In-situ observed pore formation during solidification of aluminium

Incidental porosity formation during pure aluminium solidification was visu alized in real-time with an X-ray radioscopic facility. The dynamic growth process of a 10-mm pore is observed. Its growth is divided into two sequent ial stages. In the first stage, the radius of the pore increased very fast. with time to the power of 0.52. In the second stage, the growth slowed as the pore radius changed with time to the power of 0.25. Theoretical analysi s of the pore growth based on the present observation shows that, in the in itial stage, the growth is primarily controlled by a hydrogen diffusion mec hanism; and in The second stage, growth is controlled primarily by volume s hrinkage during solidification.