Characterisation and corrosion resistance of Zn-Mn coatings electrodeposited from acidic chloride bath

Zn-Mn alloy coatings were galvanostatically electrodeposited from an acidic chloride bath. Effects of deposition current density, pH and temperature on surface morphology, microstructure and corrosion resistance of Zn-Mn coatings were studied. The coatings deposited at 10, 50 and 100 mA cm(-2) had a single eta-Zn phase structure. However, a dual phase structure of eta-Zn and epsilon-Zn-Mn with higher Mn content was found for the coatings deposited at 200 mA cm 22. The dual structure degraded the corrosion resistance of the coatings. The highest corrosion resistance was achieved for the Zn-Mn coating deposited at 100 mA cm(-2), pH 4 center dot 9 and 25 degrees C. This coating contained 4? 1 wt-% Mn and showed a unique surface morphology consisting of randomly arranged packs of very thin platelets, laid perpendicular to the surface and provided a high compactness deficient free structure.