Investigation of cathodic disbondment of phosphate, titanium and zirconium based conversion coatings applied on steel

In this study, the cathodic disbondment of conversion coatings based on phosphate, titanium and zirconium compounds was investigated on mild steel. Four samples were prepared: Bare and phosphated steel, steel with titanium based conversion coating and steel with zirconium based conversion coating. Phosphated steel showed the highest resistance to disbondment whereas the zirconium and phosphate conversion coatings illustrate the lower amounts. Due to the fact that the rate of expansion of the disbondment area increases over time, it can be inferred that the cation diffusion is dominant. Regarding the cathodic disbondment mechanism, different alkaline condition is responsible to have different disbonding areas.