Improving surface quality of LDED thin-wall Ti-6Al-4V alloy with ultralow influence on superficial layer via femtosecond laser polishing

Laser direct energy deposited (LDED) Ti-6Al-4V thin-wall components enables the lightweight development of low altitude vehicle but suffers from poor surface quality. Whereas, the specific characteristics of both material and structure limit the polishing effect of mechanical methods and the common laser polishing methods, e.g. nanosecond laser polishing (NLP), considering the structural deformation and superficial microstructure evolution. Hence, a preferable polishing method could be vital for applying such component, and the corresponding influences on overall structure and superficial microstructure need thorough investigation. In the present research, the femtosecond laser polishing (FLP) was used to improve the surface quality of LDED Ti-6Al-4V thin-wall plate, meanwhile decreasing the thermal influence, and the effects were compared to the NLP with corresponding parameters. The results reveal that FLP could decrease the surface roughness from 37.24 μm to 4.97 μm by selectively removing the peak region of melting track. Meanwhile, the depths of oxide layer and heat affected zone (HAZ) were limited within 400 nm and 5 μm, respectively, even in the air environment, and no obvious structural deformation could be observed. In contrast, NLP could result in dense cracks on surface and poorer surface quality due to the severe oxidation behavior and rapid solidification, accompanying with the formation of thick oxide layer and deep HAZ in superficial layer, and the great structural deformation could be caused. Moreover, the further wearing test confirmed the minor influence of FLP on surface layer. This work establishes FLP as a viable method for the high-precision polishing on thin-wall Ti-6Al-4V alloy in air environment, overcoming the limitations of conventional techniques for critical components. © 2025