Study On Influence Of Different Simulated Sea Water Medium On Corrosion Behavior Of 5083 Aluminum Alloy

Aluminum alloys are commonly used in marine applications where low density materials,good mechanical properties and better resistance to corrosion are desired.More and more countries use aluminum alloy as a hull structure materials of ships.However,it exists some corrosion problems restricting the development of its use in the shipping industry.AA5083-H116 is one of the aluminum alloy frequently used in vessel,when served in different seawaters environment,AA5083 has different corrosion rates,in certain sea area the AA5083 may has abnormal corrosion situation,known as the electrolyte effect.In order to solve this problem,AA5083 in different simulated sea water is studied.The corrosion effects of AA5083 in typical anions in seawater environment has been studied.In this study,the corrosion resistance of 5083 aluminum alloy in different simulated seawater environment was tested by factorial analysis method and the polarization plots,the corrosion potential,corrosion current density and the breakdown potential were examined in different concentration of C l-,HCO3-and SO42-.The corrosion behavior was analyzed by electrochemical impedance spectroscope(EIS).The results show that C l-and HCO3-can accelerate the pitting.The corrosion resistance increased with an increase in the concentration of HCO 3-and then dropped dramatically at the concentration in 90 mg·L-1,which is shows the lowest corrosion performance of AA5083,after that the corrosion resistance of AA5083 increased.SO42-can decrease corrosion current density.Meanwhile,the charge-transfer resistance of low chlorinity component is smaller than high chlorinity,and the corrosive ions can easily penetrate the native oxide film,reacting a redox reaction with the matrix.Scanning Electron Microscope(SEM)and X-ray Photoelectron Spectroscopy(XPS)was employed to study the surfa ce topography and surface composition of AA5083 in different concentration of C l-and HCO3-.The results show that ? phase with diameter in the sub-micron range,distributed along the grain boundary,fast dissolved in corrosive medium,and bring a small corrosion pore in surface.The pore size is far less than the actual visible to the naked eye of AA5083 plate formed by the corrosion pit;Mg2Si phase has no significant change in SEM observation;Iron-rich phase is widely distributed in AA5083,after soaking by electrolyte,the matrix around iron-rich phase will be corroded.More sever corrosion situation of matrix in low concentration of HCO3-than high.After long-term soaking the iron-rich phase will fall off from matrix and leave a etch pit which size is close to the actual corrosion of AA5083 plate.Uncorroded AA5083 surface is composed of Al2O3,while the surface will generate AlOOH when erosion in electrolyte.When exposed to low concentration of HCO3-the oxide film formed on the aluminum alloy will turn active,lead to high corrosion sensitivity.When exposed to high concentration of HCO3-the Al2O3 passive film will thickening,which lead to reduce corrosion rate.Scanning Kelvin Probe Force Microscopy(SKPFM)was employed to study the potential difference between matrix and intermetallic phase.The results show that when erosion by electrolyte the potential difference between matrix and intermetallic phase declined.The ? phase has a potential lower relatively to the matrix,the high reactivity of magnesium leads to the dissolution and consequently to the fast dealloying of these intermetallics.The magnesium in ? phase penetrate from oxide film to electrolyte,react with HCO3-and then generate MgCO3.When exposed to high concentration of HCO3-the potential of iron-rich phase have a little more than the matrix,when exposed to low concentration of HCO3-the potential of iron-rich phase is much more than the matrix,especially when the concentration of HCO3-in 90 mg·L-1,which is shows the highest po tential difference between iron-rich phase and the matrix;AA5083 has low corrosion rate in Q ingdao sea area because of high concentration of HCO3-in Q ingdao,and high corrosion rate in Xiamen sea area because of low concentration of HCO3-in Xiamen.