Grain size effect on deformation behaviour of Mg-Sc alloys

The effect of grain size on the flow stress and work hardening in binary Mg-Sc alloys has been investigated under conditions of uniaxial compression at 78 K and 298 K. The yield stress depends on the grain size and obeys Hall-Petch relationship. Yielding and post-yielding deformation is accomplished by both slip and twinning, organized in the form of a deformation front propagating throughout the sample. The results show similar volume fraction of twins in fine- and coarse-grained samples, suggesting no significant effect of the grain size on twinning. Modelling of mechanical properties indicates that Mg-Sc alloys deform predominantly by basal, prismatic , pyramidal slip and extension twinning. Small influence of the grain size on work hardening is interpreted due to the enhancement of slip. Analysis of σΘ characteristics shows that an increase of Sc content leads to the decrease of σΘ at corresponding flow stress. This behaviour is interpreted in terms of the combined effect of Sc on the relative activity of slip systems and stacking fault energy (SFE) of Mg-Sc alloys.