Influence of Sc Addition on Precipitation Behavior and Properties of Al-Cu-Mg Alloy

In this study, the Al-5.10Cu-0.65 Mg alloys without and with 0.2 wt% Sc addition were prepared to unveil the effect of Sc on the precipitate behavior and properties by atomic-scale scanning transmission electron microscopy. The results show that addition of Sc is able to significantly suppress the formation of the peak-hardening theta' and S precipitates but in favor of stabilizing Guinier-Preston-Bagaryatsky (GPB) zones during isothermal aging at 180 degrees C. The generation of unique GPB precursors dictating the evolution of the subsequent peak-hardening GPB zones is highly correlated with the insufficient vacancies and dragging effect of Sc to Cu in the Al-Cu-Mg-Sc alloy, thereby restricting the nucleation of theta ' and S precipitates owing to the decreased available Cu solutes. In property, 0.2 wt% Sc addition can not only enhance the corrosion resistance but also the electrical conductivity of the peak-hardening alloy. In addition, the peak-hardening Al-Cu-Mg-Sc alloy is also featured with increased strength without losing the ductility compared to its solid solution state. Further analyses indicate that the improved properties are essentially attributed to the formation of densely distributed strain-free GPB zones and smaller precipitate-free zones. The obtained results could provide a potential design strategy of high-performance alloys by Sc addition.