Acoustic and thermographic Evaluation of polymeric corrosion protective Coatings on Aluminum Alloy Airframe Structures

摘要

The goal of this work is to develop a multi-sensor nondestructive evaluation (NDE) approach to characterize aluminum alloy airframe structures under polymeric corrosion protective coatings. Two main efforts are highly relevant: (i) studying different degradation processes in the polymers to estimate the coating performance in service; and (ii) detecting and quantifying early stages of corrosion beneath an intact coating. To address these tasks we employed acoustic and thermographic NDE techniques, especially Scanning Acoustic Microscopy (SAM) and Fan Thermography. SAM can be utilized to map either coating or interface properties (C-scans). The method revealed potential to determine the curing quality of the coatings. It was also possible to detect small corrosion pits under delaminated areas. Furthermore, we evaluated the reflections of surface waves, which are generated and detected by the same probe. This provided an additional tool to examine the substrate/coating interface. Thermography was applied to detect corrosion under the coatings and sites of delamination. Fan Thermography (hot air heating) made it possible, to observe sites of decreasing adhesion over longer time periods. Both acoustic and thermographic results were correlated to electrochemical mapping of corrosion activity which was obtained by Scanning Vibration Electrode Technique (SVET).