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

Abstract

Abstract 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.