ASTM G69-12
(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 method, 2024–T3 alloy with nearly all of its nominal 4.3 % copper in solid solution, a potential of –600 to –620 mV, depending upon the rate of quenching and 7072 alloy with nearly all of its nominal 1.0 % zinc in solid solution, a potential of 885 mV (SCE) (1-3).
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. See Practice G193.
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 − 12
Standard Test Method for
1
Measurement of Corrosion Potentials of Aluminum Alloys
ThisstandardisissuedunderthefixeddesignationG69;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope example,commerciallyunalloyedaluminum(1100alloy)hasa
potential of –750 mV when measured in accordance with this
1.1 Thistestmethodcoversaprocedureformeasurementof
method, 2024–T3 alloy with nearly all of its nominal 4.3 %
thecorrosionpotential(seeNote1)ofanaluminumalloyinan
copper in solid solution, a potential of –600 to –620 mV,
aqueous solution of sodium chloride with enough hydrogen
depending upon the rate of quenching and 7072 alloy with
peroxide added to provide an ample supply of cathodic
nearlyallofitsnominal1.0%zincinsolidsolution,apotential
reactant.
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of —885 mV (SCE) (1-3).
NOTE 1—The corrosion potential is sometimes referred to as the
3.2 Because it reflects the amount of certain alloying ele-
open-circuit solution or rest potential. See Practice G193.
ments in solid solution, the corrosion potential is a useful tool
1.2 The values stated in SI units are to be regarded as
for characterizing the metallurgical condition of aluminum
standard. No other units of measurement are included in this
alloys, especially those of the 2XXX and 7XXX types, which
standard.
contain copper and zinc as major alloying elements. Its uses
1.3 This standard does not purport to address all of the
include the determination of the effectiveness of solution heat
safety concerns, if any, associated with its use. It is the
treatment and annealing (1), of the extent of precipitation
responsibility of the user of this standard to establish appro-
during artificial aging (4) and welding (5), and of the extent of
priate safety and health practices and determine the applica-
diffusion of alloying elements from the core into the cladding
bility of regulatory limitations prior to use.
of Alclad products (2).
2. Referenced Documents
4. Apparatus
2
2.1 ASTM Standards:
4.1 The apparatus consists of an inert container for the test
D1193Specification for Reagent Water
solution, a mechanical support for the test specimens that
E691Practice for Conducting an Interlaboratory Study to
insulates them electrically from each other and from ground, a
Determine the Precision of a Test Method
saturated calomel electrode (SCE), wires and other accessories
G3Practice for Conventions Applicable to Electrochemical
for electrical connections, and equipment for the measurement
Measurements in Corrosion Testing
of potential. See Note 2.
G193Terminology and Acronyms Relating to Corrosion
NOTE 2—Saturated calomel electrodes are available from several
manufacturers.Itisagoodpracticetoensuretheproperfunctioningofthe
3. Significance and Use
reference electrode by measuring its potential against one or more
3.1 The corrosion potential of an aluminum alloy depends
referenceelectrodes.Thepotentialdifferenceshouldnotexceed2or3mV.
upon the amounts of certain alloying elements that the alloy
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4.2 High-impedance(>10 Ω)voltmeterissuitableformea-
contains in solid solution. Copper and zinc, which are two of
surementofthepotential.Measurementofthispotentialshould
the major alloying elements for aluminum, have the greatest
be carried out to within 6 1 mV. Automatic data recording
effectwithcoppershiftingthepotentialinthenobleorpositive
systems may be used to permit the simultaneous measurement
direction, and zinc in the active or negative direction. For
of many specimens and the continuous recording of corrosion
potentials.
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This test method is under the jurisdiction of ASTM Committee G01 on
5. Reagents
Corrosion of Metals and is the direct responsibility of Subcommittee G01.11 on
Electrochemical Measurements in Corrosion Testing.
5.1 Purity of Reagents—Reagent grade chemicals shall be
Current edition approved May 1, 2012. Published October 2012. Originally
used in all tests. Unless otherwise indicated, it is intended that
approved in 1981. Last previous edition approved in 2009 as G69–97(2009). DOI:
10.1520/G0069-12.
2
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
3
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.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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G69−12
all reagents shall conform to the specifications of the Comm
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This document is not anASTM standard and is intended only to provide the user of anASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation:G69–97 (Reapproved 2009) Designation:G69–12
Standard Test Method for
1
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
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. See Practice G193.
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.
2. Referenced Documents
2
2.1 ASTM Standards:
D1193 Specification for Reagent Water Specification for Reagent Water
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
G3 Practice for Conventions Applicable to Electrochemical Measurements in Corrosion Testing
G193 Terminology and Acronyms Relating to Corrosion
3. Significance and Use
3.1 Thecorrosionpotentialofanaluminumalloydependsupontheamountsofcertainalloyingelementsthatthealloycontains
insolidsolution.Copperandzinc,whicharetwoofthemajoralloyingelementsforaluminum,havethegreatesteffectwithcopper
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 of –750 mV when measured in accordance with this practice,method,
2024–T3 alloy with nearly all of its nominal 4.3 % copper in solid solution, a potential of−600 to−620 mV (Note 2), of –600 to
–620 mV, depending upon the rate of quenching and 7072 alloy with nearly all of its nominal 1.0 % zinc in solid solution, a
3
potential of−885of —885 mV (SCE) (1-3).Note2—The potential depends upon the rate of quenching.
3.2 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 alcladAlclad products (2).
4. Apparatus
4.1 The apparatus consists of an inert container for the test solution, a mechanical support for the test specimens that insulates
them electrically from each other and from ground, a saturated calomel electrode (SCE) (see Note 3), (SCE), wires and other
accessories for electrical connections, and equipment for the measurement of potential. See Note 2.
NOTE 32—Saturatedcalomelelectrodesareavailablefromseveralmanufacturers.Itisagoodpracticetoensuretheproperfunctioningofthereference
electrode by measuring its potential against one or more reference electrodes. The potential difference should not exceed 2 or 3 mV.
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4.2Ahigh-impedence4.2 High-impedance(>10 Ω)voltmeterissuitableformeasurementofthepotential.Measurementofthis
1
This test method is under the jurisdiction ofASTM Committee G01 on Corrosion of Metals and is the direct responsibility of Subcommittee G01.11 on Electrochemical
Measurements in Corrosion Testing.
Current edition approved May 1, 2009.2012. Published May 2009.October 2012. Originally approved in 1981. Last previous edition approved in 20032009as
G69–97(20039). DOI: 10.1520/G0069-97R09.10.1520/G0069-12.
2
ForreferencedASTMstandards,visittheASTMwebsite,www.astm.org,orcontactASTMCustomerServiceatservice@astm.org.For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
3
All alloy designations are those of the Aluminum Association.
3
The boldface numbers in parentheses refer to the references at the end of this standar
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