1994 Volume 80 Issue 8 Pages 647-652
We investigated on shear adhesion strength of galvannealed steel (GA), focusing on interface structure. Galvanizing was performed at the several dipping conditions which was varied in the range between 0.05 and 0.18 mass % aluminium in molten zinc bath. The interface structure was evaluated employing scanning electron microscopy (SEM) and electron channeling pattern (ECP). High aluminium added to molten zinc raised the minimum interface adhesion strength of the coating around 9 mass % iron. Moreover, ruggedness with pitch of α-Fe grain size was remarkably formed at coating/substrate interface, only when the substrate sheets were galvanized in high aluminium-containing zinc-bath. The ruggedness formation seems to be caused by the difference of Γphase growth rate between on (111)-(113)-(313) α and on the plane of [010] α zone. Γphase grew slower on (111)-(113)-(313) α compared to on the plane of [010] α zone. The dependence of Γphase growth behavior on iron orientation was promoted by aluminium addition to molten zinc bath. From above mentioned results, the model that GA coating/substrate interface adhesion strength was varied with geometrical shape of the interface, which was reported previously, can be expanded to explain not only effect of iron in coating but one of aluminium in molten zinc.
