Investigation of weld parameters on ductility, onion ring and fracture behaviour of friction stir welded AA2219-T87

Friction stir welding provides better retention of ductility and plasticity in comparison to fusion welding and it increases the stability against cracking. This study aims to enhance both the ductility and strength of the welded joints. Tool profile was found to play an important role in retaining ductility, understanding the metal flow behavior and determining the fracture initiating point. The microstructure of different regions in the onion ring was inferred to correlate the strength with the metal flow pattern. The onion ring pattern strengthened the weld nugget. Shoulder and taper threaded profile tool resulted in superior mechanical properties. Microhardness results confirmed that the fracture runs through low hardness areas such as heat affected zone and thermo-mechanically affected zone. The scanning electron microscopic images revealed elongated grains and dimples, justifying ductile mode of fracture.