Friction Stir Spot Welding a Graphene-Reinforced Aluminum Alloy: The Effect of Tool Plunge Depth and Welding Time

In this work, a graphene-reinforced Al alloy was joined by friction spot welding (FSpW). The effects of welding time and tool plunge depth on the microstructure and mechanical properties of the joints were studied. Results show that FSpW is very suitable to join the graphene-reinforced Al alloy, and sound joints were obtained using wide parameter ranges. Hook bends downwards using small plunge depths of 1 mm and 1.2 mm and short welding times of 2 and 4 s, which then bends upwards at large plunge depth of 1.4 mm and prolonged welding time of 6 s. The sleeve plunge depth has a significant effect on the grain size. The grain size increases from 2.2 to 7 μm when increasing the plunge depth from 1 to 1.4 mm. Mg and C concentrations are obtained at the stir zone, and they react with each other to form Mg₂C₃. Increasing the plunge depth and the welding time decrease the hardness of the joint. The lap shear failure load of the joint first increases and then becomes stable when increasing the plunge depth, while the joint strength first increases and then decreases when increasing the welding time.