An experimental investigation and optimization of friction stir welding process for AA6082 T6 (cryogenic treated and untreated) using an integrated approach of Taguchi, grey relational analysis and entropy method

Friction stir welding is a solid state welding in which two metal parts are joined without melting with the help of frictional heat generated between the work material and non-consumable tool. Because of the poor microstructure, cracks, porosity and residual stresses in fusion welding of aircraft aluminium alloys, friction stir welding is highly attractive for joints in aircraft structures. In the present work, using Taguchi's design of experiment method, combined effect of process parameters namely tool rotation speed, welding speed (or traverse speed of tool), tool pin profile and tool shoulder diameter have been investigated for the ultimate tensile strength and percentage elongation of friction stir welded joints of AA6082 alloy. Two similar sets of experiments were performed to prepare the friction stir welded joints; first samples of AA 6082-T6 (solution heat treated and artificially aged) were friction stir welded and second cryogenic treated AA6082 alloy were friction stir welded . A comparison in the optimal conditions of two sets of experiments has also been presented. In tempered aluminium alloy, three process parameters namely tool rotation, weld speed and tool shoulder diameter are significantly affecting ultimate tensile strength, while all four parameters are significant for percentage elongation. The influence of cryogenic treatment has also been noticed on two response characteristics. An integrated approach of Taguchi method, grey relational analysis and entropy measurement method have been utilized to obtain an optimal single setting of process parameters for two response characteristics. For the friction stir welded joint of AA6082-T6 (without cryogenic treatment), a single optimal setting of process parameters was obtained corresponding to tool rotation: 1200r/min, weld speed: 35mm/min, tool pin profile, threaded cylindrical and tool shoulder diameter: 16mm. Similarly, the single optimal setting for cryogenic treated aluminium alloy (AA6082) was obtained corresponding to tool rotation: 1200r/.min, weld speed: 35mm/min, tool pin profile, cylindrical and tool shoulder diameter: 14mm.