 ACCELERATED
LIFE TESTING
Corrosion Potential Testing (ASTM G 69)
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The ASTM G69 method measures the corrosion potential of aluminum alloys.
Corrosion potential is also known sometimes as "solution potential", "rest potential"
or the "open-circuit solution". It has been used for more than 50 years to verify
the temper of aluminum (Al) alloys. It is also a useful tool for characterizing the
metallurgical condition of aluminum alloys, particularly 2XXX and 7XXX, whose major
alloying elements are copper and zinc. Although corrosion potential is not the same as
corrosion rate, it can be used to determine if galvanic corrosion will occur
when different metals and alloys are connected in an environment of aerated saltwater.
Sample/specimen preparation is important and can be done by Touchstone. If you prepare your own
samples, you must ensure during sawing/stamping you do not change the metallurgical
structure from heat. Specimen size is not important, provided the area is at least
25 mm2. Ease of handling is a consideration, however, so samples a few millimeters thick
by about 15 mm wide and 100 mm long are recommended. At least two, and possibly three specimens,
are needed for each alloy to be evaluated.
Samples are exposed to a salt water/peroxide medium along with a
saturated calomel electrode. A sample of 3003 aluminum sheet is run concurrently with
each test as a reference sample. The corrosion potential data, in millivolts,
is collected. The brazing industry has a specification not just in corrosion potential,
but in the change in potential through the thickness of the brazed sheet.
The standard practice has been to remove layers of metal by exposure
of the aluminum brazing sheet to strong caustic solution and timing
the reaction so that only a certain amount of metal is removed.
This practice suffers from being uncontrolled and unpredictable.
Sometimes the sample was destroyed, thus losing valuable data. Touchstone
Research has improved on this method by developing a technique
for removal of minute amounts of surface material in a predictable manner.
As little as 0.0005" can be removed at one step.
Additional corrosion tests are available, as well as
light microscopy, scanning electron microscopy,
metallography, failure analysis, and
mechanical testing services.
Reference: ASTM G69: Standard Test Method for Measurement of Corrosion Potentials of Aluminum Alloys
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