Evaluation of Inhibited Organic Coating Protection Against Environmentally Assisted Cracking of High Strength Aluminum Alloys

摘要

A test method is in development to assess aerospace coatings and their capacity to protect structures from environmental assisted cracking (EAC) initiation and propagation in corrosive atmospheres. EAC initiation and propagation is influenced by the complex interactions of load, environment, and alloy properties. These are explored and defined to produce a method that quantifies the crack initiation resistance provided by protective coatings for high strength aluminum alloy 7075-T651, enabling comparison between coatings. Accurate assessment of coating performance will reduce the risk associated with introducing new environmentally compliant coatings. Conventional immersion EAC testing is not well suited to study factors and interactions leading to atmospheric EAC because the bulk electrolyte conditions for immersion testing are different from those of a thin-film electrolyte. A controlled corrosive environment, unique test article geometry, static loading condition, and continuously monitoring sensor system are employed to measure onset and propagation of cracking under atmospheric conditions. Initial results demonstrate a strong dependence on inhibited primer type and galvanic coupling.