Effects of materials positioning and tool rotational speed on metallurgical and mechanical properties of dissimilar modified friction stir clinching of AA5754-O and AA2024-T3 sheets

Abstract

The performance of the modified friction stir clinched and friction stir spot welded joints of AA5754-O and AA2024-T3 Al alloy was improved by investigating the impact of material flow influencing parameters such as material positioning and tool rotational speed on the microstructure, mechanical and fracture behaviors of the joints. The results reveal that the positioning of a harder material (AA2024-T3) as the upper plate induces higher peak temperatures in the friction stir clinched (500 °C) and friction stir spot welded (475 °C) joints. This positioning favors inter-material mingling, grain coarsening with inherent higher dislocation density and tangles, and improved tensile failure loads in the AA2024-T3/AA5754-O joint than the AA5754-O/AA2024-T3 joint. The formation of partial weld-center defect declines in the AA2024-T3/AA5754-O at low tool rotational speed due to the better local heat build-up and geometric-differential flow effect in comparison with the AA5754-O/AA2024-T3 counterparts. The positioning of harder Al alloy on the top of a soft Al alloy is thus recommended for the improvement of modified friction stir clinched joints.