Friction Stir Welding of Aluminum Lithium Alloys: Experimental Investigation of Mechanical Characteristics Using Grey Relational Theory

In the current research, an aluminum alloy AA8090 is welded using the friction stir welding (FSW) technique. The main objective is to eliminate the chances of defects in the weld joint, which were observed in the conventional joining process. Experiments were planned according to the one factor at a time (OFAT) approach. The input process parameters involved during the present work are welding speed (WS), rotational speed (RS), tilt angle (TA), and dwell time (DT). However, the response variables investigated at different input parametric combinations are tensile strength (TS), percentage elongation (EL), microhardness (MH), and macroscopic structure. Due to the combination of both attributes of optimization (the higher the better in TS and the lower the better in EL), the multi-performance quality characteristics optimization approach, i.e., grey relational analysis (GRA), is implemented. The maximum TS (357 MPa) was observed at a WS of 40 mm/min, RS 500 rpm, TA 1°, and DT 10 s; however, the minimum EL was predicted at a WS of 20 mm/min, RS 500 rpm, TA 1°, and DT 20 s. The most influential parameter for the evaluation of TS is the WS; while for the investigation of EL, the most significant parameter is TA. The joining of eight series aluminum alloy poses difficulty and became a challenging task. To fulfil this gap, an attempt has been made to join the AA8090 by FSW to produce a defect-free weld.