Effects of a post-weld heat treatment on the microstructure and mechanical properties of dual-spot laser welded-brazed Ti/Al butt joints

The influence of a post-weld heat treatment (PWHT), which included a solution treatment and an artificial aging treatment, on the microstructure and mechanical properties of laser welded-brazed Ti/Al joints with Al-12Si filler was investigated. The thickness of the intermetallic compound (IMC) layer at the brazing interface increased with increasing solution treatment time at 530 °C. Si atoms diffused from the weld to the IMC layer during solution treatment, forming a Si-poor region adjacent to the brazing interface. The phases in the IMC changed from Ti(Al,Si)₃, nanograined Ti₇Al₅Si₁₂, and Ti₅Si₃ in the welded-brazed sample to Ti₇Al₅Si₁₂ with a high stacking fault density in the solution-treated sample. The net-shaped Al-Si eutectic microstructure in the fusion zone was affected by the PWHT. The size of the Si particles in the fusion zone increased with increasing solution treatment time, and the artificial aging treatment further coarsened the Si particles. The softening of the heat-affected zone (HAZ) in the Al base metal was eliminated by the PWHT. The tensile strength of the Ti/Al joint increased from 177 to 260 MPa. This result of this study indicate that the mechanical properties of Ti/Al welded-brazed joints can be improved by a PWHT.