Improved Corrosion Resistance of Galvanized Steel with a Zinc Phosphate Coating in Alkaline Solution

The corrosion activity of a zinc phosphate coating (ZP layer) on galvanized steel (GS) in alkaline solution in the presence of Ca2+ was investigated using open-circuit potential (OCP), potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) techniques. The results showed that, compared to that for the bare GS, the phosphate-coated GS presented a robust resistance to corrosion in a saturated Ca(OH)(2) solution with/without 0.5 M chloride. The GS pretreated with the phosphate coating was conducive to suppressing the rapid dissolution of the zinc layer and hydrogen evolution in the alkaline solution. The presence of Ca2+ in alkaline solution was beneficial to inhibit the dissolution of the ZP layer by precipitating calcium hydroxyzincate (Ca(Zn(OH)(3)))(2)center dot 2H(2)O) and hydroxyapatite (Ca-10(PO4)(6)(OH)(2)) at the corroding interface to form an effective barrier film.