First-principles study of work functions and micro-galvanic corrosion between Mg and Mg–Dy intermetallics

Abstract The rare earth element Dy, as an alloying element, is applied in the preparation of binary magnesium alloys and has a positive impact on the corrosion resistance and mechanical properties of magnesium alloys. However, during the solidification process of Mg–Dy alloys, second phases with different electrochemical potentials from the magnesium matrix precipitate, significantly affecting the localized corrosion of the alloy. To reveal the causes of micro-galvanic corrosion in Mg–Dy alloys, this study, based on first-principles calculations using density functional theory, calculates the work functions of different crystal planes of four second phases (Mg 1 Dy 1 , Mg 2 Dy, Mg 3 Dy, and Mg 24 Dy 5 ) in Mg–Dy alloys, and analyzes the results at the electronic level. Meanwhile, the focus was placed on comparing the work functions between the second phases and the matrix phase to determine their roles in micro-galvanic corrosion. The intrinsic potential differences between these four second phases and the magnesium matrix were determined. In addition, to verify the accuracy of the simulation results, Mg–Dy alloy samples—Sample 1 (mainly containing Mg 3 Dy) and Sample 2 (mainly containing Mg 24 Dy 5 )—were prepared, and electrochemical experiments were conducted. The calculation results indicate that the work function values of the different terminating planes of the four intermetallic phases (Mg 1 Dy 1 , Mg 2 Dy, Mg 3 Dy, and Mg 24 Dy 5 ) in Mg–Dy binary alloys are all greater than the electronic work function of the magnesium matrix, suggesting that these phases act as the anodic phases in micro-galvanic corrosion and are preferentially corroded, thereby alleviating the corrosion rate of the matrix. The experimental results showed that, compared to Sample 1 (Mg 3 Dy), Sample 2 (Mg 24 Dy 5 ) exhibited better corrosion resistance, which was consistent with the results obtained from computational analysis. This study also found that the work functions of different exposed surfaces of different crystal planes, as well as the same crystal planes, vary, and the corrosion behavior differs accordingly. The exposure of different surfaces has a significant impact on the intrinsic potential difference. These first-principles based electronic-level explanations provide insights into the micro-galvanic corrosion mechanisms of Mg–Dy alloys and offer theoretical guidance for the design and research of corrosion resistant magnesium based alloys.