Impact of tool rotational speed on the microstructural transitions and tensile properties of the dissimilar AZ80A-Mg – AA6061-Al joints fabricated by friction stir welding

Abstract Distinct AZ80A-Mg alloy with AA6061-Al alloy plates were joined using friction stir welding and investigation regarding the weld features of the fabricated joints, related to microstructural attributes and mechanical properties was carried out by employing distinctive tool rotational speeds (1600, 1400, 1200, 1000 and 800 rpm). Tool possessing cylindrical pin with tapered profile was employed at constant traverse speed of 30 mm/min and was inserted towards AA6061 alloy plate at 0.5 mm offset distance. Experimental observations revealed that employment of tool rotational speed of 1200 rpm have generated ideal amounts of frictional heat, which have softened the ingredients of both the parent metals and have contributed for the transition of the grains into dynamically recrystallized, finely refined structures being distributed evenly in nugget zone. Moreover, this joint exhibited a tensile strength of 224 MPa (nearly 77.78 % of the tensile strength of AZ80A and 72.26 % of AA6061 alloy). Presence of river like patterns, rifts, tear crinkles at the middle portions of fractured surfaces, announced the brittle category of fracture of the flaw free joint and exhibited fracture at the horizon of the thermomechanically influenced zone and the nugget zone on retreatment side, where the warped structures have fused together.