Thermal and thermo-mechanical modeling of friction stir welding of aluminum alloy 6061-T6

Friction stir welding (FSW), a new solid-state joining technique, is probably the most remarkable joining process that has been invented in this decade. This process produces low-distortion, high-quality, low-cost welds on aluminum alloys, even those difficult to weld by traditional fusion processes. In this paper, a three-dimensional finite element model of the FSW process is presented. The modeling effort includes a de-coupled heat transfer and a subsequent thermo-mechanical analysis. The temperature fields during the welding, the residual stress distribution and distortion of the workpiece after the FSW process are studied. Two unique features in FSW, namely (1) the effect of the fixture used to clamp the workpiece to the support backing plate and (2) the reduction of yield strength near the weld nugget area of the heat-treatable aluminum in the FSW process, are incorporated into the modeling. The results from the modeling are consistent with the available experimental data and trends. The model is then used to study the fabrication process of the FSW. An example is given.