The effect of solidification thermal variables on surface quality of Al–Cu ingots

A combined theoretical and experimental approach was undertaken to quantitatively determine thermal variables during solidification, i.e., transient metal/mold heat transfer coefficients, cooling rates and a driving force factor for the solidified shell distortion, given by the gradient of the cooling rate. Such thermal variables were correlated with the geometric features of the observed surface marks of Al–Cu alloys ingots in the range of pure Al and the eutectic composition. It was shown that the thermal distortion factor increases with alloy Cu content, and it is strongly dependent on the initial values of the metal/mold heat transfer coefficient. A correlation with the resulting experimental surface marks has indicated that larger depth and pitch are associated with higher thermal distortion driving forces.