Mechanisms of Corrosion Fatigue in High Strength I/M (Ingot Metallurgy) and P/M (Powder Metallurgy) Aluminum Alloys

摘要

High strength aluminum alloys are employed extensively in the primary structure of current and projected Air Force and civilian aircraft. The service lives and reliability of these aircrafts depend to a great extent on the corrosion fatigue resistance of the structural alloys. Significant efforts are underway to develop powder metallurgy (P/M) alloys that would provide improved corrosion fatigue resistance along with improvements in other mechanical properties. The objective of this study was to understand the chemical and metallurgical aspects of environmentally assisted fatigue crack growth (or corrosion fatigue) that can serve (i) as a basis for guiding the development of new and improved alloys, and (ii) as a basis for developing rational design procedures for service life predictions. The kinetics of fatigue crack growth, as a function of water vapor pressure and for water vapor-oxygen mixtures, and the accompanying fractographic observations on 7050-T7451, 7050-T651 and 7075-T651 (I/M) alloys and on 7091-T7E69 and 7091-T7E70 (P/M) alloys are described and discussed.