Microstructures and Mechanical Properties of Friction Welded Ti-6Al-4V Alloy

We investigated the relationship between the microstructure and mechanical properties of Ti-6Al-4V alloy subjected to friction welding (FW). In this work, specimens with a diameter of 15 mm and length of 50 mm were prepared, and FW was performed at a constant rotation speed (1600 rpm) and different upset lengths (1 mm and 3 mm). The electron backscattered diffraction (EBSD) method was used to analyze the grain boundary characteristic distributions (GBCDs) such as the grain size, misorientation angle, and the phase distributions for the weld zone and base material. We found that the microstructures in the weld zone were developed by a combination of continuous dynamic recrystallization and phase transformation. In addition, a decrease in the upset length led to accelerated grain refinement, and the average grain sizes in weld zone were refined from that of the base material (5.75 mu m) to 1.45 mu m and 1.85 mu m at upset lengths of 1 and 3 mm, respectively. Consequently, the maximum microhardness value increased by 320% at an upset length of 1 mm relative to the base material, and the yield and tensile strengths of the welded materials were maintained at the same levels as those of the base material. Therefore, based on the developed microstructure and mechanical properties, the application of FW to Ti-6Al-4V alloy could be obtained joints with superior performance.