Some observations for effects of copper on zinc phosphate conversion coatings on aluminum surfaces

X-Ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and electrochemical measurements have been used to characterize zinc phosphate (ZPO) conversion coatings, formed on high-purity aluminum surfaces, after dipping in coating baths containing different concentrations of Cu2+ up to 50 ppm. Significant variations in the morphology, adhesion and corrosion protection afforded by the ZPO coatings are especially observed as the Cu2+ in the bath varies from 0 to 10 ppm. Comparisons are made with the effects of surface Cu segregation on ZPO coatings formed in a previous study made on Al-2024-T3 alloy.