EIS study of corrosion behavior of AZ91 and AM50 alloys

摘要

The corrosion resistance of the alloy containing a higher content of aluminium (AZ91) in aerated, unbuffered ASTM water is better in comparison to AM50. This is observed from the higher value of the resistance R_(HF) determined from the high frequency loop of the impedance diagram which is the impedance parameter that has been found to determine more accurately the corrosion rates that can be assimilated to the charge transfer resistance. The value found for the capacitance, C_(HF) determined from the high frequency loop, C_(HF) is relatively low (20 μF/cm~2) for an expected value of the double layer capacitance, C_(dl) which indicates that an oxide-hydroxide film has been formed having some protective properties that can be attributed to a pH increase in the unbuffered electrolyte and provokes a decrease in reacting sites and/or an increase in the efficiency of the barrier film protective properties. The effect of immersion time, polarization, electrolyte content and pH, will be discussed for the two alloys including the influence of the presence and distribution of the precipitated phases.