Galvanic Corrosion of Aluminum Alloys and Carbon Composites Correlation Between Corrosion Status and Mechanical Fatigue
Abstract
Factors Affecting the Galvanic Corrosion of Aluminum Alloys and Carbon Composites Under Accelerated Environmental Testing– Correlation Between Corrosion Status and Mechanical Fatigue Summary: A wide variety of materials are used in current naval aviation systems including light weight aluminum alloys and, ever increasingly, carbon fiber composites. Understanding how these materials perform from both a corrosion and mechanical fatigue standpoint during different types of simulated environmental degradation tests is of critical importance for appropriate material choice and predicting service readiness and lifetime. Aluminum alloys are always deployed with a multi-component coating system (pretreatment + primer + paint) so it is imperative to have a good working knowledge of the optimum (i) surface pretreatment, (ii) coating composition and formation conditions and (iii) coating combinations for best overall material performance. Nonchromated pretreatment conversion coatings and primers are slowly replacing the traditional chromated systems due to the environmental unfriendliness and health hazards of the latter. Given the fact that there are now multiple non-chromated pretreatment coatings and primers that have been certified, there is a surprising dearth of knowledge about the formation, structure and, to some extent, performance of these different coatings on aluminum alloys, particularly under different environmental test conditions. The one degradation test that has typically been performed on these coatings is ASTM B117, which often is not a good predictor of “real world” performance. Therefore, one major goal of this research will be to produce new scientific insight regarding the performance of the different commercially-available trivalent chromium process (TCP) pretreatment coating systems, with and without a suitable primer, at preventing galvanic corrosion. A second major goal of the project will be to learn more about mechanisms by which carbon fiber epoxy composites (different carbon fiber modulus and matrix materials) undergo degradation and corrosion when exposed to different environmental degradation tests. The coating performance and composite properties will be assessed during four environmental degradation tests designed to simulate the different conditions airframe structures experience during service life. Greater scientific insight regarding the fundamentals of corrosion processes under different environmental exposure scenarios will lead to new materials, advanced coating systems, and improved corrosion-prevention strategies. Unique aspects of this work are (i) measurement of electrochemical parameters during the environmental testing that will provide a time-dependent measure of the corrosion status and (ii) mechanical testing of the aluminum and carbon fiber composite materials during the environmental tests, which will enable a correlation to be made between the corrosion status and material fatigue. The research will shed light on the interrelationship between the materials processing (coating system) and structure, and the life-cycle performance.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 12, 2016
- Source ID
- N000141512005
Entities
People
- Greg Swain
Organizations
- Michigan State University
- Office of Naval Research
- United States Navy