Ultralow-temperature fabrication of chromium-free zinc-aluminum coatings based on polysilazane

To avoid the health risks of Cr 6+ in traditional Dacromet coatings, developing chromium-free zinc-aluminum coatings attracts increasing attention in recent years. However, the state-of-the-art chromium-free zinc-aluminum coatings always have very high sintering temperatures over 250 °C, causing serious energy consumption. In the present work, for the first time, we report the fabrication of a novel chrome-free zinc-aluminum coating based on polysilazane. The results show that the polysilazane forms crosslinking structure via Si–O–Si backbones and the equilibrium anticorrosion effect can be achieved with a very low curing temperature less than 130 °C, which is much lower than current zinc-aluminum coatings. The zinc/aluminum particles present unique layered structure that are tightly contacted with the substrate, forming a dense structure with good barrier protection. Electrochemical characterization reveals that the coating exhibits capacitive impedance behavior at the initial stage of immersion test, indicating excellent shielding effect. As the immersion time increases, the activation corrosion of metal powder occurred under the action of corrosion medium, which plays a sacrificial anode protection role, and the resulting corrosion products can play certain shielding effect. Owing to above structural merits and electrochemical features, the developed chrome-free zinc-aluminum coating based on polysilazane demonstrates a superior corrosion resistance .