The Influence of Carbon Dioxide on the Atmospheric Corrosion of Some Magnesium Alloys in the Presence of NaCl

Abstract

The influence of ambient concentrations of carbon dioxide on the NaCl-induced atmospheric corrosion of high purity die-cast MgAl alloys (AM20 and AM60) and MgAlZn alloy (AZ91) is reported. Samples were exposed four weeks in a carefully controlled synthetic atmosphere. Relative humidity was 95%, the temperature was and the concentration of was or 350 ppm. Sodium chloride was added before the exposures The corrosion products were analyzed by gravimetry, ion chromatography, X-ray diffraction, and environmental scanning electron microscopy. Mass gain and metal loss results are reported. As expected, the combination of high humidity and NaCl is very corrosive toward the magnesium alloys investigated. The NaCl-induced corrosion is inhibited by ambient concentrations of Exposures in the absence of give rise to heavy pitting; brucite, is the dominant corrosion product. In the presence of a uniform layer of hydrated magnesium hydroxy carbonate, forms. In both environments, the corrosion rates increased in the order © 2002 The Electrochemical Society. All rights reserved.