Effect of hydrogen on dynamic precipitation in additively manufactured aluminum alloys: Evidence for HEENT mechanism

The influence of hydrogen on the dynamic precipitation and morphology of Si particles in additively manufactured Al-12Si alloys was experimentally and numerically investigated. For the first time, hydrogen was observed to transform Si precipitates from globular to plate-like morphologies, with an increase in yield strength when the hydrogen content exceeds a critical value. Computational analysis indicated that the interface of Si particles could act as potential hydrogen traps, as suggested by density functional theory (DFT) calculations. Thermodynamic insights revealed that hydrogen likely increases interfacial entropy, stabilizes coherent interfaces, and reduces interfacial energy. These findings are consistent with the HEENT mechanism, which explains how hydrogen-enhanced entropy contributes to microstructural changes and alters the mechanical properties of metals. These findings suggest that hydrogen can influence precipitate morphology through its combined effects on thermodynamic stability and kinetic processes, offering new insights into the behavior of additively manufactured aluminum alloys under hydrogen exposure. • Hydrogen transforms silicon (Si) precipitates in Al alloys to plate-like forms. • Laser Powder Bed Fusion (LPBF) Al alloys show enhanced yield strength with H effect. • Si particle trap H, increasing interfacial entropy & stabilizing coherent particles. • Thermodynamic & kinetic insights reveal role of H in anisotropic precipitate growth. • Advanced microscopy & simulation reveal H trapping and its effect on microstructure.