Phase constitution and corrosion resistance of Al-Co alloys

Al-24Co, Al-25Co, Al-26Co, Al-27Co and Al-28Co alloys (composition in atomic percent) were prepared by arc-melting in high purity argon. Each alloy was found to consist of several microstructure constituents. Precipitation sequences of different intermetallic compounds were described based on a previously published Al-Co phase diagram and non-equilibrium processes taking place during casting. Electrochemical corrosion was investigated by potentiodynamic polarization in aqueous NaCl solution at room temperature. A large amount of pitting is observed, with some of the phases being preferentially corroded. The nobility of Al-Co intermetallic compounds is discussed in terms of chemical composition and crystal structure. Conclusions towards the alloy stability are provided.