Standard Test Method for Repassivation Potential of Aluminum and Its Alloys by Galvanostatic Measurement

Importancia y uso:

5.1 This test method is designed to measure the relative effectiveness of inhibitors to mitigate pitting corrosion of aluminum and its alloys, in particular AA3003-H14, rapidly and reproducibly. The measurements are not intended to correlate quantitatively with other test method values or with susceptibility to localized corrosion of aluminum observed in service. Qualitative correlation of the measurements and susceptibility in service has been established (1).

5.2 The maximum potential reached upon initial polarization, E_B, is a measure of the resistance to breakdown of the aluminum oxide film. Lower susceptibility to initiation of pitting corrosion is indicated by a more noble potential. (See Practice G3 and Terminology G15.) This potential, as measured in this test method, is not very sensitive to the inhibitors present.

5.3 The minimum potential, E_G, following the maximum potential is a measure of the protection against continued pitting corrosion by the inhibitors. Again, a more noble potential indicates better protection. This potential is sensitive to the inhibitors present.

5.4 Visual examination of the specimens can provide information about subtleties of the pitting and inhibition mechanisms. Number of pits, pit depth, amount of deposit, and surface discoloration are some examples of recordable observations, which can assist evaluation of inhibitor effectiveness.

5.5 The presence of chloride in the test solution is critical to observation of pitting corrosion. Also, a coolant/corrosive water solution in which gas bubbles evolve spontaneously on the aluminum (indicating general corrosion) is unlikely to have a significant amount of observable pitting corrosion.

Subcomité:

D15.06

Volúmen:

15.05

Número ICS:

77.150.10 (Aluminium products)

Palabras clave:

aluminum; corrosion; electrochemical measurement; galvanostatic; localized corrosion; polarization;