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

    (Received 29 August 2013; accepted 3 January 2014)

    Published Online: 2014

    CODEN: MPCOAD

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    Abstract

    Fatigue crack growth properties of friction stir welded joints of 2024-T3 aluminum alloy were studied via constant amplitude load (increasing ΔK) testing under open air and accelerated salt fog exposure conditions. For low ΔK 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 ΔK 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 ΔKth 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 ΔKth. On the other hand, the environment in which a transverse precrack was created had a negligible effect on ΔKth because of the establishment of an equilibrium condition between corrosion-induced precrack closure and hydrogen embrittlement.


    Author Information:

    Milan, M. T.
    MIB - Materials Institute of Brazil,

    Bose Filho, W. W.
    Dept. of Materials Engineering, Engineering School of São Carlos, Univ. of São Paulo,

    Tarpani, J. R.
    Dept. of Materials Engineering, Engineering School of São Carlos, Univ. of São Paulo,


    Stock #: MPC20130036

    ISSN: 2165-3992

    DOI: 10.1520/MPC20130036

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    Author
    Title Fatigue Crack Growth Behavior of Friction Stir Welded 2024-T3 Aluminum Alloy Tested under Accelerated Salt Fog Exposure
    Symposium , 0000-00-00
    Committee E08