Effect of pre-twinning on microstructure and texture evolution in room and cryogenically deformed Mg-0.5Ca alloy

Introducing (10-12) tension twin lamellas has proved to be the most effective strategy to enhance the performance of Mg alloys. Twins can provide the preferential nucleation sites for recrystallization, hence twinning induced grain refinement can result in higher strength material based on Hall-Petch Effect. In addition, twinning can also modify the crystallographic c-axis distribution in wrought Mg alloys resulting in lower plastic anisotropy. Accordingly, in the present work, the twinning evolution in the Mg-0.5Ca (wt.%) alloy at room and cryogenic temperature was critically investigated. The samples were subjected to pre-compression (5%) at room temperature and -150 ^oC at the strain rate of 10^-3 s^-1. The microstructural and textural characterization was carried out using OM, SEM and EBSD to emphasize the twinning evolution during compression at room and low temperatures. The local lattice distortion and the localized deformation in terms of Kernel average misorientation (KAM) was also studied. The results revealed the significant grain refinement (13.7 µm, 5.61 µm and 6.02 µm of uncompressed and RT, - 150 ^oC pre-compressed, respectively), where slightly enhanced twinning fraction in the sample compressed at RT was observed. Finally, remarkable increase in the yield strength was noticed in the pre-twinned samples, which was attributed to the twinning-induced grain refinement based on the Hall-Petch relationship.