A high-strength NdFeB magnetic material and its preparation method

Abstract

The present invention discloses a high-strength NdFeB magnetic material and a preparation method thereof, and relates to the technical field of NdFeB magnetic materials. Step 1: Mix NdFeB powder with a grain boundary additive; add an ethanol solution, and disperse it ultrasonically to obtain a mixture; transfer it to a double-layer mold with a through-hole structure, set a magnetic field, wet-press mold it, and cold isostatically press it to obtain a green body; sinter and anneal it in sequence to obtain a NdFeB magnet; Step 2: Grind the surface of the NdFeB magnet; place it in a phosphoric acid solution for pretreatment; then spray a magnetic conductive coating on its surface, and solidify it to form a coating; obtain a high-strength NdFeB magnetic material. In the present application, the prepared high-strength NdFeB magnetic material has high strength and excellent corrosion resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of NdFeB magnetic materials, in particular to a high-strength NdFeB magnetic material and a preparation method thereof. Background Art

[0002] Neodymium iron boron (NdFeB) magnetic material possesses extremely high magnetic energy and coercivity and is widely used in technical fields such as motors, power generation equipment, and electronic equipment. However, due to its high brittleness at the grain boundaries, it suffers from insufficient mechanical strength (typically a bending strength of only 260-320 MPa), making it prone to fracture. This limits its application in high-stress environments such as high-speed motors.

[0003] Prior art typically introduces grain boundary additives to uniformly control the grain boundary phase to improve mechanical properties. However, the performance enhancements achieved with these additives require further refinement. Furthermore, the traditional dry-pressing followed by sintering makes it difficult to achieve uniform control of the grain boundary phase, leading to segregation or abnormal grain growth during sintering, which impacts mechanical strength. Furthermore, NdFeB materials are susceptible to environmental oxidation and electrochemical corrosion, particularly in hot, humid, or salty environments, where an oxide layer forms on the surface, leading to magnetic degradation.

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

[0005] The object of the present invention is to provide a high-strength NdFeB magnetic material and a preparation method thereof, so as to solve the problems raised in the above background technology.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] A method for preparing a high-strength NdFeB magnetic material comprises the following steps:

[0008] Step 1: Mix NdFeB powder with grain boundary additives; add ethanol solution and ultrasonically disperse to obtain a mixture; transfer the mixture to a double-layer mold with a through-hole structure, set a magnetic field, wet press, and cold isostatic press to obtain a green body; sinter and anneal it in sequence to obtain a NdFeB magnet;

[0009] Step 2: Grinding the surface of the NdFeB magnet; placing it in a phosphoric acid solution for pretreatment; then spraying a magnetic conductive coating on the surface and curing it to form a coating; thus obtaining a high-strength NdFeB magnetic material.

[0010] More optimally, the amount of the grain boundary additive added accounts for 1.2-1.5wt% of the NdFeB powder; the grain boundary additive includes NdBo alloy powder and gallium powder in a mass ratio of 1.1-1.4:0.1; the boron content in the NdBo alloy powder is 0.5-1at%.

[0011] More optimally, the volume ratio of the NdFeB powder to the ethanol solution is 1:2-3; and the ethanol solution is a 0.2-0.6 wt % myristicamine-ethanol solution.

[0012] More optimally, in step 1, the magnetic field strength is 1.5-2 T, the pressure of wet pressing is 25-28 MPa, and the pressure of cold isostatic pressing is 100-200 MPa.

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

[0014] More optimally, after grinding, the surface roughness of the NdFeB magnet is 0.4~1.6μm; the coating thickness is 10~30μm.

[0015] More optimally, the process parameters of the phosphoric acid solution pretreatment are: pretreatment at 70-75°C for 1-2 hours;

[0016] The phosphoric acid solution includes the following components: 0.5-1 wt% of tetraethyl silicate, 1-2 wt% of phosphoric acid, 2.2-2.5 wt% of isopropyl alcohol, 0.2-0.3 wt% of deionized water, 0.5-1 wt% of an aminosilane coupling agent, and the remainder is ethanol.

