Influence of processing variables on structure and porosity in stir-casting Al–Cu alloys

The influence of processing variables on the structure and porosity of stir-cast Al–10Cu alloy has been investigated experimentally. Two stir-casting conditions were considered: continuous cooling, and continuous cooling followed by isothermal stirring. Processing variables were varied as follows: stirring speed v from 340 to 995 rev min⁻¹, stirring temperature between liquidus and solidus T from 590° to 620°C, and isothermal stirring time t from 0 to 30 min. Two types of stir-cast structure are distinguished, depending on v: primary-particle agglomerations, which form at slow v, and primary particles which are nearly spherical in shape, smaller, and are relatively homogeneously distributed, which form at high v. Three types of porosity pattern are distinguished: fine trapped porosity in the matrix, coarser trapped porosity at the agglomeration boundary, and fine, shrinkage porosity within the agglomeration. These types o/porosity depend on v, T, and t.