Influence of Mg5Ga2 compound on microstructures and electrochemical properties of Mg-5%Hg-22%Ga alloy

The Mg-5%Hg-22%Ga(mole fraction) alloy was melted. Aging at 573-673 K for different times was carried out to ensure the fine dispersion of the Mg5Ga2 compound. Scanning electron microscopy (SEM), X-ray diffractometry(XRD) and energy spectrum analysis(ESA) were employed to characterize the microstructures and phases of the Mg-5%Hg-22%Ga alloy. The electrochemical and corrosion behaviors of the above alloy were studied by potentiodynamic, galvanostatic and electrochemical impedance spectroscopy (EIS) measurements. The relationship between the Mg5Ga2 compound and the electrochemical properties of the Mg-5%Hg-22%Ga alloy was discussed. The results demonstrate that the heat treatment at 573-673 K for 24 h accelerates the growth of the intergranular eutectic Mg-Mg5Ga2 and the heat treatment for 200 h prompts the transition of eutectic to dispersed linear Mg phase and Mg5Ga2 matrix. This transition enhances the electrochemical activity and corrosion resistance of the Mg-5%Hg-22%Ga alloy. In the galvanostatic tests with current density of 100 mA/cm(2), the most negative potential, -1.991 V, occurs in the sample aged for 200 h. The largest corrosion current density of 44.36 mA/cm(2) occurs in the sample aged for 24 h.