Influence of Mg Concentration on the Inhibiting Effect of CO2 on the Rate of Oxidation of Aluminum Alloys 5182 and 6016

Abstract

Oxidation of aluminum alloys during production is a well-known problem and contributes to significant metal losses. As small additions of CO2 in the oxidizing atmosphere has proven to inhibit the oxidation rate for high-Mg(≥5wt%) aluminum alloys, the present study has aimed at evaluating its effect on alloys with varying Mg concentration in combination with other alloying elements (Si and Mn), i.e. Al alloys 5182 (AlMg4.6Mn0.4) and 6016 (AlSi1.2Mg0.4). Experiments were performed by DSC-TG (Differential Scanning Calorimetry-Thermogravimetric Analysis) using three different cover gases, i.e. (i) 80% synthetic air and 20% argon, (ii) 99.999% argon and (iii) 4% CO2, 20% argon and 76% synthetic air, while monitoring the mass change and heat flux at 750°C for 7h. A significant inhibiting effect was observed for alloy 5182 during exposure to CO2, with a mass loss of -0.3%, when compared to the results obtained for synthetic air and argon having mass gains of 11.21% and 1.67%, respectively. The thickness of the oxide layer was also influenced and decreased stepwise from synthetic air, to argon and CO2. A similar effect was observed to a lesser extent for alloy 6016 due to the lower Mg concentration, decreasing the mass gain from 2.45% when heated in synthetic air to 1.61% in argon and 0.7% in CO2. The thickness of the oxide layer decreased in argon and increased to almost similar thicknesses in synthetic air and CO2. The lower mass gain in CO2 proves that CO2 has an inhibiting effect on the oxidation rate even for low-Mg alloys.