Atomic scale interactions of basal dislocations and twin boundaries with ultrathin precipitates in magnesium alloys

The aim of this work is to investigate the interaction of basal dislocations and twin boundaries with ultrafine basal disk-shaped precipitates at the atomic scale in the peak-aged Mg-1Mn-1Nd-3Zn (wt.%) alloy. With that goal, an experimental approach consisting on micropillar compression of two grains oriented favorably for basal slip and for tensile twin activation, respectively, as well as high resolution transmission electron microscopy, was put in place. First, a novel mechanism of interaction between particles and basal dislocations was observed. In particular, the movement of dislocations along basal planes led to the dissolution of the ultrathin basal precipitates in the nearby regions (within 80 nm) and to solute diffusion resulting in microsegregation of solutes at the slip lines. Hindering of basal slip due to such microsegregation prevented slip localization by promoting the consecutive activation of softer basal planes. Second, twin-precipitate interactions were found to be dependent on the twin boundary plane. In particular, bypassing of precipitates by coherent twin boundary segments were observed to lead to elastic rotations of the precipitate lattice, while the interaction of CTB/prismatic-basal intersections with precipitates resulted in precipitate shearing along prismatic planes.