A Full-Process Preparation Strategy for Fully-Dense Anisotropic ThMn12-Type Magnets

ThMn12-type SmFe12-based permanent magnets have attracted considerable attention due to their low rare-earth content and high intrinsic magnetic properties, positioning them as a key candidate system for next-generation high-performance rare-earth permanent magnets. However, the sintering of this system is hindered by its poor liquid-phase formation ability. Simultaneously, the high vapor pressure of Sm induces severe evaporation at elevated temperatures, which consequently causes the decomposition of the main phase and the formation of detrimental secondary phases. Consequently, it is challenging to obtain bulk magnets with both high density and high performance, which limits their fabrication and practical application. This study developed an integrated processing strategy of "pre-sintering combined with hot-pressing and annealing" to address the challenges in achieving both high densification and superior magnetic performance in this system. The results demonstrate that through this integrated process, fully-dense and high-performance ThMn12-type bulk magnets with low rare-earth content were successfully fabricated. Microstructural analysis revealed that the optimal magnet developed a continuous, Fe-lean, Sm-rich grain boundary phase. This structure provided effective magnetic isolation between grains, thereby yielding significantly enhanced comprehensive magnetic properties, including a maximum energy product of 10.11 MGOe, a coercivity of 8.98 kOe, and a remanence of 6.63 kGs. This study provides a critical framework through its full-process preparation strategy, delivering key insights and a practical foundation for achieving fully-dense anisotropic ThMn12-type magnets.