Characterization of Rust Layers Formed on Al-Bearing Steels Exposed to Coastal Environments

Al-bearing steels showed high corrosion resistance into coastal environments. The layer of the rusts containing Al was formed on the surface of those alloys after long periods of exposure to the coastal environments, and it was suggested that the Al plays an important role in the corrosion resistivity. In this work, we applied X-ray diffraction, electron microscopy, Raman scattering and X-ray absorption near edge structure measurements for investigating the state of Al in the rust layer. It was found that the increase in the Al content of those alloys increased amorphous and goethite type iron oxide in the rust. The Al-K XANES spectra indicated that the Al substituted goethite, α-Fe1-xAlxOOH, formed on those alloys. This action of Al has an effect on the properties of rust and serves to increase the protective ability of rust layer.