Filiform Corrosion on Polyester Powder-Coated Aluminum

Abstract

Filiform corrosion initiates and grows locally at macroscopic defects in coatings on metal substrates. While typically not detrimental to the bulk metal properties, the filiform corrosion results in threadlike filaments that propagate parallel to the surface underneath the coating. Herein, we present a study correlating the electrochemical and structural properties of polyester powder coatings onto 6022 aluminum to their associated resistance to filiform corrosion. Filiforms are propagated using a modified EN 3665 method and tracked temporally via bright field microscopy. Results including electrochemical impedance spectroscopy, open-circuit potential tracking, and potentiostatic experiments were used to evaluate coating barrier properties. Coating morphologies of pre- and post-corrosion samples are evaluated using SEM and EDX. Mechanical properties of free-standing polyester films are also characterized. The combined electrochemical and mechanical data are used to derive polyester coating design criterion to maximize resistance to filiform corrosion.