1、Designation: G47 98 (Reapproved 2011)Standard 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 originaladoptio
2、n 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 Department of Defense.1. Sco
3、pe1.1 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 materia
4、ls 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 stres
5、sed 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 u
6、se. 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:2G38 Practice for Making and Using C-Ring Stress-Corrosion Test SpecimensG4
7、4 Practice for Exposure of Metals and Alloys by Alter-nate Immersion in Neutral 3.5 % Sodium Chloride Solu-tionG49 Practice for Preparation and Use of Direct TensionStress-Corrosion Test SpecimensG139 Test Method for Determining Stress-CorrosionCracking Resistance of Heat-Treatable Aluminum AlloyPro
8、ducts 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-strai
9、n-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.
10、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 material, other stress-
11、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 direction, this method is
12、 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 the1This test method, which was developed by a joint task group with theAluminum Association, Inc., is under the
13、jurisdiction of ASTM Committee G01 onCorrosion of Metals and is the direct responsibility of Subcommittee G01.06 onEnvironmentally Assisted Cracking.Current edition approved Sept. 1, 2011. Published September 2011. Originallyapproved in 1976. Last previous edition approved in 2004 as G4798(2004). DO
14、I:10.1520/G0047-98R11.2For 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 website.3Romans, H. B., Stress Corrosion Testin
15、g, 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, pp.87118.5Sprowls, D. O., Summerson, T. J.,
16、 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.331.1Copyright ASTM Internat
17、ional, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.specimens. 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 str
18、ess, 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
19、 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 c
20、racking 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 G38)The use of C-ringspermits short-transverse tests to
21、 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
22、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 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 s
23、hall 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 mm(0.250 in.) and over, the tension specimen shall be used.6.3 Surface PreparationTest specimens shall bedegreased prior to exposure.7. Sampling and Num
24、ber 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
25、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 o
26、r 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 Specimens:7.2.1 For products stress relieved by stretching (TX51,TX510, TX511, TXX51, TXX510, TXX511), samples shall notbe taken from
27、 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 212 plate thicknesses awayfrom a side of the plate. (The side of the plate is defined as theedge parallel to th
28、e 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
29、, no less than12 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 th
30、at 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.
31、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 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
32、 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 beperpendicular to the parting plane and, if possible, centered inthe
33、width.NOTESimilar to that of typical machined part.FIG. 1 Recommended Specimen Type and Location for VariousConfigurations of Die ForgingsG47 98 (2011)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
34、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 forgingsurf
35、ace (see Fig. 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 pr
36、oduct. 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-t
37、o-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
38、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 replica
39、te 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-mm(0.125-in.) tension specimens and C-rings shall be 10 days
40、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 d
41、escribed in5.1. There shall be no interruptions except as required forperiodic inspection of specimens or changing of the 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 G49.9.1.2 C-ringsStress C-r
42、ings 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 applicatio
43、n of astress 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
44、 and by examination 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
45、-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 Failure:10.1.1 Asample shall
46、 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
47、 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 afterexpos
48、ure (ten days 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 failu
49、re. Intergranular 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 2
