Effect of tool rotation speed in friction stir spot welding on microstructure, mechanical properties and thermal conductivity of pure copper and ST14 carbon steel joint

In the present study, pure copper and plain carbon steel ST14 were bonded by point friction welding method. The welding operation was performed by a tungsten carbide pinand three rotational speeds of 1000, 1250 and 1500 rpm and a time of 60 seconds were selected for the tool. After welding, microhardness, tensile, thermal conductivity andmicrostructure tests were performed using light microscope and scanning electron microscope. The microhardness test showed that the samples with higher rotational speed, the hardness of the welding button area was higher. The results of tensile test showed that with increasing the rotational speed of the pin, the tensile strength of the specimens increased. The results of thermal conductivity test showed that with increasing the rotational speed of the pin, the coefficient of thermal conductivity decreased. The microstructural analysis of the samples showed that the connected samples with higher rotational speed, due to the increase of the inlet heat, and consequently the increase of the cooling rate, the recrystallization of the grains was faster and therefore smaller grains were formed.