A NdFeB magnetic material with high intrinsic coercivity and its preparation method

Abstract

This application relates to the field of NdFeB magnetic materials, and specifically relates to a NdFeB magnetic material with high intrinsic coercivity and a preparation method thereof, including raw materials with the following components in parts by weight: 52.5 - 57.2 parts of PrNd, 105 - 115.3 parts of Nd, 9.0 - 10.3 parts of B, 15 - 35 parts of Tb, 70 - 80 parts of Dy, 10 - 25 parts of Co, and 650 - 680 parts of Fe. By adding two rare earth elements, Tb and Dy, to the NdFeB magnetic material, this application significantly enhances the magnetocrystalline anisotropy field of the crystal, thereby greatly improving the intrinsic coercivity of the NdFeB magnetic material.

Description

Technical Field

[0001] The present application relates to the field of NdFeB magnetic materials, and in particular to a NdFeB magnetic material with high intrinsic coercivity and a preparation method thereof. Background Art

[0002] Neodymium iron boron magnetic material (NdFeB) is an alloy composed of elements such as neodymium (Nd), iron (Fe), and boron (B). NdFeB magnetic material is the third-generation rare earth permanent magnetic material developed and successfully applied in production in the 1980s of the 20th century. Due to its advantages such as high remanence, high coercivity, high magnetic energy product, and good dynamic recovery characteristics, it is currently the magnetic material with the best cost performance. Because of its excellent magnetic properties, it is known as the "magnetic king" and plays an important role in fields such as medical treatment, automobiles, household appliances, aerospace, and communication, and has broad application prospects.

[0003] Intrinsic coercivity is the core index for measuring the demagnetization resistance of magnetic materials. In the application process of NdFeB magnetic materials, high-temperature environments are often encountered. Only magnetic materials with high intrinsic coercivity can effectively resist thermally activated demagnetization and ensure that the device still maintains a stable magnetic field strength at high temperatures. However, with the continuous expansion of the application scope of NdFeB magnetic materials, the demand for optimizing the magnetic properties of NdFeB magnetic materials is also increasing. Therefore, there is an urgent need for a NdFeB magnetic material with high intrinsic coercivity. Summary of the Invention

[0004] In order to improve the intrinsic coercivity of NdFeB magnetic materials, the present application provides a NdFeB magnetic material with high intrinsic coercivity and a preparation method thereof.

[0005] In the first aspect, a NdFeB magnetic material with high intrinsic coercivity provided by the present application adopts the following technical solution:

[0006] A NdFeB magnetic material with high intrinsic coercivity includes raw materials with the following parts by weight: 52.5 - 57.2 parts of PrNd, 105 - 115.3 parts of Nd, 9.0 - 10.3 parts of B, 15 - 35 parts of Tb, 70 - 80 parts of Dy, 10 - 25 parts of Co, and 650 - 680 parts of Fe.

[0007] By adopting the above technical solution, the present application adds two rare earth elements, Tb and Dy, with relatively high contents. Tb and Dy can diffuse along the grain boundaries at high temperatures to form a (Nd, Tb)2Fe 14 B shell and a (Nd, Dy)2Fe 14The B shell wraps the main-phase grains, significantly enhancing the magnetocrystalline anisotropy field of the crystal, thereby greatly improving the intrinsic coercivity of the NdFeB magnetic material. By adding an appropriate amount of Pr, the coarsening of the grains can be inhibited, indirectly enhancing the intrinsic coercivity of the NdFeB magnetic material. The addition of Co can replace part of Fe, while increasing the Curie temperature of the magnetic material and enhancing the high-temperature stability of the magnet, it can also inhibit the formation of the Fe-Tb / Dy soft magnetic phase and delay the attenuation of the intrinsic coercivity of the magnetic material at high temperatures. Through the cooperation of various elements, the intrinsic coercivity of the NdFeB magnetic material is improved.

[0008] Preferably, the high-intrinsic-coercivity NdFeB magnetic material further includes a first additive, which is at least one of calcium and magnesium, and the dosage of the first additive accounts for 0.1-0.4 wt% of the total amount of raw materials.

[0009] By adopting the above technical solution, since adding more Tb and Dy to the NdFeB magnetic material will result in higher brittleness of the NdFeB magnetic material, in order to weaken this effect, a first additive is added to the alloy. Calcium and magnesium have strong reducibility and can reduce brittle oxides such as FeO at the grain boundaries to form more stable CaO and MgO, thereby reducing the brittle oxidation phase. Moreover, CaO and MgO are high-melting-point oxides with high stability and can be used as grain boundary strengthening phases to enhance the grain boundary bonding force and the toughness of the NdFeB magnetic material.

