Modeling of macrosegregation and microporosity formation during transient directional solidification of aluminum alloys

In this article macrosegregation and porosity formation are investigated by a numerical modeling technique and by upward vertical unidirectional solidification experiments. The local composition predicted by the macrosegregation model along the casting is used as an input parameter for simulation of the corresponding microporosity. The effects exerted by gravity upon the solute redistribution and microporosity formation are also encompassed by the model. In particular, a vertically aligned casting experiment of a binary Al–6.2 wt.%Cu alloy is considered. An X-ray fluorescence spectrometer was used to determine the segregation profiles along the casting. The experimental segregation profile and porosity evolution along the casting are compared with theoretical predictions furnished by the numerical model, by considering a transient metal/mold heat transfer coefficient profile experimentally determined. An excellent agreement between the simulated and experimental inverse copper profile has been observed. The simulation of porosity formation for an anisotropic channel has conformed better with the experimental scatter, with the experimental volumetric fraction of pores profile presenting an ascending trend from the chill to the top of the ingot.