AbstractThe cyclic stress response characteristics of Al–Li alloy 2090 aged to contain fine ordered precipitates were studied over a range of plastic strains. The specimens were cycled using tension–compression loading under total strain control. The peak aged alloy showed softening at all plastic strain amplitudes. The degree of softening was observed to be greater at higher amplitudes than at lower amplitudes. The presence of shearable matrix precipitates in the alloy results in a local decrease in resistance to dislocation movement, leading to a progressive loss of ordering contributions to hardening. The observed softening behaviour is attributed primarily to dislocation–precipitate interactions, and is a mechanical effect. The fracture behaviour of the alloy is discussed in terms of competing mechanistic effects involving plastic strain amplitude, response stress, intrinsic microstructural features, and deformation behaviour.MST/1309