ASTM G47-98(2011)
(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. , , 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.
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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Designation:G47 −98 (Reapproved 2011)
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 U.S. Department of Defense.
1. Scope G139 Test Method for Determining Stress-Corrosion Crack-
ing Resistance of Heat-Treatable Aluminum Alloy Prod-
1.1 This test method covers a uniform procedure for char-
ucts 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
4. Significance and Use
standard. The inch-pound units in parentheses are provided for
4.1 The 3.5 % NaCl solution alternate immersion test pro-
information.
vides a test environment for detecting materials that would be
1.4 This standard does not purport to address all of the
likely to be susceptible to SCC in natural outdoor
safety concerns, if any, associated with its use. It is the
environments, especially environments with marine
responsibility of the user of this standard to establish appro- 3,4,5
influences. For determining actual serviceability of a
priate safety and health practices and determine the applica-
material, other stress-corrosion tests should be performed in
bility of regulatory limitations prior to use.
the intended service environment under conditions relating to
the end use, including protective measures.
2. Referenced Documents
2 4.2 Although this test method is intended for certain alloy
2.1 ASTM Standards:
types and for testing products primarily in the short-transverse
G38 Practice for Making and Using C-Ring Stress-
stressing direction, this method is useful for some other types
Corrosion Test Specimens
of alloys and stressing directions.
G44 PracticeforExposureofMetalsandAlloysbyAlternate
Immersion in Neutral 3.5 % Sodium Chloride Solution
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 Sept. 1, 2011. Published September 2011. Originally CorrosionCrackingofMetals—AStateoftheArt,ASTMSTP518,ASTM,1972,pp.
approved in 1976. Last previous edition approved in 2004 as G47–98(2004). DOI: 87–118.
10.1520/G0047-98R11. 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 (2011)
specimens. Such pitting in tension specimens with relatively mid-plane of the plate and at least 2 ⁄2 plate thicknesses away
small cross section can markedly reduce the effective cross- from a side of the plate. (The side of the plate is defined as the
sectional area and produce a net section stress greater than the edge parallel to the rolling direction.)
nominal gross section stress, resulting in either: (1) fracture by 7.2.3 Hand Forgings—Short-transverse specimens shall be
mechanical overload of a material that is not susceptible to taken so that the stress is applied in a direction perpendicular
SCC; or (2) SCC of a material at an actual stress higher than to the forging flow lines. The region of maximum stress shall
the intended nominal test stress. The occurrence of either of be centered in the forging thickness and approximately on the
these phenomena might then interfere with a valid evaluation longitudinal center line of the forging, no less than ⁄2 the
of materials with relatively high resistance to stress corrosion. section thickness away from “as-heat treated” edges of the
forging.
6. Test Specimen
7.2.4 Die Forgings—Because of the wide variety of con-
6.1 TypeandSize—No single configuration of test specimen
figurations of die forgings, guidelines are provided for only
is applicable for the many complex shapes and sizes of
certain common types of shapes that are widely used. Short-
products that must be evaluated. A tension specimen is pre-
transverse specimens shall be taken so that the stress is applied
ferred because it more consistently provides definite evidence
in a direction perpendicular to the forging flow lines and, if
of cracking and should be used whenever the size and shape of
possible, with the region of maximum stress centered on the
the product permits; it also provides a more severe test.
parting plane. The metal flow pattern in die forgings cannot
6.1.1 Tension Specimen—The diameter of the reduced sec-
always be predicted, so only a few general rules are given, and
tion shall be 3.17 6 0.03 mm (0.125 6 0.001 in.).
they are illustrated in Fig. 1. Departures from these rules
6.1.2 C-Ring (see Practices G38)—The use of C-rings
should be made only on the basis of a study of forging flow
permits short-transverse tests to be made of sections that are
lines indicating that the intended type of test would not be
too thin or complex for practical tests with a tension specimen.
obtained. In every case, a diagram should be filed with the test
C-rings may be of various sizes as required for the product to
results to illustrate specimen locations and orientations.
be tested, but in no case less than 15.88 6 0.05 mm (0.625 6
7.2.4.1 Flanges—The centerline of the specimen shall be
0.002 in.) in outside diameter. The ratio of diameter to wall
12.70 61.27mm(0.500 60.050in.)fromthebaseofthefillet
thickness shall be kept in the range from 11:1 to 16:1.
of the flash except for flanges that are too thin, in which case,
the specimen should be centered.
