ASTM G47-98(2004)
(Test Method)Standard Test Method for Determining Susceptibility to Stress-Corrosion Cracking of 2XXX and 7XXX Aluminum Alloy Products
Standard Test Method for Determining Susceptibility to Stress-Corrosion Cracking of 2XXX and 7XXX Aluminum Alloy Products
SIGNIFICANCE AND USE
The 3.5 % NaCl solution alternate immersion test provides a test environment for detecting materials that would be likely to be susceptible to SCC in natural outdoor environments, especially environments with marine influences.3 ,4 ,5 For determining actual serviceability of a material, other stress-corrosion tests should be performed in the intended service environment under conditions relating to the end use, including protective measures.
Although this test method is intended for certain alloy types and for testing products primarily in the short-transverse stressing direction, this method is useful for some other types of alloys and stressing directions.
SCOPE
1.1 This test method covers a uniform procedure for characterizing the resistance to stress-corrosion cracking (SCC) of high-strength aluminum alloy wrought products for the guidance of those who perform stress-corrosion tests, for those who prepare stress-corrosion specifications, and for materials engineers.
1.2 This test method covers method of sampling, type of specimen, specimen preparation, test environment, and method of exposure for determining the susceptibility to SCC of 2XXX (with 1.8 to 7.0 % copper) and 7XXX (with 0.4 to 2.8 % copper) aluminum alloy products, particularly when stressed in the short-transverse direction relative to the grain structure.
1.3 The values stated in SI units are to be regarded as standard. The inch-pound units in parentheses are provided for information.
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: G47 – 98 (Reapproved 2004)
Standard Test Method for
Determining Susceptibility to Stress-Corrosion Cracking of
2XXX and 7XXX Aluminum Alloy Products
This standard is issued under the fixed designation G47; 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.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 G139 Test Method for Determining Stress-Corrosion
Cracking Resistance of Heat-Treatable Aluminum Alloy
1.1 This test method covers a uniform procedure for char-
Products Using Breaking Load Method
acterizing the resistance to stress-corrosion cracking (SCC) of
high-strength aluminum alloy wrought products for the guid-
3. Summary of Test Method
anceofthosewhoperformstress-corrosiontests,forthosewho
3.1 This test method provides a comprehensive procedure
prepare stress-corrosion specifications, and for materials engi-
foracceleratedstress-corrosiontestinghigh-strengthaluminum
neers.
alloy product forms, particularly when stressed in the short-
1.2 This test method covers method of sampling, type of
transverse grain direction. It specifies tests of constant-strain-
specimen, specimen preparation, test environment, and method
loaded, 3.18-mm (0.125-in.) tension specimens or C-rings
ofexposurefordeterminingthesusceptibilitytoSCCof2XXX
exposed to 3.5 % sodium chloride (NaCl) solution by alternate
(with 1.8 to 7.0 % copper) and 7XXX (with 0.4 to 2.8 %
immersion, and includes procedures for sampling various
copper) aluminum alloy products, particularly when stressed in
manufactured product forms, examination of exposed test
the short-transverse direction relative to the grain structure.
specimens, and interpretation of test results.
1.3 The values stated in SI units are to be regarded as
standard. The inch-pound units in parentheses are provided for
4. Significance and Use
information.
4.1 The 3.5 % NaCl solution alternate immersion test pro-
1.4 This standard does not purport to address all of the
vides a test environment for detecting materials that would be
safety concerns, if any, associated with its use. It is the
likely to be susceptible to SCC in natural outdoor environ-
responsibility of the user of this standard to establish appro-
3,4,5
ments,especiallyenvironmentswithmarineinfluences. For
priate safety and health practices and determine the applica-
determining actual serviceability of a material, other stress-
bility of regulatory limitations prior to use.
corrosion tests should be performed in the intended service
environmentunderconditionsrelatingtotheenduse,including
2. Referenced Documents
2 protective measures.
2.1 ASTM Standards:
4.2 Although this test method is intended for certain alloy
G38 Practice for Making and Using C-Ring Stress-
types and for testing products primarily in the short-transverse
Corrosion Test Specimens
stressing direction, this method is useful for some other types
G44 Practice for Exposure of Metals and Alloys by Alter-
of alloys and stressing directions.
nate Immersion in Neutral 3.5 % Sodium Chloride Solu-
tion
5. Interferences
G49 Practice for Preparation and Use of Direct Tension
5.1 A disadvantage of the 3.5 % NaCl solution alternate
Stress-Corrosion Test Specimens
immersion test is that severe pitting may develop in the
1 3
This test method, which was developed by a joint task group with the Romans, H. B., Stress Corrosion Testing, ASTM STP 425, ASTM, 1967, pp.
AluminumAssociation, Inc., is under the jurisdiction ofASTM Committee G01 on 182–208.
