Abstract
The purpose of the present research work was to study the effect of FSW parameters, including mainly the tool geometry on soundness, microstructure and mechanical properties of butt joints of AA6061 aluminum sheets. Moreover, the effect of the tool rotational speed and welding speed was as well investigated. The results showed that welding tool geometry plays a remarkable role in deciding the weld quality. Welding tool with smaller shoulder diameter has resulted in narrower weld zone. In comparison with straight shoulder and non-threaded cylindrical pin, a better weld soundness with much less tunnel defect was obtained using filet shoulder and threaded cylindrical pin. Further improvement of weld soundness was achieved using threaded taper pin. In addition to welding tool geometry, combination of both tool rotational speed and welding speed is of considerable importance for obtaining sound welds with maximum mechanical properties. Sound welded joints free from tunnels or other defects were produced using 1200rpm rotational speed, 35.5mm/min welding speed and either threaded taper pin, non-threaded taper pin or cylindrical threaded pin. However, the maximum hardness and tensile properties were obtained for the welded joint made using threaded taper pin. Hardness values of weld nugget and TMAZ of this joint were about 85% and 95% of that of the base metal. The softened HAZ in this weld, detected by the microhardness testing, was smaller than that of the other two welds. Tensile strength and elongation of this weld were 314MPa and 13.1%, which are about 7% lower than that of Al6061 base metal. Tensile properties are correlated well with microstructure and hardness where maximum tensile strength is corresponding to finer microstructure and maximum hardness in WN and TMAZ