The effect of high solid solution Mg contents (7–13 wt%) on the dynamic strain aging behavior of Al–Mg alloys

Plastic instability caused by Portevin–Le Chatelier (PLC) due to the interaction of dislocations with solute atoms, known as dynamic strain aging (DSA), remains a serious hindrance for sheet metal forming, especially for 5000 series Al alloys. Here, we investigated the DSA behavior of hot extruded Al–Mg alloys with high solid solution Mg contents varying from 7 to 13 wt% at different tensile strain rates. With increasing the Mg content and decreasing the strain rate, the critical strain for the onset of serrated stress flow increases gradually, indicating the greatly suppressed plastic instability. Moreover, serrations changes from type B to type C with increased concentrations of Mg at 5 × 10−4 s−1 and 1 × 10−3 s−1. In the Al–7Mg alloy, the critical strain exhibits an inverse behavior at lower strain rates (< 1 × 10−3 s−1) but a normal behavior at higher strain rates (> 1 × 10−3 s−1). Whereas, the inverse behavior predominates the entire range of strain rates in the Al–10Mg and Al–13Mg alloys, where the waiting time of dislocations at temporary barriers is longer than the diffusion time of Mg solutes at the critical strain. Dislocations are pinned prior to the critical strain and the first plastic instability depends on the first unpinning event.