High-strength neodymium iron boron magnetic material and preparation method thereof

Abstract

The invention discloses a high-strength neodymium iron boron magnetic material and a preparation method thereof, and relates to the technical field of neodymium iron boron magnetic materials. The method comprises the following steps: 1, mixing neodymium iron boron powder with a grain boundary additive; adding an ethanol solution, and performing ultrasonic dispersion to obtain a mixture; transferring into a double-layer mold with a through hole structure, setting a magnetic field, and carrying out wet pressing molding and cold isostatic pressing treatment to obtain a green body; sequentially sintering and annealing to obtain a neodymium-iron-boron magnet; 2, grinding the surface of the neodymium-iron-boron magnet; putting into a phosphoric acid solution for pretreatment; then spraying a magnetic conductive coating on the surface, and curing to form a coating; the high-strength neodymium iron boron magnetic material is obtained. In the invention, the prepared high-strength neodymium iron boron magnetic material has high strength and excellent corrosion resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of neodymium-iron-boron magnetic materials, and specifically to a high-strength neodymium-iron-boron magnetic material and a preparation method thereof. Background Art

[0002] Neodymium-iron-boron magnetic materials are materials with extremely high magnetic energy and coercivity, and are widely used in technical fields such as motors, power generation equipment, and electronic equipment. However, due to the relatively high brittleness of the grain boundary phase, its mechanical strength is insufficient (the flexural strength is usually only 260-320 MPa), and it is prone to fracture, which limits its application in high-stress environments such as high-speed motors.

[0003] In the prior art, grain boundary additives are usually introduced to uniformly regulate the grain boundary phase to improve mechanical properties. First, the improvement of the properties by grain boundary additives needs to be further improved. Second, traditional dry pressing and sintering are difficult to achieve uniform regulation of the grain boundary phase, and there are defects such as segregation or abnormal grain growth during sintering, which affect the mechanical strength. In addition, neodymium-iron-boron materials also have the defect of being easily oxidized and electrochemically corroded by the environment. Especially in humid or salt spray environments, an oxide layer is easily formed on the surface, resulting in attenuation of magnetic properties.

[0004] In summary, to solve the above problems, it is of great significance to prepare a high-strength neodymium-iron-boron magnetic material. Summary of the Invention

[0005] The purpose of the present invention is to provide a high-strength neodymium-iron-boron magnetic material and a preparation method thereof to solve the problems raised in the above background art.

[0006] To solve the above technical problems, the present invention provides the following technical solutions:

[0007] A preparation method of a high-strength neodymium-iron-boron magnetic material, comprising the following steps:

[0008] Step 1: Mix neodymium-iron-boron powder with a grain boundary additive; add an ethanol solution and disperse it ultrasonically to obtain a mixed material; transfer it to a double-layer mold with a through-hole structure, set a magnetic field, perform wet pressing and cold isostatic pressing treatment to obtain a green compact; sinter and anneal it in sequence to obtain a neodymium-iron-boron magnet;

[0009] Step 2: Grind the surface of the neodymium-iron-boron magnet; pretreat it in a phosphoric acid solution; then spray a magnetic conductive coating on its surface and cure it to form a coating; obtain a high-strength neodymium-iron-boron magnetic material.

[0010] Preferably, the addition amount of the grain boundary additive accounts for 1.2-1.5 wt% of the neodymium-iron-boron powder; the grain boundary additive includes neodymium-boron alloy powder and gallium powder with a mass ratio of 1.1-1.4:0.1; the boron content in the neodymium-boron alloy powder is 0.5-1 at%.

[0011] Preferably, the volume ratio of the neodymium iron boron powder to the ethanol solution is 1:2 to 3; the ethanol solution is a 0.2 to 0.6 wt% myristylamine-ethanol solution.

[0012] Preferably, in step 1, the magnetic field strength is 1.5 to 2 T, the pressure for wet pressing is 25 to 28 MPa; the pressure for cold isostatic pressing is 100 to 200 MPa;

[0013] The sintering process is as follows: in an argon atmosphere, heat up to 200 to 250 °C at a rate of 1 to 2 °C / min and hold for 5 to 10 minutes; then heat up to 1050 to 1100 °C at a rate of 10 to 15 °C / min and sinter for 2 to 3 hours; the annealing process is as follows: in an argon atmosphere, heat treat at 850 to 900 °C for 1 to 2 hours, and then heat treat at 500 to 600 °C for 1 to 2 hours.

[0014] Preferably, after grinding, the surface roughness of the neodymium iron boron magnet is 0.4 to 1.6 μm; the coating thickness is 10 to 30 μm.

