Influences of Initial Compositions,Dendrite Morphologies and Solid-Back Diffusion on Solidification Path of Al-Si-Mg Alloys

The solidification paths of ternary eutectic Al-Si-Mg alloys in the Al-rich corner were investigated by numerical calculation. The thermodynamic data needed in the calculation were obtained by direct coupling simulation program with a CALPHAD software Thermo-Calc via its TQ6-interface and COST2 database. The influences of the initial compositions, dendrite morphologies and the solid diffusion coefficients on the solidification path were analyzed. The solidification paths were calculated with assumed different solid diffusion coefficients varying in eight orders of magnitude and different dendrite morphologies including the five basic geometrical shapes of spherical, cylindrical, plate-like, inward cylindrical, inward spherical and the assumed equiaxed dendrites. The calculated results comparisons showed that initial compositions, dendrite morphologies and solid-back diffusion can significantly influence the solidification path and the type and amounts of eutectic of Al-Si-Mg alloys. The predicted solidification paths and the eutectic fraction of selected Al-Si-Mg alloys calculated with assumption of equiaxed dendrite morphology agreed well with the experimental results.