Modeling thermal behavior of chills during solidification of Al-Cu-Si alloy

The hear transfer in chills through which heat is extracted uniformly during the solidification of Al-Cu-Si alloy was investigated. The aim of the work is to estimate the localized chill-casting interfacial heat flux for various casting conditions, using measured values of temperatures at locations within the chill material, along with an "a priori" knowledge of the thermophysical proper-ties of the chill. The effect of chill location on interfacial heat flux was also investigated. A portable data logger was used for accessing the thermal history inside the casting and the chill. The heat diffusivity (root k rho Cp), thermal diffusivity (alpha = k/rho Cp) and thickness of the chill (d) were found to be important parameters controlling the heat flow across the casting-chill interface. The peak chill surface temperature was observed to decrease with increase in (d. alpha). The local solidification time decreased exponentially with increase in (d.root k rho Cp). The peak heat flux was modeled as an exponential function of the product of chill thickness and heat diffusivity (d. root k rho Cp). The time of occurrence of peak heat flux was modeled as power function of the product of chill thickness and thermal diffusivity (d.alpha). A fifth degree polynomial equation was used to describe the variation of normalized heat flux with time after occurrence of peak heat flux. The heat flux model was validated. The experimentally measured and simulated temperatures inside the chill and casting, were found to be in good agreement. All the castings were subjected to microstructure analysis. It was observed that volumetric heat capacity of the chill material had a significant effect on the secondary dendrite arm spacing (lambda(2)) of the casting.