Effect of Reversed Cyclic Stressing and Phase Transition on the Transient and Steady State Creep Behaviour of Al–22 wt% Ag Alloy

Static and completely reversed cyclic creep acceleration characteristics of Al – 22 wt% Ag alloy were investigated using a modified tensile testing machine. Different amplitudes of reversed cyclic stress (σrev) ranging from 7.2 to 10.2 MPa at different working temperatures ranging from 353 K to 413 K were performed. To get a relation between aging temperature and threshold stress (σth) for cyclic creep acceleration, aging temperatures ranged from 423 to 683 K were used. The transient creep and steady state creep parameters (n, β and έst) were calculated. Values of n, β and έst showed a dependence on aging temperature and were found to increase with increasing σrev as well as working temperature. Transmission electron microscopy (TEM) is used to investigate the microstructures formed in the aged samples. The results were explained in view of mode of interaction between the thermally induced structures during aging with moving dislocations induced by the static stress or dislocation structure induced by cyclic stress. The value of the steady state creep exponent depicts high dependence of the steady state creep stage on transient creep stage. Precipitate-dislocation interactions are suggested as the rate controlling mechanism for both transient and steady state creep stages.