Simulation of Shrinkage Porosity Formation During Alloy Solidification

Porosity due to solidification shrinkage is a troublesome defect in metal casting. It results in low yields and increased costs in production and limits the performance of cast components in service. By reliably predicting porosity in casting process simulation, porosity can be minimized or eliminated. Here, a new model for simulating the formation of shrinkage porosity during solidification is presented. The model is based on the recent discovery that shrinkage porosity nucleates and grows in regions of a casting where the solid fraction is the lowest. It calculates the feeding flows and pressure distribution in the liquid while accounting for the density variation during cooling and solidification. It predicts the location, extent and amount of all types of shrinkage porosity in a casting, including riser pipes and large internal holes, surface sinks, and distributed micro-shrinkage. Porosity predictions are presented for simple casting geometries and for a more complex Mn-steel experimental casting. The comparisons to the observations made in the experimental casting demonstrate the capability of the model to accurately predict the various types of shrinkage porosity. Numerical studies are performed to investigate the sensitivity of the predictions to various model parameters.