Effect of bath aluminum concentration on the galvanizing of hydrogen reduced hot rolled steel without acid pickling

An environmental friendly hot-rolled galvanizing process without acid pickling was provided via hydrogen reduction of hot mill scale. After reduction, the reduced specimens were directly galvanized in zinc melts with different dissolved Al contents ranging between 0.2 and 0.7 wt.%. It was found that the reduced scale exhibited superior coating wettability during galvanizing. However, the coating surface appearance varied significantly. The specimens galvanized in 0.2 wt.% and 0.4 wt.% Al melts are extremely rough caused by the formation of Fe-Zn alloys in the coating. Al depletion was observed in the zinc overlayer of these specimens. A full inhibition was obtained for specimen galvanized in the 0.7 wt.% Al bath. The coating structure was examined by scanning electron microscope (SEM) and the element distribution in the coating was studied by glow discharge optical emission spectrometry (GDOES). The possible mechanisms involved in the formation of Fe-Zn alloys were also discussed.