[0010] Since calcium and magnesium are active metals, when the addition amount of the first additive is too high, violent volatilization will occur during the melting process, resulting in splashing of the molten liquid, increasing the porosity of the magnetic material. During the sintering process, the excessive first additive may replace Nd in the lattice, disturbing the crystal structure, reducing the magnetocrystalline anisotropy, and causing a decrease in coercivity and remanence. When the addition amount of the first additive is too low, the brittle oxides cannot be fully reduced, resulting in a decrease in the magnetic properties of the NdFeB magnetic material and an increase in brittleness.

[0011] Preferably, the high-intrinsic-coercivity NdFeB magnetic material further includes a second additive, which is at least one of hafnium and titanium, and the dosage of the second additive accounts for 0.1-0.4 wt% of the total amount of raw materials.

[0012] Preferably, the second additive is hafnium.

[0013] By adopting the above technical solution, hafnium and titanium belong to transition metal elements and have a strong affinity for oxygen. Under aerobic conditions, they can preferentially combine with oxygen to form high-melting-point oxides such as HfO2 and TiO2. HfO2 and TiO2 are evenly distributed at the grain boundaries, replacing the brittle oxides that are easily formed, thereby reducing the formation of brittle phases at the grain boundaries, enhancing the grain boundary bonding force, inhibiting the initiation of cracks, and effectively improving the toughness of the NdFeB magnetic material.

[0014] Among them, hafnium preferentially combines with oxygen to form HfO2. HfO2 can form a stable strengthening phase at the grain boundaries, enhancing the binding force of the grain boundaries. HfO2 can also form a dense protective layer at the grain boundaries, effectively blocking the diffusion of oxygen into the magnetic material interior, delaying high-temperature oxidation, and improving the antioxidant performance of the NdFeB magnetic material. At the same time, the strong reducibility of hafnium can reduce the formation of brittle oxides, thereby reducing the brittleness of the grain boundaries. Hafnium can also be used as a grain growth inhibitor to inhibit the abnormal growth of grains, significantly refining the grain size of the main phase, and improving the intrinsic coercivity of the NdFeB magnetic material.

[0015] When the addition amount of the second additive is too low, the degree of grain refinement is insufficient, resulting in a decrease in intrinsic coercivity. When the addition amount of the second additive is too high, excessive hafnium or titanium may occupy the lattice positions of the main phase, replacing iron or rare earth elements, damaging the integrity of the crystal structure, reducing the magnetocrystalline anisotropy field, and causing a decrease in the magnetic properties of the NdFeB magnetic material.

[0016] Preferably, it further includes a third additive, and the third additive is at least one of methylvinylsilazane and polysilazane resin. The dosage of the third additive accounts for 1-1.5 wt% of the total amount of raw materials.

[0017] Preferably, the third additive is methylvinylsilazane.

[0018] By adopting the above technical solution, methylvinylsilazane and polysilazane resin have strong adhesion to metals. Methylvinylsilazane and polysilazane resin also have the properties of low-temperature adhesion and high-temperature ceramization. At low temperatures, methylvinylsilazane and polysilazane resin can form a temporary bonding network, enhancing the strength of the sintered green body, reducing the generation of cracks, and improving the green density and forming accuracy. During the sintering process, methylvinylsilazane and polysilazane resin crack at high temperatures to generate silicon nitride ceramics. Silicon nitride itself has lubricity and can play a role in filling the gaps between powder materials, improving the intrinsic coercivity of the NdFeB magnetic material. At the same time, the silicon nitride ceramics can cover the grain boundaries and surfaces of the NdFeB magnetic material and form a dense physical barrier to inhibit the penetration of oxygen and corrosive media, thereby improving the antioxidant and corrosion resistance of the NdFeB magnetic material.

[0019] Since methylvinylsilazane has the characteristics of low viscosity, high activity and high ceramic yield, methylvinylsilazane is preferred in this application. However, methylvinylsilazane decomposes and produces gas during pyrolysis, resulting in an increase in the porosity of the NdFeB magnetic material. The introduction of hafnium can serve as a nucleating agent to promote the uniform decomposition of methylvinylsilazane, and the surface of hafnium is highly active, capable of adsorbing the gas produced by the decomposition of methylvinylsilazane and forming high-melting-point compounds, which can be used as nanoscale filling phases during sintering, occupying the position of grain boundaries or voids, thereby reducing the porosity of the NdFeB magnetic material. At the same time, the introduction of hafnium can also enhance the interface bonding strength between the silicon nitride ceramic layer formed after high-temperature ceramicization of methylvinylsilazane and the NdFeB magnetic material.

