Corrosion Behavior Of High-strength Aluminum Alloy In Industrial Marine Atmospher

High-strength aluminum alloys are widely used in transportation,defense industry,aerospace and other industrial fields due to their advantages of high strength and low density.However,problems such as electrochemical corrosion and stress corrosion cracking（SCC）threaten the service safety of high-strength aluminum alloys and hinder their wider application in industrial fields.Traditional studies on the electrochemical and stress corrosion behavior of high-strength aluminum alloys mainly focus on the solution environment,while the more common service environment for aluminum alloys is the atmospheric environment.In addition,with the development of industry and the discharge of pollutants in coastal areas,a special industrial marine atmospheric environment has been formed.Corrosion behavior in the atmospheric environment occurs mainly in the thin electrolyte layer（TEL）adsorbed on the metal surface.At present,the research on the corrosion of aluminum alloy in the industrial marine environment is not enough,especially in the atmospheric environment.The influence of the industrial marine atmospheric environment on the corrosion mechanism of aluminum alloy is still not clear.In this work,the electrochemical and stress corrosion cracking behavior of 7050-T7451,7085-T765 and 2524-T3 aluminum alloys were studied in different environments,the changes in the morphology and composition of corrosion products were observed,and the depth distribution and geometric parameters of corrosion attack was quantitatively evaluated.The effects of different electrolyte states（solution and atmosphere）and chemical compositions of corrosion media（Cl^-and Cl^-+HSO₃^-）on the degradation behavior of high-strength aluminum alloys were compared.Qualitative/quantitative analysis of the key controlling factors of corrosion and fracture of high-strength aluminum alloys in the industrial marine atmospheric environment is carried out,which provides a basis for the environmental suitability assessment of high-strength aluminum alloys.The mechanism of sulfide aggravating the damage of high-strength aluminum alloys in the industrial marine atmospheric environment was deeply discussed.The distinction between SCC behavior and corrosion-induced mechanical property degradation（CIMPD）is briefly discussed.Finally,a method for inhibiting corrosion damage of high-strength aluminum alloys by removing corrosion products on the specimen surface is proposed,and the mechanism of reversible change of corrosion damage is also discussed.The research shows that the composition and states of the corrosion environment will affect the electrochemical and SCC controlling processes.The presence of HSO₃^-can significantly accelerate the corrosion rate and mechanical property degradation,and this effect increases with the increase of HSO₃^-concentration.The presence of sulfur species in the corrosive environment leads to the appearance of insoluble aluminum hydroxysulfate,which significantly inhibits the initiation of corrosion,accelerates the propagation of corrosion,and the resulting corrosion attack is also more conducive to stress concentration,resulting in more serious mechanical damage to the material.Compared with the solution environment,the atmospheric environment will further aggravate corrosion and SCC,change the morphology of corrosion products,and inhibit corrosion in the later stage of corrosion.The strong erosiveness of the industrial marine atmospheric environment poses a great threat to the metal materials serving in this environment.With the increase of HSO₃^-concentration,the p H value of the corrosive environment exhibits little change,while the SCC degradation is significantly promoted.This is attributed to the HSO₃^-induced buffer effect and film-induced stress effect,yielding the overshadowing effect against solution p H.With a quantitative calculation of control steps through stress-assisted degradation of 7050-T7451,SCC of the alloy is proved to be dominated by corrosion-induced hydrogen in the TEL without HSO₃^-,while the mechanical-electrochemical-hydrogen interactions controls the SCC in the presence of HSO₃^-,which indicate that the mechanical-electrochemical-hydrogen synergistic effect will be amplified in harsher corrosive environments,thereby aggravating the damage of aluminum alloys.Corrosion-induced hydrogen controls the CIMPD of 7050-T7451 alloy,but its contribution is higher in the solution than that in the TEL.The ductility of the 2524-T3 alloy can be completely restored by removing the corrosion products,eliminating the harmful brittle features,while the strength cannot be restored due to the reduction of the effective load-bearing parts.However,with the addition of sulfide,the mechanical response of the material did not change significantly after the removal of corrosion products.The research results reveal the relationship between the reversibility of mechanical damage and the morphology of corrosion product layer,corrosion attack characteristics,and the hydrogen content trapped in the matrix.