1、Designation: G 64 99 (Reapproved 2005)Standard Classification ofResistance to Stress-Corrosion Cracking of Heat-TreatableAluminum Alloys1This standard is issued under the fixed designation G 64; the number immediately following the designation indicates the year of originaladoption or, in the case o
2、f 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.INTRODUCTIONStress corrosion behavior is an important characteristic to be considered when optimizing the
3、 choiceof material for an engineering structure. Unfortunately, there is no generally accepted scale formeasuring it, and stress corrosion tendencies are difficult to define because of the complexinterdependence of the material, tensile stress, environment, and time. Conventional test-dependenttypes
4、 of laboratory stress corrosion data have only very limited applicability in mathematical modelsused for materials selection.This standard is intended to provide a qualitative classification of the relative resistance to stresscorrosion cracking (SCC) of high-strength aluminum alloys to assist in th
5、e selection of materials. Theclassification is based on a combination of service experience and a widely accepted laboratorycorrosion test.It is cautioned, however, that any such generalized classification of alloys can involve anoversimplification in regard to their behavior in unusual environments
6、. Moreover, the quantitativeprediction of the service performance of a material in a specific situation is outside the scope of thisstandard.1. Scope1.1 This classification covers alphabetical ratings of therelative resistance to SCC of various mill product forms of thewrought 2XXX, 6XXX, and 7XXX s
7、eries heat-treated alumi-num alloys and the procedure for determining the ratings.1.2 The ratings do not apply to metal in which the metal-lurgical structure has been altered by welding, forming, orother fabrication processes.1.3 The values stated in SI units are to be regarded as thestandard. The v
8、alues given in parentheses are for informationonly.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 and health practices and determine the applica-bility of
9、regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2G44 Practice for Exposure of Metals and Alloys by Alter-nate Immersion in Neutral 3.5 % Sodium Chloride Solu-tionG47 Test Method for Determining Susceptibility to Stress-Corrosion Cracking of 2XXX and 7XXXAluminumAlloyPro
10、ducts22.2 Other Documents:MIL-HANDBOOK-5 Metallic Materials and Elements forAerospace Vehicle Structures3MIL-STD-1568 Materials and Processes for Corrosion Pre-vention and Control in Aerospace Systems31This classification is under the jurisdiction of ASTM Committee G01 onCorrosion of Metals and is t
11、he direct responsibility of Subcommittee G01.06 onEnvironmentally Assisted Cracking.Current edition approved May 1, 2005. Published May 2005. Originallyapproved in 1980. Last previous edition approved in 1999 as G 64 99.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact
12、ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from Standardization Documents Order Desk, DODSSP, Bldg. 4,Section D, 700 Robbins Ave., Philadelphia, PA 19111-50981Copyright ASTM
13、 International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.MSFC-SPEC-522A Design Criteria for Controlling StressCorrosion Cracking43. Terminology3.1 Definitions:3.1.1 lotan identifiable quantity of material of the samemill form, alloy, temper, section, and si
14、ze (or thickness, in thecase of sheet and plate) traceable to a heat treat lot or lots, andsubjected to inspection at one time.3.1.2 stress-corrosion cracking (SCC)a cracking processthat requires the simultaneous action of a corrodent andsustained tensile stress. SCC in aluminum alloy productshistor
15、ically has been observed to follow an intergranular pathleading to the ultimate fracture. Thus, for the purpose of thisstandard, a fractured test specimen that reveals only pittingcorrosion or pitting plus transgranular cracking shall not beconsidered as an SCC failure (Test Method G47).4. Significa
16、nce and Use4.1 This classification involves alphabetical ratings intendedonly to provide a qualitative guide for materials selection. Theratings are based primarily on the results of standard corrosiontests.4.2 Interpretations of the SCC ratings in terms of typicalproblem areas including service exp