[0015] Preferably, the process parameters for the pretreatment with the phosphoric acid solution are: pretreat at 70 to 75 °C for 1 to 2 hours;

[0016] The phosphoric acid solution comprises the following components: 0.5 to 1 wt% tetraethyl orthosilicate, 1 to 2 wt% phosphoric acid, 2.2 to 2.5 wt% isopropanol, 0.2 to 0.3 wt% deionized water, 0.5 to 1 wt% amino silane coupling agent, and the balance is ethanol.

[0017] Preferably, the magnetic conductive coating comprises the following components: by weight, 50 parts of silicon-modified epoxy resin, 8 to 12 parts of modified magnetic powder, 10 to 12 parts of curing agent, and 0.1 to 0.5 part of defoaming agent.

[0018] Preferably, the preparation method of the modified magnetic powder is: add nanocrystalline Ni-Zn ferrite powder into the phosphoric acid solution, stir at 78 to 80 °C for 3 to 4 hours, filter and dry to obtain the modified magnetic powder; the mass ratio of the nanocrystalline Ni-Zn ferrite powder to the phosphoric acid solution is 5 to 10:100.

[0019] Preferably, the curing agent comprises isophorone diamine and a magnetic promoter in a ratio of 8:2 to 4; the preparation method of the magnetic promoter is: mix trihexyl(tetradecyl)phosphonium chloride and ferric chloride hexahydrate in equimolar amounts and stir at room temperature for 24 hours to obtain the magnetic promoter.

[0020] A high-strength neodymium iron boron magnetic material prepared by the preparation method of a high-strength neodymium iron boron magnetic material.

[0021] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: In this application, specific grain boundary additives effectively strengthen and toughen the grain boundary phase; and assist the wet pressing forming process to improve uniformity and promote the improvement of magnetism and strength; in addition, a coating with both magnetic conductivity and corrosion resistance is further coated on its surface to ensure the comprehensive performance of the high-strength NdFeB magnetic material.

[0022] In the solution, the grain boundary additive is formed by compounding neodymium-boron alloy powder and gallium powder; among them, the neodymium-boron alloy powder, as the homologous phase of the NdFeB powder, can promote the continuity of the grain boundary phase during the sintering process, reduce the direct contact of the main phase grains, thereby inhibiting intergranular fracture. It should be noted that the boron content in the neodymium-boron alloy powder needs to be limited, and the grain boundary phase is better distributed within the limited range, and the phenomenon of irregular grains appears less. Among them, introducing gallium into the grain boundary can form a low-melting-point liquid phase Nd-Ga during the sintering process to fill the grain boundary voids and enhance the interface bonding. Further, it should be noted that the ratio of the two needs to be limited. Excessive introduction of gallium will lead to too wide grain boundaries, forming a non-magnetic weak phase, which will instead reduce the coercivity. Thus, the compounding of the two not only ensures the strengthening and toughening of the grain boundary, but also avoids the excessive aggregation of the low-melting-point phase. It makes the distribution of the grain boundary phase uniform, thereby significantly improving the bending strength of the magnet.

[0023] In the solution, through the process of wet pressing forming under a magnetic field, the uniform dispersion of the grain boundary additive is promoted, effectively ensuring that the grains are oriented along the easy magnetization axis, improving the remanence and coercivity, and enhancing the magnetic properties; realizing the synchronous uniform filling of the slurry and magnetic field orientation, avoiding the problem of uneven density in the traditional dry pressing method. Through cold isostatic pressing treatment, the internal pores are eliminated, the density is increased, and the mechanical properties are strengthened; through segmented temperature-controlled sintering and annealing, the excessive growth of grains is effectively inhibited, and the magnetic domain structure is optimized.

[0024] In the solution, further to improve the corrosion resistance of the NdFeB magnet, a magnetic conductive coating is coated on its surface; to effectively ensure the magnetism, first, the thickness of the coating is limited to effectively ensure good magnetism and reduce the influence on magnetism; second, phosphoric acid is pre-used for pretreatment to form a conversion film to improve the adhesion of the coating and reduce the influence on magnetism; third, based on silicon-modified epoxy resin, a higher content of modified magnetic powder is introduced to effectively improve the magnetic conductivity. At the same time, using nanocrystalline Ni-Zn ferrite powder as the magnetic conductor, after modification, it has good interfacial compatibility with silicon-modified epoxy resin, effectively ensuring uniform magnetism. And a magnetic promoter is introduced into the curing agent of the epoxy resin, which can not only promote the crosslinking of the epoxy resin, but also improve the magnetic conductivity of the coating, reduce the magnetic circuit loss, and synergistically improve the magnetic conductivity and corrosion resistance of the coating.

