ASTM G47-98
(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
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.
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Designation: G 47 – 98
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 G 47; 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 (e) 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 3. Summary of Test Method
1.1 This test method covers a uniform procedure for char- 3.1 This test method provides a comprehensive procedure
acterizing the resistance to stress-corrosion cracking (SCC) of for accelerated stress-corrosion testing high-strength aluminum
high-strength aluminum alloy wrought products for the guid- alloy product forms, particularly when stressed in the short-
ance of those who perform stress-corrosion tests, for those who transverse grain direction. It specifies tests of constant-strain-
prepare stress-corrosion specifications, and for materials engi- loaded, 3.18-mm (0.125-in.) tension specimens or C-rings
neers. exposed to 3.5 % sodium chloride (NaCl) solution by alternate
1.2 This test method covers method of sampling, type of immersion, and includes procedures for sampling various
specimen, specimen preparation, test environment, and method manufactured product forms, examination of exposed test
of exposure for determining the susceptibility to SCC of 2XXX specimens, and interpretation of test results.
(with 1.8 to 7.0 % copper) and 7XXX (with 0.4 to 2.8 %
4. Significance and Use
copper) aluminum alloy products, particularly when stressed in
4.1 The 3.5 % NaCl solution alternate immersion test pro-
the short-transverse direction relative to the grain structure.
1.3 The values stated in SI units are to be regarded as vides a test environment for detecting materials that would be
likely to be susceptible to SCC in natural outdoor environ-
standard. The inch-pound units in parentheses are provided for
, ,
3 4 5
information. ments, especially environments with marine influences.
For determining actual serviceability of a material, other
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the stress-corrosion tests should be performed in the intended
service environment under conditions relating to the end use,
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica- including protective measures.
bility of regulatory limitations prior to use. 4.2 Although this test method is intended for certain alloy
types and for testing products primarily in the short-transverse
2. Referenced Documents
stressing direction, this method is useful for some other types
2.1 ASTM Standards: of alloys and stressing directions.
G 38 Practice for Making and Using the C-Ring Stress-
2 5. Interferences
Corrosion Test Specimens
5.1 A disadvantage of the 3.5 % NaCl solution alternate
G 44 Practice for Evaluating Stress Corrosion Cracking
Resistance of Metals and Alloys by Alternate Immersion in immersion test is that severe pitting may develop in the
specimens. Such pitting in tension specimens with relatively
3.5% Sodium Chloride Solution
G 49 Practice for Preparation and Use of Direct Tension small cross section can markedly reduce the effective cross-
sectional area and produce a net section stress greater than the
Stress Corrosion Test Specimens
G 139 Test Method for Determining the Stress-Corrosion
Cracking Resistance of Heat Ireatable Aluminum Alloy
Products Using the Breaking Load Method 3
Romans, H. B., Stress Corrosion Testing, ASTM STP 425, ASTM, 1967, pp.
182–208.
Brown, R. H., Sprowls, D. O., and Shumaker, M. B., “The Resistance of
Wrought High Strength Aluminum Alloys to Stress Corrosion Cracking,” Stress
This test method, which was developed by a joint task group with the Corrosion Cracking of Metals—A State of the Art, ASTM STP 518, ASTM, 1972, pp.
Aluminum Association, Inc., is under the jurisdiction of ASTM Committee G-1 on 87–118.
Corrosion of Metals, and is the direct responsibility of Subcommittee G01.06 on Sprowls, D. O., Summerson, T. J., Ugiansky, G. M., Epstein, S. G., and Craig,
Stress Corrosion Cracking and Corrosion Fatigue. H. L., Jr., “Evaluation of a Proposed Standard Method of Testing for Susceptibility
Current edition approved Apr. 10, 1998. Published October 1998. Originally to Stress-Corrosion Cracking of High-Strength 7XXX Series Aluminum Alloy
published as G 47 – 76. Last previous edition G 47 – 90. Products,” Stress Corrosion-New Approaches, ASTM STP 610, ASTM, 1976, pp.
