Characteristics and corrosion studies of zinc-manganese phosphate coatings on magnesium-lithium alloy

A zinc-manganese based conversion coating on magnesium-lithium alloy has been prepared from a phosphate solution at different pH values. The surface morphology and composition of the coating were characterized by scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Corrosion resistance of the coating was studied by potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS) and corrosion weight loss measurement. The experimental results indicated that the coating had large crystals that were homogeneous and ordered. The coating consists of Zn, Zn-3(PO4)(2) and MnHPO4. The corrosion resistance of the magnesium-lithium alloy was improved by the phosphate conversion treatment.