Influence of strain rate on the twin and slip activity of a magnesium alloy containing neodymium

The mechanical behavior of an extruded magnesium-manganese alloy containing 1wt% of neodymium (MN11) has been investigated at temperatures ranging from room temperature to 400°C at both quasi-static and dynamic rates. Conventional ex-situ tests, carried out in compression along the extrusion axis (EA), have been combined with in-situ tests in a scanning electron microscope (SEM) in order to elucidate the effect of a rare earth (RE) addition on the dominant deformation mechanisms. An unusually large activity of twinning was observed at room temperature in a wide range of quasi-static rates. Furthermore, the twinning activity has been found to increase at temperatures around 250°C, where clear signs of dynamic strain aging (DSA) are also apparent. The enhanced twinning activity compared to conventional Mg alloys, not containing RE elements, is attributed to an increase in the critical resolved shear stress of basal slip (CRSS_basal) due to the presence of intermetallic RE-containing particles and to the Nd atoms in solid solution. The surprising decrease of the twinning activity at dynamic rates (~10³s^-1) may be explained by a decrease in the CRSS_basal as the intermetallic RE-containg particles and the Nd solid solution strengthening become less effective with increasing strain rate.