Characterization of Mg-rich clusters in the C36 phase of the Mg-5Al-3Ca-0.7Sr-0.2Mn alloy

In this paper, characterization of clusters embedded in the C36 eutectic phase using TEM, STEM and XRD methods is presented. Disk-shaped Mg-rich clusters with sizes less than 150 nm were observed in the sand-cast Mg-5Al-3Ca-0.7Sr-0.2Mn alloy. The composition of the C36 eutectic phase was 24.1Mg-47.2Al-27.8Ca-0.9Sr and that of the Mg-rich clusters was 53.1Mg-33Al-13.1Ca-0.8Sr in at.%. The lattice parameters of the C36 phase were determined to be a0 = 5.827 Ǻ and c0 = 18.834 Ǻ, whereas for the clusters they were determined to be a0 = 5.586 Ǻ and c0 = 18.834 Ǻ. The chemical compositions of the eutectic phase and clusters, and the decrease of the lattice parameters with increasing magnesium content in the C36 phases suggest that Mg atoms occupy both Al and Ca sites in the C36 phase.