zinc phosphate conversion coatings for producing metals which exhibit enhanced corrosion prevention characteristics are prepared by the addition of a transition - metal - compound promoter comprising a manganese , iron , cobalt , nickel , or copper compound and an electrolyte such as polyacrylic acid , polymethacrylic acid , polyitaconic acid and poly - l - glutamic acid to a phosphating solution . these coatings are further improved by the incorporation of fe ions . thermal treatment of zinc phosphate coatings to generate α - phase anhydrous zinc phosphate improves the corrosion prevention qualities of the resulting coated metal .