Casting-chill interface heat transfer during solidification of an aluminumalloy

Unidirectional solidification tests on an aluminum alloy were conducted wit h a computer-controlled instrumented rig. The alloys employed in this study were poured into isolated ingot molds (made of recrystallized alumina and covered with ceramic fiber) placed on top of a steel plate, coated either w ith a graphite- or ceramic-based paint in order to avoid sticking of the ma terial. Thermal evolution during the test was captured by type-g thermocoup les placed at different positions in both the ingot and the plate. The bott om surface of the plate was either cooled with water or left to cool in air . The heat-transfer coefficients across the aluminum-steel interface were e valuated by means of a finite-difference model. It was concluded that the h eat-transfer rate depends on the conditions at the interface, such as the t ype of coating used to protect the plate, and the solidification reactions occurring on the aluminum during its solidification.