A fundamental study has been conducted of some inhibitors found to be effective in reducing galvanic corrosion between magnesium alloy AZ31B and aluminum alloy 2024-T3 in saline solutions. The object of the study was to determine the mechanism of protection afforded by the inhibitors, Mg(V03)2, BaK2(CrO4)2, and CaS, singly and in combination. The effect of these inhibitors on the polarization characteristics of the metals was determined with the electrodes isolated in separate compartments, bridging being accomplished with agar-NaC1 bridges. In this group of tests, the polarization potentials, recovery potentials, and corrosion currents were measured, the latter by means of the zero resistance ammeter circuit. Additional tests were made with the electrodes in the same beaker, corrosion currents and corrosion rates being determined under these conditions.

Correlation of results from the potential, corrosion current, and corrosion rate data indicates that the Mg(VO3)2 and BaK2CCrO4)2 polarize the aluminum strongly in the anodic direction, thereby reducing the galvanic current and the weight loss of magnesium.

Weight loss on aluminum was related to the increase in alkalinity occurring in experiments made in the same beaker.

Corrosion current measurements may serve as a useful tool for the determination of effectiveness of inhibitors, but the method should not be used indiscriminately.

Practical conclusions should only be drawn from the results obtained in experiments with both metals exposed in the same compartment. 5.8.3

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Copyright 1957 by the National Association of Corrosion Engineers.
1957
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