The investigation into vibration effect on microstructure and mechanical characteristics of friction stir spot vibration welded aluminum: Simulation and experiment

Abstract

In this study, an innovative technique is employed to modify the microstructure and increase the mechanical characteristics of the Al5083 joint made by friction stir spot welding (FSSW). In this technique entitled FSSVW (friction stir spot vibration welding), the workpiece is vibrated during FSSW. Noted processes were modeled and finite element simulation results were also analyzed. The results showed that workpiece vibration during FSSW led to grain refinement, larger weld region, and improvement of the mechanical properties, namely tensile shear strength and hardness, of the joint. Stir zone grain size decreased by about 25% and tensile shear strength value increased by about 20% by applying workpiece vibration during FSSW. The results also indicated that the tensile shear strength and hardness enhanced, as vibration frequency increased. It was concluded that the presence of vibration increased the material deformation in the stir zone and led to enhanced deformation of the material. This intensified the dynamic recrystallization and resulted in grain refinement. It was also found that tensile residual stresses developed in the stir zone of FSS and FSSV welded specimens and tensile residual stress values for FSSV welded specimens were higher than those for FSS welded specimens for about 10%. It was concluded that the effect of grain size on hardness is higher than the effect of residual stress. Higher ductility is predicted for FSSV welded specimen with higher vibration frequency and also for specimen welded with less dwell time; finite element simulation was also applied to analyze the effects of workpiece vibration during FSSW on strain distribution as well as hardness and residual stress distribution within the joint during FSSW and FSSVW processes. Finite element simulation results had good compatibility with experimental results. It was concluded that the strain values and flow velocity relating to the FSSVW process are higher than those relating to the FSSW process.

Effect of Pin Shape on Thermal History of Aluminum-Steel Friction Stir Welded Joint: Computational Fluid Dynamic Modeling and Validation

“…In Equation ( 2), Z is the Zener-Holloman parameter used for the calculation of the temperature-dependent strain rate [46][47][48][49]:…”

Study on the effect of the welding environment on the dynamic recrystallization phenomenon and residual stresses during the friction stir welding process of aluminum alloy

“…Tensile residual stresses improve the mobility of dislocations and as a result reduce the hardness, while compressive ones impede the mobility of dislocations and consequently improve the hardness. 66 Moreover, the cooling system has a noticeable influence on residual stress because of its intense influence on the thermal cycle. Therefore, the distribution of residual stress is associated with the thermal cycle and restraint intensity.…”

“…64 Voids are generated and expanded during the ductile deformation of alloys and then coalesced to generate cracks. 66 Coalescence happens through the expansion of the voids followed by elongation of the links of material among the voids. Second phase particles such as precipitates and inclusions are known as the initial places for the void generation; however, the voids can be formed around the dislocation locks.…”

Effects of Underwater Friction Stir Welding Heat Generation on Residual Stress of AA6068-T6 Aluminum Alloy

“…In the first stage, the process tool is slowly plunged into the sheets to be welded until it reaches the required depth. It is held in position for a short time while still rotating, called the dwelling stage [ 11 , 12 ]. In this stage, the material is held stationary before the tool starts to be preheated before the tool starts moving forward [ 13 ].…”