[0025] In summary, through the collaborative design of materials - processes - coatings, the present invention solves the problems of insufficient strength and toughness and easy corrosion of NdFeB magnets. On the basis of ensuring magnetism, the mechanical strength and corrosion resistance are effectively improved, and its applicability in complex environments is increased. Detailed implementation manners

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0027] It should be noted that the following parts are by weight, and there are no special restrictions on the purchasing manufacturers of all raw materials involved in the present invention. Exemplarily, in the following embodiments, the mass components of the neodymium - boron alloy powder are: 23.1% neodymium, 6.1% praseodymium, 1.18% boron, 0.24% cobalt, and the rest is iron; the gallium powder is high - purity gallium powder with a particle size of 20 - 100 nm; the boron content in the neodymium - boron alloy powder is 0.95 at%, and the particle size is 0.5 - 1 μm; the particle size of the nanocrystalline Ni - Zn ferrite powder is 10 - 100 nm; the CAS number of isophorone diamine is 2855 - 13 - 2; the model of the defoaming agent is Dow Corning DC - 1630.

[0028] In addition, without special instructions, in the following embodiments, the ethanol solution is a 0.5 wt% myristylamine - ethanol solution;

[0029] The preparation method of the modified magnetic powder material is as follows: The preparation method of the magnetic promoter is: mixing trihexyl(tetradecyl)phosphonium chloride and ferric chloride hexahydrate in an equimolar ratio, and stirring at room temperature for 24 hours to obtain the magnetic promoter;

[0030] The preparation method of the silicon - modified epoxy resin is: by weight, mixing 10 parts of epoxy resin NPEL - 128, 5 parts of bisphenol A, 0.25 parts of dibutyltin dilaurate, 4 parts of ethylene glycol monobutyl ether, and 2 parts of silicone resin SMH - 60, and stirring at 180°C for 3 hours; cooling to 140°C, adding 16 parts of ethylene glycol monobutyl ether and stirring for 4 hours, and then cooling to obtain the silicon - modified epoxy resin;

[0031] Example 1: A preparation method of a high - strength NdFeB magnetic material, comprising the following steps:

[0032] Pre - preparation: (1) Weighing the neodymium - boron alloy powder and gallium powder in a mass ratio of 1.3:0.1 and compounding them to obtain a grain - boundary additive;

[0033] (2) Based on 100 wt%, weigh the raw materials and prepare a phosphoric acid solution according to the ratio of 0.8 wt% tetraethyl orthosilicate, 2 wt% phosphoric acid, 2.5 wt% isopropyl alcohol, 0.25 wt% deionized water, 0.5 wt% amino silane coupling agent, and the rest is ethanol;

[0034] (3) Add the nanocrystalline Ni-Zn ferrite powder to the phosphoric acid solution. The mass ratio of the nanocrystalline Ni-Zn ferrite powder to the phosphoric acid solution is 10:100. Stir at 78 °C for 3 hours, filter and dry to obtain the modified magnetic powder;

[0035] (4) Weigh and mix according to the ratio of 50 parts of silicon-modified epoxy resin, 12 parts of modified magnetic powder, 11 parts of curing agent (isophorone diamine and magnetic promoter in a ratio of 8:3), and 0.2 part of defoaming agent by weight to obtain the magnetic conductive coating;

[0036] Step 1: Mix the NdFeB powder with the grain boundary additive. The addition amount of the grain boundary additive accounts for 1.4 wt% of the NdFeB powder; add an ethanol solution. The volume ratio of the NdFeB powder to the ethanol solution is 1:2. Disperse ultrasonically to obtain a mixed material; transfer it to a double-layer mold with a through-hole structure, set the magnetic field strength to 1.5 T, wet press at 28 MPa, and cold isostatic press at 150 MPa to obtain a green compact; heat it in an argon atmosphere at a rate of 2 °C / min to 200 °C and hold for 5 minutes; then heat it at a rate of 15 °C / min to 1090 °C and sinter for 2 hours; heat-treat in an argon atmosphere at 900 °C for 2 hours, and then heat-treat at 500 °C for 2 hours; obtain the NdFeB magnet;

[0037] Step 2: Grind the surface of the NdFeB magnet with a surface roughness of 0.8 μm; place it in the phosphoric acid solution and pretreat at 70 °C for 2 hours; then spray the magnetic conductive coating on its surface and cure to form a coating with a thickness of 15 μm; obtain the high-strength NdFeB magnetic material.

