1、Designation: G64 99 (Reapproved 2013)Standard Classification ofResistance to Stress-Corrosion Cracking of Heat-TreatableAluminum Alloys1This standard is issued under the fixed designation G64; the number immediately following the designation indicates the year of originaladoption or, in the case of
2、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.INTRODUCTIONStress corrosion behavior is an important characteristic to be considered when optimizing the ch
3、oiceof 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 of
4、 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 the s
5、election 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. M
6、oreover, 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 seri
7、es 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 valu
8、es 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 reg
9、ulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2G44 Practice for Exposure of Metals andAlloys byAlternateImmersion in Neutral 3.5 % Sodium Chloride Solution2G47 Test Method for Determining Susceptibility to Stress-Corrosion Cracking of 2XXX and 7XXX AluminumAlloy Products
10、2.2 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 the dir
11、ect responsibility of Subcommittee G01.06 onEnvironmentally Assisted Cracking.Current edition approved May 1, 2013. Published July 2013. Originally approvedin 1980. Last previous edition approved in 2005 as G64 99 (2005). DOI:10.1520/G0064-99R13.2For referenced ASTM standards, visit the ASTM website
12、, 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.3Available from Standardization Documents Order Desk, DODSSP, Bldg. 4,Section D, 700 Robbins Ave., Philadelphia, PA
13、 19111-5098Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1MSFC-SPEC-522A Design Criteria for Controlling StressCorrosion Cracking43. Terminology3.1 Definitions:3.1.1 lotan identifiable quantity of material of the samemill form, alloy
14、, temper, section, and size (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 alum
15、inum alloy productshistorically 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
16、 Method G47).4. Significance 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 ar
17、eas including service experience 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 A
18、list of the SCC ratings for 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 mate
19、rial selection, but numericalweights 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 su
20、sceptibility at specified 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 o
21、f tests using precracked 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
22、 lots.The highest rating 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 strengt
23、h.CEqual to or greater than 25 % of the specified minimumyield strength or 100 MPa (14.5 ksi), whichever is higher.DFails to meet the criterion for rating C.4Available from NationalAeronautics and SpaceAdministration (NASA), 300 ESt. SW, Washington, D.C.5Cook, O. H., Shaffer, I. S., Hoffner, J., and
24、 Devitt, D. F., “A Method forPredicting Stress Corrosion Cracking,” Paper No. 224 Presented at the NACECorrosion/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 St
25、andard 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.331.7Brown, B. F., “Stress Corrosion Cracking Control Measures,” NBS Monograph156, published by the U.S. Departm
26、ent of Commerce, National Bureau ofStandards, June 1977.TABLE 1 Practical Interpretation of Ratings for 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 document
27、s, such as MIL-HANDBOOK-5, MIL-STD-1568, NASC SD-24, and MSFC-SPEC-522A, should be consultedfor design 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
28、alloy, heat treatment, product form, and orientation.B High. SCC not anticipated if the total sustained 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
29、strength. This rating is designatedfor the short transverse direction in improved products used primarily 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 anti
30、cipated if there is any sustained tensile stressAin the designated test direction. This rating cur-rently is designated only for the short transverse direction in certain materials.AThe sum of all stresses including those from service loads (applied), heat treatment, straightening, forming, and so f
31、orth.G64 99 (2013)26.2 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 according toalloy type and specimen orientation as follows:Test DirectionAAlloy Type ST L and LT2XXX 10 days 40 days6X
32、XX 90 days 90 days7XXX 20 days 40 daysTABLE 2 Resistance to Stress-Corrosion Ratings for Heat-Treatable Commercial Aluminum Alloy ProductsAlloy andTemperATestDirectionBRolledPlateRodandBarCExtrudedShapesForgingsAlloy andTemperATestDirectionBRolledPlateRodandBarCExtrudedShapesForgings2011-T3, T4 LDBD
33、D7049-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
34、7075-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
35、A 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 produc
36、ts 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 d
37、irectional 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: perpen
38、dicular 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 exte
39、nsion 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
40、one class lower for thicker sections: extrusions, 25 mm (1 in.) and over; plate and forgings 40 mm (1.5 in.) and over.G64 99 (2013)3ASee 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 e
41、xcessive pitting that can lead to failureby another mechanism, as discussed in Test Method G47.7. Sampling and Number 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. The
42、 90 %conformance at a 95 % confidence level specified in 6.1 will besatisfied if 30 specimens (3 from each of 10 lots) are tested andall pass the test.7.2 If one of the 30 specimens should fail, tests of 18additional specimens, all passing, would be required to achieve90 % conformance (that is, 47 p
43、assing out of 48 total 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
44、78 total tests), and 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 1Th
45、e amount of testing 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 approp
46、riate for acceptance 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 val
47、idity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is sub
48、ject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headqua
49、rters. Your comments 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)
