Fracture Properties of Friction Stir Welded Titanium Alloy, Ti-6Al-4V

A product driven friction stir welding process has been refined to create butt-welds from two sheets of Titanium 6Al-4V (ultra fine grain). Weld specimen testing was completed on 3 different welded process conditions and the base material. This investigation includes macrostructure, microhardness, tensile properties, and fracture resistance evaluations of the weld specimens. The testing and examinations were conducted in accordance with industry standard testing specifications (e.g. ASTM E3, E407, E384, E8, E399, & E561). The weld microstructure in the stir zone is defined as refined and distorted grains of alpha in a matrix of transformed Beta containing acicular alpha. It was found that increase in alpha phase and grain refinement results in increased hardness, and increasing transformed beta in acicular alpha form which in turn results in an increase of toughness. The noted general trends in mechanical properties from “As Welded” (AW) to “Stress Relieved”(SR) conditions exhibited decrease in ultimate tensile strength and yield strength with a small increase in ductility and a large increase in fracture toughness.