Effects on the Surface Texture, Superplastic Forming, and Fatigue Performance of Titanium 6AL-4V Friction Stir Welds

• Published in: Journal of materials engineering and performance Vol. 19; no. 4; pp. 503 - 509
• Main Authors: Sanders, D. G., Ramulu, M., Edwards, P. D., Cantrell, A.
• Format: Journal Article
• Language: English
• Published: Boston Springer US 01-06-2010; Springer Nature B.V
• Subjects: Butt welded; Characterization and Evaluation of Materials; Chemistry and Materials Science; Corrosion and Coatings; Engineering Design; Fatigue (materials); Friction stir welding; Materials Science; Quality Control; Reliability; Safety and Risk; Superplastic forming; Surface layer; Texture; Titanium base alloys; Tribology; Welded joints; surface texture; fatigue; friction stir welding; titanium; superplastic forming
• ISSN: 1059-9495; 1544-1024
• DOI: 10.1007/s11665-010-9614-4

The speed and feed effects of the friction stir welding (FSW) process on the surface texture along the top of a butt welded nugget were studied. The tests were conducted using fine grain (0.8-2 μm) titanium alloy 6Al-4V with a nominal thickness of 2.5 mm. It was shown that the pin tool marks along the top surface of the weld can be highly detrimental to both the superplastic forming (SPF) characteristics and the fatigue performance of welded panels. Removing the marks by machining the top surface after FSW was found to eliminate the predominant tearing of the weld during SPF and most of the fatigue life of across the weld was also restored. Through additional development of the FSW process parameters, the butt welded nugget was made to have equivalent SPF characteristics as the parent sheet material. By using a water-cooled pin tool and other cooling techniques, it is believed that the weld zone can be kept below the beta transus temperature during FSW, which enables the formation of a grain structure that is uniquely conducive to superplastic behavior, when compared to conventional fusion welding processes.