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.

► Co-aluminide rich Al-alloys were fabricated (arc melting, casting, and free sintering). ► Fabrication method, microstructure and corrosion behaviour are strongly interrelated. ► Arc melting under argon leads to the best corrosion performance. ► Polarization behaviour and high resistance to localized corrosion are clarified. ► The very good corrosion behaviour of cobalt aluminides is demonstrated.