Solidification microstructure affecting ductility in semi-solid-cast products

The semi-solid process produces globular instead of dendritic alpha phase and extraordinarily fine fibrous aluminum-silicon eutectic structure, which apparently enables exceptionally high ductility, even when casting copper-containing and secondary alloys that would normally have limited ductility. Contrary to the experience with liquid cast products of the same alloys, semi-solid products can be given a T-5 heat treatment without loss of ductility, a significant advantage in terms of dimensional controls and treatment costs. This paper will describe solidification events that lead to the unique alpha aluminum, eutectic aluminum-silicon and secondary phase structures of semi-solid products and provide evidence to date that it is these unique characteristics that are responsible for exceptional ductility, especially in the T-5 temper.