Three-dimensional phase field simulation of spheroidal grain formation during semi solid processing of Al-7Si-0.3 Mg alloy

Abstract

The present study reports development and application of a three dimensional phase field (PF) model, to investigate the microstructure evolution mechanism responsible for generation of spheroidal primary Al grains, associated with cooling slope processed semi solid slurry of A356 aluminium alloy. The cooling slope rheoprocessing technique involves solidification of flowing melt on an inclined slope surface, where gravity assisted fluid flow and shearing action between the flowing melt and the slope surface causes formation of near spherical primary solid fragments, and subsequent isothermal globularisation of the evolving primary solid. The present PF model implements a seed density based nucleation model. The seed density requirements to simulate microstructure evolution for different simulation/melt treatment conditions of cooling slope processing have been estimated based on initial experimentation. The simulated micrograph of slope exit state i.e, at the end of cooling slope processing has been used to estimate the number density and average size of constituent α-Al grains of the generated slurry, at slope exit state. The values obtained are fed subsequently as input parameters to simulate post slurry generation isothermal globularisation process. The model predictions are validated experimentally, thus establishing its capability to predict the characteristics of semisolid slurry at different stages of cooling slope rheoprocessing, in terms of solid content (volume fraction), diameter, density, and shape factor (sphericity) of nucleated primary Al grains.