Dieless friction stir lap joining of AA 5050-H32 with AA 6061-T6 at varying pre-drilled hole diameters

The role of hole diameter on mechanical behavior and joint formation of dieless friction stir lap joints in dissimilar alloy grades of aluminum is investigated in the present article. Concurrent occurrence of mechanical interlocking along with metallurgical bonding reinforce the fabricated joints. Keyhole defect and hook defect of conventional friction stir spot welding are apparently suppressed. Hole diameter range from 3 to 3.5 mm is found to be favorable, while considering the macrostructure analysis, joint morphology analysis and load performance analysis. Appreciable fracture load up to 7 kN is obtained in lap shear test throughout the hole diameters employed. Zones present in the joint are identified, in addition the effect of size of the hole on mechanical interlocking is exposed through macrostructure analysis. The extent of recrystallization induced by frictional heat generation along with plastic deformation has affected the grain structure of the joint. Critical zones resulting in the failure of the joints are stir spot circumference and neck of the pin. A tool diameter to hole diameter ratio for successful DFSL joint fabrication is also established through the present work.