Titanium hexafluoride pretreatments are known to improve paint adhesionand function as a barrier between the coating and the hot dip galvanized(HDG) steel surface. Interactions at the zinc/pretreatment interface are ofutmost importance for the formation of pretreatment layers and the corrosionresistance of color coated hot dip galvanized steels. Removal rate of inert aluminumoxide from HDG steel samples by chemical dissolution was studied.XPS measurements showed that the surface Al2O3 layer thickness decreasedrapidly already at mild alkaline cleaning, while complete removal of Al requiredsevere etching. Low reactivity of an Al2O3-rich surface was confirmedby impaired formation of a titanium hexafluoride pretreatment layer. Grainboundaries and deformation twinnings were shown to be of importance forthe reactivity of the HDG surface and for the precipitation of the pretreatmentchemical. Helium ion microscopy images and electron probe microanalysis(EPMA) of a pretreated sample showed accumulation of the pretreatmentchemical at the grain boundaries. Al removal rate was fast at the deformationtwinnings at the grain plateaus. Slow Al removal was observed at dendritic valleysand grain boundaries. The results increase understanding of the reactivityof hot dip galvanized steel surface.
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