Effects of aging treatment on the intergranular corrosion behavior of Al–Cu–Mg–Ag alloy

Highlights: • Corrosion resistance of Al–Cu–Mg–Ag alloy follows: under-aged > peak-aged > over-aged. • The simulated matrix, θ (Al₂Cu), and the precipitations free zones (PFZ) were prepared. • The self-corrosion potentials satisfy E_Matrix > E_θ > E_PFZ. • The wider PFZ is adverse to the corrosion resistance of Al–Cu–Mg–Ag alloy. - Abstract: The effects of aging treatment on the corrosion behavior of Al–Cu–Mg–Ag alloy were studied by means of intergranular corrosion (IGC) testing, potentiodynamic polarization combined with optical microscopy (OM) and transmission electron microscopy (TEM). Corrosion testing results suggest that, the intergranular corrosion resistance properties of Al–Cu–Mg–Ag alloy decreased with increasing aging time, which is also corroborated by the potentiodynamic polarization test results for under-aged, peak-aged and the over-aged Al–Cu–Mg–Ag alloys. TEM results reveal that precipitations on the grain boundary became coarsened and distributed discontinuously with increasing aging time; widening of precipitation free zones (PFZ) is also observed. The PFZ with the lowest self-corrosion potential is preferentially attacked, and corrosion progresses along the PFZ. The corrosion resistance of over-aged Al–Cu–Mg–Ag alloy decreased because of its wider PFZ in comparison with those in other samples