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

Abstract

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 α phase and a transformed β phase, whereas the fusion zone (FZ) exhibited an acicular martensitic α′ 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 ± 6 MPa, ultimate tensile strength (UTS): 993 ± 5 MPa, percent elongation (%El): 8] compared to those prepared with 500 mm/min (YS: 909 ± 4 MPa, UTS: 956 ± 5 MPa, %El: 11). This was due to a decrease in the width of the α-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 ± 5 MPa, UTS: 922 ± 4 MPa, %El: 13) compared to higher welding speeds (YS: 892 ± 5 MPa, UTS: 938 ± 6 MPa, %El: 9) after PWHT. This is due to the formation of the diffusional product α + β phase in the FZ, as evidenced by the transmission electron microscope results.