Study of thermal cycle, mechanical, and metallurgical properties of friction stir welded aviation grade aluminum alloy

This research work presents the study of thermal cycle during friction stir welding of aviation grade aluminum alloy. In addition, mechanical and metallurgical properties of friction stir welded joints are conceptually discussed. Experimentation has been conducted in two stages. Stage I experiments has been conducted as per one-factor-at-a-time approach with varying tilt angle and dwell time. It was concluded that maximum ultimate tensile strength is obtained at 2 degrees tilt angle and 30 s dwell time by one-factor-at-a-time approach. On the basis of stage I results, full-factorial design is used for conducting main experiments by fixing the tilt angle and dwell time. Stage II has been attempted to optimize the most influencing friction stir welding parameters: rotational speed and traverse speed. It is observed that rotational speed is predominant factors for ultimate tensile strength and traverse speed for microhardness. In addition, eight thermocouples (L-shaped k type), four on the advancing side and four on the retreating side, are placed at equal distance from the centerline for measuring the temperature during the process. The optical microscope and energy beam scattered diffraction analysis have been carried out for scrutinizing the macrostructure and microstructure of friction stir welded joints. It is evident from energy beam scattered diffraction analysis that the grain size of nugget zone decreases as compared to base metal.