COUPLING OF MICROSEGREGATION MODELS TO HEAT-FLOW SIMULATIONS IN CASTINGS

Kinetic effects such as coarsening and back diffusion affect the solid ification rate and hence the rate at which latent heat of fusion is li berated. Neglecting these effects can bring about errors in macroscopi c heat flow simulation. This paper investigates whether these errors a re large enough to necessitate interactive coupling of the heat flow s imulation to kinetic models of microsegregation. An approach of 'itera tive' coupling is explored. This involves generating the thermal histo ry by macroscopic calculations using an approximate relationship betwe en the fraction of solid, f(s), and temperature, T, and then correctin g the f(s)(T) relationship by a detailed calculation of solute redistr ibution using a kinetic model of microsegregation. The corrected f(s)( T) relationship including the kinetic effects is then input to the mac roprogram and the iteration is continued until the predicted microsegr egation parameters converge. For Al-4.8% Cu alloy and Al-54% Zn alloy the predictions converge within a single iteration. This shows that th e coupling between the heat flow calculations and the solute redistrib ution calculations is weak.