Heat-pattern induced non-uniform radial microstructure and properties of Ti-6Al-4V joint prepared by rotary friction welding

Abstract

Heat-pattern (HP) induced non-uniform radial microstructure and properties of rotary friction welded Ti-6Al-4 V joint was focused in this study, the formation mechanism of which was clarified by β-reconstruction. The results show that Ti-6Al-4 V friction welded heat-pattern at different rotational speeds can be generally separated into ‘glass-like’ HP and ‘scissor-like’ HP. According to the results of β-reconstruction, the radial microstructures of ‘glass-like’ HP and ‘scissor-like’ HP are deformed α grains → deformed α grains and lamellar α’ laths → lamellar α’ laths corresponding to center→1/2R → periphery respectively, where lamellar α’ laths at periphery of ‘scissor-like’ HP have similar orientations to form α’ colony. Deformed α grains at center zone make the strength higher than that of base metal (BM) and share the similar morphology of BM compared with the lamellar α’ laths, to get the highest elongation among the three regions of center, 1/2R and periphery, reaching near 80% of BM. Whereas, lamellar α’ laths at periphery share a coarser size than that of the center zone, the strength of which is reduced and close to the BM. Compared with the deformed α grains, lamellar α’ laths are quite different from BM in morphology, which causes a significant reduction in elongation to only 62.1% of BM. Aggravating the issue further, the elongation of ‘scissor - like’ HP is reduced to only 50.3% of BM at periphery because of α’ colony. Therefore, the strength and elongation of the joint decrease gradually from center to periphery.