First-principles investigation of the binary intermetallics in Mg–Al–Sr alloy: Stability, elastic properties and electronic structure

First-principles calculations have been carried out to investigate the structural stability, elastic properties and electronic structure of the main binary phases Mg17Al12, Al2Sr, Al4Sr, Mg2Sr, MgSr and Mg17Sr2 in Mg–Al–Sr alloy, respectively. The optimized structural parameters are in very good agreement with the experimental values. Heat of formation and cohesive energy show that the Al2Sr phase is of strong alloying ability as well as good structural stability. Thermodynamic properties indicate that the Gibbs free energy of these binary phases decrease with the elevated temperature, when the temperature is above 325 K, Al2Sr and Mg17Sr2 are more stable than Mg17Al12 phases, while the temperature is above 425 K, Sr addition to the Mg–Al-based alloys can improve the heat resistance by forming Al2Sr and Mg17Sr2 phases. The densities of states (DOS) are given. The elastic parameters Cij are calculated, then bulk modulus B, shear modulus G, Young’s modulus E and Poisson’s ratio ν are derived. All the results of the analysis indicate that adding Sr to Mg–Al alloy could improve the ductility and plasticity by forming Al4Sr, Mg2Sr and MgSr phases.