ASTM G34-23

Standard Test Method for Exfoliation Corrosion Susceptibility in 2XXX and 7XXX Series Aluminum Alloys (EXCO Test)

SIGNIFICANCE AND USE
5.1 This test method was originally developed for research and development purposes; however, it is referenced, in specific material specifications, as applicable for evaluating production material (refer to Section 14 on Precision and Bias).  
5.2 Use of this test method provides a useful prediction of the exfoliation corrosion behavior of these alloys in various types of outdoor service, especially in marine and industrial environments.5 The test solution is very corrosive and represents the more severe types of environmental service, excluding, of course, unusual chemicals not likely to be encountered in natural environments.  
5.3 The exfoliation ratings were arbitrarily chosen to illustrate a wide range in resistance to exfoliation in this test. However, it remains to be determined whether correlations can be established between EXCO test ratings and realistic service conditions for a given alloy. For example, it has been reported6 that samples of Al-Zn-Mg-Cu alloys rated EA or P in a 48 h EXCO test did not develop more than a slight amount of incipient exfoliation (EA) during six- to nine-year exposures to seacoast atmospheres, whereas, ED rated materials in most cases developed severe exfoliation within a year in the seacoast atmosphere.
SCOPE
1.1 This test method covers a procedure for constant immersion exfoliation corrosion (EXCO) testing of high-strength 2XXX (see Note 2) and 7XXX series aluminum alloys.  
Note 1: This test method was originally developed for research and development purposes; however, it is referenced, in specific material specifications, as applicable for evaluating production material (refer to Section 14 on Precision and Bias).
Note 2: Some Al-Cu-Li alloys are registered in the 2xxx family. This test method has been reported as non representative of performance in outdoor atmospheres for various Al-Cu-Li alloys in both as-quenched and artificially aged tempers.2  
1.2 This test method applies to all wrought products such as sheet, plate, extrusions, and forgings produced from conventional ingot metallurgy process.  
1.3 This test method can be used with any form of specimen or part that can be immersed in the test solution.  
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

• Status: Published
• Publication Date: 30-Nov-2023
• ICS: 77.040.30 - Chemical analysis of metals
• Technical Committee: G01 - Corrosion of Metals
• Drafting Committee: G01.05 - Laboratory Corrosion Tests

Relations

• Replaces: ASTM G34-01(2018)e1 - Standard Test Method for Exfoliation Corrosion Susceptibility in 2XXX and 7XXX Series Aluminum Alloys (EXCO Test)
• Effective Date: 01-Dec-2023
• Referred By: ASTM G111-21a - Standard Guide for Corrosion Tests in High Temperature or High Pressure Environment, or Both
• Effective Date: 01-Dec-2023
• Referred By: ASTM G112-22 - Standard Guide for Conducting Exfoliation Corrosion Tests in Aluminum Alloys
• Effective Date: 01-Dec-2023
• Referred By: ASTM B221M-21 - Standard Specification for Aluminum and Aluminum-Alloy Extruded Bars, Rods, Wire, Profiles, and Tubes (Metric)
• Effective Date: 01-Dec-2023
• Referred By: ASTM B209/B209M-21a - Standard Specification for Aluminum and Aluminum-Alloy Sheet and Plate
• Effective Date: 01-Dec-2023
• Referred By: ASTM G107-95(2020)e1 - Standard Guide for Formats for Collection and Compilation of Corrosion Data for Metals for Computerized Database Input
• Effective Date: 01-Dec-2023
• Referred By: ASTM B221-21 - Standard Specification for Aluminum and Aluminum-Alloy Extruded Bars, Rods, Wire, Profiles, and Tubes
• Effective Date: 01-Dec-2023
• Referred By: ASTM G31-21 - Standard Guide for Laboratory Immersion Corrosion Testing of Metals
• Effective Date: 01-Dec-2023

Overview

ASTM G34-23: Standard Test Method for Exfoliation Corrosion Susceptibility in 2XXX and 7XXX Series Aluminum Alloys (EXCO Test) provides an internationally recognized procedure for evaluating the susceptibility of aluminum alloys to exfoliation corrosion. Originally developed for research and development, this standard is now widely referenced in material specifications to assess production materials. Using an aggressive constant immersion environment, ASTM G34-23 helps predict how high-strength 2XXX and 7XXX series aluminum alloys-commonly used in demanding structures-may perform when exposed to severe corrosive environments, such as marine and industrial atmospheres.

