Quantification of Corrosion Pitting Under Immersion and Salt Spray Environments on an As-Cast AM60 Magnesium Alloy
Martin, H. J., Alvarez, R., Horstemeyer, M., Qiang-Chandler, M., Williams, T. N., & Wang, P. (2012). Quantification of Corrosion Pitting Under Immersion and Salt Spray Environments on an As-Cast AM60 Magnesium Alloy. In David E. Laughlin (Ed.), Corrosion. NACE. 68, 571-585.
The effects of a wet saline environment on polished AM60 magnesium alloy were quantified. Experimental corrosion tests were carried out using a full immersion method and a 3.5% NaCl aqueous solution at ambient temperature. Pit characteristics were evaluated using laser beam profilometry and optical microscopy images. Three corrosion mechanisms clearly arose: localized pitting, intergranular corrosion, and general corrosion. Localized pitting was dominant at the beginning of the immersion tests but quickly became the least dominant corrosion mechanism. Intergranular corrosion became dominant at the second time period, but also quickly became less dominant. General corrosion became the dominant corrosion mechanism after 90 min and continued to be the dominant corrosion mechanism for the rest of the study. This study followed one pit throughout the study, which demonstrated that the pit characteristics of depth, area, and volume changed in an oscillating manner, due to the formation and removal of a Mg(OH)2 film. Stereological quantification was used instead of the standard weight loss method to develop a novel corrosion rate. The pit number density and mean pit surface area showed that the pits did very little growing initially before quickly and rapidly growing after the Mg(OH)2 film was removed. The nearest neighbor distance was inversely related to pit number density and showed a similar trend as the mean pit surface area.