Plasma-Sprayed YSZ/NiCrAlY Protective Coating and Its Resistance Property to Molten Al-Si Corrosion

Hot dip Al-Si alloy coating is an efficient corrosion resistant technique. However, there are serious Al-Si corrosion problems in some parts of the production line, such as sunk rolls, which are in direct contact with the Al-Si alloy melt. In this research, YSZ/NiCrAIY protective coating system was prepared by air plasma spraying (APS). The influence of main gas flow rate on the microstructure, mechanical properties, high-temperature stability and Al-Si alloy corrosion resistance of YSZ (Y-Si-Zr) coating were also investigated. The results show that the spreading uniformity, coating density and mechanical properties of the droplet firstly increase and then decrease with the increase of main gas flow rate. The coating exhibits the best surface smoothness, maximum density and optimal mechanical properties when the main gas flow rate is 40 L/min. The interface structure of YSZ coating is stable. The porosity decreases, and the density significantly increases after heat treatment at 1000 degrees C for 100 h. In addition, no diffusion or reaction zone is found at the interface between YSZ coating and Al-Si alloy melt when the coated sample is immersed in the Al-Si alloy melt for 50 h. Al-Si melt does not penetrate into the coating, but is blocked on the YSZ coating surface, indicating that APSed YSZ/NiCrAlY coating can effectively resist Al-Si melt corrosion, which can be used as one of the most potential protective coatings for parts contacting with high temperature Al-Si melt.