Developing an optimized homogenization process for sc and zr containing al-mg-si alloys

Abstract

Light-weighting of vehicles drives the development of Aluminium alloys with improved strength and formability. An opportunity to achieve this goal is using Scandium (Sc). The beneficial effects from Sc comes from the formation of nano-sized Al3Sc dispersoids. Detrimental interactions between Sc and Silicon (Si) has limited the uptake of Sc in 6xxx alloys. The first step towards developing Sc containing 6xxx-series is to understand the as-cast microstructure and the effect of subsequent heat treatment on the dispersoids. This work uses isochronal ageing trials on a series of Al-Mg-Si-(Sc)-(Zr) model alloys. The evolution of hardness and conductivity is recorded to indirectly characterize the precipitate sequence. Transmission electron microscopy is used to further characterize the morphology and kinetics of MgSi precipitates and Sc/Zr dispersoids. The precipitation of Sc was altered by the presence of Si, and hence it is concluded that a non-traditional homogenization treatment is required for these alloys.