[0020] When the amount of the third additive added is too small, the bonding force between the magnetic powder particles is weak, resulting in low strength of the pressed embryo, affecting the forming efficiency, and reducing the corrosion resistance of the resulting NdFeB magnetic material; when the amount of the third additive added is too high, it will decompose during the sintering process to produce excessive gas, destroying the uniformity of the sintering of the magnetic material, and causing the brittleness of the magnetic material to increase.

[0021] In a second aspect, the present application provides a method for preparing a high intrinsic coercivity NdFeB magnetic material, using the following technical solution:

[0022] A method for preparing a high intrinsic coercivity NdFeB magnetic material, used for preparing the above-mentioned high intrinsic coercivity NdFeB magnetic material, comprises the following steps:

[0023] S1. Melting strip: PrNd, Nd, B, Tb, Dy, Co, Fe and other raw materials are mixed according to the formula, and the mixture is melted to obtain a molten liquid, and the molten liquid is cast and stripped to obtain a strip sheet;

[0024] S2, hydrogen crushing and grinding: the stripping pieces are hydrogen crushed into coarse powder, and the coarse powder is jet milled to obtain alloy powder;

[0025] S3, pressing and molding: placing the obtained alloy powder in a mold, and pressing and molding to obtain a sintered green body;

[0026] S4. Sintering process: The green compact is sintered under the protection of nitrogen. After sintering, it is rapidly cooled to room temperature in stages and tempered to obtain NdFeB magnetic material.

[0027] By adopting the above technical solutions, through the steps of melt spinning, hydrogen decrepitation grinding, pressing and sintering, the efficient utilization of raw materials and the uniform distribution of components are realized, the formation of fine grains and the construction of an ordered magnetic domain structure are promoted, thereby significantly optimizing the magnetic properties of NdFeB magnets, including improving key indicators such as intrinsic coercivity and magnetic energy product, while improving production efficiency and quality stability, and reducing production costs, providing an efficient and reliable way for the preparation of high-performance and high-quality NdFeB magnets.

[0028] Preferably, it includes a first alloy and a second alloy. The components of the first alloy are 26.25 - 28.60 parts of PrNd, 52.50 - 57.65 parts of Nd, 4.50 - 5.15 parts of B, 7.5 - 17.5 parts of Tb, 60 - 65 parts of Dy, 5 - 12.5 parts of Co, and 325 - 340 parts of Fe. The components of the second alloy are 26.25 - 28.60 parts of PrNd, 52.50 - 57.65 parts of Nd, 4.50 - 5.15 parts of B, 7.5 - 17.5 parts of Tb, 10 - 15 parts of Dy, 5 - 12.5 parts of Co, and 325 - 340 parts of Fe;

[0029] In S1, a first ribbon is made according to the components of the first alloy, and a second ribbon is made according to the components of the second alloy;

[0030] In S2, the first ribbon and the second ribbon are hydrogen decrepitated into coarse powder, and the coarse powder is formed into alloy powder by a jet mill.

[0031] By adopting the above technical solutions, the first alloy contains 3.00 - 3.25 parts of Dy, while the second alloy contains 0.50 - 0.75 parts of Dy. By using the double main phase method of mixing the first alloy with high Dy content and the second alloy with low Dy content to prepare NdFeB magnetic materials, a composite structure of "hard magnetic phase + soft magnetic phase" can be formed, improving the magnetic properties of NdFeB magnetic materials. In the first alloy with high Dy content, Dy atoms replace Nd atoms, increasing the magnetocrystalline anisotropy field and forming a hard magnetic phase with high coercivity. The second alloy with low Dy content retains the high remanence characteristics of the Nd - Fe - B system. Due to the low content of Dy, the proportion of the Nd - rich phase in the second alloy is relatively high, which helps to form a continuous Nd - rich phase network and promote the consistent orientation of magnetic domains, thus maintaining the high remanence level of NdFeB magnetic materials. Through the synergistic effect of the hard magnetic phase and the soft magnetic phase, the hard magnetic phase, as the strengthening phase at the grain boundaries, can effectively isolate the soft magnetic phase grains, inhibit the magnetic coupling between grains, and reduce the disordered reversal of magnetic domains, thereby significantly increasing the intrinsic coercivity while maintaining the high remanence.

[0032] Preferably, in S1, the first additive or the second additive is mixed with PrNd, Nd, B, Tb, Dy, Co, and Fe and then melt spun.

[0033] By adopting the above technical solution, in S1, the first additive or the second additive is mixed with PrNd, Nd, B, Tb, Dy, Co, and Fe and then melt-spun, which can promote the uniform distribution of alloy components. The first additive can reduce the brittle oxides in the NdFeB magnetic material and form more stable compounds, and the second additive can preferentially combine with oxygen to reduce the generation of brittle oxides. Both can improve the bonding force of the grain boundaries, thereby improving the toughness of the NdFeB magnetic material.

