Corrosion Characteristics of an Al-1.78%Si-13.29%Mg Alloy in Chloride Solutions

Samples of the alloy Al-1.78%Si-13.29%Mg were immersed in aqueous 0.1M NaCl solutions up to 4 days at open circuit conditions. Morphological analysis with scanning electron microscopy (SEM) showed that the main intermetallic Al₃Fe played the role of local cathode producing dissolution of the adjacent aluminum matrix. The other intermetallic, Mg₂Si underwent selective dissolution of Mg but exhibited little morphological damage. Results with the scanning Kelvin probe force microscopy (SKPFM) technique showed a clear contrast in Volta potential between these two intermetallics and the matrix. For freshly prepared samples the Volta potential difference with respect to the matrix was about 600 mV for Al₃Fe and −300 mV for Mg₂Si. After a 19 h immersion in the chloride solution the potential difference decreased. In the case of the Mg₂Si intermetallic the Volta potential contrast to the surrounding aluminum matrix disappeared.