Abstract: By means of scanning electronic microscopy (SEM)， Xray diffraction (XRD)， electrochemical test and cupping test， the effects of Mg (15 wt.%) on the microstructure， corrosion resistance and formability of Galvalume(Zn55Al16Si) coating were studied. The SEM and XRD results revealed that MgZn2 phases appeared in the zincrich interdendritic area of Zn55Al16Si15Mg coating. The morphology of the corrosion product showed that magnesium eliminated the cracks in the corrosion product of Galvalume coating and enhanced the compactness of the corrosion product. The results of the electrochemical test showed that the corrosion rate of Zn55Al16Si15Mg coating was 341% of that of Galvalume coating， which means that the addition of magnesium markedly improved the corrosion resistance of the Galvalume coating. As a strengthening phase， MgZn2 strengthened the zincrich interdendritic area of the coating and decreased the cracks in the outer bending surface of the formed cup. As a result， the formability of Galvalume coatings was improved significantly.

Key words: Galvalume coating, microstructure, corrosion resistance, formability