On-line laser shielding of hydrogen-induced pores in arc-directed energy deposition

The detrimental effects of pollutant elements in arc-directed energy deposition (arc-DED), particularly hydrogen-induced porosity in aluminum alloys, pose critical challenges for structural integrity. While pollutant shielding is commonly employed for pore suppression, the risk of hydrogen contamination from repeated remelting of deposited layers remains largely overlooked. This study revealed that even trace surface oxides on deposited layers critically governed hydrogen pore nucleation. Microstructural characterization demonstrated a synergistic clustering mechanism among oxides, hydrogen, and pores, where oxides act as dual-functional sites for hydrogen carriers and trappers. To address this, we developed an innovative on-line laser shielding-enhanced arc-DED system integrating a high-frequency nanosecond pulsed laser with arc plasma. This hybrid approach achieved in situ oxide purification within the molten pool, reducing porosity by 98.1 % compared to conventional arc-DED. The laser-arc synergy demonstrated amplified shielding efficiency, with the arc plasma enhancing laser-induced oxide removal rate by 9.6 times. Crucially, this technology disrupted the oxide-mediated hydrogen transportation pathway while eliminating hydrogen-trapping effects in the molten pool. Implementation in Al-Zn-Mg-Cu alloys significantly improves ductility by minimizing porosity at deformation-sensitive interlayer regions. Process scalability was further verified in Al-Mg alloys, achieving comparable porosity reduction. By decoupling the dual roles of oxides in hydrogen carriers and trappers, this work establishes a paradigm-shifting strategy for pore control in arc-DED, offering a versatile platform for processing hydrogen/oxygen-sensitive metals with enhanced mechanical performance.