High-performance neodymium iron boron thick magnet and preparation method thereof
High-performance NdFeB thick magnets were prepared by grain boundary diffusion treatment and crushing and powdering methods, which solved the problems of limited grain boundary diffusion depth and poor mechanical properties in the existing technology. It achieved a balance between high coercivity and high mechanical strength, and is suitable for high-end fields such as new energy vehicles and medium and large wind turbines.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- EARTH PANDA ADVANCE MAGNETIC MATERIAL
- Filing Date
- 2026-03-13
- Publication Date
- 2026-04-24
AI Technical Summary
Existing technologies struggle to fabricate high-performance NdFeB thick magnets, especially to overcome the grain boundary diffusion depth limitation without reducing remanence, achieving a balance between high coercivity and high mechanical strength. Furthermore, traditional processes suffer from high energy consumption, high cost, or poor mechanical properties.
Thin magnets with core-shell structures are formed by grain boundary diffusion treatment. After crushing and powdering, they are oriented and sintered under pressure to prepare high-performance NdFeB thick magnets. Combined with specific heat treatment and heavy rare earth diffusion sources, the amount of heavy rare earth is reduced and the magnet performance is uniform.
A neodymium iron boron thick magnet with high coercivity and high mechanical properties has been developed, which is suitable for high-end fields such as new energy vehicles and medium and large wind turbines. It solves the problems of limited penetration depth of heavy rare earth and poor mechanical properties in traditional processes, and has broad prospects for industrial application.
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Figure CN121922450A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of rare earth permanent magnets, specifically to a high-performance neodymium iron boron thick magnet and its preparation method. Background Technology
[0002] Neodymium iron boron (Nd-Fe-B) permanent magnets, renowned for their superior magnetic energy product and coercivity, are considered the "king of magnets" and are core functional materials for modern high-end, precision equipment. With the deepening implementation of the "dual-carbon" strategy, the demand for Nd-Fe-B magnets is surging in fields such as new energy vehicle drive motors, medium and large-sized wind turbines, nuclear magnetic resonance imaging equipment, and heavy-duty industrial motors. These applications generally require magnets with a significant physical thickness (typically ≥5 mm) to meet the demands for strong magnetic field output, high load tolerance, and structural stability.
[0003] However, the preparation of high-performance NdFeB thick magnets has always faced technical bottlenecks, which seriously restricts their large-scale application in high-end fields. (1) Grain boundary diffusion technology, as a key means to reduce the amount of heavy rare earth elements and improve the coercivity of NdFeB, can only penetrate from the surface of the magnet to the shallow interior. The diffusion depth is limited. For magnets with a thickness of more than 5 mm, it is difficult to form a complete core-shell structure in the core area. In order to pursue the diffusion depth, the heat treatment time is extended, which will lead to a surge in energy consumption and cause abnormal growth of surface grains. (2) In order to avoid the problem of insufficient grain boundary diffusion depth, the overall alloying method is used to prepare thick magnets, that is, a large amount of heavy rare earth elements are directly added to the initial formula of the magnet. However, this method not only greatly increases the cost, but also significantly reduces the remanence and energy product of the magnet. (3) Another process uses the bonding magnet method to prepare thick magnets. The magnets are bonded together with glue or alloy. Although the thickness can be flexibly controlled, the mechanical properties of the magnet bonding joint are weak and easy to break.
[0004] Therefore, developing a method for preparing thick NdFeB magnets that can overcome the limitations of grain boundary diffusion thickness while taking into account high coercivity, high mechanical strength and process economy has become a technical problem that urgently needs to be solved in the field of rare earth permanent magnet materials. Summary of the Invention
[0005] In view of this, the present invention provides a high-performance neodymium iron boron thick magnet and its preparation method to solve the problems mentioned in the background art, and significantly improve the coercivity of the thick magnet without reducing the remanence, so as to meet the requirements of strong magnetic field, high mechanical stability and large load conditions.
