The deformation modes and transferability during low-cycle fatigue of Mg and Mg-3Y alloy

Mg-Y alloys show distinctly different slip/twinning activity under quasi-static monotonic loading at room temperature compared with pure Mg, as extensively reported. In this work, the influences of 3% Y addition on the deformation modes and transferability during strain-controlled tension-compression low-cycle fatigue (LCF) at room temperature of Mg sheets were studied quantitatively and statistically. The activity of various slip systems and twinning-detwinning were measured at desired fatigue stages via quasi-in-situ EBSD observations together with slip trace analysis. The results indicate that the activation of deformation modes in pure Mg was featured by the cyclic transition, i.e., tension twinning (at the compressive reversal) -> detwinning + basal slip (at the tensile reversal). In Mg-3Y alloy, basal slip dominated the cyclic deformation throughout the fatigue life span. Compared with pure Mg, Mg-3Y alloy displayed the enhanced activity of various slip systems, including basal, prismatic, and pyramidal slip systems, but lower twinning-detwinning activity. For deformation transferability, mk, which is the product of the Schmid factor (SF) and the geometric compatibility factor (m') values of the adjacent grains, was used to evaluate the slip transferability and twinning transferability at grain boundaries. Mg-3Y alloy showed a higher likelihood of slip transfer but lower twinning transferability than pure Mg. The underlying mechanisms affecting the activity of various slip systems and twinning, as well as deformation transferability and mechanical behavior, were discussed.