Enhanced Fatigue Properties of 2219 Al Alloy Joints via Bobbin Tool Friction Stir Welding

In the present study, 2219-T87 Al alloy plates, 4 mm in thickness, were subjected to bobbin tool friction stir welding (BT-FSW) under relatively high welding speeds of 200 and 400 mm/min, with the aim to analyze the effect of welding speeds on fatigue properties of the joints. The results showed that the tension–tension high-cycle fatigue performance of the BT-FSW joints at room temperature was significantly enhanced compared to that of other joints of 2xxx series Al alloys counterparts. Particularly at a high welding speed of 400 mm/min, the fatigue strength of the joint reached 78% of the base material together with a high tensile strength of 311 MPa. It was found that the joint line remnants had no effects on the fatigue properties of the BT-FSW joints due to the elimination of root flaws under the action of the lower shoulder. Most of the samples with the welding speed of 200 mm/min failed at the thermo-mechanical zone (TMAZ) during fatigue tests, attributable to the coarsened grains and precipitates, but all of the samples with high welding speed of 400 mm/min randomly failed at the nugget zone due to the improved hardness value in the TMAZ.