Corrosion-resistant magnesium alloy design based on the first-principles calculation

Second phase strengthening has been widely used in alloys designs, many of which however have been reported to enhance the galvanic corrosion of magnesium alloys. In this study, a semi-empirical model was proposed based on the first principles calculation to analyze the galvanic corrosion behaviour. Our model is validated in the case of Mg-Ge alloys, which is composed of anode Mg matrix and cathode Mg₂Ge second phase. First principles calculations on the 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 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 provides a promising perspective for designing better corrosion-resistant magnesium alloys.