ASTM_G_47-20.pdf

This 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.Designation:G47-20Standard 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 superseriptepsilon(e)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.ScopeG38 Practice for Making and Using C-Ring Stress-1.1 This test method covers a uniform procedure for char-Corrosion Test Specimensacterizing the resistance to stress-corrosion cracking(SCC)ofG44 Practice for Exposure of Metals and Alloys by Alternatehigh-strength aluminum alloy wrought products for the guid-Immersion in Neutral 3.5 Sodium Chloride Solutionance of those who perform stress-corrosion tests,for those whoG49 Practice for Preparation and Use of Direct Tensionprepare stress-corrosion specifications,and for materials engi-Stress-Corrosion Test Specimensneers.G139 Test Method for Determining Stress-Corrosion Crack-ing Resistance of Heat-Treatable Aluminum Alloy Prod-1.2 This test method covers method of sampling,type ofucts Using Breaking Load Methodspecimen,specimen preparation,test environment,and methodof exposure for determining the susceptibility to SCC of 2XXX3.Summary of Test Method(with 1.8 to 7.0 copper)and 7XXX(with 0.4 to 2.8copper)aluminum alloy products,particularly when stressed in3.1 This test method provides a comprehensive procedurethe short-transverse direction relative to the grain structure.for accelerated stress-corrosion testing high-strength aluminumalloy product forms,particularly when stressed in the short-1.3 The values stated in SI units are to be regarded astransverse grain direction.It specifies tests of constant-strain-standard.The values given in parentheses after SI units areloaded,3.18 mm(0.125 in.)tension specimens or C-ringsprovided for information only and are not considered standard.exposed to 3.5%sodium chloride(NaCl)solution by alternate1.4 This standard does not purport to address all of theimmersion,and includes procedures for sampling varioussafety concerns,if any,associated with its use.It is themanufactured product forms,examination of exposed testresponsibility of the user of this standard to establish appro-specimens,and interpretation of test results.priate safety,health,and environmental practices and deter-mine the applicability of regulatory limitations prior to use.4.Significance and Use1.5 This international standard was developed in accor-4.1 The 3.5%NaCl solution alternate immersion test pro-dance with internationally recognized principles on standard-vides a test environment for detecting materials that would beization established in the Decision on Principles for thelikely to be susceptible to SCC in natural outdoorDevelopment of International Standards,Guides and Recom-environments.especially environments with marinemendations issued by the World Trade Organization Technicalinfluences.5 For determining actual serviceability of aBarriers to Trade(TBT)Committee.material,other stress-corrosion tests should be performed in2.Referenced Documentsthe intended service environment under conditions relating tothe end use,including protective measures.2.1 ASTM Standards:2This test method.which was developed by a joint task group with theRomans,H.B.Stress Corrosion Testing.ASTM STP 425.ASTM.1967.pp.Aluminum Association.,Inc.,is under the jurisdiction of ASTM Committee G0l on182-208.Corrosion of Metals and is the direct responsibility of Subcommittee G01.06 on4 Brown,R.H.Sprowls,D.O.and Shumaker.M.B.The Resistance ofEnvironmentally Assisted Cracking.Wrought High Strength Aluminum Alloys to Stress Corrosion Cracking.StressCurrent edition approved May 1.2020.Published May 2020.OriginallyCorrosion Cracking of Metals-A State of the Art.ASTM STP 518.ASTM,1972.ppapproved in 1976.Last previous edition approved in 2019 as G47-98(2019).DOl:87-118.10.1520G0047-203 Sprowls,D.O.Summerson.T.J.,Ugiansky.G.M.Epstein.S.G,and Craig.2 For referenced ASTM standards,visit the ASTM website,www.astm.ong,orH.L.Jr.,Evaluation of a Proposed Standard Method of Testing for Susceptibilitycontact ASTM Customer Service at serviceastm.org.For Annaal Book of A.STMto Stress-Corrosion Cracking of High-Strength 7XXX Series Aluminum AlloyStandards volume information,refer to the standards Document Summary page onProducts,Stress Corrosion-New Approaches,ASTM STP 610.ASTM.1976.pp.the ASTM website.3-31.Copyright ASTM Intemational,100 Barr Harbor Drive.PO Box C700,West