Solute Clustering During Natural Ageing in Al-Cu-(Sc)-(Zr) Alloys

Solute clustering during natural ageing in Al-4wt.%Cu alloys with and without Sc and Zr has been studied. The alloys were heat treated to form Al3(Sc, Zr) dispersoids before being solutionised at 500 °C followed by a water quench. Scanning transmission electron microscopy (STEM) and atom probe tomography (APT) were used to characterize Al3(Sc, Zr) dispersoids in the Sc- and Zr-containing alloy. The APT results show that Cu segregates at the interfaces between Al3(Sc, Zr) dispersoids and the Al matrix. Solute clustering during natural ageing was quantified in situ with small-angle X-ray scattering (SAXS). The in situ SAXS results show that the presence of Al3(Sc, Zr) dispersoids significantly retards the solute clustering formation during natural ageing in the Al-Cu alloys. This could be related to the Cu segregation at the Al3(Sc, Zr) dispersoids/Al matrix interfaces, which could deplete the solid solution from Cu solute which is no more available for solute clustering. Additionally, Sc solutes could bind with vacancies which reduces the free vacancies for the diffusion of Cu.