H. Mizuno, S. Tawada, I. Aoki, Fujimi Incorporated, Kakamigahara, Gifu, Japan; J. Kitamura, Fujimi incorporated, Kakamigahara, Japan
We have already reported that MoB/CoCr coatings prepared by high velocity oxygen-fuel (HVOF) spraying have much higher durability in a molten Al-45%Zn alloy, which is mainly plated onto steel sheets for construction materials to increase corrosion resistance. Furthermore, it is found that coating structure is optimized by adjusting thickness of both topcoat of MoB/CoCr and undercoat of Co based alloy to avoid crack and/or peeling by thermal shock mainly generated by large difference of coefficient of thermal expansion between the MoB/CoCr coating (9×10-6/K) and a base substrate of austenitic stainless steel (19×10-6/K). From the study, we have clarified that insufficiently optimized specimens are damaged by mechanical failure of MoB/CoCr coatings, such as crack and peeling, at first and followed dissolution of the undercoat and substrate. However, this previous study is still insufficient in terms of the contents of molten alloy because Si addition into Al-45%Zn alloy is normally conducted in actual plating process to decrease viscosity of the alloy. In this study, influence of Si concentration in molten Al-45%Zn on durability of MoB/CoCr coatings has been quantitatively studied through micro and crystal structural analysis. Rates and mechanisms of reactions or diffusion are discussed from the quantitative study.
Summary: In this study, influence of Si concentration in molten Al-45%Zn on durability of MoB/CoCr coatings has been quantitatively studied through micro and crystal structural analysis. Rates and mechanisms of reactions or diffusion are discussed from the quantitative study.
A molten Al-45%Zn alloy is mainly plated onto steel sheets for construction materials to increase corrosion resistance.
In this application, continuous dipping rolls, such as sink-roll and stabilizer-roll, are seriously damaged by the molten alloy.
As far as we know, no good surface treatment is conducted by now.
Our developed coating will be appricable to this application.
