Effect of friction stir welding parameters on the structural integrity and mechanical behaviour of AA8090-T87 aluminium alloy under varying traverse speeds

AA8090 T87 alloy was friction stir welded with different traverse speeds of 90, 110 mm/min. at a constant rotational speed of 900 rev min−1 to peruse the effect of traverse speed on the joint strength in the stir zone. The grain size is measured by the line intercept method. Variation in traverse speed from 90 to 110 mm/min. caused variation in grain size from 32 to 24 µm in the top surface and hardness surged from 74.5 to 88.3 VHN, which was confirmed by analysing the grain size at the top surface and at 2.5 mm from the top surface for all joints in the stir zone. For the aforementioned joints, a hardness difference of 13.8 VHN was observed on the top surface of the weld and a hardness difference of 3 VHN was observed on the mid surface of the weld and tensile strength of the joint was determined to be 99.43 MPa for the 900/90 joint, the joint efficiency of 22% and 79.36 MPa for the 900/110 joint and joint efficiency of 17.4%. These hardness differences were owing to the precipitation strengthening mechanism, which occurs owing to Al–Cu–Mg precipitates and grain size variation.