In-situ construction of RE conversion coating on Mn surface and comparison of chain corrosion blocking mechanism

Abstract Different from the simple first-order oxidation behavior of other metal, Mn is prone to complex chain corrosion reaction due to its own polyvalence and Mn2+ instability. In this paper, it is found that rare earth salts can be constructed in situ on the electrolytic manganese surface to obtain a composite RE conversion coating with RE3+ and Mn2+ coexisting. The coating can improve the stability of Mn2+, effectively inhibit the bad transformation of Mn2+ to higher valence Mn3+/Mn4+, thereby blocking the chain corrosion reaction. Both La and Y conversion coating have good corrosion resistance, stability, corrosion resistance strength and durability, and their icorr are 1.638 × 10−6 A/cm2 and 2.750 × 10−6 A/cm2, which are reduced by two orders of magnitude. Although the coating performance is not much different, the formation and corrosion process are quite different due to the differences in the RE properties. The comparison of chain corrosion blocking mechanism of electrolytic manganese is of great significance not only to the passivation technology, but also to the application of RE salts in metal passivation.