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

Highlights: • ZnMo alloy coatings were electrodeposited with Mo content from 0.5 to 6 wt.%. • The corrosion rate decreased one order of magnitude using 0.5 wt.% of Mo. • TEM characterisation showed different oxide formation as a function of the Mo content. • A protective compact oxide layer formed on ZnMo (0.5–1.5 wt.%) coatings exposed to air. - Abstract: 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.