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

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 T-1 (Al2CuLi) and theta' (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, T-2 (Al6CuLi3), abundantly precipitated along grain boundaries, which badly overconsumed the atom of Li and Cu that were needed by T-1 (Al2CuLi) and theta' (Al2Cu) precipitation, and, simultaneously, deteriorated the properties at grain boundaries.