Refilled friction stir spot welding of dissimilar Q235 low-carbon steel/5052 aluminum with equal thickness

The welding characteristics of 5052 aluminum alloy and Q235 low-carbon steel sheet were systematically studied by the refilled friction stir spot welding. The effects of rotation speed and pressure speed on weld forming, tensile strength, and welded joint structure were analyzed in different welding modes. The results indicated two different connection modes: the chimeric mode and the non-chimeric mode. The corresponding depression depth are 2 and 2.4 mm, respectively. In the non-chimeric connection mode, the steel/aluminum metallurgical interface is a smooth transition, the hook structure is obvious, and the welding mechanism mainly depends on the mutual diffusion between atoms. However, in the chimeric mode, a hook structure will be formed at the metallurgical interface of steel and aluminum. The connection mechanism is determined by mechanical interlocking and mutual diffusion. The maximum strength value is 7.48 kN in non-chimeric mode. At this time, the spindle speed is 1300 r/min and the pressure speed is 1 mm/s. There were two types of fractures: the button fracture mode and the peel fracture mode.