isopropyl tri(dioctyl pyrophosphate) titanate in a mass ratio of 3:5. The multifunctional protective liquid is prepared by the following method: adding the composite coupling agent, ethyl acetate and deionized water into a reactor according to the mass ratio, heating to 45°C, stirring for 3.4 hours, then sequentially adding zinc powder, aluminum powder, nano zirconium oxide and boron nitride into the reactor, stirring for 0.5 hours, then adding acrylic resin into the reactor, heating to 55°C, stirring for 0.8 hours, and cooling to room temperature to obtain the multifunctional protective liquid.

[0029] Comparative Example 1 Same as Example 3, except that in step S1, 100 parts of NdFeB powder and 3 parts of The semi-metallic ferrimagnetic powder is mixed evenly.

[0030] Comparative Example 2 The same as Example 3, except that, in step S1, 100 parts of neodymium iron boron powder and 10 parts of semi-metallic ferrimagnetic powder are mixed uniformly according to mass parts.

[0031] Comparative Example 3 The method is the same as Example 3, except that in step S5, the composite coupling agent is γ-glycidyloxypropyltriethoxysilane.

[0032] Comparative Example 4 The method is the same as Example 3, except that in step S5, the composite coupling agent is isopropyl tris(dioctyl pyrophosphate) titanate.

[0033] Performance Testing The high performance NdFeB magnets prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were sampled and subjected to the following tests. Each group of test samples was tested 3 times and the results were averaged. The results are shown in Table 1.

[0034] Magnetic properties: Refer to the test standard: GB / T 3217-2013 (Test method for magnetic properties of permanent magnet materials) to test coercivity, remanence and maximum magnetic energy product; Corrosion resistance test: According to GB / T10124-1988 "Metal Materials Laboratory Uniform Corrosion Full Immersion Test Method", 5% HCl solution (acidic) and 3.5% NaCl solution (neutral) were selected as the corrosive media. The corrosion resistance of NdFeB magnets was tested through static immersion tests. The average corrosion rate of the magnets in different corrosive media was calculated according to the following formula; V = (m1-m2) / St, where V is the average corrosion rate of the magnet, mg·mm -2 ·h -1 m1 is the mass of the magnet before the experiment, mg; m2 is the mass of the magnet after cleaning the corrosion products and drying, mg; S is the surface area of the magnet, mm 2 ; t is the soaking time, h; The bending strength of the high-performance NdFeB magnets obtained in Examples 1 to 3 and Comparative Examples 1 to 4 was tested using a three-point bending test.

[0035] Table 1 Test results Analyzing the data in Table 1, we can see that: 1) The high performance NdFeB magnets prepared in Examples 1 to 3 have excellent corrosion resistance, comprehensive magnetic properties and mechanical properties.

[0036] 2) A comparative analysis of the performance of the high-performance NdFeB magnets obtained in combination with Example 3 and Comparative Examples 1-2 shows that when the mass ratio of the NdFeB powder to the semi-metallic ferrimagnetic powder is 100:6, the comprehensive performance of the high-performance NdFeB magnet obtained is the best. When the semi-metallic ferrimagnetic powder is too much or too little, the performance of the high-performance NdFeB magnet will decrease.

[0037] 3) A comparative analysis of the performance of the high-performance NdFeB magnets prepared in combination with Example 3 and Comparative Examples 3-4 shows that the composite coupling agent is composed of γ-glycidyloxypropyltriethoxysilane and isopropyl tris(dioctylpyrophosphate) titanate in a mass ratio of 3:5. The synergistic effect between them can improve the corrosion resistance and mechanical properties of the NdFeB magnet.

[0038] The above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit the present application. Although the above embodiments provide a detailed description of the present application, relevant technical personnel should understand that the specific implementation methods of the present application may still be modified or replaced by equivalents. Any modifications and equivalent replacements that do not depart from the spirit and scope of the present application should be included in the scope of protection of the present application.

