{10–12} extension twinning activity and compression behavior of pure Mg and Mg-0.5Ca alloy at cryogenic temperature

This study explored the deformation behavior of rolled pure Mg and Mg-0.5Ca alloy at room temperature (RT) and cryogenic temperature (CT) of −150°C. The samples were compressed at a strain rate of 10-3s-1 up to 5% strain along the rolling direction (RD). The deformed samples were examined via EBSD and analyzed concerning the loading condition and initial microstructure. The compression tests showed the temperature-insensitive hardening behavior in Mg-0.5Ca alloy. The twinning activity increased with an increase in grain size, and this was pronounced when the pure Mg samples were compressed at CT. The kernel average misorientation (KAM) analysis revealed that the twinning parent areas tend to have higher KAM values under CT deformation than the RT deformation, which links to a higher twinning activity at CT. The predominant low angle grain boundaries in the initial microstructure of pure Mg further helps to understand the profuse twinning activity in the context of existing literature. It was suggested that the higher twinned area fraction in the pure Mg sample than Mg-0.5Ca could be responsible for the temperature-dependent hardening behavior. This is presumably because the Ca element in the matrix results in a homogeneous microstructure with smaller grain size and higher Schmid factor (SF) for basal slip, leading to lower twinning dependent deformation behavior in Mg-0.5Ca than pure Mg.