Preparation method of high-performance neodymium-iron-boron magnetic powder

Abstract

The application provides a preparation method of high-performance neodymium-iron-boron magnetic powder, comprising the following steps: A) uniformly heat treating neodymium-iron-boron rapid solidification alloy cast pieces; B) hydrogen breaking and airflow grinding the neodymium-iron-boron rapid solidification alloy cast pieces obtained in step A) to obtain neodymium-iron-boron magnetic powder; C) performing HDDR treatment on the neodymium-iron-boron magnetic powder to obtain HDDR magnetic powder; D) mixing the HDDR magnetic powder with high-melting-point alloy powder to obtain mixed magnetic powder; and E) performing at least one heat treatment on the mixed magnetic powder to obtain high-performance neodymium-iron-boron magnetic powder. The preparation method provided by the application can prepare neodymium-iron-boron magnetic powder with ideal coating structure that the rare earth-rich phase uniformly wraps the main phase crystal grains, and effectively improves the magnetic performance of the magnetic powder and the subsequently prepared magnet.

Description

Technical Field

[0001] This invention relates to the field of magnetic materials technology, and in particular to a method for preparing high-performance neodymium iron boron magnetic powder. Background Technology

[0002] The demand for energy-saving retrofits has driven the explosive application of rare-earth permanent magnet motors in new energy vehicles, wind power, rail transit, and industrial robots. Neodymium iron boron (NdFeB) rare-earth permanent magnet materials, due to their excellent comprehensive magnetic properties, have become an irreplaceable core functional material in rare-earth permanent magnet motors. Coercivity, as an indicator of a permanent magnet material's ability to resist external reverse magnetic fields or other demagnetizing effects, is crucial for its service stability. However, the actual coercivity value of NdFeB magnets currently falls significantly short of its theoretical value, making improving the coercivity of NdFeB magnets a key research focus and challenge in the industry.

[0003] Theoretical calculations show that the exchange coupling length between NdFeB magnet grains is approximately 2.1 nanometers. If the grain boundary phase is non-magnetic, exceeding this thickness isolates the grains, significantly increasing coercivity. However, magnets prepared using conventional processes often exhibit discontinuous grain boundary phase distribution or direct contact between adjacent main phase particles, resulting in strong exchange coupling between the main phases. This facilitates demagnetization, promotes the propagation of demagnetization domains, and ultimately leads to low coercivity. To optimize magnet microstructure and ultimately improve coercivity, researchers have attempted various methods, including grain refinement and grain boundary reconstruction (grain boundary diffusion, dual alloying), achieving some success. However, these methods have also presented challenges, such as issues with compact density distribution and oxidation caused by grain refinement, and reduced remanence due to grain boundary reconstruction.

[0004] Recently, the academic community has begun to explore optimizing the structure of magnetic powder from the powder preparation stage, aiming to prepare high-coercivity, high-performance magnets based on high-performance NdFeB magnetic powder. Industrially, the process of rapidly solidifying cast sheets (SC sheets) + hydrogen explosion (HD) + jet milling (JM) is currently used to prepare anisotropic sintering NdFeB magnetic powder. However, the NdFeB powder particles prepared by this method have little Nd-rich phase coating on their surface and are irregularly shaped. This results in poor grain shape and sharp edges in the magnets after liquid-phase sintering, a lack of continuous grain boundaries, and weak magnetic isolation effect of the grain boundary phase, severely restricting the improvement of magnet coercivity. The magnetic powder prepared by this method can no longer meet the requirements for the research and development of high-performance magnets.

[0005] Therefore, this paper proposes a method for preparing high-performance NdFeB magnetic powder. By optimizing the powder structure during the powder preparation process, NdFeB magnetic powder with regular morphology, small and uniform size, and uniform surface coating of Nd-rich phase can be prepared. This method is of great significance for improving the coercivity of NdFeB magnets and promoting the rapid development of the NdFeB industry and the rare earth permanent magnet field. Summary of the Invention

[0006] The technical problem solved by this invention is to provide a method for preparing high-performance neodymium iron boron magnetic powder. The neodymium iron boron magnetic powder prepared in this application has a regular morphology, small and uniform size, and a surface uniformly coated with rare earth-rich phase, thereby exhibiting high coercivity.

