Corrosion mechanism of Zn–Al–Mg-coated steel in simulated polluted marine atmosphere

The corrosion behaviour of zinc–aluminium–magnesium-coated steel in a simulated polluted marine atmospheric environment was investigated. Therefore, an indoor ageing acceleration test was carefully designed by simulating a polluted marine environment. The objective was to in-depth investigate the corrosion mechanism of Zn–Al–Mg-coated steel exposed to a simulated polluted marine environment. The experiments were carried out by scanning electron microscopy for micro-morphological characterization, X-ray diffraction, electrochemical impedance spectroscopy and electrodynamic polarization curves for the aged samples. The analysis of the results obtained after an indoor accelerated ageing test shows that Zn–Al–Mg coatings generate insoluble Zn₅Cl₂(OH)₈·H₂O and Zn₄SO₄(OH)₆ during the corrosion process, which hinders the diffusion of corrosive substances into the substrate, and the insoluble substances are structurally dense and thus inhibit further corrosion. Therefore, this effectively inhibits the occurrence of further corrosion, and thus, Zn–Al–Mg coating can significantly extend the service life of Zn–Al–Mg-coated steel.