[0006] To achieve the above objectives, the present invention provides the following technical solution:
[0007] In a first aspect, the present invention provides a method for preparing a high-performance neodymium iron boron thick magnet, comprising the following steps: (1) Select a matrix material, wherein the sum of the coercivity and the maximum energy product of the matrix material is ≥58; (2) The matrix material is processed into a thin magnet, and the thin magnet is subjected to grain boundary diffusion and heat treatment using a heavy rare earth diffusion source to obtain a neodymium iron boron magnet with a core-shell structure in the main phase grains; (3) The thin magnet after grain boundary diffusion treatment is crushed and powdered to prepare magnetic powder with the main phase grains retaining a complete core-shell structure; (4) The magnetic powder is oriented, pressure sintered and tempered to obtain a thick magnet.
[0008] As a further aspect of the present invention: the coercivity of the neodymium iron boron matrix material in step (1) is ≥12 kGs and the maximum magnetic energy product is ≥46 MGOe.
[0009] As a further aspect of the present invention: the thickness of the thin magnet in step (2) is ≤5 mm; the heavy rare earth diffusion source is selected from at least one of metal Tb, metal Dy, DyHx, TbHx, DyF3 and TbF3, or a binary or multi-element alloy formed by at least one of Dy and Tb with one or more of iron, aluminum, copper and gallium.
[0010] As a further aspect of the present invention: the grain boundary diffusion process in step (2) is selected from any one of screen printing, vapor deposition, sputtering, and electrophoretic deposition; the heat treatment includes a primary heat treatment and a secondary heat treatment, wherein the temperature of the primary heat treatment is 800~1000 ℃ and the time is 3~15 h; and the temperature of the secondary heat treatment is 450~600 ℃ and the time is 3~6 h.
[0011] As a further aspect of the present invention: the heavy rare earth content in the core of the core-shell structure is less than the heavy rare earth content in the shell, and the heavy rare earth content in the core is ≤1 at.%, while the heavy rare earth content in the shell is 2~10 at.%.
[0012] As a further aspect of the present invention: the magnetic powder in step (3) is obtained by air jet milling process; the particle size of the magnetic powder is 2~10 μm, and the breakage rate of the core-shell structure of the main phase grain in the magnetic powder is ≤5%.
[0013] As a further aspect of the present invention: the orientation forming process in step (4) includes: oriented forming of the magnetic powder under a magnetic field strength of 1.5~2.5 T, and then isostatic pressing under a pressure of 150~200 MPa.
[0014] As a further aspect of the present invention: the pressure sintering in step (4) is selected from one of hot pressing sintering, spark plasma sintering or hot isostatic pressing sintering, and is carried out under vacuum or protective atmosphere, with a sintering temperature of 800~1000 ℃, a pressure of 20~400 MPa, and a holding time of 5 min~3 h; wherein, when the thickness of the thick magnet is ≤15 mm, the pressure sintering is selected from any one of hot pressing sintering, spark plasma sintering or hot isostatic pressing sintering, and when the thickness of the high-performance thick magnet is >15 mm, the pressure sintering is selected from any one of hot pressing sintering or hot isostatic pressing sintering; the protective atmosphere is selected from rare gas or nitrogen; the tempering treatment is carried out under vacuum or protective atmosphere, including two-stage tempering treatment, the temperature of the first stage tempering treatment is 800~900 ℃, and the time is 2~3 h; the temperature of the second stage tempering treatment is 480~600 ℃, and the time is 2~3 h.
[0015] As a further aspect of the present invention: the thickness of the high-performance thick magnet is ≥ 10mm.
[0016] Secondly, the present invention discloses a high-performance neodymium iron boron thick magnet, wherein the sum of the coercivity and the maximum magnetic energy product of the thick magnet is ≥65, and it is prepared by the preparation method described above.
[0017] The high-performance neodymium iron boron thick magnet has the characteristics of low remanence loss rate, high coercivity, uniformity of overall performance without thickness limitation, and good mechanical properties. It can be used in scenarios requiring strong magnetic fields, high mechanical stability and large load conditions, such as new energy vehicles, industrial motors or medical equipment.
