Abstract: Hydrogen pores in laser additive manufacturing (LAM) aluminum alloys have long been a major challenge for its application. In this study, the formation mechanisms of hydrogen pores and its kinetic behaviors were systematically investigated in laser directed energy deposited (L-DED) AlMgScZr alloy. The results indicated that hydrogen pores accumulated layer by layer at the melt pool boundaries, due to the high nucleation rate and insufficient time to escape of hydrogen pores at the melt pool boundaries. Dring the AlMgScZr powder at 150 °C/4 h enabled the significant decrease of moisture content from 0.0520 wt% to 0.0096 wt%, while the porosity of the L-DED sample only decreased from 0.51% to 0.36%. The increase of laser power decreased the porosity of L-DED sample. Except the L-DED parameters, the alloy composition exerted a more significant influence on hydrogen porosity. When the Mg content increased from 9 wt% to 14 wt%, the porosity exhibited an increase from 0.36 % to 0.52 %. Conversely, the incorporation and subsequent augmentation of Si content resulted in a significant reduction in porosity, reaching as low as 0.15% with an increase to 2 wt%. The solubility and diffusion coefficient of [H] in Al-Mg-Sc-Zr melt with different Mg and Si contents were calculated by density functional theory (DFT). It was observed that increasing the Si content led to a decrease in the nucleation zone for hydrogen pores and reduced porosity. A comprehensive porosity inhibition strategy that combines powder drying, process optimization, and composition regulation have been developed.

Key words: Laser additive manufacturing, Directed energy deposition, AlMgScZr alloy, Hydrogen, Porosity