[0017] More optimally, 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 parts of defoaming agent.

[0018] More optimally, the preparation method of the modified magnetic powder material is: adding nanocrystalline Ni-Zn ferrite powder to a phosphoric acid solution, stirring at 78-80°C for 3-4 hours, filtering and drying to obtain the modified magnetic powder material; the mass ratio of nanocrystalline Ni-Zn ferrite powder to phosphoric acid solution is 5-10:100.

[0019] More optimally, the curing agent includes isophorone diamine and a magnetic accelerator in a ratio of 8:2~4; the preparation method of the magnetic accelerator is: trihexyl (tetradecyl) phosphine chloride and ferric chloride hexahydrate are mixed in equal moles, and stirred at room temperature for 24 hours to obtain the magnetic accelerator.

[0020] A method for preparing a high-strength NdFeB magnetic material provides a high-strength NdFeB magnetic material.

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

[0022] In this scheme, the grain boundary additive is formed by combining neodymium-boron alloy powder and gallium powder. The neodymium-boron alloy powder, as a cognate phase of the neodymium-iron-boron powder, promotes grain boundary phase continuity during sintering, reduces direct contact between main phase grains, and thus inhibits intergranular fracture. It should be noted that the boron content in the neodymium-boron alloy powder needs to be limited. Within this range, the grain boundary phase is well distributed, and irregular grains are minimized. Gallium is introduced into the grain boundaries during sintering to form a low-melting-point liquid phase, Nd-Ga, which fills the grain boundary voids and strengthens interfacial bonding. Furthermore, it should be noted that the ratio of the two must be limited. Excessive gallium addition can lead to excessively wide grain boundaries, forming a weak, nonmagnetic phase that in turn reduces coercivity. This combination of the two ensures grain boundary toughening while preventing excessive aggregation of the low-melting-point phase. This uniform distribution of the grain boundary phase significantly improves the flexural strength of the magnet.

[0023] The proposed solution utilizes wet pressing under a magnetic field to promote uniform dispersion of grain boundary additives, effectively ensuring grain orientation along the easy magnetization axis, increasing remanence and coercivity, and enhancing magnetic properties. Uniform slurry filling and magnetic field orientation are synchronized to avoid the density unevenness associated with traditional dry pressing. Cold pressing eliminates internal porosity, improves density, and enhances mechanical properties. Staged temperature-controlled sintering and annealing effectively inhibit excessive grain growth and optimize the magnetic domain structure.

[0024] In the proposal, in order to further improve the corrosion resistance of NdFeB magnets, a magnetic coating is applied to their surface. To effectively ensure magnetism, the coating thickness is limited to effectively ensure good magnetism and reduce the impact on magnetism. Secondly, phosphoric acid is pre-treated to form a conversion film, which improves the adhesion of the coating and reduces the impact on magnetism. Thirdly, based on silicon-modified epoxy resin, a high content of modified magnetic powder is introduced to effectively improve magnetic permeability. At the same time, nanocrystalline Ni-Zn ferrite powder is used as a magnetic conductor. After modification, it has good interfacial compatibility with silicon-modified epoxy resin, effectively ensuring uniform magnetism. A magnetic promoter is introduced into the epoxy resin curing agent, which not only promotes the cross-linking of the epoxy resin, but also improves the magnetic permeability of the coating, reduces magnetic circuit loss, and synergistically improves the magnetic permeability and corrosion resistance of the coating.

