Microstructure and mechanical properties of strength-ductility synergetic SiC/ZK60 composites by a pre-dispersion strategy

The strength-ductility trade-off presents a significant challenge in the development of magnesium matrix composites (MMCs). A novel strategy that combines powder pre-dispersion, nano-SiC/Al master alloy sintering, stir casting, and hot extrusion combined method was introduced to prepare the strength-ductility synergetic SiC/ZK60 composites. The microstructural evolution and mechanical properties of these composites have been thoroughly investigated and compared. The results demonstrate that SiC particles are uniformly distributed within the as-solution-treated composites, and extrusion processes promote cluster refinement. Microstructural characterization shows that adding nano-SiC/Al enhances grain refinement and facilitates the precipitation of secondary phases. The grain refinement is attributed to the accelerated dynamic recrystallization (DRX) and nano-particle pinning, where particle stimulated nucleation (PSN), continue DRX (CDRX), and discontinue DRX (DDRX) are the dominant DRX mechanisms of composites. This process is further enhanced by increased nucleation sites induced by SiC, which facilitate the precipitation of MgZn₂ and Zr phases. Additionally, a microscale Al₃Zr phase precipitates within the composites due to aluminum addition. Notably, both strength and ductility, as well as elastic modulus (E) of 10SiC/ZK60 and 20SiC/ZK60 composites were improved simultaneously, with optimal ultimate tensile strength and elongation (EL) increasing by nearly 10%. Grain refinement emerges as a primary factor contributing to enhanced mechanical properties. Also, load transfer and stress release caused by multiple crack sources contribute significantly to strength and ductility strengthening, respectively.