Co-segregation of Sm/Dy elements regulates the degradation behavior of bio-magnesium alloys via a coral-like corrosion product film

Magnesium (Mg) alloys are highly promising biodegradable metals, but rapid chloride-induced corrosion severely limits practical applications. Although rare-earth (RE) alloying enhances corrosion resistance, the synergistic effects among different RE elements remain to be further elucidated. In this study, Mg-7Dy-0.3Zr- x Sm ( x = 0, 0.5, 1.0 and 1.5 wt.%) alloys were fabricated, and the effect of Sm addition on the synergistic interaction with Dy and the associated corrosion mechanism was investigated from the perspectives of microstructural characteristics and corrosion product film evolution. Results reveal that an appropriate Sm addition (0.5 wt.%) promotes the formation of stable Dy-Sm-enriched regions along grain boundaries and induces the development of a “coral-like” dense composite corrosion product film composed of Mg(OH) 2 , RE-containing oxide/hydroxide species, and Ca-P deposits. This film effectively suppresses Cl - penetration and reduces susceptibility to localized corrosion. In contrast, excessive Sm aggravates electrochemical heterogeneity, leading to more severe galvanic corrosion and thereby undermining the stability of the corrosion product film. This study emphasizes the critical role of Dy-Sm synergistic co-segregation in regulating the densification of corrosion product films, providing valuable guidance for compositional design strategies aimed at developing Mg alloys with high corrosion resistance.