Effects of heat treatment on microstructure and mechanical properties of double-sided laser-welded AA2060/AA2099 T-Joint

AA2060/AA2099 Al-Cu-Li alloys were connected via double-sided laser welding using ER4047 Al-Si filler wires, and the joint was subjected to two kinds of post-weld heat treatment: artificial aging (AA, 165 ℃ ×20 h) and solution treatment and AA (STAA, 500 ℃ ×1 h + 165 ℃ ×20 h). The principal strengthening phases of the base metals are the T1 (Al₂CuLi) and δ’ (Al₃Li) phases. The welding process resulted in the dissolution of T1 and δ’ phases, and the formation of T (AlLiSi) and Cu-rich phases in the grain boundary (GB) of the fusion zone (FZ). The δ’ phase was reprecipitated in the FZ and the T phase in the GB was characterized by an increase in the number and volume fraction when the as-welded (AW) joint was subjected to AA. In addition, the reduction of the Cu-rich phase in the GB, the reprecipitation of T1 phase in the FZ, and the spheroidization of the T phase with a uniform distribution occurred for the STAA joint. The AW joint had a tensile strength (TS) of 390 MPa and elongation (El) of 0.3%, while the AA joint had a TS of 458 MPa and El of 0.7%. The formation of the δ’ phase in the FZ and the increasing in the number and volume fraction of the T phase were responsible for the improvement of the tensile properties. The STAA joint had the highest TS of 490 MPa and El of 2.7%. The reprecipitation of the T1 and δ’ phases, and the smallest inter-particle spacing in the FZ led to the best tensile properties when the AW joint was subjected to STAA.