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Designation G47 − 98 Reapproved 2019Standard Test Method forDetermining Susceptibility to Stress-Corrosion Cracking of2XXX and 7XXX Aluminum Alloy Products1This standard is issued under the fixed designation G47; the number immediately following the designation indicates the year of originaladoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscriptepsilon ´ 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. Scope1.1 This test method covers a uniform procedure for char-acterizing the resistance to stress-corrosion cracking SCC ofhigh-strength aluminum alloy wrought products for the guid-ance of those who perform stress-corrosion tests, for those whoprepare stress-corrosion specifications, and for materials engi-neers.1.2 This test method covers method of sampling, type ofspecimen, specimen preparation, test environment, and methodof exposure for determining the susceptibility to SCC of 2XXXwith 1.8 to 7.0 copper and 7XXX with 0.4 to 2.8 copper aluminum alloy products, particularly when stressed inthe short-transverse direction relative to the grain structure.1.3 The values stated in SI units are to be regarded asstandard. The inch-pound units in parentheses are provided forinformation.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.5 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade TBT Committee.2. Referenced Documents2.1 ASTM Standards2G38 Practice for Making and Using C-Ring Stress-Corrosion Test SpecimensG44 Practice for Exposure of Metals andAlloys byAlternateImmersion in Neutral 3.5 Sodium Chloride SolutionG49 Practice for Preparation and Use of Direct TensionStress-Corrosion Test SpecimensG139 Test Method for Determining Stress-Corrosion Crack-ing Resistance of Heat-Treatable Aluminum Alloy Prod-ucts Using Breaking Load Method3. Summary of Test Method3.1 This test method provides a comprehensive procedurefor accelerated stress-corrosion testing high-strength aluminumalloy 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-ringsexposed to 3.5 sodium chloride NaCl solution by alternateimmersion, and includes procedures for sampling variousmanufactured product forms, examination of exposed testspecimens, and interpretation of test results.4. Significance and Use4.1 The 3.5 NaCl solution alternate immersion test pro-vides a test environment for detecting materials that would belikely to be susceptible to SCC in natural outdoorenvironments, especially environments with marineinfluences.3,4,5For determining actual serviceability of amaterial, other stress-corrosion tests should be performed inthe intended service environment under conditions relating tothe end use, including protective measures.1This test method, which was developed by a joint task group with theAluminum Association, Inc., is under the jurisdiction of ASTM Committee G01 onCorrosion of Metals and is the direct responsibility of Subcommittee G01.06 onEnvironmentally Assisted Cracking.Current edition approved June 15, 2019. Published June 2019. Originallyapproved in 1976. Last previous edition approved in 2011 as G47 – 98 2011. DOI10.1520/G0047-98R19.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standard’s Document Summary page onthe ASTM website.3Romans, H. B., Stress Corrosion Testing, ASTM STP 425, ASTM, 1967, pp.182–208.4Brown, R. H., Sprowls, D. O., and Shumaker, M. B., “The Resistance ofWrought High Strength Aluminum Alloys to Stress Corrosion Cracking,” StressCorrosion Cracking of MetalsA State of the Art, ASTM STP 518,ASTM, 1972, pp.87–118.5Sprowls, 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 Susceptibilityto Stress-Corrosion Cracking of High-Strength 7XXX Series Aluminum AlloyProducts,” Stress Corrosion-New Approaches, ASTM STP 610, ASTM, 1976, pp.3–31.Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade TBT Committee.14.2 Although this test method is intended for certain alloytypes and for testing products primarily in the short-transversestressing direction, this method is useful for some other typesof alloys and stressing directions.5. Interferences5.1 A disadvantage of the 3.5 NaCl solution alternateimmersion test is that severe pitting may develop in thespecimens. Such pitting in tension specimens with relativelysmall cross section can markedly reduce the effective cross-sectional area and produce a net section stress greater than thenominal gross section stress, resulting in either 1 fracture bymechanical overload of a material that is not susceptible toSCC; or 2 