Oxidation of Flash-Anodized Al-Mg Alloy in Dry Atmospheres of N2, CO2, and O2 and Humid Atmosphere of Ar

Production of anodized Al alloy is increasing with increased recycling of Al. To study recycling of anodized material, a flash-anodized 3000 series Al alloy containing 0.34 wt pct Mg was remelted in pure atmospheres of CO2, O2, and N2, and Ar with 5 mol pct H2O at 1073 K (800 °C). Hopefully, the results should be of general influence concerning dross formation and scrap remelting in the Al industry. Oxidation studies using a thermogravimetric analyser were performed. Following the treatment, the samples oxide layers were characterized. The highest oxidation rates were observed in atmospheres of O2 and CO2. However, the onset of a break-away oxidation period in O2 is delayed in comparison to CO2. Oxidation in CO2 showed substantially less MgO formation compared to O2. The main source of mass gain can be attributed to the reaction of Mg with oxygen to form MgO and MgAl x O y . Heating in N2 resulted in the lowest mass gain of all atmospheres. Experiments in humid (5 mol pct H2O) Ar atmospheres indicate that there is a minimum threshold of Mg activity to initiate oxidation via H2O. Oxidation kinetics (mechanisms) has been investigated.