An Investigation on the Thickness of Short Time Oxide Film Formed in Casting Process of Al-1Mg and Al-2Mg Alloys

As Al-Mg alloys have a great usage in various industries and the microstructures of these alloys are very sensitive todefects formation during casting، it seems a meticulous investigation of their microstrutures can be beneficial for theseindustries. Although oxygen solubility in molten aluminium alloys is said to be negligible، since aluminum alloys melt arevery sensitive to oxidation during casting، when the surface of melt is exposed to air it oxidizes quickly and an oxide film isformed on the melt surface. Then this surface oxide film can be folded and entrained into the melt due to surface turbulence. In this research، sandwiches of oxide-metal-oxide formed on a short time within the cast during solidification were used tostudy the effect of magnesium content (i. e. 1wt% and 2wt %) on the oxide film thickness. To form sandwiches of oxidemetal-oxide within the cast a certain amount of air was blown into the melt every 3 seconds during casting time by means ofa compressor at 0. 5 atmosphere pressure. Where bubbles of air reached each other، they formed a sandwich which later wasused for investigating purpose. Both the thickness of oxide films and the surface of each layer were studied via SEM. Theresults showed that the thickness of the short time oxide film varies in the range of 150-200 and 200-300 nanometers for Al-1Mg and Al-2Mg alloys، respectively. This is a new finding for this type of alloys.