Corrosion Behavior of AZ31 Magnesium Alloy in Dilute Sodium Chloride Solutions

Abstract

Corrosion behavior of AZ31 magnesium alloy in dilute NaCl solutions was studied by electrochemical techniques. Its surface film was chemically characterized by X-ray diffraction (XRD). A corrosion map in terms of electrode potential and chloride concentration [Cl^–] was obtained by using electrochemical measurements. With the map, passivation and corrosion zones were determined. The passivation zone was found to become narrow with the increasing of [Cl^–] . The values of E_ocp, open-circuit potential, in nondeaerated NaCl solutions were in the passivation zone when [Cl^–] <0.2 M and in the corrosion zone when [Cl^–] ≥0.2 M. The reduction reactions of dissolved oxygen and hydrogen evolution worked as cathodic reactions in nondeaerated solutions. By XRD analyses, Mg(OH)₂, magnesium hydroxyl carbonate, and MgO were the dominant products in the corrosion zone, whereas magnesium hydroxyl carbonate and MgO were the main components in the passivated film.