[0025] In summary, the present invention solves the problems of insufficient toughness and easy corrosion of NdFeB magnets through material-process-coating coordinated design. On the basis of ensuring magnetic properties, it effectively improves the mechanical strength and corrosion resistance, and increases its applicability in complex environments. DETAILED DESCRIPTION

[0026] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0027] It should be noted that the following parts are calculated by weight, and the purchase manufacturers of all raw materials involved in the present invention are not subject to any special restrictions. Examples include: In the following embodiments, the mass composition of the neodymium boron alloy powder is: 23.1% neodymium, 6.1% praseodymium, 1.18% boron, 0.24% cobalt, and the remainder is iron; the gallium powder is high-purity gallium powder with a particle size of 20 to 100 nm; the boron content in the neodymium boron alloy powder is 0.95 at%, and the particle size is 0.5 to 1 μm; the particle size of the nanocrystalline Ni-Zn ferrite powder is 10 to 100 nm; the CAS number of isophorone diamine is 2855-13-2; and the model of the defoaming agent is Dow Corning DC-1630.

[0028] In addition, unless otherwise specified, in the following examples, 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 as follows: trihexyl (tetradecyl) phosphine chloride and ferric chloride hexahydrate are mixed in equal moles, and stirred at room temperature for 24 hours to obtain the magnetic promoter;

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

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

[0032] Preliminary preparation: (1) Weigh neodymium boron alloy powder and gallium powder in a mass ratio of 1.3:0.1 to prepare a grain boundary additive;

[0033] (2) Based on 100 wt%, the raw materials were weighed and prepared according to the ratio of 0.8 wt% tetraethyl silicate, 2 wt% phosphoric acid, 2.5 wt% isopropyl alcohol, 0.25 wt% deionized water, 0.5 wt% aminosilane coupling agent, and the remainder ethanol to obtain a phosphoric acid solution;

[0034] (3) Adding nanocrystalline Ni-Zn ferrite powder to phosphoric acid solution at a mass ratio of 10:100, stirring at 78°C for 3 hours, filtering, and drying to obtain modified magnetic powder;

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

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

[0037] 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 magnetic conductive paint on its surface and solidify it to form a coating with a thickness of 15 μm; and obtain a high-strength NdFeB magnetic material.

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

[0039] Preliminary preparation: (1) Weigh neodymium boron alloy powder and gallium powder in a mass ratio of 1.1:0.1 to prepare a grain boundary additive;

[0040] (2) Based on 100 wt%, the raw materials were weighed and prepared according to the ratio of 0.8 wt% tetraethyl silicate, 2 wt% phosphoric acid, 2.5 wt% isopropyl alcohol, 0.25 wt% deionized water, 0.5 wt% aminosilane coupling agent, and the remainder ethanol to obtain a phosphoric acid solution;

[0041] (3) Adding nanocrystalline Ni-Zn ferrite powder to phosphoric acid solution at a mass ratio of 10:100, stirring at 78°C for 3 hours, filtering, and drying to obtain modified magnetic powder;

[0042] (4) Weigh and mix 50 parts of silicon-modified epoxy resin, 8 parts of modified magnetic powder, 12 parts of curing agent (8:4 isophorone diamine and magnetic accelerator), and 0.2 parts of defoaming agent in a ratio of 1:1 to obtain a magnetic conductive coating;

[0043] Step 1: Mix NdFeB powder with a grain boundary additive, the amount of the grain boundary additive added accounts for 1.2wt% of the NdFeB powder; add ethanol solution, the volume ratio of NdFeB powder to ethanol solution is 1:2, and ultrasonically disperse to obtain a mixture; transfer it to a double-layer mold with a through-hole structure, set the magnetic field strength to 1.5T, wet press molding at 28MPa, and cold isostatic pressing at 150MPa to obtain a green body; in an argon atmosphere, heat it to 200℃ at a rate of 2℃ / min and hold it for 5 minutes; then heat it to 1090℃ at a rate of 15℃ / min and sinter it for 2 hours; in an argon atmosphere, heat treat it at 900℃ for 2 hours, and then heat treat it at 500℃ for 2 hours to obtain a NdFeB magnet;

[0044] 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 magnetic conductive paint on its surface and solidify it to form a coating with a thickness of 15 μm; and obtain a high-strength NdFeB magnetic material.

