Electrochemical behaviour of AZ61 magnesium alloy in dilute NaCl solutions

A corrosion map in terms of electrode potential and chloride concentration [Cl−] was obtained on AZ61 magnesium alloy using electrochemical measurements, in which the alloy exhibits the corrosion and passivation zones in dilute NaCl solutions. The results are compared to those obtained on AZ31 and AZ91 alloys, in which the passivation zone of AZ61 alloy is broader than that of AZ31 alloy and gives a similar range to that of AZ91 alloy. The values of open-circuit potential on AZ61 alloy are in the passivation zone when [Cl−] is less than 0.3 mol/L. The potentiostatic polarisation of specimens depends on the chloride ion concentration and exhibits the corrosion and passivation states at various applied potentials. The current densities increase as the films flake off and are dissolved, and then drop to the low values as the new films are formed in the corrosion state. The fluctuations on the current density show the repetitive process of rupture/dissolution/repassivation on the localized surface films.