Implication of Pre-Aged Three Step T6 Treatment on the Properties of Granite and Silicon Nitride Particulates Reinforced Al7075 Matrix Composite

In the current research Al7075 (Al-5.4Zn-2.6Mg) alloy and composite prepared by dispersing 2 wt.% granite powder and 3 wt.% Si₃N₄ in Al7075 are subjected to peak aging treatment at 100, 120 and 150⁰C to obtain the maximum induced hardness by solid solution strengthening. In succession, by the results of peak aging treatment the alloy and composite are pre aged and heat treated by three step aging conditions. The results 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 100⁰C resulting in 29.88% improvement. Moreover, the composite subjected to pre-aged three step aging has resulted in improved hardness to 197.6 VHN as compared to peak hardness of 153.5 at 100⁰C resulting in 28.72% improvement. Also, the alloy and composite in this condition showed an improvement of 21.38% and 16.34% respectively in the UTS. Also, particularly composite displayed excellent wear characteristics as compared to as cast alloy. An interesting fact noticed in this work is that in three step aging the last step having higher temperature and longer 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 novel approach developed in this study will reduce the longer duration of conventional aging heat treatment and the energy consumption.

Keywords:
Al7075 alloy; step aging; pre aging; granite particle; silicon nitride; wear