A chrome-free conversion coating for magnesium-lithium alloy by a phosphate-permanganate solution

A chrome-free conversion coating on magnesium-lithium alloy was obtained from a phosphate-permanganate solution. The morphology, the composition and the corrosion resistance of this coating were examined. The thin and non-penetrating cracked morphology with some deposits existed on the phosphate-permanganate conversion coating. The main elements of the conversion coating were Mg, O, K, P and Mn. The results of the electrochemical measurements and the immersion tests demonstrated that the corrosion resistance of the magnesium-lithium alloy has been improved by the phosphate-permanganate conversion treatment.