Partial-draining and semi-dry type underwater friction stir welding set

The invention discloses a partial-draining and semi-dry type underwater friction stir welding set which comprises a gas guide rod, a friction stir head, fan blades and a gas hood, wherein the gas guide rod is a cylinder, an air channel is installed inside the cylinder, a gas inlet hole is formed at the upper end of the cylinder, the lower end of the cylinder is fixedly connected with the friction stir head, and gas outlet holes are formed in the side wall of the air channel; the fan blades are installed on the circumference of the lower end of the gas guide rod; and the gas hood is connected with the side wall of the gas guide rod, and the fan blades and the gas outlet holes are located inside an inner cavity between the gas hood and the gas guide rod. The partial-draining and semi-dry type underwater friction stir welding set is simple in structure and strong in practicality; extra compressed air sources are not needed, and a partial air environment can be formed near a welding position by means of devices of the friction stir welding set; and the formed partial air environment can effectively prevent moisture from entering weld joints, and therefore welding quality is improved further.