Anisotropic strain hardening in an extruded lean Mg-Al-Ca-Mn alloy

Compared to commercial magnesium (Mg) alloys, recently the low-alloyed Mg alloys have attracted extensive research interest for their advantages in formability, corrosion resistance, and low cost. However, their strain hardening behavior is yet fully understood. In this work, the strain hardening of an extruded lean Mg-Al-Ca-Mn alloy is qualitatively and quantitatively analyzed. As compared to the dislocation-dominated deformation along the extrusion direction (ED), the hardening along the transverse direction (TD) is significantly improved due to the activation of twinning. We quantified the specific contributions of twinning and dislocations to the net hardening effect through cyclic stress relaxation and calculations. Interestingly, the dominant hardening mechanism is always related to dislocations, even though the twin volume faction reaches similar to 40 %. This work furthers our understanding of the deformation behavior of lean Mg alloys and indicates that the strain hardening of Mg alloys can be improved if the twin morphology is properly controlled.