Abstract
Mechanical properties and visual appearance of galvannealed steel sheets are strongly influenced by steel substrate surfaces before dipping into molten Zn. It has been known that oil contamination, iron fragments and surface enrichment of oxides deteriorate the Fe–Zn reaction and result in various harmful surface defects on the galvannealed coating. In order to prepare the optimal galvannealed coating for automotive exposed panels, the steel substrate surfaces were mechanically polished by SiO2 polishing brushes.
The types of brush and pressure between the brush roll and strip are major factors for removing the appearance of visual defects on the surfaces of galvannealed coatings. The microstructure of the polished substrate, galvannealed coating and whiteness index on the surface of steel substrate were characterised by optical microscopy, scanning electron microscopy and colour difference meter.