The interaction of twins and precipitates in a Mg-7.7 at.% Al alloy

Deformation twinning has been studied in a precipitation-strengthened Mg-7.7 at.% Al alloy by transmission electron microscopy. The nature of the interaction between the twins and the second phase was found to be dependent on the relative thickness of the twin and the precipitate. Twins were observed to engulf, bypass or impinge upon the precipitates, but the precipitates themselves were not twinned. The bypass mechanism was associated with a change in the apparent habit plane of the twin, and the production of an array of 〈c + a〉 dislocations in the matrix adjacent to the twin. A model, based on basal plane slip in the twin, was invoked to explain these features.