[0034] Preferably, in S3, the third additive is mixed with the alloy powder and then pressed into a mold for forming.

[0035] By adopting the above technical solution, the third additive is mixed with the alloy powder in S3 and then pressed into a mold for forming. The third additive is in a liquid state at room temperature, can fill the pores between the alloy powders and act as an adhesive, and the addition of the third additive can reduce the friction between the magnetic powder particles, improve the fluidity of the powder in the mold, make the pressing more uniform, and contribute to improving the strength of the sintered green body.

[0036] In summary, the present application includes at least one of the following beneficial technical effects:

[0037] 1. By adding rare earth elements Tb and Dy to the NdFeB magnetic material in the present application, Tb and Dy can diffuse along the grain boundaries at high temperatures to form (Nd, Tb)2Fe 14 B shell and (Nd, Dy)2Fe 14 B shell and wrap the main phase grains, significantly enhancing the magnetocrystalline anisotropy field of the crystal, thereby greatly improving the intrinsic coercivity of the NdFeB magnetic material. And by adding Co, it can replace part of Fe, enhance the high-temperature stability of the NdFeB magnetic material while also inhibiting the formation of the Fe-Tb / Dy soft magnetic phase, and improve the magnetic properties of the NdFeB magnetic material;

[0038] 2. By adding hafnium to the NdFeB magnetic material in the present application, hafnium can preferentially combine with oxygen to form HfO2 under aerobic conditions. HfO2 belongs to high-melting-point oxides and can replace the originally easily formed brittle oxides, reduce the formation of brittle phases at the grain boundaries, enhance the bonding force of the grain boundaries, inhibit the initiation of cracks, and effectively improve the toughness of the NdFeB magnetic material. In addition, the generated HfO2 can also form a dense protective layer at the grain boundaries, effectively blocking the diffusion of oxygen into the magnetic material interior and delaying the high-temperature oxidation of the NdFeB magnetic material;

[0039] 3. In this application, by adding methylvinylsilazane to NdFeB magnetic materials, methylvinylsilazane has strong adhesion to metals and also has the properties of low-temperature adhesion and high-temperature ceramization. At low temperatures, it can form a temporary bonding network to enhance the strength of the sintered green body. At high temperatures, methylvinylsilazane undergoes pyrolysis to produce silicon nitride ceramics. The silicon nitride ceramics can cover the grain boundaries and surfaces of the NdFeB magnetic materials and form a dense physical barrier to inhibit the penetration of oxygen and corrosive media, thereby improving the oxidation resistance and corrosion resistance of the NdFeB magnetic materials. By the cooperation of hafnium and methylvinylsilazane, the influence of the increase in the porosity of the NdFeB magnetic materials caused by methylvinylsilazane can be effectively reduced. Detailed implementation mode

[0040] The raw materials in this application include the following parts:

[0041] Methylvinylsilazane: 1,1,3,3-tetramethyl-1,3-divinyldisilazane, 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasilazane, tetramethyldivinyldisilazane, etc. can be selected. In this application, tetramethyldivinyldisilazane with a CAS number of 7691-02-3 is taken as an example.

[0042] Polysilazane resin: A commercially available product with a CAS number of 475645-84-2.

[0043] The following further elaborates on this application in combination with examples and comparative examples. Example 1

[0044] A NdFeB magnetic material with high intrinsic coercivity, comprising the following components in parts by weight: PrNd 54.85 g, Nd110.15 g, B 9.65 g, Tb 25 g, Dy 75 g, Co 17.5 g, Fe 665 g.

[0045] A preparation method of a NdFeB magnetic material with high intrinsic coercivity for preparing the above NdFeB magnetic material with high intrinsic coercivity, comprising the following steps:

[0046] S1. Melting and strip casting: PrNd, Nd, B, Tb, Dy, Co, and Fe are mixed according to the formula amount, and the mixture is put into a vacuum melting furnace for melting to obtain a molten liquid. The molten liquid is cast and strip-cast to obtain strip-cast sheets.

[0047] S2. Hydrogen breaking and grinding: The strip-cast sheets are hydrogen broken into coarse powder, and the coarse powder is obtained as alloy powder after passing through a jet mill.

[0048] S3. Compression molding: The obtained alloy powder is placed in a mold and compression molded to obtain a sintered green body.

[0049] S4. Sintering process: The green compact for sintering is sintered under the protection of nitrogen. The sintering temperature is 1100 °C, and it is kept at this temperature for 3 h. After sintering, it is rapidly cooled to room temperature in stages and then tempered to obtain the NdFeB magnetic material.

