The corrosion behaviour of a recently developed Al-Li-Cu-Mg alloy thick plate was investigated using correlative immersion testing in 3.5% NaCl solution with analytical electron and ion microscopy. Intergranular corrosion was observed along grain boundaries and the particle-matrix interface of Al7Cu2(Fe, Mn) and Al20Cu2Mn3 phases from 7 min of immersion. The Li-containing Al7Cu2(Fe, Mn) phases are electrochemically more active and susceptible to de-alloying than the Al20Cu2Mn3 phases. Intergranular T1 (Al2CuLi) precipitates are attacked via selective dissolution of Li and Al. In contrast to previous observation, the dissolution rates of T1 precipitates and the adjacent alloy matrix are almost the same. •Clusters of Al7Cu2(Fe, Mn) phase act as preferred sites for corrosion initiation.•The Li-containing Al7Cu2(Fe, Mn) phases are more active than Al20Cu2Mn3 phases.•Corrosion along the particle-matrix interface is facilitated by galvanic coupling.•Intermetallic particles are de-alloyed via selective dissolution of Li and Al.•T1 (Al2CuLi) phases are dissolved at a similar rate as the adjacent alloy matrix.