[0038] Example 2: A preparation method of a high-strength NdFeB magnetic material, comprising the following steps:

[0039] Preliminary preparation: (1) Weigh and mix Nd-B alloy powder and gallium powder with a mass ratio of 1.1:0.1 to obtain the grain boundary additive;

[0040] (2) Based on 100 wt%, weigh the raw materials and prepare a phosphoric acid solution according to the ratio of 0.8 wt% tetraethyl orthosilicate, 2 wt% phosphoric acid, 2.5 wt% isopropyl alcohol, 0.25 wt% deionized water, 0.5 wt% amino silane coupling agent, and the rest is ethanol;

[0041] (3) Add nanocrystalline Ni-Zn ferrite powder into phosphoric acid solution. The mass ratio of the nanocrystalline Ni-Zn ferrite powder to the phosphoric acid solution is 10:100. Stir and process at 78 °C for 3 hours, filter and dry to obtain modified magnetic powder material;

[0042] (4) Weigh and mix according to the proportion of 50 parts by weight of silicon-modified epoxy resin, 8 parts of modified magnetic powder material, 12 parts of curing agent (isophorone diamine and magnetic promoter in a ratio of 8:4), and 0.2 part of defoaming agent to obtain magnetic conductive coating;

[0043] Step 1: Mix neodymium iron boron powder with grain boundary additive. The addition amount of the grain boundary additive accounts for 1.2 wt% of the neodymium iron boron powder; Add ethanol solution. The volume ratio of the neodymium iron boron powder to the ethanol solution is 1:2. Disperse ultrasonically to obtain a mixed material; Transfer it to a double-layer mold with a through-hole structure, set the magnetic field strength to 1.5 T, perform wet pressing at 28 MPa, and perform cold isostatic pressing at 150 MPa to obtain a green body; Heat it in an argon atmosphere at a rate of 2 °C / min to 200 °C and hold for 5 minutes; Then heat it at a rate of 15 °C / min to 1090 °C and sinter for 2 hours; Heat-treat in an argon atmosphere at 900 °C for 2 hours, and then heat-treat at 500 °C for 2 hours; Obtain a neodymium iron boron magnet;

[0044] Step 2: Grind the surface of the neodymium iron boron magnet with a surface roughness of 0.8 μm; Place it in phosphoric acid solution and pre-treat at 70 °C for 2 hours; Then spray magnetic conductive coating on its surface and cure to form a coating with a thickness of 15 μm; Obtain a high-strength neodymium iron boron magnetic material.

[0045] Example 3: A preparation method of a high-strength neodymium iron boron magnetic material, comprising the following steps:

[0046] Pre-preparation: (1) Weigh and mix neodymium boron alloy powder and gallium powder with a mass ratio of 1.4:0.1 to obtain a grain boundary additive;

[0047] (2) Based on 100 wt%, weigh raw materials and prepare phosphoric acid solution according to the proportion of 0.8 wt% tetraethyl orthosilicate, 2 wt% phosphoric acid, 2.5 wt% isopropyl alcohol, 0.25 wt% deionized water, 0.5 wt% amino silane coupling agent, and the rest is ethanol;

[0048] (3) Add nanocrystalline Ni-Zn ferrite powder into phosphoric acid solution. The mass ratio of the nanocrystalline Ni-Zn ferrite powder to the phosphoric acid solution is 10:100. Stir and process at 78 °C for 3 hours, filter and dry to obtain modified magnetic powder material;

[0049] (4) Weigh and mix according to the ratio of 50 parts of silicon-modified epoxy resin, 12 parts of modified magnetic powder, 10 parts of curing agent (isophorone diamine and magnetic promoter in a ratio of 8:2), and 0.2 part of defoaming agent by weight to obtain a magnetic conductive coating;

[0050] Step 1: Mix neodymium iron boron powder with a grain boundary additive, and the addition amount of the grain boundary additive accounts for 1.5 wt% of the neodymium iron boron powder; add an ethanol solution, and the volume ratio of the neodymium iron boron powder to the ethanol solution is 1:2, and disperse ultrasonically to obtain a mixture; transfer it to a double-layer mold with a through-hole structure, set the magnetic field strength to 2 T, wet press at 25 MPa, and perform cold isostatic pressing at 150 MPa to obtain a green compact; heat it in an argon atmosphere at a rate of 2 °C / min to 200 °C and hold for 5 minutes; then heat it at a rate of 15 °C / min to 1090 °C and sinter for 2 hours; perform heat treatment at 900 °C for 2 hours in an argon atmosphere, and then perform heat treatment at 500 °C for 2 hours; obtain a neodymium iron boron magnet;

[0051] Step 2: Grind the surface of the neodymium iron boron magnet, and the surface roughness is 0.8 μm; place it in a phosphoric acid solution and pretreat it at 70 °C for 2 hours; then spray the magnetic conductive coating on its surface and cure to form a coating with a thickness of 15 μm; obtain a high-strength neodymium iron boron magnetic material.

