Modeling of porosity formation in direct chill cast aluminum–magnesium alloys

A model of the formation of porosity during the DC casting of Al–Mg alloys was developed and incorporated as a post-processor to a commercial transient macromodel of the three dimensional heat transfer and fluid flow. The porosity model not only predicts the percentage porosity, but also the size, shape and distribution of the pores. The sensitivity of the model to process and alloy variations was evaluated, showing the importance of the cooling rate and hydrogen concentration. An experimental study of the amount of porosity in laboratory scale (250×400 mm cross-section) DC cast ingots of Al 2, 4 and 6 wt.% Mg was performed. The results from these experimental billets were used to validate the model as a function of the location in the ingot and the initial hydrogen and magnesium content. The model correctly predicted the experimentally observed trends, showing good correlation to the measured percentage porosity.