Investigation on thickness of short time oxide films in Al–1Mg and Al–2Mg alloys

Abstract

The melts of aluminium alloys are very sensitive to oxidation during casting, and the surface oxide film formed during casting can be folded and entrained into the melt due to melt surface turbulence. In this research, sandwiches of oxide–metal–oxide (OMO) formed in a very short time within the cast during solidification were investigated in order to see the effect of magnesium content (i.e. 1 and 2 wt-) on the oxide film thickness. To form OMO sandwiches within the cast, a certain amount of air was blown into the melt every 0·5 s during casting time by means of a compressor at 0·5 atm pressure. Where bubbles of air collided, they formed a sandwich which later was used for investigating purpose. Both the thickness and the surface of oxide films were studied via SEM. The results showed that the thickness of the short time oxide film varies in the range of 150–250 and 200–300 nm for Al–1Mg and Al–2Mg alloys respectively.