The growth of zinc phosphate coatings on 6061-Al alloy

Zinc phosphate coating was formed on 6061-Al alloy through a phosphating bath containing mainly ZnO, H3PO4, NaF. Yttrium oxide (Y2O3) was used as an accelerator of phosphatization to replace nitrite. The morphology, composition and the growth process of the zinc phosphate coating were investigated by SEM, EDX, XRD, FTIR and electrochemical measurements. The phosphate coating formed is composed of hopeite and metallic zinc. The formation and morphology of the zinc phosphate coating were strongly influenced by the presence of yttrium oxide (Y2O3) in the phosphating bath. The formed zinc phosphate coatings exhibited high corrosion resistance in 3% NaCl solution as shown by polarization measurement.