Investigation of casting/chill interfacial heat transfer during solidification of Al-11% Si alloy by inverse modelling and real-time x-ray imaging

Heat transfer at the casting/chill interface during solidification of Al-11% Si eutectic alloy (LM 6) was investigated. Experiments were carried out for various combinations of chill thickness, casting height and chill material. The thermal history at nodal locations in the chill was used to estimate the interfacial heat flux by inverse modelling, A new parameter called the heat flux penetration time was proposed to model the transformation of the interfacial condition from a perfect contact to a nonconforming contact. The heat transfer coefficient was modelled as a function of the chill thickness, casting height and the thermal diffusivity of the chill material. Real time x-ray imaging technique was adopted to observe the casting/chill interface during solidification of the alloy. The video pictures indicate that a gas gap forms in the case of thin chills. The formation of the gap in thick chills could not be detected. The widths of the gap formed at the interface were measured by an image analyser which revealed that the width of the gap not only varies with time but also with position along the chili surface.