ASTM D6208-07(2020)
(Test Method)Standard Test Method for Repassivation Potential of Aluminum and Its Alloys by Galvanostatic Measurement
Standard Test Method for Repassivation Potential of Aluminum and Its Alloys by Galvanostatic Measurement
SIGNIFICANCE AND USE
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, EB, 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, EG, 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.
SCOPE
1.1 A procedure to determine the repassivation potential of aluminum alloy 3003-H14 (UNS A93003) (1)2 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 standard. The values given in parentheses after SI units are provided for information only and are not considered standard.
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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
Relations
Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D6208 − 07 (Reapproved 2020)
Standard Test Method for
Repassivation Potential of Aluminum and Its Alloys by
Galvanostatic Measurement
This standard is issued under the fixed designation D6208; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope Measurements in Corrosion Testing
G15TerminologyRelatingtoCorrosionandCorrosionTest-
1.1 A procedure to determine the repassivation potential of
2 ing (Withdrawn 2010)
aluminumalloy3003-H14(UNSA93003) (1) asameasureof
G46Guide for Examination and Evaluation of Pitting Cor-
relative susceptibility to pitting corrosion by conducting a
rosion
galvanostaticpolarizationisdescribed.Aprocedurethatcanbe
G107Guide for Formats for Collection and Compilation of
used to check experimental technique and instrumentation is
Corrosion Data for Metals for Computerized Database
described, as well.
Input
1.2 The test method serves as a guide for similar measure-
ment on other aluminum alloys and metals (2-5).
3. Terminology
1.3 The values stated in SI units are to be regarded as
3.1 Definitions—Terms used in this test method can be
standard. The values given in parentheses after SI units are
found in Practice G3 and Terminology G15.
providedforinformationonlyandarenotconsideredstandard.
3.2 Symbols:
1.4 This standard does not purport to address all of the
3.2.1 E —break potential; potential at which the passive
B
safety concerns, if any, associated with its use. It is the
aluminum oxide layer breaks down.
responsibility of the user of this standard to establish appro-
3.2.2 E —protectionpotential,asmeasuredinthisgalvano-
G
priate safety, health, and environmental practices and deter-
static method; potential at which oxide layer repassivates.
mine the applicability of regulatory limitations prior to use.
3.2.3 J—current density, in A/m .
1.5 This international standard was developed in accor-
dance with internationally recognized principles on standard-
4. Summary of Test Method
ization established in the Decision on Principles for the
4.1 The test method described is an adaptation of the
Development of International Standards, Guides and Recom-
method described in FORD Motor Company standards (6).
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
4.2 An aluminum alloy specimen is polarized at fixed
current density for 20 min. in a solution of coolant and
2. Referenced Documents
corrosivewatercontainingchloride.Thepotentialasafunction
2.1 ASTM Standards:
of time is recorded.
D1193Specification for Reagent Water
4.3 The maximum potential, E , reached upon polarization
B
D3585Specification forASTM Reference Fluid for Coolant
is determined, as is the minimum potential following the
Tests
maximum potential, E .
G
G3Practice for Conventions Applicable to Electrochemical
4.4 Visual examination of the specimen may be made using
Guide G46 as a guide after disassembly and rinsing.
This test method is under the jurisdiction ofASTM Committee D15 on Engine
Coolants and Related Fluids and is the direct responsibility of Subcommittee 5. Significance and Use
D15.06 on Glassware Performance Tests.
5.1 This test method is designed to measure the relative
Current edition approved Feb. 1, 2020. Published February 2020. Originally
approved in 1997. Last previous edition approved in 2014 as D6208–07(2014). effectiveness of inhibitors to mitigate pitting corrosion of
DOI: 10.1520/D6208–07R20.
aluminum and its alloys, in particular AA3003-H14, rapidly
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
and reproducibly. The measurements are not intended to
this standard.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on The last approved version of this historical standard is referenced on
the ASTM website. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6208 − 07 (2020)
correlate quantitatively with other test method values or with 6.3 Current Supply and Recorder—A constant current sup-
susceptibility to localized corrosion of aluminum observed in plycapableofgenerating872µAcontinuouslyisrequired.The
service. Qualitative correlation of the measurements and sus- recorder must have a high input impedance (>10 Ohms), be
ceptibility in service has been established (1). capableofrecordingpotentialsof 62VwithmVaccuracy,and
have a low gain. These capabilities are typical of commercial
5.2 The maximum potential reached upon initial
potentiostat/galvanostat instruments connected to either a strip
polarization,E isameasureoftheresistancetobreakdownof
B,
chart recorder or computer, for experimental control and data
the aluminum oxide film. Lower susceptibility to initiation of
acquisition.TheschematicinFig.1showsconnectionsusinga
pitting corrosion is indicated by a more noble potential. (See
current supply and mV strip chart recorder, and Fig. X2.1
Practice G3 and Terminology G15.) This potential, as mea-
shows a schematic for using a computer and potentiostat/
sured in this test method, is not very sensitive to the inhibitors
galvanostat.
present.
