Determination of residual stresses in a friction stir welded titanium alloy by the X-ray diffraction method

摘要

Development of tools applicable to friction stir welding (FSW) and friction stir processing (FSP) of materials with high softening temperatures has recently promoted research in processing of titanium alloys; materials with high softening temperatures; via these techniques. Pertinent to this development is the evaluation of mechanical properties of the fabricated components. These mechanical properties, especially fatigue strength, can be significantly affected by residual stresses in the processed components hence there is merit in studying their distribution on a local scale. In friction stir welded (FSWed) aluminum alloys a considerable amount of work has been done to understand the residual stress distribution. In work on a FSWed Ti-6Al-4V alloy, John et al. measured transverse residual stresses through XRD and reported a distribution with highest compressive stresses in the weld center and variations through the weld thickness. Pasta and Reynolds on the other hand, used the cut compliance technique to measure the longitudinal residual stresses in a Ti-6Al-4V FSW and reported peak tensile stresses in the stirred zone (SZ) flanked by compressive residual stresses on the both the advancing side (AS) and retreating side (RS). Both John et al and Pasta and Reynolds reported residual stresses in only one in-plane direction; transverse and longitudinal respectively. In this work, residual stresses in three in-plane directions were measured in two different FSWed joints of Ti-6Al-4V to get an insight on the residual stress distribution and variation due to different FSW parameters.