As-cast grain size distribution prediction for grain refined castings via simulating free equiaxed dendrite transport during solidification

In foundry practice, as-cast microstructure is a key concern. It is well accepted that gravitydriven transport processes have an influence on the final microstructure of shape cast components. A predictive model to simulate equiaxed solidification, which treats dendrite transport in the solidifying alloy melt, at low computational cost, is presented in this article. The non-equilibrium solidification model considers nucleation from industrial inoculants, growth and transport of the equiaxed dendrites. The motion of free dendrites is computed as the combined effects of sedimentation settling and transport of free dendrites by the liquid flow due to natural convection. When free dendrites become coherent at the latter stage of solidification, the equiaxed mush of coherent dendrites is assumed to demonstrate characteristics of a porous medium, until it becomes completely solid. Simulations are used to establish the sensitivity of
the as-cast structure of Al-Si shape castings to the magnitude of mould/alloy heat transfer coefficients. It was found that the effects of dendrite sedimentation are higher for low values of this heat transfer coefficient.