[0050] Among them, the cooling after sintering of the green compact includes three stages. In the first stage, the sintering temperature is reduced from 1100 °C to 800 °C at a cooling rate of 7 °C / min and kept at this temperature for 3 h. In the second stage, the sintering temperature is further decreased from 800 °C to room temperature at a rate of 4 °C / min. The tempering process includes two stages. In the first stage, the tempering temperature is 800 °C and the tempering time is 2 h. After that, the magnetic material is cooled to room temperature using argon, and then the second stage of tempering is started. The second tempering temperature is 500 °C and the tempering time is 3 h. After the end, the magnetic material is cooled to room temperature using argon.

[0051] Example 2 - 3

[0052] Based on the preparation method of Example 1, the component ratios of the NdFeB magnetic material in Example 2 - 3 are adjusted, and the specific adjustments are shown in Table 1.

[0053] Comparative Example 1 - 3

[0054] Based on the preparation method of Example 1, the component ratios of the NdFeB magnetic material in Comparative Example 1 - 3 are adjusted, and the specific adjustments are shown in Table 1.

[0055] Performance detection test

[0056] The NdFeB magnetic materials of the above Examples 1 - 3 and Comparative Examples 1 - 3 are analyzed, and the specific detection methods are as follows:

[0057] Magnetic properties

[0058] According to GB / T3217 - 2013 "Magnetic Test Methods for Permanent (Hard Magnetic) Materials", its comprehensive magnetic properties are detected.

[0059] According to the above detection methods, the test results of Examples 1 - 3 and Comparative Examples 1 - 3 are obtained, as shown in Table 1 below.

[0060] Table 1 Data table of component ratios and performance detections of NdFeB magnetic materials in Examples 1 - 3 and Comparative Examples 1 - 3 (unit: g)

[0061]

[0062] Referring to Table 1, by comparing Examples 1-3 and Comparative Examples 1-3, it can be found that for the remanence of the Nd-Fe-B magnetic materials obtained by comparing Examples 1-3 and Comparative Examples 1-3, the remanence of Examples 1-3 is lower than that of the Nd-Fe-B magnetic materials obtained in Comparative Examples 1-3, indicating that adding Tb and Dy during the preparation process of the Nd-Fe-B magnetic materials will reduce the remanence of the Nd-Fe-B magnetic materials. By comparing the intrinsic coercivity of the Nd-Fe-B magnetic materials obtained in Examples 1-3 and Comparative Examples 1-3, it can be found that the intrinsic coercivity of the Nd-Fe-B magnetic materials obtained in Examples 1-3 has been significantly improved compared with that of the Nd-Fe-B magnetic materials obtained in Comparative Examples 1-3. Especially when the addition amount of Tb is 25 g and the addition amount of Dy is 75 g, the intrinsic coercivity of the Nd-Fe-B magnetic material is the highest, indicating that the addition of Tb and Dy can significantly improve the intrinsic coercivity of the Nd-Fe-B magnetic material while slightly reducing the remanence of the Nd-Fe-B magnetic material. Example 4

[0063] On the basis of the preparation method of Example 1, 0.3 wt% of calcium based on the total amount of raw materials was added in S1 and melted together with the raw materials in Example 4. Example 5

[0064] On the basis of the preparation method of Example 1, 0.3 wt% of magnesium based on the total amount of raw materials was added in S1 and melted together with the raw materials in Example 5. Example 6

[0065] On the basis of the preparation method of Example 1, 0.3 wt% of titanium based on the total amount of raw materials was added in S1 and melted together with the raw materials in Example 6. Example 7

[0066] On the basis of the preparation method of Example 1, 0.3 wt% of hafnium based on the total amount of raw materials was added in S1 and melted together with the raw materials in Example 7.

[0067] Performance detection test

[0068] The Nd-Fe-B magnetic materials of Examples 4-7 above were analyzed, and the specific detection methods are as follows:

[0069] Toughness

[0070] The magnet samples were respectively processed into standard-sized impact specimens with a length of 55 mm and a square cross-section of 10*10 mm according to the "GB / T 229-2007 Metallic materials - Charpy pendulum impact test method", with a V-notch in the middle of the specimen length, a V-notch included angle of 45 °, and a depth of 2 mm. And a JBS 300 digital pendulum impact testing machine was used, and a 150 J pendulum was selected for the impact toughness test to obtain the absorbed energy of the magnetic material sample.

[0071] According to the above detection method, the test results of Examples 4-7 were obtained, as shown in Table 2 below.

