Numerical and experimental investigation of microporosity formation in a ternary Al-Cu-Si alloy

Macrosegregation and porosity formation are investigated by both a numerical model and transient directional solidification experiments. The macrosegregation pattern, and the theoretical and apparent densities are presented as a function of the casting length. X-ray fluorescence spectrometry was used to determine the experimental macrosegregation profiles. The measurement of microporosity was performed by a pyknometry procedure. The local composition along an Al-6 wt%Cu-1 wt%Si casting length is used as an input parameter for simulations of microporosity evolution. The results show that the addition of 1 wt% silicon to the Al-Cu alloy composition increases significantly the volumetric fraction of pores as compared with the corresponding porosity exhibited by an Al-6 wt%Cu alloy casting. It is also shown that the use of a carbon steel chill mold induced an abnormal increase in the fraction of pores close to the casting cooled surface which was caused by a higher Fe concentration provoked by the diffusive flux of iron from the chill. (C) 2010 Elsevier B.V. All rights reserved.