Prediction of residual stresses within dissimilar Al/steel friction stir lap welds using an Eulerian-based modeling approach

Friction stir welding (FSW) was applied to fabricate dissimilar welds between 5052 aluminum alloy and DP590 dual-phase steel with a lap configuration. The interfacial formation and microstructure were investigated experimentally, and in-process thermomechanical conditions with emphasis on resultant residual stress distribution were numerically studied through a fully coupled three-dimensional (3D) Eulerian-based finite element modeling. The Al/steel thermal-mechanical interaction driven by the rotational pin penetrating the steel produced the serrated bonding interface. The brittle intermetallic layer was formed in the interface, showing distribution discontinuity along the welding direction. The simulation results showed that increasing rotation velocity resulted in higher welding temperature and cooling rate, leading to the increment in the residual stress level of the weld zone. Near interfacial residual stresses exhibited an M-shape in the Al alloy while it showed Wshape in the steel, which originated from the thermomechanical processing condition and the effect of mismatch of thermal expansion coefficient. Increasing rotation velocity decreased the near interfacial compressive stress in the steel side. Numerically predicted residual stresses were in acceptable agreement with those measured using the X-ray diffusion measurement with the cos alpha method, validating prediction reasonability. Hopefully, the current simulation work will provide a new alternative modeling strategy for predicting residual stress fields within the same or dissimilar FSW.