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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 b grains and a large number of acicular a 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.

The influence of solution treatment on the microstructure and mechanical properties of an (a+b) high temperature titanium alloy (Ti-6.5Al-2Sn-4Zr-5Mo-1W-0.2Si) are investigated by optical microscope (OM), scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and tensile tests at room and elevated temperatures. The results shows that, Ti-6.5Al-2Sn-4Zr-5Mo-1W-0.2Si alloy after simple solution treatment has good combinations of plasticity and tensile strength both at room and high temperature. With the solution temperature increasing, the volume fraction of primary a phase (ap) decreases gradually, while the volume fractions of b matrix (bt) and secondary a phase (as) increase. Room and high temperature tensile properties are insensitive with microstructure after solution treatment. With the solution temperature increasing, the content of ap phase decreases while the content and size of bt increase, which would cause the strength increase and plasticity decrease at RT and 650degC.