Effect of stress on initiation and propagation of localized corrosion in alumninium alloys

Abstract

High strength aluminium alloy AA2024 is susceptible to localized corrosion in the form of pitting and intergranular corrosion (IGC). The corrosion behaviour of this alloy is strongly influenced by the presence of different intermetallic particles. In this study, the effect of applied stress and the role of intermetallic particle removal by surface treatment on the initiation and propagation of localized corrosion are investigated. It was found that applying a stress to as polished AA2024 leads to a drop in breakdown potential. The development of micro/nano crevices adjacent to the intermetallic particles is thought to act as initiation sites for localized corrosion, lowering the breakdown potential of stressed AA2024. The electrochemical behaviour of specific intermetallic particles and the particle free matrix of AA2024 have been studied as a function of stress state using the micro-capillary electrochemical cell in combination with an in situ stressing stage. These experiments emphasized the role of intermetallic particles as the possible key contributing factor in determining the corrosion properties of the alloy under stressed conditions. In situ X-ray synchrotron microtomography experiments were used to observe the evolution of corrosion attack as a function of continuous exposure time in both unstressed and stressed AA2024. Quantitative growth rate measurements indicates that application of stresses of 70% yield strength or above has a significant effect on the localized corrosion propagation.