6.4 Electrodes:
5.3 The minimum potential, E following the maximum
G,
6.4.1 Working Electrode (WE)—Theworkingelectrode,alu-
potential is a measure of the protection against continued
minum test coupon, is cut as 51 mm × 51 mm (2 in. × 2 in.)
pitting corrosion by the inhibitors. Again, a more noble
1 1
squares from aluminum sheet 2 mm to 6 mm ( ⁄16 in. to ⁄4 in.)
potential indicates better protection. This potential is sensitive
thick. The standard material is AA3003-H14 (UNS A93003),
to the inhibitors present.
used to develop the precision and bias statements. The coupon
5.4 Visual examination of the specimens can provide infor-
is rinsed thoroughly (both sides) with methanol and placed in
mation about subtleties of the pitting and inhibition mecha-
a low temperature drying oven. No additional surface prepa-
nisms. Number of pits, pit depth, amount of deposit, and
ration is desirable. Prior to testing, a coupon is allowed to cool
surface discoloration are some examples of recordable
to room temperature. Then it is clamped to the bottom of the
observations,whichcanassistevaluationofinhibitoreffective-
O-ring joint using the matching O-ring (viton or silicone
ness.
rubber) and clamp. The clamping screw may be tightened to
5.5 Thepresenceofchlorideinthetestsolutioniscriticalto
finger tightness, if desired. Excessive tightening must be
observation of pitting corrosion. Also, a coolant/corrosive
avoided. This gives an area of 8.72 cm aluminum exposed to
water solution in which gas bubbles evolve spontaneously on
the solution.
thealuminum(indicatinggeneralcorrosion)isunlikelytohave
6.4.2 Auxiliary Electrode (AE)—Ultrafine grade graphite
a significant amount of observable pitting corrosion.
rod,6mmto8mm( ⁄4 in.) in diameter and at least 20 cm
(8in.) long.Avoid coarse grades as they can adsorb inhibitors.
6. Apparatus
6.4.3 Reference Electrode (RE)—The reference electrode
6.1 General Description—The apparatus for the electro-
can be of any convenient type, for example saturated calomel
chemical test consists of a cell, current supply, recorder, and
(Hg/HgCl)orsilverchloride(Ag/AgCl).Theelectrodemustbe
three electrodes. Fig. 1 is a generalized schematic of the
in good working order and stable in the solution to be
arrangement. More specific requirements for each component
measured.ThereferenceelectrodeisplacedinLugginprobeto
are given below.
avoid solution impedance bias. Appendix X2 contains two
suggestions for easily constructed Luggin probes.
6.2 Cell—The cell consists of a No.25 O-ring borosilicate
glassjointheldverticallyusingstandardlaboratoryclampsand
6.5 Timer—Timer with 1 s resolution out to 30 min.
ring stand. The working electrode will be clamped to the
bottom using the matching O-ring clamp and viton or silicone
7. Preparation of Apparatus
rubber gasket.
7.1 Assembly—Prior to running tests, assemble the cell and
electrodes, using an unpreparedAl specimen as the “working”
electrode using appropriate clamping. The auxiliary electrode
is positioned so that the tip is from 5 mm to 10 mm from the
working electrode surface. The Luggin probe is positioned so
that the tip is from 1 mm to 3 mm from the working electrode
surface. It is most convenient if the clamping arrangement is
such that this electrode configuration is maintained easily. The
cell is then removed and Al specimen unclamped.
8. Procedure
8.1 A corrosive water containing chloride, sulfate, and
bicarbonateispreparedbydissolvingthefollowingamountsof
anhydrous salts in distilled or deionized water,ASTM Type II
(see Specification D1193):
Sodium sulfate 592 mg
Sodium chloride 660 mg
Sodium bicarbonate 552 mg
FIG. 1 Generalized Experimental Set-up
D6208 − 07 (2020)
The solution is made up to a total weight of 1 kg with
distilled or deionized water at 20°C. A 4 kg batch size is
convenientifmanytestsaretoberun,multiplyamountsabove
byfour.Thiswillgiveasolution,whichis400ppminchloride,
sulfate, and bicarbonate.
8.2 Rinse cell, O-ring, Luggin probe (inside and out),
auxilliary electrode, and reference electrode thoroughly with
Type II water.
