Revisiting hydrogen trapping in Mg32(Al, Zn)49 approximant crystal: Influence of chemical disorder

The approximant crystal Mg₃₂(Al, Zn)₄₉ (T-phase in Al-Zn-Mg alloys) holds the potential for enhancing both strength and hydrogen embrittlement resistance in aluminum alloys when present as nano-precipitates. Our previous computational exploration indicated strong hydrogen trapping but neglected the inherent chemical disorder of this approximant crystal. This study revisits hydrogen trapping in Mg₃₂(Al, Zn)₄₉, directly including chemical disorder via special quasirandom structures. Density functional theory calculations reveal that, while chemical disorder introduces variations in trapping energies, the overall trend of strong trapping persists. Tetrahedral sites coordinated by Mg atoms exhibit particularly strong trapping, with smaller tetrahedral volumes correlating with stronger trapping due to enhanced Mg-H interactions. Multiple hydrogen occupation of these sites is also calculated, resulting in high hydrogen densities. Experimental validation using thermal desorption spectroscopy on a bulk Mg₃₂(Al, Zn)₄₉ sample confirms hydrogen trapping, reinforcing the potential of this phase for designing advanced, hydrogen-resistant aluminum alloys.