Effect of corrosion prevention compounds on fatigue life in 2024-T3 aluminum alloy

Corrosion-prevention-compound (CPC) is commonly used to prevent corrosion in the aircraft industry. The presence of corrosive environment (salt-fog, water-fog, or even dry air) on aircraft structures has detrimental effects on the fatigue of aircraft components, which may initiate and also accelerate the crack growth rate in the structures. This study describes the crack-growth results of an experimental program on 2024-T3 aluminum alloy using center-crack specimen and also investigate the effect of CPC on fatigue life. The corrosion fatigue in the presence of water vapor reduces the total fatigue life. The fatigue life of structures with the CPC treatment is shown to increase the fatigue life due to the protection from the corrosive environment (water vapor). Test results are obtained for differing stress ratios and frequencies, with and without the CPC treatment, in humid testing-environment conducted at constant amplitude fatigue loading. Micrographs of the failed-specimen surfaces are examined by scanning electron microscope (SEM) to investigate the mechanisms of failure processes and to identify the formation of crack surface along the crack-front in the crack growth region. Interestingly, two distinct failure modes are found and these are ductile and brittle fracture modes. The transition from the ductile to brittle mode can be observed clearly in this work. (c) 2006 Elsevier B.V. All rights reserved.