Effects of different aging treatments on microstructures and mechanical properties of Al-Cu-Li alloy joints welded by electron beam welding

Post-weld single aging treatment (solution treatment at 510 °C for 1 h, water quenching, and aging at 155 °C for 16 h) and post-weld double aging treatment (solution treatment at 510 °C for 1 h, water quenching, aging at 155 °C for 16 h, and aging at 130 °C for 12 h) are carried out on Al-Cu-Li alloy joints by electron beam welding (EBW) respectively. The effects of aging treatments on microstructures and mechanical properties of welded joints are investigated. Results show that the mechanical properties of welded joints are obviously improved after both aging treatments. The strength coefficient of joints is increased from 0.64 in an as-welded condition (AW) to 0.90 after post-weld double aging treatment. Microstructure analysis shows that the precipitates of the fusion zone within grains and grain boundaries are less in the AW condition. After post-weld heat treatment (PWHT), a lot of fine needle-like phases T1 (Al2CuLi) precipitate in grain boundaries of the fusion zone, and more horseshoe-shaped β′ (Al3Zr) particles precipitate within grains. In addition, grains of the fusion zone are refined after post-weld double aging treatment, which leads to an effect of grain refinement strengthening. Consequently, the mechanical properties of welded joints are greatly improved.