Heterogeneity of grain boundaries in 5xxx and 7xxx aluminum alloys and its influence on intergranular toughness

A numerical study of intergranular failure assisted by hydrogen embrittlement of precipitates along grain boundaries, as observed in aluminum alloys of the 5xxx and 7xxx series, is presented. The influence of the lengths and density of embrittled intergranular precipitates on the grain boundary’s toughness is examined. To this end, a small scale yielding problem consisting in two elastic grains with a crack emerging along the grain boundary is formulated. For a size of precipitates and ligaments smaller than the length of the fracture process zone, some reduction in the grain boundary’s toughness is observed. The magnitude of this reduction suggests that it can only partially be at the origin of the material’s embrittlement when exposed to an aqueous environment, in agreement with experimental observations.