G040012 水素マイクロプリント法を用いた7075アルミニウム合金の疲労変形における水素放出の可視化

Abstract

To improve tank safety and promote the application of aluminum alloys to high-compression hydrogen gas tank liners, it is important to clarify the fatigue properties of aluminum alloys as affected by atmospheric hydrogen. In this study, the effect of fatigue frequency and maximum applied stress on hydrogen evolution in 7075 aluminum alloy was studied by means of a hydrogen microprint technique (HMT). In fatigue deformation, accumulations of hydrogen were observed in the interface between a second phase inclusion (such as an Al_7Cu_2Fe phase) and the matrix. Hydrogen accumulations were also observed within the Al_7Cu_2Fe phase. The amount of hydrogen accumulation increased with decreasing fatigue test frequency. This shows that under elastic fatigue deformation, hydrogen diffusion is influenced by deformation rate. Hydrogen accumulation increased with increasing maximum stress, which indicates that hydrogen evolution during elastic fatigue deformation is controlled by stress-induced diffusion. Depending on the applied stress condition, stress-induced diffusion acted to shift the hydrogen diffusion route from the Al_7Cu_2Fe phase to the interface between that phase and the matrix. This result indicated that the deformation took place over a time sufficiently long for hydrogen to diffuse through that phase.