Coupling of microsegregation models to heat flow simulations in castings

Kinetic effects such as coarsening and back diffusion affect the solidification rate and hence the rate at which latent heat of fusion is liberated. Neglecting these effects can bring about errors in macroscopic heat flow simulation. The paper investigates whether these errors are large enough to necessitate interactive coupling of the heat flow simulation to kinetic models of microsegregation. An approach of 'iterative' coupling is explored. This involves generating the thermal history by macroscopic calculations using an approximate relationship between the fraction of solid, f_S, and temperature, T, and then correcting the f_S(T) relationship by a detailed calculation of solute redistribution using a kinetic model of microsegregation. The corrected f_S(T) relationship including the kinetic effects is then input to the macroprogram and the iteration is continued until the predicted microsegregation parameters converge. For Al-4.8% Cu alloy and Al-54% Zn alloy the predictions converge within a single iteration. This shows that the coupling between the heat flow calculations and the solute redistribution calculations is weak.