Predicting Residual Stresses in Friction Stir Welding of Aluminum Alloy 6061 Using an Integrated Multiphysics Model

Abstract

Experimental results in the literature show that there are two flow areas of material during the friction stir welding (FSW) process [1]; namely the “pin-driven flow” and the “shoulder-driven flow”. These areas should completely join together to create a weld with no defect. First, in order to numerically predict the local distribution of flow stress around the pin as well as the temperature, strain, and strain rate fields during FSW, a two-dimensional steady-state Eulerian multiphysics finite element model has been employed in this work for aluminum alloy 6061using the COMSOL software. In this model, the non-Newtonian flow mode of computational fluid dynamics (CFD) module, general heat transfer mode of the heat transfer module, and the plain stress mode of the structural mechanics module of the software have been coupled. Slip/stick condition between the tool and workpiece, frictional and deformation heat sources, the convectional heat transfer in the workpiece, the solid mechanics-based viscosity definition, the temperature-dependent physical properties and the Zener-Hollomon- based thermo-visco-plastic mechanical properties with a cut-off temperature of 582oC were considered. Next, the thermal history during the process predicted by the model was used as input for an elasto-visco-plastic analysis to estimate the local residual stresses distribution due to the workpiece thermal expansion effect. Finally, the predicted longitudinal and transverse residual stresses were verified by comparing to experimental data.