Modeling nucleation and growth of bubbles during foaming of molten aluminum with high initial gas supersaturation

• A nucleation and growth model is used to predict the bubble size distribution in aluminium foaming.
• Nucleation of bubbles takes place heterogeneously on conical cavities of oxide surface.
• Bubble size distributions widen with increase in initial supersaturation pressures.
• Predicted distributions show a monotonous increase whereas experimental distributions show an intermediate peak.

An idealized nucleation and growth based model was used to predict bubble size distribution in liquid aluminum foam, based on the assumption that the entire quantity of hydrogen added as TiH2 was retained in solution initially. The model considered simultaneous nucleation and growth of bubbles in the first stage, and pure bubble growth in the second stage. Bubble nucleation was found to be feasible only heterogeneously within narrow crevices in non wetting substrates. Effects of initial gas supersaturation on total expansion, final bubble size distribution, total number of bubbles, and average bubble size were investigated. Model predictions of foam characteristics were compared with experimental observations on foams prepared by dissociating TiH2 foaming agent in liquid aluminium, and good match between the two was found with respect to average cell size and total number of bubbles. Differences between model predictions and experimental observations, especially in the nature of bubble size distribution, and limitations of the model were explained.