Corrosion of Metals, and is the direct responsibility of Subcommittee G01.06 on Brown, R. H., Sprowls, D. O., and Shumaker, M. B., “The Resistance of
Environmentally Assisted Cracking. Wrought High Strength Aluminum Alloys to Stress Corrosion Cracking,” Stress
Current edition approved May 1, 2004. Published May 2004. Originally CorrosionCrackingofMetals—AStateoftheArt,ASTMSTP518,ASTM,1972,pp.
approved in 1976. Last previous edition approved in 1998 as G47 – 98. DOI: 87–118.
10.1520/G0047-98R04. Sprowls, D. O., Summerson, T. J., Ugiansky, G. M., Epstein, S. G., and Craig,
For referenced ASTM standards, visit the ASTM website, www.astm.org, or H. L., Jr., “Evaluation of a Proposed Standard Method of Testing for Susceptibility
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM to Stress-Corrosion Cracking of High-Strength 7XXX Series Aluminum Alloy
Standards volume information, refer to the standard’s Document Summary page on Products,” Stress Corrosion-New Approaches, ASTM STP 610, ASTM, 1976, pp.
the ASTM website. 3–31.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
G47 – 98 (2004)
specimens. Such pitting in tension specimens with relatively from a side of the plate. (The side of the plate is defined as the
small cross section can markedly reduce the effective cross- edge parallel to the rolling direction.)
sectional area and produce a net section stress greater than the 7.2.3 Hand Forgings—Short-transverse specimens shall be
nominal gross section stress, resulting in either: (a) fracture by taken so that the stress is applied in a direction perpendicular
mechanical overload of a material that is not susceptible to to the forging flow lines. The region of maximum stress shall
SCC; or (b) SCC of a material at an actual stress higher than be centered in the forging thickness and approximately on the
the intended nominal test stress. The occurrence of either of longitudinal center line of the forging, no less than ⁄2 the
these phenomena might then interfere with a valid evaluation section thickness away from “as-heat treated” edges of the
of materials with relatively high resistance to stress corrosion. forging.
7.2.4 Die Forgings—Because of the wide variety of con-
6. Test Specimen
figurations of die forgings, guidelines are provided for only
6.1 TypeandSize—Nosingleconfigurationoftestspecimen
certain common types of shapes that are widely used. Short-
is applicable for the many complex shapes and sizes of
transverse specimens shall be taken so that the stress is applied
products that must be evaluated. A tension specimen is pre-
in a direction perpendicular to the forging flow lines and, if
ferred because it more consistently provides definite evidence
possible, with the region of maximum stress centered on the
of cracking and should be used whenever the size and shape of parting plane. The metal flow pattern in die forgings cannot
the product permits; it also provides a more severe test.
always be predicted, so only a few general rules are given, and
6.1.1 Tension Specimen—The diameter of the reduced sec- they are illustrated in Fig. 1. Departures from these rules
tion shall be 3.17 6 0.03 mm (0.125 6 0.001 in.).
should be made only on the basis of a study of forging flow
6.1.2 C-Ring (see Practices G38)—The use of C-rings lines indicating that the intended type of test would not be
permits short-transverse tests to be made of sections that are
obtained. In every case, a diagram should be filed with the test
too thin or complex for practical tests with a tension specimen. results to illustrate specimen locations and orientations.
C-rings may be of various sizes as required for the product to
7.2.4.1 Flanges—The centerline of the specimen shall be
be tested, but in no case less than 15.88 6 0.05 mm (0.625 6
12.70 61.27mm(0.500 60.050in.)fromthebaseofthefillet
0.002 in.) in outside diameter. The ratio of diameter to wall
of the flash except for flanges that are too thin, in which case,
thickness shall be kept in the range from 11:1 to 16:1.
the specimen should be centered.
6.2 Stressing Direction:
7.2.4.2 Flat-Top Die—The tension specimen should be
6.2.1 Short-Transverse Tests:
perpendicular to the parting plane and, if possible, centered in
6.2.1.1 For specified material thicknesses of 38.10 mm
the width.
(1.500 in.) and over, the tension specimen shall be used.
6.2.1.2 For specified material thicknesses of 17.78 through
38.08 mm (0.700 through 1.499 in.), a C-ring shall be used.A
tension specimen may be used if consistent with the provisions
of Practice G49.
6.2.2 For other stress directions in materials of 6.35 mm
(0.250 in.) and over, the tension specimen shall be used.
6.3 Surface Preparation—Test specimens shall be de-
greased prior to exposure.
7. Sampling and Number of Tests
7.1 Unless otherwise specified, tests shall be performed in
the short-transverse direction; the intention is to orient the
specimen so that the applied tensile stress is perpendicular to
the metal flow lines and in the short-transverse direction
relative to the grain structure. In rolled or extruded sections
that are approximately round or square, there is no true
short-transverse direction because in a transverse plane the
grainstendtobeequiaxial;and,insuchcases,thestressshould
be directed simply in the transverse direction. If, in certain
unusual cases, the grain structure is or tends to be equiaxial
also in the longitudinal direction, the stress shall be applied in
a direction parallel to the smallest dimension of the product.
7.2 Location of Specimens:
7.2.1 For products stress relieved by stretching (TX51,
TX510,TX511,TXX51,TXX510,TXX511),samplesshallnot
be taken from the portion under the stretcher grips.
