Atomistic modeling of Mg-Al-Zn solid-liquid interfacial free energy

In this study anisotropic solid-liquid interfacial energy, gamma, of Mg-Al-Zn system is evaluated based on capillary fluctuation method. To investigate effects of temperature and solute compositions on gamma, five simulation cases, Cases I-V, are designed and divided into two group, Group I consist of Cases I-III for evaluation on solute compositions, while Group II consist of Cases I, IV and V for evaluation on temperatures. Interfacial energy stiffness of six differently oriented interfaces is evaluated, average interfacial energy, gamma(0), and anisotropic parameters of the interfaces are obtained. This study determined melting point of Mg as 964 +/- 5 K, which matches the standard value of 923 K. Evaluation on gamma(0), and gamma in high symmetric orientations gamma(Basal), gamma(PrismaticIA) and gamma(PrismaticIIA) suggests, for Cases I-V, lower gamma(0) values within 15.74-18.19 mJ/m(2) compared with elemental Mg could be related with the insufficiency of selected interatomic potential to describe the solid-liquid interface, and relation of gamma(Basal) > gamma(PrismaticIIA) > gamma(PrismaticIA) was identified. Comparisons within Group I indicate the increase of relative average equilibrium composition, (c(i)) over bar/(c(j)) over bar, will improve solute adsorption of element i on interface, which causes gamma(0), gamma(Basal), gamma(PrismaticIA) and gamma(PrismaticIIA) to decrease. As for Group II, temperature increase will result in decline of gamma(0), gamma(Basal), gamma(PrismaticIA) and gamma(PrismaticIIA), similar trend was found in Al-Sm alloy systems. Primary dendrite growth orientations for Cases I-V were determined as [0001], analysis shown increase in either temperature or (c(i)) over bar/(c(j)) over bar stabilize this preference further towards [0001].