Effect Of Sc On Electrochemical Corrosion Behavior At Normal Temperature Of Al-Cu-Li Alloy

A new generation of Sc-containing Al-Cu-Li alloy has excellent properties such as high strength,high toughness,high weldability and low anisotropy.Howerever,its local corrosion sensitivity is high,which limits its wide application in the field of national defense science and technology,such as aviation,aerospace,ship and so on.It is of great significance for study of its corrosion behavior.Al-3Cu-1Li-xSc?x=0,0.1,0.3 and 0.5?alloys were prepared by smelting.The effect of Sc on the corrosion behavior of the alloys was evaluated by open circuit potential and potentiodynamic polarization curves in sulfuric acid,NaCl with pH=2 and neutral NaCl aqueous solutions;the corrosion mechanism of the alloys was anasyled by the electrochemical impedance?EIS?and electrochemical noise?EN?techniques,combined with Mott-Schottky curve and X-ray photoelectron spectroscopy?XPS?.The results are as follows:Sc addition can eliminate the dendritic of microstructure,refine grains,increase hardness,and promote the precipitation of W?AlCuSc?phase and T₂?Al₇Cu₄Li?phase in the Al-3Cu-1Li alloy.In the sulfuric acid aqueous solution of with pH=2:the thermodynamic stability of Al-3Cu-1Li alloy increases with the increase of Sc content.Under the self-corrosion potential,the EIS of the four alloys consists of high-medium frequency capacitive arc,low-frequency inductionrc and capacitive arc.Sc does not change the corrosion mechanism of the alloys.However,it leads to an increasing in the defect concentration and a decreasing in Al oxidation degree of the alloy surface corrosion product film.The corrosion resistance of the alloy is lowered.In the 2 mol/L NaCl solution with pH=2:Sc reduces the molar activation energy of the corrosion reaction of the alloy,which makes the corrosion reaction more likely to occur.The alloy corrosion process changes from a"film failure-repassivation"process in which metal surfaces alternately occuring to severe localized corrosion.In the acidic and neutral 0.6 mol/L NaCl aqueous solution:the cathode processes of the four alloys are hydrogen evolution and oxygen absorption,respectively;the anode process is passivation and metal active dissolution,respectively.The corrosion mechanism has been changed.Compared with the acidic aqueous solution,the concentration of the point defects in the corrosion product film of the four alloys in the neutral aqueous solution is reduced by three orders of magnitude,and the corrosion resistance of the alloys is high.Cl ions are not a direct cause of pitting;the semiconductor characteristics of the alloy corrosion product film are altered by occupying the lattice interstitial sites of Al₂O₃in the corrosion product film.