Hydrogen Diffusion in Molten Aluminum A206 Casting Alloy

Porosity is usually found in the aluminum castings to some extents due to the release of hydrogen during the solidification of a casting. The presence of porosity can be detrimental to the mechanical properties and the pressure tightness of a casting. The diffusion coefficient of hydrogen in molten aluminum is one of the most important factors to understand the transmission behavior of hydrogen. The diffusion coefficients of hydrogen in molten aluminum A206 casting alloy have been determined experimentally on a specially designed laboratory apparatus in this work. A permeable crucible which contains the molten aluminum A206 casting alloy is placed in a temperature-constant vacuum furnace. According to Sievert's law, the hydrogen in the molten aluminum will diffuses unidirectional under vacuum from the place of high hydrogen concentration to the crucible/aluminum interface where the hydrogen content is low to form the concentration gradient in the melt. By solving the Fick's diffusion equation and by measuring the average hydrogen concentration in the sample, the equivalent diffusion coefficient can be obtained. The results show the diffusion coefficients of hydrogen in molten aluminum A206 cast alloy have a slightly increase with the temperatures increase from 700 degrees C to 760 degrees C. The values of (0.55-1.20) x 10(-2) cm(2)/s are estimated for the equivalent diffusion coefficient of the hydrogen in molten aluminum A206 casting alloy.