Precipitation behaviour of Al3Zr precipitate in Al–Cu–Zr and Al–Cu–Zr–Ti–V alloys

The precipitation behaviours of Al3Zr precipitate in the Al–Cu–Zr and Al–Cu–Zr–Ti–V alloys were studied by transmission electron microscopy. Metastable Al3Zr precipitates are homogeneously nucleated in dendrite centres resulting in homogeneous distribution. However, the precipitation in the interdendritic regions is complex and the precipitation morphologies, helicAl–like and stripe-like shapes, were observed, which are composed of many spherical Al3Zr precipitates. The stripe-like precipitate clusters have preferential orientations along with the 〈100〉 Al directions, which is inferred to be related to θ′(Al2Cu) and θ phases. Addition of Cu can accelerate the L12→D023 structural transformation of the Al3Zr precipitate.