Morphology and properties of hot dip Zn–Mg and Zn–Mg–Al alloy coatings on steel sheet

Hot dip coating on low carbon steel sheet samples by binary Zn–Mg alloy with low and high Mg and a ternary Zn–Mg–Al alloy, and their characterization and property evaluation have been described in this article. A good quality coating with respect to surface quality, coating structure and anti-corrosion properties was achieved at a lower bath temperature than in conventional galvanizing. Scanning electron microscopy with energy dispersive spectroscopy and X-ray diffraction studies have revealed the presence of eutectic phase mixtures in these coatings. Formation of MgZn2 has been observed on the top surface and through the cross-section of coating made from higher Mg bath. The hardness of the top surface of Zn–Mg and Zn–Mg–Al coating layers was found to be higher than Zn coating layer due to the presence of MgZn2 and other intermetallics. Steel samples coated in Zn–Mg–Al bath show better corrosion resistance properties than the ones coated in pure zinc and Zn–Mg binary baths. The correlation of these improved properties with the coating morphology has been discussed.