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 on electrodeposited zinc-nickel alloy coatings. Investigations have concentrated on producing passive surfaces from simple molybdate solutions using immersion or cathodic coating processes. Passivated surfaces have been examined using scanning electron microscopy to elucidate the coating morphology. The corrosion resistance of the treated surfaces has been assessed using simple, rapid electrochemical techniques as well as more long term salt fog immersion. Initial findings indicate molybdate-based treatment solutions improve times to white and red rust of the zinc-nickel surfaces, but as yet are surpassed by a more conventional chromate-based treatment.