[0045] Example 3: A method for preparing a high-strength NdFeB magnetic material, comprising the following steps:

[0046] Preliminary preparation: (1) Weigh neodymium boron alloy powder and gallium powder in a mass ratio of 1.4:0.1 to prepare a grain boundary additive;

[0047] (2) Based on 100 wt%, the raw materials were weighed and prepared according to the ratio of 0.8 wt% tetraethyl silicate, 2 wt% phosphoric acid, 2.5 wt% isopropyl alcohol, 0.25 wt% deionized water, 0.5 wt% aminosilane coupling agent, and the remainder ethanol to obtain a phosphoric acid solution;

[0048] (3) Adding nanocrystalline Ni-Zn ferrite powder to phosphoric acid solution at a mass ratio of 10:100, stirring at 78°C for 3 hours, filtering, and drying to obtain modified magnetic powder;

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

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

[0051] 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 magnetic conductive paint on its surface and solidify it to form a coating with a thickness of 15 μm; and obtain a high-strength NdFeB magnetic material.

[0052] Comparative Example 1: Neodymium-boron alloy powder is introduced alone as a grain boundary additive, and the rest is the same as Example 1; comprising the following steps:

[0053] Preliminary preparation: (1) Weigh NdB alloy powder as grain boundary additive;

[0054] (2) Based on 100 wt%, the raw materials were weighed and prepared according to the ratio of 0.8 wt% tetraethyl silicate, 2 wt% phosphoric acid, 2.5 wt% isopropyl alcohol, 0.25 wt% deionized water, 0.5 wt% aminosilane coupling agent, and the remainder ethanol to obtain a phosphoric acid solution;

[0055] (3) Adding nanocrystalline Ni-Zn ferrite powder to phosphoric acid solution at a mass ratio of 10:100, stirring at 78°C for 3 hours, filtering, and drying to obtain modified magnetic powder;

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

[0057] Step 1: Mix NdFeB powder with a grain boundary additive, the amount of the grain boundary additive added accounts for 1.4wt% of the NdFeB powder; add ethanol solution, the volume ratio of NdFeB powder to ethanol solution is 1:2, and ultrasonically disperse to obtain a mixture; transfer it to a double-layer mold with a through-hole structure, set the magnetic field strength to 1.5T, wet press molding at 28MPa, and cold isostatic pressing at 150MPa to obtain a green body; heat it to 200℃ at a rate of 2℃ / min under argon atmosphere, hold for 5 minutes; then heat it to 1090℃ at a rate of 15℃ / min, sinter for 2 hours; heat treat it at 900℃ for 2 hours under argon atmosphere, and then heat treat it at 500℃ for 2 hours to obtain a NdFeB magnet;

[0058] 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 magnetic conductive paint on its surface and solidify it to form a coating with a thickness of 15 μm; and obtain a high-strength NdFeB magnetic material.

[0059] Comparative Example 2: Increasing the content of gallium powder in the grain boundary additive, and the rest is the same as Example 1; comprising the following steps:

[0060] Preliminary preparation: (1) Weigh neodymium boron alloy powder and gallium powder in a mass ratio of 1:0.4 to prepare a grain boundary additive;

[0061] (2) Based on 100 wt%, the raw materials were weighed and prepared according to the ratio of 0.8 wt% tetraethyl silicate, 2 wt% phosphoric acid, 2.5 wt% isopropyl alcohol, 0.25 wt% deionized water, 0.5 wt% aminosilane coupling agent, and the remainder ethanol to obtain a phosphoric acid solution;

[0062] (3) Adding nanocrystalline Ni-Zn ferrite powder to phosphoric acid solution at a mass ratio of 10:100, stirring at 78°C for 3 hours, filtering, and drying to obtain modified magnetic powder;