8.3 Prepare the aluminum specimen as the working elec-
trode (see 5.4.2). Clamp to cell, using O-ring, and set to one
side.
8.4 Preparethetestsolutionas25vol%ofthecoolanttobe
tested, 25 vol% of the corrosive water from 6.1, and the
NOTE 1—Break potential, E , and protection potential, E , is indicated
remainder deionized or distilled water.The amount to be made B G
for each type of transient.
depends on one’s exact cell configuration. Sufficient test
FIG. 2 Two Common Potential/Time Transient Profiles After
solution is required to fill the cell (about 50 mLs) and the
Polarization
Lugginprobeassembly.FortheconfigurationsofLugginprobe
given in Appendix X2, 160 mLs is more than sufficient.
decrease.Recordthemaximumpotentialreachedinthisperiod
8.5 Fill the Luggin probe with test solution sufficient to as E . The third possibility is that the potential rises
B
cover the tip of reference electrode when inserted. Insert
continuously,thoughperhapsoscillating.Recordthemaximum
reference electrode. Gently tap Luggin to remove any bubbles potential reached throughout the run. Express potential asVv
between the tip and reference electrode. If a vertical Luggin is
SHE correcting for type of reference electrode used (see
used,asinFig.X2.2,thenbubblescanberemovedbyallowing Appendix X1).
solution to drain slowly into a waste container.
9.2 Protection Potential E —For curves similar to curveA
G
8.6 Set up current generator to output 872 µA (J = 100 in Fig. 2, asymptotic decrease in potential after break, record
µA/cm ) continuously, set recorder to a range of 62 V (other
the minimum potential reached, typically at the end of the run.
settings may be used if found to be necessary to achieve ForcurvessimilartocurveBinFig.2,thereisadecreaseafter
accurateandrepresentativepotentials,chartspeedasdesired(5 the “break” followed by a series of rises and falls, record the
mm/min is reasonable). If acquiring data by computer, set data lowest potential reached on the first fall. Typically, subsequent
acquisition rate to 1 point/s. Do not turn either generator or rises and falls are small and appear as oscillations. For curves
recorder on at this time. where the potential rises continuously, E will be equal to E .
G B
Express potential as V v SHE, correcting for type of reference
8.7 Fill cell with approximately 50 mL of test solution,
electrode used (see Appendix X1).
about 25 mm from the top of the cell. Start timer. Do not start
generator at this time. Recorder may be turned on at this time. 9.3 Curve Type—Record whether curve is asymptotic (Type
Assemble cell over Luggin probe and auxiliary electrode.
A), rising and falling (Type B), or rising only (Type C).
Attach wires to reference electrode, auxiliary electrode, and
9.4 Observations (optional)—The following are optional
working electrode. Check for bubbles in Luggin, tap gently to
observations that can be recorded as: evolution of gas bubbles
remove.
duringthetest,descriptionofsurfaceaftertest,locationofpits
8.8 At 5 min on the timer, turn on current generator, and
(for example, along scratch lines, etc. number of pits, depth of
recorder, if not already on. Record potential versus time pits, area of pits, color of deposits, location of deposits in
response for 20 min. Turn off current generator and recorder
relation to pits, and other pitting evaluations as described in
(see Note 1). Guide G46).
NOTE 1—A computer controlled system can be used in place of a
10. Report
current generator and recorder. In this case the current generator consists
of a potentiostat/galvanostate operated in galvanostatic mode. The re- 10.1 Report the following information:
corder is the computer. Software is used to control all aspects of the test
10.1.1 Report aluminum alloy tested.
protocol, including controlling the galvanostate, acquiring the data,
10.1.2 Report the average E and E of all experimental
B G
plotting, and analysis.
runs, at least two, for the formula.
8.9 Run the test in duplicate, steps 8.2 – 8.8.
10.1.3 Report type of curves obtained, A, B, or C. Report
multiple types if obtained.
9. Interpretation of Results
10.1.4 Report any visual observation made.
9.1 Break Potential, E —The graph in Fig. 2 illustrates two 10.1.5 Many other relevant test parameters are given in
B
ofthethreepossibleformsofcurveobtainedintheexperiment. Guide G107. These parameters should be recorded properly in
In Fig. 2 there is an initial rapid rise in potential followed by a laboratory notebooks for future reference.
D6208 − 07 (2020)
TABLE 1 Composition of Control Formulas
11. Precision and Bias
Specification
11.1 Precision—The precision of this test method has not AL39
Ingredient D3585
(wt %)
been determined. Round-robin testing will commence once
(wt %)
final details of the method are determined. It is expected that
Ethylene glycol 89.76 95.35
Diethylene glycol 5.00
the precision associated with the “break” potential wil
...
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