Abstract
In this study, two types of first-principles calculation models were prepared to investigate the H-atom behavior in an Al-Mg-Zn series alloy and its hydrogen embrittlement characteristics. The first calculation model, which represented a perfect crystal, was used to evaluate the Mg- and Zn-atom behavior in Al crystals. To determine the H-atom behavior in Al crystals, the formation energy and diffusion barrier of H atoms in Al crystals were also calculated. The calculation results showed that Mg and Zn atoms might have formed compounds and dissolved in Al crystals. The diffusion barrier of H atom near Zn and Mg atoms was higher than that in an ideal Al crystal. These results suggested that the H-atom absorption ability of the Al-Mg-Zn series alloy was higher than that of pure Al. The second calculation model, which consisted of two crystals, was prepared to determine the effect of H atoms near the Σ3{111} grain boundary on the embrittlement characteristics of the Al-Mg-Zn series alloy. The total energy change was investigated to evaluate the stress required to separate the grain boundary. The calculation results showed that the maximum stress required to separate the grain boundary was significantly decreased when H atoms existed near a Mg-Zn compound formed at the grain boundary. In addition, decrease ratio of grain boundary cohesive energy was about 10% when H atoms existed near a Mg-Zn compound formed at the grain boundary. These results revealed that the Al-Mg-Zn series alloy showed lower hydrogen embrittlement properties than that shown by pure Al.
