In situ observations of the kinetics of twinning-detwinning and dislocation slip in magnesium

The present study has clarified the roles of dislocation slip and twinning as the deformation mechanisms underlying the dependence of the mechanical response of pure magnesium on the sense of loading (tension vs. compression) during cyclic deformation. The details of these mechanisms were studied by monitoring the acoustic emission (AE) powered by a robust signal categorisation technique in conjunction with rapid surface imaging. Through the analysis of AE time series, the sequences of predominant deformation mechanisms in pure Mg were identified during cyclic deformation with a high degree of confidence. The AE findings were found to be in excellent agreement with direct video observations of the dislocation slip and twinning/de-twinning behaviour along the hysteresis loop. The differences between the deformation histories beginning with a first tension or compression excursion were accounted for in terms of the twinning/de-twinning - dislocation interaction and different behaviour of mechanical twins under tension and compression conditions.