Three types of strength tests, slow strain rate tensile (SSRT), fatigue life, and fatigue crack growth (FCG) tests, were performed using six types of aluminum alloys, 5083-O, 6061-T6, 6066-T6, 7N01-T5, 7N01-T6, and 7075-T6, in air and 115 MPa hydrogen gas at room temperature. All the strength properties of every material were not deteriorated in 115 MPa hydrogen gas. In all the materials, FCG rates were lower in 115 MPa hydrogen gas than in air. This was considered to be due to a lack of water- or oxygen-adsorbed film at crack tip in hydrogen gas. In 5083-O, 6061-T6 and 6066-T6, relative reduction in area (RRA) were remarkably higher in 115 MPa hydrogen gas than in air. These differences were attributed to a hydrostatic pressure produced in 115 MPa hydrogen gas. In contrast, in 7N01-T5, 7N01-T6 and 7075-T6, the values of RRA in 115 MPa hydrogen gas were nearly the same as those in air. Observation of fractured specimens inferred that the degree of such a hydrogen-induced improvement was determined by the fracture mode (e.g. cup-and-cone or shear fracture), which is dominated by the microstructure morphology.

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