Corrosion Behaviour of Magnesium Alloy Az91 and its Mmc in Nacl Solution

The corrosion behaviors of magnesium alloy AZ91C and its A1203 (short fiber)-reinforced metal matrix composite (MMC) in alkaline solutions (pH 10.5) containing chloride were compared using potentiodynamic polarization measurements, electrochemical impedance spectroscopy (EIS) and immersion tests. Dependence of polarization characteristics (corrosion potential and corrosion current density) on chloride concentration was similar for both materials. The corrosion potential Ecorr decreased linearly with the logarithm of chloride concentration, while the corrosion current density icon increased rapidly at chloride concentrations larger than 0.1%, with the /'con- for the MMC consistently higher than that for AZ91C, reaching a factor of about 3 in 3.5% sodium chloride solution. EIS data indicated that the protective film on the MMC was inferior to that on the matrix alloy. With stirring and at frequencies higher than 5 Hz, the electrode/electrolyte interface might be described by the simplified Randies model for both materials. Immersion tests showed that the corrosion rate of the MMC, in terms of weight loss, was about 7 times that of the matrix alloy. Thus the present investigation indicated that in alkaline solutions containing chloride ions, the presence of Al2O3short fibers in the alloy did not drastically alter the corrosion behavior, but significantly reduced its corrosion resistance.