Claims

1. A method for preparing high-performance NdFeB magnets, characterized in that: The following steps are involved: S1. Preparing a mixture: uniformly mixing NdFeB powder and semi-metallic ferrimagnetic powder according to parts by mass to obtain a mixture; S2. Compression molding: The mixed material is compressed under vacuum conditions to obtain a compact; S3. Sintering: Under argon protection, the compact is sintered and tempered twice to obtain NdFeB magnets; S4, pre-treating the NdFeB magnet to obtain a pre-treated NdFeB magnet; S5. Dipping in a multifunctional protective liquid: placing the pretreated NdFeB magnet into the multifunctional protective liquid for immersion for 10-30 seconds to form a multifunctional protective film on the surface of the NdFeB magnet, then taking it out, pre-curing it at 110-120°C for 5-8 minutes for leveling, and then curing it at 180-200°C for 30-40 minutes to obtain a high-performance NdFeB magnet, wherein the multifunctional protective liquid comprises the following substances in parts by weight: 35-42 parts of acrylic resin, 8-10 parts of zinc powder, 5-7 parts of aluminum powder, 5-6 parts of nano-zirconium oxide, 12-14 parts of boron nitride, 14-16 parts of a composite coupling agent, 15-18 parts of ethyl acetate, and 60-70 parts of deionized water.

2. The method for preparing a high-performance NdFeB magnet according to claim 1, wherein: In step S1, the mass ratio of the NdFeB powder to the semi-metallic ferrimagnetic powder is 100:5-7, and the NdFeB powder is Nd with an average particle size of 3-6 μm. 14 Fe80B6 powder, the semi-metallic ferrimagnetic powder is a perovskite semi-metallic ferrimagnetic powder Sr2FeReO6 with an average particle size of 1-5 μm.

3. The method for preparing a high performance NdFeB magnet according to claim 1, wherein: In step S2, the pressing pressure is 180-200 MPa.

4. The method for preparing a high performance NdFeB magnet according to claim 1, wherein: In step S3, the sintering process is: sintering at 1050-1100°C for 2-3 hours, and then cooling to room temperature at a rate of 5-6°C / min.

5. The method for preparing a high performance NdFeB magnet according to claim 1, wherein: In step S3, the secondary tempering process is as follows: heating the temperature to 900-930°C at a heating rate of 13-15°C / min for primary tempering, keeping the temperature for 1.5 hours, then cooling the temperature to 450-480°C for secondary tempering, keeping the temperature for 2 hours.

6. The method for preparing a high-performance NdFeB magnet according to claim 1, wherein: In step S4, the process conditions for pre-treating the NdFeB magnet are as follows: chamfering the NdFeB magnet with a chamfering machine for 2-3 hours, alkali washing and degreasing in a 2.5% mass concentration sodium hydroxide solution for 10-20 minutes, ultrasonic cleaning in deionized water for 3-4 minutes, then activating in a 3.5% mass concentration nitric acid solution for 0.3-0.5 minutes, and then ultrasonic cleaning in deionized water for 2-3 minutes. After drying with cold air, a pretreated NdFeB magnet is obtained.

7. The method for preparing a high performance NdFeB magnet according to claim 1, wherein: In step S5, the average particle size of the zinc powder is 0.5-1 μm, the average particle size of the aluminum powder is 0.5-2 μm, the average particle size of the nano zirconium oxide is 50-80 nm, and the average particle size of the boron nitride is 0.1-0.3 μm.

8. The method for preparing a high performance NdFeB magnet according to claim 1, wherein: In step S5, the composite coupling agent is composed of γ-glycidyloxypropyltriethoxysilane and isopropyl tris(dioctylpyrophosphate) titanate in a mass ratio of 3:

5.

9. The method for preparing a high-performance NdFeB magnet according to claim 1, wherein: In step S5, the multifunctional protective liquid is prepared by adding a composite coupling agent, ethyl acetate and deionized water to a reactor according to their mass fractions, heating to 45° C., stirring for 3-4 hours, then sequentially adding zinc powder, aluminum powder, nano zirconium oxide and boron nitride to the reactor, stirring for 0.5 hours, then adding acrylic resin to the reactor, heating to 55° C., stirring for 0.5-1 hours, and cooling to room temperature to obtain a multifunctional protective liquid.

10. A high performance neodymium iron boron magnet, characterized in that: The high-performance NdFeB magnet is prepared by the preparation method of the high-performance NdFeB magnet according to any one of claims 1 to 9.

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