Influence of Heat Treatment on the Corrosion of the Al–Mg Intermetallic Alloy in Synthetic Seawater

In this study, an Al–20 wt.% Mg alloy was synthesized to systematically correlate its electrochemical behavior in synthetic seawater with the microstructural evolution induced by heat treatment at 190, 300, and 350 °C for 6 h. The samples characterized by SEM and XRD reveal a progressive morphological evolution of the β–Al3Mg2 intermetallic phase. The open circuit potential, the potentiodynamic polarization and the electrochemical impedance spectroscopy showed that this microstructural evolution increased the microgalvanic corrosion, promoting passive-film breakdown, and reducing charge-transfer resistance. The Al–20 wt.% Mg alloy treated at 350 °C exhibited the highest corrosion current density, associated with β–Al3Mg2. These results demonstrated that controlling beta-phase precipitation through heat treatment provides an effective approach to tune the electrochemical behavior of high-magnesium aluminum alloys.