Effects of Retrogression and Re-aging (RRA) Processes on Corrosion Properties in AA 7020 Aluminium Alloy

Abstract

AA 7020 alloy, widely used in the aviation and automobile industries with its specific strength, has become a material in demand in recent years by different sectors. Heat treatment to T6 temper increases the mechanical strength by precipitating hardening (ageing). Overaging to T73 temper improves the corrosion behavior of the alloy. A RRA (retrogression and re-ageing) heat treatment is a good alternative as it improves the corrosion behaviour compared to T6 temper and provides better mechanical values than precipitates from a material in T6 temper are redissolved by a short-term heat treatment between 160 and 280 °C (retrogression) which is then followed by a re-ageing under T6 heat treatment condition.

In this study, the AA7020 alloy was retrogressed for 1, 5, 15, 30, and 45 minutes at 180, 200, and 240 °C. Before, it was re-ageing at 120 °C for 24 hours. The hardness, conductivity, and corrosion behaviour of the heat-treated samples were determined, and the microstructure was evaluated by light microscopy, scanning electron microscope (SEM), and Energy-dispersive x-ray spectroscopy (EDX) methods.