Study On Corrosion Resistant Coatings For Zinc Or Aluminum Alloys At Molten State

Hot dipping is the most economic and efficient technology to protect iron material from corrosion in nature circumstance. Hot-dip galvanizing and hot-dip aluminizing are one of the most popular hot dipping technologies which are broadly used in society. However, molten zinc or aluminium can seriously corrode hot dipping equipment. The corrosion has brought many problems such as waste of material and energy, low quality of coating and deduction of life-span. And these problems have seriously hampered the development of hot dipping. In present works, the corrosion mechanism of hot dipping equipment by molten zinc or molten aluminium has been analyzed. Many coating schemes have been designed, such as molybdenum, tungsten, Mo-30W, Co/WC, Fe-Cr-Al, MgO+ZrO₂ and Al₂O₃+TiO₂. Various analysis and testing technologies are adopted to detect the changes of samples after being corroded, including X-ray Diffraction (XRD), Electron Probe Microscopy Analysis (EPMA), Transition Electron Microscopy (TEM) and weight loss analysis by Analytical Balance. By analyzing the microstructure, phase transformation and weight loss between as sprayed and after-corrosion samples, we find that plasma spraying molybdenum coating and in-situ diffusion Fe-Cr-Al intermetallic compound coating have wonderful corrosion resistance to molten zinc and flame spraying MgO+ZrO₂ coating has wonderful corrosion resistance to molten aluminium. However, the molybdenum coating and Fe-Cr-Al coating must be used in the molten zinc and can not be used in the zinc vapor circumstance. Metal coatings can not be used in molten aluminium, either. Only ceramic coatings like MgO+ZrO₂ and Al₂O₃+TiO₂ can be used in zinc vapor and molten aluminium.