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

Abstract

AbstractThe 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 cleavage-like {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 cleavage-like 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.