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.