The dependence of the pitting potentials of aluminum alloys on the solid-state cohesion of the alloying metals

• Published in: Corrosion science Vol. 36; no. 9; pp. 1615 - 1623
• Main Author: Vijh, A.K.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.09.1994
• ISSN: 0010-938X; 1879-0496
• DOI: 10.1016/0010-938X(94)90057-4

It is shown that the pitting potentials of aluminum alloys reported by Inturi and Szklarska-Smialowska [ Corros Sci. 34, 705 (1993)] can be causatively correlated with the metal-metal bond energy, b(M-M), values of the alloying elements: high b(M-M) values raise the pitting potentials towards nobler values and vice versa. This has been interpreted as resulting from pitting being nothing but active dissolution of the bare metal sites in the micro-fissures and defects of the oxide covering the alloy, in accordance with the pioneering studies of Richardson and Wood [ Corros. Sci. 10, 313 (1970)] and Galvele et al. [U. R. Evans Conf. on Localized Corrosion, Williamsburg Dec 1971)]. Further, interpretations of pitting phenomenon being controlled by the pH of the surface oxide in relation to pH of the electrolyte solution as proposed by Natishan et al. [ J. electrochem. Soc. 135, 321 (1988)], cannot be sustained by a further analysis: such relationships between pitting potentials and pH pzc can arise because of the correlation between b(M-M) and pH pzc. Quantitatively, the slope of the correlative line between the pitting potentials of aluminum alloys and the b(M-M) values of the alloying elements has been found to be unity: no theoretical significance can be attributed to this slope at the present time, however.