Transgranular corrosion fatigue crack growth in age-hardened Al-Zn-Mg (-Cu) alloys

Stan P. Lynch, Mark Knop, Rohan T. Byrnes

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The mechanisms of transgranular corrosion fatigue in age-hardened Al-Zn-Mg (-Cu) alloys are reviewed, with an emphasis on accounting for fractographic observations. The effects of cycle frequency, solution composition, temperature, and electrode potential on crack-growth rates (and striation spacing and appearance) at intermediate to high ΔK are discussed in particular. It is concluded that corrosion fatigue, resulting in cleavagelike {100} < 110 > cracking with extensive slip on {111} planes intersecting crack fronts, can best be explained by an adsorption-induced dislocation emission mechanism (involving weakening of interatomic bonds at crack tips by adsorbed hydrogen). Solute hydrogen ahead of cracks appears to play little, if any, role in facilitating cleavagelike cracking, and the mechanisms based on decohesion are at odds with the locally high strains around cracks and the formation of nanovoids ahead of cracks.
Original languageEnglish
Pages (from-to)301 - 314
Number of pages14
JournalCorrosion Reviews
Issue number6
Publication statusPublished - 2015

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