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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.

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5083 aluminium (Al) alloy materials have extensive structural applications in transportation industries because of their high strength-to-weight ratio and corrosion resistance. However, under conventional fusion weldings, these materials are limited by their porosity, hot cracking, and distortion. Herein, friction stir welding (FSW) was performed to join a similar AA5083 alloy. A post-weld cold-rolling (PWCR) process was applied on joint samples at different thickness-reduction percentages (i.e., 10%, 20%, and 40%) to identify the effect of strain hardening on the microstructure and mechanical properties of the friction-stir-welded joint of AA5083 while considering the serration-flow behaviour at stress–strain curves and dislocation density of the post-weld cold-rolled (PWCRed) samples. FSW induced a 20% reduction in the tensile strength of the joint samples relative to the base metal. PWCR also reduced the average grain size at the nugget zone and base metal because of the increase in plastic deformation imposed on the samples. Furthermore, PWCR increased the dislocation density because of the interaction among dislocation stress fields. Consequently, the tensile strength of the friction-stir-welded joint increased with the increased cold-rolling percentage and peaked at 403 MPa for PWCRed–40%, which significantly improved the serration-flow behaviour of stress–strain and welding efficiency up to 123%.

Weight reduction is one of the most concerning issues of automotive and aircraft industries in reducing fuel consumption. Magnesium (Mg) alloys are the lightest alloys which can be used in the structure due to low density and high strength to weight ratio. Developing a reliable joining process of magnesium alloys is required due to limited ductility and low workability at room temperature. Friction stir welding (FSW) is a solid-state welding process that can be performed to produce sound joints in magnesium alloys. Researchers have performed investigations on the effect of rotation and travel speeds in FSW of AZ31B magnesium alloy. However, there is lack of study on the FSW parameters, i.e. travel speed below 50 mm/min and rotation speed lower than 1000 rpm. In this research, FSW of AZ31B magnesium alloy was performed at a constant rotation speed of 700 rpm and varied travel speeds below 50 mm/min. The results showed the development of finer grain size in stir zone with increasing of welding travel speed from 20 mm/min to 40 mm/min. It was found that the finer grain size improved the mechanical properties while maintaining the elongation at different welding parameters.