Real-Time Radiography and Modeling of Porosity Formation in an A356 Aluminum Alloy Wedge Casting

Abstract

The formation of shrinkage porosity in a wedge-shaped A356 aluminum casting is observed in real-time using video radiography. From this observation, an image-processing technique is developed to quantify the through-thickness average porosity distribution in the casting as a function of time. The solidification and cooling of the casting are simulated in order to obtain the temperature and solid-fraction fields. It is found that once the wedge becomes isolated from the in-gate, surface sinks develop until the solid-fraction at the sinking location reaches approximately 45%. Subsequently, internal porosity starts forming in the upper part of the wedge. This interdendritic porosity spreads over the region with the lowest solid-fraction and continually increases until the casting is fully solidified. The maximum porosity percentage is measured in the thermal center of the wedge. A computational model is proposed to predict the evolution of the porosity in the aluminum casting.