Abstract: Al alloys containing higher amounts of Mg (above 6 wt.%) offer improved strength and ductility compared to typical 5xxx Al-Mg alloys. However, their high-temperature deformation behaviors are less studied, which limits their further industrial developments and applications. This work aims to address this gap by systematically investigating the high-temperature flow behavior of an Al-Mg alloy containing 9 wt.% Mg. Unlike the flow curves in low-Mg Al alloys, we observe an unconventional flow behavior in this alloy under certain hot compression conditions (300 °C with 0.001 s^-1; 350 °C with 0.001 and 0.01 s^-1; 400 and 450 °C with 0.001, 0.01 and 0.1 s^-1), which is characterized by a flow stress drop immediately after yielding, without noticeable macroscopic work hardening that is considered as the driving force for dynamic recrystallization. It is revealed that Mg segregation at grain boundaries, coupled with grain boundary sliding behavior, leads to rapid nucleation and multiplication of high-density dislocations close to grain boundary regions. This avalanching-driven increase in dislocation density provides favorable conditions for sudden plastic flow, which accounts for the observed stress drop. These localized intensive dislocation activities also activate dynamic restoration processes, which mask the expected work hardening. The dependence of such flow behavior on deformation conditions and the underlying influencing factors are further discussed, which provide important insights into the processing and forming of high-Mg Al alloys at elevated temperatures.

Key words: Al-Mg alloys, Discontinuous yielding, Grain boundary sliding, Solute segregation, Dynamic recovery and recrystallization