T6 heat treatment of rheocasting 7075 Al alloy

Effects of solution heat treatment and age hardening on the microstructures and mechanical properties of rheocasting 7075 Al alloy produced by a novel technique, Gas Induced Semi-Solid (GISS) technique, were studied. This work reveals that the optimum solution heat treatment condition for the non-dendritic structured 7075 aluminium alloy was 450 °C for 4 h. Age hardening was performed at temperatures of 120 °C, 145 °C, 165 °C, and 185 °C under various time durations. The peak aging condition was the artificial aging at 120 °C for 72 h, at which a highest tensile strength of 486 MPa with 2% elongation was recorded. This higher strength was caused by higher number density and finer precipitate size of η/ phase than other aging temperatures. The main hardening phase was identified to be the η/ phase while early nucleation of η phase in the higher aging temperature specimens resulted in lower strengths of the alloy. The activation energy for the precipitate hardening process of the alloy derived in this research was 95,827 J/mol.