[0007] In view of this, this application provides a method for preparing high-performance neodymium iron boron magnetic powder, comprising the following steps:

[0008] A) The neodymium iron boron rapid solidification alloy casting sheet shown in formula (Ⅰ) is subjected to homogenization heat treatment;

[0009] B) The neodymium iron boron rapid solidification alloy casting obtained in step A) is subjected to hydrogen crushing and air jet milling to obtain neodymium iron boron magnetic powder;

[0010] C) The neodymium iron boron magnetic powder is subjected to HDDR treatment to obtain HDDR magnetic powder;

[0011] D) The HDDR magnetic powder is mixed with high melting point alloy powder to obtain mixed magnetic powder;

[0012] E) The mixed magnetic powder is subjected to at least one heat treatment to obtain high-performance neodymium iron boron magnetic powder;

[0013] RE a T 100-a-b-c B b M c (I);

[0014] RE is selected from one or more of Nd, Pr, La, Ce, Dy, and Tb;

[0015] T is selected from one or more of Fe, Co, and Ni;

[0016] M is selected from one or more of Ga, Nb, Zr, Cu, Al, V, Ti, Mo, Si, and Mn;

[0017] a, b, and c represent the weight percentages of RE, B, and M in the total population, respectively, and satisfy the following conditions: 29.0wt%≤a≤33.5wt%, 0.9wt%≤b≤1.1wt%, 0wt%≤c≤3.5wt%.

[0018] Preferably, the high melting point alloy powder is selected from one or more of Ti, Zr, V, Nb, Ta, Hf, W, Mo and Fe.

[0019] Preferably, the homogenization heat treatment is performed at a temperature of 800~1500℃, a heating rate of 5~15℃ / min, a time of 1~10h, and a vacuum degree of not less than 1×10⁻⁶. -2 Pa.

[0020] Preferably, the hydrogen crushing process specifically includes:

[0021] The neodymium iron boron rapid solidification alloy casting obtained in step A) is placed in hydrogen gas at 100~300kPa to absorb hydrogen for 0.5~5h. After the hydrogen absorption is completed, it is dehydrogenated at 200~500℃ for 1~12h.

[0022] Preferably, the particle size of the neodymium iron boron magnetic powder is 1~10μm.

[0023] Preferably, the HDDR processing procedure specifically includes:

[0024] Heating stage: The neodymium iron boron magnetic powder is placed in a hydrogen heat treatment furnace and heated to 600~1000℃ under vacuum;

[0025] Hydrogenation disproportionation stage: Introduce hydrogen gas at 10~80kPa into the hydrogen heat treatment furnace and maintain the temperature and pressure for 30~240min;

[0026] Slow dehydrogenation stage: Adjust the hydrogen pressure inside the furnace to 1~10 kPa, and continue to maintain the temperature and pressure for 30~100 min;

[0027] Recombination stage: Evacuate the furnace to a vacuum level of not less than 1×10⁻⁶. -2 Pa, keep warm for 20~60 minutes.

[0028] Preferably, the high melting point alloy powder is 1 to 10 wt% of the HDDR magnetic powder.

[0029] Preferably, the heat treatment is performed once, with a heating rate of 5-15°C / min, a temperature of 500-1000°C, and a vacuum degree of not less than 1×10⁻⁶. -2 Pa, time is 1~10h.

[0030] Preferably, the cooling method for the heat treatment is air quenching combined with air cooling.

[0031] Preferably, 30.0wt%≤a≤32.0wt%, 0.9wt%≤b≤1.1wt%, and 0.1wt%≤c≤1.0wt%.

