Scale-up modeling of the twin roll casting process for AZ31 magnesium alloy

In the present study, a 2-D finite-element method (FEM) thermal-fluid-stress model has been developed and validated for the twin roll casting (TRC) of AZ31 magnesium alloy. The model was then used to quantify how the thermo-mechanical history experienced by the strip during TRC would change as the equipment was scaled up from a laboratory size (roll diameter = 355 mm) to a pilot scale (roll diameter = 600 mm) and to an industrial scale (roll diameter = 1150 mm) machine. The model predictions showed that the thermal history and solidification cooling rate experienced by the strip are not affected significantly by caster scale-up. However, the mechanical history experienced by the strip did change remarkably depending on the roll diameters. Casting with bigger rolls led to the development of higher stress levels at the strip surface. The roll separating force/mm width of strip was also predicted to increase significantly when the TRC was scaled to larger sizes. Using the model predicted results, the effect of both casting speed and roll diameter was integrated into an empirical equation to predict the exit temperature and the roll separating force for AZ31. Using this approach, a TRC process map was generated for AZ31 which included roll diameter and casting speed.