Tortuosity but Not Percolation: Design of Exfoliated Graphite Nanocomposite Coatings for Extended Corrosion Protection of Aluminum Alloys

Abstract

Increased adoption of engineered aluminum alloys in vehicular components is imperative for automotive lightweighting, but such alloys are oftentimes prone to degradation upon exposure to corrosive environments. The design of coatings to inhibit corrosion of aluminum alloys has emerged as a critical need but given the electropositive nature of the substrates, only a sparse few options are available. In this article, we explore the corrosion resistance afforded to aluminum alloy AA7075 substrates by unfunctionalized exfoliated graphite nanocomposite coatings as a function of the exfoliated graphite loading. Detailed mechanistic understanding is developed through monitoring progression of the open circuit potential and electrochemical impedance response of the substrates over 100 days of immersion in a saline environment along with post-mortem cross-sectional scanning electron microscopy and energy dispersive X-ray spectroscopy analysis of sectioned interfaces. Electrochemical studies along with nanoindentat...