Numerical modelling of entrainment of oxide film defects in filling of aluminium alloy castings

Recent advances in understanding the filling process during casting have indicated that metal flow conditions play a key role in controlling the quality of the casting. Inappropriate filling of castings usually causes surface oxide films to be folded into the bulk liquid or broken as a result of a higher liquid metal kinematic energy, resulting in so-called 'entrainment damage'. These folded oxide film defects are entrained in aluminium alloy casting and significantly affect both static and fatigue reliabilities. In the present study, an algorithm, Oxide Film Entrainment Tracking (OFET, 2-D), has been developed, tested and validated for numerical modelling of the liquid aluminium flow and movement, fold over and entrapment of oxide films during the mould filling process of aluminium castings. The Volume of Fluid (VOF) method is employed to track the free surface of liquid metal flow. A kinematic approach has been utilised for modelling the movement and entrainment of the oxide films on the liquid metal surface. Because the oxide films on the free surface are usually very thin, the inertial forces of the films can be disregarded in comparison to other forces like gravity and pressure. The computer program based on the proposed algorithm is able to model the metal flow behaviour and oxide film defect entrainment in filling of aluminium castings.