Effect Of Thermomechanical Heat Treatment On Microstructure And Properties Of 2A97 Al-Li Alloy

The 2A97 Al-Li alloys is widely used in the aerospace due to low density,high strength and high modulus.During its long time service,2A97 Al-Li alloy must not only withstand huge load,but also face the corrosion of different environmental medias.This service state has high requirements for the strength and corrosion resistance of the alloy.A key step to obtain high strength and corrosion resistance is the thermomechanical treatment.Research on single-stage,double-stage aging system and pre-deformation process is of great significance to improve the strength,toughness and corrosion resistance and promote the applications of 2A97 Al-Li alloy.In this paper,the effects of single-stage aging,double-stage aging and pre-deformation on the microstructure,mechanical properties and corrosion behavior of 2A97 Al-Li alloy were studied by microstructure characterization,mechanical and corrosion analysis.The main conclusions are as follows:（1）The effects of experimental parameters of aging on the precipitation behaviors under the single-stage aging process of 2A97 Al-Li alloy were clarified.As the aging temperature increases,the volume fraction and the size of T₁ precipitate in the peak-aged alloy increase.when the aging temperature was 165°C,the T₁ phase consumed theθ’phase,and the precipitation ratio and size increase with the increase of aging time.The corrosion resistance of the alloy decreases with the increase of aging temperature and aging time.The alloy aged at 165°C/60 h has the best tensile properties,which has tensile strength of 549 MPa,yield strength of484 MPa,and 8.78%elongation.And the maximum depth of intergranular corrosion for the alloy is 169.84μm,and its exfoliation corrosion is EC grade.The corrosion current density of it is 5.06E-07 A·cm^-2.（2）The evolution laws of precipitation phases in 2A97 Al-Li alloy with double-stage aging which at low temperature first then high temperature and the one with high temperature first and then aging at low temperature were studied.Low temperature pre-aging is conducive to the precipitation of a large number of dispersed and uniformly distributed GP regions andδ’phases,which providing sites for the nucleation ofθ’and T₁phases.After（185°C/6 h+165°C/24 h）double-stage aging treatment,the alloy has the best comprehensive properties,with tensile strength of 552MPa,yield strength of 491 MPa and elongation of 8.2%.The corrosion resistance test of the alloy showed the maximum depth of intergranular corrosion is 146.8μm and the exfoliation corrosion is EB grade,and the self-corrosion current density is 1.03E-06 A·cm^-2.（3）The effects of pre-deformation on the microstructures and properties of 2A97 Al-Li alloy were revealed.With the increase of pre-deformation from 0%to 30%,the strength and intergranular corrosion resistance of the peak-aged alloy increased,while the elongation and exfoliation corrosion resistance decreased.When the amount of pre-deformation increases to 50%,the strength of the alloy decreases slightly.After aging,the dislocations in the grain boundaries increase the sensitivity of intergranular corrosion,which decrease the corrosion resistance.Alloy（30%-165°C/6 h）has the best comprehensive properties,with tensile strength of 642 MPa,yield strength of 616 MPa,elongation of 7.2%,maximum depth of intergranular corrosion of 124.6μm,and exfoliation corrosion of ED grade.And the self-corrosion current density of the alloy is 9.23E-07 A·cm^-2.