Friction Stir-Welded Titanium Alloy Ti-6Al-4V: Microstructure, Mechanical and Fracture Properties

• Published in: JOM (1989) Vol. 67; no. 5; pp. 1054 - 1063
• Main Authors: Sanders, D. G., Edwards, P., Cantrell, A. M., Gangwar, K., Ramulu, M.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01-05-2015
• Subjects: Chemistry/Food Science; Earth Sciences; Engineering; Environment; Physics; Fracture Toughness; Weld Nugget; Friction Stir Welding; Stress Relief
• ISSN: 1047-4838; 1543-1851
• DOI: 10.1007/s11837-015-1376-x

Friction stir welding (FSW) has been refined to create butt welds from two sheets of Ti-6Al-4V alloy to have an ultra-fine grain size. Weld specimen testing was completed for three different FSW process conditions: As welded, stress relieved, stress relieved and machined, and for the un-welded base material. The investigation includes macrostructure, microstructure, microhardness, tensile property testing, notched bar impact testing, and fracture toughness evaluations. All experiments were conducted in accordance with industry standard testing specifications. The microstructure in the weld nugget was found to consist of refined and distorted grains of alpha in a matrix of transformed beta containing acicular alpha. The enhanced fracture toughness of the welds is a result of increased hardness, which is attributed to an increase in alpha phase, increase in transformed beta in acicular alpha, and grain refinement during the weld process. The noted general trend in mechanical properties from as welded, to stress relieved, to stress relieved and machined conditions exhibited a decrease in ultimate tensile strength, and yield strength with a small increase in ductility and a significant increase in fracture toughness.