Permanent mold casting of aluminium alloys: correlation among processing, microstructure and simulation

Porosity level and local solidification time are generally acknowledged to affect both dynamic and static properties of cast aluminium alloys intended for structural applications. To analyse these effects, an investigation was carried out examining permanent mold cast A319 and A356 aluminium alloys. Step-bar castings were poured at different temperatures. The castings were sectioned and samples extracted from each step. The porosity level and the secondary dendrite arm spacing were examined using image analysis of randomly selected fields. Results were obtained for steps of thickness 5, 10, 15 and 20 mm. The riser was also sectioned where the thickness was about 35 mm. In every casting considered, porosity level and SDAS increased with section thickness. A computer simulation approach was also carried out to predict SDAS values. The simulation results showed a good correlation to experimental data.