Twinning, dynamic recrystallization, and crack in AZ31 magnesium alloy during high strain rate plane strain compression across a wide temperature

Plane strain compression (PSC) tests were carried out on as-cast AZ31 magnesium alloy samples at temperatures from 250 to 400 °C with different strain rates (≥ 10 s−1). The microstructures along the crack boundaries and secondary cracks were detected. The electron backscatter diffraction (EBSD) results indicated that twin induced dynamic recrystallization (DRX). The flow curves were analyzed using the double differentiation method and two or three minima were detected. The first set of minima is shown to identify the critical strain for twinning, while the second set indicates the critical strain for the initiation of DRX or micro-cracks, and the third set is related to the onset of micro-cracks. Twinning affects the nucleation and propagation of crack. The crack in the matrix grain is inhibited due to the preferred initiation of twinning to impede competitive crack extension. With increasing temperature, the competitive relationship between crack and DRX exists on the twin boundaries. The nucleation, growth and coalescence of voids on the grain boundaries and at grain triple junctions contributes to the formation of cracks in the fine-grained area.