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

[0064] Step 1: Mix NdFeB powder with a grain boundary additive, the amount of the grain boundary additive added accounts for 1.4wt% of the NdFeB powder; add ethanol solution, the volume ratio of NdFeB powder to ethanol solution is 1:2, and ultrasonically disperse to obtain a mixture; transfer it to a double-layer mold with a through-hole structure, set the magnetic field strength to 1.5T, wet press molding at 28MPa, and cold isostatic pressing at 150MPa to obtain a green body; heat it to 200℃ at a rate of 2℃ / min under argon atmosphere, hold for 5 minutes; then heat it to 1090℃ at a rate of 15℃ / min, sinter for 2 hours; heat treat it at 900℃ for 2 hours under argon atmosphere, and then heat treat it at 500℃ for 2 hours to obtain a NdFeB magnet;

[0065] 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 magnetic conductive paint on its surface and solidify it to form a coating with a thickness of 15 μm; and obtain a high-strength NdFeB magnetic material.

[0066] Comparative Example 3: Dry pressing was used, and the rest was the same as in Example 1; the following steps were included:

[0067] Preliminary preparation: (1) Weigh neodymium boron alloy powder and gallium powder in a mass ratio of 1.3:0.1 to prepare a grain boundary additive;

[0068] (2) Based on 100 wt%, the raw materials were weighed and prepared according to the ratio of 0.8 wt% tetraethyl silicate, 2 wt% phosphoric acid, 2.5 wt% isopropyl alcohol, 0.25 wt% deionized water, 0.5 wt% aminosilane coupling agent, and the remainder ethanol to obtain a phosphoric acid solution;

[0069] (3) Adding nanocrystalline Ni-Zn ferrite powder to phosphoric acid solution at a mass ratio of 10:100, stirring at 78°C for 3 hours, filtering, and drying to obtain modified magnetic powder;

[0070] (4) Weigh and mix 50 parts by weight of silicon-modified epoxy resin, 12 parts of modified magnetic powder, 11 parts of curing agent (8:3 of isophorone diamine and magnetic accelerator), and 0.2 parts of defoaming agent to obtain a magnetic conductive coating;

[0071] Step 1: Mix NdFeB powder with a grain boundary additive, where the amount of the grain boundary additive accounts for 1.4wt% of the NdFeB powder, to obtain a mixture; transfer the mixture into a mold, set the magnetic field strength to 1.5T, and dry-press at 20MPa to form; cold isostatically press at 150MPa to obtain a green body; heat it to 200°C at a rate of 2°C / min under an argon atmosphere and hold for 5 minutes; then heat it to 1090°C at a rate of 15°C / min and sinter for 2 hours; heat treat it at 900°C for 2 hours and then at 500°C for 2 hours under an argon atmosphere to obtain a 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 magnetic conductive paint on its surface and solidify it to form a coating with a thickness of 15 μm; and obtain a high-strength NdFeB magnetic material.

[0073] Comparative Example 4: Nanocrystalline Ni-Zn ferrite powder is directly introduced into the coating, and the rest is the same as Example 1; comprising the following steps:

[0074] Preliminary preparation: (1) Weigh neodymium boron alloy powder and gallium powder in a mass ratio of 1.3:0.1 to prepare a grain boundary additive;

[0075] (2) Based on 100 wt%, the raw materials were weighed and prepared according to the ratio of 0.8 wt% tetraethyl silicate, 2 wt% phosphoric acid, 2.5 wt% isopropyl alcohol, 0.25 wt% deionized water, 0.5 wt% aminosilane coupling agent, and the remainder ethanol to obtain a phosphoric acid solution;

[0076] (3) Weigh and mix 50 parts by weight of silicon-modified epoxy resin, 12 parts of nanocrystalline Ni-Zn ferrite powder, 11 parts of curing agent (8:3 of isophorone diamine and magnetic accelerator), and 0.2 parts of defoaming agent to obtain a magnetic conductive coating;

