The Study Of Pitting Corrosion In Aircraft Aluminum Alloy And Corrosion Inhibitor Under Electrolyte Layer In The Marine Atmosphere

Aluminum alloys are widely used in many fields,such as architecture,electronics,automotive and aerospace industries.Atmospheric corrosion of aluminum alloys is very common,especially marine atmospheric corrosion.Moisture,oxygen and corrosive media?SO₂,CO₂,NO₂?in atmosphere are the main reason for the electrochemical corrosion of aluminum alloys.Therefore,exploration on the corrosion mechanism and prevention method of aluminum alloys becomes more and more important.Experiments were carried out by using self-made adjustable and sealed atmospheric corrosion simulating cell in the controlled conditions including temperature and humidity.The local corrosion behaviors of AA6061 aluminum alloys under thin NaCl electrolyte layer were conducted by polarization curves,electrochemical impedance,and electrochemical noise.The effect of liquid film thickness on oxygen diffusion was explored by studying the Variation law of cathodic limit diffusion current density with thickness of NaCl film at different humidity.Test results show that the thinner the liquid film,the greater the cathode limited diffusion current density.But the cathode limited diffusion current density is basically unchanged when the film thickness exceeds 1000?m.This indicates that the thinner the liquid film is,the faster the diffusion rate of dissolved oxygen through the thin film is.It shows a greater oxygen reduction current under cathodic polarization.However,when the film thickness exceeds a certain range,Convection has a greater effect on oxygen transport than diffusion under thin electrolyte layer.The oxygen diffusion process is essentially the same as in the solution,so the current tends to be stable.Besides,in order to investigate the effect of Ce³⁺ions on the atmospheric corrosion of Al alloy,we added Ce³⁺ions to the thin NaCl electrolyte layer.And then electrochemical test were carried out to analyze the relationship between limited diffusion current density and thickness of thin electrolyte layer,as well as the morphological changes during the corrosion process.The initiation and propagation of pitting corrosion of Al alloy were completed in the presence or absence of Ce³⁺ions.It is found that the deposition of Ce³⁺can retard the initiation of metastable pitting on the AA6061 alloy.In the absence of Ce³⁺,more pits and corrosion products formed on the surface of aluminum alloy under the NaCl electrolyte layer.However,the result will be just the opposite when0.001mol/L Ce³⁺was added into the medium.This thesis also investigated the effect of NaCl deposition on local corrosion of aluminum alloys under high humidity environment with Ce³⁺.10×10 arrayed multi-electrodes was adopted for research and a small spray device was employed to control Ce³⁺content in the environment measured by the volume of the spray.Experimental results show that,without Ce³⁺,the accumulation of corrosion products in the central area forming a larger IR drop with the prolongation of deliquescence,which reduce the corrosion tendency of the region instead.There were less corrosion products in the surrounding area,but the corrosion there tended to be serious.This indicates that a significant polarity reversal occurred at the late stage of salt deliquescence when Ce³⁺is added to the thin electrolyte layer.