Transient memory effects during plastic strain cycling of Al-Cu alloy

Results of cyclic tests on a commercial Al-Cu alloy show the transient memory effects mainly observed in the alloy aged at 200°C. Asymmetric tests give experimental proof that the constricted loops observed during the first cycles of this material are a form of strain memory. This transient effect is associated with the back stresses caused by the misfit of θ′ lamellae in the sheared matrix lattice; it is explained by means of a simple accommodation model. The isotropic hardening component of strain-hardening can be determined from cyclic tests by a method of which an outline is presented. According to the model of dislocation shuttling used to describe the cyclic hardening, the reverse straining should repeat the forward hardening: we present experimental proof that this is indeed the case for εα > 0.008, except for a difference in stress level caused by isotropic hardening during forward straining. During saturation cycling reduction of the strain amplitude gives rise to a second memory effect: the small loops are formed by curves which closely repeat the former large-amplitude curves. As a corollary the small-amplitude peak stresses are shifted towards the first of these values, whether these are in tension or in compression