The effect of Si addition on microstructure of as-cast Mg-7Al-2.5Ca-0.4Mn- 0.25Sr alloy

The effect of Si addition on the microstructure of the as-cast Mg-7Al-2.5Ca-0.4Mn-0.25Sr alloy was investigated by using the optical microscopy (OM), the scanning electron microscope (SEM) and the X-ray diffraction (XRD). The results indicate that the micro structure of the as-cast Mg-7Al-2.5Ca-0.4Mn-0.25Sr-xSi (x=1, 2, 3) alloys are mainly composed of α-Mg matrix, AlMn phase, Mg2Ca phase, Al2Ca phase and CaMgSi phase, the volume fractions of CaMgSi phase increases with increasing the Si element. The addition of Si ranging from 1% to 3% results in the eutectic (Mg2Ca+Al2Ca) decreasing and CaMgSi phase increasing, and the morphology of the CaMgSi phase changes from hollow block shape to Chinese script shape. At the same time, the dendritic α-Mg phase structure become large. Copyright © 2013 MS&T'13®.