Conshohocken,PA 19428-2959.United StatesCopyright ASTM IntemationalG47-204.2 Although this test method is intended for certain alloyunusual cases,the grain structure is or tends to be equiaxialtypes and for testing products primarily in the short-transversealso in the longitudinal direction,the stress shall be applied instressing direction,this method is useful for some other typesa direction parallel to the smallest dimension of the product.of alloys and stressing directions.7.2 Location of Specimens:5.Interferences7.2.1 For products stress relieved by stretching(TX51,TX510,TX511,TXX51,TXX510,TXX511),samples shall not5.1 A disadvantage of the 3.5%NaCl solution alternatebe taken from the portion under the stretcher grips.immersion test is that severe pitting may develop in the7.2.2 Rolled Plate-Short-transverse specimens shall bespecimens.Such pitting in tension specimens with relativelytaken so that the region of maximum stress is centered on thesmall cross section can markedly reduce the effective cross-mid-plane of the plate and at least 2 plate thicknesses awaysectional area and produce a net section stress greater than thefrom a side of the plate.(The side of the plate is defined as thenominal gross section stress,resulting in either:(/)fracture byedge parallel to the rolling direction.)mechanical overload of a material that is not susceptible to7.2.3 Hand Forgings-Short-transverse specimens shall beSCC;or(2)SCC of a material at an actual stress higher thantaken so that the stress is applied in a direction perpendicularthe intended nominal test stress.The occurrence of either ofto the forging flow lines.The region of maximum stress shallthese phenomena might then interfere with a valid evaluationbe centered in the forging thickness and approximately on theof materials with relatively high resistance to stress corrosion.longitudinal center line of the forging,no less than the6.Test Specimensection thickness away from as-heat treatededges of theforging.6.1 Type and Size-No single configuration of test specimen7.2.4 Die Forgings-Because of the wide variety of con-is applicable for the many complex shapes and sizes offigurations of die forgings,guidelines are provided for onlyproducts that must be evaluated.A tension specimen is pre-certain common types of shapes that are widely used.Short-ferred because it more consistently provides definite evidencetransverse specimens shall be taken so that the stress is appliedof cracking and should be used whenever the size and shape ofin a direction perpendicular to the forging flow lines and,ifthe product permits;it also provides a more severe test.possible,with the region of maximum stress centered on the6.1.1 Tension Specimen-The diameter of the reduced sec-parting plane.The metal flow pattern in die forgings cannottion shall be 3.17 mm 0.03 mm(0.125 in.0.001 in.).always be predicted,so only a few general rules are given,and6.1.2 C-ring Specimen(see Practice G38)-The use ofthey are illustrated in Fig.I.Departures from these rulesC-rings permits short-transverse tests to be made of sectionsshould be made only on the basis of a study of forging flowthat are too thin or complex for practical tests with a tensionspecimen.C-rings may be of various sizes as required for theproduct to be tested,but in no case less than 15.88 mm+0.05mm(0.625 in.0.002 in.)in outside diameter.The ratio of1270127mmdiameter to wall thickness shall be kept in the range from 11:1(0.5000.050in.)to16:1.6.2 Stressing Direction:6.2.1 Short-Transverse Tests:6.2.1.1 For specified material thicknesses of 38.10 mm(a)Flange(1.500 in.)and over,the tension specimen shall be used.6.2.1.2 For specified material thicknesses of 17.78 mmthrough 38.08 mm(0.700 in.through 1.499 in.),a C-ring shallbe used.A tension specimen may be used if consistent with theprovisions of Practice G49.p1520.25mm(b)Flat-Top Die6.2.2 For other stress directions in materials of 6.35 mm(0.0600.010m)(0.250 in.)and over,the tension specimen shall be used.1.520.25mm0.060t0010n.16.3 Surface Preparation-Test 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 to(c)Boss or Small Cylindethe metal flow lines and in the short-transverse direction12.70127mmrelative to the grain structure.In rolled or extruded sections(0.5000.050in)that are approximately round or square,there is no trueshort-transverse direction because in a transverse plane theNorE 1-Similar