Abstract

An investigation has been performed to study the effects of convection streams and the movement of dendritic solid on the macrosegregation in equiaxed structure of aluminium cast ingots. The investigation combined laboratory work, metallographic examination and mathematical modelling. The laboratory work involved different superheats for Al-10%Si alloy cast ingots. The measurements of grain size of equiaxed crystals and macro-segregation distributions have been conducted to verify the solidification model by using the metallographic study combined macro/micro-structural evolution of cast ingot samples. Two-dimensional mathematical model of fluid flow and heat transfer has been developed to characterise the natural convection streams, thermal fields and macro-segregation distributions taken into account the effect of dendritic solid movements. The model predictions were compared to measurements of cooling curves and macro-segregation distributions where the reasonable agreements were found. The formation of macro-segregation phenomenon has been studied and discussed based on convection streams, the movements of dendritic solid and mushy permeability. Also, some typical cases in conventional casting processes related to increase the occurrence of dendritic solidification defects have been discussed.

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