Limitations in the use of the potentiodynamic polarisation curves to investigate the effect of Zn on the corrosion behaviour of as-extruded Mg–Zn binary alloy

The effects of Zn on corrosion behaviour of as-extruded Mg-(1-4)Zn alloys were investigated using an immersion test, a zero resistance ammeter technique, and a potentiodynamic polarisation test. As a result, it was revealed that the solutionised Zn enhanced protectiveness of the passive film, and accelerated the H₂ evolution rate of the Mg–Zn binary alloys. The acceleration of the H₂ evolution rate by addition of Zn leads to an increase in the net corrosion rate of the Mg–Zn alloy. In this research, the polarisation test was found to have some limitations for evaluating the true corrosion behaviour of passive Mg–Zn alloy.