Evaluation of Microstructure and Mechanical Properties of Friction Stir Lap Welded 6061 Aluminium Alloy at various welding speeds

In this research the AA 6061-T6 aluminium alloy plates were welded by friction stir lap welding method. The effect of welding speeds on micro- and macro-structures and mechanical properties was investigated. The welding process was conducted by welding speed in the range 20-60 mm/min at constant rotation speed of 1000 rpm. The results showed that with increasing of welding speed, tensile shear strength and joint efficiency were increased from about 126 to 132 MPa and from about 40.6 to 42.5 (%), respectively. Although average micro-hardness of the weld nugget zone (WNZ) rather than the heat affected zone (HAZ) were increase with increasing welding speed, the average grain size in the WNZ and in the HAZ was decreased from about 43 to 32 µm and from about 99 to 87 µm, respectively. Due to increasing welding speed, the EPT with an increase in welding speed the hooking and thinning defects were gradually restricted from the WNZ to the WNZ/TMAZ interface. The fracture mode within the highest tensile shear strength joints was denoted as plate separation along the hook throughout the stir zone.