Corrosion of Magnesium-Aluminum (Mg-Al) Alloys-An Interplay Between Al Content and CO2

In course of their practical applications, magnesium-aluminum (Mg-Al) alloys are frequently exposed to the ambient atmospheric, and thus, are susceptible to environmental degradation. In this study, we exposed several Mg-Al alloys (including AM20, AZ31, AM50, and AZ91) with different Al content to atmospheric environment to examine the effect of most important environmental factor, i.e., carbon dioxide (CO2) and its relation to the alloys' Al content. The surface films formed on alloys at two temperatures (-4 and 22 degrees C) were examined using auger electron spectroscopy (AES). The results show that CO2 inhibits long-term atmospheric corrosion behavior of the alloys and that the thickness of the carbon-rich layer in the surface film increases with increasing Al content. We suggest that; (a) the inhibitive effect of CO2 on the atmospheric corrosion behavior of Mg-Al systems, and (b) the positive influence of Al content on the corrosion performance of Mg-Al alloys are partly linked to the occurrence of compounds that exhibit characteristics close to that of the layered double hydroxides (LDHs)