Characterisation of oxide films formed on Co-29Cr-6Mo alloy used in die-casting moulds for aluminium

Oxide films formed at 700 °C on Co-29Cr-6Mo alloy were characterised extensively to improve the corrosion resistance of the alloy to liquid Al, enabling its use in Al die-casting moulds. Film of duplex layer consisting of an outer CoO-rich layer and an inner Cr2O3-rich layer was observed in samples subjected to oxidation for 4 h. With an increase in duration of oxidation, CoO was gradually replaced by Cr2O3, resulting in a single-layered oxide film dominantly composed of Cr2O3. The oxide film evolved with duration of oxidation treatment indicating the possibility of optimising films for Al die-casting moulds.