Control of fatigue-critical defect size by pulsed current parameters in GTAW-based wire arc additive manufacturing of Ti-6Al-4V

Abstract Wire arc additive manufacturing (WAAM) can suffer from lack of fusion (LoF) and gas porosity, which degrade fatigue performance. Although pulsed arc current has been widely used for defect reduction in welding, its mechanistic role in controlling molten-pool dynamics and fatigue-critical defect formation in Gas Tungsten Arc Welding (GTAW)-based WAAM remains insufficiently understood. This study elucidates the mechanistic role of periodically modulated arc current in controlling arc‑pressure‑driven molten‑pool dynamics and their direct influence on defect formation in GTAW‑based WAAM of Ti‑6Al‑4V. Under a constant average current, pulse frequency and current half amplitude were varied to isolate the effects of current modulation on molten‑pool behavior. High‑speed imaging was employed to directly observe molten‑pool oscillation induced by arc‑pressure variation, while internal defects were quantitatively evaluated based on extreme value statistics of fatigue‑critical maximum defect size. The results demonstrate that appropriate pulsed‑current conditions enhance molten‑pool oscillation, thereby promoting bubble escape and simultaneously reducing gas porosity and LoF without altering prior‑β grain morphology. In contrast, excessively low or high pulse frequencies, as well as excessively high peak currents that induce excessive arc pressure, weaken molten‑pool responsiveness or promote unstable molten‑pool behavior, thereby diminishing defect‑reduction effectiveness. By clarifying the influence of pulsed‑current parameters on fatigue‑critical defect size in GTAW‑based WAAM of Ti‑6Al‑4V, this study provides a practical basis for defect control and process design in WAAM.