This study demonstrates that galvanically coupling AA2024-T3 and AA7075-T6 affects localized corrosion even with the alloys’ comparable electrochemical behaviour. In situ reflected light microscopy tracked corrosion initiation and trench propagation, while zero resistance ammeter measurements quantified galvanic current density and potential. This combined approach allowed direct correlation between electrochemical signals and optically detectable surface phenomena. Galvanic coupling increased cathodic activity at AA2024-T3 intermetallic particles (IMPs) and caused the surrounding matrix to dissolve more extensively beyond the trench that formed around the particles. Local activity analysis revealed initial IMP dealloying was unaffected by galvanic coupling. However, lateral growth of trenches in both alloys was accelerated under coupling compared with electrically-isolated conditions. Correlation of optical activity with electrochemical measurements showed that trends and fluctuations in galvanic current and potential reflect different stages of local corrosion, facilitating the morphological and physicochemical interpretation of the electrochemical data.

The stability of inhibiting layers on AA2024-T3 intermetallic particles (IMPs) during re-immersion in saline following an initial immersion in a Ce(III)-containing electrolyte was investigated using in situ reflected light microscopy. Re-immersion behaviour varied due to differences in IMP composition, spatial distribution, and Ce(III) precipitation. IMPs were grouped into four categories based on whether their activity was high or low during both the immersion and re-immersion stages. Majority of the high activity particles during re-immersion had low activity during immersion. Longer immersion times (up to 72 h) and a brief delay in inhibitor supply (30 s) reduced re-immersion activity by increasing Ce(III) coverage. These findings suggest that corrosion protection systems promoting greater Ce(III) precipitation may enhance re-immersion stability.

Streaking corrosion (SC) of AA7075-T6, characterized by the rapid dissolution of an altered surface layer (ASL) formed through mechanical surface treatments, is investigated. Utilizing in situ high-resolution reflected light microscopy, we reveal that SC initiates preferentially on intermetallic particles (IMP) or pre-existing pits. Optical evidence of galvanic interactions between propagating streaks and connected IMPs is observed. Concurrent in situ open circuit potential (OCP) measurements show a characteristic pattern that correlate with SC initiation, progression, and termination. This work demonstrates the effectiveness of a simple in situ optical-electrochemical setup in tracking dynamic local corrosion processes and directly linking OCP transients to specific corrosion events.

Understanding how late an inhibitor can be released once corrosion initiated without compromising corrosion protection may help in developing more efficient anticorrosion coatings. We explored this idea through time-controlled Ce(NO₃)₃ availability to AA2024-T3 immersed in 0.05 M NaCl. Ce(NO₃)₃ was supplied at 0, 30, 60, and 180 s from the start of immersion to get a concentration of 0.001 M. Detailed visualization of surface changes at the intermetallic particle level was obtained using in-situ reflected microscopy. SEM-EDX and confocal laser microscopy confirmed the extent of intermetallic degradation and local inhibitor deposition corresponding to operando changes. When the inhibitor is supplied within 60 s of immersion, the surface changes slowdown earlier and are visually less extensive than in uninhibited systems. Furthermore, our results highlight the potential of reflected microscopy for local corrosion inhibition studies and underscore the importance of understanding the interaction between inhibitor release timing and corrosion protection.