Corrosion of Binary Mg-Al Alloys.

The corrosion behavior of single-phase Mg-Al alloys has been examined using a combination of aqueous, atmospheric and ionic liquid based techniques. Our results show preferential rapid dissolution of Mg along with redistribution and enrichment of the effectively more "noble" Al component. During aqueous free corrosion experiments immediate pH increases were measured at the solid-liquid interface in aqueous chloride. Using inductively coupled plasma mass spectroscopy the oxide/hydroxide chemical dissolution rates were determined to be 0.222 per atomic site/s for Mg²⁺ and 0.022 per atomic site/s for Al³⁺ from the elemental alloy components. Atmospheric corrosion studies measured a 60◦ contact angle decrease during 20 hour free corrosion corresponding to a small 0.04 Jm^-2 reduction in the MgO/water interfacial free energy. Rotating disk electrode and ionic liquid dissolution techniques revealed mud cracking, platelet formation and nanowire morphologies that can result from selective dissolution ofMg in single-phase Mg-Al alloys. The evolution of these morphologies is described in terms of a step-flow dissolution mechanism. [ABSTRACT FROM AUTHOR]