Abstract
M.Ing. (Mechanical Engineering)
Aluminium is an alloy material vastly used for manufacturing components in aviation, transport and a host of commercial use. Friction stir welding is a novelty solid state welding technique that was invented at The Welding Institute (TWI) of UK in 1991.
This study presents the effects of process parameters on achieving sound welds of the friction stir butt welded joint of similar AA6061-T6 Aluminium alloys. The only parameters used and varied for this study were rotational speed and feed rate. The geometry of the tool was kept constant and the material used was tool steel, W302. Friction stir welds were evaluated both by visual inspection and non-destructive testing methods. Evaluation allowed for assessment of the weld integrity by examining for the presence of weld defects. The results indicated that the welds do not have any defects. The weld macrostructure and microstructure were examined and mechanical properties evaluated. The microhardness was also evaluated which showed that optimum speeds are required to achieve uniform hardness value across the weld traverse. The base metal showed higher hardness values when compared to the weld region. However, higher rotational speeds and higher feed rates result in increased hardness values, with the highest values recorded in the weld nugget and the least values recorded in the HAZ/TMAZ interfaces with a W-shaped hardness distribution.
Couplant attenuation effect was investigated using four different types of couplants, employing Ultrasonic Testing contact pulse-echo longitudinal wave to detect weld defects. The attenuation effect was minimal when the Ultrasonic gel, oil and water were used. This was attributed to the coupling conditions such as the acoustic impedance values and the viscous properties of the couplants. Conversely, grease provided poorer frequency gain than all the couplants though it had comparable acoustic impedance values. This was attributed to its poor wetting properties and development of air pockets on contact with weld sample to be examined.