Mathematical modeling of microporosity in A356 aluminum die-castings

A 2-D axisymmetric mathematical model is currently being developed using the commercial finite element package ABAQUS to characterize the evolution of microporosity in aluminum castings. Preliminary work has focused on assessing a number of criteria functions previously proposed in the literature. Model results in the form of temperature and criteria function predictions are compared with experimentally measured temperature and porosity data obtained from a directionally chilled A356 aluminum alloy solidified under conditions resembling those found in an industrial die-casting operation. The results suggest that the Niyama function is best suited to qualitatively predict porosity of the four criteria functions examined. However, all criterion functions, including the Niyama, do not appear to be well suited to predict the amount porosity quantitatively as they fail to include the effect of varying hydrogen and inclusion content. The ultimate goal of the work is to develop a more fundamental based methodology for predicted porosity based on the evolution of the solidification microstructure and the thermodynamics of hydrogen solubility in aluminum alloys.