Analysis on Pitting Defects on Surface of Hot-dip Galvanized Sheet

In the production process of hot-dip galvanized sheet, the pitting defects always appear on the surface of the coating. Confocal laser scanning microscope, scanning electron microscopy with energy dispersive spectroscopy were used to analyze and study the pitting defects on the surface of galvanized sheet. The results show that the pitting defects protrude on the surface of the galvanized sheet, and the average diameter is about 0.6 mm, which shows dark brown. The zinc dross in the zinc pool adheres to the surface of the strip steel due to flow of zinc liquid, shaking of zinc liquid surface and vibration of belt steel, or the zinc dross particles accumulate on the roll surface. When the strip steel passes through the sink roll, stabilizing roll and straightening roll, the zinc dross adheres to the surface of the strip steel, the surface of the strip produces protuberant parts. The strip steel is squeezed by the top roll, skin-pass roll, etc., and the protuberant parts are flattened to form pitting defects.