Friction stir welding of similar and dissimilar aluminium alloys for automotive applications

Abstract

Aluminium alloys are lightweight materials relatively used in automotive industries. However, welding using the conventional welding methods is known to be difficult. In this study, the friction stir welding (FSW) known as the solid state joining process was extensively used for joining similar and dissimilar 5 mm aluminium alloy plates. The butt-joint type of similar joints (AA5083-AA5083) and dissimilar joints (AA5083- AA6061) were carried out under the same welding parameters; 1000 rpm (rotational speed) and 100 mm/min (transverse speed). Macro- and microstructural observations were acquired at the cross-section of the weld regions by stereo and optical microscopes. The microstructural study showed that the formation of ‘onion ring’ structure was detected in the nugget zone of similar joints, while wavy and distorted patterns appeared in dissimilar joints. All tensile specimens of similar welding joint showed similar fracture patterns where all fractures occurred in the thermo-mechanically affected zone (TMAZ). However, tensile specimens of dissimilar welding joint broke up at the TMAZ region as well as at Al6061 base metal at the retreating side. The tensile strength of similar joint and dissimilar joint was 22% and 19% lower compared to the base metal of Al5083 and Al6061.