A method for producing a sintered neodymium-iron-boron permanent magnet

Abstract

The application discloses a preparation method of sintered Nd-Fe-B permanent magnet, comprising the following steps: S1: alloy preparation; S2: hydrogen decrepitation treatment; S3: powder preparation: airflow milling, mechanical fusion powder regulation, powder mixing and organic additive introduction; S4: compression forming; S5: sintering treatment; S6: surface treatment, the application introduces mechanical fusion and powder mixing regulation steps after airflow milling, changes the randomness of the intermediate state of the powder into a stable and repeatable structure state, provides a reliable starting point for the grain boundary engineering; based on the regulated intermediate structure of the powder, compression and sintering are carried out, which is beneficial to forming a continuous and uniform grain boundary structure in the sintering process, and realizes more rigorous grain boundary engineering; on the basis of the grain boundary structure, the permeation treatment is implemented, the permeation path is clearer, the permeation effect is more stable, and the consistency of the magnet performance is improved.

Description

Technical Field

[0001] This invention relates to the technical field of rare earth permanent magnet material preparation, and in particular to the technical field of a method for preparing sintered NdFeB permanent magnets. Background Technology

[0002] High-performance neodymium iron boron permanent magnets typically rely on heavy rare earth elements such as Dy / Tb to enhance coercivity. However, these elements are limited in resources and expensive, and their direct addition significantly reduces remanence. Therefore, how to maintain excellent magnetic properties while reducing the amount of heavy rare earth elements has become a core issue that the industry urgently needs to address.

[0003] Chinese patent application CN201110242847.7 discloses a method for preparing high-performance sintered NdFeB with low dysprosium content. This method introduces Dy element onto the surface of air-jet milled powder particles via sputtering deposition, achieving grain boundary introduction and suppressing Dy content. The method forms a nanoscale coating layer on the powder surface through physical vapor deposition, effectively reducing the amount of dysprosium used. However, this method still has shortcomings. It simply attaches the diffused element to the powder surface and does not solve the fundamental problem of uncontrollable morphology of air-jet milled powder. Since air-jet milled powder particles are often angular and irregular in shape, and the powder system usually contains a certain proportion of ultrafine powder byproducts, the discreteness of the powder state directly affects the slippage, rearrangement, and densification behavior between particles during subsequent molding, further affecting the formation mode and spatial distribution characteristics of grain boundary phases. Differences in the intermediate structural state between different batches of powder will ultimately be amplified into fluctuations in the grain boundary structure and magnetic properties of the magnet, making it difficult to guarantee the consistent performance of this method.

[0004] Chinese patent application CN202011171110.6 discloses a method for preparing sintered NdFeB materials. This method involves pre-orientation treatment during air jet milling to ensure high orientation during the orientation pressing process, guaranteeing increased coercivity without decreasing remanence. This method improves the orientation consistency of the powder to some extent by introducing orientation control during the milling process. However, this method still has shortcomings. It fails to effectively correct morphological defects in the powder particles and does not regulate the distribution of the NdFeB-rich phase in the powder. It cannot solve subsequent problems such as uneven liquid phase wetting and poor grain boundary continuity caused by irregular morphology and uneven particle size distribution of the air jet milled powder. Because the intermediate structure of the powder is not controlled, the liquid phase wetting path is difficult to stably control during sintering, and the formation of grain boundary structures still has considerable randomness.

[0005] In existing technologies, the formation of grain boundary structures largely depends on the natural evolution during sintering or on post-sintering infiltration and diffusion processes. However, since multiple pre-processes in magnet manufacturing have a cumulative impact on grain boundary formation, it is often difficult to obtain a stable and repeatable grain boundary structure by controlling the grain boundaries only during the sintering or post-processing stages. Therefore, it is necessary to study a method for preparing NdFeB magnets that systematically controls the formation of grain boundary structures at the powder stage from the perspective of the entire manufacturing process, in order to solve the batch performance fluctuation problem caused by the randomness of powder morphology and provide a stable and controllable starting point for subsequent sintering and infiltration processes. Summary of the Invention

[0006] The purpose of this invention is to solve the problems in the prior art and to propose a method for preparing sintered NdFeB permanent magnets, which can achieve controllable powder morphology, continuous and stable grain boundary structure, and significantly improve the penetration effect and magnetic performance consistency.

[0007] To achieve the above objectives, this invention proposes a method for preparing sintered NdFeB permanent magnets, comprising the following steps: S1: Alloy preparation; S2: Hydrogen-crushed treatment; S3: Powder preparation: air jet milling, mechanical fusion powder control, powder mixing and introduction of organic additives; S4: Compression forming; S5: Sintering treatment; S6: Surface treatment.

