Dominique Thierry

Formation of Corrosion Products on Open and Confined Zinc Surfaces Exposed to Periodic Wet/Dry Conditions

Abstract The formation of corrosion products was followed during the atmospheric corrosion of open and confined zinc surfaces exposed to periodic wet and dry conditions. The periodic wet and dry exposure consisted of the immersion of samples in sodium chloride (NaCl) solutions followed by exposure to laboratory air for different time periods. Phases of the corrosion products were identified by Fourier transform infrared spectroscopy (FTIR) and x-ray diffraction (XRD), while the relative proportions of the corrosion products were determined by FTIR. Three main components were identified in the corrosion products on the zinc surfaces, namely zinc oxide (ZnO), hydrozincite (Zn5[OH]6[CO3]2), and simonkolleite (Zn5[OH]8Cl2·H2O). The wet/dry pattern of the exposure conditions was an important factor affecting the composition of the corrosion products for open zinc surfaces and zinc surfaces confined in crevices. Similar proportions of zinc oxide, simonkolleite, and hydrozincite were formed on both open and conf...

Formation of Corrosion Products on Open and Confined Metal Surfaces Exposed to Periodic Wet/Dry Conditions—A Comparison between Zinc and Electrogalvanized Steel

Abstract The formation of corrosion products during atmospheric corrosion on open and confined surfaces of electrogalvanized steel exposed to periodic wet/dry conditions was studied. The composition of the corrosion products was determined using Fourier transform infrared spectroscopy (FTIR) and extra information about the phases present was obtained by x-ray diffraction (XRD). Corrosion products that formed consisted mainly of different amounts of zinc oxide (ZnO), hydrozincite (Zn5[OH]6[CO3]2), and simonkolleite (Zn5[OH]8Cl2·H2O). These results were compared to results obtained previously for pure zinc. The wet/dry pattern of the exposure had a large influence on the composition of the corrosion products. Similar proportions of zinc oxide, simonkolleite, and hydrozincite formed on electrogalvanized steel as formed on zinc on open surfaces exposed for shorter drying times. When the drying time was longer, simonkolleite was the dominant compound on electrogalvanized steel and zinc. In contrast, zinc oxide...

In Situ Infrared Reflection Absorption Spectroscopy Studies of Confined Zinc Surfaces Exposed under Periodic Wet-Dry Conditions

In-situ infrared reflection absorption spectroscopy (IRAS) was a very powerful tool for studies of corrosion processes of the confined metals in the atmosphere.In this paper,an in-situ IRAS cell was set up and the corrosion process of zinc and water evaporation in the drying process on the confined zinc surface exposure under periodic wet dry conditions was studied by in-situ IRAS.The water thickness on the confined surface of zinc could be calculated according to the optical index.The corrosion product formed in the initial stage of the confined zinc in the purified air with the relative humidity of 50% mainly was ZnO,The amount of corrosion product on the confined zinc surface increased linearly with day,the corrosion rate decreased with time during each drying process.

Effect of Climatic Parameters on Filiform Corrosion of Coated Aluminum Alloys

Abstract The effects of temperature, relative humidity, and wet-dry transition on initiation and propagation of filiform corrosion on coated aluminum alloy 6016 (AA6016 [UNS A96016]) have been studied. Corrosion products formed in the filament were analyzed using Fourier transform infrared (FTIR)-microspectroscopy. The aluminum surfaces were tested in both milled finish and grinded conditions with chromium, phosphate, and titanium-zirconium-based pretreatment. An electrodeposited coat (ED coat) and a full paint system used for automotive applications (ED coat + topcoat) were investigated for the different combinations of mechanical finish, surface pretreatment, and coating system. In the temperature range between 5°C and 50°C, filiform corrosion, or underfilm corrosion in general, increased significantly. The effect of relative humidity and wet-dry cycling, on the other hand, seems to be strongly influenced by parameters like pretreatment, coating system, and temperature. Filiform corrosion was the highes...

Fatigue behavior of spot-welded joints in air and under corrosive environments

A bstractThe main aim of the project was to evaluate the influence of combined effects of fatigue loading and exposure to cyclic corrosion testing on the corrosion and the fatigue resistances of coated steel-based materials joined by resistance spot welding. Seven steel-based materials including cold rolled mild steels, high-strength steels, and press-hardened steels (PHS) were selected and provided by steel suppliers with different surface coatings for resistance spot welding. Panels were joined using conventional resistance spot welding in both lap-shear and T-peel designs. Joined samples were painted by e-coating following the industrial process. Metallographic characterization of the steel materials revealed that microstructures and metallic coating composition and thickness were as expected. Cross section of spot welds showed good quality and typical evolutions of hardness. Tensile tests and fatigue tests were performed on reference samples (fatigue in “air,” i.e., nonexposed to corrosion) leading to typical SN-lines as described in part I of this paper. The results were used to evaluate the influence of corrosion on tensile strength of the joined samples. Fatigue tests performed on combined and alternating corrosion and fatigue revealed that fatigue life is affected by extent of corrosion near the spot weld, with a reduction of the fatigue life at higher applied load and slight increase for lower load, compared to tests “in air.” This phenomenon was not observed for lap-shear configuration in alternated fatigue-corrosion mode.