Dynamic solidification of sand-cast aluminium alloys

Abstract

The effect of low-frequency mechanical vibration, applied during the solidification process, on the microstructure and mechanical performance of aluminium sand-casting was investigated. Both green-sand moulds and chemically bounded sand moulds were used. The vibration was applied to the moulds along the vertical axe. The investigated acceleration range was included between 0.1g and 15g. The effect of different sections and cooling rate was considered, as well as the influence of using different amplitude at constant acceleration. The microstructure and porosity of the ingots was evaluated by optical microscopy and image analysis. The mechanical properties were investigated by tensile tests performed both on cylindrical and different section flat specimens. Microstructure modification of dynamically solidified castings was achieved, consisting on a refined or a completely non-dendritic microstructure, with a globular aspect and quite rare dendrite fragments. The effective threshold acceleration in order to modify the microstructure of the different section considered was assessed. The ingots presenting modified microstructure revealed interesting mechanical performance, that means mainly higher fracture strain.