Electrochemical study on stress corrosion cracking of Al-Zn-Mg alloy

Abstract

The SCC of an Al-Zn-Mg alloy in 0.6N NaCl solution was studied by the potentiostatic SSRT (Slow Strain Rate Technique) in connection with its polarization behavior. The potential of the specimen was regulated in regions of pitting potential, unstable passive potential, and stable passive potential, which were predetermined from the polarization curve of the alloy in the same solution at 298K. The fracture surface of the specimen was observed by SEM (Scanning Electron Microscope), and the mechanism of SCC of the alloy was discussed. At the pitting potential, transgranular cracking initiates at the surface of the specimen, being followed by intergranular cracking inside of the specimen. And finally the specimen fractures mechanically, forming dimple pattern. At the passive potential, intergranular cracking occures at first. Dimple pattern is also in this case observed inside of the specimen. The transgranular cracking is considered as crack induced by pitting corrosion, and the intergranular cracking as rupture of the oxide film on grain boundaries.