AFM Characterization of Stir-Induced Micro-Flow Features within the AA6082-T6 BFSW Welds

Abstract

Bobbin Friction Stir Welding (BFSW) is a thermomechanical process containing severe plastic deformation by mechanical stirring and Dynamic Recrystallization (DRX) during recooling. Here we report the three-dimensional characteristics of the micro-flow patterns within the aluminium weld structure. The Surface topography observations by Atomic Force Microscopy (AFM) show the stirred-induced microstructural evolution where the rearrangement of dislocations at the sub-grain scale, and the subsequent High- and Low-Angle Grain Boundaries (HAGBs, LAGBs) exhibit specific alterations in grain size and morphology of the weld texture. The dislocations interaction in different regions of the weld structure also was observed in correlation to the thermomechanical behaviour of the BFSW process. These micro-flow observations within the weld breadth give a new insight into the thermomechanical characteristics of the FSW process during the stirring action where the plastic flow has a key role in the formation of the weld region distinct from the base metal.

EBSD Characterization of Bobbin Friction Stir Welding of AA6082-T6 Aluminium Alloy

“…According to the literature, the EBSD analysis for the AA6082-T6 FSW welds show a distinct partitioning effect of the DRX, mainly an ultrafine grain refined texture at the mid-SZ, altered to an elongated morphology on the flow-arms at the border and a transition region (TMAZ, HAZ) towards the BM. It is also supported by the previous works [49,61,64] that the distance of the workpiece material from the shearing field of the welding tool is the main factor in the DRX microstructure alteration.…”

Flow-Based Anatomy of Bobbin Friction-Stirred Weld; AA6082-T6 Aluminium Plate and Analogue Plasticine Model

“…The complex interaction between the rotating tool and the abutting base metal results in chaotic flow [25]. This can interfere with the identification of the actual flow mechanism and can result in the misinterpretation of the banded shear structures in the form of plastic flow lines [26].…”

Structural Anatomy of Tunnel Void Defect in Bobbin Friction Stir Welding, Elucidated by the Analogue Modelling

“…The physical size of defects is corresponding with the dynamic changes of the load during the process. Bobbin-tool FSW appears to be a thermo-mechanical process as the frictional heat combined with the high plastic deformation is used for the joining process during the rotation and movement of the bobbin tool [12][13][14]. Also, changing the parameters of the process (e.g., feeding rate and rotational speed), or features of the bobbin tool (size and geometry of pin and shoulder), or the thickness and material properties of the weld plates may lead to unknown origin defects in the weld region [10,11].…”