[0018] Compared with the prior art, the beneficial technical effects of the present invention are: (1) This invention involves crushing and pulverizing a thin magnet with a core-shell structure formed by grain boundary diffusion treatment, followed by orientation molding and pressure sintering to obtain a thick NdFeB magnet. This method ensures that the core-shell structured main phase grains are uniformly distributed throughout the magnet, with no significant coercivity gradient. It overcomes the thickness limitation of grain boundary diffusion and allows for the flexible fabrication of magnets with a thickness of 10 mm or more according to actual needs. This fundamentally solves the technical bottleneck of limited penetration depth of heavy rare earth atoms and large differences in magnetic properties between the core and surface of thick magnets in traditional surface grain boundary diffusion technology. Compared with the overall alloying process that adds a large amount of heavy rare earth elements to the raw materials, this invention significantly reduces the amount of heavy rare earth elements used, and increases the coercivity of the magnet by more than 7 kOe compared to the untreated magnet without reducing remanence.
[0019] (2) The NdFeB thick magnet of the present invention has high mechanical properties and is suitable for complex working conditions. Compared with traditional bonded magnets, it significantly improves bending strength and has better mechanical properties, avoiding magnet breakage. At the same time, the pressure sintering is low-temperature controllable, which limits the thermodynamic factors of heavy rare earth atom diffusion and avoids the destruction of the core-shell structure of the main phase grains due to excessively high vacuum sintering temperature. This solves the dilemma of "magnetic properties and mechanical properties cannot be obtained simultaneously" in the preparation of existing thick magnets. It is widely applicable to high-end fields such as new energy vehicle drive motors and medium and large wind turbines, and has broad prospects for industrial application. Attached Figure Description
[0020] Figure 1 The scanning electron microscope image of the high-performance neodymium iron boron thick magnet prepared in Example 1 of the present invention shows the core-shell structure morphology of the main phase grains.
[0021] Figure 2 The line scan analysis results of the high-performance neodymium iron boron thick magnet prepared in Example 1 of the present invention are shown. The scanning path extends from the grain core, through the shell, and to another grain core. The line scan curve reflects the difference in the content of heavy rare earth elements between the core and the shell. Detailed Implementation
[0022] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
[0023] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.
[0024] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.
[0025] In this invention, the "damage rate" of the core-shell structure of the main phase grains in the magnetic powder refers to the proportion of grains whose core-shell structure is damaged during the crushing and powdering process. The detection method is as follows: Take an appropriate amount of magnetic powder sample, disperse it and observe it under a scanning electron microscope using backscattered electron imaging mode; randomly select 10 different locations, with no less than 50 main phase grains at each location, and count the number of grains with obvious shell damage, missing or incomplete shells. Calculate the damage rate using the following formula: Damage rate (%) = (Number of shell-damaged grains / Total number of grains counted) × 100%.
[0026] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
[0027] Example 1 This embodiment provides a method for preparing a high-performance neodymium iron boron thick magnet, specifically including the following steps: (1) Grain boundary diffusion treatment: N52 neodymium iron boron with a coercivity and maximum energy product of 64.20 was selected as the matrix material and processed into a thin magnet with a thickness of 1 mm. The thin magnet was acid-etched in a 2% nitric acid solution for 3 min, then ultrasonically cleaned in ethanol and dried at room temperature to obtain the magnet substrate for grain boundary diffusion.
[0028] Metal Tb was deposited on the surface of the magnet substrate using magnetron sputtering. The working gas pressure was 0.8 Pa, the gas flow rate was 16 sccm, and the Tb target (purity greater than 99.9%) was sputtered for 1.5 h with a sputtering power of 120 W, resulting in a coating thickness of 3.13 μm.
[0029] The coated magnet is then subjected to heat treatment, which includes a primary heat treatment and a secondary heat treatment: the primary heat treatment temperature is 900℃, and the holding time is 3 h; the secondary heat treatment temperature is 480℃, and the holding time is 3 h. After the above heat treatment, a thin magnet with a core-shell structure of main phase grains is obtained.