[0052] Comparative Example 1: Introduce neodymium boron alloy powder alone as a grain boundary additive, and the rest is the same as in Example 1; it includes the following steps:

[0053] Pre-preparation: (1) Weigh neodymium boron alloy powder as a grain boundary additive;

[0054] (2) Calculate by 100 wt%, weigh raw materials and prepare a phosphoric acid solution according to the ratio of 0.8 wt% tetraethyl orthosilicate, 2 wt% phosphoric acid, 2.5 wt% isopropanol, 0.25 wt% deionized water, 0.5 wt% amino silane coupling agent, and the rest is ethanol;

[0055] (3) Add nanocrystalline Ni-Zn ferrite powder to the phosphoric acid solution, and the mass ratio of the nanocrystalline Ni-Zn ferrite powder to the phosphoric acid solution is 10:100, stir at 78 °C for 3 hours, filter and dry to obtain modified magnetic powder;

[0056] (4) Weigh and mix according to the ratio of 50 parts of silicon-modified epoxy resin, 12 parts of modified magnetic powder, 11 parts of curing agent (isophorone diamine and magnetic promoter in a ratio of 8:3), and 0.2 part of defoaming agent by weight to obtain a magnetic conductive coating;

[0057] Step 1: Mix neodymium iron boron powder with grain boundary additives. The addition amount of the grain boundary additives accounts for 1.4 wt% of the neodymium iron boron powder. Add an ethanol solution. The volume ratio of the neodymium iron boron powder to the ethanol solution is 1:2. Disperse ultrasonically to obtain a mixed material. Transfer it to a double-layer mold with a through-hole structure. Set the magnetic field strength to 1.5 T and perform wet pressing at 28 MPa, and then perform cold isostatic pressing at 150 MPa to obtain a green compact. Heat it in an argon atmosphere at a rate of 2 °C / min to 200 °C and hold for 5 minutes. Then heat it at a rate of 15 °C / min to 1090 °C and sinter for 2 hours. Perform heat treatment at 900 °C for 2 hours in an argon atmosphere, and then perform heat treatment at 500 °C for 2 hours to obtain a neodymium iron boron magnet.

[0058] Step 2: Grind the surface of the neodymium iron boron magnet to a surface roughness of 0.8 μm. Place it in a phosphoric acid solution and pretreat it at 70 °C for 2 hours. Then spray a magnetic conductive coating on its surface and cure to form a coating with a thickness of 15 μm to obtain a high-strength neodymium iron boron magnetic material.

[0059] Comparative Example 2: Increase the content of gallium powder in the grain boundary additives, and the rest is the same as in Example 1. It includes the following steps:

[0060] Preliminary preparation: (1) Weigh a neodymium boron alloy powder and gallium powder with a mass ratio of 1:0.4 and compound them to obtain grain boundary additives.

[0061] (2) Based on 100 wt%, weigh raw materials and prepare a phosphoric acid solution according to the ratio of 0.8 wt% tetraethyl orthosilicate, 2 wt% phosphoric acid, 2.5 wt% isopropyl alcohol, 0.25 wt% deionized water, 0.5 wt% amino silane coupling agent, and the rest is ethanol.

[0062] (3) Add nanocrystalline Ni-Zn ferrite powder to the phosphoric acid solution. The mass ratio of the nanocrystalline Ni-Zn ferrite powder to the phosphoric acid solution is 10:100. Stir and process at 78 °C for 3 hours, filter and dry to obtain modified magnetic powder.

[0063] (4) Weigh and mix according to the ratio of 50 parts of silicon-modified epoxy resin, 12 parts of modified magnetic powder, 11 parts of curing agent (isophorone diamine and magnetic promoter in a ratio of 8:3), and 0.2 part of defoaming agent by weight to obtain a magnetic conductive coating.

