Study on the microstructure and mechanical properties of 2A97 Al-Li alloys laser beam welded T-joints

Successive mode and simultaneous mode were used in two-side and two-beam DISK laser welding for T-joints of 1.5 mm-thickness 2A97-T3 aluminum-lithium alloy, and the microstructure, hardness distribution and tensile properties of T-joints obtained by two modes were investigated in comparison. The results show that, for simultaneous-mode joints and the heat conduction welding side in successive-mode joints, the fusion zone (FZ) micro-hardness are 61%-67% of base metal's (BM). The softening of FZ is attributed to the dissolution of the precipitate phase. However, the micro-hardness of the deep penetration weld in successive-mode joints is higher, indicating that the heat conduction welding process has a strengthening effect on the deep penetration weld. The tensile strength of the skin and the stringer of successive welding T-joints reach 415 and 337 MPa respectively, approximately 84.8% and 68.9% of the BM's, while that of simultaneous welding T-joints are 90.6% and 59.4% of the BM's respectively. For successive-mode T joints, the fracture occurs in transition zone (TZ) on the side of heat conduction weld, indicating that TZ on the side of heat conduction weld is the weakest part in T-joints.