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 MgZn(2) 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 MgZn(2) 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. (C) 2010 Elsevier B.V. All rights reserved.