Unusual ageing behaviour of friction-stir welded Al–Cu–Mg alloy

Abstract The conventional peak-ageing treatment of friction-stir welded AA2519 resulted in precipitation of a stable θ-phase instead of the expected strengthening dispersion of θ″ and θ′ thus degrading material strength. This phenomenon was attributed to acceleration of the precipitation kinetics due to grain refinement and over-ageing effect associated with the weld thermal cycle.