Understanding the interaction of {10–12} twins and Mg17Al12 precipitates in magnesium alloys via high-resolution electron microscopy

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The interactions between {10 1‾ 2} twins and basal precipitates in the Mg–8Al-0.5Zn alloys have been investigated using high-resolution transmission electron microscopy. The underlying interaction mechanisms at different twinning processes were analyzed in detail. In the process of twin propagation, the twin tip can traverse across multiple basal precipitates in the form of nucleation of new twins on the opposite side of the precipitates and continuously expand in the grain. Such re-nucleation events are suggested to be driven by the local stress concentration arising from the twin impinging upon the precipitate. During twin thickening, the precipitates undergo a small elastic deflection rather than plastic shearing when the twin engulf them. Furthermore, a large number of I1 stacking faults are activated at the twin-precipitate interface to accommodate the twinning shear. The orientation relationship (OR) of the precipitates inside the twin is changed from Burgers to [2 1‾1‾ 0]α//[11 1‾]β, (0 1‾ 10)α//(011)β, (0001)α//(2‾ 11‾)β when they are engulfed by twin.