[0032] This application provides a method for preparing high-performance NdFeB magnetic powder. First, a rapidly solidified NdFeB alloy casting is subjected to homogenization heat treatment. Then, the resulting alloy casting is subjected to hydrogen crushing and air jet milling to obtain NdFeB magnetic powder. Next, the obtained magnetic powder undergoes HDDR treatment. Finally, the anisotropic HDDR magnetic powder is mixed with high-melting-point alloy powder and heat-treated to obtain high-performance NdFeB magnetic powder. In this application, the air-jet milled magnetic powder undergoes HDDR treatment to allow the nanoscale grains to grow and extrude the rare-earth-rich phase around the particles, forming a compositional distribution where the rare-earth-rich phase uniformly coats the main phase grains. Then, the high-melting-point alloy is uniformly mixed with the HDDR magnetic powder to prevent the rare-earth-rich phase extruded around the particles from melting and causing the particles to stick together. The added high-melting-point alloy also inhibits grain growth during the subsequent magnetic powder sintering process, fully utilizing the advantages of fine grains to improve coercivity. The method for preparing high-performance magnetic powder provided by this invention can mass-produce highly anisotropic HDDR magnetic powder with consistent orientation. At the same time, it can optimize the composition distribution of the magnetic powder to improve its coercivity, avoid the use of heavy rare earth elements, and is simple and easy to operate, making it convenient for production applications. Attached Figure Description

[0033] Figure 1 This is a schematic diagram illustrating the principle of preparing high-performance neodymium iron boron magnetic powder according to the present invention. Detailed Implementation

[0034] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0035] To prepare high-performance NdFeB magnetic powder with consistent orientation and high coercivity, this application optimizes the powder structure during the powder preparation process, effectively improving the anisotropic orientation of the NdFeB magnetic powder and ultimately enhancing its coercivity. Specifically, this invention discloses a method for preparing high-performance NdFeB magnetic powder, including the following steps:

[0036] A) The neodymium iron boron rapid solidification alloy casting sheet shown in formula (Ⅰ) is subjected to homogenization heat treatment;

[0037] B) The neodymium iron boron rapid solidification alloy casting obtained in step A) is subjected to hydrogen crushing and air jet milling to obtain neodymium iron boron magnetic powder;

[0038] C) The neodymium iron boron magnetic powder is subjected to HDDR treatment to obtain anisotropic HDDR magnetic powder;

[0039] D) The anisotropic HDDR magnetic powder is mixed with high melting point alloy powder to obtain mixed magnetic powder;

[0040] E) The mixed magnetic powder is subjected to at least one heat treatment to obtain high-performance neodymium iron boron magnetic powder;

[0041] RE a T 100-a-b-c B b M c (I);

[0042] RE is selected from one or more of Nd, Pr, La, Ce, Dy, and Tb;

[0043] T is selected from one or more of Fe, Co, and Ni;

[0044] M is selected from one or more of Ga, Nb, Zr, Cu, Al, V, Ti, Mo, Si, and Mn;

[0045] a, b, and c represent the weight percentages of RE, B, and M in the total population, respectively, and satisfy the following conditions: 29.0wt%≤a≤33.5wt%, 0.9wt%≤b≤1.1wt%, 0wt%≤c≤3.5wt%.

[0046] The specific preparation process of the high-performance NdFeB magnetic powder in this application is as follows: Figure 1 As shown, specifically: NdFeB rapid solidification alloy sheets are homogenized by heat treatment to obtain coarsened columnar crystal alloy castings. Then, the alloy castings are broken by hydrogen crushing and air jet milling. After HDDR treatment, nanoscale grains are engulfed and grown. Finally, the refined grains are mixed with high melting point alloy powder and heat treated to prevent powder particles from sticking together and inhibit grain growth, which is conducive to obtaining high-performance NdFeB magnetic powder with consistent orientation.

