Effect of process conditions on superplastic forming behaviour in Ti–6Al–4V friction stir welds

Abstract

Friction stir welding of Ti–6Al–4V was performed on 5 mm thickness sheet. Wide ranges of processing conditions were tested, and an experimentally determined process window was established for this given material, thickness and tooling configuration. Welds made within this process window were also superplastically formed. It was found that the weld parameters influence joint quality in terms of microstructure, penetration and void formation in addition to process traits such as loads and tool wear. Furthermore, since the microstructure of the weld could be altered with the welding parameters, the degree of superplasticity in the joints could also be controlled. Finally, experimental observations were compared to a proposed analytic process model in an attempt to establish trends between the weld characteristics and the welding conditions used. Reasonable correlations were observed between the analytic model and experimental results.