Production of rheocast slurries by partial melting through alternative thermomechanical treatments

The production of alloys with rheocast structure, where the primary phase consists of globularized particles, by partial melting, involves grain recrystallization and secondary phases melting. In the process known as SIMA (Strain Induced Melt Activation), the raw material is cold deformed by a two-step rolling, making it little efficient. This work investigates the production of thixotropic material, by alternative thermomechanical treatments, of an Al-3.35wt%Cu alloy. Two treatments, which avoid the hot deformation step of SIMA, are performed: Recrystallization and Partial Melting (RAP) and Overaging (OAT) processes. In the first, the as-cast, dendritic, alloy is cold deformed at ambient temperature and then heated to a constant temperature in the mushy zone, to obtain the rheocast structure. In the second, the alloy undergoes a solution and precipitation heat treatment, before cold-deformation, with the aim of obtaining second phase precipitated particles with size and interparticle spacing favourable to the increasing of the nucleation rate of recrystallized grains, during heating of the alloy. It was found that the two routes produce globularized structures, with grain reduction of 85 % and 90 % for RAP and OAT, respectively, with respect to initial grain sizes. In general, OAT process resulted in more rounded and smaller globules than RAP