Indexation of coordinated bursts of plasticity in Mg-4Zn via high-energy X-rays

Our understanding of grain-level bursts of plasticity in polycrystals remains limited by current techniques. By employing a modified Synchrotron transmission X-ray Laue diffraction method (beam size larger than the grain size), we tracked grain rotations for the first 1 % of tensile strain, in 4400 time steps. We indexed 33 grains and quantified the magnitude and frequency of intermittent bursts of grain rotation. We interpret these events in terms of bursts of plastic deformation. The events are highly coordinated amongst nearby grains, and their frequency and magnitude, as well as the number of grains participating, peaked at around the onset of full plasticity. At this point, 7 out of the 10 indexed grains with orientations favorable for twinning showed significant drops in diffracted intensity (a mean value of 8 %), due to twin induced re-orientation. For other orientations, 20 out of 23 grains displayed bursts attributable to lattice dislocation glide (interpreted in terms of basal and prismatic 〈a〉 slip). The mean value of the magnitude of these bursts is ～0.08°, implying accumulated shear strains of the order of 3 × 10^–3. These bursts, in many cases, were due to the activation of more than a single slip/twin system within the grain, and co-ordination amongst neighboring grains also involved collaboration between slip and twinning events.