| An innovative method which determines the equivalent diffusion coefficient of the hydrogen in molten aluminum is presented in this paper. The molten aluminum is placed in a permeable porous crucible and is maintained at a predetermined temperature. The vacuum is created outside of the crucible and the hydrogen in the molten aluminum will diffuses through the porous crucible wall out due to the hydrogen concentration difference at the aluminum melt/crucible interface. The hydrogen contents in the molten aluminum decrease as the vacuuming time extends. The relationship between equivalent diffusion coefficient and average hydrogen contents can be determined by solving Fick's diffusion equation at polar coordinate under certain initial and boundary conditions. Experiments were carried out to test the hydrogen contents in molten aluminum foundry alloy at different times. The equivalent diffusion coefficients of the hydrogen in molten A357 alloy have been obtained by combination of the testing data and computation. The values of (9.4-10.2)x10-3 cm2/s are estimated for the equivalent diffusion coefficient between the temperature of 700 and 730 °C. |
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