Microstructure and corrosion performance of Al-32%Co alloys

Al-32 (wt%)Co alloys have been prepared by casting, arc melting under argon and free sintering. The received microstructures have been explained in terms of solidification sequences and solid state diffusion processes. Corrosion experiments in 3.5% NaCl at 25 °C showed that the alloys exhibit high resistance to localized corrosion regardless of the preparation method. Nevertheless, the preparation method strongly influences the obtained microstructure and, consequently, the corrosion behaviour. The latter is controlled by competing processes taking place simultaneously, such as active dissolution and pitting of the (Al) phase, passivation of the adjacent Al9Co2 and pseudopassivation of (Al) induced by interaction with its adjacent intermetallic phase. The positive effect of the intermetallic phases on the corrosion performance of the alloys is noted.