13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- that the surface quality in the oxidation ceramics coating layer processes plays an important part in fatigue damage of aluminum alloy. In additional, the fracture-resistant of the different fracture appearances is different under the different oxidation ceramics coating layer methods. The different oxidation ceramics coating layer methods cause unavoidably the different surface quality. The oxidation ceramics coating layer with sealing hole can much easily avoid the surface defects such as shrinkage cavity. And the shrinkage cavity causes unavoidably the stress concentration and fatigue life degradation of materials. At the same time, the residual stress affects on the fatigue life of Al 2024-T4 alloy to exist the different results in three oxidation ceramics coating processes. 4. Summary Fatigue life of aluminum alloys may be either affected by relative higher humidity when the cycle is over than 2×106 or improved by the appropriate oxidation ceramics coating layer technology. For example, the effect of micro-arc oxidation with sealing hole process on the fatigue life of Al 2024-T4 alloy is positive and the effect of other micro-arc oxidation processes, such as micro-arc oxidation process and hard oxidation process, on the fatigue life of Al 2024-T4 alloy is negative. Therefore, the micro-arc oxidation ceramics coating layer with sealing hole technology is not only to enhance the fatigue strength but also to avoid the harmful or negative effect of the relative humidity on the fatigue life of Al 2024-T4 alloy. Acknowledgements The authors would like to thank the projects (Grants No: 11072124,11272173) supported by NSFC. References [1] Q.Y. Wang, C. Bathias, N. Kawagoishi, Effect of inclusion on subsurface crack initiation and giga-cycle fatigue strength. Int J Fatigue, 24 (2002) 1269–1274. [2] X.D. Li, X.S. Wang, H.H. Ren, Y.L. Chen, Z.T. Mu, Effect of prior corrosion state on the fatigue small cracking behavior of 6165-T6 aluminum alloy. Corros Sci, 55 (2012) 26-33. [3] K. Jones, D.W. Hoeppner, Prior corrosion and fatigue of 2024-T3 aluminum alloy. Corros Sci, 48 (2006) 3109-3122. [4] W.F. Xu, J.H. Liu, Microstructure and pitting corrosion of friction stir welded joints in 2219-O aluminum alloy thick plate. Corros Sci, 51 (2009) 2743-2751. [5] N. Kawagoishi, K. Kariya, Y. Nu, S. Furumoto, E. Kondo, Effect of humidity on fatigue strength of age-hardened Al alloy under rotating bending. Key Eng Mater, 452-453 (2011) 745-748. [6] N. Kawagoishi, T. Fukudome, K. Kariya, Q. Chen, M. Goto, Fatigue strength of age-hardened and extruded Al alloy under high humidity (Rotating bending and ultrasonic loading). Trans Japan Soc Mech Eng A, 76 (2010) 1651-1658. [7] H.M. Nykyforchyn, V.I. Pokhmurskii, M.D. Klapkiv, M.M. Student, J. Ippolito, Electrochemical characteristics of PEO treated electric arc coatings on lightweight alloys. Adv Mater Research, 138 (2010) 55-62. [8] B. Lonyuk, I. Apachitei, J. Duszczyk, The effect of oxide coatings on fatigue properties of 7475-T6 aluminium alloy. Surf & Coat Tech 201 (2007) 8688-8694. [9] N.P. Wasekar, A. Jyothirmayi, L.R. Krishna, G. Sundararajan, Effect of micro arc oxidation coatings on corrosion resistance of 6061-Al alloy. J Mater Eng & Perform, 17 (2008) 708-713. [10] N. Kawagoishi, K. Hayashi, N. Yan, S. Furumoto, E. Kondo, Effect of humidity on fatigue strength of age-hardened Al alloy under rotating bending. Key Eng Mater, 452-453 (2011) 745-748.
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