Electron beam welding (EBW) offers significant production efficiency advantages for Ti alloys in aerospace applications. However, the formation of martensitic α' in the weld joint reduces toughness and fatigue properties, posing safety challenges. To address these issues, this study investigates the effects of annealing below the β transus temperature (mill annealing, MA) and above the β transus temperature (beta annealing, BA) on the microstructure and mechanical properties of EBWed Ti-6Al-4V (Ti64). EBW produced α' in both the fusion zone (FZ) and heat-affected zone due to rapid heating and cooling. MA transformed α' into an α+β basketweave structure, but did not eliminate microstructural gradients. Conversely, BA produced a homogenized microstructure across all regions, characterized by a transformed β phase with a coarse α+β basketweave structure dominantly oriented with prismatic plane. Both annealing processes reduced the amount of low-angle grain boundaries in the FZ compared to the EBWed condition. BA achieved superior mechanical improvements, including a 20 % increase in tensile toughness, a 56 % improvement in fatigue life, and a 100 % improvement in impact toughness. These enhancements are attributed to uniform strain distribution and enhanced fracture resistance facilitated by the basketweave structure. Therefore, this study suggests that BA is the obtimal heat treatment for Ti64 weld joint, significantly improving fatigue cycle and impact toughness, and is refommened for aerospace structural applications.

A cryogenic-temperature–non-circular drawing sequence (CT-NCD) at 123 K was designed to investigate the effects of the deformation stress mode on the twin activation of a commercial pure titanium (CP-Ti) for manufacturing a high-strength CP-Ti wire. A cryogenic tensile test was conducted using a digital image correlation camera in a cryogenic chamber. The cryogenic-tensile strength of CP-Ti was improved by 58.5% and strain was improved by 52.1% when compared with the tensile-test results at room temperature. The CT-NCD was conducted in the cryogenic chamber and the results were compared with those of the room-temperature wire drawing (RT-WD). The numerical and experimental results confirmed that the CT-NCD sequence continued to produce faultless CP-Ti wires. The mechanical properties of the CT-NCD wire showed that the strength increased by 12.6% with comparable ductility, and micro-Vickers hardness increased by 17.4% when compared with that of the RT-WD. The twin map obtained through electron-backscattering diffraction showed that the twinning of the CT-NCD wire significantly increased when compared with that of the RT-WD due to temperature and process effects. From the numerical analysis results, the NCD sequence generated more tensile twin than WD owing to the deformation stress mode change by a die shape. It was concluded that the proposed CT-NCD sequence affects twin activation by deformation stress mode from the die design and temperature changes, compared to the conventional RT-WD, resulting in grain refinement and mechanical property enhancement. Based on the results, CT-NCD is considered useful for manufacturing the high-strength CP-Ti wire for industrial applications.