Structural stability of intermetallic compounds of Mg-Al-Ca alloy

Abstract

A first-principles plane-wave pseudopotential method based on the density functional theory was used to investigate the energetic and electronic structures of intermetallic compounds of Mg-Al-Ca alloy, such as Al 2Ca, Al 4Ca and Mg 2Ca. The negative formation heat, the cohesive energies and Gibbs energies of these compounds were estimated from the electronic structure calculations, and their structural stability was also analyzed. The results show that Al 2Ca phase has the strongest alloying ability as well as the highest structural stability, next Al 4Ca, finally Mg 2Ca. After comparing the density of states of Al 2Ca, Al 4Ca and Mg 2Ca phases, it is found that the highest structural stability of Al 2Ca is attributed to an increase in the bonding electron numbers in lower energy range below Fermi level, which mainly originates from the contribution of valence electron numbers of Ca(s) and Ca(p) orbits, while the lowest structural stability of Mg 2Ca is resulted from the least bonding electron numbers near Fermi level.