Investigation on mechanical properties of friction stir welding of 2 mm thick aluminium alloy sheet

The objective on the research was to investigate the mechanical properties and microstructure of joining between identical aluminium alloys of AA6061-T6 and AA1100 by using friction stir welding (FSW) process. Due to the unstable stirring process of welding, microhardness test was conducted to measure the hardness distribution across the weld nugget. The mixing of two distinct materials was influenced by tool rotation speed. Therefore, microstructure analysis was carried out to investigate the grain size and shape. At the heat affected zone (HAZ), the grain size of AA6061-T6 increased, on the while those of AA1100 decreased. In the weld nugget, a hook defect in the aluminium alloy joining was detected. By using monotonic tensile load, the different weld line directions were observed with the expansion in tool rotation. The joints failure was consistent on the area of AA1100 series. Furthermore, two specimens were investigated, one through the 1xxx aluminium series and the other through 6xxx aluminium series. Inspection of the weld nugget hardness indicates the non-homogenous material intermixing during the stirring process that is confirmed by the results of microhardness measurement.