Electrochemical evaluation of advanced anodized aluminum and chromate-free conversion coatings

In the present study, electrochemical evaluation of advanced surface modification methods for different metallic materials was performed using electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), cyclic polarization and other electrochemical techniques. This dissertation comprises four chapters. Chapter 1 is an overview of different corrosion protection technologies and electrochemical methods that can be used to characterize the corrosion behavior of different metals and alloys.;In chapter 2, the long-term (365 days) corrosion resistance of anodized Al 6061-T6 produced by two different hard anodizing (type III) processes was evaluated using EIS and SEM. The results suggest that these anodized samples were very corrosion resistant. Since the oxide layers of anodized Al 6061 are subject to thermal cycling in the semiconductor industry, the protective properties of the oxide layers that were subjected to thermal cycling treatments at 120, 160 and 200°C were evaluated. The thermal cycling treatment can produce considerable damage of the outer porous oxide layer and the inner barrier layer.;The objective of the study in Chapter 3 was to determine the optimum process parameters for producing highly protective cerium-based conversion coatings on galvanized steels using an optimum treatment solution. The optimum combination of three factors was determined through 23 factorial design experiments.;Stainless steels provide good corrosion resistance through the formation of a chromium-rich oxide film on the metal surface. However, many types of stainless steels are susceptible to localized corrosion such as pitting corrosion and crevice corrosion. The objective of the study in Chapter 4 was to determine the corrosion resistance of three different stainless steels and a nickel-based alloy that were treated by an optimized treatment solution containing hydrogen peroxide, colloidal silica and silane.