Electrochemical impedance spectroscopy of chitosan coated magnesium alloys in a synthetic sweat medium

Pure magnesium and/or its alloys (AZ31E, AZ91E) are the optimum shell materials for electronic products that contact the hands of the users, and are corroded by the sweat solution (0.1% urea, 0.5% NaCl and 0.5% lactic acid). The corrosion behavior of the tested electrodes was investigated in artificial sweat solution as function of immersion time. In the electrochemical cell Mg or its alloy acts as the anode and NaCl in sweat solution is the corrosive medium. Results showed that the most corroded electrode was pure magnesium while the least corroded was AZ91E alloy. Chitosan was used as coating with different concentrations for AZ91E alloy to protect it against corrosion. The results were carried out using various electrochemical techniques such as potentiodynamic polarization, electrochemical impedance (EIS) and surface examination via scanning electron microscope (SEM). After coating AZ91E alloy with 5% chitosan the formed film was thicker than that formed on the uncoated one and its thickness increased with increasing chitosan concentration. The micrographs showed that the coated AZ91E alloy has superior corrosion resistance properties as compared to the uncoated alloy and that corrosion decreases with increasing the polymer concentration. EIS and polarization results were confirmed by SEM micrographs.