Atomic ordering at the interfaces between liquid Al and solid MgO: An Ab Initio molecular dynamics study

Magnesia (MgO) particles inevitably exist in Al-Mg based alloys and can act as potential nucleation sites during solidification processing. In this paper we investigated the effect of MgO substrates on the atomic ordering in the liquid Al adjacent to the liquid Al/solid MgO interfaces using an ab initio molecular dynamics approach. We found that at thermal equilibrium, on the O-terminated MgO{1 1 1} surface forms an Al-terminating layer that contains vacancies and is thus atomically rough. In contrast, we found that both Mg-terminating MgO{1 1 1} and MgO{0 0 1} substrates are stable in liquid Al. The analysis suggests that the MgO{1 1 1} substrate with a new Al-terminating layer has much less templating power for atomic ordering in the liquid Al compared with that of the Mg-terminated MgO{1 1 1} substrate. In addition, there is also little atomic ordering in the liquid Al adjacent to the MgO{0 0 1} substrate due to the chemical interaction between the substrate surface and the liquid Al.