Influence of Third Alloying Element on Dislocation Slip and Twinning Activities in Mg-Nd-Based Alloys

In the present study, the influence of Zn or Al addition as a third alloying element on the deformation mechanisms of Mg-Nd-based alloys was investigated by quasi in situ tensile tests. Distinct mechanical behaviors were observed between Mg-1.0 Zn-1.7 Nd (ZN12, in wt.%) and Mg-1.0 Al-1.7 Nd (AN12) alloys. The ZN12 alloy showed a lower yield strength and higher fracture strain compared to the AN12 sample. A considerable number of slip traces, corresponding to basal and non-basal dislocations, were formed at the early deformation stage of the ZN12 sample. On the contrary, only a few grains in the AN12 sample showed obvious slip traces. To minimize the effect of grain size and texture on the activation of deformation modes, the grains were categorized into several groups based on their grain sizes and Schmid factors. By comparing the grains in the same group, it was found that basal and non-basal slip are preferred in the ZN12 sample compared to the AN12 sample. High activity of tensile twinning was observed in both samples. However, half of the twins were activated after yielding in the ZN12 sample, while a majority of the twins were formed at a higher strain in the AN12 sample.