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Mathematical modeling of microporosity in A356 aluminum alloy Vo, Phuong

Abstract

Die cast aluminum wheels are one of the most difficult automotive castings to produce because of stringent cast surface and internal quality requirements. As part of a collaborative research agreement between researchers at the University of British Columbia and Canadian Autoparts Toyota Inc., work has been underway to predict heat transport and porosity formation in die cast A356 wheels. 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 criteria functions, including the Niyama, do not appear to be well suited to predict the amount of porosity quantitatively as they fail to include the effect of varying hydrogen and inclusion content. A 2-D axisymmetric mathematical model incorporating flow through the interdendritic network and the thermodynamics of hydrogen solubility has been developed. This model has been successfully applied to the prediction of the amount of porosity in a series of test castings with varying hydrogen content.

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