Experimental and optimization studies of ultrasonic‑assisted friction stir weldments of AA2014‑T651 using graph theory

Joining of Al-Cu based alloys such as AA2014-T651 is very difficult by fusion welding techniques due to liquefaction and solidification cracks. Therefore, solid state welding namely Friction Stir Welding (FSW) is most suitable to join these alloys. The main objective of this work is to identify the most influenced process parameters such as rotation speed of the tool, and tool traverse speed and their levels for fabricating the
weldments by FSW process with using ultrasonic vibrations (UAFSW). A set of experiments were carried out using the plain cylindrical and taper threaded cylindrical tool pin profile at different levels of process parameters and experimental results were collected. A graph theory and utility concept was proposed and found an optimal working condition for better weldment properties. The UAFSW process enhanced the AA2014-
T651 weldment mechanical characteristics at 1100 rev/min of tool rotation speed, and 40 mm/min of tool traverse speed. The tensile strength, yield strength, percentage of elongation, impact strength and micro hardness were found to be 431.69 MPa, 307.47 MPa, 11.66 %, 8.32 J, and 139 HV respectively at optimal working condition. The weld joint obtained using a taper threaded tool pin profiled with ultrasonic vibration exhibits 95% joint efficiency compared to the weldments made by plain cylindrical taper tool pin profile with ultrasonic vibration. The measured characteristics have been correlated with microstructure and fracture features. The optimized responses were verified by the validation test.