Understanding the galvanic corrosion of the Q phase/Al couple using SVET and SIET
Abstract The galvanic corrosion of the Q phase/Al couple in 0.1 M NaCl solutions has been studied using the scanning vibrating electrode technique (SVET) the scanning ion selective electrode technique (SIET) and energy dispersive X ray spectroscopy (EDX) The galvanic corrosion of the Q phase/Al couple was found to be dependent on pH and immersion time. Current density maps obtained by SVET shows that the anodic oxidation processes emerge from Al in a localized manner in pH 2 and 6 solutions but is initiated in a uniform manner in pH 13 solution, whereas, the cathodic processes are more homogeneously distributed over the Q phase at pH 2, 6 and 13. It is seen that the Q phase remains cathodic in the Q phase/Al couple in acidic, neutral and alkaline solutions indicating that the galvanic polarity of the Q phase is independent of pH. The effect of the galvanic corrosion was largest at pH 2 and 13 compared to pH 6. The pH map obtained by SIET indicates that the galvanic activity of the Q phase/Al couple proceeds via heavy alkalization of the Q phase surface with the generation of appreciable amounts of OH ions. The enrichment of Cu indicated by EDX is responsible for the observed cathodic activity of the Q phase in the Q phase/Al couple.
Journal of Materials Science Technology