Interplay between the effects of deformation mechanisms and dynamic recrystallization on the failure of Mg-3Al-1Zn

Abstract

This work focuses on the relationship between deformation mechanisms, dynamic recrystallization (DRX), and failure mechanisms in Mg-3Al-1Zn under tension at relatively low temperatures (25–200 °C). The loading orientation was selected to favor either prismatic slip, basal slip, or extension twinning as the primary active deformation mechanism upon yielding. The tensile response was accurately simulated at various temperatures using visco-plastic self-consistent crystal plasticity modeling coupled with optimization under constraints. The relative deformation mechanism activities were predicted to gain insight into the role of microstructure evolution and DRX in failure. Extensive microstructural investigation was performed to identify characteristics of failure and categorize them according to slip, twin, and DRX activities, in an attempt to ultimately provide insights for achieving better formability at low temperatures. Failure processes were categorized according to four primary microstructural features observed during deformation prior to failure: (1) extension twinning without DRX, (2) extension twinning with DRX, (3) contraction twinning followed by double twinning, and (4) abundant DRX and high microcrack density along DRX regions. Prismatic slip was found to promote homogeneous DRX via the continuous DRX mechanism, resulting in ductile fracture. Similarly, basal slip allows for high elongation to failure but low yield strengths while promoting discontinuous DRX, whereas extension twinning contributed to quasi-brittle failure at low temperatures and minimal DRX activity. As the yield strength becomes orientation-independent at 150 °C, with increased elongation, transition from twinning-to slip-dominant microstructures, and higher DRX activity, the findings indicate that the flow anisotropy in Mg-3Al-1Zn can be mitigated beginning at 150 °C.