Non-chrome-containing conversion coatings for zinc and zinc alloys

The primary function of all conversion coating systems is to provide for a surface that accepts applied coatings and resists corrosion as insurance against any breaks in the applied coating. By far, the greatest success in this regard has been achieved by the chromium-based conversion coating systems, which have been in wide use for more than 70 years. Any attempts to duplicate this success must, by necessity, be based upon a process that has its chemistry aligned as closely as possible with that of the chromium-based systems. Of the approaches taken, only that of the permanganate-based system approaches that of the chromium based-system in all respects, and it is the only heavy-metal system that has no environmental problems associated with its use.