Anti-corrosion Performance of Zinc-Aluminum Composite Coating on Fasteners

An anti-corrosion system of sherardizing and zinc-aluminum film composite coatings was designed and investigated in order to meet the needs of the corrosion protection of the metallurgical equipment in Zhanjiang.The Zn-Al film was prepared using a process of dip coating,drying and roasting.The corrosion performance of the Zn-Al film was tested by electrochemical methods.The results showed that a Zn-Al film with relatively good performance could be obtained when the Zn-Al film was prepared by dip coating in the coating solution composed of 285 g/L flake zinc,65 g/L flake aluminum,30 g/L sodium molybdate and so on,followed by drying at 70～80 ℃ and roasting at 300 ℃.Relative to the base metal 40Cr steel,both the Zn-Al film and zinc impregnation layer were anodic,the self-corrosion potential and self-current density of Zn-Al film and zinc impregnation layer were lower than those of 40Cr steel.The Zn-Al film showed a passivation region in the electrode potential range from -0.8 V～-0.3 V (Ag/AgCl) in 3.5% NaCl.