Influence of stir zone temperature and axial force on defect formation and their effect on weld efficiency during friction stir welding of AA1100: A simulation and experimental investigation

Achieving good weld quality is of prime objective of every industry. Therefore, it is essential to understand the underlying mechanism of defect formation and its impact on weld quality. In the current work, a simulation through a coupled Eulerian-Lagrangian model is carried out to investigate the influence of peak temperature developed at the stirred zone and axial force on defect formation during friction stir welding to understand the thermophysical interaction between the tool and the workpiece. Also, an attempt has been made to correlate the numerically predicted defect and its quantum with the experimental weld strength for different process parameters. The developed model is validated with experimentally observed axial force, weld flash, and defects. The highest weld strength of 90.6 MPa (85% weld efficiency) is achieved at 600 rpm and 160 mm/min weld speed and is confirmed with the almost defect-free condition. A unique way is established to study material flow mechanism on both sides of the weld center line in the thickness direction for similar material. For a few parameters, defects (cavity and void) are observed, but their distribution did not significantly hamper the weld quality, and weld efficiency is in the range of 70-75%. Lower weld efficiency of 58% is found only for tunneling defects. A descendent of weld strength was observed while increasing rotational speed from 600 rpm to 1500 rpm, which has been correlated with stir zone peak temperature, axial force, and defects.