2013 年 63 巻 2 号 p. 57-64
For a high-purity Al–Zn–Mg–Cu alloy plate with a main composition comparable to 7075 aluminum alloy, the slow strain rate tensile (SSRT) test was carried out in humid air to examine the change of hydrogen embrittlement behavior with temper from underaged (UA) to overaged (OA). The relationship between the fracture response and the processes of hydrogen-transport and -enrichment was discussed. UA material showed a high embrittlement susceptibility accompanied by intergranular cracking (IGC), while OA material revealed a relatively small increase in ductility as a local elongation, leading to transgranular dimple-type fracture. No effect of pre-exposure to enhance the IGC initiation of UA was observed. It is supported that IGC will initiate when a local site along grain boundaries are situated in a hydrogen atmosphere with a given high level of concentration. The hydrogen transport can depend on both lattice diffusion and dislocation transport, and the latter is however assessed to play a determinant contribution to attain the critical concentration. The increased ductility of OA material is attributed to the formation of fine dimples induced by a hydrogen-enrichment at the interface between precipitates and matrix in grains.