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. - Highlights: • Al–24Co to Al–28Co alloys were prepared by arc-melting in high purity argon. • Precipitation sequences of different intermetallic compounds have been observed. • Anodic alloy dissolution takes place by galvanic mechanism. • Nobility of Al–Co intermetallic compounds increases with increasing Co concentration.