Investigation of coating cracking and fatigue strength of 7050-T74 aluminum alloy with different anodize coating thicknesses
Creators:Goetz, John M.
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Publisher:The Ohio State University
Series/Report no.:The Ohio State University. Department of Mechanical Engineering Honors Theses;2005
The benefits of applying anodize coatings to aluminum alloys for corrosion protection have been widely recognized. Despite their many advantages, anodize coatings are believed to be a detriment to the fatigue properties of the substrate aluminum. Additionally, there is relatively little scientific knowledge of how to optimize such coatings, and the impact of varying coating thickness is not understood. This project involves the study of four anodize thicknesses ranges deposited on a 7050-T74 aluminum substrates. Through the use of rotary bend fatigue experiments and tensile cracking experiments, the effect of increasing anodize thickness has been examined. Scanning electron microscopy has also been used to relate the measured strengths to the cracking patterns observed at the failure surfaces. Through the fatigue experiments, it was found that the thinnest anodize coatings yielded the highest fatigue lives. The tensile cracking experiments with acoustic emission measurements indicate that when compared to the thinner coatings, the thickest coatings have a higher cohesive strength. This research project has provided much needed insight into the field of anodic coatings for structural applications. More importantly, the results of this project quantify the extent to which the mechanical and coating properties of anodized 7050 aluminum alloy are affected by varying coating thickness. The information gained through this research project is aimed at helping Goodrich make an educated decision on the optimum thickness for the anodize coating of the 7050 aluminum alloy.
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