Solute strengthening of prismatic slip, basal slip and image twinning in Mg and Mg–Zn binary alloys

Mg–Zn binary alloys with concentrations between 0 and 2.8 wt% Zn have been prepared and processed via hot rolling and annealing to produce specimens with a strong basal texture and a range of grain sizes. These have been deformed in three different strain paths: tension, compression and shear, in order to promote the dominance of prismatic slip, image twinning and basal slip, respectively. This experimental data has been used to create Hall–Petch plots for each deformation mode. It has been found that the prismatic slip system has a plateau in its Hall–Petch plot above grain sizes of ∼30 μm, and solute softening of the prismatic system was found to be operative only at grain sizes above ∼50 μm. In compression, the stress required to activate twinning was found to be insensitive to Zn concentration. It is proposed that solute softening and anomalous Hall–Petch behaviour of prismatic slip be understood in terms of the dominance of the cross-slip stress in coarse grained materials. The effect of grain size on the relative strength of basal slip, prismatic slip and image twinning is also discussed.