Corrosion behavior of aluminum alloys intended for sacrificial anode application in seawater
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The corrosion behavior of several commercial aluminum sacrificial anode alloys were studied. Laboratory-scale experiments were conducted to establish the galvanic current output characteristics of the alloys when coupled to HY-80 steel in synthetic seawater. Also direct weight loss measurements of corrosion rates and potentiostatic polarization behavior were obtained, and the mode and distribution of corrosive attack on the various anode alloys were studied by scanning electron microscopy. All the alloys studied show similar galvanic current characteristics as a function of time, with an initially high current density which falls of to a stable value, primarily due to the accumulation of calcareous deposits on the cathodes. The corrosion patterns developed by each alloy are distinctly different, both on the macroscopic and microscopic scale. The commercial alloy Galvalum I macroscopically exhibits attack preferentially on specimen edges, while Reynode II tends to form vertically elongated dissolution cavities on the broad specimen surfaces, and KA-90 tends to profusely pit. These different behaviors can be rationalized in terms of the observed anodic polarization characteristics of the respective alloys. All the alloys show distinct crystallographic attack on the microscopic scale, but the details of dissolution morphology are quite different for each alloy.
NPS Report NumberNPS-69Ps-78-002
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