Effect of chromate primer on corrosion fatigue in aluminum alloy 7075

✍ Scribed by Sarah E. Galyon Dorman; Yongwon Lee

• Publisher: Elsevier
• Year: 2011
• Tongue: English
• Weight: 498 KB
• Volume: 10
• Category: Article
• ISSN: 1877-7058
• DOI: 10.1016/j.proeng.2011.04.203

✦ Synopsis

The Center for Aircraft Structural Life Extension (CAStLE) at the United States Air Force (USAF) Academy has undertaken work to produce a standardized test method for determining the effect of a corrosion inhibitor containing chromate on small scale fatigue damage. CAStLE is specifically focusing their research on the effect of chromate primers on the pit-to-crack transition and crack growth under the USAF damage tolerant flaw size (1.5 mm). Quantifying the chromate effect on the small damage scale is necessary to provide a baseline to compare the efficacy of new and safer coatings on fatigue life. To correctly account for these factors, bare and chromate primered test specimens of AA7075-T651 were produced with a center hole and a corrosion pit at the edge of the hole, and subsequently fatigued using representative environments and loading schemes until a thumbnail crack of approximately 1 mm radius was produced. How chromate coatings effect fatigue crack growth is dependent on enough chromate leaching from a coating to reduce the fatigue crack growth rate (FCGR) in the time it takes to grow from a 300 m pit to a 1 mm fatigue crack. The current results suggest that the amount of chromate required to leach from the primer to affect FCGR may be highly dependent on the amount of chloride present.