The role of precipitates upon the electrochemical stability of aluminium

Whilst the electrochemical stability of a metal is typically described in terms of equilibrium thermodynamics, in an engineering context, a likelihood of corrosion as predicted by thermodynamics is not as useful as knowing the kinetic response (i.e. how fast a metal reacts in a certain environment). This work presents a discrete effort towards developing an improved understanding and representation of kinetic stability for aluminium-based metals, as an engineering alternative to Pourbaix diagrams. The overall study will assess the environmental envelope for passivity of aluminium, and account for the influence of microstructural heterogeneities (grain size, precipitates and crystallinity), which are not presently considered in equilibrium thermodynamics. In prior work we presented kinetic stability diagrams for pure aluminium with different grain size and grain boundary density. In the present study, we convey preliminary kinetic stability diagrams as a function of pH and potential for Al-4wt%Cu alloys with different precipitate size distribution and density - to elucidate the effect of precipitate state upon electrochemical kinetics.