Key Topics

• Purpose of the EXCO Test: Assesses the susceptibility of wrought aluminum alloys (2XXX and 7XXX series) to exfoliation corrosion under controlled laboratory conditions.
• Test Method: Involves continuous immersion of specimens in a corrosive solution composed of sodium chloride, potassium nitrate, and nitric acid, maintained at 25 °C ± 3 °C.
• Applicability: Suitable for all wrought products (sheet, plate, extrusions, forgings) produced from conventional ingot metallurgy, as well as any part that can be fully immersed in the test solution.
• Exfoliation Corrosion: Defined as subsurface corrosion that spreads laterally along grain boundaries, forming layered damage that can compromise structural integrity.
• Visual Rating System: Specimens are classified as showing no attack (N), pitting (P), or various degrees of exfoliation (EA to ED) based on comparison to standard reference photographs.
• Precision and Bias: The method is highly repeatable for highly susceptible alloys, but ratings for intermediate levels of resistance may vary between laboratories due to subjective interpretation.

Applications

• Material Qualification and Quality Control: Frequently referenced in aluminum alloy material specifications, the ASTM G34-23 test method is vital for qualifying and monitoring high-strength aluminum materials used in critical applications.
• Research and Product Development: Provides a reproducible benchmark for comparing the exfoliation corrosion resistance of new alloy formulations or tempers during early-stage research.
• Outdoor Service Prediction: Offers valuable insight into the anticipated performance of 2XXX and 7XXX aluminum alloys in service environments prone to severe corrosion, helping users select appropriate alloys or surface treatments for marine or industrial applications.
• Failure Assessment: Used as a diagnostic tool to evaluate the corrosion resistance of in-service components suspected of degradation due to exfoliation.
• Regulatory and Procurement Compliance: Satisfies requirements from industry bodies, government agencies, and contractual agreements where proven corrosion resistance is mandatory.

Related Standards

• ASTM D1193 - Specification for Reagent Water: Defines water purity requirements for solution preparation.
• ASTM E3 - Guide for Preparation of Metallographic Specimens: Procedures for preparing samples for inspection and classification.
• ASTM G112 - Guide for Conducting Exfoliation Corrosion Tests in Aluminum Alloys: Supplemental guidance for exfoliation corrosion testing.
• ASTM G193 - Terminology and Acronyms Relating to Corrosion: Definitions of corrosion-related terms used throughout ASTM G34-23.

By following ASTM G34-23, laboratories and industries can ensure consistent evaluation of aluminum alloys' resistance to exfoliation corrosion, supporting safer material selection and enhanced service life in demanding environments. This standard stands as an important resource for metallurgists, quality assurance professionals, and engineers involved in the selection and validation of corrosion-resistant aluminum materials.

