ASTM G69-97(2009)
(Test Method)Standard Test Method for Measurement of Corrosion Potentials of Aluminum Alloys
Standard Test Method for Measurement of Corrosion Potentials of Aluminum Alloys
SIGNIFICANCE AND USE
The corrosion potential of an aluminum alloy depends upon the amounts of certain alloying elements that the alloy contains in solid solution. Copper and zinc, which are two of the major alloying elements for aluminum, have the greatest effect with copper shifting the potential in the noble or positive direction, and zinc in the active or negative direction. For example, commercially unalloyed aluminum (1100 alloy) has a potential of −750 mV when measured in accordance with this practice, 2024–T3 alloy with nearly all of its nominal 4.3 % copper in solid solution, a potential of −600 to −620 mV (Note 2), and 7072 alloy with nearly all of its nominal 1.0 % zinc in solid solution, a potential of − 885 mV (SCE) (1-3).
Note 2—The potential depends upon the rate of quenching.
Because it reflects the amount of certain alloying elements in solid solution, the corrosion potential is a useful tool for characterizing the metallurgical condition of aluminum alloys, especially those of the 2XXX and 7XXX types, which contain copper and zinc as major alloying elements. Its uses include the determination of the effectiveness of solution heat treatment and annealing (1), of the extent of precipitation during artificial aging (4) and welding (5), and of the extent of diffusion of alloying elements from the core into the cladding of alclad products (2).
SCOPE
1.1 This test method covers a procedure for measurement of the corrosion potential (see Note 1) of an aluminum alloy in an aqueous solution of sodium chloride with enough hydrogen peroxide added to provide an ample supply of cathodic reactant.
Note 1—The corrosion potential is sometimes referred to as the open-circuit solution or rest potential.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3 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.
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Designation:G69–97 (Reapproved 2009)
Standard Test Method for
Measurement of Corrosion Potentials of Aluminum Alloys
ThisstandardisissuedunderthefixeddesignationG69;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscript
epsilon (ϵ) indicates an editorial change since the last revision or reapproval.
1. Scope copperinsolidsolution,apotentialof−600to−620mV(Note
2), and 7072 alloy with nearly all of its nominal 1.0% zinc in
1.1 Thistestmethodcoversaprocedureformeasurementof
solid solution, a potential of−885 mV (SCE) (1-3).
thecorrosionpotential(seeNote1)ofanaluminumalloyinan
aqueous solution of sodium chloride with enough hydrogen
NOTE 2—The potential depends upon the rate of quenching.
peroxide added to provide an ample supply of cathodic
3.2 Because it reflects the amount of certain alloying ele-
reactant.
ments in solid solution, the corrosion potential is a useful tool
NOTE 1—The corrosion potential is sometimes referred to as the for characterizing the metallurgical condition of aluminum
open-circuit solution or rest potential.
alloys, especially those of the 2XXX and 7XXX types, which
contain copper and zinc as major alloying elements. Its uses
1.2 The values stated in SI units are to be regarded as
include the determination of the effectiveness of solution heat
standard. No other units of measurement are included in this
treatment and annealing (1), of the extent of precipitation
standard.
during artificial aging (4) and welding (5), and of the extent of
1.3 This standard does not purport to address all of the
diffusion of alloying elements from the core into the cladding
safety concerns, if any, associated with its use. It is the
of alclad products (2).
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
4. Apparatus
bility of regulatory limitations prior to use.
4.1 The apparatus consists of an inert container for the test
2. Referenced Documents
solution, a mechanical support for the test specimens that
insulates them electrically from each other and from ground,
2.1 ASTM Standards:
saturated calomel electrode (SCE) (see Note 3), wires and
D1193 Specification for Reagent Water
accessories for electrical connections, and equipment for the
3. Significance and Use
measurement of potential.
3.1 The corrosion potential of an aluminum alloy depends
NOTE 3—Saturated calomel electrodes are available from several
upon the amounts of certain alloying elements that the alloy
manufacturers.Itisagoodpracticetoensuretheproperfunctioningofthe
contains in solid solution. Copper and zinc, which are two of
reference electrode by measuring its potential against one or more
reference electrodes. The potential difference should not exceed 2 or 3
the major alloying elements for aluminum, have the greatest
mV.
effectwithcoppershiftingthepotentialinthenobleorpositive
direction, and zinc in the active or negative direction. For
4.2 A high-impedence (>10 Ω) voltmeter is suitable for
example, commercially unalloyed aluminum (1100 alloy) has
measurement of the potential. Measurement of this potential
apotentialof−750mVwhenmeasuredinaccordancewiththis
should be carried out to within 6 1 mV. Automatic data
practice, 2024–T3 alloy with nearly all of its nominal 4.3%
recording systems may be used to permit the simultaneous
measurementofmanyspecimensandthecontinuousrecording
of corrosion potentials.
