FIRST-PRINCIPLE CALCULATIONS OF STRUCTURAL STABILITIES AND ELASTIC PROPERTIES OF Al2Sr AND Mg2Sr PHASES

Structural stabilities, elastic properties and electronic structures of Mg17Al12, Al2Sr and Mg2Sr phases have been determined from first-principle calculations by using CASTEP and DMOL programs based on the density functional theory. The calculated formation heats and cohesive energies indicated that Al(2)three phases Mg2Sr is a phase with the best plasticity. The calculations of the density of states (DOS) and Mulliken electronic populations showed that the reason of Al2Sr having the highest structural stability attributes to Al2Sr phase having the more covalent bonds compared with Mg17Al12 and Mg2Sr phases, while Mg17Al12 phase having more stable structure is the result of coaction of ionic and covalent bonds.Sr has the strongest alloying ability as well as the highest structural stability. The calculated Gibbs free energy showed that the structural stabilities of Mg17Al12, Al2Sr and Mg2Sr change with elevated temperature, when the temperture is above 423 K, Al2Sr is more stable than Mg17Al12 phase, and Sr addition to the Mg-Al base alloys can improve the creep properties. The calculated bulk modulus (B), anisotropy values (A). Young's modulus (E), shear modulus (C) and Poisson ratio (v) showed that Mg2Sr is ductile, on the contrary, Mg17Al12 and Al2Sr are both brittle, and among the result of co-action of ionic and covalent bonds.