Localized corrosion of 6056 T6 aluminium alloy in chloride media

The corrosion behaviour of 6056 T6 aluminium alloy was investigated in 1 M NaCl solution. Pitting and intergranular corrosion were found to be dependent on each other since intergranular corrosion nucleated on pit walls and spread from them. Coarse intermetallic Al–Si–Mg-containing particles were found to be nucleation sites for pits. Pits first developed within the grains and grew up through microscopic crystallographic tunnels. The intergranular corrosion mechanism of 6056 T6 alloy appeared to consist of preferential dissolution of the anodic Si and Cu depleted zone along grain boundaries whereas Cu–Si–Mg rich intergranular precipitates functioned as local cathodes and stimulated the dissolution of the depleted zone.