Intergranular stress corrosion crack propagation in hot-rolled AZ31 Mg alloy sheet

The susceptibility to stress corrosion cracking (SCC) of hot-rolled AZ31 Mg alloy sheets with different levels of deformation were evaluated by constant extension rate tensile (CERT) testing in distilled water. The normalised macroscopic SCC susceptibilities of the materials, characterised in terms of the normalised UTS and elongation-to-failure, were relatively consistent; however, the predominant mode of SCC propagation was strongly dependent on the microstructure. For all materials, cracks were initiated by localised film rupture and dissolution. Crack propagation through fine-grained, recrystallised regions was intergranular, whereas crack propagation through the larger, original grains was transgranular and tended to follow {101¯2} twin boundaries. In both cases, the crack propagation mechanism was a form of hydrogen embrittlement.