By using an X-ray temperature gradient stage, in situ observations were made of the nucleation and growth kinetics of H porosity during the directional solidification of Al-7wt%Si. The effect of altering the solidification rate, upon the growth rate and morphology of the resultant porosity, was characterized by tracking individual pores using video images. It was found that increasing the solidification rate caused the pore radius to decrease and the pore density to increase. The results were used to develop a model for the evolution of H pores during the solidification of cast Al-Si alloys. This involved analysing the diffusion-limited growth of pores in spherical coordinates. The deterministic solution of the grain nucleation and growth was used as a sub-model in order to calculate the parameters which depended upon the solid fraction.

Diffusion-Controlled Growth of Hydrogen Pores in Aluminium-Silicon Castings - in situ Observation and Modelling. R.C.Atwood, S.Sridhar, W.Zhang, P.D.Lee: Acta Materialia, 2000, 48[2], 405-17