Understanding hydrogen-induced pore formation and release in Al-Cu alloy L-PBF process with auxiliary preheating

• The influence of preheat temperature on hydrogen-induced pore formation in Al-2139 alloy L-PBF was systematically investigated. • A normalized-enthalpy framework was introduced to quantitatively link melt pool lifetime, porosity, and hydrogen content in Al-2139 L-PBF. • Prolonged melt pool lifetime promoted hydrogen-induced pore growth, while higher energy input enhanced hydrogen degassing. • TDS and SEM-ECCI analyses revealed that hydrogen desorption and the disappearance of stacking-fault bundles were consistent with the mitigation of yield-point behavior after heat treatment. Laser powder bed fusion (L-PBF) enables the fabrication of high-strength aluminum alloys, but hydrogen-induced porosity remains a major challenge due to the large solubility gap between liquid and solid phases. This study systematically examined how preheat temperature influences hydrogen-related pore formation and evolution in the L-PBF of Al-2139 alloy. A dimensionless normalized enthalpy was introduced to integrate the effects of laser energy input, preheating, and material properties, enabling quantitative evaluation of melt pool lifetime, porosity, and hydrogen content. Thermodynamic calculations and simulations revealed that increased porosity is closely associated with prolonged melt pool lifetime, whereas hydrogen content decreases with higher energy input due to vapor-jet-driven degassing. Thermal desorption spectroscopy confirmed hydrogen release at 150–350 °C, and SEM-ECCI revealed stacking-fault bundles linked to hydrogen-modified slip. The yield-point phenomenon observed in the as-built specimens disappeared after heat treatment, consistent with hydrogen desorption and reduced dislocation pinning. The normalized-enthalpy framework provides a quantitative basis for controlling hydrogen behavior and optimizing preheat-assisted L-PBF of aluminum alloys.