Al₂(Mg,Ca) phases in Mg-Al-Ca ternary system: First-principles prediction and experimental identification

First-principles calculations of three Laves phase structures at Al₂Ca and Al₂Mg compositions predict the existence of Al₂(Mg,Ca) Laves phase. To validate this prediction, a diffusion couple between Mg-30 wt.%Ca alloy and pure Al was assembled and heat-treated at 688 K for 2 weeks. From the cross section of the diffusion couple, backscatter electron microscopy coupled with electron probe microanalysis indicated the existence of Al₂(Mg,Ca). Two Laves phases, i.e. C36-Al₂(Mg,Ca) and C14-Al₂(Mg,Ca), were identified by indexing the electron backscatter diffraction pattern with predicted lattice parameters by first-principles calculations and by diffraction analysis using transmission electron microscopy independently.