Abstract

Porosity formation in A356 aluminium plate castings was studied experimentally and theoretically. Analysis of a model introduced in this paper led to the formulation of a pressure index, P*, which was expressed in terms of the thermal parameters G, Vs and tf (where G is the thermal gradient, Vs is the solidus velocity and tris the local solidification time), and the alloy's physical constants. The index, determined from the effects of local pressure drops based on Darcy's law and surface tension within the interdendritic liquid, was employed to estimate the formation of porosity in A356 alloy castings. The experimental and theoretical results indicated that porosity content is inversely proportional to P*, and that porosity content tends to decrease with increasing G0.38/V1.62 when this parameter is less than 0.05°C0.38 min1.62 cm−2. As the value of G0.38/V1.62 is increased over approximately 0.05 °C0.38 min1.62 cm−2, the porosity content was found to be independent of this parameter.

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