Yet Another Marked Difference among Impurities as Modifier Elements for Refinement of Eutectic Si in Al-Si Alloys

Abstract

First principles calculations have been carried out in conjunction with lattice dynamics to evaluate free energies of ternary intermetallic phases, Al₂Si₂X (X = Ca, Sr, Ba, Eu, Y, Yb). The most stable crystal structure is identified for each X as a function of temperature. It is found that some of the intermetallic phases are stable over wide temperature range, thereby giving ability to modify and refine Al-Si eutectic phases with better mechanical properties. Substitution energy of the intermetallic phase is evaluated to aiming at examining the magnitude tolerance of the intermetallic phases with respect to deviation of chemical composition. Finally, the role of Al₂Si₂X as a modifier is examined from a solely geometric viewpoint, which provides yet another possible factors among many behind the X species dependence on modification of eutectic Si without using existing theories.