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: G34 − 23
Standard Test Method for
Exfoliation Corrosion Susceptibility in 2XXX and 7XXX
Series Aluminum Alloys (EXCO Test)
This standard is issued under the fixed designation G34; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope 2. Referenced Documents
2.1 ASTM Standards:
1.1 This test method covers a procedure for constant im-
D1193 Specification for Reagent Water
mersion exfoliation corrosion (EXCO) testing of high-strength
E3 Guide for Preparation of Metallographic Specimens
2XXX (see Note 2) and 7XXX series aluminum alloys.
G112 Guide for Conducting Exfoliation Corrosion Tests in
NOTE 1—This test method was originally developed for research and
Aluminum Alloys
development purposes; however, it is referenced, in specific material
G193 Terminology and Acronyms Relating to Corrosion
specifications, as applicable for evaluating production material (refer to
Section 14 on Precision and Bias).
2.2 ASTM Adjunct:
NOTE 2—Some Al-Cu-Li alloys are registered in the 2xxx family. This
Adjunct to G34 Test Method for Exfoliation Corrosion
test method has been reported as non representative of performance in
Susceptibility in 2XXX and 7XXX Series Aluminum
outdoor atmospheres for various Al-Cu-Li alloys in both as-quenched and
Alloys (EXCO Test) (Digital PDF illustrations of appear-
artificially aged tempers.
ance classifications – 6 glossy photos (B&W))
1.2 This test method applies to all wrought products such as
sheet, plate, extrusions, and forgings produced from conven-
3. Terminology
tional ingot metallurgy process.
3.1 Definitions:
1.3 This test method can be used with any form of specimen
3.1.1 exfoliation corrosion, n—subsurface corrosion that
or part that can be immersed in the test solution.
proceeds laterally from the sites of initiation along planes
parallel to the surface forming corrosion products that force
1.4 This standard does not purport to address all of the
metal away from the body of the material, giving rise to a
safety concerns, if any, associated with its use. It is the
layered appearance resembling the pages of a book (Terminol-
responsibility of the user of this standard to establish appro-
ogy G193).
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
4. Summary of Test Method
1.5 This international standard was developed in accor-
dance with internationally recognized principles on standard-
4.1 This test method provides an accelerated exfoliation
ization established in the Decision on Principles for the
corrosion test for 2XXX and 7XXX series aluminum alloys
Development of International Standards, Guides and Recom-
that involves the continuous immersion of test materials in a
mendations issued by the World Trade Organization Technical
solution containing 4 M sodium chloride, 0.5 M potassium
Barriers to Trade (TBT) Committee.
nitrate, and 0.1 M nitric acid at 25 °C 6 3 °C (77 °F 6 5 °F).
The susceptibility to exfoliation is determined by visual
examination, with performance ratings established by refer-
1 ence to standard photographs.
This test method is under the jurisdiction of ASTM Committee G01 on
Corrosion of Metals and is the direct responsibility of Subcommittee G01.05 on
Laboratory Corrosion Tests.
Current edition approved Dec. 1, 2023. Published December 2023. Originally
ɛ1
approved in 1972. Last previous edition approved in 2018 as G34 – 01 (2018) . For referenced ASTM standards, visit the ASTM website, www.astm.org, or
DOI: 10.1520/G0034-23. contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Colvin, E. L., and Murtha, S. J., “Exfoliation Corrosion Testing of Al-Li Alloys Standards volume information, refer to the standard’s Document Summary page on
2090 and 2091,” Proceedings of the Fifth International Aluminum-Lithium the ASTM website.
Conference, Williamsburg, VA, Materials and Component Engineering Publications Available from ASTM International Headquarters. Order Adjunct No.
Ltd, U.K., March 24–31, 1989, p. 1251. ADJG003402-E-PDF. Original adjunct produced in 1980.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G34 − 23
5. Significance and Use
NaCl (4.0 M)
KNO (0.5 M)
5.1 This test method was originally developed for research
HNO (0.1 M)
and development purposes; however, it is referenced, in
Dissolve 234 g of NaCl, 50 g of KNO in water, and add
specific material specifications, as applicable for evaluating
6.3 mL of concentrated HNO (70 weight %). Dilute to 1 L.
production material (refer to Section 14 on Precision and Bias).
This solution has an apparent pH of 0.4.
5.2 Use of this test method provides a useful prediction of
7.4 The solution shall be maintained at a temperature of
the exfoliation corrosion behavior of these alloys in various
25 °C 6 3 °C (77 °F 6 5 °F).
types of outdoor service, especially in marine and industrial
environments. The test solution is very corrosive and repre- 8. Sampling
