INVESTIGATION OF BRIGHT STREAK ON THE COATING SURFACE OF HOT-DIP GALVANNEALED IF STEEL

To improve the surface quality of hot-dip galvannealed IF steel in industrial continuous galvanizing line,the morphology and formation mechanism of a bright streak have been investigated by optical microscopy,scanning electron microscopy and energy dispersive spectrometer. The coating morphology,cross-section and the substrate morphology after removing the zinc coating are different between the streak site and the normal site. It is obvious that the streak is caused by the micro-cracks in the surface and subsurface of the substrate. And the micro-cracks are caused by Al2O3.