[0030] (2) Preparation of thick magnets: The thin magnets after grain boundary diffusion treatment were subjected to hydrogen crushing and air jet milling in sequence: the hydrogen crushing process was: hydrogen absorption at 300℃ for 2h, and dehydrogenation at 500℃ for 3h; the air jet milling process was: rotation speed of 3800rpm, to obtain NdFeB magnetic powder with an average particle size (SMD) of 3.12 μm. The damage rate of the core-shell structure of the main phase grains in the magnetic powder was tested to be 4.33%. The obtained magnetic powder was oriented and pressed into shape under a magnetic field strength of 2T, and then subjected to isostatic pressing at 150 MPa to obtain a green blank. The green blank was placed in a hot pressing sintering furnace and sintered under a protective atmosphere of 99.99% pure argon gas at a sintering temperature of 950℃, a pressure of 40 MPa, and a holding time of 0.5h. After sintering, tempering treatment was performed, and the tempering process was: primary tempering at 900℃ for 2h, and secondary tempering at 480℃ for 2h. After sintering and tempering, the magnets were processed to obtain a 15 mm thick neodymium iron boron magnet with a coercivity and a maximum energy product of 71.29.
[0031] Compositional analysis of the core and shell of the main phase grains was performed using energy dispersive spectroscopy (EDS), and the results are as follows: Figure 2 The line scan curve is shown. The path of this line scan is... Figure 1The white arrow points from the grain core, through the shell, and extends to the core of another grain. The results show that the heavy rare earth element (HREE) content in the core is approximately 0.82 at.%, while the HREE content in the shell is approximately 2.85 at.%, with the core content being significantly lower than the shell content.
[0032] Example 2 This embodiment provides a method for preparing a high-performance neodymium iron boron thick magnet. The preparation steps are the same as in Example 1, except that the final neodymium iron boron thick magnet has a thickness of 30 mm and a coercivity and maximum energy product of 71.28.
[0033] Example 3 This embodiment provides a method for preparing a high-performance neodymium iron boron thick magnet, specifically including the following steps: (1) Grain boundary diffusion treatment: N52 neodymium iron boron matrix material with a coercivity and maximum energy product of 64.20 was selected and processed into a thin magnet with a thickness of 3 mm. The thin magnet was acid etched in a 2% nitric acid solution for 3 min, and then ultrasonically cleaned in ethanol and dried at room temperature to obtain the magnet substrate for grain boundary diffusion.
[0034] Tb is plated onto the surface of the magnet using a screen printing process. 95 An Al5 diffusion source was applied to the surface of the magnet and dried at 100 °C for 20 min. After coating, the magnet was 1.2 wt.% heavier than the substrate.
[0035] The coated magnet is then subjected to heat treatment, which includes a first-stage heat treatment and a second-stage heat treatment. The first-stage heat treatment is carried out at a temperature of 900 ℃ and a holding time of 9 h. The second-stage heat treatment is carried out at a temperature of 480 ℃ and a holding time of 3 h, resulting in a thin magnet with a core-shell structure in the main phase grains.
[0036] (2) Preparation of thick magnets: The thin magnets after grain boundary diffusion treatment were subjected to hydrogen crushing and air jet milling in sequence: the hydrogen crushing process was: hydrogen absorption at 300℃ for 2h, and dehydrogenation at 500℃ for 3h; the air jet milling process was: the classifier wheel speed was 3200rpm, and NdFeB magnetic powder with an average particle size (SMD) of 3.66 μm was obtained. The damage rate of the core-shell structure of the main phase grains in the magnetic powder was detected to be 4.02%. The obtained magnetic powder was oriented and pressed into shape under a magnetic field strength of 2T, and then subjected to isostatic pressing at 150 MPa to obtain a green blank. The green blank was loaded into a hot pressing sintering furnace and sintered under a protective atmosphere of 99.99% argon gas. The sintering temperature was 950 ℃, the pressure was 40 MPa, and the holding time was 0.5 h. After sintering, tempering treatment was performed. The tempering process was: primary tempering at 900 ℃ for 2h, and secondary tempering at 480 ℃ for 2h. The sintered and tempered magnets were processed to obtain a 15 mm thick NdFeB magnet with a coercivity and a maximum energy product of 70.70.
