Corrosion of the WC-12Co and enamel coatings in liquid Zn-55Al alloy at 640 °C

•Enamel coating provides higher corrosion resistance than WC-12Co coating.•Co-Zn solid solution forms firstly at the corrosion front of the WC-12Co coating.•Dissolution of Co-Al, Co-Zn phase and decarburization of WC degrade WC-12Co.•γ-Al2O3 grows on enamel coating can delay Ca dissolution and form CaAl4O7.•CaAl4O7 interlayer prevents Al permeation and provides high corrosion resistance. Corrosion behavior of the WC-12Co and enamel coatings in liquid Zn-55Al alloy is investigated comparatively. Serious corrosion consumes over 40 μm of the WC-12Co coating after 100 h immersion. Co dissolution occurs firstly by forming Zn-Co solid solution and then intermetallic compounds. WC is decarburized and reacts with Al to form WAl5 at high temperature. The enamel coating suffers quite slight corrosion. Porous γ-Al2O3 layer develops at surface, which then reacts with the enamel to form a continuous CaAl4O7 interlayer that prevents the further invasion of Al and provides the high corrosion resistance.