ASTM D6208-07

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).

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 G 3 and Terminology G 15.) This potential, as measured in this test method, is not very sensitive to the inhibitors present.

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.

Visual examination of the specimens can provide information about subleties 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.

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.

1.1 A procedure to determine the repassivation potential of aluminum alloy 3003-H14 (UNS A93003) (1) as a measure of relative susceptibility to pitting corrosion by conducting a galvanostatic polarization is described. A procedure that can be used to check experimental technique and instrumentation is described, as well.

1.2 The test method serves as a guide for similar measurement on other aluminum alloys and metals (2-5).

1.3 The values stated in SI units are to be regarded as the standard. Values given in parentheses are for information only.

1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.