Synergistic effect of Cu and Si on hot-dipping galvalume coating

The coating microstructures and thicknesses of the iron panels galvanized in galvalume baths containing 0.0, 0.1, 0.5 and 1.0 wt.%Cu for 10 s, 30 s, 60 s, 180 s, 300 s and 600 s have been studied detailedly. The results indicate that Cu can effectively control the Fe–Al reactivity by the synergistic effect with Si. The addition of Cu makes Si be enriched in the reaction region during the hot-dipping. It promotes the formation of the τ5 phase and hinders the growth of the Fe2Al5 phase. The diffusion path model was introduced to studying the effects of Cu and Si in the present study. The addition of 0.5–1.0 wt.%Cu in galvalume bath forms a stable diffusion path, iron substrate/Fe2Al5/FeAl3/τ5/overlay. The violent reaction between the iron substrate and the Al–Zn liquid is under control by the compact intermetallic layer, and it decreases the thickness of the intermetallic layer.