A feasibility research on friction stir welding of a new-typed lap–butt joint of dissimilar Al alloys

A new-typed joint configuration, called lap–butt joint of dissimilar aluminum alloys, consisted of a single AA6063 plate of 4 mm thick and two overlap AA5052 plates of 2 mm thick. As needed as some engineering applications, the lap–butt joint was successfully welded through the friction stir welding technique using a designed tool of W9Mo3Cr4 V with some geometric improvements. The optimum work conditions and a process map were obtained after the welding process parameter optimization experiments. The process window was built aiming to choose the suitable processing conditions to pursue the high-quality lap–butt joints. The effects of welding parameters, especially the value of pin off-set, on weld-formation, microstructures and mechanical tensile properties of the lap–butt joints of dissimilar aluminums were investigated. The parameter of pin off-set played a very important role and exerted stronger influence upon the joint quality. Three typical micro flow-patterns of plasticized materials were found in the weld-zones: circumfluence, laminar-flow and turbulent-flow. Some weld-defects and the morphologies of ‘onion rings’ were detected.