Quantification of the influence of increased pre-stretching on microstructure-strength relationships in the Al–Cu–Li alloy AA2195

Abstract

The effect of increasing pre-stretching to higher levels, than are currently used in industrial practice, has been investigated on the strength, microstructure, and precipitation kinetics seen during artificial ageing an Al–Cu–Li alloy AA2195 - focussing on the behaviour of the main strengthening phase, T1. Increasing the pre-strain level, to the maximum obtainable before plastic instability (15%), resulted in an increase in the T8 yield strength to ∼ 670 MPa with a corresponding reduction in ductility from ∼11 to 7.5%. Microstructure data have been used to deconvolute and model the effects of increasing pre-strain on the main strengthening components that contribute to this large strength increase. The precipitation strengthening model proposed by Dorin et al. [1] has been successfully employed to calculate the strengthening contribution of the T1 phase and the increase in strength due to strain hardening has been modelled using X-ray line broadening measurements of dislocation density, using the modified Williamson–Hall approach. Refinement of the T1 phase was observed to continue to higher pre-strains than previously thought, but it is predicted that this leads to a reduction in the strengthening contribution from precipitation. In contrast a low level of recovery was observed during stretching, and artificial ageing, resulting in an increasing contribution form strain hardening with pre-strain. Thus, it is shown that increasing the pre-strain prior to ageing results in a reduction in the strengthening provided by the T1 phase, in favour of an increase in the strain hardening contribution.