Re-Examination of Oxidation in Al-Mg Alloys Containing High Contents of Mg at High Temperatures Using Phase Diagrams

Abstract

In this study, the oxidation of Al–Mg alloys with Mg content ranging from 3 mass% to 5 mass% at a high temperature was re-examined using phase diagrams was re-examined using phase diagrams plotted using thermodynamic software. The as-cast microstructures of all examined alloys showed the formation of the β–Al3Mg2 phase, and especially, its phase fraction considerably increased with increasing Mg content up to 5 mass% from 3 mass%. After oxidation at 500 °C under the ambient atmospheric conditions for 50 h, all the oxidized cross-sections had coarse and dark areas nonuniformly distributed in the matrix, which were found to be the oxide clusters containing Mg-based oxides. With increasing Mg content, the higher Mg content was involved in promoting the growth of Mg-oxide clusters and possibly associated with the change in the fraction of the β–Al3Mg2 phase. The Al–5 mass%Mg alloy formed higher fractions of MgO and spinel during the oxidation.