The evolution of phase constitution and microstructure in iron-rich 2:17-type Sm-Co magnets with high magnetic performance

Iron-rich 2:17-type Sm-Co magnets are important for their potential to achieve high coercivity and maximum magnetic energy product. But the evolution of phase structure, which determines magnetic properties, remains an unsolved issue. In this study, the phase constitution and microstructure of solution-treated 2:17-type Sm-Co alloys are studied. The increase of Fe content promotes the ordering transformation from the 1:7H phase to partially ordered 2:17R and lamellar Zr-rich 1:3R phase. This ordering transformation is mainly due to the competitive atoms occupation of Zr, Fe and Sm in the 1:7H phase. To ease this competition, we modify Sm content in iron-rich 2:17-type Sm-Co magnets. Different solution precursors and corresponding cellular structures are observed. Solution precursor with 1:7H, partially ordered 2:17R, 2:17H and 1:3R phase evolves into uneven and incomplete cellular structures, while solution precursor with partially ordered 2:17R phase forms larger cell size with less lamellar phase, thus poor coercivity and magnetic energy product. However, solution precursors with single 1:7H phase evolve into uniform cellular structures and perform high coercivity and magnetic energy product. Our results indicate if a single 1:7H phase could be obtained in solution-treated 2:17-type Sm-Co magnets with higher iron content, much higher magnetic properties could be achieved.