Materials Performance

AUG 2018

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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57 MATERIALS PERFORMANCE: VOL. 57, NO. 8 AUGUST 2018 the solution increased the rate of penetra- tion. As the corrosion time increased, the number of pits continued to increase, and the corroded area continued to expand. In addition, under the alternating cyclic load, the sample specimen had directional dam- age that led to the formation of small cracks along the grain boundar y, which tended to connect with each other, as shown in Figure 2. At the same time, due to the stress con- centration, the fatigue damage was further extended near the corrosion pits. Many transmission channels for corrosive media were formed around the corrosion pits, which promoted the development of addi- tional corrosion pits. The emergence and d e v e l o p m e n t o f t h e p i t s c a u s e d t h e mechanical properties of the material to decline, which further affected the initia- tion of fatigue cracks and the expansion of fatigue cracks affecting the fatigue life of materials. Crack Deflection and Bifurcation In this study, the presence of corrosion pits in the direction of the arrows was con- sidered. As illustrated by the white dotted arrows in Figure 3, the main crack propa- gated along pit edges intersecting its origi- nal propagation path, which caused it to def lect. The pits led to a decrease in the mechanical properties of the surrounding area so that the fatigue crack expanded in the corrosion zone where expansion resis- tance was small . Bifurcation occurred when the fatigue crack path def lected . Whether a bifurcated crack will extend far- ther depends on the conditions at the crack tip. The bifurcation of the crack in Figure 3 was due to the presence of two corrosion pits during the original crack propagation, which led to further expansion of the crack. The propagation of the fatigue crack pro- ceeded in the direction of the least resis- tance, causing it to propagate in both directions. Conclusions Based on the simplified TWIST gust load spectrum S1, the corrosion/fatigue alternation test of 2024-T4 aluminum alloy showed that the fatigue life decreased with the increase of corrosion time (h) in the alternating process. The number and area of the crack sources increased and the number and density of the pits increased, which led to the decrease of the material's local mechanical properties and the accel- eration of the fatigue crack propagation. Furthermore, in the process of fatigue crack growth, the fatigue crack propaga- tion path can be def lected and/or bifur- cated due to the existence of corrosion pits. References 1 X.D. Li, et al., "Effect of Prior Corrosion State on the Fatigue Small Cracking Behavior of 6151-T6 Aluminum Alloy," Corros. Sci. 55, 2 (2012): pp. 26-33. 2 C.Y. Men, et al., "Correlations Between Stress Corrosion Cracking, Grain Boundary Pre- cipitates and Zn Content of Al–Mg–Zn Al- loys," J. Alloys and Compounds 655 (2016): pp. 178-187. 3 X.H. Zhao, et al., "The Cracking Behaviors of Anodic Films on 1050 and 2024 Aluminum Alloys after Heating up to 300 °C," J. Alloys and Compounds 479, 1-2 (2009): pp. 473-479. 4 H. Fadaee, M. Javidi, "Investigation on the Corrosion Behaviour and Microstructure of 2024-T3 Al Alloy Treated via Plasma Electro- lytic Oxidation," J. Alloys and Compounds 604, (2014): pp. 36-42. 5 S.H. Xu, Y.D. Wang, "Estimating the Effects of Corrosion Pits on the Fatigue Life of Steel Plate Based on the 3D Profile," Int. J. Fatigue 72 (2015): pp. 27-41. 6 ASTM E647, "Standard Test Method for Mea- surement of Fatigue Crack Growth Rates" (West Conshohocken, PA: ASTM, 2015). 7 ASTM G34-01, "Exfoliation Corrosion Sus- ceptibility in 2XXX and 7XXX Series Alumi- num Alloys (EXCO Test)" (West Consho - hocken, PA: ASTM, 2013). FUSHENG WANG is an assistant experi- mentalist with the Sino-European Institute of Aviation Engineering, Civil Aviation Uni- versity of China, Tianjin, China, email: In this position, Wang's main research direction is fatigue failure analyses. Wang holds a master's degree in materials engineering from Tian- jin University. XUNTAO ZHANG is a student at the Sino- European Institute of Aviation Engineer- ing, Civil Aviation University of China, email: As a post- graduate student since 2016, Zhang's main research direction is the fatigue properties and corrosion resistance of aluminum alloy. Zhang holds a bachelor's degree in engi- neering in aircraft power from the Civil Aviation University of China. AILUN WANG is a student at the Sino- European Institute of Aviation Engineer- ing, Civil Aviation University of China, email: As a post- graduate student since 2015, Wang's main research direction is the fatigue properties of aluminum alloy. Wang has a master's degree in aeronautical engineering from the Civil Aviation University of China. YAJUN CHEN is an associate professor with the Sino-European Institute of Avia- tion Engineering, Civil Aviation University of China, email: As an associate professor, Chen's main research direction is aeronautical structure and material failure analyses. Chen holds a Ph.D. in material processing engineering from the Tianjin University and has coau- thored a paper on multiaxial fatigue behaviors of 2024-T4 aluminum alloy under different corrosion conditions. FIGURE 3 Special crack propagation behavior. Corrosion-Fatigue Effect on the Life of Aluminum Alloy

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