Numerical study on the micro-galvanic corrosion of AZ31 magnesium alloy

In combination with a moving mesh technique and a level set function, the corrosion behavior of AZ31 magnesium alloy with a continuous β phase network and the discrete β phase around the a phase in a sodium chloride solution was investigated by finite element method. The distributions of potential and the concentrations of chloride ions and magnesium ions on the interface of magnesium/chloride solution during the corrosion progress were obtained by solving the Nernst-Planck function. The feasibility of this simulation method was validated with scanning ion-selective electrode experiments. Simulation results show that when the β phase is a discrete distribution around the a phase, the corrosion rate of the a phase adjacent to the β phase is the highest, a indented corrosion pit form at this place and chloride ions are enriched, which leads to the acceleration of the corrosion rate of the a phase. Finally, the β phase is removed from the alloy into the solution. However, when the β phase is a continuous distribution around the a phase, the solving process tends to be halted after the a phase is totally dissolved and only the continuous β phase is exposed to the chloride solution. Results of scanning ion-selective electrode experiments indicate that this simulation method can predict the electrochemical corrosion of magnesium alloys well.