7.2.2 Rolled Plate—Short-transverse specimens shall be
NOTE—Similar to that of typical machined part.
taken so that the region of maximum stress is centered on the
FIG. 1 Recommended Specimen Type and Location for Various
mid-plane of the plate and at least 2 ⁄2 plate thicknesses away Configurations of Die Forgings
G47 – 98 (2004)
7.2.4.3 Boss or Small Cylinder—The C-ring specimen 9.3.1 Interim Inspection:
should be centered on the parting plane and with the outside
Visuallyinspectspecimenseachworkingdayforevidenceof
diameter of the ring being 1.52 6 0.25 mm (0.060 6 0.010 in.)
cracking without removal of corrosion products. Inspection
from the forging surface (see Fig. 1). may be facilitated by wetting the specimen with the test
7.2.4.4 Large Cylinder—The centerline of tension speci-
solution and by examination at low magnifications.
mens shall be 12.70 6 1.27 mm (0.500 6 0.050 in.) from the
9.3.2 Final Examination—Perform final examination at a
base of the flash. If a C-ring is required, its outside diameter
magnification of at least 10X on all surviving specimens after
shall be 1.52 6 0.25 mm (0.060 6 0.010 in.) from the forging
cleaning them in concentrated (70%) nitric acid (HNO)at
surface (see Fig. 1).
room temperature followed by a water rinse. Section and
7.2.5 Extruded, Rolled, or Cold Finished Rod, Bar, and
metallographically examine any C-ring that is considered
Shapes:
suspect, as evidenced by linear pitting, to determine whether or
7.2.5.1 Width-to-Thickness Ratio Greater than 2—Short-
not SCC is present. Similar examination of fractured or
transverse specimens shall be taken so that the region of
cracked tension specimens also can be useful to verify SCC as
maximum stress is centered in the section thickness, at least
the cause of failure.
onesectionthicknessawayfromthesidesoftheproduct.Inthe
case of complex configurations for which the grain direction-
10. Interpretation of Results
ality cannot be predicted, specimen location shall be deter-
10.1 Criterion of Failure:
mined by means of macroetched transverse sections to ensure
10.1.1 Asample shall be considered to have failed the test if
a short-transverse specimen and to avoid regions of nearly
one or more of the specimens fail, except that the retest
equiaxial (transverse) grain flow.
provisions of Section 11 shall apply.
7.2.5.2 Width-to-Thickness Ratio of 2 or Less—Specimens
10.1.2 A specimen that has fractured or which exhibits
shall be centered in the section thickness so that the region of
cracking shall be considered as a stress corrosion failure unless
maximum stress application will be at least one half the section
proved otherwise by the provisions of 10.2 and 10.3.
thickness away from a fabricated surface, if possible. These
10.2 Macroscopic Examination—Cracking should be
specimens shall be considered to have a “transverse” orienta-
clearly differentiated from lined-up pitting. If the presence of
tion to the grain structure. When C-rings are required, they
SCC is questionable, metallographic examinations should be
shall be taken so that the region of maximum tensile stress is
performed to determine whether or not SCC is present.
3.18 6 0.25 mm (0.125 6 0.010 in.) from the product surface.
7.3 NumberofSpecimens—For each sample, which shall be
NOTE 1—When a specimen fractures within a relatively short time after
uniform in thickness and grain structure, a minimum of three exposure (ten days or less), metallographic examination is not necessary
because such rapid failures are characteristically due to SCC.
adjacent replicate specimens shall be tested.
10.3 Metallographic Examination:
8. Test Environment
10.3.1 Aspecimen that reveals intergranular cracking, even
8.1 Corrosion Test Environment—Specimens shall be ex-
when accompanied by transgranular cracking, shall be consid-
posedtothealternate10-minimmersion—50-mindryingcycle
ered as an SCC failure. Intergranular fissures that are no deeper
in accordance with Practice G44.
than the width of localized areas of intergranular corrosion or,
8.2 Length of Exposure—The test duration for 3.18-mm
in the case of C-rings, not deeper than those in unstressed or
(0.125-in.) tension specimens and C-rings shall be 10 days for
compressively stressed surfaces, shall not be considered as an
2XXX alloys or 20 days for 7XXX alloys, unless cracking
SCC failure. In the case of tension specimens, the depth of
occurssooner.Forspecimenstobetestedinthelongtransverse
intergranular fissures may be compared to those in an un-
direction, the test duration should be 40 days. Longer non-
stressed specimen when available.
standard test durations are likely to cause failures of the
10.3.2 A specimen that reveals only pitting corrosion (that
3.18-mm tension specimens as a result of severe pitting as
is, no intergranular attack), or pitting plus transgranular crack-
described in 5.1. There shall be no interruptions except as
ing, shall not be considered as an SCC failure.
required for periodic inspection of specimens or changing of
the solution.
NOTE 2—Transgranular cracking in the absence of intergranular attack
only occurs in pitted specimens under extremely high stress (intensity)
9. Procedure
and, for t
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