Research on Influence of Aluminum Content on the Microstructure and Corrosion Resistance of Zn-Al coatings

The surface morphology of three kinds of Zn-Al coatings with different aluminum powder content were observed under SEM.The self-corrosion potential and current,anode passivation and impedance of the coatings immersed for 24 hours in 3.5% NaCl solution were analyzed by means of the potentiodynamic polarization and electrochemical impendence spectrum.The results show that with increase of content of aluminum,Zn-Al coating gradually becomes brighter and more smooth,the self-corrosion potential and current of the coating turns more positive and reduces in sequence,respectively.The passivation in the polarization curve of the coating doesn't exist when the content of aluminum comes to 50%.The fitting value of EIS of the coatings immersed for 24 hours in 3.5% NaCl solution shows that the coating with high aluminum content has greater impedance value and lower water infiltration amount because of oxidation film on it.