[0072] Table 2 Data Sheet of Component and Performance Detection of Nd-Fe-B Magnetic Materials in Example 1 and Examples 4-7

[0073]

[0074] Referring to Table 2, by comparing Example 1 with Examples 4-7, it can be seen that for the Nd-Fe-B magnetic materials obtained in Examples 4-7, adding calcium, magnesium, titanium, and hafnium in S1 improves the toughness of the Nd-Fe-B magnetic materials compared to those obtained in Example 1. However, the difference in toughness of the Nd-Fe-B magnetic materials obtained between Examples 4-7 is not significant. By further comparing the intrinsic coercivity of the Nd-Fe-B magnetic materials obtained in Example 1 with that of the Nd-Fe-B magnetic materials obtained in Examples 4-7, it can be found that for the Nd-Fe-B magnetic materials obtained in Examples 4-6, there is no significant improvement in the intrinsic coercivity compared to Example 1, while the intrinsic coercivity of the Nd-Fe-B magnetic materials obtained in Example 7 has been improved to a certain extent. This shows that the introduction of hafnium can not only improve the toughness of Nd-Fe-B magnetic materials but also enhance the intrinsic coercivity of Nd-Fe-B magnetic materials. This is because hafnium can act as a grain growth inhibitor to inhibit the abnormal growth of grains, resulting in a significant refinement of the main phase grain size, thereby enhancing the intrinsic coercivity of Nd-Fe-B magnetic materials.

[0075] Examples 8-9

[0076] Based on the preparation method of Example 4, the addition amount of calcium in Examples 8-9 was adjusted, and the specific adjustment is shown in Table 3.

[0077] Comparative Examples 4-5

[0078] Based on the preparation method of Example 4, the addition amount of calcium in Comparative Examples 4-5 was adjusted, and the specific adjustment is shown in Table 3.

[0079] The Nd-Fe-B magnetic materials of Examples 8-9 and Comparative Examples 4-5 were subjected to the above performance detection, and the test results are shown in Table 3.

[0080] Table 3 Data Sheet of Proportion of Calcium Usage and Performance Detection of Example 4, Examples 8-9 and Comparative Examples 4-5

[0081]

[0082] Referring to Table 3, by comparing Example 4, Examples 8-9 and Comparative Examples 4-5, it can be seen that when the calcium dosage accounts for 0.1-0.3 wt% of the total raw materials, the toughness of the obtained NdFeB magnetic material is in an ideal state. When the calcium dosage ratio is too high, the toughness of the obtained NdFeB magnetic material decreases. This may be because calcium will increase the porosity of the NdFeB magnetic material during the melting process, reducing the density of the NdFeB magnetic material and resulting in a decrease in the toughness of the NdFeB magnetic material. When the calcium dosage ratio is too low, many brittle oxide phases in the grain boundary are not reduced, resulting in a decrease in the toughness of the NdFeB magnetic material.

[0083] Examples 10-11

[0084] Based on the preparation method of Example 5, the addition amount of magnesium was adjusted in Examples 10-11, and the specific adjustment is shown in Table 4.

[0085] Comparative Examples 6-7

[0086] Based on the preparation method of Example 5, the addition amount of magnesium was adjusted in Comparative Examples 6-7, and the specific adjustment is shown in Table 4.

[0087] The NdFeB magnetic materials of Examples 10-11 and Comparative Examples 6-7 were subjected to the above performance tests, and the test results are shown in Table 4.

[0088] Table 4 Performance test data table of the magnesium dosage ratio of Example 5, Examples 10-11 and Comparative Examples 6-7

[0089]

[0090] Referring to Table 4, by comparing Example 5, Examples 10-11 and Comparative Examples 6-7, it can be seen that when the magnesium dosage accounts for 0.1-0.3 wt% of the total raw materials, the toughness of the obtained NdFeB magnetic material is in an ideal state. Especially when the magnesium dosage accounts for 0.3 wt% of the total raw materials, the toughness of the obtained NdFeB magnetic material is optimal. When the magnesium dosage ratio is too high, the toughness of the obtained NdFeB magnetic material decreases. This may be because magnesium will volatilize at high temperature, increasing the porosity of the NdFeB magnetic material and affecting the density of the NdFeB magnetic material, resulting in a decrease in the toughness of the NdFeB magnetic material. When the magnesium dosage ratio is too low, many brittle oxide phases in the grain boundary are not reduced, resulting in a decrease in the toughness of the NdFeB magnetic material. Example 12

[0091] Based on the preparation method of Example 7, 12 g of tetramethyldivinyldisilazane was added in S3 in Example 12, and the tetramethyldivinyldisilazane and the alloy powder were placed in a mold for pressing. Example 13

[0092] Example 13 Based on the preparation method of Example 7, 12 g of polysilazane resin was added in S3, and the polysilazane resin and alloy powder were placed in a mold for pressing.

