Inhibition of Ce3+ on Stress Corrosion Crack of High Strength Aluminum Alloy
Wen-ting LI1, Hao-wei WANG2, Jun YU1, Ze-hua DONG1,3,*(), Xing-peng GUO1
1 Hubei Key Laboratory of Materials Chemistry and Service Failure, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan 430074, China 2 AVIC Special Vehicle Research Institute, Jingmen 448000, Hubei, China 3 School of Chemical and Food Sciences, Hubei Institute of Arts, Xiangyang 433500, Hubei, China
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.
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