[0064] Step 1: Mix neodymium iron boron powder with grain boundary additives. The addition amount of the grain boundary additives accounts for 1.4 wt% of the neodymium iron boron powder. Add an ethanol solution. The volume ratio of the neodymium iron boron powder to the ethanol solution is 1:2. Disperse it by ultrasonic wave to obtain a mixed material. Transfer it to a double-layer mold with a through-hole structure. Set the magnetic field strength to 1.5 T, perform wet pressing at 28 MPa, and perform cold isostatic pressing at 150 MPa to obtain a green compact. Heat it in an argon atmosphere at a rate of 2 °C / min to 200 °C and hold for 5 minutes. Then heat it at a rate of 15 °C / min to 1090 °C and sinter for 2 hours. Heat-treat it in an argon atmosphere at 900 °C for 2 hours, and then heat-treat it at 500 °C for 2 hours to obtain a neodymium iron boron magnet.

[0065] Step 2: Grind the surface of the neodymium iron boron magnet, and the surface roughness is 0.8 μm. Place it in a phosphoric acid solution and pre-treat it at 70 °C for 2 hours. Then spray a magnetic conductive coating on its surface and cure it to form a coating with a thickness of 15 μm to obtain a high-strength neodymium iron boron magnetic material.

[0066] Comparative Example 3: Use dry pressing, and the rest is the same as in Example 1. It includes the following steps:

[0067] Pre-preparation: (1) Weigh neodymium boron alloy powder and gallium powder with a mass ratio of 1.3:0.1 and compound them to obtain grain boundary additives.

[0068] (2) Based on 100 wt%, weigh raw materials and prepare a phosphoric acid solution according to the ratio of 0.8 wt% tetraethyl orthosilicate, 2 wt% phosphoric acid, 2.5 wt% isopropyl alcohol, 0.25 wt% deionized water, 0.5 wt% amino silane coupling agent, and the rest is ethanol.

[0069] (3) Add nanocrystalline Ni-Zn ferrite powder to the phosphoric acid solution. The mass ratio of the nanocrystalline Ni-Zn ferrite powder to the phosphoric acid solution is 10:100. Stir and process it at 78 °C for 3 hours, filter and dry it to obtain modified magnetic powder.

[0070] (4) Weigh and mix according to the ratio of 50 parts of silicon-modified epoxy resin, 12 parts of modified magnetic powder, 11 parts of curing agent (isophorone diamine and magnetic promoter in a ratio of 8:3), and 0.2 part of defoaming agent to obtain a magnetic conductive coating.

[0071] Step 1: Mix the NdFeB powder with the grain boundary additive. The addition amount of the grain boundary additive accounts for 1.4 wt% of the NdFeB powder to obtain a mixed material. Transfer it to a mold, set the magnetic field strength to 1.5 T, and dry press it at 20 MPa to form a green compact. Perform cold isostatic pressing at 150 MPa to obtain a green body. Heat it in an argon atmosphere at a rate of 2 °C / min to 200 °C and hold for 5 minutes. Then heat it at a rate of 15 °C / min to 1090 °C and sinter for 2 hours. Heat-treat it in an argon atmosphere at 900 °C for 2 hours and then at 500 °C for 2 hours to obtain the NdFeB magnet.

[0072] Step 2: Grind the surface of the NdFeB magnet to a surface roughness of 0.8 μm. Place it in a phosphoric acid solution and pretreat it at 70 °C for 2 hours. Then spray a magnetic conductive coating on its surface and cure it to form a coating with a thickness of 15 μm to obtain a high-strength NdFeB magnetic material.

[0073] Comparative Example 4: In the coating, directly introduce nanocrystalline Ni-Zn ferrite powder, and the rest is the same as in Example 1. It includes the following steps:

[0074] Pre-preparation: (1) Weigh and mix neodymium-boron alloy powder and gallium powder with a mass ratio of 1.3:0.1 to obtain a grain boundary additive.

[0075] (2) Based on 100 wt%, weigh the raw materials and prepare a phosphoric acid solution according to the ratio of 0.8 wt% tetraethyl orthosilicate, 2 wt% phosphoric acid, 2.5 wt% isopropyl alcohol, 0.25 wt% deionized water, 0.5 wt% amino silane coupling agent, and the rest is ethanol.

[0076] (3) Weigh and mix according to the ratio of 50 parts of silicon-modified epoxy resin, 12 parts of nanocrystalline Ni-Zn ferrite powder, 11 parts of curing agent (isophorone diamine and magnetic promoter in a ratio of 8:3), and 0.2 part of defoaming agent to obtain a magnetic conductive coating.

