Electrodeposition And Performance Study Of Sn-Zn Alloy Coatings

Tin-Zinc alloy coatings have been widely used as both functionalcoatings and protective coatings in industrial fields such as electronics,automobile, shipbuilding, aerospace, etc., because of its superior corrosionresistance, good wear resistance and impact molding formability, lowcontact resistance and excellent solderability. In this paper, Sn-Zn alloywith Zn content of3~30wt%were electrodeposited onto Cu and steel. Theeffect of bath composition, pH, temperature, cathodic current density,stirring rate on morphology and composition of Sn-Zn deposits wereinvestigated. The corrosion behavior and anti-corrosion performance ofvarious Sn-Zn deposits were also studied.It was determined that lower cathodic current density, faster stirringrate, higher temperature, would contribute to increase Sn content in Sn-Znalloy deposits. So Sn-Zn alloy electrodeposition follows principles ofnormal co-deposition type. In Cyclic voltamery study, the presence ofcitrate acid in bath narrowed the gap of deposition potential for Sn and Znwith0.282V. PEG600affected the kinetics of deposition by inhibitingdiffusion of Sn(II) and Zn(II). The result of transient current studiesshowed that electrocrystallization of Sn-Zn on Cu substrates was acombination of instantaneous nucleation and diffusion controlled growth.A variety of electrochemical techniques were introduced tocharacterize the corrosion behavior of Sn-Zn deposits. OCP-t curvesshowed that more negative OCP attributed to higher Zn content in deposits.The major reaction of corrosion was Zn dissolution. EIS analysis showedthat, for deposits with Zn content of3~13wt%, corrosion reaction was controlled by charge transfer process. While for deposits with Zn contentof18~27wt%, corrosion reaction was controlled by mass transfer process.Data of polarization curves showed that, in comparision with deposits withZn content of18~27wt%, those with Zn content3~13wt%has higherlinear polarization resistance Rpand lower corrosion current density icorr.After456h salt spray test, there were no visible red rust on deposits ofSn-3Zn and Sn-22Zn, indicating Sn-3Zn and Sn-22Zn had the bestanti-corrosion performance.