Comparative assessment on weldability of Al 6061 to polycarbonate for dissimilar sheets placement in friction stir lap welding using sensor signals

The thermoplastic polymers and precipitation hardened aluminium alloys are highly popular in the aerospace and automobile sectors as a replacement of metallic materials to improve the strength to weight ratio. Thus, the unlike aluminium alloy to polycarbonate assembled structures are often necessary for which mechanical fastening and adhesive bonding are the primary methods for joining as fusion welding processes are inadequate. However, the dissimilar joint efficiency is found to be less. Thus, the ultrasonic and friction welding processes are developed. The friction stir welding is one such advanced material stirring technique without any melting of base materials. The present work addresses metallic aluminium (Al6061) to polycarbonate sheet materials joining using friction stir welding in overlap configuration using tapered H13 tool steel. The thrust force with associated tool stirring torque has been acquired in real time during plunging followed by welding phase. The weld bead profile with respective force-torque signals was analysed for the process monitoring. The tensile test has been carried out on the lap welds. The weld interface of the unlike sheets have also been scrutinised. Initially, the aluminium sheet was partially overlapped on polycarbonate for the parametric study. The highest joint efficiency was found to be 40.2% at 1400 rpm tool rotational speed and 75 mm/min traverse speed due to improper material mixing at the weld interface. Therefore, the feasibility of the process have been tested by placing thermoplastic polycarbonate over aluminium alloy through which the joint efficiency was further improved (48.57%) at comparatively low tool rotational speed (1100 rpm) with lower welding speed (55 mm/min) as the minute metallic particles uniformly mixed with melted and solidified polycarbonate due to more uniform torque in the welding phase. The tool stirring torque and axial thrust was found to be higher in this overlap position.