Underlying causes of poor mechanical properties of aluminum-lithium alloy electron beam welded joints

Abstract

The measured tensile strength for the electron beam welded joint of 2195 aluminum-lithium alloy was only 60% of BM, corresponding to a drastic softening effect within the welded zone. Although hole defect worsened the tensile strength for the welded joint, the strengthening phase deficiency within welded zone, including T1 (Al2CuLi) and θ' (Al2Cu), was indeed the underlying cause for the poor mechanical properties of aluminum-lithium alloy electron beam welded joint. The primary reasons for strengthening phase deficiency were proposed. Measured by chemical testing method, the Li content within the welded zone was merely 0.71%, which was attributable to the excessive temperature up to 3573 K in melt pool, indicating that the Li evaporation loss was as high as 36%. The Li evaporation loss was the most crucial factor for the barren precipitation of strengthening phases. The high-density dislocation clusters within the welded zone suggested a too fast cooling rate during solidification process. The brittle quasi-crystal phase, T2 (Al6CuLi3), abundantly precipitated along grain boundaries, which badly overconsumed the atom of Li and Cu that were needed by T1 (Al2CuLi) and θ' (Al2Cu) precipitation, and, simultaneously, deteriorated the properties at grain boundaries.