Residual Stress Distribution and Mechanical Properties of TA15/BTi-6431S Titanium Alloy Welding Joints by Ultrasonic Impact Treatment

Abstract

TA15 (Ti-6.5Al-2Zr-1Mo-1V) and BTi-6431S (Ti-6.5Al-3Sn-3Zr-3Mo-3Nb-1W-0.2Si) titanium alloy plates were welded through gas tungsten arc welding (TIG) and different ultrasonic impact treatment (UIT) were conducted on the weldment. The effects of ultrasonic impact treatment (UIT) on the microstructure and residual stress distribution and mechanical properties for the welding joint were investigated through optical microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and tensile tests. After TIG welding, the structure of welding joint is composed of fusion zone (FZ), heat-affected zone (HAZ) and base metal. The FZ is widmannstatten structure with coarse β grains and a large number of acicular α due to the fast cooling rate. The microstructure in the HAZ shows a gradual change because of the presence of temperature gradients during welding. The residual stress after TIG is mainly tensile stress and the maximum longitudinal stress appears in the centerline of welding joint. The UIT process shows dramatic influence on residual stress distribution. After employing UIT twice, the residual stress near the welding joint shows a uniform distribution and the maximum tensile stress changes to compressive stress. However, the tensile properties at room temperature almost remain unchanged after UIT.