Influence of precipitation on yield elongation in Mg-Zn alloys

The effect of precipitation on yield elongation in an extruded Mg-4.5 wt% Zn alloy is investigated. The yield plateau is shown to disappear in the presence of precipitation and it is subsequently proposed that two criteria need to be satisfied for a distinct yield plateau: (1) the initial propagation of twins is autocatalytic in that twinning in one grain should stimulate twinning in an adjacent grain; (2) the twins that initially form should display an appreciable aspect ratio. These two criteria can also explain why the yield elongation decreases with an increase in grain size and deformation temperature.