The Research of the Auxiliary Power of Q235 Steel Friction Stir Welding Technology and Joint Microstructure’s Observation

Abstract

Friction Stir Welding (FSW) is a new and developing technology that has been used succefully in the joining of aluminum and aluminum alloys.To demonstrate the feasibility of the auxiliary power of Q235 steel friction stir welding, we used orthogonal test method to design auxiliary power FSW parameter,then welded 200mm×80mm×4mm of Q235 with the parameter. The result shows that the rotating 1200 r/min, the stay time 10s and the heating temperature 700 °C,the welding joint tensile strength can reach 332.19 MPa. Analysing the parameter fracture morphology,we found that the fracture is divided into three levels: the upper part is the ductile fracture; the middle part is the combination of the ductile fracture and the brittle fracture;the lower part is the majority of the brittle fracture, and exists the local ductile fracture. Analysing the microstructure,we found that welding joint is divided into the base zone, the heat affected zone,the thermo-mechanically affected zone and the stir zone,and the microscopic organization of every area is influenced by the heat and the force on the area. The microhardness of stir area improves 12% on average than the base’s.The microhardness of the heat affected zone and the thermo-mechanically affected zone decreases , comparing to the base’s.