to that of typical machined partgrains tend to be equiaxial:and,in such cases,the stress shouldFIG.1 Recommended Specimen Type and Location for Variousbe directed simply in the transverse direction.If.in certainConfigurations of Die ForgingsCopyright ASTM Intemational24G47-20lines indicating that the intended type of test would not be9.Procedureobtained.In every case,a diagram should be filed with the test9.1 Method of Loading:results to illustrate specimen locations and orientations.9.1.1 Tension Specimens-Stress tension specimens in con-7.2.4.1 Flanges-The centerline of the specimen shall bestant strain-type fixtures,as in Fig.3 of Practice G49.12.70 mm 1.27 mm(0.500 in.0.050 in.)from the base of9.1.2 C-ring Specimens-Stress C-ring specimens by athe fillet of the flash except for flanges that are too thin,inmethod that provides constant strain and produces a tensilewhich case,the specimen should be centered.stress on the ring outside diameter in accordance with Practice7.2.4.2 Flat-Top Die-The tension specimen should be per-G38.pendicular to the parting plane and,if possible,centered in the9.2 Magnitude of Applied Stress-Stress specimens to onewidth.or more levels as specified or as required to determine7.2.4.3 Boss or Small Cylinder-The C-ring specimencomparative stress corrosion resistance.The application of ashould be centered on the parting plane and with the outsidestress less than about 103 MPa(15 ksi)is not practicable.diameter of the ring being 1.520.25 mm(0.0600.010 in.)9.3 Examination of Specimens:from the forging surface(see Fig.1).9.3.1 Interim Inspection-Visually inspect specimens each7.2.4.4 Large Cylinder-The centerline of tension speci-working day for evidence of cracking without removal ofmens shall be 12.70 mm 1.27 mm(0.500 in.0.050 in.)corrosion products.Inspection may be facilitated by wettingfrom the base of the flash.If a C-ring is required,its outsidethe specimen with the test solution and by examination at lowdiameter shall be 1.52 mm 0.25 mm(0.060 in.0.010 in.)magnifications.from the forging surface(see Fig.1).9.3.2 Final Examination-Perform final examination at a7.2.5 Extruded,Rolled,or Cold Finished Rod.Bar,andmagnification of at least 10X on all surviving specimens afterShapes:cleaning them in concentrated(70%)nitric acid(HNO3)at7.2.5.1 Width-to-Thickness Ratio Greater than 2-Short-room temperature followed by a water rinse.transverse specimens shall be taken so that the region of9.3.2.1 C-ring Specimens-For any sample that exhibitsmaximum stress is centered in the section thickness.at leastlined-up pitting,section and metallographically examine atone section thickness away from the sides of the product.In theleast one of the replicate C-ring specimens to determinecase of complex configurations for which the grain direction-whether or not SCC is present.An example of lined-up pittingality cannot be predicted,specimen location shall be deter-is shown in Fig.2.mined by means of macroetched transverse sections to ensure9.3.2.2 Tension Specimens-Metallographic examination ofa short-transverse specimen and to avoid regions of nearlyfractured or cracked tension specimens can be useful to verifyequiaxial(transverse)grain flow.SCC as the cause of failure:that is,to differentiate SCC from7.2.5.2 Width-to-Thickness Ratio of 2 or Less-Specimensthe interferences described in Section 5.shall be centered in the section thickness so that the region ofmaximum stress application will be at least one half the section10.Interpretation of Resultsthickness away from a fabricated surface,if possible.These10.1 Criterion of Failure:specimens shall be considered to have atransverseorienta-10.1.1 A sample shall be considered to have failed the test iftion to the grain structure.When C-rings are required,theyone or more of the specimens fail,except that the retestshall be taken so that the region of maximum tensile stress isprovisions of Section 11 shall apply.3.18 mm+0.25 mm(0.125 in.0.010 in.)from the productsurface.7.3 Number of Specimens-For 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 Environment-Specimens shall be ex-posed to the alternate 10 min immersion-50 min drying cyclein accordance with Practice G44.8.2 Length of Exposure-The test duration for 3.18 mm(0.125 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 forFIG.2 Photograph Showing Example of Lined-up Pitting onperiodic inspection of