Stress-assisted coalescence of pits has been examined in Al-Li-Cu alloy AA2096 after several aging heat treatments at 160°C in an alternate immersion 0.6M NaCl test. Pit formation was governed by electrochemical factors. Specifically, pits were formed in the matrix adjacent to bands of Al-Fe-Cu constituent particles in all tempers. Stress corrosion cracking (SCC) susceptible tempers exhibited pronounced pit coalescence promoted by stress and facilitated by intergranular corrosion. SCC resistant tempers also experienced stress dependent pit coalescence that was hypothesized to be promoted by pit tunneling and ductile rupture of remaining ligaments. The ramifications of larger corrosion fissures towards SCC are as follows: SCC susceptible tempers may experience higher applied stress intensities owing to larger (i.e., longer and deeper) fissures at a given remote stress in addition to possibly exhibiting greater stage II crack velocities.

Subject
Pits, Constituents, Crack growth, Intergranular stress corrosion cracking, Stress intensity, Geometry, Crack initiation, Fissures, Stress, Localized corrosion, Alloys, Stress corrosion cracking, Alternate immersion tests
Keywords:
aluminum-lithium-copper alloys, environmental cracking, stress corrosion crack initiation, pit coalescence, corrosion fissures
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2000
Association for Materials Protection and Performance (AMPP)
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