Characterization and corrosion behavior of binary Mg-Ga alloys

Four binary cast Mg-Ga alloys containing 1, 2, 3 and 4 wt% Ga were studied in terms of microstructure and degradation behavior. The alloys present two types of intermetallics: (i) the second phase Mg5Ga2, which volume increases with the amount of Ga in the alloy, and (ii) inclusions containing impurities. For the first time, the binary Mg-Ga system is analyzed paying particular attention to the effect of secondary phases (Mg5Ga2) and impurities on the localized corrosion mechanism using AFM/SKPFM. Inclusions containing impurities reveal a high Volta potential difference, enough to form an active galvanic couple. However, localized electrochemical activities decrease with time leading to uniform degradation. For short immersion times, there is no clear influence of the element Ga on the corrosion behavior, measured by electrochemical and hydrogen evolution tests. However, for longer immersion times, increasing the amount of Ga in the alloy shows a clear negative effect. Electrochemical measurements reveal that higher Ga containing alloys form faster an oxide layer which is not stable.