The components of the equipment for processing the Al melts into the molded parts can be markedly corroded by the molten Al. In this study

a 4 μm CrN coating or CrN/TiN multilayer coating for providing the physical and chemical barriers between the molten reactive Al and the steel substrate were deposited by Cathodic Arc Evaporation onto 10 mm-thick heat-resistant steel plates. The dipping tests were conducted in a 700℃ A356 melt for 1 to 21 h at intervals of 3 h. The damage of the coated steel was evaluated by the plane-view and cross-sectional metallography. Experimental results indicate that after certain incubation period

the coated steel was locally attacked

forming hemispherical pits on both CrN and CrN/TiN coated steels. The incubation time for the pit nucleation on the CrN coated steel was shorter than that for the CrN/TiN coated steel. Once the obvious pits formed

the pitted areas increased with dipping time

regardless of the type of coating. After 21 h of dipping

the coating that remained adhering to the steel substrate showed no reaction with the molten Al. The different incubation time of the distinct coatings can be explained by their different coating microstructures. That is

the CrN/TiN coating displayed a finer columnar structure than the CrN coating did. The structural refinement resulted from the multilayer coating process reduced the density of the coating defects. Consequently

the CrN/TiN coating retarded the pit nucleation more effectively than the CrN coating.