Hydrogen embrittlement of 7075, 7175 and 7475 alloys was investigated by a tensile test of cathodically charged specimens. Hydrogen permeation behaviors for these alloys are similar to each other and are characterized by an increase only in a region of under-aging states. Embrittlement is shown in a similar aging region and is proportional to a permeated hydrogen content, although it is merely shown for a very thin plate specimen because permeation is limited to a surface layer within a depth of a few microns. However, some differences in embrittling degree are found among these alloys. That is, embrittlement of 7075 alloy is prominent, while that of 7475 alloy is negligible. This discrepancy is attributed to a difference in distribution of inclusions related to the impurity contents. Dependences of embrittlement to strain rate and temperature were also examined.
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