Microporosity prediction in aluminum alloy castings

Abstract

A comprehensive methodology that takes into account solidification, shrinkage-driven interdendritic fluid flow, hydrogen precipitation, and porosity evolution has been developed for the prediction of the microporosity fraction and distribution in aluminum alloy castings. The approach may be used to determine the extent of gas and shrinkage porosity, i.e., the resultant microporosity which occurs due to gas precipitation and that which occurs when solidification shrinkage cannot be compensated for by the interdendritic fluid flow. A solution algorithm in which the local pressure and microporosity are coupled is presented, and details of the implementation methodology are provided. The models are implemented in a computational framework consistent with that of commonly used algorithms for fluid dynamics, allowing a straightforward incorporation into existing commercial software. The results show that the effect of microporosity on the interdendritic fluid flow cannot be neglected. The predictions of porosity profiles are validated by comparison with independent experimental measurements by other researchers on aluminum A356 alloy test castings designed to capture a variety of solidification conditions. The numerical results reproduce the characteristic microporosity profiles observed in the experimental results and also agree quantitatively with the experimentally measured porosity levels. The approach provides an enhanced capability for the design of structural castings.