sents the more severe types of environmental service,
8.1 Sampling procedures are not considered applicable to
excluding, of course, unusual chemicals not likely to be
this test method, as they are often covered by product specifi-
encountered in natural environments.
cations. It is assumed that the test specimens are removed from
5.3 The exfoliation ratings were arbitrarily chosen to illus- representative samples of materials.
trate a wide range in resistance to exfoliation in this test.
9. Test Specimens
However, it remains to be determined whether correlations can
be established between EXCO test ratings and realistic service 9.1 Specimens may be of any practical size or shape.
conditions for a given alloy. For example, it has been reported
Nevertheless, for the results to be of most significance a
that samples of Al-Zn-Mg-Cu alloys rated EA or P in a 48 h specimen size of at least 50 mm by 100 mm (2 in. by 4 in.), or
EXCO test did not develop more than a slight amount of
the equivalent, is recommended.
incipient exfoliation (EA) during six- to nine-year exposures to
9.2 The edges of sawed specimens need not be machined,
seacoast atmospheres, whereas, ED rated materials in most
but specimens obtained by blanking or shearing shall have
cases developed severe exfoliation within a year in the seacoast
edges dressed by machining or filling to a depth equal to the
atmosphere.
thickness of the specimen to remove cold-worked metal.
9.3 Remove the cladding of alclad sheet by machining the
6. Apparatus
test surface; remove or mask the cladding on the back side
6.1 Any suitable glass, plastic, or similarly inert container
(non-test surface) also.
can be used to contain the solution and specimens during the
9.4 When removing test specimens from extrusions and
period of test. Depending upon the shape and size of the
forgings, take care to avoid specimen locations underneath
specimens, rods or racks of glass, plastic, or any inert sub-
flanges, ribs, etc., where the grain structure is usually variable.
stance shall be used to support the specimen above the bottom
of the container. The container should be fitted with a loose-
10. Standardization
fitting cover to reduce evaporation.
10.1 To provide an indication when some inadvertent de-
viation from the correct test conditions occurs, it is necessary
7. Reagents
to expose to the test at regular intervals a control specimen of
7.1 Purity of Reagents—The test solution shall be prepared
a material with known resistance. This control should exhibit
with reagent grade sodium chloride (NaCl), potassium nitrate
the same degree of exfoliation each time it is included in the
(KNO ), and nitric acid (HNO ).
3 3
test.
7.2 Purity of Water—Distilled or deionized water shall be
10.2 The control may be any material of the alloy type
used to prepare test solution. The water purity must conform to
included in the scope of this test method, preferably one with
Specification D1193, Type IV reagent water, except that for
an intermediate degree of susceptibility (Fig. 1 and Fig. 2).
this method, the values of chloride and sodium can be
disregarded. 11. Procedure
11.1 Degrease the specimens with a suitable solvent.
7.3 A test solution of the following composition shall be
used:
11.2 Mask the back surfaces of the specimens to minimize
corrosion of non-test areas. Protective coatings must have good
adherence to avoid crevice corrosion beneath the coating; also,
they should not contain leachable ions or protective oils that
Ketcham, S. J., and Jeffrey, P. W., “Exfoliation Corrosion Testing of 7178 and
7075 Aluminum Alloys” (Report of ASTM G01.05 Interlaboratory Testing Program
will influence the corrosion of the test surface. (See Figs. 1-6.)
in Cooperation with the Aluminum Association); and Sprowls, D. O., Walsh, J. D.,
11.3 Use the solution in sufficient quantity to provide a
and Shumaker, M. B., “Simplified Exfoliation Testing of Aluminum Alloys,”
Localized Corrosion—Cause of Metal Failure, ASTM STP 516, ASTM, 1972.
volume-to-metal surface area ratio of 10 mL ⁄cm to
Sprowls, D. O., Summerson, T. J., and Loftin, F. E., “Exfoliation Corrosion 2 2 2
30 mL ⁄cm (65 mL ⁄in. to 200 mL ⁄in. ). Include all exposed
Testing of 7075 and 7178 Aluminum Alloys—Interim Report on Atmospheric
metal area in the determination of total surface area.
Exposure Tests” (Report of ASTM G01.05.02 Interlaboratory Testing Program in
Cooperation with the Aluminum Association); and Lifka, B. W. and Sprowls, D. O.,
11.4 Use fresh solution at the start of each test. Do not
“Relationship of Accelerated Test Methods for Exfoliation Resistance in 7XXX
change the solution even though the pH increases during the
Series Aluminum Alloys With Exposure to a Seacoast Atmosphere,” Corrosion in
Natural Environments, ASTM STP 558, ASTM, 1974. test. It is normal for the pH to increase from the initial apparent
G34 − 23
