The effect of Mn incorporation on zirconium conversion coating with and without organic coating

In this paper, manganese ion was added to a hexafluorozirconic acid based conversion coatingto study how this additive affects corrosion resistance, morphology and composition of the coating. The properties of the coated surface was examined EIS tests for comparing the corrosion resistance of differently coated samples and AFM to evaluate surface morphology.The higher charge transfer resistance of conversion coating was observed in the presence of 0.01 g/l Mn ion in the solution as reported by EIS results. According to AFM, more uniformity was observed for zirconium conversion coating containing 0.01 g/l Mn ion compared to that with no Mn. The organic coating applied on the Zr conversion coating without Mn ion showed the highest corrosion resistance with |Z| 0.01 Hz = 1.34 x 1010 after 6 weeks immersion in corrosive media. Consequently, although a certain additive such as MnSO4 may modify conversion coating characteristics, it can not necessarily improve corrosion performance in an organic coated system