[0008] Preferably, the alloy preparation in step S1 includes: preparing NdFeB alloy material by spun lapping, wherein the NdFeB alloy material has a brittle intergranular fracture microstructure, wherein the grain boundaries are enriched with low-melting-point rare earth phases, and the volume fraction and morphology of the grain boundary phase are set such that: in the subsequent crushing process, cracks extend along the grain boundaries and expose fresh grain interfaces, and the grain interfaces directly constitute the grain boundary liquid phase diffusion channels in the further heat treatment process.

[0009] Preferably, step S3, air jet milling, includes: performing air jet milling on the hydrogen-treated NdFeB alloy material to obtain micron-sized NdFeB alloy material powder; during the air jet milling process, some ultrafine powder by-products are also generated, and the ultrafine powder by-products are enriched with NdFeB-rich phase components.

[0010] Preferably, the mechanical fusion powder control in step S3 includes: between the air jet milling and pressing steps, mixing the micron-sized NdFeB alloy powder obtained by air jet milling with ultrafine powder by-products; applying high shear force and controlled friction force to the air jet milled mixed powder under inert atmosphere conditions, so that controlled contact and interaction occur between powder particles. The conditions for applying high shear force and controlled friction force are set as follows: modifying the surface of powder particles to reduce sharp corners and irregular structures, so that the powder morphology tends to be uniform; causing the NdFeB-rich phase to plastically spread and form a coating or semi-coating structure on the surface of the main phase particles; and controlling the intermediate structural state of the powder, so that it changes from a random state after air jet milling to a controllable state that is conducive to subsequent molding and grain boundary structure formation.

[0011] Preferably, the powder mixing and organic additive introduction in step S3 includes: between the mechanical fusion treatment and the compression molding step, mixing the powder after mechanical fusion treatment, and introducing a small amount of organic additive during the mixing process; the organic additive is used to improve the flowability, molding stability and the synergistic rearrangement behavior between particles during the compression molding process, and the standard for the amount of organic additive added is: it does not affect the control effect of the intermediate structure of the powder obtained by mechanical fusion treatment, and can be removed in the subsequent compression molding and sintering process.

[0012] Preferably, the sintering process in step S5 includes: sintering the pressed structure. During the sintering process, the neodymium-rich phase coated on the powder surface wets and migrates, promoting the formation and continuous distribution of grain boundary phases. This is used to form a grain boundary structure with expected continuity and spatial distribution characteristics inside the magnet. The grain boundary phases are arranged in a hexagonal honeycomb pattern in space. A single grain boundary phase surrounds a main phase grain to form a hexagonal outline, and adjacent hexagons share the grain boundary edge.

[0013] Preferably, the method further includes step S7: infiltration treatment, which includes: performing infiltration treatment on the basis of the grain boundary structure to allow the infiltrated components to enter the interior of the magnet along the grain boundary structure, thereby improving the magnetic properties, mechanical reliability and stability of the magnet; the infiltration treatment includes at least one of solid phase infiltration, liquid phase infiltration, gas phase infiltration or physical deposition followed by diffusion infiltration.

[0014] The beneficial effects of this invention are as follows: By introducing mechanical fusion and powder mixing control steps after air jet milling, this invention transforms the randomness of the intermediate state of powder into a stable and repeatable structural state, providing a reliable starting point for grain boundary engineering. Based on the controlled intermediate powder structure, pressing and sintering facilitate the formation of a continuous and uniform grain boundary structure during sintering, achieving more rigorous grain boundary engineering. Infiltration treatment is then performed on the basis of this grain boundary structure, resulting in a clearer infiltration path, more stable infiltration effect, and improved magnet performance consistency. The method has a clear process path, strong compatibility with existing powder metallurgy processes, and is suitable for large-scale manufacturing. Due to the more controllable grain boundary structure, the magnet has potential improvements in mechanical reliability, thermal stability, and long-term service stability. After sintering, the magnet's microstructure exhibits a near-ideal hexagonal honeycomb structure, with controllable grain boundary thickness, and the batch fluctuation of coercivity after infiltration can be reduced to within 3%.