[0037] Energy dispersive spectroscopy (EDS) was used to analyze the composition of the core and shell of the main phase grains. The results showed that the heavy rare earth content in the core was about 0.78 at.% and the heavy rare earth content in the shell was about 7.88 at.%, with the content in the core being significantly lower than that in the shell.
[0038] Example 4 This embodiment provides a method for preparing a neodymium iron boron thick magnet. The preparation steps are the same as in Example 3, except that the final neodymium iron boron thick magnet has a thickness of 40 mm and a coercivity and maximum energy product of 70.21.
[0039] Example 5 This embodiment provides a method for preparing a neodymium iron boron thick magnet, specifically including the following steps: (1) Grain boundary diffusion treatment: N52 neodymium iron boron matrix material with a coercivity and maximum magnetic energy product of 64.20 was selected and processed into a thin magnet with a thickness of 5 mm. The thin magnet was acid etched in a 2% nitric acid solution for 3 min, and then ultrasonically cleaned in ethanol and dried at room temperature to obtain the magnet substrate for grain boundary diffusion.
[0040] Tb is plated onto the surface of the magnet using a screen printing process. 95 An Al5 diffusion source was applied to the surface of the magnet and dried at 100 °C for 20 min. After coating, the magnet was 1.21 wt.% heavier than the substrate.
[0041] The coated magnet is then subjected to heat treatment, which includes a first-stage heat treatment and a second-stage heat treatment. The first-stage heat treatment is carried out at a temperature of 900°C for 15 hours, and the second-stage heat treatment is carried out at a temperature of 480°C for 3 hours, resulting in a thin magnet with a core-shell structure in the main phase grains.
[0042] (2) Preparation of thick magnets: The thin magnets after grain boundary diffusion treatment were subjected to hydrogen crushing and air jet milling in sequence. The hydrogen crushing process was: hydrogen absorption at 300℃ for 2h, and dehydrogenation at 500℃ for 3h. The air jet milling process was: the classifier wheel speed was 3500rpm, and NdFeB magnetic powder with an average particle size (SMD) of 3.36 μm was obtained. The damage rate of the core-shell structure of the main phase grains in the magnetic powder was detected to be 3.98%. The obtained magnetic powder was oriented and pressed into shape under a magnetic field strength of 2T, and then subjected to isostatic pressing at 150 MPa to obtain a green blank. The green blank was loaded into a hot pressing sintering furnace and sintered under a protective atmosphere of 99.99% pure argon gas at a sintering temperature of 950℃, a pressure of 40 MPa, and a holding time of 0.5h. After sintering, tempering treatment was performed. The tempering process was: primary tempering at 900℃ for 2h, and secondary tempering at 480℃ for 2h. The sintered and tempered magnets were processed to obtain a 15 mm thick NdFeB magnet with a coercivity and a maximum energy product of 69.89.
[0043] Energy dispersive spectroscopy (EDS) was used to analyze the composition of the core and shell of the main phase grains. The results showed that the heavy rare earth content in the core was about 0.91 at.% and the heavy rare earth content in the shell was about 9.16 at.%, with the content in the core being significantly lower than that in the shell.
[0044] Comparative Example 1 This comparative example provides a method for preparing a neodymium iron boron magnet, which specifically includes the following steps.
[0045] N52 magnet blanks with a thickness of 15 mm and a maximum coercivity and energy product of 64.20 were selected and acid-etched in a 2% nitric acid solution for 3 min. After acid etching, the blanks were ultrasonically cleaned in ethanol and dried at room temperature to obtain magnet substrates for grain boundary diffusion.
