Influence of carbon addition on the microstructure and damage mechanisms of an AZ91D alloy

Abstract

The effect of carbon and SiC addition in combination with heat treatment on the mechnanical properties of a commercial AZ91 alloy was studied in this work. Different additions of carbon and SiC were considered for the as-cast and heat-treated conditions. The three-dimensional geometry of the Mg–Al particle structure was characterized by X-ray tomography and scanning electron microscopy. The addition of 0.17% SiC or 0.08% carbon led to an increase in the volume fraction of the Mg–Al particles. However, the addition of SiC caused a signficant drop of the ultimate strength and ductility, whereas 0.08% carbon significantly increased the mechanical properties. The homogenization process at 420 ​°C during 24 ​h led to dissolution and more homogeneous distribution of the Mg–Al particles, what caused an increase in the ductility of the alloy. The combination of homogenization with addition of SiC or carbon led to optimal mechanical behaviour, as more fine and homogenoeus Mg–Al particle structure and grain structure were achieved.