Influence of Deaerated Condition on the Corrosion Behavior of AZ31 Magnesium Alloy in Dilute NaCl Solutions

Abstract

The corrosion behavior of AZ31 Mg alloy in the nondeaerated and deaerated dilute NaCl solutions was investigated by electrochemical measurements. The cathodic reaction of AZ31 Mg alloy depends on the hydrogen evolution and the oxygen reduction in nondeaerated media, while that is dominanted by the hydrogen evolution in deaerated media. In the potentiostatic measurements in deaerated media, the current density reached a peak during the initial immersion and then showed a stepwise decrease getting into the passivation state by a homogeneous distribution of the Mg(OH)₂ product with increasing polarization time. It revealed that AZ31 alloy has a better corrosion resistance in deaerated media after long immersion. In the 0.01 mol/L solution, passivation zone was observed in deaerated media polarization up to −1.35 V (vs. SCE) while the corrosion and passivation zones were occurred in nondeaerated media. Potentiodynamic measurements in the 0.01 mol/L NaCl solution containing various concentrations NaHCO₃ showed that the corrosion behavior of AZ31 alloy depends on the NaHCO₃ concentration. It means that the presence of CO₂ naturally in nondeaerated media may affect the corrosion process.