The corrosion resistance of three types of iron phosphate coatings on cold-rolled steel was examined. The alkali metal phosphating baths studied were three of the types most commonly encountered in industrial finishing operations. Coating composition was varied by using different accelerators in the phosphating bath. The components of each of the phosphate coatings were deduced by stripping test panels in a solution of 6 M HCl inhibited by Sb2O3. The stripping solution was then analyzed for the concentrations of ferrous iron, ferric iron, and phosphate. In the second part of the study, painted steel test panels were exposed to 5% salt fog as in ASTM B-117. Corrosion resistance was found to be strongly related to coating composition. Corrosion performance suffered as the fraction of ferrous salts in the coating increased.

Subject
Zinc rich coatings, Coatings, Chlorate, Composition, Salts, Spray coating, Iron, Phosphates, Sodium, Salt spray corrosion testing, Corrosion resistance, Accelerators, Phosphating
Keywords:
iron phosphate, coating composition, corrosion resistance
NACE International
1992
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