SCC extension of 7075 series aluminum alloys under mixed-mode I–II loading

Stress corrosion cracking (SCC) behavior of 7075 and 7175 aluminum alloys under the mixed-mode I–II loading in 3.5%NaCl solution was investigated to determine the effect of specimen orientation and mode II component on SCC extension. The mode I fracture toughness K1C is found to be strongly dependent on the orientation relative to the rolling direction, while K2C shows less pronounced anisotropy. It is also found that SCC initiation and crack growth rate in the S–L specimen is retarded by the intervension of increasing mode II component. The effect of mode II component is more pronounced in 7175 having a larger grain size in the thickness direction than 7075. The SCC extension behavior under the mixed-mode loading can be explained by a hydrogen embrittlement model incorporating hydrogen accumulation at grain boundaries with the crack tip stress condition.