Morphology

thickness and phase constituent of phosphate chemical conversion coating on the die casting AZ91D magnesium alloy were investigated by SEM（scanning electron microscope）and XRD（X-ray diffraction）

and the corrosion resistance of the coating and the matrix alloy were examined in salt spray and damp testing.In addition

the formation mechanism of the coating was described.The results indicate that the phosphate chemical conversion coating exhibits micro-net like structure with some micro-crack and 7.6 μm in thickness as well as uniform distribution

showing excellent protection for the matrix alloy.The coating is composed of amorphous phase

and the chemical compositions in the coating mainly include P

O

Al

Ba

F

Mg elements.The salt spray and damp testing verify that the coating can distinctly improve the corrosion resistance of the AZ91D magnesium alloy matrix.