ASTM G34-01(2007)
(Test Method)Standard Test Method for Exfoliation Corrosion Susceptibility in 2XXX and 7XXX Series Aluminum Alloys (EXCO Test)
Standard Test Method for Exfoliation Corrosion Susceptibility in 2XXX and 7XXX Series Aluminum Alloys (EXCO Test)
SIGNIFICANCE AND USE
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).
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.4 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.
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 reported5 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.
SCOPE
1.1 This test method covers a procedure for constant immersion exfoliation corrosion (EXCO) testing of high-strength 2XXX 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).
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 and health practices and determine the applicability of regulatory limitations prior to use.
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: G34 − 01(Reapproved 2007)
Standard Test Method for
Exfoliation Corrosion Susceptibility in 2XXX and 7XXX
Series Aluminum Alloys (EXCO Test)
ThisstandardisissuedunderthefixeddesignationG34;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope 2.2 ASTM Adjuncts:
Illustrations (Enlarged Glossy Prints)
1.1 This test method covers a procedure for constant im-
mersion exfoliation corrosion (EXCO) testing of high-strength
3. Terminology
2XXX and 7XXX series aluminum alloys.
3.1 Definitions:
NOTE 1—This test method was originally developed for research and
3.1.1 exfoliation—corrosion that proceeds laterally from the
development purposes; however, it is referenced, in specific material
sites of initiation along planes parallel to the surface, generally
specifications, as applicable for evaluating production material (refer to
at grain boundaries, forming corrosion products that force
Section 14 on Precision and Bias).
metal away from the body of the material giving rise to a
1.2 This test method applies to all wrought products such as
layered appearance (Terminology G15).
sheet, plate, extrusions, and forgings produced from conven-
4. Summary of Test Method
tional ingot metallurgy process.
4.1 This test method provides an accelerated exfoliation
1.3 Thistestmethodcanbeusedwithanyformofspecimen
corrosion test for 2XXX and 7XXX series aluminum alloys
or part that can be immersed in the test solution.
that involves the continuous immersion of test materials in a
1.4 This standard does not purport to address all of the
solution containing 4 M sodium chloride, 0.5 M potassium
safety concerns, if any, associated with its use. It is the
nitrate, and 0.1 M nitric acid at 25 6 3°C (77 6 5°F). The
responsibility of the user of this standard to establish appro-
susceptibility to exfoliation is determined by visual
priate safety and health practices and determine the applica-
examination, with performance ratings established by refer-
bility of regulatory limitations prior to use.
ence to standard photographs.
2. Referenced Documents
5. Significance and Use
2.1 ASTM Standards: 5.1 This test method was originally developed for research
D1193 Specification for Reagent Water
and development purposes; however, it is referenced, in
E3 Guide for Preparation of Metallographic Specimens specific material specifications, as applicable for evaluating
G15 Terminology Relating to Corrosion and Corrosion Test-
productionmaterial(refertoSection14onPrecisionandBias).
ing (Withdrawn 2010)
5.2 Use of this test method provides a useful prediction of
G112 Guide for Conducting Exfoliation Corrosion Tests in
the exfoliation corrosion behavior of these alloys in various
Aluminum Alloys
types of outdoor service, especially in marine and industrial
environments. The test solution is very corrosive and repre-
sents the more severe types of environmental service,
This test method is under the jurisdiction of ASTM Committee G01 on excluding, of course, unusual chemicals not likely to be
Corrosion of Metals and is the direct responsibility of Subcommittee G01.05 on
encountered in natural environments.
Laboratory Corrosion Tests.
Current edition approved May 1, 2007. Published May 2007. Originally
approved in 1972. Last previous edition approved in 2001 as G34–01. DOI:
10.1520/G0034-01R07. Available from ASTM International Headquarters. Order Adjunct No.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or ADJG003402. Original adjunct produced in 1980.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Ketcham, S. J., and Jeffrey, P. W., “Exfoliation Corrosion Testing of 7178 and
Standards volume information, refer to the standard’s Document Summary page on 7075AluminumAlloys” (Report ofASTM G01.05 Interlaboratory Testing Program
the ASTM website. in Cooperation with the Aluminum Association); and Sprowls, D. O., Walsh, J. D.,
The last approved version of this historical standard is referenced on and Shumaker, M. B., “Simplified Exfoliation Testing of Aluminum Alloys,”
www.astm.org. Localized Corrosion—Cause of Metal Failure, ASTM STP 516, ASTM, 1972.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G34 − 01 (2007)
5.3 The exfoliation ratings were arbitrarily chosen to illus- 9. Test Specimens
trate a wide range in resistance to exfoliation in this test.
9.1 Specimens may be of any practical size or shape.
However, it remains to be determined whether correlations can
Nevertheless, for the results to be of most significance a
be established between EXCO test ratings and realistic service
specimen size of at least 50 by 100 mm (2 by 4 in.), or the
conditions for a given alloy. It is an ongoing activity of the
equivalent, is recommended.
