A Combined Electrochemical Impedance Spectroscopy and X-Ray-Computed Tomography Study of the Effect of a Silyl Ester on Delamination and Underfilm Pit Formation in a Coated AA7050 Sample

Recently, encapsulated silyl esters have been shown to act as efficient healing agents for self-healing anticorrosive coatings. While the positive protective effects were irrefutable, the actual protection mechanism has not been clarified yet. In the present proof-of-concept study, x-ray-computed μ-tomography and electrochemical impedance spectroscopy (EIS) have been combined to clarify the protection mechanisms of a silyl ester on a coated aluminum alloy (AA)7050 (UNS A97050). The results show that the silyl ester protects the damaged coating-metal system by delaying the delamination initiation and growth kinetics while at the same time decreasing the underfilm pit growth. The study demonstrates the potential of x-ray-computed μ-tomography to follow delamination front line and underfilm pits in coated metallic samples. The combination of tomography with EIS led to an improvement in the understanding of the two mechanisms by which the silyl ester prolongs the protection in the event of local scratch damage.