[0077] Step 1: Mix the NdFeB powder with the grain boundary additive. The addition amount of the grain boundary additive accounts for 1.4 wt% of the NdFeB powder. Add an ethanol solution with a volume ratio of NdFeB powder to ethanol solution of 1:2 and disperse it ultrasonically to obtain a mixed material. Transfer it to a double-layer mold with a through-hole structure, set the magnetic field strength to 1.5 T, and wet press it at 28 MPa. Perform cold isostatic pressing at 150 MPa to obtain a green body. Heat it in an argon atmosphere at a rate of 2 °C / min to 200 °C and hold for 5 minutes. Then heat it at a rate of 15 °C / min to 1090 °C and sinter for 2 hours. Heat-treat it in an argon atmosphere at 900 °C for 2 hours and then at 500 °C for 2 hours to obtain the NdFeB magnet.

[0078] Step 2: Grind the surface of the NdFeB magnet to a surface roughness of 0.8 μm; place it in a phosphoric acid solution and pretreat it at 70 °C for 2 hours; then spray a magnetic conductive coating on its surface and cure it to form a coating with a thickness of 15 μm; obtain a high-strength NdFeB magnetic material.

[0079] Comparative Example 5: In the coating, isophorone diamine is used alone as the curing agent, and the rest is the same as in Example 1; it includes the following steps:

[0080] Pre-preparation: (1) Weigh a grain boundary additive by compounding neodymium-boron alloy powder and gallium powder with a mass ratio of 1.3:0.1;

[0081] (2) Based on 100 wt%, weigh the raw materials and prepare a phosphoric acid solution according to the ratio of 0.8 wt% tetraethyl orthosilicate, 2 wt% phosphoric acid, 2.5 wt% isopropyl alcohol, 0.25 wt% deionized water, 0.5 wt% amino silane coupling agent, and the rest is ethanol;

[0082] (3) Add nano-crystalline Ni-Zn ferrite powder to the phosphoric acid solution, and the mass ratio of nano-crystalline Ni-Zn ferrite powder to the phosphoric acid solution is 10:100. Stir and process at 78 °C for 3 hours, filter and dry to obtain a modified magnetic powder material;

[0083] (4) Weigh and mix according to the ratio of 50 parts of silicon-modified epoxy resin, 12 parts of modified magnetic powder material, 11 parts of isophorone diamine, and 0.2 part of defoaming agent by weight to obtain a magnetic conductive coating;

[0084] Step 1: Mix the NdFeB powder with the grain boundary additive, and the addition amount of the grain boundary additive accounts for 1.4 wt% of the NdFeB powder; add an ethanol solution, and the volume ratio of the NdFeB powder to the ethanol solution is 1:2. Disperse ultrasonically to obtain a mixed material; transfer it to a double-layer mold with a through-hole structure, set the magnetic field strength to 1.5 T, wet press and form at 28 MPa, and perform cold isostatic pressing at 150 MPa to obtain a green compact; heat it in an argon atmosphere at a rate of 2 °C / min to 200 °C and hold for 5 minutes; then heat it at a rate of 15 °C / min to 1090 °C and sinter for 2 hours; perform heat treatment at 900 °C for 2 hours in an argon atmosphere, and then perform heat treatment at 500 °C for 2 hours; obtain an NdFeB magnet;

[0085] Step 2: Grind the surface of the NdFeB magnet to a surface roughness of 0.8 μm; place it in a phosphoric acid solution and pretreat it at 70 °C for 2 hours; then spray a magnetic conductive coating on its surface and cure it to form a coating with a thickness of 15 μm; obtain a high-strength NdFeB magnetic material.

[0086] Performance Test 1: The high-strength Nd-Fe-B magnetic materials prepared in the examples and comparative examples were subjected to relevant performance tests. Among them, the flexural strength test was carried out with reference to GB / T31967.2 at a rate of 0.5 mm / min; the magnetic property A was measured using a gaussmeter, and then it was immersed in a 3.5 wt% aqueous sodium chloride solution for 72 hours. After cleaning and drying, the magnetic property B was further tested. The obtained data are shown in the following table:

[0087] Conclusion: It can be seen from the data in the above table that: in this application, the flexural strength is effectively improved by a specific proportion of grain boundary additives, and the corrosion resistance is further improved by the coating. Comparing the data of Example 1 with Comparative Examples 1-5, in Comparative Example 1, only a single Nd-B alloy powder was used, resulting in insufficient grain boundary liquid phase and a decrease in properties such as strength; in Comparative Example 2, the increase in the content of gallium powder led to non-magnetic weaknesses and a decrease in related properties; in Comparative Example 3, dry pressing was used, resulting in poor compactness and grain boundary segregation, and a decrease in properties; in Comparative Example 4, the nanocrystalline Ni-Zn ferrite powder was not modified, resulting in poor compatibility and a decrease in related properties; in Comparative Example 5, the curing agent had no magnetic promotion effect, leading to a decrease in magnetic conductivity and adhesion, and a decrease in related properties.