[0015] The features and advantages of the present invention will be described in detail through embodiments and in conjunction with the accompanying drawings. Attached Figure Description

[0016] Figure 1 This is a flowchart of a method for preparing a sintered NdFeB permanent magnet according to the present invention; Figure 2 This is a mechanical fusion powder control diagram of a method for preparing sintered NdFeB permanent magnets according to the present invention; Figure 3 This is a diagram of the plastic spreading structure of the neodymium-rich phase after mechanical fusion powder control in the preparation method of sintered neodymium iron boron permanent magnets according to the present invention. Figure 4 This is a diagram of the internal grain boundary structure of the magnet after sintering treatment, according to the preparation method of the sintered NdFeB permanent magnet of the present invention. Detailed Implementation

[0017] Example 1 See Figure 1 , Figure 2 and Figure 3 The present invention discloses a method for preparing sintered NdFeB permanent magnets, comprising the following steps: S1: Alloy preparation; S2: Hydrogen-crushed treatment; S3: Powder preparation: air jet milling, mechanical fusion powder control, powder mixing and introduction of organic additives; S4: Compression forming; S5: Sintering treatment; S6: Surface treatment; The alloy preparation in step S1 includes: preparing NdFeB alloy material by lapping, wherein the NdFeB alloy material has a brittle intergranular fracture microstructure, wherein the grain boundaries are enriched with low-melting-point rare earth phases, and the volume fraction and morphology of the grain boundary phase are set such that, in the subsequent pulverization process, cracks propagate along the grain boundaries and expose fresh grain interfaces, which directly constitute the grain boundary liquid phase diffusion channels in the further heat treatment process. The air jet milling in step S3 includes: processing the hydrogen-crushed NdFeB alloy material. Neodymium iron boron alloy material is subjected to air jet milling to obtain micron-sized neodymium iron boron alloy material powder. During the air jet milling process, some ultrafine powder byproducts are simultaneously generated. These ultrafine powder byproducts are enriched with neodymium-rich phase components. Step S3, mechanical fusion powder control, includes: between the air jet milling and molding steps, mixing the micron-sized neodymium iron boron alloy material powder obtained from air jet milling with the ultrafine powder byproducts; and applying high shear force and controlled friction force to the air jet milled mixed powder under an inert atmosphere to precipitate the powder… Controlled contact and interaction occur between the particles. The conditions for applying high shear force and controlled friction are set as follows: the surface of the powder particles is modified to reduce sharp corners and irregular structures, making the powder morphology more uniform; the neodymium-rich phase undergoes plastic spreading and forms a coating or semi-coating structure on the surface of the main phase particles; the intermediate structure of the powder is regulated, transforming it from a random state after air jet milling to a controllable state that is conducive to subsequent molding and grain boundary structure formation. The powder mixing and organic additive introduction in step S3 include: between the mechanical fusion treatment and the pressing step, the powder after mechanical fusion treatment is mixed, and a small amount of organic additive is introduced during the mixing process; the organic additive is used to improve the flowability, molding stability and the synergistic rearrangement behavior between particles during the pressing process. The standard for the amount of organic additive added is: it does not affect the regulation effect of the intermediate structure of the powder obtained by mechanical fusion treatment, and it can be removed in the subsequent pressing and sintering process.

[0018] Example 2 See Figure 1 , Figure 2 , Figure 3 and Figure 4 The present invention discloses a method for preparing sintered NdFeB permanent magnets, comprising the following steps: S1: Alloy preparation; S2: Hydrogen-crushed treatment; S3: Powder preparation: air jet milling, mechanical fusion powder control, powder mixing and introduction of organic additives; S4: Compression forming; S5: Sintering treatment; S6: Surface treatment; The alloy preparation in step S1 includes: preparing NdFeB alloy material by spun ladle method. The NdFeB alloy material has a brittle intergranular fracture microstructure, wherein low-melting-point rare earth phases are enriched at the grain boundaries. The volume fraction and morphology of the grain boundary phase are set such that, in subsequent pulverization, cracks propagate along the grain boundaries and expose fresh grain interfaces. These grain interfaces directly constitute the grain boundary liquid phase diffusion channels in the further heat treatment process. The air jet milling in step S3 includes: performing air jet milling on the hydrogen-crushed NdFeB alloy material to obtain micron-sized NdFeB alloy material powder; the air jet milling process simultaneously produces... The process generates a portion of ultrafine powder byproducts, which are enriched with NdFeB-rich components. Step S3, involving mechanical fusion and powder control, includes: between the air-jet milling and pressing steps, mixing the micron-sized NdFeB alloy powder obtained from air-jet milling with the ultrafine powder byproducts; applying high shear force and controlled friction to the air-jet milled mixture under an inert atmosphere to induce controlled contact and interaction between powder particles. The conditions for applying high shear force and controlled friction are set as follows: modifying the surface of the powder particles to reduce sharp corners and irregular structures, making the powder morphology more uniform; and ensuring that the powder particles... The neodymium-rich phase undergoes plastic spreading and forms a coated or semi-coated structure on the surface of the main phase particles; the intermediate structural state of the powder is regulated, transforming it from a random state after air jet milling into a controllable state that is conducive to subsequent molding and grain boundary structure formation. Step S3, powder mixing and the introduction of organic additives, includes: between the mechanical fusion treatment and the molding step, mixing the powder after mechanical fusion treatment, and introducing a small amount of organic additives during the mixing process; the organic additives are used to improve the flowability, molding stability, and synergistic rearrangement behavior between particles during molding. The standard for the amount of additive is: it should not affect the control effect of the intermediate structure of the powder obtained by mechanical fusion treatment, and it should be removed in the subsequent pressing and sintering process. The sintering treatment in step S5 includes: sintering the pressed structure. During the sintering process, the neodymium-rich phase coated on the powder surface wets and migrates, promoting the formation and continuous distribution of the grain boundary phase, which is used to form a grain boundary structure with expected continuity and spatial distribution characteristics inside the magnet. The grain boundary phase is arranged in a hexagonal honeycomb pattern in space. A single grain boundary phase surrounds a main phase grain to form a hexagonal outline, and adjacent hexagons share the grain boundary edge.

