Dissociative hydrogen adsorption on inner surface of pore in aluminum is estimated based on statistical thermodynamics with experimental and first-principles calculational data. The relationship among hydrogen gas pressure, the amount of surface adsorbed hydrogen atoms, and the reduction of surface energy are derived with including the deviation from ideal gas for hydrogen at high pressure. The reduction of surface energy is found to depend on a small amount of difference in hydrogen adsorption energy.

In the development of high strength aluminum alloys, hydrogen embrittlement is a crucial problem. In order to understand hydrogen embrittlement, it is inevitable to know hydrogen trapping states in the alloys and it can be identified using thermal desorption spectrometry of hydrogen. We numerically simulated thermal desorption spectra of hydrogen in aluminum which are reported for a cylindrical specimen and for a plate specimen, and interpreted the desorption peaks included in them on the basis of the trap site concentration and the trap energy. As a result, we found that the peak at the lowest-temperature side can result from grain boundaries, although it was confirmed that the reported interpretation for other peaks is reasonable. In addition, we obtained the result showing the possibility that the trap site concentration of dislocations and vacancies changes during the process of heating the specimens.

Hydrogen embrittlement sensitivity (HES) of Al–Zn–Mg base alloys with high amount of zinc was studied by preparing the alloys without and with hydrogen charging. In order to clarify the effect of source of hydrogen entry on HES, we compared tensile properties between conventional strain rate testing (CSRT) in an ultrahigh vacuum atmosphere, and slow strain rate testing (SSRT) in a humid air atmosphere. It was clarified that the HES of the Al–Zn–Mg alloys varied depending on the source of hydrogen entry. Namely, internal hydrogen introduced during the melting and cast process lowers strength of the alloys. On the other hand, external hydrogen introduced from the alloy surface during SSRT under humid air raised the HES in the alloy with high strength. The HES caused by internal hydrogen was increased when the Al–Zn–Mg alloy contained high amount of hydrogen plus 0.1% of iron. The HES caused by external hydrogen was increased when the peak-aged Al–Zn–Mg alloy contained 0.1% of iron.

The effect of hydrogen on the mechanical properties of high-Zn Al–Zn–Mg base alloys with different amount of internal hydrogen was investigated using the micro-indentation. The amounts of internal hydrogen for high-Zn Al–Zn–Mg base alloys were 0.12 mL/100 g and 0.33 mL/100 g, respectively. A micro-indentation using a Berkovich indenter was performed at loading rate of 70 mN/s. The indenter was loaded to a maximum value of 1200 mN, and then was maintained for 30 s. Below the critical strain rate at which interaction between hydrogen and dislocation affects, it was found that the loading curvature decreased under the influence of hydrogen. In addition, the activation energy required for the dislocation motion tended to decrease as the amount of internal hydrogen increased. Thus, the displacement during the holding time increased since the mobility of the dislocation motion was promoted. From these results, it was shown that the effect of internal hydrogen on the mechanical properties of aluminum alloy could be evaluated by micro-indentation.

Hydrogen embrittlement sensitivity of a high-Zn containing Al–Zn–Mg–Cu series alloy in T6 temper was evaluated by tensile testing at various strain rates in humid air (HA) and dry nitrogen gas (DNG). The elongation of Al–10Zn–2.6Mg–1.6Cu–0.2Cr alloy in HA was smaller than that in DNG due to hydrogen embrittlement. Quasi-cleavage fracture caused a loss of elongation at medium strain rates (10⁻³–10⁻⁴ s⁻¹), and smooth intergranular cracking degraded ductility largely at slow strain rates (10⁻⁵–10⁻⁶ s⁻¹). These results indicate that the higher content of Zn in Al–Zn–Mg–Cu series alloy increase hydrogen embrittlement sensitivity, and exhibits hydrogen embrittlement even when the strain rate is 10⁻³ s⁻¹.

Severe cold rolling was applied to a 7075 aluminum alloy and tensile tests were made to evaluate mechanical properties of the rolled specimens. The sheet specimens of 6.8 mm thick were solution-treated at 480°C for 1 h, water-quenched and subsequently rolled to 0.7 mm in thickness at room temperature. A part of the rolled sheet was solution-treated again, and heat treated at 120°C for 24 h (T6). Tensile test pieces were made from these sheet specimens and the tensile tests were made at initial strain rates of 1.67×10⁻⁶ and 1.67×10⁻⁷ s⁻¹ in dry nitrogen gas (DNG) and in humid air (HA) where the relative humidity was controlled to be above 90%. The ultimate tensile strength was about 640 MPa, which is far higher than the specimen treated in T6 condition, and it does not depend on initial strain rate and test environment. It is noted that the specimen tested in the humid air shows relatively high elongation at the lower strain rate of 1.67×10⁻⁷ s⁻¹. This result indicates that the cold-rolled specimen has excellent resistance to hydrogen embrittlement in humid air.

Effects of electroless Ni–P plating on the fatigue strength of commercial A5052 and A2017aluminum alloys were investigated using the rotary bending fatigue testing machine. Electroless Ni–P plating drastically improved the fatigue strength of the A5052 alloy in H14 condition by suppressing the generation of fatigue crack. It also improved the fatigue strength of the T4-tempered A2017-T4 alloy in the high stress region, but the fatigue strength in the low stress region was the same as that of the non-processed specimens. Such fatigue strength was supposed to originate from the hydrogen embrittlement by the hydrogen introduced into the specimen during the plating.

Micropore growth and void initiation and growth behaviors of 5052 aluminum alloys during tensile deformation were observed by means of X-ray computed tomography (CT) using the X-ray image beamline (BL20XU) of the Japanese synchrotron radiation facility (SPring-8). Tensile tests were carried out in ambient and wet conditions. In 5052 alloy tensile tested in wet condition, the drop of stress followed by the maximum stress was remarkable, and the fracture strain was reduced in comparison with those of 5052 alloy tested in ambient condition. The number of fine micropores and voids decreased in 5052 alloy when plastic deformation started and the decrease in the amount of fine micropores and voids in the wet condition was less than those in ambient condition. These might be caused by the acceleration of micropore growth and void initiation and growth during tensile testing in wet condition.