Alloy composition and metal/mold heat transfer efficiency affecting inverse segregation and porosity of as-cast Al-Cu alloys

Porosity is one of the most important defects in metals casting. In this study, macrosegregation and porosity formation were investigated by a numerical model and by solidification experiments. The local composition along the length of Al-Cu castings was calculated by the macrosegregation model and used as an input parameter for simulation of microporosity. The effects exerted by gravity upon the solute redistribution and microporosity are also encompassed by this model. X-ray fluorescence spectrometry was used to determine the segregation profiles. The measurement of microporosity was performed using pyknometry analysis. The results have demonstrated that both the decrease on alloy solute content and the increase on metal/mold heat transfer coefficient are connected to lower porosity levels at regions closer to the casting surface. (C) 2008 Elsevier Ltd. All rights reserved.