[0019] Example 3 See Figure 1 , Figure 2 and Figure 4 The present invention discloses a method for preparing sintered NdFeB permanent magnets, comprising the following steps: S1: Alloy preparation; S2: Hydrogen-crushed treatment; S3: Powder preparation: air jet milling, mechanical fusion powder control, powder mixing and introduction of organic additives; S4: Compression forming; S5: Sintering treatment; S6: Surface treatment; S7: Infiltration treatment; The alloy preparation in step S1 includes: preparing NdFeB alloy material by spun ladle method. The NdFeB alloy material has a brittle intergranular fracture microstructure, wherein the grain boundaries are enriched with low-melting-point rare earth phases. The volume fraction and morphology of the grain boundary phase are set such that, in subsequent pulverization, cracks propagate along the grain boundaries and expose fresh grain interfaces. These grain interfaces directly constitute the grain boundary liquid phase diffusion channels in the further heat treatment process. The air jet milling in step S3 includes: performing air jet milling on the hydrogen-crushed NdFeB alloy material to obtain micron-sized NdFeB alloy material powder. During the air jet milling process, some ultrafine powder by-products are generated simultaneously. The ultrafine powder by-products are enriched with NdFeB-rich phase components. The powder mixing and organic additive introduction in step S3 includes: between the mechanical fusion treatment and the molding step, performing powder mixing treatment on the powder after mechanical fusion treatment, and introducing a small amount of organic additives during the powder mixing process. The organic additives are used to improve the flowability, molding stability and molding process of the powder. The cooperative rearrangement behavior between particles, the standard for the amount of organic additive added is: it does not affect the regulation effect of the intermediate structure of the powder obtained by mechanical fusion treatment, and can be removed in the subsequent pressing and sintering process. The sintering treatment in step S5 includes: sintering the pressed structure. During the sintering process, the neodymium-rich phase coated on the powder surface wets and migrates, promoting the formation and continuous distribution of the grain boundary phase, which is used to form a grain boundary structure with expected continuity and spatial distribution characteristics inside the magnet. The grain boundary phase is arranged in a hexagonal honeycomb pattern in space. A single grain boundary phase surrounds a main phase grain to form a hexagonal outline, and adjacent hexagons share the grain boundary edge. The infiltration treatment in step S7 includes: performing infiltration treatment on the basis of the grain boundary structure, so that the infiltrated component enters the interior of the magnet along the grain boundary structure, which is used to improve the magnetic properties, mechanical reliability and stability of the magnet. The infiltration treatment includes at least one of the following treatment methods: solid phase infiltration, liquid phase infiltration, gas phase infiltration or diffusion infiltration after physical deposition.

