Numerical model to predict the position, amount and size of microporosity formation in Al–Cu alloys by dissolved gas and solidification shrinkage

This paper presents a numerical and experimental analysis of the formation of interdendritic microporosities during unidirectional solidification of Al 4.5 wt.% Cu alloy. A model, based on the method of finite difference is applied to simulate the solidifying process, permitting the determination of structural parameters, as primary and secondary dendrite arm spacing, permeability of the interdendritic channels and the formation of microporosity between the dendritic arms. The model permits the prediction of microporosity due to metal shrinkage during solidification and due to the evolution of hydrogen resulting from the difference in its solubility in the liquid and solid phases, including determination of their dimensions and locations. The model allows establishing the minimum gas content and the ideal thermal conditions to minimize microporosity formation. To test and optimize the model developed, experimental testing was performed, using a specially built unidirectional solidifying oven and in situ measurements of the hydrogen content in the liquid metal. Using optical microscopy, the primary and secondary interdendritic spacing were obtained, also including determination of microporosity dimensions and locations. Results obtained are presented with the application of the model for Al 4.5 wt.% Cu alloy solidification under different conditions.