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Abstract
Hydrogen can dissolve to a significant extent in molten aluminium and is the main cause of gas porosity in castings. The effect of intensive melt shearing on hydrogen concentration in molten aluminium alloy has been studied by both reduced pressure test and direct hydrogen measurement, and the results show that intensive melt shearing has a significant degassing effect for the LM24 aluminium alloy melt. By applying intensive melt shearing, the hydrogen concentration in the liquid alloy was reduced from 0·16 to 0·08 mL/100 g, and the density index Di was reduced from 12·40 to 2·96%. It was also found that shearing speed, shearing time and holding time after shearing could influence the degassing efficiency. In addition, pressurised melt filtration was also carried out to understand the mechanism of reduced porosity by intensive melt shearing, particularly the role of oxide in the formation of porosity, and the microstructure refinement.
The authors would like to thank Dr M. Xia and Dr H. Li for their help in the experiments and useful discussions on degassing. The authors would also like to thank FOSECO for providing ‘ALSPEK H’ for directly measuring the hydrogen concentration. The financial support from EPSRC and TSB of the UK is gratefully acknowledged.