Effects of Solution Temperature and Immersion Time on the Semiconducting Behaviors of Passive Films Formed on AZ31B Alloy

The influences of solution temperature and immersion time on formed passive film semiconducting behaviors of AZ31B Mg alloy in sodium hydroxide electrolyte (pH=12) under steady-state terms has been investigated applying electrochemical measurements such as Mott–Schottky, impedance spectroscopy and potentiodynamic polarization tests. Mott– Schottky measurements showed the formed passive film on AZ31B magnesium alloy indicates an n-type semiconducting characteristics regardless the immersion time and electrolyte temperature, and the figured donor density rises exponentially by increasing solution temperature and immersion time. While, potentiodynamic polarization data showed that the alloy corrosion and passive current density diminishes as a result of increasing immersion time. Furthermore, the data obtained from impedance spectroscopy revealed that the passive film the reciprocal capacitance being proportional to its thickness, rises by increasing immersion time. It was found that despite the increase in thickness and resistance of passive layer with prolonged immersion time, long immersion times led to favor a less hydrated oxide film the transformation into a more hydrated phase followed via rising the film donor concentration.