An experimental investigation of torque and force generation for varying tool tilt angles and their effects on microstructure and mechanical properties: Friction stir welding of AA 6061-T6

Friction stir welding (FSW) has evolved as a very promising joining process for light weight material fabrication. Weld characteristics of FSW AA6061-T6 samples in terms of mechanical properties of weldment have been studied by varying the tool tilt angles for taper and taper threaded tool. Torque and different forces (Z force, X force) generated at the tool-workpiece interface are experimentally measured and analyzed to assess the effect of tilt angles. It is observed that torque and forces associated with FSW increases as tilt angle increase. Torque and vertical force (Z force) attained by the taper threaded tool is higher than that of taper tool whereas welding force (X force) for taper threaded tool is found to be less compared to taper tool. Fluctuation of welding force increases with increase in tilt angle for taper tool but taper threaded tool exhibits an opposite behavior. The onion ring structure for taper tool is not prominent, where as a clear layered, stacked onion ring formation can be observed for taper threaded tool. Comparatively improved tensile properties are achieved for taper threaded tool at higher tilt angles. EDS analysis reveal the presence of higher amount of iron percentage at nugget for welded specimens those experienced higher X force fluctuation and exhibit brittle failure under tensile loading.