SEM study of intermetallic phases growth in a hot-dip galvanizing process

The influence of both the cooling rate and the base Steel roughness upon the Al-rich phase was análized For this, Steel sheets were coated in a simulator of the hot-dip galvanized process working at 470 ºC up to reaching an average roughness valué of 1.30 or 0.90 pan; besides, either an air or water spray flow was used in order to obtain cooling rotes between 7 and 22 ºC s-1, respectively. The galvanized píate surfaces were characterized by means of SEM and XRD analysis. From the experimental results the following conclusions could be drawn: a) the Al-rich phase growths as an intermetallic (AlsFez), that crystallizes forming an orthorombic lattice in which increasing cooling rotes do not change the morphology but stop the growing of the crystals, and b) an increase of the Steel roughness makes that outburst structures but not the Al-rich phase develops at the bottom of pits