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The initial micro-galvanic corrosion behavior of Mg‒30wt%Ca alloy only containing Mg 2 Ca and α-Mg was studied by immersion testing in a 0.9% NaCl solution at 37 °C. The quasi-in situ SEM and TEM results show that Mg 2 Ca corroded easier than α-Mg, indicating that Mg 2 Ca acted as an anode. The work function (Φ) for Mg 2 Ca calculated by first-principles is significantly lower compared to that for α-Mg. The Volta potential measured by a scanning Kelvin probe force microscope reveals that the Mg 2 Ca had a relatively low Volta potential (ψ) value. The lower Φ and ψ values for Mg 2 Ca indicate a lower electrochemical nobility, which is consistent with the experimental phenomenon. [ABSTRACT FROM AUTHOR]