Understanding the environmentally assisted cracking (EAC) initiation and propagation of new generation 7xxx alloys using slow strain rate testing

• Published in: Corrosion science Vol. 199; p. 110161
• Main Authors: Aboura, Y., Garner, A.J., Euesden, R., Barrett, Z., Engel, C., Holroyd, N.J.H., Prangnell, P.B., Burnett, T.L.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Ltd 01-05-2022; Elsevier BV
• Subjects: Aluminum base alloys; Crack initiation; Environmentally assisted cracking; Environmentally Assisted Cracking (EAC); Fractography; Grain boundaries; Grain structure; High strength aluminium alloys; Hydrogen Embrittlement; Intergranular fracture; Slow strain rate; Stress Corrosion Cracking (SCC); Stress Corrosion Cracking (SCC); High strength aluminium alloys; Fractography; Hydrogen Embrittlement; Environmentally Assisted Cracking (EAC)
• ISSN: 0010-938X; 1879-0496
• DOI: 10.1016/j.corsci.2022.110161

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.
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•Strain rates as low as 10-8 s-1 were utilised to assess the EAC performance of aluminium alloy 7xxx series in humid air.•The complete sequence of EAC was presented through high-resolution fractography of well-preserved fracture surfaces.•Thick plate AA 7085 and AA 7449 were more susceptible to EAC in humid air compared to AA7050 in their T7651 tempers.•AA7050 high resistance to EAC in humid air was attributed to the difficulty of growing short cracks during EAC initiation.