Evaluation of crystal structure and tensile properties at the micro level of friction stir weld developed with n-MQL

Friction stir welding of AA2014 alloy requires cooling techniques to prevent premature weld failure by carrying away the excess heat. In this study, minimum quantity lubrication technique is explored for the first time with graphene nanofluid. This study aims to develop instant grain refinement and reprecipitation. FSW is performed at the optimized parameters i.e., 1200 rpm and 72 mm/min. The retention of precipitates in HAZ and entanglement of dislocations in NZ are obtained through the instant quenching action of n-MQL. The evolution of microstructure and precipitation in the developed weld zones are studied using TEM. The microscopic results also present the developed substructures such as subgrains, cell wall, orowan loops etc. Crystal structure in the nugget zone is analysed using Rietveld refinement method. The results reveal a 100 % match with Al 0.99 Cu 0.01 . The crystallite size in nanometers and the microstrain are deduced using Scherrer method and W-H plot. The local tensile properties of each weld zone are analysed in detail using flat microtensile test. The weld center with recrystallized grains exhibits the lowest ultimate tensile strength, yield strength and % elongation. The current study presents the influence of dynamic recovery and recrystallisation on the local tensile properties of the weld.