[0047] Specifically, this application will first present RE as follows: a T 100-a-b-c B b M c The NdFeB rapid-solidification alloy casting shown undergoes homogenization heat treatment. The original grain size of the rapid-solidification alloy casting is small, and the broken HDDR magnetic powder particles contain many original grains with different orientations. The grains refined after direct HDDR processing and subsequent recombining inherit the texture orientation of the original grains, resulting in a chaotic grain texture orientation and low orientation consistency in the HDDR magnetic powder particles, leading to poor anisotropy in the final magnetic powder. Based on this, this application first performs homogenization heat treatment on the rapid-solidification alloy to increase the grain size of the original rapid-solidification alloy casting, reducing the number of original grains with different orientations in the broken HDDR magnetic powder particles, effectively improving the grain orientation consistency in the final HDDR magnetic powder particles. Simultaneously, it effectively avoids the polycrystalline orientation disorder that exists after heat treatment of the uniformly mixed HDDR magnetic powder in subsequent preparation processes, thus enabling the preparation of highly anisotropic magnetic powder with highly consistent grain orientation.

[0048] In this application, the chemical formula of the neodymium iron boron rapid-solidification alloy casting is RE. a T 100-a-b-c B b M c ;

[0049] RE is selected from one or more of Nd, Pr, La, Ce, Dy, and Tb;

[0050] T is selected from one or more of Fe, Co, and Ni;

[0051] M is selected from one or more of Ga, Nb, Zr, Cu, Al, V, Ti, Mo, Si, and Mn;

[0052] a, b, and c represent the weight percentages of RE, B, and M in the total population, respectively, and satisfy the following conditions: 29.0wt%≤a≤33.5wt%, 0.9wt%≤b≤1.1wt%, 0wt%≤c≤3.5wt%.

[0053] More specifically, 30.0wt%≤a≤32.0wt%, 0.9wt%≤b≤1.1wt%, and 0.1wt%≤c≤1.0wt%.

[0054] The NdFeB rapid solidification alloy castings described in this application are obtained by lamination in a rapid solidification furnace. In this application, the thickness of the NdFeB rapid solidification alloy castings is 200~300μm.

[0055] During the homogenization heat treatment process, the temperature is 800~1500℃, the heating rate is 5~15℃ / min, the time is 1~10h, and the vacuum degree is not less than 1×10⁻⁶. -2 Pa; more specifically, the homogenization heat treatment is performed at a temperature of 900~1200℃, a heating rate of 5~10℃ / min, and a time of 4~8h.

[0056] This application further processes the aforementioned NdFeB rapid solidification alloy castings with hydrogen breakage and air jet milling to obtain NdFeB magnetic powder. Hydrogen breakage (HD) causes the NdFeB alloy to absorb hydrogen and form hydrides, leading to alloy breakage. The rare earth-rich phase is hydrogenated first, causing intergranular fracture. Therefore, most HD powders are single crystals, and the powder particles are coated with a rare earth-rich phase. However, in the subsequent air jet milling process, the rare earth-rich phase on the outside of the main phase particles is easily detached. This is because the size of the powder after hydrogen breakage is larger than the target particle size (the target particle size is ~2.5μm). Ultimately, under continuous air jet milling, although the powder size meets the target, the ideal particle composition distribution after hydrogen breakage is also destroyed. Therefore, if the directly pressed blank is sintered and densified, the distribution of non-ferromagnetic grain boundaries is discontinuous, the grains are in direct contact, the magnetic isolation between grains is weakened, and the coercivity is low. Extensive research by the applicant indicates that only the intrusive growth of nanoscale grains formed after subsequent HDDR treatment can expel the rare-earth-rich phase around the particles, resulting in an ideal compositional distribution where the rare-earth-rich phase uniformly coats the main phase grains. Because the main phase grains are well coated with the rare-earth-rich phase, the demagnetizing coupling between the sintered main phase grains is effectively enhanced, greatly improving the coercivity of the magnet. The hydrogen breakup process described in this application specifically involves: placing a homogenized heat-treated NdFeB rapidly solidified alloy casting in 100-300 kPa hydrogen gas to absorb hydrogen for 0.5-5 hours, followed by dehydrogenation at 200-500°C for 1-12 hours; more specifically, placing the homogenized heat-treated NdFeB rapidly solidified alloy casting in 200-300 kPa hydrogen gas to absorb hydrogen for 1-5 hours, followed by dehydrogenation at 300-500°C for 5-10 hours. The magnetic powder after hydrogen crushing is then subjected to air jet milling until the powder particle size is 1~10μm, more specifically 1~5μm.

