Grain Refinement of Liquid Metal by Cavitation Process: Modelling
Haghayeghi, L. Nastac, “Grain Refinement of Liquid Metal by Cavitation Process: Modelling”, Metals and Materials International, Vol.19, 2013, PP.959-967.
An investigation was carried out on the grain refinement of molten AA5754 Aluminum alloy through intensive shearing. The results show intensive shearing via cavitation decreases the grain size significantly. The above hypothesis for structure refinement was evaluated and an experiment was performed to ensure the creditability of this assumption. Finally, it was simulated by computational fluid dynamics (CFD) modelling. It was understood that shearing is the responsible mechanism for creation of cavitation bubbles and further collapse of them. It was also concluded the pressure which generated from the collapse of the bubble is well enough for braking the oxide layer and wetting them. It was proved that breaking of the oxide layer wets the impurity particles upon collapse of cavitation bubbles and provides additional nuclei and additional grain refinement. The suggested mechanism includes improved wetting by breaking the oxide layer through fatigue via continuous hitting of the micro-jets, local undercooling upon the collapse of cavitation bubbles, and pre-solidification inside fine capillaries.