Task Group on Exfoliation Corrosion of Aluminum Alloys
9.2 The edges of sawed specimens need not be machined,
(G01.05.02.08) to maintain outdoor exposure tests for this
but specimens obtained by blanking or shearing shall have
purpose. For example, it has been reported that samples of
edges dressed by machining or filling to a depth equal to the
Al-Zn-Mg-CualloysratedEAorPina48-hEXCOtestdidnot
thickness of the specimen to remove cold-worked metal.
develop more than a slight amount of incipient exfoliation
(EA) during six- to nine-year exposures to seacoast atmo-
9.3 Remove the cladding of alclad sheet by machining the
spheres, whereas, ED rated materials in most cases developed
test surface; remove or mask the cladding on the back side
severe exfoliation within a year in the seacoast atmosphere. It
(non-test surface) also.
is anticipated that additional comparisons will become avail-
9.4 When removing test specimens from extrusions and
able as the outdoor tests are extended.
forgings, take care to avoid specimen locations underneath
flanges, ribs, etc., where the grain structure is usually variable.
6. Apparatus
6.1 Any suitable glass, plastic, or similarly inert container
10. Standardization
can be used to contain the solution and specimens during the
10.1 To provide an indication when some inadvertent de-
period of test. Depending upon the shape and size of the
viation from the correct test conditions occurs, it is necessary
specimens, rods or racks of glass, plastic, or any inert sub-
to expose to the test at regular intervals a control specimen of
stance shall be used to support the specimen above the bottom
a material with known resistance. This control should exhibit
of the container. The container should be fitted with a loose-
the same degree of exfoliation each time it is included in the
fitting cover to reduce evaporation.
test.
7. Reagents
10.2 The control may be any material of the alloy type
included in the scope of this test method, preferably one with
7.1 Purity of Reagents—The test solution shall be prepared
with reagent grade sodium chloride (NaCl), potassium nitrate an intermediate degree of susceptibility (Fig. 1 and Fig. 2).
(KNO ), and nitric acid (HNO ).
3 3
11. Procedure
7.2 Purity of Water—Distilled or deionized water shall be
used to prepare test solution.The water purity must conform to 11.1 Degrease the specimens with a suitable solvent.
Specification D1193, Type IV reagent water, except that for
11.2 Mask the back surfaces of the specimens to minimize
this method, the values of chloride and sodium can be
corrosionofnon-testareas.Protectivecoatingsmusthavegood
disregarded.
adherence to avoid crevice corrosion beneath the coating; also,
7.3 A test solution of the following composition shall be they should not contain leachable ions or protective oils that
used:
willinfluencethecorrosionofthetestsurface.(SeeFigs.1-6.)
NaCl (4.0 M)
11.3 Use the solution in sufficient quantity to provide a
KNO (0.5 M)
3 2
volume-to-metal surface area ratio of 10 to 30 mL/cm (65 to
HNO (0.1 M)
200 mL/in. ). Include all exposed metal area in the determina-
Dissolve 234 g of NaCl, 50 g of KNO in water, and add 6.3
tion of total surface area.
mL of concentrated HNO (70 weight %). Dilute to 1 L. This
solution has an apparent pH of 0.4.
11.4 Use fresh solution at the start of each test. Do not
change the solution even though the pH increases during the
7.4 The solution shall be maintained at a temperature of 25
test.ItisnormalforthepHtoincreasefromtheinitialapparent
6 3°C (77 6 5°F).
value of 0.4 to about 3 during the first several hours depending
upon the amount of corrosion that occurs.
8. Sampling
11.5 Immerse the specimens in the solution using rods or
8.1 Sampling procedures are not considered applicable to
racks of inert material to support the specimens above the
this test method, as they are often covered by product specifi-
bottom of the container. Place the test surface upward in a
cations. It is assumed that the test specimens are removed from
horizontal position to prevent loss of exfoliated metal from the
representative samples of materials.
surface of the specimen. Do not concurrently immerse in the
same container alloys containing less than 0.25 % copper with
Sprowls, D. O., Summerson, T. J., and Loftin, F. E., “Exfoliation Corrosion
those containing greater amounts of copper.
Testing of 7075 and 7178 Aluminum Alloys—Interim Report on Atmospheric
Exposure Tests” (Report of ASTM G01.05.02 Interlaboratory Testing Program in 11.6 The following maximum periods of exposure are
Cooperation with theAluminumAssociation); and Lifka, B.W. and Sprowls, D. O.,
recommended for testing the alloy types indicated:
“Relationship of Accelerated Test Methods for Exfoliation Resistance in 7XXX
2XXX Series 96 h
Series Aluminum Alloys With Exposure to a Seacoast Atmosphere,” Corrosion in
7XXX Series 48 h
Natural Environments, ASTM STP 558, ASTM, 1974.
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