Molecular insight into the pathway to crystallization of aluminum

We use molecular simulations to study the onset of crystallization in a liquid of Al, cooled at a temperature 20% below the melting point. We show that Al nucleates into a random packing of the hexagonal close-packed and the face-centered cubic phases. Body-centered cubic clusters, which usually form during the nucleation of simple fluids, are not observed during the crystallization of Al. Throughout nucleation and growth, Al nuclei are always strongly faceted, in sharp contrast with the spherical crystallites observed for simple fluids. Our results demonstrate that the pathway to crystallization of Al strongly departs from that of simple fluids.