As-cast microstructure of Al-Zn-Mg-Cu-Zr alloy containing trace amount of Sc

It has been reported that the element scandium (Sc) is the most effective modificator which can significantly refine the grain size, prohibit recrystallization process and increase the strength. Adding trace of Sc in 7000 series aluminum alloys is considered to be an effective way to modify its microstructure and promote mechanical properties. In order to study the effect of Sc element on as-cast microstructure of Al-Zn-Mg-Cu-Zr alloy, ingots containing different amounts of Sc were prepared by ferrous-mold cast. Microstructures were characterized by means of differential scanning calorimeter (DSC), X-ray diffraction (XRD), optical microscope (OM) and scanning electrical microscope (SEM). The results indicate that when the Sc level exceeds a critical concentration, Al-3(Sc,Zr) primary phase would form in the melt and act as an efficient nucleant, resulting in very refined grain and an equiaxed grain structure. Sc element reduces the number of eutectic phases formed during solidification, coupled with an increase in the concentration of major alloying elements retained in the solute. This behavior suggests possible benefits in improving the integrated properties of terminal products.