Grain boundary alloy regulation of double-sided laser beam welding aluminum–lithium alloys T-joint

2060-T8 and 2099-T83 are both new third-generation aluminum-lithium (Al–Li) alloys which have excellent specific strength, elastic modulus, and fatigue resistance. However, double-sided laser beam welding of Al–Li alloys has a larger tendency to form hot crack and porosity. In this work, grain boundary alloy regulation of double-sided laser beam welding Al–Li alloys T-joint was performed using new welding wires under optimized parameters. Optimization of the composition of new welding wire shows that when Si content is 5.41 % and Cu content is 6.17 %, T (LiAlSi) phase size is controlled below 1 μm to suppress its stress concentration problem, and θ (Al₂Cu) phase is evenly distributed along the grain boundaries in an approximate grid pattern, all of which have excellent precipitation strengthening effects on grain boundaries. Furthermore, the potential crack source formed by the solidification shrinkage of intergranular liquid phase can also be filled and repaired by Al–Si divorced eutectics. Therefore, hot crack and porosity defects are effectively suppressed. The maximum average hoop tensile strength of the T-joints is 405.2 MPa, reaching 80 % of the skin base material. The maximum average longitudinal compressive load of the T-joints is 95.4 kN. Nevertheless, excessive Si content in welding wire leads to a significant increase in the size of T phase, which promotes the stress concentration problem and crack propagation at T phase interface, and weakening of precipitation strengthening of T phase on grain boundaries. The excessive Cu content also leads to uneven distribution of θ phase and the increase of porosity in weld zone.