Effect of Mo addition on corrosion of Zn coatings electrodeposited on steel

ZnMo coatings with Mo content from 0.5 to 6 wt.% were electrodeposited on steel from citrate electrolytes. Electrochemical studies of their corrosion behaviour performed in a 5 wt.% NaCl showed that the low Mo content (∼0.5-1.5 wt.%) enhances corrosion protection significantly, whilst higher contents barely improve the corrosion properties in comparison to pure zinc coatings. Microstructural and phase characterisation indicate that the formation of a continuous and compact thin oxide film on the surface of the ZnMo (0.5-1.5 wt.%) coatings is the key factor affecting the high corrosion resistance of such coatings.