The microstructure evolution and embrittlement mechanism in the heat-affected zone of thick-plate titanium alloys fabricated by gas metal arc welding

The efficient gas metal arc welding (GMAW) of thick-plate titanium alloys contributes to the application and promotion of large titanium alloy structural parts. However, the severe embrittlement behavior in the heat-affected zone (HAZ) seriously harms the service performance. In the current work, the microstructure evolution and tensile properties in HAZ are systematically analyzed by employing the thermal-mechanical simulation tests, and the embrittlement mechanism is innovatively elucidated for the first time by discussing the resistance and impetus to dislocation slip. The results showed that as it got closer to weld metal, the α phase underwent the transformation of “α_p + α_s→α_p+α’→ghost α+α’→α’ + α_GB”. Furthermore, the resistance to dislocation slip increased gradually due to the more severe lattice distortion, the higher density of high-angle grain boundaries (HAGBs), and the more intensive strain concentration, while the impetus decreased gradually due to the reduced Schmid factor (SF) of {0001}<11$\bar{2}$0> slip system. These led to the most severe embrittlement behavior occurring at the near-weld metal. The current work provides a valuable theoretical guide for welding quality optimization of large titanium alloy structural parts.