Effect of Microstructure on the Performance of Corrosion Resistant Alloys
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Corrosion by pitting in aluminum alloys is a very complex process that canbe affected by various factors such as chemical composition and microstructureof the alloys. The electrochemistry and distribution of second phases populating the alloy are the main factors that significantly influence the corrosion ofaluminum alloys.The purpose of the present work is to contribute to a deeper understanding of how the chemical composition and microstructure affect the ability of analuminium alloy to form a passive layer and its susceptibility to localized corrosion. To carry out the experiment, samples of alloys 3003, 5049, 6061, and 6063were prepared. The open circuit potential transient technique was utilized toinvestigate the corrosion potential of alloys under study. The ability of alloys toform the passive layer and the corrosion parameters such as corrosion potentialwere determined using potentiodynamic polarization measurement.In this study, the corrosion behvaiour of alloys was explored as a function oftime using the salt spray test. For each type of alloy, we considered 26 samples,prepared from tubes, and tested in a salt spray chamber in the duration of 49days. At specified intervals, two samples of each alloy were taken out fromthe chamber. The type of corrosion and the corrosion rate were investigatedthrough this test. As pitting is the main corrosion process, the depth of tendeepest pits were measured using optical microscopy. Also, the cross section ofthe deepest pit was analyzed to see if the alloy is susceptible to intergranularcorrosion.Statistical analysis was carried out in order to investigate the variation ofcorrosion rate during exposure and to predict the lifetime of a component. Inparticular, the Extreme Value theory, the Gumbel distribution, was employed toplot the probability paper of the extreme pit depth occurrence. In addition, theGumbel distribution theory was utilized to extrapolate data to longer exposuretimes.