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The stress corrosion cracking (SCC) susceptibility of 7A04 high strength aluminum alloy in 3.5% (mass fraction) NaCl solution and the Ce3+ inhibition of SCC were investigated by slow stress rate test(SSRT), using constant current polarization, electrochemical noise (ECN) and electrochemical impedance spectroscopy (EIS) techniques. The inhibition mechanism of Ce3+ ions on the initiation and propagation of cracking was also analyzed. The results indicate that both anodic and cathodic galvanostatic polarizations can accelerate the SCC of 7A04, the former increases anodic dissolution but the latter accelerates hydrogen embrittlement of crack tip. SCC susceptibility of 7A04 can be reduced effectively by the addition of cerium ions, the fracture time is delayed and slowed down, but only during the initiation other than the propagation stage of cracking. Ce3+ ions can restrain the initiation of metastable pitting on the surface of 7A04 specimen, which therefore increase the induction time of the cracking since that the micro pits are usually the source of cracking.However, once the crack begins to propagate or the specimen is notched, the addition of cerium ions can rarely inhibit the cracking process. This is possibly attributed to that the radius of Ce3+ ion is too large to diffuse into the crack tip or it is hard to form protective CeO2 layer, Ce3+ ion therefore fails to rehabilitate the active alloy at the crack tip and further reduce the SCC developing rate of 7A04. SEM also indicates that the crack initiation of smooth 7A04 specimens is mainly induced by metastable or stable pits.

The corrosion behavior of X65 carbon steel under different deposits in CO2 saturated formation water was studied by weight loss measurements, electrochemical measurements, wire beam electrode and microscopic analysis. The results show that the corrosion rate of the steel slightly decreases by being covered with sand, clay or ferrous carbonate. However, covered with ferrous sulfide, elemental sulfur or mixture, the corrosion rate obviously accelerates, especially in the specimen covered with elemental sulfur. The corrosion rate of the specimen covered with mixture deposits also significantly increases, in which elemental sulfur plays a dominant role. The significant increase in corrosion rate of the specimen covered with elemental sulfur is attributed to the self-catalytic action of elemental sulfur on the cathodic reaction of steel corrosion. The current and potential distributions of wire beam electrodes indicate that the potentials of the electrodes covered with mixture deposits are more positive than those without deposits. During the corrosion, severe localized corrosion occurs on the electrodes under mixture deposits. The current and potential maps of wire beam electrodes can effectively reflect the localized corrosion behavior of the steel under deposits due to the change of local environment.

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