Metallurgical Insights into the Sensitization of Al-Mg Alloy Structural Components in High-Speed Vessels: A Field Study

The sensitization behavior of Al-Mg alloys (AA 5xxx series) used in marine vessel structures was investigated through a comprehensive combination of analytical techniques. Exclusively field-retrieved samples of a special marine-grade AA 5xxx and conventional AA 5086 after prolonged exposure (>20 y) in an operational environment were examined. Scanning electron microscopy was used for microstructural characterization, while the alloy’s susceptibility to intergranular corrosion (IGC) was evaluated as per ASTM G67-18. It is critical to note that the present research incorporated external environmental and operational variables that influence the sensitization kinetics in ship structures, enabling an assessment of their relative importance. Results indicate that sensitization progression is strongly dependent on each vessel’s operational and maintenance history, leading to distinct evolution patterns even among vessels of the same class. The transformation kinetics of Mg-rich phases were found to be highly sensitive to local environmental conditions, with samples exhibiting comparable degrees of sensitization displaying notably different microstructural morphologies. These findings underscore the need for an integrated evaluation framework that combines environmental exposure, operational history, and microstructural analysis to more accurately predict the sensitization behavior of marine Al-Mg alloys.