Addition of Mo in the Zn based alloy coating in the citrate solution and investigation of its corrosion behavior

In this work, Zn-Co-Mo coatings were electrodeposited on mild steel substrate from a citrate solution at current densities of 5, 7.5 and 10 mA.cm-2 and pH values of 4.5, 5, and 5.5. The coated samples were studied by scanning electron microscope and potentiodynamic polarization. The corrosion behavior of the coatings was related to the molybdenum content and formation of local anodes and cathodes. According to the results, a distinct range of current and pH was recognized to provide high quality and corrosion resistant coatings. The percentage of molybdenum as an alloying element plays an important role in the improvement of the corrosion properties of the coating. The formed coating at pH of 5.5 with 13 wt. % Mo showed the lowest corrosion current density with a value of 0.5 µA.cm-2.The molybdenum coating also showed a passive-like behavior in the anodic region due to the presence of molybdenum in the coating composition.