[0046] Tb is plated onto the surface of the magnet using a screen printing process. 95 An Al5 diffusion source was applied to the surface of the magnet and dried at 100 °C for 20 min. After coating, the magnet was 1.2 wt.% heavier than the substrate.
[0047] The coated magnet was then subjected to heat treatment, which included a primary heat treatment and a secondary heat treatment: the primary heat treatment temperature was 900℃, and the holding time was 30 h; the secondary heat treatment temperature was 480℃, and the holding time was 3 h. After the above heat treatment, a 15 mm thick magnet with diffusion treatment was obtained, and the sum of its coercivity and maximum energy product was 64.88.
[0048] Comparative Example 2 This comparative example provides a method for preparing a neodymium iron boron magnet, which specifically includes the following steps.
[0049] (1) Grain boundary diffusion treatment: N52 neodymium iron boron with a coercivity and maximum energy product of 64.20 was selected as the matrix material and processed into a thin magnet with a thickness of 3 mm. The thin magnet was acid-etched in a 2% nitric acid solution for 3 min, then ultrasonically cleaned in ethanol and dried at room temperature to obtain the magnet substrate for grain boundary diffusion.
[0050] Tb is plated onto the surface of the magnet using a screen printing process. 95 An Al5 diffusion source was applied to the surface of the magnet and dried at 100 °C for 20 min. After coating, the magnet was 1.21 wt.% heavier than the substrate.
[0051] The coated magnet was then subjected to heat treatment, which included a primary heat treatment and a secondary heat treatment: the primary heat treatment temperature was 900℃, and the holding time was 9 h; the secondary heat treatment temperature was 480℃, and the holding time was 3 h. After the above heat treatment, a thin magnet with a core-shell structure of the main phase grains was obtained.
[0052] (2) Preparation of thick magnets: The thin magnets after grain boundary diffusion treatment were subjected to hydrogen crushing and air jet milling in sequence. The parameters of hydrogen crushing and air jet milling were the same as in Example 3. Neodymium iron boron magnetic powder with an average particle size (SMD) of 3.66 μm was obtained. The damage rate of the core-shell structure of the main phase grains in the magnetic powder was 4.02%.
[0053] The obtained magnetic powder was oriented and pressed into shape under a magnetic field strength of 2 T, and then subjected to isostatic pressing at 150 MPa to obtain a green blank. The green blank was placed in a vacuum sintering furnace and sintered at 1050℃ for 5 h, followed by heat treatment. The heat treatment included a primary heat treatment and a secondary heat treatment: the primary heat treatment temperature was 900℃, and the holding time was 3 h; the secondary heat treatment temperature was 480℃, and the holding time was 3 h. The sintered and tempered magnet was processed to obtain a neodymium iron boron magnet with a thickness of 15 mm, whose coercivity and maximum energy product summed to 64.13.
[0054] Comparative Example 3 This comparative example provides a method for preparing a neodymium iron boron magnet, specifically including the following steps: (1) Grain boundary diffusion treatment: N52 neodymium iron boron with a coercivity and maximum energy product of 64.20 was selected as the matrix material and processed into a thin magnet with a thickness of 3 mm. The thin magnet was acid-etched in a 2% nitric acid solution for 3 min, then ultrasonically cleaned in ethanol and dried at room temperature to obtain the magnet substrate for grain boundary diffusion.
[0055] Tb is plated onto the surface of the magnet using a screen printing process. 95 An Al5 diffusion source was applied to the surface of the magnet and dried at 100 °C for 20 min. After coating, the magnet was 1.2 wt.% heavier than the substrate.
[0056] The coated magnet was then subjected to heat treatment, which included a primary heat treatment and a secondary heat treatment: the primary heat treatment temperature was 900℃, and the holding time was 9 h; the secondary heat treatment temperature was 480℃, and the holding time was 3 h. After the above heat treatment, a thin magnet with a core-shell structure of the main phase grains was obtained.
