Evolution of microstructure and properties of Al–Zn–Mg–Cu–Sc–Zr alloy during aging treatment

Abstract

As one of the most efficient trace element to improve the mechanical properties of alloys, scandium (Sc) has attracted much attention for aluminum alloys in recent years. In this study, a new kind of Al–Zn–Mg–Cu–Sc–Zr alloy has been designed, and the evolution of microstructure and properties during the processes including homogenization, hot extrusion, solid solution and aging has been investigated. The alloy aged at 120 °C reveals a dual-peak aging phenomenon which is attributed to the overlap of the formation of Guinier–Preston (GP) zones and η′ phases. Consequently, excellent mechanical properties can be obtained (UTS = 747 MPa, YS = 721 MPa and EI = 10.9%) when the alloy is aged at 120 °C for 15 h. The improvement of the mechanical performance is mainly attributed to the grain refinement by the primary Al3(Sc, Zr) and the dispersion strengthening of the secondary Al3(Sc, Zr). Thus, the combined additions of Sc and Zr play an important role for the strengthening of the alloy.