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The present study investigates the effect of joining parameters on the microstructural and mechanical characteristics of dissimilar friction stir spot welding (FSSW) between AA 1050 Al and 22MnB5 hot stamped boron steel. Mechanical performance has been evaluated by shear and microhardness testing. Optical microscopy has been used to investigate the microstructure generated in the different FSSW regions. A macrostructural examination has revealed the creation of mechanical interlocking in the Al steel connections. No volumetric defects or any other imperfection has been found in all FSSW connections. Shear failure load has increased with increasing both tool rotational speed and plunge depth for all FSSW connections. Higher plunge depth has improved the mechanical interlocking between lower and upper sheet due to the formation of a larger secondary flash. Encouraging results have been obtained using coated WC-Co tools in terms of durability and joint performance.

In this paper the effect of tool geometry and welding parameters on friction stir welded lap joints with AA2099-T83 and AA2060-T8E30 aluminium alloys has been investigated through the study of the material flow and weld formation along with the reaction forces during friction stir welding (FSW) for various sets of welding parameters and two FSW tools with different geometrical features. The results showed that welding parameters and tool probe geometry strongly affect the characteristics of the typical defect features (hook and cold lap defects) of the friction stir welded lap joints. From the relationship established between the welding parameters, tool probe geometry and the hook and cold lap defect formation, some guidelines are concluded with the objective of guaranteeing appropriate FSW lap joint properties.

The main goal of this investigation is to study the flow pattern and mixing which take place during dissimilar friction stir welding (FSW). Aspects such as the origin of onion rings and development of welding defects are considered. An evaluation of the impact of welding parameters (rotational speed) on material mixing of AA 7075-T6 and AA 2024-T3 (3 mm thickness) dissimilar butt welds was performed. The 'stop action' technique has been employed in order to acquire a close snap shot of the flow and mixing in one of the samples which showed limited mixing but optimal mechanical performance and surface condition. A non-stable rotational flow inside the threads has been identified in this sample due to the formation of a cavity on the rear of the pin. This fact gave rise to characteristic bands in the longitudinal section but it was not enough for developing an onion ring-like mixing pattern.