[0088] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a high-strength neodymium iron boron magnetic material, characterized in that: It includes the following steps: Step 1: Mix neodymium iron boron powder with grain boundary additives; Add an ethanol solution, disperse ultrasonically to obtain a mixed material; transfer it to a double-layer mold with a through-hole structure, set a magnetic field, perform wet pressing to form a green body, and perform cold isostatic pressing treatment to obtain a green compact; sinter and anneal it successively to obtain a neodymium iron boron magnet; Step 2: Grind the surface of the neodymium iron boron magnet; pretreat it in a phosphoric acid solution; then spray a magnetic conductive coating on its surface and cure to form a coating; Obtain a high-strength neodymium iron boron magnetic material.

2. The preparation method of a high-strength neodymium iron boron magnetic material according to claim 1, characterized in that: The addition amount of the grain boundary additive accounts for 1.2 - 1.5 wt% of the neodymium iron boron powder; the grain boundary additive includes neodymium boron alloy powder and gallium powder with a mass ratio of 1.1 - 1.4:0.1; the boron content in the neodymium boron alloy powder is 0.5 - 1 at%.

3. The preparation method of a high-strength neodymium iron boron magnetic material according to claim 1, characterized in that: The volume ratio of the neodymium iron boron powder to the ethanol solution is 1:2 - 3; the ethanol solution is a 0.2 - 0.6 wt% myristylamine-ethanol solution.

4. The preparation method of a high-strength neodymium-iron-boron magnetic material according to claim 1, characterized in that: In Step 1, the magnetic field strength is 1.5 - 2 T, the pressure for wet pressing is 25 - 28 MPa; the pressure for cold isostatic pressing treatment is 100 - 200 MPa; The sintering process is as follows: under an argon atmosphere, heat up at a rate of 1 - 2 °C / min to 200 - 250 °C and hold for 5 - 10 minutes; then heat up at a rate of 10 - 15 °C / min to 1050 - 1100 °C and sinter for 2 - 3 hours; the annealing process is as follows: under an argon atmosphere, perform heat treatment at 850 - 900 °C for 1 - 2 hours, and then perform heat treatment at 500 - 600 °C for 1 - 2 hours.

5. The preparation method of a high-strength neodymium iron boron magnetic material according to claim 1, characterized in that: In Step 2, after grinding, the surface roughness of the neodymium iron boron magnet is 0.4 - 1.6 μm; the coating thickness is 10 - 30 μm.

6. The preparation method of a high-strength neodymium iron boron magnetic material according to claim 1, characterized in that: The process parameters for the phosphoric acid solution pretreatment are: pretreat at 70 - 75 °C for 1 - 2 hours; The phosphoric acid solution includes the following components: 0.5 - 1 wt% tetraethyl orthosilicate, 1 - 2 wt% phosphoric acid, 2.2 - 2.5 wt% isopropyl alcohol, 0.2 - 0.3 wt% deionized water, 0.5 - 1 wt% amino silane coupling agent, and the rest is ethanol.

7. The preparation method of a high-strength neodymium iron boron magnetic material according to claim 1, characterized in that: The magnetic conductive coating includes the following components: by weight, 50 parts of silicon-modified epoxy resin, 8 - 12 parts of modified magnetic powder, 10 - 12 parts of curing agent, and 0.1 - 0.5 part of defoaming agent.

8. The preparation method of a high-strength neodymium-iron-boron magnetic material according to claim 7, characterized in that: The preparation method of the modified magnetic powder is: add nanocrystalline Ni-Zn ferrite powder to a phosphoric acid solution, stir at 78 - 80 °C for 3 - 4 hours, filter and dry to obtain the modified magnetic powder; the mass ratio of the nanocrystalline Ni-Zn ferrite powder to the phosphoric acid solution is 5 - 10:

100.

9. The preparation method of a high-strength neodymium-iron-boron magnetic material according to claim 7, wherein: The curing agent includes isophorone diamine and a magnetic promoter with a ratio of 8:2 - 4; the preparation method of the magnetic promoter is: mix trihexyl(tetradecyl)phosphonium chloride and ferric chloride hexahydrate in equimolar amounts and stir at room temperature for 24 hours to obtain the magnetic promoter.

10. A high-strength neodymium iron boron magnetic material prepared by the preparation method of a high-strength neodymium iron boron magnetic material according to any one of claims 1 - 9.

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