[0057] According to the present invention, the magnetic powder obtained above is then subjected to HDDR treatment to obtain anisotropic HDDR magnetic powder. This application uses HDDR treatment on the magnetic powder to cause the nanoscale grains within the particles to grow and merge, extruding the rare-earth-rich phase around the particles, forming an ideal compositional distribution where the rare-earth-rich phase uniformly coats the main phase grains. The specific process of the HDDR treatment is as follows:

[0058] The heating stage involves placing the neodymium iron boron magnetic powder in a hydrogen heat treatment furnace and heating it to 600-1000°C under vacuum.

[0059] The steps of the hydrogenation disproportionation stage are as follows: introduce hydrogen gas at 10~80kPa into the hydrogen heat treatment furnace and maintain the temperature and pressure for 30~240min;

[0060] Steps for the slow dehydrogenation stage: Adjust the hydrogen pressure inside the furnace to 1~10 kPa, and continue to maintain the temperature and pressure for 30~100 min;

[0061] The steps of the recombination stage are as follows: Evacuate the furnace to a vacuum level of not less than 1×10⁻⁶.-2 Pa, keep warm for 20~60 minutes.

[0062] This application then mixes the HDDR-treated magnetic powder with high-melting-point alloy powder to obtain mixed magnetic powder; HDDR treatment causes the rare-earth-rich phase of the magnetic powder to redistribute and easily leads to direct contact between the main phase grains, which is detrimental to coercivity; at the same time, when the heat treatment temperature reaches about 900℃, RE2Fe 14 B grain boundaries are in a molten state, making it easy for particles to stick together during magnetic powder heat treatment. This invention, by adding a high-melting-point alloy and uniformly mixing it with HDDR magnetic powder, prevents the rare-earth-rich phases squeezed around the particles from melting and sticking together. The added high-melting-point alloy also inhibits grain growth during subsequent magnetic powder sintering, fully utilizing the advantages of fine grains to improve coercivity. In this application, the high-melting-point alloy powder is specifically selected from one or more of Ti, Zr, V, Nb, Ta, Hf, W, Mo, and Fe, and its content is 1~10wt% of the HDDR magnetic powder. More specifically, the content of the high-melting-point alloy powder is 2~5wt% of the HDDR magnetic powder. Introducing too much high-melting-point alloy powder will reduce remanence.

[0063] This application concludes by subjecting the mixed magnetic powder to at least one heat treatment to obtain a high-performance neodymium iron boron magnet; this achieves the effect of high-melting-point alloy powder inhibiting the growth of magnetic powder grains, resulting in a fine-grained effect. In this application, the heat treatment is performed once, with a heating rate of 5~15℃ / min, a temperature of 500~1000℃, and a vacuum degree of not less than 1×10⁻⁶. -2 The heat treatment process takes 1 to 10 hours, and the cooling method is gas quenching followed by air cooling. More specifically, the heating rate is 8 to 12 °C / min, the temperature is 700 to 900 °C, and the vacuum degree is not less than 1 × 10⁻⁶. -2 Pa, time is 4~8h.

