Effect Of Sealing Treatment On Corrosion Resistance Of Thermal Sprayed Metal Base Coatings

The casing pipe in the deep-sea drilling platform is in service in the deep-sea environment,it is extremely susceptible to severe seawater corrosion,which shortens its service life.The effective method to expand its service life is to prepare a protective coating on the surface of the casing pipe by thermal spraying technology.However,the thermal spraying coating has defects such as pores and micro cracks,which will seriously affect the corrosion resistance of the coating.Therefore,it is very important to seal the protective coating of the casing pipe.Sealing treatment is to infiltrate the sealants into the pores of the coating by dipping,ultrasonic and brushing,so as to reduce the pore defects of the coating and improve the corrosion resistance of the protective coating.In this paper,Fe-based amorphous and Al-based alloys with excellent corrosion resistance are selected as corrosion resistant coating materials.Fe-based amorphous coating and Al-based coating are deposited on the substrate surface by atmospheric plasma spraying and oxygen-acetylene flame spraying.The coating was sealed by three sealing methods,namely dipping,ultrasonic and brushing coating.The microstructure changes of the coating before and after sealing were characterized by X-ray diffractometer(XRD)and scanning electron microscope(SEM).Electrochemical experiments and salt spray tests on the coatings were carried out to study of the effects of sealing treatment on the corrosion performance of the coatings,which provides a scientific basis for the accurate formulation of thermal sprayed corrosion resistant coating on the surface of the casing pipe in the marine environment.The main conclusions are as follows:There are pores and a small amount of microcracks in the Fe-based amorphous coating,and the bonding strength between the coating and the substrate is low.The surface pores of the iron-based amorphous coating after brushing and sealing have been filled,effectively preventing the penetration of the corrosive solution into the coating.The structure of the Al-based coating is loose and porous,the bonding strength between the coating and the substrate is well.The surface structure of the Al-based coating after brushing and sealing is dense and showing a flat state.Electrochemical test results show that the three sealing treatment methods have improved the corrosion resistance of Fe-based amorphous coatings and Al-based coatings to a certain extent,and the corrosion resistance effect is:brush sealing is better than immersion sealing.Dip sealing is better than ultrasonic sealing.In the salt spray corrosion test,the quality loss of the Fe-based amorphous coating after sealing is small,the corrosion rate of the coating is relatively slow,and it shows good corrosion resistance.Both the AlCu coating and AlSi coating after sealing have increased weight,while the corrosion rate of the Al coating and AlMg coating after sealing has shown a downward trend.