Effect of RE Addition on the Solidified Process and Microstructure of Al-7Si-0.3Mg Alloys

The solidification process and microstructure of Al-7Si-0.3Mg alloy with different rare earth (RE) additions have been studied by using thermal analysis, optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The results showed that the addition of RE enhanced the liquidus temperature and decreased the growth temperature of eutectic Si, which lead to obvious increase in solidification interval of the studied alloy. In addition, the grain size of primary α-Al had no obvious change, and the mean area of eutectic Si particles decreased with increasing RE content to 1.6 wt.%. The RE-rich compounds with different compositions were obtained with increasing RE concentration in Al-7Si-0.3Mg alloys. The method of phase diagram calculation helps to clarify the formation and growth mechamism of different RE-rich phases during solidification.