Evolution of Residual Stresses in Friction Stir Welded Joints of AA7039

The gradient in microstructural morphology due to the mixture of strain-free recrystallized, partially recrystallized and uncrystallized grains in nugget, TMAZ and HAZ regions is a typical characteristic of FSW microstructure. This microstructural diversity typically contributes to the formation of residual stresses. The present study suggests how tool parameters like shoulder diameter and pin diameter affect thermal characteristics, microstructure evolution and residual stress generation during friction stir welding of AA 7039. The residual stresses were measured experimentally by XRD scan implementing the sin2ψ method. Also, a simulation model of the FSW of AA7039 sheet was developed in ANSYS APDL to estimate the residual stresses theoretically and compared with the experimentally observed trend. The study revealed that the specimen welded with 29 mm shoulder diameter and 7 mm pin diameter exhibited a maximum specimen temperature during welding and experimental residual stress value of 154 MPa (tensile). On the other hand, a specimen welded with 19 mm shoulder diameter and 8 mm pin diameter reveals a reduction in residual stress of 94 MPa(tensile). The simulated residual stress values are also well corroborated with the experimental observations. © 2022, The Institution of Engineers (India).