Atomic Ordering at the Liquid-Al/MgAl2O4 Interfaces from Ab Initio Molecular Dynamics Simulations

MgAl2O4 spinel particles exist inevitably in Al-Mg alloy melts and may act as potential substrates for heterogeneous nucleation of solid aluminum during solidification processing. In this paper, we investigated systematically the atomic ordering of liquid Al adjacent to liquid-Al/MgAl2O4{1 1 1} interfaces using an ab initio molecular dynamics simulation technique. Our simulations revealed that the interaction between the liquid metal and the spinel surface results in the formation of an ordered metal layer that terminates the substrate. This new terminating layer is positively charged, chemically bonded to the substrate, topologically rough, and structurally coupled with the metal sublayers beneath the outmost oxygen layer. The present results may shed new light on the role of spinel particles in Al-Mg alloys and on heterogeneous nucleation processes in general.