specimens or changing of the solution.C-ring SpecimenCopyright ASTM Intemational3G47-2010.1.2 A specimen that has fractured or which exhibitsintergranular fissures may be compared to those in an un-cracking shall be considered as a stress corrosion failure unlessstressed specimen when available.proved otherwise by the provisions of 10.2 and 10.3.10.3.2 A specimen that reveals only pitting corrosion(that10.2 Macroscopic Examination-Cracking should beis,no intergranular attack),or pitting plus transgranularclearly differentiated from lined-up pitting.If the presence ofcracking,shall not be considered as an SCC failure.SCC is questionable in accordance with 9.3.2.1 for C-ringNorE 2-Transgranular cracking in the absence of intergranular attackspecimens and 9.3.2.2 for tension specimens,metallographiconly occurs in pitted specimens under extremely high stress(intensity)examinations should be performed to determine whether or notand,for the purpose of this test method,is not considered as a criterion ofSCC is present.SCC.NorE 1-When a specimen fractures within a relatively short time after11.Retesting and Resamplingexposure(ten days or less).metallographic examination is not necessary11.1 Retesting shall be permitted only if a single specimenbecause such rapid failures are characteristically due to SCC.fails by SCC,in which case three replicate specimens shall be10.3 Metallographic Examination:tested.If any retest specimen fails,the sample shall be10.3.1 A specimen that reveals intergranular cracking,evenconsidered to have failed the test.when accompanied by transgranular cracking.shall be consid-ered as an SCC failure.Intergranular fissures that are no deeper11.2 If any failure is due to improper preparation of thethan the width of localized areas of corrosion or,in the case ofspecimen or to incorrect testing technique,or if the specimen isC-rings,not deeper than those in unstressed or compressivelyfound to be not representative of the material,the specimenstressed surfaces,shall not be considered as an SCC failureshall be discarded and another specimen substituted.(see Fig.3).In the case of tension specimens,the depth of11.3 When resampling.the required specimens shall betaken from the original sample if possible,or from anothersample of the same lot of material.12.Report12.1 Report the following information:100m12.1.1 Results of all tests,including type and size ofspecimen,orientation of specimen and number of replicates,stress level,and times to failure.12.1.2 Identification of alloy,temper,product form,andthickness of materials tested,including reference to applicablespecifications.12.1.3 Any deviation from the procedures outlined above.Width of13.Precision and Bias13.1 Precision:Localized13.1.1 The precision of data generated using this testmethod was evaluated by way of an interlaboratory testCorrosionprogram among seven laboratories using aluminum alloy 7075plate in three tempers;relatively susceptible T651,a moreresistant T7X51(similar to commercial T7651).and highlyresistant T7351.13.1.2 The procedure and raw data are described in detail inASTM STP 610.3 The tests were conducted using fivereplicate,short transverse specimens tested at various stresslevels that were chosen based on the expected performance ofthe individual tempers.Each of the seven laboratories con-ducted the test twice so that there were a total 140 specimensin for each combination of temper and stress level.The datahave been analyzed with respect to fraction of specimenssurviving the standard test period of 20 days.Although threedifferent specimen types were included in the testing,theanalysis has been conducted only for 3.18 mm(0.125 in.)diameter tensile bars as described in Practice G49.Reproduc-ibility was evaluated by comparing the seven laboratoriesagainst each other,and repeatability was evaluated by compar-In this example,the depth of the intergranular fissure is greater than the width ofthe localized attack and the specimen would be considered an SCC failure.ing the two runs conducted by each laboratory.Treating theFIG.3 Metallographic Cross-section Showing Measurement ofthree tempers separately,the following conclusions can beDepth of Intergranular Fissure and Width of Localized Attackdrawn.Copyright ASTM Intemationa4G47-20TABLE 1 Calculations of Variance for Fraction of 7075-T7X51 Plate SCC Specimens Surviving in the Interlaboratory