SCC of a material at an actual stress higher thanthe intended nominal test stress. The occurrence of either ofthese phenomena might then interfere with a valid evaluationof materials with relatively high resistance to stress corrosion.6. Test Specimen6.1 Type and SizeNo single configuration of test specimenis applicable for the many complex shapes and sizes ofproducts that must be evaluated. A tension specimen is pre-ferred because it more consistently provides definite evidenceof cracking and should be used whenever the size and shape ofthe product permits; it also provides a more severe test.6.1.1 Tension SpecimenThe diameter of the reduced sec-tion shall be 3.17 6 0.03 mm 0.125 6 0.001 in..6.1.2 C-Ring see Practices G38The use of C-ringspermits short-transverse tests to be made of sections that aretoo thin or complex for practical tests with a tension specimen.C-rings may be of various sizes as required for the product tobe tested, but in no case less than 15.88 6 0.05 mm 0.625 60.002 in. in outside diameter. The ratio of diameter to wallthickness shall be kept in the range from 111 to 161.6.2 Stressing Direction6.2.1 Short-Transverse Tests6.2.1.1 For specified material thicknesses of 38.10 mm1.500 in. and over, the tension specimen shall be used.6.2.1.2 For specified material thicknesses of 17.78 through38.08 mm 0.700 through 1.499 in., a C-ring shall be used. Atension specimen may be used if consistent with the provisionsof Practice G49.6.2.2 For other stress directions in materials of 6.35 mm0.250 in. and over, the tension specimen shall be used.6.3 Surface PreparationTest specimens shall bedegreased prior to exposure.7. Sampling and Number of Tests7.1 Unless otherwise specified, tests shall be performed inthe short-transverse direction; the intention is to orient thespecimen so that the applied tensile stress is perpendicular tothe metal flow lines and in the short-transverse directionrelative to the grain structure. In rolled or extruded sectionsthat are approximately round or square, there is no trueshort-transverse direction because in a transverse plane thegrains tend to be equiaxial; and, in such cases, the stress shouldbe directed simply in the transverse direction. If, in certainunusual cases, the grain structure is or tends to be equiaxialalso in the longitudinal direction, the stress shall be applied ina direction parallel to the smallest dimension of the product.7.2 Location of Specimens7.2.1 For products stress relieved by stretching TX51,TX510, TX511, TXX51, TXX510, TXX511, samples shall notbe taken from the portion under the stretcher grips.7.2.2 Rolled PlateShort-transverse specimens shall betaken so that the region of maximum stress is centered on themid-plane of the plate and at least 21⁄2 plate thicknesses awayfrom a side of the plate. The side of the plate is defined as theedge parallel to the rolling direction.7.2.3 Hand ForgingsShort-transverse specimens shall betaken so that the stress is applied in a direction perpendicularto the forging flow lines. The region of maximum stress shallbe centered in the forging thickness and approximately on thelongitudinal center line of the forging, no less than1⁄2 thesection thickness away from “as-heat treated” edges of theforging.7.2.4 Die ForgingsBecause of the wide variety of con-figurations of die forgings, guidelines are provided for onlycertain common types of shapes that are widely used. Short-transverse specimens shall be taken so that the stress is appliedin a direction perpendicular to the forging flow lines and, ifpossible, with the region of maximum stress centered on theparting plane. The metal flow pattern in die forgings cannotalways be predicted, so only a few general rules are given, andthey are illustrated in Fig. 1. Departures from these rulesshould be made only on the basis of a study of forging flowlines indicating that the intended type of test would not beNOTE 1Similar to that of typical machined part.FIG. 1 Recommended Specimen Type and Location for VariousConfigurations of Die ForgingsG47 − 98 20192obtained. In every case, a diagram should be filed with the testresults to illustrate specimen locations and orientations.7.2.4.1 FlangesThe centerline of the specimen shall be12.70 6 1.27 mm 0.500 6 0.050 in. from the base of the filletof the flash except for flanges that are too thin, in which case,the specimen should be centered.7.2.4.2 Flat-Top DieThe tension specimen should be per-pendicular to the parting plane and, if possible, centered in thewidth.7.2.4.3 