Microstructures, tensile properties and work hardening behavior of SiCp/Mg-Zn-Ca composites

Abstract

The SiCp/Mg-4Zn-0.5Ca composite was fabricated by semi-solid stirring assisted ultrasonic vibration and followed by ultra-slow-speed (0.01 mm s−1) extrusion at 280 °C. The results show that the as-extruded composite exhibits a typical bimodal microstructure consisted of ∼96.2% ultrafine dynamic recrystallization (DRXed) grains (∼0.86 μm) and relatively coarse unDRXed regions in a shape of elongated strips. Large amount of nanoscale MgZn2 dynamically precipitated during ultra-slow-speed extrusion. The DRXed regions are thought propitious to the nucleation and growth of precipitate as compared with that of unDRXed regions. Compared with previous works on particle reinforced Mg matrix composites, the as-extruded SiCp/Mg-4Zn-0.5Ca composite not only possess high yield strength (322.7 MPa) and ultimate tensile strength (409.1 MPa), but also exhibit excellent ductility (10.1%). The ultrafine DRXed grains and large amount of dynamic precipitated nanoscale MgZn2 are thought responsible for the superior strength of present composite. A typical linear hardening stage appears in the work hardening rate curve of as-extruded composite. Compared with the hinder effect of SiCp and dynamic precipitated nanoscale MgZn2 on the movement of dislocations, the ultrafine DRXed grains play a main role on aggravating the dynamic recovery rate in stage Ⅲ.