Experimental investigations of stress-relaxation ageing behaviour of AA6082

Abstract

Stress-relaxation ageing behaviour of peak-aged aluminium alloy 6082 (AA6082-T6) has been experimentally investigated with initial loading in both elastic and plastic regions in this study. The stress-relaxation ageing tests with various initial strain levels were carried out at 160 °C for up to 12 h and room temperature tensile tests were performed subsequently. Selected samples have been examined using transmission electron microscopy (TEM) to study microstructural evolution during the process. The results show that the total stress relaxed after 12 h test increases significantly with increasing initial strain levels. The initial strain levels contribute little effect on yield strength evolution during stress-relaxation ageing, as softening from the coarsening of β′′ precipitates is balanced by hardening from dislocations. Stress-relaxation mechanisms of the material have been analysed on the basis of creep stress exponent. In the elastic region, a creep stress exponent of 3 with a threshold stress of 70.1 MPa has been obtained, indicating a dislocation glide controlled creep mechanism; while in the plastic region, a decreasing threshold stress with increasing initial strain levels has been proposed to achieve a positive creep stress exponent.