Microstructure and corrosion behavior of cast Fe-B alloys dipped into liquid zinc bath

The corrosion behavior of cast Fe-B alloys in a liquid zinc bath was examined. As a result, the as-cast Fe-3.5B alloy displays the best corrosion resistance in all tested specimens owing to its netlike structure of eutectic Fe₂B against the liquid zinc. XRD and EDS results indicate that the main phases in the corrosion layer are determined to be δ, ζ and η from the matrix to the zinc zone, respectively. The corrosion process is controlled by the diffusion of zinc atoms and the dissolution mechanism. According to the observations, only three steps occur in the whole dissolution process: the preferential dissolution of α-Fe, the formation of intermetallic compounds, and the spalling of Fe₂B caused by cracks that mainly result from the internal stress produced by Fe/Zn phase transformation. The continuous netlike Fe₂B phase delays the further reaction of Fe/Zn and hinders the diffusion of zinc atoms between the substrate and liquid zinc effectively, improving corrosion resistance of Fe-B alloy in comparison with 1Cr18Ni9Ti stainless steel.