Hydrogen behaviour during stress-corrosion cracking of an AZ31 magnesium alloy

Hydrogen behaviour during stress-corrosion cracking in an AZ31 magnesium alloy was studied by using hydrogen microprint technique (HMT), which is a method to visualize points of hydrogen emission from metals. Tensile test specimens were prepared from an extruded bar of the AZ31 magnesium alloy and deformed in tension at an initial strain rate of 8.3 × 10-3 s-1 or 8.3 × 10-6 s-1 under different environmental conditions. When the specimen was tested at a strain rate of 8.3 × 10-6 s-1 in a 4% NaCl solution, it exhibited brittle transgranular stress-corrosion with almost no macroscopic plastic deformation. HMT was applied to the specimen that was pre-strained in the NaCl solution, and it was revealed that hydrogen evolved from the surface of the specimen along slip lines after 5% plastic deformation. This result represents an evidence of accelerated diffusion of hydrogen by dislocation motion, which may be related to the brittle stress-corrosion cracking accompanied by plastic deformation in the localized area at a crack tip.