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.