Atomic force microscopy, scanning electron microscopy and electrochemical characterization of Al alloys, conversion coatings, and primers used for aircraft

Characterization of the metal–coating interface is crucial to the understanding and prediction of the performance of corrosion protective coatings. To date, such characterization has been incomplete and performed on a scale of measurement that gives little microscopic-scale information. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) have the ability to provide such information. We present in this work the use of such methods to examine the interface between steel and marine coatings and to image the surface of untreated aircraft aluminum alloys. We have also imaged these aircraft alloys after chromate/phosphate pretreatment. AFM and SEM have also been used to investigate the changes in surface morphology, which accompany changes in the samples due to exposure. Electrochemical noise methods, electrochemical impedance spectroscopy measurements, and Prohesion^TM testing were performed in parallel with the AFM/SEM measurements. The results, along with implications for aircraft coatings, are discussed.