Undermining pitting that may form the surface give the appearance of incipient exfoliation (Keller’s Etch; 100×).
FIG. 1 Examples of Pitting Corrosion
value of 0.4 to about 3 during the first several hours d
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM 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.
´1
Designation: G34 − 01 (Reapproved 2018) G34 − 23
Standard Test Method for
Exfoliation Corrosion Susceptibility in 2XXX and 7XXX
Series Aluminum Alloys (EXCO Test)
This standard is issued under the fixed designation G34; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
ε NOTE—Adjunct description/stock number updated editorially and editorial changes made throughout in November 2020.
1. Scope
1.1 This test method covers a procedure for constant immersion exfoliation corrosion (EXCO) testing of high-strength 2XXX (see
Note 2) and 7XXX series aluminum alloys.
NOTE 1—This test method was originally developed for research and development purposes; however, it is referenced, in specific material specifications,
as applicable for evaluating production material (refer to Section 14 on Precision and Bias).
NOTE 2—Some Al-Cu-Li alloys are registered in the 2xxx family. This test method has been reported as non representative of performance in outdoor
atmospheres for various Al-Cu-Li alloys in both as-quenched and artificially aged tempers.
1.2 This test method applies to all wrought products such as sheet, plate, extrusions, and forgings produced from conventional
ingot metallurgy process.
1.3 This test method can be used with any form of specimen or part that can be immersed in the test solution.
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.
2. Referenced Documents
2.1 ASTM Standards:
D1193 Specification for Reagent Water
E3 Guide for Preparation of Metallographic Specimens
This test method is under the jurisdiction of ASTM Committee G01 on Corrosion of Metals and is the direct responsibility of Subcommittee G01.05 on Laboratory
Corrosion Tests.
Current edition approved Oct. 1, 2018Dec. 1, 2023. Published November 2018December 2023. Originally approved in 1972. Last previous edition approved in 20132018
ɛ1
as G34 – 01 (2013).(2018) . DOI: 10.1520/G0034-01R18E01.10.1520/G0034-23.
Colvin, E. L., and Murtha, S. J., “Exfoliation Corrosion Testing of Al-Li Alloys 2090 and 2091,” Proceedings of the Fifth International Aluminum-Lithium Conference,
Williamsburg, VA, Materials and Component Engineering Publications Ltd, U.K., March 24–31, 1989, p. 1251.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G34 − 23
G112 Guide for Conducting Exfoliation Corrosion Tests in Aluminum Alloys
G193 Terminology and Acronyms Relating to Corrosion
2.2 ASTM Adjunct:
Adjunct to G34 Test Method for Exfoliation Corrosion Susceptibility in 2XXX and 7XXX Series Aluminum Alloys (EXCO
Test) (Digital PDF illustrations of appearance classifications – 6 glossy photos (B&W))
3. Terminology
3.1 Definitions:
3.1.1 exfoliation—exfoliation corrosion, n—subsurface corrosion that proceeds laterally from the sites of initiation along planes
parallel to the surface, generally at grain boundaries, surface forming corrosion products that force metal away from the body of
the material, giving rise to a layered appearance resembling the pages of a book (Terminology G193).
4. Summary of Test Method
4.1 This test method provides an accelerated exfoliation corrosion test for 2XXX and 7XXX series aluminum alloys that involves
the continuous immersion of test materials in a solution containing 4 M sodium chloride, 0.5 M potassium nitrate, and 0.1 M nitric
acid at 25 °C 6 3 °C (77 °F 6 5 °F). The susceptibility to exfoliation is determined by visual examination, with performance
ratings established by reference to standard photographs.
5. Significance and Use
5.1 This test method was originally developed for research and development purposes; however, it is referenced, in specific
material specifications, as applicable for evaluating production material (refer to Section 14 on Precision and Bias).
5.2 Use of this test method provides a useful prediction of the exfoliation corrosion behavior of these alloys in various types of
outdoor service, especially in marine and industrial environments. The test solution is very corrosive and represents the more
severe types of environmental service, excluding, of course, unusual chemicals not likely to be encountered in natural
environments.
5.3 The exfoliation ratings were arbitrarily chosen to illustrate a wide range in resistance to exfoliation in this test. However, it
remains to be determined whether correlations can be established between EXCO test ratings and realistic service conditions for
a given alloy. It is an ongoing activity of the Task Group on Exfoliation Corrosion of Aluminum Alloys (G01.05.02.08) to maintain
outdoor exposure tests for this purpose. For example, it has been reported that samples of Al-Zn-Mg-Cu alloys rated EA or P in