[0064] The method for preparing high-performance NdFeB magnetic powder provided by this invention can mass-produce highly anisotropic HDDR magnetic powder with consistent orientation. At the same time, it can optimize the composition distribution of the magnetic powder to improve the coercivity of the magnetic powder, avoid the use of heavy rare earth elements, and is simple and easy to operate, making it convenient for production and application.

[0065] To further understand the present invention, the preparation method of high-performance neodymium iron boron magnetic powder provided by the present invention will be described in detail below with reference to the embodiments. The scope of protection of the present invention is not limited by the following embodiments.

[0066] Example 1

[0067] Chemical formulas prepared by rapid solidification furnaces are classified into (PrNd) by mass percentage. 25.77 Ce 5.88 Al 0.15 Cu0.2 Ga 0.1 Co 0.2 Zr 0.2 Fe bal. B 0.88 The prepared rapid solidification alloy castings were placed in a vacuum heat treatment furnace and heated to 1080℃ at a heating rate of 10℃ / min. After holding at this temperature for 4 hours, the castings were quenched by air and cooled to room temperature. The castings were then placed in a hydrogen heat treatment furnace and 200 kPa hydrogen was introduced to absorb hydrogen for 4 hours. After dehydrogenation at 450℃ for 10 hours, the castings were then milled by air jet mill to obtain powder with a particle size of 1~3μm.

[0068] The powder was placed in a fully automated hydrogen heat treatment furnace for HDDR treatment: first, the temperature was raised to 800℃, and after introducing 50 kPa H2, the temperature and pressure were maintained for 4 hours. Then, the hydrogen gas was extracted to 5 kPa, and the temperature and pressure were maintained for another 90 minutes. Finally, a vacuum was drawn to 1×10⁻⁶. -2 After holding the powder at a pressure below Pa for 40 minutes, it was quenched by air and cooled to room temperature to obtain HDDR powder. Hf was added at 2% of the weight of HDDR powder and mixed evenly. The powder was then placed in a vacuum heat treatment furnace and heated to 700℃ at a heating rate of 10℃ / min. After holding at this temperature for 3 hours, it was quenched by air and cooled to obtain heat-treated HDDR magnetic powder.

[0069] After mixing magnetic powder with epoxy resin, PPMS testing showed that the magnetic powder had Br = 13.6 kGs, Hcj = 12.6 kOe, and DOA = 0.625 (DOA = (Br) (∥) -Br (⊥) ) / Br (∥) The larger the DOA value, the stronger the anisotropy of the magnetic powder, the better the orientation of the magnetic powder, and the higher the remanence.

[0070] To compare the advantages of this invention, magnetic powder obtained by conventional hydrogen-broken gas milling and HDDR treatment of rapidly solidified alloy castings was used as Comparative Example 1. The magnetic powders prepared in Example 1 and Comparative Example 1 were tested, and the performance data of Example 1 and Comparative Example 1 are compared in the table below:

[0071] Table 1. Performance data of NdFeB magnetic powder prepared by different methods

[0072]

[0073] The comparison shows that the magnetic properties and orientation of the embodiment are significantly higher than those of the comparative example. The present invention has obvious advantages, and can prepare an ideal coating structure to improve the performance of magnetic powder while enhancing anisotropy.

[0074] Example 2

[0075] Chemical formulas prepared by rapid solidification furnaces are classified into (NdPr) by mass percentage. 31 Cu0.2 Al 0.1 Zr 0.2 Co 0.5 Ga 0.1 Fe bal . B 0.9 The prepared rapid solidification alloy castings were placed in a vacuum heat treatment furnace and heated to 1100℃ at a heating rate of 10℃ / min. After holding at this temperature for 4 hours, the castings were quenched by air and cooled to room temperature. The castings were then placed in a hydrogen heat treatment furnace and 200 kPa hydrogen was introduced to absorb hydrogen for 4 hours. After dehydrogenation at 450℃ for 10 hours, the castings were then milled by air jet mill to obtain powder with a particle size of 1~3 μm.

