Controlled nucleation method for formation of semisolid feedstock

A Controlled Nucleation method has been developed to produce feedstock for semisolid forming, without forced convection. By controlling grain nucleation and growth, fine-grained and non-dendritic microstructures that are suitable for semisolid casting can be generated. The method has been applied to hypoeutectic and hypereutectic aluminium-silicon casting alloys, aluminium wrought alloys and a magnesium alloy. Parameters such as pouring temperature, cooling rate and grain refiner addition have been controlled to achieve copious nucleation, nuclei survival and dendritic growth suppression during solidification. The influences of the controlling parameters on the formation of thixotropic structure are different for each of these alloy groups. The as-cast structures were then partially remelted and isothermally held. Semisolid thixotropic structures were developed and ready for semisolid casting.