The contribution of hydrogen evolution processes during corrosion of aluminium and aluminium alloys investigated by potentiodynamic polarisation coupled with real-time hydrogen measurement

Abstract

Water reduction, which leads to the evolution of hydrogen, is a key cathodic process for corrosion of many metals of technological interest such as magnesium, aluminium, and zinc; and its understanding is critical for design of new alloys or protective treatments. In this work, real-time hydrogen evolution measurement was coupled with potentiodynamic measurements on high-purity aluminium and AA2024-T3 aluminium alloy. The results show that both materials exhibit superfluous hydrogen evolution during anodic polarisation and that the presence of cathodically active alloying elements enhances hydrogen evolution. Furthermore, it was observed for the first time that superfluous hydrogen evolution also occurs during cathodic polarisation. Both the anodic and cathodic behaviours can be rationalised by a model assuming that superfluous hydrogen evolution occurs locally where the naturally formed oxide is disrupted. Specifically, during anodic polarisation, oxide disruption is due to the combined presence of chloride ions and acidification, whereas during cathodic polarisation, such disruption is due to alkalinisation. Furthermore, the presence of cathodically active alloying elements enhances superfluous hydrogen evolution in response to either anodic or cathodic polarisation, and results in ‘cathodic activation’ of the dissolved regions.