Recent Developments in Slurry Formation

Abstract

Despite the proven improvement in the quality of products formed by semisolid processing, providing both better surface finish and mechanical properties after heat treatment, the main obstacle to progress in the industrial use of thixoforming are due to the additional costs involved in. 1. The production of solid billets having the correct internal structure, e.g., by the MHD process 2. The reheating, melting, and soaking of the billet to reformthe semisolid structure 3. The scrap produced by each thixoformed article, which must be returned to the billet manufacturer for reconstitution as appropriate billets These cost problems have led back in recent years to a reconsideration of the rheoforming route (the production of semisolid alloy slurry on site followed by immediate injection of slurry into the die), that was originally used at MIT, thus bypassing casting of solid by MHD. The UBE process [35] has been developed whereby rapid cooling of the aluminum alloy in a cylindrical steel crucible forms a semisolid billet. The semisolid billet and crucible are then transferred to the die casting machine by robot arm, where the billet is dropped into the shot sleeve for immediate injection. The scrap from the operation is collected ready for remelting in the holding furnace on site for further casting. This route clearly obviates the need for MHD stirring to produce a nondendritic structure, and the heating and partial melting of billets prior to injection.