Influence of 1.0 wt% Li on Precipitates in Al-Zn-Mg-Cu Alloy

Microstructure control always plays a key role in enhancing properties of high-strength Al alloys. Attempts to improve the microstructure of 7000 series alloys by addition of 1.0 wt% Li have been made for a long time, but unsystematically. This article compares the microstructural features of 1.0 wt% Li-containing Al-Zn-Mg-Cu alloy with those of Li-free Al-Zn-Mg-Cu alloy by using differential scanning calorimetric (DSC) techniques, Vickers microhardness and transmission electron microscopy (TEM). The results show the dominance of Guinier Preston (GP) zones, η′or ηphases in 1.0 wt% Li-containing Al-Zn-Mg-Cu alloy, and confirm the capability of Li to retard the rate of precipitates growth and coarsening.