Short-Time Oxidation of Al–Mg in Dynamic Conditions

Abstract

In this research, an attempt was made to investigate the short-time oxidation of Al–Mg melt using oxide/metal/oxide sandwich method. Samples were produced by controlled blowing of bubbles with the pressure of 0.2 atm through the aluminum melt containing 1, 3 and 5.5 weight percent of Mg at 670 °C. Various characteristics of dynamically formed oxide films such as wrinkles, folds, holes, cracks and re-oxidation patterns were studied through microscopic analysis. It appeared that re-oxidation patterns are the main features of the dynamically formed oxide films. Also, separation of oxide films in the oxide/oxide interface and loose connections with the paired metal were other important phenomena. Thickness of the oxide films was measured to be 19, 31 and 51 nm for Al–1 Mg, Al–3 Mg, and Al–5.5 Mg samples, respectively. Thermodynamic-based considerations revealed the formation of MgO, MgAl2O4 and Al2O3 as possible product of the oxidation within the range of this study. However, MgAl2O4 was only detected in Al–1 Mg and Al–3 Mg samples based on XRD analysis while there was no evidence of Al2O3 formation at all. Furthermore, MgO was the main oxide in both Al–3 Mg and Al–5.5 Mg sandwich samples. High concentration and activity of magnesium at the surface of the melt along with the turbulent situation and short time duration of the oxidation process can be considered as the main discrepancy cause between thermodynamics and experimental results.