STP610

    Corrosion Thresholds for Interference Fit Fasteners and Cold-Worked Holes

    Published: Jan 1976


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    Abstract

    Empirical relationships were obtained between fastener interference or hole expansion and the stress-corrosion thresholds of aluminum alloys. Tensile and stress-corrosion threshold properties were determined for single heats of 2024-T3, 7075-T6, 7075-T76, and 7050-T76 extruded bar used in the studies. The various fastener and hole expansion systems, with a range of interference levels to over 10 mils, were installed in the principal grain directions of each alloy. Specimens were subjected to 3.5 percent sodium chloride alternate immersion and seacoast exposures, then analyzed by visual and metallographic techniques.

    The residual tensile stresses created around the holes appeared to rise sharply with increasing amounts of interference, approaching a theoretical limit. Even low interference fits of a few mils caused stress corrosion under the more susceptible conditions. Crack initiation tended to occur further from the hole as interference increased; wet sealant installation helped to reduce galvanic reactions in the vicinity of the hole. Estimated stress corrosion potential over a range of interference fits in aluminum alloys is presented.

    Keywords:

    stress corrosion, aluminum alloys, fasteners, cold worked holes, residual stress, metallographic examination


    Author Information:

    Kaneko, RS
    Development engineer and group engineer, Materials and Processes, Lockheed-California Company, Burbank, Calif.

    Simenz, RF
    Development engineer and group engineer, Materials and Processes, Lockheed-California Company, Burbank, Calif.


    Paper ID: STP28684S

    Committee/Subcommittee: G01.06

    DOI: 10.1520/STP28684S


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