Investigating the Corrosion Resistance of Multi-cation Zinc Phosphate Conversion Coatingusing Transition Metals and Alkaline Earth Metals

Two kinds of phosphate conversion coatings, including zinc phosphate coating and zinc–calciumphosphate coating, were prepared on the surface of AZ۳۱ alloy in phosphate baths. The morphologies of thesecoatings were observed using scanning electron microscopy. The corrosion resistance of the coatings wasevaluated by potentiodynamic polarization technique. The results show that the flowerlike Zn–Ca phosphateconversion coatings are mainly composed of hopeite (Zn₃(PO₄)₂·۴H₂O). They have a quite different morphologyfrom the dry-riverbed-like Zn phosphate coatings that consist of MgO, MgF₂, Zn or ZnO and hopeite. Both of thezinc and zinc–calcium phosphate coatings can remarkably reduce the corrosion current density of the substrates.The Zn–Ca coating exhibits better corrosion resistance than the Zn coating.

کلیدواژه ها:

Corrosion ، conversion coverage ، Color primer