  A variety of chromate-free conversion coatings are being actively
investigated to improve the corrosion performance of light-weight alloys for
aerospace and defense applications. Advancing conversion coating, however,
requires an in-depth understanding of the underlying corrosion mechanisms in
order to rationally design sustainable coatings. Here, we present a multiscale
modeling approach to predict corrosion performance of metallic materials, with
a focus on localized corrosion of Cu-containing aluminum alloys coated with
ZrO2 layer. First-principles and transition-state theory are used to implement
the kinetics model, which includes electrolyte-metal interfacial reactions. The
modeling framework systematically characterizes and couples multiple
electrochemical and physical (e.g., transport) phenomena to explore
interrelationships between pit morphology, surface chemistry, and local
environment. This multiscale model can quantitatively link the corrosion rate
of ZrO2-coated aluminum alloys with the evolution of interfacial reactions
during immersion, which is very difficult to establish using in situ
experiments. We have evaluated the presented multiscale model using available
experimental data. The rate of corrosion and pit stability were quantitatively
assessed for various environmental parameters and applied potentials. Results
show that Zr-based conversion coating strongly enhances the corrosion
performance of aluminum alloys due to zirconium involvement in interfacial
kinetics.
