Effect of plastic deformation on the ageing behaviour of an Al-Cu-Mg alloy with a high Cu/Mg ratio

The effect of tensile strain ranging from 1% to 7% on the decomposition sequence and mechanical properties of an AA2519 alloy with low Si content is studied. Pre-straining promotes the precipitation of theta'- and Omega(1)-phases at dislocations and suppresses the precipitation of GP-zones and theta ''-phase. The aspect ratio (AR) of the homogeneously nucleated Omega(1)-phase is higher than that of the Omega(n)-phase nucleated on the theta'-phase/A1 interfaces by a factor of similar to 4. Replacement of theta ''-phase by a dispersion of theta'- and Omega(n)-phases took place under peak-ageing condition and thus imparted only a minor hardening effect, despite a seven-fold increase in the volume fraction of the strengthening precipitates. An increase in the yield stress by 30% with increasing pre-strain from 1% to 7% is attributed to an increase in the lattice dislocation density. Over-ageing leads to replacement of the Omega(11)-phase by the theta'-phase.