ASTM G47-22

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Designation: G47 − 20 G47 − 22
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. 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
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 values given in parentheses after SI units are provided for
information only and are not considered standard.
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:
G38 Practice for Making and Using C-Ring Stress-Corrosion Test Specimens
G44 Practice for Exposure of Metals and Alloys by Alternate Immersion in Neutral 3.5 % Sodium Chloride Solution
G49 Practice for Preparation and Use of Direct Tension Stress-Corrosion Test Specimens
G139 Test Method for Determining Stress-Corrosion Cracking Resistance of Heat-Treatable Aluminum Alloy Products Using
Breaking Load Method
3. Summary of Test Method
3.1 This test method provides a comprehensive procedure for accelerated stress-corrosion testing high-strength aluminum alloy
This test method, which was developed by a joint task group with the Aluminum Association, Inc., is under the jurisdiction of ASTM Committee G01 on Corrosion of
Metals and is the direct responsibility of Subcommittee G01.06 on Environmentally Assisted Cracking.
Current edition approved May 1, 2020Dec. 1, 2022. Published May 2020January 2023. Originally approved in 1976. Last previous edition approved in 20192020 as
G47–98 (2019). –20. DOI: 10.1520/G0047-20.10.1520/G0047-22.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. 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
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product forms, particularly when stressed in the short-transverse grain direction. It specifies tests of constant-strain-loaded, 3.18
mm (0.125 in.) tension specimens or C-rings exposed to 3.5 % sodium chloride (NaCl) solution by alternate immersion, and
includes procedures for sampling various manufactured product forms, examination of exposed test specimens, and interpretation
of test results.
4. Significance and Use
4.1 The 3.5 % NaCl solution alternate immersion test provides a test environment for detecting materials that would be likely to
3,4,5
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.
4.2 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.
5. Interferences
5.1 A disadvantage of the 3.5 % NaCl solution alternate immersion test is that severe pitting may develop in the specimens. Such
pitting in tension specimens with relatively small cross section can markedly reduce the effective cross-sectional area and produce
a net section stress greater than the nominal gross section stress, resulting in either: (1) fracture by mechanical overload of a
material that is not susceptible to SCC; or (2) SCC of a material at an actual stress higher than the intended nominal test stress.
The occurrence of either of these phenomena might then interfere with a valid evaluation of materials with relatively high
resistance to stress corrosion.
6. Test Specimen
6.1 Type and Size—No single configuration of test specimen is applicable for the many complex shapes and sizes of products that
must be evaluated. A tension specimen is preferred because it more consistently provides definite evidence of cracking and should
be used whenever the size and shape of the product permits; it also provides a more severe test.
6.1.1 Tension Specimen—The diameter of the reduced section shall be 3.17 mm 6 0.03 mm (0.125 in. 6 0.001 in.).
NOTE 1—Experience has shown that tension specimens with diameters larger than 3.17 mm (0.125 in.) are less sensitive to initiation and may require
longer exposure periods, and that tension specimens with smaller diameters may be more prone to the interferences described in 5.1. For a more detailed
discussion on the effects of tension specimen diameter, see 5.3 in Practice G49 or Sprowls et. al.
6.1.2 C-ring Specimen (see Practice G38)—The use of C-rings permits short-transverse tests to be made of sections that are too
thin or complex for practical tests with a tension specimen. C-rings may be of various sizes as required for the product to be tested,
but in no case less than 15.88 mm 6 0.05 mm (0.625 in. 6 0.002 in.) in outside diameter. The ratio of diameter to wall thickness
shall be kept in the range from 11:1 to 16:1.
6.2 Stressing Direction:
6.2.1 Short-Transverse Tests:
6.2.1.1 For specified material thicknesses of 38.10 mm (1.500 in.) and over, the tension specimen conforming to 6.1.1 shall be
used.
6.2.1.2 For specified material thicknesses of 17.78 mm through 38.08 mm (0.700 in. through 1.499 in.), a C-ring shall be used.
A tension specimen conforming to 6.1.1 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.
