OH Min-suk POSCO Technical Research Laboratories

Spoluautoři Kim Sang-Heon, KIM Su-Young, KIM Tae-Chul , KIM Jong-Sang

In this work, we investigated the effect of Mg and Al composition on microstructural properties and corrosion resistance in hot-dip Zn-Mg-Al ternary alloy coated steel sheets. Alloy coated steels with various coating composion of 0~5 wt% Mg and 0.2~23 wt% Al were fabricated by hot-dip simulator for comparison. Cross-sectional analysis in microstructure indicated that Mg and Al containing Zn alloy coated layers consist of Zn single phase, Zn/Al, Zn/MgZn2 binary eutectic and Zn/Al/MgZn2 ternary eutectic phases. Large Zn-Al eutectoid surrounded by MgZn2 was also observed in the coating layers with high Al composition (>10 wt%). When increasing Mg (3 wt%) higher than Al (2~2.5 wt), a volume of Zn/MgZn2 binary eutectic lamellar structure in the coating layer was evidently increased. Zn-Mg-Al coated steels with 3 wt% of Mg and 2~5 wt% of Al showed the highest corrosion resistance in plat surface area, while those with 3 wt% of Mg and 2 wt% of Al showed the highest corrosion resistance in cut-edge area in salt spray test and cyclic corrosion test. Analysis on the corrosion product clearly indicated that Mg played a key role in increasing corrosion resistance. Mg in the Zn/MgZn2 eutectic mixture preferentially dissoluted and readily formed dense and ordered barrier layer hindering galvanic current, resulting in increase of corrsion resistance in Zn-Mg-Al coated steel sheets.