First-principles study of hydrogen segregation at the MgZn2 precipitate in Al-Mg-Zn alloys

Hydrogen embrittlement susceptibility of high strength 7xxx series Al alloys has been recognized as the critical issues in the practical use of Al alloys. In spite of the recent improvement of experimental technique, the hydrogen distribution in Al alloys is still unclear. Focusing on the interface between MgZn2 precipitates and an Al matrix, which is considered as one of the important segregation sites in these alloys, we investigated the stable eta-MgZn2-Al interface, and the possible hydrogen trap sites in MgZn2 and at the eta-MgZn2-Al interface via first-principles calculation. Most of the interstitial sites inside the MgZn2 crystal were not possible trap sites because their energy is relatively higher than that of other trap sites. The trap energy of the most favorable site at the eta-MgZn2-Al is approximately - 0.3 eV/H, which is more stable that of the interstitial site at the grain boundary. The interface between MgZn2 and Al is likely to be a possible trap site in Al alloys. Moreover, hydrogen atoms do not tend to be trapped around Zn, but a trap site around Mg is favorable; this observation is consistent with previous experimental observations.