Electrochemical performance and corrosion resistance of Zn-Al pseudo-alloy coatings in chlorine ion-containing environment

The corrosion behavior and electrochemical characteristics of pure Zn and Zn-Al pseudo-alloy coatings in chlorine ion-containing environment were investigated by salt spray test and electrochemical impedance spectroscopy (EIS). The surface morphologies and phase compositions of the coatings and the corrosion products were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). A preliminary discussion was carried out on the corrosion mechanisms of the two kinds of the coatings. It is found that the corrosion product layer on the pure zinc coating sample is loose and porous with prolonging test time, the main corrosion products are Zn ₅(OH) ₈Cl ₂H ₂O, ZnO and Zn ₅(CO ₃) ₂(OH) ₆, and some areas in the corrosion product layer have cracked after salt spray testing for 768 h. A compact corrosion product layer forms on the zinc-aluminum pseudo-alloy coating with the time prolonging, and the main corrosion products consist of Zn ₅(OH) ₈Cl ₂H ₂O, Zn _0.71Al _0.29(OH) ₂ (CO ₃) _0.145·xH ₂O and ZnAl ₂O ₄. EIS results indicate that the charge transfer resistance of the two coatings increases during the corrosion process. The impedance of the zinc-aluminum pseudo-alloy coating is significantly greater than that of the pure zinc coating, showing a better corrosion resistance.