Effect of impurity elements on the corrosion behavior of Mg-Al alloys: A first principles study

Abstract

Magnesium-aluminum (Mg-Al) alloys are promising lightweight materials but are prone to severe corrosion induced by trace impurities (Fe, Ni, Cu) even at ppm levels. This study systematically investigated the corrosion mechanisms of impurity-containing second phases in Mg-Al alloys using first-principles calculations. The work functions and surface energies of impurity-induced phases (Bcc(Al,Fe), Al₁₃Fe₄, Mg₂Ni, Mg₂Cu) and common phases (Mg₁₇Al₁₂, Al₈Mn₅, Al₁₁Mn₄) were calculated. Results reveal that all impurity phases exhibit higher average work functions (Φ) than α-Mg, acting as cathodic sites to drive micro-galvanic corrosion. The maximum work function hierarchy follows: Bcc(Al,Fe) > Al₈Mn₅ > Mg₂Ni > Mg₁₇Al₁₂> Mg₂Cu. Mn substitution in Fe-containing phases reduces their cathodic activity by lowering work function disparities. Notably, the corrosion effect of impurities may also be affected by the inversion of electrochemical nobility. This study establishes a direct correlation between electronic work function differences and corrosion susceptibility, providing atomic-scale insights for designing high-purity Mg-Al alloys through impurity control strategies.