Unveiling the homogenization microstructure evolution and its effect on cellular structure for Fe-rich Sm-Co-Fe-Cu-Zr magnets

The solution-treated Fe-rich 2:17-type Sm-Co-based magnets generally contain an inhomogeneous microstructure, which hinders the development of the complete cellular structure required for high-performance magnets. Here, the microstructure evolution of Sm(CobalFe0.31Cu0.07Zr0.025)7.7 magnet during the solution treatment is systematically investigated. Unlike the normal Fe-medium magnets, it was interestingly found that the initial-stage solution-treated Sm(CobalFe0.31Cu0.07Zr0.025)7.7 magnet possesses a profuse lamellar-type microstructure. Within the lamellar-type microstructure, there are three microregions exhibiting an obvious difference in composition and 2:17R ordering degree. Further, various 1:3R phases precipitated within the lamellar-type microstructure. With the disappearance of lamellar-type microstructure, the 1:7H phase increased substantially, and the distribution of defect-aggregated cell boundaries became uniform, promoting the homogeneous precipitation of 1:5H cell boundary phases during aging. The current study reveals a typical microstructural evolution in Fe-rich 2:17-type Sm-Co-based magnets during solution treatment.