Finite Element Simulation of Residual Stresses in Friction Stir Welding of AA2219 Plates

Friction stir welding (FSW) is a solid-state welding process in which the temperatures never exceed the melting point of the work-piece material. The process is widely used in the aerospace industry for welding aluminum alloys, and aluminum–lithium alloys are used in the fabrication of propellant tanks. Knowledge of the residual stresses developed due to the welding process is an important parameter used in the design of propellant tanks. The present work details the finite element simulation of friction stir welding of two flat plates made of AA2219 material, a material used for fabrication of the propellant tanks used in the launch vehicles of ISRO. The simulation is performed using a nonlinear, fully coupled thermal-structural finite element analysis using ANSYS (version 18.1) code. The computational model involves two work-plates and the FSW tool modeled using three-dimensional solid elements and the effect of the fixtures supporting the work-piece is brought in using appropriate structural and thermal boundary conditions. The constitutive models used for the analysis are capable of simulating the frictional heat generation and the associated temperature-dependent mechanical response of the material. The entire sequence of operations involved in the welding process from the initial plunge of the tool to the final removal of clamps after cooling is simulated. It is seen that the predicted temperatures on the work-piece fall with 70–90% of the melting temperature of this particular alloy. The predicted residual stress pattern shows a characteristic M-shaped distribution along the width of the work-piece which agrees well with results reported in the literature.