Damage cause analysis of coating failure of pot roll for hot-dip aluminizing

Abstract

Hot-dip aluminized steel is produced by immersing cold-rolled steel in a molten aluminum bath for a certain period. However, the pot rolls immersed in the aluminum bath suffer significant surface damage due to the reactions with the molten bath. This study identified the cause of surface damage of the stabilizer roll used for continuous hot-dip plating of aluminum at 660 °C. The damage was caused by molten Al infiltrating a defective structure with interconnected pores and splat boundaries. This molten Al dissolves the metal components of both the coating and substrate. As the lower part of the coating melts and liquefies, repetitive external frictional forces lead to the formation and growth of cracks in the upper coating. That eventually leads to the upper part of the coating partially or entirely detaching, resulting in surface defects in the form of pits. Possible ways to extend the lifetime of the port rolls to suppress such damage have been proposed.