17、erience are given in Table1. Practical experience has shown that SCC problems withaluminum alloys generally have involved situations where thedirection and magnitude of the tensile stresses resulting frommanufacturing or use, or both, of the material were notrecognized.4.3 Alist of the SCC ratings f
18、or the heat-treatable aluminumalloy products is given in Table 2. Revisions to the table will berequired as new materials become available and additional testresults are accumulated.4.4 These alphabetical ratings are not suitable for direct usein mathematical models for material selection, but numer
19、icalweights and confidence factors can be devised on the basis ofexperience and judgment of the materials engineer.55. Basis of Classification5.1 The stress corrosion ratings for new or additionalmaterials shall be based on laboratory tests of standard smoothspecimens for susceptibility at specified
20、 stress levels. The3.5 % NaCl alternate immersion test (Practice G44) waschosen for the laboratory test because it is widely used foraluminum alloys and is capable of detecting materials thatwould be likely to be susceptible to SCC in natural environ-ments.65.2 Other types of tests using precracked
21、specimens ordynamic loading have promise7as alternative or supplemen-tary methods, but they presently require better understandingand standardization.6. Test Method6.1 To rate a new material and test direction, stress-corrosion tests shall be performed on at least ten random lots.The highest rating
22、assigned shall be that for which the testresults show 90 % conformance at the 95 % confidence levelwhen tested at the following stresses:AEqual to or greater than 75 % of the specified minimumyield strength.BEqual to or greater than 50 % of the specified minimumyield strength.CEqual to or greater th
23、an 25 % of the specified minimumyield strength or 100 MPa (14.5 ksi), whichever is higher.DFails to meet the criterion for rating C.6.2 Specimens shall be exposed by alternate immersion in3.5 % sodium chloride solution in accordance with PracticeG44.6.3 The length of exposure shall be selected accor
24、ding toalloy type and specimen orientation as follows:4Available from NationalAeronautics and SpaceAdministration (NASA), 300 ESt. SW, Washington, D.C.5Cook, O. H., Shaffer, I. S., Hoffner, J., and Devitt, D. F., “A Method forPredicting Stress Corrosion Cracking,” Paper No. 224 Presented at the NACE
25、Corrosion/78 International Corrosion Conference in Houston, TX, March 610,1978.6Sprowls, 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 Al
26、uminum AlloyProducts,” Stress Corrosion-New Approaches, ASTM STP 610, ASTM, 1976, pp.331.7Brown, B. F., “Stress Corrosion Cracking Control Measures,” NBS Monograph156, published by the U.S. Department of Commerce, National Bureau of Stand-ards, June 1977.TABLE 1 Practical Interpretation of Ratings f
27、or Resistance to SCCNOTE 1The stress levels mentioned below and the test stresses mentioned in 6.2 are not to be interpreted as “threshold” stresses, and are notrecommended for design. Other documents, such as MIL-HANDBOOK-5, MIL-STD-1568, NASC SD-24, and MSFC-SPEC-522A, should be consultedfor desig
28、n recommendations.Rating InterpretationA Very high. SCC not anticipated in general applications if the total sustained tensile stressAis less than 75 % of the minimum specified yield strength forthe alloy, heat treatment, product form, and orientation.B High. SCC not anticipated if the total sustain
29、ed tensile stressAis less than 50 % of the minimum specified yield strength.C Intermediate. SCC not anticipated if the total sustained tensile stressAis less than 25 % of the minimum specified yield strength. This rating is designatedfor the short transverse direction in improved products used prima
30、rily for high resistance to exfoliation corrosion in relatively thin structures where appre-ciable short transverse stresses are unlikely.D Low. SCC failures have occurred in service or would be anticipated if there is any sustained tensile stressAin the designated test direction. This rating cur-re
31、ntly is designated only for the short transverse direction in certain materials.AThe sum of all stresses including those from service loads (applied), heat treatement, straightening, forming, and so forth.G 64 99 (2005)2Test DirectionAAlloy Type ST L and LT2XXX 10 days 40 days6XXX 90 days 90 days7XX
32、X 20 days 40 daysASee Footnote B, Table 2.These exposure periods are believed to be long enough todetect susceptibility to intergranular SCC in each instance, yetshort enough to avoid excessive pitting that can lead to failureby another mechanism, as discussed in Test Method G47.7. Sampling and Numb
