The corrosion behavior of several commercial aluminum sacrificial anodealloys were studied. Laboratory-scale experiments were conducted to establishthe galvanic current output characteristics of the alloys when coupled toHY-80 steel in synthetic seawater. Also direct weight loss measurementsof corrosion rates and potentiostatic polarization behavior were obtained, andthe mode and distribution of corrosive attack on the various anode alloyswere studied by scanning electron microscopy. All the alloys studied show similar galvanic current characteristics as a function of time, with aninitially high current density which falls of to a stable value, primarilydue to the accumulation of calcareous deposits on the cathodes. Thecorrosion patterns developed by each alloy are distinctly different, bothon the macroscopic and microscopic scale. The commercial alloy Galvalum Imacroscopically exhibits attack preferentially on specimen edges, whileReynode II tends to form vertically elongated dissolution cavities on thebroad specimen surfaces, and KA-90 tends to profusely pit. These differentbehaviors can be rationalized in terms of the observed anodic polarizationcharacteristics of the respective alloys. All the alloys show distinctcrystallographic attack on the microscopic scale, but the details ofdissolution morphology are quite different for each alloy.
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