A quasi-passivated film formed on as-solutionized Mg-Sm-Zn-Zr alloy in NaCl solution

• Published in: Corrosion science Vol. 198; p. 110136
• Main Authors: Feng, Yu-Jun, Li, Qian, Zhao, Tian-Liang, Pan, Fu-Sheng
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Ltd 15.04.2022; Elsevier BV
• Subjects: Alloys; Corrosion; Corrosion currents; Corrosion potential; Corrosion resistance; Magnesium; Magnesium base alloys; Passivation; Rare earth; Samarium; Sodium chloride; Solid solution; Surface film; Thickness; Zinc; Zirconium base alloys; PBR; Ebreak; icorr; Surface film; Rare earth; Solid solution; EIS; Corrosion resistance; RE; SCE; EDS; SKP; Mg; XPS; SEM; Magnesium; UHP; TEM; PDP; OCP; FIB; OM; Passivation
• ISSN: 0010-938X; 1879-0496
• DOI: 10.1016/j.corsci.2022.110136

Benefiting from a quasi-passivated film, as-solutionized Mg-Sm-Zn-Zr alloy exhibits an extraordinary corrosion resistance over currently reported Mg alloys. The breakdown potential and corrosion current density are respectively −1.208 VSCE and 3.9 μA/cm2 after 24 h immersion in 0.6 M NaCl solution. The film consists of an outer layer, an intermediate layer and a Zn-rich layer. The oxide of solute element Sm strengthens the intermediate layer, which plays the primary role of impeding corrosion, by filling the vacancies left by the selective dissolution of Mg. An approximate linearity exists between the film resistance and the thickness of the intermediate layer. [Display omitted] •A quasi-passivated film is formed on as-solutionized Mg-Sm-Zn-Zr alloy in NaCl solution.•The tri-structure film is composed of outer, intermediate and Zn-rich inner layer.•The in-situ transformation of Sm in intermediate layer plays the critical role.•Protectiveness of the surface film is nearly linear to the thickness of the intermediate layer.•The inner Zn-rich layer is formed by a dissolution-reduction process.