This test method is under the jurisdiction of ASTM Committee G01 on
Corrosion of Metals and is the direct responsibility of Subcommittee G01.11 on
5. Reagents
Electrochemical Measurements in Corrosion Testing.
Current edition approved May 1, 2009. Published May 2009. Originally
5.1 Purity of Reagents—Reagent grade chemicals shall be
approved in 1981. Last previous edition approved in 2003 as G69–97(2003). DOI:
used in all tests. Unless otherwise indicated, it is intended that
10.1520/G0069-97R09.
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 boldface numbers in parentheses refer to the references at the end of this
the ASTM website. standard.
3 5
All alloy designations are those of the Aluminum Association. Round-robin test conducted by G01.11 (unpublished results).
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
G69–97 (2009)
all reagents shall conform to the specifications of the Commit- bemeasured).Furtherpreparationconsistsoffilingwithalong
tee onAnalytical Reagents of theAmerican Chemical Society, lathe file. Original flat surface specimens are also filed with
where such specifications are available. Other grades may be long lathe file to remove the original mill scale oxide layer.
used, provided it is first ascertained that the reagent is of 8.3 No filing or machining is needed to prepare specimens
sufficiently high purity to permit its use without lessening the that have original flat surface, representative of its metallurgi-
accuracy of the determination. calstructure,ortopreparespecimensthataretoothintopermit
5.2 Purity of Water—The water shall be distilled or deion- more than minimal removal of metal; these include clad
ized conforming to the purity requirements of Specification products with thin claddings which are to be measured.
D1193, Type IV reagent water. 8.4 The surfaces of all products selected for measurement,
5.3 Sodium Chloride (NaCl). including those with no previous preparation, are abraded dry
5.4 Hydrogen Peroxide (H O ) (30 %)—In case of uncer- with No. 320 grade aluminum oxide or silicon carbide cloth
2 2
tainty (for example, whenever freshly opened reagent is not and then with No. 00 steel wool.
used), the concentration of hydrogen peroxide in the reagent
NOTE 4—Caution:Clad products with thin claddings should only be
shall be confirmed by chemical analysis as described inAnnex
abraded lightly except to remove the cladding for measurement of the
A1. In no case shall reagent containing less than 20%
core.
hydrogen peroxide be used.
8.5 Following mechanical preparation, the specimen is
cleaned,ordegreased,inaninertsolvent(forexample,acetone
6. Solution Conditions
or perchloroethylene).
6.1 The test solution shall consist of 58.56 0.1 g of NaCl
8.6 All parts of a specimen and its electrical connection to
and 96 1 mL of 30% hydrogen peroxide reagent per 1 L of
be exposed in the test solution, except for the area of the
aqueous solution. (This solution is 1 M with respect to
specimen prepared for measurement, are masked off. Any
concentration of sodium chloride.)
material that masks a surface physically and electrically and
6.2 The hydrogen peroxide reagent shall be added just
that is inert in the test solution may be used (see Annex A2).
before measurements are made because it decomposes upon
standing.
9. Procedure
6.3 Freshly prepared solution shall be used for each set of
9.1 For corrosion potential measurements, the test speci-
measurements.
mens and the reference electrode are immersed in the appro-
6.4 Not less than 500 mLof solution shall be used for each
priate quantity of test solution; the test specimens are con-
set of measurements.
nected to the positive terminal of the equipment for measuring
6.5 The total exposed area of all the specimens of the same
potential, and the reference electrode to the negative terminal.
composition in each set of measurements shall not exceed 100
2 9.2 Care should be taken to ensure that all the unmasked
mm per 100 mL of solution.
area of each test specimen prepared for measurement is
6.6 The temperature of the test solution shall be maintained
exposed to the test solution and that any other unmasked area
at 256 2°C.
is not exposed. Care should also be taken to ensure that any
unmaske
...
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