On the AA2198-T851 alloy microstructure and its correlation with localized corrosion behaviour

Highlights: • The relationship between pH and formation of corrosion rings in Al alloys. • The formation of primary and secondary severe localized corrosion pits. • Similarity between corrosion propagation and slip mechanism. • Crystallographic corrosion features and morphology in AA21998-T851. • Relationship between orientation dependent striations/bands and the T1 phase. - Abstract: The corrosion behaviour of AA2198-T851 alloy has been investigated using a combination of immersion tests and different microscopy techniques. Results showed that severe localized corrosion initiated within 1 h of corrosion immersion test in 0.01 mol L⁻¹ NaCl solution. The corrosion mechanism in this alloy is intragranular and it propagates crystallographically. The propagation occurs through grain orientation dependent bands and it can be likened to the movement of dislocation through slip planes. Corrosion rings around stable pits result from pH variations. Secondary pits form around primary pits within corrosion rings and are preceded by hydrogen evolution.