[0077] Step 1: Mix NdFeB powder with a grain boundary additive, the amount of the grain boundary additive added accounts for 1.4wt% of the NdFeB powder; add ethanol solution, the volume ratio of NdFeB powder to ethanol solution is 1:2, and ultrasonically disperse to obtain a mixture; transfer it to a double-layer mold with a through-hole structure, set the magnetic field strength to 1.5T, wet press molding at 28MPa, and cold isostatic pressing at 150MPa to obtain a green body; in an argon atmosphere, heat it to 200℃ at a rate of 2℃ / min and hold it for 5 minutes; then heat it to 1090℃ at a rate of 15℃ / min and sinter it for 2 hours; in an argon atmosphere, heat treat it at 900℃ for 2 hours, and then heat treat it at 500℃ for 2 hours to obtain a 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 magnetic conductive paint on its surface and solidify it to form a coating with a thickness of 15 μm; and obtain a high-strength NdFeB magnetic material.

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

[0080] Preliminary preparation: (1) Weigh neodymium boron alloy powder and gallium powder in a mass ratio of 1.3:0.1 to prepare a grain boundary additive;

[0081] (2) Based on 100 wt%, the raw materials were weighed and prepared according to the ratio of 0.8 wt% tetraethyl silicate, 2 wt% phosphoric acid, 2.5 wt% isopropyl alcohol, 0.25 wt% deionized water, 0.5 wt% aminosilane coupling agent, and the remainder ethanol to obtain a phosphoric acid solution;

[0082] (3) Adding nanocrystalline Ni-Zn ferrite powder to phosphoric acid solution at a mass ratio of 10:100, stirring at 78°C for 3 hours, filtering, and drying to obtain modified magnetic powder;

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

[0084] Step 1: Mix NdFeB powder with a grain boundary additive, the amount of the grain boundary additive added accounts for 1.4wt% of the NdFeB powder; add ethanol solution, the volume ratio of NdFeB powder to ethanol solution is 1:2, and ultrasonically disperse to obtain a mixture; transfer it to a double-layer mold with a through-hole structure, set the magnetic field strength to 1.5T, wet press molding at 28MPa, and cold isostatic pressing at 150MPa to obtain a green body; in an argon atmosphere, heat it to 200℃ at a rate of 2℃ / min and hold it for 5 minutes; then heat it to 1090℃ at a rate of 15℃ / min and sinter it for 2 hours; in an argon atmosphere, heat treat it at 900℃ for 2 hours, and then heat treat it at 500℃ for 2 hours to obtain a 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 magnetic conductive paint on its surface and solidify it to form a coating with a thickness of 15 μm; and obtain a high-strength NdFeB magnetic material.

[0086] Performance Test 1: The high-strength NdFeB magnetic materials prepared in the Examples and Comparative Examples were subjected to relevant performance tests. The flexural strength test was conducted according to GB / T31967.2 at a rate of 0.5 mm / min. Magnetic properties (A) were measured using a gaussmeter. The materials were then immersed in a 3.5 wt% sodium chloride aqueous solution for 72 hours, rinsed, and dried before being tested for magnetic properties (B). The resulting data are shown in the following table:

[0087]

[0088] Conclusion: The data in the above table show that the present invention effectively improves the bending strength by using a specific proportion of grain boundary additives, and further improves its corrosion resistance by coating. Comparing the data of Example 1 with Comparative Examples 1 to 5, Comparative Example 1 uses only a single neodymium boron alloy powder, resulting in insufficient liquid phase at the grain boundaries and reduced strength and other properties; in Comparative Example 2, the gallium powder content is increased, resulting in non-magnetic weaknesses and reduced related properties; in Comparative Example 3, dry pressing is used, resulting in poor density, grain boundary segregation, and reduced performance; in Comparative Example 4, the nanocrystalline Ni-Zn ferrite powder is not modified, resulting in poor compatibility and reduced related properties; in Comparative Example 5, the curing agent has no magnetic promoter, resulting in reduced magnetic permeability and adhesion, and reduced related properties.

