Corrosion-induced embrittlement in ZK60A Mg alloy

A Diffusion-based Corrosion Layer (DCL) in Mg alloys composed of partially oxidized alloy is present between the corrosion product and the uncorroded bulk metal. This layer has different mechanical properties compared to the bulk (lower elastic modulus and ductility) that change gradually from the bulk to the surface. We investigate, experimentally and computationally, mechanisms that play a role in corrosion-induced embrittlement of ZK60A Mg alloys. We find that the DCL may assist in crack initiation and propagation under loading because of its graded mechanical properties and strong, seamless bonding to the bulk. Tensile tests on specimens with different post-treatments identify the role played by the DCL in lowering ductility, and separate it from the role played by hydrogen embrittlement (HE) or/and corrosion surface defects. The DCL effect on embrittlement dominates HE and other corrosion-induced effects in this alloy. A peridynamic model of a structure with a pit with various damage distributions through the surface damage layer reveals that this layer produces a structure with lower ductility. Remarkably, the model shows that the largest embrittlement occurs when the damage layer is seamlessly bonded to the bulk, which is what is observed experimentally in the case of the DCL.