Corrosion Behavior Of Zn-Cu-Ti Alloy Coating In Simulated Service Environment

International Marine resources are in a state of intense competition,corrosion protection of Marine engineering facilities has been included in the national strategy,to raise the level of attention to Marine corrosion protection,and promote the Marine corrosion prevention industry at the national level,the development of low-cost,high-performance new alloy anticorrosive coating under the Marine atmosphere corrosion environment has important engineering practical and scientific significance.Zn-Cu-Ti and other metal materials have been used in the field of metal corrosion protection,and have great potential advantages in corrosion resistance compared with Zn-Al-based alloy materials.However,there are few reports on Zn-Cu-Ti alloy coatings.Therefore,it is necessary to study the related corrosion problems of Zn-Cu-Ti anticorrosive coatings under simulated Marine atmosphere environment.In this thsis,Zn-Cu-Ti coating was prepared on Q235 substrate by arc spraying process.Corrosion electrochemistry and corrosion path of Zn-Cu-Ti coating corroded at different times in 3.5%wt.%Na Cl neutral salt spray were studied.The general rule of open-circuit voltage,Tafel polarization curve and AC impedance changing with corrosion was analyzed,and the mechanism of corrosion protection mechanism evolution and corrosion type evolution process of Zn-Cu-Ti coating were investigated.At the same time,the corrosion process and corrosion mechanism of Zn-Cu-Ti coating in the solution of 3.5 wt.%Na Cl with p H 3 were studied,so as to promote the practical application of Zn-Cu-Ti coating in different Marine and atmospheric environments.Specific research contents are as follows:（1）The electrochemical behavior of arc spraying Zn-Cu-Ti coating in 3.5 wt.%Na Cl neutral salt spray at different time was studied by electrochemical method.According to the open circuit potential（OCP）,the corrosion process of coating can be divided into five stages:surface oxide dissolution stage,corrosion product deposition stage,coating stable dissolution stage,occluded corrosion cell formation and development stage and accelerated corrosion stage.By polarization curve fitting found that corrosion potential E_corr,on the whole,with the increase of corrosion time gradually,and the corrosion current density I_corrdecreases.During the whole corrosion process,the EIS was analyzed by four different equivalent circuits,and it was found that the total resistance Rt was up to 3641Ωcm²at 30d corrosion,and the comprehensive corrosion resistance was the best.The total resistance R_tis positively correlated with the corrosion rate,and the trend of OCP is highly similar.R_tdecreases first,then increases,and then decreases with the corrosion time.（2）The corrosion path of arc spraying Zn-Cu-Ti coating in 3.5 wt.%Na Cl neutral salt spray was studied.Cl^-and O elements permeate along the interlayer gap and are preferentially etched near the interlayer gap to form pitting corrosion.With the deepening of corrosion,due to the enrichment of Cl^-and the difficulty of oxygen diffusion,occluded cell corrosion occurs,and Cl^-and H⁺penetrate into the matrix,leading to the formation of galvanic corrosion.Cu₂O formed at the early stage of corrosion reacts with Cl^-to form Cu Cl.With the enrichment of Cl^-,Cu₂Cl（OH）₃gradually formed.In the process of coating corrosion,the sacrificial anode plays a leading role in protecting the cathode in the early stage,and the protection of the corrosion product layer plays a leading role gradually,and the protection of the corrosion product layer plays an absolute leading role in the later stage.（3）The corrosion time of arc sprayed Zn-Cu-Ti coating in 3.5wt.%Na Cl solution with p H 3 is studied.It is found that two typical corrosion processes of Zn-Cu-Ti coating are pitting corrosion,and the other is pitting corrosion to occluded cell corrosion and then to atypical heterogeneous corrosion.But the corrosion rate of pitting corrosion is much higher than that of pitting corrosion to block cell corrosion and then to atypical non-uniform corrosion corrosion,so the main corrosion failure form of Zn-Cu-Ti coating is pitting corrosion.The corrosion electrochemical parameters were fitted.It was found that with the increase of corrosion time,the corrosion potential and total resistance R_tshowed a downward trend,and the maximum value of total resistance R_twas 701.20Ωcm².The difference between the corrosion mechanism of Zn-Cu-Ti coating in simulated neutral Marine atmosphere environment and Marine acid rain environment is that the former sacrificial anode protects the cathode and the corrosion product layer,while the latter pitting sacrificial anode protects the cathode absolutely.This thesis contains 37 figures,8 tables and 150 references.