Characterization Studies on 7075 Aluminium Alloy Under As-Cast and in Multiple Step T6 Conditions

In the present investigation AA7075 (Al–5.4Zn–2.6 Mg) alloy is subjected to peak aging treatment at 100, 120 and 150 °C to obtain the maximum induced hardness due to solid solution strengthening. In succession, by the results of peak aging treatment the alloy is heat treated by two step and three step aging under non-pre aged and pre-aged conditions. The results of this modified aging treatment indicated that pre-aged three step aging has resulted in enhanced alloy hardness of 185.6 VHN as compared to peak hardness of 142.9 at 100 °C resulting in 29.88% improvement. Also the alloy in this condition showed an improvement of 21.38% in UTS and displayed excellent wear characteristics as compared to as cast alloy. An important observation in this work is that in two or three step aging the last step having higher temperature and duration of aging has resulted always a better hardness and hence has improved mechanical properties. This may be due to increased aging kinetics during heat treatment. The method developed in this study is advantageous in reducing the long duration of conventional aging heat treatment and the energy consumption.