NUMERICAL AND EXPERIMENTAL ANALYSIS OF MACROSEGREGATION DURING UPWARD AND DOWNWARD SOLIDIFICATION OF A TERNARY Al-Cu-Si ALLOY

摘要

In this article macrosegregation phenomena in ternary Al-Cu-Si alloys are investigated by a numerical modeling technique and by upward and downward unidirectional solidification experiments. In particular, vertically aligned casting experiments of a ternary Al-8wt%Cu-3wt%Si alloy samples are considered. An X-ray fluorescence spectrometer was used to determine the segregation profiles along the castings. The experimental segregation profiles are compared with theoretical predictions furnished by the numerical model, with transient metal/mold heat transfer coefficient profiles being determined in each experiment. The numerical method consists of an explicit/implicit time integration scheme for coupling solutal and thermal fields. It has been observed that the numerical predictions generally conform to the experimental segregation measurements. The model is able to compute the inverse (Cu) solute concentration profile, which occur for upward solidification. For downward solidification only a small region of inverse (Cu) segregation close to the casting surface has been detected. For both solidification arrangements, no macrosegregation has been observed for the silicon content along the length of the directionally solidified casting, except for a short initial transient of normal (upward) and inverse (downward) segregation.