Thermal contact conductance effect in modeling of resistance spot welding process of aluminum alloy 6061-T6

In this study, a finite element model was developed based on the thermal contact conductance for predicting the nugget formation during the welding process in aluminum alloy 6061-T6. Since the strength of spot welded joints is completely dependent on nugget dimensions, an axisymmetric coupled structural-thermal-electrical finite element model was built and utilized to predict the nugget size. The thermal contact conductance, which is considered as a function of temperature and surface roughness, was applied in the contact area between electrode-workpiece and workpiece-workpiece. The results were validated by the data obtained from the nugget experimental measurement tests on the aluminum alloy and the previous study on steel. The obtained data from finite element model enjoys good agreement with the experimental nugget measurement tests. The results indicate that in the modeling of aluminum alloys spot welding, the thermal contact conductance has a major role in nugget enlargement during the welding process and cannot be ignored. In addition, it was shown that by increasing the welding heat input to the nugget zone, the contact resistance at the interfaces (electrode-sheet and sheet-sheet) will be decreased. As a result of that, the height of the nugget increases with a higher rate comparing to its diameter. Furthermore, in this study, the effects of spot welding parameters such as the welding current and the welding time are investigated on nugget dimensions.