The cyclic stress-strain behavior of polycrystalline Al-5wt.%Mg

Abstract

Push-pull fatigue tests have been carried out on binary Al-5wt.%Mg specimens in the annealed and cold-worked conditions at constant plastic strain amplitudes between 4 × 10 −5 and 2 × 10 −2 to characterize the cyclic stress-strain response and the strain-fatigue life behaviour. The annealed material hardens substantially at all strain levels and, at saturation, exhibits a constant plateau stress of 270 MPa for plastic strain amplitudes between approximately 10 −4 and 2 × 10 −3. The high degree of cyclic hardening is related to the formation of a high density of fine dislocation loops. Intense slip bands are also observed to penetrate the bulk of the specimen. The strain-fatigue life plots of the annealed and cold-worked material reveal a two-slope behaviour. The high fatigue life exponent at low plastic strain amplitudes is thought to be due to rapid crack initiation in isolated surface slip bands.