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

Highlights: • 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.