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 Corrosion
Cracking of Metals—A State of the Art, ASTM STP 518, ASTM, 1972, pp. 87–118.
Sprowls, D. O., Summerson, T. J., Ugiansky, G. M., Epstein, S. G., and Craig, H. L., Jr., “Evaluation of a Proposed Standard Method of Testing for Susceptibility to
Stress-Corrosion Cracking of High-Strength 7XXX Series Aluminum Alloy Products,” Stress Corrosion-New Approaches, ASTM STP 610, ASTM, 1976, pp. 3–31.
G47 − 22
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 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 from a side of the plate. (The side of the plate is defined as the edge parallel
to the rolling direction.)
7.2.3 Hand Forgings—Short-transverse specimens shall be taken so that the stress is applied in a direction perpendicular to the
forging flow lines. The region of maximum stress shall be centered in the forging thickness and approximately on the longitudinal
center line of the forging, no less than ⁄2 the section thickness away from “as-heat treated” edges of the forging.
7.2.4 Die Forgings—Because of the wide variety of configurations of die forgings, guidelines are provided for only certain
common types of shapes that are widely used. Short-transverse specimens shall be taken so that the stress is applied in a direction
perpendicular to the forging flow lines and, if possible, with the region of maximum stress centered on the parting plane. The metal
flow pattern in die forgings cannot always be predicted, so only a few general rules are given, and they are illustrated in Fig. 1.
NOTE 1—Similar to that of typical machined part.
FIG. 1 Recommended Specimen Type and Location for Various Configurations of Die Forgings
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Departures from these rules should be made only on the basis of a study of forging flow lines indicating that the intended type of
test would not be obtained. In every case, a diagram should be filed with the test results to illustrate specimen locations and
orientations.
7.2.4.1 Flanges—The centerline of the specimen shall be 12.70 mm 6 1.27 mm (0.500 in. 6 0.050 in.) from the base of the fillet
of the flash except for flanges that are too thin, in which case, the specimen should be centered.
7.2.4.2 Flat-Top Die—The tension specimen should be perpendicular to the parting plane and, if possible, centered in the width.
7.2.4.3 Boss or Small Cylinder—The C-ring specimen should be centered on the parting plane and with the outside diameter of
the ring being 1.52 6 0.25 mm (0.060 6 0.010 in.) from the forging surface (see Fig. 1).
7.2.4.4 Large Cylinder—The centerline of tension specimens shall be 12.70 mm 6 1.27 mm (0.500 in. 6 0.050 in.) from the base
of the flash. If a C-ring is required, its outside diameter shall be 1.52 mm 6 0.25 mm (0.060 in. 6 0.010 in.) from the forging
surface (see Fig. 1).
7.2.5 Extruded, Rolled, or Cold Finished Rod, Bar, and Shapes:
7.2.5.1 Width-to-Thickness Ratio Greater than 2—Short-transverse specimens shall be taken so that the region of maximum stress
is centered in the section thickness, at least one section thickness away from the sides of the product. In the case of complex
configurations for which the grain directionality cannot be predicted, specimen location shall be determined by means of
macroetched transverse sections to ensure a short-transverse specimen and to avoid regions of nearly equiaxial (transverse) grain
flow.
7.2.5.2 Width-to-Thickness Ratio of 2 or Less—Specimens shall be centered in the section thickness so that the region of maximum
stress application will be at least one half the section thickness away from a fabricated surface, if possible. These specimens shall
be considered to have a “transverse” orientation to the grain structure. When C-rings are required, they shall be taken so that the
region of maximum tensile stress is 3.18 mm 6 0.25 mm (0.125 in. 6 0.010 in.) from the product surface.
7.3 Number of Specimens—For each sample, which shall be uniform in thickness and grain structure, a minimum of three adjacent
replicate specimens shall be tested.
8. Test Environment
8.1 Corrosion Test Environment—Specimens shall be exposed to the alternate 10 min immersion—50 min drying cycle in
accordance with Practice G44.
FIG. 2 Photograph Showing Example of Lined-up Pitting on C-ring
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