Effects of Crystallographic Orientation on Corrosion Behavior of Magnesium Single Crystals

The corrosion behavior of magnesium single crystals with various crystallographic orientations was examined in this study. To identify the effects of surface orientation on the corrosion behavior in a systematic manner, single-crystal specimens with ten different rotation angles of the plane normal from the [0001] direction to the direction at intervals of 10A degrees were prepared and subjected to potentiodynamic polarization and potentiostatic tests as well as electrochemical impedance spectroscopy (EIS) measurements in 3.5 wt.% NaCl solution. Potentiodynamic polarization results showed that the pitting potential (E-pit) first decreased from -1.57 V-SCE to -1.64 V-SCE with an increase in the rotation angle from 0A degrees to 40A degrees, and then increased to -1.60 V-SCE with a further increase in the rotation angle to 90A degrees. The results obtained from potentiostatic tests are also in agreement with the trend in potentiodynamic polarization tests as a function of rotation angle. A similar trend was also observed for the depressed semicircle and the total resistances in the EIS measurements due to the facile formation of MgO and Mg(OH)(2) passive films on the magnesium surface. In addition, the amount of chloride in the passive film was found first to increase with an increase in rotation angle from 0A degrees to 40A degrees, then decrease with a further increase in rotation angle, indicating that the tendency to form a more protective passive film increased for rotation angle near 0A degrees [the (0001) plane] or 90A degrees [the plane].