6.2 Stressing Direction:
7.2.4.2 Flat-Top Die—The tension specimen should be per-
6.2.1 Short-Transverse Tests:
pendicular to the parting plane and, if possible, centered in the
6.2.1.1 For specified material thicknesses of 38.10 mm
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
degreased 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.
NOTE 1—Similar to that of typical machined part.
7.2.2 Rolled Plate—Short-transverse specimens shall be
FIG. 1Recommended Specimen Type and Location for Various
taken so that the region of maximum stress is centered on the Configurations of Die Forgings
G47−98 (2011)
7.2.4.3 Boss or Small Cylinder—The C-ring specimen 9.3 Examination of Specimens:
should be centered on the parting plane and with the outside 9.3.1 Interim Inspection: Visually inspect specimens each
diameter of the ring being 1.52 6 0.25 mm (0.060 6 0.010 in.) working day for evidence of cracking without removal of
from the forging surface (see Fig. 1). corrosion products. Inspection may be facilitated by wetting
7.2.4.4 Large Cylinder—The centerline of tension speci- the specimen with the test solution and by examination at low
mens shall be 12.70 6 1.27 mm (0.500 6 0.050 in.) from the magnifications.
base of the flash. If a C-ring is required, its outside diameter 9.3.2 Final Examination—Perform final examination at a
shall be 1.52 6 0.25 mm (0.060 6 0.010 in.) from the forging magnification of at least 10X on all surviving specimens after
surface (see Fig. 1). cleaning them in concentrated (70%) nitric acid (HNO)at
7.2.5 Extruded, Rolled, or Cold Finished Rod, Bar, and room temperature followed by a water rinse. Section and
Shapes: metallographically examine any C-ring that is considered
7.2.5.1 Width-to-Thickness Ratio Greater than 2—Short- suspect, as evidenced by linear pitting, to determine whether or
transverse specimens shall be taken so that the region of not SCC is present. Similar examination of fractured or
maximum stress is centered in the section thickness, at least cracked tension specimens also can be useful to verify SCC as
onesectionthicknessawayfromthesidesoftheproduct.Inthe the cause of failure.
case of complex configurations for which the grain direction-
10. Interpretation of Results
ality cannot be predicted, specimen location shall be deter-
mined by means of macroetched transverse sections to ensure 10.1 Criterion of Failure:
a short-transverse specimen and to avoid regions of nearly 10.1.1 Asample shall be considered to have failed the test if
equiaxial (transverse) grain flow. one or more of the specimens fail, except that the retest
7.2.5.2 Width-to-Thickness Ratio of 2 or Less—Specimens provisions of Section 11 shall apply.
shall be centered in the section thickness so that the region of 10.1.2 A specimen that has fractured or which exhibits
maximum stress application will be at least one half the section cracking shall be considered as a stress corrosion failure unless
thickness away from a fabricated surface, if possible. These proved otherwise by the provisions of 10.2 and 10.3.
specimens shall be considered to have a “transverse” orienta-
10.2 Macroscopic Examination—Cracking should be
tion to the grain structure. When C-rings are required, they
clearly differentiated from lined-up pitting. If the presence of
shall be taken so that the region of maximum tensile stress is
SCC is questionable, metallographic examinations should be
3.18 6 0.25 mm (0.125 6 0.010 in.) from the product surface.
performed to determine whether or not SCC is present.
7.3 Number of Specimens—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
adjacent replicate specimens shall be tested. because such rapid failures are characteristically due to SCC.
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-
ered as an SCC failure. Intergranular fissures that are no deeper
posedtothealternate10-minimmersion—50-mindryingcycle
in accordance with Practice G44. than the width of localized areas of intergranular corrosion or,
in the case of C-rings, not deeper than those in unstressed or
8.2 Length of Exposure—The test duration for 3.18-mm
compressively stressed surfaces, shall not be considered as an
(0.125-in.) tension specimens and C-rings shall be 10 days for
SCC failure. In the case of tension specimens, the depth of
2XXX alloys or 20 days for 7XXX alloys, unless cracking
intergranular fissures may be compared to those in an un-
occurssooner.Forspecimenstobetestedinthelongtransverse
stressed specimen when available.
direction, the test duration should be 40 days. Longer nonstan-
10.3.2 A specimen that reveals only pitting corrosion (that
dard test durations are likely to cause failures of the 3.18-mm
is, no intergranular attack), or pitting plus transgranular
tension specimens as a result of severe pitting as described in
cracking, shall not be considered as an SCC failure.
5.1. There shall be no interruptions except as 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 ex
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