[0057] (2) Preparation of thick magnets: Five thin magnets after grain boundary diffusion treatment were taken and glued together to obtain a thick magnet with a thickness of 15 mm. The sum of its coercivity and maximum energy product is 67.29.
[0058] Comparative Example 4 This comparative example provides a method for preparing a neodymium iron boron magnet, specifically including the following steps: N52 neodymium iron boron (NdFeB), with a coercivity and maximum energy product sum of 64.20, was selected as the matrix material and processed into a thin magnet with a thickness of 3 mm, serving as the basic stacked unit. Tb was then uniformly laid on the surface of the thin magnet. 95 Al5 alloy powder was used, with the powder layer thickness controlled to be uniform and consistent, ranging from 50 to 100 μm, ensuring no localized accumulation or voids of alloy powder on the magnet surface. Subsequently, a 3 mm thick N52 thin magnet was stacked on top of this alloy powder layer, ensuring tight adhesion between the substrate material and the alloy powder layer. This powder-stacking process was repeated until a total of 5 layers were stacked, constructing a layered magnet blank assembly with a total thickness of 15 mm. Tb was sandwiched between each layer. 95 Al5 alloy powder was used as the diffusion source layer. The above-mentioned stacked magnet blank assembly was subjected to pressure heat treatment at 60 MPa, with a first-stage heat treatment temperature of 900℃ and a holding time of 9 h; and a second-stage heat treatment temperature of 480℃ and a holding time of 3 h, to reduce the Tb at the interfaces of each magnet layer. 95 Al5 alloy powder undergoes interfacial alloying with the matrix material to ultimately prepare an integrated magnet with a thickness of 15 mm, whose coercivity and maximum energy product sum to 69.83.
[0059] Performance testing The magnetic properties of the magnets in Examples 1-5 and Comparative Examples 1-4 were tested according to the requirements of GB / T3217-2013 Permanent Magnet (Hard Magnet) Materials - Magnetic Test Methods, and the results are listed in Table 1. Simultaneously, the bending strength of the magnets in Examples 1-5 and Comparative Examples 1-4 was tested according to the requirements of GB / T 31967.2-2015 Physical Properties Test Methods for Rare Earth Permanent Magnet Materials Part 2: Determination of Bending Strength and Fracture Toughness, and the results are listed in Table 1.
[0060] A comparison of the data in Table 1 reveals that the technology of this invention can significantly improve the performance of thick magnets: the remanence retention of the thick magnets obtained in Examples 1-5 is all 95% or higher, with a large increase in coercivity and high bending strength; the sum of the coercivity and maximum energy product of the thick magnets is ≥65. Comparative Examples 1 and 2 have lower coercivity, and while the magnets in Comparative Examples 3 and 4, compared to Examples 1-5, have a bending strength lower than those in Examples 1-5, even though the sum of the coercivity and maximum energy product of magnets of the same thickness is ≥65, their mechanical properties are poor. The technical solutions of Examples 1-5 were used to prepare neodymium iron boron materials with high coercivity and high mechanical properties, and their performance is not limited by thickness.
[0061] Table 1 Performance test results of the magnet Remanence Br (kGs) Remanence retention rate (%) Coercivity (kOe) Maximum magnetic energy product (MGOe) Flexural strength (MPa) N52 NdFeB matrix material 14.45 / 13.60 50.60 362 Example 1 14.31 99.03 23.17 48.12 321 Example 2 14.28 98.82 23.02 48.26 318 Example 3 14.12 97.30 22.67 48.03 322 Example 4 14.11 96.96 22.88 47.33 328 Example 5 14.08 97.44 22.06 47.83 312 Comparative Example 1 14.16 97.92 17.72 47.16 343 Comparative Example 2 13.84 95.78 18.11 46.02 315 Comparative Example 3 13.62 94.26 22.85 44.44 59 Comparative Example 4 13.54 93.70 23.55 46.28 118 The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0062] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention, and no reference numerals in the claims should be construed as limiting the scope of the claims.
[0063] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.
