Effects of chromium addition on corrosion resistance of Fe-3.5B alloy in liquid zinc

The effects of chromium addition on the corrosion resistance of Fe-3.5B alloy in liquid zinc bath at 520°C have been investigated. The results show that the matrix of as-cast Fe-3.5B alloy transforms into α-(Fe, Cr) solid solution while the eutectic Fe₂B changes into M₂B-type boride gradually with the increasing chromium addition. The corrosion resistance of Fe-3.5B alloy can be greatly enhanced by 5wt.% chromium addition that still maintains the netlike structure of boride in it. EDX analysis reveals that the Cr element can enrich in the Γ-Fe₃Zn₁₀Cr_x (x=1.09 to 1.37) phase of the interface to hinder the diffusion of zinc atoms favorably. The Cr addition has no effect on the Vickers hardness of δ and ζ in the corrosion layer basically. Corrosion mechanism of Fe-3.5B alloys with various Cr additions includes the following processes: the superficial dissolution of Cr at the interface, dissolution of the Cr-depleted zones of the matrix corroded by liquid zinc, and the spalling of boride which lost the supporting role of the matrix completely. The corrosion process is mainly controlled by the diffusion of liquid zinc atoms.