33、er of Tests7.1 The method of sampling various mill product forms, theselection of test specimens, and the minimum number of testsper lot shall be in accordance with Test Method G47. The90 % conformance at a 95 % confidence level specified in 6.1will be satisfied if 30 specimens (3 from each of 10 lo
34、ts) aretested and all pass the test.TABLE 2 Resistance to Stress-Corrosion Ratings for Heat-Treatable Commercial Aluminum Alloy ProductsAlloy andTemperATestDirectionBRolledPlateRodandBarCExtrudedShapesForgingsAlloy andTemperATestDirectionBRolledPlateRodandBarCExtrudedShapesForgings2011-T3, T4 LDBDD7
35、049-T76 LDDADLTDD LT ADSTDDDDSTDDCD2011-T8 LDA 7149-T73 L AALTDADDLTDDSTDA ST BA2014-T6 L A A A B 7050-T74 L ADAALT BEDBEBELT ADST D D D D ST BDBB2024-T3, T4 L A A AD7050-T76 L A A ADLT BEDBEDLT A B ADST D D DDST C B CD2024-T6 LDADA 7075-T6 L A A A ALTDBDAELT BEDBEBESTDBDD STDDDD2024-T8 L A A A A 70
36、75-T73 L A A A AT AAA T AAAST B A B C ST A A A A7075-T74 LDD DALT ASTDD DB2124-T8 L ADDD7075-T76 L ADADLT A LT ADADST BDDDST CDCD2219-T3, T37 L ADAD7175-T74 LDD DALT BDBDLT AST DDDDSTDD DB2219-T6 LDDA 7475-T6 L ADDDLTDALTBESTEE EAST DDD D2219-T8, T87 L A A A A 7475-T73 L ADDDLT A A A A LT AST A A A
37、A ST ADDD6061-T6 L A A A A 7475-T76 L ALT A A A A LT ADDDST A A A A ST C7005-T53, T63 LDDA A 7178-T6 L ADADLT AEAELT BEDBEDSTDDDD STDDDD7039-T64 L ADAD7178-T76 L ADADLT AEDAEDLT ADADST DDDDST CDCD7049-T73 L ADA A 7079-T6 L ADAALT ADAA TBEDBEBEST ADBA SDDDDAThe ratings apply to standard mill products
38、 in the types of tempers indicated, including stress-relieved tempers, and could be invalidated in some cases by applicationof nonstandard thermal treatments or mechanical deformation at room temperature by the user.BTest direction refers to orientation of the stressing direction relative to the dir
39、ectional grain structure typical of wrought materials, which in the case of extrusions andforgings may not be predictable from the geometrical cross section of the product.L Longitudinal: parallel to direction of principal metal extension during manufacture of the product.LTLong Transverse: perpendi
40、cular to direction of principal metal extension. In products whose grain structure clearly shows directionality (width-to-thickness ratiogreater than two) it is that perpendicular direction parallel to the major grain dimension.STShort Transverse: perpendicular to direction of principal metal extens
41、ion and parallel to minor dimension of grains in products with significant grain directionality.CSections with width-to-thickness ratio equal to or less than two, for which there is no distinction between LT and ST.DRating not established because the product is not offered commercially.ERating is on
42、e class lower for thicker sections: extrusions, 25 mm (1 in.) and over; plate and forgings 40 mm (1.5 in.) and over.G 64 99 (2005)37.2 If one of the 30 specimens should fail, tests of 18additional specimens, all passing, would be required to achieve90 % conformance (that is, 47 passing out of 48 tot
43、al tests). Iftwo of the original 30 specimens should fail, tests of 33additional specimens, all passing, would be required (that is, 61passing out of 63 total tests); if three should fail, tests of 48additional specimens, all passing, would be required (that is, 75passing out of 78 total tests), and
44、 so forth. (These calculationswere based on the exact binomial distribution for a populationproportion.)7.2.1 The additional specimens shall be selected from othernonfailing lots or from additional lots (3 specimens per lot).7.3 The results of all tests shall be reported.NOTE 1The amount of testing
45、specified in 7.1 and 7.2 was selected asa basis for classifying different materials. However, this amount of testingis not sufficient to ensure that every production lot of a material will havea specified capability for resistance to SCC. Nor should it be construed asbeing appropriate for acceptance
46、 tests of production materials.8. Keywords8.1 alphabetical stresscorrosion ratings; heattreatablealuminum alloys; laboratory corrosion tests; practical interpre-tation of ratings; service experience; stress-corrosion trackingASTM International takes no position respecting the validity of any patent
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49、 will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax),