[0020] This invention transforms the randomness of the intermediate state of powder into a stable and repeatable structural state by introducing mechanical fusion and powder mixing control steps after air jet milling, providing a reliable starting point for grain boundary engineering. Based on the controlled intermediate powder structure, pressing and sintering facilitate the formation of a continuous and uniform grain boundary structure during sintering, achieving more rigorous grain boundary engineering. Infiltration treatment is then performed on the basis of this grain boundary structure, resulting in a clearer infiltration path, more stable infiltration effect, and improved magnet performance consistency. The method has a clear process path, strong compatibility with existing powder metallurgy processes, and is suitable for large-scale manufacturing. Due to the more controllable grain boundary structure, the magnet has potential improvements in mechanical reliability, thermal stability, and long-term service stability. After sintering, the magnet's microstructure exhibits a near-ideal hexagonal honeycomb structure, with controllable grain boundary thickness, and batch fluctuations in coercivity after infiltration can be reduced to within 3%.

[0021] The above embodiments are illustrative of the present invention and are not intended to limit the present invention. Any simple modifications to the present invention are within the scope of protection of the present invention.

Claims

1. A method for preparing a sintered NdFeB permanent magnet, characterized in that: Includes the following steps: S1: Alloy preparation; S2: Hydrogen-crushed treatment; S3: Powder preparation: air jet milling, mechanical fusion powder control, powder mixing and introduction of organic additives; S4: Compression forming; S5: Sintering treatment; S6: Surface treatment.

2. The method for preparing a sintered NdFeB permanent magnet as described in claim 1, characterized in that: The alloy preparation in step S1 includes: preparing NdFeB alloy material by spun lamination. The NdFeB alloy material has a brittle intergranular fracture microstructure, wherein low-melting-point rare earth phases are enriched at the grain boundaries. The volume fraction and morphology of the grain boundary phase are set such that, in the subsequent crushing process, cracks extend along the grain boundaries and expose fresh grain interfaces. The grain interfaces directly constitute the grain boundary liquid phase diffusion channels in the further heat treatment process.

3. The method for preparing a sintered NdFeB permanent magnet as described in claim 1, characterized in that: The air jet milling process in step S3 includes: performing air jet milling on the hydrogen-treated NdFeB alloy material to obtain micron-sized NdFeB alloy material powder; during the air jet milling process, some ultrafine powder by-products are generated, and the ultrafine powder by-products are enriched with NdFeB-rich phase components.

4. The method for preparing a sintered NdFeB permanent magnet as described in claim 1, characterized in that: The mechanical fusion powder control in step S3 includes: between the air jet milling and pressing steps, mixing the micron-sized NdFeB alloy powder obtained by air jet milling with ultrafine powder by-products; applying high shear force and controlled friction force to the air jet milled mixed powder under inert atmosphere conditions, so that controlled contact and interaction occur between powder particles. The conditions for applying high shear force and controlled friction force are set as follows: modifying the surface of powder particles to reduce sharp corners and irregular structures, so that the powder morphology tends to be uniform; causing the NdFeB-rich phase to plastically spread and form a coating or semi-coating structure on the surface of the main phase particles; and controlling the intermediate structural state of the powder, so that it changes from a random state after air jet milling to a controllable state that is conducive to subsequent molding and grain boundary structure formation.

5. The method for preparing a sintered NdFeB permanent magnet as described in claim 1, characterized in that: The powder mixing and organic additive introduction in step S3 includes: between the mechanical fusion treatment and the compression molding step, the powder after mechanical fusion treatment is mixed, and a small amount of organic additive is introduced during the mixing process; the organic additive is used to improve the flowability, molding stability and the synergistic rearrangement behavior between particles during the compression molding process, and the standard for the amount of organic additive added is: it does not affect the control effect of the intermediate structure of the powder obtained by mechanical fusion treatment, and can be removed in the subsequent compression molding and sintering process.

6. The method for preparing a sintered NdFeB permanent magnet as described in claim 1, characterized in that: The sintering process in step S5 includes: sintering the pressed structure. During the sintering process, the neodymium-rich phase coated on the powder surface wets and migrates, promoting the formation and continuous distribution of grain boundary phases. This is used to form a grain boundary structure with expected continuity and spatial distribution characteristics inside the magnet. The grain boundary phases are arranged in a hexagonal honeycomb pattern in space. A single grain boundary phase surrounds a main phase grain to form a hexagonal outline, and adjacent hexagons share the grain boundary edge.

7. The method for preparing a sintered NdFeB permanent magnet as described in claim 1, characterized in that: It also includes step S7: infiltration treatment, which includes: performing infiltration treatment on the basis of the grain boundary structure to allow the infiltrated components to enter the interior of the magnet along the grain boundary structure, so as to improve the magnetic properties, mechanical reliability and stability of the magnet; the infiltration treatment includes at least one of solid phase infiltration, liquid phase infiltration, gas phase infiltration or physical deposition followed by diffusion infiltration.

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