a 48 h EXCO test did not develop more than a slight amount of incipient exfoliation (EA) during six- to nine-year exposures to
seacoast atmospheres, whereas, ED rated materials in most cases developed severe exfoliation within a year in the seacoast
atmosphere. It is anticipated that additional comparisons will become available as the outdoor tests are extended.
6. Apparatus
6.1 Any suitable glass, plastic, or similarly inert container can be used to contain the solution and specimens during the period
of test. Depending upon the shape and size of the specimens, rods or racks of glass, plastic, or any inert substance shall be used
to support the specimen above the bottom of the container. The container should be fitted with a loose-fitting cover to reduce
evaporation.
7. Reagents
7.1 Purity of Reagents—The test solution shall be prepared with reagent grade sodium chloride (NaCl), potassium nitrate (KNO ),
and nitric acid (HNO ).
Available from ASTM International Headquarters. Order Adjunct No. ADJG003402-E-PDF. Original adjunct produced in 1980.
Ketcham, S. J., and Jeffrey, P. W., “Exfoliation Corrosion Testing of 7178 and 7075 Aluminum Alloys” (Report of ASTM G01.05 Interlaboratory Testing Program in
Cooperation with the Aluminum Association); and Sprowls, D. O., Walsh, J. D., and Shumaker, M. B., “Simplified Exfoliation Testing of Aluminum Alloys,” Localized
Corrosion—Cause of Metal Failure, ASTM STP 516, ASTM, 1972.
Sprowls, D. O., Summerson, T. J., and Loftin, F. E., “Exfoliation Corrosion Testing of 7075 and 7178 Aluminum Alloys—Interim Report on Atmospheric Exposure Tests”
(Report of ASTM G01.05.02 Interlaboratory Testing Program in Cooperation with the Aluminum Association); and Lifka, B. W. and Sprowls, D. O., “Relationship of
Accelerated Test Methods for Exfoliation Resistance in 7XXX Series Aluminum Alloys With Exposure to a Seacoast Atmosphere,” Corrosion in Natural Environments, ASTM
STP 558, ASTM, 1974.
G34 − 23
7.2 Purity of Water—Distilled or deionized water shall be used to prepare test solution. The water purity must conform to
Specification D1193, Type IV reagent water, except that for this method, the values of chloride and sodium can be disregarded.
7.3 A test solution of the following composition shall be used:
NaCl (4.0 M)
KNO (0.5 M)
HNO (0.1 M)
Dissolve 234 g of NaCl, 50 g of KNO in water, and add 6.3 mL 6.3 mL of concentrated HNO (70 weight %). Dilute to 1 L.
3 3
This solution has an apparent pH of 0.4.
7.4 The solution shall be maintained at a temperature of 25 °C 6 3 °C (77 °F 6 5 °F).
8. Sampling
8.1 Sampling procedures are not considered applicable to this test method, as they are often covered by product specifications. It
is assumed that the test specimens are removed from representative samples of materials.
9. Test Specimens
9.1 Specimens may be of any practical size or shape. Nevertheless, for the results to be of most significance a specimen size of
at least 50 mm by 100 mm (2 in. by 4 in.), or the equivalent, is recommended.
9.2 The edges of sawed specimens need not be machined, but specimens obtained by blanking or shearing shall have edges dressed
by machining or filling to a depth equal to the thickness of the specimen to remove cold-worked metal.
9.3 Remove the cladding of alclad sheet by machining the test surface; remove or mask the cladding on the back side (non-test
surface) also.
9.4 When removing test specimens from extrusions and forgings, take care to avoid specimen locations underneath flanges, ribs,
etc., where the grain structure is usually variable.
10. Standardization
10.1 To provide an indication when some inadvertent deviation from the correct test conditions occurs, it is necessary to expose
to the test at regular intervals a control specimen of a material with known resistance. This control should exhibit the same degree
of exfoliation each time it is included in the test.
10.2 The control may be any material of the alloy type included in the scope of this test method, preferably one with an
intermediate degree of susceptibility (Fig. 1 and Fig. 2).
11. Procedure
11.1 Degrease the specimens with a suitable solvent.
11.2 Mask the back surfaces of the specimens to minimize corrosion of non-test areas. Protective coatings must have good
adherence to avoid crevice corrosion beneath the coating; also, they should not contain leachable ions or protective oils that will
influence the corrosion of the test surface. (See Figs. 1-6.)
2 2
11.3 Use the solution in sufficient quantity to provide a volume-to-metal surface area ratio of 10 mL ⁄cm to 30 30 mL mL/cm⁄cm
2 2
(65 mL ⁄in. to 200 200 mL mL/in.⁄in. ). Include all exposed metal area in the determination of total surface area.
11.4 Use fresh solution at the start of each test. Do not change the solution even though the pH increases during the test. It is
normal for the pH to increase
...