[0093] Comparative Example 8

[0094] Comparative Example 8 Based on the preparation method of Example 1, 12 g of tetramethyldivinyldisilazane was added in S3, and the tetramethyldivinyldisilazane and alloy powder were placed in a mold for pressing.

[0095] Performance Detection Test

[0096] The NdFeB magnetic materials of the above Examples 12 - 13 and Comparative Example 8 were analyzed, and the specific detection methods were as follows:

[0097] Corrosion Resistance

[0098] A neutral salt spray test was carried out. An aqueous sodium chloride solution with a concentration of 5 wt% was used to spray the magnetic material sample, and the test temperature was 35°C. Since the corrosion reaction of NdFeB magnetic materials in neutral salt spray is mainly oxidation and exfoliation, the weight loss rate after 144 h was used as the detection basis for the corrosion resistance of the magnetic material sample. The weight loss rate after 144 h = (mass before immersion - mass after immersion) / mass before immersion.

[0099] The NdFeB magnetic materials of Examples 12 - 13 and Comparative Example 8 were subjected to the above performance detection, and the test results are shown in Table 5.

[0100] Table 5 Performance Detection Data Sheet of Example 7, Examples 12 - 13 and Comparative Example 8

[0101]

[0102] Referring to Table 5, by comparing Example 7, Examples 12 - 13 and Comparative Example 8, it can be seen that in Examples 12 - 13, tetramethyldivinyldisilazane and polysilazane resin were added respectively on the basis of Example 7, significantly reducing the weight loss rate of NdFeB magnetic materials in the salt corrosion reaction, indicating that the corrosion resistance of NdFeB magnetic materials has been significantly improved. Among them, the weight loss rate of the NdFeB magnetic material in Example 12 is less than that of the NdFeB magnetic material in Example 13, indicating that adding tetramethyldivinyldisilazane on the basis of the preparation method of Example 7 makes the corrosion resistance of NdFeB magnetic materials better. This is because tetramethyldivinyldisilazane has higher fluidity at low temperatures and can wrap the magnetic powder particles more evenly. At high temperatures, the vinyl groups of tetramethyldivinyldisilazane can participate in cross-linking, and compared with polysilazane resin, the ceramization yield is higher. Therefore, the obtained NdFeB magnetic materials have stronger corrosion resistance.

[0103] By comparing Example 7, Example 12 and Comparative Example 8, it can be found that the absorption work of the NdFeB magnetic material obtained in Comparative Example 8 is the lowest. Since hafnium is not introduced into the NdFeB magnetic material in Comparative Example 8, the brittle oxidation phase at the grain boundaries cannot be reduced, resulting in an increase in the brittleness and a decrease in the toughness of the NdFeB magnetic material. However, the weight loss rate of the NdFeB magnetic material obtained in Comparative Example 8 is between that of Example 7 and Example 12, indicating that through the combination of hafnium and tetramethyldivinyldisilazane, the toughness of the NdFeB magnetic material can be improved while further enhancing the corrosion resistance of the NdFeB magnetic material. Example 14

[0104] On the basis of the preparation method of Example 1, 1.5 g of calcium and 1.5 g of hafnium were added in S1 and melted together with the raw materials in Example 14. Example 15

[0105] On the basis of the preparation method of Example 1, 1.5 g of magnesium and 1.5 g of hafnium were added in S1 and melted together with the raw materials in Example 15.

[0106] The NdFeB magnetic materials of Examples 14 - 15 were subjected to the above performance tests, and the test results are shown in Table 6.

[0107] Table 6 Performance test data of Examples 7 and Examples 14 - 15

[0108]

[0109] Referring to Table 6, by comparing Example 7 and Examples 14 - 15, it can be seen that the absorption work of the NdFeB magnetic materials obtained in Examples 14 - 15 is greater than that of the NdFeB magnetic material obtained in Example 7, indicating that adding composite calcium and hafnium or magnesium and hafnium during the preparation of the NdFeB magnetic material can improve the toughness of the NdFeB magnetic material. This is because calcium and magnesium have strong reducibility, which can reduce the brittle oxides at the grain boundaries and generate more stable CaO and MgO, while hafnium can preferentially combine with oxygen, and the generated HfO2 can replace the originally easily formed brittle oxides. Through the synergistic effect of the two, the toughness of the NdFeB magnetic material is further improved. Example 16

[0110] Example 16 Based on the preparation method of Example 1, the NdFeB magnetic material is divided into a first alloy and a second alloy. The components of the first alloy are PrNd 27.425 g, Nd 55.075 g, B 4.825 g, Tb 12.5 g, Dy 62.5 g, Co 8.75 g, and Fe 332.5 g. The components of the second alloy are PrNd 27.425 g, Nd 55.075 g, B 4.825 g, Tb 12.5 g, Dy 12.5 g, Co 8.75 g, and Fe 332.5 g. In S1, a first strip casting sheet is made according to the components of the first alloy, and a second strip casting sheet is made according to the components of the second alloy. In S2, the first strip casting sheet and the second strip casting sheet are hydrogenated and crushed into coarse powder, and the coarse powder is formed into alloy powder by air jet milling.