Test ProgramApplied StressAverageRepeatabilityReproducibilityOverallFraction SurvivingVarianceVarianceVariance172 MPa25k90.8860.00570.06520.0709241 MPa35 ksi0.7710.07430.1120.186310 MPa45 ksi0.5570.03710.08760.125TABLE 2 Calculations of Standard Deviation of 7075-T7X51 Plate SCC Specimens Surviving in the Interlaboratory Test ProgramApplied StressAverageRepeatabilityReproducibilityOverallFraction SurvivingStandard DeviationStandard DeviationStandard Deviation172 MPa25k50.8860.07560.2550.266241 MPa35 ksi0.7710.2730.3350.432310 MPa45 ksi0.5570.1930.2960.35313.1.2.1 T65/-Overall,for this susceptible temper,137 outcombinations of material and environment.In the first case,theof 140 specimens failed at stress levels of 103 MPa and 172vast majority of specimens will fail quickly,while in theMPa(15 ksi and 25 ksi)making calculations of variance notsecond case,the vast majority of specimens will survive themeaningful.Since at least three of five specimens failed in eachduration of the test.Variability in results will tend to be highestgroup and the passing specimens were at two differentwhen material and environment combine to produce a situationlaboratories,the qualitative observation can be made that allof intermediate performance such that some but not all of thelaboratories produced similar results.specimens fail.The T7X51 material tested in this program fell13.1.2.2 77X5/-This temper with intermediate resistanceinto the category.had a mixture of failing and surviving specimens making the13.1.4 The statement on precision included in previouscalculations shown in Table 1 and Table 2 meaningful.Theversions of this test method was based on time-to-failurecalculations show that,depending on the stress level,reproducibility,or laboratory-to-laboratory differences,is re-criteria.That analysis is included in this version as Appendixsponsible for from 60%to 92 of the variance withX1.repeatability causing the remainder.The variance does depend13.1.5 Information relevant to the repeatability and repro-somewhat on applied stress level as probability of failureducibility of the stressing methods and environment called outwould be most consistent at either low stress levels where therein this test method can be found in the precision and biasare very few,if any failures,or at high stress levels where most,statement of Test Method G139.if not all,specimens fail.13.1.2.3 T735/-All specimens of this temper survived at13.2 Bias-The procedure in Test Method G47 has no biasbecause the result of the pass-fail stress-corrosion cracking testthe single stress level of 296 MPa(43 ksi).making calculationsis defined only in terms of this test method.of variance not meaningful.However,as with the susceptibleT651 temper,the qualitative observation can be made that eachlaboratory produced the same result.14.Keywords13.1.3 The results of this interlaboratory test program agree14.1 accelerated testing:aluminum alloys;corrosion;heat-with general experience,which indicates that SCC data will betreatable aluminum alloys;stress-corrosion cracking:tensionmost consistent under either relatively severe or relatively mildtestingAPPENDIX(Nonmandatory Information)X1.TIME-TO-FAILURE ANALYSIS OF INTERLABORATORY TEST PROGRAM DATAX1.1 Previous versions of Test Method G47 used a state-X1.2 The graph in Fig.X1.I shows data from the interlabo-ment on precision that was based on time-to-failure of speci-ratory test program described in STP 610and Section 13 ofmens.This statement on precision has been changed becausethis test method.The data in plot show that variability of thethe criteria given in the test method for differentiating samplesdata increase as survival time increases.These data agree withis based on specimens passing or failing(not cracking orthe statements made in Section 13 that combinations ofcracking)during defined exposure periods.Although the time-material,stress,and environment that produce intermediateto-failure analysis is not directly relevant to results producedlevels of resistance will give the highest variability.Combina-by the current procedure,it is included in this appendixtions of the same factors that produce either low or highbecause it may provide useful information in certain situations.resistance will produce less variability because the specimenswill either all fail relatively quickly or will not fail at all.Copyright ASTM Intemational