The Investigation of Strength-Ductility Mechanism of Bimodal Size SiCp/Mg-Zn Matrix Composite

Mg-Zn-Al matrix composites reinforced with bimodal-size SiCp (average size of similar to 8 mu m and similar to 60 nm) are fabricated by semi solid stirring casting process and extrusion process. The influence of bimodal size SiCp on microstructure and texture evolution, mechanical properties as well as work hardening behavior of Mg-Zn-Al matrix composites are investigated. The results reveal that the area fraction of unrecrystallization (unDRX) region decreases from 12.8 % of matrix alloy to 5.2 % of 9 wt% m-SiC+1 wt% n-SiC/Mg-6Zn-3Al-0.5Ca(M9N1) composite, and the average grain size (AGS) is reduced sharply with addition of SiCp, which decreases from 7.3 mu m of matrix alloy to 0.9 mu m of M9N1 composite. The addition of micron SiCp (m-SiCp) promotes the generation of nano precipitates, and the precipitate size is reduced further after the addition of nano SiCp (n-SiCp). The intensity of basal texture decreases firstly and then increases with the addition of m- and n-SiCp because of the pinning effect from n-SiCp and nano precipitates for grain boundary. The bimodal-size SiCp particles have been observed to significantly enhance the strength of the composite. The M9N1 composite demonstrates exceptional performance, and its yield strength and ultimate tensile strength is 322 MPa and 360 MPa, respectively. The exceptional strength of the composite can be attributed to various strengthening mechanisms, including grain refinement, precipitate strengthening, dislocation strengthening, and the load transfer effect.