A comparison of time-scales governing the interaction and growth of hydrogen bubbles with a solidifying front

Elongated hydrogen porosity appears in aluminum based cast components and can lead to crack initiation. In this study, a comparison between the growth rates of hydrogen bubbles and the solidifying front during the process of engulfment is presented. Extending upon a previously developed order estimate for the ratio of growth rates of the two interfaces, it is found that dimensionless grouping leads to two distinct time scales that correspond to solidification and hydrogen diffusion. The analysis proves the hypothesized thought-experiment and explains the mechanism of hydrogen bubble elongation. The scaling prediction is also validated with available experimental studies, and shows that the rate of elongation varies directly with the pore radii and inversely with the cooling rates.