Fatigue Crack Growth Behavior of Friction Stir Welded 2024-T3 Aluminum Alloy Tested under Accelerated Salt Fog Exposure

Author(s)

Milan, M. T. ; Bose Filho, W. W. ; Tarpani, J. R.

• Document type: Journal article
• Source: MATERIALS PERFORMANCE AND CHARACTERIZATION; v. 3, n. 3, p. 20-pg., 2014-01-01.

Abstract

Fatigue crack growth properties of friction stir welded joints of 2024-T3 aluminum alloy were studied via constant amplitude load ( increasing Delta K) testing under open air and accelerated salt fog exposure conditions. For low Delta K values, longitudinal crack growth in the weld line center was slower under corrosion fatigue than by air because of the prevalence of corrosion-induced crack closure. On the other hand, growth rates of transverse crack crossing the weld nugget were not affected by the environment aggressiveness because of a balance between hydrogen embrittlement and corrosion inducing crack closure along with welding compressive residual stresses. For intermediate Delta K values, propagation rates 5 times faster were observed for both longitudinal and transverse cracks under salt fog ambient as a result of hydrogen-induced embrittlement, which is favored by larger crack tip openings allowing local corrosive medium access. As the final catastrophic fracture approaches, longitudinal and transversal crack propagation rates under corrosion fatigue approximated the values observed in air testing, as time, under the 30-Hz loading frequency applied, was scarce for an effective interaction between crack tip fresh material and the hostile environment. For longitudinal cracks, precracking in air resulted in fatigue-corrosion limit factor Delta K-th slightly lower than that obtained in salt fog precracked specimens, as the corrosive role played by the salt fog environment along the precrack introduction contributed to crack-closure effect, so increasing the apparent value of Delta K-th. On the other hand, the environment in which a transverse precrack was created had a negligible effect on DKth because of the establishment of an equilibrium condition between corrosion-induced precrack closure and hydrogen embrittlement. (AU)