Experimental investigation of overhang structure surface roughness characterization and oxidation characteristic in L-PBF aircraft hydraulic channels

Laser powder bed fusion (L-PBF), as one of the additive manufacturing technologies, has become one of the most promising techniques for producing components with complex geometries. While L-PBF enhances design freedom for aircraft hydraulic channels, challenges such as improving surface quality and oxidation behavior in overhang structures remain critical issues. This research experimentally investigates the effects of key process parameters, including laser power density, spot diameter, and layer thickness, on the surface roughness and oxidation behavior of the top overhang surfaces of hydraulic channels. The formation mechanisms of incompletely molten particles and microcracks on overhang surfaces are revealed. The microstructure of the overhang surfaces is examined using scanning electron microscopy (SEM), and the distribution of oxygen in fully and partially molten regions is examined using energy dispersive spectroscopy (EDS) to clarify the relationship between incomplete melting and oxidation. Experimental results show that higher laser power densities not only exacerbate surface roughness but also promote oxidation in incompletely molten areas. For hydraulic channels with a diameter of 10 mm, the spot diameter of 130 μm, and layer thickness of 40 μm effectively reduce surface roughness at the top of the channel. Compared to unmelted and fully molten regions, the oxygen level in partially molten regions is much higher. Both the oxygen content in molten and incompletely molten regions decreases with increasing layer count during fabrication. Using fresh powder reduces both the surface roughness of overhang structures and the oxide content. This study provides theoretical insights and practical guidance for the application of L-PBF technology in aircraft hydraulic channels.