The superplastic deformation behavior and microstructure evolution of electron beam welded 5A90 aluminum lithium alloy were investigated. The results indicated that the electron beam weld joint had good superplasticity under a suitable deformation condition. The elongation increased first and then decreased with increasing deformation temperature and initial strain rate,and the maximal elongation of 171.1% was obtained at the temperature of 450 ℃ and the strain rate of 5 × 10^(-3) s^(-1).The microstructure observation indicated that the fine equiaxed dendrite of weld bead transformed into coarse equiaxed in the initial stage( strain ε≤0.7),then refined in the later stage of superplastic deformation.The eutectic structure gradually decreased with the increase of strain. While the microstructure of HAZ was refined and equiaxed with the increase of strain.
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