Galvanic Corrosion of Aluminum Coupled to Passivating and Non-Passivating Alloys

M.S. University of Hawaii at Manoa 2016.Includes bibliographical references.Galvanic corrosion of 6061-T6 aluminum-coupled metals was studied in marine, volcanic, and rainforest environments. In addition to field research, galvanic couples were subjected to the chloride-containing GM-9540P accelerated corrosion test. The galvanic couple types included 6061-T6 Al with Ti-6Al-4V, 316 stainless steel, silver, copper, 1018 steel, and Mg AZ31B connected via insulating fasteners. In this research, galvanic corrosion currents were measured through portable data loggers connected to each metal in the aluminum-coupled specimens. The total corrosion on an anode in a galvanic couple results from galvanic corrosion between the anode and the cathode plus additional simultaneous local corrosion on the anode caused by cathodic reactions occurring on the anode. The value of the total corrosion rate, that is, local corrosion and galvanic corrosion, was determined by mass loss of the galvanically-coupled aluminum coupons. The local corrosion was determined using the difference between the total corrosion rate and the galvanic corrosion rate, as determined from the galvanic current data and Faraday’s law. The mass loss of the coupons was also compared to those of uncoupled aluminum coupons which were not subjected to galvanic corrosion. Corroded aluminum samples were subjected to surface analysis using SEM/EDXA and XRD. Potentiodynamic polarization and pH experiments were also conducted in order to study the mechanisms of galvanic corrosion for the couples described above