Corrosion-Fatigue Crack Growth in Age-Hardened Al Alloys: Examples of Failures and Explanations for Fractographic Observations

Abstract:

The characteristics of corrosion-fatigue in age-hardened Al alloys, e.g. brittle striations on cleavage-like facets, are described, with reference to two examples of component failure. Mechanisms of corrosion fatigue (and explanations for fracture-surface features) are then reviewed. New observations of corrosion-fatigue crack growth for 7050-T7451 alloy compact-tension specimens tested in aqueous environments using a constant (intermediate) ΔK value but different cycle frequencies are then described and discussed. These observations provide additional support for a hydrogen-embrittlement process involving adsorption-induced dislocation-emission from crack tips.

• Periodical: Advanced Materials Research (Volumes 891-892)
• Pages: 248-253
• DOI: https://doi.org/10.4028/www.scientific.net/AMR.891-892.248
• Online since: March 2014
• Authors: Rohan Byrnes*, Noel Goldsmith, Mark Knop, Stan Lynch
• Keywords: Adsorption-Induced Dislocation-Emission (AIDE), Aluminium Alloy, Corrosion Fatigue, Cycle Frequency, Failures, Fractography, Mechanism

References

[1] R.P. Gangloff, Environment sensitive fatigue crack tip processes and propagation in aerospace aluminium alloys, pp.3401-3433 in: Fatigue '02, A. Blom (Ed. ), EMAS, UK, 2002, and references therein.

[2] N.J.H. Holroyd, D. Hardie, Factors controlling crack velocity in 7000 series aluminium alloys during fatigue in an aggressive environment, Corr. Sci., 23 (1983) 527-546.

DOI: 10.1016/0010-938x(83)90117-8

[3] S.P. Lynch, Mechanisms of fatigue and environmentally assisted fatigue, pp.174-213 in: J.T. Fong (Ed. ), Fatigue Mechanisms, ASTM STP 675, (1979).

DOI: 10.1520/stp35890s

[4] S.P. Lynch, Mechanistic and fractographic aspects of stress-corrosion cracking (SCC), pp.3-89, and Hydrogen embrittlement phenomenon and mechanisms, pp.90-130, in: V.S. Raja, T. Shoji (Eds. ), Stress Corrosion Cracking, Woodhead Publishing Limited, Cambridge, 2011. Republished in Corrosion Reviews, 30 (2012).

DOI: 10.1533/9780857093769.1.3

[5] A.D.B. Gingell, J.E. King, The effect of frequency and microstructure on corrosion fatigue crack propagation in high strength aluminium alloys, Acta mater., 45 (1997) 3855-3870.

DOI: 10.1016/s1359-6454(97)00033-5

[6] J.S. Warner, S. Kim, R.P. Gangloff, Molybdate inhibition of environmental fatigue propagation in Al-Zn-Mg-Cu, Int. J. of Fatigue, 31 (2009) 1952-(1965).

DOI: 10.1016/j.ijfatigue.2009.01.016

[7] R.E. Stoltz, R.M. Pelloux, Mechanisms of corrosion fatigue crack propagation in Al-Zn-Mg alloys, Metall. Trans., 3 (1972) 2433-2441.

DOI: 10.1007/bf02647046

[8] S.P. Lynch, Mechanisms and kinetics of environmentally assisted cracking: current status, issues, and suggestions for future work, Metall. Mater. Trans. A, 44A, (2012) 1209-1229.

DOI: 10.1007/s11661-012-1359-2

[9] N.T. Goldsmith, Deep focus: a digital image processing technique to improve focal depth in light microscopy, Image Analysis and Stereology, 19 (2000) 163-167.

DOI: 10.5566/ias.v19.p163-167

[10] N.H. Grinberg, Stage-II fatigue crack growth, Int. J. of Fatigue, 6 (1984) 229-242.

DOI: 10.1016/0142-1123(84)90054-9

[11] S.P. Lynch, Progression markings, striations, and crack-arrest markings on fracture surfaces, Mat. Sci. Engng A, A468-470 (2007) 74-80, and references therein.

DOI: 10.1016/j.msea.2006.09.083