A novel phosphate conversion film on Mg–8.8Li alloy

The super light Mg–Li alloys exhibit excellent formability due to the addition of lithium, but the corrosion resistance is deteriorated. A novel conversion film is developed to improve the corrosion resistance. The surface morphology of conversion film was observed using scanning electron microscopy (SEM). The chemical composition was analyzed by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The corrosion behaviors of Mg–8.8Li alloy and conversion film were investigated with electrochemical and immersion tests. The experimental results indicated that the Mg–8.8Li alloys with and without the protection of conversion film can both be used in NaOH solution safely. But the Mg–8.8Li substrate was susceptible to corrode in NaCl and Na2SO4 solutions, and the conversion film can prevent them from corroding. Compared with the NaCl solution, the Na2SO4 solution was a strong corrosive medium to the conversion film.