Abstract

PEO film growth exhibits a preference for the matrix over IMPs. • IMP-associated defects compromise PEO film integrity and thus its corrosion resistance. • Alkaline etching pretreatment benefits the corrosion resistance of PEO film. Third-generation Al–Cu–Li alloys exhibit high specific strength but suffer from high corrosion susceptibility. While plasma electrolytic oxidation (PEO) films provide corrosion protection for Al–Cu–Li alloys, their barrier integrity may be compromised by coarse intermetallic particles (IMPs). Based on quasi-in-situ high-resolution electron microscopy and electrochemical analysis, the present study reveals that IMPs are selectively excluded during the PEO process. This exclusion leads to the local films with compromised thickness and compactness, with the degradation further exacerbated by Cu redistribution, which, consequently, results in reduced corrosion resistance. To address these issues, alkaline etching pretreatment was proposed, effectively reducing the surface density of IMPs and thus significantly restoring the initial barrier integrity and enhancing the corrosion resistance of the resulting PEO film. Specifically, compared to the polished state, the corrosion current density of the PEO film on the etched substrate decreases by ∼3.5-fold (from 1.13 × 10 −7 A/cm 2 to 3.29 × 10 −8 A/cm 2 ), while the total impedance increases by an order of magnitude (from 1.48 × 10 5 Ω·cm 2 to 1.51 × 10 6 Ω·cm 2 ). Download: Download high-res image (164KB) Download: Download full-size image