[0111] The NdFeB magnetic material of Example 16 is subjected to the above performance tests, and the test results are shown in Table 7.

[0112] Table 7 Data table of performance tests for Example 1 and Example 16

[0113]

[0114] Referring to Table 7, by comparing Example 1 and Example 16, it can be seen that compared with the single main phase method in Example 1, in Example 16, the NdFeB magnetic material is prepared by a double main phase method in which a first alloy with a high Dy content and a second alloy with a low Dy content are mixed, which can form a composite structure of "hard magnetic phase + soft magnetic phase", significantly improving the magnetic properties of the NdFeB magnetic material. The first alloy with a high Dy content can provide a hard magnetic phase with high coercivity, and the second alloy with a low Dy content can maintain the high remanence level of the NdFeB magnetic material, enabling the NdFeB magnetic material to significantly improve the intrinsic coercivity while maintaining a high remanence.

[0115] This specific embodiment is only an interpretation of the present application and does not limit the present application. Those skilled in the art can make modifications to this embodiment without creative contributions according to needs after reading this specification, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A high intrinsic coercivity NdFeB magnetic material, characterized in that: The invention relates to a raw material comprising the following components in parts by weight: 52.5-57.2 parts of PrNd, 105-115.3 parts of Nd, 9.0-10.3 parts of B, 15-35 parts of Tb, 70-80 parts of Dy, 10-25 parts of Co, and 650-680 parts of Fe; the raw material further comprises a second additive, wherein the second additive is hafnium, and the amount of the second additive accounts for 0.1-0.4wt% of the total amount of the raw material; the raw material further comprises a third additive, wherein the third additive is methylvinylsilazane, and the amount of the third additive accounts for 1-1.5wt% of the total amount of the raw material; A method for preparing a high intrinsic coercivity NdFeB magnetic material comprises the following steps: S1, melt-spinning strip: PrNd, Nd, B, Tb, Dy, Co, and Fe are mixed according to the formula, and the mixture is melted to obtain a molten liquid, and the molten liquid is cast and spun to obtain a spun strip sheet; S2, hydrogen crushing and grinding: the strips are hydrogen crushed into coarse powder, and the coarse powder is jet milled to obtain alloy powder; S3, pressing and molding: placing the obtained alloy powder in a mold, and pressing and molding to obtain a sintered green body; S4, sintering process: sintering the green compact under the protection of nitrogen, cooling it to room temperature in stages after sintering, and tempering it to obtain NdFeB magnetic material; Comprising a first alloy and a second alloy, wherein the components of the first alloy are 26.25-28.60 parts of PrNd, 52.50-57.65 parts of Nd, 4.50-5.15 parts of B, 7.5-17.5 parts of Tb, 60-65 parts of Dy, 5-12.5 parts of Co, and 325-340 parts of Fe, and the components of the second alloy are 26.25-28.60 parts of PrNd, 52.50-57.65 parts of Nd, 4.50-5.15 parts of B, 7.5-17.5 parts of Tb, 10-15 parts of Dy, 5-12.5 parts of Co, and 325-340 parts of Fe; In S1, a first stripping sheet is manufactured according to the composition of a first alloy, and a second stripping sheet is manufactured according to the composition of a second alloy; In S2, the first belt-spinning pieces and the second belt-spinning pieces are hydrogen-crushed into coarse powder, and the coarse powder is jet-milled to form alloy powder.

2. A high intrinsic coercivity NdFeB magnetic material according to claim 1, characterized in that: The invention also includes a first additive, which is at least one of calcium and magnesium. The amount of the first additive is 0.1-0.4wt% of the total amount of the raw material.

3. A high intrinsic coercivity NdFeB magnetic material according to claim 2, characterized in that: In S1, the first additive or the second additive is mixed with PrNd, Nd, B, Tb, Dy, Co, and Fe and then melt-spinned.

4. The high intrinsic coercivity NdFeB magnetic material according to claim 1, characterized in that: In S3, the third additive is mixed with the alloy powder and then placed in a mold for compression molding.

Images