From heterogeneous nucleation to homogeneous spatial distribution of hardening precipitates: An in situ TEM study on cold-rolled AA2024-T3 (Al–Cu–Mg).

The transition from heterogeneous nucleation of nanoscale hardening S-phase precipitates on dislocation lines in cold-rolled aluminium alloy 2024 (Al–Cu–Mg) to a spatially homogeneous distribution during artificial ageing is studied by means of in situ and ex situ transmission electron microscopy (TEM). Three stages of precipitate evolution following nucleation on dislocation lines are established: (i) Growth and coalescence on dislocation lines, (ii) Ostwald ripening controlled by pipe diffusion, and (iii) Ostwald ripening controlled by volume diffusion. Whilst Ostwald ripening controlled by pipe diffusion is active (stage (ii) and transition from stage (ii) to stage (iii)) dislocation annihilation and/or re-arrangement can occur. [ABSTRACT FROM AUTHOR]