Study On Low Pressure Cold Sprayed Zn-Al-Al₂O₃ Composite Coating And Its Corrosion Resistance

With the continuous deepening of China’s maritime power strategy,the Chinese navy has an increasing demand for marine engineering equipment.In this context,the corrosion resistance of steel structures in the marine environment has received extensive attention.Zn-Al coating has the function of cathode isolation and anode sacrifice,which is one of the most effective means of steel protection.Cold spraying technology has received extensive attention due to its high spraying efficiency,small thermal impact on the substrate,and high coating density.This paper,focuses on Zn-Al-Al₂O₃and Zn-Al-Al₂O₃-La₂O₃cold spray coatings,using SEM/EDS technology,salt spray test,electrochemical test and other methods,the effects of Al,La₂O₃,annealing temperature and annealing time on the microstructure and corrosion resistance of the coating were studied.The relevant results have important theoretical significance for the industrial application of cold sprayed Zn-Al composite coatings in the field of marine equipment.The research shows that:（1）The Zn-Al-Al₂O₃composite coating combines well with the substrate,its density is better than that of the Zn-Al₂O₃coating,and the Zn₆₀Al₃₀（Al₂O₃）₁₀coating has the best density;With the increase of Al content,the corrosion resistance of Zn-Al-Al₂O₃experienced a process of first increasing and then decreasing,and the corrosion resistance of Zn₆₀Al₃₀（Al₂O₃）₁₀coating reached the highest value;（2）In the early stage of corrosion,the anodic dissolution of Zn is the main reason for the Zn₉₀（Al₂O₃）₁₀and Zn₈₀Al₁₀（Al₂O₃）₁₀composite coatings;When the content of Al in the Zn-Al-Al₂O₃composite coating is greater than or equal to 20%,the corrosion of the composite coating includes two basic processes:the anodic dissolution of Zn and the barrier effect of the Al passivation film on the coating surface.The surface of Zn₆₀Al₃₀（Al₂O₃）₁₀coating is more likely to form dense corrosion product Zn₅（OH）₈Cl₂·H₂O,which prevents the corrosion medium from further eroding the substrate;（3）After annealing at x℃（x=150,200,250）for 2h,the Zn₆₀Al₃₀（Al₂O₃）₁₀composite coating consists of（Zn）,α-Al and Al₂O₃;When the annealing temperature increased to 300～350℃,the microstructure and composition of the Zn₆₀Al₃₀（Al₂O₃）₁₀composite coating changed to（Zn）,α-Al,α＇-Al and Al₂O₃;（4）Increasing the annealing temperature can improve the density and corrosion resistance of the Zn₆₀Al₃₀（Al₂O₃）₁₀composite coating,especially the annealing process at 350℃for 2h is the best;The prolongation of annealing time can effectively improve the density of the coating,but has little effect on the corrosion resistance;（5）The addition of La₂O₃powder can effectively improve the density of Zn-Al-Al₂O₃-La₂O₃composite coatings;With the increasing of La₂O₃,it will lead to the decrease of powder yield in the process of spraying and the coating thickness will decrease.