Prediction of as-cast grain size distribution from a model of equiaxed solidification with free dendrite transport

As-cast microstructure is one of the essential engineering concerns for aerospace materials. Movement of equiaxed dendrites during solidification has a significant influence on the final microstructure of shape cast components. The authors have developed a predictive model of equiaxed solidification which treats dendrite transport in the solidifying alloy melt, at low computational cost. The non-equilibrium model considers nucleation from industrial inoculants, growth and movement of dendrites. The motion of free dendrites is computed as the combined effects of sedimentation settling of denser dendrites and transport of small dendrites by liquid flow due to natural convection. When free dendrites become coherent at the latter stage of solidification, the resultant equiaxed mush of coherent dendrites is assumed to have become 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/material heat transfer coefficients.