Application of EIS to assess the effect of rare earths small addition on the corrosion behaviour of Zn–5% Al (Galfan) alloy in neutral aerated sodium chloride solution

Abstract

The effect of rare earth metal (Gd, Dy, Er, and Y) small additions on the corrosion behaviour of Zn–5% Al (Galfan) alloy has been investigated. The corrosion resistance of Zn–5Al–0.1Gd, Zn–5Al–0.1Dy, Zn–5Al–0.1Er, and Zn–5Al–0.1Y alloys has been assessed by electrochemical impedance spectroscopy (EIS) measurements carried out in a 0.1 M NaCl solution, at approximately neutral pH, without stirring and in contact with the air. For comparison, the electrochemical tests have also been carried out on the Galfan alloy. EIS results showed that rare earths’ addition significantly improves the corrosion behaviour of Galfan. This improvement is most likely due to enhanced barrier properties of the corrosion products layer and additional active corrosion protection originated from the inhibiting action of the lanthanide ions entrapped as oxides/hydroxides in this surface layer.