Sequentially combined thermo-mechanical and mechanical simulation of double-pulse MIG welding of 6061-T6 aluminum alloy sheets

Double-pulse MIG (DP-MIG) welding is an efficient aluminum alloy jointing technique, which can form heterogeneous aluminum alloy welded sheets with different microstructure and mechanical properties. In order to accurately analyze and predict mechanical properties of welded structures, the geometrical features, local material properties and residual stresses of different welded zones should be synthetically considered in the numerical simulation. This work proposes a sequentially combined thermal-mechanical and mechanical simulation to accurately characterize the mechanical properties of the welded joint through the finite element analysis (FEA) method. The thermo-mechanical simulation was carried out to analyze the transient temperature field and residual stress distribution, which are conductive to build mechanical simulation model with detailed geometric features, the corresponding local material properties as well as attached residual stress. Subsequently, the mechanical simulation was performed to investigate the stress distribution of the welded joint. The deformation behavior and load-carrying capacity of the welded joint from numerical simulation are all in good agreement with corresponding experimental study, which indicates the feasibility and superiority of the developed sequentially combined thermal-mechanical and mechanical simulation method. Also, the stress distribution of the welded joints analyzed by numerical simulation reveals that the fracture evolution mechanism depends on whether the reinforcement has been removed from the welded specimen. The existence of the weld reinforcement leads to the increase of shear stress under tensile condition; hence, the fracture morphology includes equiaxed dimples and elongated dimples. When the reinforcement is removed, the mechanism is trans-granular and inter-granular mixed fracture in the welded zone; otherwise, trans-granular fracture occurs in the heat-affected zone.