[0076] The powder was placed in a fully automated hydrogen heat treatment furnace for HDDR treatment: first, the temperature was raised to 840℃, and after introducing hydrogen gas at 50 kPa, the temperature and pressure were maintained for 4 hours. Then, the hydrogen gas was removed, the pressure was reduced to 3 kPa, and the temperature and pressure were maintained for another 90 minutes. Finally, a vacuum was drawn to 1×10⁻⁶. -2 After holding the powder at a pressure below Pa for 40 min, it was quenched by air and cooled to room temperature to obtain HDDR powder. Nb was added at 2% of the weight of HDDR powder and mixed evenly. The powder was then placed in a vacuum heat treatment furnace and heated to 750℃ at a heating rate of 10℃ / min. After holding at this temperature for 4 h, it was quenched by air and cooled to obtain heat-treated HDDR magnetic powder.

[0077] After mixing magnetic powder with epoxy resin, PPMS testing showed that the magnetic powder had Br = 14.3 kGs, Hc = 14.6 kOe, and DOA = 0.723 (DOA = (Br) (∥) -Br (⊥) ) / Br (∥) The larger the DOA value, the stronger the anisotropy of the magnetic powder, the better the orientation of the magnetic powder, and the higher the remanence.

[0078] To compare the advantages of the present invention, magnetic powder obtained by conventional hydrogen-broken gas milling and HDDR treatment of rapidly solidified alloy castings was used as Comparative Example 2. The magnetic powders prepared in Example 2 and Comparative Example 2 were tested, and the performance data of Example 2 and Comparative Example 2 are compared as follows:

[0079] Table 2. Performance data of NdFeB magnetic powder prepared by different methods

[0080]

[0081] The comparison shows that the magnetic properties and orientation of the embodiment are significantly higher than those of the comparative example. The present invention has obvious advantages, and can prepare an ideal coating structure to improve the performance of magnetic powder while enhancing anisotropy.

[0082] Example 3

[0083] Nd chemical formula, determined by mass percentage, was prepared using a rapid solidification furnace. 26 Dy 4.1 B 1.1 Co 1.0 Fe bal. The prepared rapid solidification alloy castings were placed in a vacuum heat treatment furnace and heated to 1080℃ at a heating rate of 10℃ / min. After 5 hours, the castings were quenched by air and cooled to room temperature. The castings were then placed in a hydrogen heat treatment furnace and 200 kPa hydrogen was introduced to absorb hydrogen for 4 hours. After dehydrogenation at 450℃ for 10 hours, the castings were milled by air jet mill to obtain powder with a particle size of 1~3 μm.

[0084] The powder was placed in a fully automated hydrogen heat treatment furnace for HDDR treatment: first, the temperature was raised to 840℃, hydrogen gas was introduced at 50 kPa, and the temperature and pressure were maintained for 4 hours. Then, the hydrogen gas was removed, the pressure was reduced to 3 kPa, and the temperature and pressure were maintained for another 90 minutes. Finally, a vacuum was drawn to 1 x 10⁻⁶. -2 After holding the powder at a pressure below 45 min, it was quenched in air and cooled to room temperature to obtain HDDR powder. Zr was added at 2% of the weight of the HDDR powder and mixed evenly. The powder was then placed in a vacuum heat treatment furnace and heated to 800℃ at a heating rate of 10℃ / min. After holding at 800℃ for 4 h, it was quenched in air and cooled to obtain heat-treated HDDR magnetic powder.

[0085] After mixing magnetic powder with epoxy resin, PPMS testing showed that the magnetic powder had Br = 13.2 kGs, Hcj = 16.2 kOe, and DOA = 0.654 (DOA = (Br) (∥) -Br (⊥) ) / Br (∥) The larger the DOA value, the stronger the anisotropy of the magnetic powder, the better the orientation of the magnetic powder, and the higher the remanence.

