Introduction

Abstract

A heterogeneous microstructure is intentionally developed in 2A97-T3 aluminium–copper–lithium alloy during solidification and thermomechanical processes to obtain good mechanical properties. As a consequence, the alloy is susceptible to localized corrosion. Electron microscopy was employed to observe intermetallic particles and their periphery and the initiation and development of intermetallic particle induced localized corrosion in 2A97-T3 aluminium–copper–lithium alloy. In-situ optical microscopy monitoring, energy dispersive X-ray spectroscopy and electron backscatter diffraction were also used to provide supportive evidence. Compared with the small number of continuous localized corrosion events, discontinuous localized corrosion event is relatively common. They are associated with corroded Al2Cu IM particles and Al–Cu–Fe–Mn-(Si) IM particles, as well as corrosion pits that are formed by particle fall-out due to dissolution of surrounding aluminium matrix. Discontinuous localized corrosion is confined within the shallow near-surface region of aluminium matrix. Triggered immediately after immersion, hydrogen gas evolution developed in form of bubbling at a continuous localized corrosion site which is associated with severe surface etching and sub-surface attack. Intergranular corrosion initiated from the corrosion pit bottom, connects to the corrosion pit via small openings, and developed into the large network buried underneath the alloy surface. T1 phase precipitate remnant and corroded IM particles at grain boundary induced dissolution in the periphery of the particle, drive intergranular corrosion to propagate. Copper is much less oxidized than aluminium and lithium during grain boundary attack, and therefore accumulated at the corrosion product – aluminium matrix interface in the intergranular corrosion filament. Then, the copper enrichment band acts as further local cathode to support reduction reactions.