Effect Of Deformation And Aging Treatment On The Corrosion Behavior And Microstructure Of The Al-4.0Cu-0.9Li Alloy

The Al-Cu-Li alloy is a typical heat-treatable strengthened alloy with good performance of low density,high specific strength and high elastic modulus,which is widely used in the aerospace and military industry.However,Al-Cu-Li alloys are vulnerable to localized corrosion that often leads to material failure in the service environment.Thermo-mechancial treatment(TMT)process is one of the common methods to improve the comprehensive performance of Al-Cu-Li alloys.In this work,we conducted Vickers hardness test,standard intergranular corrosion experiment,electrochemical experiment,combined with scanning electron microscopy,electron backscatter diffraction,transmission electron microscopy and other characterization methods to systematically study the effect of the T8 process with different pre-deformation,double-stage aging process with pre-aging and TMT process with pre-aging and pre-deformation on the mechanical property,corrosion resistance and microstructure of the Al-4.0Cu-0.9Li alloy.The conclusions are as follow:(1)Compared with direct artificial aging process,the T8-treated alloy with pre-deformation have faster aging response speed and higher peak hardness,which is due to the formation of more T₁precipitates promoted by the pre-deformation process.As the increase in the grain anisotropy of the alloy after deformation,the corrosion resistance is different in the cross section and rolling plane.In the cross section,the corrosion resistance of the alloy first becomes worse and then becomes better with the increase of deformation.The corrosion resistance of the alloy with 5%deformation becomes worse due to the formation of more T₁precipitates which are corrosive.When the deformation is more than 5%,on the one hand,the grains are elongated along the rolling direction,resulting in the corrosion path becomes longer;on the other hand,more corrosion-resistant small-angle grain boundaries are formed,so the corrosion resistance of the alloy is improved.On the rolling plane,the corrosion resistance of the alloy with large deformation(over 50%)becomes worse because the elongated grains along the rolling direction provide continuous corrosion channels.(2)Compared with the single-stage aging treatment,double-stage aging process with natural ageing can increase the peak hardness value of the alloy due to the precipitation of more T₁phase in the Al matrix caused by the natural aging.The effect of natural aging on the corrosion resistance of the alloy is different at different artificial aging temperatures.When the artificial aging temperature is 160°C,natural aging can promote the precipitation of the T₁phase and strengthen the galvanic effect between the T₁phase and the composite phase to reduce the corrosion resistance of the alloy.When the artificial aging temperature is up to 180?and 200?,the precipitation of the composite phase is almost completely suppressed because of the natural aging and high-temperature artificial aging,leading to the failure of the galvanic effect between the T₁phase and the composite phase.Furthermore,high-temperature aging process can also promote the growth and discontinuous distribution of the grain boundary precipitated phases to significantly reduce the corrosion potential difference between the grain boundaries and the matrix,thereby improving the corrosion resistance of the alloy.(3)The TMT process includes artificial aging,deformation and natural aging at the same time.The alloy treated by TMT process has a better mechanical propertity because of the formation of more T₁phases.However,the precipitation of more T₁phases and the continuous distribution of grain boundary precipitates grain boundaries make the alloy prone to localized corrosion,leading to its corrosion resistance decreased.