[0086] To compare the advantages of the present invention, magnetic powder obtained by conventional hydrogen-broken gas milling and HDDR treatment of rapidly solidified alloy castings was used as Comparative Example 3. The magnetic powders prepared in Example 3 and Comparative Example 3 were tested, and the performance data of Example 3 and Comparative Example 3 are compared as follows:

[0087] Table 3. Performance data of NdFeB magnetic powder prepared by different methods

[0088]

[0089] The comparison shows that the magnetic properties and orientation of the embodiment are significantly higher than those of the comparative example. The present invention has obvious advantages, and can prepare an ideal coating structure to improve the performance of magnetic powder while enhancing anisotropy.

[0090] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0091] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing high-performance neodymium iron boron magnetic powder, comprising the following steps: A) The neodymium iron boron rapid solidification alloy casting sheet shown in formula (Ⅰ) is subjected to homogenization heat treatment; B) The neodymium iron boron rapid solidification alloy casting obtained in step A) is subjected to hydrogen crushing and air jet milling to obtain neodymium iron boron magnetic powder; C) The neodymium iron boron magnetic powder is subjected to HDDR treatment to make the nanoscale grains in the particles grow together and squeeze the rare earth-rich phase to the surrounding of the particles, forming an ideal compositional distribution in which the rare earth-rich phase uniformly coats the main phase grains, and thus obtaining HDDR magnetic powder. The specific process of HDDR processing is as follows: Heating stage: The neodymium iron boron magnetic powder is placed in a hydrogen heat treatment furnace and heated to 800~840℃ under vacuum; Hydrogenation disproportionation stage: Introduce hydrogen gas at 10~80kPa into the hydrogen heat treatment furnace and maintain the temperature and pressure for 30~240min; Slow dehydrogenation stage: Adjust the hydrogen pressure inside the furnace to 1~10 kPa, and continue to maintain the temperature and pressure for 30~100 min; Recombination stage: Evacuate the furnace to a vacuum level of not less than 1×10⁻⁶. -2 Pa, keep warm for 20~60 minutes; D) The HDDR magnetic powder is mixed with a high-melting-point metal powder to obtain a mixed magnetic powder; the content of the high-melting-point metal powder is 2-5 wt% of the HDDR magnetic powder. E) The mixed magnetic powder is subjected to at least one heat treatment to obtain high-performance NdFeB magnetic powder; the heat treatment is performed once, the heating rate is 5~15℃ / min, the temperature is 500~1000℃, and the vacuum degree is not less than 1×10⁻⁶. -2 Pa, time is 1~10h; RE a T 100-a-b- B b (Ⅰ); RE is selected from one or more of Nd, Pr, La, Ce, Dy, and Tb; T is selected from one or more of Fe, Co, and Ni; a and b represent the weight percentages of RE and B in the total population, respectively, and satisfy the following conditions: 29.0wt%≤a≤33.5wt%, 0.9wt%≤b≤1.1wt%; The high-melting-point metal powder is selected from Zr, Nb, or Hf.

2. The preparation method according to claim 1, characterized in that, The homogenization heat treatment is performed at a temperature of 800~1500℃, a heating rate of 5~15℃ / min, a time of 1~10h, and a vacuum degree of not less than 1×10⁻⁶. -2 Pa.

3. The preparation method according to claim 1, characterized in that, The hydrogen crushing process is specifically as follows: The neodymium iron boron rapid solidification alloy casting obtained in step A) is placed in hydrogen gas at 100~300kPa to absorb hydrogen for 0.5~5h. After the hydrogen absorption is completed, it is dehydrogenated at 200~500℃ for 1~12h.

4. The preparation method according to claim 1, characterized in that, The particle size of the neodymium iron boron magnetic powder is 1~10μm.

5. The preparation method according to claim 1, characterized in that, The cooling method for the heat treatment is air quenching combined with air cooling.

6. The preparation method according to claim 1, characterized in that, 30.0wt%≤a≤32.0wt%, 0.9wt%≤b≤1.1wt%.

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