1、Designation: G 47 98 (Reapproved 2004)Standard Test Method forDetermining Susceptibility to Stress-Corrosion Cracking of2XXX and 7XXX Aluminum Alloy Products1This standard is issued under the fixed designation G 47; the number immediately following the designation indicates the year of originaladopt
2、ion or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscriptepsilon (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.
3、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 mate
4、rials 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 2XXX(with 1.8 to 7.0 % copper) and 7XXX (with 0.4 to 2.8 %copper) aluminum alloy products, particularly when st
5、ressed 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 it
6、s use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2G 38 Practice for Making and Using the C-Ring Stress-Corrosion Test Spe
7、cimensG 44 Practice for Exposure of Metals and Alloys by Alter-nate Immersion in Neutral 3.5% Sodium Chloride SolutionG 49 Practice for Preparation and Use of Direct TensionStress-Corrosion Test SpecimensG 139 Test Method for Determining the Stress-CorrosionCracking Resistance of Heat-Treatable Alum
8、inum AlloyProducts Using the 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
9、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. Signi
10、ficance 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 outdoor environ-ments, especially environments with marine influences.3,4,5Fordetermining actual serviceability of a materi
11、al, other stress-corrosion tests should be performed in the intended serviceenvironment under conditions relating to the end use, includingprotective measures.4.2 Although this test method is intended for certain alloytypes and for testing products primarily in the short-transversestressing directio
12、n, 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 relatively1This test method, which was deve
13、loped 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 May 1, 2004. Published May 2004. Originallyappro
14、ved in 1976. Last previous edition approved in 1998 as G 47 98.2For 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 standards Document Summary page onthe ASTM websit
15、e.3Romans, H. B., Stress Corrosion Testing, ASTM STP 425, ASTM, 1967, pp.182208.4Brown, 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, p
16、p.87118.5Sprowls, 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, A
17、STM, 1976, pp.331.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.small cross section can markedly reduce the effective cross-sectional area and produce a net section stress greater than thenominal gross section stress, resulting in
18、either: (a) fracture bymechanical overload of a material that is not susceptible toSCC; or (b) 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 r
19、esistance 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
20、 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 G 38)The use of C-ringspermits short-transverse tests to be made of secti
21、ons 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
22、 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 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. Ate
23、nsion specimen may be used if consistent with the provisionsof 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 PreparationTest specimens shall be de-greased prior to exposure.7. Sampling and Number of Tests7.
24、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 secti
25、onsthat 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
26、equiaxialalso in the longitudinal direction, the stress shall be applied ina 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 notbe taken from the portion u
27、nder 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 212 plate thicknesses awayfrom a side of the plate. (The side of the plate is defined as theedge parallel to the rolling dire
28、ction.)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 than
29、12 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
30、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 fro
31、m these rulesshould be made only on the basis of a study of forging flowlines indicating that the intended type of test would not beobtained. 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
32、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 beperpendicular to the parting plane and, if possible, centered inthe width.NOTESimi
33、lar to that of typical machined part.FIG. 1 Recommended Specimen Type and Location for VariousConfigurations of Die ForgingsG 47 98 (2004)27.2.4.3 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
34、.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.
35、 1).7.2.5 Extruded, Rolled, or Cold Finished Rod, Bar, andShapes:7.2.5.1 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 the
36、case 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 R
37、atio 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 structu
38、re. 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
39、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 G 44.8.2 Length of ExposureThe test duration for 3.18-mm(0.125-in.) tension specimens and C-rings shall be 10 days for2XXX allo
40、ys 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 non-standard test durations are likely to cause failures of the3.18-mm tension specimens as a result of severe pitting asdescribed in 5
41、.1. There shall be no interruptions except asrequired for periodic inspection of specimens or changing ofthe solution.9. Procedure9.1 Method of Loading:9.1.1 Tension SpecimensStress tension specimens in“constant strain”-type fixtures, as in Fig. 3 of Practice G 49.9.1.2 C-ringsStress C-rings by a me
42、thod that providesconstant strain and produces a tensile stress on the ring outsidediameter in accordance with Practice G 38.9.2 Magnitude of Applied StressStress specimens to oneor more levels as specified or as required to determinecomparative stress corrosion resistance. The application of astres
43、s less than about 103 MPa (15 ksi) is not practicable.9.3 Examination of Specimens:9.3.1 Interim Inspection:Visually inspect specimens each working day for evidence ofcracking without removal of corrosion products. Inspectionmay be facilitated by wetting the specimen with the testsolution and by exa
44、mination at low magnifications.9.3.2 Final ExaminationPerform final examination at amagnification of at least 10X on all surviving specimens aftercleaning them in concentrated (70%) nitric acid (HNO3)atroom temperature followed by a water rinse. Section andmetallographically examine any C-ring that
45、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 Failure:10.1.1 A sample shall be consid
46、ered 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
47、 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 d
48、ays or less), metallographic examination is not necessarybecause such rapid failures are characteristically due to SCC.10.3 Metallographic Examination:10.3.1 A specimen that reveals intergranular cracking, evenwhen accompanied by transgranular cracking, shall be consid-ered as an SCC failure. Interg
49、ranular fissures that are no deeperthan the width of localized areas of intergranular corrosion or,in the case of C-rings, not deeper than those in unstressed orcompressively stressed surfaces, shall not be considered as anSCC failure. In the case of tension specimens, the depth ofintergranular fissures may be compared to those in an un-stressed specimen when available.10.3.2 A specimen that reveals only pitting corrosion (thatis, no intergranular attack), or pitting plus transgranular crack-ing, shall not be considered as an SCC failure.NOTE 2Transgran
