Evaluation of formability and material characteristics of aluminum alloy friction stir welded tube produced by a novel process

Ultra-thin wall tubes were produced using a hybrid process combining friction stir welding and spinning. For this novel processing technique, rolled plates were coiled and FSW to form cylinders, and then the cylinders were subjected to spinning to get target tubes. To evaluate the formability of the tubes, a relationship between the microstructure and the plastic deformation was examined, and hydraulic bulge performances were analyzed by finite element simulation. The experiment results show that the fine-equiaxed grains are generated both in the weld nugget and base material during tube forming. The tube exhibits high formability and presents a two times higher elongation compared to extruded tube. The homogeneous microstructure of the tube leads to uniform deformation and the tube performs a uniform circumferential wall thickness distribution during hydraulic bulging. The simulation results suggest that the regions near and opposite the weld nugget occur large circumferential stress, which lead to a great thinning of the tube at final stage of hydraulic bulging as observed in the experiment.