Metallurgical and Mechanical Characterization of Double-Sided Friction Stir Welded Thick AA5083 Aluminum Alloy Joints

In this paper, double-sided friction stir welding was employed to join the thick AA5083 alloy plates. The effects of rotational speed, traverse speed and pin length on the join features were evaluated. For this purpose, macro- and microstructural evolutions, and mechanical properties such as microhardness, tensile strength and fracture toughness were studied. According to the results, the stirring action and generated heat led to the fragmentation of Al6(Mn, Fe) particles and dissolution of Al3Mg2 compounds in the stir zone (SZ). The SZ grain size was much smaller than that of the other zones; however, the hardness remained almost the same alongside the joint area (~ 80 HV). An increase in rotational speed at a low traverse speed caused the increase in the grain size of the SZ; however, at a high traverse speed, it did not have any important effect on the average grain size. The highest double-sided failure energy of the joints was obtained by the traverse speed of 80 mm/min, the rotational speed of 1000 rpm and the pin length of 6 mm. In order to study the resistance to crack growth, fracture toughness (three-point bending) test was done. The results show that the KQ obtained for the optimum welded sample is about 11.5% higher than that of the base metal.