Insights on the Al-Cu-Fe-Mn intermetallic particles induced pitting corrosion of Al-Cu-Li alloy

The pitting corrosion and surface modifications of aluminium alloy AA2050-T8 (Al-Cu-Li) resulting from immersion in 0.1 M NaCl at open circuit potential were studied by time-of-flight secondary ion mass spectrometry (ToF-SIMS). ToF-SIMS chemical mapping showed a local distribution of chlorides and hydroxides in the pits enriched in Cu and Fe. Preferential sites of corrosion initiation were evidenced in the alloy matrix close to Al-Fe-Cu-Mn intermetallic particle. A formation of an oxide-hydroxide layer with different composition and/or higher thickness was evidenced over IMP than the alloy matrix. LiO dissolved from the oxide layer but metallic lithium was still present in the matrix.