On the friction stir welding of alloy AA2014 under n-MQL cooling condition

Friction stir welding (FSW) of AA2014 alloy requires cooling to prevent the dissolution of precipitates. The sustainable minimum quantity lubrication technique with graphene nanofluid is employed in this study for cooling purposes. FSW was carried out at 1200 rpm and 72 mm/min. A tool with a square pin was used. The microstructural evolution of the FSW joint under uniaxial tensile load is explored in detail for the first-time using electron backscatter diffraction. The results show that the grains undergo discontinuous dynamic recrystallisation during FSW and continuous dynamic recrystallisation during tensile deformation. Pole figures reveal the shear texture formed by plastic deformation. Tensile deformation has reduced local grain misorientation remarkably and thereby the dislocation accumulation. A significant increase of 94.5% is observed in grain size. Tensile deformation transforms a significant number of sub-grains with low-angle grain boundaries into stable grains with high-angle grain boundaries. The stable recrystallized grains with HAGBs and subgrains with LAGBs significantly influence the mechanical properties of the weld.