Initiation of basal slip and tensile twinning in magnesium alloys during nanoindentation

The present study addresses the challenge of determining the stress required for the initiation of deformation modes in Mg alloys. Nanoindentation is employed to detect the onset of basal slip and tensile twinning. A Mg-6 wt. % Zn alloy and a series of Mg-Gd binary alloys with concentrations between 0.3 and 4 wt. % Gd are examined in the extruded state. Nanoindentation tests were conducted on {101¯0} and {112¯0} crystal planes using a 5 μm radius spherical indenter. It is shown that the initial yielding point in the load trace corresponds to the appearance of basal slip lines on the sample surface. A pop-in event is seen to accompany the appearance of twinning. We find that the addition of Zn strengthens the basal slip but shows mild influence on twin initiation. For alloying with Gd, an impact on basal slip and twinning is only seen at the highest solute levels. A means of examining the alloying effect on twin growth is proposed and revealed that solute Zn has a greater impact on twin growth than initiation.