Localized corrosion in AA2024-T351 aluminium alloy: Transition from intergranular corrosion to crystallographic pitting

The relationship between intergranular corrosion and crystallographic pitting in AA2024-T351 aluminium alloy during immersion in 3.5 wt.% NaCl solution is investigated. It is found that intergranular corrosion occurs first and crystallographic pitting initiates from the crevice wall behind the intergranular corrosion front. Propagating away from the grain boundaries, crystallographic pitting develops into selected grain interior. Due to copper enrichment along the pit walls, the crystallographic pits in the AA2024 alloy are characterized with relatively irregular pit walls on a much finer dimension compared to the well-defined half-cube shape crystallographic pits in pure aluminium.