Abstract
The effect of heat treatments on the SCC susceptibility of Al-Zn-Mg alloy in 0.6N NaCl solution was investigated by the potentiostatic SSRT (Slow Strain Rate Technique) in connection with its polarization behavior. Solutiontreated, peak-aged and over-aged specimens were tested, and the potential of these specimens was regulated in the region of pitting corrosion, unstable passivity and stable passivity respectively, which were found from their polarization curves in 0.6N NaCl solution at 298K. And the fracture surface of specimen was observed by a scanning electron microscope (SEM).At the pitting potential, all these specimens fracture transgranularly at first, being followed by intergranular cracking inside of the specimen. Transgranular cracking is considered as the crack induced by pitting corrosion, and intergranular cracking as the rupture-growth of the oxide film on grain boundaries. The fracture ratio of intergranular cracking to dimple pattern for over-aged specimen is smaller than that of solution-treated specimen. It is explained from the viewpoint of the growth of oxide film.
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