来源：ACS Publications
Chloride-induced film breakdown critically limits the application of rare-earth-containing magnesium alloys, yet the concentration-dependent transition from passivation to localized corrosion remains insufficiently understood. Here, the corrosion behavior of an as-cast Mg-9Gd-3Y-0.6Zn-0.5Zr alloy in 0–5.0 wt % NaCl solutions was investigated using quasi-in situ SEM, SKPFM, cross-sectional SEM/EDS, XPS, electrochemical testing, and first-principles calculations. Increasing NaCl concentration accelerated corrosion, with the icorr rising from 33.57 μA cm–2 in pure water to 1156.42 μA cm–2 in 5.0 wt % NaCl, while the interfacial resistance decreased from 3210.0 to 15.8 Ω cm2. Within the examined concentration range, a pronounced corrosion-mode transition occurred around 0.5 wt % NaCl, changing from relatively uniform dissolution with rare-earth-assisted MgO/Mg(OH)2 film repair to severe microgalvanic pitting around RE-rich second phases. XPS and cross-sectional EDS indicate that Gd/Y oxides contribute to film densification at low chloride levels but become insufficient under high chloride attack. DFT calculations further reveal that increasing Cl– coverage changes OH– adsorption from competitive to cooperative behavior, promoting nonprotective Mg–Cl–OH products. These results clarify the chloride-controlled balance between RE-assisted passivation and microgalvanic corrosion.