Fatigue behavior and fractography in friction stir welding zones of dissimilar aluminum alloys (AA5086-H32 with AA6061-T6)

Abstract

Dissimilar aluminum alloys of AA5086-H32 with AA6061-T6 were welded by friction stir welding method using three different values of linear and rotating speed; V = 50, 75 and 90 mm/min., N = 680, 920 and 1500RPM. Tensile test was used to determine the efficiency of welded samples. The microstructure, hardness, XRD analysis and fatigue tests were studied for the welded sample with the highest tensile strength. The fatigue test was studied in the welding and the nearby region at a distance of x=5, 10 and 15 mm from the welding line. The fractured fatigue surface was analyzed using SEM. The welding speed used has an effect on the efficiency of the welded samples where the maximum welding efficiency (82%) was obtained at N = 680 and V = 75 mm/min. The microstructural analysis indicated that there is a significant elongation and bending in the grains of the thermo-mechanical affected zone (TMAZ) in the advance side (AA5086-H32) of the weld compared to the retreating side (AA6061-T6). The results of XRD and EDS indicated that there is no transition of phases between the two alloys. The maximum value of hardness was at the weld line and started to decrease away from it, hence the values of hardness at the advance side was higher compared to the retreating side. Fatigue strength of the welded samples was less than the wrought alloys.