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 associ ated with constituent particles in the alloys.:Pitting is attributed to the galvanic coupling of constituent particles:to the matrix. To better unders tand the mechanism and kinetics of pitting, two model alloys were used in t his study, emulating the Cu, Fe, Mn containing constituent particles, to me asure the open circuit potential and galvanic current density associated wi th 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 p article size and limiting current density. The much higher limiting cathodi c current density for both of-the model alloy-aluminum couples in an acidif ied, versus a neutral, solution indicated that galvanic corrosion of the pa rticle-matrix couple contributed not only to the nucleation but also to the growth of pits in aluminum alloys. (C) 1999 Elsevier Science Ltd. All righ ts reserved.