Multi-modal 3D image-based simulation of hydrogen embrittlement crack initiation in Al-Zn-Mg alloy

Abstract

In Al-Zn-Mg alloy, hydrogen leads to degradation of mechanical properties. It is indispensable to suppress this phenomenon called hydrogen embrittlement (HE) for increasing the strength of Al-Zn-Mg alloy. Intergranular fracture (IGF) mainly occurs when HE affects this alloy. In order to suppress HE, we need to understand the initiation behavior of IGF. Heterogeneous distribution of stress, strain and hydrogen concentration in polycrystalline material have an influence on the IGF initiation. In the present study, distribution of stress, strain and hydrogen concentration in actual fractured regions were investigated by employing a crystal plasticity finite element method and hydrogen diffusion analysis using a 3D-image-based model. This model was created based on 3D polycrystalline microstructure data obtained from X-ray imaging technique. By combining in-situ observation of tensile test of the same sample by X-ray CT with the simulation, we compared distribution of stress, strain and hydrogen concentration with actual crack initiation behavior. Based on this, the condition for intergranular crack initiation were discussed. As a result, it is revealed that stress load perpendicular to grain boundary induced by crystal plasticity dominate intergranular crack initiation. In addition, accumulation of internal hydrogen induced by crystal plasticity had little impact on crack initiation.