Effects of friction stir welding process on the microstructure and mechanical properties of AA8090-T87 aluminium alloy

AA8090 aluminium lithium alloy which is employed in the fuselage of airplane and in the cryogenic fuel tank was successfully welded using friction stir welding technique. Nine set of experiments were conducted by employing 700 rpm, 900 rpm, and 1100 rpm rotation speed with varying traverse speeds of 30 mm min(-1), 50 mm min(-1), 70 mm min(-1) to arrive at the best possible combination of inputs and obtain better joint efficiency. The macroscopic, microscopic and mechanical property analysis were performed to determine the effectiveness of the joint. Based on the results of the aforementioned studies, the best combination of input parameters such as rotational speed and traverse speed for the welded specimens were determined as 700 rpm and 30 mm min(-1), 700 rpm and 70 mm min(-1) respectively. Tensile strength of 700 rpm and 30 mm min(-1), 700 rpm and 70 mm min(-1) joints were found as 238.1 MPa and 222.56 MPa, micro hardness of the afore-mentioned joints were 107.3 VHN and 123.1 VHN and are subjected to microstructural analysis using scanning electron microscopy and electron back scattered diffraction techniques in stir zone and in heat affected zone. The above studies revealed the reason for the deviation in the grain size, increase in micro hardness, tensile strength owing to precipitate formation in the grains, and grain refinement in the weld zone.