Investigation of welding parameter dependent microstructure and mechanical properties in friction stir welded pure Ti joints

Commercial purity titanium plates with 2 mm in thickness were successfully friction stir butt-welded at a welding speed ranged from 50 to 300 mm/min. The measured peak temperatures during all the welding processes were below the α/β phase transformation point. The microstructural characterization revealed that the stir zone has an equiaxial grain structure and low density of dislocations at lower welding speed, but a high density of dislocations at higher welding speed. The optimized tensile property was obtained for the specimen welded at 200 mm/min. The mechanical properties related to the microstructural evolution were investigated and discussed by comparing with the Al (fcc) and IF steel (bcc) results.