Microstructure and Mechanical Properties of Friction Stir Welded Dissimilar Titanium Alloys: TIMET-54M and ATI-425

Abstract

Weight reduction in automobiles and in aerospace industries can profoundly register for the behemoth change in the consumption of the fossil fuels and, in turn, CO2 emission. With a promising hope in hindsight for weight reduction, we have successfully produced butt joints of friction stir welded (FSWed) dissimilar, and rather novice, α-β titanium alloys—ATI-425 and TIMET-54M. The study presented in this article encompasses the microstructural and mechanical properties of the joints for two cases, (1) ATI-425 on the advancing side; and (2) TIMET-54M on the advancing side. The evolution of microstructure and concomitant mechanical properties are characterized by optical microscopy, microhardness, and tensile properties. A detailed description of the microstructural evolution and its correlation with the mechanical properties have been presented in this study. Our investigations suggest that mixing patterns are dependent on the location (advancing, or retreating) of the alloying sheet. However, the microstructure in the weld nugget (WN) is quite similar (grain boundary α, and basket weave morphology consisting of α + β lamellae) in both cases with traces of untransformed β. The thermo-mechanically affected zone (TMAZ) on the either side of the weld is primarily affected by the microstructure of the base material (BM). A noticeable increase in the hardness values in the WN is accompanied by significant deflection on the advancing and retreating sides. The tensile properties extracted from the global stress strain curves are comparable with minimal difference for both cases. In both cases, the fracture occurred on the retreating side of the weld.

Keywords

• dissimilar α-β titanium alloys
• FSW
• microstructure
• mechanical properties