Influences of Chloride on Microstructure and Corrosion Behaviour of Al-Mg-Si alloys in neutral solution

The influences of Cl- concentration on the corrosion behaviour of Al-Mg-Si alloy were studied by using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electrochemical analysis. The results show that the microstructures primarily consist of precipitate free zone (PFZ), largesize MgSi-riched dispersed phase and beta' precipitates. The corrosion type and corrosion behaviour of Al-Mg-Si are greatly affecting by Cl- concentration. With the increase in Cl- concentration, the open circuit potential (OCP) and corrosion resistance of the alloy decrease. In 1.0 wt. % NaCl solution, slight pitting corrosion occurs around MgSi phase. In 3.5 wt. % NaCl solution, obvious intergranular corrosion (IGC) and hemispherical pitting corrosion appear. In 5.5 wt. % NaCl solution, corrosion kinetic of the Al-Mg-Si alloy are significantly enhanced, making it susceptible to severe overall corrosion. High concentration of Cl- leads to rapid dissolution of the passivation film and serious corrosion.