Growth and corrosion behavior of rare earth film on hot-dip galvanized steel

Hot-dip galvanized(HDG) steel sheets were treated for 30 s-24 h by the rare earth aqueous solution containing 20 g/L Ce(NO3)3·6H2O, and the growth behavior and corrosion resistance of the rare earth film were investigated by SEM, EDS, AES and NSS. The results reveal that the rare earth film becomes thick while the mass gain of the samples does not distinctly change due to the zinc dissolution with the increase of treatment time. The film grows up more quickly and is apt to cracking in the vicinity of zinc grain boundaries, and eventually the film partly warps and flakes off with increasing film thickness. The NSS results show that the corrosion resistance of the film is dominated by both the film thickness and the cracks. With increasing treatment time, the corrosion resistance of the film increases within 1 h due to the increased film thickness and decreases after 1 h because the cracking and flaking off gradually become dominant factor.