Global and local mechanical properties and microstructure of Bobbin tool friction-stir-welded Al–Li alloy

AA2198-T851 sheets were welded by bobbin tool friction stir welding using a rotational speed of 800 rpm and welding speed of 42 mm min(-1). The microstructure and precipitates within the joint were characterised by transmission electron microscopy. The global and local mechanical behaviour was determined using a digital image correlation system. Specific attention was given to the relationship between the local microstructure and properties across the joint, which govern the global strength and ductility of the welds. A lower global elongation of the joint is caused by the premature strain localisation in the softened zone.