Evaluation of slip behavior of mobile dislocations in an Al-Mg-Si alloy by <i>in-situ</i> tensile-testing transmission electron microscopy

In this study, mobile dislocations within annealed commercial-purity aluminum (A1050) and peak-aged Al-0.6mass%Mg-0.94mass%Si alloy (6M9S) with needle-shaped β” precipitates were dynamically observed by in-situ tensile-testing transmission electron microscopy, and then correlated with their deformation and strengthening mechanisms. Homogeneous slip of mobile dislocations along primary and secondary slip systems was observed in A1050, whereas a localized slip with many slip traces occurred in 6M9S due to the dispersed β” precipitates. After further straining, however, a widening of the localized slip regions was detected in 6M9S because segmented β” precipitates are no longer sheared by dislocations. Such a slip behavior of mobile dislocations supports a strengthening mechanism of 6M9S; i.e. β” precipitates sheared by leading dislocations possess less resistance to the subsequent dislocations, but small pieces of segmented and then rotated β” become non-shearable, resulting in a strengthening through Orowan mechanism.