Microstructure and mechanical properties of friction stir welded AA2014 alloy under n-MQL

Dissolution of precipitates by excess heat from friction stir welding (FSW) diminishes the joint quality of precipitation strengthened AA2014 alloy. Minimum quantity lubrication (MQL) technique is employed in this study to dissipate the unwanted heat. Graphene nanofluid prepared using two-step method with graphene nanoplatelets in water is used as the coolant. The development of grain structure and precipitation is studied using optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction and differential scanning calorimetry. The results show that the distinct thermal cycles occurring at each combination of rotational speed and welding speed transform the precipitates differently, thereby regulating the weld properties. The formation of precipitate free zones has been successfully eliminated. n-MQL has been observed to develop stable theta precipitates that produce higher weld properties. The process window for superior properties is established at the rotational speed of 1200 r/min and welding speed of 72 mm/min.