Tailoring the Microstructure and Mechanical Property of Mg-Zn Matrix Composite via the Addition of Al Element

The semi-solid stir casting method is adopted to prepare 10 wt% SiC_p/Mg–6Zn–0.5Ca–xAl (x = 0, 1, 3 and 5 wt%) composites, and the microstructure evolution and mechanical property of composites with various Al content are investigated. The results show that the addition of 3 wt% Al improves the distribution of SiC_p, whereas the SiC_p cluster occurs again with Al content greater than 3%. An abnormal phenomenon of twinning is observed in the cast composites in this work. The SiC_p/Mg–6Zn–0.5Ca composite possesses the highest twin content of ~ 23%, for which tension twins (TTW) and compression twins (CTW) account for ~ 19% and ~ 3%, respectively. The CTW is only observed in ZXA600 composite. The addition of Al has an inhibiting effect for the generation and growth of twins. The content of twin decreases firstly and then increases with increase of Al content. The lowest twin content is obtained as Al increases to 3 wt%. It is found the existence of twin is detrimental to the mechanical property of composites. As-cast SiC_p/Mg–6Zn–0.5Ca–3Al composite with the lowest twin content exhibits the optimal mechanical property of yield strength, ultimate tensile strength and elongation for 100 MPa, 188 MPa and 4.4%, respectively. The outstanding mechanical property is attributed to the uniform distribution of SiC_p, the low twin content and the well-distributed fine second phases.