Heat transfer at the casting/chill interface during solidification of commercially pure Zn and Zn base alloy (ZA8)

Casting/chill interfacial heat transfer during solidification of commercially pure zinc and ZA8 alloy against copper, hot die steel, stainless steel and aluminium instrumented chills was investigated. The peak heat flux strongly depends on the thermophysical properties of chill, chill surface condition and superheat of the casting material. Contact angles of alumina coating measured on various substrates suggested that the adhesion of the coating material on copper chill was significantly better as compared to other chill materials. The heat flux curve in the case of coated chills is characterised by a double peak indicating remelting of the solidified casting shell. The second peak in the HTC curve is lower for high conductivity and higher for low conductivity chills as compared to the first peak. It is possible that solid shell formation and remelting occurred in the case of high thermal conductivity chills, whereas shell remelting did not happen in lower thermal conductivity chills.