Transition of atmospheric corrosion behavior and mechanism of Q420 weathering steel on the Sichuan-Tibet Plateau: critical elevation effect

Extreme environmental conditions on the Sichuan-Tibet Plateau, particularly intense radiation and temperature fluctuations, pose significant challenges to authentic corrosion monitoring. To address this, this study proposes a comprehensive strategy combining Fe-Ti dual-element resistance sensing with survival analysis. Continuous thickness loss rate data for Q420 weathering steel were acquired spanning the entire elevation gradient of the plateau by eliminating temperature interference. On this basis, the Mantel test was employed to analyze environmental characteristics, and a survival analysis model was constructed using a 5% thickness loss as the failure criterion. It was identified that temperature, temperature difference, time of wetness, and PM 10 are primary risk factors, whereas elevation functions as a significant protective factor. Notably, the survival curves separate clearly around 3000 m, indicating a critical elevation effect in atmospheric corrosion. Microscopic characterization confirms the underlying mechanism driving this transition. Below 3000 m, the rust layer is thick, porous, and dominated by γ-FeOOH. In contrast, the layer transforms into a thin and dense structure dominated by α-FeOOH above this threshold, which exhibits significantly enhanced protective performance. These findings provide a scientific basis for differentiated corrosion protection design for engineering projects on the plateau.