Study On The Micro-Arc Oxidation Of Plating Of Aluminum Doping Lanthanide On Q235 Steel

Mild steel is widely used in fabrication of reaction vessels, store tanks, petroleum refineries and so on. However, its poor wear and corrosion performance greatly restricts its application in practice. Many kinds of surface modification techniques are developed to improve for its wear and corrosion performance of mild steel. In this paper, Al plating doping a small amount of lanthanide was prepared on Q235 steel in molten salt firstly and then ceramic coating was fabricated on Al plating by micro-arc oxidation (MAO) methods in order to improve surface performance of Q235 steel.Ceramic coating was obtained in different electrolytes. The influence of variety and concentration of addition, treatment time, oxide voltage on the behavior of MAO process and corrosion resistance of ceramic coating was studied, the optimum processing parameters were found. Microstructure of ceramic coating was observed by SEM. The element composition and phase components of ceramic coating were determined by EDS and XRD, respectively. The corrosion behavior of ceramic coating was assessed by weigh loss measurements and potentiodynamic polarization tests in 3.5 wt% sodium chloride(NaCl) solution, respectively. The analysis of electrochemical impedance spectroscopy (EIS) showed details of corrosion performance with different exposure time in 3.5 wt% NaCl solution and the mechanism of forming ceramic coating was also discussed.The result showed that ceramic coating easily formed in silicate electrolyte, and breakdown voltage was 30～40 V lower in the silicate electrolyte than that of aluminate electrolyte. Corrosion potential of ceramic coating fabricated in aluminate electrolyte suffered a increase in the positive direction. The addition of ingredient into electrolyte influenced the morphological feature and corrosion resistance of ceramic coating. Oxide voltage and treatment time had a great effect on the forming rate of ceramic coating. SEM reveals the porous nature of the deposit and the size of pores and roughness of surface increased with prolonged treatment time and increased oxide voltage, ranging from 1μm to 2μm(in diameter), while the number of pores decreased. The coating is mainly composed ofγ-Al₂O₃,α-Al₂O₃ and so on. The corrosion rate in 3.5 wt% NaCl solution was significantly reduced by the formation of ceramic coating on mild steel in different kinds of electrolyte.