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AA7075 alloys susceptibility to exfoliation corrosion is related to distribution and size of precipitate within grain boundary, continuity within grain boundary and electrochemical behaviour. Distribution and size of precipitate in the grain also effects the conductivity of the material. The effect of different temperatures and time periods of RRA temper on exfoliation corrosion of AA7075 alloy is examined in this study. Exfoliation corrosion (EXCO) solution was prepared in accordance with ASTM G34-97 standard and the samples were kept in the solution for 48 h. After the samples were processed in the solution, the susceptibility of the alloy to exfoliation corrosion, its electrical conductivity and pH values of the solution were determined using microstructure scanning. It was determined that exfoliation corrosion resistance value and electrical conductivity changed in relation to chosen temperature and time of RRA temper.

Significantly changed intergranular corrosion (IGC) and exfoliation corrosion (EFC) behaviors of the equal-channel-angular-pressed (ECAPed) Al–Cu alloy were discovered through immersion test, electrochemical measurements, and microstructure observation. The ECAPed alloys with ultra-fine grained (UFG) α(Al) matrix and extremely refined θ-phase particles displayed obvious decreased IGC sensitivity, but deteriorated susceptibility to EFC. The decreased IGC sensitivity of ECAPed alloys presented decreased IGC propagation depths in immersion test in NaCl + H2O2 solutions and increased polarization resistance in electrochemical impedance spectrum test in MIL-H-600 solution. The reason for the decreased IGC sensitivity was the breakage of the net structure of θ phase during ECAP process, which destroys the continuity of IGC propagation channel. The deteriorated susceptibility to EFC of ECAPed alloys in EXCO solution presented gradual evolution from serious IGC attack into obvious lamellar EFC, and finally complete dissolution of surface grains. Meanwhile, the EFC propagation depths were sharply decreased with the increasing ECAP passes. This phenomenon was caused by the aspects ratio evolution of deformed grains and the gradually decreased IGC sensitivity of the ECAPed alloys.

Corrosion behaviour of different tempers (namely NA, UA, PA and OA) of AlZnMgCuZrSc alloy was studied by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), optical microscopy (OM) and transmission electron microscopy (TEM). Over aged (OA) can decrease the susceptibility to exfoliation due to the discontinuous distribution of the η precipitates at the grain boundaries, cause a negative shift of the corrosion potential (Ecorr), and lead to the prolonging of the time of the appearance of two time constants in impedance diagrams. In addition, AlZnMgCuZrSc alloy with over aged treatment has an enhanced resistance to exfoliation corrosion.

The exfoliation corrosion behavior of an Al–Zn–Mg–Cu–Zr alloy containing Sc artificially aged at 120 °C for 24 h is studied by macroscopic observation techniques and electrochemical impedance spectroscopy (EIS) measurements. After 48 h immersion, the blisters start bursting and delamination initiates, along with the appearance of two time constants in the impedance diagrams. According to the simulation by equivalent circuit, the corrosion rate decreases sharply and then reaches a steady state, which is due to the change of the solution pH and oxide layer thickness, as well as the accumulation of corrosion products.