Method for preparing high-performance double-main-phase sintered mixed rare earth iron boron magnet through two-step diffusion method

Abstract

The invention discloses a method for preparing a high-performance double-main-phase sintered mixed rare earth iron boron magnet through a two-step diffusion method, and belongs to the technical fieldof rare earth magnetic material preparation. Components of two main-phase alloys are RE-Fe-B (RE is Nd or Pr) and (Nd, MM)-Fe-B respectively, MM being mixed rare earth. The method is characterized inthat, to begin with, with a PrHoFe alloy quick-setting sheet serving as a diffusion source, the surfaces of (Nd, MM)-Fe-B hydrogen decrepitation powder particles are uniformly coated with a layer PrHo-rich compound, thereby improving the coercive force by utilizing higher anisotropic fields of Pr2Fe14B and Ho2Fe14B; and then, with a ZrCu alloy quick-setting sheet serving as the diffusion source, the surfaces of the powder particles subjected to the first-step diffusion are evenly coated with a Zr-rich layer to prevent growth of MM-containing main phase grains and suppress mutual diffusion withthe other main phase in the two main phases in the sintering process, thereby obtaining high coercive force.

Description

Technical field: [0001] The invention provides a method for preparing a high-performance dual main phase sintered mixed rare earth iron boron magnet by a two-step diffusion method, which belongs to the technical field of rare earth magnetic material preparation. Background technique: [0002] As the third-generation rare earth permanent magnet material that has attracted much attention, sintered NdFeB magnets have been widely used in electronics, electrical machinery, aerospace, transportation and other fields due to their excellent comprehensive magnetic properties. One of the important basic functional materials. However, as the demand for sintered NdFeB magnets continues to increase, a large amount of rare earth elements Pr, Nd, Dy, Tb, etc. are consumed, which also leads to an increase in their prices. Therefore, the use of highly abundant rare earths, especially unseparated mixed rare earths, to prepare magnets is of great significance for realizing cost control, environmen...

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Problems solved by technology

However, during the diffusion process, the diffusion depth of heavy rare earth elements or low-melting point alloys in the bulk magnet matrix is ​​limited, which makes the grain boundary diffusion technology have certain defects.

Therefore, it is better to introduce diffusion elements on the surface of powder particles by a certain technology to realize the diffusion of elements formed by the diffusion source on the surface of the powder, which is more effective in improving the coercive force. The current reports are mainly on the diffusion of heavy rare earth elements such as Dy and Tb in jet milled powder. , including thermal resistance evaporation deposition method (such as patent 201710624106.2), magnetron sputtering method (such as patent 201110242847.7) and rotary evaporation diffusion method (such as patent 201710852677.1), but these methods all diffuse the jet mill powder, because the jet mill powder Fine particles can easily lead to severe oxidation of the powder and affect the performance of the magnet. At the same time, the cost of diffusing heavy rare earth elements such as Dy and Tb is too high. The thermal resistance evaporation deposition method and the magnetron sputtering method require high equipment and are not easy to control the cost and realize industrialization. ; and for the rotary evaporation diffusion method, because the distance between the diffusion source and the diffused airflow mill powder is relatively long, and the agglomeration of the airflow mill powder is more serious when heated, it will lead to poor diffusion effect and limited performance for improving the final magnet.

[0004] In order to prepare high-performance mixed rare earth iron boron magnets, we use the double alloy method to prepare magnets, but for the (MM, Nd)-Fe-B main phase with a high amount of mixed rare earth substitution, due to the high content of mixed rare earths. Its performance is poor, especially because the magnetic crystal anisotropy field is significantly reduced after MM is replaced, resulting in low coercive force, and the grains are easier to grow during the sintering process. Severe interdiffusion occurs during sintering and heat treatment leading to severe deterioration of magnet properties

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