Unraveling the role of tensile stress in corrosion and the formation of oxide films on sensitized Al-Mg alloys

Intergranular corrosion (IGC) significantly damages the strength of Al-Mg alloys with a Mg content > 3 wt% when these alloys are serviced in marine environments. Although a dense oxide film can prevent the degradation of Al alloys, the influence of tensile stress on the properties of the oxide film is unclear. Here, the oxide films formed on a sensitized 5083 Al-Mg alloy under constant elastic and plastic tensile stresses are investigated. Pitting corrosion and intergranular corrosion occurred on the alloy surface. Tensile stress accelerated the anodic dissolution on the alloy surface and promoted intergranular corrosion, weakening the corrosion resistance of the oxide film. A heterogeneous oxide film was found on sensitized Al-Mg alloy, with the oxide film formed on the IGC region was thicker than that on the alloy matrix due to local alkalization. Tensile stress caused dislocations near the grain boundaries, but did not change the composition of the oxide film in the region subjected to intergranular corrosion. Density-functional theory calculations suggest that tensile stress destroyed the oxide film and weakened the electronic interactions between the oxide film and the alloy matrix, fostering the propagation of intergranular corrosion. Our findings clarify the mechanisms of oxide film formation on Al-Mg alloys under constant tensile stress in aqueous solution.