The cyclic stress-strain response of precipitation hardened Al-15 wt.% Ag alloy

Abstract

Al-15 wt.% Ag alloy, heat-treated so as to contain GP zones, and thermomechanically treated in two different modes, has been strain-cycled in order to explore its cyclic stress-strain response. Observations of the deformation and fracture behavior have been made by transmission- and scanning electron microscopy. The alloy containing GP zones does not soften under constant cyclic plastic strains and this observation supports the “disordering” mechanism of cyclic softening in those alloys which do soften. Instead, cyclic strain-induced γ precipitates are nucleated and grown, even at comparatively short lives, and give rise to large degrees of hardening; over a small range of strain, the cyclic stress-strain curve shows a negative slope on account of this precipitation. The growth kinetics of the precipitates have been analysed in detail and shown to be consistent with vacancy-enhanced diffusion. The thermomechanically treated alloys are extraordinary resistant to cyclic softening. In addition, cyclic response under random and incremental loading has been studied and differences and similarities with respect to behavior under constant strain cycling have been documented.