Influence of indentation size on the corrosion behaviour of a phosphate conversion coated AZ80 magnesium alloy

The service performance of magnesium alloy wheel hub was simulated by studying the effect of surface defect size on the corrosion resistance of a calcium phosphate conversion coated AZ80 magnesium alloy. The surface defects were produced with different sizes using a Film Impactor. The corrosion behaviour was studied using electrochemical, hydrogen evolution and immersion tests. The microstructures were characterized using a scanning electron microscope and a laser confocal microscope. Phases and the corrosion products were analyzed using XRD and XPS. The size of the surface defects influenced the corrosion resistance of the coating and the corrosion initiation area. The coating provided no protection for an indentation larger than 2.7 mm. The corrosion mechanism of the coating was also clarified.