In situ observations were made of the nucleationand growth kinetics of hydrogen porosity during the directionalsolidification of aluminium-7 wt percent silicon (Al7Si) withTiB_2 grain refiner added, using an X-ray temperature gradientstage (XTGS). The effect of altering the solidification velocity onthe growth rate and morphology of the porosity formed wascharacterized by tracking individual pores with digital analysis ofthe micro-focal video images. It was found that increasing thesolidification velocity caused the pore radius to decrease and poredensity to increase. Insight gained from the experimental resultswas used to develop a computational model of the evolution ofhydrogen pores during solidification of aluminium-silicon castalloys. The model solves for the diffusion-limited growth of thepores in spherical coordinates, using a deterministic solution ofthe grain nucleation and growth as a sub-model to calculate theparameters that depend upon the fraction solid. Sensitivity analysiswas carried out to assess the effects of equiaxed grain density, poredensity, initial hydrogen content and cooling rate. The modelagrees with the experimental results within the resolution limits ofthe XTGS experiments performed.
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