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.

Automated summary

Excessive heat generated during friction stir welding (FSW) causes dissolution of precipitates and reduces the joint quality of AA2014 alloy. To dissipate the unwanted heat, minimum quantity lubrication (MQL) technique is used, with a graphene nanofluid prepared using two-step method as the coolant. The effects of different thermal cycles on grain structure and precipitation are investigated, and it is found that the formation of precipitate free zones can be eliminated by appropriate combinations of rotational speed and welding speed. The development of stable theta precipitates through n-MQL leads to higher weld properties, with the favorable process window established at a rotational speed of 1200 r/min and welding speed of 72 mm/min.