3D study of the structure of primary crystals in a rheocast Al–Cu alloy

An Al-10.25 wt.% Cu alloy was mechanically stirred at 1000 rpm while being cooled to and isothermally held at 619°C for various times before casting. The microstructure of as-cast materials consists of pseudo-particles and pseudo-clusters in two-dimensional (2D) views. Serial sectioning was performed and it was found that pseudo-particles belonging to a pseudo-cluster were connected in three dimensions and a pseudo-cluster was actually a single primary particle. A three dimensional (3-D) model of such a primary particle was constructed from 2D sections which showed the complexity of its structure. It is suggested that the theories based on agglomeration and disagglomeration of particles during rheocasting be re-examined in light of the experimental results.