Annual Book of ASTM Standards, Vol 03.02. 3–31.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
G47
nominal gross section stress, resulting in either: (a) 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 (b) 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 ⁄2the
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-
figurations of die forgings, guidelines are provided for only
6.1 Type and Size—No single configuration of test specimen
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 G 38)—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 6 1.27 mm (0.500 6 0.050 in.) from the base of the fillet
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.
7.2.4.3 Boss or Small Cylinder—The C-ring specimen
6.2.1.2 For specified material thicknesses of 17.78 through
should be centered on the parting plane and with the outside
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 G 49.
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
grains tend to be equiaxial; and, in such cases, the stress should
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), samples shall not
be taken from the portion under the stretcher grips.
7.2.2 Rolled Plate—Short-transverse specimens shall be
taken so that the region of maximum stress is centered on the
mid-plane of the plate and at least 2 ⁄2 plate thicknesses away
NOTE 1—Similar to that of typical machined part.
from a side of the plate. (The side of the plate is defined as the
FIG. 1 Recommended Specimen Type and Location for Various
edge parallel to the rolling direction.) Configurations of Die Forgings
G47
diameter of the ring being 1.52 6 0.25 mm (0.060 6 0.010 in.) Visually inspect specimens each working day for evidence of
from the forging surface (see Fig. 1). cracking without removal of corrosion products. Inspection
7.2.4.4 Large Cylinder—The centerline of tension speci- may be facilitated by wetting the specimen with the test
mens shall be 12.70 6 1.27 mm (0.500 6 0.050 in.) from the solution and by examination at low 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
one section thickness away from the sides of the product. In the
the cause of failure.
case of complex configurations for which the grain direction-
ality cannot be predicted, specimen location shall be deter-
10. Interpretation of Results
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 A sample 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-
tion to the grain structure. When C-rings are required, they 10.2 Macroscopic Examination—Cracking should be
shall be taken so that the region of maximum tensile stress is clearly differentiated from lined-up pitting. If the presence of
3.18 6 0.25 mm (0.125 6 0.010 in.) from the product surface. SCC is questionable, metallographic examinations should be
7.3 Number of Specimens—For each sample, which shall be performed to determine whether or not SCC is present.
uniform in thickness and grain structure, a minimum of three
NOTE 1—When a specimen fractures within a relatively short time after
adjacent replicate specimens shall be tested.
exposure (ten days or less), metallographic examination is not necessary
because such rapid failures are characteristically due to SCC.
8. Test Environment
10.3 Metallographic Examination:
8.1 Corrosion Test Environment—Specimens shall be ex-
10.3.1 A specimen that reveals intergranular cracking, even
posed to the alternate 10-min immersion—50-min drying cycle
when accompanied by transgranular cracking, shall be consid-
in accordance with Practice G 44.
ered as an SCC failure. Intergranular fissures that are no deeper
8.2 Length of Exposure—The test duration for 3.18-mm
than the width of localized areas of intergranular corrosion or,
(0.125-in.) tension specimens and C-rings shall be 10 days for
in the case of C-rings, not deeper than those in unstressed or
2XXX alloys or 20 days for 7XXX alloys, unless cracking
compressively stressed surfaces, shall not be considered as an
occurs sooner. For specimens to be tested in the long transverse
SCC failure. In the case of tension specimens, the depth of
direction, the test duration should be 40 days. Longer non-
intergranular fissures may be compared to those in an un-
standard test durations are likely to cause failures of the
stressed specimen when available.
3.18-mm tension specimens as a result of severe pitting as
10.3.2 A specimen that reveals only pitting corrosion (that
described in 5.1. There shall be no interruptions except as
is, no intergranular attack), or pitting plus transgranular crack-
required for periodic inspection of specimens or changing of
ing, shall not be considered as an SCC failure.
the solution.
NOTE 2—Transgranular cracking in the absence of intergranular attack
9. Procedure
only occurs in pitted specimens under extremely high stress (intensity)
and, for the purpose of this text method, is not considered as a criterion of
9.1 Method of Loading:
SCC.
9.1
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