Study on localized corrosion mechanism of 2195 Al-Li alloy in 4.0% NaCl solution (pH 6.5) using a three-electrode coupling system Localized corrosion morphologies of 2195 Al-Li alloy with various heat treatment in 4.0% NaCl solution (pH 6.5) were investigated, and its corrosion mechanism was studied using a three-electrode coupling system of a (Al) substituting for the precipitate-free zone (PFZ), simulated bulk h 0 (Al 2 Cu) and T1 (Al 2 CuLi). h 0 acts as cathodic zone in the alloy. At the initial stage, T1 phase is active with respect to h 0 and a (Al), and endures the main anodic current, indicating that anodic dissolution occurs on T1. However, its potential moves to positive direction with immersion time, due to dealloying of Li from T1. As a result, the main anodic dissolution occurs on a (Al) at a later stage. At this stage, as only T1 and a (Al) are coupled, T1 is cathodic to a (Al). In real 2195 alloy, T1 phase is very tiny, and anodic dissolution of T1 and PFZ occurs alternately. These results show that its intergranular corrosion or intersubgranular corrosion is caused by alternate anodic dissolution of T1 phase and PFZ along grain and subgrain boundaries.

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Ni‐Si3N4 nanocomposite films with both the consecutive Ni crystallites and dispersed Si3N4 particles in the nanometer range have been fabricated using DC electroplating technique, and characterized by scanning electron microscopy (SEM), transmission electron microscope (TEM), and X‐ray diffraction (XRD). The corrosion resistance of the Ni‐Si3N4 nanocomposite film has been compared to that of pure Ni coating through polarization. Meanwhile, the corrosion process of Ni‐Si3N4 nanocomposite film in neutral 3.5% NaCl solution has been investigated using electrochemical impedance spectroscopy (EIS). The results show that the Ni‐Si3N4 nanocomposite film is more resistant to corrosion than the pure Ni coating. The corrosion of Ni‐Si3N4 nanocomposite film is controlled by electrochemical step, and the whole corrosion process is divided into two sequential stages. The main corrosion type of Ni‐Si3N4 nanocomposite films in neutral 3.5% NaCl solution is pitting.

A Cr(III) contained conversion coating on AA2024-T3 was prepared in solution containing Cr 2 (SO 4 ) 3 and K 2 ZrF 6 . Its composition was analysed using X-ray photoelectron spectroscopy, and its corrosion resistance was characterised by electrochemical measurements and neutral salt spray exposure. To investigate its self-repairing effect, the coupling current between a small uncoated sample and a large coated sample was monitored through an artificial scratch cell. The coating mainly consists of zirconium oxide and chromium oxide and hydroxide; no Cr(VI) species is detected. It improves the corrosion resistance by hindering the anodic process as well as the cathodic process. Meanwhile, it possesses self-repairing effect, which is generated from the release of Cr(III) species from the coating, migration and then deposition on the nearby scratch area.

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