Corrosion Properties of Steel Sheet with Zinc-Base Alloy Coatings

Steel sheets with three kinds of zinc alloy coatings, that is, pure zinc coating, Galfan coating and Zn-Al-Mg coating, were hot-dipping galvanized by a hot-dip process simulator (HDPS). Alloying elements content as mass percent in the three coatings is Zn-0.2%Al, Zn-5%Al and Zn-2%Al-2%Mg, respectively. Corrosion behavior of the steel sheets with zinc-base alloy coating was studied by total immersion test. Corrosion resistance of the zinc-base alloy coatings dipped with different times was analyzed by means of electrochemical measurement and scanning electron microscope (SEM) analysis. The results show that the Zn-Al-Mg coating has the largest corrosion current density at the early stage of immersion. Along with increasing immersing time, corrosion current density of the Zn-Al-Mg decreases but that of the pure zinc coating and the Galfan coating increases. For the Galfan coating, diffusion characteristics could be found for the Nyquist curve, which means higher corrosion rate. However, for the Zn-Al-Mg coating, limited diffusion characteristics could be found for the Nyquist curve, which means corrosion product covered the surface enhances the corrosion resistance.