Effect of Welding Speed and Post-Weld Heat Treatment on Microstructural and Mechanical Properties of Alpha plus Beta Titanium Alloy EB Welds

The current work aims to examine the influence of various welding speeds (500, 700, and 800 mm/min) on the microstructure and mechanical characteristics of electron beam-welded Ti-6Al-4V alloy joints. The base metal microstructure was composed of a slightly elongated & alpha; phase and a transformed & beta; phase, whereas the fusion zone (FZ) exhibited an acicular martensitic & alpha;& PRIME; microstructure. This is due to faster cooling rates in the FZ associated with electron beam welding. The welds prepared with a 800 mm/min welding speed showed higher strength and lower ductility [yield strength (YS): 959 & PLUSMN; 6 MPa, ultimate tensile strength (UTS): 993 & PLUSMN; 5 MPa, percent elongation (%El): 8] compared to those prepared with 500 mm/min (YS: 909 & PLUSMN; 4 MPa, UTS: 956 & PLUSMN; 5 MPa, %El: 11). This was due to a decrease in the width of the & alpha;-platelets in the FZ owing to faster cooling rates at higher welding speeds. For all welding speeds, samples that underwent post-weld heat treatment (PWHT) displayed a noteworthy reduction in both UTS and hardness values compared to all the as-welded samples. However, the welds at lower welding speeds showed lower strength and higher ductility (YS: 868 & PLUSMN; 5 MPa, UTS: 922 & PLUSMN; 4 MPa, %El: 13) compared to higher welding speeds (YS: 892 & PLUSMN; 5 MPa, UTS: 938 & PLUSMN; 6 MPa, %El: 9) after PWHT. This is due to the formation of the diffusional product & alpha; + & beta; phase in the FZ, as evidenced by the transmission electron microscope results.