Effect Of Li Containing Precipitates On Plastic Deformation Behavior And Microstructure Evolution Of AA2099 Al-Li Alloy

At present,the third generation Al-Li alloy has been widely used in the fuselage skin,pillars and floor beams of domestic C919 medium-sized passenger aircraft.The results show that the excellent comprehensive mechanical properties of the third generation Al-Li alloys are due to the precipitation of Li containing precipitates(including Al Li(?)phase,Al₃Li(??)phase,Al₂Cu Li(T₁)phase and Al₆Cu Li₃(T₂)phase)during heat treatment/hot working.In view of this,the typical third generation Al-Li alloy AA2099 was taken as the research object in this paper,and the precipitation of different lithium containing precipitates was realized by adjusting the heat treatment process,subsequently,X-ray diffraction(XRD),electron backscatter diffraction(EBSD),transmission electron microscopy(TEM)and crystal plastic finite element simulation(CPFEM)were used to study the influence of different Li containing phases on the plastic deformation behavior and microstructure evolution of AA2099 Al-Li alloy under uniaxial compression at 250?and room temperature,the main conclusions are as follows:1)Under the condition of uniaxial compression at medium temperature,the flow stress curve of the AA2099 sample in solid solution state appears obvious strain hardening behavior,and in the later stage of strain,the orientation of the crystal deflects slowly to<110>direction;The yield behavior of the AA2099 sample containing??phase after deformation is similar to that of solid solution AA2099 Al-Li alloy,and at the later stage of strain,the crystal orientation also deflects slowly to<110>orientation;The true stress-strain curve of the AA2099 sample containing T₁phase after deformation decreases gradually after reaching the peak stress,and the speed of crystal orientation deflection to<110>crystal direction increases gradually at the later stage of strain;AA2099 alloy with T₂phase has the minimum mechanical response and texture characteristics.2)Under uniaxial compression at room temperature,the flow stress curve of the AA2099 sample in solid solution state shows obvious work hardening phenomenon,the texture types are mainly S{123}<634>(59°,37°,63°)and copper{112}<111>(90°,35°,45°);The flow stress curve of the AA2099 sample containing??phase is similar to that of the solid solution state,the texture types are mainly brass{011}<211>(35°,45°,0°)and S{123}<634>(59°,37°,63°);the peak stress of the AA2099 sample containing T₁phase is the highest,but the texture strength is the weakest.There is only a small amount of Goss{011}<100>(0°,45°,0°)orientation;For AA2099 with T₂phase,its mechanical response is the weakest,and the main texture types are S{123}<634>(59°,37°,63°)and cube{001}<100>(0°,0°,0°).3)Based on the uniaxial compression experimental data at room temperature and the finite element theory of crystal plasticity,the crystal plasticity constitutive models of AA2099 Al-Li alloy with different lithium containing precipitates is established;Based on the results of microstructure characterization,a three-dimensional Realistic polycrystalline finite element model reflecting the grain morphology of AA2099 Al-Li alloy is established;Based on the"trial and error"method,the crystal plastic material parameters of AA2099Al-Li alloy with different Li containing precipitates are determined.The predicted mechanical behavior and texture evolution of AA2099 Al-Li alloy under uniaxial compression at room temperature are in good agreement with the experimental results.