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.

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.

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.