Friction stir welding device

The invention relates to a friction stir welding device. The friction stir welding device comprises a stirring head, a sub-zero treatment unit and a control unit, wherein the sub-zero treatment unit comprises a low-temperature tempering box, a sub-zero treatment box, a liquid nitrogen storage tank and a liquid delivery pipe; the low-temperature tempering box and the sub-zero treatment box are sequentially arranged above a workpiece welding seam and regularly move in the welding direction; the liquid delivery pipe is used for connecting the sub-zero treatment box to the liquid nitrogen storage tank; the control unit is connected with the sub-zero treatment box and the low-temperature tempering box respectively for controlling the temperature rising and reducing rates, the soaking time and the processing temperature of the sub-zero treatment box and the low-temperature tempering box. According to the friction stir welding device, the sub-zero treatment box and the low-temperature tempering box are arranged above the workpiece welding seam, so that cold and hot circular treatment combining sub-zero treatment and low-temperature tempering is performed on a workpiece during friction stir welding in real time, the thermal stress produced in the welding process is reduced through the cold and hot circular treatment, the dimensional stability of a weldment is improved and the mechanical performance of the weldment is improved.