Effect of superplastic deformation on microstructure and mechanical properties of 2A97 Al-Li alloy
2A97 Al-Li alloy was superplastic deformed to a series of true strains for 0.4,0.7,0.9 and 1.1 at 430℃with strain rate of 2×10-3 s-1.The room-temperature tensile test and fracture morphology analysis were carried out,and the effect of superplastic deformation on microstructure was studied by electron backscattering diffraction(EBSD)and scanning electron microscope(SEM).The results show that,with the increase of superplastic deformation,the small angle grain boundary changes to the large angle grain boundary through dynamic recrystallization,and the grain morphology evolves from strip to equal.At the true strain stage of 0-0.9,the average dislocation density decreases from 0.6×1013 m-2 to 0.2×1013 m-2 due to dynamic recrystallization,but increases to 0.3×1013 m-2 due to coordinating grain boundary slip when the true strain reaches to 1.1.The tensile strength decreases at true strain stage of 0-0.4,and increases at true strain stage of 0.4-1.1.The elongation variation is opposite significantly.The strength decreases because of the dynamic crystallization softening at true strain stage of 0-0.4;at the stage of 0.4-1.1,strength decreasing attributes to solid solution strengthening from second phases dissolution,grain boundary strengthening and precipitation strengthening.However,the area fraction of cavity increases from 0.09%to 0.47%,and second phases coarsen,leading to the decrease of elongation.
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