Boss or Small CylinderThe C-ring specimenshould be centered on the parting plane and with the outsidediameter 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 CylinderThe centerline of tension speci-mens shall be 12.70 6 1.27 mm 0.500 6 0.050 in. from thebase of the flash. If a C-ring is required, its outside diametershall be 1.52 6 0.25 mm 0.060 6 0.010 in. from the forgingsurface see Fig. 1.7.2.5 Extruded, Rolled, or Cold Finished Rod, Bar, andShapes7.2.5.1 Width-to-Thickness Ratio Greater than 2Short-transverse specimens shall be taken so that the region ofmaximum stress is centered in the section thickness, at leastone section thickness away from the sides of the product. In thecase of complex configurations for which the grain direction-ality cannot be predicted, specimen location shall be deter-mined by means of macroetched transverse sections to ensurea short-transverse specimen and to avoid regions of nearlyequiaxial transverse grain flow.7.2.5.2 Width-to-Thickness Ratio of 2 or LessSpecimensshall be centered in the section thickness so that the region ofmaximum stress application will be at least one half the sectionthickness away from a fabricated surface, if possible. Thesespecimens shall be considered to have a “transverse” orienta-tion to the grain structure. When C-rings are required, theyshall be taken so that the region of maximum tensile stress is3.18 6 0.25 mm 0.125 6 0.010 in. from the product surface.7.3 Number of SpecimensFor each sample, which shall beuniform in thickness and grain structure, a minimum of threeadjacent replicate specimens shall be tested.8. Test Environment8.1 Corrosion Test EnvironmentSpecimens shall be ex-posed to the alternate 10-min immersion50-min drying cyclein accordance with Practice G44.8.2 Length of ExposureThe test duration for 3.18-mm0.125-in. tension specimens and C-rings shall be 10 days for2XXX alloys or 20 days for 7XXX alloys, unless crackingoccurs sooner. For specimens to be tested in the long transversedirection, the test duration should be 40 days. Longer nonstan-dard test durations are likely to cause failures of the 3.18-mmtension specimens as a result of severe pitting as described in5.1. There shall be no interruptions except as required forperiodic inspection of specimens or changing of the solution.9. Procedure9.1 Method of Loading9.1.1 Tension SpecimensStress tension specimens in “con-stant strain”-type fixtures, as in Fig. 3 of Practice G49.9.1.2 C-ringsStress C-rings by a method that providesconstant strain and produces a tensile stress on the ring outsidediameter in accordance with Practice G38.9.2 Magnitude of Applied StressStress specimens to oneor more levels as specified or as required to determinecomparative stress corrosion resistance. The application of astress less than about 103 MPa 15 ksi is not practicable.9.3 Examination of Specimens9.3.1 Interim InspectionVisually inspect specimens eachworking day for evidence of cracking without removal ofcorrosion products. Inspection may be facilitated by wettingthe specimen with the test solution and by examination at lowmagnifications.9.3.2 Final ExaminationPerform final examination at amagnification of at least 10X on all surviving specimens aftercleaning them in concentrated 70 nitric acid HNO3atroom temperature followed by a water rinse. Section andmetallographically examine any C-ring that is consideredsuspect, as evidenced by linear pitting, to determine whether ornot SCC is present. Similar examination of fractured orcracked tension specimens also can be useful to verify SCC asthe cause of failure.10. Interpretation of Results10.1 Criterion of Failure10.1.1 Asample shall be considered to have failed the test ifone or more of the specimens fail, except that the retestprovisions of Section 11 shall apply.10.1.2 A specimen that has fractured or which exhibitscracking shall be considered as a stress corrosion failure unlessproved otherwise by the provisions of 10.2 and 10.3.10.2 Macroscopic ExaminationCracking should beclearly differentiated from lined-up pitting. If the presence ofSCC is questionable, metallographic examinations should beperformed to determine whether or not SCC is present.NOTE 1When a specimen fractures within a relatively short time afterexposure ten days or less, metallographic examination is not necessarybecause such rapid failures are characteristically due to SCC.10.3 Metallographic Examination10.3.1 A specimen that reveals intergra
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