Analyzing Galvanic Corrosion Behavior of Metal Alloys Based on First-Principles Simulations

Abstract

Galvanic corrosion behaviors of alloys have usually been investigated through experiments, where the measured polarization curves, the corrosion potential and current could differ a lot between different literature. Herein, we proposed a semi-empirical model based on the mixed potential theory and first principles calculation to analyze the galvanic corrosion of the metal alloys. Our model is further validated in the case of Mg-Ge alloys, which is composed of anode Mg matrix and cathode Mg2Ge second phase. The combination of the large anode equilibrium potential difference between Mg and Mg2Ge, and the Schottky barrier across the interface indicates that the Mg2Ge second phase can prevent the Mg grain from serving as the cathode and impede the electron transfer between the Mg grains. First principles calculations on the kinetics of hydrogen evolution reaction upon Mg2Ge reveal that the rate-determining step is the hydrogen adsorption, which is extremely energetically unfavored but an inevitable intermediate state. The estimated exchange current of the hydrogen evolution upon Mg2Ge is about 3 orders of magnitude smaller than that on pure Mg, indicating the depressed galvanic corrosion of the Mg-Ge alloys is also the result of the low hydrogen exchange current upon Mg2Ge. Moreover, some typical intermetallics, such as MgZn2 and MgSc, were selected to compare the corrosion properties of different Mg alloys, which is in close agreement with the experimental observations. Our model to predict the galvanic corrosion behavior provides a promising perspective for designing better corrosion-resistant metal alloys.