Microstructural Analysis and Defect Evaluation during Friction Stir Welding of AA6063 Aluminium Pipes

In the present work, the AA6063 aluminium pipes having 5 mm wall thickness were welded by friction stir welding (FSW) using high speed steel (HSS) tool of tapered cylindrical pin profile. The tool rotational speed of 900 and 1120 rpm and circumferential speed of pipes were chosen as 1.57 mm/s and 2.38 mm/s. FSW experiments were performed using varying tool shoulder diameter, tool rotational speed and pipe circumferencial speed. The second pass of FSW experiments was also performed. The defects were investigated and the effects of process parameters and the number of passes on the microstructure and microhardness were investigated. The presence of tunnel defect was observed in samples and the size of tunnel was significantly reduced in the second pass.