Corrosion Morphologies in Different Welding Zones of Friction-Stir Welded (FSW) Aluminum Alloy AA5086AA5086, AA6061AA6061, and Dissimilar AA5086AA6061 Joints Exposed in Various Atmospheric Environments

Abstract

Similar and dissimilar joints of AA6061-T6 and AA5086 have been exposed in mild and severe marine, volcanic (with acid rain), rainforest, and arid atmospheric environments in the Hawaiian islands. The severe marine environment on the Marine Corps Base Hawai'i (MCBH) shows high humidity and rainfall and high chloride ion concentrations; whereas, the mild marine site on Coconut Island is characterized by a significant lower chloride ion concentration. Samples near the Kilauea Volcano on the Big Island are under exposure of acid rain, variable humidity, and sulfur dioxide plume. The rainforest at the Lyon Arboretum in Manoa represents the wet climate with high rainfall, high humidity and time of wetness, and low chloride ion concentrations. In contrast, the dry climate in Waipahu shows low humidity and rainfall, low time of wetness, and low chloride ion concentrations. The impact of the atmospheric environment on the severity of the corrosion has been studied in different welding zones of each type of sample. The focus was to show the dissilimarities in morphology of the parent material, the weld nugget, the heat affected zone (HAZ), and the thermo-mechanically affected zone (TMAZ). The microstructure and chemical composition of the different welding zones before and after the exposure to the environment have been characterized using Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Analysis (EDXA). In addition to the field tests, laboratory tests have been performed to study galvanic corrosion between the different welding zones using the zero-resistance ammeter (ZRA) technique.