STP610: Learning from Experience of the Stress-Corrosion Failure of High-Strength Aluminum Alloy Forgings

    Cina, B
    Chief metallurgist and senior physicist, Materials and Process Engineering, Engineering Division, Israel Aircraft Industries Ltd., Lod,

    Kaatz, T
    Chief metallurgist and senior physicist, Materials and Process Engineering, Engineering Division, Israel Aircraft Industries Ltd., Lod,

    Pages: 11    Published: Jan 1976


    Abstract

    Despite the extensive literature on the subject and the known methods for preventing stress corrosion, the users of high-strength aluminum alloys are still on occasion faced with this problem particularly in wrought components. Examples from actual experience with aircraft forgings are cited to emphasize the susceptibility of the transverse direction, particularly at parting lines, and the complex and often unpredictable role of residual stresses. Despite the absence of a specific short transverse direction, cylindrical forgings can show considerable susceptibility in their single transverse direction. Attention is drawn to the possibly dangerous combination of stresses resulting from heat treatment, machining, and interference assemblies.

    It is shown that the mere presence at the surface of a forging of residual compressive stresses resulting from heat treatment is no guarantee that stress-corrosion failure will not initiate from such a surface.

    Residual stresses developed along the inside diameter of a blind hole on quenching are a major unknown, and methods for obviating such difficulties are discussed.

    In addition to the factors known to affect stress-corrosion susceptibility, there would also seem to be a batch factor whereby some apparently small and temporary modification in manufacturing procedure can increase the susceptibility to stress corrosion significantly.

    An example is quoted of the minute amount of moisture found sufficient to initiate a stress-corrosion failure.

    The necessity is discussed and emphasized for determining the nature and gradient of residual stresses adjacent to potentially critical surfaces as a stage in the qualification of prototype forgings.

    Keywords:

    stress corrosion, cracking (fracturing), aluminum alloys, forgings, residual stress, quenching, assembly stresses, machining, blind holes, corrosive medium


    Paper ID: STP28670S

    Committee/Subcommittee: G01.06

    DOI: 10.1520/STP28670S


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