Heterogeneity of aging response in friction stirred Al-Cu-Li alloy.

Friction stirred materials have unavoidable heterogeneity in the processed microstructure, which is more severe in the transverse direction of the run and deteriorates structural strength. Effect of post friction stir pre-stretching and aging on this microstructural heterogeneity in an Al-Cu-Li alloy sheet is investigated using highly resolved local tensile behaviour. Local stress-strain curves, at 1 mm spacing were obtained using transverse tensile tests accompanied by a continuous strain measurement using digital image correlation and the hybrid model was used for strain hardening analysis. Local mechanical and strain hardening behaviour is correlated with microstructural information obtained from transmission electron microscopy and differential scanning calorimetry. Aging with and without pre-stretch, both effectively increased the global strength, but the aging response was heterogeneous in all the cases due to variation in solute content and the strain hardening ability within the processed region. Direct aging enhanced the microstructural heterogeneity and led to strain localization, while strain hardening during pre-stretch contributed more strength to the weaker regions, enhanced T1 precipitation and thus effectively reduced the strength heterogeneity. This study provides insight into detailed mechanical behaviour information within a friction stir processed material which can be applied to strengthen structures produced with friction stir technology. • Aging response of friction stirred Al-Cu-Li sheet improves with pre-stretch. • Precipitate phases are pre-stretch sensitive and control flow heterogeneity. • The aging response is limited by the local solute availability. • Dislocation accumulation during pre-stretch strengthens weaker regions. [ABSTRACT FROM AUTHOR]