Study On Corrosion Behavior And Mechanism Of Casting Al-2.5Li-Mg System Alloy

Cast Al-Li alloys have good microstructure and mechanical properties due to their low density,high specific stiffness,low fatigue crack growth rate,good low temperature performance and easy processing,and meet the requirements of weight loss.It has been widely used.Since the service conditions of Al-Li alloys in aviation are long-term humid and salt fog environments,corrosion is prone to occur,and currently there is little research on the corrosion resistance of cast Al-Li alloys.Therefore,in this paper,the corrosion properties of cast Al-2.5Li-Mg alloys with different element contents are systematically studied,and on this basis,the corrosion mechanism of the alloy is discussed in depth.The structure and surface morphology of the Al-2.5Li-Mg alloy were characterized by XRD,SEM and other technical means.CHI660 E Electrochemical Workstation was used to test the electrochemical corrosion performance of Al-2.5Li-Mg alloys,and M470 scanning electrochemical microscope was used to test the micro-area corrosion behavior of the alloy to illustrate its corrosion mechanism.The results show that the corrosion resistance of Al-2.5Li-Mg alloy in 0.9% Na Cl solution is related to the added elements.When the other components are the same,an increase in the magnesium content within a certain range will reduce the corrosion resistance of the cast Al-2.5Li-Mg series alloy.The corrosion current density and electrode potential are respectively-6.214 Acm^-2 and-0.82 V when they contain 1.5wt.%Mg,they changed to-5.617 Acm^-2 and-0.961 V when it contains 5.0wt.%Mg.The corrosion resistance of the alloy decreases after adding copper to the Al-2.5Li-Mg series alloy,the alloy corrosion current density and electrode potential become-5.973 Acm^-2 and-0.664 V,respectively.After adding copper and nickel elements together,the corrosion resistance of the alloy is improved,the alloy corrosion current density and electrode potential become-6.211 Acm^-2 and-0.785 V respectively.The addition of copper and scandium reduces the corrosion resistance of the alloy,the corrosion current density and electrode potential of the alloy changes to-6.183 Acm^-2 and-0.673 V respectively.Based on the immersion corrosion test of the alloy,combined with the results of the scanning electrochemical microscope and the analysis of the corrosion morphology,the five-component alloys were soaked in 0.9% Na Cl solution for 1 hour,2 hours,4 hours,16 hours,96 hours and 192 hours,as the magnesium content increases,the magnesium content in the second phase of the Al-Li-x Mg alloy is higher and the degree of corrosion is more serious;however,the corrosion mechanism is pitting corrosion;the corrosion resistance of the Al-Li-x Mg alloy added with copper is reduced,but the corrosion resistance of the alloy is improved when copper and nickel are added at the same time,that are galvanic corrosion;the addition of copper and scandium reduces the corrosion resistance of Al-Li-x Mg alloy,and the corrosion mechanism is galvanic corrosion and pitting corrosion.