Experimental and numerical modeling of equiaxed solidification in metallic alloys

Nucleation undercoolings are measured for the primary dendritic structure and for the eutectic structure in aluminum-copper samples solidified during electromagnetic levitation. The recorded cooling curves are used to determine the heat extraction rate and the solidification times. Metallurgical characterizations consist of composition measurements using a scanning electron microscope (SEM) equipped with energy-dispersive X-ray spectrometry and analyses of SEM images. The distribution maps drawn for the average copper composition, the volume fraction of the eutectic structure and the dendrite arm spacing reveal strong correlations. An equiaxed solidification model based on mass and heat balances is developed for the interpretation of the measurements. The model predicts the effect of diffusion in the liquid and in the solid, as well as the consequences of the recalescences occurring immediately after the nucleation of the primary dendritic structure and the eutectic structure. The nucleation undercooling of the eutectic structure is shown to be a key parameter for a quantitative prediction of the fraction of phases in the solidified samples.