Effect of added magneisum on the coating properties of galvanized steel sheets

Abstract

The effect of a small amount of added Mg on the microstructure, Fe-Al inhibition layer, corrosion resistance and welding properties of hot-dip galvanized and galvannealed steel sheets were investigated. Both the microstructure and distribution of Mg were measured by scanning electron microscopy, transmission electron microscopy, glow discharge spectrometer and electron probe micro analyzer. A thin Mg layer was inhomogeneously precipitated between the Zn-coating and Al inhibition layer. During the annealing process around 470-510 °C, the Mg layer was completely diffused into the inside and/or extreme surface of the Zn coating. The corrosion resistance of galvannealed steel sheets produced in a commercial galvanizing line was significantly improved by adding a small amount of Mg into the molten zinc pot. Fe content, the formation of the Fe-Al inhibition layer and weldability were also influenced by the Mg addition.