Structure-controlled slow dynamics in Al-Mg melts

Abstract

Molecular dynamics simulation was employed to investigate the dynamical and structural properties of Al-Mg melts with the Al concentration systematically changed. The results show that the viscosity of Al₆₇Mg₃₃ abnormally surpasses that of Al₈₅Mg₁₅ below 550 K, inconsistent with the tendency at high temperatures. The evolution of the icosahedral order population is found to account for this dynamic behavior. Structural analysis shows a preferred bonding between Al and Mg atoms in the nearest neighbor shells, while a repelling tendency between them in the second shells, leading to the prepeak emergence in the partial static structure factors. The formation of icosahedral clusters is constrained in the Al-rich compositions because of the lack of sufficient Mg atoms to stabilize the clusters geometrically. These results demonstrate the structural consequence through the interplay between geometric packing and chemical interaction. These findings are crucial to understanding the structure-dynamic properties in Al-Mg melts.