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.

An integrated multiphysics model for friction stir welding of 6061 Aluminum alloy

“…It predicted strain at all points of the work piece for the first time, compared to other CFD-based models which predicted strain only on limited streamlines. The model was successfully applied to predict the distribution of microstructure and residual stress around the pin [40,41], as it predicts Figure 13: Values of temperature (K) and shear strain rate (s-1) in different regions using the present model with the weld speed of 13.33 mm/sec and the rotational speed of 41.66 rev/sec, along with corresponding results from [55] (Fig. 12)…”

“…The authors recently reported some advantages of the integrated multiphysics modeling in directly predicting microstructure and residual stress after FSW based on the main process parameters (weld speed and rotational speed) [40,41]. There are two different regimes of material flow during FSW; namely "pin-driven flow" and "shoulder-driven flow".…”

A mathematical and experimental analysis of friction stir welding of steel

“…Lagrangian analysis including mesh deformation and also the error in estimating the residual stresses arising from the fact that dynamic recrystallization is taking place in the SZ as a result of high temperatures and strains rate can result in partial strain relaxation [127] . Some work has been reported which has calculated the temperature using a CFD technique and then transferred the data into an FEM model to calculate the strain and residual stresses [127] . The numerical analysis applied to aluminium alloy 6061 used a coupled system of the CFD module with steady state Eulerian multi-physics FEM with a sticking/slipping assumption between the tool and workpiece.…”