ZK60镁合金自持式搅拌摩擦焊工艺

Self-reacting friction stir welding process of ZK60 magnesium alloy

采用直径为16 mm且表面刻有逆时针旋转的螺旋槽的轴肩,直径为6 mm的圆柱形光面搅拌针且沿长度方向加工三个对称平台的自持式搅拌摩擦焊搅拌头,成功进行了3 mm厚ZK60镁合金薄板自持式搅拌摩擦焊,研究了焊接参数对接头表面成形、缺陷的形成及力学性能的影响。研究结果表明,搅拌头旋转速度为600r/min不变,焊接速度较低时,接头上、下表面产生沟槽缺陷,增大焊接速度获得表面无缺陷的接头,过分增加焊接速度,在前进侧和后退侧分别形成线状缺陷和孔洞缺陷,接头的力学性能随焊接速度的增大线增大后减小;采用焊接速度为400 mm/min不变,采用较低的搅拌头旋转速度时,接头表面鱼鳞纹均匀、成形美观、接头表面和内部均无缺陷,旋转速度过分增大,鱼鳞纹粗糙,在前进侧和后退侧接头内部分别产生线状缺陷和孔洞缺陷,接头力学性能随搅拌头旋转速度增大而减小。接头最大的抗拉强度为270 MPa,断后伸长率为8. 92%,接头强度系数达到87%。

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%.