On the ageing of a hyper-eutectic Zn-Al alloy

Zinc alloys are widely used in different fields, like handles and locking, fashion and design as well as automotive or electronics, thanks to their good mechanical and technological properties combined with low cost and easy formability. A limit to a wider use of these alloys is the aging phenomenon that causes a drop in their mechanical properties in time. In order to improve their use in competition with more expensive copper and aluminum alloys, in the last years the research has been addressed to develop new Zn-alloys compositions. One of these new alloys, containing 15 wt% of Aland 1 wt% of Cu, appears to be suitable for both foundry and plastic deformation forming processes, as resulted from preliminary laboratory and industrial trials. Being a newly developed alloy, many properties have still to be investigated, to better understand the effective potentiality for a proper industrial application. In this paper the ageing behavior of die-cast Zn-15Al-1 Cu hyper-eutectic alloy was studied by means of tensile tests and microstructural analyses. It was demonstrated that the alloy suffers from a drop in mechanical properties, in particular at the very beginning of soaking at high temperature. A first analysis of the microstructure by optical and scanning electron microscope was not able to fully point out the causes of the aging phenomenon.