NON-CHROMATE CONVERSION COATING TREATMENTS FOR ELECTRODEPOSITED ZINC-NICKEL ALLOYS

Molybdate-based conversion coating solutions have been examined as to their suitability as possible replacements for chromate formulations o n electrodeposited zinc-nickel alloy coatings. Investigations have con centrated on producing passive surfaces from simple molybdate solution s using immersion or cathodic coating processes. Passivated surfaces h ave been examined using scanning electron microscopy to elucidate the coating morphology. The corrosion resistance of the treated surfaces h as been assessed using simple, rapid electrochemical techniques as wel l as more long term salt fog immersion. Initial findings indicate moly bdate-based treatment solutions improve times to white and red rust of the zinc-nickel surfaces, but as yet are surpassed by a more conventi onal chromate-based treatment.