Investigation of defect formation during friction stir welding of aluminum alloys

Friction stir welding (FSW) is a widely used material joining process. A lot of study has been done in this field but the formation of defects in the process has not been adequately explored. In this work, an attempt has been made to study the defects that are observed during the friction stir welding process. Sheets of aluminum 1100 alloy have been welded together at different parameter values. The welds obtained were cut along the cross-section, polished and observed under the optical instruments to get insight into the defects that were formed during the FSW process. Macro as well as micro sized defects, have been observed in different regions of the welding zone. It was observed that mainly four types of defects were formed during the friction stir welding. The defects produced during the process can be attributed to the thermal stresses and improper mixing of material during the welding. Micro size tunneling defects are observed in welds produced with low tool rotation speed, and this signifies improper mixing of material.