Effects of CO₂ Cover Gas and Yttrium Additions on the Oxidation of AlMg Alloys

AlMg alloys are known to suffer from problematic oxidation that can result in significant dross formation and loss of Mg from the melt. Historically, beryllium has been used to minimize the oxidation as it forms a protective BeO layer at the oxide-metal interface that inhibits further oxidation of the Mg. Alternative protection agents to beryllium are desired due to its strong negative health impacts. The purpose of this paper is to summarize findings in respect to the effectiveness of CO₂ cover gas and yttrium additions as alternatives to beryllium; by examining the rate and product of oxidation using thermogravimetric analysis, electron microscopy and EDS. It was found that additions of as little as 5% CO₂ to air atmosphere can reduce the oxidation of a 5% Mg alloy to nearly the same extent as beryllium additions, while the addition of 100 ppm of yttrium was found to have a limited impact on the oxidation.