A mechanistic study on the passivation degradation of 5083 Al alloy exposed to seawater tidal zone

Purpose This study aims to investigate the effect of sensitization treatment on the corrosion behavior of 5083 aluminum alloy under long-term exposure in the natural seawater tidal zone and elucidate the corresponding corrosion mechanism. Design/methodology/approach Sensitized and nonsensitized AA5083 samples were exposed to the Zhoushan seawater tidal zone for two years, with their corrosion morphologies and element distribution characterized by scanning electron microscopy/energy dispersive spectroscopy, and their electrochemical properties were tested using potentiodynamic polarization and electrochemical impedance spectroscopy in 3.5 Wt.% NaCl solution. Findings Sensitization treatment and tidal zone exposure both degrade the corrosion resistance of AA5083, and their synergistic effect further aggravates the corrosion degree. Sensitized AA5083 shows more severe localized corrosion with more and deeper pits, looser corrosion product layers with more cracks after tidal zone exposure, accompanied by Mg enrichment near pitting areas due to the preferential dissolution of grain boundary β phase (Al3Mg2). Electrochemical tests reveal that sensitized samples have more negative corrosion potential, higher self-corrosion current density and lower impedance, indicating stronger corrosion tendency and faster corrosion kinetics. The corrosion product layer formed during exposure can slightly inhibit further corrosion and increase the impedance of exposed sensitized samples compared with unexposed ones. Originality/value This study conducts long-term natural seawater tidal zone exposure tests on sensitized AA5083, making up for the deficiency of previous studies relying on laboratory simulation or nonsensitized samples, and the results provide important theoretical and engineering references for the corrosion protection of AA5083 marine structures considering sensitization factors.