Ionic Inhibition of Environental Fatigue Crack Growth in 7075-T6


Article Preview

The objective of this study is to quantify and understand the effectiveness of a hexavalent chrome replacement ion to inhibit environmentally assisted fatigue crack propagation (EFCP) in high strength aluminum alloys. Addition of molybdate (MoO4 2-) to bulk-low chloride solution effectively inhibits EFCP in peak aged 7075, comparable to that of CrO4 2-. The effectiveness of inhibition depends strongly on loading variables: .K, R, and frequency as explained qualitatively by mechanical instability of a crack tip passive film that otherwise hinders production and uptake of embrittling hydrogen. The critical loading frequency (and crack tip strain rate), below which film stability and inhibition occur, increases with increasing inhibitor concentration, but only for low stress ratio loading, perhaps due to occluded crack transport and reaction considerations. Molybdate could be a beneficial replacement for chromate and a candidate for inhibitor release from a tailored coating.



Key Engineering Materials (Volumes 345-346)

Edited by:

S.W. Nam, Y.W. Chang, S.B. Lee and N.J. Kim




J. S. Warner et al., "Ionic Inhibition of Environental Fatigue Crack Growth in 7075-T6", Key Engineering Materials, Vols. 345-346, pp. 989-994, 2007

Online since:

August 2007




[1] R.P. Gangloff. in Fatigue '02, Anders Blom, ed., Engineering Materials Advisory Services, West Midlands, UK, pp.3401-3433 (2002).

[2] Z.M. Gasem. Frequency Dependant Environmental Fatigue Crack Propagation in the 7XXX Alloy/Aqueous Chloride System. Ph.D. Dissertation, University of Virginia, Charlottesville, VA (1999).

[3] Z.M. Gasem, R. P Gangloff. in Chemistry and Electrochemistry of Corrosion and Stress Corrosion Cracking, R.H. Jones, ed., TMS, Warrendale, PA, pp.501-521 (2001).

[4] S.E. Gaylon. The Effects of CPC on the Initiation and Growth of Corrosion Fatigue Cracks in AA7075-T6. MS Thesis, University of Virginia, Charlottesville, VA (2006).

[5] X.F. Lui, S.J. Huang, H.C. Gu. Corrosion Science. 45, pp.1921-1938 (2003).

[6] X.F. Lui, S.J. Huang, H.C. Gu. International Journal of Fatigue. 24, pp.803-809 (2002).

[7] B. Davo, A. Conde, J.J. de Damborenea. Corrosion Science. 47, pp.1227-1237 (2005).

[8] M.A. Jakab. Corrosion Inhibition by Metal Ions Delivered from Amorphous Alloys. Ph.D. Dissertation, University of Virginia, Charlottesville, VA (2006).

[9] R.P. Gangloff, D.C. Slavik, R.S. Piascik, R.H. Van Stone, in Small Crack Test Methods, ASTM STP 1149, J.M. Larsen and J.E. Allison, eds., ASTM International, West Conshohocken, PA, pp.116-168 (1992).


[10] K.S. Ferrer, R.G. Kelly. Corrosion. 58, pp.452-459 (2002).

[11] MP Ciccone. The Effect of Corrosion Product Formation on Fatigue Crack Closure of AA7075-T6511 and AA 7055-T7451. MS Thesis, University of Virginia, Charlottesville, VA (2005).

[12] K.R. Copper, R.G. Kelly. J. Chromatography A. 850, pp.381-389 (1999).

[13] M.A. Jakab, P. Presuel-Moreno, J.R. Scully. Corrosion. 61, pp.246-263 (2005).

[14] A. Turnbull and D.H. Ferriss, Corrosion Science, 27, pp.1323-1350 (1987).

[15] R.P. Gangloff. in Embrittlement by the Localized Crack Environment, R.P. Gangloff, ed., TMS-AIME, Warrendale, PA, pp.265-290 (1984).

[16] K. Aramaki. Corrosion Science. 47, pp.1285-1298 (2005).