Microstructure and corrosion behaviors of conductive Hf/HfN multilayer coatings on magnesium alloys

Both high corrosion resistance and electrical conductivity are required for the surface coatings of the magnesium alloys as used in electronics or aerospace applications. In this study, anticorrosive yet conductive Hf/HfN multilayer coatings are deposited on magnesium alloys via magnetron sputtering. The microstructural characterizations reveal that the growth of nano-scale pinholes along with the columnar structure of Hf sublayers have been completely suppressed by introducing the nanocrystalline HfN sublayers. The optimized Hf/HfN multilayer coated magnesium alloy exhibits a positive corrosion potential of -0.51 V vs SCE and low corrosion current density of 0.01 mu A/cm(2) in electrochemical system, and few corrosion pits after 48 h salt spray test, while maintaining the fine electronic conductivity similar to magnesium alloy. The desirable performance was attributed to the multilayer structure induced by nanocrystalline HfN interlayer, which resulted in decreased coating porosity, confined pathway and increased energy barrier for corrosion media.