Influence of the Welding Speed on the Friction Stir Welding of Thick Al 6061-T6 Alloy Using a Bobbin Tool

The joints fabricated using BTFSW for Al 6061-T6 aluminium alloy of 6 mm thickness were investigated by varying welding speed in the present paper. The different welding speeds examined were 20, 31.5, 50 and 120 mm/min, with the rotation speed maintained at a steady 380 rev/min. Sound joints without internal defects were obtained at a lower welding speed of 20 and 31.5 mm/min while void was observed at a higher welding speed of 50 and 120 mm/min. The weld nugget zone of all the joints showed fine and equiaxed grain. The grains within the welding nugget area decreased size as the welding speed incremented. Findings of tensile testing showed an increase in strength for lower welding speed and a further decrease in strength for higher welding speed. The research indicated that successful BTFSW joints were achieved within a limited range of welding speed, suggesting a narrow operating window of optimal welding speed for BTFSW.