Effect of manganese addition on the appearance, morphology, and corrosion resistance of hot-dip galvanized zinc coating

The study investigates the effect of manganese addition in the hot-dip galvanized zinc coating on steel. The Zn[sbnd]Mn hot-dip coatings were prepared under ambient conditions on a steel sheet using a custom-made galvanization simulator. The Zn[sbnd]Mn hot-dip coatings were always covered with oxides formed during the withdrawal, giving patchy coloration. A novel approach is demonstrated to prevent patchy coloration due to these oxides and produce alloy coated surfaces with homogeneous coloration. The microstructures of the alloy coated sheets were investigated to identify the effect of the Mn addition. The microstructure changes in the alloy coating due to increasing Mn addition were correlated to the composition, hardness of the individual intermetallic layers, and the basal texture. Compared to the hot-dip Zn coating, Mn addition decreased the corrosion rate (i_corr from potentiodynamic polarization test) in the alloy coating by 65%. The Mn addition also controlled the degree of the white rust formation and prolonged the life of the alloy coated steels in accelerated salt spray test (> 300 h of exposure, ASTM B117). The bend test results show that Mn addition does not affect the deformation tolerance of the hot-dip alloy coatings.