A crystallographic investigation on the growth of Al4Sr crystals under a high magnetic field

Abstract

A high magnetic field (HMF) was applied to the solidification process of hypereutectic Al–Sr alloy to crystallographically investigate the growth of Al4Sr crystals. The results show that the primary Al4Sr crystals exhibit typically a platelike shape in three dimensions, irrespective of whether a HMF is applied or not. They are externally bound by the faceted {001} and {011} planes (the {001} planes correspond to the large-area surfaces of the platelike shape). With the application of a HMF, the primary Al4Sr crystals tend to be distributed uniformly in the specimen and align vertically (i.e., with the longer axes parallel to the HMF direction in the observation section). Moreover, they tend to orient preferentially with the ⟨001⟩ direction (i.e., c-axes) perpendicular to the HMF direction. The platelike shape results because the {011} planes have a higher reticular density and thus faster growth rates than the {001} planes. The uniform distribution and the preferential orientations of the primary Al4Sr crystals are ascribed to the magnetic viscosity resistance force and the magnetization energy associated with the magnetocrystalline anisotropy of the Al4Sr crystals.