Charpy Impact Testing of Friction Stir Welded Titanium Joints

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 microstructure, notched bar impact testing, and examinations of fracture surfaces of the Titanium 6Al-4V weld specimens. The experimental setup and implementation of material testing was in accordance with ASTM test methods specifications. 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. The absorbed energy to completely fracture the notched specimens during the Charpy impact test in the parent material is more than the energy required to fracture through the center of the friction stir welds.