SVET investigation into use of simple molybdate passivation treatments on electrodeposited zinc coatings

Chromate replacement in passivation processes has formed the basis of much research, molybdates having already been studied as one entirely chromium free alternative. Molybdate conversion coatings from three different solutions have been examined using the scanning vibrating electrode technique (SVET) to determine whether molybdates are capable of 'self-repair', one of the beneficial features of chromates. Additionally, morphological studies and neutral salt spray corrosion tests have been used to characterise the samples. Chromate passivated samples have been used as the standard against which the molybdates have been assessed throughout the study. SVET line scans conducted over a period of ∼74 min suggest that molybdates are capable of some form of self-repair when damaged. However, the anodic potential perturbation during repassivation is larger than that observed with chromates.