Abstract
A numerical model for predicting microporosity formation in aluminium castings has been developed, in which the redistribution of hydrogen between solid and liquid phases, and Darcy flow in the mushy zone were taken into account. For simulating the nucleation and growth of hydrogen pores, the pore radius is assumed to be a function of the secondary dendrite arm spacing, whereas the pore growth assumes equilibrium hydrogen activity between pore, liquid and solid. One of the key features of the model is that it uses a two-stage approach to porosity prediction. In the first stage, the volume fraction of porosity is calculated based on the reduced pressure, whereas, in the second stage, at fractions solid greater than grain coalescence fSC, an increment in the fraction porosity is calculated based on the volume of liquid trapped within a continuous solid network, which is estimated using a correlation based on the Niyama criterion. The model has been implemented within the commercial software package, ABAQUS, which has been used as a platform to solve the thermal field. The numerical model has been applied to a simple cylinder-shaped test casting, and the simulated results have been evaluated by comparing with the experimental results.
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