Influence of ageing on corrosion behaviour of Al-Mg-Si alloys in chloride and acid media

Abstract

This paper deals with studies on corrosion behaviour of two Al-Mg-Si alloys containing excess Si in 1 (N) NaCl and 0.1 (N) inorganic acids. Intergranular corrosion and immersion tests were carried out as per standards (MIL-H-6088F, ASTM G-31). Intergranular corrosion was assessed using optical, scanning and transmission electron microscopy. The effects of isothermal and isochronal ageing on corrosion resistance in 0.1 (N) HCl and on hardness changes were studied. The studies showed that the amount of intergranular attack in NaCl solution increases with ageing time and is maximum at peak aged condition. Segregation of Si particles and Mg2Si at the grain boundary contributes to intergranular corrosion. Corrosion rate was higher in HCl than in HNO3 and H2SO4 solutions, however it was maximum in 0.1(N) HCl during its peak aged period