Effect of Welding Parameters on Junction Structure and Fracture Behavior of Friction-Stir-Welded Joints of 2024 Aluminum Alloys

In this paper, the effect of welding speed and tool rotation speed on the junction structure and fracture behavior of friction-stir-welded joints was investigated with use of 2024 aluminum alloys of 3.2 mm thick. Results show that the formation of junction structure is more affected by tool rotation speed than by welding speed due to the differences of heat input levels. When welding speed is at 100 mm/min and tool rotation speed is in the range of 400-600 r/min, the joint junction structure causes complete bonding with no welding defects. While under improper welding parameters, the junction structure causes the precipitate aggregation on the bonding line and the partial bonding with the appearance of both tunnel defects and kissing bond defects. Meanwhile, the results of tensile tests show that the tensile fracture of all FSW joints occur at the weld center. The failure mode of joints with defects-free junction structure characterized by shear fracture is ductile. While the failure mode of joints with defects-existent junction structure characterized by layered fracture surface is brittle. Furthermore, that heterogeneous microstructure, precipitate aggregation and welding defects converge inside the junction structure is the main factor affecting the tensile properties and fracture behavior of the friction-stir-welded joint.