Hydrogen, porosity and oxide film defects in liquid Al
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This article reports results from an experiment where a bubble of air was held at a constant temperature in a liquid Al melt, with the volume of the bubble monitored continuously using real-time X-ray equipment. When the H content of the surrounding melt was low, the volume of the trapped air bubble reduced with time, as the O and N in the bubble atmosphere reacted with the Al to form Al2O3 and AlN. When the H content of the melt was increased to about 0.3 ml 100 g−1 Al, the H in solution passed into the air bubble causing its expansion. In an Al casting the same effect would cause an entrained double oxide film defect to act as a site for the growth of H-driven gas porosity. The way in which the oxide film defects might behave in forming H porosity has been discussed.
KeywordsOxide Film Liquid Metal Small Bubble Bubble Volume Metal Stream
The authors wish to thank Professor John Campbell of the University of Birmingham, United Kingdom, and Professor John T. Berry of the Mississippi State University, Mississippi, USA, for helpful discussions in connection with the work. The authors also wish to thank Mr. A. Caden for his technical support, and the Ministry of Science, Research and Technology of the Islamic Republic of Iran for its financial support.
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