Yielding behaviour and Hall­–Petch relationship in ultrafine-grained Al–Mg binary alloys

This study investigates yielding behaviour, Hall–Petch relationship and strengthening mechanism of ultrafine-grained Al–Mg binary alloys. Ultrafine-grained Al–Mg samples reveal unusual discontinuous yielding and extra Hall–Petch strengthening. The critical grain size to separate the extra Hall–Petch strengthening from the conventional Hall–Petch strengthening becomes larger as the Mg content is higher, indicating that dislocation sources in the ultrafine-grained structure becomes more difficult to activate by solute atoms of Mg. It is also found that the Lüders elongation in the discontinuous yielding becomes less pronounced by Mg addition, suggesting that enhancement of work hardening ability by addition of solute atoms is effective to avoid the occurrence of unwanted discontinuous yielding in ultrafine-grained metals.