Galvanic coupling of model alloys to aluminum — a foundation for understanding particle-induced pitting in aluminum alloys

Pitting corrosion in aluminum alloys has been shown to be intimately associated with constituent particles in the alloys. Pitting is attributed to the galvanic coupling of constituent particles to the matrix. To better understand the mechanism and kinetics of pitting, two model alloys were used in this study, emulating the Cu, Fe, Mn containing constituent particles, to measure the open circuit potential and galvanic current density associated with particle–matrix couples. The rate of corrosion reaction at the particle–matrix couple was found to be controlled by the limiting cathodic current density and the particle size. The total corrosion current increased with particle size and limiting current density. The much higher limiting cathodic current density for both of the model alloy–aluminum couples in an acidified, versus a neutral, solution indicated that galvanic corrosion of the particle–matrix couple contributed not only to the nucleation but also to the growth of pits in aluminum alloys.