Roles of Slip and Twinning on Indentation Formations in Magnesium Alloy Single Crystals

Indentation tests using a spherical indenter were applied to six hexagonal close-packed structure single crystals - pure Mg, Mg–0.5 at%Al, Mg–0.5 at%Zn, Mg–0.5 at%Y, Mg–0.9 at%Y, and pure Zn single crystals – to investigate the roles both slips and twinning induce on the formation of indentation. When indented on (0001), all single crystals displayed circular morphology without slip lines or twins. Mg and Mg alloys’ indentation sizes were found dependent on critical resolved shear stress (CRSS) for basal slip in (0001) indentations, while Zn (0001) indentation size depends on CRSS for both basal and second order pyramidal slips. Conversely, when indented on (1010) and (1210), all single crystals displayed indentations elongated to [0001] surrounded by basal slip lines. Also, {1012} twins were observed in Mg–0.5 at%Al and Mg–0.5 at%Zn but were scarce in Mg–Y. Pure Zn displayed second order pyramidal slips. Sizes of both (1010) and (1210) indentations were found dependent on CRSS for basal slips and for {1012} twins.