Understanding the environmentally assisted cracking (EAC) initiation and propagation of new generation 7xxx alloys using slow strain rate testing
Yasser Aboura, Alistair Garner, Ryan Euesden, Zak Barrett, Christian Engel, N.J.H. Holroyd, P.B. Prangnell, Timothy L. Burnett
Abstract
New generation (new-gen) 7xxx series alloys have recently been shown to have higher susceptibility to environmental assisted cracking (EAC) in humid air, compared to AA7050, in T7651 tempers. Hydrogen (H)-EAC fracture features of brittle intergranular (IG) and transgranular (TG) fracture modes were observed with humidity levels as low as 20%. Initiation was favoured at sites of intermetallic particle clusters with gas pores. The higher performance of AA7050 was attributed to the difficulty of initiation in this alloy, where the grain structure, combined with an intrinsic resistance of the grain boundaries to IG-EAC, made the attainment of sustained cracking difficult.