Claims
1. A method for preparing a high-performance neodymium iron boron thick magnet, characterized in that, Includes the following steps: (1) Select a matrix material, wherein the sum of the coercivity and the maximum energy product of the matrix material is ≥58; (2) The matrix material is processed into a thin magnet, and the thin magnet is subjected to grain boundary diffusion and heat treatment using a heavy rare earth diffusion source to obtain a neodymium iron boron magnet with a core-shell structure in the main phase grains; (3) The thin magnet after grain boundary diffusion treatment is crushed and powdered to prepare magnetic powder with the main phase grains retaining a complete core-shell structure; (4) The magnetic powder is oriented, pressure sintered and tempered to obtain a thick magnet.
2. The method for preparing high-performance NdFeB thick magnets according to claim 1, characterized in that, The coercivity of the matrix material described in step (1) is ≥12 kGs and the maximum magnetic energy product is ≥46 MGOe.
3. The method for preparing high-performance NdFeB thick magnets according to claim 1, characterized in that, The thickness of the thin magnet in step (2) is ≤5 mm; the heavy rare earth diffusion source is selected from metal Tb, metal Dy, and DyH. x TbH x At least one of DyF3 and TbF3, or a binary or multi-element alloy formed by selecting at least one of Dy and Tb with one or more of iron, aluminum, copper, and gallium.
4. The method for preparing high-performance NdFeB thick magnets according to claim 1, characterized in that, The grain boundary diffusion process in step (2) is selected from any one of screen printing, vapor deposition, sputtering, and electrophoretic deposition. The heat treatment includes a primary heat treatment and a secondary heat treatment. The temperature of the primary heat treatment is 800~1000 ℃ and the time is 3~15 h. The temperature of the secondary heat treatment is 450~600 ℃ and the time is 3~6 h.
5. The method for preparing high-performance NdFeB thick magnets according to claim 1, characterized in that, The heavy rare earth content in the core of the core-shell structure is less than that in the shell, and the heavy rare earth content in the core is ≤1 at.%, while the heavy rare earth content in the shell is 2~10 at.%.
6. The method for preparing high-performance NdFeB thick magnets according to claim 1, characterized in that, The magnetic powder in step (3) is obtained by air jet milling; the particle size of the magnetic powder is 2~10 μm, and the breakage rate of the core-shell structure of the main phase grains in the magnetic powder is ≤5%.
7. The method for preparing high-performance NdFeB thick magnets according to claim 1, characterized in that, The orientation forming process in step (4) includes: oriented forming of the magnetic powder under a magnetic field strength of 1.5~2.5 T, and then isostatic pressing under a pressure of 150~200 MPa.
8. The method for preparing high-performance NdFeB thick magnets according to claim 1, characterized in that, The pressure sintering in step (4) is selected from one of hot pressing sintering, spark plasma sintering, or hot isostatic pressing sintering, and is carried out under vacuum or a protective atmosphere. The sintering temperature is 800~1000 ℃, the pressure is 20~400 MPa, and the holding time is 5 min~3 h. When the thickness of the thick magnet is ≤15 mm, the pressure sintering is selected from any one of hot pressing sintering, spark plasma sintering, or hot isostatic pressing sintering. When the thickness of the thick magnet is >15 mm, the pressure sintering is selected from any one of hot pressing sintering or hot isostatic pressing sintering. The protective atmosphere is selected from rare gas or nitrogen. The tempering treatment is carried out under vacuum or a protective atmosphere and includes two-stage tempering treatment. The temperature of the first stage tempering treatment is 800~900 ℃ and the time is 2~3 h. The temperature of the second stage tempering treatment is 480~600 ℃ and the time is 2~3 h.
9. The method for preparing a high-performance NdFeB thick magnet according to claim 1, characterized in that, The thickness of the thick magnet is ≥ 10 mm.
10. A high-performance neodymium iron boron thick magnet, characterized in that, The thick magnet is prepared by any one of claims 1 to 9, and the sum of its coercivity and maximum magnetic energy product is ≥65.