[0089] Finally, it should be noted that the above descriptions are merely 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 aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing high-strength NdFeB magnetic material, characterized in that: The following steps are involved: Step 1: Mix NdFeB powder with grain boundary additives; An ethanol solution is added and ultrasonically dispersed to obtain a mixture; the mixture is transferred to a double-layer mold with a through-hole structure, a magnetic field is set to 1.5-2T, wet pressing is performed at a pressure of 25-28MPa, and cold isostatic pressing is performed to obtain a green body; the green body is sequentially sintered and annealed to obtain a NdFeB magnet; Step 2: Grind the surface of the NdFeB magnet; pre-treat it in a phosphoric acid solution; then spray a magnetic conductive coating on its surface and solidify it to form a coating; Obtain high-strength NdFeB magnetic material; The amount of the grain boundary additive added is 1.2-1.5wt% of the NdFeB powder; the grain boundary additive comprises NdB alloy powder and gallium powder in a mass ratio of 1.1-1.4:0.1; the NdB alloy powder is a homologous phase of the NdFeB powder, and the boron content of the NdB alloy powder is 0.5-1at%; The volume ratio of the NdFeB powder to the ethanol solution is 1:2-3; the ethanol solution is a 0.2-0.6 wt % myristic amine-ethanol solution.

2. The method for preparing a high-strength NdFeB magnetic material according to claim 1, wherein: In step 1, the pressure of the cold isostatic pressing treatment is 100~200MPa; The sintering process is as follows: in an argon atmosphere, the temperature is raised to 200-250°C at a rate of 1-2°C / min and maintained for 5-10 minutes; then the temperature is raised to 1050-1100°C at a rate of 10-15°C / min and sintered for 2-3 hours; the annealing process is as follows: in an argon atmosphere, heat treatment is performed at 850-900°C for 1-2 hours, and then heat treatment is performed at 500-600°C for 1-2 hours.

3. The method for preparing a high-strength NdFeB magnetic material according to claim 1, wherein: In step 2, after grinding, the surface roughness of the NdFeB magnet is 0.4-1.6 μm; the coating thickness is 10-30 μm.

4. The method for preparing a high-strength NdFeB magnetic material according to claim 1, wherein: The process parameters of the phosphoric acid solution pretreatment are: pretreatment at 70-75°C for 1-2 hours; The phosphoric acid solution includes the following components: 0.5-1 wt% of tetraethyl silicate, 1-2 wt% of phosphoric acid, 2.2-2.5 wt% of isopropyl alcohol, 0.2-0.3 wt% of deionized water, 0.5-1 wt% of an aminosilane coupling agent, and the remainder is ethanol.

5. The method for preparing a high-strength NdFeB magnetic material according to claim 1, wherein: 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 parts of defoaming agent.

6. The method for preparing a high-strength NdFeB magnetic material according to claim 5, wherein: The modified magnetic powder material is prepared by adding nanocrystalline Ni-Zn ferrite powder to a phosphoric acid solution, stirring the solution at 78-80°C for 3-4 hours, filtering, and drying to obtain the modified magnetic powder material; the mass ratio of the nanocrystalline Ni-Zn ferrite powder to the phosphoric acid solution is 5-10:

100.

7. The method for preparing a high-strength NdFeB magnetic material according to claim 5, wherein: The curing agent includes isophorone diamine and a magnetic accelerator in a ratio of 8:2-4. The preparation method of the magnetic accelerator is as follows: trihexyl (tetradecyl) phosphine chloride and ferric chloride hexahydrate are mixed in equal moles, and stirred at room temperature for 24 hours to obtain the magnetic accelerator.

8. A high-strength NdFeB magnetic material prepared according to the method for preparing a high-strength NdFeB magnetic material according to any one of claims 1 to 7.

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