An examination of microstructural evolution and homogeneity in a magnesium AZ80 alloy processed by high-pressure torsion

A magnesium AZ80 alloy with an initial grain size of ~250 μm was processed by high-pressure torsion for up to 12 turns at room temperature. The processing produced increased hardness and significant grain refinement with average grain sizes of ~320 and ~200 nm at the edges of the discs after 1 and 12 turns, respectively. Microstructural examinations on different planes along the thickness direction of the discs revealed the presence of shear bands and twin boundaries and there were significant inhomogeneities even after 12 turns. The results show the presence of well-defined vortices having similarities to the well-established Kelvin-Helmholtz shear instabilities in fluid flow.