Friction Stir Spot Welding between Copper and AA6061-T6 with the Aid of Interlayer: An Experimental Study

A commercial sheet of pure Copper (Cu) and an Aluminum alloy sheet (AA 6061-T6) were joined at a thickness of 2 mm using Friction Stir Spot Welding with an intermediate layer (IL-FSSW) with a pinless tool. The present work was conducted according to various parameters in terms of rotation speed, feed rate, soaking time, the stability of the plunge depth (2 mm), and the diameter of the welding tool (12 mm). The welding process parameters were optimized based on the Taguchi method, using the design of experiments (DOE). The results proved that the utmost shear force was fulfilled at a rotating speed of 1800 RPM, feed rate of 15 mm/min, soaking time of 20 sec, and shear force of 3908 N (Cu above Al sheet). Under the same arrangement of sheets, the maximum microhardness was 157Hv at 1120 rpm, 15 mm/min feed, 10 s soaking time, and 10 sec preheating in the stir zone (SZ). There was a change in the microstructure of the Weld spot and the base metal. The pictures showed the difference in the size of the crystalline grains of the cross-section of the weld joint and different zones. The microstructure was analyzed using light microscopy, scanning electron microscopy SEM, EDS, and XRD examination to determine the phases. The results showed a change in the grain size according to regions and that intermetallic compounds (IMCs) led to a brittle fracture in the welded samples.