Self-reacting friction stir welding process of ZK60 magnesium alloy

ZK60 magnesium alloy plate with 3 mm in thickness was successfully welded by self reacting friction stir welding process using the tools with the diameter of 16 mm and 3 mm of the shoulder and the pin,respectively. The self-reacting friction stir welding tools are featured of counterclockwise scrolled shoulder and smooth cylindrical pin with three symmetrical flats longitudinally distributed. The effects of the parameters on the surface appearance,flaws forming,and mechanical properties were investigated. It was shown that the grooves in the bottom and top surface of the joint appear,and the sound joint with the good surface quality and without internal flaws was obtained at the higher welding speed by using the constant rotation speed of the tool 600 r/min. The linear defect and the holes were observed on the retreating side（ RS） and the advancing side（ AS） of the joint respectively when the welding speed was excessively increased. And the tensile strength and the elongation of the joint firstly increase and then decrease with the increase of the welding speed at the constant rotation speed of the tool. The highest tensile strength and the elongation of the joint were reach up to 270 MPa and 8. 92% of the joint,respectively,and the joint efficiency reaches 87%.